CDMA Access Channel Parameters

Access Channel Parameters

Access Channel ParametersAccess Channel Parameters

Access Channel ?Overview

Access Channel is a Reverse CDMA Channel used by mobile stations for communicating to the base station.

The Access Channel is used by the mobile station to initiate communicat- ion with the base station and to respond to Paging Channel messages.

In additioanlly, the Access Channel may be used to transmit user’s short messages.

The messages transmitted on the Access Channel can be classified into two types, the Request Messages and the Response Messages.

Example of Request Messages:

Origination Message, Registration Message, Order Message, etc.

Example of Response Messages:

Response Message, Order Message, etc.


Access Channel Structure

1.2288Mcps

4.8KbpsAccess

Channel Bits

14.4Ksps

Long Code

Generator

Long Code Mask

1.2288Mcps

28.8Ksps 28.8Ksps

64-ary Orthogonal Modul

ation

Convolutional Coding

R=1/3

Symbol Repetition

Block Interleaving

307.2Kcps

D

1/2 chip

FIR Filter

QPSK

I-PN （ 1.2288Mcps)

Q-PN （ 1.2288Mcps)

FIR Filter


FeaturesThe mobile station transmits on the Access Channel using a Random Access procedure.

64-ary orthogonal modulation

Spreading and channelizing with Long PN code

Fixed data rate: 4800bps

Frame length: 20ms

Maximum 32 Access Channels shall be supported per Paging Channel

The mobile station supports only one Access Channel.

Long code mask

41 33

32 28 27 25 24 9 8 0

110001111 ACN PCN BASE_ID PILOT_PN

ACN : Access Channel Number (0~31)

PCN : Paging Channel Number (1~7)

BASE_DI : Base Station ID (0~65535)

PILOT_PN : Pilot PN offset index


Access Channel Frame Structure

ACH Frame

Access Channel Slot

0.02x[(1+PAM_SZ)+(3+MAX_CAP_SZ)] sec, 96x[(1+PAM_SZ)+(3+MAX_CAP_SZ)] bits

20ms, 96bits

Access Channel Message Capsule

Access Channel Message

MSG_LENGTH

Padding

Message Body CRC

88 x Nf bits

8 x MSG_LENGTH

8bits 2 - 842bits 30bits

. . . . . .

Access Channel Preamble ACH Frame Body T ACH Frame Body T. . .

1+PAM_SZ Frames, 96x(1+PAM_SZ) bits

Nf Frames, 96xNf bits (Not exceeding 3+MAX_CAP_SZ Frames)

Nf: Number of Access Channel frames needed for message transmission

T: Encoder Tail Bits (8bits)

ACH Frame ACH Frame ACH FrameACH Frame

T T


Random Access ProcedureOverview

In the CDMA system, the mobile stations use the random access proced-ure to make a low probability of collision among the probes sent by each mobile station.

The mobile station shall begin the access probe transmission at the timing posterior to the start of an access channel slot by a random PN chips.

System Time

Access Channel Slot Access Channel Slot

The actual start of transmission is deferred from the beging of the access channel slot for PN chips.


Access Attempt

System Time

Access Probe Sequence 1 Seq 2 Seq 3

Seq MAX_REQ_SEQ (15 max)

Access Attempt

RS RS PD

Request message ready for transmission

Request Attempt

PD PD

PD : Persistence Delay

RS : Random Sequence backoff delay


System Time

Access Probe Sequence 1 Seq 2 Seq 3 Seq 4

Seq MAX_RSP_SEQ (15 max)

Access Attempt

RS RS RS

Response message ready for transmission

Response Attempt

RS : Random Sequence backoff delay


System Time

IP (Initial Power)

Access Probe 1 + NUM_STEP

(16 max)

Access Probe Sequence

TA RT

PI

Select Access Channel (RA), initialize transmit power

Access Probe Sequence

RT

Access Probe 3

Access Probe 2

Access Probe 1

TA TA

PI

PI : Power Increment

TA : Acknowlogment response timeout

RT : Probe backoff


System Time

Access Channel Slot and Frame Boundary

Access Probe

PN Randomization Delay = RN chips = RN 0.8138 s

Access Probe

One Access Channel Slot

Access Channel Preamble (Modulation Symbol 0)

Access Channel Message Capsule

Access Channel Frame (20 ms)

1 + PAM_SZ (1 – 16 frames)

3 + MAX_CAP_SZ (3 – 10 frames)

4 + PAM_SZ + MAX_CAP_SZ (4 – 26 frames)

Actual Access Probe Transmission


Vari-able

Name Generation Range Units

IP Initial Open-loop PowerIP = – mean input power (dBm) + offset power + NOM_PWR – 16×NOM_PWR_EXT + INIT_PWR + interference correction

dBm

PD Persistence DelayDelay continues slot-by-slot until persistence

test (run every slot) passes.- slots

PI Power IncrementPI = PWR_STEPs + change in mean input power + change in interference correction

dB

RA Access Channel NumberRandom between 0 and ACC_CHANs; generated before every access probe sequence or every access probe.

0~31 -

RN PN Randomization DelayHash using ESN between 0 and 2PROBE_PN_RAN – 1; generated once at the beginning of each access sub-attempt.

0~511 chips

RS Sequence BackoffRandom between 0 and 1 + BKOFF; generated before every sequence (except the first sequence).

0~16 slots

RT Probe BackoffRandom between 0 and 1 + PROBE_BKOFF; generated before subsequent probes.

0~16 slots

TA Ack Response TimeoutTA = 80 (2 + ACC_TMO); timeout from end of slot

160~1360 ms


Parametersmax_req_seq

Maximum number of access probe sequences for a request.

Range: 1~15 Default: 2

backoff

Backoff range between access probe sequences.


max_rsp_seq

Maximum number of access probe sequences for a response.


nominal_pwr

Nominal transmit power offset.

Range: - 8 ~ +7dB


nom_pwr_ext

Extended nominal transmit power offset. For Band Class 0, set to “0”; for Band Class 1, set to “1”.

initial_pwr

Initial power offset.

Range:-16 ~ +15dB

pwr_step

Power increase step size.

Range: 0~7dB Default: 3

num_step

One less than number of probes in an access probe sequence.

Range:0~ 15 Default: 9

acc_timeout

access response ack timeout.



probe_backoff

Backoff between access probe transmissions.


preamble_size

One less than Access Channel preamble size.

Range: 0~15 Default: 3 Units: frames

max_cap_size

Three less than maximum frames in an Access Channel message capsule.

Range:0~7 Default: 7 Units: frames

probe_pn_random

Time randomization parameter for Access Channel probes.



Persistence TestOverview

The persistence test is used to control the Access Channel load, and may be used to provide access priority for some mobile stations.

For request access probe sequences only, before first probe transmissi-on in an access probe sequence, the mobile station shall perform the persistence test.

If the test passes, the mobile station shall begin to transmit the first access probe in that slot; if the test fails, the mobile station shall defer to transmit the first access probe slot-by-slot until persistence test passes.

The value of the Persistence Delay (PD) is determined by the persistence test duration.


Persistence test procedureThe mobile station computes a variable P depending on the parameters (PSIST, REG_PSIST and MSG_PSIST) received from the base station via the Access Parameters Message.

The mobile station shall generate a ramdom number RP, 0<RP<1, using a specific algorithm.

The persistence test is said to pass when RP is less than the current value of P for the type of this access attempt.

If RP greater than or equal to the current value of P, the mobile station shall defer the access probe transmission to next access channel slot, and shall perform the persistent test with new random number RP.

The base station can adjust the persistence test delay by change the PSIST, REG_PSIST and MSG_PSIST parameters. The value of P is smaller, the persistence test delay is longer.


Variable P calculationIf the Access Channel request is a registration, P shall be computed by

If the Access Channel request is a message transmission, P shall be computed by


If the Access Channel request is other than a registration or a message transmission, P shall be computed by

where ACCOLCp (0~15) is access overload class indicator.

The access overload class 0 ~ 9 are assigned to commercial mobile stations, the access overload class 10 is assigned to test mobile station, the access overload class 11 is assigned to emergency mobile station, and the access overload class 12~15 are reserved.


RP Generation

RP = Zn / m

Zn = a Zn-1 mod m

Z0 = ( ESN RANDOM_TIME ) mod m

a = 75 = 16807

m = 231 – 1 = 2147483647

where RANDOM_TIME shall be the least-significant 32-bits of SYS_TIMEs stor

ed from the Sync Channel Message.


Parameterspsist_0_9

Persistence for overload classes 0~9.


psist_10

Persistence for overload class 10 (test mobile stations).


psist_11

Persistence for overload class 10 (emergency mobile stations).


psist_12 ~ 15

Persistence for overload class 12~15 (Reversed).



msg_psist

Persistence modifier for access channel message transmissions.


reg_psist

Persistence modifier for access channel registration transmissions.


minor_psist

Persistence for minor overload class.

Range: 0~7 Default:

major_psist

Persistence for major overload class.

Range: 0~7 Default:


critical_psist

Persistence for critical overload class.

Range: 0~7 Default:

Date post:	29-Nov-2014
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CDMA Access Channel Parameters

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