"Radio Network Planning"
Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. Chapter 7 Radio Network Planning for WCDMA 7.1 Overview With the emergence of 3G mobile communication technology, the construction of the UMTS network will bring a profound evolution, which makes higher requirements for network planning. At present, the public is greatly interested in this new technology. The construction of 3G mobile communication network is in the ascendant. This new mobile communication technology is different from the traditional GSM network planning in terms of essence. Worldwide people are developing new planning tool and algorithm and designing new work flow. Comparison between UMTS network planning and GSM network planning: 1. GSM network planning The GSM network planning is based on radio wave propagation analysis. According to the transmitting power and antenna configuration of BTS, its coverage area is calculated. Normally, only the downlink coverage area is calculated, so the GSM technology does not take uplink coverage area into consideration. The next step is performed by network planning engineers to analyze the required cell capacity. According to the calculated cell area, the traffic of cells can be estimated with the help of electronic map, and then the required channel numbers are calculated through traffic models (such as Erlang-B or Erlang-C). Next, it is the frequency distribution for BTSs, and the same frequency can only be reused among enough-distanced cells, to avoid interference. To expand the network in the future, the network planning engineer just needs to distribute new channels to the corresponding cells. As long as there is appropriate frequency in the overall frequency planning and the expansion does not exceed the maximum capacity of the BTS, the network does not require other adjustments. Otherwise, new BTSs or sectors should be added, and new frequency calculation and channel distribution are required. 2. UTMS network planning Compared with the GSM network planning, the UMTS network planning features the following differences: Cell breathing: 2004-08-30 Confidential Information of Huawei. No Page7-1, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. The CDMA network is totally different from the GSM network. Since channels and users are not separated for consideration, there is tight relation between coverage and capacity. The cell with more traffic has less coverage area. In the CDMA network, more traffic means more interferences. This kind of effect of dynamic change of cell area is called as “cell breathing”. This can be illustrated through the following visual example. In a birthday party of a friend, many guests come. More people taking will cause it is harder to hear the voice of opposite party clearly. If in the beginning, you can talk with a friend at another end of the room, you can not hear what he is saying at all when the room is very noisy. It indicates that the “cell radius” of talking area is shortened. The UMTS network planning engineer faces a network changing dynamically. In UMTS network planning, the network expandability should be taken into consideration first of all. The network planning engineer can not simply add frequency to the related cell as planning GSM network. In the beginning of network planning, a determined traffic signal redundancy should be taken into consideration, and this redundancy will be used as “compensation” to the interference caused by increased traffic. This shows that, from the very beginning, it is required to construct the network with smaller cells or more NodeBs, resulting in higher investment cost. If the traffic signal surplus is too small, there is only one way: adding NodeBs when expanding. The network planning engineer should notice the above issues, because enhancing transmitting power simply can not reduce the receiving signal deterioration caused by traffic incensement. Enhancing transmitting power can only improve the receiving signal of a cell but will add interference to the adjacent cells. As a result, the whole network communication quality will be influenced. To enhance transmitting power, the valid range or capacity (for the CDMA network, they are homonymous) of the CDMA cell is limited. When the UMTS network transmitting power is doubled, the cell capacity is increased by 10%. The enhanced transmitting power raises the valid range of cell, but to satisfy the requirements of remote mobile subscribers, it is necessary to enhance transmitting power by multiple times, which will influence the talking quality of other mobile subscribers. Let’s return to the above party example. You can enhance your voice to continue the conversation with the friend at another end of the room, but at the same time, other guests also raise voice to talk with others. As a result, the whole room is submerged in noise. The corresponding relationship between transmitting power and cell capacity is gradual. Since the UMTS cell load is subject to saturate, the UMTS network planning engineer must reduce the full-load ratio. The detailed parameters depend on different services and how much the network carrier would like to risk. Usually, the full-load factor is preset as 60% in network design. Here, the “cell breathing” effect is used. The adjacent cells can mutually compensate load, called as soft load. Due to cost, the network capacity can not be increased on a large scale. The mathematical demonstration on the 2004-08-30 Confidential Information of Huawei. No Page7-2, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. UMTS service with large scale data transmission shows that, as data transmission volume increases, it is more possible for a service cell to borrow capacity from the adjacent cells. This result is satisfied. Near-far effect: Another typical issue of the CDMA network is near-far effect. Since all the subscribers in the same cell share the same frequency, it is important that each subscriber in the whole system transmits signal at the minimum power. Let’s return to the above party example. If someone is shouting in the room, the conversation among all the other guests will be influenced. In the CDMA network, this problem can be solved through power control. For example, the UMTS network uses closed loop power control at frequency 1500 Hz. For GSM network, however, the power control works at 2 Hz and is for uplink only. This kind of fast power control mechanism has been implemented in the UMTS hardware. But the network planning engineer will face the other case of this problem. When a subscriber is far away from the NodeB, he needs a majority of transmitting power, resulting in power shortage for other subscribers. This means that the cell capacity is related to the actual subscriber geographical distribution. When subscriber density is rather large, statistics average value can be used to solve this problem. When subscriber quantity is small, it is necessary to perform dynamic analysis to the network through simulations. Uplink and downlink: The UMTS network traffic is asymmetrical, that is, the data transmission quantity in the network uplink differs from that in downlink. The network planning engineer should calculate values in two directions and then combine them together properly. In this way, the network planning work will be very complicated. Uplink is a typical limit factor for the valid coverage range of UMTS cell, or we can say that uplink is coverage-limited and downlink is capacity-limited. The transmitting power in uplink is provided by UE and the one in downlink is provided by NodeB. The above problems also occur in the existing CDMA network. For the UMTS network, these problems are more complicated. The UMTS network can satisfy different services with different requirements in communication quality and traffic at the same time, including simple voice service and packet service up to 2Mbps. Integrated services: In fact, the UMTS network should satisfy requirements of different services at the same time. So, the network planning engineer should take different services into consideration. For the service with low communication quality requirement, the UMTS cell has rather large coverage. For the service with high communication quality 2004-08-30 Confidential Information of Huawei. No Page7-3, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. requirement, the cell has very small coverage. So, in the actual work, the network planning engineer should not just consider UMTS cell radius, because different services correspond to different cell radiuses. If the minimum cell radius, that is, the service with highest communication quality requirement, is used as the standard for network planning, the network establishment cost will be very high and it is not realistic. The UMTS network planning engineer should start from the cell radius of middle-class service. As a result, the actual valid range of the cell can only satisfy the requirement of high-class service partially. At present, many network planning software companies have started to develop valid algorithms for this kind of new UMTS network integrated service. Other differences: Compared with GSM network, the UMTS network features other differences. The GSM network solves capacity problem with sector partition method. The cell with too much traffic is divided into multiple sectors, and antennas are added correspondingly. This method is also used for the UMTS network, but its effect is not enough. The change of cell coverage will cause the near-far effect mentioned above, and overlapped sectors will interfere mutually because they use the same frequency. The declination angle (mechanical or electronic) of antenna plays an important role in the UMTS network. It can reduce the interference among adjacent cells and raise cell capacity implicitly. In the actual application, large declination angle can be chosen to solve this problem. In the WCDMA system, multi-path propagation is not a negative factor but an ideal result, because receiver can combine the signal with delay of at least 1 Chip (the UMTS network chip transmission rate is 3.84 Mcps, that is, 1 Chip=0.26 microsecond, equal to 78 meters) into valid signal. In addition, the UMTS network also uses the soft handover. In this case, a mobile subscriber can connect to several cells. This method solves network signal fluctuation, but raises network traffic. The traditional Erlang model is not applicable any more. Compared with 2G traditional GSM network, the UMTS network features many differences. Especially, the UMTS network can run asynchronously, which causes “non-orthogonality” of transmission channel. Let’s return to the party example again. Even if the perfect planning can be made theoretically, that is, planning the person to talk in the certain time, it is impossible to reach that ideal goal factually, because the watches of all the guests can not be synchronous exactly. Through the above analysis, we can clearly see that the UMTS network planning needs more cost, compared with the current mobile communication network planning. The UMTS network planning is rather complicated, because many system parameters are 2004-08-30 Confidential Information of Huawei. No Page7-4, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. closely related to each other and should be calculated at the same time. In the current mobile communication network, however, these parameters are calculated separately. 7.2 3G Network Planning Procedure Compared with the second generation mobile communication, it is difficult to forecast different service models in the third generation system network owing to introduction of several kinds of high bit rate services. As for radio network planning, in any case, it is required to calculate the link budget, capacity and number of NodeBs, estimate the coverage of base station and design the parameters. In addition, it is required to design the whole network, calculate the number of channel units, capacity of transmit lines, RNCs, MSCs and other units in a base station. In network planning, performance measurements (such as dropped call rate and GOS) should be introduced to measure the network performance. High-bit rate services are provided at the cell area where base stations are covered equably, while low-bit rate services are provided to the edge of cell. The coverage can be designed as continuous coverage or hotspot coverage. You should estimate coverage of base station carefully according to different services and different implemented policies. Radio network planning can be divided into the following phases: Preparation Phase 1) Confirming Coverage Object 2) Confirming Capacity Object 3) Confirming Coverage Policy Estimation Phase 1) Estimating Cell Service Amount 2) Estimating Cell Capacity 3) Estimating Coverage Area 4) Calculating Capacity and Link budget Design and Adjustment Phase 5) Wireless Coverage Optimization Adjustment 6) Control Channel Power Design 7) Pilot Design 8) Soft Handover Parameter Design 9) PN Offset Handover After the above phases, you get to know the radio network features and confirm control channel allocation and design handover parameters, and then you may analyze the coverage of base station in detail. As for some cell, inter-cell interference vs. total interference ratio is unique. During the process of planning, you can continually take an analysis to the network and evaluate the interference ratio to estimate the coverage in different cells. Such iterative process may be repeated until the convergence of 2004-08-30 Confidential Information of Huawei. No Page7-5, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. coverage is achieved. Design tools can be adopted to realize the process automation and in the meantime detect leaks in the coverage. Usually, the coverage in 3G network service is not equable, which would lower network performance. On the one hand, the interference in the service-intensive area gets more, resulting in low quality. On the other hand, it is not necessary to get high quality, for it will result in a waste of resources. System effectiveness can be improved with the method of self-adapting controlling cell radius, antenna direction and uplink received power threshold. Cell radius can be varied with pilot power adjustment. If signal-interference ratio (SIR) is higher than the required value, cell radius can be increased. If not, cell radius can be decreased. The uplink/downlink cell radius can be balanced by increasing/decreasing uplink received power threshold. In the configuration of separate sectors, the communication quality of the base station can be balanced by changing central angle of each sector. 7.3 3G Radio Network Antenna 7.3.1 Introduction In 3G system (including WCDMA and cdma2000), which is as a new generation mobile communication system, multi-access mode has changed from TDMA/FDMA to CDMA/FDMA. However, as far as the wireless signal is concerned, it’s still facing the difficulties in making use of frequency resources efficiently and decreasing network interferences and transforming electrical signals with the utmost of efficiency. A antenna is a communication system bridge between a user terminal and a base station control equipment, widely applying to cellular mobile communication system. As the communication technology is developing, antennas will be on progress consequentially. The mobile communication system in the seventies adopted omnidirectional antennas or angle reflector antennas, for the reason that a few carriers and base stations can meet the demands of few users in a mobile communication system of a city. As the economy goes forward, the amount of mobile terminals, whose demands can not be met by the old base stations, is boosting so rapidly. Especially as the development of digital cellular technology goes, new antennas are required to be configured to improve the multi-path fading, site assignment and multi-channel network in metropolis. Plate type antennas are widely applying to 2G digital cellular system thanks to the features of low section, light framework, easy setting and good electrical specifications. From the middle 80’s to the late 90’s, vertical polarization (VP) antennas are usually adopted. A cell is usually divided into 3 sectors, each of which demands 3 antennas, so 9 antennas should be set in a cell. However, too many antennas will result in many problems, such as high setting cost. In addition, the optimum diversity reception gains are unable to be achieved with diversity reception antennas set, saying nothing of that 2004-08-30 Confidential Information of Huawei. No Page7-6, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. the antennas are unable to be set in some base stations. In that case, the technology of dual polarized antennas emerges as the times require. In 3G phase, as the wireless technology grows and the signal detection varies, the cellular network should be adjusted and optimized, which demands new base station antennas, such as self-adapting control antenna and intellectualized antenna. 7.3.2 3G Network Structure 3G system, a board-band CDMA system, inherits the features of narrowband CDMA system in the aspect of network structure. Thanks to code division multiple access, frequency reuse is not a big problem any longer. The network interference sources from itself, related to the amount of calling users at the same time. In a metropolis, three-sector base stations are commonly configured. In suburb, town and road, three-sector base stations or omni-directional base stations are configured as required and in arterial traffic, two-sector base stations are commonly configured, as shown in Figure 7-1. Section cell Section cell Omnidirectional cell cell Omnidirectional Figure 7-1 3G Network Structure For 3G (WCDMA), the channels per carrier are decided together by OVSF code and scrambling code, so capacity of the channels per carrier is great. You should set the number of the carriers and traffic channels in each base station based on the requirements of practical traffic distribution in engineering design. When implementing multi-carrier, you should pay attention to the followings in designing radio network: 1) Optimize hard handover to minimize the possibility of call drops. 2) Avoid isolated multi-carrier base station and implement multi-carrier in central cells to avoid hard handover. 3) Avoid heavy-traffic cells of being edge cells where hard handover occurs. 2004-08-30 Confidential Information of Huawei. No Page7-7, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. 7.3.3 3G Radio Network Typical Antennas You have several options to choose 3G typical antenna base on the following principles: 1) Properly choosing half-power beam width and gain of antenna based on the number of base station sectors, traffic density and coverage requirements. 2) Adopting duplexer to save antenna locations. 3) Adopting dual polarization antennas in the dense urban areas. The adjustment of antenna direction is the same as that in 2G engineering. The main lobe direction and angle of tilt of the directional antennas should be properly adjusted to the traffic distribution and communication quality requirements. When setting antennas, you should note that the isolation between antennas should meet the requirements of horizontal and vertical isolation to avoid interference. The setting height of antenna is up to the coverage. Therefore, it should be properly considered according to the coverage, interference, isolation and future development requirements. The antennas used in 3G network are similar to those used in 2G network, whose requirements are as follows: Sector antenna gain: 13-16 dBd Omnidirectional antenna gain: 9-10 dBd Sector antenna half-power beam width: 60-65 degrees or 90 degrees Omnidirectional antenna deviation in roundness: < +/- 1 dB Voltage standing wave ratio (VSWR): <1.5 Impedance: 50 ohm (unbalanced type) Maximum input: >500W Antenna diversity: Space diversity or polarization diversity is taken as standard configurations. 7.3.4 3G Smart Antenna (SA) 1. Principles of SA By adopting SDMA that signals differ in the direction of transmission path, SA reduces the effects of time delay spread, Rayleigh fading, multi-path, channel interference, distinguishes the signals from the same frequency and timeslot, and combines with other multiple access technologies to maximize the use of frequency spectrum resources. 2004-08-30 Confidential Information of Huawei. No Page7-8, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. The SA in base stations is a kind of array antenna comprising multiple antenna cells. By adjusting the weight scope and phase of each signal and changing array pattern, it can cancel interferences and increase S/N. In addition, it can measure a user’s direction so that a beam is directed to the user. 1 2 N ....... ... ..... W11 W12 W1N Wm1 Wm2 Wmn ¡Æ ¡Æ USER1 USERm Figure 7-2 SA Pattern From the Figure 7-2, it can be shown that the array antenna is composed of N antenna units, each of which has a corresponding weigher, totaling M groups of weighers and forming beams in M directions. M indicates the number of users, which can be greater than the number of antenna units. The dimension of array antenna and the number of antenna units decide the maximum gain and the minimum beam width, which means that the dimension of array antenna and antenna gain should keep balance with the antenna side lobe performance. By adjusting the signal phase and amplitude received from each antenna, SA combines them to a desired beam. This is called beam forming, which can form all kinds of beams, such as scanning beam, multi-beam, shaped beam and the beam with zero position controlled. According to the pattern, there are two types of SA: self-adapting pattern and shaped pattern. The key technology of SA is to identify the signal angle of arrival (AOA) and the implement of digit-shaped. The algorithms to identify the signal AOA are MUSIC algorithm, ESPRIT algorithm, maximum likelihood algorithm, etc. The implementation of digit-shaped is to choose the optimum weight coefficient to get the optimum beam. For self-adapting algorithm, the first step is to set rules, which commonly are maximum likelihood, maximum S/N, minimum mean square error (MMSE), minimum square error. You should choose one of them according to the specific conditions. Beam forming SA pattern is shown in the Figure 7-3. 2004-08-30 Confidential Information of Huawei. No Page7-9, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. Figure 7-3 Beam Forming SA Principle Pattern 2. Applications of SA in 3G The application example of SA in 2G network indicates that SA can efficiently prevent from interference. According to the 3G criteria, the SA application is required to improve the network capacity and performance, and take the technical factors, such as “converged beam”, “self-adapting beam forming” and “beam handover”, into consideration. “Converged beam” is applied to special areas, aiming at enlarging coverage and increasing capacity. Such beam does not associate with a user, nor does it trace mobile users in the coverage. However, by increasing link scope and converging beams, it can reduce transmission power of mobile users and according increase capacity. If mobile user enters the area with great transmission attenuation, the converged beam will point to the mobile user and rest on him. If a mobile user enters the area with good coverage which converged beams become unnecessary, the mobile user will be in the charge of common pilot channel. “Self-adapting beam forming”, applying to downlink, is in favor of link budget for individual user and a group of users to improve the system performance. In poor transmission conditions, such as cell edge (basement), the coverage is required to be spread to users with an aim to improve link scope. “Beam handover system” can switch users between narrow beams to form narrow sectors without handover loss. Because the capacity in 3G system increases as the number of sectors increases, four 30-degree beams coverage can substitute one 120-degree one, resulting in increasing capacity by 2 to 4 times. Users are switched between beams without the requirement of any special auxiliary channel. There are several options to apply SA in 3G. Beam handover SA is an option in starting phase. In network design, SA can reduce the external network interference (such as one frequency interference, adjacent frequency interference and other-system 2004-08-30 Confidential Information of Huawei. No Page7-10, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. interference) and the internal network interference as well. The order of magnitude depends on the amount of beams. 7.4 3G Handover Design 7.4.1 Introduction As the mobile station (MS) gets out of the service cell and goes into another service cell, the link between the former base station and the MS will be substituted for the link between the new base station and the MS. Handover, in mobility management, is mostly performed by RRC layer protocol in 3G. 1. Protocol state The UE state can be classified into IDLE state and CONNECTED state. The IDLE state can be classified into UTRAN IDLE, GPRS IDLE and GSM IDLE, three of which has CONNECTED state. The UTRAN CONNECTED state can be classified into four states: URA-PCH, CELL-PCH, CELL-FACH and CELL-DCH. Handover, generally speaking, is that UE is transferred from one communication connection to another one in the CONNECTED state. In this text, handover refers to that UE in CELL-DCH state, unless otherwise specified. 2. Handover Classification According to the setup and release of radio link between MS and network, handover can be classified into softer handover, soft handover and hard handover. Soft handover refers to that a MS begins to connect with a new base station, the communication between the mobile station and the former base station is still on. Soft handover is only applying to the CDMA cells with the same frequency. The difference between soft handover and softer handover is, softer handover is performed in the same NodeB where the maximum gain ratio combination of diversity signals are implemented, while soft handover is performed between two NodeBs, diversity signals selective combination in RNC. Hard handover consists of intra-frequency handover, inter-frequency handover and inter-system handover. Note that soft handover refers to the intra-frequency handover, but not all intra-frequency handovers are soft handovers. If the target cell and the former cell have the intra-frequency but belong to different RNC, and there is no Iur interface between RNCs, the intra-frequency hard handover will occur. Besides, the internal code handover in the same cell is also hard handover. 2004-08-30 Confidential Information of Huawei. No Page7-11, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. Inter-system hard handover consists of the handover between FDD mode and TDD mode, the handover between WCDMA system and GSM system in R99, and the handover between WCDMA and cdma2000 in R2000. The startup compress mode is required to measure inter-frequency and inter-system for inter-frequency hard handover and inter-system hard handover. According to the purpose, handover can be classified into edge handover, urgent handover at poor quality, urgent handover at quick level decrease, interference handover, velocity sensitivity handover, charge handover, layered/leveled handover, etc. The typical process of handover is measurement control → measurement report → handover decision→ handover implementation → new measurement control. In the phase of measurement control, the network informs UE of the measurement parameters through the sent measurement control message. In the phase of measurement report, the measurement report message is sent to the network by UE. In the phase of handover decision, the network makes a handover decision according to the measurement report. In the phase of handover implementation, UE and the network go along the signalling procedure and make a response to signalling. 7.4.2 Measurement Procedures In WCDMA system, there are intra-frequency measurements, inter-frequency measurements, inter-RAT measurements, traffic volume measurements and UE-internal measurements. The same type of measurements may be adopted in different functions or processes of UTRAN, such as cell reselection, handover and power control. The UE shall support a number of measurements running in parallel. The UE shall also support that each measurement is controlled and reported independently of every other measurement. Cells that the UE is monitoring (e.g. for handover measurements) are grouped in the UE into three different categories: 1.Cells, which belong to the active set. User information is sent from all these cells. The cells in the active set are involved in soft handover or softer handover. 2.Cells, which are not included in the active set, but are monitored according to a neighbour list assigned by the UTRAN belong to the monitored set. 3.Cells detected by the UE, which are neither included in the active set nor in the monitored set belong to the detected set. Reporting of measurements of the detected set is only required for intra-frequency measurements made by UEs in CELL_DCH state. 2004-08-30 Confidential Information of Huawei. No Page7-12, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. In IDLE mode, the UE shall perform measurements according to the measurement control information included in System Information Block Type 11 on BCCH. In CELL-FACH, CELL-PCH or URA-PCH state, the UE shall perform measurements according to the measurement control information included in System Information Block Type 12 on BCCH, while in CELL-DCH state, according to the measurement control information transmitted by UTRAN. The measurement results will pass two smoothness processing. The first processing is on the physical layer, with an aim to filter fast fading and report the measurement results from physical layer to higher layer; The second processing is done before event evaluation, when the higher layer takes weighted average on the measurement results reported from the physical layer, based on the time, to confirm the coefficient of filter. 1. UE Measurement P-CCPCH RSCP RSCP, Received Signal Code Power, is a measured received power of a code from P-CCPCH in TDD cell. The reference point of RSCP is the antenna connector at UE. SIR S/N is defined as (RSCP/ISCP) (SF/2).Measuring SIR should be in DPCCH after the combination of wireless link. The reference point of SIR is the antenna connector at UE. Where: RSCP, Received Signal Code Power, is a received power of pilot bit in a code. ISCP, Interference Signal Code Power, is a received signal interference measured in pilot bits. Only non-orthogonality of the interference is concerned in measurement. SF=Spreading Factor. P-CPICH RSCP Received Signal Code Power is a code power measured in P-CPICH. The reference point of RSCP is the antenna connector at UE. If transmission diversity is adopted in , the received code power from each antenna should be measured separately, then added, and sequentially be the power of the whole received codes in P-CPICH. UTRA carrier RSSI RSSI = Received Signal Strength Indicator, a broadband received power within relative channel width. The measurement will be taken at the downlink of UTRAN. The reference point of RSSI is the antenna connector at UE. GSM carrier RSSI 2004-08-30 Confidential Information of Huawei. No Page7-13, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. RSSI = Received Signal Strength Indicator, a broadband received power within relative channel width. The measurement will be taken at the BCCH carrier of GSM. The reference point of RSSI is antenna connector at UE. CPICH Ec/No Ec/No refers to ratio of the received energy of each code to noise power density in a channel. Ec/No has something in common with RSCP/RSSI. The measurement will be taken at basic CPICH. The reference point of Ec/No is the antenna connector at UE. If basic CPICH adopts transmission diversity, the received energy of each code (Ec) from each antenna should be measured separately. The value of adding the received energy of each code on basic CPICH will be Ec. BLER of transmission channel c It refers to the evaluation of Block Error Rate (BLER) of transmission channel. The evaluation of BLER is based on CRC of each transmission block after the combination of wireless link. Only the transmission channel with CRC requires the evaluation of BLER. In the connection mode, BLER can be measured in any transmission channel. In the idle mode, the BLER on the transmission channel PCH should firstly be measured if BLER needs measuring. UE transmitting power It refers to the transmitting power of the whole UE at a carrier. The reference point of UE transmitting power is the antenna connector at UE. In UE, in addition to the measurements above mentioned, there are the measurements in the aspects of time and order, which would not be described here. 2. RNC Measurement RSSI RSSI, Received Signal Strength Indicator, refers to a broadband received power within UTRAN uplink carrier channel bandwidth at the access point of UTRAN. The reference point of RSSI measurement is the antenna connector. SIR S/N is defined as (RSCP/ISCP)SF. Its measurement should be taken in DPCCH after the combination of wireless link at Node B. In the compression code, SIR should not be measured at transmitting interval. The reference point of SIR measurement is the antenna connector. Where: RSCP, Received Signal Code Power, refers to a received power in a code. 2004-08-30 Confidential Information of Huawei. No Page7-14, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. ISCP, Interference Signal Code Power, refers to a received signal interference. Only non-orthogonality of interference is concerned in measurement. SF refers to the spreading factor used in DPCCH. SIRerror SIRerror = SIR – SIRtarget_ave, where: SIR refers to the SIR measured at UTRAN in dB. SIRtarget_ave = refers to the average value of SIRtarget during a period of time. This period of time is the same as that when counting the average value of SIR error. The average value of SIRtarget is arithmetic average, SIRtarget_ave in dB. Transmitting carrier power The transmitting carrier power is the ratio (0…100%) of the whole transmitting power to the maximum transmitting power, where the whole transmitting power [W] is related to the average power [W] of a carrier at an access point of UTRAN. The maximum transmitting power is related to the average transmitting power [W] of a carrier at an access point of UTRAN under the condition that each cell is on the maximum power .The measurement may be taken at any transmitting carrier from the access point of UTRAN .The reference point of measuring transmitting carrier frequency is the antenna connector. The carrier frequency of each branch should be measured in case of transmitting diversity. transmitting code power Transmitting code power goes under the condition of given carrier, given scrambling and channel code. You can take measurements at DPCCH of any specific wireless link from the access point of UTRAN, to show the pilot bit power at DPCCH. All time slots should be involved in the measurement of transmitting power in the compression mode. For example, the time slot of transmitting interval should be involved. The reference point of measuring transmit code power is the antenna connector. The transmitting code power [W] of each branch should be measured and added in case of transmitting diversity. BER of transmission channel BER of transmission channel is to evaluate the mean bit error rate of DPDCH data after the combination of wireless link. The BER of transmission channel (TrCH) is as a result of measuring the puncture bits of channel coding input terminal at Node B. The evaluation of transmission channel BER may be reported at the end of each TTI at TrCH. The reported transmission channel BER should be a BER evaluation at the latest TTI of the current TrCH. Only the BER of transmission channel through channel coding are needed to be reported. BER of physical channel 2004-08-30 Confidential Information of Huawei. No Page7-15, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. BER of physical channel is to evaluate the mean bit error rate of DPCCH data after the combination of wireless link at Node B. BER of physical channel may be reported at the end of each TTI of all sent transmission channels. The reported BER of physical channel should be a mean BER evaluation at the latest TTI of each transmission channel. Other measurements: round trip time, transmission time delay, leading accesses, etc. 7.4.3 Co-frequency Handover The WCDMA handover algorithm is briefed as follows. WCDMA soft handover algorithm adopts Ec/Io of pilot CPICH to be a measurement value of handover, which is reported to RNC through three-layer signaling. The following terms are used for describing handover: Active set: The cells in active set are connected to MS in the form of soft handover. Neighboring set/Monitoring set: They both list the cells which are measured by MS continually, but the pilot Ec/Io in these cells are not mature enough to enter active set. WCDMA handover algorithm WCDMA soft handover algorithm is briefed as shown in Figure 7-4: Figure 7-4 WCDMA soft handover algorithm scheme common mechanism 2004-08-30 Confidential Information of Huawei. No Page7-16, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. If during the period of ΔT, pilot _Ec/Io> optimum pilot _Ec/Io reports range hysteresis event 1A, and active set is not full, the cell enters active set, which is called event 1A or wireless link addition. If during the period of ΔT, pilot _Ec/Io> optimum pilot _Ec/Io reports range hysteresis event 1B, the cell will be deleted from active set, which is called event 1B or wireless link deletion. If during the period of ΔT, active set is full, optimum alternate pilot _Ec/Io> former worst pilot _Ec/Io + _Ec/Io + hysteresis event 1C, the strongest alternate cell (the strongest cell in monitoring set) will substitute for the weakest cell in active set. Such event is called event 1C or the combination of wireless link addition and deletion. Supposing there are at most two cells in active set as shown in Figure 5-20. Where: Reporting range indicates a threshold value of soft handover; Hysteresis event 1A indicates adding hysteresis; Hysteresis event 1B indicates removing hysteresis; Hysteresis event 1C indicates replacing hysteresis; ΔT indicates trigger time; Optimum pilot _Ec/Io indicates the highest value of cell measurement in active set; Former worst pilot _Ec/Io indicates the highest value of cell measurement in active set; Optimum alternate pilot _Ec/Io indicates the highest value of cell measurement in monitor set; Pilot _Ec/Io is a measured and filtered value. 7.4.4 Handover between WCDMA System and GSM System The WCDMA criteria and GSM criteria support the bidirectional handover between WCDMA and GSM. As a result of coverage and load balancing, such handovers are used. In the early WCDMA configuration, it is necessary to hand off to GSM system for continuous coverage, and the handover from GSM to WCDMA can be used to reduce the load in GSM cell. Due to load, the bidirectional handover is significant as the service of WCDMA network grows. The inter-system handover is triggered by source RNC/BSC. From the point view of received system, the inter-system handover is similar to the inter-RNC handover or the inter-BSC handover. 2004-08-30 Confidential Information of Huawei. No Page7-17, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. 1. Compression mode If WCDMA adopts a way of continuous sending and receiving, but no WCDMA signal gap is generated, MS can not take inter-system measurement through one receiver. In this regard, the compression mode is significant for the inter-frequency measurements and the inter-system measurements. The introduction of compression mode is to take alien frequency measurement or alien-system measurement at FDD. The reason for that is a set of transceiver can only work on a group of transceiver frequency at the same time. If you want to measure the signals with other frequencies, you should power off the transceiver and hand off the frequency to target frequency for measurement. To ensure the normal transmission of downlink signals, the former signals should be transmitted during the transmission time left, which is called downlink compression mode. As the measurement frequency is close to the uplink transmitting frequency, to ensure good measurement, the uplink signal transmit should be stopped at the same time, which is called uplink compression mode. The compression mode is shown in the following figure. One frame (10 ms) Transmission gap available for inter-frequency measurements Figure 7-5 Compression Mode Diagrammatic Sketch Fast power control can not be used during the period of compression mode gap, so some interleaved gain will be lost; In this regard, during the compression frame, higher Eb/No is demanded to decrease capacity. The process of typical inter-system handover is as follows: The inter-system handover trigger is implemented at RNC, for example MS is out of WCDMA coverage range; RNC commands MS to begin with the inter-system measurements in compression mode; 2004-08-30 Confidential Information of Huawei. No Page7-18, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. RNC chooses the target GSM cell based on the MS measurements; RNC sends a handover command to MS. The handover from GSM system to WCDMA system sources from the BSC of GSM. Due to discrete transmission and receiving, the compression mode is not required for the measurement value of WCDMA from GSM. 7.4.5 Inter-frequency Handover in WCDMA Most of UMTS operators have 2 ~ 3 available FDD carrier, where: one frequency is enough to operate, while the other ones will be used to meet the demands of increasing capacity. We can adopt two different ways on how to use the frequencies: For the site with high capacities, several frequencies can be used at the same site, or, different frequencies can be used in macro-cell layer and micro-cell layer. These schemes should be supported for the inter-frequency handover at WCDMA carrier. The same as the inter-system handover, inter-frequency handover requires the compression mode measurement. 7.4.6 Handover Design The soft handover design consists of the configuration of the soft handover-related parameters and the control of soft handover rate. As WCDMA adopts soft handover-related threshold, it ensures a relatively stable configuration of the parameters such as the threshold. But the control of the handover rate is identical with IS-95, which is about 30% to 40%, because too much soft handover will not only increase the cost on the radio resources, but also reduce the capacity of the down link when the soft handover is increased to a certain degree. On the down links, the system interference will be increased along with the increase of the soft handover link. In case that the system interference exceeds the diversity gain of the soft handover, the soft handover will bring no benefit to the system capacity. In this regards, a well-prepared design is demanded before performing the soft handover in WCDMA. We can keep the soft handover rate in a suitable range by providing enough diversity in the up/down link. Parameters with regard to the network performance: Reporting Range: It is used to set the events 1a and 1b, namely the parameter R in formulas 1a-1 and 1a-2, 1b-1 and 1b-2. The bigger the R value is, the wider the soft handover area is. That is because the bigger the R value is, the easier it is to access ACTIVE SET. 2004-08-30 Confidential Information of Huawei. No Page7-19, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. W, which is used to calculate the cell quality of the active set is the value adopted for different cells. You will use it when you calculate the formulas 1a-1, 1a-2, 1b-1 and1b-2. Hystersis: The magnetic hysteresis value in the event report. Like in GSM, the purpose of introducing this value is to avoid the Ping-pong effect as possible. If the value is set too big will result in that the handover may occur difficultly, but if it is set too small, the Ping-pong effect may not be avoided. Reporting deactivation threshold: The maximum number of cells in the active set when the event is effective, is less than the maximum number of cells in the active set by 1. It is actually used to confirm the maximum number of cells in the active set (only for 1A event). If the value is set too big, the system interference may exceed the diversity gain of the soft handover, otherwise. If it is set too small, it may fail to fully use the diversity gain of soft handover. Reporting activation threshold: The minimum cell number of the active set when the event is effective (only for 1C event). Time to trigger: Try to avoid the impact of fast fading. If this value is too big, the handover may be delayed while if it is too small, the handover may occur frequently. Amount of reporting: The maximum amount of reporting after the event report changes to the cycle report. It is often used together with the Reporting interval. Reporting interval: Reporting cycle after the event report changes to the cycle report. It is used together with the amount of reporting. In using it, we should try to avoid over-adding the signaling flow. Reporting Cell Status: It is used to indicate the cell composition principle of the measured result, including the maximum number of reporting cells and the attributes of the reporting cell. 7.5 WCDMA Power Control Planning 7.5.1 Introduction In the WCDMA system, radio resource management includes power management, mobility management, load management, channel allocation and reconfiguration, and AMR mode control. Of which, the power management is a link of great importance. Power is the ultimate radio resource of the WCDMA system, so the only method to make fully use of the radio resources is to strictly control the use of power. In terms of power management, the QoS of a subscriber can be improved by increasing the transmit power of the subscriber; however, such improvement may result in deteriorating other subscriber’s receiving quality due to the self-interference feature of 2004-08-30 Confidential Information of Huawei. No Page7-20, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. the CDMA system. WCDMA adopts the broadband spreading technology with all signals sharing the same spectrum and the signal energy of each MS is allocated within the frequency band, thus for other MSs it is a kind of wideband noise. Therefore, the use of power in the CDMA system is conflicting. In addition, there are such effects as shadow, multi-path fading and remote loss in the radio environment. The position of a cellular MS in the cell is random and changes frequently, so the path loss will fluctuate greatly, especially in the multi-cell DS/CDMA system, where all the cells adopt the same frequency. Theoretically, the address codes allocated by different subscribers are orthogonal, but in fact it is hard to guarantee them, thus causing mutual interference among the channels and serious “near-far effect” and “corner effect”. Near-far effect occurs in the uplink. If all the subscribers in the cell transmit signals to the BS with the same power, then the signals of the MS near the BS are strong while the signals of the MS far from the BS are weak. In such a case, the weak signals will be masked by the strong signals. Corner effect occurs in the downlink. When the MS is at the corner of the cell, the interference will be twice more than that in the vicinity of the cell. When the interference is severe, the communication quality of the MS will be lowered promptly. Therefore, on the basis of ensuring QoS for subscribers, how to effectively control power, how to reduce the transmit power as much as possible, and how to reduce the system interference and increase the system capacity are the key to WCDMA technologies. The WCDMA system has such functions as forward power control (i.e. control of the BS transmit power) and reverse power control (i.e. control of the MS transmit power}, of which the reverse power control is especially important, because with it, the system capacity and communication quality may be ensured and the fading and near-far effect may be avoided to a great extent. 7.5.2 Principles of Power Control Implementation 1. Features of fast power control The mode of power control implementation in the WCDMA system is greatly different from that in the GSM system. Fast power control is a very important concept integrated in the WCDMA system. The radio propagation environment is severe. In the typical cellular mobile communication environment, the transmitting signals between the BS and the MS usually reach respective receivers after many times of reflections, dispersions and refractions. In this way, it is easy to cause multi-path fading of the signal. Fast fading will cause great impact on the receiving quality of the slow mobile receiver. In the GSM system, the MS reports the measurement result every 480 ms, and the frequency of the power control does not exceed twice per second. Therefore, for the GSM system, the 2004-08-30 Confidential Information of Huawei. No Page7-21, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. multi-path fading is counteracted through frequency hopping. For the WCDMA system, in the uplink the DPCCH will divide a 10 ms radio frame into 15 timeslots, each of which includes a power control command (TPC_cmd).As the speed of power control is higher than that of fast fading, the receiving quality of the slow MS is effectively ensured. In other words, the fast power control brings some gain to the slow MS by avoiding fast fading. Table 7-1 gives a comparison of the required Eb/Io values and required relevant transmit power changes for the slow and fast power control in the case of three different motion conditions. Table 7-1 Changes of slow and fast power control in the case of three different conditions Fast power control Gain of fast power Required Eb/Io Slow power control (1500 Hz) control ITU Pedestrian A 3Km/h 11.3dB 5.5dB 5.8dB ITU Vehicular A 3Km/h 8.5dB 6.7dB 1.8dB ITU Vehicular A 50Km/h 6.8dB 7.3dB -0.5dB Another two advantages of fast power control are that it can quickly adjust the power of the MS to avoid far-near affect to a great extent and the fast adjustment of the power reduces the interference to other cells and MSs. 2. Power control implementation In the WCDMA system, power control may be divided into inner loop power control and outer loop power control. The inner loop power control is to converge the received SIR to the target SIR by controlling the transmit power of physical channels. In the WCDMA system, relevant power adjustment commands are sent out by estimating the received Eb/No (ratio of bit energy to interference power spectrum density). There is certain mapping relationship between Eb/No and SIR. For instance, for the 12.2 kbps voice service, the typical value of Eb/No is 5.0 dB. If the chip rate is 3.84 Mcps, the processing gain will be 10 log10 (3.84M/12.2k) = 25 dB. So, the SIR is -20 dB (= 5 dB-25 dB), that is, the Carrier-to-Interference Ratio (C/I) is more than –20 dB. The outer loop control mechanism is to dynamically adjust the SIR target value of the inner loop control, so as to ensure that the communication quality always meets the requirements (i.e. the specified FER/BLER/BER value).The outer loop control is conducted in the RNC. The radio channels are complex, so the power control based only on the SIR value cannot reflect the real quality of the links. For instance, based on the same FER, the requirements of static subscribers, low speed subscribers (3 km/H) and high speed subscribers (50 km/H) for SIR are different. The communication quality is finally measured with FER/BLER/BER, so it is necessary to dynamically adjust the SIR target value according to the actual FER/BLER value. 2004-08-30 Confidential Information of Huawei. No Page7-22, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. The inner power control may be subdivided into open loop power control and closed loop power control. The former aims to providing the estimates of the initial transmit power. It estimates the path loss and the interference level according to the measurement result, so as to calculate the process of initial transmit power. In the WCDMA system, the open loop power control is adopted in both the uplink and downlink. In the WCDMA-FDD system, the fast fading conditions in the uplink and downlink are absolutely irrelevant because the frequency spacing between the uplink and the downlink is large. Therefore, the path loss estimates obtained through the open loop power control according to the downlink signals are inaccurate for the uplink. The method to solve this problem is to introduce the fast closed loop power control mechanism. The closed loop power control mechanism is to rapidly adjust the power in the uplink/downlink during the communication period, thus making the link quality converged to the target SIR. Two algorithms may be adopted for the closed loop uplink power control in 3GPP protocol. In the two algorithms, the step length of the uplink power control is 1 dB or 2 dB. In the DPCCH, the step adjustment of the power control is dpcch = tpc*TPC_cmd.TPC_cmd is the synthesized TPC command from different algorithms. The power of DPDCH is set according to the power offset between the DPDCH and the DPCCH. Differences between the two modes are: The open loop is not closed. It estimates the downlink interference according to the uplink interference, or estimates the uplink interference according to the downlink interference. In comparison, the closed loop is a closed feedback loop. The initial transmit power of the open loop power control is set by the RNC (uplink) or the UE (downlink), while the closed loop power control is completed by Node B with RNC only giving the target SIR value of the inner loop power control. 2004-08-30 Confidential Information of Huawei. No Page7-23, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. Transmitting signal Receiving signal Receiving signal Generate power control Power control parameter (P or SIR) instruction according to instruction insertion estimation a certain algorithm Via Via transmission transmission channel link Receiving signal demodulation Power control instruction abstraction WE generation Adjust transmitting power Receiving signal according to a certain algorithm Transmitting signal Figure 7-6 Basic structure of the closed loop power control mechanism 3. SSDT (Site Selection Diversity Transmission) In the soft handover, there are two or more BSs in the downlink transmitting signals to an UE simultaneously, which occupies additional system resources (transmit power), causing additional interference and reducing the forward capacity. Therefore, careful selection of the power control algorithm during the soft handover is important to improve the system capacity. Another algorithm of the power control in the soft handover is SSDT (site selection diversity transmission), according to which, the BS with minimum path loss will transmit signals, while other BSs will only receive signals of the uplink and transmit DPCCH. In this way, the total transmit power and additional interference may be reduced. SSDT is an optional macro diversity method in the software handover mode. The specific SSDT implementation method is as follows: Firstly, the UE selects a cell from ACTIVE SET as the PRIMARY CELL, and all other cells fall into the NON PRIMARY CELL. SSDT is to transmit signals from the PRIMARY CELL in the downlink, so as to reduce the interference resulted from the multi-channel transmission in the soft handover mode. Secondly, it is required to implement the site address selection promptly if there is no network intervention, so as to maintain the advantages of the soft handover. To select PRIMARY CELL, a temporary identity code should be allocated to each cell. Then, the UE will notify other cells in ACTIVE SET of the identity code of PRIMARY CELL on a regular basis. NON PRIMARY CELL selected by the UE will turn off the transmit power, and the identity code of PRIMARY CELL will be transmitted via 2004-08-30 Confidential Information of Huawei. No Page7-24, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. the uplink FBI domain of the uplink. The SSDT activation, stopping and ID code allocation are implemented by the upper signaling. SSDT is initiated by the network according to ACTIVE SET of the soft handover. Once it is determined to adopt SSDT, the network will notify the cell and the UE of the message that SSDT is activated in the period of current soft handover. Otherwise, TPC will still operate in the usual mode, that is, each cell controls the transmit power according to the TPC instruction of the uplink. The allocation of temporary identity code should be implemented by the network and notified to all the cells in ACTIVE SET and the UE for site address selection. The UE measures the Received Signal Code Power of Common Pilot Channels (RSCP of CPICHs) transmitted by the cells within ACTIVE SET on a regular basis to select the PRIMARY CELL. The cell with highest RSCP of CPICHs is the PRIMARY CELL. 7.5.3 Planning of the Power Control Parameters In the 3G system, the design criteria of the network planning is based on the SIR optimization and the activity set management. How to set proper RSCP of CPICHs, SIR target value of various services and handover area (changes to the activity set scope), and how to determine the coverage and quality of each service area are the mandatory tasks of the network planning. In the WCDMA system, the inner loop power control is implemented by NODE-B. The inner loop power control makes convergence to the target SIR, which is determined by the outer loop power control. Therefore, the power control parameters planning is mainly reflected by the outer loop parameters planning. With the research to and experiment on the relevant parameter settings of the outer loop power control, the outer loop power control can satisfy the requirements for the control accuracy and the control speed. Specific parameters involving the outer loop power control are as follows: Time factor of BLER report: The target BLER value divided by the time factor is the pieces N to be measured; BLER measurement report parameters; Maximum pieces to be observed: This parameter is used to control the upper limit of the pieces N to be measured; SIR-converged lagging value: Check the SIR lagging value (one of measurement report parameters) converged by SIR; Control parameters of the SIR measurement report: SIR measures the filter factor used by the SIRerr; Uplink outer loop power control parameters: SIR variation range, SIR adjustment factor, SIR target value falling step length, SIR maximum falling step length; 2004-08-30 Confidential Information of Huawei. No Page7-25, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. Uplink soft capacity control parameters: voice quality level and corresponding BLER values;; Default CPICH power downlink power balancing parameters: Trigger/Stop the threshold of DPB process, adjustment period and proportion of the downlink power balancing Downlink outer loop power control parameters: Trigger and stop the thresholds of downlink outer loop power control; Inner loop power control parameters: Initial SIR value, adjustment step length, algorithm mode selection; The above parameters are provided by OM, and there is a close link among them. 7.6 WCDMA Radio Network Structure and Resource Planning 7.6.1 Basic Network Structure 1. Network structure The basic network structure of WCDMA has been described in the prior chapter. It is divided into core network and access network. This chapter introduces the structure features of UTRAN and some key technologies and network parameters affecting the radio network structure from the perspective of network planning. Types of areas and the relationships among them 1) Types of areas include: Location Areas; Routing Areas; UTRAN Registration Areas; Cell Areas. 2) Relationships among the areas are shown as Figure 7-7: 2004-08-30 Confidential Information of Huawei. No Page7-26, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. Figure 7-7 Relationships among the areas The classification of location areas and routing areas in the WCDMA system is similar to that in the GSM and GRPS systems. 2. Cell structure The Node B of Huawei WCDMA system supports omnidirectional, 31, 32, 34, 61, 62 and 64 (combined cabinet) cell configurations. The cell structure of WCDMA is similar to that of GSM with different titles. “Cell” is similar to the “BS” in the GSM, while “SECTOR” is equal to the cell in the GSM system. For instance: What are 3*1, 3*2, 3*4, 6*1, 6*2 and 6*4? The first digit is the number of sectors supported by each cell; the second digit is the number of carrier frequencies supported by each sector. 3*1 means the BS supports 3 sectors, each of which has one carrier frequency; 6*4 means the BS supports 6 sectors, each of which has 4 carrier frequencies. The cell structure planning is to evenly provide high bit rate within the cell area, or the data rate of the cell boundary may be lower than that of the area near the BS, thus the cell area will be larger. The number of cells is calculated according to the capacity and the link budget. A network may be coverage-limited or capacity-limited. Capacity limited means the maximum cell radius cannot support the total traffic flow. Then, the number of cells may be calculated according to the number of subscribers supported by the cell per sq.km. Coverage limited means there is enough capacity in the cell to support all the traffic flow. Then, the number of required BSs may be calculated according to the maximum cell area. 2004-08-30 Confidential Information of Huawei. No Page7-27, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. 3. Hierarchical structure of the air interface According to the protocol, the air interface may functionally form a hierarchical structure. From bottom to top, they are physical layer, link layer and network layer. The physical layer fulfills the coding, modulation and spread spectrum of the physical channel. The link layer may be subdivided into two sub-layers: Medium Access Control (MAC) and Link Access Control (LAC).The former determines the resources provided by the physical layer, while the latter completes the establishment, maintenance and release of the logic link connection. The network layer includes such functions as call control, mobility management and radio resource management. 4. Channel allocation and reconfiguration The channel allocation includes the following types: Connection-oriented channel configuration: Fundamental Channel Configuration (FRC) and Dynamic Channel Reconfiguration (DCCC) Cell-oriented channel configuration: Cell code resource allocation, cell channel resource allocation and uplink scramble allocation Of which: Fundamental channel configuration: Allocate the channel types and bandwidth according to the service request; and configure the parameters of each layer of the channel according to the QoS. Dynamic channel configuration: During the communication, dynamically change the channel configurations according to current service status, including the channel types and the parameters of each layer of the channel Cell channel resource allocation: Common channel is the resource in the cell, including RACH, FACH, DSCH and CPCH. Cell code resource management: Cell downlink code resource allocation policy and code resource maintenance. Uplink scramble allocation: The uplink scramble includes the scramble reserved for the common channels RACH and CPCH, and the scramble allocated to the UE with dedicated channel. If RRC is connected or RAB sets up the request, the fundamental channel configuration entity determines the channel type according to the service type and rate requirements, and configures parameters of each layer of the channel according to the QoS. It makes a request to the call admission control entity for admission control according to the channel configuration parameter (QoS).If it is permitted, then go ahead; or the process of the channel setup is failed. 2004-08-30 Confidential Information of Huawei. No Page7-28, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. The dedicated channel is used to allocate the uplink scrambles; while the cell code resource maintenance entity is used to allocate the downlink channel code. The common channel is used to allocate the common channel parameters. If the channel is set up successfully, the dynamic channel configuration entity will monitor the traffic flow for the specific service, and make dynamic adjustment to the channel parameters. The cell channel resources are allocated according to the current cell service and the load conditions, so as to adjust the resource configuration of the cell common channel and optimize the system performances. The cell code resource management entity is used to maintain the cell code resources. 7.6.2 Hierarchical Network Structure 1. Basic concept of the hierarchical network structure Similar to the GSM system, the cell may be divided into macro cell (umbellate cell), micro cell and pico cell according to the features and scope of the cell services. The macro cell, micro cell and pico cell form a hierarchical network structure (HCS). The third generation mobile communication system should be able to support the services with wide coverage in various radio operation environments. The cell type varies with the requirements: Continuous coverage should be ensured for the large cell, while the small cell needs high spectral efficiency and capacity. The cell with small coverage is used to the terminal with low mobility and high capacity, while the cell with large coverage is used to the terminal with high mobility and low capacity. In addition, cells should be able to operate on other cells of different types. The coverage area of micro cell is hundreds meters, while the coverage area of macro is one or just over one kilometers. In the rural area, it can provide the micro cell with continuous coverage and the fast mobile subscribers with services. The pico cell covers an indoor scope with the radius of several meters. The satellite cell provides global continuous coverage. The traffic should be based on the minimum available cell. There are two methods to design multi-layer cell in the CDMA system: Different hierarchical cells operating on the same band, or different hierarchical cells operating on the different bands. The multi-layer structure also can be applied to the multi-operator environment. 2. Micro cell and macro cell with the same frequency The frequency reusability factor is 1. The processing gain of the system enables subscribers to bear the interference from the cells of different layers. The intra-layer interference is controlled by the power control, while the inter-layer interference is 2004-08-30 Confidential Information of Huawei. No Page7-29, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. controlled by the spatial isolation. Generally, the attenuation of the micro cell is larger than that of the macro cell, because its antenna is lower. Soft handover can offset the attenuation valley of the boundary of micro cell. 3. Micro cell and macro cell with different frequencies It is easy to manage when the cells of different layers adopt different frequencies, because there is no interference among the layers. The disadvantage of this method is that it needs large spectrum. At least 15 MHz bandwidth is required if the WCDMA system is divided into three layers. The impact on the total spectral efficiency from the non-linear power amplifier depends on the neighboring channel interference and the link performance deterioration. The increase of the neighboring channel interference will reduce the spectral efficiency. Although different carrier frequencies are adopted in the multi-layer cells, interference will occur between neighboring channel carriers if the capacity is high. 4. Antennas selection and parameters setting of the hierarchical network Similar to the GSM system, the traffic of the hierarchical network should be deployed as much as possible to the cell with minimum coverage area; that is, the macro cell is used to satisfy the requirements of the system for wide coverage, while the micro cell and the pico cell are used to absorb the traffic and the data traffic. For this purpose, as to the engineering parameters setting, the antenna and the transmit power of the macro cell are high; while the antenna and the transmit power of the micro cell are low; as to the software parameters setting, it is easier for the MS to access the micro cell and the pico cell. Most of the data traffic is convergent in the pico cell, so higher QoS of the pico cell should be ensured for higher service rate. 7.6.3 Mobility Management 1. Cell selection and re-selection 1) MS status According to the protocol, five statuses are available for the MS (UE): IDLE, CELL_DCH, CELL_FACH, CELL_PCH and URA_PCH. In the CELL_DCH status, the cell-crossing is judged by the measurement report, and the location is updated by the handover process. In the CELL_FACH and CELL_PCH statuses, the cell-crossing is judged by the UE cell reselection, and the location is updated by CELL UPDATE. 2004-08-30 Confidential Information of Huawei. No Page7-30, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. In the URA_PCH status, the cell-crossing is judged by the UE URA, and the location is updated by URA UPDATE. 2) Mobility management policy in the IDLE status When the UE starts up, it will carry out PLMN selection, cell selection and location registration. Upon the completion of the cell selection, the cell re-selection will be carried out. If a new cell is selected to stay, the location registration will be carried out for the new location area entry. If access and immediate cell evaluation are required, then initiate the access in the optimized cell. If the MS is in the CELL_DCH status, the UE crosses the cell through the handover flow. 3) Potential subscriber control The stay cell selection by the MS is determined by adjusting the parameters of the cell reselection, so as to adjust the cell load direction and achieve the load self-adaptive adjustment. 2. Random access procedure Random access procedure is a process: A MS requests the access system, then the network responses and allocates a service channel to the MS. The random access is carried out when the MS begins to transmit power; or when synchronization loss for some reasons occurs; or when message packets should be transmitted. The random access is fulfilled after following steps are completed: 1) synchronization between the code and frame; 2) search for the cell parameters, such as the random access code; 3) evaluation of the downlink path loss and random access to the initial power level. The optimal criterion for the random access procedure is the process rate and the low transmission power. The requirement for the random access procedure speed is determined by the requirement for the initial synchronization time. The number of access channels is depending on the involved access load. In addition, it also will be affected by the information transmitted in the random access status. Too high transmission power will reduce the capacity of the CDMA system, and the transmit power in the random access status cannot be controlled by the fast closed loop power control, so it is most important to make the total transmit power in the random access status minimum. If the initial transmission power is lowest, there is a long time for the access attempt. On the other hand, the high transmission power in the initial access will cause interference to other subscribers during the fast synchronization. The least information that needs to be transmitted in the random access attempt is the identity numbers of the MSs of some types. A kind of typical random access information 2004-08-30 Confidential Information of Huawei. No Page7-31, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. includes the pre-field, the synchronization and the data. The data should include at least the MS identity number, while the pre-field is the unmodulated wideband spread spectrum signal. 3. Call Admission Control Call Admission Control is a part of the load management. The call admission control algorithm is used to accept new calls as many as possible on the basis of ensuring the existing QoS. Its principle is: Current Status of the Cell Resources + Service Request YES/NO. The current status of the cell resources is depending on the uplink interference and the downlink load; while the requested service is depending on the QoS. 4. SNRS migration The structure shown in the left figure may occur for some reasons, such as the handover, cell update, URA update, RRC reconnection and direct retry. To save Iur interface resource and reduce the time delay, it is required to migrate the Iu interface as shown in Figure 7-8, that is, SNRS migration. The SNRS migration may effectively reduce the traffic of the Iur interface and improve the adaptability of the system. Figure 7-8 SNRS migration 7.6.4 Factors Affecting the Network Structure 1. Universal antenna and smart antenna (narrow-beam antenna) Smart antenna is widely used in the WCDMA system. In some relevant articles, it is also called self-adaptive antenna or narrow-beam antenna. The smart antenna adopts the concept of SDMA, monitoring and extracting the space information of every subscriber via the self-adaptive array antenna. It separates the signals of different directions without any interference according to the differences of the antenna array in the incident signal direction. In fact, it makes the communication 2004-08-30 Confidential Information of Huawei. No Page7-32, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. resources are no longer restricted by the time domain, the frequency domain and the code domain, and extended to the space domain. The advantages of the smart antenna are: The result of antenna beam forming is equal to increase the gains of the antenna; the antenna beam forming algorithm may take the multi-path transmission into consideration, avoiding the multi-path communication from affecting the digital wireless communication system with the performance enhanced; the antenna beam forming greatly reduces the multiple access interference. In this way, the communication capacity can be expanded in multiple. It also can improve the channel multiplexing rate of the communication system and the BS coverage area, and solve the increasingly serious interference problems (like common channel and multi-path fading). In addition, it can optimize the network structure. 2. The transmission models of GSM, CDMA and WCDMA and the affects of radio transmission on the system structure From the perspective of signal transmission, in the same frequency band range, the signals of the GSM, CDMA and WCDMA transmitted in the space have the same features, including the path loss, the slow and fast fading from the transmitter to the receiver. However, the transmission bandwidth in the WCDMA reaches 5M or more, so the multi-path fading performance is powerful. Its signal frequency band is far larger than the relevant bandwidth of the channel. The multi-path components may be separated, making fully use of the multi-path diversity receiving technology. 3. Parameters The network planning structure is realized by setting proper network engineering parameters and the network functional parameters. Different antenna gains, antenna heights, antenna types, network connection parameters, power control parameters, handover parameters and service rates are set for the cells of different layers of the hierarchical network. 4. Power control The power control plays an important role in the CDMA network performance and the network capacity. 5. Coverage The maximum cell coverage is determined by the link budget. Besides the data rate and the Eb/N performance, such specific factors as the cable loss, the antenna gain and the receiver noise should be calculated. In addition, the affects of the soft handover 2004-08-30 Confidential Information of Huawei. No Page7-33, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. gain and asymmetric traffic should be taken into consideration. Different service coverage area has different service rate requirements. The design basis of the hierarchical network is as follows: Outdoor in the rural: Terminal speed 250 kmph, 144 Kpbs at least, 384 Kpbs optimal Outdoor in the urban or suburb: Terminal speed 150 Kmph, 384 Kpbs at least, 512 Kpbs optimal Indoor or outdoor with a small area: Terminal speed 10 Km, 2 Mbps at least. Real-time fixed time delay: BER--, time delay 20-300 ms. Non-real time variable time delay: BER--, time delay 150 ms. Erl/km2 may be adopted for in a geometrical area. The data traffic may be Mbps/km2. The BS adopts multi-subscriber detection technology to provide a favorable coverage and lower the transmit power of the MS. The increase of the data rate will reduce the coverage area of the uplink. It differs from the narrowband system. 7.6.5 Radio Resource Planning 1. WCDMA frequency resource The W-CDMA spectral efficiency is related to the link performance. According to the theoretical analysis and the emulation, the uplink capacity is 2 to 2.5 times of the downlink capacity. Besides the antenna diversity in the BS, the uplink adopts the multi-subscriber signal detection technology, which provides almost two times capacity than the common receiver. In the downlink, two BSs transmit to the same MS the signals, which are not orthogonal, but only cause multi-path diversity. For the spectral efficiency, the bandwidth of 15- to 20-MHz is required for each cell to support an effective 2-Mbps subscriber. 2. Relationship between the resource planning and the network structure The WCDMA carrier interval is 200 KHz, ranging from 4.2 MHz to 5.4 MHz. The carrier intervals are adopted according to the interference to obtain proper protection for the neighboring channels. The bandwidth of 15 MHz may be divided for the use of three cells. The interval between different operators may be longer to avoid interference among them. 2004-08-30 Confidential Information of Huawei. No Page7-34, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. 7.7 3G Network Capacity Estimation 7.7.1 Introduction In the WCDMA system, the capacity of the uplink is lower that of the downlink, because the BS has better receiving technologies than the MS, such as the antenna diversity and multi-subscriber detection. In the UMTS, the downlink capacity is considered more important than the uplink capacity because the asymmetrical traffic is closely related to download services. In the 3G, more consideration is given to the downlink capacity. The factors causing the differences between the capacity uplink and the downlink capacity are the orthogonal code and the BS transmit diversity. WCDMA system adopts long extended code to distinguish cells in the downlink and subscribers in the uplink. 7.7.2 Downlink Orthogonal Code The downlink orthogonal code will affect the capacity, so it is considered to adopt irregular short code, which is orthogonal in the case of one path. Part of the orthogonality will disappear in case of multi-path, causing mutual interference among the subscribers in the cell. In the GSM system, there is no mutual interference in the same cell, because the time domain is orthogonal. 7.7.3 Link Budget To estimate the maximum area of the cell, it is required to carry out RLB ( Radio link budget) calculation. In the RLB, it is necessary to consider such factors as antenna gain, cable loss, diversity gain and fading margin. The RLB calculation result is the maximum allowed transmission path loss, based on which the cell radius and the number of required sites may be obtained. Compared with the TDMA-based radio access system (like the GSM system), the WCDMA system has some special problems in the link budget, including interference margin, fast fading margin, transmit power increasing and soft handover gain. 7.7.4 Capacity and Coverage Analysis If the maximum allowable path loss of a cell is known, it is easy to calculate the coverage area of the cell with the known transmission model. If the coverage area of the cell is known, it is required to select such sites as the channel elements, sector and carrier frequency and site density (cell radius) to configure, so as to satisfy the traffic requirements. The cell radius is also closely related to the number of access subscribers. Therefore, the coverage is correlative with the capacity, and the network operator should know the subscriber distribution and the growth trend, because it will 2004-08-30 Confidential Information of Huawei. No Page7-35, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. directly affect the coverage. The network should be configured properly to meet the traffic requirements and reduce the network cost as much as possible. The number of carrier frequencies, number of sectors, cell load, number of subscribers and cell radius will affect the final result. 7.7.5 Soft Capacity The number of required cells may be calculated with the available spectrum, subscribers amount forecast and traffic density information. The traffic density is indicated by erl. The calculation is conditional on the given congestion. If the congestion is caused by the hardware, then the result may be obtained in Table B. If the maximum capacity is caused by the interference, then the capacity is defined as soft capacity. For the system with soft capacity restriction, it cannot be calculated with Ireland Table. The total channel capacity is larger than the average number of the channels of each cell. The neighboring cells share a part of interference, so more traffic may be processed if the congestions are the same. If the interference from the neighboring cell is less, there will be more available channels in the middle cell as shown in Figure 7-9. Small Small Small Even load Huge load Small Small Small Figure 7-9 Interference sharing in the WCDMA If the cell has few channels, that is, there are high bit rate real-time subscribers, then the average load should be reduced to ensure low congestion. With the reduction of average load, there is additional capacity to be provided to the neighboring cell for use. This part of capacity is borrowed from the neighboring cell, so the interference sharing provides soft capacity. It is important for the high bit rate real-time subscribers to connect as shown in the figure. The soft capacity depends on the transmission environment (i.e. network planning). The value of is of great importance, and determined by the equipment radio resource management algorithm. In the WVDMA system, all subscribers share the interference source in the space channel, so the analysis cannot be conducted separately. The mutual affects among subscribers result in the changes of transmit power, which in turn cause further changes and repeating mutual affects. Forecast processing repeats unless it is stable. In the WCDMA system, the uplink/downlink fast power control, soft handover/softer 2004-08-30 Confidential Information of Huawei. No Page7-36, Total37 Spreading without Permission Error! Use the Home tab to apply 标题 1 to the text that you Basic Principles of WCDMA System want to appear here. handover and orthogonal downlink channels will affect its performance. Unlike the GSM, the BS sensitivity is depending on the number of subscribers and the rate of subscribers. It is constant in the GSM. The interference planning and capacity planning are even more important in the 3G. 7.7.6 Planning Conclusion The WCDMA cell capacity (at full load) is inversely proportional to the cell coverage radius. Under certain I/C, reducing the cell radius can improve the cell capacity. Essentially, it is to offset the cell capacity loss caused by the system noise. Reducing the cell capacity can increase the coverage radius. Of course, the coverage area should be subject to the radio coverage conditions. In the cell planning, it is required to determine proper coverage radius to meet the cell capacity requirements. The cell coverage requirements for the capacity in the urban and rural are different. In the urban, there are many hot areas and the unit area traffic demand is high. In such a case, to solve the capacity problem is a main task. Whereas, in the rural area, the traffic demand is low and the main task is to solve the coverage problem. The CDMA system features soft capacity and can satisfy this requirement. The unit area capacity may be improved by the cell splitting and multi-sector. Such improvement may be realized easier in the CDMA cell, which dynamically changes the cell coverage by controlling the pilot transmit power. 2004-08-30 Confidential Information of Huawei. No Page7-37, Total37 Spreading without Permission