Underwater wireless optical communication (UWOC) is a promising technology for the massive data transmission of the Internet of Underwater Things (IoUT) due to its high speed, low latency, and wide range of applications. However, UWOC systems face significant challenges, such as oceanic turbulence and pointing errors. Given the increasing number of underwater optical devices, interference is another challenge for the UWOC. Therefore, this paper proposes a multihop UWOC system based on rate-splitting multiple access (RSMA) with relay selection over the Weibull-generalized Gamma (WGG)-distributed oceanic thermocline turbulence channel with pointing error. The RSMA scheme is used to realize communication between a source and multiple users. Multihop relays are deployed to extend the communication distance, and relay selection is applied to improve the channel quality of underwater wireless optical links. The statistical characterization of the system is analyzed, including the probability density function (PDF) and the cumulative distribution function (CDF) of the instantaneous signal-to-noise ratio (SNR) under relay selection. Based on the statistical results, an exact closed-form expression for the outage probability is given. Moreover, the asymptotic expression of the outage probability under high SNR is provided, and the diversity order is obtained based on the asymptotic analysis of the outage probability. Simulation results are given to verify our derived expressions. The outage performance of the proposed system under various system configurations, including air bubble levels, thermohaline gradients, pointing error levels, target rates, power allocation, the number of parallel relays, and the number of hops, is analyzed. Additionally, the RSMA-based system is compared with the non-orthogonal multiple access (NOMA)-based system. It has been demonstrated that the RSMA-based system outperforms the NOMA-based system.

As a promising underwater communication technique for the Internet of Underwater Things (IoUT), underwater wireless optical communication (UWOC) has attracted increasing interest due to its low-link delay, high-transmission rate, and wide applications. In underwater environments, path loss, ocean turbulence fading, and pointing error fading seriously damage UWOC performance. Thus, relaying schemes have been proposed to mitigate fading in wireless optical links. In this article, we present a relay-assisted multihop vertical UWOC system employing multiple-input-multiple-output (MIMO) technology in conjunction with the equal gain combing (EGC) method over layered cascaded Gamma-Gamma turbulence channels with pointing errors. For the proposed system, we consider both fixed gain amplify-and-forward (AF) relaying and decode-and-forward (DF) relaying. The cumulative distribution function (CDF) and the probability density function (PDF) of the end-to-end instantaneous signal-to-noise ratio (SNR) are derived with the help of the single-variate Fox-H function and the bivariate Fox-H function. Further, we give the closed-form expressions of the outage probability and the ergodic channel capacity. Moreover, we provide the asymptotic analysis of the outage probability to obtain more insights into the diversity order. The diversity order is shown to depend on the turbulence parameters of each layer, the number of laser sources and photodetectors, the pointing error parameters, and the number of hops. Finally, Monte-Carlo simulation results are utilized to validate our derived results.

Different from previous literature assuming either single reconfigurable intelligent surface (RIS) or multiple RISs at given locations, this letter first studies a multi-user millimeter wave (mmWave) massive multiple-input multiple-output (MIMO) system aided by multiple RISs following Poisson point processes. Then we derive an accurate closed-form expression for the spectral efficiency of an arbitrary user and an approximation for the ergodic spectral efficiency of the cell. Moreover, we consider the hardware impairment and model a practical phase-dependent amplitude for each reflecting element. Finally, the simulation results verify the derivations and demonstrate that RISs can provide greater performance gain than the active nodes and require different deployment strategy, which is related to the number of RISs.

In this study, the authors investigate the intra‐physical functional splits of 5G new radio protocol stack proposed by different groups. Based on the location of the digital beamforming block, the radio units (RUs) are divided into two categories: Category A and Category B. Two implementation modes of hybrid beamforming at the physical layer are considered, in which digital beamforming is performed either at the distributed unit (DU), as in the Category A RU based hybrid beamforming (HBF‐A) scheme, or at the RUs, as in the Category B RU based hybrid beamforming (HBF‐B) scheme. To maximise the weighted sum rate, the authors formulate the problems of jointly designing hybrid beamforming, analogue combining and fronthaul compression strategies for both HBF‐A and HBF‐B. The formulated problems are simplified by adopting the codebook‐based design, and further tackled by leveraging the majorisation–minimisation algorithm. Finally, numerical results confirm that the HBF‐A scheme outperforms the HBF‐B scheme in the large power regime. Compared with the HBF‐A method, the HBF‐B method is more sensitive to changes in system parameters, such as the compression noise and the number of receive antennas, in the large power regime, while it is less sensitive in the small power regime.

Present day requirements of high quality audio and video surveillance has instigated research interests in wireless multimedia sensor networks (WMSN). In order for the WMSN to achieve trademark performance in audio and video surveillance applications, certain design requirements must be met. In this work, we identify vital design issues affecting diversity gain in conditions especially, where channel fading characteristics fluctuate rapidly. We apply the cooperative communication technique in WMSN to create a framework that optimizes diversity gain in an environment where channel state information (CSI) is unknown. We then discuss promising research directions for optimizing diversity gain and noncoherent communication efficiency in cooperative WMSN.

ABSTRACT In this paper, we investigate the optimal sensing settings for a cognitive radio (CR) network consisting a number of CR users and a fusion center (FC). Our objective is to maximize the channel utilization under the constraint that the signals from the primary user (PU) are sufficiently protected. We focus on the utilization of the channel in which PUs dynamically enter the network with burst nature. Thus, we apply the average error probability (AEP) as the metric of channel utilization. Moreover, in order to protect the PU signal from being interfered, the missing detection probability is applied as the constraint function. Assuming that counting rules are utilized in the FC, we derive the false alarm probability, the missing detection probability, and the AEP in the maximum a posteriori (MAP) fashion. Then, after proving the monotonic properties of the objective function and the constraint function, we propose an efficient algorithm named Algorithm I that can derive the optimal settings for maximizing the channel utilization. Moreover, a simplified algorithm named Algorithm II is also proposed to minimize the AEP, supposing that perfect synchronization exists between the CR users and the PU. Finally, we show our numerical results and compare our optimal results with those found by exhaustive searches. We conclude that our Algorithm I produces optimal results very close to those found by exhaustive searches. Performance comparison between Algorithms I and II is also provided in terms of the AEP and the probability of missing detection. Copyright © 2012 John Wiley & Sons, Ltd.

In this study, the authors investigate the optimal sensing settings that can maximise the throughput of the cognitive radio (CR) users under the constraint that the signals from the primary users (PUs) are sufficiently protected. They focus on the throughput at the data link layer where end-to-end delivery of data packets is considered. Consequently, the throughput is defined as the rate at which correct data are received. They reconsider the tradeoff between the sensing settings and the throughput. They also separately perform optimisation on the throughput when cooperative spectrum sensing (CSS) is/is not used. In order to evaluate the throughput, they further derive the exact symbol-error-rate (SER) expressions in the presence of co-channel interference. After proving that the throughput functions are unimodal, they proposed two efficient and effective algorithms that can derive the optimal settings for maximising the throughput. Finally, the authors show that their numerical results and compare optimal results with those found by exhaustive searches. They conclude that their algorithms produce optimal results very close to those found by exhaustive searches.

Transmission error because of fading in the cognitive radio–fusion centre (CR–FC) links can severely degrade the performance of cooperative spectrum sensing. In this study, the upper and lower bounds of the overall false alarm probability and overall detection probability are derived as functions of the bit-error probabilities (BERs) of the CR–FC links. Based on these bounds, the constraints that the BERs of the CR–FC links should satisfy are addressed given the target overall false alarm probability or overall detection probability. Furthermore, channel coding schemes and cooperative schemes that provide reliable transmissions in the CR–FC links are studied. Particularly, inspired by the cluster-based cooperative spectrum sensing, a multi-user cooperative scheme is proposed. Finally, the relationship between the overall detection probability and the overall false alarm probability is investigated when the SNR of the primary user signal at each CR node is small.

Turbo (iterative) decoding can be implemented with a large family of soft-input soft-output (SISO) algorithms, including suboptimal but practical algorithms such as the soft-output Viterbi algorithm (SOVA) and max-log-MAP algorithm. The performance with these practical algorithms can be improved with simple scaling factor methods. However, their theoretical analysis was mainly based on the relaxed assumption proposed by Papke et al. that the extrinsic information is Gaussian distributed. This study proposes a novel scaling factor approach for reducing both the overestimation of reliability values and the correlation between the intrinsic and extrinsic information. Explicit formulae for computing the scaling factors are derived based on mathematical statistics. A key difference compared to the scaling factor method of Papke et al. is that the proposed scaling factors can be computed off-line. The numerical results show that when implemented in the decoding algorithm of block component codes, the proposed scaling factor approach improves the performance of turbo decoding over additive white Gaussian noise and Rayleigh fading channels. It is superior than the method by Papke et al. in both performance and complexity.

Optimal transmit/receive diversity (TRD) is one of the most important configurations for wireless multiple-input multiple-output (MIMO) systems, due to its good performance and ease of implementation. Though investigated intensively, the performance of optimal TRD in general correlated fading with cochannel interference is still not well understood. Since the optimal TRD's output instantaneous signal-to-interference-plus-noise ratio (SINR) is equal to the largest sample eigenvalue of a quadratic form involving signal and interference channel matrices, directly determining the probability density function (pdf) of this eigenvalue has been a prevailing approach in the literature. Given the nonlinearity involved in the quadratic form, however, finding such a pdf is not simple except for some special channel conditions. In this paper, we formulate the problem, in a totally different framework, as testing the positive-definiteness of a random matrix whereby the theory of matrix-variate distributions can be invoked to obtain exact solutions in terms of special functions. The solutions are very general including most of existing results as a special case and allowing for the correlation structures of both signal and interferers to be arbitrary at both transmitter and receiver ends. Numerical results are presented to validate the theoretical analysis.

Dual-hop transmission systems employing fixed-gain amplify-and-forward (AF) relaying have been studied recently over Nakagami fading channels. These analyses, however, either have imposed certain constraints on the fading parameters or have not been totally accurate when evaluating the diversity order of the systems. In this letter, we will develop a methodology for evaluating the diversity order of such systems. The methodology can be easily extended to analyze fixed-gain AF relaying with multiple relays.

This paper investigates the diversity performance of wireless relay networks with multiple parallel relays communicating with the destination over orthogonal channels. The networks under consideration employ two signal-to-noise ratio (SNR) thresholds and multiple hard-decision detections (HDD) at the destination. One SNR threshold is used to select transmitting relays in the second phase: a relay retransmits to the destination if its received SNR is larger than the threshold, otherwise, it remains silent. The other threshold is used at the destination for detection: the destination makes a hard decision on the received signal from a relay if its SNR is higher than the threshold, otherwise, the destination makes an erasure decision. Then the destination simply combines all the hard-decision results and makes the final binary decision based on majority voting. Focusing on the decode-and-forward (DF) relaying protocol, the paper derives the end-to-end bit error and outage probabilities, and presents the diversity analysis of the proposed method. It is shown that the full diversity order can be achieved by setting appropriate thresholds even when the destination does not know the exact or average SNRs of the source-relay links. The diversity analysis is further extended to multi-hop cooperation and/or with the presence of a direct link where multiple thresholds are needed.

Cooperative communications has been recognised as an effective technique to combat multi-path fading impairment and to provide additional diversity advantage for small-size and low-power-consumption mobile terminals. A class of decode-and-forward (DF) relaying serial cooperative communications, in which each node is assumed to be able to determine whether the received signals can be successfully decoded or not, has recently been proposed and analysed over Rayleigh fading channels. Since the Nakagami fading channels represent a wide variety of realistic channels, such serial cooperative networks should be investigated over such channels before putting into real applications. In this paper, we analyse the performance of such serial cooperative transmission systems thoroughly over dissimilar Nakagami fading channels. We derive a closed-form symbol-error-rate expression for the case of M-ary phase shift keying (PSK) modulation. Moreover, we evaluate the system diversity property and investigate the achievable diversity order under two specific channel conditions. Finally, we perform simulations to verify the theoretical findings.

This letter presents a new look at the problem of energy detection with and without diversity schemes. The impact of channel fading and/or diversity scheme on the probability of missing detection is quantified and then the definition, sensing gain, is proposed based on the analytical result. The sensing gain proposed in this letter determines the slope of the probability of missing detection versus average signal-to-noise ratio (SNR) curve, at high SNR, in a log-log scale. Our result shows that the sensing gain just has a relationship with the type of channel fading and/or diversity scheme and is totally irrelevant with the false alarm probability which is preset.

We analyze the performance of cooperative communication systems with opportunistic decode-and-forward for relaying and selection combining receiver at the destination. We derive an exact closed-form expression for the outage of the system over dissimilar Nakagami fading channels. Also, we study its asymptotic outage performance, based on which the optimum power allocations for the source and the relays are determined. Finally, we verify the theoretical results by simulations.

We analyze the performance of cooperative communication systems with opportunistic decode-and-forward for relaying and selection combining receiver at the destination. We derive an exact closed-form expression for the outage of the system over dissimilar Nakagami fading channels. Also, we study its asymptotic outage performance, based on which the optimum power allocations for the source and the relays are determined. Finally, we verify the theoretical results by simulations.

We analyze a serial cooperative transmission system with DF relaying over Nakagami fading channels. We consider a system in which the simple receivers will not estimate the amplitude of the received signals. Hence, signals are combined with equal gain before decoding. Moreover, the relays use a simple protocol when relaying the messages — they re-transmit the message if they can decode the received message correctly; otherwise, they do not transmit anything and remain idle. We will derive an exact expression for the asymptotic symbol error rate of the system and evaluate the diversity properties.

In this paper, we investigate the orthogonal space-time block codes communication systems with various M-ary modulation schemes over independent identically distributed (i.i.d) Nakagami-q (Hoyt) fading channels. We derive exact closed-form expressions of the system performances in terms of symbol error rate (SER). These expressions are composed of Lauricella's multivariate hypergeometric functions, which are easily evaluated numerically.

The performances of orthogonal space–time block codes (OSTBCs) over Rician–Nakagami channels are investigated. In particular, we derive closed-form symbol error probability (SEP) expressions for OSTBC systems in which M-ary phase-shift-keying modulation and M-ary quadrature-amplitude modulation are used. These SEP results are expressed in terms of Lauricella's multivariate hypergeometric functions, which can be easily evaluated numerically. When the Rician–Nakagami channel degenerates to the Rician–Rayleigh channel, or equivalently the Rayleigh fading channel, the closed-form SEP expressions are rewritten in terms of higher transcendental functions, that is, Gauss hypergeometric function and Appell hypergeometric function.

Optimum combining (OC) is a powerful means for combatting co-channel interference. Its performance, however, is difficult to analyze. The prevailing methodology in current use is to neglect the influence of additive white Gaussian noise (AWGN). Inclusion of AWGN into the analysis usually leads to mathematical intractability, except for some extreme cases. In this letter, we formulate the problem in the framework of hypergeometric functions, so that their good properties can be exploited to enable the analysis to account for the influence of AWGN and co-channel interference simultaneously. We obtain closed-form solutions to the characteristic function (CHF) of the signal-to-interference-plus-noise ratio at the OC output for three important operational scenarios in Rayleigh fading, although the general solution still needs further effort to simplify. The assumptions made here are that both signal and interferers suffer from Rayleigh fading, and the number of interferers is not less than the number of antennas. The use of resulting CHF formulas is illustrated through their application to the bit-error and outage performance evaluation of OC.

The exact performance analysis for optimum combining of faded signals is a difficult problem in the presence of both interferers and noise. This letter derives exact closed-form expressions for the probability density function and outage probability of output signal-to-interference-plus-noise ratio with a Rayleigh fading signal in the presence of additive noise and correlated equal-power Rayleigh interferers. These exact expressions are expressed in form of a determinant with entries of scalar variate hypergeometric functions.

It was suggested by Battail that a good long linear code should have a weight distribution close to that of random coding, rather than a large minimum distance, and a turbo code should be also designed using a random-like criterion. In this paper, we first show that the weight distribution of a high-rate linear block code is approximately Gaussian if the code rate is close enough to one, and then proceed to construct a low-rate linear block code with approximately Gaussian weight distribution by using the turbo-coding technique. We give a sufficient condition under which the weight distribution of multicomponent turbo block (MCTB) codes (multicomponent product (MCP) codes, respectively) can approach asymptotically that of random codes, and further develop two classes of MCTB codes (MCP codes) satisfying this condition. Simulation results show that MCTB codes (MCP codes) having asymptotically Gaussian weight distribution can asymptotically approach Shannon's capacity limit. MCTB codes based on single parity-check (SPC) codes have a far poorer minimum distance than MCP codes based on SPC codes, but we show by simulation that when the bit-error rate is in the important range of 10/sup -1/-10/sup -5/, these codes can still offer similar performance for the additive white Gaussian noise channel, as long as the code length of the SPC codes is not very short. These facts confirm in a more precise way Battail's inference about the "nonimportance" of the minimum distance for a long code.

We consider the minimum cyclotomic coset representatives and derive some of their properties. The results allow more precise estimates of the dimension of Bose-Chaudhuri-Hocquenghem (BCH) and classical Goppa codes of a given designed minimum distance, and more precise estimates of the true designed distance of BCH codes and the minimum distance of classical Goppa codes.