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A space-time coding array (STCA) system transmits an identical waveform with a small time offset across the array elements. It shares the characteristics of high angular resolution and instant wide angular coverage, leading to the low probability of interception as seen in the traditional multiple-input and multiple-output radar. Angle-time two-dimensional matched filter is required in the STCA. However, the sidelobe level (SLL) of the multi-dimensional ambiguity function in the range and angle domains is not as low as that desired in practical applications and the range resolution decreases as the number of elements increases. Here, two kinds of subarray-based time-delay methods are proposed to improve the resolution and reduce the SLL of the ambiguity function for STCA. Both the regular and irregular subarrays are considered, which increase the degrees of freedom and thus enhance the range resolution. Moreover, the SLL of the ambiguity function is reduced. Simulation results are provided to demonstrate the effectiveness of the proposed methods.

Successive relaying is a bandwidth-efficient scheme in cooperative networks. In this study, a novel distributed space-time coding (DSTC) transmission scheme for a two-path successive relay network is proposed that enjoys threshold-based selection relaying protocol. A new beamforming method is also employed alongside the proposed DSTC transmission scheme. Three scenarios are considered in this study. In the first scenario, single-input–single-output (SISO) relays are considered. In the second and third scenarios, multiple-input–multiple-output (MIMO) relays are used, but in the second case a transmission scheme named as quasi-DSTC scheme alongside employing space-time coding at each relay is proposed. A closed-form expression for the end-to-end bit error rate (BER) of the system is derived and it is shown that regardless of the fading in inter-relay channel, the proposed scheme achieves full diversity order even when there are decoding errors at the relay nodes. Simulation results show a significant saving in power of about 2.5, 3, and 4 dB at BER ( 10 − 4 ) compared with other conventional methods in the case of using SISO relays, MIMO relays in the second and third scenarios, respectively.

In this study, a rate-varying space-time pre-coding scheme for a multiple-input multiple-output system in a fast-fading channel is proposed. In particular, unlike the traditional fixed rate space-time coding scheme, the transmitter which has no channel state information keeps choosing a pre-coding matrix randomly at each space-time symbol period to deliver the information until it is successfully decoded by the receiver. Since the number of received symbol vectors needed to successfully decode the information is determined by the channel realisation, the coding rate of the proposed scheme can adapt to the fast-fading channel. The exact expression of the equivalent signal-to-noise ratio gain after the post-combining and zero-forcing equalisation at the receiver side is derived, and a design criteria to achieve optimal performance in terms of average error probability and ergodic capacity under the mean power constraint is provided. Based on this, a minimal variance pre-coding (MVP) scheme is designed, which is compared with an intuitive Gaussian pre-coding scheme. It is shown that the MVP scheme has better performance and could adapt to different channel conditions.

This study investigates the cooperative multicast of scalable video over dedicated relay-based cellular networks. Different layers in a scalable video tend to have different transmission quality requirements, and legacy cellular network has limitations in providing homogeneous service quality within its coverage area. The authors propose two realistic cooperative transmission schemes with a capacity performance analysis for scalable video over dedicated relay-based cellular networks. The proposed transmission schemes with multiple antennas at an evolved node B and the dedicated relay utilise the combinations of beamforming and space-time coding in order to enhance the multicast performance of scalable video. The proposed schemes ensure that the received base layer (BL) of scalable video guarantees the minimum video quality to all user terminals throughout the cell coverage with given outage probability, while the terminals inside the relay coverage can achieve better video quality by receiving both the BL and additional enhancement layer data according to the received channel condition. The antennas configuration and the video type determine which multicast scheme to choose.

Adaptive power allocation (PA) algorithms with different criteria for a cooperative multiple-input multiple-output network equipped with distributed space-time coding are proposed and evaluated. Joint constrained optimisation algorithms to determine the PA parameters and the receive filter are proposed for each transmitted symbol in each link, as well as the channel coefficients matrix. Linear receive filter and maximum-likelihood detection are considered with amplify-and-forward and decode-and-forward cooperation strategies. In these proposed algorithms, the elements in the PA matrices are optimised at the destination node and then transmitted back to the relay nodes via a feedback channel. The effects of the feedback errors are considered. Linear minimum mean square error expressions and the PA matrices depend on each other and are updated iteratively. Stochastic gradient algorithms are developed with reduced computational complexity. Simulation results show that the proposed algorithms obtain significant performance gains as compared with existing PA schemes.

In this study, the authors evaluate the outage probability performance of an amplify-and-forward cooperative relay network where the relays are equipped with cognitive radios. When the number of available relays is more than four the authors use the channel conditions in order to select the best four cognitive relays from a set of M cognitive relay nodes and then they are used for cooperation between the source and the destination nodes. Expressions for outage probability are determined for a frequency flat Rayleigh-fading environment from the received signal-to-noise ratio with perfect and imperfect spectrum acquisition. In addition, a modified distributed quasi-orthogonal space–time block coding scheme with increased code gain distance is considered for use within the proposed cognitive relay network. To utilise the available spectrum opportunities with the modified quasi-orthogonal space–time block code, the code matrix can be adapted to the number of available relays. Simulation results show that the four relay selection improves the system performance. This is confirmed by the outage probability analysis. The simulations also show that the modified code can significantly enhance the performance of the system and improve the reliability of the link as compared with the conventional distributed quasi-orthogonal space–time block coding.

Distributed space-time coding (DSTC) with an efficient relaying protocol, referred to as amplify-and-forward and decode-and-forward (DF-AF) selection relaying, has not received much attention yet. In the DF-AF selection relaying-aided DSTC transmissions, each relay could adaptively process the received signal according to its decoding state to improve the performance. In this study, the authors analyse the pairwise error probability (PEP) performance, the diversity order and the union bound on the error probability of the DSTC with DF-AF selection relaying in cooperative wireless sensor networks. More specifically, by introducing a random variable vector to denote the decoding state of the relays, the upper bounds of PEP are derived first for the DSTC with DF-AF selection relaying based on the Chernoff bound. Then, the diversity order and the union bound on the error probability are obtained based on the upper bounds of PEP. Finally, simulation results verify the theoretical analysis and demonstrate that the DSTC with DF-AF selection relaying has better error performance than the DSTC with DF protocol and the DSTC based on AF protocol.

In this study, the authors develop a distributed space–time coding scheme for a two-way relay network that contains multiple distributed relay nodes. Both the time and frequency asynchronous nature of the distributed system are considered in the design. Distributed convolutional coding is employed to handle multiple timing errors in the networks. The authors prove that under perfect frequency synchronisation, the proposed scheme can achieve both spatial and multipath diversity by linear receivers, such as linear zero-forcing or minimum mean-square-error receiver, thus providing a low decoding complexity. The authors further find that frequency asynchronism has little effect on the designed scheme and show that the diversity can still be achieved almost surely (in the measured theoretic sense) under both time and frequency asynchronous scenarios. The authors also provide numerical results to corroborate the proposed studies.

Space-time coding with receive combiner bank (STC-RCB), in which a bank of receive combiners is added before the space-time decoder for interference-plus-noise suppression, is proposed. Without loss of generality, the author consider space-time block code (STBC) to be the representative of STC and study the performance for (STBC-RCB). The author derive the output signal to interference-plus-noise ratio (SINR) (of the space-time decoder) for STBC-RCB under multi-user cochannel interference. By regarding STBC as a special case of STBC-RCB, the author also derive the output SINR for STBC under multi-user cochannel interference. Simulation results show that the output SINR of STBC-RCB can be much larger than that of STBC, also, they show that STBC-RCB can adopt the appropriate receive combining strategy in the RCB to further improve the performance.

Multiple input multiple output (MIMO) techniques are widely employed in modern wireless systems. The most prominent approaches to MIMO communication are space-time coding (STC) and spatial multiplexing (SM). Less studied is a hybrid technique called adaptive MIMO switching (AMS), which may be employed by fixing the transmission rate and selecting between space-time block coding and SM transmission modes based on instantaneous channel conditions to achieve the most efficient link. This study presents a hardware implementations of a selector algorithm and a detector employing it. The detector is designed for a 2×2 MIMO system and was implemented on an Altera Cyclone II FPGA. In addition, two transmission protocols with decision feedback from the receiver to the transmitter via a low-rate feedback channel are introduced and the feasibility of switching for high-data-rate transmissions is discussed.

This study presents a new blind carrier frequency offset (CFO) estimation technique for multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems employing space-time coding (STC). CFO estimation is crucial for OFDM systems to avoid the performance degradation because of the inter-carrier interference that results when the CFO is not estimated and compensated accurately. Based on the assumptions that the data symbols are selected from a constant modulus constellation and the channel is varying slowly over time, a new blind CFO estimator is proposed by minimising the power difference between all subcarriers in two consecutive STC blocks. Therefore the proposed system exploits all subcarriers in time and frequency domain, which provides a remarkable performance improvement over other techniques reported in the literature. The complexity of the proposed estimator is substantially reduced by approximating the cost function by a sinusoid that can be minimised using direct closed-form computations within one OFDM symbol period. Monte Carlo simulations are used to assess the performance of the proposed system by means of mean squared error (MSE) in both static and time-varying frequency-selective fading channels. The simulation results demonstrate that the proposed estimator can eliminate the MSE error floors that usually appear at moderate and high signal-to-noise ratios for the estimators that work only in frequency domain.

Error propagation from the relay to the destination is a major drawback of digital relaying protocols that substantially diminishes the cooperative diversity gain of the system. Appropriately designed selection relaying schemes can effectively mitigate this phenomenon and improve the diversity order, especially when the source-relay channel state information (CSI) is not available at the destination. In this study, the authors investigate the SNR-based selection relaying scheme in a multi-relay cooperative network that employs the distributed space-time coding (DSTC) strategy. The authors present a closed-form expression for the end-to-end bit error probability (BEP) of the system. It is demonstrated that the orthogonality of the space-time coded signals transmitted by the relays is not preserved under the error propagation from the relays to the destination and this gives rise to intersymbol interference at the destination. The SNR loss and intersymbol interference caused by the error propagation substantially diminish the diversity order of the system. The error propagation can be effectively mitigated by employing appropriate thresholds at the relays. The authors derive a closed-form expression for the optimal threshold that minimises the end-to-end BEP of the system. The authors also analyse the asymptotic behaviour of the BEP and demonstrate that by employing the optimal threshold the full diversity order is achieved. Furthermore, the authors propose a class of thresholds that are independent of the network geometry and also provide full diversity order. By employing these thresholds, each relay node can decide to forward or remain silent independent of other relay nodes.

Designed is an error-resilient, yet high-throughput interleave division multiplexing based space-time code suitable for multi-source co-operation. Its achievable rate, power efficiency and flexibility have been characterised.

A downlink (base-to-mobile) multicarrier direct-sequence code-division multiple-access (MC DS-CDMA) system employing multiple antennas at both the base station and each of the mobile terminals is investigated, when communicating over fast time-varying fading channels resulting in time-selective fading. In the considered multiantenna MC DS-CDMA, space-time spreading (STS) based on the family of orthogonal variable spreading factor (OVSF) codes is proposed in order to achieve the time diversity because of the time-selective fading, in addition to the transmit/receive diversity. In this contribution, the closed-form expressions for the single-user bit-error rate (BER) are derived, in order to gain insight into the achievable BER performance of the multiantenna MC DS-CDMA. The BER performance of the multiantenna MC DS-CDMA system is investigated, when communicating over correlated time-selective Rayleigh fading channels. The study and performance results show that the multiantenna MC DS-CDMA using OVSF codes-assisted STS constitutes a high-efficiency downlink space-time transmission scheme. It is capable of achieving the full diversity provided by the time-selective fading and multiple transmit/receive antennas. Furthermore, the proposed multiantenna MC DS-CDMA is capable of achieving a self-balance between the time diversity achieved and the multiuser interference suppression capability, when using low-complexity correlation detection.

Satellite-MIMO, space-time coded for capacity gain, is investigated, and complementary cumulative distribution function outage and capacity predictions are provided using a verified physical-statistical MIMO land mobile-satellite channel model. Capacity results obtained for a single satellite, single antenna terminal (SISO), a dual satellite, single antenna terminal (2×1 MISO) and a dual satellite, dual antenna terminal (2×2 MIMO) system are compared, showing the benefit of satellite-MIMO.

The effect of imperfect channel estimation on the bit error rate (BER) of multiple-input multiple-output communication systems utilising space-time coding is investigated. A multipath channel is considered and a given level for the channel estimation error is assumed. The receiver employs an equaliser to reduce the ISI in the received signal. A closed-form expression for the SNR at the output of the equaliser that employs the results of the channel estimation is derived. The theoretical SNR derived is used as a basis to assess the performance of the system. Results are applicable to any channel estimation technique. Analysis shows that the deterioration of performance in the multiple transmit antenna scheme outweighs the benefits achieved over the single antenna case when the SNR and channel estimation error are large. The degradation in the transmit diversity scheme exceeds 8 dB to achieve a BER of 10/sup -4/ when the channel estimation error is 5% relative to the perfect channel estimation case.

Space-time coding (STC) employing ternary phase shift keying (TPSK) for highly reliable wireless communications is explored. STC-TPSK is one of the effective schemes for achieving coding gains without losing attractive features of TPSK, such as superior error rate performance and good spurious characteristics. This study verifies that STC-TPSK outperforms both STC-BPSK and STC-QPSK over Rayleigh fading channels.

The performance of a quasi-orthogonal space-time block code with antenna selection is considered. Transmit antenna selection as well as receive antenna selection is studied. A new selection rule is proposed that minimises the average bit error ratio and achieves full diversity even if only a simple zero-forcing receiver is used.

In most commercial wideband code division multiple access systems, the transmitted signal in the downlink channel is spread by orthogonal codes to accommodate different users. However, frequency selective fading destroys the orthogonality and causes multiple access interference. Application of a chip level decision feedback equaliser with the Alamouti transmit diversity scheme is proposed to restore the orthogonality of the received spreading sequences.

A serially concatenated space-time code (SCSTC) that enables efficient high-speed transmission in a band-limited channel is proposed. The performance of the proposed system is compared with that of conventional bandwidth-efficient trellis coded modulation schemes, such as serially concatenated trellis coded modulation (SCTCM) and turbo trellis coded modulation (turbo-TCM), and a significant performance improvement is shown.

A space-time-code (STC) blind receiver is proposed. The receiver has the advantages of constrained minimum output energy (CMOE) blind multiuser detectors and space-time (ST) 2D-Rake receivers and overcomes their limitations. It can make full use of spatial, temporal and code signatures involved in the desired user's signal to suppress multiuser access interference and combine multipath components.

Simulation results for the comparative performance of a number of space-time coding (STC) schemes in a multiple-input-multiple-output (MIMO) channel are presented, and compared with a single-antenna benchmark and two-antenna space-time transit diversity (STTD) scheme. Both the space-time trellis coding (STTC) and BLAST approaches offer high spectral efficiencies, but STTC outperforms BLAST in terms of its power efficiency.