The transfer of data

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1.1 Introduction to Wireless Technology

Wireless communication is the transfer of data through signals in a space. The distances can be short or long for signals. Wireless communication can be termed as "wireless".

It includes various types of communications like Radio, Mobile, Broadband, GPRS, etc.., and Other wireless devices includes Headphones, Keyboards, Mouse, etc..,

Wireless communication can be via:

  • Radio frequency communication,
  • Microwave communication, for example long distance or range communication via highly directional antennas, or short distance or range communication via Infrared Data Association (IrDA).

Types of Wireless Networks:

  • One-to-One Communication,
  • One-to-Many Communication,
  • Broadcasting,
  • Cellular and other wireless networks.

1.2 History Wireless Technology


The world's first wireless telephone conversation held in 1880, when Alexander Graham Bell and Charles Sumner Tainter originated and patented the photophone, a telephone that transmitted audio conversations wirelessly over modulated light beams (which are narrow projections of electromagnetic waves), which are limited availability of sunlight and good weather. Same as free-space optical communication and the photophone needs a clear line for sight without any obstacles between receiver and transmitter. It would be few decades before the photophone's principals found their applications first in military communications and later in fiber-optic communications.


This technology came into public use to refer a radio transceiver. In the field of wireless communication the term "telegraphy" used in the early stage, now is used to describe modern wireless communication such as in cellular and wireless broadband Internet. This is implemented in various devices, such as "wireless remote control" ,"wireless energy transfer", consideration of the specific technology (e.g. Radio, Infrared, Bluetooth, Ultrasonic). Guglielmo Marconi and Karl Ferdinand Braun were awarded in the year 1909 Nobel Prize for the contribution to wireless telegraphy in physics.

Early wireless work

Eight years before Hertz's experiments, David E. Hughes transmitted radio signals over a few hundred yards by means of a clockwork keyed transmitter. As this was before Maxwell work was understood, Hughes' contemporaries dismissed his achievement as mere "Induction". In 1885, T. A. Edison used a vibrator magnet for induction transmission. In 1888, Edison deploys a system of signaling on the Lehigh Valley Railroad. In 1891, Edison got the wireless patent for the proposed method using inductance.

In the history of wireless technology, the demonstration of electromagnetic waves theory by Heinrich Hertz in 1888 was very crucial. From the research of James Clerk Maxwell and Michael Faraday the theory of electromagnetic waves was already predicted. Hertz explained that electromagnetic waves can be transmitted and be caused to travel through space in straight lines and that they were able to substantiate the theory by receiving the transmitted signals over an experimental apparatus. The practical applications for wireless radio communication and radio remote control technology were later developed by later inventors, such as Nikola Tesla.

The electromagnetic spectrum

All AM and FM radio and electronic equipment make use of the electromagnetic spectrum. In America, the frequencies which are available to use for communication are treated as the public resource are regulated by the FCC (Federal Communications Commission). This determines the frequency ranges that can be used for a specific purpose and a specific user. If there is no such control then this might result in chaos for example, imagine a scenario where airlines didn't have specific frequencies to work under and an amateur radio operator was interfering with the pilot's ability to land an airplane. Thus arrangements need to be made to control or alternative arrangements such as a privatized electromagnetic spectrum. Thus specifying a specific frequency band for specific purpose, i.e. Wireless communication spans the spectrum from 9kHz to 300GHz. (Also see Spectrum management).

1.3 Applications of wireless technology

  • Security systems
  • Television remote control
  • Cellular telephony (phones and modems)
  • WiFi
  • Wireless energy transfer

Security systems

Wireless technology may substitute traditional hard wired implementations of security systems in home or office buildings.

Television remote control

Modern TVs use wireless (generally infrared) remote control devices. Now a day's radio waves are also used.

Cellular telephony (phones and modems)

Perhaps the best known example for a wireless technology is the cellular telephone and modems. These devices use radio waves to allow the operators to make phone calls from any location in worldwide. Operators can be applied on anywhere that there is a cellular telephone site to arrange the equipment which is required to receive and transmit the signals is used to transfer both voice and information to and from these devices.


Wireless fidelity is termed as Wi-Fi. It is a wireless local area network (LAN) technology that enables laptop's, PC's, PDA's, and other instruments to connect easily to the internet. Technically it is known as IEEE 802.11 a,b,g,n, Wi-Fi is less costlier and reaching the speeds of standard Ethernet and regular wire-based LAN technologies. The Wi-Fi hot spots have become popular over the past few years. Various businesses companies/ agencies charge customers a monthly/yearly fee for service, while others companies have started offering it for free of cost in an effort to maximize the sales of their goods.

Wireless energy transfer

It is a process of transferring electrical energy from a power source to the load without any cord and which (the load) might not have any built in power source.

Computer Interface Devices

Many computer peripherals manufacturers turned to wireless technology on the bases of the consumer's satisfaction. Originally these units were used to be bulky, with limited transmitters or receivers to connect between a computer, keyboard and mouse, thus in recent generations have used small and high quality devices. These systems have becoming so ubiquitous that some users have started complaining on wired peripherals. Wireless devices generally tend to have a slightly slower response of time when compared to wired counterparts, however the gap has been constantly decreasing. Initial concerns over the security of wireless keyboards have already been addressed with the maturation of the technology in the field.

Many scientists complained on this technology for the reason wireless technology interferes with their experiments, that influence them to make use less optimal devices because of the optimum one is not available on a wired version. This has become especially predominant among scientists who generally use trackballs as the number of models in production are steadily decreasing.

1.4 Introduction to CDMA and GSM


Code division multiple access (CDMA) is a channel access method utilized by various radio communication technologies. There is no confusion with the mobile phone standards named as cdmaOne and CDMA2000 (which are referred as simply "CDMA"), which use CDMA as an underlying channel access method.

The basic concept in data communications are the idea of allowing several transmitters to send bulk of data simultaneously on a single communication channel. This allows several operators to share different frequencies of a bandwidth. This concept is known as multiplexing. CDMA makes spread-spectrum technology and special coding scheme (where every transmitter is assigned a unique code) to allow multiple operators to be multiplexed over a same channel. By contrast, time division multiple access (TDMA) which divides access by time, whereas frequency-division multiple access (FDMA) which divides access by frequency.

An analogy to the problem of multiple access is a room (channel) in which people wish to communicate with each other. To avoid confusion, people could take turns speaking (time division), speak at different pitches (frequency division), or speak in different languages (code division). CDMA is analogous to the last example where people speaking the same language can understand each other, but not other people. Similarly, in radio CDMA, each group of users is given a shared code. Many codes occupy the same channel, but only users associated with a particular code can understand each other.

CDMA is a modulation and multiple access schemes based on spread-spectrum communication. In this scheme, multiple operators share the same frequency band at the same time, by spreading the spectrum of their transmitted signals, so that each user's signal is pseudo-orthogonal to the signals of the other users.


Which conducting early tests on new Global System Mobile (GSM) technology it was considered to use Time Division Multiple Access (TDMA) technology, its property of working with a variety of suppliers and ease of pitching the product faster into the market place. Major corporate mobile players lie Siemens and Ericsson hold their hands out for support. Finally GSM digital standard after being gone through series of tests came to existence in 1988.

Right from the first day of GSM technology worldwide coverage came into the mind for any new system that would be any utility to the GSM. Like other 2G systems GSM is quite good in voice calls, but data and internet application is not that good with the GSM.A data call is made in the same way as the voice call that is, when the user makes a data call a circuit switched connection gets established which remains till the session expiration when the user disconnects. If the user wants to reconnect he has to make again a dial in.

1.5 Difference between GSM and CDMA

Before deciding which technology is superior, let's talk a little more about both the technologies:

  • CDMA: Both information and audio are divided from signals using codes and transmitted using a wide-range frequency.Because of this, some more space is left fortransferring the information (this is one of the major reasons why CDMA technology is preferred for 3G or 3rd generation, which gets multimedia applications and faster broadband access). 14% in the world market prefers CDMA. For the 3rd generation CDMA uses 1x EV-DO (wireless broadband)& EV-DV. It has a lot of operators in Asian countries, especially in South Korea.
  • GSM: Even though it is said to be as "the latest technology" in various countries, GSM is older than CDMA (and TDMA also). Thisdoesn't mean that CDMA is superior orbetter than GSM. Roaming readiness and fraud prevention are two major advantages from GSM technology. GSM has large number of operators in the cell phone technology in worldwide, with 73% of the world market. GSM has a very strong presence in the various countries of Europe.

TDMA technology has a least number of operators from the three major digital technologies (GSM, CDMA and TDMA) because it is gradually being replaced to CDMA or GSM. There starts, GSM (vs.) CDMA war. At one side of a room, a GSM user says it is best "because it has a SIM chip, it is a mostly used technology in world market, it is more secure and advanced". On the other side of a room, CDMA operators say it is best"because it has a 3rd generation chosen technology since CDMA is more advanced..."

In the beginning, GSM was superior to CDMA.GSM had more services/advantages and allowed maximum data transfer. But CDMA has advantages of the dominating standard, soon deliver the samefeatures which wasfound in GSM. Nowadays, it is impossible to say that GSM services are superior to CDMA. Multimedia information, video, audio, digital camera, high-speed Internet access & even PDA function are some of the features we found on both the technologies. A new CDMA 1XRTT technology, which previews what 3rd generation cell phones will bring, more advanced than an EDGE, technology in the starting of 3rd generation, allowing higher transfer rates.

Even the GSM SIM card has an advantage, that allows you to change your cell phone number rather than cell phone and keep your phone list, is being replaced by some CDMA userswith aservice which allows to store your phone book in operator's database, allowing user to recover their phone book even if their cell phone is stolen by someone (which is impossible with GSM cell phones, since your cell phone is stolen with yourSIM card also). Notice that nowadays a new accessory called as SIM backup has released, which allows user to backup the information which is stored in your SIM card. Also some GSM users are offering similar backup service.

So, nowadays both CDMA & GSM technologies are equip rated in technology, but this picture would not be like that in the future. Apteral, CDMA evolution is wider and in a few years it will become superior to GSM. This means, that GSM users will disappear? Not at all. GSM will be migrate over CDMA & the war will continue, because of the existing CDMA users interested to use 1xEV-DO and 1XEV-DV services for their 3rd generation network and the present GSM users have opted for the different technology, called as a WCDMA. Even though the present GSM users will migrate to WCDMA, they can use their existing GSM network. So operators won't feel anything new or unknown when the users shift to the new generation (3G),independently from the services they choose.

1.6 CDMA Receivers

A CDMA receiver that separates the signals by means of a correlator which uses the particular type of binary sequence to despread the signals and collects the energy of a desired signal. Other operators, signals whose spreading codes which do not match this sequence, are not despread in the bandwidth. As a result, contribute only to the noise. These signals will represent a self-interference which generated by the system. The output of a correlator is sent to narrow-bandwidth filter. This filter allows all of the desired signal's energy to pass through, but it reduces the interfering of signal's energy by the ratio of the bandwidth before correlator to the bandwidth after correlator. This reduction will improve the signal-to-interference ratio of a desired signal. This ratio is also known as processing gain. The signal to noise ratio is determined by the ratio of a desired signal power to the sum of all of the other signal powers. It is enhanced by a processing gain or the ratio of spread bandwidth to baseband data rate.

CDMA users are uniquely identified by a code sequence embedded as an address within the carrier waveform, which gives the receiver the capability of selective addressing. To recover a signal, the receiver correlates the sum of incoming signals against address sequences. This process maximizes the output for the signal matching the address sequence. However the receiver must have the knowledge of the address sequence.

To achieve isolation between CDMA users, it is necessary to select code sequences with properties by which a correlation process would build up the signal of the matching sequence while maintaining the low correlation values for non-matching sequences. Gold code sequences have a bound on the cross correlation values for any pair of sequences, taken over the full sequence period. Furthermore a single Gold code set can produce a large number of sequences that take on uniformly low-cross correlation values. Such properties make Gold codes attractive for CDMA applications. Gold code sequences have a period of 2m -1, where m is the length of shift register used to generate the Gold code. The cross-correlation value of two such sequences are no larger than 2{(m+2)/2} + 1. From a single old code generator, we can produce a total of 2m+1 new sequences. A particular code is chosen to modulate data for a particular channel and the modulated is extracted using the same code at the receiver.

Acquisition algorithms are used to acquire a particular channel, where in the code and frequency ambiguity about the multiplexed signal is resolved. Synchronization algorithms are used to maintain the receiver synchronization with the incoming signal.

1.7 CDMA Signals

In a CDMA system, each and every signal consists of a different pseudorandom of binary sequence (called as a spreading code) which modulates a carrier and spreading spectrum of the waveform. A huge number of CDMA signals will share the same frequency of spectrum. If CDMA is viewed in either of the frequency domain or time domain, the multiple access signals can overlap with each other. Anyway, the use of the statistically orthogonal is spreading codes which separate the various signals in the code space.

1.8 CDMA Signal Processing

In the demodulation of CDMA signals, the different paths can be independently received, that greatly reduces the severity of the multipath fading. However, multipath fading is not completely eliminated because occasionally there may be multiple paths that cannot be independently processed by the demodulator. Different operators in CDMA employ signals that have very small cross-correlation. Thus, correlators can extract individual signals from a mixture of signals even though they are transmitted simultaneously in the same frequency band. CDMA systems employ wideband signals with good cross-correlation properties, which mean the output of a filter matched to one user's signal is small when it receives a different user's signal as input.

In direct-sequence spread-spectrum systems, a high-rate antipodal pseudorandom spreading sequence modulates the transmitted signal so that the bandwidth of the resulting signal is roughly equal to the rate of the spreading sequence. The cross-correlation of the signals is then largely determined by the cross-correlation properties of the spreading signals. Although CDMA signals overlap in both time and frequency domains, they can be separated, based on their spreading waveforms. Spreading rates can be chosen to exceed the coherence bandwidth so that the channel becomes frequency selective. For instance, different spectral components are affected unequally by the channel, and only parts of the signal are affected by fades. Expressing the same observation in time domain terms, multipath components are resolvable at a resolution equal to the chip period and can be combined coherently, for example, by means of a rake receiver.

Coherent combination of multipath components requires an estimate of the channel impulse response. Such an estimate can be calculated from a training sequence or by means of a pilot signal.

1.9 Purpose and Outline of thesis

The origins of Spread spectrum are in military field and navigation systems. Techniques developed to provide efficient data communication proved for CDMA mobile technology.

To meet data communication requirements for commercial mobile standards like GSM, implementation of a multi-channel CDMA receiver offering a data rate of 9600 bps is illustrated.

The CDMA receiver consists of a Soft Correlator, Acquisition & Synchronization algorithms and Data Extractor. This paper presents a brief overview of CDMA receiver, mathematical model, and functional block diagram with implementation details and its results. The features of ADSP2189M processor, in relevance to the CDMA receiver implementation, like Serial ports, General-purpose flags, Timer, BDMA mode and multi-instruction in single cycle, are highlighted


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