RAB drop rate improvement - L1,L2,L3 TIMERS TUNING

Radio LINK SUPERVISION TIMER Trials – L1 Timers

UE SIDE L1 TIMERS

›T313 (Proposing changes from 3 to 10)

›N313 (Proposing changes from 100 to 200)

RNC SIDE L1 TIMERS

›rlFailureT (proposing changes from 10 to 20)

›DCHRCLostT (proposing changes from 50 to 90)

›ninsyncind/noutsyncind (proposing changes to 1 and 256 respectively)

BACKGROUND

• Radio connection supervision (RCS) strategy contains some system constant ruling the algorithm to supervise the connection at L1 (phisycal), L2 (RLC) and L3 (RRC) level in order to understand the best moment to release the connection

• Those system constant were originally configured for a certain traffic profile and certain kind of mobiles, and they are not fitting anymore for the current advanced mobiles (tipically Smartphones) and their traffic profile (tipically MultiRabs)

• A new RCS strategy has been considered for better handling the current 3G traffic

L1 Timer (UE side) N313 : number of consecutive “out of sync” after that Ue starts t313“Out of sync” generation is Ue dependant, generally when the Ue measures a SIR < target SIR.(the SIR is measured according to a sliding window of 160 ms  according to motorola information)According to specification Ues switches off the transmitter when is “out of Sync”.T313: After n313 consecutive “out of service”, the UE starts T313 and doesn’t  stop it until it Measures an “in Sync” that is SiR> SIR TargetN315: number of consecutive “in Sync” for the Ue to stop T313  and the Radio Link FailureProcedureTimer for Radio Link Failure in DL = n313*10 (ms)+ t313 . After this timer expiry the call is
droppedL1 Timer (proposed value)It is recommended to align themProposed valuesDchRcsLostT = 90 (9 sec) / rlFailureT = 20 (2 sec)T313 = 10 sec / N313 = 200UL RLS (DchRcLostT+ rlFailureT+(noutsyncind*10ms)) = 9 +2+2.56 = 13.56 secDL RLS (T313 + N313*10ms) = 10 + 200*10ms = 12 secimproved rlc settings             
Involved Parameters›The parameters involved in the change are listed below:–UeMaxDat – the parameter determines the number of transmissions of a PDU before a SDU is discarded or reset procedure is initiated. The number of transmissions is equal to MaxDat - 1.–UeTimerPoll – the parameter defines the maximum time for the transmitter to receive a STATUS PDU corresponding to a poll that it has sent before polling again. It is started when the poll is transmitted. A new poll is sent when this timer expires and no status is received.–UeMaxRst – the parameter determines the maximum number of transmissions of reset PDU equals MaxRst-1.

–UeTimerRst – the parameter defines the timer used for retransmission of reset PDU.–RncMaxDat – the parameter determines the number of transmissions of a PDU before a SDU is discarded or reset procedure is initiated. The maximum number of transmissions of a PDU equals MaxDat-1.–RncTimerPoll – the parameter defines.the maximum time for the transmitter to receive a STATUS PDU corresponding to a poll that it has sent before polling again. It is started when the poll is transmitted. A new poll is sent when this timer expires and no status is received.–RncMaxRst – the parameter determines the maximum number of transmissions of a reset PDU. The maximum number of transmissions of a reset PDU equals MaxRst-1.All parameters are system constants and may only be changed by Ericsson personnel.›Note that the parameter values for UeMaxDat, UeTimerRst and UeMaxRst are coded, for example setting parameter UeMaxRst = 4 means that that the UE will use UeMaxRst = 12. •Current TELECOM settings for SRB:Timerpoll (both sides RNC and Ue)=160MaxDat(both sides RNC and Ue)= 40rncMaxRST = 1UeMaxRST= 0 (means 1)rncTimerRST=550UeTimerRST= 10 (means 550)Total L2 timer (both UL or DL)= Timerpoll*(MaxDat-1)+TimerRST*(MaxRST-1)
= 160*(39)+ (1-1)(550) = 6,24sec = 160*(39)+ (1-1)(550) = 6,24sec = 160*(39)+ (1-1)(550) = 6,24sec = 160*(39)+ (1-1)(550) = 6,24secIn our opinion L2 supervision timers need to be made more robust (longer timeouts) to handle temporary bad radio, and it is suggested to align them with L3 supervision timersL2 Timers : proposed valuesOn RNC side there is no limit on maxDat, so use that to increase the timeout- On UE side maxDat is limited, set it to the max value (15) and then increase timerPoll to get the timeout length wanted.UeRC=2 / UeRcRb=2,3,4 (UeRc=speech and DCH 2,3,4 associated with speech)rncMaxDat  proposed = 50  ueMaxDat  proposed = 15(40)rncMaxRST proposed = 3  ueMaxRST proposed =4(12)rncTimerPoll  proposed = 270  ueTimerPoll  proposed = 200In this case the RLC supervision timing will lastIn RNC (270*49) + (3-1)*550 = 14.33 secondsIn Ue (39* 200)+(12-1)*550 = 13.85 secondsWe’re proposing to change them on pure speech (uerc=2, ueRcRb=2,3,4), and on Speech + Ps 0/0, and to all active multiRab associated with Speech.After looking at the performances, we would like to extend to all PS RABs as wellL3 Timers•L3 Timers start when a rrc procedure takes place (i.e. Radio Bearer / Radio Bearer Setup complete  -  active set / active set update complete)•The more classical example is L3 soft handover procedureAfter sending an rrc active set update, if the RNC doesn’t receive an active set update complete by the UE within timer: tRrcActiveSetUpdate the call is dropped , even if the Ue should recover the L1 or the L2  levels. So L3 timers (in particular the soft handover)  should expiry only after the L1 and L2 timers have expiried (Ue / RNC has had all time considered useful to recover The connection)•Actual value of  tRrcActiveSetUpdate in network = 5 seconds•Proposed value= 10 seconds.rab setup/release  

tRrcRABEst & tRrcRABRel timers›Background–Timers for RB setup and RB release are suggested to be increased. That way, more time is allowed for RAB reconfigurations, such as switch from single-RAB to multi-RAB or vice versa, and the risk for drops during RAB reconfiguration is reduced.–RAB setup and release is supervised by the following timers:›tRrcRABEst for RAB setup›tRrcRABRel for RAB release–The timers set the time for RRC RESPONSE. It has been seen in field trials that retainability can be improved by increasing the timer values.
–Both timers are system constants and may only be changed by Ericsson personnel.›In order to align all L3 timers, we propose the following changes–Change tRrcRABEst from 5 to 10 (5s à 10s)–Change tRrcRABRel from 6 to 12 (6s à 12s)››Connection to other improvements:After the RB setup/release (supervised by timer tRrcRABEst  or tRrcRABRel) an RB reconfiguration is done if RLC parameters need to be changed between UeRc:s. This procedure is supervised by hardcoded timers (establish: 5s, release 6s). To avoid this timer supervised RRC procedure it is recommended to align RLC settings for UeRc as much as possible. This minimizes the risk for dropped call. See section