Researches On Link Adaptation In Multiuser OFDM System

The resource of spectrum is the most invaluable resource in the wireless communication. As the increasing of the demand for wireless data service, the research that how to furthest improve data transmit rate in the limit bandwidth, i.e. that how to furthest improve the using efficient of spectrum become the research hotspot of mobile communication. While Link Adaptation has better superiority in improving data transmit rate and the using efficient of spectrum, so LA(Link Adaptation) became one of the key techniques in the present and future mobile communication system. Based on the key technology research in B3G-TDD systems, Link Adaptation in multi-user OFDM systems are researched in this dissertation.OFDM is one of the key techniques to effectively combat frequency selective fading. The principle of OFDM scheme is simply introduced in this dissertation. Because of the characteristic of multi-carrier of OFDM, OFDM can combat multi-path interfere and transmit high data rate, communicate at the same time for different users as well, i.e. has the ability of multi-user/multi-access. The disser~+ation analyzes several common multi-access techniques of OFDM, including OFDMA, OFDM-TDMA and OFDM-CDMA.In the system of adaptive OFDM, Adaptive modulation is to choose different modulation mode in each sub-carrier, which realizes link adaptation in both frequency domain and time domain. Impacts of the factors including frequency group, time interval are analyzed.Based on research of adaptive modulation in OFDM system, this dissertation focus on the link adaptation in multi-user system. First, optimization aim of multi-user resource allocation and optimization algorithm of mathematic expression are introduced, but this optimization algorithm is too complex, so the sub-optimization algorithms that are close to the...