Rate control with distributed joint diversity and power control for wireless networks

Two rate control algorithms with distributed joint diversity and power control are proposed for wireless networks. We prove that with the proposed algorithms, the allowed transmitting rate can converge to the individual rate requirement with which the QoS requirement can be satisfied, and each user can share the bandwidth according to the pre-specified setting so that certain fairness can be maintained among the users in the same cell. Simulation results also show that the scheme with rate control gains larger throughput than the scheme without rate control.     

Throughput and resource optimization for adaptive coding‐based random access networks with correlated sources

Modern wireless communication networks frequently have lower application throughput due to higher number of collisions and subsequent retransmission of data packets. Moreover, these networks are characterized by restricted computational capacity due to limited node‐battery power. These challenges can be assessed for deploying fast, reliable network design with resource‐restrained operation by means of concurrent optimization of multiple performance parameters across different layers of the conventional protocol stack. This optimization can be efficiently accomplished via cross‐layer design with the aid of network coding technique and optimal allocation of limited resources to wireless links. In this paper, we evaluate and analyze intersession coding across several source–destination pairs in random access ad hoc networks with inherent power scarcity and variable capacity links. The proposed work addresses the problem of joint optimal coding, rate control, power control, contention, and flow control schemes for multi‐hop heterogeneous networks with correlated sources. For this, we employ cross‐layer design for multiple unicast sessions in the system with network coding and bandwidth constraints. This model is elucidated for global optimal solution using CVX software through disciplined convex programming technique to find the improved throughput and power allocation. Simulation results show that the proposed model effectively incorporates throughput and link power management while satisfying flow conservation, bit error rate, data compression, power outage, and capacity constraints of the challenged wireless networks. Finally, we compare our model with three previous algorithms to demonstrate its efficacy and superiority in terms of various performance metrics such as transmission success probability, throughput, power efficiency, and delay.     

Performance enhancement of adaptive orthogonal modulation in wireless CDMA systems

Recent research in wireless code-division multiple-access systems has shown that adaptive rate/power control can considerably increase network throughput relative to systems that use only power or rate control. In this paper, we consider joint power/rate optimization in the context of orthogonal modulation (OM) and investigate the additional performance gains achieved through adaptation of the OM order. We show that such adaptation can significantly increase network throughput, while simultaneously reducing the per-bit energy consumption relative to fixed-order modulation systems. The optimization is carried out under two different objective functions: minimizing the maximum service time and maximizing the sum of user rates. For the first objective function, we prove that the optimization problem can be formulated as a generalized geometric program (GGP). We then show how this GGP can be transformed into a nonlinear convex program, which can be solved optimally and efficiently. For the second objective function, we obtain a lower bound on the performance gain of adaptive OM (AOM) over fixed-modulation systems. Numerical results indicate that relative to an optimal joint rate/power control fixed-order modulation scheme, the proposed AOM scheme achieves significant throughput and energy gains.     

Cross‐Layer Resource Allocation in Multi‐interface Multi‐channel Wireless Multi‐hop Networks

In this paper, an analytical framework is proposed for the optimization of network performance through joint congestion control, channel allocation, rate allocation, power control, scheduling, and routing with the consideration of fairness in multi‐channel wireless multi‐hop networks. More specifically, the framework models the network by a generalized network utility maximization (NUM) problem under an elastic link data rate and power constraints. Using the dual decomposition technique, the NUM problem is decomposed into four subproblems — flow control; next‐hop routing; rate allocation and scheduling; power control; and channel allocation — and finally solved by a low‐complexity distributed method. Simulation results show that the proposed distributed algorithm significantly improves the network throughput and energy efficiency compared with previous algorithms.     

Cross-Layer MAC Protocol and Holistic Opportunistic Scheduling with Adaptive Power Control for QoS in WiMAX

Providing quality of service (QoS) to different service classes with integrated real-time and non-real-time traffic is an important issue in broadband wireless access networks. Opportunistic MAC (OMAC) is a novel view of communication over spatiotemporally varying wireless link whereby the multi-user diversity is exploited rather than combated to maximize bandwidth efficiency or system throughput. It combines cross-layer design features and opportunistic scheduling scheme to achieve high utilization while providing QoS support to various applications. Channel characteristics, traffic characteristics and queue characteristics are the essential factors in the design of opportunistic scheduling algorithms. In this paper, we propose a cross-layer MAC scheduling framework in WiMAX point-to-multipoint (PMP) systems and a corresponding opportunistic scheduling algorithm with an adaptive power control scheme to provide QoS support to the heterogeneous traffic. Extensive simulation experiments have been carried out to evaluate the performance of our proposal. The simulation results show that our proposed solution can improve the performance of the WiMAX PMP systems in terms of packet loss rate, packet delay and system throughput.     

Bit loading with BER-constraint for multicarrier systems

We present discrete adaptive bit loading algorithms for multicarrier systems with uniform (nonadaptive) power allocation operating in a frequency selective fading environment. The algorithms try to maximize the overall throughput of the system while guaranteeing that the mean bit error rate (BER) remains below a prescribed threshold. We also study the impact of imperfect subcarrier signal-to-noise ratio information on throughput performance. Results show that the proposed algorithms have approximately the same throughput and mean BER as the optimal allocation while having a significantly lower computational complexity relative to other algorithms with near-optimal allocations. Moreover, when compared with algorithms that employ approximations to water filling, the computational complexity is comparable while the overall throughput is closer to the optimum.     

Performance of OFDMA Multicell Systems with Opportunistic Beamforming

The opportunistic beamforming (OB) technique in multicellular OFDMA networks is investigated in this paper. Three cross-layer radio resource management (RRM) algorithms for OFDMA operational scenarios are considered. These algorithms build upon typical network planning practices for OFDMA systems. The first two implement an OFDMA network with opportunistic rate adaptation while the third one aims at a network which guarantees QoS provision through power control on carrier basis. The RRM algorithms are based on typical OFDMA resource allocation targets such as minimization of transmit power, maximization of throughput and interference averaging. Then, the OB concept is combined with the considered RRM algorithms and a comparative performance analysis between the two types of networks (omni and opportunistic beamforming) is performed in terms of throughput, blocking probability and fairness. The paper aims at providing a useful insight into the way the OB technique affects the performance of different OFDMA networks based on large scale simulations. The simulation results suggest that OB is preferred for OFDMA systems with opportunistic rate adaptation rather than power controlled systems which offer QoS provision. According to the presented results, OB provides to OFDMA systems with opportunistic rate adaptation a ??13% throughput gain and ??75% gain in terms of blocking probability. In addition, it is shown that the combination of OB with interference averaging RRM algorithms has a minor beneficial impact only on the system fairness.     

Resource scheduling scheme for 5G mmWave CP-OFDM based wireless networks with delay and power allocation optimizations

In this paper, to optimize the average delay and power allocation (PA) for system users, we propose a resource scheduling scheme for wireless networks based on Cyclic Prefix Orthogonal Frequency Division Multiplexing (CP-OFDM) according to the first fifth-generation standards. For delay minimization, we solve a throughput maximization problem that considers CP-OFDM systems with carrier aggregation (CA). Regarding PA, we consider an approach that involves maximizing goodput using an effective signal-to-noise ratio. An algorithm for jointly solving delay minimization through computation of required user rates and optimizing the power allocated to users is proposed to compose the resource allocation approach. In wireless network simulations, we consider a scenario with the following capabilities: CA, 256-Quadrature Amplitude Modulation, millimeter waves above 6 GHz, and a radio frame structure with 120 KHz spacing between the subcarriers. The performance of the proposed resource allocation algorithm is evaluated and compared with those of other algorithms from the literature using computational simulations in terms of various Quality of Service parameters, such as the throughput, delay, fairness index, and loss rate.     

System evaluation of optimal downlink beamforming with congestion control in wireless communication

We investigate the use of congestion control and joint optimal downlink beamforming, power control, and access point allocation, in a multi-cell wireless communication system. The access points of the system employ smart antennas and single antennas are used at the terminals. The possibility to send messages to multiple terminals at the same frequency in the same time slot is exploited. We show how previously proposed algorithms for optimal downlink beamforming easily can be extended to determine also the optimal access point for each mobile terminal. In order to assign resources, optimal beamforming requires a feasible set of mobiles, i.e. that all admitted users can be offered the required signal-to-interference-and-noise ratio. Therefore, an algorithm for deciding which mobile terminals to admit or reject from a congested system is proposed and evaluated. Using the proposed congestion algorithm, joint optimal downlink beamforming is evaluated and the throughput increase as compared to decentralized beamforming algorithms and other congestion control strategies is assessed from a system point of view. The results show that the proposed strategy can almost double the throughput compared to decentralized beamforming algorithms and give a fivefold increase in throughput compared to conventional beamforming without any interference suppression.     

Contrôle de puissance dans les réseaux ad-hoc

In an ad-hoc network, mobile stations communicate with each other using multi-hop wireless links. There is no stationary infrastructure such as base stations. Each node in the network also acts as a router, forwarding data packets for other nodes. In this architecture, mobile stations have a multi-hop path, via other mobile stations acting as intermediaries or relays, to indirectly forward packets from source to destination. Adjusting the transmitted power is extremely important in ad-hoc networks due to at least the following reasons. The transmitted power of the radio terminals determines the network topology. The network topology in turn has considerable impact on the throughput (fraction of packets, sent by a source, and successfully received at the receiver) performance of the network. The need for power efficiency must be balanced against the lifetime of each individual node and the overall life of the network. Power control problem can be classified in one of three categories. The first class comprises of strategies to find an optimal transmitted power to control the connectivity properties of the network. The second class of approaches could be called power aware routing. Most schemes use some shortest path algorithm with a power based metric, rather than a hop count based metric. The third class of approaches aim at modifying the mac layer. We use distributed power control algorithms initially proposed for cellular networks. We establish a classification of power control algorithms for wireless ad-hoc networks. We evaluate these algorithms in anIeee 802.11b multi-hop wireless ad-hoc LAN environment. Results show the advantage of power control in maximizing signal-to-interference ratio and minimizing transmitted power.     

双向能量协作的中继系统功率分配算法

在无线中继系统中,考虑源节点和中继节点都是能量采集的,而源与中继之间可以进行能量协作,即可双向传递能量,针对瑞利衰落信道场景以最大化系统吞吐量为目标,联合优化源节点的发射功率、中继节点的发射功率以及传递的能量值,提出了双向能量传递的最优功率分配算法。本文根据场景模型建立了最优化问题,利用凸优化知识求得最优解的形式,假设能量传递无损耗情况下提出了理想功率分配方案;然后以此为基础,在满足能量因果性和数据因果性的条件下,对传递的能量和发送的功率进行优化。仿真结果表明,本文提出的双向能量传递的功率分配算法优于其它的功率分配算法,能有效的提高系统吞吐量。      

Dynamic resource scheduling (DRS): a multimedia QoS framework for W‐CDMA

Multi‐media support is an important feature of third generation (3G) wireless communication systems, and Quality of Service (QoS) is a crucial issue, as in any other networking environment. In this paper, the QoS issues in the wireless last‐mile is investigated for 3G systems based on Wideband‐Code division multiple access (W‐CDMA). Supporting multiple rates in the CDMA environment introduces the power assignment problem, which is coupled with the bandwidth and error QoS parameters. Also, multi‐media traffic flows should be classified and serviced in such a way to provision delay guarantees. In this paper, a new framework, namely dynamic resource scheduling (DRS), is described and extensively studied. In order to serve multi‐media services with different requirements, a family of nine algorithms has been developed within the DRS framework. These algorithms can be categorized with respect to single or prioritized queuing architectures, fixed or variable rate bandwidth and power allocation, and variable spreading gain or multi‐code spreading strategies. The paper presents the performance of the DRS algorithms in comparison with each other and with conventional scheduled‐CDMA (S‐CDMA) and proposed schemes in the W‐CDMA standard. The performance for error and throughput QoS provisioning and power control dynamics are explored; advantages, disadvantages and limitations of the algorithms are discussed. The DRS framework is concluded to be a promising QoS architecture, with a simple, flexible, scalable structure that can be configured according to a given traffic scenario. Copyright © 2004 John Wiley & Sons, Ltd.     

Maximum-throughput delivery of SVC-based video over MIMO systems with time-varying channel capacity

In this paper, we present a novel scalable video transmission strategy over multi-input multi-output (MIMO) wireless systems with time-varying channel capacity. It is a great challenge to simultaneously guarantee the QoS for video delivery and maximize the system throughput over time-varying MIMO channel. We demonstrate that, by making full use of estimated channel state information (CSI) through feedback, a cascade of adaptive operations can be designed to satisfy maximum throughput for scalable video over MIMO systems. These operations include power allocation based on water-filling (WF), adaptive channel selection (ACS), and novel throughput maximizing power reallocation (PR). The proposed ACS transmission scheme enables overall increase in data throughput among enhancement layers by adaptively launching base layer bit-stream to proper sub-channel. Then, after initial power allocation with WF and proper adaptive mode selection, we obtain the surplus power across enhancement layer sub-channels which can be reallocated to some sub-channels by the proposed PR scheme. With such power reallocation, certain enhancement layers will be able to reach new level of QAM modulation through PR so as to maximize the system data throughput. We present in this paper some detailed analysis on these adaptive operations. We also present some simulation results to demonstrate that maximum throughput video transmission over MIMO wireless systems indeed can be achieved based on scalable video coding (SVC) and a sequence of appropriately designed adaptive operations.     

Zero-forcing methods for downlink spatial multiplexing in multiuser MIMO channels

The use of space-division multiple access (SDMA) in the downlink of a multiuser multiple-input, multiple-output (MIMO) wireless communications network can provide a substantial gain in system throughput. The challenge in such multiuser systems is designing transmit vectors while considering the co-channel interference of other users. Typical optimization problems of interest include the capacity problem - maximizing the sum information rate subject to a power constraint-or the power control problem-minimizing transmitted power such that a certain quality-of-service metric for each user is met. Neither of these problems possess closed-form solutions for the general multiuser MIMO channel, but the imposition of certain constraints can lead to closed-form solutions. This paper presents two such constrained solutions. The first, referred to as "block-diagonalization," is a generalization of channel inversion when there are multiple antennas at each receiver. It is easily adapted to optimize for either maximum transmission rate or minimum power and approaches the optimal solution at high SNR. The second, known as "successive optimization," is an alternative method for solving the power minimization problem one user at a time, and it yields superior results in some (e.g., low SNR) situations. Both of these algorithms are limited to cases where the transmitter has more antennas than all receive antennas combined. In order to accommodate more general scenarios, we also propose a framework for coordinated transmitter-receiver processing that generalizes the two algorithms to cases involving more receive than transmit antennas. While the proposed algorithms are suboptimal, they lead to simpler transmitter and receiver structures and allow for a reasonable tradeoff between performance and complexity.     

Cross-Layer Scheduling and Power Control Combined With Adaptive Modulation for Wireless Ad Hoc Networks

Efficient resource management is a major challenge in the operation of wireless systems, especially energy-constrained ad hoc networks. In this paper, we propose a cross-layer optimization framework to jointly design the scheduling and power control in wireless ad hoc networks. We study the system performance by combining scheduling, power control, and adaptive modulation. Specifically, the transmitted power and constellation size are dynamically adapted based on the packet arrival, quality of service (QoS) requirements, power limits, and channel conditions. A key feature of the proposed method is that it facilitates a distributed implementation, which is desirable in wireless ad hoc networks. The performance of our proposed methodology will be investigated in ad hoc networks supporting unicast as well as multicast traffic. Simulation results will show that the proposed scheme achieves significant gains in both the single-hop throughput and power efficiency compared with the existing method, which implements the scheduling through a central controller, and adopts power control with fixed modulation     

Optimal Power and Rate Control for Minimal Average Delay: The Single-User Case

Contemporary wireless systems combine aspects of network theory such as scheduling, throughput, and delay as well as information theory aspects such as capacity, coding, and power control. Design of such systems requires joint optimization of both network and physical layers. In this paper, we analyze a single-user communication system composed of a transmitter preceded by a queue used for retransmissions, Gaussian block-fading channel, and a receiver. The system average delay is optimized by using combined power/rate control under average power constraints. Dynamic programming is used for calculating the optimized policies using numerical analysis as well as analytic analysis for asymptotically large buffer size. Asymptotic results are obtained for all combinations of fixed or variable power and rate controls. The most important result extends the "water-filling" result for systems with average delay constraint     

An efficient resource optimization scheme for D2D communication

With the rapid development of wireless technologies, wireless access networks have entered their Fifth-Generation (5G) system phase. The heterogeneous and complex nature of a 5G system, with its numerous technological scenarios, poses significant challenges to wireless resource management, making radio resource optimization an important aspect of Device-to-Device (D2D) communication in such systems. Cellular D2D communication can improve spectrum efficiency, increase system capacity, and reduce base station communication burdens by sharing authorized cell resources; however, can also cause serious interference. Therefore, research focusing on reducing this interference by optimizing the configuration of shared cellular resources has also grown in importance. This paper proposes a novel algorithm to address the problems of co-channel interference and energy efficiency optimization in a long-term evolution network. The proposed algorithm uses the fuzzy clustering method, which employs minimum outage probability to divide D2D users into several groups in order to improve system throughput and reduce interference between users. An efficient power control algorithm based on game theory is also proposed to optimize user transmission power within each group and thereby improve user energy efficiency. Simulation results show that these proposed algorithms can effectively improve system throughput, reduce co-channel interference, and enhance energy efficiency.     

Cross-Layer Antenna Beamforming and Power Control in Wireless Uplinks

We consider backlog-driven power control and antenna beamforming as a means to maximize network throughput in a wireless uplink, where a base station receives with an antenna array from single-antenna wireless users. Throughput maximization gives rise to an optimization problem which is in general non-concave. We introduce a cross-layer, alternating maximization algorithm searching for the optimal solution, and a variant of the algorithm with reduced complexity. The algorithm alternates between a power control step and a beamforming step. Simulation results illustrate the convergence of the proposed scheme to a locally optimal pair of power vector and beamforming matrix, and quantify its throughput gains in a system with stochastic arrivals.     

Fair channel-adaptive rate scheduling in wireless networks with multirate multimedia services

In this paper, we study the fundamental problem of allocating with efficiency and fairness the available resources in a code-division multiple-access wireless system that supports multirate multimedia services. Our proposed approach adopts the use of dynamically assigned data rates that match the channel capacity in order to improve the system throughput and overcome the problems associated with the location-dependent and time-dependent errors and channel conditions, the variable system capacity and the transmission power limitation. We introduce and describe two new algorithms, namely the channel adaptive rate scheduling (CARS) and fair channel adaptive rate scheduling (FCARS) algorithms. CARS improves the system throughput by adjusting the transmission rates according to the varying channel conditions and performs an iterative procedure to determine the power index that a user can accept by its current channel condition and transmission power. Based on the assignment of CARS, FCARS achieves the objective of fairness by further compensating the lagging users, while still maintaining all the constraints imposed by the system. The performance evaluation process confirms that our approach achieves, simultaneously, the design objectives of both high throughput and fairness and demonstrate the corresponding improvements.     

PMCAP/CDMA系统中一种新的多址干扰控制技术

多址干扰(MAI)是限制CDMA系统容量的瓶颈,而在无线通信系统中,为了实现数据的高速无差错传输,混合ARQ已经得到越来越多的应用。该文利用第二类混合ARQ(HARQ type-II)中每次重传的数据分组有不同的纠错能力和抗多址能力的特性,提出了一种新的联合区分多址干扰控制方法。仿真结果显示该方法在CDMA系统中有比传统方法更好的性能。