A coefficient vector technique implemented on a differential distributed space time block coding (DDSTBC) scheme is presented in this paper to improve on the computation complexity of existing DDSTBC schemes. The full mapping scheme and differential technique for utilizing the co-efficient vectors in a two-relay cooperative network is presented and comparison is made between the proposed technique and the traditional unitary matrices based technique. Results obtained from the numerical and simulation analysis conducted, showed that the proposed method presents an improvement in terms of computation complexity and BER performance. The proposed scheme was extended to accommodate networks with four and eight relay nodes utilizing square-real orthogonal codes.

Present day requirements of high quality audio and video surveillance has instigated research interests in wireless multimedia sensor networks (WMSN). In order for the WMSN to achieve trademark performance in audio and video surveillance applications, certain design requirements must be met. In this work, we identify vital design issues affecting diversity gain in conditions especially, where channel fading characteristics fluctuate rapidly. We apply the cooperative communication technique in WMSN to create a framework that optimizes diversity gain in an environment where channel state information (CSI) is unknown. We then discuss promising research directions for optimizing diversity gain and noncoherent communication efficiency in cooperative WMSN.

An iterative pilot‐aided channel estimation technique for space–frequency block coded (SFBC) multiple‐input multiple‐output orthogonal frequency division multiplexing systems is proposed. Traditionally, when channel estimation techniques are utilised, the SFBC information signals are decoded one block at a time. In the proposed algorithm, multiple blocks of SFBC information signals are decoded simultaneously. The proposed channel estimation method can thus significantly reduce the amount of time required to decode information signals compared to similar channel estimation methods proposed in the literature. The proposed method is based on the maximum likelihood approach that offers linearity and simplicity of implementation. An expression for the pairwise error probability (PEP) is derived based on the estimated channel. The derived PEP is then used to determine the optimal power allocation for the pilot sequence. The performance of the proposed algorithm is demonstrated in high frequency selective channels, for different number of pilot symbols, using different modulation schemes. The algorithm is also tested under different levels of Doppler shift and for different number of transmit and receive antennas. The results show that the proposed scheme minimises the error margin between slow and high speed receivers compared to similar channel estimation methods in the literature.

So far, complex valued orthogonal codes have been used differentially in cooperative broadband networks. These codes however achieve less than unitary code rate when utilized in cooperative networks with more than two relays. Therefore, the main challenge is how to construct unitary rate codes for non-coherent cooperative broadband networks with more than two relays while exploiting the achievable spatial and frequency diversity. In this paper, we extend full rate quasi-orthogonal codes to differential cooperative broadband networks where channel information is unavailable. From this, we propose a generalized differential distributed quasi-orthogonal space-frequency coding (DQSFC) protocol for cooperative broadband networks. Our proposed scheme is able to achieve full rate, and full spatial and frequency diversity in cooperative networks with any number of relays. Through pairwise error probability analysis we show that the diversity gain of our scheme can be improved by appropriate code construction and sub-carrier allocation. Based on this, we derive sufficient conditions for the proposed code structure at the source node and relay nodes to achieve full spatial and frequency diversity.

In this paper, a source-assisting differential distributed space time block coding (SA-DDSTBC) scheme is proposed for cooperative networks. Firstly, in most existing works on distributed space time block coding (DSTBC), the destination node is assumed to have perfect channel state information (CSI), thus, signal recovery is straight forward. In practice however, some scenarios exist whereby the destination node is unable to acquire CSI. Consequently, this work incorporates differential concepts with DSTBC to facilitate signal recovery in cooperative networks operating in environments where CSI acquisition is impractical. Secondly, different from most works on DSTBC which assume that the source-destination link is unavailable, the proposed scheme employs a source-assisting (SA) strategy that exploits the additional diversity path provided by the source-destination link. The numerical and simulation results obtained illustrate that compared to the conventional DSTBC schemes, the proposed SA-DDSTBC scheme achieves non-coherent signal recovery and improved BER and diversity performance with negligible increase in decoding complexity.

We propose co-efficient vector based differential distributed quasi-orthogonal space time block codes (DQSTBC) for cooperative networks utilizing the decode-and-forward protocol. In our work, we employ rotated constellation quasiorthogonal codes which guarantee full code-rate and full diversity in cooperative networks with more than two relay nodes.

Combination of STBC with OFDM has gained considerable interest and has become a promising technique for future wireless communications. However, such systems require the knowledge of the Channel State Information (CSI) at the receiver. In this paper, a new channel estimation approach is proposed using dedicated pilot subcarriers defined at fixed intervals to estimate the channel parameters. Once channel parameters at the pilot subcarriers have been estimated using known pilot symbols at the receiver, the iterative channel estimation process is initiated, and data symbols positioned at adjacent data subcarriers are recovered. Subsequently, the recovered data symbols become the new set of pilots which are then used to re-estimate the channel parameters and recover the next adjacent STBC block. Another major novel contribution of the paper is the proposal of a new group decoding method that reduces the processing time significantly via the use of subcarrier grouping for transmitted data recovery. The OFDM symbols are divided into groups to which a set of pilot subcarriers are assigned and used to initiate the channel estimation process. Designated data symbols contained within each group of the OFDM symbols are decoded simultaneously in order to improve the decoding time duration.