CDMA and GSM

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INTRODUCTION

When we talk about cellular services, there are two main cellular data transmission technologies which are present in today's life it is: Code Division Multiple Access (CDMA) and Global System for Mobile Communications (GSM). It is no doubt that GSM is the most popular technology worldwide. Although CDMA has a lower number of users compared to GSM, but it is seriously popular in countries like China and India.

CDMA stands for code division multiple access. It is such type of channel access method which is utilized by different types of radio communication technologies. It employs analog to digit conversion and uses spread spectrum technology. it is a form of multiplexing which allows the uses of a particular frequency for a number of signals and optimizing the use of available bandwidth. In this technology every channel uses the full available spectrum. Individual conversation is encoded with a pseudo random digital sequence.

In India, CDMA mobile services were launched in December 2002 and in these seven years the Indian cellular market has seen some major competition between it and GSM technology.

GSM, which stands for Global system for mobile/wireless communication, is the world standard for digital cellular communication for voice, fax, SMS and Data transmission. GSM is the name of a standardization group established in 1982 to create initially a common European mobile telephone standard that would formulate specifications for a pan-European mobile cellular radio system operating at 900/1800 MHz. GSM is not a new technology.

It was invented before CDMA but it has a reputation as the latest mobile technology.It's often claimed that it's a better technology because it uses a SIM chip, allowing users to switch handsets and operators more easily.

Properties of GSM

* Good subjective speech quality

* Low terminal and service cost

* Support for international roaming

* Ability to support handheld terminals

* Support for range of new services and facilities

* Spectral efficiency

* ISDN compatibility

GSM operators in India

CDMA_Market_05

Why I prefer CDMA:

It is no doubt that today the total number of users of GSM has far greater than the cdma.According to a survey the total number of users of GSM is about over 3 billion people across more than 212 countries and by comparison, there are over 502 million CDMA users worldwide. But if we take a conscious look on these two markets then we found that at the early stage CDMA has no multimedia messages, video, high transfer rate of data but after it, it stands in the market and gave the unbelievable result. Now currently CDMA also has the same features like as multimedia messages, video, high- speed internet access, digital camera and even PDA functions, which were available in GSM.

In the field of technology it is impossible to declare that which wireless technology is best because in some view cdma is best and in some part gsm.

On the subject of its signal it depends on where the users are, but 9 times out of 10 CDMA will provide better coverage than GSM, especially inside buildings that GSM can't penetrate.

since bandwidth is the major problem in the modern times the CDMA has a very clear advantage over the GSM in these terms and also the number of channels (users) that can be allocated in a given bandwidth is comparatively higher for CDMA than for GSM.

Further the cost of setting up a CDMA network is also comparatively less than the GSM network.

If we take a look on the below mathematical calculation of these two technology we will have some clue that which technology is better.

GSM= work with SIMcards ( ATT,T-mobile) some areas have better coverage than CDMA (Verizon, Sprint, Alltel ect), the Problem with GSM is that its bandwith is not as fast as CDMA since Data travels quicker on CDMA's devices due to less steps to follow :

GSM= Data - SIMcard - device= response

CDMA= Data - Device= Response (wider bandwith as well)

So we would say that CDMA is better than GSM.

It is the new wireless technology and day by day its users are increasing and there is possibility that many of the new technology will be developed. It is the growing features of today's wireless technology so for the future enhancement our group has chosen this topic.

TECHNOLOGY USED IN CDMA

Basically, both CDM and GSM technologies address differently the same fundamental problem of mobile communication, how to divide the finite frequency of air waves between multiple users at the same time, or, how to make more than one person to carry on a conversation on the same frequency without causing mutual interference. In technical jargon, GSM (TDMA) does it by chopping up the channel into sequential time slices. Each user of the channel takes turns transmitting and receiving in a round-robin fashion. In reality, only one person is actually using the channel at any given moment, but he only uses it for short bursts. CDMA on the other hand, uses a special type of digital modulation called Spread Spectrum, which takes the user's voice stream bits and splatters them across a very wide channel in pseudo-random fashion. The receiver undoes the randomization in order to collect the bits together in a coherent order.

Code-division multiple access is a form of multiplexing, which allows numerous signals to occupy a single transmission channel, optimizing the use of available bandwidth. CDMA employs analog-to-digital conversion (ADC) in combination with spread spectrum technology. The technology is used in ultra-high-frequency cellular telephone systems in the 800 MHz and 1.9 GHz bands. IS-95 uses CDMA. http://searchmobilecomputing.techtarget.com/news/929575/Mobile-and-Wireless-Protocols#4 (UHF)

IS 95 :

The CDMA technology based on the IS-95 protocol standard .It was first developed by QUALCOMM.

The CDMA technology, used in the Interim Standard IS-95, maximizes spectrum efficiency and enables more calls to be carried over a single 1.25 MHz channel. In a CDMA system each digitized voice is assigned a binary sequence that directs the proper response signal to the corresponding user. The receiver demodulates the signal using the appropriate code. The resulting audio signal will contain only the intended conversation, eliminating any background noise. This allows more calls to occupy the same space in the communication channel, thereby increasing capacity. As a simple, example let us assume a user is talking into a mobile phone on a CDMA network. The transmitted portion of a voice signal has frequency components from approximately 300~3400 Hz. This analog signal is digitally encoded, using QPSK (Quadrature Phase Shift Keying), at 9600 bps. The signal is then spread to approximately 1.23 Mbps using special codes that add redundancy. Some of these codes include a device ID that is unique to the phone (like a serial number). Next the signal is broadcast over the channel. When broadcast, the signal is added to the signals of the other users in the channel. On the receiving end, the same code is used to decode the incoming signal. The 9600 bps signal is obtained and the original analog signal is reconstructed. When the same code is used on another user's signal, the redundancy is not removed and the signal remains at 1.23 Mbps.

http://www.wirelessdevnet.com/channels/wireless/training/mobilewirelesstoday4.html

SPREAD SPECTRUM:

CDMA employs analog to digital signal conversion in combination with spread specrum technology. In this technology audio is first digitized (ADC) into binary elements.The frequency of the transmitted signal is then made to vary according to a defined pattern, 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. There are trillions of possible frequency-sequencing codes. this enhances privacy and makes cloning difficult. The technology is used in ultra high frequency cellular telephone systems in the 800 MHZ and 1.9 GHZ bands.

http://www.bee.net/mhendry/vrml/library/cdma/cdma.htm

MULTIPLEXING:

CDMA is form of multiplexing (access to the same resource will be given to the more than one user) which allows the use od a particular frequency of a number of signals, optimizing the use of available bandwidth. It is a cellular technology that uses the spread spectrum technology. In CDMA technology every channel uses the full available spectrum. Individual conversion are encoded with a pseudo random digital code.

CDMA ONE:

cdmaOne technology improves quality of service through the use of soft handoffs, which greatly reduce the number of dropped calls and ensure a smooth transition between cells. In soft handoff, a connection is made to the new cell while maintaining the connection with the original cell. This transition between cells is one that is almost undetectable to the subscriber. cdmaOne technology also takes advantage of multipath fading to enhance communications and voice quality. Using a rake receiver and other improved signal-processing techniques, each mobile station selects the three strongest multipath signals and coherently combines them to produce an enhanced signal.

Optical multimedia CDMA system with novel multiplexing techniques

Four novel multiplexing techniques (VSM, PSM, RPM, OIM) of an optical multimedia CDMA system have been proposed by using prime codes with different code lengths. PSM and VSM have the advantages of easily adding and controlling the inserting code system, but with a limited successful number. RPM can dynamically add the inserting codes into the original codes at the price of a complicated algorithm and lower multiplexing speed. For example, VSM, PSM, RPM, and OIM can insert the number of inserting P3-code to be 2, 3, 4, and 15 into the simultaneous number of original P7-code being 7 with the successful number of 10 for the original P7-code system. So OIM is the best model to process the multimedia CDMA system.

WCDMA :

W-CDMA (Wideband Code Division Multiple Access), is an air interface standard found in 3G mobile telecommunications networks. W-CDMA transmits on a pair of 5 MHz-wide radio channels, while CDMA2000 transmits on one or several pairs of 1.25 MHz radio channels. Though W-CDMA does use a direct sequence CDMA transmission technique like CDMA2000, W-CDMA is not simply a wideband version of CDMA2000. The W-CDMA system is a new design by NTT DoCoMo, and it differs in many aspects from CDMA2000. From an engineering point of view, W-CDMA provides a different balance of trade-offs between cost, capacity, performance, and density; it also promises to achieve a benefit of reduced cost for video phone handsets. W-CDMA may also be better suited for deployment in the very dense cities of Europe and Asia. However, hurdles remain, and cross-licencing of patents between Qualcomm and W-CDMA vendors has not eliminated possible patent issues due to the features of W-CDMA which remain covered by Qualcomm patents.[5]

W-CDMA has been developed into a complete set of specifications, a detailed protocol that defines how a mobile phone communicates with the tower, how signals are modulated, how datagrams are structured, and system interfaces are specified allowing free competition on technology elements.

High Speed Packet Access:

High Speed Packet Access (HSPA) is a collection of two mobile telephony protocols, High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), that extend and improve the performance of existing WCDMA protocols.

These improvements lead to a better utilization of the existing radio bandwidth provided by WCDMA.

HSPA improves the end-user experience by increasing peak data rates up to 14 Mbit/s in the downlink and 5.8 Mbit/s in the uplink. It also reduces latency and provides up to five times more system capacity in the downlink and up to twice as much system capacity in the uplink, reducing the production cost per bit compared to original WCDMA protocols. HSPA increases peak data rates and capacity in several ways:

Shared-channel transmission, which results in efficient use of available code and power resources in WCDMA

A shorter Transmission Time Interval (TTI), which reduces round-trip time and improves the tracking of fast channel variations

Link adaptation, which maximizes channel usage and enables the base station to operate close to maximum cell power

Fast scheduling, which prioritizes users with the most favorable channel conditions

Fast retransmission and soft-combining, which further increase capacity

16QAM (Quadrature Amplitude Modulation), which yields higher bit-rates

CDMA 2000:

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. The set of standards includes: CDMA2000 1X, CDMA2000 EV-DO Rev. 0, CDMA2000 EV-DO Rev. A, and CDMA2000 EV-DO Rev. B. The successor to CDMA2000 is LTE, part of the competing 3GPP family.

SPATIAL MULTIPLEXING:

Spatial multiplexing is a transmission technique in MIMO (multiple-input and multiple-output) wireless communication to transmit independent and separately encoded data signals, so-called streams, from each of the multiple transmit antennas. Therefore, the space dimension is reused, or multiplexed, more than one time.

Its characteristics are:

Several different data bits are transmitted via several independent (spatial) channels.

No bandwidth expansion.

Space-time equalization needed in the receiver.

The data streams can be separated by the equalizer, if fading processes of the spatial channels are (nearly) independent.

Spatial Diversity-

it is a way to fight against fades. If a radio signal is received through one channel in a deep fading environment then there is a possibility of losing that signal, if lost then there is nothing that can be done to recover. That is why diversity technique is used to improve system performance in the presence of fading channel. In this technique, signals are transmitted and received through a number of channels instead of only one channel. The main idea behind diversity is that when several copies of the same signals are passed through different channels then they experience independent fading of each other-there will be high probability that some signals will undergo deep fades while other may not. When these signals reach the receiver then there will be significant energy to make a decision that what was actual sent.

http://hubpages.com/hub/spatial-multiplexing-spatial-diversity

Td scdma

TD-SCDMA (time division synchronous code division multiple access) is a mobile telephone standard for wireless network operators who want to move from a second generation (2G) wireless network to a third-generation (3G) one. Supporting data transmission at speeds up to 2 Mbps, TD-SCDMA combines support for both circuit-switched data, such as speech or video, and also packet-switched data from the Internet. The standard combines time division multiple access (TDMA) with an adaptive, synchronous-mode code division multiple access (CDMA) component.

TD-SCDMA was developed by the China Academy of Telecommunications Technology (CATT) in collaboration with Datang and Siemens.

http://searchmobilecomputing.techtarget.com/definition/TD-SCDMA

Other protocols used in cdma is is-93(work in mobile station) is-97(work in base station) is 834,53,41,124

IMPORTANCE OF THE TECHNOLOGY

Coverage: The most important factor is getting service in the areas where we will be using phone. Upon viewing competitors' coverage maps you may discover that only GSM or CDMA carriers offer cellular service in your area. If so, there is no decision to be made, but most people will find that they do have a choice.

Data Transfer Speed: With the advent of cellular phones doing double and triple duty as streaming video devices, podcast receivers and email devices, speed is important to those who use the phone for more than making calls. CDMA has been traditionally faster than GSM, though both technologies continue to rapidly leapfrog along this path. Both boast "3G" standards, or 3rd generation technologies.

Subscriber Identity Module (SIM) cards: In the United States only GSM phones use SIM cards. The removable SIM card allows phones to be instantly activated, interchanged, swapped out and upgraded, all without carrier intervention. The SIM itself is tied to the network, rather than the actual phone. Phones that are card-enabled can be used with any GSM carrier.

The CDMA equivalent, a R-UIM card, is only available in parts of Asia but remains on the horizon for the U.S. market. CDMA carriers in the U.S. require proprietary handsets that are linked to one carrier only and are not card-enabled. To upgrade a CDMA phone, the carrier must deactivate the old phone then activate the new one. The old phone becomes useless.

Roaming: For the most part, both networks have fairly concentrated coverage in major cities and along major highways. GSM carriers, however, have roaming contracts with other GSM carriers, allowing wider coverage of more rural areas, generally speaking, often without roaming charges to the customer. CDMA networks may not cover rural areas as well as GSM carriers, and though they may contract with GSM cells for roaming in more rural areas, the charge to the customer will generally be significantly higher.

International Roaming: If you need to make calls to other countries, a GSM carrier can offer international roaming, as GSM networks dominate the world market. If you travel to other countries you can even use your GSM cell phone abroad, providing it is a quad-band phone (850/900/1800/1900 MHz). By purchasing a SIM card with minutes and a local number in the country you are visiting, you can make calls against the card to save yourself international roaming charges from your carrier back home. CDMA phones that are not card-enabled do not have this capability, however there are several countries that use CDMA networks. Check with your CDMA provider for your specific requirements.

Comparison table

Feature

NMT

GSM

UMTS (3GSM)

IS-95 (CDMA one)

CDMA 2000




Roaming

Scandinavia

Worldwide, 200+ countries

Worldwide

Limited

Limited

Handset interoperability

None

SIM card

SIM card

None

RUIM (not commonly implemented)

Operator locking

Monopoly

Unlockable

Unlockable

ESN

ESN

Common Interference

None

Interferes with some electronics, such as amplifiers

None

None

None

Signal quality/coverage area

Good coverage due to low frequencies

Good coverage indoors on 850/900MHz. Repeaters possible. 35km hard limit.

Smaller cells and lower indoors coverage on 2100MHz; equivalent coverage indoors and superior range to GSM on 850/900MHz.

Unlimited cell size, low transmitter power permits large cells

Unlimited cell size, low transmitter power permits large cells

Frequency utilization/Call density

Very low density

0.2MHz = 8 timeslots. Each timeslot can hold up to 2 calls through interleaving.

5MHz = 2 Mbit/s. Each call uses 1.8-12 kbit/s depending on chosen quality and audio complexity.

? Comparable to UMTS

? Comparable to UMTS

Battery life

Low, due to high transmitter power (1 watt)

Very good due to simple protocol, good coverage and mature, power-efficient chipsets.

Lower due to high demands of WCDMA power control and young chipsets.

Lower due to high demands of CDMA power control.

Lower due to high demands of CDMA power control and young chipsets.

Handoff

Hard

Hard

Soft

Soft

Soft

Breathing

No

No

Yes

Yes

Yes

Intellectual property

Scandinavian telecom operators

Concentrated among a few manufacturers

Concentrated among a few manufacturers

Qualcomm

Qualcomm

Future Enhancement

Since bandwidth is a major problem in modern times, CDMA has a very clear advantage over GSM in these terms. The number of channels (users) that can be allocated in a given bandwidth is comparatively higher for CDMA as compared to GSM.

Cost

The cost of setting up a CDMA network is also comparatively less than the GSM network. Due to these advantages there is high probability that CDMA tech-nology will dominate the future of mobile communications.

GSM is better or CDMA is more superior is certainly a debatable issue. As per the present scenario, it is probably an understatement to say that cell phones have become the single greatest tool in business as well as personal communication

SECURITY

When CDMA was launched there was no way to access audio,video and internet Bluetooth and wi-fi activity.

The main importance of this technology in oAll users use same frequency and may transmit simultaneously

_ Narrowband message signal multiplied by wideband spreading signal, or codeword

_ Each user has its own pseudo-codeword (orthogonal to others).

_ Receivers detect only the desired codeword. All others appear as noise.

_ Receivers must know transmitter's codeword.

Time

Code Division Multiple Access (CDMA) is an increasingly popular method for handling higher volumes of calls. This spread spectrum technique is resistant to inference and jamming, provides for more calls to be made on a single frequency, allows for frequency reuse, and permits soft handoffs. Evolution Data Optimized, or Evolution Data Only (EV-DO) is designed as an evolution of the CDMA 2000 standard that supports higher bandwidths, enabling a wider range of wireless data services.

In a CDMA system, your encoded voice is digitized and divided into packets. These packets are tagged with "codes." The packets then mix with all of the other packets of traffic in the local CDMA network as they are routed towards their destination. The receiving system only accepts the packets with the codes destined for it.

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