Cellular-Planning and Optimization

CDMA Concept In CDMA timing plays an important role. All the base stations are synchronised with satellite time. The base stations will start their transmission with reference to the satellite clock. All the base stations will not transmit at the same instant. With reference to the satellite clock, each base station will offset it’s timing by a certain offset. All base stations will have different offsets. So even if transmission is occurring in a neighbouring cell using the same PN code, then though this come as an interference to the user in the existing cell but it will not effect the receiver in decoding the right information. This is because, information is decoded by correlating the PN codes, since the neighbour base station is offset in time, it will not correlate with the code used in this cell. CDMA Capacity The factors deciding capacity are Processing Gain Signal to Noise Ratio Voice Activity Factor Frequency Reuse Efficiency Capacity in CDM...

Spread Spectrum Technique All of the modulation and demodulation techniques strive to achieve greater power and/or bandwidth efficiency in a stationary additive white Gaussaian noise channel. Since bandwidth is a limited resource, one of the primary design objectives of all modulation schemes is to minimize the required transmission bandwidth. Spread spectrum techniques on the other hand employ a transmission bandwidth that is several orders of magnitude greater than the minimum required signal bandwidth. While this system is very bandwidth inefficient for a single user, the advantage of spread spectrum technique is that many users can simultaneously use the same bandwidth without significantly interfering with one another. In a multiple-user multiple access interference environment, spread spectrum systems becomes very bandwidth efficient. There are two types of spread spectrum techniques are used Direct Sequence Frequency Hopping. Direct Sequence is adopted by CDMA ...

Introduction To Cellular Communication To provide wireless communication access to subscribers we need a pair of RF channels per active call. In a large city with several thousand subscribers number of channels required would be so large that they cannot be accommodated on one site. Also there is a limit to availability of spectrum. If an operators get a 5 MHz band, then he has only 25 channels to use with 25 channels loaded at one site he can offer cellular service to 2000 subscribers at most. To overcome this limitation, you have to create zones of coverage, which are called as cells. Cellular Structure Cells in cellular system are hexagons. The actual cell covered by a base station takes a very different shape depending upon the terrain obstructions and transmitting antenna characteristics. The cells are of different sizes and shapes to cover a den sly populated area, smaller cells are used. Where a large cells cover a low subscriber density areas. On the highways ...