Traffic-based topology control algorithm for energy savings in multi-hop wireless networks

This paper presents a traffic-based topology control algorithm for multi-hop wireless networks, in order to optimize the global energy consumption while maximizing the aggregate throughput. Contrary to major related works, we do not consider that reducing transmission powers implies reducing interferences and that the traffic is uniformly distributed among the links. Thus, we propose to dynamically calculate the transmission power of nodes depending on the traffic. First, we redefine the N-hop interference model for varying transmission powers. Then, we define a function giving the minimum interference according to the transmission powers. We propose several algorithms minimizing this function: global optimization, local optimization, and distributed optimization for a limited computation cost. Our first algorithm is used as a reference for limited cases. We show by simulation that our heuristics are relevant compared to existing works.     

New transmission scheme to enhance throughput of DF relay network using rate and power adaptation

This paper presents a new transmission scheme for a decode and forward (DF) relay network using continuous power adaptation while independent average power constraints are provisioned for each node. To have analytical insight, the achievable throughputs are analysed using continuous adaptation of the rates and the powers. As shown by numerical evaluations, a considerable outperformance is seen by continuous power adaptation compared to the case where constant powers are utilised. Also for practical systems, a new throughput maximised transmission scheme is developed using discrete rate adaptation (adaptive modulation and coding) and continuous transmission power adaptation. First a 2-hop relay network is considered and then the scheme is extended for an N-hop network. Numerical evaluations show the efficiency of the designed schemes.     

Adaptive multirate CDMA for uplink throughput maximization

We determine the optimal adaptive rate and power control strategies to maximize the total throughput in a multirate code-division multiple-access system. The total throughput of the system provides a meaningful baseline in the form of an upper bound to the throughput achievable with additional restrictions imposed on the system to guarantee fairness. Peak power and instantaneous bit energy-to-noise spectral density constraints are assumed at the transmitter with matched filter detection at the receiver. Our results apply to frequency selective fading in so far as the bit energy-to-equivalent noise power spectral density ratio definition can be used as the quality-of-service metric. The bit energy-to-equivalent noise power spectral density ratio metric coincides with the bit-error rate metric under the assumption that the processing gains and the number of users are high enough so that self-interference can be neglected. We first obtain results for the case where the rates available to each user are unrestricted, and we then consider the more practical scenario where each user has a finite discrete set of rates. An upper bound to the maximum average throughput is obtained and evaluated for Rayleigh fading. Suboptimal low-complexity schemes are considered to illustrate the performance tradeoffs between optimality and complexity. We also show that the optimum rate and power adaptation scheme with unconstrained rates is in fact just a rate adaptation scheme with fixed transmit powers, and it performs significantly better than a scheme that uses power adaptation alone.     

Distributed power control for multiuser cognitive radio networks with quality of service and interference temperature constraints

One of the most challenging problems in dynamic resource allocation for cognitive radio networks is to adjust transmission power of secondary users (SUs) while quality of service needs of both SUs and primary users (PUs) are guaranteed. Most power control algorithms only consider interference temperature constraint in single user scenario while ignoring the interference from PUs to SUs and minimum signal to interference plus noise ratio (SINR) requirement of SUs. In this paper, a distributed power control algorithm without user cooperation is proposed for multiuser underlay CNRs. Specifically, we focus on maximizing total throughput of SUs subject to both maximum allowable transmission power constraint and SINR constraint, as well as interference temperature constraint. To reduce the burden of information exchange and computational complexity, an average interference constraint is proposed. Parameter range and convergence analysis are given for feasible solutions. The resource allocation is transformed into a convex optimization problem, which is solved by using Lagrange dual method. In computer simulations, the effectiveness of our proposed scheme is shown by comparing with distributed constrained power control algorithm and Nash bargaining power control game algorithm. Copyright © 2014 John Wiley & Sons, Ltd.     

Rate selection based medium access control for full-duplex asymmetric transmission

The realization of full-duplex wireless communication is predictable. And asymmetric transmission is a practical and low-cost application scenario, where full-duplex access point (FD_AP) can communicate with two users simultaneously to receive and send packets. While, in an asymmetric transmission, the transmit power of uplink sender decides the uplink and downlink rates because of the inter-client interference, which accordingly restricts the throughput. Besides, the size of packets in uplink and downlink is generally unequal. Therefore, a WIFI network with a FD_AP and half-duplex users is studied in this paper, and a medium access control (MAC) protocol based on power control and rate selection (PCRS) is proposed. PCRS MAC employs a received signal strength based rate selection strategy to select different rates and power for uplink and downlink transmission. Then, FD_AP can establish efficient and reliable full-duplex asymmetric transmission. Simulation results show that PCRS can improve the throughput and the probability of successful asymmetric communication as compared to the distributed coordination function (DCF) and a simple full-duplex MAC protocol without PCRS. Besides, PCRS MAC also maintains a high level of fairness.

     

Joint rate regulation and power control for cochannel interference limited wireless networks

Centralized and distributed algorithms for joint rate regulation and power control are proposed for the wireless networks where the cochannel interference limits the capacity. The goal of the proposed algorithms is maximizing the data rate while minimizing the transmitting power on each hop of the wireless networks. The distributed algorithm simulates the operation of the centralized algorithm in a distributed fashion and need not measure the link gains for all transmission links and interference links. We prove that the distributed algorithm can find the maximal transmitting rate and the minimal transmitting power as the centralized algorithm does. Simulation results also show that the proposed distributed algorithm outperforms the previous distributed algorithm in the data rate achieved. Copyright © 2011 John Wiley & Sons, Ltd.     

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.     

一种基于分布式功率控制的侧行链路高谱效传输机制

第五代(5th Generation, 5G)无线通信系统除了支持蜂窝通信,还支持侧行链路(Sidelink, SL)通信,即两个用户设备(User Equipment, UE)之间可以直接通信,而不需要经过基站中转,有利于降低传输时延、提升资源利用率。在现有的SL分布式系统中,主要通过简单的能量测量进行干扰规避,资源复用准则欠佳,导致中高用户密度场景下吞吐受限。为此,提出了一种基于分布式功率控制的SL高谱效传输机制。各发送UE基于目标链路的信道状态信息(Channel State Information, CSI)和其他干扰链路的CSI进行功率优化,以实现局部范围内多个通信链路的和吞吐最大化;进一步,设计了广播式的CSI测量上报机制能实现多链路的分布式功率控制和资源选择。仿真结果表明,所提方案相比于现有的SL分布式资源分配机制,在中高用户密度下可获得30%～100%的吞吐增益;此外,所提方案相比于现有WiFi的载波侦听多址(Carrier Sense Multiple Access, CSMA)分布式信道接入机制,在中高用户密度下可获得50%～200%的吞吐增益。     

基于速率约束的OFDM中继链路能效最优资源分配策略

该文研究解码转发(DF)模式的OFDM中继链路的能效最大化资源分配问题。与现有典型的固定速率最小化发射功率或无约束最大化能效算法不同,该文考虑电路功率消耗的前提下,将问题建模为以最大化系统能效为目标,同时考虑用户最小速率需求、源节点S和中继节点R各自总发射功率约束下的联合子载波配对和最优功率分配问题。证明了速率和功率联合约束条件下中继链路全局能效最优解的唯一性,在此基础上提出一种低复杂度联合最优资源分配策略。仿真结果表明,该文所提方案能够在最小速率和S/R节点最大发射功率约束下自适应分配功率资源,实现系统能效最优,并能够降低链路的中断概率。     

Spectrum efficiency sub-carrier and energy efficiency power allocation for downlink multi-user CoMP in multi-cell system

Coordinated multi-point transmission/reception （CoMP） was proposed currently as an effective technology to improve cell-edge throughput in next-generation wireless systems. Most of the existing work discussed clustering methods mostly to maximize the edge user throughput while neglecting the problem of energy efficiency, such as those algorithm clustering base stations （BSs） of better channel condition and BSs of worse channel condition together. In addition, BSs usually increase the transmit power to achieve higher throughput without any considering of interference caused to other users, that may result in energy waste. The authors focus on the throughput maximizing problem while fully considering energy saving problem in CoMP systems. A coefficient is defined to describe the fitness of clusters. Then a sub-carrier allocation algorithm with clustering method is put forward for CoMP downlink, which can save the transmit power of BS and increase the throughput. Furthermore a power allocation scheme is proposed based on non-cooperation game; in which the transmit power is decreased by BSs generally to reach the Nash equation （NE）. Simulation shows that the proposed sub-carrier allocation scheme and power allocation algorithm are better than the existing ones on users＇ throughput while consumes much less energy.     

A scheme for throughput maximization in a dual-class CDMA system

This work focuses on the problem of efficient exploitation of the available bandwidth in order to provide high bit rates on the wireless link, as will be required in future wireless systems interfacing to broadband fixed networks. In particular, the uplink of a CDMA system with two user classes is considered. One of the classes consists of delay-intolerant users requiring support for a constant information bit rate, while the other consists of delay-tolerant users needing support for an information bit rate larger than a given value. It is assumed that when not transmitting information, synchronization contact is maintained with the base station at a given rate. The objective is to maximize the throughput of the delay tolerant users, while ensuring that the interference to other cells is as low as possible by minimizing the sum of all of the transmit powers used by the mobiles. Two transmission modes for the delay-tolerant users are considered. In the first mode, all of the users are allowed to transmit information when they wish. In the second mode, the transmissions of the delay-tolerant users are scheduled, so that only a limited number of them are transmitting information at any given time instant. It is shown that the second transmission mode, which is a time-scheduled scheme for the delay-tolerant users (with hybrid CDMA/TDMA as a special case), affords a better throughput while imposing the same average power requirements as conventional transmission. The results in this paper can be interpreted using results from previous work based on information theory     

Power Control for Distributed MAC Protocols in Wireless Ad Hoc Networks

In centralized wireless networks, reducing the transmission power normally leads to higher network transport throughput. In this paper, we investigate power control in a different scenario, where the network adopts distributed MAC layer coordination mechanisms. We first consider widely adopted RTS/CTS based MAC protocols. We show that an optimal power control protocol should use higher transmission power than the "just enough" power in order to improve spatial utilization. The optimal protocol has a minimal transmission floor area of Theta(d_{ij}d_{max}), where d_{max} is the maximal transmission range and d_{ij} is the link length. This surprisingly implies that if a long link is broken into several short links, then the sum of the transmission floors reserved by the short links is still comparable to that reserved by the long link. Thus, using short links does not necessarily lead to higher throughput. Another consequence of this is that, with the optimal RTS/CTS based MAC, rate control can at best provide a factor of 2 improvement in transport throughput. We then extend our results to other distributed MAC protocols which uses physical carrier sensing or busy-tone as the control signal. Our simulation results show that the optimal power controlled scheme outperforms other popular MAC layer power control protocols.     

Optimizing the throughput‐lifetime tradeoff in wireless sensor networks with link scheduling,rate adaptation,and power control

Throughput and lifetime are usually conflicting objectives in designing wireless sensor networks; hence, the right balance needs to be found. With this aim in view, we address in this paper the problem of minimizing the frame length defined within a time division multiple access scheme and the problem of maximizing network lifetime subject to a maximum frame length. The pursued solution in either case leverages a wide range of parameters related to coverage, routing, transmission power, and data rate. Furthermore, it is consistent with the physical interference model. To this end, we rely on column generation technique to derive near‐optimal solutions even when the integrality constraints on coverage and flow variables are enforced. Moreover, we propose a polynomial‐time heuristic algorithm to solve efficiently the underlying NP‐hard problem of concurrent link selection with discrete power control and rate adaptation. Simulation results show that our heuristic algorithm leads to solutions within 3% of optimality while saving around 99% of computation time. Besides, the results illustrate the significant impact of power control and rate adaptation on throughput and lifetime improvement. Interestingly, we found that network lifetime can be significantly prolonged when traffic demands are sufficiently low at the affordable cost of small decrease in throughput. Copyright © 2015 John Wiley & Sons, Ltd.     

混合蜂窝和端到端网络中的分布式功率控制算法

该文针对蜂窝模式和端到端模式混合网络,提出了一种端到端分布式功率控制方法。该算法以最大化系统频谱效率为目标,以凸优化工具为基础,提出了分布式功率控制的具体算法。在算法设计中考虑了混合网络中不同通信模式之间的有害干扰,提出了有效的干扰避免方法,从而提高了系统吞吐量。仿真结果对算法的收敛性和性能进行了验证。     

Combined power and rate adaptation for wireless cellular systems

We extend the throughput optimization technique of Qiu and Chawla (1999) for adaptive modulation, to combine power and rate adaptation in wireless cellular systems. We develop new combined power and rate control algorithms for wireless multimedia systems, in which the transmitted powers and rates of different media users are adapted based on the signal-to-interference power ratio. Using simulations, we show that with appropriately chosen power and rate limits, our proposed combined power and rate control algorithms can achieve a higher throughput when compared to previously proposed algorithms with power control only.     

On the usefulness of outer-loop power control with successive interference cancellation

Multiuser detection (MUD) performance can be significantly better than the conventional matched filter receiver in CDMA systems. Further, since optimal MUD is exponentially complex, research has mainly focused on suboptimal approaches such as successive interference cancellation (SIC). SIC requires a geometric distribution of received powers to achieve equal performance for all received signals. We propose a power control scheme for SIC to achieve this profile (or the profile corresponding to any desired and achievable set of error rates) based on frame-error rate (FER) or bit-error rate (BER). Specifically, we derive the relationship between received power and BER for linear SIC and show that for unlimited mobile powers, a deterministic distributed BER-based outer-loop power control drives the received powers to the optimal power profile. The convergence of the deterministic BER-based algorithm is examined in the absence of inner loop power control errors. The simulated performance of a stochastic version of this algorithm is examined using instantaneous FER measurements. The stochastic algorithm is shown to provide unbiased estimates of the true power updates and converge to the optimal power vector provided the mobiles have unlimited power. We consider power limits for specific mobiles and find that individual mobile limits do not affect the performance of other signals. We examine the impact of system loading, multiple FER targets, error correction, and inner loop power control error on the performance of the algorithm.     

Throughput Gains Using Rate and Power Control in Cooperative Relay Networks

In this letter, we use power and rate adaptation to maximize the throughput in cooperative relay networks when limited feedback links to the transmitter nodes exist. We observe that, for a finite rate of feedback, the throughput maximizing outage probability can be relatively high. This suggests using higher rate codes and allowing some outages in an effort to increase the overall network throughput. Our analysis also reveals that the relaying transmission paradigm offers significant throughput gains over direct transmission for any rate of the feedback link. Our work not only demonstrates the power of cooperative coding, but also suggests the importance of network protocols incorporating feedback to allow for throughput maximization     

Rate-adaptive indoor infrared wireless communication systems usingrepeated and punctured convolutional codes

We propose a rate-adaptive transmission scheme using repeated and punctured convolutional codes for indoor infrared wireless communications. The proposed system uses a coding scheme consisting of an outer punctured convolutional code and an inner repetition code, and varies code rate, i.e., bit rate adaptively depending on channel conditions. We show that the proposed system can realize communications in worse channel conditions at the expense of bit rate, while maximizing the throughput available to a user on his position     

Spreading and power allocation for multiple antenna transmission using decorrelating receivers

We propose a new scheme for multiple antenna transmission in the context of spread-spectrum signaling. The new scheme consists of using shifted Gold sequences to modulate independent information on the multiple antennas. We show that this strategy of using multiphase spreading (MPS) on different antennas greatly improves the throughput over currently known spread-spectrum multiple-antenna methods. We also find the optimal power allocation strategy among multiple transmit antennas for a fixed rate of channel state information, which might be provided via a feedback link, at the transmitter. We demonstrate the differences in optimal power distribution for maximizing capacity and minimizing probability of outage. When the transmission from the two antennas uses orthogonal spreading, we find that optimizing the power does not give much gain over the equal power transmission. However, when the transmissions are not orthogonal as in the case of MPS, then allocating power to maximize throughput gives considerable gain over equal power transmission. We also consider the effect of imperfections in the feedback channel on the optimal power allocation and show that our power allocation scheme is robust to feedback errors.     

EPCM – an efficient power controlled MAC protocol for mobile ad hoc network

To reduce interference and to save a significant amount of energy, a control of transmission power is employed in Mobile Ad hoc Network. Many researchers have reported numerous transmission power control schemes to achieve the objective. Some of those techniques use higher transmission power for control packets (Request To Send/Clear To Send) and lesser power for Data and ACK packets. These schemes, though save some amount of energy, achieve least aggregate throughput due to poor spatial reuse and hidden terminal interference. In this paper, an efficient Power Controlled Medium Access Control (EPCM) scheme is evinced, which uses uniform interference aware and minimum transmission power for both Control and Data packet. The performance of EPCM is evaluated and compared with three reported Medium Access Control protocols which are based on transmission power control schemes and is observed that the proposed protocol achieves better throughput and minimal energy consumption while avoiding the hidden terminal problem.