09 Wcdma Rno Access Procedure Analysis.pdf

09 WCDMA RNO Access Procedure Analysis WCDMA Access Procedure ReviewReview Access is associated with the call setup success rate of the network Mastering the access procedure can increase this KPI wit[.]

WCDMA Access Procedure

Access is associated with the call setup success rate of the network Mastering the access procedure can increase this KPI with the access parameters optimization

Random access procedure

Physical channel about access

PRACH access slot

Structure of the random-access transmission

Each random-access transmission consists of one or several

preambles of length 4096 chips and a message of length 10

Structure of the random-access transmission

The preamble-to-preamble distance τ p-p shall be larger than or equal to the minimum preamble-to-preamble distance

Structure of the random-access transmission

when AICH_Transmission_Timing is set to 0

τ p-p,min = 15360 chips (3 access slots)

Random access procedure

Physical channel about access

Random access procedure

Concepts in random access procedure

Preamble Signature

AC (Access Class)

ASC (Access Service Class)

RACH sub channels

Access slot set

The preamble signature corresponding to a signatures consists of 256 repetitions of a length

16 signature Ps(n) shown as the following table UE gets signature from system info type5.

Access Class

The SIMs/USIMs of all the UEs are allocated with one of Access Class 0~9 In addition, one or more special access classes (Access Class 11~15) might be allocated to the SIM/USIM storage information of the UEs with high priority, as shown below:

Access Class 13 - Public Utilities;

Different from Access Class 0~9 and 11~15, the control information of Access Class 10 is sent to UEs by means of air interface signalling, indicating whether the UEs belonging to Access Class 0~9 or without IMSI can be accessed to the network in case of emergency calls For the UEswith Access Class 11~15, they cannot initiate the emergency calls when Access Class 10 and Access Class 11~15 are all barred

Access Service Class

The PRACH resources (access timeslots and preamble signatures in FDD mode) can be classified into several ASCs One ASC defines a partition of certain PRACH resources

The ASCs are numbered within the range 0<= i <=7, and the maximum number of ASCs is 8 "0" indicates the highest priority and "7" indicates the lowest priority.

AC to ASC mapping In case the UE is member of several ACs it shall select the ASC for the highest AC number

ASC 1st IE 2nd IE 3rd IE 4th IE 5th IE 6th IE 7th IE

Access Slot Set

Access slot set 1 contains PRACH slots 0 – 7 and starts τp-a chips before the downlink P-CCPCH frame for which SFN mod 2 = 0 Access slot set 2

contains PRACH slots 8 - 14 and starts (τp-a –2560) chips before the downlink P-CCPCH frame for which SFN mod 2 = 1

RACH sub channels

14 13

12 11

10 9

8 7

2 1

0 7

6 5

4 3

6

14 13

12 11

10 9

8 5

5 4

3 2

1 0

7 6

4

8 14

13 12

11 10

9 3

7 6

5 4

3 2

1 0

2

11 10

9 8

14 13

12 1

7 6

5 4

3 2

1 0

0

11 10

9 8

7 6

5 4

3 2

1 0

Sub-channel number SFN modulo 8 of

corresponding

P-CCPCH frame

A RACH sub-channel defines a sub-set of the total set of uplink access

slots There are a total of 12 RACH sub-channels

Random access procedure

Before random-access procedure, Layer 1 shall receive the following information from the RRC layers:

The preamble scrambling code

The message length in time, either 10 or 20 ms

The AICH_Transmission_Timing parameter [0 or 1]

The set of available signatures and the set of available RACH sub-channels for each ASC

The power-ramping factor Power Ramp Step

The parameter Preamble Retrans Max

Preamble_Initial_Power

The Power offset P p-m = Pmessage-control – Ppreamble

The set of Transport Format parameters, This includes the power offset between the data part and the control part of the random-access message for each Transport Format

Random access procedure

Layer 1 shall also receive the following information from the MAC layers :

The Transport Format to be used for the PRACH message part.

The ASC of the PRACH transmission.

The data to be transmitted

Random access steps

1 Derive the available uplink access slots in the next full access slot set and Randomly select one access slot

2 Randomly select a signature from the set of available signatures within the given ASC

3 Set the Preamble Retransmission Counter to Preamble Retrans Max

4 Set the parameter Commanded Preamble Power to Preamble_Initial_Power

Random access steps

5 Transmit a preamble using the selected uplink access slot, signature, and preamble transmission power.

6 Check the corresponding AI, if received positive AI, send the message part and set L1 status “RACH message transmitted”

If received negative AI, set L1 status “Nack on AICH received”.

7 If no AI received, select the next access slot, signature and decrease the preamble retransmission counter by one, increase the preamble power by power ramp step Check if the counter more than 0 and the preamble power less than the maximum allowed If true, send a preamble again Otherwise, set L1 status “No ack on AICH”

Random access procedure

Physical channel about access

Parameters optimization

Preamble_Initial_Power = DL_Path_Loss + UL_interference +

the initial PRACH transmission power according to the open loop power

too big, the initial transmission power will be too big, but the access process will become shorter; if it is set too small, the access power will satisfy the requirements, but the preamble requires multiple ramps, which will lengthen the access process

PRACH Power Ramp Step

power by the UE before it receives the NodeB capture indication.

big, the access process will be shortened, but the probability of wasting power will be bigger; if it is set too small, the access process will be lengthened, but some power will be saved It is

a value to be weighed.

Maximum Preamble Retransmit Times

retransmission times of the UE within a preamble ramp cycle

big, the access process will be shortened, but the probability of wasting power will be bigger; if it is set too small, the access process will be lengthened, but some power will be saved It is

a value to be weighed.

Maximum Preamble Cycle Times

Mmax defines the maximum times of the random access preamble cycle When the UE transmits a preamble and has reached the maximum retransmit times (PreambleRetransMax), if the UE has not received the capture indication yet, it will repeat the access attempt after the specified waiting time; but the maximum cycle times cannot exceed Mmax.

too small, the UE access success rate will be influenced; if it is set too big, the UE will probably try access attempt repeatedly within a long time, which will increase the uplink interference.

RRC Setup Procedure

Parameters optimization

T300 and N300

DPDCH Power Control Preamble Length (PCPreamble)

Successive Synchronization Indication Times (NInSyncInd)

Successive Out-of-sync Indication Times (NOutSyncInd)

Radio Link Failure Timer Duration (TRLFailure)

N312 and T312

N313, N315, T313

T300 and N300

After the UE transmits RRC CONNECTION REQUEST message, the T300

timer will be started, and the timer will be stopped after the UE receives RRC CONNECTION SETUP message Once the timer times out, if RRC CONNECTION REQUEST message is retransmitted less than the number of times specified by the constant N300, the UE repeats RRC CONNECTION REQUEST; otherwise it will be in the idle mode

Influence on the network performance: The T300 setting should be considered together with the UE, UTRAN processing delay and the propagation delay The bigger T300 is, the longer time the UE T300 will wait for The bigger N300 is, the higher success probability of the RRC connection setup will be, and the longer RRC setup time will probably be It will likely be that a UE repeats the access attempt and the connection setup request transmission, and consequently other users will be influenced seriously

if it is the confirmation mode, the retransmission may cause more serious data delay If this parameter is set improperly, it will lead to data loss and retransmission delay, which will consequently influence the service rate and the transmission delay.

This parameter defines the successive synchronization indication times required for the NodeB to trigger the radio link recovery process The radio link set remains in the initial state until it receives NInsyncInd successive synchronization indications from L1, then NodeB triggers the radio link recovery process, which indicates that the radio link set has been synchronized Once the radio link recovery process is triggered, the radio link set is considered to be in the synchronized state

Influence on the network performance: The bigger this parameter is, the stricter the synchronization process will be, and the more difficult the sync will be; the smaller it is, the easier the synchronization will be However, if the link quality is bad, a simple synchronization requirement will lead to the waste of the UE power and the increase of uplink interference; in the radio link maintenance process, this parameter is used together with the successive out-of-sync indication counter

NOutSyncInd defines the successive out-of-sync indication times that are required to receive to start the timer TRlFailure When the radio link set is in synchronized state, the NodeB will start the timer TRlFailure after it receives NOutsyncInd successive out-of-sync indications The NodeB should stop and reset the timer TRlFailure after receiving NInsyncInd successive sync indications If the timer TRlFailure times out, the NodeB will trigger the radio link failure process, and indicate the radio link set that is out-of-sync

Influence on the network performance: If this parameter is set too small, the link out-of-sync decision will be likely to occur; if it is set too big, out-of-sync will not be likely to occur, but, if the link quality is bad, it will result in waste of the UE power and increased uplink interference In the radio link maintenance process, this parameter is adopted together with the successive synchronization indication counter

This value defines the timer TRlFailure duration When the radio link set is in synchronized state, NodeB should start the timer TRlFailure after it receives NOutsyncInd successive out-of-sync indications; and NodeB should stop and reset the timer TRlFailure after receiving NInsyncInd successive sync indications If the timer TRlFailure times out, NodeB will trigger the radio link failure process, and indicate the radio link set that is out-of-sync

Influence on the network performance: If the timer is set too short, there will few chances for link synchronization; if it is set too long, the radio link failure process will probably be delayed, and the downlink interference will be increased

N312 and T312

When the UE starts to set up the dedicated channel, it starts the T312 timer, and after the UE detects N312 synchronization indications from L1, it will stop the T312 timer Once the timer times out, it means that the physical channel setup has failed

Influence on the network performance: The bigger N312 is, the more difficult the dedicated channel synchronization will be; the longer T312 is, the bigger the synchronization probability will be, but the longer the synchronization time will be

N313, N315, T313

After the UE detects N313 successive out-of-sync indications from L1, it will start the T313 timer And after the UE detects N315 successive sync indications from L1, it will stop the T313 timer Once the timer times out, the radio link fails

Influence on the network performance: The bigger N313 is, the more difficult it will be to start T313, which will reduce the out-of-sync probability; the smaller N315 is, the longer T313 will be, and the bigger the link recovery probability will be These three parameters should be used together

RAB Setup Procedure

Appendix: MOC signaling process

Appendix: MOC signaling process

Inital Direct Transfer

RRC

RANAP RANAP

DCCH

Direct Transfer

RANAP RANAP

Direct Transfer

:

Direct Transfer DCCH ::

Direct Transfer DCCH ::

RRC Downlink

RRC

RRC

Uplink RRC

RRC

RRC

RRC

RANAP RANAP

Direct Transfer (Call Proceeding) Inital Direct Transfer

Appendix: MOC signaling process

Establishment

Q.AAL2 Q.AAL2

NBAP

Ready

Appendix: MOC signaling process

UE

Node B

DCCH : Radio Bearer Setup

DCCH : Radio Bearer Setup Complete

Q.AAL2 Q.AAL2

Appendix: MOC signaling process

RRC

RANAP RANAP

Direct Transfer (Alerting)

(Connect) RRC

RRC

RANAP RANAP

Direct Transfer (Connect Acknowledge) RRC

RANAP RANAP

Direct Transfer (Rlease Complete)

RANAP RANAP Direct Transfer

(Release)

RANAP RANAP Direct Transfer

Appendix: MOC signaling process

UE

Node B Serving RNS Serving

RANAP RANAP

RANAP RANAP

Iu Release Command

Iu Release Complete

Q.AAL2 Q.AAL2

Q.AAL2

Release Complete

Q.AAL2 Q.AAL2

NBAP

NBAP Complete

Random access procedure: physical channels, detailed random access procedure, access parameters optimization.

RRC setup procedure and parameters optimization.

RAB setup procedure and the whole UE outgoing call procedure.