Unit - 6CDMA Technology

System overview

• Code division multiple access (CDMA)

• 1989

• Qualcomm IS-95

• Also called wideband spread spectrum

• 3G cellular– Time Division Synchronous CDMA [TD-CDMA]– Multicarrier CDMA [MC-CDMA]– Wideband CDMA [W-CDMA]

Evolution of 3G CDMA• CDMA2000

– Approved for IMT-2000 3G standards• (International Mobile Telecommunications)

– Backward compatible with TIA/EIA-95-B• (Telecommunication industry association)• (Electronic Industries Alliance)

– Data services up to 2 mbps– Multimedia, advanced radio technologies– 2 versions

• cdma2000 1xEV : 2.4 mbps– EV: Evolution; – provides higher speeds implemented in two phases

• cdma2000 1xEV-DV: 3 mbps – EV-DV: Evolution data and voice only– Integrates voice and data on the same carrier

Evolution of 3G CDMA

• First form of CDMA was IS-95 – Dual mode of operation in 800 MHz– Compatible with AMPS and CDMA

• Additional features in IS-95A describes – Wideband 1.25 GHz– Power controls, registration, handoff, voice service

procedures– Compatibility

• Cdmaone - group of all CDMA technologies

CDMAone Network components

Wireless Intelligent Network

Mobile Station (MS)

Wireless Priority Service Center (WPSC)

Signaling

Signaling and User Data

Home Location Register (HLR)/Authentication Center

(AC)

Visitor Location Register (VLR)

PSTN/ISDN

MSC

Mobile Switching Center (MSC)

Inter-Working Function (IWF)

*FC+DN

Base Station (BS)

FC – Feature CodeDN - Directory Number

CDMA Basics• Based on wideband spread spectrum

digital techniques• Separation of signals in time and

frequency domain– Transmission on same frequency at same

time • Signals are spread over entire bandwidth• Encoded and broadcasted• Other than the intended receiver discard

the signal as if it is noise• Receiver demodulates the signal if it is

above the threshold SNR

Multiple Access

FDMA

• FDMA - frequency division multiple access– spectrum divided into

narrowband channels– each user given a channel

for use– transmission confined to

signal power within channel– selective filters used used

at both ends to distinguish other channels

– reuse distance must be far away

TDMA

• TDMA - Time division multiple access– spectrum divided into

timeslots – each user given a timeslot

for use– transmission confined to

the time slot– BTS and MS require

synchronization– Increases spectral

efficiency at expense of each user's total data rate

CDMA• CDMA - Code division

multiple access– Each mobile has

continuous use of entire spectral allocation

– Spreads its transmitted energy out over the entire bandwidth of allocation

– Uses unique code for each transmitted signal

– MS and BTS are able to distinguish between signals transmitted simultaneously over the same frequency allocation

– CDMA can be combined with TDMA and FDMA to increase capacity

Comparison of access technology

CDMA Example

CDMA Basics

• For CDMA standard carrier and channel are differentiated

• carrier– carrier frequency may be divided by means of codes

into 64 different channels

• channel– cannel carry information related to a separate and

distinct conversation or data connection in digital form

• In TDMA carrier is divided into timeslots and each timeslot serves as channel

CDMA Advantages/Disadvantages• Advantages

– Increased cellular communications security. – Simultaneous conversations. – Smaller phones – Low power requirements and little cell-to-cell

coordination needed by operators. – Extended reach - beneficial to rural users situated

far from cells. • Disadvantages

– CDMA is relatively new, and the network is not as mature as GSM

– CDMA cannot offer international roaming, a large GSM advantage

3G Wireless Systems & Standards

3G Wireless Standards & Systems

CDMA 2000(Successor of IS-95)

1xRTT 3xRTT

1x EVDO 1x EVDV

UMTS

CDMA- Code Division Multiple Access

UMTS- Universal Mobile Telecommunications System

RTT- Radio Transmission Technology

FDD W-CDMA TDD W-CDMA

FDD- Frequency Division Duplex

TDD- Time Division Duplex

EV- Evolution DO- Data Only DV- Data and Voice.

CDMA Frequency bands

• Cellular bands– Uplink - 824 MHz to 849 MHz– Downlink - 869 MHz to 894 MHz– 20 MHz separation– Only some of the frequencies will be used

• 1900 MHz PCS Band– 1200 Channels– 60 KHz channel spacing – 80 MHz separation

CDMA Frequency bands

Transmitter CSMA PCS Channel

Number N

Center frequency for

CDMA Channel MHZ

TDMA PCS Channel

Number N

TDMA PCS Channel

Frequency (MHz)

Mobile station

0 <= N <= 1199

1850 + 0.05 N

1 <=N<= 1999

1849.980 + 0.03 x N

Base Station

0 <= N <= 1199

1930 + 0.05 N

1 <=N<= 1999

1930.020 + 0.03 x N

N = Frequency reuse factor

Frequency Planning Issues

• If N = 1, one carrier per base station

• Carrier is chosen form list of preferred CDMA channels

• Same channel used throughout the base station

• If number of base stations increase system capacity but decreases performance

CDMA Network and system architecture

• Based on TIA Committee– TR-45

• Develops system performance, compatibility, interoperability, service standards for cellular bands

– TR-46 • Co-ordinates the same activities in PCS band

– TR-45.3• Deals with NA-TDMA

– TR-45.5• Deals with CDMA

CDMA Reference architecture• IS-95 CDMA similar to GSM architecture• CDMA2000 uses network access interfaces for an all-IP network• Messaging between CDMA system elements is through SS7

protocols

MS

RBS

MSC MSC

BSC IWF

OSS

HLR

HLR HLR

HLRHLR

PSTNPSTN

PDNPDN

PLMNPLMN

Ai

Pi

Mi

O

FBC

E

AL

Um

H G

CDMA2000 MSC-BSC interface functional planes

Physical facilities

Transport protocolsTransport protocols Transport protocolsTransport protocols

MobilityMgmt

MobilityMgmt

Trans.FacilityMgmt

Trans.FacilityMgmt

Trans.Facility

Mgmt

Trans.Facility

Mgmt MobilityMgmtMobilityMgmt

RadioRsrc Mgmt

RadioRsrc Mgmt

CallProcSupp

Services

CallProcSupp

Services

RadioRsrc Mgmt

RadioRsrc Mgmt

Call ProcSupp

services

Call ProcSupp

services

MSC BSC

CDMA2000 MSC-BSC interface functional planes

• MSC to BSC interface– Supports 4 functional planes

• Call processing & supplementary services– Call origination, termination waiting etc.

• Radio resources management– Maintenance of link during handoff

• Mobility management– Registration/de-registrations, authentication, voice

privacy

• Transmission facility management– Transport of voice, data, signaling information

Major network components of cdma2000

BSS

PSTNPSTN

PDPD

MSC/VLR

Nodes

BSC RBS

PacketCore

Network

SubscriberDevice

Network nodes in CDMA2000

BSS

PSTNPSTN MSC/VLR

MPS

BSC RBS

IWF

SubscriberDevice

PPCS HLR/AC UM/VMS

PCN

PDNPDN

GPS

MSC/VLR

• MSC – Serves as interface between PSTN and BSS– Call establishment functions to and from users– Provides mobility and roaming– Registration, authentication, location updating, call

handoffs, routing

• VLR– Temporary database– Call control and routing

IWF

• Gateway between cellular network and PDN

• Supports circuit-switched data calls for dial-up ISP– Routed to PSTN users

• Uses Ethernet for signaling between itself and MSC

• For CDMAone – IWF incorporated in PCN (Packet core network)

Mobile positioning system (MPS)

• Based on GPS for emergency services• Ability to locate the caller known as

– Enhanced 911 or E911 technology– Location based services – Location specific marketing tools

• Phase 1– Able to tell a local public safety answering point (PSAP)

– Location of cellular antenna handling the emergency call

• Phase 2– Forms a mobile assisted GPS to find latitude and longitude of

mobile within 50 to 100 mtrs

Unified Messaging/Voice mail service

• Developed by Ericsson

• Integrates email and voice mail access

• Messaging waiting indication using sms

• Multiple message retrieval modes including the use of DTMF or WAP browser

• Connects PDN and MSC

HLR/AC• Co-located in CDMA2000• HLR

– Subscriber information database– For subscriber device activity– Has ESN (electronic serial number), service plan,

overseas access details– Identification of MSC where mobile was last registered

• AC– Authentication for mobile subscribers whey first registered– Uses shared secret data (SSD)

• Keys, ESN, random number provided by AC and broadcast to SD– A-key stored in SD and AC

• Compares values calculated at AC and SD determines mobile status with system

PPCS and other nodes

• Pre paid calling service (PPCS)

• Information about subscriber’s allocation minutes and balance for communication

• Updates billing details

• PPAS (Prepaid administration system) provides balance information to PPCS system

• Increased system functionality for roaming

BSS• BSC

– One per cell– Provides interface to circuit switched core network (PSTN)

through MSC– Provides interface to packet switched networks like PCN,

PDN and other networks through MSC– More than one BSS in CDMA2000 – Combination of all CDMA BSSs and radio network

management system is called CDMA radio access network – C-RAN

• RBS– Interface between BSC and subscriber devices via the

common air interface– RBS to GPS antenna receiver

• Timing, frequency references – Monitor and manage operations of RBS, alarm indications– Power supplies and environmental control units

PLMN subnetwork

• For CDMA2000 it provides mobile wireless communication services

• Consists of several functional subnetworks– CCN (circuit core network)– PCN (Packet core network)– SNN (Service node network)– C-RAN (CDMA- Random access network)– Access to PSTN and PDN through these

subnetworks

Circuit Core Network (CCN)

• Provides switching functions for call completion between MS and PSTN

• Major element in CCN is MSC– Concerned with completion of voice calls

between subscriber and PSTN– MSC is basically extension of PSTN– MSC provides circuit switching, call charging,

roaming, maintenance etc

CDMA Radio Access Network (C-Ran)

• Interface between wireless cellular subscriber and CCN

• Consists of– Multiple base station subsystems

(BSSs)

– Radio network manager (RNM)• Supports operation and management• Support for multiple BSSs

PCN

• Standard interface for wireless Packet switched data services

• Between C-Ran and PDN• Links to various IP networks from C-Ran• Has 3 main hardware nodes

– Authentication, Authorization, Accounting (AAA) server

– Home agent (HA)– Packet data serving node (PDSN)

Cdma2000 PCNPDNPDN

AAA Server

Home Agent(HA)

PDSN

BSS #3

BSS #2

BSS #1

Subscriberdevices

Subscriberdevices

Subscriberdevices

Subscriberdevices

IPNetwork

IPNetwork

PDSN

• PDSN provides IP transport capability to connect to C-Ran and then to PDN

• PDSN connects to C-Ran through the Aquater

interface (R-P interface)• Setup, maintenance, termination, of nodes• Point of connection to radio network and IP

network and provides IP service management • Facilitates wireless mobile IP functionality• Serves as foreign agent to register network

visitors

AAA sever

• Data bases contain user profile on AAA server

• Define QoS for PDSN

• Accounting information for billing

• Can be configured for billing

Home agent (HA)

• Packet forwarding over IP network• Packet from PDSN SD via C-RAN• HA + PDSN

– Authenticates mobile IP registration from MS– Location information maintenance – Packet tunneling– Assign temporary address for a visitor

• Wireless LAN serving node (WSN) used with PCN

Network management system (NMS)

• Manage operations of entire network

• Has NOC (Network operations centre)– Provide control points

• Eg. AT & T – NOC at Seattle

• Layers of management– Highest level is network management system– Sub-network management system– Lowest level is network element management

system

Network Management

• Entire network management and monitoring (Highest level)

• Computer based, integrated graphical view, modular software application for maintenance

• Provides operator with QOS and corrective measures for errors

• 5 functions of wireless network management system– Network surveillance / Fault maintenance– Performance measurement– Trouble management– Configuration management– Security management

Functions of wireless network management system

• Fault maintenance (management)– Detection, isolation, repairs devices degradation or downtime– Uses tools for repair

• Performance management– Gathering, reporting, analyzing performance statistics

• Trouble management– Display description that affect network – Communicate information between operator and maintenance

section• Configuration management

– Support administration and configuration of network– Support installation, interconnection of nodes

• Security management– Manage user accounts– Control and set user based access tools

Sub-network management

– Management of circuit, packet, radio network

– Concerned with CDMA System

• CDMA MSC

– Provides• Fault management• Performance management• Configuration management• Software management• Hardware management

– Provides access to operator to manage one or more MSCs

– PCN network management system• Manages PCN nodes of CDMA

system• Statistics administration• Online documentation• Backup, restore function• Network topology maps • Database of PCN nodes

– C-RAN management system• Manages CDMA Base station

system• Configure radio, network

parameters• Monitors C-RAN alarm and

performance• Install, upgrade software• Manage user security and backup

Element management

• Refers to ability to interface directly with network element through a “Craft” dataport

• Uses element specific software, technician control through remote connection

• Software driven element management for initial deployment, installation, testing of RBS for diagnostic and trouble shooting during alarm

Base station system (BSS)

System communication links

PSTN

PSTN

PDN

PDN

BSC RBSs

Packet coreInterface nodes

MSC/VLR

Servicenodes

Subscriberdevice

ChannelizedT1/E1/J1

ChannelizedT1/E1/J1

UnchannelizedT1/E1/J1

Ethernet overSONETFiber link

Ethernet (10/100 mbps)

A

A1

A2

A5

Abis Um

A10

A11

System communication links

• CDMA Equipment vendors use OFC– SONET signals delivered at 155.52mbps

• Channelized T1/E1/J1 with control information over A interface between MSC-BSC

• Signaling protocol over T1/E1/J1 timeslots between MSC and other elements like AUC, HLR

• Ethernet to carry data between service nodes and PDN at 10/100 mbps

• Unchannalized T1/E1/J1 between BSC and RBS• Ethernet at 10/100 mbps rates from PCN to PDN• For 3G CDMA C-RAN connected higher data rates by

T-Carrier

Subscriber device

• Wireless phone/data devices• Performs CDMA encoding/decoding, vocoding• Each subscriber has band or set of radio bands

for various operating modes• 2 groups

– Portable devices for mobile voices connectivity first, data next

– Laptop, PDA using WLL for high speed internet access

• VOIP capability – For video conferencing

CDMA BASICS

CDMA Channel concept

• CDMAone, cdma2000 use CDMA to provide additional user capacity over limited radio spectrum

• Accomplished by spread spectrum encoding technique– All channels occupy same frequency spectrum– To differentiate channels Walsh spreading codes are

used for channel encoding• Coded channels used specifically for CDMA

– Provides precise timing control, overhead information

• Other channels used for traffic

Walsh Code

• Each Walsh code has 64 binary bit combination of 0s and 1s

• All zeros Walsh code is W064 has equal number of 0s and

1s• All 64 combinations are orthogonal to each other• Creates 64 distinct communication channels in same

frequency spectrum• Walsh coded signals appear as broadband noise for

CDMA receiver except for the one receiver that is used for demodulation

• Forward and reverse channels encoded differently

Basic spectrum spreading operation

Data in Data out

Exclusive OR

Spreading

sequence

1

0

1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 0

0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 1 0

Data

Orthogonal sequence

Output

CDMA Transmitter CDMA Receiver

Walsh encoding & decoding

• 2 types of pseudorandom noise (PN) codes are used by IS-95 communication system– Short PN codes

• Time shifted both to identify CDMA base station and time synchronization signals to subscriber device

– Long PN codes• Provide data scrambling on forward traffic channel• Providing differentiation between forward and

reverse link channels

Forward logical channels

• Between CDMA BS and SD

• IS-95 has 1.25 MHz bandwidth

• IS-95 occupies same bandwidth as 42 AMPS or NA-TDMA (North American TDMA) Channels

• IS-95 can be overlaid on earlier generation cellular systems

Basic spreading procedure on forward channels

1. Digital signal to be spread is transmitted over a particular forward channel

• Uses exclusive ORing of signal + Walsh code (Wi64)

2. Scrambling in I and Q lines using short PN spreading codes

• Short PN codes are not orthogonal but have good cross correlation and auto correlation

• Generated by 2 linear feed back shift registers (LFSR)

3. Resulting PN spreading codes are repeating binary sequences of approximately equal number of 1s and 0s and length of 32,768

4. I and Q signals are passed through baseband filters and applied to RF quadrature modulator IC

• Converts output signal to UHF band frequency

5. The signal is linearly combined with other forward channel signals, amplified and composite passband signal

• Transmitted over air interface

Basic spreading procedure on forward channels

Base bandfilter

Base bandfilter

I channel Pilot PNAt 1.2288 mcps

Walsh code Wi64

Q channel Pilot PNAt 1.2288 mcps

To QPSK RF Modulator

Channel-Dependentsymbol

CDMA base station timing offset reuse pattern

15

15

CDMA base station timing offset reuse pattern

• Short PN spreading codes helps to differentiate base stations transmitting on same frequency

• All CDMA base station use same short PN code sequence but offset by 64 bit increment

• 512 offsets possible• Timing synchronization through GPS to achieve

system time that has required accuracy• 4 types of logical channels in forward direction

– Pilot channel– Synchronization channel– Paging channel– Traffic/power channel

Pilot channel• The pilot channel is always code channel zero.• It is both a demodulation reference for the mobile

receivers, and for handoff level measurements• It must be present in every station. • It carries no information. • It is pure short code, with no additional cover or

information content.• All stations use the same short code, and thus have the

same pilot waveform. • They are distinguished from one another only by the

phase of the pilot.• The air interfaces stipulate that pilot phases always be

assigned to stations in multiples of 64, giving a total of 512 possible assignments

Generation of Pilot channel signal

Base bandfilter

Base bandfilter

I channel Pilot PNAt 1.2288 mcps

Walsh code W064

Q channel Pilot PNAt 1.2288 mcps

To QPSK RF Modulator

Channel-Dependentsymbol

I channel

Q channel

Synchronization channel• The sync channel carries a repeating message that

identifies the station, and the absolute phase of the pilot sequence.

• The data rate is always 1200 bps. • The interleave period is equal to the period of the short

code. – This simplifies finding frame boundaries, once the mobile has

located the pilot. • The Sync Channel carries a single, repeating message

that conveys the timing and system configuration information to the mobile station.

• The mobile station can derive accurate system time by synchronizing to the short code.

• The short code synchronization and the pilot offset, which is part of the sync message, fix system time.

Paging channel

• The paging channel is the vehicle for communicating with mobile stations when they are not assigned to a traffic channel.

• Its primary purpose is to convey pages, that is, notifications of incoming calls, to the mobile stations.

• It carries the responses to mobile station • Successful accesses are normally followed by an

assignment to a dedicated traffic channel.• The paging channel may run at either 4800 or 9600 bps. • Each base station must have at least one paging

channel per sector, on at least one of the frequencies in use.

• All paging can be done on one frequency, or it can be distributed over multiple frequencies.

Traffic/power channel• Traffic channels are assigned dynamically, in response

to mobile station accesses, to specific mobile stations. • The mobile station is informed, via a paging channel

message, which code channel it is to receive • The traffic channel always carries data in 20 ms frames.• Frames at the higher rates include CRC codes to help

assess the frame quality in the receiver.• The 800 bps reverse link power control subchannel is

carried on the traffic channel• Each base station participating in a soft handoff makes

its own power control decision, independent of the others

CDMA Reverse logical channels

• Mobile-to-cell direction of communication• Carries traffic and signaling• Active only during calls to the associated mobile station

or the associated base station• The channels used in the reverse link are

– Traffic Channel - carries data and speech. The data rate on the Traffic channel is variable, hence each frame may have a different rate.

– Access channel - carries control messages and requests to the base station

• These channels share the same assigned CDMA frequency

• Each of these channels is assigned a distinct user long PN code sequence for spreading the spectrum of the signal

Access channels

• Used by mobile stations for communicating to the base station.

• Used for short signaling message exchanges, such as call originations, responses to pages, and registrations.

• It is a slotted random access channel• Consists of a sequence of all-zero frames that is sent at

the 4800 bps rate followed by message• Access Channel frame contains 96 bits (20 ms frame at

4800 bit/s). • Each Access Channel frame consists of 88 information

bits and eight Encoder Tail Bits.

Access channels

To QPSK Modulator

Access channel generation• Separation of Users

– The reverse CDMA Channel uses a very long period spreading code, in distinct phases.

• Orthogonal Modulation – Reverse link data modulation is 64-ary orthogonal, and is applied prior to the

spreading. – The 64-ary orthogonal sequences are the same Walsh functions that are used in the

Forward CDMA Channel– Each period of the Walsh sequence (a Walsh Chip) is four PN chips in duration. The

modulation symbol rate is thus always 4,800 sps or cps (chips per second)• Spreading

– Each Reverse CDMA Channel is spread by both the channel-unique Long Code and the Short Code, which has I- and Q-components

– The spreading is quadrature, that is, from a single binary-valued symbol stream, two binary sequences are generated by mod 2 addition of the short code PN sequences

– The effect of adding long and short codes is to produce a supersequence that has an extraordinarily long period, about 257, or 3700 years at the 1.2288 MHz spreading rate

• RF Modulation – The two coded, covered, and spread streams are vector-modulated on the RF carrier.

The Q-axis modulation is delayed by 1/2 chip. – The spreading modulation is thus offset QPSK.

Traffic/power control channel• Support both voice and data in 2 rate sets RS1 &

RS2• Reverse CDMA Channel are mobile-unique that is,

each station has a unique Long Code Mask, based on its electronic serial number.

• Whenever the mobile is assigned to traffic, it uses its specific long code mask.

• The traffic channel always carries data in 20 ms frames.

• Frames at the higher rates of Rate Set RS1, and in all frames of Rate Set 2, include CRC codes to help assess the frame quality in the receiver.

CDMA Frame format

• The CDMA Rate Families– IS-95 defines the 9600 bps family of rates (Rate Set 1)

• 9600, 4800, 2400, and 1200 bps• Can select one of the four rates every 20 ms frame

– 14400 bps family of rates (Rate Set 2)• 14400, 7200, 3600, and 1800 bps• Can select one of the four rates every 20 ms frame

– Extended rates (extended Rate Set 1)• Adds 19200, 38400, and 76800 bps• At most four rates can be active• Can select one of the four active rates every 20 ms frame

CDMA Forward channel

CDMA Frame format

• CDMA takes 20 ms segments of digital samples of a voice signal

• Encodes them through the use of speech coder into variable frames

• 20ms frames outputs at either Rate set 1 or Rate set 2

• Pauses in speech is encoded with lower bit rates

CDMA Forward Frame format

Rate set 2 (14.4 kbps)267 information bits, 12 CRC bits, 9 Tail bits

(288 bits)

Frame (20 ms)

Rate set 2 traffic channel structure

Forward channel frame format

• Of 4 forward logical channels– Pilot channel

• No frame format and is continuous RF signal– Traffic channel

• Frame duration = 20ms with variable bit rates depending on rate sets• Further divided into 16 groups of 1.25 ms power control• Power control bits transmitted over forward traffic channels are randomly

inserted into 1.25 ms stream– Sync channel has configuration and timing information

• 32 bit frame = 1 SOM bit + 31 data bits• 1 bit start of message (SOM) (1 for 1st frame and 0 for others)• Data rate 1200 bps and duration = 26.666 ms• 3 sync channel frames = 1 sync channel super frame = 80 ms

– Paging channel• Transmit over head information and MS Specific message• Paging slot = 80 ms = 8 half frames of 10 ms• Half frame has – SCI (Synchronized capsule indicator) bit = SOM• Can use only 2 successive slots

CDMA Paging channel structure

Maximum F-PCH slot cycle

163.84 x R Bits, 163.84 s

F-PCHSlot 0

F-PCHHalf frame

F-PCHHalf frame

F-PCHHalf frame

F-PCHSlot n

F-PCHSlot 2047

F-PCHHalf frame

F-PCHHalf frame

SCIF-PCH

Half frame body SCIF-PCH

Half frame body SCIF-PCH

Half frame body SCIF-PCH

Half frame bodySCI

F-PCHHalf frame body SCI

F-PCHHalf frame body

80 ms 0.08 x R Bits

8 F-PCH half frames

10 ms 0.01 x R Bits

PCH frame size

First new capsuleIn slot synchronized

Abutted messages Unsynchronized capsules

synchronizedcapsules

Layer 2 encapsulated PDU padding encapsulated PDU Layer 2

encapsulated PDU Padding

= 0 = 0 = 0= 1 = 1

F-PCH Msg capsule F-PCH Msg capsule F-PCH Msg capsule F-PCH Msg capsule

Reverse channel frame formats

• Divided into 20ms traffic channels frames• Subdivided into 1.25ms power control groups• Coded bits from convolutional encoder are

repeated• For maximum data all 16 power channels used

– Else 8 channels and for lesser data 4 or 2 channels can be used

• A masking pattern used for reducing interference at mobile station

• Random access protocol is used for accessing the same channel

CDMA Reverse channel variable data rate transmission

13 14 15 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 1 2 3 4

13 14 15 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 1 2 3 4

13 14 15 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 1 2 3 4

13 14 15 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 1 2 3 4

B0 B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11 B12 B13

Start of PCG 15

Only 2 power control groups are transmitted during a 1200 bps frame

Only 4power control groups are transmitted during a 2400 bps frame

Only 8 power control groups are transmitted during a 4800 bps frame

Random masking pattern is derived from mobile station’s ESN

All power control groups are transmitted during a 9600 bps frame

20 ms frame = 16 power control groups

1.25 ms = 5.1 power control group

CDMA system (Layer 3) operations

System Determination

substrate

Pilot channel acquisitionsubstrate

Sync channelDetermination

substrate

Timing changesubstrate

Power-up Or any other state

Mobile stationIdle state

CDMA System selected

Receives sync channel message

Acquisition pilot channel

CDMA Mobile station initialization state

CDMA system (Layer 3) operations

CDMA Mobile station call processing states

Power up

Mobile stationInitialization

state

Mobile stationIdle state

System Accessstate

Mobile station Control on

Traffic channel state

Initializationtask

Mobile stationHas fully acquired System timing

Receives a paging channelMessage requiring anAcknowledgement or responseOriginates a call or performs registration

Directed to a traffic channel

End use of traffic channel

MS idle handoff operationWith NGHBR_config equalTo ‘011’ or unable to receivePaging channel message

Receives an ack to an access channel transmission other than anMessage or a page response message

Begin analog mode operation

end analog mode operation

CDMA System access state flow chart

Update overheadInformationsubstrate

Page response substrate

MS Order Message response

substrateRegistration access

substrate

MS OriginationAttempt substrate

MS Messagetransmission

substrate

PACA Cancel substrate

Enter MS Control on The traffic channel

State Or go to analog

(Enter MS Idle state, MS Control on trafficChannel state orGo to analog

Enter MS Idle state

Received msg or Order requiring an Ack or response

Registrationaccess

UserGeneratedData burst

msg

User initiated

call

UserCanceleda PACACall

GPM 5 received aGeneral page msg

GPM

User initiated a callOr PACA call Re-originated

GPM

GPM

GPM

CDMA Mobile station control on traffic channel flow chart

Traffic channelInitialization

substrate

Warning for order

substrate

conversationsubstrate

Waiting for msanswer

substrate

releasesubstrateSystem determination

substrateOf the mobile station

Initialization state

MS terminated callAnd layer 3 receives a Forward dedicated Channel acquiredindication From layer 2

Receives a maintenanceOrder or an alertWith information msg

MS stationAnswersUsers call

Receives a maintenance order or alert with info msg

Receives Releaseorder

Receives Release order

Receives Alert withInfo msg

Enter from system access stateMS originated callAnd layer 3 receivesA forward dedicatedChannel acquired Indication from layer 2

MS terminated callBypass ordered by BSAnd layer 3 receivesForward dedicated channelAcquired information from Layer 2

MS User initiatesDisconnect or MSBase station receivesRelease order

Registration

• Process where CDMA MS informs cellular system through BS about its – Identification– Location– Status– Slot cycle– Other information

• 10 types of registration– 5 are autonomous that are independent of

roaming status

Types of registration

• Power up registration– When CDMA MS power on

• Power off registration– When CDMA MS power off

• Time based registration– When various timers expire– Forces to register at regular intervals

• Distance based registration– When distance between MS & BS exceeds certain limit– Forced registration

• Zone based registration– When MS enters into new zone– Has list of all zones MS bvisited

Types of registration

• Parameter change registration– When specific parameters change– Independent of roaming status

• Ordered registration– When requested by BS through issue of order message

• Implicit registration– When MS sends an origination message BS locates MS– Considers as implicit registration

• Traffic channel registration– When BS has registration information for a MS during assigning

a traffic channel• User zone registration

– When MS selects an active zone

Call establishment

• Requires tasks like– Mobile initialization state– Idle state– Access state– Traffic state

Mobile initialization state

• MS power ups and enters this state

• MS searches a pilot channel using short PN Codes in 15 sec

• Synchronizes to pilot channel

• After locating searches for sync channel and PN codes

• Decodes sync channel and aligns to timing of BS

Idle state

• After initialization moves to idle state

• Ready and waits for data/cal

• Monitors radio channel quality constantly

• Uses sleep mode to conserve battery power (slot-mode)

• Monitor neighboring calls during handoff

Access state

• Enters active state when MS receives ack, originates a call, during registration

• Randomly attempts to access system

• Gets access through paging channel

• Uses backoff if it faces collision during access

• Access level provides the request power level

Access StateAccess probe sequence #1

Access probesequence #N

Access probesequence #3

Access probesequence #2

Random backoffDelay RS1

Random backoffDelay RS2

Access probe 1

Access probe 2

Access probe 3

Access probe N

Random delay

Random delay

Details of Access Probe sequence

Power

Access attempt

• Access probe = access channel preamble + access channel message capsule

• 2 types of access message – Response message– Request message

• MS sends series of sequence of access probes of increasing power level

Traffic state

• Enters traffic state when information is exchanged between MS and BS

• Transmit signaling/voice information on RTC/FTC

• Signaling can be– Blank and burst: 1.25 ms speech data +

signaling message burst – Dim and burst: during low speech activity

Mobile originated call

• MS Sends access msg on access channel• Monitors paging channel for response• On successful response FTC is assigned

according a walsh code• BS receiver is assigned a RTC + long PN code• BS sends paging channel msg to MS on RTS• MS configures itself and begins to transmits

preamble over RTC• BS uses FTC to acknowledge the preamble• MS begins sending traffic information

Mobile originated callSend service request message

Assign MS to FTC

Send Preamble (setup information

Setup call (dial digits)Acknowledge receipt of preamble on FTC

Begin communication

BS originated call timelineSend page message on paging channel (PgC)

Send acknowledge

Assign MS to FTC

Acknowledge preamble

Start transmitting null information

Send Preamble

Send alert (ring signal) message

MS rings and subscriber presses send

MS sends connection message

Connect call and start conversation

Mobile terminated call

• BS Sends msg to MS on paging channel• MS sends ack on access channel• BS receives ack and sets up FTC• BS assigns receiver to mobile RTC• BS sends null traffic on FTC• MS sends preamble on RTC• BS acknowledges the preamble• MS sends null traffic• BS sends alert message for ring tone and

display of calling number information

Call termination

• By BS or MS• If by MS

– MS sends call termination message to BS, stops transmitting on RTC

– Returns to initialization state

• If by BS– BS sends call termination message– MS stops transmitting on RTC– Return to initialization state

Call Handoff

• Handoff can occur in 3 states– Idle state– Access state– Traffic state

• Procedure of handoff depends on present state of mobile

• All cases are mobile assisted handoff (MAHO)

Idle/Access Handoff

• Idle handoff– Mobile is in idle state and moves to another sector/cell – If received signal strength of other pilot channel is twice the

current PC, MS listens to new PgC– It is Hard handoff because signal is interrupted for a short time

• Access handoff– Mobile is in access state– Handoff occurs while sending probes or before sending probes– In access entry handoff, mobile does a hard idle handoff from

one PgC to other – If new PgC has better signal than previous it enters access state

Soft Handoff• Handoff takes place when mobile is in

conversation on FTC• Possible only when both sector/cell has same

frequency and only in traffic state• Far-near problem• In CDMA system, mobile is connected to nearest

base station (strongest signal with lowest power)• 3 types of soft handoffs

– Softer– Soft– Soft softer

Soft Handoffs in CDMA

• Soft handover can be used when cells operated on the same frequency are changed.

• Softer handover is where the radio links that are added and removed belong to the different sectors of same cell

• Soft-softer handoff is where the radio links that are added and removed belong to the two sectors of same cell and sector of adjacent cell

Soft/softer Handoff Vs Handoffs in other systems

• Soft/softer handoff– No interruption of

conversation– High speed data

transmission is associated with loss

– Improved system performance

– Reduced transmit power

• Other systems– Has interruption in

communication links– High speed data

transmission is lossless

– Low performance– Requires high

transmission power

Hard handoff

• Happens during intercarrier handoff

• Interruption of signal

• Two types– Hand-down

• Between 2 different carriers in same cell

– Handover• Between 2 different carriers in two different cells

Hand-down handoff

• Known as Pocketed implementation• CDMA provider uses second CDMA carrier in

individual or noncontiguous cells • This provides additional capacity during high

traffic growth• MS using 2nd carrier• Exiting pocket of 2nd carrier cell must be handed

off to common carrier to continue the call• First hand down call to common carrier before

exiting pocketed area• Then soft handoff can be performed

Hand-down handoff

MS

Two carrier cellsSingle carrier cells

Power control

• Adjacent and co-channel interference do not cause problem

• Interference is from other mobiles using same frequency at same time

• Near-far effect• Fading and shadowing problems• To overcome these, power control is necessary• Forward link uses frame error rate (FER) to make power

control decisions because RSS may be good, but frames may have errors– Forward link power control– Reverse open loop – Fast closed loop

Forward link power control

• FTC is controlled according to information transmitted to BS

• FTC transmits at nominal level and reduces its output power level gradually as required

• MS reports FTC FER regularly and does adjustments to control power level

Reverse open loop

• Path loss (signal attenuation) is same between BS and MS in either direction

• MS makes open loop estimate without feedback from BS about power level required

• RSS is measured and transmits a low level signal if pilot is strong and vice-versa

Fast closed loop

• Forward and reverse channels fade differently• Fast Closed loop scheme (for overcoming

fading) is employed on forward channel• Power control bit is transmitted every 1.25ms• BS receives signal and if value is above average

SNR bit is set to 1 else 0• This is continued till correct value is achieved• Called inner-loop power control