1. An Introduction to CDMA Air Interface: IS-95A

2. Contents
Introduction
Forward CDMA Channel
Reverse CDMA Channel

3. CDMA Around the World

4. IS-95 Interfaces
A Interface (BSC-MSC) .. This interface is between the BSC and the MSC. It supports both the control plane and user plane
Abis Interface (BTS-BSC)—This is the interface between the BSC and BTS. This is internal interface and generally proprietary
B Interface (MSC-VLR) This interface is defined by TIA IS-41
C Interface (MSC-HLR) This interface uses IS-41 messaging as well
D Interface (HLR-VLR) – HLR-VLR signaling is based on IS-41 as well. It sits on top of SS7

5. IS-95 interface (cont..)
E Interface (MSC-MSC)– Inter MSC signaling is defined in IS-41
L interface (MSC-IWF) This interface allows the ability for circuit switched data in second generation networks
Um Interface (BS-MS) – This is the air interface between the mobile and the network

6. Multiple Access CDMA Benefits of CDMA:
unique digital codes are used to differentiate subscribers
codes are shared by both MS and BS
all users share the same range of radio spectrum
Benefits of CDMA:
Capacity increases: 4 to 5 times (GSM)
Improved call quality
Simplified system planning
Enhanced privacy
Improved coverage characteristics
Increased talk time for portables
Bandwidth on demand

7. CDMA There are two CDMA common air interface standards:
Cellular ( MHz) - TIA/EIA/IS-95A
PCS ( MHz) - ANSI J-STD-008
They are very similar in their features, with exceptions of the frequency plan, mobile identities, and related message fields.
IS-95A
45 MHz spacing for forward & reverse channel
Permissible frequency assignments are on 30 kHz increments

8. Forward CDMA Channel of IS-95A
From BSS to MS
It carries traffic, a pilot signal, and overhead information.
Pilot is a spread but unmodulated
Pilot and overhead channels establish the system timing and station identity.
Pilot channel is also used in the mobile-assisted handoff (MAHO) process as a signal strength reference.

9. Overhead Channels
There are three types of overhead channel in the forward link:
pilot, is required in every station
sync
paging
Pilot channel
pure short code with no additional cover or information content
always code channel zero
a demodulation reference for the mobile receivers and for handoff level measurements
carries no information
all stations use the same short code, distinguished by the phase

10. Overhead Channels Sync Channel
sync channel carries timing and system configuration information
data rate is always 1200 bps

11. Overhead Channels Paging channel
used to communicate with MSs when they are not assigned to a traffic channel
successful accesses are normally followed by an assignment to a dedicated traffic channel
paging channel may run at either 4800 or 9600 bps
each BS must have at least one paging channel per sector, on at least one of the frequencies in use

12. Traffic Channel Traffic channels Timing
assigned dynamically, in response to MS accesses, to specific MS
always carries data in 20 ms frames
carry variable rate traffic frames, either 1, 1/2, 1/4, or 1/8 of 9600 bps
rate is independently variable in each 20 ms frame
the 800 bps reverse link power control subchannel is carried on the traffic channel by puncturing 2 from every 24 symbols transmitted.
Timing
all base stations must be synchronized within a few microseconds

13. Handoff Steps in a handoff
Starting in a state where only one cell is supporting the call in question.
Informing the candidate cell of the imminent handoff
Signaling the mobile to begin executing the handoff.
New cell beginning to service the mobile
Mobile beginning to use the new cell
Entering the mid-handoff state (prolonged only in CDMA)
Mobile discontinuing use of the old cell
Old cell stopping service to the mobile
Ending in a state where the new cell is supporting the call in question

14. Primary and Signaling Traffic
172 bits
9600 bps Primary Traffic only MM =0
Primary Traffic = 171 bits
Dim & Burst with rate 1/2
primary & signaling traffic MM =1 TT =0 TM
=00
Primary Traffic
= 80 bits
Signaling Traffic
= 88 bits
Dim & Burst with rate 1/4
primary & signaling traffic MM =1 TT =0 TM
=01
Primary Traffic
= 40 bits
Signaling Traffic
= 128 bits MM =1
Dim & Burst with rate 1/8
primary & signaling traffic TT =0 TM
=10
Primary Traffic
= 16 bits
Signaling Traffic
= 152 bits
Blank & Burst with
signaling traffic only MM =1 TT =0 TM
=11
Signaling Traffic = 168 bits
80 bits
4800 bps primary
traffic only
Primary Traffic = 80 bits
40 bits
2400 bps primary
traffic only
Primary Traffic = 40 bits
16 bits
1200 bps Primary
traffic only
Primary Traffic = 16 bits

15. Secondary Traffic 172 bits MM =1 TT TM =00 Primary Traffic = 80 bits
Dim & Burst with rate
1/2 primary &
Secondary traffic MM =1 TT TM
=00
Primary Traffic
= 80 bits
Signaling Traffic
= 88 bits
Dim & Burst with rate
1/4 primary &
Secondary traffic MM =1 TT TM
=01
Primary Traffic
= 40 bits
Signaling Traffic
= 128 bits
Dim & Burst with rate
1/8 primary &
Secondary traffic MM =1 TT TM
=10
Primary Traffic
= 16 bits
Signaling Traffic
= 152 bits
Blank & Burst with
Secondary traffic only MM =1 TT TM
=11
Signaling Traffic = 168 bits

16. Sync Channel
Signaling on all channels use a synchronized bit-oriented protocol.
Sync channel is used during the system acquisition stage.
Sync channel frame length is the length of pilot PN sequence.
Only the Sync Channel Message is sent on the sync channel. MS
obtains information from Sync Channel Message
adjusts its timing to normal system timing
begins monitoring its Paging Channel

17. Paging Channel Data rate: 2400, 4800, 9600 bps
One 9600 bps Paging Channel can support 180 pages/sec.
Paging Channel conveys four major types of messages:
overhead
paging
order
channel assignment
Configuration of the system is conveyed in four overhead messages:
System Parameter Message
Access Parameter Message
Neighbor List Message
CDMA Channel List Message

18. Overhead Messages System Parameter Message: Access Parameter Message
configuration of the Paging Channel
registration parameters
parameters to aid pilot acquisition
Access Parameter Message
configuration of the Access Channel
control parameters used to stabilize the Access Channel
Neighbor List Message
time offset of the pilot
basic neighbor configuration
CDMA Channel List Message
CDMA frequency assignment that contain Paging Channels

19. Paging Channel Messages
Page Message:
contains pages to one or more mobile stations.
Order Message:
a broad class of messages used to control a particular MS.
Channel Assignment Message:
let BS to assign a MS to the traffic channel
change Paging Channel Assignment

20. Access Channel
Access Channel provides communications from MS to BS when MS is not using a Traffic Channel.
All Access Channel use 4800 bps mode
Access Channel Message:
call origination
response to pages
orders
registrations
Control of Access Channel transmission is accomplished through the Access Parameter Message sent on the Paging Channel

21. Framing and Signaling on the Traffic Channel
Both forward & reverse Traffic Channels use 20 ms frames.
Frames can be sent at 9600, 4800, 2400, or 1200 bps
Signaling
blank-and-burst signaling:
sent at 9600 bps
replace one or more frames of primary traffic data
dim-and-burst signaling:
sends both signaling and primary traffic data in a frame
degradation in voice quality is essentially undetectable

22. Traffic Channel Messages & Service Option
Four types of control messages on the Traffic Channel
messages controlling the call itself
messages controlling handoff
messages controlling forward link power
messages for security and authentication
IS-95 supports different user applications, called service options
Two different service options can be simultaneous supported:
primary traffic
secondary traffic
MS can specify the desired service option at call origination.

23. IS-95 Standard Forward Link Reverse Link Pilot Channel Sync Channel
Paging Channels (max. 7)
Traffic Channels
Power Control Sub-Channel
Reverse Link
Access Channels