In this paper, a delay diversity orthogonal frequency-division multiplexing (DD OFDM) transmission scheme in amplify-and-forward (AF) full-duplex relay systems is investigated. One direct source-to-destination link, one relay forwarding link, and residual self-interference are considered in the system. The necessary cyclic prefix length is investigated and a suitable AF relay protocol in the full-duplex relay OFDM system is proposed. This paper demonstrates that the AF relay link and the direct source-to-destination link can be combined to provide spatial diversity. The key is that the DD OFDM scheme is used to transform the spatial diversity into increased channel frequency diversity that is further exploited by using the bit-interleaved coding. The bit error rate performance of the proposed system is verified by simulation results.

In this paper, we study the precoder design problem for MIMO-OFDM systems with insufficient cyclic prefix (CP) using statistical channel state information (CSI) at the transmitter. In our previously proposed channel independent precoding scheme, an interference nulling based precoding structure is studied, which can assist to either cancel interblock interference (IBI) or separate the subspace occupied by IBI from the subspace used for information symbols. In this work, we consider a robust precoder design which combines statistical CSI at the transmitter and the interference nulling based precoding structure to gain a better performance compared to the channel independent precoding scheme. Statistical channel state information at the transmitter in the form of covariance matrix of the MIMO-OFDM channel matrix is utilized to perform the robust precoding. The design criterion for the precoder design is to minimize the maximum average mean squared error (MSE) of all the transmitted symbols during one OFDM block interval. To achieve this goal, the precoder design exhibits a similar procedure to the optimized design framework for MIMO transceivers for either perfect or statistical CSI with no interference effect, but with a distinct equivalent channel. Since the average MSEs are set equal using this precoder, the BER performance is better than our previously proposed channel independent precoder and the simulation validates this result.

In this paper, a new interference nulling based channel independent precoding for MIMO-OFDM systems of nttransmit and nrreceive antennas with insufficient cyclic prefix (CP) is proposed. By employing the notion of interference nulling, we show that our proposed channel independent precoding scheme can eliminate the inter-block interference (IBI) caused by the insufficient CP with higher bandwidth efficiency than the conventional zero-padded or a sufficient CP added block transmission system when nr≤ nt. It is also shown that when nr>; nt, the IBI can be eliminated without the need of any zero-padding or adding CP or precoding when the OFDM block length is not too small.

This paper proposes an interference alignment (IA) based precoder design for OFDM with insufficient cyclic prefix (CP) when only the statistics of channel coefficients is known at the transmitter. This precoding not only performs the inter-block interference (IBI) separation and elimination as in our previously proposed channel independent IA based precoding schemes, but also minimizes the MSE in a linear MMSE receiver and therefore improves the BER performance.

In this paper, a channel independent precoding for MIMO-OFDM systems of nttransmit and nrreceive antennas with insufficient cyclic prefix (CP) is proposed. By empolying the interference alignment (IA) idea, we show that our proposed channel independent precoding scheme can eliminate the interblock interference (IBI) caused by the insufficient CP with a higher bandwidth efficiency than the conventional zero-padding or adding a sufficient CP when nr≤ nt. It is also shown that when nr>; nt, the IBI can be eliminated without any zero-padding or adding CP or precoding when the OFDM block length is not small.