CDMA TECHNOLOGY

Presentation by- Niranjan Kumar Sharma

ECE Final Year, MNIT Jaipur

Acknowledgement Mobile communication history Multiple Access methods CDMA Switch Overview Call Flow Advantages, Disadvantages

“Appreciation can make a day, even change a life. Your willingness to put it into words is all that is necessary”.•I thank God Almighty for the successful completion of my training.• •I express my sincere gratitude to Dr. Vineet sahula , Head of the Department, Electronics & Communication Engineering. I am deeply indebted to Dr. Kamalesh Kumar Sharma, for their valuable advice and guidance. I am also grateful to all other members of the faculty of Electronics & Communication department for their co-operation.•I am grateful to TATA Teleservices Limited. for giving me the opportunity to undergo this Training Program. • NIRANJAN KUMAR SHARMA

1st.Generation(1980s)

Analog

NMT CT0TACS CT1AMPS

2nd. Generation(1990s)

Digital

GSMDECTDCS1800 CT2PDCPHSIS-54IS-95IS-136UP-PCS

IMT-2000CDMA2000W-CDMA

3rd. Generation(2000s)

1946 Mobile communication Appeared St. Louis USA 1946to1970 Slow growth of mobile networks all over world.

1970 BELL LAB introduced Cellular Principle. 1979 AMPS System in US

Analogue technology used. Technologies incompatible. Modules cumbersome & heavy. 1980s TACS & NMT systems introduced by Europe

& Nordic countries. 1990s Digital Systems introduced.

1946- 1960s 1980s 1990s 2000s Appeared 1G 2G 3G

Analog Digital Digital

Multi Multi Unified Standard Standard Standard Terrestrial Terrestrial Terrestrial

& Satellite

◦ AMPS: Advanced Mobile Phone Service

(US, 800 MHz Band)◦ TACS: Total Access Communication System

(UK , 900 MHz Band)

◦ NMT450: Nordic Mobile Telephone Service

(Scandinavian, 450 MHz & 900 MHz Band)

◦ DAMPS: Digital AMPS

(US, 800 MHz Band, IS-54 IS-136)

◦ CDMA: Code Division Multiple Access System

(US, 900 MHz Band, 1S-95)

◦ GSM: Global System For Mobile Communication.

(Europe, 900 / 1800 MHz Band)

IMT-2000: International Mobile Telecommunications in 2000

CDMA2000: IMT Multi‑Carrier  W-CDMA: Wideband Code Division Multiple Access)

LTE Advanced: long-term evolution WiMAX-Advanced: Worldwide Interoperability

for Microwave Access

High Capacity Support of global roaming across multiple

wireless and mobile networks Tolerance for interference Privacy Mixture of a variety of infrastructures Flexible Quality of Service (QoS)

MULTIPLEACCESSMETHOD

FDMA TDMA CDMA

FDMA is used for standard analog cellular. Each user is assigned a discrete slice of the RF

spectrum. FDMA permits only one user per channel since it

allows the user to use the channel 100% of the time. Therefore, only the frequency “dimension” is used to define channels.

Time Division Multiple Access A user’s channel is a specific frequency But only allotted for a certain duration It belongs to the user for certain time slots in

repeating sequence. Numbers of users are much greater Grouper Special Mobile (GSM) uses this technique

Code Division Multiple Access Each user is assigned a binary, Direct Sequence

code during a call. The DS code is a signal generated by linear

modulation with wideband Pseudorandorn Noise (PN) sequences.

As a result, DS CDMA uses much wider signals than those used in other technologies.

There is no time division, and all users use the entire carrier, all of the time.

CDMA is a “spread spectrum” technology, which means that it spreads the information contained in a particular signal of interest over a much greater bandwidth than the original signal.

The standard data rate of a CDMA call is 9600 bits per second (9.6 kilobits per second).

This initial data is “spread,” including the application of digital codes to the data bits, up to the transmitted rate of about 1.23 megabits per second.

The signal occupies a bandwidth much greater than that which is necessary to send the information.

The bandwidth is spread by means of a code which is independent of the data.

The receiver synchronizes to the code to recover the data. The use of an independent code and synchronous reception allows multiple users to access the same frequency band at the same time.

Frequency hopping. The signal is rapidly switched between different frequencies within the hopping bandwidth

Time hopping. The signal is transmitted in short bursts pseudo-randomly, and the receiver knows beforehand when to expect the burst.

Direct sequence. The digital data is directly coded at a much higher frequency. The code is generated pseudo-randomly, the receiver knows how to generate the same code, and correlates the received signal with that code to extract the data.

CDMA is a Direct Sequence Spread Spectrum system.

The CDMA system works directly on 64 kbit/sec digital signals. These signals can be digitized voice, ISDN channels, modem data, etc.

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

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

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

The carrier is received and amplified. The received signal is mixed with a local carrier to

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

the anticipated signal. The receiver acquires the received code and

phase locks its own code to it. The received signal is correlated with the

generated code, extracting the Information data.

The main Problem with Direct Sequence is the Near-Far effect.

when a non- reference user is closer to the receiver then the reference-user, it is possible that the interference caused by this non-reference user (however suppressed) has more power the reference user.

It equals 1 if the two codes are identical It equals 0 of the two codes have nothing in

common Intermediate values indicate how much the codes

have in common. Auto-Correlation: The correlation of a code with a

time-delayed version of itself.

The 850MHz CDMA band is most popularly used all over the world

This band works between 824-849MHz used for the Reverse link communication 869-894MHz used for the Forward link communication each of 25MHz.

The total band of 25MHz is divided into small channels of 30KHzeach.An actual CDMA carrier will be using a multiple of the 30KHz channels.

This means for an actually utilized bw of 1.23MH will need 41*30KHz channels.

Relationship between the channel numbers and actual freq. Reverse link frequency =(825+N0.03)MHz Forward link frequency=(870+N0.03)MHz N=CDMA Channel Number

mutually orthogonal The user signal (or control channel) is

multiplied by the Walsh code. The Walsh code provides each user or channel

with an unique identifier and, in DS spreading, spreads the frame across the entire 1.23MHz bandwidth.

CDMA uses unique spreading codes to spread the baseband data before transmission

It must be deterministic. The subscriber station must be able to independently generate the code.

It must appear random to a listener without prior knowledge of the code

The cross-correlation between any two codes must be small

The code must have a long period

The PN Short Code is used only for tracking the mobile that means to calculate the round trip delay or path delay for the mobile.

Used for Quadrature Spreading Repeat every 26.67 msec (clock rate of

1.2288Mcps)

Repeats every 41 days (clock rate of 1.2288Mcps) The functions of a long code: Scramble the forward CDMA channel Control the insertion of power control bit Spread the information on the reverse CDMA channel to identify the mobile stations

The MS is the mobile subscriber equipment, which can originate and receive calls and communicate with the BTS.

The BTS transmits and receives radio signals, realizing communication between the radio system and the mobile station.

Base Transceiver Station (BTS) control and management 

call connection and disconnection  mobility management  stable and reliable radio link provision for the

upper-layer services power control radio resource management.

The MSC implements the service switching between the calling and called subscribers.

One MSC is connected with multiple BSCs. The MSC can also be connected to the PSTN, ISDN

or other MSCs. It provides the interface between the radio

network and PSTN.

It is a database for mobile subscriber management, the HLR (Home Location Register) is responsible for storing subscription information.

It stores the authentication information. It also prevents unauthorized subscribers from

accessing the system and prevents the radio interface data from being stolen.

It is a dynamic database, stores the temporary information

VLR is used to store the subscriber information of all the MSs in its local area, which can be used to establish the incoming/outgoing call connections, to support basic services, supplementary services and mobility management.

Handover occurs when a call has to be passed from one cell to another as the user moves between cells.

In a traditional "hard" handover, the connection to the current cell is broken, and then the connection to the new cell is made. This is known as a "break-before-make" handover.

it is possible to make the connection to the new cell before leaving the current cell. This is known as a "make-before-break" or "soft" handover.

Soft handovers require less power, which reduces interference and increases capacity.

The number of “Effective” traffic channels includes the traffic carrying channels

The number of “Actual” traffic channels includes the effective traffic channels, plus channels allocated for soft handoff.

The number of “Physical” traffic channels includes the Pilot channels, the Sync channels, the Paging channels, the Soft Handoff Overhead channels and the Effective (voice and data) traffic channels.

Pilot Channel The pilot channel is used by the mobile unit to obtain initial system synchronization and to

provide time, frequency, and phase tracking of signals from the cell site.   Sync Channel This channel provides cell site identification, pilot transmit power, and the cell site pilot

pseudo-random (PN) phase offset information. With this information the mobile units can establish the System Time as well as the proper transmit power level to use to initiate a call.

  Paging Channel The mobile unit will begin monitoring the paging channel after it has set its timing to the

System Time provided by the sync channel. Once a mobile unit has been paged and acknowledges that page, call setup and traffic channel assignment information is then passed on this channel to the mobile unit.

  Forward Traffic Channel This channel carries the actual phone call and carries the voice and mobile power control

information from the base station to the mobile unit.

Access Channel When the mobile unit is not active on a traffic

channel, it will communicate to the base station over the access channel. This communication includes registration requests, responses to pages, and call originations.  

Reverse Traffic Channel This channel carries the other half of the actual

phone call and carries the voice and mobile power control information from the mobile unit to the base station.

Types Of Call

On Net Call Off Net Call

Local STD Local STD

onOn Net Call-call in same networkOff Net Call-call in other network

• The mobile user when decides to make a call, enters the desired phone number. This initiates an access probe. The mobile uses the access channel and attempts to contact the serving base station.

• Since no traffic channel has been established, the mobile uses open loop power control. Multiple tries are allowed at random times to avoid collisions that can occur on the access channel. Each successive attempt is made at a higher power level. After each attempt, the mobile listens to the paging channel for a response from the base stations.

Once the access request has been received by the base station, the base station responds with an assignment to a traffic channel (Walsh code). The base station initiates the land link, and conversation takes place.

Call termination can be initiated either from the mobile or the land side. In either case the transmissions are stopped, the Walsh code is freed, and the land line connection is broken. The mobile unit resumes monitoring the page channel of the current serving cell.

Interim Standard 95 (IS-95) is the first CDMA-based digital cellular standard by Qualcomm. The brand name for IS-95 is cdmaOne. IS-95 is also known as TIA-EIA-95.

It is a 2G mobile telecommunications standard that uses CDMA, a multiple access scheme for digital radio, to send voice, data and signaling data (such as a dialed telephone number) between mobile telephones and cell sites.

CDMA2000 (also known as IMT Multi‑Carrier (IMT‑MC)) is

a family of 3G mobile technology standards, which use CDMA channel access, to send voice, data, and signaling data between mobile phones and cell sites.

W-CDMA (Wideband Code Division Multiple Access)

 It uses the DS-CDMA channel access method and the FDD duplexing method to achieve higher speeds and support more users compared to most time division multiple access (TDMA) and time division duplex (TDD) schemes used before.

1. It has high capacity.2. It has the capability of using signals that arrive in the receivers

with different time delays.3. It is interference limited multiple access system.4. It uses unique spreading codes due to which it has low noise

level.5. High capacity increases as well as extended battery life for

handsets.6. Increased cellular communications security.7. Simultaneous conversations.8. Increased efficiency, meaning that the carrier can serve more

subscriber.9. Smaller phones.10. Low power requirements and little cell-to-cell coordination needed

by operators.

1. It causes ‘near-far’ problem i.e. a transmitter ”near” the receiver sending a different code than the receiver’s desired code produces in the receiver a signal comparable wit that of a ”far” transmitter sending the desired code.

2. Synchronization of the receiver and the transmitter is complex.

3. Due to its proprietary nature, all of CDMA’s flaws are not known to the engg. Community.

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

5. CDMA cannot offer international roaming,a large GSM advantage.

In a world of finite spectrum resources, CDMA enables many more people to share the airwaves at the same time than do alternative technologies. The CDMA air interface is used in both 2G and 3G networks. 2G CDMA standards are branded cdmaOne and include IS-95A and IS-95B. CDMA is the foundation for 3G services: the two dominant IMT-2000 standards, CDMA2000 and WCDMA, are based on CDMA.

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