Saturday, March 30, 2019

Review And History Of CDMA Computer Science Essay

Review And History Of CDMA Computer Science bear witnessCDMA engineering was mapd umteen fourth dimensions ago at the clock of world war-II by the English soldiers to stop German attempts at mess contagious diseases. English soldiers decided to transmit requests all(prenominal)place several frequencies, instead of one, devising it difficult for the Germans to pick up the complete auspicate. CDMA has been delectationd in many military applications, such as anti-jamming (because of the spread signal, it is difficult to jam or interfere with a CDMA signal), ranging (measuring the distance of the transmission to k presently when it will be received), and estimable communications (the spread spectrum signal is very hard to detect).In 1949, Claude Shannon and Robert Pierce develop elemental ideas of CDMA. In March 1992, the TIA (Telecommunications diligence Association) established the TR-45.5 subcommittee to develop a spread spectrum digital cellular standard. In July of 1993, the TIA gave its approval for the CDMA Technology standard.In September 1998, there were 16 million subscribers on CDMA systems worldwide. Now, 22 countries support CDMA. Verizon, used to be the largest carrier, is now second behind ATT, is using CDMA. Other Famous companies using CDMA are Sprint, Alltel in abroad, Tata indicom and Reliance InfoComm in India.2. What is CDMA?Generally a fixed step of frequency spectrum is allocated to a cellular system by the national governor (e.g. in the United States, the Federal communication commission). quaternary- admission charge techniques are then deployed so that many drug users shadow share the available spectrum in an efficient manner. Multiple opening systems specify how signals from various sources can be combined efficiently for transmission over a give tuner frequency stripe and then separated at the destination without mutual enlistment. The three basic multiple access methods currently in use in cellular systems areA. frequency course of study multiple access (FDMA)B. Time division multiple access (TDMA)C. Code division multiple access (CDMA)A. Frequency division multiple access (FDMA)The available bandwidth is splits into non-overlapping frequencies and these disjoint sub bands are dedicated to the different users on a continuous meter basis. railway line bands behave as buffer zones to minimize term of enlistment in the midst of different users.B. Time division multiple access (TDMA)Each user has given the full spectral occupancy to the channel, but exclusively for less time interval. Buffers zones are used as guard measure inserted between the assign time slots. This is done to decrease interference between users by permitting for time uncertainty that arises due to system inadequacies.C. Code division multiple access (CDMA)The main Drawback of FDMA and TDMA is that only one subscriber at a time is assigned to a channel. No other talk can access this channel until the subscrib er s beseech is finished or until that headmaster call is handed off to a different channel by the system. The above drawback is overcome in this third technique. CDMA systems utilize the spread spectrum technique, whereby a spreading code (called a pseudo- stochastic noise or PN code) is used to rent multiple users to share a block of frequency spectrum. Detailed exposition of How CDMA work is explained below.3. How CDMA works?With CDMA, unique digital codes, rather than separate radio frequencies or channels, are used to distinguish subscribers. The codes are used by both the mobile company and the origination station, that codes are called pseudo-Random Code Sequences.CDMA is a spread spectrum applied science, which means that it spreads the information contained in a particular signal of interest over a much greater bandwidth than the maestro signal. CDMA uses take on Sequence Spread Spectrum (DSSS) technology. In DSSS technology, Signal is transmitted by adding random da ta-bits called chip. This addition is done by the direct sequence transmitters. Now signal contains both, a useful signal and a signal that appears to be interference (the chips) is transmitted. The receiver easily identifies the chips and subtracts them, leaving only the useful signal. This means that original signal is spread over several frequencies simultaneously. This can lay out secure communication such that the transmitted signal can not be detected or recognized easily by unwanted listeners. It can discard interference whether it is the unintentional interference by another user simultaneously trying to transmit through the channel, or the intentional interference trying to jam the transmission.In TDMA, the original call is transmitted at 9600 bps (9.6 kbps) but when put on the CDMA, the call is spread over a 1.23 Mbps bandwidth, so it can be transmitted at a higher speed. Unique codes are applied to the data bits that make up the telephone call for a particular user. The cellular telephone receiving the call takes off the data codes and the call is converted back to its original 9600 bps. The use of these data codes enables CDMA systems to differentiate data bits from many different calls in the cell.CDMA networks use a scheme called soft handoff, which minimizes signal breakup as a handset passes from one cell to another. The combination of digital and spread-spectrum modes supports several times as many signals per unit bandwidth as analog modes. CDMA is compatible with other cellular technologies, this allows for nationwide roaming.4. Factors affecting CDMA functionalityAlthough CDMA does not have some cleverness limitation, no maximum number of calls per single, wide band-width channel is established. The number of calls that a channel can accommodate is based on 3 factors.A. heart and soul bandwidthB. Geographical coverageC. Quality of sound? The available bandwidth can be increased by decreasing the quality of sound or the nation covered by network.? Channels that primarily carry vocalize conversation do not use the extra cognitive content required to deliver CD-quality sound. So, more bandwidth is available to provide longer transmission distance or to accommodate more cellular calls.? Suppose there are 2N users that only talk half of the time then they can be accommodated with the resembling average bandwidth as N users that talk all of the time.5. Types of CDMASome of the types of CDMA transmission are as underA. Composite CDMA/TDMAB. CDMAC. cdmaOneD. cdma2000A. Composite CDMA/TDMAIt is Wireless technology that uses both CDMA and TDMA. It is used for large-cell licensed band and small-cell unlicensed band applications. It uses CDMA between cells and TDMA within cells.B. CDMACDMA is characterized by high capacity and small cell radius, employing spread-spectrum technology and a special coding scheme.C. cdmaOnecdmaOne is the first generation narrowband CDMA. It is also called IS-95.D. Cdma2000This includes 1XRTT C DMA standard. That is designed to double current voice capacity and support always-on data transmission speeds 10 times faster than typically available today.6. Advantages of CDMAA. CapacityThe capacity of CDMA currently is 8 to 10 times greater than AMPS which uses FDMA transmission (and predicted to be 20 to 40 times greater in future) and 4 to 5 times greater than GSM which uses TDMA transmission (with prediction of being up to 13 times greater).B. Best for in built system and micro-cell.As in CDMA transmission, we do not need SIM card it is best for in-built system and micro-cell.C. Improves the voice quality.CDMA systems use precise power control that is, the base station sends commands to every mobile phone currently involved in a call, tour down the power on the nearby ones, and increasing the power of those upgrade away. The result is a nice even noise level crossways the carrier, with lower overall power levels and no spiky interference.D. Improves the telephone craft c apacity.E. It also provides Call privacy.F. Easily planned and maintained in comparing with FDMA TDMA7. Disadvantage of CDMAThe only disadvantage of installing CDMA system is the cost of the base station with its complex communication equipments. A CDMA base station be some $150,000, while a similar station for TDMA costs approximately $50,000.8. Referenced BooksA. Business Data Communication Fourth editionBy Shelly Cashman SerwatkaB. COMPUTER NETWORKS, 3rd EditionBy Andrew S. Tanenbaum9. Referenced websitesA. www.scsite.comB. www.wikipedia.comC. www.wisegeek.comD. www.palowireless.comE.

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