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This paper investigates distributed cell-free massive multiple-input multiple-output with non-ideal user equipment hardware under spatially correlated channels. By employing the use-and-then-forget technique, a lower capacity bound is derived based on the established generalized UE hardware impairments model. In addition, maximum ratio combining can be used to derive a closed-form expression of the spectral efficiency (SE), which offers novel insights into the impact of non-ideal UE hardware on network performance. Furthermore, a max–min SE fairness problem with UE hardware impairments is established where the optimization variables are data power and large-scale fading decoding (LSFD) vectors. Since this is a non-convex problem, we devise an iterative alternating optimization algorithm based on the bisection search to acquire the globally optimal solution. Numerical results indicate that the recommended joint data power control and LSFD design algorithm provides higher SE for the weakest UE, thus significantly enhancing the total SE of the network. [ABSTRACT FROM AUTHOR]

With the recent advancement of vehicular ad-hoc networks (VANETs) or the internet of vehicles (IoVs), vehicles are getting more powerful and generating huge amount of traffic data, including computation-intensive and delay-sensitive applications in the vehicular edge computing (VEC) networks, which are difficult to be processed by an individual vehicular node. These resource-demanding tasks can be transferred to another vehicular node with idle computing resources for processing. Due to high mobility and limited resources of vehicular nodes, it is challenging to execute lengthy computation-intensive tasks until completion within the delay constraint. There is a need to provide an efficient task offloading strategies to support these applications. In this paper, an efficient distributed task offloading scheme is proposed to select nearby vehicles with idle computing resources, to process the tasks in parallel by considering some vital metrics, including link reliability, distance, available computing resources, and relative velocity. In order to complete the lengthy computation-intensive tasks in vehicular edge computing networks, a task is divided into several subtasks before offloading. The performance of the proposed scheme is evaluated in several VEC network conditions. Results show that the proposed computation task offloading scheme achieves better performance in latency, throughput, resource utilization and packet delivery ratio than the existing schemes. [ABSTRACT FROM AUTHOR]

One objective of this paper is to propose a novel class of sequence pairs, called “quasi-orthogonal Z-complementary pairs (QOZCPs)”, each depicting Z-complementary property for their aperiodic auto-correlation sums and also having a low correlation zone when their aperiodic cross-correlation is considered. Construction of QOZCPs based on Successively Distributed Algorithms under Majorization Minimization (SDAMM) is presented. Another objective of this paper is to apply the proposed QOZCPs in fully polarimetric radar systems and analyse the corresponding ambiguity functions. It turns out that QOZCP waveforms are much more Doppler resilient than the known Golay complementary waveforms. [ABSTRACT FROM AUTHOR]

A mobility-aware dynamic caching optimization problem (MDCP) is modelled for optimal caching when the contents’ popularity may vary over time. The $\mathcal {NP}$ -hardness of MDCP is proved. For the problem's solution, first, by providing a reformulation, the optimum of MDCP can be computed in up to medium-scale system scenarios. In addition, a time-efficient algorithm is developed for large-scale scenarios. The results of performance evaluation are provided. [ABSTRACT FROM AUTHOR]

Caching is an effective way to address the challenges due to explosive data traffic growth and massive device connectivity in fifth-generation (5G) networks. Currently, few works on caching pay attention to the impact of the time duration for which content is stored, called retention time, on caching optimization. The research on retention time is motivated by two practical issues, i.e., flash memory damage and storage rental cost in cloud networks, together giving rise to the storage cost. How to optimize caching contents taking the storage cost into consideration is a challenging problem, especially for the scenarios with cache-enabled mobile nodes. In this paper, a retention-aware caching problem (RACP) in vehicular networks is formulated, considering the impact of the storage cost. The problem’s complexity analysis is provided. For symmetric cases, an optimal dynamic programming (DP) algorithm with polynomial time complexity is derived. For general cases, a low complexity and effective retention aware multi-helper caching algorithm (RAMA) is proposed. Numerical results are used to verify the effectiveness of the algorithms. [ABSTRACT FROM AUTHOR]

This paper considers the co-existence of two important communication techniques, non-orthogonal multiple access (NOMA) and mobile edge computing (MEC). Both NOMA uplink and downlink transmissions are applied to MEC, and analytical results are developed to demonstrate that the use of NOMA can efficiently reduce the latency and energy consumption of MEC offloading. In addition, various asymptotic studies are carried out to reveal the impact of the users’ channel conditions and transmit powers on the application of NOMA to MEC are quite different from those in conventional NOMA scenarios. Computer simulation results are also provided to facilitate the performance evaluation of NOMA-MEC and also verify the accuracy of the developed analytical results. [ABSTRACT FROM AUTHOR]

In this paper, a novel codebook design method for sparse code multiple access (SCMA) is proposed and an analytical framework to evaluate the bit error rate (BER) performance is developed. In particular, to meet the codebook design criteria based on the pairwise error probability, a novel codebook with large minimum Euclidean distance employing the star quadrature amplitude modulation signal constellations is designed. In addition, with the aid of the phase distribution of the presented SCMA constellations, BER of SCMA system over downlink Rayleigh fading channel is obtained in closed-form expression. The simulation and analytical results show that the presented SCMA codebook outperforms the existing codebooks and low-density signature, and the proposed design is more efficient for the SCMA codebook with large size and/or high dimension. Moreover, the derived theoretical BER results match well the simulation results, especially in the high signal-to-noise ratio regimes. [ABSTRACT FROM AUTHOR]

Conventional wireless caching assumes that content can be pushed to local caching infrastructure during off-peak hours in an error-free manner; however, this assumption is not applicable if local caches need to be frequently updated via wireless transmission. This paper investigates a new approach to wireless caching for situations in which the cache content has to be updated during on-peak hours. Two non-orthogonal multiple access (NOMA)-assisted caching strategies are developed, namely, the push-then-deliver strategy and the push-and-deliver strategy. In the push-then-deliver strategy, the NOMA principle is applied to push more content files to the content servers during a short time interval reserved for content pushing during on-peak hours and to provide more connectivity for content delivery, compared with the conventional orthogonal multiple access (OMA) strategy. The push-and-deliver strategy is motivated by the fact that some users’ requests cannot be accommodated locally and the base station has to serve them directly. These events during the content delivery phase are exploited as opportunities for content pushing, which further facilitates the frequent update of the files cached at the content servers. It is also shown that this strategy can be straightforwardly extended to device-to-device caching, and various analytical results are developed to illustrate the superiority of the proposed caching strategies compared with OMA based schemes. [ABSTRACT FROM AUTHOR]

This paper investigates distributed MIMO precoding design to maximize the weighted sum rate in a heterogeneous network where the multiple input multiple output full-duplex (MIMO-FD) small cells reuse the downlink spectrum of the macro base-station (BS) to exchange backhaul information. The multi-antenna BS transmits signals to the cellular users using the dirty paper coding technique and the MIMO-FD small cells apply FD precoding structures to effectively balance the received signal, the self-interference (SI), and the co-channel interference (CCI). Since the optimization problem is shown to be nonconvex, obtaining the global optimum is challenging. A low-complexity solution with distributed implementation is introduced with proved convergence. By applying the successive convex approximation technique and the duality between the broadcast channel and the multiple access channel, the original nonconvex problem is decomposed into a sequence of convex subproblems, which can be solved analytically and separately at each small cell and macro BS with limited channel state information exchange. Simulation results confirm the convergence and demonstrate the benefits of the introduced algorithm. It is shown that the SI and CCI can be suppressed effectively with sufficient cancellation power and number of transmit antennas at the FD small cells. [ABSTRACT FROM AUTHOR]

The achievable rate of full-duplex (FD) small-cell systems with massive multiple-input multiple-output (MIMO), in which a low-power base station (BS) equipped with large antenna arrays sends/receives data to and from multiple half-duplex (HD) users at the same time on the same frequency, is investigated. The BS uses imperfect channel state information (CSI) obtained from received pilots, nonideal hardware, and a linear transmitter and receiver, i.e., zero-forcing (ZF) or maximum-ratio transmission/maximum-ratio combining (MRT/MRC), to process the signals. The approximate closed-form expressions of the achievable rate for both the ZF and MRT/MRC processing are derived and used to analyze the effect of the number of antennas and the hardware imperfection on the self-interference (SI), which is a bottleneck of the FD systems. To maximize the spectral efficiency (SE) and the energy efficiency (EE) of this system, two nonconvex power-allocation optimization problems are formulated and solved by utilizing the sequential convex approximation technique and the fractional programming technique. Two iterative algorithms are proposed with proved local convergence. Numerical results illustrate that the analytical approximation of achievable rate matches well with the Monte Carlo simulation. It is also shown that the ZF processing has greater ability to suppress SI, compared with MRT/MRC processing. The proposed power-allocation algorithms are shown to increase the SE and EE significantly, compared with the uniform power-allocation scheme when the BS is equipped with moderately large antenna arrays. [ABSTRACT FROM PUBLISHER]

Energy efficiency (EE) optimization of wireless systems has attracted increasing attention recently due to its beneficial impacts on the environment and operational savings. Max-min user energy-efficient precoding for multicell multiple-input–multiple-output (MIMO) cooperative networks is investigated. The optimization problem is a nonconvex fractional programming problem, and optimal solutions are hard to find. Two different local optimization methods, namely, block coordinate descent and sequential convex approximation, are proposed to transform the original problem into a series of convex subproblems. In the former method, the relationship between the user rate and the minimum mean square error (MMSE) is utilized, and optimization of the transmitter matrix is formulated as a semidefinite program; the latter method is based on the convex approximation of the nonconvex rate function. The fractional subproblem is transformed into a parameterized subtractive form by exploiting the generalized fractional programming theorem in both methods. Two iterative-fairness-based energy-efficient algorithms are proposed with proved local convergence. Numerical results illustrate that the proposed max-min EE algorithms can improve EE with a performance loss in terms of the sum rate at a high signal-to-noise ratio (SNR) and achieve EE fairness among base stations with different transmit power levels. [ABSTRACT FROM PUBLISHER]

Nonorthogonal multiple access (NOMA) represents a paradigm shift from conventional orthogonal multiple-access (MA) concepts and has been recognized as one of the key enabling technologies for fifth-generation mobile networks. In this paper, the impact of user pairing on the performance of two NOMA systems, i.e., NOMA with fixed power allocation (F-NOMA) and cognitive-radio-inspired NOMA (CR-NOMA), is characterized. For F-NOMA, both analytical and numerical results are provided to demonstrate that F-NOMA can offer a larger sum rate than orthogonal MA, and the performance gain of F-NOMA over conventional MA can be further enlarged by selecting users whose channel conditions are more distinctive. For CR-NOMA, the quality of service (QoS) for users with poorer channel conditions can be guaranteed since the transmit power allocated to other users is constrained following the concept of cognitive radio networks. Because of this constraint, CR-NOMA exhibits a different behavior compared with F-NOMA. For example, for the user with the best channel condition, CR-NOMA prefers to pair it with the user with the second best channel condition, whereas the user with the worst channel condition is preferred by F-NOMA. [ABSTRACT FROM AUTHOR]

In this paper, rate and subcarrier bandwidth adaptation (RSBA) on the average spectral efficiency of orthogonal frequency-division multiplexing (OFDM) systems using $M$-ary quadrature amplitude modulation ($M$-QAM) is investigated in the presence of frequency-selective and very rapidly time-varying fading channels. The closed-form expressions for rate and capacity with perfect channel state information (CSI) and imperfect CSI are derived. In this paper, imperfect CSI is caused jointly by channel estimation error and unavoidable delay between when CSI is estimated and when the estimation results are used for actual transmission. The capacity with perfect CSI is just a special case of imperfect CSI. Based on the closed-form expressions of the maximum capacity, optimal RSBA algorithms with perfect and imperfect CSI are proposed, respectively. Theoretical and numerical results show that the RSBA scheme can improve the system performance effectively under the perfect-CSI case. It can make a tradeoff between intercarrier interference (ICI) and transmission efficiency by considering the cyclic prefix. The results also show that the RSBA scheme is effective in repelling the impact of outdated CSI, as well as in reducing the impact of channel estimation error, but to a lesser extent. [ABSTRACT FROM AUTHOR]

The outage performance of a dual-hop mobile ad hoc network (MANET), which employs amplify-and-forward (AF) relaying in a Rayleigh fading environment in the presence of a Poisson field of interferers at the destination, is investigated. All mobile users are assumed to follow the Poisson arrival model along the highway and can only communicate with each other via a stationary base station or a mobile relay station. Under this MANET model, a single-integral expression for the exact outage probability and a tight lower bound are both derived. The impacts of transmitting power, path-loss exponent, and spatial density of interferers on the performance of dual-hop systems are found. It is revealed that the outage probability of each hop, as a function of distance, transmitting power, etc., has a different impact on the end-to-end outage probability. The outage probability floor is derived when the transmission power at the source/relay becomes large. The optimal power allocation for the dual-hop link is obtained. The behavior of the outage probability during the communication process between the moving nodes is investigated. The analytical results are validated with Monte Carlo simulation. [ABSTRACT FROM AUTHOR]

In this paper, a new conditional power and rate adaptation scheme for orthogonal frequency-division multiplexing (OFDM) systems is proposed in the presence of carrier frequency offset (CFO), with perfect and imperfect channel state information (CSI). The conventional adaptive scheme is shown to be a special case of the conditionally adaptive scheme technique that enables the resulting nonconvex optimization problem, which is solved in a feasible way. It leads to a solution for optimal power adaptation that maximizes the spectral efficiency of an OFDM system using $M$-ary quadrature amplitude modulation (MQAM) under average power and instantaneous bit error rate (BER) constraints. Closed-form expressions for the average spectral efficiency (ASE) of adaptive OFDM systems are derived for perfect and imperfect CSI cases. The theoretical results and computer simulations show that range of the conditional adaptation becomes narrow and the performance of constant power and continuous rate is very close to that of the conditionally adaptive power and continuous rate for higher CFO or high signal-to-noise ratio (SNR) values. [ABSTRACT FROM AUTHOR]

Due to frequent handovers in broadband wireless communications for the high-speed railway system, communication interruption caused by handover failures could seriously degrade the users' experience. Aiming at reducing the handover failure probability, this paper proposes an effective handover scheme based on the distributed antenna system (DAS) and mobile-relay-aided two-link architecture, i.e., ground–relay link and relay–onboard link, where the mobile relay is mounted on top of the moving train. In addition, an antenna selection scheme with optimal power allocation is proposed to improve handover performance. Our simulation and analysis results show that the DAS structure with macrodiversity can reduce the unnecessary handovers, as well as reduce the handover failure and link outage probabilities compared with the traditional cell without DAS. In addition, the proposed DAS with an antenna selection scheme performs better in terms of handover failure and link outage probabilities than that of DAS with a equal power allocation (EPA) scheme. [ABSTRACT FROM PUBLISHER]

Abstract: In this paper, a novel simplified iterative decoding scheme based on the so-called joint early detection-early stopping (JEDES) technique, is investigated for short-frame turbo coding applications. The proposed scheme attains a lower complexity than existing schemes by carefully integrating two known techniques: early detection and associated built-in cyclic redundancy check. Our analysis and simulation results show that for a frame size of 49bits, the proposed JEDES scheme can achieve a complexity saving of over 30% with little performance loss at practical bit and frame error rates compared with previous results. For a longer frame size 169, the proposed JEDES scheme can approach the GENIE scheme with nearly the same complexity reduction. [ABSTRACT FROM AUTHOR]

The distribution of the interservice time, which is the interval between the end of a call served and the start of the succedent call served by a portable, is a crucial parameter for modeling and cost analysis for location management in personal communication service (PCS) networks. The interservice time differs from the interarrival time due to the busy-line effect. However, in the literature, most of the cost analyses for location management were carried out by ignoring the busy-line effect, i.e., by identifying the interservice time with the interarrival time, because, so far, there is no analytical result for the interservice time distribution considering the busy-line effect. In this paper, we develop an analytical model to investigate the busy-line effect on the interservice time distribution. Closed-form analytical formulas for the interservice time are derived. A numerical study shows that a big discrepancy exists between the interarrival time and the interservice time. Based on the analytical results for the interservice time, the impact of the busy-line effect on modeling of portable movements in PCS networks is further evaluated. An analytical result for the distribution of the number of cell-boundary crossings during the interservice time is obtained. Both analytical results and numerical examples indicate that the busy-line effect has influence on the distribution of the number of cell-boundary crossings during the interservice time. Therefore, cost analysis for location management without considering the busy-line effect may lead to unreliable results. The results presented in this paper pave the way for modeling location management and portable movements in PCS networks. [ABSTRACT FROM AUTHOR]

Abstract: Generalized Steiner systems were first introduced by Etzion and used to construct optimal constant weight codes over an alphabet of size with minimum Hamming distance , in which each codeword has length and weight . As to the existence of a , a lot of work has been done for , while not so much is known for . The notion GDD was first introduced by Chen et al. and used to construct . The necessary condition for the existence of a is . In this paper, it is proved that there exists a for any prime power and . By using this result, the known results on the existence of optimal quaternary constant weight codes are then extended. [Copyright &y& Elsevier]

In this correspondence, previous work on(P, V, M) code sequences, which are sequences with a zero-correlation zone (ZCZ) that can be used to accurately and efficiently perform channel estimation in multiple-antenna communication systems, are noted. In addition, extensions of ZCZ sequence sets based on perfect sequences, almost-perfect sequences, and perfect arrays are presented. It is shown that those ZCZ sets based on perfect sequences/arrays are optimal with respect to theoretical bounds. [ABSTRACT FROM AUTHOR]

Focuses on a study on the construction of a class of pseudonoise sequences based on Gordon-Mills-Welch sequences. Construction of low correlation zone sequences; Proof of the main theorem on on pseudonoise sequences; Conclusion.

Summary: The orthogonal time frequency space (OTFS) transmission scheme was shown to outperform orthogonal frequency division multiplexing (OFDM) under the doubly dispersive channel. In this paper, the linear precoding is studied for multiple‐input and multiple‐out (MIMO) OTFS systems, in which a spatial‐Doppler domain singular value decomposition (SVD) precoding scheme is proposed. At the transmitter, the Doppler domain symbols from different spatial streams are precoded before projected onto multiple antennas for transmission. At the receiver, multipath components of the transmitted symbols in the delay‐Doppler grid are combined by using maximal ratio combining (MRC) strategy, so as to achieve the multipath diversity gain and increase the reception reliability. The achievable rate and complexity of the proposed scheme are analyzed, revealing that it can increase the achievable rate while reducing the detector complexity as well. The simulation results confirm that the SVD‐based precoding significantly enhances the error performance of the MIMO‐OTFS with MRC‐based detector. [ABSTRACT FROM AUTHOR]

Summary: The exponential growth of various applications requires deploying an ever‐growing number of network services. A generalized service deployment framework for Open Shortest Path First (OSPF) networks is proposed in this paper. The framework includes placing programmable routers, distributing different types of services on these routers, and leading traffic flow through them according to the predetermined sequence order requirement. However, it is not possible to direct all the traffic flows through the required service nodes along the shortest path with a single and suitable set of link weights. To address the issue, multiple topology routing (MTR) technique is incorporated to have various logical topologies with multiple sets of link weights. Correspondingly, the problem of jointly optimizing Placement of programmable routers, Distribution of different types of services among these routers, and Link Weights setting based on MTR (shortened to PD‐LW‐MTR) and its mixed integer linear programming formulation are presented in this paper. A novel decomposition algorithm is also proposed to address this problem efficiently. Experiment results validate the correctness and feasibility of our algorithm. It is also shown that the optimization algorithm can obtain near‐optimal solution and just only a few logical topologies over multiple sets of link weights are necessary for traffic flows to guarantee service order requirements. [ABSTRACT FROM AUTHOR]

In this article, we revisit the problem of how to provide “native” IP multicast support to enterprise distributed applications in today's clouds, without touching either the application implementation or the underlying network hardware. We propose SDM, Software-Defined IP Multicast, to explore the idea of performing Multicast-to-Unicast (M2U) and Unicast-to-Multicast (U2M) translations at the virtualized network edge. At the data plane, with novel architecture designs, SDM achieves efficient M2U and U2M translations by only using Open vSwitch (OVS), an OpenFlow-compatible open-source software switch widely deployed in modern clouds. At the control plane, SDM dynamically adopts multicast trees respecting the join and leave of receivers with flexible cost-based algorithms. SDM is very easy to deploy and use, as its required features are already supported by off-the-shelf OVS software (version 2 2.3) and the OpenFlow protocol (version 2 1.1). Performance evaluations of its control-plane algorithms also imply that SDM is flexible to construct through-put and latency/height optimized multicast trees respecting task requirements. [ABSTRACT FROM AUTHOR]

In this paper, the existing ad hoc on demand multipath distance vector (AOMDV) routing scheme for vehicular ad hoc networks (VANETs) is extended to a reliable low-latency multipath routing (RLLMR) scheme based on multipath link reliability, capable of determining the reliable routes preemptively. Here, the link reliability refers to the probability that a direct transmission link among any two vehicles remains constantly available for a specific period of time, which can be computed based on the position, route, and velocity of the vehicles to facilitate the reliable routing process in VANETs. In the proposed RLLMR scheme, the mathematical distribution of vehicles movements and link breakages is also considered to increase the reliability of the vehicular networks. The simulation results show that proposed RLLMR scheme performs better compared to existing schemes in terms of latency, reliability, throughput, and energy consumption at the cost of marginally increased routing overhead. [ABSTRACT FROM AUTHOR]

This paper considers a challenging communication scenario, in which users have heterogenous mobility profiles, e.g., some users are moving at high speeds and some users are static. A new non-orthogonal multiple-access (NOMA) transmission protocol that incorporates orthogonal time frequency space (OTFS) modulation is proposed. Thereby, users with different mobility profiles are grouped together for the implementation of NOMA. The proposed OTFS-NOMA protocol is shown to be applicable to both uplink and downlink transmission, where sophisticated transmit and receive strategies are developed to remove inter-symbol interference and harvest both multi-path and multi-user diversity. Analytical results demonstrate that both the high-mobility and the low-mobility users benefit from the application of OTFS-NOMA. In particular, the use of NOMA allows the spreading of the high-mobility users’ signals over a large amount of time-frequency resources, which enhances the OTFS resolution and improves the detection reliability. In addition, OTFS-NOMA ensures that low-mobility users have access to bandwidth resources which in conventional OTFS-orthogonal multiple access (OTFS-OMA) would be solely occupied by the high-mobility users. Thus, OTFS-NOMA improves the spectral efficiency and reduces latency. [ABSTRACT FROM AUTHOR]

Grant-free transmission is an important feature to be supported by future wireless networks since it reduces the signaling overhead caused by conventional grant-based schemes. However, for grant-free transmission, the number of users admitted to the same channel is not capped, which can lead to a failure of multi-user detection. This paper proposes non-orthogonal multiple-access (NOMA) assisted semi-grant-free (SGF) transmission, which is a compromise between grant-free and grant-based schemes. In particular, instead of reserving channels either for grant-based users or grant-free users, the focus here is on an SGF communication scenario, where users are admitted to the same channel via a combination of grant-based and grant-free protocols. As a result, a channel reserved by a grant-based user can be shared by grant-free users, which improves both connectivity and spectral efficiency. Two NOMA assisted SGF contention control mechanisms are developed to ensure that, with a small amount of signaling overhead, the number of admitted grant-free users is carefully controlled and the interference from the grant-free users to the grant-based users is effectively suppressed. Analytical results are provided to demonstrate that the two proposed SGF mechanisms employing different successive interference cancelation decoding orders are applicable to different practical network scenarios. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the outage performance of hybrid automatic repeat request with chase combining (HARQ-CC) assisted downlink non-orthogonal multiple access (NOMA) systems. A closed-form expression of the individual outage probability and the diversity gain are obtained firstly. Based on the developed analytical outage probability, a tradeoff between the minimum number of retransmissions and the transmit power allocation coefficient is then provided for a given target rate. The provided simulation results demonstrate the accuracy of the developed analytical results. Moreover, it is shown that NOMA combined with the HARQ-CC can achieve a significant advantage when only average channel state information is known at the transmitter. Particularly, the performance of the user with less transmit power in NOMA systems can be efficiently improved by utilizing HARQ-CC. [ABSTRACT FROM AUTHOR]

Abstract: An explicit expression is derived for the symbol error rate (SER) of the star MQAM system considered by Ioannis and Aris [Closed-form SER expressions for star MQAM in frequency non-selective Rician and Nakagami-m channels. Int J Electron Commun AEU 2005;59:417–20]. [Copyright &y& Elsevier]

Comments on the article `On the Minimization of Overhead in Channel Impulse Response Measurement.' Description on the article; Response of the authors to the commentary.

The optimum designs of multihop networks operating in an interference-limited environment are studied in this paper. The objective is to identify the optimum operation parameters that can maximize the end-to-end throughput of a multihop link in the network. The optimum designs are performed with respect to two parameters, the number of hops, and the signal-to-interference ratio (SIR) threshold for successful transmission. Under a fixed total transmission power, more hops means shorter distance for each hop, but also less power per hop and longer delays. A higher SIR threshold can achieve a higher throughput by employing high-order modulations, but at the cost of a higher outage probability. We capture these tradeoff relationships by deriving the throughput, which is expressed as an explicit function of a number of system parameters. It is shown through theoretical analysis that the throughput is quasi-concave in the number of hops or the SIR threshold, and the optimum design parameters that can maximize the throughput are obtained analytically and verified through simulations. [ABSTRACT FROM AUTHOR]

The performance of $L$- branch scan-and-wait combining (SWC) reception systems over arbitrarily correlated and not necessarily identically distributed Nakagami- $m$ fading channels is analyzed and evaluated. First, a fast convergent infinite series representation for the SWC output signal-to-noise ratio (SNR) is presented. This expression is used to obtain analytical expressions in the form of infinite series for the average error probability performance of various modulation schemes for integer values of $m$ as well as the average number of paths estimation and the average waiting time (AWT) of $L$-branch SWC receivers for arbitrary values of $m$. The numerically obtained results have shown that the performance expressions converge very fast to their exact analytical values. It was found that the convergence speed depends on the correlation and operating SNR values as well as the Nakagami $m$- parameter. In addition to the analytical results, complementary computer simulated performance evaluation results have been obtained by means of Monte Carlo error counting techniques. The match between these two sets of results has verified the accuracy of the proposed mathematical analysis. Furthermore, it is revealed that, at the expense of a negligible AWT, the average error probability performance of SWC receivers is always superior to that of switch-and-examine combining receivers and, in certain cases, to that of maximal-ratio combining receivers. [ABSTRACT FROM PUBLISHER]

In a cellular network, the network coverage is partitioned into nonoverlapping areas called registration areas to facilitate location management (LM) that keeps track of the location of a user equipment (UE) unit. In the second-generation Global System for Mobile Communications (GSM) and the third-generation Universal Mobile Telecommunications System (UMTS), a registration area is called a location area (LA) in the circuit-switched domain or a routing area (RA) in the packet-switched domain. In the fourth-generation Long-Term Evolution (LTE), a registration area is called a tracking area (TA). To tackle the drawbacks of the LA/RA-based LM scheme used in GSM and UMTS, which is intrinsically a static scheme, LTE adopts a dynamic LM scheme called a TA list (TAL)-based scheme. Under the TAL-based scheme, the network allocates to a UE unit a group of TAs referred to as a TAL instead of only a single TA. The UE can move freely within the allocated TAL without performing any location updates that are called TA updates (TAUs) in LTE. Only when moving into a TA that is not included in the allocated TAL does the UE need to perform a TAU, and afterward, the network will allocate, to the UE, a new TAL. The performance of the TAL-based scheme relies on the allocated TAL. If the allocated TAL is inappropriate with respect to the UE's mobility and traffic characteristics, the TAL-based scheme may produce adverse effects. To find an optimal TAL allocation method for global UE units that exhibit weak regularity in their mobility, this paper develops an embedded Markov chain approach to analyze the signaling cost of the TAL-based scheme. This paper distinguishes itself from existing studies in the following aspects. First, this paper follows LTE technical specifications, that is, the number of TAs in a TAL can vary and, furthermore, is upper bounded, whereas existing studies partially or completely ignore this stipulation. Second, this paper emphasizes the impact of a call handling model that dictates whether a TAU occurs after the completion of a call by considering two call handling models, i.e., a call plus location update and a call without location update. Third, as for the dependence among the cell residence time, the TA residence time, and the TAL residence time, this paper proposes the use of a fluid flow model to describe this dependence, which is simple but does not compromise accuracy. Analytical formulas for the total signaling cost of the TAL-based scheme due to TAU and paging operations, as well as formulas that are useful in designing an optimal paging scheme, are derived, and their accuracy is validated through Mont Carlo simulation. Then, numerical studies are carried out to investigate the impact of diverse parameters on the signaling cost, revealing that the network can allocate, to a UE unit, an optimal TAL that is consistent with the UE's mobility and traffic characteristics to minimize the signaling cost of the TAL-based scheme. [ABSTRACT FROM AUTHOR]

The optimum designs of linear multihop networks that can minimize the end-to-end transmission delays are studied in this paper. In multihop networks, more hops mean a shorter transmission distance per hop but more overheads; thus, it is critical to identify the optimum number of hops that can minimize the end-to-end delay. Two network configurations are considered: one with deterministic equidistant relays and the other with random relays uniformly distributed between the source and destination. The average end-to-end delays of both networks operating in the presence of noise and/or interference are expressed as functions of a number of system parameters, such as channel propagations, noise, interference, protocol overhead, and the geometric distributions of the relays. Based on the analytical results, the optimum number of hops for various system configurations is obtained. It is shown that networks with equidistant relays can achieve a shorter end-to-end delay than those with uniformly distributed relays. [ABSTRACT FROM AUTHOR]

GSM-R is predicted to be obsoletd by 2030, and a suitable successor is needed. Defined by the International Union of Railways, the Future Railway Mobile Communication System (FRMCS) contains many future use cases with strict requirements. These use cases should ensure regular communication not only in network coverage but also in uncovered scenarios. There is still a lack of standards on off-network communication in FRMCS, so this article focuses on off-network communication and intends to provide reference and direction for standardization. We first provide a comprehensive summary and analysis of off-network use cases in FRMCS. Then we give an overview of existing technologies (GSM-R, TETRA, DMR, LTE-V2X, and NR-V2X) that may support off-network communication. In addition, we simulate and evaluate the performance of existing technologies. Simulation results show that it is possible to satisfy the off-network communication requirements in FRMCS with enhancements based on LTE-V2X or NR-V2X. Finally, we give some future research directions to provide insights for industry and academia. [ABSTRACT FROM AUTHOR]

In this paper, we consider underlay cognitive radio (CR) networks with one primary receiver, one cognitive transmitter–receiver pair, and one energy harvesting relay. The transmission power of the secondary source is opportunistically determined by its interference to the primary receiver, and the relay transmission is powered by the energy harvested from the radio-frequency observations at the relay. For the considered CR networks with simultaneous wireless information and power transfer (SWIPT), we derive analytical expressions for the outage probability, as well as their high signal-to-noise ratio (SNR) approximations in closed form. The developed analytical results demonstrate that the use of SWIPT will not cause any loss in diversity gain, but the outage probability achieved by the SWIPT-CR scheme asymptotically decays as \log \mboxSNR/\mboxSNR, whereas a decaying rate of \mbox1/\mboxSNR is achieved by a conventional CR network. Computer simulation results are also provided to demonstrate the accuracy of the presented analysis. [ABSTRACT FROM AUTHOR]

In this paper, a downlink single-cell non-orthogonal multiple access (NOMA) network with uniformly deployed users is considered and an analytical framework to evaluate its performance is developed. Particularly, the performance of NOMA is studied by assuming two types of partial channel state information (CSI). For the first one, which is based on imperfect CSI, we present a simple closed-form approximation for the outage probability and the average sum rate, as well as their high signal-to-noise ratio (SNR) expressions. For the second type of CSI, which is based on second order statistics (SOS), we derive a closed-form expression for the outage probability and an approximate expression for the average sum rate for the special case two users. For the addressed scenario with the two types of partial CSI, the results demonstrate that NOMA can achieve superior performance compared to the traditional orthogonal multiple access (OMA). Moreover, SOS-based NOMA always achieves better performance than that with imperfect CSI, while it can achieve similar performance to the NOMA with perfect CSI at the low SNR region. The provided numerical results confirm that the derived expressions for the outage probability and the average sum rate match well with the Monte Carlo simulations. [ABSTRACT FROM AUTHOR]

In this paper, we consider a cloud radio access networks (C-RANs) in which base stations (BSs) are uniformly distributed inside a disk. The outage probability and the ergodic rate achieved by these C-RANs are analyzed, where stochastic geometry is used to capture the randomness of BS locations. Compared with existing studies to C-RANs, more accurate analytical results are developed by applying the Gauss–Chebyshev integration, as confirmed by our simulation results. [ABSTRACT FROM PUBLISHER]

The dual-function radar communication (DFRC) is an essential technology in Internet of Vehicles (IoV). Consider that the road-side unit (RSU) employs the DFRC signals to sense the vehicles’ position state information (PSI), and communicates with the vehicles based on PSI. The objective of this paper is to minimize the maximum communication delay among all vehicles by considering the estimation accuracy constraint of the vehicles’ PSI and the transmit power constraint of RSU. By leveraging convex optimization theory, two iterative power allocation algorithms are proposed with different complexities and applicable scenarios. Simulation results indicate that the proposed power allocation algorithm converges and can significantly reduce the maximum transmit delay among vehicles compared with other schemes. [ABSTRACT FROM AUTHOR]

SUMMARY: In this paper, resource allocation problem in orthogonal frequency division multiple access‐based cognitive radio (CR) systems to maintain minimum transmission rate constraints of CR users (CRUs) with the specified interference thresholds is investigated. Firstly, a single primary user (PU) CR system is considered, and a suboptimal resource allocation algorithm to maximize the sum transmission rate of all CRUs is proposed. Secondly, the single‐PU scenario is extended to multiple‐PU case, and an asymptotically optimal resource allocation algorithm is proposed using dual methods subject to constraints on both interference thresholds of PUs and total transmit power of all CRUs. Analysis and numerical results show that, in contrast to classical resource allocation algorithms, the proposed algorithm can achieve higher transmission rate and guarantee each CRU's minimum transmission rate in both scenarios. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Quasi-complementary sequence sets (QCSSs) can be seen as a generalized version of complete complementary codes (CCCs), which enables multicarrier communication systems to support more users. The contribution of this work is two-fold. First, we propose a systematic construction of Florentine rectangles. Secondly, we propose several sets of CCCs and QCSSs, using Florentine rectangles. The CCCs and QCSSs are constructed over $\mathbb {Z}_{N}$ , where $N\geq 2$ is any integer. The cross-correlation magnitude of any two of the constructed CCCs is upper bounded by $N$. By combining the proposed CCCs, we propose asymptotically optimal and near-optimal QCSSs with new parameters. [ABSTRACT FROM AUTHOR]

In this paper, we develop an approach of embedded Markov chain to analyze the signaling cost of a movement-based location management (MBLM) scheme. This approach distinguishes itself from those developed in the literature in the following aspects. 1) It considers the location area (LA) architecture used by personal communication service (PCS) networks for location management. 2) It considers two different call handling models that determine after a call whether a location update should be performed. 3) It considers the effect of the call holding time on the call handling models. 4) It proposes to use a fluid flow model to describe the dependence between the cell and the LA residence time. We derive closed-form analytical formulas for the signaling cost, whose accuracy is manifested by a simulation. Based on the analytical formulas, we conduct a numerical study to evaluate the influence of various parameters on the signaling cost. The formulas can contribute to the implementation of the MBLM scheme in PCS networks including Fourth-Generation (4G) Long-Term Evolution. The modeling approach developed in this paper can be exploited to model other location management schemes. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate the user fairness power allocation (PA) for video transmission in a non-orthogonal multiple access (NOMA)-assisted wireless system with a pair of users. Considering that video transmission is usually delay-sensitive, the video quality can be adaptively adjusted based on the network conditions. First, a new performance metric, called the average video quality degradation probability, is proposed to describe the adaptive video quality. Then, based on the principles of NOMA and user queue model, the average video quality degradation probability of both users is derived. Next, a bisection search based power allocation (PA) algorithm is proposed to balance the video quality between the NOMA pair. Simulation results demonstrate that the proposed NOMA scheme is more effective to achieve the user fairness compared with the fixed NOMA scheme, the fractional transmit power allocation (FTPA) based NOMA scheme, the achievable rate fairness (ARF) NOMA scheme, and the optimized time division multiple access (TDMA) scheme. [ABSTRACT FROM AUTHOR]

Abstract: Phishing attack is growing significantly each year and is considered as one of the most dangerous threats in the Internet which may cause people to lose confidence in e-commerce. In this paper, we present a heuristic method to determine whether a webpage is a legitimate or a phishing page. This scheme could detect new phishing pages which black list based anti-phishing tools could not. We first convert a web page into 12 features which are well selected based on the existing normal and fishing pages. A training set of web pages including normal and fishing pages are then input for a support vector machine to do training. A testing set is finally fed into the trained model to do the testing. Compared to the existing methods, the experimental results show that the proposed phishing detector can achieve the high accuracy rate with relatively low false positive and low false negative rates. [Copyright &y& Elsevier]

Variable-weight optical orthogonal code (OOC) was introduced by Yang for multimedia optical CDMA systems with multiple quality of service (QoS) requirements. In this paper, four general constructions for optimal cyclic packings and optimal variable-weight OOCs are presented. Many new infinite classes of optimal (v, W,1,Q)-OOCs are obtained. New infinite classes of optimal (v, W,1,Q)-OOCs for \vert W\vert \geq 4 are easily obtained by the constructions. [ABSTRACT FROM AUTHOR]

Abstract: Radio frequency identification is a contactless, low power, and low cost wireless communication technology. Like barcode, it can be stuck to a product, animal, instrument and etc.; there are lots of applications being used practically in the real world. During communication, all tags and reader are shared with the same communication channel. The tag collision arbitration is a significant issue for reducing the communication overhead during tag identification. In this paper, we propose a fast tag identification algorithm named as Enhanced Anti-collision Algorithm (EAA). EAA uses counter and stack to reduce tag collisions efficiently. Compared to other existing methods, our method not only uses fewer timeslots but reduce the length of a timeslot for identifying tags. [Copyright &y& Elsevier]

Abstract: In this paper, we proposed a modified turbulent particle swarm optimization (named MTPSO) model for solving planar graph coloring problem based on particle swarm optimization. The proposed model is consisting of the walking one strategy, assessment strategy and turbulent strategy. The proposed MTPSO model can solve the planar graph coloring problem using four-colors more efficiently and accurately. Compared to the results shown in , not only the experimental results of the proposed model can get smaller average iterations but can get higher correction coloring rate when the number of nodes is greater than 30. [ABSTRACT FROM AUTHOR]