CDMA 120 – cdmaOne and CDMA2000 Concepts and Terminology phần 7 ppsx

CDMA 120 – cdmaOne and CDMA2000 Concepts and Terminology

Section 6: Call Processing and Registration

80-13321-1 X11

© 2002 QUALCOMM Incorporated 6-7

CDMA 120

cdma university Section 6-7 Access Channel Processing Probe Probe Probe

Time

Power

MMT98010699Ac.emf

Description of the Access Channel

The Access Channel is transmitted at 4800 bps. Most access transmissions require only

120-180 milliseconds.

The Access Probing Process

To access the system, a mobile randomly selects an Access Channel and transmits a probe

(message) without any coordination with the Base Station or other mobiles. If the probe is not

acknowledged, the mobile will transmit the same probe at a random time later, generally at a

higher level of power. After several retransmissions, the mobile will declare an access failure and

reinitialize. The access attempt may not be granted due to a shortage of resources. This is referred

to as a blocked call.

Priority Access Channel Assignment (PACA)

High priority subscribers may be placed in a queue when a Traffic Channel is not available to grant

their access request. When a Traffic Channel becomes available, the high priority subscriber will

be connected and notified much like an incoming call.

CDMA 120 – cdmaOne and CDMA2000 Concepts and Terminology

Section 6: Call Processing and Registration

80-13321-1 X11

© 2002 QUALCOMM Incorporated 6-8

CDMA 120

cdma university Section 6-8 Traffic Channel Message Structure

Rate 1/2 Primary +

Signaling

80 bits

Primary Traffic

88 bits

Signaling or

Secondary Traffic

1

MM

1

1

TT

0

2

TM

00

12 bits 8 bits

CRC Tail

Rate 1/4 Primary +

Signaling

40 bits

Primary Traffic

128 bits

Signaling or

Secondary Traffic

1

MM

1

1

TT

0

2

TM

01

12 bits 8 bits

CRC Tail

Rate 1/8 Primary +

Signaling

16 bits

Primary Traffic

152 bits

Signaling or

Secondary Traffic

1

MM

1

1

TT

0

2

TM

10

12 bits 8 bits

CRC Tail

Blank and Burst 168 bits

Signaling Traffic

1

MM

1

MM - Mixed Mode

0 = Primary Only

1 = Primary + Signaling

or Secondary

TT - Traffic Type

0 = Signaling

1 = Secondary

TM - Traffic Mode

00 = 80 / 88

01 = 40 /128

10 = 16 / 152

11 = 168

1

TT

0

2

TM

11

12 bits 8 bits

CRC Tail

MMT98010678Ag.emf

Frame Formats

The Traffic Channel carries user voice, user data, and call control signaling. This is accomplished

using a multiplex option. Signaling on the Traffic Channel is important for the handoff and power

control processes.

Traffic Channel Message Structure

Most Traffic Channel messages fit into a single frame. cdmaOne systems allow for messages to be

much longer than a single frame. In this case, the message will be divided into segments and placed

in separate frames.

Call Failure

If either the Forward or Reverse link becomes degraded, many frames may arrive in error.

If the link degrades significantly, the audio signal may be muted. Both the mobile and the Base

Station will tolerate such a poor quality link for about 5 seconds, then discontinue the call. This is

referred to as a dropped call.