Compressed Mode

Topics to be covered What is Compressed Mode? Where it is used? Compressed Mode Interfaces and PRBs Methods of CM Signaling Diagrams Handling of Special cases during CM

What is Compressed Mode? Compressed Mode is a state when reception and

transmission of UE and BTS is halted in order to perform measurements in other WCDMA frequencies or RATs.

The measurements involve InterFrequency HO or InterSystem HO measurements.

InterFrequency HO measurements HHO is an Interfrequency HO. HHOs are difficult for a MS in a CDMA system. Two options available:

- Dual Mode Receiver- Compressed Mode.

InterSystem HO measurements InterSystem HOs are HOs between two different RATs. Before, UE can start any HO, it must measure the quality of the new

cell/carrier. UE need to :

- know the frequency in which the new cell in the other system is transmitting.

- measure the signal strength of the new carrier. Two modes:

- Dual Mode receiver

- Compressed Mode

Compressed Mode Interfaces and PRBs

HA3

MCC BRMRRC, IUB, IUR, L2

Compressed Mode Interfaces and PRBs

HA3 determines whether there is need to apply CM for individual UE and hence controls preparing, activation and deactivation of CM usage for an UE.

MCC prepares, activates or deactivates CM by request of HA3. MCC sends configuration and control messages to BTS (Iub), DRNC (RNSAP), UE (RRC) and L2.

BRM determines compressed Mode pattern parameters and used compressed mode method. BRM also checks whether the CM is possible to apply for an UE.

Parameters from HC Reason for CM

- Uplink DCH quality

- UE Uplink Tx Power - CPICH RSCP- Downlink RL Tx Power- CPICH Ec/No- Fast moving UE in HCS- Service/Load or IMSI based handover

Measurement Purpose- FDD Measurement- TDD Measurement- GSM Carrier RSSI Measurement- GSM initial BSIC identification

Signalling Diagram of Compressed Mode

RRMSRNC-HCSRNC-AC/PSBTSUE

CM required

CM on

NBAP/RNSAP: RL Reconfiguration Commit

RRC: Ph/Tr reconfiguration

RRC: Measurement Control

RRC: Measurement Report

RRC: Measurement Report

RRC: Measurement Control

CM off

NBAP/RNSAP: RL Reconfiguration procedure/CM command

RRC: Ph/Tr reconfiguration

Measurement Done

Uu Iub

NBAP/RNSAP: RL Reconfiguration Prepare

NBAP/RNSAP: RL Reconfiguration Ready

DRNCIur

NBAP/RNSAP: Compressed Mode Command

Types of Frame Gap used in CM

Normal Frame Normal Frame

CM Frame CM Frame

15 timeslots

8 timeslots 7 timeslots 8 timeslots 7 timeslots

Normal Frame Normal Frame

CM Frame CM Frame

15 timeslots

11 timeslots 7 timeslots 12 timeslots

Single Frame

Double Frame

Methods for Compressed Mode Higher Layer Scheduling (HLS): DCH user data transmitted in the channel

is reduced. Lower bit rate TFCS is constructed.

- HLS ½

- HLS ¾

SF/2: Temporarily doubles the physical channel data rate in the radio channel.

Compressed Mode Pattern Parameters

D O C U M E N T T Y P E

T y p e U n i t O r D e p a r t m e n t H e r eT y p e Y o u r N a m e H e r e T y p e D a t e H e r e

T r a n s m i s s i o n

T r a n s m i s s i o n g a p 2

g a p 2

T G S N T G S N

T G L 2 T G L 2

T G p a t t e r n 2

# T G P R C

g a p 1

T r a n s m i s s i o n T r a n s m i s s i o n

g a p 1

T G D T G D

T G P L 1 T G P L 2

T G p a t t e r n 1 T G p a t t e r n 2

T G L 1 T G L 1

# 1 # 2 # 3 # 4 # 5

T G p a t t e r n 1T G p a t t e r n 1 T G p a t t e r n 2 T G p a t t e r n 1 T G p a t t e r n 2

Frame structure types in CM

Slot # (Nfirst - 1)

TPC

Data1TFCI Data2 PL

Slot # (Nlast + 1)

PL Data1TPC

TFCI Data2 PL

transmission gap

Slot # (Nfirst - 1)

TPC

Data1TFCI Data2 PL

Slot # (Nlast + 1)

PL Data1TPC

TFCI Data2 PL

transmission gap

TPC

(a) Frame structure type A

(a) Frame structure type B

Examples of CM methods in Downlink

Examples of CM methods in Uplink

Higher layer scheduling (Double Frame):

Halving the spreading factor (Single Frame):

CM on

CM on

CM off

CM off

Gaps

Certain TFCs are not allowed to use

SF/2 Original SF

Gaps

t

P

10 ms

Compressed mode by HLS

Higher layer scheduling decreases transport channel capacity and that is why it can be used only for NRT.

It can not be used for circuit switched and RT PS (conversational and streaming) data TrChs.

Advantage is that it does not cause any extra load to the cell. Disadvantage is that it really decreases capacity of PS data channel.

Compressed mode by SF/2 SF/2 can be used both in downlink and uplink. It allows single frame method.

Used for AMR.

  During the compressed mode, original spreading code is used in normal frames between

gapped frames and new spreading code, which is taken from one step higher level from OVSF tree is used during the compressed frames.

Alternative scrambling code allows the usage of channelization codes of normal channelization code tree again and now those channelization codes are always free.

Signalling Diagram in case of HLS

RRM

CM detected

CM method selected

RNC-RRMRNC-RRCRNC-MACRNC-NBAPBTSUE

PhCh & TrCh prm

PhCh & TrCh prm

RRC: Physical/Transport Channel Reconfiguration

RRC: Physical/Transport Channel Reconfiguration Complete

TrCh prm & TFC restrictions

Uu Iub

NBAP: RL Reconfiguration Prepare

NBAP: RL Reconfiguration Ready

NBAP: RL Reconfiguration Commit

Compressed mode activation and measurement

CM off & TrCh prmRRC: Physical/Transport Channel Reconfiguration procedure or Measurement Control

CM off & TrCh prm

CM off & PhCh & TrCh prmNBAP: RL Reconfiguration procedure or CM Command

Signalling Diagram in case of SF/2

RRM

CM detected

CM method selected

RNC-RRMRNC-RRCRNC-MACRNC-NBAPBTSUE

PhCh prm

PhCh prm

RRC: Physical Channel Reconfiguration

RRC: Physical Channel Reconfiguration Complete

Uu Iub

NBAP: RL Reconfiguration Prepare

NBAP: RL Reconfiguration Ready

NBAP: RL Reconfiguration Commit

Compressed mode activation and measurement

CM offRRC: Physical Channel Reconfiguration procedure or Measurement Control

CM offNBAP: RL Reconfiguration procedure or CM Command

TFS Subsets for TFCS Construction

= TFS restriction class 1 = no restriction 384 384 = TFS restriction class 2 256 256 256 -

128 128 128 - 128 -64 64 64 - 64 - 64 -

32 32 32 32 32 32 32 32 32 3216 16 - - - - - - - - - -

8 8 - - - - - - - - - - - -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 8 16 32 64 128 256 384 DCH bit rate 336 96 176 336 336 336 336 336 TB size

128 12864 64 64 -48 - - - 32 32

32 32 32 - 32 - 24 -16 16 16 16 16 16 16 16 16 16 16 -

8 8 - - - - - - - - 8 8 8 8 8 80 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 8 16 32 64 128 0 8 16 32 DCH bit rate336 176 336 336 336 336 336 336 336 336 TB size

DC

H T

TI =

20

ms

DC

H T

TI =

40

ms

DC

H T

TI =

10

ms

Handling of special cases during the CM RAB establishment, modification or release. SF = 4 is not allowed. Relocation. Hard HandOver (HHO). DCH needs to be released or downgraded due to pre-emption function

or enhanced overload control function. Inactivity timer of PS DCH expires but other active DCHs are present. Inactivity timer of last PS DCH expires. CM is not supported in case of PS NRT with 8/8 kbps. (CR 665)

Power Control During Compressed Gaps, PC performs worst. Also compressed frames

may be lost if PC is not set correctly.

To avoid this, a parameter called RPP (Recovery Period Power) is used. It specifies the uplink PC algorithm applied during recovery period after each transmission gap in the CM.

During Recovery Period, PC is allowed to recover SIR as close as possible to target SIR.

Order of Execution of CM methods Downlink

- SF/2- SF/2 with Alternative Scrambling Code- HLS ½- HLS ¾

Uplink- SF/2- HLS ½ - HLS ¾

References Packet Scheduler SFS. 3GPP spec 25.211 - Physical

channels and mapping of transport channels

3GPP spec 25.215 – Physical Layer Measurements