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Vehicle tracking is one of the important applications of the wireless sensor network (WSN), and sensor scheduling is essential in WSN for achieving an efficient tracking process. Traditional centralized sensor scheduling frameworks cannot meet real-time requirements of vehicle tracking in WSN, because of task overloading caused by limited resource consumption and communication bandwidth. To solve this problem, this letter proposes a multiagent distributed sensor scheduling framework in WSN. This letter first proposes a preactivation-based vehicle tracking model to preactive some sensors in order to reduce unnecessary resource consumption. Then, this letter develops a fully decentralized multiagent reinforcement learning (FDMARL) algorithm to design our multiagent sensor scheduling framework. The simulation results show the convergence and the superiority of our proposed FDMARL-aided sensor scheduling algorithm.

The collision channel without feedback (CCw/oFB) introduced by Massey and Mathys, depicts a scenario where multiple users share a communication channel but have arbitrary time offsets, and can never learn these time offsets due to the lack of feedback. This paper considers an extension of the CCw/oFB, which allows the receiver to use successive interference cancellation (SIC) to cancel the interference caused by those collided packets whose contents have been known by the receiver. We derive the zero-packet-loss throughput regions of this model for both the unsynchronized and slot-synchronized cases. Given an arbitrary number of users and a packet alphabet of arbitrary size, it is shown that these two regions coincide, and the outer boundary of this common region is the set of all points with only nonnegative components that add up to one. It is further shown that all points on this outer boundary with only rational components can be achieved without packet loss in the slot-synchronized case. The constructive proofs are based on a joint design of protocol sequences, identification/location algorithm and erasure correcting codes. These findings indicate that the negative impact of the lack of time synchronization on the throughput performance can be removed by the help of SIC.

Performance optimization of the inter-satellite link is the key to improve the performance of satellite networks. This article proposes a dynamic power allocation method for the inter-satellite link of Low Earth Orbit (LEO)/Medium Earth Orbit (MEO) satellites based on the computing power of LEO satellites. A utility function is designed according to the transmission characteristic of the inter-satellite link. The existence of the Nash Equilibrium (NE) of the utility function is proved based on the super-modular game theory. The LEO satellite obtains its balanced solution of the transmission power through the Newton iteration method. In this process, based on the initial orbit parameters of the satellite and the satellite operating time, the inter-satellite link distance is predicted through the spherical geometric relationship between the LEO/MEO satellites, so that the signal-to-interference and noise ratio (SINR) can be estimated in advance. The MEO satellite controls the penalty factor to enhance the utility of the entire network. Simulation results show that the proposed power allocation method achieves the purpose of saving power resources while improving system performance.

A multichannel conflict-avoiding code of length $L$ and weight $w$ for $M$ orthogonal channels, denoted by MC-CAC(M, L, w), is used for deterministic multiple-access without feedback. When the number of simultaneously active users is less than or equal to w, an MC-CAC(M, L, w) is able to provide a hard guarantee that each active user has a successful transmission within every consecutive $L$ time slots. An upper bound on the number of potential users, or codewords, that an MC-CAC(2, L, 3) can support is derived in this paper. By means of (hooked) Skolem sequences, we propose a new construction that can provide a series of optimal MC-CAC(2, L, 3)s in the sense that the code sizes achieve the obtained upper bounds.

Small World Effect (or Six Degrees of Separation theory) has generated significant influence in the world. Many researchers and institutes have done lots of work on the study of it. We model Small World Effect by random process and Graph, calculate the probability that any two people i and j in the world can contact each other after n steps (forwarding messages by intermediaries) based on different R (average number of acquaintances everyone has in the world).When R=50 or 80, if n≥5, the probability is 0.848 and the search is very likely to happen. When R=150, n=4, this probability is 0.99994, that is, after 4 steps, any two people in the world will establish connection almost surely. In the sense of Dunbar's number (R=150), six degrees of separation becomes four degrees of separation. We propose the concepts of (directed) Random Fuzzy Graph for the very first time which can describe the fact of recognition among people best, because the relation among persons is random and fuzzy.

This paper considers a multiple-access system with multiple-packet reception (MPR) capability $\gamma $ , i.e., a packet can be successfully received as long as it overlaps with $\gamma -1$ or fewer other packets at any instant during its lifetime. To efficiently utilize the MPR capability, this paper generalizes $p$ -persistent carrier-sense multiple access (CSMA) to consider that a user with carrier sensing capability $c$ adopts the transmission probability $p_{n}$ if this user has sensed $n$ ongoing transmissions for $n=0,1,\ldots ,c-1$ . This paper aims to model the characteristics of such CSMA and to design transmission probabilities for achieving maximum saturation throughput. To this end, we first formulate such CSMA as a parameterized Markov decision process (MDP) and use the long-run average performance to evaluate the saturation throughput. Second, by observing that the exact values of optimal transmission probabilities are in general infeasible to find, we modify this MDP to establish an upper bound on the maximum throughput, and modify this MDP again to propose a heuristic design with near-optimal performance. Simulations with respect to a wide range of configurations are provided to validate our study. The throughput performance under more general models and the robustness of our design are also investigated.

This letter proposes a new feedback-free solution that can put collisions to good use for decoding among asynchronous transmitters. Our key idea is to jointly exploit physical-layer network coding that allows a receiver to extract the bitwise XOR information out of time-overlapping signals, and a protocol-sequence-based scheme that allows each transmitter to deterministically determine which and when source packets contribute to the transmitted signal. In the application of group-based event detection, our design enables all source packets from asynchronous transmitters to be decoded within a quite short time duration. Simulation results show that our design, with low energy consumption, outperforms both conventional and state-of-the-art schemes in terms of the worst-case detecting delay.

This paper considers random access in a communication channel, which is shared by $N$ active users with saturated traffic. Following a slotted ALOHA-type protocol, each active user attempts to transmit in every slot with a common probability. It is assumed that the channel has the multiple-packet reception capability to enable the correct reception of up to $M$ ( $1 \leq M ) time-overlapping transmissions. To support mission- and time-critical applications that require reliable delivery within a strict delivery deadline $D$ (in units of slot), the aim of this paper is to achieve the maximum deadline-constrained reliability. First, we prove the uniqueness of the optimal transmission probability for any $1\leq M and any $D\geq 1$ . Second, we show it can be computed by a fixed-point iteration for all the cases. Third, for real-life scenarios where $N$ may be unknown and changing, we develop a distributed algorithm for $M>1$ , which allows each active user to dynamically tune its transmission probability based on a method for estimating $N$ . Simulation results verify our analysis and show that the proposed tuning algorithm is effective with near-optimal performance. In addition, as a special case (i.e., $D=1$ ) of our study, the issue of saturation throughput maximization is completely addressed for the first time.

In secure spatial modulation systems, an active antenna-group (AAG) selection of maximizing the average secrecy rate (SR) is proposed to avoid the disadvantage that conventional AAG selection scheme of minimizing bit error ratio at desired receiver may lead to a substantial SR loss. However, due to the limited active antenna pattern and finite-alphabet inputs, it is very hard for us to optimize the SR without closed-form expression. To address the two issues, first, by exploiting the relationship between minimum mean-square error and mutual information, the expression of SR in the low signal-to-noise ratio (SNR) region is derived. Using the expression, the problem of maximizing SR (Max-SR), called Max-SR I, is converted to integer programming problem. In the high SNR region, we derive an asymptotical lower bound for SR, and find the fact that the Max-SR can be reduced to maximizing the difference of Bob’s minimum Euclidean distance and Eve’s one, called Max-SR II. Through this conclusion, we can find the relationship between SR and bit-error rate. Furthermore, Max-SR III is proposed to overcome the disadvantage of the SR performance loss for the above two asymptotical algorithms in the moderate SNR region, where an approximate expression is exploited as the efficient metric to design AAG. Numerical results show that the SR performance of the proposed Max-SR III is close to that of optimal exhaustive search method, and the Max-SR I and Max-SR II can achieve acceptable SR performance with extremely low complexity.

This paper considers multichannel slotted ALOHA for unicast in an ad hoc network. Under a deadline-constrained scenario that a packet is required to be transmitted to an intended recipient within a strict delivery deadline $D$ (in unit of slot) and retransmission is not allowed, we obtain the optimal channel selection probabilities and the optimal transmission probability that maximize the reliability. In particular, the throughput maximization can be studied as the case of $D =1$ . Furthermore, by noting that there is a tradeoff between reliability and throughput when $D>1$ , we obtain the optimal schedule that maximizes the reliability subject to a throughput constraint and the one that maximizes the throughput subject to a reliability constraint.

The absence of a regional, open water vessel collision risk assessment system endangers maritime traffic and hampers safety management. Most recent studies have analysed the risk of collision for a pair of vessels and propose micro-level risk models. This study proposes a new method that combines density complexity and a multi-vessel collision risk operator for assessing regional vessel collision risk. This regional model considers spatial and temporal features of vessel trajectory in an open water area and assesses multi-vessel near-miss collision risk through danger probabilities and possible consequences of collision risks via four types of possible relative striking positions. Finally, the clustering method of multi-vessel encountering risk, based on the proposed model, is used to identify high-risk collision areas, which allow reliable and accurate analysis to aid implementation of safety measures.

In this paper, the problem of content caching in 5G cellular networks relying on social-aware device-to-device communications (DTD) is investigated. Our focus is on how to efficiently select important users (IUs) and how to allocate content files to the storage of these selected IUs to form a distributed caching system. We aim at proposing a novel approach for minimizing the downloading latency and maximizing the social welfare simultaneously. In particular, we first model the problem of maximizing the social welfare as a many-to-one matching game based on the social property of mobile users. We study this game by exploiting users’ social properties to generate the utility functions of the two-side players, i.e., content providers (CPs) and IUs. Then we model the problem of minimizing the downloading latency as a many-to-many matching problem. For solving these games, we design a many-to-one IU selection (MOIS) matching algorithm and a many-to-many file allocation (MMFA) matching algorithm, respectively. Simulation and analytical results show that the proposed mechanisms are stable, and are capable of offering a better performance than other benchmarks in terms of social welfare and network downloading latency.

Medium-scale or large-scale receive antenna array with digital beamforming can be employed at receiver to make a significant interference reduction but leads to expensive cost and high complexity of the RF-chain circuit. To deal with this issue, classic analog-and-digital beamforming (ADB) structure was proposed in the literature for greatly reducing the number of RF-chains. Based on the ADB structure, in this paper, we propose a robust hybrid ADB scheme to resist directions of arrival (DOAs) estimation errors. The key idea of our scheme is to employ null space projection (NSP) in the analog beamforming domain and diagonal loading (DL) method in digital beamforming domain. The simulation results show that the proposed scheme performs more robustly, and moreover, it has a significant improvement on the receive signal-to-interference-plus-noise ratio compared to NSP ADB scheme and DL method.

Millimeter wave (mmWave) communication has been regarded as one of the most promising technologies for the future generation wireless networks because of its advantages of providing a ultra-wide new spectrum and ultra-high data transmission rate. To reduce the power consumption and circuit cost for mmWave systems, hybrid digital and analog (HDA) architecture is preferred in such a scenario. In this paper, an artificial noise (AN) aided secure HDA beamforming scheme is proposed for mmWave multiple input single output (MISO) system with low resolution digital-to-analog converters (DACs) and finite-quantized phase shifters on radio frequency. The additive quantization noise model for AN aided HDA system is established to make an analysis of the secrecy performance of such systems. With the partial channel knowledge of eavesdropper available, an approximate expression of secrecy rate (SR) is derived. Then using this approximation formula, we propose a two-layer alternatively iterative structure (TLAIS) for optimizing digital precoder (DP) of confidential message (CM), digital AN projection matrix (DANPM) and analog precoder (AP). The inner-layer iteration loop is to design the DP of CMs and DANPM alternatively given a fixed matrix of AP. The outer-layer iteration loop is between digital baseband part and analog part, where the former refers to DP and DANPM, and the latter is AP. Then for a given digital part, we propose a gradient ascent algorithm to find the AP vector. Given a matrix of AP, we make use of general power iteration (GPI) method to compute DP and DANPM. This process is repeated until the terminal condition is reached. Simulation results show that the proposed TLAIS can achieve a better SR performance than existing methods, especially in the high signal-to-noise ratio region.

Powerline communication (PLC) is an attractive approach to providing information transfer services for future smart grids. However, due to high attenuation and interference, it is a great challenge to achieve reliable transmissions over PLC channels. In this letter, we propose an opportunistic decode-and-forward-based multiple-relaying (ODFR) scheme to enhance the performance of PLC networks, where the optimal relay is selected dynamically for data forwarding. Specifically, we first formulate the cumulative distribution functions (CDFs) of the received signal-to-noise ratio by exploiting statistical properties of the PLC channels. Then, drawing upon this derived CDF, we further develop the closed-form expressions of outage probability and approximate capacity for the proposed ODFR scheme. Simulations validate the consistency of our analytical results with Monte Carlo simulations.

Relying on the special mathematical properties among the access patterns of users, deterministic grant-free access can achieve ultra-high reliability within a finite time duration, and thus is favorable in coping with the challenge in ultra-reliable low-latency communications (URLLC) for 5G. Recently, interference canceling (IC) codes, proposed for access under the successive interference cancellation technique at the physical layer, have been becoming a hot research topic. However, it is difficult to obtain IC codes by the current mathematical tools or traditional search algorithms. To fill this gap, we put forth a deep reinforcement learning (DRL) based algorithm to search IC codes, with carefully designed metrics and reward functions as per the underlying mathematical constraints. The search results indicate that the algorithm can efficiently discover IC codes, while the simulation results indicate that the discovered IC codes yield significantly lower failure probability than the random access protocol given the same latency requirements, and thus are more suitable for URLLC.

Mobile edge computing (MEC) is a promising technology that sinks cloud computing down to the edge of the cellular network, so as to reduce latency and network congestion. In this paper, we investigate computing offloading problem for MEC-assisted heterogeneous vehicular networks where both vehicles and road unit sides (RSUs) can provide computation services. With the goal of maximizing the total computation rate, we design two computing offloading schemes, namely serial and parallel offloading schemes, and formulate the optimization problem as a Markov decision process (MDP) problem. To solve it, we propose a deep reinforcement learning (DRL) based vehicular edge computing (VEC) offloading solution. Simulation results show that the proposed parallel offloading scheme outperforms other solutions in terms of the total computation rate at the cost of high computation delay.

Conflict-avoiding codes (CACs) were introduced by Levenshtein as a single-channel transmission scheme for a multiple-access collision channel without feedback. When the number of simultaneously active source nodes is less than or equal to the weight of a CAC, it is able to provide a hard guarantee that each active source node transmits at least one packet successfully within a fixed time duration, no matter what the relative time offsets between the source nodes are. In this paper, we extend CACs to multichannel CACs for providing such a hard guarantee over multiple orthogonal channels. Upper bounds on the number of codewords for multichannel CACs of weights three and four are derived, and constructions that are optimal with respect to these bounds are presented., 12 pages. Accepted for publication in IEEE Transaction on Information Theory

In this paper, we consider a multiuser uplink status update system, where a monitor aims to timely collect randomly generated status updates from multiple end nodes through a shared wireless channel. We adopt the recently proposed metric, termed age of information (AoI), to quantify the information timeliness and freshness. Due to the random generation of the status updates at the end node side, the monitor only grasps a partial knowledge of the status update arrivals. Under such a practical scenario, we aim to address a fundamental multiuser scheduling problem: how to schedule the end nodes to minimize the network-wide AoI? To solve this problem, we formulate it as a partially observable Markov decision process (POMDP), and develop a dynamic programming (DP) algorithm to obtain the optimal scheduling policy. By noting that the optimal policy is computationally prohibitive, we further design a low-complexity myopic policy that only minimizes the one-step expected reward. Simulation results show that the performance of the myopic policy can approach that of the optimal policy, and is better than that of the baseline policy.

The fifth generation and beyond wireless communication will support vastly heterogeneous services and user demands such as massive connection, low latency and high transmission rate. Network slicing has been envisaged as an efficient technology to meet these diverse demands. In this paper, we propose a dynamic virtual resources allocation scheme based on the radio access network (RAN) slicing for uplink communications to ensure the quality-of-service (QoS). To maximum the weighted-sum transmission rate performance under delay constraint, formulate a joint optimization problem of subchannel allocation and power control as an infinite-horizon average-reward constrained Markov decision process (CMDP) problem. Based on the equivalent Bellman equation, the optimal control policy is first derived by the value iteration algorithm. However, the optimal policy suffers from the widely known curse-of-dimensionality problem. To address this problem, the linear value function approximation (approximate dynamic programming) is adopted. Then, the subchannel allocation Q-factor is decomposed into the per-slice Q-factor. Furthermore, the Q-factor and Lagrangian multipliers are updated by the use of an online stochastic learning algorithm. Finally, simulation results reveal that the proposed algorithm can meet the delay requirements and improve the user transmission rate compared with baseline schemes.

Transparent topology is common in many mobile ad hoc networks (MANETs) such as vehicle ad hoc networks (VANETs), unmanned aerial vehicle (UAV) ad hoc networks, and wireless sensor networks due to their decentralization and mobility nature. There are many existing works on distributed scheduling scheme design for topology-transparent MANETs. Most of them focus on delay-unconstrained settings. However, with the proliferation of real-time applications over wireless communications, it becomes more and more important to support delay-constrained traffic in MANETs. In such applications, each packet has a given hard deadline: if it is not delivered before its deadline, its validity will expire and it will be removed from the system. This feature is fundamentally different from the traditional delay-unconstrained one. In this paper, we for the first time investigate distributed scheduling schemes for a topology-transparent MANET to support delay-constrained traffic. We analyze and compare probabilistic ALOHA scheme and deterministic sequence schemes, including the conventional time division multiple access (TDMA), the Galois field (GF) sequence scheme proposed in \cite{chlamtac1994making}, and the combination sequence scheme that we propose for a special type of sparse network topology.We use both theoretical analysis and empirical simulations to compare all these schemes and summarize the conditions under which different individual schemes perform best.

Ultra-reliable and low-latency communication (URLLC) is of capital importance for the 5G wireless networks and has received a lot of attention recently. Motivated by the hard delay requirement for URLLC, we aim at devising medium access control (MAC) schemes that can guarantee packet transmissions within a bounded delay. The model we considered is a multi-channel single-hop ad hoc network in which each node has packets to broadcast to other nodes. This broadcast scenario is common, and has been extensively studied in various scenarios such as safety message broadcast in vehicular ad hoc networks (VANETs). Most of the existing MAC schemes employ backoff algorithms to handle transmission failures caused by channel collisions, and thus cannot provide a hard guarantee on transmission delay. Moreover, these schemes rely on time synchronization and coordination among the nodes, which would cause heavy overhead for control message exchange. In this paper, we focus on devising MAC schemes to provide a hard guarantee on broadcast delay, without time synchronization and cooperation among the nodes. We employ the sequence scheme in which each node is pre-assigned a periodic sequence to schedule transmissions and receptions at each time slot. These sequences are referred to as schedule sequences. Since each node starts its transmission schedule independently, there exist relative time offsets among the schedule sequences they use. Previous sequence schemes for broadcast are only conducted in the single channel context. Our objective is to design schedule sequences such that in a multi-channel system, each node can transmit at least one packet to each of its neighbors successfully within a common period, no matter what the time offsets are. The sequence period should be designed as short as possible. In this paper, we analyze the lower bound on sequence period, and propose a sequence construction method by which the period can achieve the same order as the lower bound. We also consider the random scheme in which each node transmits or receives on a channel at each time slot with a pre-determined probability. The frame length and broadcast completion time under different schemes are compared by numerical studies.

International audience; Among typical range-free localization schemes for sensor networks, DV-Hop has its distinguishing advantage of the capability to localize unknown nodes, which have less than three or even no neighbor anchors. However, existing DV-Hop based localization methods have not considered the problem of packet collisions, which can frequently happen during the throughout-whole-network broadcast of numerous data packets at the first two steps of DV-Hop. In order to effectively improve the success rate of packet transmission between nodes, this paper proposes a medium access control (MAC) method based on Chinese Remainder Theorem (CRT) protocol sequence for DV-Hop localization. First, a broadcasting strategy is designed for the proposed MAC method. Then, dedicated procedures for both anchor nodes and unknown nodes are presented to implement the designed MAC method in DV-Hop localization. Through simulation and evaluation, the performance of DV-Hop localization with the proposed MAC method is thoroughly investigated. Simulation results show that when the number of protocol sequences is larger than a certain number, the proposed MAC method can provide DV-Hop with better localization accuracy than E-CSMA/CA, while keeping similar localization time.

In cognitive radio networks, establishing a communication link between a pair of secondary users (SUs) requires them to rendezvous on a commonly available channel. Asynchronous channel hopping sequences with full rendezvous diversity (AFCHS) enable a pair of SUs to meet on every channel without requiring clock synchronization, and hence minimize rendezvous failures due to the appearance of primary user signals. Maximum conditional time-to-rendezvous (MCTTR) and maximum time-to-rendezvous (MTTR) are two primary metrics for evaluating the worst-case time-to-rendezvous of AFCHS under two extreme scenarios. In this letter, we derive lower bounds on the MCTTR and MTTR of AFCHS, and then propose a scheme with the minimum MCTTR and small MTTR. When the number of channels is odd, the proposed scheme has the minimum MTTR.

In this paper, we investigate the secrecy energy efficiency (SEE) optimization of the multiple-input single-output (MISO) system. First, transmission beamforming vector is designed to achieve the SEE maximization subject to the constraints of transmission power, minimum secrecy rate threshold and harvested energy threshold. The optimization problem belongs to the category of fractional optimization, which is non-convex and is very difficult to tackle. In order to solve the optimization problem, we propose an algorithm that can obtain a near-optimal solution, which consists of outer-tier and inner-tier iterations. For the outer-tier iteration, we first employ the Dinkelbach method to convert the fractional objective function into a polynomial form, and then transform the optimization problem into a difference of concave (DC) programming. For the inner-tier iteration, we employ the first-order Taylor expansion and successive convex approximation (SCA) method to solve the DC optimization problem. Then, we analyze the computational complexity of the proposed algorithm. In addition,we prove that the rank relaxation is tight. The simulation results show that the SEE performance of our proposed algorithm is obviously superior to that of secrecy rate maximization scheme and zero-forcing scheme.

Protocol sequences are periodic zero-one sequences for the scheduling of packet transmissions in a time-slotted channel. A special class of protocol sequences, called shift-invariant sequences, plays a key role in achieving the information-theoretic capacity of the collision channel without feedback. This class of shift-invariant protocol sequences has the property that the pairwise Hamming crosscorrelation functions are invariant to relative delay offsets. However, the common period of shift-invariant sequences grows exponentially as a function of the number of supported users. In this paper, we consider a family of protocol sequences, whose period increases roughly as a quadratic function of the number of the users, and show that it is close to shift-invariant by establishing a bound on the pairwise Hamming crosscorrelation. The construction is based on the Chinese remainder theorem (CRT), and hence the constructed sequences are called CRT sequences. Applications to collision channel allowing successive interference cancellation at the receiver are discussed.

Protocol sequences are deterministic binary sequences of a common period, which enjoy some special Hamming cross-correlation property by design. In contrast to random or contention-based medium access control schemes, a protocol sequence-based scheme can serve to provide at least a certain number of contention-free packet transmissions within a bounded delay for each asynchronous user in a feedback-free multiple access system. However, all protocol sequence-based schemes in the literature require that all sequence entries are mapped to slots with the same time duration, which produces a relatively low channel utilization. To overcome this inefficiency that is undesirable in delay-constrained wireless sensor networks, building on the idea of combining sequence-based access and carrier sensing, this paper proposes a new protocol sequence-based scheme, called the PS-CS. We derive the theoretical average throughput, average access delay, worst-case delay, and average energy consumption of the PS-CS. It is shown that the PS-CS produces average throughput close to the optimal capacity of ${p}$ -persistent carrier sense multiple access (CSMA), and enjoys smaller access delay than the optimal ${p}$ -persistent CSMA. In addition, we study the energy-delay tradeoff, impact of carrier sensing fault and channel error, and how to modify the PS-CS to support real-time downlink for feedback control.

Protocol sequences are binary and periodic sequences used for deterministic multiple access in a collision channel without feedback. In this paper, we focus on user-irrepressible (UI) protocol sequences that can guarantee a positive individual throughput per sequence period with probability one for a slot-synchronous channel, regardless of the delay offsets among the users. As the sequence period has a fundamental impact on the worst-case channel access delay, a common objective of designing UI sequences is to make the sequence period as short as possible. Consider a communication channel that is shared by M active users, and assume that each protocol sequence has a constant Hamming weight w. To attain a better delay performance than previously known UI sequences, this paper presents a CRTm construction of UI sequences with $$w=M+1$$ , which is a variation of the previously known CRT construction. For all non-prime $$M\ge 8$$ , our construction produces the shortest known sequence period and the shortest known worst-case delay of UI sequences. Numerical results show that the new construction enjoys a better average delay performance than the optimal random access scheme and other constructions with the same sequence period, in a variety of traffic conditions. In addition, we derive an asymptotic lower bound on the minimum sequence period for $$w=M+1$$ if the sequence structure satisfies some technical conditions, called equi-difference, and prove the tightness of this lower bound by using the CRTm construction.

With the further development of Internet of Things technology, the highly integrated IoT communication technology has been widely used. The wearable device has been transformed from concept to actual product, and has also begun to develop into the medical industry, such as wrist blood glucose controller, sound wave. Stimulating insulin secretors, wearable defibrillators, wearable alternating electric fields for brain tumor treatment, iontophoresis, smart glasses to help people with Alzheimer's disease find items. Based on the Internet of Things technology, the conditions for establishing a regional health service system from residents (bottom floor) to medical institutions (top level) are becoming more and more mature. The content of this research institute will also be widely applied and promoted in regional residents' health services.

In this paper, we study completely irrepressible (CI) sequences. For a slot-asynchronous communication system supporting $K$ users with such sequences, a key feature is that each user is guaranteed to be able to send out at least one contention-free packet in one common sequence period. This is a desirable property since it provides a bounded delay guarantee for medium access control (MAC) layer contention, in contrast to random access schemes. Generalizing previous studies on CI sequences, we investigate systems endowed with multiple-packet reception (MPR) capability $\gamma$ , $\mbox{2} \leq \gamma . That is, a packet transmission is successful if and only if the total number of transmissions in the channel at any point in time during its transmission is less than or equal to $\gamma$ . We investigate the minimum period $L$ of CI sequences for MPR as $L$ is a fundamental factor that affects the worst-case delay. The main result is that $L$ is asymptotically upper bounded by $\mbox{2}K^2/(\gamma-\mbox{2})$ when $\gamma \geq \mbox{3}$ . For $\gamma = \mbox{2}$ , the corresponding bound is $\mbox{2}K^2$ . In contrast, the bound for the single-packet reception system $(\gamma=\mbox{1})$ is $\mbox{4}K^2$ . Simulation results verify our analysis and present comparative studies between CI sequences and random access in an application of group-based detection in a wireless sensor network.

Consider a time-slotted communication channel that is shared by $K$ active users transmitting to a single receiver. It is assumed that the receiver has the ability of the multiple-packet reception to correctly receive up to $\gamma$ ( $1 \leq \gamma ) simultaneously transmitted packets. Each user accesses the channel following a deterministic binary sequence, called the protocol sequence, and transmits a packet within a channel slot if the sequence value is equal to one. If the users are not time synchronized, the relative shifts among them can cause significant fluctuation in throughput. If the throughput of each user is independent of relative shifts, then the adopted protocol sequence set is said to be throughput-invariant (TI). If we define worst-case system throughput as the minimal system throughput that can be guaranteed for any set of relative shifts, then TI sequences maximize it and hence are of fundamental interest. This paper investigates TI sequences for $\gamma \geq 1$ . Several new results are obtained including throughput value as a function of the duty factors, a lower bound on the sequence period, a construction that achieves the lower bound on the sequence period, and theorems on the intrinsic structure that establish connections with some other families of binary sequences.

In this paper, a Kriging-assisted discrete global optimization method is presented for computationally expensive black-box problems. KDGO employs Kriging to approximate the landscape of a black-box model, and utilizes a novel infilling strategy to capture the promising discrete samples. In the infilling strategy, a multi-start knowledge mining approach is introduced, including Optimization, Projection, Sampling and Selection. Firstly, a multi-start optimization is used to capture the promising solutions in the continuous design range. Secondly, all these potential solutions are projected to a predefined matrix and a grid sampling method suitable for low and high-dimensional space is proposed to get the promising discrete samples. Thereafter, the k-nearest neighbors (KNN) search strategy and expected improvement (EI) criterion are jointly used to select the candidate samples. The algorithm keeps running to update Kriging and find the most promising samples until the satisfactory solution is obtained. KDGO is primarily developed to solve time-consuming black-box problems with various discrete cases including binary, integer, non-integer, uni/multimodal and box/inequality-constrained types. After the comparison tests on 20 representative benchmark cases, KDGO proves that it can build a reasonable balance between exploitation and exploration. Besides, compared with the existing 6 methods, KDGO has significant advantages on computational efficiency and robustness. Finally, KDGO is used for structure optimization of a blended-wing-body underwater glider, and gets the satisfactory design.

A large-scale fully-digital receive antenna array can provide very high-resolution direction of arrival (DOA) estimation, but resulting in a significantly high RF-chain circuit cost. Thus, a hybrid analog and digital (HAD) structure is preferred. Two phase alignment (PA) methods, HAD PA (HADPA) and hybrid digital and analog PA (HDAPA), are proposed to estimate DOA based on the parametric method. Compared to analog phase alignment (APA), they can significantly reduce the complexity in the PA phases. Subsequently, a fast root multiple signal classification HDAPA (Root-MUSIC-HDAPA) method is proposed specially for this hybrid structure to implement an approximately analytical solution. Due to the HAD structure, there exists the effect of direction-finding ambiguity. A smart strategy of maximizing the average receive power is adopted to delete those spurious solutions and preserve the true optimal solution by linear searching over a set of limited finite candidate directions. This results in a significant reduction in computational complexity. Eventually, the Cramer-Rao lower bound (CRLB) of finding emitter direction using the HAD structure is derived. Simulation results show that our proposed methods, Root-MUSIC-HDAPA and HDAPA, can achieve the hybrid CRLB with their complexities being significantly lower than those of pure linear searching-based methods, such as APA.

This paper considers a media access control (MAC) scheme, which employs Reed-Solomon codes for error-correction, protocol sequences for packet scheduling, and successive interference cancellation (SIC) for demodulation. The construction of the protocol sequences is based on the Chinese remainder theorem (CRT), and a bound on the pairwise Hamming cross-correlation is established. After proving some properties of Hamming cross-correlation of CRT sequences, we illustrate how to allocate the code rates for a system with SIC. A lower bound on system throughput is established.

With the introduction of several new coding tools and technology for depth maps in 3D-HEVC, the coding efficiency is improved at the expense of computational complexity. Meanwhile, the inter-view correlation is not considered and used well for depth maps, while it is developed maturely in texture video coding. Therefore, in this paper, we propose an early determination scheme for the best prediction mode of depth maps in dependent views. The proposed algorithm can early determine the Merge mode as the best one and if it is all other candidates would be skipped by taking advantage of the inter-view information and the intermediate RD-cost comparison. Experimental results show that the proposed algorithm can provide about 22.1% remarkable time reduction with almost no BDBR increased compared with the state-of-the-art algorithm.

In this paper we investigate the identification and synchronization problems on a multiple access collision channel. Following Massey's lead, solutions to these problems are addressed by protocol sequences. This paper considers two different levels of user synchroneity: frame-synchronous access and slot-synchronous access. For the identification problem, we study user-detectable sequences. These are sequences with the cross-correlation property that allows each active user be detected within a bounded delay basing only on the channel activity information observed. Furthermore, we investigate the synchronization problem for delay-detectable sequences under the slot-synchronous access assumption. The goal of the synchronization problem is to determine the offset relations among all the active users. Sequences that allow such determination can be viewed as a special subset of user-detectable sequences. For both of these sequence families, it is desirable that the sequence length should be as short as possible. Hence, it is important to derive the minimum sequence lengths for these respective families. This is an extremely difficult open problem. Nevertheless, lower and upper bounds on these minimum lengths are presented in this paper under different levels of synchroneity assumptions. In addition, the performance of these sequences is demonstrated via numerical simulation.

Without requiring time synchronization, protocol sequences can be used to design a simple and reliable channel access protocol for mobile ad hoc networks. This paper focuses on completely irrepressible (CI) sequences, which can be employed to allow each user to have at least one successful packet transmission within each sequence period for a completely asynchronous channel. Previous numerical studies have shown by using carefully designed CI sequences, the average delay performance can be improved than using ALOHA-type schemes. To gain a unique insight into the characteristics of the protocol, we present an analytical model for the delay performance of CI sequences. The accuracy of our analytical model is verified via numerical results.

In wavelength-division multiplexing (WDM) networks, wavelength reservation protocols are employed to establish end-to-end lightpaths between source-destination node pairs. In this paper, we propose a new reservation scheme that is targeted for application in large-scale WDM core optical networks requiring wavelength-continuity, such as the CORONET Continental US (CONUS), initiated by DARPA. The proposed scheme is a hybrid between the source-initiated reservation (SIR) and destination-initiated reservation (DIR), and is designed to reduce the backward blocking due to contentions among concurrent set-up requests. In the scheme, the protocol first tries to reserve a suggested wavelength that is associated with the chosen lightpath as the set-up request is propagated from source to destination; if this reservation fails, the node before the destination then reserves a wavelength by using a prioritized selection and echoes the request back to the source. Simulation results show that the hybrid approach can reduce the blocking probability significantly. In addition, the impact of aggressiveness, that is, the number of wavelengths a single request attempts to select in the destination initiated phase, and how it should be set, are also studied in this paper.

In this paper, we propose a novel directional modulation (DM) scheme based on random frequency diverse arrays with artificial noise (RFDA-DM-AN) to enhance physical layer security of wireless communications. Specifically, we first design the RFDA-DM-AN scheme by randomly allocating frequencies to transmit antennas, thereby achieving two-dimensionally (i.e., angle and range) secure transmissions, and outperforming the state-of-the-art one-dimensional (i.e., angle) phase array (PA) based DM scheme. Then we develop the closed-form expression of a lower bound on the ergodic secrecy capacity (ESC) of our RFDA-DM-AN scheme. Based on the theoretical lower bound derived, we further optimize the transmission power allocation between the useful signal and artificial noise (AN) in order to enhance the ESC. Simulation results show that 1) our RFDA-DM-AN scheme achieves a higher secrecy capacity than that of the PA based DM scheme, 2) the lower bound derived is shown to approach the ESC as the number of transmit antennas N increases and precisely matches the ESC when N is sufficiently large, and 3) the proposed optimum power allocation achieves the highest ESC compared with other power allocations in the RFDA-DM-AN.

A channel is asynchronous if all users can start to transmit at an arbitrary point in time. Protocol sequences are used for multiple access in the collision channel without feedback. In this paper, we consider protocol sequence sets with the property that each user is able to successfully send at least one packet in each sequence period for the asynchronous channel. Such sequence sets are said to be completely irrepressible (CI). We analyze the class of CI sequences with the minimum number of ones in each period and derive lower bound on the minimum period. Moreover, if the sequence structure satisfies some technical conditions, which are called equi-difference, we improve the lower bound and present a construction that asymptotically meets this lower bound. We also show that the deterministic sequences proposed in this paper yield better performance in terms of average delay than the random approach.

Slotted CSMA/CA is employed in the beacon enabled IEEE 802.15.4 to resolve collisions in the contention access period with a low energy cost. To address the problem of excessive contentions at the beginning of each superframe, IEEE 802.15.4/2006 assigns each uncompleted transmission an additional random backoff delay before accessing the channel in the next superframe, by using deference mechanisms. Previous simulation studies have shown that deference mechanisms bring a significant impact on the delay performance of slotted CSMA/CA. In this paper, we develop an analytical model to predict the actual delay performance, and verify our evaluation by using simulation results.

Topology-transparent scheduling is a deterministic medium access control protocol for mobile ad hoc networks and wireless sensor networks. This approach only depends on two parameters: the number of nodes in the network and the maximum size of neighborhood. An attractive property is that each node can guarantee a bounded delay in which several packets can be successfully transmitted, no matter which nodes are its neighbors. In this paper, we study conflict-avoiding codes (CACs) and strongly conflict-avoiding codes (SCACs) based scheduling for slot-synchronized and asynchronous network, respectively, since it is difficult for mobile nodes to achieve frame-synchronization. The effect of synchronization on maximal delay is examined. In addition, we investigate average delay and average energy consumption by simulation.

Broadcast is one of the most fundamental services provided by the communication protocol for wireless sensor networks. In this paper, we design an energy-aware reliable deterministic broadcast scheduling protocol by using user-irrepressible (UI) protocol sequences. Each user transmits a packet in a time slot if and only if the sequence value is equal to one. A collision occurs if two or more users transmit at the same slot. UI sequences ensure that each user can receive at least one packet error-free from each other within the sequence period. Moreover, it does not require any time synchronization among the users. In the protocol, a new construction of UI sequences is presented and a sleeping mechanism is proposed. Simulation results show that the new protocol has a significant energy saving compared with traditional UI-sequences-based schemes. In addition, the delay can in fact be reduced by employing new UI sequences instead.

This paper proposes a carrier-sensing multiple access protocol for asynchronous multiple-packet reception (MPR), which enables wireless receivers to correctly decode partially time-overlapping packets. Unlike previous studies, which require back-off nodes to constantly monitor the channel, our design requires only that each node sense the number of transmitting nodes after the completion of the back-off period for determining whether to begin transmission in the next time slot. In addition, we develop an analytical model to evaluate relevant parameters and performance metrics of the proposed protocol. Our model relies on the channel-sensing probability of a node in a randomly chosen slot, rather than channel-accessing probability adopted in previous models for asynchronous MPR. The results are validated through numerical study under a variety of network conditions. We also show that the proposed protocol is quite robust to imperfect estimation in channel sensing, and is more energy-efficient than other similar threshold-based protocols.

We consider the slot-synchronized collision channel without feedback, in which K active users all transmit their packets to one sink. It is assumed that the channel has the ability of the multiple-packet reception (MPR), i.e., can accommodate at most (1 � 1. For both design objective, we establish a lower bound on sequence period and prove the lower bound can be achieved by some construction. I. INTRODUCTION A. System Model

Protocol sequences are used for distributed multiple accessing in the collision channel without feedback. In this paper we consider user-detectable sequences with the property that each active user can be detected by looking at the channel activity only, within some bounded delay. It is important in some applications such as ad hoc networks. Some lower and upper bounds of its minimum period are investigated in this paper. In addition, we display some interconnections with some other sequence designs.

The limited bandwidth and the finite battery power of mobile devices represent one of the greatest limitations of current WPANs. In this paper, an analytical model for the energy efficiency of the IEEE 802.15.4 slotted CSMA/CA which can be studied as slotted non-persistent CSMA was proposed and validated. Key to the accuracy of the model is a careful study of the idle period after last collision, which has been studied by Zhang et al. (2006). Specifically, a distributed mechanism to improve the energy efficiency for contention control in IEEE 802.15.4 was also present and evaluated and show that power saving and throughput maximization can be jointly achieved. Simulation results indicate that our mechanism is very effective and robust. This mechanism can be used to extend the standard 802.15.4 access mechanism without requiring any additional hardware.

In this paper, we present a way to estimate the performance of successful requests in contention access period (CAP) of IEEE 802.15.3 accounting for dual carrier-orthogonal frequency division multiplexing-ultra wide band (DC-OFDM-UWB). It is important for a piconet coordinator (PNC) to schedule traffic of a piconet and will determine the duration of contention free period (CFP). Simulation results show that the analysis accurately predicts the performance of CAP in UWB PHY. This research should provide helpful insight to the implementation of UWB-based IEEE 802.15.3 wireless networks