Performance study of mobile WiMAX network with changing scenarios under different modulation and coding

WiMAX—the Worldwide Interoperability for Microwave Access is a promising technology for offering high‐speed data, video and multimedia services over mobile platform evolving toward all IP networks. The increasing demand of WiMAX for VoIP and high‐speed multimedia is due to the simplicity of installation and cost reduction compared with the traditional wired DSL cable. The challenges to service providers lie with the Quality of Service (QoS) under varying fading environment while at the same time maximizing for resource utilization. In this paper, a rigorous and comprehensive performance study of mobile WiMAX has been made with respect to adaptive modulation and coding techniques considering the variation in the speed of the mobile, path‐loss, scheduling services and application type for comparing with the fixed type of modulations. The OPNET 14.5.A modeler for WiMAX platform has been used as simulator for adaptation at the physical layer of the transmission in WiMAX OFDMA structure. Observation reveals that dynamic adaptation of modulation and coding schemes based on channel condition enables better QoS while consuming low overall bandwidth of the system. Copyright © 2011 John Wiley & Sons, Ltd.     

WiMAX中基于跨层设计的SNR阈值区间可变式自适应调制编码机制

 IEE 802.16标准在物理层定义了多种可选的调制和编码方式,并可采用基于信道状态信息的自适应调制编码机制。本文提出一种新的适用于全球微波接入互操作网络的信噪比阈值区间可变式自适应调制编码机制,其自适应调制-编码模式不仅取决于物理层信道状态信息,还与高层多媒体服务流的目标误包率这一重要服务质量参数有关。与传统型和改进型自适应调制编码机制相比,信噪比阈值区间可变式自适应调制编码机制能够在满足各类业务目标误包率的同时获得较好的系统有效数据传输速率。     

基于AMC和HARQ的大气激光通信跨层系统性能研究

针对大气激光通信中由大气湍流引起的系统性能下降问题,研究了基于物理层自适应调制编码(AMC)和数据链路层混合自动请求重传(HARQ)的大气激光通信跨层系统性能。在建立了大气湍流信道瞬时信噪比模型的基础上,建立了大气激光通信AMC-HARQ系统模型,并推导了系统误包率和频带利用率公式,最后在双伽马信道模型下进行了仿真分析。仿真结果表明,大气激光通信AMC-HARQ系统能够在保证一定误包性能的条件下,大大提高系统频带利用率,提高单一应用AMC时的系统误包性能。随着重传次数增加,误包率和频带利用率均提高,但频带利用率增幅随重传次数增加而减小。     

联合自适应调制编码与ARQ的跨层设计

为了提高无线系统数据速率,目前广泛地采用物理层自适应调制编码(AMC)和链路层自动重发请求(ARQ)协议相结合的跨层设计,这种设计方法能大大提高系统频谱利用率。本文在瑞利衰落信道模型下,在给定包时延和丢包率的情况下,推导出了联合AMC和ARQ的跨层设计频谱利用率的公式。同时也与纯AMC和纯ARQ的情况作了比较。     

Utility‐based probabilistic call admission control for complete fairness in wireless networks

Resource reservation or the other prioritization strategies adopted by Call Admission Control (CAC) schemes in wireless networks lead to unfair resource allocation to users belonging to different service classes (SCs) due to high divergence among the respective call blocking probabilities (CBPs). In this paper, we propose dynamic optimization of probabilistic CAC (P‐CAC) schemes to assure CAC fairness among users of different SCs in wireless networks. The approach is based on users utility combined with fairness optimization, aiming at dynamically determining the probability value in the P‐CAC scheme. This optimal probability is adjusted to network ongoing traffic, CBPs of each SC, prioritization levels characterizing the SCs supported, and the users risk aversion, which reflects their behavior toward the perceived QoS. The existence and uniqueness of the optimal probability that leads to absolute fairness among the users of a wireless network are proven. Copyright © 2012 John Wiley & Sons, Ltd.     

Packet Loss Fair Scheduling Scheme for Real‐Time Traffic in OFDMA Systems

In this paper, we propose a packet scheduling discipline called packet loss fair scheduling, in which the packet loss of each user from different real‐time traffic is fairly distributed according to the quality of service requirements. We consider an orthogonal frequency division multiple access (OFDMA) system. The basic frame structure of the system is for the downlink in a cellular packet network, where the time axis is divided into a finite number of slots within a frame, and the frequency axis is segmented into subchannels that consist of multiple subcarriers. In addition, to compensate for fast and slow channel variation, we employ a link adaptation technique such as adaptive modulation and coding. From the simulation results, our proposed packet scheduling scheme can support QoS differentiations while guaranteeing short‐term fairness as well as long‐term fairness for various real‐time traffic.     

Dynamic pricing for load‐balancing in user‐centric joint call admission control of next‐generation wireless networks

Next‐generation wireless networks (NGWN) will be heterogeneous, comprising of a number of radio access technologies (RATs) co‐existing in the same geographical area. In NGWN, joint call admission control (JCAC) algorithms are required to select the most appropriate RAT for each incoming call. It is envisaged that these JCAC algorithms will be user‐centric (i.e. will consider users' preferences in making RAT selection decisions) in order to enhance user satisfaction. However, user‐centric JCAC algorithms can lead to highly unbalanced traffic load among the available RATs in NGWN because users act independently, and most of them may prefer to be connected through a particular RAT. Highly unbalanced traffic load in NGWN will result in high overall call blocking/dropping probability and poor radio result utilization. To address this problem, we propose dynamic pricing for balancing traffic load among available RATs in heterogeneous wireless networks where users' preferences are considered in making RAT selection decisions. By dynamically adjusting the service price in each of the available RATs, the proposed user‐centric JCAC scheme evens out the unbalanced traffic load caused by independent users' preferences. The JCAC scheme uses fuzzy multiple attribute decision‐making (MADM) technique to select the most appropriate RAT for each incoming call. We develop a Markov model to evaluate the overall call blocking/dropping probability and percentage load in each RAT in heterogeneous wireless networks. Performance of the proposed JCAC scheme is compared with that of a scheme that does not use dynamic pricing. Simulation results are given to show the effectiveness of the proposed JCAC scheme. Copyright © 2009 John Wiley & Sons, Ltd.     

大气激光通信自适应系统中LDPC的识别

从大气激光通信信道 模型出发,结合大气激光通信特殊的调制方式,利用接收解调软判决序列的后验概率信息 ,导出大气激光通信 自适应系统中低密度奇偶校验码(LDPC)的识别算法公式。仿真结果表明, 当识别正确率为 0.8时, 在强湍流条件下, 算法公式比传统算法性能提高约1.2dB;在弱湍流条件下,算法公 式 比传统算法性能提高约1.5dB;并 且随着码率的降低和码长的增加,识别成功率均有提高。因此,所提算法公式能够进一步抑 制大气湍流影响,提高系统性能。     

Adaptive coding and modulation scheme for satellite‐UMTS TDD systems based on a photogrammetric channel estimation method

The conventional wireless communication systems are designed to overcome the worst‐case channel, using the huge amount of redundant bits to assure communications performance and quality of services. Those systems cannot achieve the optimum spectrum and power efficiency. This paper presents an adaptive coding and modulation scheme used in the user terminals of the third‐generation satellite communication system. A three‐state photogrammetric channel estimation method is introduced for tracing the variations of large‐scale environments. The mobile user terminal dynamically switches the suitable coding and modulation schemes according to the result of photogrammetric channel estimator in order to maximize the power efficiency and data throughput. The real measurement data were used to validate our proposed method. The results show that the proposed method not only reduces the system complexity, but also mitigates the power control requirements and increases the data throughput for the land mobile satellite personal communication systems. Copyright © 2006 John Wiley & Sons, Ltd.     

Flexible block‐wise loading algorithm for effective resource allocation and reduction of uplink feedback information in OFDMA systems

Adaptive modulation and coding (AMC) is a well‐known technique that selects a suitable modulation level and coding rate according to the user's channel quality. The utilization of AMC in downlink (DL) requires the channel information of each user on DL to properly select the modulation and coding scheme (MCS) level. However, under a practical OFDMA system environment, it is unsuitable to feedback all the channel information over the whole frequency resources due to the limited uplink bandwidth. In this paper, to optimize the performance of the AMC system and to reduce the uplink feedback requirement, we propose a flexible block‐wise loading (FBL) algorithm combined with a novel channel quality information (CQI) feedback scheme requiring less number of CQI feedback bits, which is suitable for the general OFDMA system with AMC. The proposed FBL algorithm dynamically allocates groups of sub‐carriers to each user in DL based on the channel quality information encapsulated in a newly defined feedback signal format. As a result, the sector throughput and outage performance is improved due to the flexibility on the sub‐channel allocation and increased accuracy on the CQI feedback information by the proposed FBL algorithm. Copyright © 2008 John Wiley & Sons, Ltd.     

Packet Scheduling Algorithm Considering a Minimum Bit Rate for Non‐realtime Traffic in an OFDMA/FDD‐Based Mobile Internet Access System

In this letter, we consider a new packet scheduling algorithm for an orthogonal frequency division multiplexing access/frequency division duplex (OFDMA/FDD)‐based system, e.g., mobile broadband wireless access or high‐speed portable internet systems, in which the radio resources of both time and frequency slots are dynamically shared by all users under a proper scheduling policy. Our design objective is to increase the number of non‐realtime service (e.g., WWW) users that can be supported in the system, especially when the minimum bit rate requirement is imposed on them. The simulation results show that our proposed algorithm can provide a significant improvement in the average outage probability performance for the NRT service, i.e., significantly increasing the number of NRT users without much compromising of the cell throughput.     

Bit error rate performance of orthogonal frequency‐division multiplexing relaying systems with high power amplifiers and Doppler effects

This paper analyzes the bit error rate performance of orthogonal frequency‐division multiplexing systems in mobile multihop relaying channels. We considered the uplink scenario and quantified the effects of mobile channel impairments such as Doppler shift due to user mobility per hop, high power amplifier distortions when amplifying the transmitted/relayed orthogonal frequency‐division multiplexing symbol per hop, and the cumulative effects of these impairments on multihop relaying channels. It was shown that the resulting intercarrier interference due to the cumulative effects of the phase noise generated by these impairments per hop becomes very significant in a multihop relaying communication system and severely degrades the bit error rate performance of the system. Simulation results agree well with and validate the analysis. Copyright © 2011 John Wiley & Sons, Ltd.     

Resource allocation in orthogonal frequency division multiple access‐based cognitive radio systems with minimum rate constraints

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

Cross-layer design based on RC-LDPC codes in MIMO channels with estimation errors

In this paper, we propose a cross-layer design framework combining adaptive modulation and coding (AMC) with hybrid automatic repeat request (HARQ) based on rate-compatible low-density parity-check codes (RC-LDPC) in multiple-input multiple-output (MIMO) fading channels with estimation errors. First, we propose a new puncturing pattern for RC-LDPC codes and demonstrate that the new puncturing pattern performs similar to the random puncturing but is easier to apply. Then, we apply RC-LDPC codes with the new puncturing pattern to the cross-layer design combing AMC with ARQ over MIMO fading channels and derive the expressions for the throughput of the system. The effect of channel estimation errors on the system throughput is also investigated. Numerical results show that the joint design of AMC and ARQ based on RC-LDPC codes can achieve considerable spectral efficiency gain.     

Research on application of variable coding modulation system based on Digital Video Broadcasting ‐ Satellite ‐ 2nd Generation in data transmission of near‐earth remote sensing satellite

In order to make full use of the link resources for data transmission from near‐earth remote sensing satellites, variable coding modulation (VCM) system is used to fully utilize the system link margin to improve the satellite data transmission performance. By analyzing the dynamic link under the VCM data transmission system, the contribution of the VCM system to the satellite data link optimization is studied from the perspective of engineering application, which can provide reference for the data link design of remote sensing satellites. Applying the flow design, for the currently adopted transmission system of X band, compared with traditional constant coding modulation (CCM) system, the average link performance of VCM system can be increased by 42.1% in single‐station transmission mode and 53.3% in dual‐station relay mode through the exampled analysis.     

Nth best relay selection with network coding in two‐way relay systems

In this paper, we propose an Nth best relay selection (Nth‐RS) scheme for analog network coding in two‐way relay systems. In traditional two‐way single‐relay selection schemes, only the best one is selected to forward network‐coded signals. However, in practical applications, the best relay may be unavailable because of the scheduling or overload constraints. In this case, we investigate a more general scheme, where the Nth best but available relay is selected. To evaluate the transmission of reliability, the expression of outage probability in exponential–integral form and its asymptotic expression in closed form are presented. Moreover, the upper bound and lower bound of outage probability are also derived. The analysis reveals that the diversity order of Nth‐RS equals to (M ? N + 1), where M is the number of relay nodes, and the results are verified by simulations. In order to improve system performance, transmit power between sources and relay is optimally allocated to minimize the upper bound of outage probability under total power constraint. Simulation results show that Nth‐RS scheme with proposed power allocation can achieve substantial improvement over equal power allocation scheme. Copyright © 2012 John Wiley & Sons, Ltd.     

Performance analysis of switch‐and‐stay combining in two‐way relay systems with analog network coding and time‐division broadcast protocols

In this paper, we consider switch‐and‐stay combining (SSC) in two‐way relay systems with two amplify‐and‐forward relays, one of which is activated to assist the information exchange between the two sources. The system operates in either analog network coding (ANC) protocol where the communication is only achieved with the help of the active relay or time‐division broadcast (TDBC) protocol where the direct link between two sources can be utilized to exploit more diversity gain. In both cases, we study the outage probability and bit error rate (BER) for Rayleigh fading channels. In particular, we derive closed‐form lower bounds for the outage probability and the average BER, which remain tight for different fading conditions. We also present asymptotic analysis for both the outage probability and the average BER at high signal‐to‐noise ratio. It is shown that SSC can achieve the full diversity order in two‐way relay systems for both ANC and TDBC protocols with proper switching thresholds. Copyright © 2014 John Wiley & Sons, Ltd.     

Packet splitting and adaptive modulation based on CSI of time domain for decode‐and‐forward cooperative OFDM systems in different channel model

Cooperative communications obtain the transmission and channel diversity gains by using the relay node. However, since cooperative communications transmit the redundancy signal to obtain the transmission diversity gain, the transmission rate is degraded. Moreover, since cooperative communications add the interference in the relay node, the diversity gain is also degraded. The packet splitting has been proposed based on the channel state information of the time domain to obtain the good system performance without the redundancy signal. Moreover, the adaptive modulation has been proposed to improve the transmission rate. In this paper, we propose the combination method with the packet splitting and the adaptive modulation based on the channel state information of the time domain to improve the bit error rate and throughput performances for decode‐and‐forward cooperative orthogonal frequency division multiplexing systems in the different channel model. From the computer simulation results, we determine the optimum weight and threshold for the proposed method. Moreover, the proposed method shows the good bit error rate and throughput performances.     

A new methodology for the determination of the co‐ordination area around stations of the fixed service (FS) with respect to mobile Earth stations on board vessels (ESVs)

The extensive use of Earth stations located on board sea going vessels (ESVs) has created the necessity for the development of a new type of co‐ordination area around the fixed service receivers (FSRs) operating in frequency bands C and Ku. To date there is not a single method concerning the calculation of the co‐ordination area around the FSRs, which takes into account the mobility of the interfering stations. This paper addresses an in‐depth analysis of the interference produced to the FSRs by the ESVs and proposes a new method for the development of the co‐ordination area around the FSRs, taking into account parameters such as the velocity of the ESVs and their frequencies of passage from specific locations. Simulations performed for three different operational scenarios prove the validity of the new methodology. Copyright © 2005 John Wiley & Sons, Ltd.