Module 3�CDMA TECHNOLOGY� �

Ms. Deeksha Bekal Gangadhar

Assistant Professor,

Department of Electronics & Communication

MITE

Introduction to CDMA

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• Developed by Qualcomm Corporation in 1989 and continued into the early 1990s during which it was accepted for use as an air interface standard Commercially deployed in the year 1995.
• In 1992, TIA adopted IS-95 as the CDMA air interface standard for the digital transmission technologies known as wideband spread spectrum.
• The first CDMA commercial network began operation in Hong Kong in 1995.
• Other forms of CDMA are:
• ➢ Time Division CDMA (TD-CDMA)
• ➢ Time Division Synchronous CDMA (TD-SCDMA)
• ➢ Multicarrier CDMA (MC-CDMA)
• ➢ Wideband CDMA (W-CDMA)

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� Evolution of 2G CDMA

• The first form of CDMA, IS-95, specified a dual mode of operation in 800-MHz cellular band for both AMPS and CDMA.
• First standard defined mobile station and base station requirements that would ensure the compatibility for both AMPS and CDMA.
• The next standard IS-95A describes the structure of wideband 1.25MHz CDMA channels and the operations necessary to provide power control, call processing, handoffs and registration procedures for proper system operations
• Along with the voice, circuit switched data services were provided at 14.4 kbps over these first CDMA systems.
• With additional features, new standard, TIA/EIA-95-B accepted in 1999, provided the compatibility of 1.8 to 2.0-GHz CDMA PCS systems with IS-95A.
• These systems provided packet-switched data service at rates up to 64 kbps known as 2.5G CDMA technology.
• These early forms of CDMA are grouped together called cdmaOne, trademark of the CDMA Development Group.

� Evolution of 2G CDMA

Evolution of 3G CDMA

• Cdma2000
• Cdma2000 was one of five proposals the ITU approved for IMT-2000 third- generation(3G) standards.
• Provides support for data services up to 2 mbps, multimedia services and advanced radio technologies.
• 2 phases- 1) 1xRTT( 1X radio transmission technology) happening over a standard 1.25MHz cdma channel.
• 2) CDMA2000 1xEV (Evolutionary)
• there are 2 versions– 1xEV-DO(data only)
• -- 1xEV-DV (Data and Voice)
• 1XEV –DO support asymmetrical peak data rates of 2.4mbps – downlink and 153 kbps in uplink
• 1XEV –DV can support integrated voice and data at speeds up to 3mbps over all IP network architecture.

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CDMA basics:

• CDMA is a multiple access technology that is based on the use of wideband spread spectrum digital techniques that enable the separation of signals that are concurrent in both time and frequency.
• All signals share the same frequency spectrum simultaneously.
• The signals transmitted by the mobile stations and the base stations within the cell are spread over the entire bandwidth of a radio channel and encoded in such a way as to appear as broadband noise signals to every other mobile or base station receiver.

• The Identification and subsequent demodulation of individual signals occur at a receiver through the use of a copy of the code used to originally spread the signal at the transmitter.
• This process has the net effect of demodulating the signal intended for the receiver while rejecting all other signals as broadband noise.
• Since a specific minimum level of signal-to-noise ratio is necessary to provide for a certain level of received signal quality, the level of background noise or interference from all system transmissions ultimately limits the number of users of the system and hence the capacity.

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comparison of different techniques

CDMA Frequency Bands

• Initially CDMA systems were deployed in existing Cellular Frequency Bands (Band Class0) and Personal Communication Service(PCS) Bands (Band class1) in United States.
• Later 3G CDMA systems were allowed in 1710-1755MHz and 2110-2155MHz Advanced Wireless Service (AWS) bands
• A frequency separation of 45MHz between the forward and reverse channels is employed when used in cellular bands.
• Mobile station transmit frequency band is 824-849 MHz and the base station transmit frequency band is 869-894MHz.

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CDMA and NA-TDMA PCS channel numbers and carrier frequencies

CDMA Frequency Bands

useable CDMA channel numbers and assigned frequencies for Band Class1.

CDMA Frequency Bands

Preferred set of CDMA frequency assignments for Band Class1

Frequency Planning Issues

• Since the frequency reuse factor is N=1, CDMA frequency planning is relatively simple compared to analog cellular systems.
• For a system that only requires one carrier per base station that carrier must be chosen from the list of preferred CDMA channels.
• The same channel should be used by all the base stations throughout the system to take advantage of soft and softer handoff capabilities.
• Additional system capacity can be added by the addition of new base stations or by increasing the number of base station carriers.

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CDMA Network and System Architecture

Initial CDMA (IS-95) Reference Architecture

CDMA Network and System Architecture

• Messaging between CDMA system network element is through the use of protocols similar to SS7.
• TIA/EIA-634-B is an open interface standard that deals with signaling between the MSC and BSC over the A interface.
• TIA/EIA-41-D describes the protocols used between the other core network elements (MSC, VLR, HLR, AC, etc).

CDMA Network and System Architecture

• Messaging between CDMA system network element is through the use of protocols similar to SS7.
• TIA/EIA-634-B is an open interface standard that deals with signaling between the MSC and BSC over the A interface.
• TIA/EIA-41-D describes the protocols used between the other core network elements (MSC, VLR, HLR, AC, etc).

cdma2000 MSC-BSC interface functional planes

Network architecture of CDMA

Packet Network architecture of CDMA

Packet Network architecture of CDMA

• Mobile- service switching center and visitor location register
• Interworking Function:
• Mobile Positioning System
• Unified messaging/Voice mail service
• HLR/AC
• PPCS(prepaid calling services) and Other nodes
• Base station subsystem
• BSC
• RBS
• PLMN (Public land mobile) subnetwork
• Circuit core network
• CDMA Radio Access network
• Packet Core Network
• AAA (Authentication authorization accounting)
• HA (Home aget)

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Packet Network architecture of CDMA

• Mobile- service switching center and visitor location register
• Interworking Function:
• Mobile Positioning System
• Unified messaging/Voice mail service
• HLR/AC
• PPCS and Other nodes
• Base station subsystem
• BSC
• RBS
• PLMN subnetwork
• Circuit core network
• CDMA Radio Access network
• Packet Core Network

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Packet Network architecture of CDMA

• Network Management
• System Communication Links
• Subscriber Devices

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Mobile- service switching center and visitor location register

• The CDMA mobile-services switching center (MSC) serves as the interface between the public switched telephone network and base station subsystem.
• The MSC performs functions necessary for the establishment of calls to and from the system’s mobile subscribers.
• Provides functionality needed to permit subscriber mobility and roaming.
• Subscriber registration and authentication, location updating functions, call handoffs and call routing for roaming subscribers.

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• Typically VLR function is colocated with the MSC.
• Its function is to provide a database containing temporary information about registered subscribers that may be needed by the MSC in the performance of call control operations and the provisioning of subscriber services for the mobiles currently registered In the MSC/VLR service area.

Interworking Function:

• In CDMA system IWF is the only gateway between the wireless network and the PDN.
• It provides the direct connection to the PDN for packet data calls.
• The IWF node supports circuit-switched data calls by providing internal modems for connections to dial-up internet service providers(ISPs).
• These circuit switched data calls are routed to the PSTN through the MSC.
• The IWF typically uses Ethernet for the signaling between itself and the MSC and for the exchange of packet data between itself and the PDN.
• In CDMA2000 the IWF’s packet data transfer function is augmented by the packet core network(PCN) element.

Mobile Positioning System

• In CDMA system mobile positioning system can determine the geographic position of a mobile subscriber.
• MPS is based on Global positioning system(GPS) and is to be used for emergency services.
• The ability to locate the caller is known as Enhanced 911 or E911.
• For phase 1 of the wireless E911 program, the cellular system must be able to tell a local public safety answering point (PSAP) the location of the cellular antenna that is handling the emergency call.

• In phase 2 of the first implementations of this location determining system, the MPS uses a form of mobile-assisted GPS and triangulation to determine the latitude and longitude of the mobile within 50 to 100 meters
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Unified Messaging /Voice Mail Service

• Ericsson Corporation’s new cdma2000 systems contain a unified messaging / voice mail service (UM/VMS) node that integrates e-mail and voice mail access.
• This node provides messaging waiting indication using short message service (SMS) and multiple message retrieval modes including the use of DTMF or WEB browser.
• UM/VMS node connects to the PDN and the MSC in Ericsson’s system.

HLR/AC

• The HLR/AC are typically colocated in cdma2000 systems.
• The HLR holds subscriber information in a database format that is used by the system to manage the subscriber device (SD) activity.
• The type of information contained in the HLR includes the SD electronic serial number (ESN), details of the subscriber’s service plan, any service restrictions and the identification of the MSC where the mobile was last registered.

• The AC provides a secure database for the authentication of mobile subscribers when they first register with the system and during call origination and call termination.
• The AC uses shared secret data (SSD) for authentication calculations.
• Both the AC and SD calculate SSD based on the authentication key , ESN and random number provided by the AC and broadcast to the SD.
• The A-key is stored in the SD and also at the AC and never transmitted over the air.
• The AC or MSC/VLR compares the values calculated by the AC and the SD to determine the mobile’s status with the system.

PPCS and Other nodes:

• The prepaid calling service node provides a prepaid calling service using the subscribers home location area MSC.
• This node provides the MSC with information about the subscriber with account balance information.
• The PPCS node is usually associated with a prepaid administration computer system that provides the necessary database to store subscriber information and update it as needed.
• The prepaid administration system (PPAS) provides the subscriber account balance information to the PPCS system.
• Other additional nodes may be added to the system to provide increased system functionality like intersystem roaming.

Base station subsystem:�

• The BSS consists of one BSC and all the radio base stations controlled by the BSC.
• The BSS provides the mobile subscriber with an interface to the circuit switched core network(PSTN) through the MSC and an interface to public data network (PDN) through the Packet core network(PCN).
• There can be more than one BSS in a cdma2000 system.
• The combination of all the CDMA BSS’s and the radio network management system that oversees their operation is known as the CDMA radio access network or C-RAN.

BSC

• It is the interface between the MSC, the packet core network(PCN), other BSSs in the same system, and all of the radio base stations that it controls.
• It provides routing of data packets between the PCN and the RBSs , radio resource allocation, system timing and synchronization, system power control, all handoff procedures , and processing of both voice and data as needed.

RBS

• The cdma2000 RBS provides the interface between the BSC and the subscriber devices via the common air interface.
• The functions provided by the RBS include CDMA encoding and decoding of the subscriber traffic and system overhead channels and the CDMA radio links to and from the subscribers.

• The typical RBS contains an integrated GPS antenna and receiver that is used to provide
• system timing and frequency references,
• a computer-based control system that monitors and manages the operations of the RBS
• provides alarm indications as needed,
• communications links for the transmission of both system signals and subscriber traffic between itself and the BSC, and
• power supplies and environmental control units as needed.

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PLMN subnetwork

• A cdma2000 PLMN provides mobile wireless communication services to subscribers and typically consists of several functional subnetworks.
• These subnetworks are known as the circuit core network (CCN), Packet core network (PCN), service node network(SSN), and CDMA radio access network (C-RAN)

Circuit core network

• The CCN provides the switching functions necessary to complete calls to and from the mobile subscriber to the PSTN.
• The major network element in the CCN is the MSC.
• This portion of the system is primarily concerned with the completion of voice calls between the subscriber and the PSTN.
• The MSC is basically an extension of the PSTN that services the various cells and associated radio base stations within the cells.
• The MSC provides circuit switching and provides features such as call charging, subscriber roaming support, and maintenance of subscriber databases.

CDMA Radio access network

• In cdma2000, the CDMA C-RAN provides the interface between the wireless cellular subscriber and CCN.
• The CCN consists of the MSC and other system components involved with connections to the PSTN for all circuit-switched voice and data calls.
• The C-RAN can consist of multiple base station subsystems (BSSs) and some form of radio network manager (RNM) system.
• The RNM system provides operation and management (O&M) support for multiple BSSs.

Packet Core Network

• In cdma2000, the PCN provides a standard interface for wireless packet-switched data service between the C-RAN and public data network(PDN).
• The PCN provides the necessary links to various IP networks to and from the C-RAN.
• The PCN typically consists of three main hardware node:

- Authentication, authorization and accounting(AAA)

- Home agent (HA)

- Packet data serving node (PDSN).

Packet core Network architecture of CDMA

• In a cdma2000 cellular system, the packet data serving node (PDSN) provides the needed IP transport capability to connect the C-RAN and hence the subscriber to public data network.
• The PDSN connects to the C-RAN through the Aquater Interface (also known as the radio-packet R-P interface).
• The PDSN also interfaces the C-RAN with the home agent and the authentication, authorization and accounting nodes.
• In such a capacity, it sets up, maintains, and terminates secure communications with the home agent and the authentication, authorization and accounting nodes.

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• It further serves as a point of connection to the radio network and the IP network and provides IP service management to offered IP traffic.
• Also facilitate wireless mobile IP functionality, it also serves as a foreign agent to register network visitors.
• The AAA server both authenticates and authorizes the subscriber device to employ the available network services and applications.
• To facilitate this operation the AAA server manages a database that contains user profiles.

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• The user profile information will also include information about quality of service for the PDSN.
• The AAA server receives accounting information from the PDSN node that together with session information can be used for billing of the subscriber.
• An AAA server configured primarily for billing purposes.
• The PDSN may send accounting information to the billing AAA server and use a different AAA server for authentication and authorization.

• In cdma2000 system, the home agent (HA) has the task of forwarding all packets that are destined for the subscriber device to the PDSN over an IP network.
• The PDSN then sends the packets to the SD via the C-RAN and the common air interface.
• To be able to perform this operation the HA is conjunction with the PDSN authenticates mobile IP registrations from the mobile subscriber, performs SD registration, maintains current location information for the SD , and performs necessary packet tunneling.

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Packet tunneling:

• IP packets destined for a perticular SD’s permanent address are rerouted to the SD’s temporary address.
• If the SD is registered in a foreign network (not its home network) , then the SD has been assigned a temporary dynamic IP address by the foreign agent(this functionality is provided by the foreign network PDSN) and this temporary address is sent to the HA.

• A recent addition to the elements of the PCN is a wireless LAN serving node(WSN).
• This node provides IP transport capability and connectivity between the wireless network and wireless LAN enabled subscriber devices through wireless LAN access points.

Network interface architecture of CDMA

CDMA Channel Concept

Forward logical channels

• The IS-95 CDMA forward channels exist between the CDMA base station and the subscriber devices.
• IS-95 signal occupies a bandwidth of approximately 1.25 MHz
• AMPS and NA-TDMA -30 khz

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Basic Spreading procedure used on CDMA Forward Channels

Forward logical channels

• The four types of logical channels in the forward direction are:

➢ Pilot channel

➢ Synchronization channel

➢ Paging channel

➢ Traffic/Power Control channel

Pilot channels

• The CDMA Pilot channel is used to provide a reference signal for all the SDs within a cell.
• The short PN spreading code is used to identify the base station and the Pilot signal is transmitted at a fixed output power usually 4-6dB stronger than any other channel.

Generation of the CDMA Pilot Channel Signal

Synchronization Channel

• Used by the system to provide initial time synchronization.
• This process increases the data rate to 4.8kbps.
• The sync message includes the system and network identification codes, identification of paging channel data rates, the offset value of the short PN spreading code and the state of the long PN spreading code.

Generation of the CDMA Synchronization Channel Signal

Paging Channels

• Used to page the SDs when there is a mobile-terminated call and to send control messages to the SDs wen call setup is taking place.

Generation of the CDMA Paging Channel Signal

Traffic/Power Control Channels

• The CDMA Forward Traffic Channels carry the actual user information.

Generation of the CDMA forward Traffic/Power Channel for 9.6kbps Traffic

Traffic/Power Control Channels

• The CDMA Forward Traffic Channels carry the actual user information.

Generation of the CDMA forward Traffic/Power Channel for 14.4kbps Traffic

Access Channels

• The CDMA access channels are used by the mobile to answer pages and to transmit control information for call setup and tear down.
• An access message at 4.8kbps undergoes the familiar convolutional encoding, symbol repetition and block interleaving that raises the data rate to 28.8kbps.

Traffic/Power Control Channels

• The CDMA Reverse Traffic/Power Control Channels support both voice and data.

CDMA Frame Format

• The basic system frame size is 20ms.
• The first IS-95 systems used the 8-kbps Qualcomm-Coded Excited Linear Prediction (QCELP) speech encoder that produced 20ms frame outputs of either 9600, 4800, 2400, or 1200 bps (Rate Set 1) with the addition of overhead bits for error correction. The actual net bit rates are 8.6, 4.0, 2.0, or 0.8kbps.
• A second encoder, the 13-kbps QCELP13 encoder produced the outputs of 14.4, 7.2, 3.6 and 1.8 kbps (Rate Set 2), with a net maximum bit rate of 13.35 kbps.
• The speech encoder makes use of pauses and gaps in the user’s speech to reduce its output from a nominal 9.6 or 14.4kbps to lower bit rates and 1.2 or 1.8kbps during silence.

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Forward Channel Frame Formats

• Pilot Channel does not employ a frame format.
• The Forward Traffic Channel frames are 20ms in duration and contain a varying number of information bits, frame error control check bits and tail bits depending upon the rate set and the data rate.
• Power control bits transmitted over the Forward Traffic Channels are randomly inserted into the data stream of each 1.25ms power control group yielding a power control signal rate of 800bps.

Sync Channel

• The CDMA Forward Synchronization Channel provides the mobile or subscriber device with system configuration and timing information.
• A Sync Channel message is typically broken up into sync channel frames of 32 bits each.
• The Sync Channel frame consists of Start Of Message (SOM) bit and 31 data bits.
• The start of Sync Channel is indicated by a SOM bit set to 1 in the first frame and 0 in subsequent frames of the same message.
• At a data rate of 1200 bps, a Sync Channel frame is 26.666ms in duration.

Paging Channel

• The Forward Paging Channels are used to transmit system overhead information and mobile station specific messages.
• Its data rate can be either 4800 or 9600 bps.
• The Paging Channel is formatted into 80-ms paging slots of eight half frames of 10-ms duration.
• Each half frames starts with a Synchronized Capsule Indicator (SCI) bit that is functionally similar to SOM bit.
• The CDMA system uses the mobile station’s ESN to determine the correct slot to use for paging of the mobile.

Paging Channel

Reverse Channel Frame Formats �Traffic Channel

• The Reverse Traffic Channel is divided into 20ms traffic channel frames.
• It is logically subdivided into sixteen 1.25-ms power control groups and variable data rates are sent.
• The coded bits from the conventional encoder are repeated before interleaving when the speech characteristics are such that the encoded data rate is less than the maximum.
• The data burst randomizer generates a random masking pattern for the gating pattern that is tied to the mobile station’s ESN

Reverse Channel Frame Formats �Traffic Channel

CDMA Reverse Channel Variable Data Rate Transmission

Access Channel

• Reverse Access Channel is used by the mobile station to communicate with the base station.
• It is used for short message exchanges, like responses to commands from the base station, for system registrations and for call origination requests.
• Its data rate is 4.8kbps using a 20ms frame that contains 96 information bits.
• Every access channel message is typically composed of several Access Channel frames.

CDMA System (Layer 3) Operations

• Spread spectrum technology is used to implement CDMA cellular systems.
• Few more advantages of CDMA are better immunity to interference and multipath propagation, a frequency reuse factor of N=1, the ability to perform soft handoffs and extremely precise power control.
• The last feature affords increased battery life since the mobile is always operated at the minimum output power needed for satisfactory system performance.

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Initialization/Registration

Initialization/Registration

CDMA Mobile Station Call Processing States

Initialization/Registration

• Power up Registration
• Power down Registration
• Time based Registration
• Distance based Registration
• Zone based Registration
• Parameter-change Registration
• Ordered Registration
• Implicit Registration
• Traffic Channel Registration
• User zone Registration

Call Handoff

• Idle/access handoff
• Soft handoff
• Softer handoff
• soft handoff
• soft softer handoff
• Hard handoff

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Idle/ Access Handoff :

• If the mobile is in the idle state and moves from the coverage area of one sector/cell into another sector/cell, an idle handoff can occur.
• When the RSS of a different pilot channel is determined to be twice as strong than the current PC, the mobile will start listening to the paging channel associated with the stronger PC.

Softer handoff: handoff is between two sectors of the same cell.

Soft handoff: can occurs between two different cells.

Soft-softer handoff: can occur when the motion of the mobile gives it a handoff choice between two sectors of the same cell and a sector from an adjacent cell.

Hard Handoff:�

• A CDMA mobile in the traffic state can experience a hard handoff.
• This will occur for the case of an intercarrier handoff.
• Intercarrier handoff causes the radio link to be abruptly interrupted for a short period