Studies On Several Key Technologies In MIMO-OFDM Of The Next Generation Mobile Communicaition Systems

The next generation mobile communication systems also called B3G (Beyond 3G/4G)can support services with data rates up to 100 Mbps and even higher. To obtain such high daterates and high capacity transmissions we need to improve the spectrum efficiency evidently.The multiple transmitting and receiving antenna system (MIMO) exploits the space resourceto improve the channel capacity effectively without additional frequency spectrum andtransmission power. Orthogonal Frequency Division Multiplexing (OFDM) is amultiple-carriers technique, of which the orthogonal carriers can be used to exploit thefrequency spectrum efficiently.The actual reasons of using MIMO system is to obtain the multiplexing gain and/ordiversity gain. The multiplexing gain can improve the system capacity and meanwhile thediversity gain can strengthen the system reliability. A typical MIMO multiplexing technique isBell laboratories layered space-time (BLAST) architecture. Encoding of BLAST is very easyand the corresponding research mainly focuses on the detection algorithms. There are twokinds of diversity techniques, i.e. transmitting diversity and receiving diversity respectievly.Generally speaking, using the transmitting diversity technique we don't need to know thechannel state information (CSI) at the transmitting antennas, but with the CSI we can obtainmuch better system performance. Using the OFDM technique we can resolve easily theproblem of frequency-selective fading in MIMO system. On the other hand, MIMO-OFDMtechnique can improve the capacity greatly by allocate the power appropriately amongdifferent carriers and transmitting antennas.This dissertation aims to tackle several tough issues of MIMO-OFDM technique such asBLAST detection algorithm, closed loop diversity technique and power allocation. The thesiswork can be summarized as follows.Propose an efficient ML detection algorithm. According to simulation results thisalgorithm has better bit error rate (BER) performance with significant reduction in thecomputational complexity.Propose a new iterative V-BLAST detection algorithm with low computational complexity. Simulation results demonstrate that the performance of the new algorithm is notfully satisfactory but with advantage of simplicityPropose an efficient iterative V-BLAST detection algorithm, Simulation resultsdemonstrate that the proposed algorithm has the same performance with the traditionaliterative V-BLAST detection algorithm and its computational complexity is reduced greatly.Propose an efficient transmit diversity with partial closed-loop scheme. Simulationresults show that in case of a high signal noise ratio (SNR), with only 10% occupation of thefeedback channel, the proposed new scheme has the same performance of the traditional ones.A novel algorithm for power allocating in OFDM-STBC system is proposed. Theproposed algorithm has optimized performance of overall BER which has been certifiedthough mathematic method. To reduce the computational complexity a new simplifiedalgorithm is also proposed, of which the performance is analyzed.