Design and Analysis of a Dynamic Space-Code Multiple Access with Large Area Synchronous Scheme Using the Smart Antenna System
Ng, Chee Kyun (2007) Design and Analysis of a Dynamic Space-Code Multiple Access with Large Area Synchronous Scheme Using the Smart Antenna System. PhD thesis, Universiti Putra Malaysia.
The most important property in wireless systems, when it comes to increase the system capacity and spectrum efficiency, is eliminating interference. Code Division Multiple Access (CDMA) is considered interference-limited system. Spatial filtering using smart antenna has emerged as a promising technique to improve the performance of cellular communication systems; hence, Space Division Multiple Access (SDMA) has recently received increasing interest in improving the performance of wireless systems. These interference-limited systems are susceptible to time of arrival (TOA) and angle of arrival (AOA) of individual user signals, thus, a non-uniform traffic can severely degrade the performance of CDMA and SDMA systems. In this thesis, new approach of the joint multiple access system arising from the combination of CDMA and SDMA systems is designed, and its system performances are then investigated. An innovative approach to eliminate the existing interferences in this joint multiple access system is proposed. The spreading sequences of Large Area Synchronous Even Ternary (LAS-ET) which exhibited an interference free window (IFW) in their correlation are exploited here. The spatial signature from smart antenna narrower beam is exploited to drive all the multipath propagation signals to arrive within the IFW in reverse link transmission. The size of IFW is adaptable with the size of smart antenna beamwidth through dynamic space code (DSC) algorithm. Hence, this double signatures scheme forms a novel multiple access scheme called Dynamic Space Code Multiple Access (DSCMA) system. From the nature of spatial filtering of smart antenna systems, a dynamic sequence reuse assignment is possible in DSCMA to increase its spectrum efficiency. The non-zero pulse intervals and sequence length of LAS-ET are arranged in even numbers which has demonstrated some performance improvements in ternary phase shift keying (TPSK) signalling. On the other hand, the combined spreading sequence and spatial signature scheme also prompts a possibility of developing a novel Space Division Duplexing (SDD) scheme. The reverse and forward links are transmitted within a narrower beam of smart antenna, and both links are distinguished by different LAS-ET sequences. The simulation results indicate that the reverse link system capacity in DSCMA using LAS-ET spreading sequences together with smart antenna system is increased dramatically compared to traditional binary spreading sequences. The results also showed that the spectrum efficiency of DSCMA is increased when the number of elements in smart antenna system is increased. Finally, it can be concluded that the system capacity and spectrum efficiency are increased significantly from DSCMA using smart antenna systems due to its perfect interference cancellation scheme.
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