Adaptive Modulation The Key Technologies In Wireless Mimo-ofdm Systems

With the constant growth of all kinds of wireless business, the system capacityand data rate will be put forward higher demand. Therefore, Multiple Input MultipleOutput plus Orthogonal Frequency Division Multiplex (MIMO-OFDM) architectureis adopted frequently in future mobile communication system. OFDM technology canreduce the influence of multi-path fading. MIMO technology can improve the channelcapacity several times with multi-antenna.To achieve higher transmission rate and system capacity, Adaptive Modulationtechnology is applied to the MIMO-OFDM system in this thesis. Without the channelcoding, the MMSE Soft Interference Cancellation detector and MMSE SuccessiveInterference Cancellation detector can achieve better system capacity compared withother detecters. If LDPC channel coding is applied, the performance of adaptivemodulation can be improved more than 2.0 dB compared with fixed modulation,when the system capacity is 132Mbps.With the Doppler shifts estimation technology, the moving speed can beobtained to adjust the adaptive modulation cycle and reduce the feedback information.In this thesis, a Doppler shifts estimation algorithm based on channel covariancefunction is popularized to MIMO-OFDM system. In the simulation of B3G system, itcan effectively estimate the moving speed up to 250km/h within 200ms.Channel estimation technology is one of the pivotal technologys of the wirelesstransmission, and also the key to get the channel quality in the adaptive modulationsystem. Based on the introduction of the channel estimation which replace the 2-Dtime-frequency filter by concatenated two 1-D filters, this thesis presents theimplement scheme of the channel estimation of the B3G downlink on the C languageplatform, and also the simulation results of the whole link.