theory of planning

UMTS Workshop Day 1: Theory & PlanningSlide title In CAPITALS 50 pt Slide subtitle 32 pt
UMTS Workshop
Day 1: Theory & Planning
Damian Dimarzio, GSDC Australia
Top right corner for field-mark, customer or partner logotypes. See Best practice for example.
Slide title 40 pt Slide subtitle 24 pt Text 24 pt Bullets level 2-5 20 pt
Ericsson Confidential
WCDMA theory
WCDMA Concepts
UTRAN architecture
WCDMA Radio Network Features & Products
RBS Product Overview
Idle mode behaviour
Hardware Dimensioning
WCDMA theory
WCDMA Concepts
UTRAN architecture
Idle mode behaviour
frequency
All users transmit at the same time
AMPS, NMT, TACS
spreading code
IS-95, cdma2000, WCDMA
time slot
position within the time slot
Several users share the
Time
Concepts
There are three basic air interface multiple access techniques, frequency, time and code division multiple access.
Frequency Division Multiple Access (FDMA) is very common in the first generation of Mobile Communication systems, for example TACS. The available spectrum is divided into physical channels of equal bandwidth. One physical channel is allocated per subscriber. The physical channel allocated to the subscriber is used during the entire duration of the call and is unavailable for use by another subscriber during this time.
In Time Division Multiple Access (TDMA) the available spectrum for one carrier, is divided in time. The subscriber is allocated a set amount of time referred to as a time slot. Subscribers can only use the air interface for this amount of time. An example of a system that uses this principle is D-AMPS, which explains why D-AMPS is sometimes called TDMA. Since other mobile telephony systems that use TDMA, for example GSM, also split the available frequency band into several distinct carriers, in a sense they are hybrids using both TDMA and FDMA
Wideband Code Division Multiple Access (WCDMA) allows many subscribers to use the same frequency at the same time. In order to distinguish between the users the information undergoes a process known as spreading. That is the information is multiplied with long and short codes, hence WCDMA is referred to as a spread spectrum technology. This technology was first developed by the military to avoid the possibility of their signals being jammed or listened to by the enemy.
Both signals combined
Both signals are
Concepts
If multiple users transmit a spread spectrum signal at the same time, the receiver will still be able to distinguish between the users provided each user has a unique code that has a sufficiently low cross correlation with the other codes. Cross correlating the code signal with a narrow band signal will spread the power of the narrow band signal thereby reducing the interfering power in the information bandwidth. The spread spectrum signal 1 receives a narrow band interference signal 2. At the receiver the spread spectrum signal is despread while the interference signal is spread, making it appear as a background noise compared to the despread signal. The ratio between the transmitted bandwidth to information bandwidth is called the processing gain GP
Fundamental Capacity Limitation is available RF transmit power
One RF power budget must be split between all Mobile Stations!
Fixed portion of RF power Budget allocated to Common Channels
SSMA interference from other Base Stations
Increases noise level in cell
Traffic channel power is allocated based on Mobile Station needs
More power allocated to distant MS’s; less to nearby MS’s
WCDMA uses fast power control on the downlink traffic channels
UL Factors
Intracell interference from other mobiles in the same cell, many to one scenario
Intercell interference from other mobiles in other cells and adjacent frequencies
Intersystem Interference from other systems like GSM
Concepts
The most important factor that limits the downlink capacity of a CDMA system is the available RF transmit power since the base station is powered by one power source which must be divided between all mobiles. A fixed portion of this power must be used to transmit the common channels over the entire coverage area of the cell that is pilot, broadcast and paging channels.
Another factor that influences the capacity in the downlink is interference from other base stations since this will increase the required signal level at the mobile to achieve the minimum Eb/No and hence increase the demand for power at the base station. As networks grow and begin to use hierarchy topologies with a resultant increase in the number of base stations in the network this will become a greater problem.
Another factor that must be remembered is that the traffic channel power is allocated according to the needs of the mobile, distant mobiles will require more power than those closer to the base station. In other words the downlink could accommodate a large amount of close mobiles but only a small numbers of distant ones. This power is adjusted in the same way as mobile power is, using fast power control.
The more traffic on the cell, the more noise generated.
More power is required in UL and DL to achieve the required Eb/No.
The cell shrinks because power is a finite resource.
BS 1
BS 2
Concepts
Near-Far Ratio, terrain, RF obstacles, “Corner” effects, etc
Multipath fading cancellation
Concepts
As with all radio transmissions the CDMA signal will be subjected to multiple reflections, diffractions and attenuations caused by natural objects such as buildings, hills etc resulting in what is known as multipath propagation. This will have two effects on the received signals at each end.
1. The bit energy for a single chip will be split by the various paths and arrive at different time intervals. The delay between these various arrivals is typically 1 to 2 µs in urban and suburban areas and up to 20 µs in hilly areas.
Since the WCDMA chip rate is 3.84 Mcps then the time duration of each chip will be 1/3.84·106 = 0.26 µs. If the time difference in these multi path components is at least 0.26 µs the WCDMA receiver can combine these to obtain multipath diversity. How this is achieved will be explained later.
2. For certain time delay positions there are usually many paths nearly equal in length along which the radio signal travels. For example paths with a length difference of half a wavelength ( at 2 GHz = 7 cm) will result in both signals canceling each other out. This type of fading is known as fast or Rayleigh fading and takes place as the receiver moves across even short distances.
Each RAKE finger tracks a different multipath component
Sliding correlator used to obtain a correlation peak for each multipath component
Also used to track other cells during soft handover
Searcher finger is used to measure other cells (for handover)
Power measurements of neighbouring BS
Sum of individual multipath components:
maximum ratio
strongest select
equal gain
Concepts
Pilot Pollution Definition
Pilot pollution definition is the detection of many high power pilots as compared to Best Serving Pilot that do not contribute to the received signal.
All other signals received that exceed the Active Set Size act as interference which degrades the performance of the system.
Concepts
Downlink: Channelization Codes used to distinguish data (and control) channels coming from each cell
(Also called channelisation, short or Walsh codes)
CC1 , CC2, CC3
Uplink: Channelization Codes used to distinguish data (and control) channels coming from each UE
Concepts
Adapts user bit-rate to code length
In reality, multipath, small timing errors diminish the usable code space
Example: 8 users; one 8-bit code per user
Chip Rate = 3.840 Mcps
1
1-1
11
1-11-1
1-1-11
11-1-1
1111
1-11-11-11-1
1-11-1-11-11
1-1-111-1-11
1-1-11-111-1
11-1-111-1-1
11-1-1-1-111
1111-1-1-1-1
11111111
Concepts
(Also called PN, long or gold codes)
Downlink: Scrambling Code used to distinguish each cell (assigned by operator – SC planning)
Uplink: Scrambling Code used to distinguish each UE (assigned by network)
SC3
SC4
SC5
SC6
SC1
SC1
SC2
SC2
Concepts
Downlink Scrambling Codes
Downlink Scrambling Codes
Each Cell is assigned one and only one Primary Scrambling Code (of 512)
Secondary Scrambling Codes may be used over part of a cell, or for other data channels
Primary SC0
8192 Downlink Scrambling Codes
Each code is 38,400 chips of a 218 - 1 (262,143 chip) Gold Sequence
Primary SC7
Primary SC504
Primary SC511
Concepts
Code allocation corresponds to
Dedicated Traffic Connection
UE-specific Scrambling Code(s)
Uplink Scrambling Code Type depends on the Application
Concepts
SC6 + CC1 + CC2 + CC3 + CC4
4 data channels
SC2 + CC4 + CC5 + CC6 + CC7
2 data channels
Concepts
WCDMA theory
WCDMA Concepts
UTRAN architecture
Idle mode behaviour
Iu
Iu
Architecture
If we have a closer look at the UMTS Radio Access Network (UTRAN) or WCDMA RAN we can see how the various components are interconnected using defined interfaces.
For the purpose of this course we will be concentrating on the interface between the User Equipment (UE) and the Node B, that is the Uu or Air Interface.
The main interfaces of UTRAN are Iu, Iur, and Iub. Iu is the interface between UTRAN and core network. There are two types of interfaces in the Iu interface. The Iu interface towards the packet-switched (PS) (GPRS) and the Iu interface towards the circuit-switched (CS) (MSC). The Iu interface supports several functions such as establishing, maintaining and releasing radio access bearers (RAB), performing intrasystem and intersystem handover, location services by transferring requests from the CN to UTRAN, and location information from UTRAN to CN. Iur interfaces radio network controllers and is required to support inter RNC soft handover. The Iub is a logical interface that connects base station (node B) to radio network controller.
WCDMA theory
WCDMA Concepts
UTRAN architecture
Idle mode behaviour
TE
MT
UTRAN
RAB
RABs
In order to allow rational design of UMTS network, the overall end-to-end QoS requirements need to be broken down to specific sub-service requirements for the individual building blocks of the network -> bearer services.
each bearer service on a certain layer offers its specific services using services provided by lower layers
The role of the Radio Bearer Service is to cover all the aspects of the radio interface transport.
The Iu-Bearer Service together with the Physical Bearer Service provides the transport between UTRAN and CN. Iu bearer services for packet traffic shall provide different bearer services for a variety of QoS requirements.
Traffic class
Conversational class
conversational RT
Streaming class
streaming RT
Interactive class
RABs
Each user will with a certain probability belong to a certain class of users with identical QoS profiles
Probability distribution of the QoS class membership of all users is referred to as service mix
Challenge for the operator: which service mix needs to be specified for the capacity definition of the system; important parameters:
pricing strategy for services for revenue maximization
competition in the different services and QoS classes
Traffic Class ['conversational', 'streaming', 'interactive', 'background']
Definition: Type of application for which the Radio Access Bearer service is optimized.
Purpose: By including the traffic class itself as an attribute, UTRAN can make assumptions about the traffic source and optimize the transport for that traffic type. In particular, buffer allocation may be based on traffic class.
The type of application is indicated by reference to the UMTS traffic classes.
RABs
A radio access bearer (RAB) connection via UTRAN is realised by two concatenated segments, the Iu bearer connection and the radio bearer connection and slides 4-7 illustrate the mapping of radio bearer connections on logical, transport and physical channels.
Each of the RABs (note: the discussion below only concerns the user plane in the right part of slides 4-4) is mapped onto one or more radio bearers. More than one radio bearer may be used if the user data can be separated into different subflows with different error protection needs.
Each radio bearer is mapped on one radio link control (RLC) entity.
Each RLC entity in the RNC communicates with its peer entity in the UE with one or more logical channels. Depending on the service required from the RLC, logical channels are configured for operation in Transparent Mode (TM), Unacknowledged Mode (UM) or Acknowledged Mode (AM) (the option of using different logical channels for transfer of data and control PDUs (Protocol Data Units) in the RLC AM data is not used in UTRAN P1).
The logical channels carrying user plane traffic, i.e. DTCHs are mapped onto dedicated (DCH) or common (RACH/FACH) transport channels as specified for each multiplexing option. A radio bearer may have more than one multiplexing option, where each option specifies a particular mapping on dedicated or common physical channels.
Radio bearers using TM RLC for support of CS services require dedicated transport and physical channels, while radio bearers using AM RLC for support of best effort packet data services can use either dedicated or common physical channels.
The radio bearer logical channel, DTCH, is multiplexed with other logical channels on the RACH and FACH transport channels used for transfer over the common physical channels PRACH and S-CCPCH
User data at the UTRAN service access points is represented as RAB SDUs (Service Data Units). Each RAB SDU is transferred via the Iu interface in the payload field of a Iu user plane PDU (Protocol Data Unit).
The SDU size can be specified as one or more fixed sizes per RAB or as a variable size with a specified maximum.
A RAB SDU may be structured in RAB subflow SDUs, in which case the number of bits per subflow SDU is specified in the SDU format information provided in the “RAB assignment request”.
Higher layer data units i.e. RAB or RAB subflow data units or RRC messages are mapped on SDUs of the RLC layer. These SDUs are within the RLC layer mapped onto RLC PDUs. The mapping depends on the RLC mode (TM, UM or AM, called TrD, UMD or AMD for RLC PDUs) used to handle the data flow for each RAB connection or RRC message.
Each RLC PDU is mapped onto one and only one transport block.
On dedicated transport channels, the transport block size is the same as the RLC PDU size except in the case of multiplexing of logical channels on the same transport channel.
UL: Interactive 64 kbps PS RB
DL: Interactive PS RB on HS-DSCH
Interactive 384/HS kbps PS RAB (optional)
UL: Interactive 384 kbps PS RB
DL: Interactive PS RB on HS-DSCH
RABs
Used for channel estimation
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Pilot Symbol Data (10 symbols per slot)
1 timeslot = 2560 Chips = 10 symbols = 20 bits = 666.667 uSec
Channels
PCH (Paging Channel)
FACH (Forward Access Channel)
Used for transmission of idle-mode control information to a UE
Dedicated Transport Channels
DCH (Dedicated Channel)
Used for BLER measurements
Channels
Dedicated Transport Channels
DCH Dedicated Channel
Used for BLER measurements
Channels
SCH - Synchronization Channel
DPDCH - Dedicated Physical Data Channel
DPCCH - Dedicated Physical Control Channel
Dedicated Connection Channels
AP-AICH - Acquisition Preamble Indicator Channel
CD/CA-AICH - Collision Detection Indicator Channel
CSICH - CPCH Status Indicator Channel
PRACH - Physical Random Access Channel
AICH - Acquisition Indicator Channel
Channels
WCDMA theory
WCDMA Concepts
UTRAN architecture
Idle mode behaviour
WCDMA theory
WCDMA Concepts
UTRAN architecture
Idle mode behaviour
Macro
Products
RBS 3106/3206
Products
Micro
Coverage
Capacity
Micro
Products
Dual Band and RRU Support
Output Power: 20 to 120 W configurations
Channel Element: UL/DL 1536/1536 CE
Supports: Tx-diversity, 4-way RX-diversity,
HSDPA and Enhanced Uplink
Products
Channel Element: UL/DL 768/768 CE
Supports: 2-way RX-diversity, HSDPA and E-UL
Products
MU
TRX
PA
LNA/Filters
Products
Main Unit Configurations
HW prepared: E-UL and 6 RRUs
RRU Configurations
Products
Channel Element: UL/DL 128/128
Products
Micro allready exists for the 2100 MHz band in the P3 release. New are the 1900 and 850 MHz band.
From 40000 to 540000 subs
Mixed traffic: 20 mE voice, 3.1 mE 64 kbps UDI & 142 bps packet data
Up to 768 RBSs per node
Max Iub traffic from 50 Mbps to 675 Mbps
Main
Products
Handover 76/1553-HSD 101 02/4
Idle Mode Behavior and Connected Mode Behavior in CELL_FACH State 71/1553-HSD 101 02/4
IP Infrastructure for O&M 2/1553-HSD 101 02/3
Load Sharing 3/1553-HSD 101 02/4
Power Control 80/1553-HSD 101 02/4
Security Management 78/1553-HSD 101 02/3
Synchronization 84/1553-HSD 101 02/3
UE Positioning 89/1553-HSD 101 02/3
Handling of License Control 90/1553-HSD 101 02/4
HSDPA Overview 91/1553-HSD 101 02/4
HSDPA User Plane 93/1553-HSD 101 02/4
HSDPA Migration and Activation 95/1553-HSD 101 02/4
Neighbouring Cell Support 92/1553-HSD 101 02/4
CPI documents on:
cpistore.ericsson.se
WCDMA theory
WCDMA Concepts
UTRAN architecture
Idle mode behaviour
CELL_FACH mode
User Equipment (UE) in Connected Mode (has an RRC Connection to radio network)
UE uses the common transport channels RACH or FACH
If the parameter interFreqFDDMeasIndicator = 1, the UE will evaluate cell reselection criteria on inter-frequency cells (0)
CELL_DCH mode
User Equipment (UE) in Connected Mode (has an RRC Connection to radio network)
UE uses dedicated channels for transmitting data and signalling
Idle Mode Behaviour
System Information
System parameters are broadcast on BCCH. It has information regarding Idle Mode Behaviour.
The System Information elements are broadcast in System Information Blocks (SIB’s). Each SIB contains a specific collection of information.
Idle Mode Behaviour
Paging
System Information Broadcast
Idle Mode Behaviour
PLMN Selection
PLMN selection performed upon power on or upon recovery from lack of coverage
If there is no last registered PLMN, or if it is unavailable, the UE will try to select another PLMN “AUTOMATICALLY” or “MANUALLY” depending on its operating mode
Manual mode
UE displays all PLMNs (allowed and not allowed) by scanning all frequency carriers
The user makes a manual selection and the UE attempts registration on the PLMN
Automatic mode
Each PLMN in the user-controlled PLMN list in the USIM, in order of priority
Each PLMN in the operator-controlled PLMN list in the USIM
Other PLMNs according to the high-quality criterion
Roaming
Roaming is a service through which a UE is able to obtain services from another PLMN
The UE in Automatic mode, having selected and registered a Visited PLMN (VPLMN) periodically attempts to return to its Home PLMN (HPLMN) according to a timer. Default = 30mins
Idle Mode Behaviour
Start
Suitable cell found
Idle Mode Behaviour
Cell Selection
UE looks for a suitable cell in the selected PLMN and camps on to it
Cell search procedure
Primary scrambling code is obtained from CPICH
UE then monitors the paging and system information, performs periodical radio measurements and evaluates cell reselection criteria
Strategies used for the cell selection process:
Initial Cell Selection: UE has no knowledge of the WCDMA radio channels
UE scans all WCDMA radio frequency channels to find a suitable cell with the highest signal level and read BCCH
The PLMN is determined from the mcc and mnc in the MIB in BCCH
Stored Information Cell Selection: UE knows the carrier frequencies that have previously been used
Idle Mode Behaviour
Squal = Qqualmeas - qQualMin (for WCDMA cells)
Srxlev = Qrxlevmeas - qRxLevMin – Pcompensation (for all cells)
Where Pcompensation = max(maxTxPowerUL – P,0)
Cell selection criteria (S criteria) is fulfilled when
Squal>0 ( for WCDMA cells only)
and Srxlev>0
Idle Mode Behaviour
Cell Reselection
Allows UE’s to move between cells in idle and cell_FACH connected mode
Always camp on the best cell the UE performs the cell reselection procedure in the following cases:
When the cell on which it is camping is no longer suitable
When the UE, in “camped normally” state, has found a better neighbouring cell than the cell on which it is camping
When the UE is in limited service state on an acceptable cell
Idle Mode Behaviour
Rev A
Ericsson Proprietary
R(Serving) = Qmeas(s) + qHyst(s)
R(Neighbour) = Qmeas(n) – qOffset(s,n)
Derived from the averaged received signal level for GSM cells
Derived from CPICH Ec/Io or CPICH RSCP for WCDMA cells depending on the value of qualMeasQuantity (2, Ec/Io)
qHyst(s) = qHyst1 when ranking based on CPICH RSCP (4)
qHyst(s) = qHyst2 when ranking based on CPICH Ec/Io (4)
qOffset(s,n) = qOffset1sn when ranking based on CPICH RSCP
qOffset(s,n) = qOffset2sn when ranking based on CPICH Ec/Io
The above two values are 0 for WCDMA cells and 7 for GSM cells
Idle Mode Behaviour
Idle Mode Behaviour
Rev A
Location and Routing Area updating
Location Area = The area to which the Core Network sends a paging message for circuit switched.
Routing Area = The area to which the Core Network sends a paging message for packet switched.
If the Location Area Identity (LAI) or Routing Area Identity (RAI) read on system information is different to the one stored on the USIM, the UE performs a LA or RA registration update
Three types of registration update
Normal
IMSI attach/detach - used if att = 1 (1)
UE sends “attach” or “detach” messages when the UE is powered on or off
Idle Mode Behaviour
Core Network informs a UE of a terminating service request
RAN informs all UE’s that the system information has been modified
Paging messages sent to all UE’s in LA or RA
Discontinuous Reception: UE listens to PICH at predefined times only
Discontinuous Reception (DRX) cycle = (2^k) * 10 (ms)
where k = cnDrxCycleLengthCs (7) for CS and cnDrxCycleLengthPs (7) for PS
Idle Mode Behaviour
WCDMA theory
WCDMA Concepts
UTRAN architecture
Idle mode behaviour
The Transmitter adapts the output power according to Pathloss
Goal is that all users should experience the same SIR which corresponds to a target BLER.
Regulates power output to maintain good connection quality good connection quality
Minimize UL and DL transmitted power to reduce interference, and increase capacity
No PC on pilot or some CCH
Power Control
Power Control
1. Open-Loop Power Control (Initially, No signaling)
Performed in the uplink and downlink to calculate a minimum starting power for setting up a connection.
Common channels (RACH/FACH)
Transmit at calculated power,
Power Control
- Uplink
Initial preamble from UE uses the UL power calculated as:
P_PRACH = L_PCPICH + RTWP + constantValueCprach
RTWP is UL interference measured by the RBS
If the RBS does not detect the preamble, the UE sends a new preamble with an UL power that is powerOffsetP0 higher than the previous preamble.
When the RBS detects a preamble, it sends acknowledgement indication (AI) to the UE, which then sends the RACH control part of the message with an UL power that determined by the last preamble and an offset powerOffsetPpm.
1
2
2
3
This open loop power control function ensures that the random access does not cause too much interference
Power Control
Rev A
Downlink Initial Power Setting on DCH
This open loop power control function calculates the initial DL power of the physical channel that carries user data (DPDCH) and the physical channel that carries information needed to keep the connection running.
P_DL_DPDCH = primaryCpichPower + (dlInitSirTarget – Ec/No_PCPICH) + cBackOff + 10 log (2/SF_DL_DPDCH)
where:
primaryCpichPower is DL power for PCPICH in the cell where the connection is established
Ec/No is the measured DL Ec/No reported by the UE
When the EcNo is not available (e.g. at IRAT HO), the default Ec/No is set to ecNoPcpichDefault
dlInitSirTarget is the signal-to-interference target for the DL DPDCH
SF_DL_DPDCH is the spreading factor for the DL connection
cBackOff is used to provide a more conservative initial output power or to increase the call setup reliability
When in SHO:
where:
cSho is a function of the Soft HO margin + initShoPowerParam
Initial DL power at DCH establishment
Power Control
WCDMA supports fast (1500 Hz) quality based closed loop power control. It enables the power transmitted to be kept as low as possible, though still maintaining the quality of the connection. The receiver orders the transmitter to increase or decrease the output power, thus maintaining the SIR close to the target value. Since it is fast, the Rayleigh fading can be tracked even for quite highly mobile users. It also means that rapid changes in the interference can be handled. The benefit of quality base power control is that it minimizes the interference in the system i.e. it maximizes capacity.
In addition to quality based power control, WCDMA also supports outer loop power control. This is done by monitoring the transport block CRC after diversity combining in the RNC and changing the SIR-target, which is used by the fast quality based power control. So that a certain bit error rate (BER) or frame error rate (FER) is achieved. The SIR-target is needed in order to reach a certain BER of FER and depends on the channel model.
Open-loop power control is used to adjust the transmit power of the physical Random-Access channel. This power value is calculated by the UE based on the path loss from the base station, the uplink interference value and the required SIR (uplink interference value and SIR and sent by the base station on the broadcast channel).
Uplink Initial Power Setting on DCH
This open loop power control function determines the initial UL power at connection establishment
P_UL DPDCH
P_UL DPCCH
P_UL_DPCCH_INIT= primaryCpichPower + RTWP + ulInitSirTarget – 10 log (SF_DPCCH) + cPO
where:
primaryCpichPower is DL power for PCPICH in the cell where the connection is established
RTWP is the total UL interference measured by the RBS
ulInitSirTarget is the signal-to-interference target for the DL DPCCH
SF_DPCCH is the spreading factor for the UL connection
cPO is used to provide a more conservative level to minimize excessive UL interference
Power Control
2. Outer-Loop Power Control (slow)
maintains the required Block Error Rate (BLER) for a service by modifying the SIR target
Dedicated channels
If the BLER measured (DL@UE, UL@RNC) is below/ above the minimum acceptable BLER,
UE/RNC increase/reduce SIR target.
3. Inner-Loop Power Control UL/DL (fast)
minimizes the power and interference of ongoing connections by maintaining a minimum SIR.
Dedicated channels
Performed 1500 times per second,
Adjust (up or down) the Tx power to reach the SIR target.
Power Control
1
2
3
4
Estimate UL quality
slow fading
Power Control
UL Outer Loop PC have two possible regulator algorithms:
Constant step regulator ulOuterLoopRegulator = [CONSTANT STEP]
Jump regulator
ulOuterLoopRegulator = [JUMP]
sirMax
sirMin
Initial targets for SIR regulation is decided at UL initial power setting
Anti-windup prevents the RNC to change the UL SIR target if the UE cannot increase/decrease its output power further, i.e. already transmits on max. / min power.
Power Control
Jump Regulator
Increases UL SIR target whenever a transport block is erroneously received and decreases the UL SIR target whenever a transport block is correctly received
Power Control
- Constant Step Regulator
Increases UL SIR target whenever a transport block is erroneously received and decreases the UL SIR target whenever a certain number of transport block are correctly received
Power Control
Uplink Inner Loop Power Control
If estimated UL SIR >= target UL SIR, then RBS send power DOWN command
If estimated UL SIR < target UL SIR, then RBS send power UP command
UE always power UP/DOWN in steps of 1 dB
In SHO:
if all radio links in active set send power UP command, the UE powers UP by 1 dB
If at least one radio link in the active set sends power DOWN command, the UE powers DOWN by 1 dB.
Power Control
Transmit
No
Yes
No
Yes
Power Control
BS
Power Control
If we look at this scenario from the perspective of the mobile output power we can see the three power controls in action.
At initial connection the mobile makes four attempts known as access pre-ambles at increasing power levels until the base station receive power target is achieved. This will be signaled by the Base Station with an acquisition indicator channel. Then the UE sends the message on RACH. Connection is then established and inner or fast power control can take over to maintain this target. As you can see this is constantly adjusted at a rate of 1500 times per second. In the case of IS-95 this rate was only 800 times per second.
At some time later the base station receives a command to increase the receive power target as part of the outer loop process. In other words the FER has increased. Inner-loop power control will then be used to ramp the mobile power up to achieve this new level and maintain this.
Power Control
Channel Switching
dlCodeAdm
70 (%)
70 (%)
beMarginDlCode
pwrAdm
75 (%)
75 (%)
pwrAdmOffset
10 (%)
10 (%)
beMarginDlPwr
10 (%)
10 (%)
maximumTransmissionPower
minPwrMax
primaryCpichPower
aichPower
ulInitSirTargetHigh
ulOuterLoopRegulator
Jump
Jump
sirMin
Handover
WCDMA theory
WCDMA Concepts
UTRAN architecture
Idle mode behaviour
Handover Types
Soft Handover
In DCH mode, MS has concurrent traffic connections with two BS’s
Softer Handover
Similar to Soft Handover, but between two sectors of the same cell
Inter-Radio Access Technology (IRAT) Handover
CS Handover from a WCDMA system to another system
Traffic and Control Channels are Disconnected and must be Reconnected (hard handover)
Inter-frequency Handover (IFHO)
When the MS must change WCDMA carrier frequency during the Handover
Traffic and Control Channels are Disconnected and must be Reconnected (hard handover)
Inter-RAT Cell Change
manages PS UE mobility between cells using WCDMA RAN and cells using GSM/GPRS
Cell Reselection
manages UE mobility between WCDMA cells with same frequency, different frequency and between WCDMA cells and GSM/GPRS cells, when the UE is in idle mode or CELL_FACH state.
Handover
As with all mobile communications networks CDMA must be capable of handing over connections from one cell to another to maintain the connection as the mobile is moving. Four different type of handovers are supported by the CDMA system.
Inter RAT Handover (RAT = Radio Access Technology)
For example a call could move from a CDMA base station to a GSM base station or to a Cdma2000 base station.
Inter frequency handover
This describes what happens when a connection is handed from one CDMA carrier frequency to another. This type of handover is the type employed in GSM systems.
Soft Handover
This type of handover is unique to CDMA. During this type of handover the mobile is connected to two or more cells. This is achieved by using the fingers of the Rake receiver. The advantage of this type of handover is that there is no distinct break in connection and hence it should be less noticeable than a hard handover and the likelihood of a dropped connection is reduced. The disadvantage of this type of handover is that additional resources are required for the same connection.
Softer Handover
This type of handover is similar to Soft handover, however this time the cells belong to the same base station which have identical timing.
Handover
Before we look at how this problem is solved it is useful to look at the different handover scenarios that can occur. Handovers between sectors on cells that are connected to the same are referred to as “inter-Node” handovers, these can be either hard or soft.
When the target sector is controlled by another RNC the handover is termed “inter-RNS”. It should be noted that if this is a soft handover the Iur interface is used to pass information between the RNSs. This interface is not used if a hard handover is performed.
The last scenario that needs to be considered is when the handover is occurring between sectors on the same base station or node B. This type of handover is called “intra-Node” or softer.
As is shown in the above figure, it is composed of core network, wireless access net and users terminals. For the core network, it is mainly based on two kinds of networks in the 2nd generation of mobile communication GSM network based on MAP and CDMA based on IS-41.
When fast power control is used, soft handover is essential
Allows MS to operate in most conservative power control mode
Soft handover provides performance benefits
“Seamless” coverage at cell fringes
Handover may be less noticeable to the user
Soft handover also degrades system capacity
Uses redundant physical layer resources from adjacent or overlapping cells
Handover
SSMA is used to distinguish all transmitters in a Cellular CDMA system
That is PN codes are used to separate multiple transmitters on the same frequency.
Fast power control is required to sustain SSMA performance
Since these PN codes are not orthogonal and do not provide perfect separation fast power control is required to maintain these interfering signals at an equal level.
When fast power control is used, soft handover is essential
to avoid excessive interference during handover.
time
the MS causes excessive interference to BS2
BS2 Receive Power Target
UE responding to BS1
Handover
CDMA systems must use soft or softer handover to reduce interference caused by near-far problems resulting from mobiles penetrating the coverage area of adjacent cells without being power controlled while in that cell.
The diagram above shows what the effect of using hard as opposed to soft or softer handover in a CDMA system would be. As the mobile moves away from BS 1 towards BS 2 there will come a time before the hard handover is performed, that the signal received at BS 2 exceeds its received power target and will start to cause excessive interference to other mobiles in that sector. Since the mobile is not connected to BS 2 it has no way of reducing this power. This excessive interference at BS 2 and could result in wiping out connections on BS 2.
Once the connection undergoes a hard handover to BS 2, power control messages from BS 2 can be used to reduce the power to the power target and reduce the interference, however this period of interference would be unacceptable.
Soft and softer handovers allow the mobile to be taken into power control before the received signal exceeds the target and eliminate this excessive interference.
Results from the existing American CDMA system (IS-95) have shown that each call uses an average of 1.9 resources for each connection. This high value indicates that without soft or softer handover this near-far problem would be very common.
Measurement criteria
Active set (SHO)
Monitored set (cells measured by UE but which does not belong to active set (Intra/Inter frequency and Inter-RAT frequencies)
Measurement
Rev A
Compare with measurement criterion
f1
f1
f2
Handover
9/15/2003
14
Rev A
WCDMA Soft Handover Process
One finger of the RAKE receiver is constantly scanning neighboring Pilot Channels.
When a neighboring Pilot Channel reaches the t_add threshold, the new BS is added to the active set
When the original Base Station reaches the t_drop threshold, originating Base Station is dropped from the active set
Monitor Neighbor BS Pilots
Handover
From existing CDMA systems it has been shown that Softer handover occurs in about 5-15% of connections and Soft handover in about 20-40% of connections.
Cell 1
T_ADD
T_REPLACE
t
t
t
T_DROP
Handover
The graph above shows the received signal to interference ratio Eb/No against time of three cells. The various ‘t_add’ and ‘t_drop’ thresholds can clearly be seen. The whole process of moving from connected only to cell 1 through soft handover with cell 1 and 2 to soft handover with cell 2 and 3 to finally being connected to only cell 3 can be clearly seen.
It should be noted that unlike hard handover this ‘t_add’ is is a couple of dB lower than the serving cell, hence soft handover will occur before the signal level at the neighbor exceeds that of the serving cell.
Event cause:
Radio Link addition / replacement due to measurements related to best cell in Active Set
Event 1a and 1b
reportingRange1a
hysteresis1a
timeToTrigger1a
UE sends Measurement Report message for EVENT 1a and the cell is added to AS. If AS is full maxActiveSet, the cell will replace the worst cell in the current AS, provided the reported cell has better quality
Handover
9/15/2003
14
Rev A
Event cause:
Radio Link removal from due to measurements related to best cell in Active Set
Event 1a and 1b
reportingRange1b
hysteresis1b
timeToTrigger1b
UE sends Measurement Report message for EVENT 1b and the cell is removed from the AS (one cell is always kept in AS to maintain connection).
Handover
9/15/2003
14
Rev A
*
Event 1c, non-active Primary CPICH becomes better than active Primary CPICH
Event cause:
Radio Link substitution due to measurements related to least good cell in AS while the AS is full
hysteresis1c
timeToTrigger1c
UE sends Measurement Report message for EVENT 1c and the cell replaces the least good cell in the AS.
Event 1c
Rev A
Event cause:
ANY cell (AS or monitored) becomes better than the current best cell in the AS.
hysteresis1d
timeToTrigger1d
UE sends Measurement Report message for EVENT 1d. If the cell already belongs to AS, no action is taken by RNC. Else, the cell will be added to the AS, and if the AS is full, the least good cell will be replaced.
Event 1d
Rev A
(DCCH)
Handover
Compressed Mode
The physical channel is reconfigured to create transmission and reception gaps.
Data compression can be accomplished by:
Decreasing the Spreading Factor by 2:1
Increases Data Rate so bits get through twice as fast!
Puncturing bits
UE then tunes to other frequencies (GSM) to conduct measurements
Signaling required to prepare for the measurements
Additional UE and network processing load
Recommendation:
Avoid going in and out of compressed mode
Handover
*
Event 2d, Quality of current used frequency is below a threshold
Event cause:
Initiation of inter-frequency or inter-RAT measurement due to bad quality or signal strength
UE sends Measurement Report message for EVENT 2d and depending on how parameter HoType [IFHO / GSM / None] is set for cells in AS, this will trigger compressed mode measurements, and possibly Event 2b or 3a.
UsedFreqThresh2d
Hysteresis2d
timeToTrigger2d
Rev A
*
Event 2f, Quality of current used frequency is above a threshold
Event cause:
Termination of inter-frequency or inter-RAT measurement due to good quality or signal strength
UE sends Measurement Report message for EVENT 2f and any compressed mode measurements are terminated.
UsedFreqRelThresh2f
UsedFreqThresh2d
Hysteresis2f
timeToTrigger2f
Rev A
Transfer ongoing calls to another RAT or WCDMA frequency
Benefits
Use GSM networks as coverage fall back
Use WCDMA network to offload GSM network at high traffic load
Maintains UE radio connections when radio environment requires move to another frequency
P4 Enhancement
Handover
Summary
Inter-frequency handover allows for an ongoing call to be transferred from one WCDMA frequency to another in a case where a UE is moving out of coverage of the source frequency. The feature covers functions for both inter-frequency handover for UEs on dedicated channel and for inter-frequency cell re-selection in connected mode on common channel and in idle mode.
Benefits
This feature maintains UE radio connections in a situation where the radio environment requires that the connection is moved to another frequency.
Description
Inter-frequency handover on dedicated channel
Inter-frequency handover is supported for both CS and PS connections on dedicated channel. Both intra-RNC and inter-RNC Handover are supported.
Compressed mode measurements are triggered by any of the following events:
· Low Ec/No (signal quality)
· Low RSCP (signal strength)
· High UE Tx Power
If start of compressed mode was triggered by event 2d (Ec/No or RSCP) the related handover or cell change event (2b) will be triggered on the same quantity that triggered start of measurements. If start of compressed mode was instead triggered by event 6a, event 2b will be triggered by RSCP adjusted by an offset compared to if compressed mode was triggered by event 2d on RSCP. RSCP is used for event 2b in this case since UE Tx power is not considered a robust enough measurement to trigger handover.
Since a compressed mode pattern for combined GSM and inter-frequency measurements is not defined in the 3GPP standard, the preferred handover type is operator definable for each UTRAN cell. The system will read the preferred handover type for the source cell, and perform related measurements if this handover type is allowed for the service. If the connection is in soft handover, i.e. the active set is larger than 1, and one or more of the active set cells allow inter-frequency handover, this will be the preferred handover type.
The handover evaluation is based on measurements on non-source frequencies belonging to neighbouring cells through the use of compressed mode (SF/2 or Higher Layer Scheduling) or non-compressed mode, depending on the UE capabilities. The SRNC instructs the UE via the RBSs involved in the active set (in relevant cases involving the DRNC) to start measurements, and the UE sends the measurement report to the SRNC, which decides on the target cell and frequency and schedules the handover execution.
After a successful inter-frequency handover, one radio link on the target frequency has been successfully established and the radio link(s) that existed towards the UE on the source frequency has been released.
If compressed mode has been activated for the UE to perform inter-frequency measurements, the UE will be ordered to stop compressed mode when switching to the target frequency.
WCDMA RAN P4 utilizes timing re-initialised inter-frequency handover. In case the admission control algorithm in the CRNC rejects the inter-frequency handover execution, the SRNC will either try to perform inter-frequency handover to another cell or to wait for some time before making another attempt in the same cell.
The supported compressed mode types are spreading factor reduction (SF/2) for guaranteed bitrate services and Higher Layer Scheduling (HLS) for non-guaranteed bitrate services. Neighbour cell measurements without compressed mode are supported for UEs with dual receivers.
Relation between inter-frequency and GSM handover
Since a compressed mode pattern for combined GSM and inter-frequency measurements is not defined in the 3GPP standard, the preferred handover type is operator definable for each UTRAN cell. The system will read the preferred handover type for the active set cell(s), and perform related measurements if this handover is allowed for the service. Inter-frequency handover has priority over GSM handover, i.e. inter-frequency handover will be performed if at least one of the active set cells prefers this handover type and this handover type is supported/allowed for the service type. If neither inter-frequency nor GSM handover is allowed for the service, neighbour cell measurements and handover will not be performed.
Inter-frequency cell re-selection in connected mode on common Channel and in idle mode
Inter-frequency cell re-selection for idle mode and for connected mode on common channel is supported for both intra-RNC and inter-RNC use cases.
Mobility Management in these UE modes is controlled by a series of parameters that are broadcasted as part of System Information. Based on these parameters, the UE will perform radio measurements and decide on the preferred carrier. The decision is based on measured values of the Ec/No and RSCP in the source and target cells, where operator definable thresholds decide when a cell re-selection to another carrier should be attempted. The cell re-selection parameters are configurable on cell level. Also GSM cells may be included as target cells.
Neighbour cell definition
32 inter-frequency neighbour cells can be defined per UTRAN cell.
Parameters
The following parameters are provided to allow the user to influence inter-frequency handover and cell re-selection:
Events 2d and 6a (start IF measurements)
· Ec/No and RSCP (combined measurements) thresholds for WCDMA source cell
· Hysteresis values for Ec/No and RSCP in WCDMA source cell
· Max UE Tx power
Event 2f and 6b (stop IF measurements)
· Ec/No and RSCP thresholds for WCDMA source cell
· Max UE TX power
Event 2b (IF Handover):
· Ec/No and RSCP thresholds for WCDMA target cell
· RSCP threshold for WCDMA source cell at start of measurements due to high UE Tx power
· Hysteresis values for WCDMA source cell
· Time-to-trigger value for 2b
· Individual cell offset
· The number of times the system should try IF HO if first attempt fails
· Time interval between IF HO attempts
The absolute value of the event 2d threshold is configurable on cell level, while event 2f and 2b are configurable as a relative offsets (separate for Ec/No and RSCP) between event 2d and the respective event threshold on RNC level. Thresholds for event 6a and 6b are configurable on RNC level. The event 2b threshold when measurements were started by event 6a, is set relative to the 2b threshold used when measurements were started by low RSCP. Individual cell offset is configurable on cell level.
GSM Handover & Cell Re-selection
Summary
The feature "GSM Handover" provides support for Inter Radio Access Technology Handover, Cell Change and Cell Reselection for interoperability with GSM, whereby Circuit Switched (CS) and/or Packet Switched (PS) calls can be transferred to and from GSM networks without loss of context. This feature provides the required functions on the WCDMA side, while the feature FAJ 121 57 "GSM - WCDMA Cell Reselection and Handover" in GSM BSS R9.1 provides the corresponding functions on the GSM/BSS side.
Benefits
· Maintains intersystem mobility with retained UE calls and PDP contexts
· Allows use of GSM Networks as a fall back in case of lost coverage in the WCDMA network.
· Allows use of the WCDMA network to offload the GSM network in case of high traffic load in that network.
Description
WCDMA RAN supports cell re-selection between WCDMA and GSM in idle mode, and inter-RAT transfer for the following services to and from WCDMA:
· Voice (Conversational RAB for AMR speech)
· Packet (Interactive RAB up to 384 kbps packet data)
Inter system transfer for the Multi-RAB is also supported, and the procedure is essentially a handover of the CS part, followed by a cell re-selection of the PS part. Until Dual Transfer Mode (DTM) is available in GSM, the PS part will be suspended after transfer from WCDMA to GSM.
UTRAN is configured to not trigger compressed mode on 384 and 128 kbps, but instead perform a down-switch to 64 kbps before compressed mode is activated. The down-switch is triggered by high downlink code power for the connection, indicating that the UE is approaching the limit of WCDMA coverage. A 2d event received when the connection rate is above 64 kbps will be memorized by the RNC, and compressed mode will be triggered when 64 kbps is reached.
Inter-RAT transfer of Circuit Switched Data (Non-transparent 57.6 kbps steaming RAB) is supported from WCDMA to GSM.
The WCDMA to GSM transfer for the PS RAB on dedicated channel is done by forcing the UE to GPRS (cell change), while on common channel the transfer is done by a UE initiated cell re-selection. In both cases, the UE will perform a Routing Area update and re-initiate the connection from GPRS standby state. For GSM to WCDMA transfers, the UE will perform a Routing Area update and re-initiate the connection form idle mode.
GSM handover is supported over the Iur interface.
Inter-RAT handover/cell change algorithm in WCDMA RAN:
The UE on DCH makes measurements on the Monitored Set. The Monitored Set is based on neighbour cell information defined per cell. Some of these neighbour cells may be GSM cells. If the active set contains more than one cell, the monitored set is created by cyclically adding neighbouring cells from each of the active set cells. The list of neighbouring cells sent to the UE may contain up to 32 cells.
Compressed mode measurements are triggered by any of the following events:
· Low Ec/No (signal quality)
· Low RSCP (signal strength)
· High UE Tx Power
If start of compressed mode was triggered by event 2d (Ec/No or RSCP) the related handover or cell change event (3a) will be triggered on the same quantity that triggered start of measurements. If start of compressed mode was instead triggered by event 6a, event 3a will be triggered by RSCP adjusted by an offset compared to if compressed mode was triggered by event 2d on RSCP. RSCP is used for event 3a in this case since UE Tx power is not considered a robust enough measurement to trigger handover.
Since a compressed mode pattern for combined GSM and inter-frequency measurements is not defined in the 3GPP standard, the preferred handover type is operator definable for each UTRAN cell. The system will read the preferred handover type for the source cell, and perform related measurements if this handover type is allowed for the service. If the connection is in soft handover, i.e. the active set is larger than 1, and one or more of the active set cells allow inter-frequency handover, this will be the preferred handover type.
If the preferred handover type is not supported for the service, measurements related to the alternative type will be performed. If none of the handover types are allowed for the service, neighbour cell measurements and handover will not be performed.
The supported compressed mode types are spreading factor reduction (SF/2) for guaranteed bitrate services and Higher Layer Scheduling (HLS) for non-guaranteed bitrate services. Neighbour cell measurements without compressed mode are supported for UEs with dual receivers.
For the handover trigger criteria from GSM to WCDMA, see the GSM/GPRS feature mentioned above.
Inter-RAT cell re-selection algorithm in WCDMA RAN:
A UE in idle mode or connected mode on a common channel makes measurements on neighbour cells as indicated by the broadcasted system information received from the source cell. Some of these target cells may be GSM cells.
If such measurements indicate that the criteria for a Cell Reselection are met, and that the preferred cell is a GSM cell, the UE starts the appropriate procedures to inform the system about its imminent inter-RAT cell re-selection, including the new target cell identity.
By use of HCS parameters in the broadcasted system information, thresholds for both Ec/No and RSCP may be used to trigger cell re-selection to GSM.
Neighbour cell definition
The feature includes the possibility to define up to 64 GSM/GPRS cells as neighbour cells for any UTRAN cell. Both own and foreign PLMN cells are managed. The maximum number of GSM cells included in the neighbouring cell list sent to the UE is however 32, and the possibility to define 64 is related to the support for shared networks; see FAJ 121 246 R2, "Shared Network Support". A defined neighbour cells is identified by individual cell ID, and each neighbour cell may have an individual cell offset in order to adjust cell borders according to the cell plan.
Parameters
Events 2d and 6a (start GSM measurements)
· Ec/No and RSCP (combined measurements) thresholds for WCDMA source cell Ec/No or RSCP threshold for WCDMA source cell
· Max UE Tx power
Events2f and 6b (stop GSM measurements)
· Ec/No and RSCP thresholds for WCDMA source cell l
· Max UE TX power
Event 3a (GSM Handover)
· Min RSCP for WCDMA source cell at start of measurements due to high UE Tx power
· Hysteresis values for WCDMA source cell
· Time-to-trigger value for 3a
· Individual cell offset
· The number of times the system should try GSM HO if first attempt fails
· Time interval between GSM HO attempt
The absolute value of the event 2d threshold is configurable on cell level, while event 2f and 3a are configurable as relative offsets (separate for Ec/No and RSCP) between 2d and the respective event threshold on RNC level. Thresholds for event 6a and 6b are configurable on RNC level. The event 3a threshold when measurements were started by event 6a, is set relative to the 3a threshold used when measurements were started by low RSCP. Individual cell offset is configurable on cell level.
Operator configurable parameters for Cell Re-selection in idle mode and on common channel include:
· Signal strength threshold for GSM target cell
· Hysteresis value for WCDMA source cell
Ranking offset for GSM target cell in relation to WCDMA source cell
Slide title 40 pt Slide subtitle 24 pt Text 24

theory of planning

Documents