Orthogonal time sequency multiplexing (OTSM) is a recently proposed modulation technique that outperforms orthogonal frequency division multiplexing (OFDM) in high-mobility and doubly spread channel conditions. Integrating intelligent reflecting surfaces (IRS) can further boost OTSM performance by effectively combining multi-path signals. This paper investigates the combination of OTSM and IRS to develop a generalized input-output relationship in both the time domain and delay-sequency (DS) domain, considering the presence of in-phase and quadrature-phase imbalances (IQI) at the receiver. To mitigate these imbalances, we apply a zero-padding (ZP) strategy in the DS domain, which not only suppresses time-domain interference but also enables dual pilot insertion for the estimation of IQI and channel parameters in the delay-time domain, followed by compensation in the time domain. Our analysis demonstrates that receiver IQI significantly degrades the bit error rate (BER) performance, particularly with increasing gain mismatch parameters. However, with the proposed compensation techniques, the BER performance approaches that of an ideal, imbalance-free scenario.

Orthogonal time frequency space (OTFS) is an emerging two-dimensional modulation method that has the potential to overcome the drawbacks of conventional orthogonal frequency division multiplexing, specifically in millimeter-wave and high-Doppler wireless environments. Intelligent reflecting surface (IRS) is a novel technology that has acquired considerable attention in the wireless communication research field due to its unique capability to significantly improve channel conditions. In this paper, we are taking advantage of both OTFS and IRS and present a general time-domain and delay Doppler input-output relation with in-phase (I) and quadrature-phase (Q) imbalances at the receiver. The effect of receiver IQ imbalance on bit error rate (BER) performance is also explored. The investigation confirms that with an increase in the gain mismatch parameter, the BER performance degrades.

Performance of space shift keying (SSK) modulation in cooperative decode-and-forward (DF) Relaying scheme using simultaneous wireless information and power transfer (SWIPT) is analyzed over the Rayleigh fading channel. SWIPT eliminates the need for frequent battery replacement at the relay in cooperative communications whereas SSK is a low complexity modulation technique to enhance data rate and minimize inter-channel interference, inter antenna synchronization requirement and the number of radio frequency chains. Closed-form and Upper bound expression for average bit error probability (ABEP) are derived with multiple DF relays with a direct link. Numerical and computer simulation results are presented with the discussion. Results demonstrate system performance improvement due to the combined effect of energy harvesting with SSK modulation.

Outage performance of cooperative relay networks using opportunistic decode-and-forward (DF) relaying in η-μ, κ-μ and mixed η-μ and κ-μ fading channels is analyzed. In DF relaying, a relay is allowed to forward the message from source only if the message is correctly decoded. The destination node combines both the direct signals from the source and the indirect signals from the relays using maximal-ratio diversity combining technique. In our analysis, exact closed-form expressions for the outage probability are obtained in η-μ, κ-μ and mixed η-μ and κ-μ fading channels, respectively. Numerical examples are provided to show the effect of number of relays, transmission rate and fading parameters on the outage probability. Numerical results are verified with Monte Carlo simulations.

A high‐data‐rate differential chaos shift keying (DCSK) scheme based on spatial modulation (SM), spatially modulated DCSK (SM‐DCSK), is proposed. By employing multiple transmit antennas and using transmit antenna index as information‐carrying unit, the proposed scheme offers a higher data rate compared with the conventional DCSK scheme. In particular, with two transmit antennas, the proposed scheme transmits a DCSK modulated bit from a selected antenna and hence can double the data rate. At the receiver, the maximum received signal is used to retrieve the block of transmitted bits. Mathematical expression for the conditional error probability of the proposed system is derived based on Gaussian approximation. The error probability of the antenna number estimation and the error probability of the transmitted bit estimation are evaluated numerically. Symbol error rate of the proposed scheme is compared with that of the quadrature chaos shift keying scheme. Numerical and simulation results are presented as a function of system parameters.

Differential chaos shift keying (DCSK) modulation‐based transmit antenna selection (TAS) schemes are proposed to reduce the effect of signal fading with less hardware complexity at the receiver. The transmitter adopts DCSK modulation and employs multiple antennas, whereas the receiver can have single/multiple antennas. On the basis of receiver structure/specifications some TAS schemes are presented. In particular, for multiple transmit antennas and single receive antenna system DCSK‐TAS scheme is proposed and for multiple transmit and multiple receive antenna system, two schemes, i.e. DCSK‐joint antenna selection and DCSK‐TAS/equal gain combining (DCSK‐TAS/EGC), are proposed. The probability of error of the proposed schemes is numerically evaluated in the presence of perfect feedback and feedback error in Nakagami‐ m fading channels. The proposed schemes completely outperform the conventional DCSK scheme with one transmit and one receive antenna. The results show that the DCSK‐TAS/EGC has the best error performance among the proposed schemes. Throughput of the proposed schemes is also presented and compared. The error performance of the proposed schemes are numerically evaluated and plotted for the parameters of interest. The simulation results verify the theoretical results.

Performance of multihop communication systems with regenerative relays using decode-and-forward (DF) relaying in η-μ fading channels is analyzed. In our analysis, novel closed form expressions of performance metrics: moments of end-to end signal to noise ratio, amount of fading, outage probability and average bit error rate (ABER) of Gray coded rectangular quadrature amplitude modulation (RQAM) signals are obtained for multihop communication systems in independent and non identically distributed η-μ fading channels. Numerical results are provided to illustrate the system's performance and the impact of number of hops and fading parameters on the performance is analyzed and discussed. Numerical analysis is verified by Monte Carlo simulation.

Performance of quadrature amplitude modulation (QAM) scheme in two-wave with diffuse power (TWDP) fading environment is analyzed. Closed-form expressions for the exact average symbol error rate (ASER) of general order rectangular QAM (RQAM) and cross QAM (XQAM) schemes are presented using moment generating function of TWDP fading distribution. Obtained ASER expressions are in the form of Appell's (Φ1(·)) and Lauricella's (Φ1(3)(·)) hypergeometric functions which can be numerically evaluated using either integral or series representation. Further, closed-form expression for the nth order moment of the received signal-to-noise ratio is derived. Numerical results show excellent agreement with simulation results.

Performance of an L-independent branch and a dual correlated branch, selection combining (SC) receivers are analyzed over Hoyt fading channels. Exact analytical expressions, for the probability density function (PDF), moments and outage probability of the combiner output signal-to-noise ratio (SNR), and average bit error rate for binary, coherent and non-coherent modulations are obtained for each type of SC receiver. Upper bounds on the truncation errors of PDF expressions containing infinite series are obtained too. Numerical and simulation results are plotted and the effect of L and correlation on the performance is studied and compared with available results.

Performance of an L branch maximal ratio combining (MRC) receiver has been analyzed in equally correlated η-μ fading channels. For the combiner output signal-to-noise ratio, analytical expressions for the probability density function, moments and outage probability have been obtained. For the MRC receiver, expressions for the average bit error probability for binary, coherent and non-coherent modulations have been presented. Numerical results have been plotted to illustrate the effect of fading correlation and diversity order (L) on the receiver performance. Both numerical and Monte Carlo simulation results have been found to be closely matching.

Performance of an L-selection combining (SC) receiver has been analyzed in κ-μ and η-μ fading channels. Moments of the SC receiver output signal-to-noise ratio and average bit error rate for binary, coherent and non-coherent modulations have been obtained analytically. Both numerical evaluation and computer simulation results have been generated to validate the obtained mathematical expressions. A study on the effect of the order of diversity on the system performance has also been presented.

Average symbol error rate (ASER) of an equal gain combining (EGC) receiver with an arbitrary number of branches in exponentially correlated, Nakagami-m fading channels has been derived for binary, differential phase-shift keying (DPSK) and noncoherent frequency-shift keying (NCFSK) modulations. A Parseval's theorem based approach has been used. Numerical and simulation results have been found to be in close agreement. Results show that for a given ASER, as expected, exponentially correlated fading requires a higher SNR with respect to independent fading. For a given number of branches L, increase in SNR required (SNR penalty) with respect to independent fading is less for higher values of fading parameter m while for a given m, SNR penalty is more for higher L

Using a Gil-Palaez lemma-based approach, we derive a general expression for the bit-error rate of a predetection equal gain combining receiver for coherent binary phase-shift keying modulation in exponentially correlated, Nakagami-m fading channel for an arbitrary number of branches. The obtained expressions are different for even and odd numbers of branches. Numerical results have been corroborated with simulations.