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CDMA

Presentation by:Hira RasabHuma Chaudhry

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Contents

• Introduction

• CDMA Signal ▫ Transmission ▫ Reception

• CDMA Evolution

• CDMA Core Elements

• CDMA ▫ VOICE call▫ SMS▫ EVDO

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Introduction to CDMA

•CDMA (Code-Division Multiple Access) refers to any of several protocols used in wireless communications.

•As the term implies, CDMA is a form of multiplexing, which allows numerous signals to occupy a single transmission channel, optimizing the use of available bandwidth.

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CDMA[1]

• For radio systems there are two resources, frequency and time. • Division by frequency, so that each pair of communicators is allocated part of the

spectrum for all of the time.• Division by time, so that each pair of communicators is allocated all (or at least a

large part) of the spectrum for part of the time .• In Code Division Multiple Access (CDMA), every communicator will be allocated

the entire spectrum all of the time. CDMA uses codes to identify connections.

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•CDMA employs analog-to-digital conversion (ADC) •Audio input is first digitized into binary elements. •The frequency of the transmitted signal is then made

to vary according to a defined pattern (code),▫ so it can be intercepted only by a receiver whose

frequency response is programmed with the same code, so it follows exactly along with the transmitter frequency.

Introduction to CDMA (ctd..)

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CDMA fundamentals..

•CDMA network work on 800MHz and 1.8GHz frequency.

•CDMA phones are activated remotely, by the carrier, using the phone's serial number, known as the ESN.

•The CDMA channel is nominally 1.23 MHz wide.

•CDMA networks handoff Scheme: soft handoff.

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CDMA Evolution

• IS-95A – Voice – Data up to 14.4 kbps• IS-95B – Voice – Data up to 115 kbps• CDMA2000 1X – 2X Voice Capacity – Data up to 307 kbps on

a single carrier – IMT-• 1xEV-DO – Optimized high speed data up to 2.4 Mbps on a

single carrier – IMT-2000• Compliant• 1xEV-DV – Integrated Voice and Data with Downlink rates up

to 4.8 Mbps

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Generating a CDMA signal[5]

There are five stages in generating a CDMA signal.

• analog to digital conversion• vocoding• encoding and interleaving• channelizing the signals• conversion of the digital signal

to a Radio Frequency (RF) signal

The use of codes is a key part of this process.

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Generating a CDMA signal

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How compression works

•As people pause between syllables and words when they talk,▫ CDMA takes advantage of these pauses in speech

activity by using a variable rate vocoder.

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Variable Rate Vocoder

•A CDMA vocoder varies compression of the voice signal into one of four data rates based on the rate of the user's speech activity:

Full, 1/2, 1/4 and 1/8.

•The vocoder uses its full rate when a person is talking very fast.

• It uses the 1/8 rate when the person is silent or nearly so.

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Vocoder types

•CDMA systems can use either an 8 kbps or a 13 kbps vocoder. ▫8kbps vocoder maximize capacity.

• The 13 kbps vocoder was later developed to provide a more land-line quality voice signal. ▫ slight reduction in capacity, better voice quality.

•Recently the CDMA community adopted a new 8 kbps vocoder: usually referred to as the EVRC (Extended Variable Rate Coding).▫ It combines the quality of 13 kbps vocoding with the

capacity of the 8kbps data rate.

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Encoding and interleaving

•Encoders and interleavers are built into the BTS and the phones.

Purpose: •To build redundancy into the signal so that

information lost in transmission can be recovered.

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How encoding works•Example: The type of encoding done at this stage is

called "convolutional encoding.”•A digital message consists of four bits (A, B, C, D) of

vocoded data.• Each bit is repeated three times. •These encoded bits are called symbols.

•The decoder at the receiver uses a majority logic rule. ▫Thus, if an error occurs, the redundancy can help

recover the lost information.

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Burst errors

•A burst error is a type of error in received digital telephone signals.

• Burst errors occur in clumps of adjacent symbols. •These errors are caused by fading and interference.

Encoding and interleaving reduce the effects of burst errors.

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How interleaving works

• Interleaving is a simple but powerful method of ▫reducing the effects of burst errors and recovering lost

bits. In the example discussed here the symbols from each group are interleaved (or scrambled) in a pattern that the receiver knows.

•De-interleaving at the receiver unscrambles the bits, spreading any burst errors that occur during transmission.

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Channelizing

•The encoded voice data is further encoded to separate it from other encoded voice data.

•The encoded symbols are then spread over the entire bandwidth of the CDMA channel.

•This process is called channelization.

•The receiver knows the code and uses it to recover the voice data.

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Kinds of Codes used in CDMA

CDMA uses two important types of codes to channelize users.

•Walsh codes channelize users on the forward link (BTS to mobile).

•Pseudorandom Noise (PN) codes channelize users on the reverse link (mobile to BTS).

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Walsh codes

•Walsh codes provide a means to uniquely identify each user on the forward link.

•Walsh codes have a unique mathematical property--they are "orthogonal."

• In other words, Walsh codes are unique enough that the voice data can only be recovered by a receiver applying the same Walsh code.▫ All other signals are discarded as background noise.

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PN codes

•Pseudorandom Noise (PN) codes uniquely identify users on the reverse link.

•A PN code is one that appears to be random, but isn't.

• The PN codes used in CDMA yield about 4.4 trillion combinations of code. This is a key reason why CDMA is so secure.

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Code channels used in CDMA

•A code channel is a stream of data designated for a specific use or person. ▫This channel may be voice data or overhead control

data.

•Channels are separated by codes.

•The forward and reverse links use different types of channels.

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Forward link channels

•The forward link uses four types of channels to transmit voice and control data to the mobile.

•The types of forward link channels are:

▫Pilot▫Sync▫Paging▫Traffic

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Reverse link channels

•The reverse link uses two types of channels to transmit voice and control data to the BTS.

•The types of reverse link channels are:

▫Access▫Traffic

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States of an MS [6]

Channels used in call Setup[5]

CDMA

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Channels used For Call Processing

1. Forward Channels

1. Pilot Channel2. Paging Channel3. Synchronous Channel4. Forward Traffic Channel

Reverse Channels1. Access Control Channel2. Reverse Traffic Channel

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Forward Link Channels

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Call Processing - Pilot

•The BTS constantly transmits the pilot channel.

•The mobile uses the pilot signal to acquire the system.

• It then uses the pilot signal to monitor and adjust the power needed in order to transmit back to the BTS.

Pilot Ch

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Call Processing - Sync

•The BTS constantly transmits over the sync channel so the mobile can synchronize with the BTS.

• It provides the mobile with the system time and the identification number of the cell site.

•The mobile ignores the sync channel after it is synchronized.

Sync Ch

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Call Processing - Paging

•CDMA uses up to seven paging channels.• The paging channel transmits overhead information

such as commands and pages to the mobile. •The paging channel also sends commands and traffic

channel assignment during call set-up. ▫The mobile ignores the paging channel after a traffic

channel is established.

Paging Ch

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Call Processing - Traffic

•Base station assigns a forward and reverse traffic channel to the mobile when it is in conversation.

Forward link traffic channel

•CDMA uses between fifty-five and sixty-one forward traffic channels to send both voice and overhead control data during a call.

•Once the call is completed, the mobile tunes back in to the paging channel for commands and pages.

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Reverse link channels

•The reverse link uses two types of channels to transmit voice and control data to the BTS.

•The types of reverse link channels are:

•Access•Traffic

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Reverse link channels

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Call Processing – Access Channel

The mobile uses the access channel when not assigned to a traffic channel.

The mobile uses the access channel to:

•Register with the network•Originate calls•Respond to pages and commands from the base station• Transmit overhead messages to the base station

Access Ch

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Reverse link traffic channel

•The reverse traffic channel is only used when there is a call.

•The reverse traffic channel transmits voice data to the BTS.

• It also transmits the overhead control information during the call.

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CDMA used for

Signal generation

Termination

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CDMA Signal Transmission

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Generating a CDMA signal[2]

•There are five steps in generating a CDMA signal. analog to digital conversionvocodingencoding and interleavingchannelizing the signalsconversion of the digital signal to a Radio Frequency

(RF) signal

•The use of codes is a key part of this process

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Vocoding

Voice Compression

•The second step of CDMA signal generation is voice compression.

• CDMA uses a device called a vocoder to accomplish voice compression.

•Vocoders are located at the BSC and in the phone.

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CDMA Signal Transmission

Signal transmission consists of the following steps:

1. A pseudo-random code is generated, different for each channel and each successive connection.

2. The Information data modulates the pseudo-random code (the Information data is “spread”).

3. The resulting signal modulates a carrier. 4. The modulated carrier is amplified and broadcast.

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Signal Reception

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Signal Reception

Signal reception consists of the following steps: 1. The carrier is received and amplified. 2. The received signal is mixed with a local carrier to

recover the spread digital signal. 3. A pseudo-random code is generated, matching the

anticipated signal. 4. The receiver acquires the received code and phase locks

its own code to it. 5. The received signal is correlated with the generated code,

extracting the Information data.

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Mobile Station States[6]

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Mobile Station StatesPower Up

InitializationState

AccessState

TrafficState

Synchronization

Paging Loss

Call originationor page response

Page response completed

End of call

IdleState

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1. Initialization:

Acquire pilot channel of the selected CDMA system.

Process synch channel for synchronization

2. Idle:

Monitor paging channel for overhead and mobile directed messages

Ready to move to access state to originate a call or respond to a page request

MS states Discussed:

Mobile switched On..

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4. Traffic:MS communicates with the base station

using forward and reverse traffic channelsPaging and access channels are no longer

monitoredAlert with info is used for order message

3. Access:MS sends messages to the base station and gets responses in the paging channel.This can be a call origination or a page response.

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CDMA Architecture [Some Imp N/W ELEMENTS]

• Some of the important identities used in CDMA networks are as listed below:

▫ MSID: An MSID (Mobile Station Identity) can be in one of the two forms – the MIN (Mobile Identification Number) number identifying a subscription in CDMA network; or the IMSI (International Mobile Station Identity.e.g, 410530428521442.

▫ ESN: The Electronic Serial Number (ESN) is the number assigned by the manufacturer to the Mobile Equipment. For example, the ESN of a handset is 15FED16F.

▫ MSCID: MSC Identity is assigned to each of the network elements (e.g. MSC, HLR, SMSC etc.) in an CDMA network.

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MDN: Mobile Directory Number is an addressable (or dial able) number on which the subscriber can be called on.e.g, +924238521442.

MSCIN: MSC Identity Number is the Global Title address (or the number) assigned to the MSC.

HLR- with the help of MSC keeps the location of the subscriber updated.

VLR- downloads the copy of the subscriber’s data from HLR when the user enters the different location Area. It has the location ID named as “Cell No.(identification of the BTS serving the cell)” e.g, 41053000030270.

AUC- is used to keep a check on the authenticity of the user.

CDMA [Some Imp N/W ELEMENTS.. (contd.)

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• Voice▫ I\C and O\G

CDMA

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MS visiting diff Locations

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MS moving on different N/WsIf an MS moves from VLR1 TO VLR2

1

•-on entering the VLR2, a “Location Update” msg. is sent to the N/W, and then the requestNotification msg. from VLR2, is sent to the HLR

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•HLR updates the VLR2 by referring to MIN of MS in DB and doing the following process:

2.1

•--it send a RegCancel Req. to VLR1, which then removes the record of the Subscriber and sends response to HLR

2.2

•After VLR1 has removed the MS record, HLR sends the Subscriber details and a ReqNot msg. to allow VLR2 to update the information for the MS requesting

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Once the MS is registered in VLR2-

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Call to a user visiting a different Network:

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Call to a user in VLR2

1. When a call is made:

2. The GatewayMSC sends notification to the HLR which is serving that MDN

3. HLR identifies the MIN is in a different network and sends a ReqRoute msg. to the

serving MSC (to establish a path for G-MSC to Serving MSC for the communication

to take place).

4. The serving MSC identifies the MIN and checks the availability of the MS (either

busy or on waiting)

5. When available, the MSC assigns the TLDN (from a pool of available

numbers) ,and sends the TLDN to the HLR

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Call to a user in VLR2..(CTD)

6. The HLR on receipt of the response from the serving MSC, sends the TLDN to the calling Party (the GMSC) for association b/w TLDN and MIN then allocates voice path for communication purpose

7. the serving MSC then releases the TLDN, for reuse.

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Call FROM a Mobile User

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A Call FROM a Mobile User

1. A call initiation request is sent to the RCC (Rev. Command Channel).

2. Along with this, the MS transmits its MIN, Electronic Serial Number(ESN) and the phone number of the called party.

3. The MS also transmits the Station Class Mark (SCM) which indicates the maximum transmitter power level for the particular user

4. The BS forwards the data to the MSC, which validates the data and makes connection to the called party through the PSTN (Public Switched Telephone Network)

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An Incoming Call:

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A Call TO a Mobile User

• The MSC dispatches the request to all BS. The Mobile Identification Number(MIN) is broadcasted as a paging message over all FCCs (Forward Command channels) throughout the service area

• The MS receives the paging message from the BS it is monitoring. It responds by identifying itself over the RCC (Reverse Command Channel).

• The BS conveys the handshake to the MSC.

• The MSC instructs the BS to move to an unused voice channel.

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• The BS signals the MS to change over to an unused FVC (Forward Voice Channel) and RVC (Rev. voice Channel) for the allocation of channels

• A data message called alert is transmitted over the FVC to instruct the mobile for ringing.

•Thereby, completing the call setup.

A Call TO a Mobile User… (ctd..)

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• While the call is in progress, the MSC or the BS, adjust the transmitted power in order to maintain the call quality.

A Call TO a Mobile User… (ctd..)

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Data

SMS handling

CDMA

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Short Message Delivery Point-To-Point Bearer Service Usage in CDMA

SMS

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N\W infrastructure for SMS:

•The network infrastructures that need to deploy SMS service use the same ones to deploy voice call service with the additional one being▫that is Short Message Service Centre (SMSC).

•SMSC responsible to handle all request related to the SMS service.

• It will identify the SMS request from the originating mobile phone number, process the request and finally, send to request to the proper destination phone number.

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•The complete network infrastructures which involved on the SMS service are;

•Base Transceiver Station (BTS)•Base Station Controller (BSC)•Mobile Switching Centre•Home Local Register (HLR) or Visitor Local Register

(VLR)•Short Message Service Centre (SMSC)• Intelligent Network (IN)

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• A message that is sent by subscriber will be forward to the BTS, BSC and MSC and HLR/VLR.

• MSC will identify what kind of service is requested by subscriber, and once it finds out that it is a messaging service, the MSC will forward the request to SMSC for next processing.

• SMSC will validate the phone number whether it is right to make a messaging service by checking the balance on Intelligent Network (IN). If it has sufficient balance, it will deducted and then deliver the message to the destination phone number.

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In case of CDMA networks, each MS belongs to one and only one Message Center (MC or the SMSC).

SMS being a store-and-forward type of application, it is the responsibility of the Home MC of any given CDMA subscriber, to store & subsequently deliver the terminating message to the subscriber.

When a CDMA user originates a Short Message, there are two methods of routing the message to it’s destination.

One method is called as the “Direct” method & the other is called as “Indirect” method of routing.

In case of the “Direct” method, the Originating MSC delivers the message to the Destination subscriber’s MC.

In case of “Indirect” method, the message is first delivered to Originator’s MC & then forwarded to the Destination subscriber’s MC.

Ultimately, the message gets deposited in the destination subscriber’s MC for delivery.

MCMCIndirect

DirectSMDPP

SMDPP

SMDPP / SMPP

SMDPP

Origination Home

Destination Home

Network Network

SMDPP: Short Message Delivery Point-To-Point Bearer Service

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SMS DELIVERY Scenario [6]

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SMS Call Flows (A) explains the successful SMS delivery scenario.a. MS ‘B’ registers at MSC/VLR-2. MSC sends ‘REGNOT’ message to the HLR with

it’s own address (PC/SSN) as ‘SMSAddress’ to the HLR.b. HLR Stores the ‘SMSAddress’ and sends ‘regnot’ response to the MSC/VLR-2.c. MS ‘A’ sends an SMS for MS ‘B’. The MSC-1 delivers the message to the MC of

MS ‘B’ (i.e. MC-2) through the IS-41 message called as SMDPP (Short Message Delivery Point-to-Point).

d. The Message Center sends ‘smdpp’ response to acknowledge the receipt of the message.

MSC-1 MC-2 MSC-2HLR-2

REGNOT (SMSAddress)

regnot (profile)

A

B

SMDPP (SMS Bearer, MDN)

smdpp (ACK)

SMSREQ (MDN)

smsreq (MIN, SMSAddress)

SMDPP (MIN, SMS Bearer)

smdpp (ACK)

a

b

c

d

e

f

g

h

Img Courtesy; http://www.3gpp2.org/Public_html/specs/index.cfm

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e. The MC-2 sends ‘SMSREQ (SMS Request)’ message to the HLR of MS ‘B’, to find out the subscriber’s current location & status.

f. If HLR finds that the MS ‘B’ is registered, it sends ‘smsreq’ response with the MIN & the ‘SMSAddress (the address of the serving MSC)’ to the MC-2.

g. On receipt of response to ‘SMSREQ’ the MC-2 sends ‘SMDPP’ message to the MSC identified by the ‘SMSAddress’.

h. The MSC-2 pages the MS ‘B’ & delivers the message & sends successful response to the MC-2 in ‘smdpp’ message.

MSC-1 MC-2 MSC-2HLR-2

REGNOT (SMSAddress)

regnot (profile)

A

B

SMDPP (SMS Bearer, MDN)

smdpp (ACK)

SMSREQ (MDN)

smsreq (MIN, SMSAddress)

SMDPP (MIN, SMS Bearer)

smdpp (ACK)

a

b

c

d

e

f

g

h

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SMS Procedure (B) the first unsuccessful SMS delivery attempt.

SMS

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SMS Call Flows (B) explains the first unsuccessful SMS delivery attempt.a. MS ‘B’ de-registers from MSC/VLR-2. MSC sends ‘MSINACT’ message to the HLR, which

indicates to HLR that the MS ‘B’ is not available any more.b. HLR marks the MS ‘B’ as ‘Inactive’ and sends ‘msinact’ response to the MSC/VLR-2.c. MS ‘A’ sends an SMS for MS ‘B’. The MSC-1 delivers the message to the MC of MS ‘B’ (i.e.

MC-2) through the IS-41 message called as SMDPP (Short Message Delivery Point-to-Point).

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d. The Message Center sends ‘smdpp’ response

to acknowledge the receipt of the message.

e. The MC-2 sends ‘SMSREQ (SMS Request)’ message to the HLR of MS ‘B’, to find out the subscriber’s current location & status.

f. HLR finds that the MS ‘B’ is marked as ‘Inactive’ and sends ‘smsreq’ response with the ‘SMSAccessDeniedReason’ parameter set to a value indicating that the SMS to this MS (‘B’) can not be delivered at this moment.

g. The HLR also sets a flag called ‘SMS Delivery Pending Flag (SMDPF)’ indicating that there was an attempt to deliver an SMS to this MS, but, it was not delivered.

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d. After some time when the MS ‘B’ turns ‘ON’, it performs “Power-Up Registration”. The MSC/VLR-2 sends ‘REGNOT’ to the HLR.

e. HLR responds to ‘REGNOT’ with the subscriber’s profile.

The HLR also finds that, against ‘this’ MIN, the SMDPF flag is set.

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d. Because the SMDPF flag for MS ‘B’ was set, the HLR sends a message called ‘SMSNOT (SMS Notification)’ to the Home MC of MS ‘B’. The ‘SMSNOT’ message includes the MIN, MDN & the SMSAddress.

e. The MC-2 responds with ‘smsnot’ to the HLR. On receipt of the ‘smsnot’ message, the HLR resets the SMDPF flag.

f. On receipt of SMSNOT, the MC-2 comes to know that the MS ‘B’ is now available & is located at the MSC identified by the ‘SMSAddress’ received in ‘SMSNOT’. The MC-2 retries the delivery of message by sending ‘SMDPP’ message to the MSC-2.

g. On successful delivery of message to MS ‘B’, the MSC sends the ‘smdpp’ response message to the MC-2. If the originating MS had requested for delivery acknowledgement, then the MC-2 forms the delivery confirmation message to be sent to MS ‘A’ & goes ahead with SMS delivery call flow for message delivery confirmation to MS ‘A’.

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• EVDO

CDMA

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EV-DO

•EVDO is short for evolution data optimized.

•The official name, defined by the Telecommunication Industry Association, is "CDMA2000, High Rate Packet Data Air Interface".

•This is another wireless service that like DSL is always on. It is used just like any other high speed Internet access service.

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• There are many telecommunication services which can be optimized by Telecommunication Company to gain as much as revenue instead of traditional service (such as voice call and SMS) and one of them is Data Service e.g. mobile broadband internet service.

• The term of Data Service is usually associated with wireless or mobile broadband internet services which include CDMA 1x 2000, GPRS, EVDO or 3G services.

• For Data Service, Telecommunication Companies need to insert new network infrastructures to the existing network e.g. Packet Data Service Node (PDSN), SGSN/GGSN and charging system to charge the subscribers while they utilize the services.

Companies evolving to EVDO

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[3]CDMA call flow for Data Service

• The call flow of Data Service e.g mobile broadband internet service is just like voice call flow.

• The difference is type of service which be retrieved by subscribers. Therefore, Data Service call flow will be routed to the network infrastructures where voice call served and then route to Data Service’s networks element to have internet service.

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Data Service Call flow (continued…)

•Then, the AAA server or charging system will assign certainty tariff once they noticed that the phone number used by subscribers to make a Data Service is a valid number.

• Finally, PDSN will request internet traffic and then forward back to the subscribers. In this section, subscriber will be able to browse to internet.

Firewall was installed to protect internal network keep secure

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Img. Courtesy:http://www.tek.com/ir/whitepaper/WP_CDMA.pdf

EV-DO1x Architecture

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The Radio Access Network (RAN)• The Radio Access Network is the mobile subscriber’s entry point for

communicating either data or voice content. • It consists of:

▫ The air link▫ The cell site tower/antenna and the cable connection to the Base Station Transceiver

Subsystem (Um)▫ The Base Station Transceiver Subsystem (BTS)▫ The communications path from the Base Station Transceiver Subsystem to the base station

controller (Abis)▫ The Base Station Controller (BSC)▫ The Packet Control Function (PCF)

• The RAN has a number of responsibilities that impact the network’s delivery of packet services in particular. The RAN must map the mobile client identifier reference to a unique link layer identifier used to communicate with the PDSN, validate the mobile station for access service, and maintain the established transmission links.

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PCF

• The Packet Control Function (PCF) routes IP packet data between the mobile station within the cell sites and the Packet Data Serving Node (PDSN).

• During packet data sessions, it will assign available supplemental channels as needed to comply with the services requested by the mobile and paid for by the subscribers.

• The PCF maintains a “reachable” state between the RN and the mobile station, ensuring a consistent link for packets; buffers packets arriving from the PDSN when radio resources are not in place or insufficient to support the flow from the PDSN.

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The Core CDMA Network Elements’ Role in EVDO[4]

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1. The Packet Data Serving Node (PDSN/FA)

• The PDSN/FA is the gateway from the RAN into the public and/or private packet networks. In a simple IP network, the PDSN acts as a standalone Network Access Server (NAS), while in a mobile IP network it can be configured as a Home Agent (HA) or a Foreign Agent (FA).

• The PDSN does the following activities:▫ Manage the radio-packet interface between the BSS and the IP network

by establishing, maintaining and terminating link layer to the mobile client

▫ Terminate the PPP session initiated by the subscriber▫ Provide an IP address for the subscriber (either from an internal pool or

through a DHCP server or through an AAA server)

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PDSN (CNTD…)

▫• Perform packet routing to external packet data networks or packet routing to the HA which optionally can be via secure tunnels

▫• Collect and forward packet billing data▫• Actively manage subscriber services based on the

profile information received from the SCS server of the AAA server

▫• Authenticate users locally, or forward authentication requests to the AAA server

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2. The AAA Server

•The AAA (Authentication, Authorization, and Accounting) server is used to

• authenticate •and authorize

•users for network access and to store subscriber usage statistics for billing and invoicing.

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3. The Home Agent

• The Home Agent (HA) supports seamless data roaming into other networks that support 1xRTT.

• The HA provides an anchor IP address for the mobile and forwards any mobile-bound traffic to the appropriate network for delivery to the handset.

• It also maintains user registration, redirects packets to the PDSN and (optionally) tunnels securely to the PDSN.

• Lastly, the HA supports dynamic assignment of users from the AAA and (again optionally) assigns dynamic home addresses.

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Interfaces used to communicate

• In order to obtain packet data services, the mobile performs registration

•with the serving wireless network on the ▫A1 interface

•and then with the packet network on the▫A10/A11 interface.

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Communication Setup

•

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Data Flow Procedure in EV-DO

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Future of CDMA service providers..

•Future concern: •CDMA market competitor WiMAX

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References:

1. http://www.umtsworld.com/technology/cdmabasics.htm2. http://www.bee.net/mhendry/vrml/library/cdma/cdma.htm3. http://www.wisegeek.com/what-is-evdo.htm4. http://www.wikinvest.com/stock/Starent_Networks_Corp_%28STAR%29/Network_Functions5. http://www.cdmauniversity.com/prodtech/cdma/training/cdma25/m5/m5p03.html6. http://adaptive.ucsd.edu/2003_salih_CDMA2000.ppt

Bibliography:

• http://en.wikipedia.org/wiki/Code_division_multiple_access• http://ipandtelephone.blogspot.com/2007/04/cdma-call-flows.html• http://www.slideshare.net/mukesh2686/call-processing-in-cdma• http://www.cdmaonline.com/interactive04/workshops/terms1/1030.htm• http://en.wikipedia.org/wiki/Rake_receiver• http://www.evdoinfo.com/content/view/37/61/• http://www.cisco.com/en/US/solutions/ns341/ns973/starent/datasheet_c78-582253.pdf

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Thank You!