Effective bandwidth of multimedia traffic in packet wireless CDMA networks with LMMSE receivers: a cross-layer perspective

We propose a novel concept of cross-layer effective bandwidth that characterizes the unified resource usage taking into account both physical layer linear minimum mean square error (LMMSE) receivers and statistical characteristics of the packet traffic in code division multiple access (CDMA) networks. Based on the concept of cross-layer effective bandwidth, we develop an optimal connection admission control (CAC) scheme for variable bit rate packet traffic with QoS constraints at both physical and network layers. By introducing a small signal-to-interference ratio (SIR) outage probability using the concept of cross-layer effective bandwidth, the capacity of CDMA networks in the proposed CAC scheme can be increased significantly compared to some existing schemes. The effectiveness of the proposed approaches is demonstrated by numerical examples.     

A cross-layer framework for multi-layer-video multicast with QoS requirements in multirate wireless networks

We propose a cross-layer framework for efficient multi-layer-video multicast with rate adaptation and quality-of-service (QoS) requirements in multirate wireless networks. We employ time division multiple access at the physical layer to transmit different video layers' data. The multicast sender then dynamically regulates the transmission rate and time-slot allocation based on the channel state information (CSI) and loss QoS requirements imposed by upper protocol layers. Under our proposed cross-layer framework, we first design a rate adaptation algorithm to fulfill the diverse loss QoS requirements for all video layers while achieving high multicast throughput. We then develop a time-slot allocation scheme which synchronizes data transmission across different video layers. Also conducted are simulation results to validate and evaluate our designed adaptive multicasting schemes under the proposed cross-layer framework.     

无线视频错误控制技术研究

无线视频传输中误码和丢包会导致视频质量的严重下降,研究了视频传输中的错误控制相关技术。对已有的无线视频错误控制方法进行了详细分析,在此基础上提出了一种更加有效的无线视频传输中的错误控制框架。将无线误码丢包和拥塞丢包准确区分,改进了以往算法带宽估计公式不准确的问题。并且对视频内容根据在解码端重要性的不同区分保护。在错误控制的同时进行了拥塞控制。     

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.     

A Cross-Layer Adaptive Modulation and Coding Scheme for Energy Efficient Software Defined Radio

In this paper, a simple and novel cross-layer adaptive modulation and coding (AMC) scheme, which increases the energy efficiency of the wireless communication system is proposed. Traditionally, AMC has been used to improve MAC-layer performance in terms of coded bit error rate, packet error rate, and throughput. The modulation and coding scheme is switched according to signal-to-noise ratio thresholds at the PHY layer. We extend the approach, proposing a framework for energy-efficient cross-layer AMC that captures the impact of both MAC layer and PHY layer parameters on the AMC switching criteria. Cross-layer designs are naturally suited to software defined radio applications. Not only are they readily implemented in software, but also they are integral to the radio components. They can optimize performance of the radio either for a given configuration or adaptively. Through examples of WLAN physical layer and Frequency Domain Equalized systems, we demonstrate our AMC scheme and verify its effectiveness by simulation.     

RED theory for quality of service provisioning in wireless communications

In this paper, we study the performance limit of a wireless communication system over a fading channel. The system under study consists of 1) a finite‐buffer discrete‐time queueing system on the link layer; and 2) a rate‐adaptive channel coding system on the physical layer. The objective of this paper is to analyze the relationship among data rate (R), packet error probability (E), and delay bound (D) under the interaction between the link layer and the physical layer. In our analysis, we consider three types of packet errors; that is, 1) packet drop due to full buffer; 2) packet drop due to delay bound violation; and 3) packet decoding error due to channel noise. We obtain an upper bound on the packet error probability. Furthermore, by minimizing the packet error probability over the transmission rate, we obtain an optimal rate control policy that guarantees the user‐specified data rate and delay bound. In the case of constant arrival, the optimal rate control policy results in a rate‐error‐delay triplet; then, by varying data rate and delay bound, we obtain rate‐error‐delay Pareto‐optimal surface, which serves as the performance limit of the system under study. Copyright © 2012 John Wiley & Sons, Ltd.     

Improving link layer performance on satellite channels with shadowing via delayed two-copy selective repeat ARQ

This paper focuses on improving performance of land mobile satellite channels (LMSCs) at high band (Ka-band or EHF band), where shadowing is the primary impediment to reliable data transmission. Compared with multipath fading, shadowing exists on a longer time scale; hence, interleaving to combat shadowing introduces unacceptably large decoding delay. We use Lutz's model to investigate bit-error rate/packet-error rate (BER/PER) performance of interleaving with various forward error correction (FEC) coding as a function of different channel parameters to demonstrate its limited effectiveness for combatting burst errors whose mean duration significantly exceed a link layer (LL) packet. We propose a delayed two-copy selective repeat ARQ (DTC-SR-ARQ) scheme, whereby two copies of a packet are sent-the second with a delay relative to the first-in every transmission or retransmission. Closed-form expressions for mean transmission time, success probability, and residual loss probability are provided and simulations used to validate the analysis. Furthermore, the issue of optimum delay is addressed as well, and a simple yet effective strategy is suggested to support transmission control protocol (TCP) traffic over this data link layer. DTC-SR-ARQ is shown to achieve much shorter additional delay than interleaving and compared with normal SR-ARQ, reduces mean transmission time at expense of a small increase in residual packet loss probability. Furthermore, ns2 simulation results show that for TCP traffic, DTC-SR-ARQ acquires higher end-to-end throughput than normal SR-ARQ.     

Cross-layer QoS Analysis of Opportunistic OFDM-TDMA and OFDMA Networks

Performance analysis of multiuser orthogonal frequency division multiplexing (OFDM-TDMA) and orthogonal frequency division multiple access (OFDMA) networks in support of multimedia transmission is conducted in this work. We take a cross-layer approach and analyze several quality-of-service (QoS) measures that incilude the bit rate and the bit error rate (BER) in the physical layer, and packet average throughput/delay and packet maximum delay in the link layer. The authors adopt a cross-layer QoS framework similar to that in IEEE 802.16, where service classification, flow control and opportunistic scheduling with different subcarrier/bit allocation schemes are implemented. In the analysis, the Rayleigh fading channel in the link layer is modeled by a finite-state Markov chain, and the channel state information (CSI) is assumed to be available at the base station. With the M/G/1 queueing model and flow control results, the analysis provides important insights into the performance difference of these two multiaccess systems. The derived analytical results are verified by extensive computer simulation. It is demonstrated by analysis and simulation that OFDMA outperforms OFDM-TDMA in QoS metrics of interest. Thus, OFDMA has higher potential than OFDM-TDMA in supporting multimedia services.     

Payload Length and Rate Adaptation for Multimedia Communications in Wireless LANs

We provide a theoretical framework for cross-layer design in multimedia communications to optimize single-user throughput by selecting the transmitted bit rate and payload size as a function of channel conditions for both additive white Gaussian noise (AWGN) and Nakagami-m fading channels. Numerical results reveal that careful payload length adaptation significantly improves the throughput performance at low signal to noise ratios (SNRs), while at higher SNRs, rate adaptation with higher payload lengths provides better throughput performance. Since we are interested in multimedia applications, we do not allow retransmissions in order to minimize latency and to reduce congestion on the wireless link and we assume that packet loss concealment will be used to compensate for lost packets. We also investigate the throughput and packet error rate performance over multipath frequency selective fading channels for typical payload sizes used in voice and video applications. We explore the difference in link adaptation thresholds for these payload sizes using the Nafteli Chayat multipath fading channel model, and we present a link adaptation scheme to maximize the throughput subject to a packet error rate constraint.     

基于D2D通信系统中的一种跨层中继选择算法

在D2D通信系统与蜂窝网络共存的场景下,引入中继节点可有效提高D2D链路的吞吐量和D2D用户对蜂窝用户的干扰。文中基于译码转发模式,结合跨层协作通信的思想,提出了一种基于物理层和数据链路层的跨层中继选择算法。该算法结合物理层的信道状态信息和数据链路层的队列状态信息,两个参数进行最优中继节点的选择。并最终通过仿真验证表明,基于跨层中继选择算法可提高通信系统的吞吐量,同时降低了通信系统的平均时延和数据包错误率。     

Performance analysis of DS-CDMA with slotted ALOHA random access for packet PCNs

In this paper, we present a discrete time Markov chain based analytical framework for the study of Direct-Sequence Code-Division-Multiple-Access (DS-CDMA) with slotted ALOHA random access protocols (DS-CDMA-S-ALOHA) for packet Personal Communications Networks (PCNs). It incorporates both the random access and the random errors associated with DS-CDMA-S-ALOHA protocols into a unified framework. The key feature is that it distinguishes between the two stages in the transmission process, namely the access stage and the reception stage, which characterize the random access and the random errors associated with DS-CDMA-S-ALOHA protocols respectively. Two DS-CDMA-S-ALOHA protocols are presented and analyzed. The performance of the protocols and the effects of the design parameters, namely the packet retransmission probability and the forward error correction code rate of the Bose-Chaudhuri-Hocquenghem (BCH) block codes are evaluated numerically and compared with a bandwidth equivalent conventional multi-channel slotted ALOHA system. The results show that, by proper design, the DS-CDMA-S-ALOHA protocols can double the throughput with respect to that of a bandwidth equivalent conventional multi-channel slotted ALOHA system.     

Cross-Layer Performance Study of Cooperative Diversity System With ARQ

In this paper, a cross-layer design of a wireless communication system is proposed by considering a quadrature signaling (QS)-based cooperative diversity (CD) system employing truncated stop-and-wait automatic repeat request (ARQ) for error control. The proposed CD-ARQ scheme employs selection relaying at the partner, and all the transmission channels are assumed to exhibit Nakagami-$m$ fading. To analyze the cross-layer performance of the proposed scheme, a Markov model is developed by capturing the effects of correlated transmission errors of the Nakagami-$m$ fading cooperative channels. Based on the analysis, the effective cooperative channel of QS-CD-ARQ is uncorrelated when the normalized Doppler shift of at least one of the user-to-destination channels is higher than 0.2. Performance metrics (e.g., channel efficiency, packet loss rate, throughput, average delay, and jitter) are taken into account in the study. Our numerical results show that the QS-CD-ARQ scheme outperforms both an incremental-relaying-based CD system and a non-cooperative system if the average of the received signal is higher than the receiver sensitivity and if the channel between users is better than the direct transmission channel. In addition, QS-CD-ARQ provides the lowest packet loss rate with the lowest delay among all the schemes for any number of maximum retry limits. Moreover, compared with a scheme that employs incremental relaying, the proposed QS-CD-ARQ scheme is less complex to implement.      

OFDM系统中基于自适应调制和ARQ的PHY-MAC跨层设计

设计了一种适用于正交频分复用（OFDM）的跨层自适应算法。此算法结合自适应调制（AM）和有限自动重传请求（ARQ）技术，能够根据不同的信道状态在物理层和数据链路层联合进行性能优化，可以在保证上层吞吐量一定的条件下提供更小的丢包率。仿真结果表明，通过跨层结构设计的系统和传统的分层结构设计的系统相比有一定的性能增益，在进行高速传输时此增益更为显著。     

Estimation of accurate effective loss rate for FEC video transmission

We propose an algorithm for adjusting data transmission parameters, such as the packet size and the code rate of forward error correction (FEC), to obtain maximum video quality under dynamic channel conditions. When determining transmission parameters, it is essential to calculate an accurate effective loss rate that reflects FEC recovery failures and over-deadline packets. To this end, we analyze the delays caused by FEC coding and the potential packet size variations. In our analysis, we consider the effect of delayed transmission of video packets incurred by the parity packets as well as the encoder and decoder buffers. With the analysis reflecting the delay effect, we are able to accurately estimate the delay patterns of all video packets. Based on the analysis results, we establish an accurate model for estimating the effective loss rate. Simulations show that the proposed effective loss rate model accurately estimates the effective loss rate and significantly improves the reconstructed video quality at the receiver.     

Performance analysis of cross layer design with imperfect channel information in distributed antenna systems

In this paper, based on the imperfect channel state information (CSI), a cross layer design (CLD) scheme is developed for distributed antenna system (DAS) by combining adaptive modulation (AM) at the physical layer and automatic repeat request (ARQ) at the data link layer. The performance of DAS with CLD is investigated over composite fading channel which considers large-scale path loss and small-scale Rayleigh fading. With the performance analysis, the probability density function of the estimated signal-to-noise ratio (SNR) is derived, and then, the switching thresholds under a target packet error rate constraint are further derived. According to these results, and using numerical calculation, the closed form analytical expressions of average packet error rate and spectrum efficiency of DAS with CLD are, respectively, achieved, which will provide better evaluation way for the DAS performance. To decrease the performance loss caused by the conventional single estimation in the presence of imperfect CSI, the multi-estimation method is proposed to increase the system performance by exploiting previous channel estimation information. Numerical results corroborate our theoretical analysis, and the simulation is in consistence with the theoretical result. Moreover, the system performance can be increased by decreasing the estimation error and/or path loss. Especially, the multi-estimation method can enhance the performance effectively and enable the system to tolerate large estimation errors.     

New cross-Layer design approach to ad hoc networks under Rayleigh fading

We propose a new cross-layer design employing the predictability of Rayleigh channels to improve the performance of ad hoc networks. In addition, we propose a Markov model for Rayleigh channels and an innovative Markov model for IEEE 802.11 distributed coordination function. By combining these two models, we derive the theoretical expressions for network throughput, packet processing rate, packet loss probability, and average packet delay under Rayleigh channels. The simulation of the proposed cross-layer design is also carried out. It is shown that the new approach improves the network throughput, reduces unnecessary packet transmissions and therefore reduces packets lost. We also show that there is a close match between the analytical and the simulation results which confirms the validity of the analytical models.     

一种环境感知的无线Mesh网络自适应QoS路径选择算法

本文针对如何改善无线多跳Mesh网络的服务质量,满足无线多媒体业务对数据传输的带宽、时延、抖动的要求等问题,研究了一种基于无线信道状态和链路质量统计的MAC层最大重传次数的自适应调整算法。该算法通过对无线Mesh网络的无线信道环境的动态感知,利用分层判断法区分无线分组丢失的主要原因是无线差错还是网络拥塞导致,实时调整MAC层的最佳重传次数,降低无线网络中的分组冲突概率。基于链路状态信息的统计和最大重传策略,提出了一种启发式的基于环境感知的QoS路由优化机制HEAOR。该算法通过动态感知底层链路状态信息,利用灰色关联分析法自适应选择最优路径,在不增加系统复杂度的基础上,减少链路误判概率,提高传输效率。NS2仿真结果表明,HEAOR算法能有效减少重路由次数,降低链路失效概率,提高网络的平均吞吐率。本文提出的方法不仅能够优化MAC层的重传,而且通过发现跨层设计的优化参数实现对路径的优化选择。      

Joint QoS control for video streaming over wireless multihop networks: A cross-layer approach

In this paper, we propose a novel cross-layer framework for jointly controlling and coding for multiple video streams in wireless multihop networks. At first, we develop a cross-layer flow control algorithm that works at the medium access control (MAC) layer to adjust each link's persistence probability and at the transport layer to adjust flow rates. This proposal is designed in a distributed manner that is amenable to online implementation for wireless networks, and then, a rate-distortion optimized joint source-channel coding (JSCC) approach for error-resilient scalable encoded video is presented, in which the video is encoded into multiple independent streams and each stream is assigned forward error correction (FEC) codes to avoid error propagation. Furthermore, we integrate the JSCC with the specific flow control algorithm, which optimally applies the appropriate channel coding rate given the constraints imposed by the transmission rate obtained from the proposed flow control algorithm and the prevailing channel condition. Simulation results demonstrate the merits and the need for joint quality of service (QoS) control in order to provide an efficient solution for video streaming over wireless multihop networks.     

Optimal resource allocation for wireless video over CDMA networks

We present a multiple-channel video transmission scheme in wireless CDMA networks over multipath fading channels. We map an embedded video bitstream, which is encoded into multiple independently decodable layers by 3D-ESCOT video coding technique, to multiple CDMA channels. One video source layer is transmitted over one CDMA channel. Each video source layer is protected by a product channel code structure. A product channel code is obtained by the combination of a row code based on rate compatible punctured convolutional code (RCPC) with cyclic redundancy check (CRC) error detection and a source-channel column code, i.e., systematic rate-compatible Reed-Solomon (RS) style erasure code. For a given budget on the available bandwidth and total transmit power, the transmitter determines the optimal power allocations and the optimal transmission rates among multiple CDMA channels, as well as the optimal product channel code rate allocation, i.e., the optimal unequal Reed-Solomon code source/parity rate allocations and the optimal RCPC rate protection for each channel. In formulating such an optimization problem, we make use of results on the large-system CDMA performance for various multiuser receivers in multipath fading channels. The channel is modeled as the concatenation of wireless BER channel and a wireline packet erasure channel with a fixed packet loss probability. By solving the optimization problem, we obtain the optimal power level allocation and the optimal transmission rate allocation over multiple CDMA channels. For each CDMA channel, we also employ a fast joint source-channel coding algorithm to obtain the optimal product channel code structure. Simulation results show that the proposed framework allows the video quality to degrade gracefully as the fading worsens or the bandwidth decreases, and it offers improved video quality at the receiver.     

Efficient channel utilization for real-time video in OVSF-CDMA systems with QoS assurance

In this paper, the utilization of real-time video service in the downlink of an orthogonal variable spreading factor code division multiple access (OVSF-CDMA) system is studied. By modeling the video traffic and wireless channel as a joint Markov modulated process, and properly partitioning the states of the Markov process, an adaptive rate allocation scheme is proposed for real-time video transmission with quality of service provisioning while achieving high channel utilization. The scheme is applicable for packet switching and frame-by-frame real-time video transmission, and incorporates both the physical layer and network layer characteristics. For QoS provisions, the closed form expressions of packet delay and loss probability are derived based on the Markov model. Analytical and simulation results demonstrate that the proposed scheme can significantly improve the channel utilization over the commonly used effective bandwidth approach.