This paper develops a detection scheme based on the implicit pilot-symbol-assisted architecture of M-ary frequency-shift-keying (FSK) modulation in amplify-and-forward (AF) multiple-relay networks. It is shown that, at the expense of the low spectral efficiency inherent in FSK modulation, every transmitted symbol from the source to the destination can be used as a pilot symbol. In the proposed detection scheme, the destination combines the signals from the source and the relays to perform detection by using the estimated channels obtained from the implicit pilot symbols. Using the Gaussian approximation for the effective noise at the destination, an upper bound of the approximated bit-error-rate (BER) is provided. Simulation results reveal that the proposed scheme can significantly improve the BER performance when compared to previously proposed schemes in a temporally-correlated fading environment. The simulation results also verify the obtained upper bound on the approximated BER.

This paper develops a detection scheme based on implicit pilot-symbol-assisted architecture for non-coherent amplify-and-forward (AF) relay networks. The networks use M-ary frequency-shift-keying (FSK) modulation and multiple relays to assist communication from a source to a destination. Built on the fact that every transmitted symbol from the source to the destination can be considered as a pilot symbol, the destination combines the signals from the source and the relays to perform detection by using the estimated channels obtained from the implicit pilot symbols. A tight upper bound on the bit-error-rate (BER) of the developed scheme is obtained and used to show that the proposed scheme achieves a full diversity order. Moreover, simulation results reveal that the proposed scheme can significantly improve the BER performance when compared to previously proposed schemes in a temporally-correlated fading environment.

An incremental relaying protocol based on the adaptive decode-and-forward relaying scheme is presented for a cooperative wireless network with binary frequency-shift keying modulation. To reduce error propagation and satisfy bit-error-rate (BER) requirement, the proposed protocol employs two thresholds. One threshold is used to select reliable relays: if a relay is requested to re-trnsmit, it will do so if its decision variable is larger than the threshold; otherwise, it remains silent. The other threshold is used at the destination as follows: the destination sends a request to re-transmit if the decision variable corresponding to a received signal is smaller than the threshold, otherwise, the destination sends a request to stop re-transmissions. The destination combines the signals from the requested relays and from the source to make the final decision. Very-tight closed-form upper bounds for both the average BER and throughput are derived for the proposed protocol. Based on the obtained BER and throughput expressions, the problem of choosing optimal thresholds to maximise the throughput while the BER meets a given constraint is investigated. Simulation results show that our proposed protocol leads to a considerable improvement in the performence of cooperative diversity systems.

A relaying technique based on single relay selection is studied for multiple-relay networks using hierarchical modulation for unequal error protection. A single relay selection scheme achieves a higher bandwidth efficiency while maintaining the same diversity order as when all the relays are selected in a multiple-relay network. Specifically, a cooperative network with one source, K relays, and one destination is considered in which two different protection information classes are modulated by a hierarchical 2/4-amplitude shift keying (ASK) constellation at the source. After selecting a relay to cooperate with the source, based on the instantaneous received SNR, the selected relay decides to retransmit both classes by using a hierarchical 2/4-ASK constellation, or the more protection class by using a 2-ASK constellation, or remains silent. The approximated bit error rate (BER) of each information class is derived. Optimal thresholds are chosen to minimize the BER of one class while satisfying the BER constraint of the other. Analytical and simulation results show that the optimal thresholds can improve the error performance significantly.

This paper considers a cooperative network in which binary frequency-shift-keying (BFSK) modulation is employed to facilitate noncoherent communications between a source and a destination with the help of K relays. Proposed is an adaptive cooperative scheme that employs two thresholds as follows. One threshold is used to select retransmitting relays: a relay retransmits to the destination if its decision variable is larger than the threshold, otherwise it remains silent. The other threshold is used at the destination for detection: the destination marks a relay as a retransmitting relay if the decision variable corresponding to the relay is larger than the threshold, otherwise, the destination marks it as a silent relay. Then the destination combines the signals from the retransmitting relays and from the source to make the final decision. The average end-to-end (e2e) bit-error-rate (BER) is derived in a closed-form expression for single-relay and two-relay networks. The problems of selecting optimal thresholds or jointly optimal thresholds and power allocation to minimize the average BER are investigated. Simulation results are provided to validate our analysis. Compared to the previously proposed piecewise-linear (PL) detection scheme, our proposed scheme yields a superior performance under a wide range of channel conditions when optimal thresholds or jointly optimal thresholds and power allocation are employed.

A relaying technique based on single-relay selection is studied for multiple-relay networks when hierarchical modulation is employed for unequal error protection. A single-relay selection scheme achieves a higher bandwidth efficiency while maintaining the same diversity order as when all the relays are selected in a multiple-relay network. Specifically, a cooperative network with one source, K relays, and one destination is considered in which two different protection information classes are modulated by a hierarchical 2/4-amplitude shift keying (ASK) constellation at the source. After selecting a relay to cooperate with the source, based on the instantaneous received signal-to-noise ratio, the selected relay decides to retransmit both classes by using a hierarchical 2/4-ASK constellation, or the more protection class by using a 2-ASK constellation, or remains silent. The approximated bit error rate (BER) of each information class is derived. Optimal thresholds are chosen to minimise the BER of one class while the BER of the other class satisfies a requirement. Numerical and simulation results are provided to validate the analysis. The results also show that the optimal thresholds can improve the error performance significantly.

This paper studies a relaying technique in cooperative networks using hierarchical modulation. Hierarchical modulation is useful in applications that require different protection classes of the information. In particular, a cooperative network with one source, one relay, and one destination is considered. Two different protection classes are modulated by a hierarchical 2/4-amplitude shift keying (ASK) constellation at the source. Based on the instantaneous received signal-to-noise ratio (SNR) at the relay, the relay decides to retransmit both classes by using a hierarchical 2/4-ASK constellation, or the more protection class by using a 2-ASK constellation, or remains silent. Optimal thresholds are chosen to minimize the bit-error-rate (BER) of the less protection class while the BER of the more protection class meets a given requirement. Numerical and simulation results are provided to verify the analysis. The results show that the optimal thresholds improve the performance significantly.

A design method is introduced for linear dispersion (LD) space-time codes in wireless relay networks under Rayleigh fading channels. The codes are designed with a stochastic quasi-gradient algorithm to minimize the upper bound of the average pairwise error probability. Simulation results show that the optimized codes achieve a coding gain of about 2 dB over codes that are randomly generated based on the isotropic distribution.

This paper applies the sigma mapping of M-QAM in linear diversity-embedded space-time block codes (LDE-STBC) to achieve different diversity levels and various coding gains for unequal error protection (UEP). By controlling the basis vectors of sigma mapping, the bit error rate (BER) performance of each bit in a layer can be made to satisfy its quality-of-service (QoS) requirement. Moreover, with the low decoding complexity offered by sigma mapping, highly-flexible codes can be designed.