Design and simulation of a variable-width trellis MAP ICI equalizer
In the high mobility scenario, the wireless communication systems that adopts Orthogonal frequency-division multiplexing (OFDM) transmission scheme will experience rapid channel variations such as high-speed railway. It is considered that will induce inter-carrier interference (ICI) and BER performance degradation due to the orthogonality between subcarriers is destroyed in OFDM transmission systems. In order to eliminate the distortions, the research topics in the field of channel compensations are attractive for many years. The channel equalization techniques can be classified into time-domain and frequency-domain methods. The goal of this thesis is design a low complexity ICI cancellation scheme in frequency-domain, which is easier to be implemented in practical. The most common technique to deal with the distortion causing by the ICI is focus on the channel frequency response (CFR) matrix. It is known that the MAP receiver based on BCJR algorithm offers optimal BER performance but the computational complexity is too high to implement in practical systems. From empirical observations, a measure which is called ICI indicator was introduced to indicate the ICI level on each subcarrier , which offers more precise ICI measurements than conventional methods. Armed with the ICI indicator, the modified BCJR algorithm can achieve better balance between computational complexity and BER performance. However the previous works haven’t mentioned the explorations on hardware. The goal of this thesis will modify BCJR algorithm with the help of the ICI indicator to make it more appropriate to implement on hardware. We can show some advantages on hardware through the contributions of this thesis. Discussions and simulation results both on software and hardware will also be provided in the thesis. This thesis is organized as follows. Chapter1will introduce background and motivations. Chapter2 gives an introduction of OFDM-based system model over doubly selective fading channels. Besides, a measurement which is called ICI indicator is also provided in chapter2. Chapter 3 will give an introduction of BCJR algorithm and discussion of simplified versions. MAP ICI equalizer based on simplified BCJR and incorporate with ICI indicator is also provided. Chapter 4 gives hardware design units of variable-width trellis MAP ICI equalizer. Chapter5 will give simulation results and discussions both on software and hardware. Finally, the conclusion of this thesis will be provided in Chapter6.