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.

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.

This paper introduces a computationally efficient pilot aided channel estimation method for space-frequency block coding (SFBC) Orthogonal Frequency Division Multiplexing (OFDM) systems under frequency selective channels. The proposed method, simulated under WiMax requirements, is based on the use of eight pilots defined in the standard to estimate the channel parameters at constant interval. The pilots are also coded in the same SFBC format to simplify the estimation computations, but can be modulated by different modulation scheme to reduce the estimation error. The method offers tradeoff between accurate channel estimation and efficient bandwidth usage as more pilots would allow the algorithm to perform a more accurate estimation but at the cost of less transmitted data. Performances are evaluated for high mobility applications and with pilots modulated using different modulation schemes. Simulation results are presented for different number of antenna at the receiver, different values of Doppler shifts and different modulations for pilot and data subcarriers.

This paper describes a channel estimation scheme for Multiple Input Multiple Output (MIMO)-Orthogonal Frequency Division Multiplexing (OFDM) systems based on training sequence. We first develop an approach to channel estimation which is crucial for the decoding of the transmitted data. We then discuss the implementation of the proposed method for WiMax systems under various channel conditions. The efficiency of the new algorithm is demonstrated through the simulation of the MIMO-OFDM system for two and four transmit antennas and different number of receive antennas. The Space-Time Coding with 192 information subcarriers per codeword is used as defined in the WiMax standard. Through simulations, it is shown that the proposed method has between 1.5 dB and 2dB loss compared to the ideal case where the channel coefficients are known at the receiver. In summary, with the proposed channel estimation technique, combining diversity using Space-Time Codes with OFDM is proved to be a promising technique for the present and future wireless communications.