Date post: | 19-Dec-2015 |
Category: |
Documents |
Upload: | lara-mcgowan |
View: | 214 times |
Download: | 0 times |
WCDMA Radio Functionalities
Chapter 11
OBJECTIVES:Upon completion of this chapter the student will be able to:
List the UTRAN functions
Describe soft and softer handover
Describe handover to and from GSM (inter-system handover)
Describe admission and congestion control
Describe channel rate switching
Describe (intra-system) inter-frequency handover
WCDMA Radio Network Design
ll aa nn kkBB
iioonnaall llyy
ttnneettnnII
EN/LZT 123 6039 P1E
11 WCDMA Radio Functionalities
11 WCDMA Radio Functionalities
Table of Contents
Topic Page
INTRODUCTION......................................................................193
RADIO ACCESS BEARERS (RABS) AND SERVICES................................193
RADIO NETWORK FUNCTIONALITIES......................................................194
TRANSPORT NETWORK FUNCTIONALITY...............................................195
OTHER SERVICES......................................................................................196
FUNCTIONALITY STILL UNDER STANDARDIZATION..............................196
RADIO NETWORK FUNCTIONALITY....................................198
ADMISSION CONTROL...............................................................................198
BLOSSOMING AND WILTING.....................................................................198
CHANNEL SWITCHING...............................................................................199
CONGESTION CONTROL...........................................................................199
DOWNLINK POWER ALLOCATION...........................................................200
DOWNLINK POWER DRIFT PREVENTION................................................200
POWER CONTROL.....................................................................................201
RADIO CONNECTION SUPERVISION........................................................201
SOFT/SOFTER HANDOVER.......................................................................202
SYNCHRONISATION FUNCTIONS........................................203
FRAME AND NODE SYNCHRONISATION.................................................203
NETWORK SYNCHRONISATION...............................................................203
OTHER SERVICES/FUNCTIONALITY STILL UNDER STANDARDIZATION...............................................................204
GSM INTEROPERABILITY..........................................................................204
GSM HANDOVER........................................................................................204
CAPACITY IMPROVING FEATURES..........................................................205
TRANSMIT DIVERSITY...............................................................................206
IMPROVED POSITIONING..........................................................................207
EN/LZT 123 6039 P1E – I –
WCDMA Radio Network Design
– ii – EN/LZT 123 6039 P1E
11 WCDMA Radio Functionalities
INTRODUCTION
The functions/functionalities of UTRAN can roughly be divided into
Radio Access Bearers (RABs) and services
Radio network functionalities
Transport network functionalities
Synchronization functions
RAN management functions
Other services
Functionality still under standardization
This chapter concentrates on the radio network functionalities but some information about other functions are given.
RADIO ACCESS BEARERS (RABS) AND SERVICES
Conversational RAB for AMR speechThis RAB supports AMR speech, 12.2 kbps (full rate). Support for voice activity detection and silence descriptor is provided by utilizing DTX. DTX is used independently in the uplink and the downlink.
Interactive RAB. This RAB supports packet switched best effort services up to 384 kbps (384 kbps in downlink and 64 kbps in uplink) with and without prioritization. Transport formats for lower rates than 384 kbps are supported as well. The channel rate switching functionality decides which transport format to use.
Conversational RAB for UDI 64 kbps service (circuit data)RAB to support UDI guaranteed 64 kbps circuit switched service. This RAB can be used for circuit switched based multimedia applications using e.g. H.324M.
Streaming RAB for NT CS data. RAB used e.g. to support fax and V.90 modem service.
Multiple simultaneous RABs2 simultaneous RABs per UE is supported. The multiple RABs can be a mix of RABs for circuit and packet switched services.
EN/LZT 123 6039 P1E – 193 –
WCDMA Radio Network Design
Emergency call This function provides support for Emergency Calls. The support includes prioritization of the call.
PositioningA Cell based positioning method, i.e.; the position is determined with granularity of cell. Positioning with a better accuracy e. g. based on Round Trip Time measurements is also provided.To exploit GPS capability UTRAN can also offer the possibility to send the GPS parameters transparently between the CN and the UE.
Transparent Message TransferTransfer of control plane messages e. g. connection management, mobility management and Short Message Services (SMS), transparently through the UTRAN between core network and UE is supported.
Cell Broadcast Possibility to broadcast localized information, e.g. SMS cell broadcast
RADIO NETWORK FUNCTIONALITIES
These are treated in more detailed in a section that follows but the more important functionalities are
Soft and softer Handover A UE in soft handover mode is communicating with two or more RBSs, while a UE in softer handover communicates with multiple sectors at the same RBS. The soft/softer handover functionality includes decision on how many cell carriers to connect in soft/softer handover and functionality for setting up and releasing connections between the RBS and the UE. Soft/softer handover is supported for dedicated channels. During soft handover the macro diversity combining is conducted in the RNC. For softer handover, maximum ratio combining is conducted in the RBS.
Handover to and from GSM. The feature (inter system handover) planned for the first releases is based on congestion and on loss of coverage.
Admission and Congestion Control Admission control blocks new incoming calls as well as handover attempts when the load in the system is high. The admission functionality is also capable of including priority, for instance emergency calls, in the admission decision.Congestion control is used to resolve overload in both the uplink and the downlink. In case of overload, congestion
– 194 – EN/LZT 123 6039 P1E
11 WCDMA Radio Functionalities
control reduces bit rates of delay tolerant existing connections or as a second option, removes existing connections.
Channel switchingChannel switching includes channel type and rate switching. Channel type switching is used to switch between common and dedicated channels both in the uplink and downlink. The activation of the switching is based on data activity in order to assure an efficient usage of the dedicated channel resources. The channel rate switching functions allows for changes of transport format on the air interface, e.g. to increase/decrease the bit rate. The activation of the switching is based on changes in a user’s bit rate demand, due to addition or removals of RABs.
Inter-frequency handoverThe system supports inter-frequency HO between cellcarriers on different frequencies. The handover could be initiated both for capacity reasons, e.g. load sharing, and for mobility reasons.
TRANSPORT NETWORK FUNCTIONALITY
ATM interfacesThere are a number of different ATM interfaces available for both RNC and RBS:E1: 2MbpsJ1: 1.5Mbps, T1: 1.5Mbps, E3: 34Mbps, T3: 45Mbps, STM-1: 155Mbps
ATM PVC and PVP including VC cross connectAll logical ATM links for Iu and Iub are set up as permanent virtual ATM connections. These are then used either for user plane with AAL2 or AAL5, control plane with AAL5 or O&M with IP over AAL5.The PVCs and PVPs can be set up either directly between two nodes or via a third (or more) node(s), i.e. includes cross connect functionality.PVPs are used when handling a set of PVC as a single entity e.g. for cross connect and VP shaping. PVPs are normally used for connection of UTRAN nodes to ATM backbone networks.
Switched AAL2 connections AAL2 switched connections are used on Iu for circuit and
EN/LZT 123 6039 P1E – 195 –
WCDMA Radio Network Design
speech connections and on Iub for all connections RBS-RNC.
ATM on fractional transmission over E1/T1.This is mainly used at smaller installations in the initial phase of UTRAN introduction, when capacity requirements are low. The function “ATM on fractional” on E1/T1 interfaces allows for using parts of STM transmission connections (e.g. E1, T1 etc) for ATM traffic.
Link redundancyFor control plane and O&M signaling the 1+1link redundancy is achieved by a loss less switch over. For user plane the data is distributed over both (all) links (1+1 or n+1). User plane links can hence be configured for optimal cost with some service degradation at loss of a link, or for maximal availability with over provisioning of link capacity.
Circuit emulation for transmission sharing (for E1/T1/J1)The Circuit emulation function allows STM connections terminated on E1/T1/J1 port (or a fractional of it) to be carried over ATM using ATM AAL1.
OTHER SERVICES
These services include
SMS cell broadcast
GSM interoperability
GSM handover
Inter-frequency handover
Packet data scheduling
Transmit diversity
Improved positioning
FUNCTIONALITY STILL UNDER STANDARDIZATION
Packet data up to 2 Mbps
Support for TDD
Other Radio Network capabilities
– 196 – EN/LZT 123 6039 P1E
11 WCDMA Radio Functionalities
Adaptive antennas
Interference Cancellation
Hierachichal Cell Structure (HCS)HCS is used to achieve high capacity at a low cost in high traffic density areas by introducing different cell layers in the system, i.e. macro layer, micro layer and perhaps also a pico layer.
Access to multiple MSC/SGSN from one RNC. (Virtual RNC)The system allows for one physical RNC node to be connected to several MSCs and SGSNs.
IP transport network
EN/LZT 123 6039 P1E – 197 –
WCDMA Radio Network Design
RADIO NETWORK FUNCTIONALITY
The radio network functions provide a means for a fully mobile WCDMA network with high quality. Further, as power is the common shared resource in WCDMA. A large effort is put on different power management schemes in order to assure good performance. Some of the radio network functions are described below.
ADMISSION CONTROL
Guarantees the overall Quality of Service bycontrolling the number of users
New users blocked above this point
interference
Capacity / LoadPlanned load
Planned coverageCoverage
User added
Admission threshold
Figure 11-1 Admission control
Admission control blocks new incoming calls as well as handover attempts when the load in the system is high (Figure 11-1). By doing that, the call dropping probability is reduced. Admission control is used in both the uplink and the downlink. The admission decision is based on air interface load, by using measurements of uplink interference, downlink output power as well as the actual number of users. The admission functionality is also capable of including priority, for instance emergency calls, in the admission decision.
BLOSSOMING AND WILTING
Blossoming and wilting enables to gradually increase the output power at start up (or gradually power decrease at shut down) instead of initially letting the RBS transmit with maximum output power. This ensures graceful start up/shut down, to retain existing calls. This functionality has been proven to be very usefull in Ericsson’s commercial IS-95 networks.
– 198 – EN/LZT 123 6039 P1E
11 WCDMA Radio Functionalities
CHANNEL SWITCHING
Channel switching includes channel type and rate switching. Channel type switching (Figure 11-2) is used to switch between common and dedicated channels both in the uplink and downlink. The activation of the switching is based on data activity in order to assure an efficient usage of the dedicated channel resources.
Release dedicated channel
Random-AccessRequest
Random-Access Channel
Packet Packet Packet
Dedicated Channel
TTime-out
Switch to common
Switch todedicated
Random-AccessRequest
User 1 User 2
Figure 11-2 Channel type switching
The channel rate switching functions allows for changes of transport format on the air interface, e.g. to increase/decrease the bit rate. The activation of the switching is based on changes in a user’s bit rate demand, due to addition or removals of RABs.
CONGESTION CONTROL
Figure 11-3 Congestion control
EN/LZT 123 6039 P1E – 199 –
WCDMA Radio Network Design
Congestion control is used to resolve overload in both the uplink and the downlink (Figure 11-3). It uses the same measurements as the admission control. In case of overload, congestion control reduces bit rates of delay tolerant existing connections or as a second option, removes existing connections.
DOWNLINK POWER ALLOCATION
This functionality allows for the possibility to set the output power of the common control channels as well as the possibility to set different maximum output powers of the downlink channels traffic channels (depending on the RAB). Since the downlink output power defines the coverage for individual channels, it is possible to design the system in such a way that the downlink data rate can be higher than the uplink data rate for users on cell border.
DOWNLINK POWER DRIFT PREVENTION
During period of soft handover, the output power from the different RBSs may drift apart. This feature offers a modified type of power control during the soft handover periods in order to prevent the drift (Figure 11-4).
UP / DOWN(closed loop)
RBS1 RBS2
FER/BERDataComb.
MRC
Mitigation of power drift
Figure 11-4 Power control during soft handover
– 200 – EN/LZT 123 6039 P1E
11 WCDMA Radio Functionalities
POWER CONTROL
F a s t q u a l i t y b a s e d p o w e r c o n t r o l- Im p r o v e s c a p a c i t y .
O u t e r lo o p p o w e r c o n t r o l
O p e n lo o p p o w e r c o n t r o l
F le x ib lep o w e r a l lo c a t io n
B lo s s o m&
w i l t
Figure 11-5 Power control
The power control is one of the most important functions in a WCDMA network (Figure 11-5). Ericsson’s products support three different types power control, namely inner loop power control, outer loop power control and open loop power control.
The inner loop power control is C/I based and consists of two parts. In the uplink, the quality of the received signal is compared to an Eb/Io target. Based on the comparison a power control command is transmitted to the UE. In the downlink, the output power per TCH is adjusted according to the power control command from the UE.
The purpose of the outer loop power control is to adjust the Eb/Io so that the quality of a connection meets the set FER/BER target. The uplink outer loop is conducted after diversity combining.
The open loop power control is used when transmitting on common channels.
RADIO CONNECTION SUPERVISION
The purpose of this function is to detect lost radio connections. The lost connections are released to free up the resources.
EN/LZT 123 6039 P1E – 201 –
WCDMA Radio Network Design
SOFT/SOFTER HANDOVER
A lg o r ith m- R e la t iv e th re s h o ld s
m in im iz e s th e n u m b e r o fm o b ile s in s o ft h a n d o v e r
T im e
C /I
A d d B D e le te A
A d dm a rg in
D ro pm a rg in
B A
Figure 11-6 Soft/softer handover
A UE in soft handover mode is communicating with two or more RBSs (Figure 11-6), while a UE in softer handover communicates with multiple sectors at the same RBS. The soft/softer handover functionality includes decision on how many cell carriers to connect in soft/softer handover and functionality for setting up and releasing connections between the RBS and the UE. Soft/softer handover is supported for dedicated channels. Any combination of soft and softer handover is possible up to four handover legs in the active set.
During soft handover, the macro diversity combining, namely selection diversity, is conducted in the RNC. For softer handover , maximum ratio combining is conducted in the RBS. The soft handover functionality is also supported when a UE moves from one RNS to another.
– 202 – EN/LZT 123 6039 P1E
11 WCDMA Radio Functionalities
SYNCHRONISATION FUNCTIONS
FRAME AND NODE SYNCHRONISATION
Node synchronisation aligns the TX/RX parts of the RBSs with the RNC and is necessary for soft handover. Frame synchronisation guarantees that the same frame (sent from the RNC in UTRAN) is transmitted over the air interface at the same time from RBSs in macro diversity operation. Another objective is to select/combine correct UE frames (from different RBSs) in the RNC.
NETWORK SYNCHRONISATION
Synchronises the UTRAN nodes to the transport network node(s) with respect to clock references in order to regain and distribute synchronisation references in a master-slave approach within UTRAN (primarily RNC-RBS). The transport network can either be built with external ATM/PDH/SDH equipment or with direct connections, i.e. own fibre/copper lines or microwave systems.
EN/LZT 123 6039 P1E – 203 –
WCDMA Radio Network Design
OTHER SERVICES/FUNCTIONALITY STILL UNDER STANDARDIZATION
GSM INTEROPERABILITY
Handover from WCDMA to GSM means that WCDMA can be deployed in islands overlaying GSM. As the demand for WCDMA increases, those islands can be expanded. To be able to limit the initial deployment to large cities, the initial investment in WCDMA can be kept low. Handover from GSM to WCDMA allows access to WCDMA services. Further, if RANOS is used, the management functions for intersystem support can be added in order to make the operation and maintenance efficient and easy.
GSM HANDOVER
Inter frequency measurements are needed tosupport inter system handover
Compressed mode supports these measurements
Inter system
WCDMAGSM
time for measurementsTf = 10 ms
SF=SF0
SF=SF0/2SF=SF0
Compressed mode
Figure 11-7 Inter system handover
This function provides the means for intersystem handover from UTRAN to GSM and from GSM to UTRAN. Handover to GSM is triggered due to loss of WCDMA coverage. Handover from GSM may be triggered in order to access UMTS services1. To conduct intersystem handover, measurements are needed on the GSM system. Compressed mode is supported in order to conduct such measurements (Figure 11-7).
1 The availability of handover from GSM to UTRAN is dependent of the GSM standardisation.
– 204 – EN/LZT 123 6039 P1E
11 WCDMA Radio Functionalities
CAPACITY IMPROVING FEATURES
Inter-frequency Handover
MicroMacro
• Support of multiple carriers in high capacity regions• Load sharing to increase performance
Load distributed between carriers
Figure 11-8 Inter frequency handover
This function supports handover between cell-carriers belonging to different WCDMA frequency layers (Figure 11-8). To be able to measure the quality on other frequencies prior to inter- frequency handover compressed mode is utilised.
Packet Data Scheduling
extra capacitycan be givento packet datausers
load
time
max planned load
• Load sharing in time results in a high capacity• Smooth interference levels in the system
Figure 11-9 Packet scheduling
Packet data scheduling of interactive RABs is used to assure that the planned spectrum is used efficiently (Figure 11-9). This is achieved by continuously update the transport format for the interactive RABs. The aim is to maximize the bit rate for the packet data users, without exceeding the capacity that the system is planned to handle. This functionality relies on the
EN/LZT 123 6039 P1E – 205 –
WCDMA Radio Network Design
same measurements that are used for admission and congestion control.
TRANSMIT DIVERSITY
As transmit diversity improves the downlink capacity, it can be viewed as one expansion possibility. In areas with high capacity demand, it is of course also possible to use it at initial deployment.
Open Loop Transmit Diversity
On
Off 15 dB
10 dB
Figure 11-10 Transmit diversity (STTD)
To enjoy the benefits of transmit diversity, the RBS must have the proper installed hardware. The usage of Space Time Transmit Diversity (STTD) improves downlink capacity (Figure 11-10). The largest gain is expected in environments where the users are moving slowly. STTD transmits nearly the same information from two antennas at nearly the same time. The two antennas experience different fading patterns, which results in a diversity gain since the fast fading is combated. It is possible to switch on/off the TX diversity.
– 206 – EN/LZT 123 6039 P1E
11 WCDMA Radio Functionalities
IMPROVED POSITIONING
The positioning function provides different alternatives with different accuracy as well as different costs. The most basic one, is when UTRAN provides the position using the stored cell information.
Positioning
For a higher accuracy, positioning based on Round Trip Time (RTT) measurements can be used. In order to further improve the accuracy achieved by RTT measurements, RBSs outside the current active set can also be used.
In order to exploit GPS capability, UTRAN can also offer the possibility to send the GPS parameters transparently from the CN to the UE and from the UE to the CN.
EN/LZT 123 6039 P1E – 207 –
WCDMA Radio Network Design
ll aa nn kkBB
iioonnaall llyy
ttnneettnnII
– 208 – EN/LZT 123 6039 P1E