Review And History Of CDMA Computer Science Essay

Review And History Of CDMA Computer Science EssayCDMA technology was utilize some successions ago at the meter of world war-II by the English soldiers to stop German attempts at jamming transmissions. English soldiers decided to pass on shows over several frequencies, instead of one, making it difficult for the Germans to pick up the complete signal. CDMA has been utilise in many military applications, such as anti-jamming (because of the unfold signal, it is difficult to jam or interfere with a CDMA signal), ranging (measuring the blank space of the transmission to k without delay when it will be received), and secure communications (the spread spectrum signal is real hard to detect).In 1949, Claude Shannon and Robert Pierce develop basic ideas of CDMA. In March 1992, the TIA (Telecommunications Industry 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 Technolog y standard.In September 1998, there were 16 million subscribers on CDMA remainss 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 amount of frequence spectrum is allocated to a cellular system by the national regulator (e.g. in the United States, the Federal communication commission). Multiple-access techniques are then deployed so that many users mass share the available spectrum in an efficient manner. Multiple access systems specify how signals from different sources can be combined efficiently for transmission over a given up radio frequence band and then separated at the destination without mutual incumbrance. The three basic three-fold access methods currently in use in cellular systems areA. Frequency division multiple access (FDMA)B. Time division multip le 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 time basis. Channel bands behave as buffer zones to minimize interference between different users.B. Time division multiple access (TDMA)Each user has given the full spectral occupancy to the channel, but lone(prenominal) for less time interval. Buffers zones are used as guard times inserted between the assigned 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 conversation can access this channel until the subscriber s war cry is finished or until that original claim 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-random noise or PN code) is used to allow multiple users to share a block of frequency spectrum. Detailed Description 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 base shoes, that codes are called pseudo-Random Code Sequences.CDMA is a spread spectrum technology, which means that it spreads the information contained in a particular signal of interest over a much great bandwidth than the original signal. CDMA uses Direct Sequence Spread Spectrum (DSSS) technology. In DSSS technology, Signal is ancestral by adding random data-bits called chip. This rise to power is done by the direct sequence transmitters. Now signal contains both, a usefu l signal and a signal that appears to be interference (the chips) is transmitted. The receiver easy identifies the chips and subtracts them, leaving only the useful signal. This means that original signal is spread over several frequencies simultaneously. This can deliver 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 capacity limitation, no maximum piece 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. Total bandwidthB. Geographical coverageC. Quality of die? The available bandwidth can be increased by decreasing the quality of sound or the area covered by network.? Channels that primarily expect voice conversation do not use the extra capacity 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 same 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 limited coding scheme.C. cdmaOnecdmaOne is the first generation narrowband CDMA. It is similarly called IS-95.D. Cdma2000This includes 1XRTT CDMA standard. That is designed to double current voice capacity and support always-on data transmission speeds 10 times instant(prenominal) th an 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, turning down the power on the nearby ones, and increasing the power of those except away. The result is a nice even noise level across the carrier, with lower overall power levels and no spiky interference.D. Improves the telephone traffic capacity.E. It also provides Call privacy.F. Easily planned and maintained in comparison with FDMA TDMA7. Disadvantage of CDMAThe o nly disadvantage of installing CDMA system is the cost of the base station with its complicated communication equipments. A CDMA base station costs approximately $150,000, while a similar station for TDMA costs approximately $50,000.8. Referenced BooksA. Business selective information 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. www.indiastudychannel.com