Inter-carrier Interference Cancellation In Multicarrier Systems Research

Next generation wireless communications system commits itself to provide mobile users with better-quality, high-speed wireless multi-media services, which results in a great concern at multi-carrier modulation (MCM) technology and multi-access technology. Orthogonal frequency division multiplexing (OFDM), which is a typical MCM technology, theoretically could completely eliminate the inter-symbol interference (ISI) by using cyclic prefix (CP). Multi-access technology can provide access services for multiple users at the same time, which can be easily combined with MCM technology.Currently, WiMAX, which supports broadband wireless access technology, attracts the extensive attention of the industry. WiMAX, based on the standard of wireless metropolitan area network (WMAN), have broad application prospects and can provide high-speed data, voice and video services both in fixed and mobile environments. Orthogonal frequency division multiple access (OFDMA) is a mainstream technology of IEEE 802.16e (WiMAX) standard, which support mobility. This paper mainly concerns OFDMA uplink system whose subcarriers are interleaved.Due to the increase in users'data rates and velocity, multipath effects and Doppler spread and so on, in the wireless transmission channel, will result in more serious ISI, inter-carrier interference (ICI), as well as multi-access interference (MAI), which is one of the main problems in the research.The main work and conclusions of this paper are as follows:Research OFDM system model and time-varying multi-path channel model; Analyzing the mechanism of the ICI from the frequency and time domain, respectively; Analyze the relationship between SIR and the Doppler frequency shift, and the relationship between the SINR and SNR, and the energy distribution of ICI in theory and simulation.This paper also study OFDMA systems which is based on the WiMAX technology and whose uplink subcarriers are interleaved; Synthetically analyze MAI and ICI, and change OFDMA system into OFDM model to be dealt with ICI and the MAI; Introduce several existing elimination methods of ICI: interference self cancellation algorithm, frequency domain tap-filter algorithm, frequency domain equalization algorithm, match filter algorithm, and compare the complexity of these methods and simulation.This paper, combining with iterative thought as Turbo Code and on the basis of classic MMSE algorithm, proposes a serial interference cancellation scheme based on random subcarrier allocation. This scheme can eliminate ICI and MAI well. This paper also compare several types of algorithm.When the number of subcarriers is big, the complexity of computing after changing the algorithm system will greatly reduce, with bit error rate performance guaranteedBecause of the introduction of the cyclic prefix, traditional CP-OFDM systems reduced channel information capacity, and rectangular pulses in the time domain leads to the waste of spectrum. Then this paper researches another multi-carrier system OFDM/OQAM, whose pulse shaping takes in account the time-frequency characteristics of the channel. This system also can resist the ISI and ICI well and overcome two inherent flaws of CP-OFDM system. Finally, this paper compares the performance of CP-OFDM system and OFDM/OQAM system in several channel environments by simulation. It can be foreseen that the combination of OFDM/OQAM system and OFDMA will have a broad application prospects.