Inspired by the concept of Space-Time Shift Keying (STSK), the further evolved philosophy of Space-Time-Frequency Shift Keying (STFSK) was proposed for Multiple-Input-Multiple-Output (MIMO) wireless communications, where a beneficial diversity gain may be gleaned from three different domains, namely the space-, time- and frequency-domain. In this paper we proposed soft-detected STFSK in order to conceive its iterative decoding aided version combined with channel codes. Our results showed that the STFSK soft demodulator, which iteratively exchanges extrinsic information with channel codes, may decrease the required transmit power by approximately 3 dB at the Eb/N0of 10-5, compared to hard-decision STFSK. Furthermore, the detection complexity of both the hard- and the soft-decision STFSK demodulator is quantified in terms of the number of multiplications and additions required for each detection iteration.

Slow Frequency Hopping Multiple Access (SFHMA) is capable of providing inherent frequency diversity and of beneficially randomising the effects of cochannel interference. It may also be advantageously combined with our novel Space-Time-Shift Keying (STFSK) scheme. The proposed system's area spectral efficiency is investigated in various cellular frequency reuse structures. Furthermore, it is compared to both classic Gaussian Minimum Shift Keying (GMSK) aided SFHMA as well as to GMSK assisted Time Division/ Frequency Division Multiple Access (TD/FDMA). The more sophisticated third-generation Wideband Code Division Multiple Access (WCDMA) and the fourth generation Long Term Evolution (LTE) systems were also included in our comparisons. We demonstrate that the area spectral efficiency of the STFSK aided SFHMA system is higher than those of the GMSK aided SFHMA and TD/FDMA systems as well as that of the WCDMA, but it is only 60% that of the LTE system.

The rationale of our design is that although much of the literature of cooperative systems assumes perfect coherent detection, the assumption of having any channel estimates at the relays imposes an unreasonable burden on the relay station. Hence, non-coherently detected Reed-Solomon (ReS) coded Slow Frequency Hopping (SFH) assisted M-ary Frequency Shift Keying (FSK) is proposed for cooperative wireless networks, subjected to both partial-band interference and Rayleigh fading. Erasure insertion (EI) assisted ReS decoding based on the joint maximum output-ratio threshold test (MO-RTT) is investigated in order to evaluate the attainable system performance. Compared to the conventional error-correction-only decoder, the EI scheme may achieve an E_b/N_0 gain of approximately 3 dB at the Codeword Error Probability, P_w, of 10^{-4}, when employing the ReS(31,20) code combined with 32-FSK modulation. Additionally, we evaluated the system's performance, when either equal gain combining (EGC) or selection combining (SC) techniques are employed at the destination's receiver. The results demonstrated that in the presence of one and two assisting relays, the EGC scheme achieves gains of 1.5 dB and 1.0 dB at the P_w of 10^{-6}, respectively, compared to the SC arrangement. Furthermore, we demonstrated that for the same coding rate and packet size, the ReS(31,20) code using EI decoding is capable of outperforming convolutional coding, when 32-FSK modulation is considered, whilst LDPC coding had an edge over the above two schemes.

The rationale of our design is that although much of the literature of cooperative systems assumes perfect coherent detection, the assumption of having any channel estimates at the relays imposes an unreasonable burden on the relay station. Hence, non-coherently detected Reed-Solomon (ReS) coded Slow Frequency Hopping (SFH) assisted M-ary Frequency Shift Keying (FSK) is proposed for cooperative wireless networks, subjected to both partial-band interference and Rayleigh fading. Erasure insertion (EI) assisted ReS decoding based on the joint maximum output-ratio threshold test (MO-RTT) is investigated in order to evaluate the attainable system performance. Compared to the conventional error-correction-only decoder, the EI scheme may achieve a gain of approximately 3 dB at the Eb/N0of 10-4, when employing the ReS(31,20) code combined with 32-FSK modulation. Additionally, we evaluated the system's performance, when either equal gain combining (EGC) or selection combining (SC) techniques are employed at the destination's receiver. The results demonstrated that in the presence of one and two assisting relays, the EGC scheme achieves gains of 1.5 dB and 1.0 dB at the Eb/N0of 10-6, respectively, compared to the SC arrangement.

Hybrid-Automatic-Repeat-reQuest (HARQ) has become an indispensable technique in reliable communications systems. However, its performance is inevitably affected by the channel's fading correlation. In this paper, we proposed a novel relay-switching aided HARQ scheme in order to mitigate the detrimental effects of correlated fading without unduly increasing the system's complexity and delay. Our results show that the proposed relay-switching regime operates efficiently in correlated channels, hence significantly reduces the error floor of turbo-coded HARQ. Additionally, a HARQ scheme using Segment Selective Repeat (SSR) is incorporated in the relay-switching scheme for achieving further improvements. Quantitatively, the proposed relay-switching aided turbo-coded HARQ scheme using SSR may achieve an approximately 2 dB gain, compared to the conventional amplify-and-forward aided turbo coded HARQ arrangement using Chase Combining.

Systematic Luby transform (SLT) codes constitute rateless codes, which are capable of adaptively adjusting their code rate depending on the channel quality without any explicit channel state information (CSI) at the transmitters. SLTs are also suitable for space time collaboration-aided relay networks. In this study, an iterative decoding-aided SLT scheme is combined with 16 quadrature amplitude modulation (QAM) transmission in a wireless relay-aided network. The bit error ratio (BER) results and extrinsic information transfer (EXIT) charts are provided to evaluate the performance of the proposed scheme. The simulation results show that the proposed scheme using amplify-and-forward (AF) relaying achieves a 2.5 dB gain at a BER of 10−5, while the attainable improvement is nearly 6 dB for decode-and-forward (DF) relaying, compared to the non-iterative detection scheme operating without the relay's assistance. Moreover, the AF relaying-aided SLT coded 16-QAM scheme is more beneficial, when the relay station is close to the source. By contrast, the DF relaying performs best near the mid-point between the source and the destination. Additionally, a modified Hybrid Automatic-Repeat-reQuest (HARQ) protocol using incremental redundancy is applied along with the SLT-coded 16-QAM scheme in order to enhance the achievable throughput and energy efficiency of cooperative networks. This arrangement reduces the total transmit power by about 5%, compared to the classic HARQ scheme.

Inspired by the concept of the Space-Time Shift Keying (STSK) modulation, in this paper we proposed the Space-Frequency Shift Keying (SFSK) modulation as well as the Space-Time-Frequency Shift Keying (STFSK) concept which spreads the transmit signal not only across the space and time domains, but also the frequency domain. The performance of STSK modulation is degraded by about 2 dB, when the channel changes from uncorrelated frequency-flat fading to the frequency-selective environment of the 6-tap COST207 model. By contrast, as a benefit of Frequency Shift keying, the SFSK and STFSK schemes are capable of maintaining their performance also in frequency-selective fading environments. Finally, we demonstrate that the STSK and SFSK schemes constitute special cases of the STFSK modulation.

Hybrid Automatic-Repeat-reQuest (ARQ) schemes are capable of maintaining reliable communications for transmission over hostile wireless channels. In coherent detection aided schemes, the achievable performance substantially depends on the accuracy of channel state information (CSI). In this paper, the impact of imperfect CSI on Reed-Solomon (RS) coded HybridARQ systems is investigated for transmission over block-Rayleigh fading channels. The corresponding goodput equation is derived and used to evaluate the system's performance. The effects of code rate and channel quality are also visualized. Furthermore, the results are utilized for the optimization of the pilot versus data symbols power allocation in order to maximize the system's goodput. Quantitatively, the proposed scheme provides a 2.5 dB Eb/N0gain at a given goodput for the (255/223) RS code defined over the GF(256).

Channel estimation (CE) plays an important role in determining the achievable performance of coherently detected communications systems. In this paper, the impact of imperfect CE on Reed-Solomon coded Hybrid Automatic-Repeat-Request (ReS/H-ARQ) systems is investigated for transmission over correlated Rayleigh fading channels. The proposed scheme invokes Amplify-and-Forward relaying, where the benefits of multiple cooperative stations are also quantified. Both the corresponding bit error probability and goodput are characterized. The system parameters are adjusted for maximizing the attainable system performance. An optimum pilot power allocation scheme is proposed, which reduces the required bit-energy by 4 dB for the (255/223) Reed-Solomon code defined over the Galois field GF(256) without reducing the goodput.

Systematic Luby Transform (SLT) codes constitute rateless codes, which are capable of adaptively adjusting their code rate depending on the channel quality without explicit channel state information (CSI) at the transmitters. SLTs are also suitable for space-time collaboration aided relay networks. In this paper, an iterative decoding aided SLT scheme is combined with 16-QAM transmission in a wireless relay aided network. The Bit Error Ratio (BER) results and Extrinsic Information Transfer (EXIT) charts are provided to evaluate the performance of the proposed scheme. The simulation results show that the proposed scheme using amplify-and-forward (AF) relaying achieves a 2.5dB gain at a BER of 10-5, while the attainable improvement is nearly 6dB for decode-and-forward (DF) relaying, compared to the non-cooperative scheme, where the 16-QAM and the SLT decoder work independently. Moreover, the AF relaying aided SLT coded 16-QAM scheme is more beneficial, when the relay station is close to the source. By contrast, the DF relaying performs best near the mid-point between the source and destination. In addition, a modified Hybrid Automatic-Repeat-reQuest (HARQ) protocol using incremental redundancy is applied along with the SLT coded 16-QAM scheme to enhance the achievable throughput and energy efficiency of cooperative networks. This arrangement reduces the total transmit power by about 8%, compared to the classic HARQ scheme.

Systematic Luby Transform (SLT) codes constitute rateless codes, which are capable of adaptively adjusting their code rate depending on the channel quality without any explicit channel state information (CSI) at the transmitters. In this paper, we investigate the performance of an SLT coded wireless system communicating over a correlated fading channel within an 802.11b network. The simulation results show that the SLT coded system can achieve a 3 dB gain in term of fading deviation when fading correlation changes from 1 Hz to 5 Hz. Moreover, it is found that a system employing an SLT code can provide similar performance to other rateless codes, namely the Luby Transform (LT) code and the Random Linear Fountain Code (RLFC). However, this level of performance is achieved with a reduced number of decoding operations. A 20% reduction is achieved when the standard deviation of the fading amplitude is 10 dB and the communication distance is 7 m. Greater reductions are observed under more benign propagation conditions.