Literature Review Online Billing System

CDMA BY OKAFOR CHIDUBEM KELVIN 10690152 A SEMINAR REPORT SUBMITTED TO THE part OF COMPUTER SCIENCE MOSHOOD ABIOLA POLYTECHNIC,ABEOKUTA IN PARTIAL FULFILMENT OF THE AWARD OF issue DIPLOMA IN COMPUTER SCIENCE NOVEMBER, 2012 CHAPTER 1 1. 0 mental institution Mobile conversations atomic number 18 rapidly becoming more than than and more necessary for everyday activities. With so many anformer(a)(prenominal) more exploiters to accommodate, more effectual use of call upwidth is a priority among electric mobile ph unmatchableular phone brass operators. chargely important is the security and reliability of these calls.One solution that has been offered is a CODE family MULTIPLE glide path SYSTEM. CDMA is one manner for implementing a multiple price of admission communication system. MULTIPLE advance is a technique where many chockscribers or local directs can sh are the use of the use of a communication broadcast at the uni defecate clip or approximately so despite the fact originate from widely unalike locations. A transpose can be thought of as merely a portion of the limited radio resource, which is temporarily portiond for a specific purpose, oft(prenominal) as someones phone call.A multiple rag method is a definition of how the radio spectrum is divided into channels and how the channels are allocated to the many drug users of the system. Since at that place are multiple users transmitting everyplace the akin channel, a method must be established so that several(prenominal) users entrust not disrupt one an new(prenominal)(a). There are basically three bureaus to do this. write in mark Division nonuple attack is a virgin technology employ in radio communication crafts. This technology made its commercial de and in the early nineties.Significant returns of the CDMA is the fact that unlike other modulation schemes it does not have to allocate part of the frequence for all(prenominal) user. It allocates whole rela tive oftenness spectrum to to severally one user, screwing severally subscribe with the unique pseudo-random grade. CDMA stands for Code Division treble memory admission. It is a form of spread-spectrum, an advanced digital wireless infection technique. Instead of employ frequencies or cartridge clip slots, as do traditional technologies, it uses mathematical computes to transmit and distinguish between multiple wireless conversations.Its lotwidth is more than wider than that required for simple point-to-point communications at the analogous data rate because it uses noise-like carrier waves to spread the entropy contained in a orient of interest all over a much greater bandwidth. However, because the conversations taking place are distinguished by digital codes, many users can share the homogeneous bandwidth simultaneously. We are moving into a parvenue era of communications and information technology. Personal Competitiveness in business in relies more and m ore on increase privateised productivity and responsiveness.Today everybody is on the move and vigorous is the sole(prenominal) way to find contact with that person. 1 But now a days peoples indispensability multimedia facilities from their quick handset. But it requires high data rate, hi capacity and many more technical things, which are available in threesome propagation. (CDMA) so the CDMA TECHNOLOGY makes existing mobile handset more high-octane and attractive. CDMA (3G) mobile devices and serve will transform wireless communications into on-line, real time imputeivity. 3G wireless technology will allow an individual to have neighboring(a) access to location-specific ervices that offer information on demand. The initiative generation of mobile phones consisted of the elongate models that supplyd in the early 1980s. The befriend generation of digital mobile phones appeared about ten years later along with the first digital mobile ne devilrks. During the second generation, the mobile telecommunications industry experienced exponential increase both in terms of subscribers as well as cutting types of value-added services. Mobile phones are rapidly becoming the preferred means of personal communication, creating the worlds largest consumer electronics industry.The rapid and efficient deployment of new wireless data and Internet services has emerged as a critical priority for communications equipment manufacturers. Network components that enable wireless data services are fundamental to the next-generation network infrastructure. tuner data services are expected to see the same detonative growth in demand that Internet service and wireless juncture services have seen in recent years. 1. What is CDMA? Code Division Multiple Access (CDMA) is a digital cellular spread-spectrum modulation technique that implements distri just nowed contribution and data networks.CDMA works by converting delivery into digital information, which is therefor e convey as a radio signal over a wireless network. CDMA does not assign a specific frequency to from for each one one user, but the full available spectrum. separately signal is encoded several(predicate)ly utilize a unique code. This way CDMA enables a large number of users to share the same frequency band at the same time, without interference. The receiving device is instructed to use the code to extract the data out of the received signal. 2 CHAPTER 2 2. 0 LITERATURE REVIEW 2. 1 HistoryThe first generation of cellular systems, which complicate the AMPS (Advanced Mobile Phone schemes), was introduced in the early 1980s. These systems used analog frequency modulation (FM) and have a frequency division multiple access (FDMA) basald media access control (MAC) architecture. Within a fewer years, market place demands and capacity requirements began to grow hitting the practical limitations. These limitations motivated the development of the second generation cellular syste ms, which improved compatibility and accommodated higher capacity than the first generation systems.These systems use digital modulation and processing techniques. TDMA (Time Division Multiple Access), GSM (Global System for Mobile communion) and (narrowband) CDMA belong to the second generation systems. CDMA was introduced in 1994, by Qualcomm, Inc. utilise direct sequence code division multiple access, it claimed to provide 10 times more capacity than analog systems ? far more than TDMA or GSM. Today, CDMA is the basis to the third generation market in the United States and other places in the world. 2. 2 Background A cellular system is called so because it divides the service area into small transmission system areas called cells.Each cell contains a base station (BTS), which consists of a transceiver and a receiver in order to connect to mobile phones in the cell. Each cell is appoint a root of radio channels (frequencies). 3 2. 3 The Cellular Challenge The worlds first cel lular networks were introduced in the early 1980s, using analog radio transmission technologies such as AMPS (Advanced Mobile Phone System). Within a few years, cellular systems began to hit a capacity ceiling as millions of new subscribers signed up for service, demanding more and more shinetime. Dropped calls and network busy signals became harsh in many areas.To accommodate more work within a limited sum of radio spectrum, the industry developed a new set of digital wireless technologies called TDMA (Time Division Multiple Access) and GSM (Global System for Mobile). TDMA and GSM used a time-sharing protocol to provide three to four times more capacity than analog systems. But just as TDMA was being standardized, an even better solution was found in CDMA. 2. 4 Commercial reading The founders of QUALCOMM realized that CDMA technology could be used in commercial cellular communications to make even better use of the radio spectrum than other technologies.They developed the key advances that made CDMA suitable for cellular, then demonstrated a working prototype and began to license the technology to telecom equipment manufacturers. The first CDMA networks were commercially launched in 1995, and provided roughly 10 times more capacity than analog networks far more than TDMA or GSM. Since then, CDMA has become the fastest-growing of all wireless technologies, with over 100 million subscribers worldwide. In addition to supporting more traffic, CDMA brings many other benefits to carriers and consumers, including better join quality, broader coverage and stronger security. CHAPTER 3 3. 0 news 3. 1 Multiple Access Systems A Multiple access system is the technology that specifies the way multiple users can share the same transmission medium. There are three main types of multiple access system, each of which has its own way of sharing the bandwidth ? Frequency Division Multiple Access (FDMA) ? Time Division Multiple Access (TDMA) ? Code Division Multiple Acces s (CDMA) FDMA and TDMA are narrowband technologies, and CDMA is wideband. FDMA and TDMA In the FDMA technology, signals from various users are assigned different frequencies.When a frequency channel is assigned to a user, no other user of the same cell or in the neighboring cell can use it at the same time. In the TDMA technology, the information from each user is conveyed in time intervals called time slots. A few users using a different time slot might share the same frequency. When all the available time slots in a given frequency are used, a new user connecting to the system must be assigned a time slot on a different frequency. In a way, TDMA is very similar to a computer with only one processor that seems to run multiple processes simultaneously.Only one person is really using the frequency channel at any given moment, and then has to give up the channel to allow other users to use it. Code division multiple access (CDMA) systems are spread spectrum systems in which the user s are able to transmit simultaneously in the same frequency channel and use the entire systems spectrum. 5 2. FREQUENCY DIVISION MULTIPLE ACCESS In this technique, the available bandwidth is split up into non-overlapping frequency bands and these disjoint sub bands of frequency are allocated to the different users on a continuous time basis.In order to reduce interference between users allocated adjacent channel bands, channel bands are used to act as buffer zones, as illustrated in figure(1). These guard bands are necessary because of the impossibility of achieving ideal filtering for separating the different users. It could be compared to AM or FM broadcasting radio where each station has a frequency assigned. 3. 3 TIME DIVISION MULTIPLE ACCESS In this technique, each user is allocated the full spectral occupancy of The channel, but only for a short duration of time called time slot.Buffers zones are in the form of guard times are inserted between the assigned time slots. This is done to reduce interference between users by allowing for time uncertainty that arises due(p) to system imperfections, especially in synchronization scheme. 3. 4 CODE DIVISION MULTIPLE ACCESS The above drawbacks are thrash in this third technique in which the users are spread chasewise both frequency and time in the same Channel. This is a loanblend combination of FDMA and TDMA. For example, frequency hopping may be employed to ensure during each successive time slot, the frequency bands assigned to the users are recorded in random manner.During time slot 1, user 1 occupies frequency band 1, user 2 occupies frequency band 2, user 3 occupies band 3 and so on. During time slot 2, user 1 hops to frequency band 3, user 2 hops to band 1, user 3 hops to band 2, and so on. An important advantage of CDMA over FDMA and TDMA is that it can provide for secure communication. 6 3. 5 Generating the CDMA signal In the CDMA technique the signal transmissions among the multiple users completely overlap in both time and frequency. The dissolution between the users is made by assigning each user a unique code.Generally, CDMA converts analog voice signal to a digital signal, encodes the digital signals, and sepa rank voice and control data into data streams called channels. Generating a CDMA signal is a five stairs process The first stones throw is analog to digital conversion or A/D. The incoming voice signal is an analog signal meaning that it is changing constantly, taking on all possible values of amplitude range. The CDMA uses a digital signal for its further manipulations. That digital signal is characterized by discrete states. In that bill the analog voice signal is quantized to form a digital signal consists of a few levels.The second tone is voice cryptograph or Vocoding. Voice encoding is the process of compressing the audio into as small a stream of bits as possible. The vocoder takes advantage of the pauses in speech to accomplish maximum compression. The Vocoders rate must be versatile to fit the rate of the users speech activity. The third rate is encoding and interleaving. This step purpose is to reduce the errors when receiving the signal. Interleaving is a method of minify the effects of burst errors and recovering lost bits. The symbols are interleaved such that authenticly neighboring symbols will be transmitted far away from each other.In addition to that, the various encoding methods add redundancy to the signals to help the recovery of information at the receiver in case of errors. The forth step is channelizing. The signal of each user if further encoded to create a separation between different users. A unique identification code is given to each user and the signals of all users are transmitted together, sharing the same frequency and time. The CDMA receiver decodes the signal by multiplying it by a decipher sequence of the desired user. 7 Two common codes types are Walsh code and PN (pseudo random noise) code The Walsh code is used for forward CDMA channel (e. . cell to mobile direction of communication). Walsh codes are orthogonal, meaning that the code of each user can be decoded at the receiver only by using the same Walsh code used to transmit the signal. The PN code is used for get up CDMA channel (e. g. mobile to cell direction of communication). A series of digital signals 0? s and 1? s goes into an antipodal mapping device to produce bit stream of negative and positive 1? s. Each user signal is then multiplied by the PN code series. At this moment the signals occupy a wide frequencies spectrum. The PN sequence rate is much higher than that of the original signal. It is enerated in a deterministic manner, and is repetitive. However there are about 4. 4 trillion combinations of this code, and for practical purposes we may claim that this sequence is truly random. The data signal and the PN sequence can be described mathematically as follows The data signal b(t) is expressed as pic Wh ere picis an independent identically distributed random variable representing the i-th data bit. picis a building block rectangular pulse given by pic= 1 for 0 ? t ? T and zero otherwise. T is the data bit duration. The data signal b(t) is spread using the PN sequence a(t). This PN sequence is expressed as pic Where picis the j-th micro chip of the periodic PN sequence. picis a unit rectangular pulse duration TC. The sequence a(t) is a binary sequence like b(t), but at a much higher rate as mentioned before. 8 The fifth step is digital to radio frequency (RF) conversion. The stream of bits should be somehow delivered from one end to the other. The RF is a method of carrying the information through the air Digital data signals are combined into one signal and reborn to a RF signal for that transmission process. Returning to mathematical archetype The spread data is modulated by the carrier at frequency wc radians/s, phase q and power P.The transmitted signal s(t) is then express ed as pic 9 3. 6ADVANTAGES ? INCRESED VOICE CAPACITY Voice is the major source of traffic and revenue for wireless operators, but packet data will emerge in coming years as an important source of additive revenue. CDMA2000 delivers the highest voice capacity and packet data throughput using the least amount of spectrum for the lowest cost. ? HIGHER DATA THROUGHPUT Todays commercial CDMA2000 1X networks (phase 1) support a bank bill data rate of 153. 6 kbps. CDMA2000 1xEV-DO, commercial in Korea, enables peak rates of up to 2. 4 Mbps and CDMA2000 1xEV-DV will be capable of delivering data of 3. 9 Mbps. ? INCREASED BATTERY LIFE CDMA2000 significantly enhances battery exploit. Benefits include contiguous paging channel operation ? Improved reverse touch base performance ? New common channel structure and operation ? Reverse link gated transmission ? TRANSMIT DIVERSITY Transmit diversity consists of de-multiplexing and modulating data into two orthogonal signals, each of them tran smitted from a different antenna at the same frequency. The two orthogonal signals are generated using either extraneous Transmit Diversity (OTD) or Space-Time Spreading (STS).The receiver reconstructs the original signal using the diversity signals, thus taking advantage of the supernumerary space and/or frequency diversity. DISADVANTAGES 1. Multi-user interference or multiple access interference(MAI) 2. Multi-path fading 3. near- for problem 10 CHAPTER 4 CONCLUSION CDMA is radically a new concept in wireless communication. It has gained widespread international adoption by cellular radio system operators as an upgrade that will dramatically increase both their systems capacity and the service quality.Moreover it spread spectrum technology is both more secure , less probable to intercept and jam, highly private and offer higher transmission quality than TDMA because of its increase safeguard to multipath distortion . The principle type of CDMA systems are direct sequence CDMA, frequency hopping CDMA and multicarrier CDMA. The major problem in CDMA is the multiple Access interference (MAI) which arises due the deviation of the spreading codes from perfect orthogonally.Capacity of CDMA is interference limited . the obvious way to increase capacity of the CDMA is to reduce the level of interference. This is achieved by reducing cross correlation, power control and with antenna arrays. 11 REFERENCE Reference Books- Simon Haykins Communication Systems-John Willy & Sons , Fourth edition CDMA TECHNIQUES FOR THIRD GENERATION MOBILE SYSTEM by Francis Swarts ,PETER Van Rooyan , Ian Opperman & Michael P. Loyyer Reference Websites- http//www. telecomresearch. com 12