Research On Inter-Cell Interference Mitigation In TD-OVCDMA System And The Analysis Of Coded Overlapped Time Division Multiplexing System

Professor Daoben Li proposed a new networking design structure based on four-color theorem, which used generalized complementary sequence to distinguish cells. Each cell still uses the same frequency range, but the complementary codes among adjacent cells are different, that is corresponding to the four-color principle, each code represents a color. Each cell has the same spectrum efficiency under this condition, and the frequency reuse factor is 1. Moreover, this networking design can completely eliminate the Adjacent Cell Interference (ACI). However, the interference signal still appear away from one cell size and the propogation isolation degree to the nearest interference cell is only17.41dB, which differs by 8.1dB from ITU-LTE required minimum 25.51dB.As a result, it is necessary to take some measures to mitigate the Inter-Cell Interference (ICI). The first half of this thesis mainly researches the effect of iterative interference cancellation technology adopted in Interleaved Division Multiple Access (IDMA) to reduce ICI. As the application of overlapped multiplexing principle in time domain, the second half of this thesis analyses the performance of coded Overlapped Time Division Multiplexing (OVTDM) system.Chapter one outlines the present situation of the mobile communication and ICI mitigation technology in LTE.Chapter two studies the performance of Product Code on mitigating ICI. And describe in detail a new intra-frequency networking solution applied in TD-LTE-A system, which is based on four-color theorem. Describe TD-OVCDMA link level simulation platform from the perspective of transmitter structure and Rake receiver solution. Then from the analysis of simulation results, S interleaver can improve the performance of TD-OVCDMA system to a certain degree; but when distinguishing cell signals with different interleaver patterns and treat the interference signal as noise, the interleaver has little improvement in mitigating ICI.Chapter there introduces iterative interference cancellation technology which is applied in IDMA. And by imitating the ways of IDMA, we distinguish the service signal from interference signal with different interleaver patterns in TD-OVCDMA system. At the same time, evaluate the schemes of Joint Detection (JD), Minimum Mean Square Error (MMSE) detection technology and treating ICI as noise, compared with IDMA under intra-frequency network structure. For the weak interference-17.41dB, JD technology gains a little and treating the interference signal as noise scheme is a little bit better than IDMA algorithm; IDMA algorithm is more efficient for the strong interference signal than the weak one. Moreover, under the condition of short frame, IDMA algorithm has no significant iteration gain after three iterations.Chapter four mainly focuses on evaluating the performance of two coding schemes of Overlapped Time Division Multiplexing (OVTDM) system. One is using Turbo Product Code (TPC) as Forward Error Correcting (FEC) code, the other uses conventional Turbo code provided by Long Term Evolution (LTE) as a standard of comparison. Through analyzing uncoded OVTDM signal structure and its Bit Error Rate (BER) in low-to-moderate Signal to Noise Ratio (SNR), utilizing an FEC with fast iterative convergence behavior is a good choice. TPC satisfies the property of fast iterative convergence and is easy to be realized in hardware implementation, while turbo code is a relatively mature channel coding scheme in LTE. Simulation results show that TPC plus OVTDM (TPC-OVTDM) scheme outperforms LTE Turbo plus OVTDM (LTE-Turbo-OVTDM), TPC plus Quadrature Amplitude Modulation (TPC-QAM) and LTE Turbo plus QAM (LTE-Turbo-QAM) under the condition of short interleaver depth and same spectral efficiency. Moreover, with the increase of spectral efficiency, the TPC-OVTDM scheme can achieve greater coding gain. Furthermore, through comparing the performance of TPC-QAM with LTE-Turbo-QAM, the error correcting capability of TPC is better than that of LTE Turbo code. In addition, the TPC-OVTDM scheme makes system's cardinality of signal constellation increase polynomially with spectral efficiency, rather than that of QAM signal which grows exponentially.