UMTS radio access network dimensioning

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					                                                                                   A multi-service dimensioning methodology is

                                                                                   essential in order to propose a cost-effective

H. Ramzi                                                                           radio access network solution to operators.




UMTS radio access network dimensioning




       Introduction                                                               Among the various elements of a UMTS network, the
                                                                                  Radio Access Network (RAN) is a major part of the oper-
In recent months, the mobile telecom world has moved for-                         ator’s investment (see Figure 1). Hence one of the key
ward into the “UMTS era”. Governments have identified                             issues for the operator’s partner (supplier) is to propose
the number of Universal Mobile Telecommunications                                 a cost-effective RAN solution.
System (UMTS) licenses to be awarded and have defined                             This article highlights how UMTS differs from the Global Sys-
the associated legal framework. Standardization bodies are                        tem for Mobile Communication (GSM) and the main steps
fine-tuning the latest versions of the standards. Regula-                         involved in dimensioning a UMTS radio access network.
tors are setting up UMTS license award processes (beauty
contests, auctions or a mix of the two). Operators are set-
ting up critical size consortia through acquisitions or                                  What is Different about UMTS?
alliances to compete for UMTS licenses. Content providers
are building up and enhancing their mobile services and                           UMTS uses different technologies than GSM, and this
applications portfolios. Investors are carefully analyzing                        directly affects dimensioning of the UMTS RAN. The main
the UMTS value chain and its associated business plans.                           differences are:
Suppliers are optimizing their solutions (time to market,
technical features, commercial issues, etc). The press is                         • New multiple access technique: Wideband Code Divi-
speaking highly about the capabilities of UMTS, and hence                           sion Multiple Access (WCDMA).
kindling user interest in UMTS.                                                   • Multi-service traffic environment.
Operators that already own a UMTS license or are can-                             • Asynchronous Transfer Mode (ATM) transport in the
didates for one are now looking for reliable business part-                         RAN (UMTS Release ’99).
ners that can provide end-to-end UMTS solutions
(i.e. user terminals, radio access network, core and                              New Multiple Access Technique
backbone networks, service integrator capabilities and                            One of the key aspects in cellular networks is the multi-
content provider capabilities).                                                   ple access technique adopted on the air interface
                                                                                                     between the user equipment and the
                                                                                                     Node B. The chosen technique must
  Fig. 1    UMTS radio access network                                                                optimally divide the available radio
                                                                                                     spectrum (MHz) into a number of
                                                                                                     channels and define how these chan-
                                                                                                     nels are allocated to the many users
                   Radio Access                                                       ISDN           (subscribers) accessing the network.
                                              B
                     Network              No
                                            de
                                                                                                     WCDMA has been chosen for the air
                                                  RN




                                                                                                     interface to meet the constraints of the
                                                   C




                           B
                         de
                       No                 Iu-b                                                       UMTS radio interface: variable bit
                                                                    Core
                                                       Iu-r        Network
                                                                                                     rates, variable Quality of Service
             de
               B
                                            de
                                              B                                                      (QoS), etc.
           No                             No
                                  No
                                    de
                                      B                                                              To illustrate this technique, one can
                                                       RN
                                                        C




                                                                                                     imagine a “cocktail party”. Picture a
                                                                                     Internet
                              B
                                                                                                     large room with a number of partygoers
                            de
                          No
                                              B               Iu                                     who would like to simultaneously
                                            de
                                          No
                                                                                                     hold a conversation with a “super
                                                                                                     translator” in the middle of the room.



                   Alcatel Telecommunications Review - 1 st Quarter 2001     55    UMTS radio access network dimensioning
  Fig. 2    Cocktail party                                                           As the number of partygoers increases further, partygoers
                                                                                     must move closer to the translator to be heard, or must speak
                                                                                     more loudly. As a result, partygoers at the edges of the room
                                                                                     are no longer served by the cell. However, if partygoers start
                                                                                     to speak more loudly, the noise continues to increase. Thus
                                                                                     a stringent discipline needs to be implemented within the
                                 Tra Supe                                            room to resolve this problem. The translator (Node B) solves
                                    nsl r
                                       ato
                                           r                                         the noise problem by requesting that each individual
                                                                                     speaks loudly enough to be heard, but no louder. Thus power
                                                                                     control is needed to operate a WCDMA system.
                                                                                     As the useful signal is conveyed over a wide frequency band
                                                                                     (5 MHz), two multipaths can be “easily” distinguished and
                                                                                     combined by the receivers (inherent frequency diversity of
                                                                                     WCDMA). This is carried out by a Rake receiver. As two adja-
                                                                                     cent cells can use the same carrier, one user equipment can
                                                                                     be connected simultaneously to two Node Bs to benefit from
                                                                                     two-path diversity. WCDMA thus supports soft handover.
Each partygoer is carrying on a conversation in his or her
own unique language with the super translator (see Fig-
ure 2). The room corresponds to the coverage area of one                               Tab. 1      Main characteristics of WCDMA affecting the design
cell; the partygoers correspond to user equipment in the                              • WCDMA is a noise limited system
cell; the translator corresponds to the Node B; and each                              • Coverage depends on the amount of traffic in the cell
language corresponds to a given code.                                                 • No frequency planning is needed (users are differentiated by codes)
Each person sees the other conversations as noise, which
                                                                                      • Path diversity (known as “macrodiversity”) thanks to soft handover.
should do no more than cause a slight rise in the “noise
floor” or interference level. This is done by “spreading” the
transmitted signals using a direct spreading techniques,                             Hence, a specific WCDMA power budget is needed.
such as WDCMA.
As more partygoers (user equipment) enter the room                                   Different Traffic and QoS Constraints: Multi-service
(cell), the room gets noisier. The translator (Node B) hears                         Environment
more noise and so do the other partygoers. Ultimately, the                           UMTS will give subscribers access to a great variety of
noise level increases to the extent that it interferes with                          services and applications, which can be grouped into
conversations. Hence, the system capacity (simultaneous                              three main categories: always-on applications, media
number of users) is limited by the level of noise in the room                        applications and M-commerce applications, as shown in
(cell). Consequently, WCDMA is a noise-limited technique.                            Figure 3.


  Fig. 3    Typical UMTS user services



               Always-on                                                               Media                          Fun
                                                                                                                      • Games (Hangman, Poker, Quiz, …)
                                                Directories                                                           • Screen Saver
                                                • Yellow/White Pages                                                  • Ring Tone
                                                • International Directories                                           • Horoscope
      Mobile Office                             • Operator Services                                                   • Biorhythm
      • E-mail
      • Agenda                                                                          Music
      • IntraNet/InterNet                                                               • Downloading of music
      • Corporate Applications                                                          files or video clips
      • Database Access
                                       Transportation                  News
                                       • Flight/train Schedule         (general/specific)                           Location services
                                       • Reservation                   • International/National News                • Traffic Conditions
                                                                       • Local News                                 • Itineraries
                                                                       • Sport News                                 • Nearest Restaurant, Cinema, Chemist,
                                                                       • Weather                                    Parking;, ATM ...
                                                                       • Lottery Results
                         Vertical application                          • Finance News
                         • Traffic Management                          • Stock Quotes
                         • Automation                                  • Exchange Rates
                         • Mobile Branches                                                                            M-commerce
                         • Health

                                                                                           Non physical                                         Physical
                                                                                           • On-line Banking                                    On-line Shopping
                                                                                           • Ticketing                                          On-line Food
                                                                                           • Auction
                                                                                           • Best Price




               Alcatel Telecommunications Review - 1 st Quarter 2001            56     UMTS radio access network dimensioning
Each service requests a minimum bit rate                               Fig. 4      RAN dimensioning
to provide the quality of service that the
user (human or machine) expects. How-                                    INPUTS :                                                       OUTPUTS :
ever, these services are conveyed over the                               Regulators/Operators                                           A Radio Access Network solution, i.e.:
                                                                         requirements in terms of :            R.A.N                    • Node B : Number and configuration
RAN onto a standard set of bearer services.                              • Coverage,                                                    • RNC : Number and configuration
A typical set of bit rates (to be provided by                            • Traffic,
                                                                                                               Design                   • Transmission Links capacities : Mbit/s
                                                                         • QoS                                                          • Architecture : Topology
FDD/WCDMA) is as follows:

• Adaptive MultiRate (AMR) speech
  (4.75 to 12.2 kbit/s) ➜ circuit-switched
                                                                                                ALCATEL PRODUCTS PORTFOLIO :
  12.2 kbit/s.                                                                                  • Evolium™ products range
• Real-time 64 kbit/s (circuit-switched) ➜                                                      • Litespan products range
                                                                                                • DSLAM products range
  Non-real-time 64 kbit/s (packet                                                               • Broadband Wireless Access solutions
  switched).                                                                                    • Optinex™ products range
                                                                                                  etc
• Real-time 128 kbit/s and real-time
  144 kbit/s (circuit-switched) ➜ Non-real-
  time 144 kbit/s (packet-switched).
• Real-time 384 kbit/s (circuit-switched)
  ➜ Non-real-time 384 kbit/s (packet switched).                                                        UMTS RAN Dimensioning: Methodology

Throughput is not the only criterion on which the user bases                                   The aims of radio access network dimensioning are to:
his or her opinion of quality of the delivered service. Max-
imum delay and data error rates (Bit Error Ratio, Block                                        • Estimate the number and configuration of the various
Error Rate, Frame Erasure Rate) are also critical param-                                         network elements required to provide a mobile service
eters. Hence, services are also classified into:                                                 in a given region (at national or regional level), with roll-
                                                                                                 out spread over several phases (e.g. 5 years).
•    Conversational: very delay-sensitive, symmetric.                                          • Propose a RAN topology.
•    Streaming: delay sensitive, very asymmetric.
•    Interactive: round-trip-delay sensitive, asymmetric.                                      A combination of these two aspects should lead to a cost-
•    Background: most delay-insensitive, asymmetric.                                           effective solution, as shown in Figure 4.

     Tab. 2      Main characteristics of the multi-service environment                         Inputs
                                                                                               For each phase of the roll-out plan, three types of input
    • A set of bit rates: AMR (4.75 to 12.2 kbit/s); 64 kbit/s, 144 kbit/s, 384 kbit/s.
                                                                                               data are required:
    • Circuit-switched and packet-switched.
    • Asymmetry between the uplink and downlink bit rates.                                     Coverage
    • Variable QoS: mean throughput, maximum throughput, blocking probability,                 • Regions to be covered (e.g. areas with more than
      maximum delay.
                                                                                                 500 000 inhabitants).
                                                                                               • Partitioning of the region into subareas (e.g. business,
Hence, a multi-service traffic model is needed.                                                  residential).
                                                                                               • Identification of the class of each subarea (e.g. dense
Different Transport Technology: ATM Transport (Release 99)                                       urban, urban, suburban, rural). This directly translates
As a consequence of the multi-service environment, the links                                     into propagation conditions.
between network elements have to be multi-service “pipes”,
supporting variable bit rates and able to support variable QoS.                                Traffic
Release 99 of the UMTS standards assumes that ATM trans-                                       • Spectrum availability (e.g. 3 x 15 MHz).
port is used for the radio access network. Hence, one has                                      • Subscriber density per subarea (e.g. 500 subscribers
to consider the overheads inherent to ATM when evaluating                                         per km2).
the link capacity over the Iu-b, Iu-r, Iu-cs and Iu-ps inter-                                  • Subscriber profile.
faces. One must also consider the inherent Virtual Cir-
cuit/Virtual Path (VC/VP) grooming capabilities of an ATM                                      Quality of Service
transport network when designing the transmission net-                                         • Coverage probability (e.g. 95% probability of the
work topology.                                                                                   strength of the signal received within the cell being
It should be noted that Iu-r is a new interface which did not                                    above a given threshold).
exist in GSM. This interface allows soft handover between                                      • Blocking probability, maximum delay, minimum
two “adjacent” Node Bs managed by two different Radio                                            throughput.
Network Controllers (RNC), as shown in Figure 1.                                               • Service level per subarea (e.g. deep indoor coverage for
                                                                                                 a dense urban subarea, that is, a mobile service can be
     Tab. 3      Main characteristics of ATM transport technology                                provided even in a meeting room without windows).
    • Inherent overheads
                                                                                               Process
    • VC/VP grooming capabilities
                                                                                               Once all the above information has been assembled for a
                                                                                               given phase and a given subarea, the process of deriving
Hence, a new RAN architecture is needed.                                                       the number and configuration of the various network ele-



                    Alcatel Telecommunications Review - 1 st Quarter 2001                 57    UMTS radio access network dimensioning
ments can commence using the proce-                Fig. 5    Node B dimensioning process
dure outlined below.
                                                        Multiservice
                                                        Traffic Mix
Node B dimensioning
The aim of Node B dimensioning is to
determine:

• cell range;                                                              Required number
                                                                           of simultaneous
• number of carriers per sector;                                               channels         WCDMA            Cell range
                                                             Traffic                                                           Cell
• required common baseband capacity.                        Analysis                          Link Budget
                                                                                                                 Number of    count
                                                                                                Analysis          carriers
Coverage and capacity are closely linked                                                                         per sector
when using WCDMA. Hence, the Node B
dimensioning process should deal simul-
taneously with both the coverage and
capacity, as well as taking into account
the multi-service traffic mix. Figure 5                 Iterative process until convergence
shows the principle of the Node B
dimensioning process, which is applied
independently to the uplink (user equip-
ment to Node B) and to the downlink (Node B to user                • Step 5 bis: A propagation model (e.g. Okumura-Hata
equipment).                                                          or Walfish-Ikegami) is applied which reflects the con-
The analysis for the uplink comprises the following steps:           straints of the subarea in order to calculate the cell
                                                                     range. In turn, this is used to derive the site area cov-
• Step 1: Assume a typical cell range R0, which gives the            ered by a Node B taking into account the QoS con-
  cell area.                                                         straints, which then leads to the calculated cell
• Step 2: Estimate the average traffic captured within the           range and thus the cell area.
  cell area based on the traffic inputs.                           • Step 6: Continue the iteration until the calculated cell
• Step 3: Derive the number of simultaneous channels                 range equals the assumed cell range.
  (codes) required to convey the peak traffic per service,         • Step 7: Check that the cell load (i.e. noise rise) is below
  which leads to the number of channels required to sup-             a certain level. If not, add a new carrier to split the
  port the peak mix of traffic. Figure 6 illustrates the             traffic.
  problem.
• Step 4: A statistical approach is then used to calculate         The analysis for the downlink comprises the following
  the aggregate rise in noise generated by this traffic mix.       steps:
• Step 5: The aggregate noise rise is fed into the multi-ser-
  vice power budget, which is used to determine the Max-           • Step 1: Assume a typical cell range, and thus the cell
  imum Allowable Path Loss (MAPL) or attenuation. The                area.
  power budget takes into account the performance of the           • Step 2: Based on traffic inputs, identify the average
  products involved (e.g. transmitted power, feeder losses,          traffic captured within this cell area.
  antenna gain, sensitivity) and degradation of the radio path     • Step 3: Determine the required number of simulta-
  (propagation attenuation, shadowing effects, multipath             neous channels (codes) needed to convey the peak traf-
  effects) when calculating the MAPL, as shown in Figure 7.          fic for each service.


  Fig. 6   Required number of simultaneous channels

                                     Air interface "pipe"                                        Peak Traffic = worst case




   Video-
   conferencing                                                      Average traffic
   Voice, SMS                                                                                                                  Number
   Shopping on line                                                                                                            of radio
   Web browsing                                                                                                                resources
   File transfer
                                                                                             Aggregate traffic
   Interactive games



                                                                       Busy hour




             Alcatel Telecommunications Review - 1 st Quarter 2001    58    UMTS radio access network dimensioning
• Step 4: Calculate the mean power                 Fig. 7    Power budget
  required for one user of each service.
• Step 5: Based on a knowledge of                                                 Antenna Gain
  the uniform distribution of user                                                                        Radio Path Degradation :
                                                                                                      Attenuation, shadowing, Multipath
  equipment over the cell area (with
  or without soft handover), use a
  statistical approach to determine
  the aggregate Node B transmit
  power corresponding to the traf-                 Feeder Losses
  fic mix.                                                                 BS
                                                            Sensitivity
• Step 6: The aggregate Node B trans-
  mit power is fed into the multi-service
  power budget, which is used to
  determine the MAPL and hence the
  cell range
• Step 7: The iteration is continued
                                                                                        Sensitivity
  until the assumed cell range leads to
  the maximum transmit power of the
  Node B

Having calculated the cell ranges for
both the uplink and downlink, the
most limiting link is selected. The analysis for the non-                   uplink and the transmitted power on the downlink.
limiting link (uplink or downlink) is then repeated, tak-                 • Consistent multi-service power budget analysis.
ing into account the selected cell range (i.e. decrease user              • No a priori assumptions are made about the limiting
equipment transmit power or decrease the Node B                             link (uplink or downlink), neither for coverage nor for
transmit power).                                                            capacity.
In summary, The Node B dimensioning methodology                           • One absolute cell range for all services, ensuring con-
developed by Alcatel involves:                                              tinuous coverage for all services.

• Consistent multi-service traffic analysis.                              Figure 8 shows some screenshots from the Alcatel
• Statistical approach to determine the noise rise on the                 UMTS radio dimensioning tool.


  Fig. 8   Screenshots taken from the Alcatel UMTS radio dimensioning tool




             Alcatel Telecommunications Review - 1 st Quarter 2001   59    UMTS radio access network dimensioning
  Fig. 9   Screenshots of radio network planning tool




                   Up to


                                        Database                                 Coverage prediction




                 Traffic map                                Pilot coverage                               Soft handover areas




Radio network planning study                                                  management limitation constraint, it is possible to cal-
Having dimensioned the Node B, the next stage is to carry                     culate the minimum number of RNCs required to han-
out a Radio Network Planning (RNP) study. This requires                       dle the Node Bs (number of Node Bs ÷ maximum num-
accurate data (RNP databases) related to the area being                       ber of Node Bs per RNC). This is designated NR1.
studied, including such information as topography and                     •   Step 2: From the average traffic assumptions provided
morpho-class (urban, suburban, rural, etc). RNP studies                       as input and from the traffic limitation constraint, one
are generally focused on key target areas (“hot spots”)                       can determine the minimum number of RNCs required
and are carried out before site search or site acquisition.                   to handle the average traffic (NR2av).
Both new sites and existing GSM sites can be considered.                  •   Step 3: Knowing the average traffic per RNC, it is pos-
These studies are carried out using a specialized RNP tool.                   sible to calculate the peak traffic to be handled per
It should be mentioned that in GSM, RNP studies were                          RNC (statistical distribution function). It is important
mainly focused on predicting the coverage area. How-                          to check that the traffic capacity of the RNC being
ever, in the case of UMTS, the RNP studies consider not                       considered is sufficient to carry this peak traffic. If
only the coverage, but also noise rise analysis, capac-                       not, N R2av is increased, or a larger configuration is
ity planning, soft handover areas, etc, as shown in Fig-                      considered, and a new peak traffic per RNC is cal-
ure 9.                                                                        culated.
                                                                          •   Step 4: Number of required RNCs is NR; the greater of
RNC Dimensioning                                                              NR1 and NR2peak is selected.
Dimensioning of the RNC is largely conditioned by its                     •   Step 5: Knowing the peak user traffic per RNC, it is pos-
characteristics. The ones affecting the dimensioning                          sible to calculate the incoming aggregate traffic on the
process are:                                                                  Iu-b interface (number of STM-1s) as well as the aggre-
                                                                              gate outgoing traffic on the Iu-cs, Iu-ps and Iu-r inter-
• Traffic limitations, that is, the maximum throughput per                    faces (cf. next paragraph). Hence, a final check is made
  RNC:                                                                        on the connectivity limitation constraint.
  - maximum circuit-switched throughput (Erlangs);
  - maximum packet-switched throughput (Mbit/s).
• Management limitations, that is, the maximum number
  of Node Bs managed by an RNC.                                               Fig. 10 Iu-b dimensioning
• Connectivity limitations, that is, the maximum number
  of connections towards the Iu-b, Iu and Iu-r interfaces.                                                 ATM                   O&M
                                                                              Calculated by means of    Overheads               Traffic
                                                                              an analytical approach      Factor
The traffic limit for a given RNC is a tradeoff between the
circuit-switched throughput and packet-switched
throughput.                                                                    Average        Peak                                           Total
                                                                                Traffic      Traffic                                      Throughput
Dimensioning the RNC comprises the following five
steps:
                                                                                Soft          30%                   Signaling
• Step 1: Node B dimensioning determines the total                            Handover                                Factor
  number of Node Bs for the target area. Based on the



             Alcatel Telecommunications Review - 1 st Quarter 2001   60       UMTS radio access network dimensioning
 Fig. 11 Iu-cs and Iu-ps dimensioning                                                dimensioning. The total capacity required for the Iu-r inter-
                                                                                     face is a proportion of the total Iu user traffic.
                                 ATM
                              Overheads
                                Factor                                               Architecture
                                                                                     The purpose of “Architecture” is to propose an overall
                                                                                     topology for the radio access network, that is, to identify
     RNC          CS & PS                                Total                       RNC locations, to define the type of interconnection
 Dimensioning       Peak                                 I u-cs and I u-ps
                   Traffic                               Throughput                  between the Node Bs and the RNC (daisy chain, star,
                  per RNC
                                                                                     ring), and, if necessary, to identify transmission nodes.
                                          Signaling                                  Here we look at several possible RAN transmission solu-
                                            Factor                                   tions which take into account UMTS traffic from the
                                                                                     Node Bs and GSM traffic from the Base Transceiver Sta-
                                                                                     tion (BTS). Node Bs generate ATM cells that are mapped

Interface Dimensioning                                Fig. 12 Multiplexing of GSM and UMTS traffic within an SDH node
Iu-b
The Iu-b interface is dimensioned by
                                                                                                     de
calculating the capacity of the “pipe”                                                             No
coming from the Node B. This pipe                                                                   B               de
                                                                                                                  No
                                                                                                                   B                  BTS
should convey:
                                                                    de               de
                                                                  No
                                                                   B               No
• Peak user traffic (aggregated),                                                   B
  including soft handover traffic.
• Overheads for ATM/ATM Adaptation                                                                                                             RN
                                                                                                                                                   C
  Layer (AAL), signaling and Opera-
                                                            de
                                                                                             Tr Ba ra
  tions and Maintenance (O&M).                            No
                                                                                               an ck di
                                                                                                (o



                                                           B                                      sm bo o S
                                                                                                   pt
                                                                                                     ic


                                                                                                      is ne DH
                                                                                                        /


                                                                                                        si
There are two steps in this process:                                                                      on )

• Step 1: Alcatel has developed an ana-                                 BTS
  lytical approach to determine the
  aggregate peak traffic at Node B
  level. This approach requires the fol-
                                                                                                                            BS
  lowing parameters as inputs: number                                                                                         C
  of users of service i (active or not);
  channel bit rate for service i; session
  inter-arrival rate for service i; session
  length for service i; activity factor for
  service i; and percentage of users in
  soft handover.                                      Fig. 13 ATM concentration of GSM and UMTS traffic
• Step 2: The ATM/AAL, signaling and
  O&M overheads are then added to the
  peak traffic calculated in Step 1 (see
  Figure 10).                                                                                               de
                                                                                                         No
                                                                                                          B            de
                                                                                                                    No
                                                                                                                     B
Iu-cs and Iu-ps
                                                                                 de           de             de
The dimensioning process for Iu-cs and                                        No
                                                                               B           No             No
                                                                                            B              B                                   S
Iu-ps calculates the peak user through-                                                                                                     BT
put for both the circuit-switched and
                                                                                                                                                   RN
packet-switched streams. Hence, the                                                                                                                    C
total throughputs for both these streams
                                                            de                                             Tra
(i.e. Iu-cs and Iu-ps) can be determined                 No
                                                          B
                                                                                                   (op         n
                                                                                                      tic Back smis
by adding the ATM/AAL, signaling and                                                                     /ra bo sio
                                                                                                             dio ne n
O&M overheads (see Figure 11).                                                                                   SD
                                                                                                                    H)
                                                                                 S
                                                                              BT
Iu-r
The Iu-r interface carries the traffic
generated by users in soft handover
between two Node Bs managed by dif-
                                                                                                                                 BS
                                                                                                                                  C




ferent RNCs. Iu-r user traffic is a portion
of the Iu-b user traffic. Margins for
ATM/AAL overheads and signaling have
to be taken into account, as for Iu



                Alcatel Telecommunications Review - 1 st Quarter 2001         61      UMTS radio access network dimensioning
onto Plesiochronous Digital Hierarchy             Fig. 14 UMTS is ATM concentrated, while GSM is SDH multiplexed
(PDH) or Synchronous Digital Hier-
archy (SDH) frames, whereas voice
                                                                                                    de
traffic generated by the BTS are                                                                 No
                                                                                                  B               de
mapped onto channeled E1 (PDH).                                                                                No
                                                                                                                B
                                                                         de          de              de
Case 1                                                                No
                                                                       B          No              No
                                                                                   B               B
Both GSM and UMTS traffic are mul-                                                                                                       S
                                                                                                                                      BT
tiplexed within an SDH node. ATM                                                                                                              RN
traffic generated by the Node Bs is                                                                                                                C
conveyed over PDH or SDH and mul-                      de                                            Tra
                                                    No                                     (op           n
tiplexed together with GSM traffic                   B                                          tic Back smis
                                                                                                   /ra bo sio
coming from BTS within an SDH node                                                                     dio ne n
                                                                                                           SD
(e.g. Add/Drop Multiplexer; ADM).                                                                             H)
The aggregate streams (SDH VCs) are                                      S
                                                                      BT
transparently conveyed over the SDH
transmission backbone (see
Figure 12).
This architecture is recommended if




                                                                                                                          BS
                                                                                                                             C
SDH nodes already exist in the net-
work at the Point Of Concentration
(POC), and if overall UMTS traffic at
this point is quite low (< 30 x E1) and
does not require any ATM concentra-
                                                 Fig. 14b UMTS is ATM concentrated while GSM is SDH multiplexed (optimized)
tion.

Case 2
Both GSM and UMTS traffic are                                                                                       de
aggregated within an ATM switch.                                                                                 No
                                                                                                                  B
GSM traffic, adapted in AAL-1 (circuit                                 de                          de
                                                                    No             de           No
emulation) and encapsulated in ATM                                   B          No
                                                                                 B               B
cells, is concentrated together with
UMTS traffic generated by Node Bs                                                                                                            RN
within an ATM switch. The aggre-                                                                                                               C
                                                         de
gated stream is then carried on the                   No
                                                       B                                          Tra
                                                                                          (op         n
transport backbone. This minimizes                                                           tic Back smis
the bandwidth required in the trans-                                                            /ra bo sio
                                                                                                    dio ne n
mission backbone (see Figure 13).                                                                       SD
                                                                        S                                  H)
This architecture is recommended if                                  BT
the SDH nodes already exist, UMTS
traffic is very high and there is only
a moderate amount of GSM traffic (a
few E1s). It becomes mandatory if the
                                                                                                                        BS
                                                                                                                          C




existing transport backbone cannot
support the new UMTS “incoming”
traffic without a capacity upgrade.

Case 3
UMTS traffic (ATM) is concentrated within an ATM                              Fig. 15 RAN architecture
switch, while GSM traffic is multiplexed within an SDH
node. The aggregated ATM stream is then multiplexed
                                                                                                                         Rural
within an SDH node together with the GSM traffic (see                                      Suburban                                 Node B
Figure 14).
This architecture is recommended if SDH nodes already                                                                Transmission
exist, UMTS traffic is very high and GSM traffic is very                         Node B                                  Node
high. No ATM engineering is needed for GSM traffic in
                                                                                 Core                                               1xE1
this case. GSM traffic is treated independently.                                Network                                2xE1
Figure 14b shows an optimized implementation of this                                                           RNC
                                                                                                    RNC
case based on the Alcatel O-MSN (Optinex™ Multi-ser-
vice Node). An ATM switch – IP/SDH/ATM (ISA)                                                            4xE1
board – is integrated in the SDH node and internal SDH                        Node B
multiplexing (no external cabling) is performed.
                                                                                                Urban




            Alcatel Telecommunications Review - 1 st Quarter 2001      62     UMTS radio access network dimensioning
         Typical RAN Dimensioning Results                                                           Conclusion

Let us assume an area to be covered made up of three                                         Dimensioning is the first step in the design of a UMTS
subareas – urban, suburban and rural – with rollout                                          Radio Access Network. It is important to note that it is
spread over three phases. Typical examples of RAN                                            very different from GSM dimensioning. The characteris-
dimensioning results related to this area are given in                                       tics of UMTS introduce greater complexity and make the
Tables 4 to 6.                                                                               RAN designers’ task more interesting!
                                                                                             In order to propose a cost-effective RAN solution to its
                                                                                             partners, Alcatel has developed an innovative multi-ser-
  Tab. 4      Node B results showing the number and con-                                     vice dimensioning methodology which addresses the spe-
              figuration of network elements in the RAN                                      cific features of UMTS.
                      Phase 1                  Phase 2                   Phase 3             The technical parameters involved in this methodology,
                                                                                             as well as the process itself, are regularly enhanced based
 Urban          S333            0        S333            0        S333             8
                                                                                             on feedback from simulations and field trials conducted
                S222            0        S222            6        S222             6
                                                                                             by Evolium SAS, the joint Alcatel-Fujitsu venture. s
                S111         10          S111            4        S111             4
 Suburban       S222            0        S222            0        S222             10
                                                                                              Bibliography
                S111         20          S111          30         S111             20
 Rural           01             0         01             0         01              12         1. H. Biscéré: “RNC and UTRAN Interfaces dimensioning”,
 * Cumulative figures                                                                            September 2000.
 S333 Three-sector site with three carriers per sector                                        2. Y. Dupuch: “UMTS Radio dimensioning rules”, September
 S222 Three-sector site with two carriers per sector                                             2000.
 S111 Three-sector site with one carrier per sector
 O1 Omnidirectional site with one carrier                                                     3. M. Bourguignon: “UTRAN Transmission network solu-
 Bold figures indicate upgraded sites (additional carrier) from the previous                     tions”, November 2000.
 phase.



  Tab. 5      RNC results showing the number and configura-                                               Hani Ramzi is Director of Mobile Network
              tion of the network elements in the RAN                                                     Design within the Alcatel Mobile Communication
         Phase 1                       Phase 2                      Phase 3                               Division in Vélizy, France.
 Large RNC            0     Large RNC             0          Large RNC         1
 Medium RNC           0     Medium RNC            1          Medium RNC        1
 Small RNC            1     Small RNC             1          Small RNC             0

 The figures in bold represent the upgraded RNC (in capacity)


  Tab. 6      RAN interface results

    lu (lu-cs+lu-ps)                 Phase 1          Phase 2            Phase 3

    Large BSC                                                            70 Mbit/s

    Medium BSC                                        50 Mbit/s          50 Mbit/s

    Small BSC                       30 Mbit/s         30 Mbit/s



These figures are provided to illustrate the types of output.
Accurate figures are derived on a case-by-case basis.

Architecture
Figure 15 shows a typical RAN architecture.




                 Alcatel Telecommunications Review - 1 st Quarter 2001                  63    UMTS radio access network dimensioning