Cdma Technology System Used In Mobile Computer Science Essay

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Code division multiple access is a channel access method utilized by various radio communication technologies. It should not be confused with the mobile phone   standards called cdmaOne and CDMA2000 (which are often referred to as simply "CDMA"), which use CDMA as an underlying channel access method.

One of the basic concepts in data communication is the idea of allowing several transmitters to send information simultaneously over a single communication channel. This allows several users to share a bandwidth of different frequencies. This concept is called multiplexing. CDMA employs spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code) to allow multiple users to be multiplexed over the same physical channel. By contrast, time division multiple access (TDMA) divides access by time, while frequency-division multiple access (FDMA) divides it by frequency. CDMA is a form of "spread-spectrum" signaling, since the modulated coded signal has a much higher data bandwidth than the data being communicated.

CDMA (Code-Division Multiple Access) refers to any of several protocols used in so-called second-generation (2G) and third-generation (3G) 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.

The technology is used in ultra-high-frequency (UHF) cellular telephone systems in the 800-mhz and 1.9-ghz bands.

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Now a day's importance of CDMA technology

One of the important wireless technologies widely in use today is CDMA which has been adopted by many service providers.

For anybody aspiring to start their career in the wireless communication industry, the knowledge of the CDMA technology is a must.

This course provides the basic knowledge on the working of the CDMA technology.

The cellular industry is about 90% of the way through the process of defining standards for the transition to digital radio, in order to gain much greater capacity and reduce service costs. That process, which involves by now several man-centuries of effort on the part of all the major cellular manufacturers, has concentrated upon a more established architecture known as TDMA (time division multiple access).

Modulation technique

Asynchronous CDMA's main advantage over CDM (Synchronous CDMA), TDMA and FDMA is that it can use the spectrum more efficiently in mobile telephony applications. (In theory, CDMA, TDMA and FDMA have exactly the same spectral efficiency but practically, each has its own challenges - power control in the case of CDMA, timing in the case of TDMA, and frequency generation/filtering in the case of FDMA.) TDMA systems must carefully synchronize the transmission times of all the users to ensure that they are received in the correct timeslot and do not cause interference.

Most modulation schemes try to minimize the bandwidth of this signal since bandwidth is a limited resource. However, spread spectrum techniques use a transmission bandwidth that is several orders of magnitude greater than the minimum required signal bandwidth. One of the initial reasons for doing this was military applications including guidance and communication systems. These systems were designed using spread spectrum because of its security and resistance to jamming.

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CDMA is a spread spectrum multiple access technique. A spread spectrum technique is one which spreads the bandwidth of the data uniformly for the same transmitted power.

Spreading code is a pseudo-random code which has a narrow Ambiguity function unlike other narrow pulse codes.

In CDMA a locally generated code runs at a much higher rate than the data to be transmitted. Data for transmission is simply logically XOR (exclusive OR) added with the faster code.

The figure shows how spread spectrum signal is generated. The data signal with pulse duration of Tb is XOR added with the code signal with pulse duration of Tc. (Note: bandwidth is proportional to 1 / T where T = bit time) Therefore, the bandwidth of the data signal is 1 / Tb and the bandwidth of the spread spectrum signal is 1 / Tc. Since Tc is much smaller than Tb, the bandwidth of the spread spectrum signal is much larger than the bandwidth of the original signal.


Code Division Multiplexing (Synchronous CDMA)

Synchronous CDMA exploits mathematical properties of orthogonally between vectors representing the data strings.

For example, binary string "1011" is represented by the vector (1, 0, 1, 1). Vectors can be multiplied by taking their dot product, by summing the products of their respective components.

If the dot product is zero, the two vectors are said to be orthogonal to each other (note: if u=(a,b) and v=(c,d), the dot product u·v = a*c + b*d). Some properties of the dot product aid understanding of how W-CDMA works.

Asynchronous CDMA

The previous example of orthogonal Walsh sequences describes how 2 users can be multiplexed together in a synchronous system, a technique that is commonly referred to as Code Division Multiplexing (CDM).

The set of 4 Walsh sequences shown in the figure will afford up to 4 users, and in general, an NxN Walsh matrix can be used to multiplex N users.

Multiplexing requires all of the users to be coordinated so that each transmits their assigned sequence v (or the complement, -v) so that they arrive at the receiver at exactly the same time.

Thus, this technique finds use in base-to-mobile links, where all of the transmissions originate from the same transmitter and can be perfectly coordinated.

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What is benefit of CDMA Technology?

Outstanding Voice and Call Quality

CDMA filters out background noise, cross-talk, and interference so you can enjoy crystal-clear voice quality, greater privacy, and enhanced call quality. QUALCOMM's CDMA variable rate vocoder translates voice into digital transmissions, zeroes and ones, at the highest translation rates possible (8kbps or 13kbps). 

Greatest Coverage for Lower Cost

CDMA's spread spectrum signal provides the greatest coverage in the wireless industry, allowing networks to be built with far fewer cell sites than is possible with other wireless technologies.

Longer Talk Time, Longer Battery Life and Smaller Phones

You can leave your phone on with CDMA. CDMA uses power control to monitor the amount of power your system and handset need at any time. 

Greater Capacity

CDMA allows the largest number of subscribers to share the same radio frequencies, helping service provider's increase their profitability. You can leave your phone on with CDMA. CDMA uses power control to monitor the amount of power your system and handset need at any time. 

Reduced Background Noise and Interference

CDMA combines multiple signals and improves signal strength. This leads to the near elimination of interference and fading.

Improved Security and Privacy

CDMA's digitally encoded, spread spectrum transmissions resist eaves dropping. Designed with about 4.4 trillion codes, CDMA virtually eliminates cloning and other types of fraud. 

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Difference between CDMA Technology and GSM Technology

Serial number

CDMA Technology

CDMA Advantage

GSM Technology

CDMA Disadvantage


CDMA stands for code division multiple access it use cdma

Techniques as access mechanism.

GSM is stands for global system for mobile communication. It use tdma & fdma techniques as access mechanism.


CDMA phone instruments are dedicated to the service Provider.

GSM phone instruments are portable across service Providers through SIM cards.


in CDMA the entire frequency band is available to the End-user. So, the Frequency Re-use factor is 1 in CDMA.

In GSM, the entire frequency band is not available to the end-user.


in cdma we allocate a

Unique code for every user separately and allocate bandwidth to user.

In gsm we divide bandwidth in to time slots for better utilization of bandwidth.


 Here the handset is network locked. You have to buy a complete package from the service provider that includes both, the handset and the connection (prepaid / post-paid).

If you opt for GSM technology, you have the freedom to choose handset separately from the wide variety of big handset companies like Nokia, Motorola, Sony Ericsson, etc who retail their products in the market. 


You cannot change the service provider and still keep the same handset.

You even enjoy the freedom to switch the service provider and still continue with the same handset. 


Here you need to check for International roaming tie ups if you travel abroad frequently. You do not enjoy the freedom like GSM mobiles.

To save yourself from roaming charges from your service provider, you can purchase a local SIM card with call value and a local number in the country you are visiting. 

CDMA Advantages:

-->The first and the most important advantage in CDMA is the cost of calls is lower than GSM. Although this difference is becoming transparent day by day still roaming costs will remain low.

-->CMDA services in India are backed up India's most wealthy companies Tata and Reliance. 

-->Right now the call quality is better than GSM. But as soon as the subscriber base increases the call quality will start going low because of the way in which CDMA system works.


-->although many handsets are available in CDMA service u don't find as much variety as u would in GSM handsets.

--> The biggest disadvantage for CDMA handsets is they aren't compatible with GSM handsets. U cannot use a CDMA handset with a SIM card. So u gotta stick around with one handset for a long time.

-->Another disadvantage is that in CDMA only 2 service providers are there Reliance and Tata. While Tata is still improving so u gotta stick to Reliance u has no option? Offcourse Reliance is too increasing day by day.

--> The web based services like messenger, downloading ringtones etc from websites are not yet available in CDMA services yet. 

What is soft handoff?

Soft handoff technology is used by code-division multiple access (CDMA) systems. Older networks use frequency division multiplex (FDM) or time division multiplex (TDM). In CDMA, all repeaters use the same frequency channel for each mobile phone set, no matter where the set is located. Each set has an identity based on a code, rather than on a frequency (as in FDM) or sequence of time slots (as in TDM). Because no change in frequency or timing occurs as a mobile set passes from one base station to another, there are practically no dead zones. As a result, connections are almost never interrupted or dropped.

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Hard Hand Off

Hard Hand Off, used in CDMA systems, describes a hand-off involving a frequency change. The hard hand-off is a break before make hand-off just like in other wireless systems and must be used where the current and hand-off candidate base stations do not use the same RF channel. See also soft hand-off.

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Security issues

Parameter Negotiation

After the call has been set up using the protocols H.225 and Q.931, the H.245 protocol is now used to negotiate the parameters of the call. It uses the H.245 control channel, which is always open.

Each side starts out by announcing its capabilities: e.g. whether it can support video or conference calls, which codec's it supports, bit rate etc.

once each side knows what the other one can handle, two unidirectional data channels are set up and a codec and other parameters assigned to each one

after all negotiations are complete, data flow can begin using RTP, which is managed by RTCP, which handles congestion control and audio/video synchronisation

When either party hangs up, the Q.931 call signalling channel is used to tear down the connection.

SIP - Session Initiation ProtocoL

This application-layer protocol describes how to set up Internet telephone calls, videoconferences, and other multimedia connections. SIP is a single module, designed to interwork well with existing Internet applications.C:\Users\HEMANT GUPTA\Desktop\sip_proxy2.gif


A VPN consists of a set of computers that interconnect over an insecure network such as the Internet and make use of encryption and other protocols to provide security. At each private site LANs link workstations, servers and databases under the control of an IT department.

CDMA Data Channel

The authentication system with TIA/EIA/IS-95 standard in cellular phone provides authentication, signalling message encryption, and voice privacy. To

Provide these services, The CAVE (Cellular Authentication and Voice Encryption Algorithm), CMEA (Cellular Message Encryption Algorithm), and PN sequence (private long code mask) were used. In an effort to enhance the authentication process and to protect sensitive subscriber information (such as PINS), a method is needed to encrypt certain fields of selected traffic channel signalling messages.


Data traffic has increased exponentially, unlike voice traffic, which shows only a linear increase. As a consequence of this, many packet-switching network operators started showing interest in carrying voice over their data networks. The amount of additional bandwidth required for voice is negligible since the packet networks are already built for the data trifurcations are being invented regularly.


This is the telephony world's implementation of VoIP. It includes a large number of protocols for speech coding, call setup, signalling, data transport and other important areas.



Implementation of CDMA transmitter for a multi-standard SDR base band platform

It is clear now that it is virtually impossible to adopt or impose on a single standard for all wireless networks. Hence, software defined radio (SDR) technology emerged which addresses this issue. This paper describes the design of CDMA digital transmitter for a multi-standard SDR base band platform. The platform consists of reconfigurable and reprogrammable hardware platform which provide different standards with a common platform. This paper focus also on the methods of generate VHDL model of CDMA transmitter. This model can be implemented with Field Programmable Gate Array (FPGA).

Radio channels are 5 MHz wide.

Chip rate of 3.84 Mbps

Supported mode of duplex: frequency division (FDD)

Employs coherent detection on both the uplink and downlink based on the use of pilot symbols and channels .

Supports inter-cell asynchronous operation.

Variable mission on a 10 ms frame basis.

Multimode transmission.

Adaptive power control based on SIR (Signal-to-Interference Ratio).

Multiuser detection and smart antennas can be used to increase capacity and coverage.

Multiple types of handoff (or handover) between different cells including soft handoff, softer handoff and hard handoff.

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