Wcdma radio functionality

UMTS Presentation - 1

UMTS Radio Features Presentation

Praveen Gupta, MobileStack,[email protected]


Admission control overview

Guarantees the overall Quality of Service by controlling the number of users

Interference

Capacity / Load

Planned load

Planned coverageCoverage

New users blocked above this point

User added

Admission threshold


Admission control purpose & algorithm description

Purpose:– This algorithm selectively denies access requests in order to limit the

load.

Algorithm description:– When new resources are required for a radio connection (Radio Link

set-up or modification), the Radio Connection Coordination algorithmrequests admission.

This requests includes parameters specifying the requested amount of resources. Admission Control checks if the requested amount of resources is available.


Characteristics of admission control

The RBS regularly reports measurements values of transmitted power By knowing the connections, the RNC keeps track of ASE, RBS HW and DL code usageHandover legs have higher priority than new callsDifferent thresholds for different services At high load, interactive users may be offered lower datarates than under normal load conditions


Congestion control overview

Bitrate

Over load is resolved by:

Delaying packetsCall removal


Congestion control purpose & algorithm description

Purpose: This algorithm solves overload situations. An overload situation occurs due to fluctuations in the UL interference and the used DL power.

Algorithm description : The algorithm is only triggered in case of (near) overload in a cell. The algorithm acts in case the transmitted Carrier Power measurement (DL Power) indicates overload. It is possible to set different thresholds for different services.


Example 1: Congestion control work flow

DL power or UL interferenceexceeded

Restrict access

Order admission to block

Interactive users insystem?

Move user to common ch Remove user

Set timer

Wait for command

No

Allow admissionand access

Message: over-load resolved

At overload, alterconnection with highest DL power

Yes

Timer expired


Enhanced Capacity control

Admission control checks HW resources in both UL & DL

Directed retry at call set-up to GSM in case of admission denial in WCDMA

Load balancing between different frequencies


P(Startvalue)

Open loop

P(SIR-Target,UL)

P(SIR-Target, DL)

Closed loop

DL-TPC UL-TPC

SIR-Target,DL

BLER-Measured,DL

DL-Outer

BLER = Block Error Rate

SIR = Signal to Interferenc

TPC = Transmit Power Co

e Ratio

ntrol

loop

RNC

SIR-Target,UL

SIR-Error,UL

UL-Outer loop

Power control overview


Power control purpose & reason

Purpose:The purpose is to minimize the transmit power while maintaining the quality of radio links. There are three different types power control:– Inner loop power control – Outer loop power control– Open loop power control.

Reason:Power control– Maintains the quality of the connections– Reduces power consumption– Minimizes interference – Improves the coverage and capacity of the system


Power control over timeInner-loop power Control

(Initial Receive Power Target)

RBS Receive Power Target

Inner-loop power Control(Updated Receive Power Target by Outer-loop power Control)

RBSReceive Power

Open-loop Power ControlAccess Preambles

timeDPCHRACHAccess Preambles

1500 updates/sec

The PRACH is “power controlled” by means of preamble ramping


Channel type switching overview

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


Channel type switching purpose & reason

Purpose:To optimize the channel usage for best effort packet switched users (Interactive users). To determine if it is necessary to switch UE connected substates e.g. from a common to a dedicated channel.

Reason:For best effort traffic for a particular user there is large variations in time in the offered traffic (bursty nature of traffic). It is not efficient for the air-interface to keep up resources for a dedicated channel continuously. This function saves also battery for connected UEs, which are not transferring data.


Channel rate switching

Change bit rate when moving away from RBS:

- UL supported by UE- DL supported in RNC

Advantage: Higher coverage and higher capacity B

it ra

te

Change of bit rate at high load

- Reduce bitrate for Interactive users- Reduce bitrate for voice users by changing AMR mode

Advantage: Lower blocking probability

Distancefrom RBS

orLoad in the cell


Adaptive Multi Rate (AMR) Rate Selection

Selection of the AMR mode at call set up About four combinations of simultaneous modes defined by the standard is supportedThe modes range from around 4.75 kbps up to 12.2 kbps

12.2

Bit rate for a user[kbps]

7.954.75

XX

X

Distancefrom RBS

orLoad in the cell


Adaptive Multi Rate (AMR) Rate Control

Possible to change the AMR mode for coverage and capacity reasons dynamically.The AMR switching and rate control optimises the usage of the air-interface by adapting the AMR rates for coverage and capacity reasons.

12.2

Bit rate for a user[kbps]

7.954.75

Distancefrom RBS

orLoad in the cell


Transmit Diversity - Open loop- Introduced to combat fading with up to 5dB gain in the downlink

On

Off15 dB

10 dBOn


Open Loop Transmit Diversity

Coverage & capacity gain– additional diversity effect -> less transmitted power -> less

interference in the system

The same information is transmitted from the two antennas. For each antenna the information is coded in a different way.

The total transmitted power is split between the two antennas.


Open Loop Transmit Diversity- Space-Time Transmit Diversity (STTD)

AB

b0 b1 b2 b3

b0 b1 b2 b3

-b2 b3 b0 -b1

Antenna A

Antenna BChannel bits

STTD encoded channel bitsfor antenna A and antenna B.

The signals from the two antennas are spread and scrambled with the same code and simultaneously transmittedThe two signals experience different fading patterns and the RAKE receiver observes the sum of the two faded orthogonal signalsThe resulting signal has a smoother fading pattern than the two original signalsUsed on all DL channels (except SCH and CPICH).


Open Loop Transmit Diversity- Time Switched Transmit Diversity (TSTD)

In TSTD the transmission alternates between the antennasUsed on Synchronization Channel (SCH)TSTD is implemented as a part of STTD

b0 b1 b2 b3

b0 b2Antenna A

Antenna BChannel bits

b1 b3


Transmit diversity - Closed-loop

Closed-loop Transmit Diversity (DPCH, PDSCH only)– UE sends Feedback Information (FBI) Bits to the RBS over the DPCCH– FBI bits tell the RBS how to adjust antenna gain (only mode 2) and phase (both

mode 1 and mode 2) for optimal reception at the UE– Mode 1 supported in P4

Σ

DPCCH

DPDCHMUX

DCH (or PDSCH)

Σ

CPICH2

CPICH1

Decode FBICalculateGains, Phases

Antenna 1

Antenna 2• S/P Demux• Channelization• Scrambling• I/Q Modulation


TX diversity modes mapped on physical channels

Application of Tx diversity modes on downlink physical channel types"X" – can be applied, "–" – not applied

Physical channel type Open loop mode Closed loopTSTD STTD Mode

P-CCPCH – X –SCH X – –S-CCPCH – X –DPCH – X XPICH – X –PDSCH – X XAICH – X –CSICH – X –


Blossoming and wilting

The purpose of the blossoming (at cell addition) and wilting (at cell removal) is to allow cells to be added or removed from the radio network with minimum disturbance to the network.

RBS1 RBS2

WiltingBlossoming

Output power gradually decreased (wilting) Output power gradually increased (blossoming)


Micro cell support overview

MicroMacro

Support of micro cells to:– cover white spots or to– increase capacity in hot-spot areas

Advanced load sharing to increase performance by distributing usersbetween different cells

The micro cell can be deployed in: – different frequency as the macro cell – the same frequency band as the macro cell


Micro cell evolution scenario

At some cell radius macrocell (i.e. roof-top antennas) capacity growth is limited due to poor RF isolation.

Microcells can be added in same or different frequency depending on:– rate of traffic increase– distance macro-hot spot– UE velocity

Ultimately there will be a complete micro-layer

f2

f2

f2


Connection set-up/release description

Connection Setup and Release includes establishment and release of control plane connections between the UE and UTRAN, and between the UE and the Core Networks.

It also covers Radio Access Bearer establishment according to the requested Quality of Service between a Core Network and a UE with established signalling connection, as well as release of existing Radio Access Bearers.

The functions consists of two subfunctions

– Signaling Connection Setup and Release

– Radio Access Bearer Setup and Release


Radio connection supervisionBenefit:

– Allows an efficient resource utilization– Guarantees that users are not charged for time when they did not have network contact.

Description:This feature continuously monitors the status of the radio connection for all connected UEsand disconnects those for which a reasonable quality cannot be maintained and/or the contact has been lost.

The meter for the "unacceptable quality" depends on measurements performed on up-link physical channels as well as duration of disturbance or loss of contact. Typically the meters are set such that the quality is considered unacceptable only when there has been no working contact with the UE for a few seconds for DCH connected and several minutes for cell connected.

If the quality is considered unacceptable or the UE is considered lost, the radio network will request the deletion of all connections towards this UE. Thereby all Radio bearers and RAB'sallocated for this UE are disconnected. Logical, HW and SW resources related to these channels/bearers are also released.


Soft/softer Handover overview

Algorithm–Relative thresholds minimizes the

number of mobiles in soft handoverB A

Time

C/I

Add B Delete A

Add margin Drop

margin


Soft HandoverSoft handover essential for power controlSoft handover reception

– combines signals from RBS in the RNC

RBS 1 RBS 2

RNC


Softer Handover

Softer handover reception– combines signals from two or more sectors in one RBS

RBS


Characteristics of soft/softer handover

RNC controls the UE measurements (i.e. what to measure, report type, what to report and the monitoring set)UE measures on CPICH (Ec/No, RSCP or path loss)UE evaluates measurements (event driven or periodic)RNC evaluates which cells to add/replace/remove from active set (max size is 4)RNC executes the handover decision and provides UE with new neighbor list


Paging

Purpose: Paging enables the CN to page UEs for terminating service request or for the UTRAN to reach the UE to trigger a UE state transition. The function will also broadcast modified system information to all UEs. The following cases are handled by the paging function: – CN originated when UE in idle mode – CN originated when UE in connected mode. – UTRAN originated to trigger a UE state transition.– UTRAN originated to trigger a UE to read updated system in-

formation.


Cell Update

Purpose: Using common or paging channels are important to allow an efficient management of resources for always connected low intensity packet traffic. The feature "Cell Update" is used to allow mobility, cell reselection ("hard handover") and efficient paging of UE's in such states.

Benefit:– Support the mobility for UE's on common or paging channels.– Provide a high success rate and efficient management of

resources for paging to CELL_PCH connected UE's (PCH is Paging Channel).


URA_PCH State

Idle Mode

RRC Connected Mode

Idle

URA_PCH Cell_PCH

Cell_FACH Cell_DCH

New state called WCDMA RAN Registration Area (URA_PCH State)Benefit:– Reduce signaling in

WCDMA RAN due to updates of location of moving mobiles

– Simplified paging– Lower UE battery

consumption


Intersystem Handover GSM - WCDMA

WCDMA

GSM

WCDMA

Dual mode


Why GSM Interoperability - why GSM Handover?

For service and coverage– Initially to provide “seamless service” to UMTS users

For load sharing between frequencies and Radio Access Technologies (RAT)– Increase capacity pool size– GSM network full used

For fair behavior in shared network solutions

To allow access to unique bearers


GSM Intersystem Handover

Inter frequency measurements are needed to support inter system handoverCompressed mode supports these measurements

– 3 different types of compressed mode

Compressed mode

time for measurementsTf = 10 ms

SF=SF0

SF=SF0/2SF=SF0

Inter system

WCDMAGSM


Compressed Mode - 3 different types

Different alternatives with different impactsLower spreading factor

+ Same user data rate- Power increase- Need to allocate a code with half spreading factor

1) Allocate code in the same code tree - remain code orthogonality2) Allocate code in another code tree - easy to get codes

Puncturing+ Same user data rate can be used+ Remain on the same spreading factor (code)- Power increase- Weakens Forward Error Correction (FEC) codingHigher layer scheduling+ Power increase can be avoided- Lower user data rate


Control of Inter Radio Access Technology Cell Reselection

UMTS to GSM :Neighbour Cell ListQuality measure

• CPICH (RSCP or CPICH Eb/N0)For each neighbour Cell Reseletion criteria

• Serving cell quality limit to start neighbor cell measurements• Minimum required signal level to allow selection• Minimum required quality of to allow selection

(For FDD cells) • Offset between serving cell and neighbor cell• Hysteresis of the serving cell for ranking of cells• Time to trigger cell reselection


BSC

RNC

Real time changes of Connection & Cell

Link adaptation and control as well as inter-system, service based load sharing.

Based on existing and currently standardized, Iur-g, interfaces.

Functionality for: - Handover Control- Admission Control- Load Control- Service Differentiation

Ensure full utilization of spectrum and system at maximum performance.

Intersystem Traffic ControlAlways Best Connected

GSM/EDGE

WCDMA

Core Network


Load Balance GSM-UMTSSystem Features for Traffic Control and Efficiency as Function of Time

Time

• Symmetric Handover Algorithms in GSM and WCDMA• Congestion triggered Handover from GSM to WCDMA• System preference based Handover from GSM to WCDMA• Coverage based Handover from WCDMA to GSM• Cell Reselection Idle& PS• Congestion hold-down

•Congestion triggered Handover WCDMA to GSM•System preference based Handover from WCDMA to GSM

• Real time load Balancing, Iur-g• O&M load Management

• Self Configuring Radio Network with Dynamic Cell Reselection Control

Dual-mode Handsetpenetration(GSM/EDGE-WCDMA)

• Combined Configuration Management, CCM• Service based Directed Retry• Load Control

100%Achieved Load-balancing Efficincy


Transparent message transfer

Supports the transfer of signaling and other messages between a UE and the core network nodes, MSC and SGSN.Basic feature required for UE signaling, e.g. for call set-up Provides support for SMS

DescriptionIn UMTS, the radio access network need to transfer signaling messages (Non Access Stratum) transparently between the UE and either of the core network domains for establishing and releasing calls. Such transparently transferred messages are also used for other purposes, e.g. LA/RA updating and support SMS services.


System Information distribution

Allows the UE to get access to updated System Information, which in turn is necessary for correct network behavior.DescriptionThe system information is regularly broadcast to the UE's on Broadcast Channel. The information is relates to:– Power control, both Common and dedicated channels, e.g. UL

interference – RRC connection parameters e.g. timers and counters – Adjacent cell configuration parameters.– UE Measurements e.g. to support handover evaluation – Location Area and Routing Area– Common channel configuration– Cell selection and re-selection


Node and network synchronization

Node synchronization:The Node Synchronization function contains four sub-functions:– Holding of and generation of node reference time in the RNC and the

RBSs, – Measurement of phase difference between the frame reference time in

the RNC and the frame reference time in each RBS.– A database of measured phase differences to each RBS is held, and an

estimate of the accuracy of each of the measurement. – Supervision of drifting frame reference times in the nodes.

Generation of node reference time and phase measurement are handled by a device, the Timing Unit (TU), present in both RNC and RBS.


Node and network synchronization

Network synchronization:The RBS and RNC internal clocks can be synchronized either to:

– the transport network or to – an external high stability clock reference.

RBSs and RNCs both have stable clocks locked to the reference carried over the transmission network. The clocks, besides synchronizing internal functions in the node, also generate sync to the outgoing transmission links and to the radio transmission. It is possible to cascade up to 5 clocks (Nodes)One primary and up to seven secondary synchronization reference links can be configured for each nodeThe network synchronization (clock) function can be configured to be redundant or non-redundant.


Integrity protection and ciphering mode control

Integrity protection handles: – the control of integrity protection of control plane data– co-ordination of integrity keys between different core

networks (PS and CS). The integrity protection maintains access link data integrity between the SRNC and UE.

Ciphering Mode Control handles:– the control of ciphering of user plane and control

plane data– co-ordination ciphering keys between different core

networks (PS and CS). The ciphering is performed for secure data confidentiality between the SRNC and UE


IOT certification for Iu/Iur

Iu is the most common 3G multi-vendor interface

Enables an operator to choose (several) RAN suppliers

RAN RAN

3G CN 3G CN

Vendor-A3G system

Vendor-B3G system

Iu IuIu Iu


High Speed Downlink Packet Access (HSDPA)

Requirements– High peak data rates (8-10 Mbps)– Higher throughput – Lower delay

Introduction of a new High Speed Downlink Shared Channel (part of 3GPP Rel.5)– Exists in downlink only– Always associated with a dedicated physical channel (DPCH) pair

DPCH

HS-DSCH


Mulitcode to allow bit rates >384 kbit/s

One user has more than one channelization codeOne user can than have several data streams to achieve bit rates above 384kbit/s

Data 2TFCIData 1 TPC PilotPrimaryDPCCH/DPDCH

Data 4Data 3AdditionalDPCCH/DPDCH

Data NData N-1AdditionalDPCCH/DPDCH


The use of codes in WCDMASingle cell view:– all mobiles need to share the same frequency carrier in WCDMA– orthogonal codes separate between the users and between

different communication channels to one user (multi-code operation)Channelization codes

Network view:– nearly orthogonal codes to distinguish between the

communication channels from different RBS’s– One scrambling code per sector and per carrier e.g a 3x2 RBS

has 6 scrambling codesScrambling codes


Multiple scrambling codes overview

Each sector/carrier (cell) broadcasts a unique cell ID code -> downlink scrambling code

With multiple scrambling codes -> there is more than one downlink scrambling code per sector/carrier (cell)

Cell #1, ID code 1

Cell #2, ID code 1

Cell #1, ID code 2

Cell #2, ID code 2

Cell #3, ID code 1

Cell #3, ID code 2


Multiple scrambling code benefitMultiple scrambling codes gives more than one channelization code tree per sector/carrierThe problem with code shortage is removed.

1

11 10

1111 1100 1010 1001

11111111 11110000 11001100 11000011 10101010 10100101 10011001 10010110

1

11 10

1111 1100 1010 1001

11111111 11110000 11001100 11000011 10101010 10100101 10011001 10010110


Power Scheduling

Extra capacity can be given to packet data users

load

time

max planned load

Load sharing in time results in a high capacity– Continuous update of the transport format for the interactive RABs both in UL and DL– The aim is to maximize the bit rate for the interactive users

Smooth interference levels in the system– Optimize the usage of the radio capacity in the system e.g DL power, without exceeding

the maximum planned load

Wcdma radio functionality

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