Distributed Power Control And Performance Analysis For Mobile Cellular Communication Systems

For cellular mobile communication systems, power control is one of the mostessential elements. For FDMA/TDMA systems, it is used to reduce co-channelinterference, allowing a more "dense" reuse of frequency resources and thus highercapacity. For CDMA systems, in order to effectively solve the near/far effect and thecorner problems, power control is especially important. In the absence of powercontrol, the capacity of CDMA systems is very low, even lower than that of mobilesystems based on FDMA technology. One of the reasons for the use of power controlboth in FDMA/TDMA and in CDMA systems is to prolong battery life of themobiles by using a minimum transmission power. In this thesis, distributed powercontrol of the cellular mobile systems and the system performance adopting powercontrol are analyzed in details.Some problems such as time-delay and signal measurement difficult exist when distributed power control schemes are applied to the practical cellular mobile communication systems. Thereby improving the iteration speed of distributed power control schemes is the focus the researchers concerned. Firstly, a novel SIR-based distributed power control scheme fitted for FDMA or TDMA systems is developed in this thesis. Analysis results show that the iteration speed can be improved significantly with the proposed scheme either for 1-D or for 2-D cellular systems.It is foreseen that the 3G and 4G mobile communication systems will provide wideband services such as high-speed data, video and high quality images, and most of these services will be provided through downlink transmission, which makes the downlink power control as important as the uplink power control. In this thesis, for the downlink of OVSF-CDMA and MC-CDMA cellular systems, a rate assignment algorithm, i.e. GRS (Greedy Rate Scheduling) scheme, is proposed. It is proved that the GRS can maximize system throughput while simultaneously minimizing the transmission powers. Based on the GRS, a distributed combined power and rate control algorithm is proposed. Analysis and simulation results show that in the practical cellular systems, the steady transmission power is little affected by the orthogonalized factor under light and heavyload. However, under the middle traffic load, the steady transmission power increases notably with the increase of the orthogonalized factor. Analysis and simulation results show that each user can transmit data with its highest data rate under light load, but under middle and heavy traffic load, the average data rate will decrease rapidly with the increase of the orthogonalized factor.For CDMA systems, in order to achieve higher capacity, combined power and rate control has been extensively investigated. In general, it is difficult to consider simultaneously the specific characteristics of voice and data users as can be seen from the published literatures. In this thesis, four priority-based combined power and rate control algorithms are proposed for the uplink of cellular system with integrated voice and data traffic. The four algorithms are: PBCPRC (Priority-Based Combined Power And Rate Control) , PBSPC (Priority-Based Selective Power Control) , SIRPBCPRC (SIR and Priority-Based Combined Power And Rate Control) and improved SIRPBCPRC. Their common characteristic is that, when allocating system resources, all voice users are assigned higher priority based on the real-time characteristics of voice service. Simulation results demonstrate that, compared with the corresponding schemes without priority, the four proposed priority based schemes make the outages of voice users much lower (even near to zero) at the cost of transmission data rates. At the same time, our comprehensive assessment shows that, considering different performance measures, the improved SIRPBCPRC algorithm is the best under heavy load.Power control has a crucial impact on the capacity of CDMA systems. In this thesis, the capacity of a wideband multirate OVSF-CDMA system adopting MRC RAKE receiver in the presence of fading and power-control error is analyzed. The corrected numerical results are given, with respect to the nontrivial errors found in a paper published by an international journal abroad. More important, theoretical provenance is given to explain the phenomenon that the optimal received-power-ratio is a fixed value in the corrected numerical results.In this thesis, for the uplink of a single cell multirate CDMA system, the performance of a linear SIC (Successive Interference Cancellation) receiver is analyzed. The capacity limits of a conventional single-user detection receiver, a system with linear SIC receiver, and a system with perfect SIC receiver are derivedin closed form for an Additive White Gaussian Noise (AWGN) channel.