Improving Efficiency of Timeslot Assignment for Non‐realtime Data in a DVB‐RCS Return Link: Modeling and Algorithm

This paper presents a dynamic resource allocation algorithm with multi‐frequency time‐division multiple access for the return link of interactive satellite multimedia networks such as digital video broadcasting return channel via satellite systems. The proposed timeslot assignment algorithm, called the very efficient dynamic timeslot assignment (VEDTA) algorithm, gives an optimal assignment plan within a very short period. The optimality and computational efficiency of this algorithm demonstrate that it will be useful in field applications.     

A real-time algorithm for timeslot assignment in multirate return channels of interactive satellite multimedia networks

Since the digital video broadcast-return channel via satellite (DVB-RCS) standard was released in 2000, developing an interactive satellite multimedia (ISM) network has become a hot issue. In order to provide high-speed multimedia services using a DVB-RCS system, it is important to efficiently and dynamically assign the timeslots to a number of terminals according to their various demands. Also, it is imperative to improve the degradation of link quality due to rain-fade attenuation in Ka-band satellite communications. As a result, multirate superframe structures should be implemented for a relatively low data rate at the cost of stable connection to terminals in rain-fade regions and a relatively high data rate to terminals in clear-sky regions. Timeslot scheduling in this environment is studied in this paper. We mathematically formulate the timeslot assignment problem as a nonlinear integer programming problem and develop an efficient real-time solution algorithm. Extensive simulation results show that our algorithm successfully finds a feasible solution with optimality gap less than 0.05% within about 5 ms at Pentium III PC. We believe that our algorithm can be utilized as a guideline in developing real-time timeslot assignment algorithms for ISM networks.     

Dynamic resource allocation for DVB‐RCS networks

To provide high‐speed multimedia services using the digital video broadcasting‐return channel satellite (DVB‐RCS) standard, it is imperative to efficiently assign timeslots according to user demands and dynamically take into account the variations of the propagation conditions. In satellite networks operating above 10 GHz, rain fading constitutes the dominant factor deteriorating the quality of service. In this paper, a novel two‐phase resource allocation scheme for a DVB‐RCS compliant satellite network is proposed. The scheme operates in two phases, the resource calculation and the resource assignment. In the resource calculation phase, based on a dynamic channel model, an efficient algorithm is presented to determine the superframe design that maximizes system throughput. In the resource assignment phase, a novel Hybrid Bin‐packing algorithm is introduced maximizing the utilization of the multi‐frequency time division multiple access frame. The proposed algorithm has been compared with existing schemes exhibiting significantly better results with regard to overall system throughput. Copyright © 2008 John Wiley & Sons, Ltd.     

AG‐DPA: Assignment game–based dynamic power allocation in multibeam satellite systems

Dynamic power allocation is the key technology to maintain the link quality and improve the system throughput in multibeam satellite systems. Many numerical optimization algorithms have been proposed to optimize the power allocation schemes among beams. However, current metaheuristic algorithms, most of which are off‐line iterative methods, are not appropriate in nonuniform traffic demands and time‐varying channels due to the high computational complexity. To solve this problem, an assignment game–based dynamic power allocation (AG‐DPA) is proposed to achieve the suboptimality with low complexity in multibeam satellite systems. The key idea of the proposed AG‐DPA is to model the DPA problem into an assignment game model where the competitive equilibrium is achieved. Further, an adaptive price factor is introduced to make a trade‐off between algorithm performance and complexity. Simulation results show the effectiveness of the proposed AG‐DPA algorithm.     

A cross‐layer optimization for maximum‐revenue‐based multicast in multichannel multiradio wireless mesh networks

Given a video/audio streaming system installed on a multichannel multiradio wireless mesh network, we are interested in a problem concerning about how to construct a delay‐constrained multicast tree to support concurrent interference‐free transmissions so that the number of serviced mesh clients is maximized. In this paper, we propose a heuristic approach called cross‐layer and load‐oriented (CLLO) algorithm for the problem. On the basis of the cross‐layer design paradigm, our CLLO algorithm can consider application demands, multicast routing, and channel assignment jointly during the formation of a channel‐allocated multicast tree. The experimental results show that the proposed CLLO outperforms the layered approaches in terms of the number of serviced mesh clients and throughputs. This superiority is due to information from higher layers can be used to guide routing selection and channel allocation at the same time. As a result, the CLLO algorithm can explore more solution spaces than the traditional layered approaches. In addition to that, we also propose a channel adjusting procedure to enhance the quality of channel‐allocated multicast trees. According to our simulations, it is proved to be an effective method for improving the performance of the proposed CLLO algorithm. Copyright © 2013 John Wiley & Sons, Ltd.     

Perfect match model‐based link assignment to design topology for satellite constellation system

In satellite constellation network, the satellites visible from one satellite are more than communication terminals (CTs) equipped. Each inter‐satellite link (ISL) would occupy one CT on each of two satellites connected by this ISL. Therefore, a fundamental problem considering link assignment is how to assign limited CTs for each satellite to establish ISLs with its visible satellites. Link assignment scheme based on perfect match model (LAS‐PMM) is proposed to make full use of huge bandwidth provided by CT. In LAS‐PMM, the problem of assigning all the CTs of each satellite to establish ISLs is modeled as a perfect matching problem, where a perfect matching is searched over a mixed complete bipartite graph. Simulation results show that LAS‐PMM is better than the regular and greedy LASs, in terms of CT utilization and average node‐to‐node distance. Copyright © 2015 John Wiley & Sons, Ltd.     

Frequency resource allocation strategy with QoS support in hybrid cellular and Device‐to‐Device networks

Hybrid networks, comprising a conventional cellular network overlaid with Device‐to‐Device (D2D), offer efficient way to improve system throughput. In this paper, a novel orthogonal frequency‐division multiple access channel‐assignment method is proposed for hybrid network. The proposed approach is optimal in terms of throughput and is subjected to a sensible QoS requirement, which guarantees that macrocell and D2D achieve a prescribed data rate and outage probability, respectively. Our solution consists of two phases. In the first phase, the minimum sub‐channels are allocated to the macrocell to satisfy their data rate requirements. This problem is mapped to the 0‐1 Knapsack Problem and solved by integer programming based Lagrange dual approach. In the second phase, the redundant sub‐channels are allocated to D2D pairs to maximize the throughput of D2D networks. An interference management scheme is proposed to guarantee the outage probability of D2D communications. A cluster is taken as the unit for frequency reuse among D2D pairs. The problem of clustering is mapped to the MAX k‐CUT problem in graph theory and is solved by graph‐based heuristic algorithm. Extensive simulations demonstrate the superior performance of the proposed solution compared with the existing scheme. Copyright © 2014 John Wiley & Sons, Ltd.     

TDMA时隙分配对业务时延性能的影响分析

 在TDMA通信系统中,时隙分配是影响业务时延性能的重要因素,包括时隙数量分配(带宽分配)、时隙分配周期(TDMA帧长)和时隙位置分配三方面.本文针对可变速率和固定速率两类业务,基于随机服务系统理论和交通流理论建立了业务时延模型,得到了平均时延的解析式,分析了时隙数量、时隙位置和TDMA帧长度对业务时延影响的规律和特点.结果表明时隙位置分配越均匀,越能改善业务的平均时延和时延抖动性能;而在传统的时隙连续分配方式下,增加时隙数量分配对时延性能提高非常有限.在DVB-RCS卫星系统等具有较长帧设计的TDMA系统中,采用时隙均匀分配方式能够有效提高业务时延性能.计算机仿真验证了建模分析的正确性.     

Adaptive frequency‐hopping schemes for CR‐based multi‐link satellite networks

In this paper, we study two dynamic frequency hopping (DFH)–based interference mitigation approaches for satellite communications. These techniques exploit the sensing capabilities of a cognitive radio to predict future interference on the upcoming frequency hops. We consider a topology where multiple low Earth orbit satellites transmit packets to a common geostationary equatorial orbit satellite. The FH sequence of each low Earth orbit–geostationary equatorial orbit link is adjusted according to the outcome of out‐of‐band proactive sensing scheme, performed by a cognitive radio module in the geostationary equatorial orbit satellite. On the basis of sensing results, new frequency assignments are made for the upcoming slots, taking into account the transmit powers, achievable rates, and overhead of modifying the FH sequences. In addition, we ensure that all satellite links are assigned channels such that their minimum signal‐to‐interference‐plus‐noise ratio requirements are met, if such an assignment is possible. We formulate two multi‐objective optimization problems: DFH‐Power and DFH‐Rate. Discrete‐time Markov chain analysis is used to predict future channel conditions, where the number of states are inferred using k‐means clustering, and the state transition probabilities are computed using maximum likelihood estimation. Finally, simulation results are presented to evaluate the effects of different system parameters on the performance of the proposed designs.     

A delay‐centric parallel multi‐path routing protocol for cognitive radio ad hoc networks

In this paper, we develop a delay‐centric parallel multi‐path routing protocol for multi‐hop cognitive radio ad hoc networks. First, we analyze the end‐to‐end delay of multi‐path routing based on queueing theory and present a new dynamic traffic assignment scheme for multi‐path routing with the objective of minimizing end‐to‐end delay, considering both spectrum availability and link data rate. The problem is formulated as a convex problem and solved by a gradient‐based search method to obtain optimal traffic assignments. Furthermore, a heuristic decentralized traffic assignment scheme for multi‐path routing is presented. Then, based on the delay analysis and the 3D conflict graph that captures spectrum opportunity and interference among paths, we present a route discovery and selection scheme. Via extensive NS2‐based simulation, we show that the proposed protocol outperforms the benchmark protocols significantly and achieves the shortest end‐to‐end delay. Copyright © 2015 John Wiley & Sons, Ltd.     

A coordinated multi‐point‐based quality of service provision resource allocation scheme with inter‐cell interference mitigation

The paper investigates resource allocation via power control for inter‐cell interference (ICI) mitigation in an orthogonal frequency division multiple access‐based cellular network. The proposed scheme is featured by a novel subcarrier assignment mechanism at a central controller for ICI, which is further incorporated with an intelligent power control scheme. We formulate the system optimization task into a constrained optimization problem for maximizing accepted users' requirements. To improve the computation efficiency, a fast yet effective heuristic approach is introduced for divide and conquer. Simulation results demonstrate that the proposed resource allocation scheme can significantly improve the network capacity compared with a common approach by frequency reuse. Copyright © 2014 John Wiley & Sons, Ltd.     

Performance evaluation of TCP‐based applications over DVB‐RCS DAMA schemes

Transmission Control Protocol (TCP) performance over Digital Video Broadcasting—Return Channel via Satellite (DVB‐RCS) standard is greatly affected by the total delay, which is mainly due to two components, propagation delay and access delay. Both are significant because they are dependent on the long propagation path of the satellite link. The former is intrinsic and due to radio wave propagation over the satellite channel for both TCP packets and acknowledgements. It is regulated by the control loop that governs TCP. The latter is due to the control loop that governs the demand assignment multiple access (DAMA) signalling exchange between satellite terminals and the network control center, necessary to manage return link resources. DAMA is adopted in DVB‐RCS standard to achieve flexible and efficient use of the shared resources. Therefore, performance of TCP over DVB‐RCS may degrade due to the exploitation of two nested control loops also depending on both the selected DAMA algorithm and the traffic profile. This paper analyses the impact of basic DAMA implementation on TCP‐based applications over a DVB‐RCS link for a large set of study cases. To provide a detailed overview of TCP performance in DVB‐RCS environment, the analysis includes both theoretical approach and simulation campaign. Copyright © 2009 John Wiley & Sons, Ltd.     

Power allocation scheme based on sum capacity maximization for signal‐to‐leakage‐and‐noise ratio precoded multiuser multiple‐input single‐output downlink

This paper proposes a power allocation scheme to maximize the sum capacity of all users for signal‐to‐leakage‐and‐noise ratio (SLNR) precoded multiuser multiple‐input single‐output downlink. The designed scheme tries to explore the effect of the power allocation for the SLNR precoded multiuser multiple‐input single‐output system on sum capacity performance. This power allocation problem can be formulated as an optimization problem. With high signal‐to‐interference‐plus‐noise ratio assumption, it can be converted into a convex optimization problem through the geometric programming and hence can be solved efficiently. Because the assumption of high signal‐to‐interference‐plus‐noise ratio cannot be always satisfied in practice, we design a globally optimal solution algorithm based on a combination of branch and bound framework and convex relaxation techniques. Theoretically, the proposed scheme can provide optimal power allocation in sum capacity maximization. Then, we further propose a judgement‐decision algorithm to achieve a trade‐off between the optimality and computational complexity. The simulation results also show that, with the proposed scheme, the sum capacity of all the users can be improved compared with three existing power allocation schemes. Meanwhile, some meaningful conclusions about the effect of the further power allocation based on the SLNR precoding have been also acquired. The performance improvement of the maximum sum capacity power allocation scheme relates to the transmit antenna number and embodies different variation trends in allusion to the different equipped transmit antenna number as the signal‐to‐noise ratio (SNR) changes.Copyright © 2013 John Wiley & Sons, Ltd.     

Practical cross‐layer routing and channel assignment in cognitive radio ad hoc networks

In the heterogeneous and unreliable channel environment of cognitive radio ad hoc networks (CRAHNs), a multipath route with channel assigned is preferable in both throughput and reliability. The cross‐layer multipath routing and channel assignment in CRAHNs is becoming a challenging issue. In this paper, this problem is characterized, formulated, and shown to be in the form of mixed integer programming. For this Non‐deterministic Polynomial‐time (NP)‐hard problem, the deficiency of the widely used linearization and sequential fixing algorithm is first analyzed. The main contribution of this paper is the development of a new backtracking algorithm with feasibility checking to search optimal solutions and a heuristic algorithm with high feasible solution‐obtained probability (HHFOP) for distributed application in CRAHNs. Through feasibility checking and solution bounds validating, backtracking algorithm with feasibility checking cuts off unnecessary searching space in early stage without loss of optimal solutions, making it much more efficient than brute searching. For practical application in CRAHNs with polynomial complexity, HHFOP first computes the maximal‐supported throughput through link‐channel assignment and link‐capacity coordination for each candidate path. Then the paths are combined, and the route throughput is optimized. Extensive simulation results demonstrate that HHFOP can achieve a high feasible solution‐obtained probability with little throughput degradation compared with linearization and sequential fixing algorithm, indicating its practicability for distributed applications in CRAHNs. Copyright © 2013 John Wiley & Sons, Ltd.     

Bandwidth guaranteed call admission in TDMA/CDMA ad hoc wireless networks

This paper first studied the timeslot assignment problem in time division multiple access/code division multiple access (TDMA/CDMA) wireless ad hoc networks. Given a path P, we prove that a timeslot assignment providing one unit of bandwidth on P can be found in O(P) time if such an assignment exists. The results have been extended to the case that P can provide two units of bandwidth. Based on the timeslot assignment for the special cases, an efficient slot assignment algorithm with O(P²k) is proposed for general cases, where k is the number of slots in a TDMA frame. Then, the timeslot assignment algorithm is integrated into a quality of service (QoS) call admission scheme for QoS call requests. Extensive simulations are conducted and the results have demonstrated the superior performance of our method.     

星上MF-TDMA系统信道管理方法

MF-TDMA被广泛应用于现代宽带通信卫星系统的上行链路设计中,而时隙分配算法是系统资源利用率的重要保证。针对MF-TDMA时隙分配复杂,时隙资源浪费严重等难题,该文给出一种可动态调整载波信道的MF-TDMA系统时隙分配算法,算法将天基移动通信系统用户接入时隙分配问题分解为载波确定和载波内时隙分配两个部分,并针对用户终端载波确定问题,给出一种带载波调整的RCP算法(RCP-A)算法,解决现有方法在多业务多用户条件下资源浪费大、使用率低的问题;针对载波内时隙分配问题,采用基于倒序时隙编号时隙资源树管理方式,解决业务因时隙分配而带来的时延抖动问题;并给出了适合星上处理能力的时隙资源管理其实现方法。仿真测试显示,该实现方法适合于星上MF-TDMA无线资源管理器。     

On energy‐efficient performance‐guaranteed channel assignment in cognitive radio‐based wireless mesh networks

In recent years, in order to make efficient use of spectrum resources, much attention has been given to solving the problem of channel assignment in cognitive radio‐based wireless mesh networks (CR‐WMNs). Current approaches focus mainly on avoiding interference in order to enhance performance in terms of throughput. WMNs are intended to provide low‐cost multimedia communication. Therefore, in order to provide low‐cost real‐time communication, channel assignment in CR‐WMNs should take into consideration not only the issue of throughput, but also energy consumption and delays. In this paper, we first define an optimization problem to maximize the end‐to‐end throughput per unit of energy consumption while minimizing, as well as guaranteeing, the delay constraint specified for a data stream. Based on this, we then propose a novel distributive heuristic channel assignment approach to solve the optimization problem in a self‐organized manner. Finally, we present the simulation results to evaluate the performance of the proposed solution in terms of end‐to‐end throughput per unit of energy consumption and delays. Copyright © 2015 John Wiley & Sons, Ltd.     

Multiple gateway placement in large‐scale constellation networks with inter‐satellite links

Multiple gateways are required in large satellite constellation networks (LSCNs) with inter‐satellite links (ISLs), and their placement may greatly affect the system performance. Gateway placement can be optimized to achieve better network performance under the non‐uniform ground demand distribution. This paper formulates a gateway placement optimization model for LSCN with ISLs, aiming at achieving an optimal overall performance including delay, traffic peak, and load balance. The constraints of potential gateway location, gateway‐satellite connectivity, and max hop‐count are considered. A genetic algorithm (GA)‐based method is proposed to solve the integer optimization problem with the help of quasi‐evenly distributed reference layout. A Starlink‐like constellation with ISLs is adopted in the simulation. The simulation results show that the optimized layout has better performance than the reference layout. Additionally, the locations with high user demand or at the middle of ocean are preferred by gateways. The network performance is jointly influenced by gateway placement, demand distribution, constellation configuration, node, and link capacities. The abnormally high ISL hop‐count is found in the south Indian Ocean, which is caused by constellation and ISL configuration.     

Preference‐based zone selection in 802.16 networks

We examine a new problem called the Zone Selection Problem (ZSP) in wireless Orthogonal Frequency‐Division Multiple Access (OFDMA)‐based systems. We consider the case where the mobile station (MS) informs the base station of its preferences regarding possible working modes supported by the system. In Worldwide Interoperability for Microwave Access (WiMAX) systems, which are used as a practical reference system for constraints and specific modes of operations, each working mode must be assigned at a different time interval called a Zone. Such zone may, in the downlink subframe, define a specific transmission scheme, which can be either single‐input single‐output or one of the multiple‐in multiple‐out (MIMO) modes supported by the system. We define ZSP as a problem where the base station assigns MSs to zones in a way that optimizes the system utilization (in terms of resource usage) while trying to satisfy the preferences of the users as much as possible. This makes ZSP a bi‐objective optimization problem. We derive assignment costs from physical channel models that integrate specific MIMO schemes and channel conditions. We provide an exact solution to ZSP by using a combinatorial optimization abstraction. We propose a simplified and practical mode ranking approach that enables the MS to define its preferences regarding operation in the optional MIMO modes in the system. We prove that ZSP is NP‐hard and describe two heuristic solutions: a greedy approach and a local search approach. Simulation results show the performance of the exact algorithms on a realistic WiMAX system assumptions and present the trade‐off between the user preferences and system preferences. Copyright © 2016 John Wiley & Sons, Ltd.     

一种基于容忍度的优先级动态轮询协议

根据利用卫星平台进行战场超视距情报数据转发的应用需求,针对卫星高速数据链的业务特点,提出了一种基于容忍度的优先级动态轮询协议;设计了帧结构和基于容忍度的优先级动态时隙分配算法及其流程;最后利用Opnet仿真软件仿真验证。仿真结果表明,改进后的协议通过容忍度函数实现了不同业务量、不同优先等级下时隙的动态调整,既可以使高优先级业务时延性能得到保障,又不会"饿死"低优先级请求,获得了较好的"公平性"。