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					                                                                                               WCDMA Radio Interface
        Basic Principles of WCDMA System                                                                Technology




   Chapter 5 WCDMA Radio Interface Technology

             In the WCDMA system, the mobile UE connects with the fixed system network through
             a radio channel on the radio interface. Called Uu interface, this interface is one of the
             most important interfaces in the WCDMA system. The radio interface technology is the
             core one in the WCDMA system, which shows the core technologies and main
             differences of all kinds of 3G mobile communication systems.
             By learning the WCDMA radio interface, we can understand the operating principle
             between the UE and the WCDMA network systems and get known to the
             communication procedures. Learning this chapter is also the precondition of the
             WCDMA radio network planning.

5.1 Overview of the WCDMA Radio Interface
5.1.1 Protocol Structure of Radio Interfaces

             Figure 5-1 shows the protocol structure of UTRAN radio interfaces related to the
             physical layer. From the perspective of protocol structure, the WCDMA radio interface
             is composed of the following three layers: Physical layer, medium access control layer
             and radio resource control layer. In terms of protocol layer, the WCDMA radio interface
             has three channels: Physical channel, transport channel and logical channel.

             Layer 3
                                               Radio Resource Control (RRC)
                         Control/measure




                                                                                                   Logical channel
             Layer 2
                                                         Medium Access Control (MAC)

                                                                                                   Transport channel

             Layer 1                                            Physical layer                     Physical channel


                                               Figure 5-1 Physical Structure of Radio Interfaces


             The circles among different layers/sub-layers in the Figure are Service Access Points
             (SAPs).
             The physical layer provides data transmission services required by the upper layer.
             These services are accessed by using the transport channel through MAC sub-layer.



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             The physical layer provides services for the MAC layer through a transport channel,
             while the proprieties of transmission data determine what kind of transport channel
             should be used and how to transmit. The MAC layer provides the RRC layer with
             services through a logical channel, while the proprieties of the transmitted data
             determine the type of the logical channel. In the Medium Access Control (MAC) layer,
             the logical channel is mapped as a transport channel. MAC layer should select proper
             Transport Format (TF) for each transport channel, according to the transient source
             rate of logical channels. The selection of transmission format relates tightly to the
             transport format combination set of each connection (defined by receiver control
             module).
             RRC layer also provides services for upper layers (non-access stratums) through
             Service Access Points (SAPs). The SAPs are used by the upper layer protocol and the
             RANAP of the Iu interface respectively on the UE side and the UTRAN side. All
             signaling of upper layers (including mobility management, calling control and
             conversation management) are compressed into RRC messages, and then are sent
             on radio interfaces.
             The RRC layer configures such protocol entities of lower layers as physical channels,
             transport channels and logical channels by using the control interfaces between it and
             lower layer protocols. The RRC layer also uses control interfaces to control commands
             in real-time, for example, it requires the lower layers to perform specific measurement,
             and asks them to use the same interfaces to report measurement interfaces and error
             information.
             Logical channel: Carrying user services directly. According to the types of the carried
             services, it falls into two types: Control channel and service channel.
             Transport channel: It is the interface of radio interface layer 2 and physical layer, and
             is the service provided for MAC layer by the physical layer. According to whether the
             information transported is dedicated information for a user or common information for
             all users, it is divided into dedicated channel and common channel.
             Physical channel: It is the ultimate embodiment of all kinds of information when they
             are transmitted on radio interfaces. Each kind of channel which uses dedicated carrier
             frequency, code (spreading code and scramble) and carrier phase (I or Q) can be
             regarded as a dedicated channel.
             At the transmitting end, the data flows from MAC and upper layers are transmitted in
             radio interfaces, reused and mapped by channel coding, transport channel and
             physical channel, spread and modulated by physical channel, and then formed the
             data flows of radio interfaces to be transported on the radio interfaces. At the receiving
             end, it is a reverse process.
             This chapter gives a brief introduction to logical channels and transport channels, and
             focuses on the process of physical channels and layers. By learning the process of


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              physical channels and layers, we can deeply understand the operating principle of
              WCDMA radio interfaces, and get known to the WCDMA network planning.

5.1.2 Spreading Spectrum and Scrambling

              On radio interfaces, after source coding and channel coding, the data flow continues to
              spread spectrum, scramble and modulate.




                           Figure 5-2 Relation between Spreading Spectrum and Scrambling Code


              The code word used for spreading spectrum is called channelization code, for which
              OVSF (Orthogonal Variable Spreading Factor) code is used. The code word used for
              scrambling is called scramble, which adopts GOLD sequence.

             1. Spreading spectrum and channelization code

              Channelization code is used to distinguish the transmission from the same source,
              that is, different physical channels of the same terminal between the downlink
              connection and upper-link one of a sector. The spread spectrum/channelization of
              UTRAN is based on orthogonal variable spreading factor (OVSF) technology.
              OVSF can change the spreading factor and keep the orthogonality between different
              spreading codes with various lengths. Code words can be selected from the code tree
              shown below. If one connection uses variable spreading factors, it can use correctly
              the code tree for dispreading according to the minimum spreading factor. Therefore,
              just select the channelization codes from the branch of the code tree directed by the
              minimum spreading factor code.




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                                        Figure 5-3 Structure of channelization code tree


             2. Scramble

              Scramble is used to separate the terminals or BSs, and it is used after spreading
              spectrum, so it does not change the bandwidth of signals but only separate the signals
              from different sources. After scrambling, the problem that several transmitters use the
              same code word spreading spectrum is solved. Figure 5-2 shows the relation between
              spreading spectrum and channelization chip rate in UTRA. After the spread spectrum
              of channelization code, it already reaches chip rate, so the scrambling code does not
              affect the symbol rate.
              The table below summarizes the functions and features of the scrambling codes and
              channelization codes.




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                       Table 5-1 Functions and Features of the Scrambling Codes and Channelization Codes.

                                        Channelization code                               Scrambling code

                              Uplinks: Distinguish physical data
                              (DPDCH) and control channels (DPCCH).       Uplinks: Distinguish terminals
              Purpose
                              Down links: Distinguish the down links of   Down links: Distinguish cells
                              different users in the same cell.
                                                                          Uplinks: 10 ms = 38400 chips or =66.7 us = 256
                                                                          chips
                              4~256 chips (1.0-66.7 us)
              Length                                                      For advanced BS receipt, option 2 can be
                              The down links contain 512 chips
                                                                          selected.
                                                                          Down links: 10 ms = 38400 chips
                              Quantity of code words under a
              Quantity of                                                 Uplinks: Several million
                              scrambling word is equal to that of
              code words                                                  Down links: 512
                              spreading factors
                              OVSF (Orthogonal Variable Spreading         Long 10 ms code: Gold code
              Code cluster
                              Factor)                                     Short code: Extended S (2) code cluster
              Spreading
                              Yes, transport bandwidth is added.          No, transport bandwidth is not affected.
              spectrum


5.2 Logical Channel
             For the types of logical channels, please see Figure 5-4:




                                                  Figure 5-4 Types of logical channels



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             1. Control channel

              The following control channels are only used to transmit the information of control
              plane:
              Broadcast Control Channel (BCCH): Downlink channel used to broadcast system
              messages.
              Paging Control Channel (PCCH): Downlink channel used to send paging messages.
              Common Control Channel (CCCH): Bidirectional channel used to send control
              messages between the network and UE. This channel is mapped to RACH/FACH
              transport channel. Identifiers of long UTRAN UE (U-RNTI, including SRNC) are
              required in this channel, which ensures the uplink messages to be sent to the correct
              SRNC.
              Dedicated Control Channel (DCCH): Bidirectional channel used to send control
              messages between the network and UE. This channel is allocated by the network to
              the point-to-point dedicated channel of the UE when RRC is built.

             2. Traffic channel

              The following traffic channels are only used to transmit the information of user plane:
              Dedicated Traffic Channel (DTCH): Bidirectional point-to-point channel dedicated for
              one UE and used to transport user information.
              Common Traffic Channel (CTCH): Point-to-multipoint down link used to transport the
              dedicated user information for all or a group of UEs.

5.3 Transport Channel
5.3.1 Types of Transport Channels

              A transport channel is used at the physical layer to provide services for the upper layer.
              It defines the mode and features of data transmission on air interfaces.
              It is divided into two types: Dedicated channel and common channel. The main
              difference between them is: Resources in the common channel are shared by all users
              or a group of users within a neighborhood, while resources in the dedicated channel
              are defined by the dedicated code on specific frequency, and they are used only for
              individual users.

5.3.2 Dedicated Transport Channel

              Only one kind of dedicated transport channel exists, that is, Dedicated Channel (DCH).
              The Dedicated Channel (DCH) is an uplink or downlink channel. In the whole or part of
              the neighborhood, DCH uses beam-forming antenna to transmit.



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5.3.3 Common Transport Channel

             Totally, there are the following six transport channels: BCH, FACH, PCH, RACH,
             CPCH and DSCH.
                 BCH (Broadcast Channel): It is a downlink transport channel, which is used to
                  broadcast the dedicated information in the system or in a cell. The BCH always
                  transmits in the whole cell, and it has a separate transport format.
                 FACH (Forward Access Channel): it is a downlink transport channel. In the whole
                  or part of the cell, FACH uses beam-forming antenna to transmit.
                 PCH (Paging Channel): It is a downlink transport channel, which always transmits
                  in the whole cell. The transmission of the PCH associates with that of page
                  indication generated by the physical layer so as to support the effective dormant
                  mode program.
                 RACH (Random Access Channel): it is an uplink transport channel. It always
                  receives information in the whole cell. It features collision and adventure, using
                  open loop power control.
                 CPCH (Common Packet Channel): it is an uplink transport channel, and it
                  associates with the dedicated channel of a downlink. This dedicated channel is
                  used to provide CPCH power control of the uplink and CPCH control commands
                  (such as emergency).It features initial collision and adventure, using open loop
                  power control.
                 DSCH (Downlink Shared Channel): it is a downlink transport channel shared by
                  some UEs, associating with one or more DCHs. In the whole or part of the cell,
                  DSCH uses beam-forming antenna to transmit.

5.3.4 Indicator

             The WCDMA protocol defines a series of indicators for the transport channel. In fact,
             an indicator is a fast lower-layer signaling entity. It does not occupy any entity block but
             is implemented directly in the physical layer by the physical channel.
             There are the following related indicators: Acquisition Indication (AI), Access Preamble
             Indication (API), Channel Assignment Indication (CAI), Collision Detection Indication
             (CDI), Paging Indication (PI) and Status Indication (SI). Indicators can be either binary
             or ternary. Their mapping to the indicator channel is determined by the physical
             channel. The physical channel used to transmit indicators is called Indicator Channel
             (ICH).

5.3.5 Mapping from the Logical Channel to the Transport Channel

             The transport channel serves the logical channel. From Figure 5-5, we can see the
             mapping relation between the logical channel and the transport channel.



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                         Figure 5-5 Mapping between the logical channel and the transport channel


5.4 Physical Channel
5.4.1 Relevant Concepts of the Physical Channel

             The physical channel is defined by a specific carrier frequency, scramble,
             channelization code (optional), time bucket from beginning to end (there is time
             duration) and the corresponding phase of the uplink. The duration is defined by the
             beginning and end time, measured by using the integer times of chip.
             Radio frame: It is a processing frame containing 15 timeslots. The length of a radio
             frame is 38400 chips.
             Timeslot: It is a unit composed of some bit fields, 2560 chips in length.
             The default duration of a physical channel lasts from the beginning hour to end hour.
             The non-consecutive physical channels will be noted clearly.
             The transport channel (more abstract high-layer than the physical layer) can be
             mapped to the physical layer. For the physical layer, it maps the data from a Coded
             Composite Transport Channel (CCTrCH) to the physical channel. Besides the data, it
             also maps channel control commands and physical signaling.
             Like the physical channel, the physical signaling is also an entity based on air features,
             but no transport channel or indicator is mapped to physical signaling. The physical
             signaling can support the functions of the physical channel.

5.4.2 Architecture of the Uplink Physical Channel

             The uplink physical channel is divided into two types: Uplink dedicated physical
             channel and uplink common physical channel.
             The uplink dedicated physical channel is divided into uplink Dedicated Physical Data
             Channel (uplink DPDCH) and uplink common physical channel.


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              The uplink common physical channel is divided into Physical Random Access Channel
              (PRACH) and Physical Common Packet Channel (PCPCH).

             1. DPDCH/DPCCH

              Figure 5-6 shows the frame structure of the uplink dedicated physical channel. Each
              frame is 10 ms long, divided into 15 timeslots. And each timeslot is 2560 chips long,
              and corresponds to a power control period.
              The DPDCH is a dedicated transport channel. There may be zero, one or more
              DPDCHs in a radio link.




                                        Figure 5-6 Channel architecture of the DPCH


              The Dedicated Physical Control Channel (DPCCH) includes the following: The known
              pilot bits used to support channel estimation for the relevant detection, Transmit Power
              Control (TPC), FeedBack Information (FBI) and an optional Transport Format
              Combination Indicator (TFCI). There is only one DPCCH in each radio link.
              The parameter “k” in Figure 5-6 determines the number of bits of each uplink
              DPDCH/DPCCH. It relates to the Spreading Factor (SF) of the physical channel. 1
                        k
              SF=256/2 The SF of the DPDCH ranges from 256 to 4. The SF of the uplink DPCCH
              is always 256, that is, there are 10 bits for each uplink DPCCH timeslot.

             2. PRACH

              The physical random access channel is used to transport RACH.
              The transmission of the RACH is based on the timeslot ALOHA mode with fast
              acquisition indication. The UE may begin to transport in a time offset defined in
              advance, indicated as access timeslots. Every two frames have 15 access timeslots,
              at an interval of 5120 chips. Figure 5-7 shows the quantity of the access timeslots and
              the interval between them. The information about the availability of the access timeslot
              in the current cell is provided by the high-layer information.

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                               Figure 5-7 The access timeslot quantity and interval of the RACHs


             The structure of the random access transmission is shown in Figure 5-8. It includes
             one or more 4096-chip preambles and a 10-ms or 20-ms message part.




                                   Figure 5-8 Structure of the random access transmission


                 Preambles for the RACH
             The preamble of the random access transmission is 4096 chips long, and it is 256
             times repetition of a signature with the length of 16 chips. Totally, there are 16 different
             signatures.
                 RACH message part
             Figure 5-9 shows the structure of the random access messages. The 10-ms message
             is divided into 15 timeslots, with T slot=2560 chips. Each timeslot contains two parts:
             One is the data part, where the RACH transport channel is mapped; the other is
             control part, which is used to transport the control information of layer 1.The data part
             and control part are transmitted concurrently. A 10-ms message is composed of one
             radio frame, while a 20-ms message is of two 10-ms radio frames. The length of the
             message part is determined by the signatures and/or timeslot, which is configured by
             the high layer.
                                             k
             The data part contains 10*2 bits, where k = 0, 1, 2, 3.For the message data part, they
             correspond respectively to 256, 128, 64 and 32 spreading factors.


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              The control part includes eight known pilot bits used to support the channel estimation
              for the relevant detection and two TFCI bits, which corresponds to 256 spreading
              factors for the message control part. In the random access message, the total of TFCI
              bits is 15*2=30 bits. The value of TFCI corresponds to a specific transport format of
              the current random access information. In case that the PRACH is 20 ms long, the
              TFCI will repeat in the second radio frame.




                                   Figure 5-9 Structure of the random access message


             3. PCPCH

              The Physical Common Packet Channel (PCPCH) is used to transport CPCH.
                 The transmission of the CPCH
              The transmission of the CPCH is based on the DSMA-CD (Digital Sense Multiple
              Access-Collision Detection) mode with fast acquisition indication. The UE may begin
              to transport at the predefined time offset corresponding to the frame border of the BCH
              received by the current cell. The timing and structure of the access timeslot is the
              same as that of the RACH. The structure of the CPCH random access transmission is
              shown in Figure 5-10.The CPCH random access transmission includes the following
              parts: One or more 4096-chip-long Access Preambles (APs), one 4096-chip-long
              Collision Detection Preamble (CD-P), one 0-timeslot-long or 8-timeslot-long DPCCH
              Power Control Preamble (PC-P) and one variable Nx10 ms message.




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                               Figure 5-10 Structure of the CPCH random access transmission


                 Access preambles of the CPCH
             Like the RACH preamble part, the feature sequence of the RACH are used here, but
             fewer than the RACH preambles. You can select a scramble from different code
             segments of the Gold code which consists of the RACH preamble scrambles, and you
             can also use the same scramble if the signature is shared.
                 Collision detection preamble part of the CPCH
             Like the RACH preamble part, the CPCH collision detection preamble part uses the
             feature sequence of the RACH. You can select a scramble from different code
             segments of the Gold code which consists of RACH and CPCH preamble scrambles.
                 Power control preambles of the CPCH
             The Preamble part of power control is called Power Control Preamble (PC-P) of the
             CPCH. The length of the power control preamble (Lpc-preamble) is a high-layer parameter,
             and can have zero or eight timeslots.
                 CPCH messages
             Figure 5-11 shows the frame structure of the uplink common physical channel. Each
             frame is 10 ms long, divided into 15 timeslots. And T slot = 2560 chips, equal to a power
             control period.




                           Figure 5-11 The frame structure of uplink PCPCH data and control part

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                                            k
              The data part contains 10*2 bits. Here, k = 0, 1, 2, 3, 4, 5, 6, which corresponds
              respectively to 256, 128, 64, 32, 16, 8 and 4.
              Each message contains N_Max_frames 10 ms frames at most.N_Max_frames is a
              high layer parameter. Each 10 ms frame is divided into 15 timeslots, with T slot=2560
              chips. And each timeslot contains two parts: The data part used to transport high-layer
              information and the control part of the layer 1 control information. The data part and
              control part are transmitted concurrently.
              The spreading factor of the CPCH message control part is 256.
              The Dedicated Physical Control Channel (DPCCH) includes the following: The known
              pilot bits used to support channel estimate for the relevant detection, Transmit Power
              Control (TPC), FeedBack Information (FBI) and an optional Transport Format
              Combination Indicator (TFCI).

5.4.3 Structure of the Downlink Physical Channel

             1. DPCH

              Only one kind of downlink dedicated physical channel exists, that is, downlink
              Dedicated Physical Channel (downlink DPCH).
              Within a downlink DPCH, the dedicated data is generated at layer 2 or higher layer (i.e.
              DCH) and is transmitted by time multiplexing together with the control information
              (including the known pilot bits, TPC instruction and an optional TFCI) generated by
              layer 1.Therefore, the downlink DPCH can be regarded as a time multiplexer between
              the downlink DPDCH and DPCCH.
              Figure 5-12 shows the frame structure of the downlink DPCH. Each frame is 10 ms
              long, divided into 15 timeslots. And Tslot=2560 chips, corresponding to a power control
              period.




                                    Figure 5-12 Frame Structure of the Downlink DPCH




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              The parameter “k” in Figure 5-12 determines the total number of bits in each uplink
              DPCH timeslot. It relates to the Spreading Factor (SF) of the physical channel, that is,
                           k
              1 SF = 512/2 So, the SF ranges from 512 to 4.
              There are the following two kinds of downlink DPCHs: One is TCFI included (i.e.
              services occurred simultaneously), and the other one is TFCI excluded (i.e. fixed rate
              services).

             2. The DL-DCCH of CPCH

              The spreading factor of the DL-DPCCH (message control part) is 512. Figure 5-13
              shows the frame structure of the DL-DPCCH of the CPCH.




                               Figure 5-13 Frame structure of the downlink DPCCH of the CPCH


              The DL-DPCCH of the CPCH is composed of known pilot bits, TFCI, TPC commands
              and CPCH Control Command (CCC). The CPCH control command is used to support
              CPCH signaling. There are two types of CPCH control commands: Layer 1 control
              command (message start indication) and high-layer control command (i.e. emergency
              abort command).

             3. CPICH

              The CPICH is a downlink physical channel with fixed rate (30 kbps, SF=256), used to
              transport the predefined bit/symbol sequence. Figure 5-14 shows the frame structure
              of the CPICH.




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                                              Figure 5-14 Frame structure of the CPICH


             When the transmit diversity () is used in any downlink channel of a cell, the two
             antennas will use the same channelization code and scramble to transmit CPICH. In
             this case, for antenna 1 and 2, the predefined symbol sequences are different, as
             shown in Figure 5-15. Without the transmit diversity, the symbol sequence of antenna
             1 in the figure will be used.
                 Antenna 1      A A A A A A A A A A A A A A A A A A A A A A A A



                 Antenna 2      -A -A A A -A -A A A -A A -A -A A A -A -A A A -A -A A A -A -A

                                  slot #14                       slot #0                           slot #1

                             Frame#i                                             Frame#i+1
                                                    Frame Boundary


                                  Figure 5-15 Modulation mode used for the CPICH (with A = 1+j)


             There are two types of CPICH: Primary and secondary CPICH. They have different
             purposes in the physical characteristics.
                   Primary Common Pilot Channel (P-CPICH)
                    The Primary Common Pilot Channel (P-CPICH) has the following characteristics:
                    -    The same channelization code always used
                    -    Primary scrambles used
                    -    Only one CPICH in each cell
                    -    Broadcasting in the whole cell
             The primary CPICH is the phase reference for the following downlink channels: SCH,
             primary CCPCH, AICH and PICH. It is also the default phase reference for other
             downlink physical channels.
                   Secondary Common Pilot Channel (S-CPICH)
                    The Secondary Common Pilot Channel (S-CPICH)                             has   the following
                    characteristics:
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                  -    Any channelization code with SF = 256 can be used
                  -    Primary or auxiliary scrambles may be used
                  -    Zero, one or more secondary CPICHs may exist in every cell
                  -    Transmission allowed in the whole or part of the cell
                  -    The secondary CPICH may be the reference for the secondary CCPCH and
                       downlink DPCH. In this case, the high-layer signaling will notify the UE.

             4. P-CCPCH

              The CCPCH is a downlink physical channel with fixed rate (30 kbps, SF=256), used for
              BCH transportation.
              Figure 5-16 shows the frame structure of the P-CCPCH. Compared with the downlink
              DPCH, it does not have TPC commands, TFCI or pilot bits. Within the first 156 chips of
              each timeslot, the P-CCPCH does not transmit. However, in this period, the primary
              and secondary SCHs transmit.




                                      Figure 5-16 Frame structure of the P-CCPCH


              When diversity antennas are used in the UTRAN and open loop diversities are used to
              transmit P-CCPCH, the data part of the P-CCPCH is encoded via STTD. Except #14,
              the last two bits of an even timeslot are performed STTD coding together with the first
              data bits of the next timeslot. The last two bits of the timeslot #14 are not performed
              STTD coding, but are transmitted from the two antennas with the same power, as
              shown in Figure 5-17. The high-layer signaling determines whether the P-CCPCH is
              performed STTD coding. Furthermore, by modulating the SCH, the high-layer
              signaling also points out whether the STTD codes exist on the P-CCPCH. During the
              period of power-on and handoff between cells, the UE can ensure whether the STTD
              codes exist on the P-CCPCH by receiving the high-layer message, demodulating the
              SCH or through the combination of the above two methods.




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                                 Figure 5-17 STTD codes of the P-CCPCH data symbols


             5. S-CCPCH

              Secondary CCPCH is used to transmit FACH and PCH. There are two kinds of
              S-CCPCHs: TECI included and TFCI excluded. Whether the TFCI is transmitted is
              determined by the UTRAN. Therefore, it is mandatory for all UEs to support the TFCI
              using. The possible rate set is the same as that of the downlink DPCH. Please see
              Figure 5-18 for the frame structure of the S-CCPCH.




                                      Figure 5-18 Frame structure of the S-CCPCH


              The parameter “k” in Figure 5-18 determines the total number of bits in each downlink
              CCPCH timeslot. It relates to the Spreading Factor (SF) of the physical channel,
                       k
              SF=256/2 .So, the SF ranges from 256 to 4.
              The FACH and PCH can map the same or different S-CCPCHs. If they map the same
              S-CCPCH, they can map the same frame. The main difference between the CCPCH
              and a downlink dedicated physical channel is that the CCPCH is not controlled by
              inner loop power. And the main difference between the P-CCPCH and the S-CCPCH
              is: The P-CCPCH has a pre-defined fixed rate, while the S-CCPCH can support a
              variable rate by containing TFCI. Furthermore, the P-CCPCH can transmit
              consecutively in the whole cell, however, the S-CCPCH can use the same method as


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              that of the DCH to transmit in narrow beams (only valid for the S-CCPCH of the
              transport FACH).

             6. SCH

              The Supplemental Channel (SCH) is a downlink channel used for cell search. It
              contains two channels: Primary SCH and Secondary SCH. The 10 ms radio frame of
              the primary and secondary SCHs is divided into 15 timeslots, each 2560 chips in
              length. Figure 5-19 shows the structure of the SCH radio frame.




                                 Figure 5-19 Structure of the Synchronization Channel (SCH)


              The primary SCH includes a 256-chip-long modulation code and a Primary
              Synchronization Code (PSC), which is indicated with Cp in Figure 5-19, and
              transmitted once every timeslot. The PSCs of each cell in the system are the same.
              The secondary SCH transmits repeatedly one 256-chip-long modulation code with 15
              series and one SSC together with the Primary SCH. In Figure 18, the SSC is indicated
                      i,k
              with cs , of which i = 0, 1,…, 63 is the serial number of the scramble group, and k = 0,
              1, 2,…,14 is the timeslot number. Each SSC is a code selected from 16 different
              256-chip-long codes. The sequence of the secondary SCH indicates which code
              group the uplink scramble belongs to.
              When the transmit diversity is used, the TSTD method will be adopted.

             7. PDSCH

              The Physical Downlink Shared Channel (PDSCH) is used to transport the Downlink
              Shared Channel (DSCH).
              One PDSCH corresponds to a root PDSCH channelization code or a channelization
              code under it. The PDSCH is allocated within a radio frame, on the basis of a signal
              UE. Within a radio frame, the UTRAN can allocate different PDSCHs to different UEs
              under the same PDSCH root channelization code, on the basis of code multiplexing.
              Within the same radio frame, multiple parallel PDSCHs with the same spreading factor
              can be allocated to a signal UE. This is a special example of multi-code transport. The
              frames of all PDSCHs under the same PDSCH root channelization code are
              synchronous.
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              Within different radio frames, the PDSCHs allocated to the same UE can have
              different spreading factors.
              The structure of the PDSCH frame and timeslot is shown in Figure 5-20.




                                       Figure 5-20 Frame structure of the PDSCH


              For radio frames, each PDSCH always associates with a downlink DPCH. The
              PDSCH need have neither the same spreading factor as the associated DPCH, nor
              frame alignment.
              The DPCCH part of the associated DPCH transmits all information related to layer 1,
              that is, the PDSCH does not carry any layer 1 information. To notify the UE that there
              are data to be decoded on the DSCH, two possible signaling methods, or the TFCI
              field or the high-layer signaling carried by the associated DPCH will be used.
              If the signaling method based on the TFCI is used, the TFCI will inform the UE of the
              PDSCH channelization code as well as of the transient PDSCH-related transport
              format parameters.
              In other cases, information will be given by the high-layer signaling.

             8. PICH

              The Paging Indicator Channel (PICH) is a physical channel with fixed rate (SF=256),
              used to transport paging indicators (PIs). The PICH always associates with a
              S-CCPCH which is the mapping of a PCH transport channel.
              Figure 5-21 shows the frame structure of the PICH.A PICH frame is 10 ms long,
              including 300 bits (b0, b1, …, b299).Of which, there are 288 bits (b0, b1, …, b287) used to
              transport the paging indicator. The left 12 bits are not used, which are reserved for the
              future.




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                                            Figure 5-21 Structure of the PICH


             9. AICH

              The Acquisition Indication Channel (AICH) is a physical channel used to transport the
              acquisition indicators (AIs). The AIs correspond to the signatures on the PRACH.
              Figure 5-22 shows the structure of the AICH. The AICH consists of 15 consecutive AS
              sequences, each 5120 chips in length. Each timeslot is composed of two parts: One is
              Access Indication (AI) consisting of 32 real value symbols (a 0, …, a31); the other is the
              free part of the consecutive 1024 bits, which is not the formal composition of the AICH.
              The non-transmit part of the timeslot is reserved for the future CSICH or other physical
              channels.
              The spreading factor of the AICH channelization code is 256.
              The phase reference of the AICH is the P-CPICH.




                                         Figure 5-22 Frame structure of the AICH


             10. AP-AICH

              The Access Preamble Acquisition Indication Channel (AP-AICH) is a physical channel
              with a fixed rate (SF = 256) used to transport the API of the CPCH. The API
              corresponds to the AP signature transmitted by the UE.
              The AP-AICH and the AICH can use the same or different channelization codes. The
              phase reference of the AP-AICH is the P-CPICH. Figure 5-23 shows the structure of
              the AP-AICH. The AP-AICH uses a 4096-chip-long part to transmit the API, followed
              by a 1024-chip-long free part which is not the formal composition of the AP-AICH. And
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              this free part of the timeslot is reserved for the future CSICH or other physical
              channels.
              The spreading factor of the AP-AICH channelization code is 256.




                                          Figure 5-23 Structure of the AP-AICH


             11. CD/CA-ICH

              Collision Detection/Channel Assignment Indication Channel (CD/CA-ICH) is a physical
              channel with a fixed rate (SF = 256). When the CA is inactive, it is used to transport the
              CDI, or when the CA is active, it is used to transport the CDI/CAI. Figure 5-24 shows
              the structure of the CD/CA-ICH. The CD/CA-ICH and the AP-AICH can use the same
              or different channelization codes.
              The CD/CA-ICH uses a 4096-chip-long part to transmit the CDI/CAI, followed by a
              1024-chip-long free part which is reserved for the CSICH or other physical channels.
              The spreading factor of the CD/CA-ICH channelization code is 256.




                                         Figure 5-24 Structure of the CD/CA-ICH


             12. CSICH

              The CPCH Status Indication Channel (CSICH) is a physical channel with a fixed rate
              (SF=256), used to transport the CPCH status information.
              The CSICH always associates with a physical channel used to transmit the AP-AICH
              of the CPCH, and uses the same channelization code and scrambling code as this
              channel. Figure 5-25 shows the frame structure of the CSICH. The CSICH consists of
              15 consecutive ASs, each 40 bits in length. Each timeslot is composed of two parts:
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             One is a 4096-chip-long free point, the other is Status Indication (SI) consisting of 8
             bits (b8i,….b8i+7), of which i is the access timeslot number. The CSICH uses the same
             modulation as the PICH. And its phase reference is also the P-CPICH.




                            Figure 5-25 Structure of the CPCH Status Indication Channel (CSICH)


5.4.4 Mapping from the Transport Channels and Physical Channels

             In the UTRAN, the data generated by the high layer is air transmitted by a transport
             channel of the different physical channels in the mapping physical layer. Therefore, the
             physical layer is required to have a variable rate-supported transport channel for
             providing broadband services, and at the same time, several services can be
             multiplexed to the same connection in it.
             A physical channel together with one or more physical data channels constitutes a
             Coded Composite Transport Channel (CCTrCH). In a given connection, there may be
             more CCTrCHs, but only one physical control channel.
             The mapping relation between transport channels and physical channels is shown in
             Figure 5-26.




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                        Figure 5-26 Mapping relation between transport channels and physical channels


5.4.5 Spreading and Modulation of Physical Channels

             1. Spreading of the uplink channels

              When spreading spectrum is applied in the physical channel, it includes the following
              two operations: The first is channelization operation. Each data symbol is converted
              into some chips, so the bandwidth of the signaling is enhanced. The number of chips
              converted from the data symbols is called spreading factor. The second is scramble
              operation. In this operation, scrambles are added to the spreading signals. In
              channelization operation, the data symbol of I and Q channels respectively multiply by
              the orthogonal spreading factor. And in scramble operation, the signals of I and Q
              channels multiply by the scrambles of the complex value. Here, I and Q represent the
              real part and imaginary part.

              1)   DPCH

              Figure 5-27 shows the spreading spectrum principle of the uplink DPCCH and DPDCH.
              The binary DPCCH and DPDCH used for spreading spectrum are indicated via real
              sequence, that is, the binary 0 is mapped as the real +1, and the binary 1 is mapped
              as the real -1.The DPCCH spreads to the dedicated chip rate via the channelization
                                   th
              code cc, and the n DPCCH (DPDCHn) spreads to the dedicated chip rate via the

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             channelization code cd,n. One DPCCH can transmit simultaneously together with six
             parallel DPDCHs.




                            Figure 5-27 Spreading spectrum of the uplink DPCCH and DPDCH


             After channelization, the spreading signals of the real value are performed
             emphasized processing. The DPCCH is processed via the gain factor                 βc, and
             DPDCH via      βd. After emphasized processing, the power distribution rate of the
             DPCCH and DPDCH can be adjusted.

             2)   PRACH
                 Preambles for the PRACH
             The PRACH preambles include the code of the multiplex value.
                  PRACH messages
             Figure 5-28 describes the principle of spreading spectrum and scrambling of the
             PRACH messages, which include data part and control part. The binary data and
             control part used for spreading spectrum are indicated via real sequence, that is, the
             binary 0 is mapped as the real +1, and the binary 1 is mapped as the real -1.The
             control part spreads to the dedicated chip rate via the channelization code c c, while the
             data part spreads to the dedicated chip rate via the channelization code c d.
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                     The data part of a
                     PRACH message


                   The control part of a
                    PRACH message




                                                Figure 5-28 Spreading spectrum of the PRACH messages


              After channelization, the spreading signals of the real value are performed
                                                                                                             d,   and the
                                           c.

              After emphasized processing, the code streams of the I and Q channels become those
              of the complex value. And then, the signals of this complex are scrambled via S r-msg,n
              code. The 10 ms scrambles correspond to the messages part of the 10 ms radio frame,
              e.g. the first scramble corresponds to the starting part of radio frame messages.

              3)      PCPCH
                    Preambles for the PCPCH
              The PCPCH preambles include the code of the multiplex value.
                    PCPCH messages
              Figure 5-29 describes the principle of spreading spectrum of the PRACH messages,
              which is the same as that of the PRACH messages.




                   The data part of a
                   PCPCH message


                   The control part of a
                    PCPCH message




                                                Figure 5-29 Spreading spectrum of the PCPCH messages


             2. Modulation of the uplink channel

              The chip rate of the modulation code is Mcps.
              In the uplink, the chip sequences of the complex value generated by spreading are
              modulated in QPSK mode, as shown in Figure 5-30.


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                                                Separate the real
                                                                               Pulse




                                                 imaginary part
                                                  part from the
                   Chip sequence of                                           formed
                    complex values
                     generated by
                  spreading spectrum                                           Pulse
                                                                              formed




                                                         Figure 5-30 Uplink modulation


             3. Spreading spectrum of the downlink channels

              Figure 5-31 describes the spreading spectrum for all downlink physical channels
              except the SCH, e.g. the P-CCPCH, S-CCPCH, CPICH, AICH, PICH, PDSCH and
              downlink DPCH. The physical channel without spreading spectrum includes a
              sequence of a real value symbol. The symbols of all the channels except the AICH
              may have the following values: +1, -1 and 0, of which 0 represents DTX
              (Discontinuous Transmission).
              Each pair of symbols are divided into I channel and Q channel after the serial-parallel
              conversion. The rule for division is that the symbols with even numbers are allocated
              to the I channel and those with odd numbers are allocated to the Q channel. After
              spreading spectrum, phase justification and additional aggregation, the I and Q
              channels of a real value become the sequence of a complex value. This sequence is
              scrambled by the scrambling code Sdl,n of the complex value.




                  All downlink physical
                channels except the SCH




                        Figure 5-31 Spreading spectrum for all downlink physical channels except the SCH


              Figure 5-31 describes how the different downlinks combine. The signals of the
              complex value after spreading spectrum (the arrow S in Figure 5-32) are emphasized
              via the emphasized factor G. The complex P-SCH and S-SCH are emphasized
              respectively by Gp and Gs. All the downlink physical channels are combined together
              through complex emphasis.




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                                   Figure 5-32 Spreading and Modulation of the SCH and P-CCPCH


             4. Modulation of the downlink channels

              The chip rate of the modulation code is 3.84 Mcps.
              In the downlink, the chips of the complex value generated by spreading are modulated
              in QPSK mode, as shown in Figure 5-33.



                                                                            Pulse
                                                   the imaginary
                                                   real part from
                                                   Separate the




                   Chip sequence of                                        formed
                    complex values
                                                        part




                 generated by spreading
                       spectrum                                              Pulse
                                                                            formed




                                              Figure 5-33 Modulation of the downlink channels


5.5 Physical layer Procedures
5.5.1 Synchronous Procedure

             1. Cell search

              During the cell search, the UE searches a cell and determines the downlink scrambles
              are synchronous with the frames of the common channel. Generally, it has the
              following three steps:
              Step 1: Timeslot synchronization
              At this step, the UE uses the primary synchronization code of the SCH to get the
              timeslot synchronization of this cell. Typically, it uses a matched filter to match the
              primary synchronization code which is common for all cells. The timeslot timing of this
              cell can be got from the wave peak value output by the detection matched filter.
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              Step 2: Frame synchronization and code set identification
              At this step, the UE uses the secondary synchronization code of the SCH to get the
              timeslot synchronization, and identifies the cell set found at the first step, which is
              implemented by correlating the signals received and all possible secondary
              synchronization code sequences, and identifying the maximum correlation value. The
              periodical shift of the sequence is unique, so if the code set is the same as the frame
              synchronization, it can be confirmed.
              Step 3: Scramble identification
              At this step, the UE finds the definite primary scramble used by the cell. The primary
              scramble is got by correlating all codes in the identified code set on the CPICH
              through symbols. After identifying the primary scramble, the primary CCPCH can be
              detected, so the specific BCH information of the system and cell can be read.
              If the UE has received some related information about the scrambles, step 2 and 3 can
              be simplified.

             2. Common channel synchronization

              The radio frame timing of all common physical channels can be confirmed after the cell
              search. During the cell search, the radio frame timing of the P-CCPCH can be got, and
              then the timing for these channels can be confirmed, according to the related timing
              relation between the P-CCPCH and other common physical channels.

             3. Dedicated channel synchronization

              After synchronizing the common channels, during the establishment of services and
              other correlations, the UE can synchronize uplink and downlink dedicated channels,
              according to the corresponding protocol specification.

5.5.2 Paging Procedure

              After registering a network, the UE is allocated to a paging group. If there is paging
              information sent to any UE belonging to this paging group, the Paging Indicator (PI)
              will appear periodically in the Paging Indicator Channel (PICH).
              After detecting the PI, the UE will decode the next PCH frame transmitted in the
              S-CCPCH to check whether there is paging information sent to it. When the PI
              receiving indication judgment is less reliable, the UE is also required to decode the
              PCH. The paging intervals are shown in Figure 5-34.




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                        Paging indication


                                                                      Paging messages




                                     Figure 5-34 Relationship between the PICH and PCH


             The less the PI appears, the less the UE is waken from the hibernating mode, and the
             longer the battery lives. Obviously, the compromising solution lies on the time
             corresponding to the call from the network. However, increased PI intervals can not
             infinitely extend the service life of batteries, so in free mode, the UE still has other
             tasks for processing.

5.5.3 Random Access Procedure

             During the random access procedure of the CDMA system, the near-far effect should
             be suppressed, because the power required for sending is unknown in the initialization
             transmission. The transmit power, set by using the principle of open loop power control
             and according to the absolute power got by measuring the received power, fluctuates
             greatly. The RACH of UTRAN has the following operation procedures:
                The UE decodes the BCH so as to find the usable RACH sub-channels and
                 scrambles as well as signatures.
                The UE selects a RACH sub-channel randomly from the usable access group as
                 well as a signature from the usable signatures.
                The UE measures the downlink power level, and sets initial power level for the
                 uplink RACH.Sending the selected signature in the access preamble
                The UE decodes the AICH, views the transmit power of the enhanced preamble
                 for the 1dB times step length provided by the base station. The preamble will be
                 resent in the next access timeslot.
                After detecting the AICH of the base station, the UE begins to send 10 ms or 20
                 ms messages transmitted by the RACH.
             The RACH procedures are shown in Figure 5-35. The UE keeps sending the preamble
             until it receives the confirmation of the AICH, then sends the messages.




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                                                                                        AICH


                                                                                           RACH




                                    PACH                    AICH                 PRACH
                                   Preamble               Preamble               message


                    Figure 5-35 Power change of the PRACH preamble and transmission of the messages


             When the RACH transmits data, spreading factors and data rates are variable
             between frames, which is indicated by the TFCI of the PRACH control part.Usable
             spreading factors range from 256 to 32, therefore, a signal frame in the RACH may
             have 1200 signaling symbols, which can be mapped as 600 or 400 bits according to
             the channel codes.For the maximum bit, its reachable coverage area is smaller than
             that transmitted with the minimum rate, especially when the RACH does not use
             macro diversity in the dedicated channel.

5.5.4 Access Procedure of the CPCH

             The operation of the uplink Common Packet Channel (CPCH) is similar to that of the
             RACH, but they differ in the CPCH and the first layer Collision Detection (CD) which is
             similar to the preamble symbol structure of the PRACH.




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                                                                                     CD/CA-ICH




                                                                                        AP-AICH




                                                                                           CPCH




                     CPCH preamble    AP-ICH      CPCH-CD     CPCH CAI      CPCH message

                                      Figure 5-36 Access procedure of the CPCH


             To reduce collision and interference, the CPCH Status Indication Channel (CSICH) is
             added in the new protocol version for the CPCH. The CSICH is an independent
             channel of the BS for transmission, which has indicator bits to indicate different CPCH
             status. When all the CSICH are occupied, it avoids unnecessary access attempt so
             that the throughput of the CPCH is enhanced. Only when the CSICH indicates that
             free CPCH part is available, can the UE send random access preambles on the uplink
             CPCH.
                Before the UE detects the AICH, operations of the CPCH are the same as those
                 of the RACH, as shown in Figure 5-36.
                After that, the UR sends another feature sequence Collision Detection (CD)
                 preamble with the same power level. This feature sequence is chosen randomly
                 from the given feature sequence set.
                Then, the BS will send the same feature sequence in the CD Indication Channel
                 (CD-ICH) to respond to the UE. In this way, the collision probability of the first
                 layer can be reduced.
                After receiving the correct response from the BS on the CD Indication Channel
                 (CD-ICH), the UE will transmit the CPCH messages, which may last several
                 frames.
                The CPCH Channel Assignment Indication channel (CPCH-CAI) is an option of
                 the system. It indicates the UE to use the unoccupied CPCHs in the form of
                 channel assignment. CA messages and collision detection messages are sent in
                 parallel.
             Why is the CPCH required to use the collision detection mechanism, while not
             required in the RACH?

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              First, the long-time transmission requires the collision detection mechanism of the
              physical layer. During the RACH procedure, only one RACH message may be lost due
              to collision, however, during the CPCH procedure, an undetected collision may cause
              several frames lost as well as extra interference.
              Secondly, the fast power control of the CPCH helps reduce the interference caused by
              data transfer, at the same time, it also emphasizes the importance of adding collision
              detection mechanism into the CPCH. If a UE adjusts the power via the power control
              command used for other UEs, and sends the data within several frames, it will cause
              serious interference in the cell, and more serious during the high rate data
              transmission.
              Before the transmission of CPCH messages, there is a segment of length-optional
              power control preamble for choosing. To quicken the convergence speed of power
              control, the power control preambles of eight timeslots use 2dB step length.
              The CPCH must restrict the maximum duration for transmission, because the CPCH
              does not support soft handoff and compressed mode for measuring within the
              frequency and the system. Too long transmission may cause call dropping and strong
              interference. The UTRAN set maximum CPCH transmission during service
              negotiation.

5.5.5 Downlink Transmit Diversity

             1. Space Time Transmit Diversity (STTD) based on space and time block codes

              The downlink open loop transmit diversity adopts the Space Time Transmit Diversity
              (STTD) based on the space and time block codes. In the UTRAN, STTD codes are
              optional, but the supporting for the STTD on the UE is mandatory.
              STTD codes are used in four consecutive channel bit blocks. The diagram of the
              general STTD encoder for the channel bits b0, b1, b2, b3 is shown in Figure 5-37.
              Channel encoding, rate matching and interleaving are performed in the non-diversity
              mode.




                               Figure 5-37 Diagram of the general modules for STTD encoder




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             2. Time Switched Transmit Diversity (TSTD) used for the SCH

              The TSTD can be used for the SCH. In the UTRAN, the TSTD used for the SCH is
              optional. But on the UE, supporting for the TSTD is mandatory.
              Figure 5-38 shows the structure of the SCH by using TSTD. In even-number timeslots,
              both the PSC and the SSC transmit on antenna 1, while in odd-number timeslots, both
              of them transmit on antenna 2.




                                       Figure 5-38 Structure of the SCH by using TSTD.


             3. Closed loop transmit diversity

              The general structure of the transmitter supporting DPCH closed loop transmit
              diversity is shown in Figure 5-39. Channel encoding, interleaving and spreading
              spectrum are the same as those of non-diversity mode. The compound signals after
              spreading are sent to two transmitter antennas, and are weighted by the specific
              weighting factors w1 and w2 of the antennas. Weighting factors are determined by the
              UE, and are notified of the transceiver in the UTRAN cell by using D bits of the FBI
              field in the downlink DPCCH.
              The key of a closed loop transmit diversity is calculation of the weighting factors, and it
              is divided into the following two modes, according to different calculation methods of
              weighting factors:
                  Mode 1 uses phase justification: The dedicated pilot symbols (orthogonal) used
                   by the two antennas to transmit DPCCH are different.
                  Mode 2 uses phase/amplitude justification: The dedicated pilot symbol used by
                   the two antennas to transmit DPCCH are the same.




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                Figure 5-39 General structure of the downlink transmitter supporting DPCH closed loop transmit
                                                             diversity


             Table 5-2 summarizes possible modes of open and closed loop transmit diversity
             applied in different types of downlink physical channels. The STTD and closed loop
             mode are forbidden to be used in the same physical channel at the same time. What is
             more, if any downlink physical channel uses a transmit diversity, the P-CCPCH and
             the SCH will also use it.
             Furthermore, the mode of a transmit diversity used on the PDSCH frame must be the
             same as that used on the associated DPCH. Within the duration of the PDSCH frame
             and a timeslot before this PDSCH frame, the mode (open or closed loop) of a transmit
             diversity used the associated DPCH cannot be changed. However, it is allowed to
             convert closed loop mode 1 into closed loop mode 2, or vice versa.
             The “√” under the modes of downlink physical channels indicates the mode can be
             used, and the “×” indicates it cannot.

                              Table 5-2 Types of physical channels and modes of transmit diversities

                                                 Open loop transmit diversities
                Types of physical channels                                           Closed loop transmit diversity
                                                   TSTD                  STTD
                        P-CCPCH                     X                     √                        X
                          SCH                       √                     X                        X
                        S-CCPCH                     X                     √                        X
                         DPCH                       X                     √                        √
                          PICH                      X                     √                        X
                         PDSCH                      X                     √                        √
                          AICH                      X                     √                        X
                         CSICH                      X                     √                        X


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posted:4/13/2012
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