A Multi-Hop Resource Reservation Scheme for Seamless Real-Time QoS Guarantee in WiMedia Distributed MAC Protocol

In this paper, a multi-hop range conflict-free resource reservation scheme for UWB (Ultra Wide Band) WPAN (Wireless Personal Area Network) with D-MAC (Distributed Medium Access Control) is proposed. Unlike the centralized IEEE 802.15.3 MAC, the D-MAC UWB specified by WiMedia Alliance supports DRP (Distributed Reservation Protocol) mechanism which makes all devices be self-organized and removes the SOP (Simultaneous Operating Piconet) problem, i.e., packet collisions between overlapped piconets in the centralized IEEE 802.15.3 MAC. However, since each device’s mobility perspective in multi-hop environment has not been taken into account in the current WiMedia D-MAC, it may cause a “mobile” hidden node problem. In addition, once a DRP conflict occurs due to the mobile hidden node problem, only one of the DRP reservations involved in that DRP conflict maintains the reserved MASs, while the other DRP reservations must be terminated and DRP negotiations for them have to be re-started although only a few MASs are overlapped. Such DRP termination and renegotiation time delays due to the DRP conflicts can be a critical problem to the mobile devices transceiving real-time QoS traffic streams. Therefore, we propose a mechanism to prevent and resolve multi-hop range DRP conflicts due to each device’s mobility in D-MAC environment and demonstrate its guaranteed Seamless QoS and prioritized real-time QoS performances via numerical analyses.     

A Distributed Cooperative MAC Protocol for QoS Improvement and Mobility Support in WiMedia Networks

A Distributed Medium Access Control (D-MAC) protocol based on UWB for high-rate Wireless Personal Area Networks is specified by the WiMedia Alliance. D-MAC protocol is suitable for ubiquitous connection in home networks, military/medical applications due to its inexpensive cost, low power consumption, high data rate, and distributed approach. In contrast to IEEE 802.15.3, D-MAC makes all devices have the same functionality. And its networks are self-organized and provide devices with functions such as access to the medium, channel allocation to devices, data transmission, quality of service and synchronization in a distributed manner. D-MAC fundamentally removes the problems of the centralized MAC approach revealed at IEEE 802.15.3 MAC by adopting a distributed architecture. However, the current D-MAC can’t prevent QoS degradations, occurred by mobile nodes with low data rate due to bad channel status, which cause critical problems in QoS provisioning to isochronous streams and mobile applications. Therefore, we propose a distributed cooperative MAC protocol for multi-hop WiMedia networks using virtual MIMO links. Based on instantaneous Channel State Information among WiMedia devices, our proposed protocol can intelligently select the transmission path with higher data rate to provide advanced QoS with minimum delay for real-time multimedia streaming services.     

Wireless USB Cluster Tree based on Distributed Reservation Protocol for Mobility Support

Wireless USB (WUSB) is the USB technology merged with WiMedia PHY /MAC. WUSB can be applied to wireless personal area network applications as well as PAN applications like wired USB. However, due to mobility of WUSB devices in multi-hop environment, DRP (distributed reservation protocol) reservation conflicts happen frequently among WUSB devices with three-hop distance. To solve this problem in large scale WUSB networks, we propose a new DRP reservation scheme using dual role devices and a new Operation Info bits for three-hop mobility support. It is shown by simulation and numerical results that throughputs of WUSB devices at three-hop range hidden DRP reservation conflicts are largely increased.     

Distributed quality of service routing protocol for multimedia traffic in WiMedia networks

Ultra-wideband (UWB) technology has emerged as a solution for the wireless interface between medical sensors and personal servers in future telemedicine systems. The WiMedia Alliance has specified a distributed medium access control protocol based on UWB for high-rate WPANs. In the cases of some applications, data traffic between the source device and destination device is transmitted via one or more intermediate links before it reaches the destination device. However, when all data frames do not transmit in the current DRP reservation block, a relay device cannot transmit the received data frame from the source device in the current DRP policy, until the next DRP duration reserved for forwarding to the destination device begins. This policy increases end-to-end latency between the source device and destination device significantly. Therefore, in this paper, we propose a novel reservation-based routing protocol to minimize the end-to-end delay between source and destination. The proposed routing protocol utilizes the number of medium access slots and hop-count to decide the optimal route between the source device and destination device. The simulation results show that the proposed protocol can enhance the throughput and delay performance and improve energy efficiency by minimizing the packet drop and collision.     

Combining the rate adaptation and quality adaptation schemes for wireless video streaming

Video streaming service over wireless networks is a challenging task because of the changes in the wireless channel conditions that can occur due to interference, fading, and station mobility. Moreover, the IEEE 802.11 WLAN standard does not contain any specifications for the rate adaptation scheme which are useful for improving the wireless link utilization. To provide efficient wireless video streaming service, the rate adaptation scheme should be applied at the low layer and the quality adaptation scheme should be considered at the high layer. To meet this requirement of wireless video streaming, we propose a new cross-layer design for video streaming over wireless networks. This design includes the rate adaptation scheme in the data link and physical layers and the quality adaptation scheme in the application layer. The rate adaptation scheme adjusts the data transmission rate based on the measured RSSI at the sender-side and informs the quality adaptation scheme about the rate limits. Then the quality adaptation scheme utilizes this rate limits to adjust the quality of the video stream. Through performance evaluations, we prove that our cross-layer design improves the wireless link utilization and the quality of the video stream simultaneously.     

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.     

A Multi-channel Scheduling Scheme for Collision-Free High-Rate WPANs

Ultra wide-band (UWB) technologies are being feverishly developed in the technical community. UWB devices are expected to operate at rates of up to 0.5 Gb/s and communicate with other devices at a range of up to 10 m. Thus, UWB technologies are being developed as core technology for high-speed wireless personal area networks. The salient features of UWB networks—high-rate communications, low interference with other radio systems, and low power consumption—bring many benefits to users. Thus, they enable consumers to experience new applications such as wireless universal serial bus for connecting personal computers to their peripherals and the consumer–electronics in people’s living rooms. However, if multiple WiMedia logical link protocol Service Sets (WSSs) coexist in an adjacent area, various conflicts among independent WSSs can occur frequently. In order to solve this problem, we propose a multi-channel scheduling scheme (MCS) for the coexistence of adjacent WSSs. The proposed MCS scheme can scan new idle channel and detect its time offset where a WSS device can transmit a new beacon frame and data frames without conflicts. We also evaluate the performance of the proposed MCS scheme through various simulations in terms of several metrics. Simulation results demonstrate that the MCS scheme can minimize the possibility of data frame collisions by efficiently managing the multiple available channels in a hybrid manner combining proactive and reactive methods.     

UWB网络中分布式资源预留协议的设计与实现

分布式资源预留协议是UWB网络中一种重要的信道接入机制,其实现能为研究UWB网络性能提供仿真基础.本文分析了ECMA-368标准中的分布式资源预留协议体系,从结构体系、资源预约处理等方面着手,提出了一种在NS2仿真平台上实现该协议的设计方案.仿真结果表明,该方案有效地实现了DRP的基本功能,保证了资源的预留和节点之间业务流的可靠传输,为UWB网络仿真平台的实现打下了基础.     

Adaptive Self-Learning Resource Allocation Scheme for Unlicensed Users in High-Rate UWB Systems

In this paper, we investigate a dynamic sub-band allocation for spectrum sharing in the multiuser OFDM-UWB systems while respecting the system constraints and the distributed MAC architecture. The contribution of this work is twofold: first we propose a dynamic spectrum allocation scheme based on an analytical study by deriving a multiuser optimization problem to find the optimal allocation solution. Based on an adaptive and low-complexity approach, the proposed scheme shares the available resources among unlicensed UWB users while taking into consideration the QoS requirements and the channel conditions. Then we extend the proposed scheme to allow the coexistence of a maximum number of secondary users in one channel while maintaining all the constraints support. This leads to a time-frequency allocation approach that exploits information laying in different layers, allowing a cross-layer design. This new approach improves the system performance compared to WiMedia solution and offers a considerable gain for users that have strict QoS requirements.     

AF双向中继网络中一种新的中继选择算法

通过高信噪比条件下AF双向中继网络总速率的近似表达,给出了链路增益乘积和系统总速率之间的关系式。基于此关系式提出一种最大化链路增益乘积中继选择算法(Maximum Relay Selection,MRS),在中继处引入门限,将链路质量超过门限的中继选出建立可靠候选集。在建立的可靠候选集中以两跳链路增益乘积最大化为标准,实现最佳中继选择。通过仿真将该中继选择算法与现有AF双向中继网络3种不同中继选择算法进行性能比较。仿真结果表明,该中继选择算法能在同时保证AF双向中继网络两跳链路质量的前提下,提高系统的总速率。     

Cross-Layer Modeling for QoS-Driven Multimedia Multicast/Broadcast over Fading Channels in [Advances in Mobile Multimedia]

In this article we propose a cross-layer design model for multimedia multicast/broadcast services to efficiently support the diverse quality of service requirements over mobile wireless networks. Specifically, we aim at achieving high system throughput for multimedia multicast/broadcast while satisfying QoS requirements from different protocol layers. First, at the physical layer, we propose a dynamic rate adaptation scheme to optimize the average throughput subject to the loss rate QoS constraint specified from the upper-layer protocol users. We investigate scenarios with either independent and identically distributed (i.i.d.) or non-i.i.d. fading channels connecting to different multicast receivers. Then, applying the effective capacity theory at the data link layer, we study the impact of the delay QoS requirement (i.e., QoS exponent) on the multimedia data rate of mobile multicast/broadcast that our proposed scheme can support. Also presented are simulation results which show the trade-off among different QoS metrics and the performance superiority of our proposed scheme as compared to the other existing schemes.     

Optimal transmission of high definition video transmission in WiMedia systems

WiMedia systems are developed for indoor high-data-rate wireless systems. The H.264/AVC, a high-efficiency video coding technique, is considered for high definition (HD) video application. Considering the transmission of H.264/AVC based HD video over WiMedia, in this paper, we will propose a cross-layer architecture and an analytical model to calculate the optimal payload length with the constraints in error criteria, retransmission mechanism, and the delay budget. Besides, the required minimum reservation slots in WiMedia are also investigated to optimize the transmission performance of HD video.     

A Cross Layer Routing Protocol for Multihop Cellular Networks

We propose a cross-layer routing protocol for a Code Division Multiple Access (CDMA) Multihop Cellular Network (MCN). In designing the routing protocol for MCN, multiple constraints are imposed on intermediate relay node selection and end-to-end path selection. The constraints on relay nodes include willingness for cooperation, sufficient neighbourhood connectivity and the level of interference offered on the path. Path constraints include end-to-end throughput and end-to-end delay. A facile incentive mechanism is presented to motivate the cooperation between nodes in call forwarding. In addition, we present a route resilience scheme in the event of dynamic call dropping. In particular, a fast neighbour detection scheme for route resilience is proposed. Instead of using periodic HELLO messages as in traditional ad-hoc routing, the proposed neighbour detection scheme adopts an explicit handshake mechanism to reduce neighbour detection latency. We conclude the paper by demonstrating the superior performance of the proposed routing protocol compared with the other well known routing algorithms.     

分布式Alamouti空时码的信道容量及最优资源分配方案

该文针对基于译码转发协议的分布式Alamouti空时码(DF-DASTC)系统的信道容量以及最优资源分配策略问题。利用退化中继信道模型,推导得到了DF-DASTC系统在衰落信道下的信道容量闭式解。以DF-DASTC信道容量最大化为目标,对该系统在固定带宽分配时,中继及信源节点的最优功率分配方案进行了研究,推导得到了DF-DASTC系统的最优功率分配方案的闭式解。利用凸优化理论,将以DF-DASTC信道容量最大化为目标函数的多目标优化问题转换为非线性不等式约束的单目标凸优化问题,进一步得到了可变带宽分配时的DF-DASTC系统的最优带宽和功率分配策略。理论分析和系统仿真表明,该文所提出的资源分配策略,比平均分配的资源方案具有更大的信道容量。另外,该文的最优资源分配策略适用于具有多个中继节点的无线中继网络,具有普适性。     

Cross-Layer Analysis of Joint Rate and Power Adaptation in Nakagami Fading Channels with Multiple-User Contention

Adaptively adjusting transmit rate and power concurrently to enhance goodput and save energy is a challenging issue in a wireless local area network (WLAN) because goodput enhancement and energy saving are usually two contradictory goals. In this paper, we propose channel-driven rate and power adaptation (CDRPA) schemes and develop a physical (PHY)/medium access control (MAC) cross-layer analytical method incorporating the impacts of Nakagami fading channel and the carrier sense multiple access (CSMA) MAC protocol. The CDRPA scheme has much lower computation complexity than the energy-optimal complete-search scheme. In a multiuser contention scenario, we analyze the energy efficiency and the goodput of the power-first and rate-first CDRPA schemes as well as the energy-optimal complete-search adaptation scheme. At the cost of lower goodput, the power-first scheme has better energy efficiency than the rate-first CDRPA scheme, whereas if the goodput is the main concern, the rate-first CDRPA scheme shall be chosen due to better goodput performance. More interestingly, we find that the power-first CDRPA scheme can achieve about the same goodput and energy efficiency as the energy-optimal complete-search link adaptation scheme.     

协作通信系统中基于频谱效率优化的跨层设计

为改善协作分集系统的频谱效率,提出一种改进的跨层设计方案,对协作通信系统物理层的自适应调制编码（AMC）技术和链路层的混合自动重传(HARQ)协议进行联合优化设计。该方案利用少量比特的反馈,使得仅当目的节点通过直接信道不能正确译码分组时或者当直接信道处于深度衰落时触发中继节点转发协作伙伴数据。给出了所提方案基于瑞利衰落信道、解码转发（DF）条件下频谱效率的表达式,然后搜索在任意信噪比条件下使频谱效率最大化的调制与编码方案。通过计算机仿真对理论分析进行了验证。理论分析和仿真表明该跨层设计在中低信噪比(SNR)可进一步提升协作通信系统的频谱效率。      

Dual-Hop Non-regenerative OFDM Relay Systems with Chunk-Based Power Allocation

In this paper, we propose dual-hop non-regenerative Orthogonal Frequency Division Multiplexing (OFDM) relay systems without signal buffering and processing delay due to Fast Fourier Transform (FFT) and Inverse FFT (IFFT) at the Relay Node (RN). One scheme uses per subcarrier Power Allocation (PA) at Source Node (SN) and per chunk PA at RN to improve the achievable rate. Another scheme employs per chunk PA at both SN and RN. Numerical results in mobile communication environments show that both schemes improve the achievable rates compared to conventional simple amplify-and-forward relay systems with per subcarrier PA at RN. In particular, the latter scheme can obtain almost the same or slightly higher achievable rates by selecting an appropriate chunk size in severe frequency selective channel and by setting any chunk size in highly frequency-correlated channels. Therefore, chunk-based PA at both SN and RN can be found a beneficial PA for dual-hop OFDM relay systems in terms of competitive achievable rates and relatively small amount of required channel information to calculate allocated power.     

Cross-Layer Radio Resource Allocation for Multicarrier Air Interfaces in Multicell Multiuser Environments

Packet scheduling over shared channels is one of the most attractive issues for researchers dealing with radio resource allocation in wireless networks as modern systems' different traffic types, with different application requirements, need to coexist over the air interface. Recently, attention has been attracted to multicarrier techniques and the application of cross-layer approaches to the design of wireless systems. In this paper, a radio access network using a multicarrier air interface is considered in a multicell multiuser context. We propose a new cross-layer scheduling algorithm that manages channel, physical layer, and application-related information; we compare its performance with a previously published cross-layer strategy and with simpler well-known channel-aware or channel-unaware techniques and then discuss its optimization. We investigate the performance in terms of perceived user quality and fairness in the presence of mixed realistic traffic composed of H.264 video streaming with tight bounds on the delay jitter and file transfer protocol (FTP) data. To support video traffic, application-suited buffer-management techniques are also considered in conjunction with scheduling, and link adaptation is implemented at the physical layer to better exploit channel fluctuations. The role of scheduling and resource-allocation functionalities are discussed. It is shown that the cross-layer strategy proposed guarantees the same performance obtained by the previously published algorithm while reducing complexity. Moreover, under heavily loaded conditions, the cross-layer scheduling strategy provides a significant gain with respect to simple channel-aware or channel-unaware techniques.     

Distributed differential space-time coding for wireless relay networks

Distributed space-time coding is a cooperative transmission scheme for wireless relay networks. With this scheme, antennas of the distributive relays work as transmit antennas of the sender and generate a space-time code at the receiver. It achieves the maximum diversity. Although the scheme needs no channel information at relays, it does require full channel information, both the channels from the transmitter to relays and the channels from relays to the receiver, at the receiver. In this paper, we propose a differential transmission scheme, which requires channel information at neither relays nor the receiver, for wireless relay networks. As distributed space-time coding can be seen as the counterpart of space-time coding in the network setting, this scheme is the counterpart of differential space-time coding. Compared to coherent distributed space-time coding, the differential scheme is 3dB worse. In addition, we show that Alamouti, square real orthogonal, and Sp(2) codes can be used differentially in networks with corresponding numbers of relays. We also propose distributed differential space-time codes that work for networks with any number of relays using circulant matrices.     

Cross-layer design scheme for multihop communications

A cross-layer design scheme for wireless communications is proposed and the performance evaluated. The scheme combines a truncated automatic repeat request (ARQ) protocol at the data link layer and multihop transmission at the physical layer. Closed-form solutions are derived for the average throughput and the average number of transmissions required to send a packet when the channel surfers from Nakagami-m fading. Finally, the improvement, when the cross-layer design is implemented is shown.