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This paper devises a novel group frequency-hopping (FH) scheme for OFDM modulated multiuser system, in order to optimize the resource reuse efficiency and resolve the performance degradation due to the deep fading in the same time. In the OFDM modulated multiuser system, the traditional FH schemes can work in a multipath fading environment and achieve a moderate bit-error-rate (BER). However, when the deep fading subcarriers exist, the traditional schemes present poor performance, because the deep fading subcarriers become dominant factor in determining the overall BER performance. To solve this problem, this paper proposes a novel group FH scheme. The scheme reorganizes the frequency domain sequences of the deep fading subcarriers and then forms them into a short-OFDM frame, which is allocated dynamically and adaptively to the subcarreirs of idle users to transmit. Computer simulation results show the superiority of the proposed scheme over the traditional schemes in the BER performance.

In this paper, we consider the problem of blind channel estimation for single-input, single-output (SISO) system. Our main aim is to provide a new consideration in the subspace-based blind channel estimation. Instead of utilizing the noise subspace, as usually the case, we propose a new algorithm that makes use of the signal subspace signature. The new algorithm is shown to give a comparable performance with that of the noise subspace-based methods. A similar idea can be applied straightforwardly to single-input multiple-output (SIMO) and multiple-input multiple-output (MIMO) systems.