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Narrowband interference (NBI) is one of the most important problems in an OFDM system, which not only degrades the signal performance on the overlapped subcarriers, but also affects the signal performance on the nearby subchannels due to the spectral leakage effect of DFT demodulation at the receiver. In this paper, we consider the NBI problem caused by narrow band digital communication systems, and propose a novel NBI cancellation method. We consider the NBI reconstruction problem including NBI central frequency and its bandwidth estimation. Simulation results show that this method can achieve about 6dB signal to interference plus noise ratio (SINR) gain if the interference bandwidth is about twice of that OFDM bins and the system SINR is about 0 dB. As the bandwidth of NBI decreases', more SINR gain will be obtained. Meanwhile, We also consider the system implementation problem, it has shown that its implementation complexity is not high based on the current digital signal processing techniques. If zoom FFT is employed in our system, the calculation complexity can be reduced considerably (1). Index Terms--narrowband interference cancellation, OFDM, WLAN

In this paper, we present a multiple symbol differential detection method for the differential encoding scheme of MPSK signals by using two transmit antennas. Compared to the conventional detection method proposed by Tarokh and Jafarkhani, the new detection method keeps the advantages such as providing full spatial diversity and no requirement on channel state side information at the receiver etc.. Moreover, it can provide a certain coding gain with relatively low complexity. The scheme can be considered as the extension of multiple-symbol differential detection schemes to two transmit antennas. Keywords--Antenna arrays, differential detection, space-time codes, transmit diversity

Multirate multimedia information with different quality of service may be required at the same time in future communication system. In this paper, we propose a new class of trellis coded modulation (TCM) schemes, which can carry two different rates multimedia information only using the same signal constellation. The transmitted information bit number per symbol in the proposed TCM is not an integer and greater than that of the conventional TCM. An interesting character of the proposed multirate TCM is that it can provide different error protection for the two rates information. We also present the design criterion and the existence of noncatastrophic multirate TCM. Some theoretical and simulation results have shown that it can provide a certain coding gain compared with the corresponding uncoded modulation schemes. Keywords--Trellis coded modulation,multirate TCM, multimedia communications, multirate information transmission

Modulated codes as an effective technique to mitigate the intersymbol interference (ISI) have been studied recently, which can transfer the multipath interference into implicit diversity and provide a certain coding gain compared with the ideal additive white Gaussian noise (AWGN) channel. Turbo codes have been proved as an extremely powerful error correction coding technique for AWGN, which can be used to approach the channel capacity. In this paper, we propose a joint turbo coding and modulated coding for the ISI channels with AWGN and investigate its performance by simulation. Simulation results show that the proposed joint coding method is an effective technique to mitigate the ISI and strong noise simultaneously. In addition, it can approach the limit of ISI channel information rate. Keywords -- Turbo code, modulated code, intersymbol interference

In this paper, we propose a block coded modulation (BCM) technique to reduce the peak to average power ratio (PAPR) in OFDM systems. In the proposed technique, binary blocks are mapped to M-ary blocks and M-ary blocks of small sizes with low PAPR are selected. Large size M-ary blocks with low PAPR are constructed by using the selected small size M-ary blocks. Similar to trellis coded modulation, with this technique variable rates ranging from 1 to a rate much higher than 1 of BCM can be obtained upon different requirements of the random error correction capability in the system, given that the PAPR is below a fixed value. PAPR gain is defined by comparing with the uncoded OFDM system. Optimal coding gain for the BCM given a PAPR gain is also obtained in various cases. Keywords: OFDM systems, peak-to-average power ratio, coded modulation