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Wireless Model-Based Predictive Networked Control System Over Cooperative Wireless Network

Owing to their distributed architecture, networked control systems (NCSs) are proven to be feasible in scenarios where a spatially distributed feedback control system is required. Traditionally, such NCSs operate over real-time wired networks. Recently, in order to achieve the utmost flexibility, scalability, ease of deployment, and maintainability, wireless networks such as IEEE 802.11 wireless local area networks (LANs) are being preferred over dedicated wired networks. However, conventional NCSs with event-triggered controllers and actuators cannot operate over such general purpose wireless networks since the stability of the system is compromised due to unbounded delays and unpredictable packet losses that are typical in the wireless medium. Approaching the wireless networked control problem from two perspectives, this work introduces a practical wireless NCS and an implementation of a cooperative medium access control protocol that work jointly to achieve decent control under severe impairments, such as unbounded delay, bursts of packet loss and ambient wireless traffic. The proposed system is evaluated on a dedicated test platform under numerous scenarios and significant performance gains are observed, making cooperative communications a strong candidate for improving the reliability of industrial wireless networks.

A distributed MAC protocol for full duplex radio

Recent advances in antenna and circuit design enable radios that operate in full duplex mode on a single channel with very low residual self-interference. In this paper, the use of such full duplex radios in a wireless local area network (WLAN) is explored. Different scenarios in which the full duplex transmission can be exploited are studied. A distributed full duplex MAC design based on IEEE 802.11 DCF that adopts to the traffic conditions is proposed. The proposed MAC design works for both ad hoc and infrastructure modes of WLAN and takes into consideration new interference and contention during full duplex transmissions. OPNET simulations comparing the performance of the proposed MAC with traditional half duplex based IEEE 802.11 DCF show that the new MAC protocol provides up to 88% throughput gain in a heavily loaded network.

Dynamic resource scheduling schemes for W-CDMA systems

W-CDMA is the strongest candidate for the air interface technology of third-generation wireless communication systems. Dynamic resource scheduling is proposed as a framework that will provide QoS provisioning for multimedia traffic in W-CDMA systems. The DRS framework monitors the traffic variations and adjusts the transmission powers of users in an optimal manner to accommodate different service classes efficiently. Variable and optimal power allocation is suggested to provision error requirements and maximize capacity, while prioritized queuing is introduced to provision delay bounds. A family of DRS algorithms has been devised along these dimensions for obtaining different levels of QoS. The DRS schemes are discussed in terms of queuing and bandwidth allocation with an emphasis on their impact on delay QoS.

Half-duplex or full-duplex relaying: A capacity analysis under self-interference

In this paper multi-antenna half-duplex and full-duplex relaying are compared from the perspective of achievable rates. Full-duplexing operation requires additional resources at the relay such as antennas and RF chains for self-interference cancellation. Using a practical model for the residual self-interference, full-duplex achievable rates and degrees of freedom are computed for the cases for which the relay has the same number of antennas or the same number of RF chains as in the half-duplex case, and compared with their half-duplex counterparts. It is shown that power scaling at the relay is necessary to maximize the degrees of freedom in the full-duplex mode.

Cooperation in Wireless Sensor Networks: Design and Performance Analysis of a MAC Protocol

Cooperative communications is one of the promising techniques to enhance the performance of wireless networks. The extent of performance improvement needs to be carefully investigated, especially for wireless sensor networks, due to the overhead and energy costs involved with cooperation and the dependency on energy consumption models. In this paper, we propose a cooperative medium access control protocol, COMAC that enables cooperation in a realistic scenario using 802.11g based radios and leverages cooperative communications by making use of the overheard packets from neighboring nodes of a sender node. In an effort to determine the conditions under which cooperation is preferable, we evaluate COMACs performance in comparison with standard 802.11 through detailed simulations, considering different physical layer data rates, varying transmission ranges, networks of different sizes and various energy consumption models. COMAC is shown to provide robustness to the wireless channel impairments, resulting in increased transmission range and improved packet success ratio in point-to- point scenarios. Throughput and energy efficiency performance is also quantified for multi-point-to-point scenarios with varying number of contending nodes. It is shown that cooperation with COMAC can provide significant enhancement in throughput, up to 23 times non-cooperative 802.11, together with energy savings of 50% even for high circuit energy consumption cases.

Rate distortion optimized joint ARQ-FEC scheme for real-time wireless multimedia

In this paper, we investigate rate distortion optimized streaming of H.264 coded video sequences over time-varying wireless channels. Our main objective is to minimize average end-to-end distortion to satisfy a certain quality of service (QoS) by considering the media and channel characteristics such as packet importance, packet dependencies, decoding deadlines, channel state information and channel capacity. In particular, we propose a sender-driven optimized joint ARQ-FEC scheme that decides on packet transmissions, re-transmissions as well as the FEC rate used in each transmission. The optimized joint ARQ-FEC scheme along with packet scheduling aims to minimize a weighted sum of distortion and total transmission cost under capacity constraints. The other objective in this paper is to satisfy the QoS of the optimized joint ARQ-FEC scheme without minimizing end-to-end distortion. We improved two approximate algorithms that use the media and channel characteristics to transmit the best selected and FEC coded packet. The real-time simulation results with H.264 sequences demonstrate the efficacy of the all proposed algorithms over the classical error recovery scheme uses ARQ and FEC.

Throughput Analysis of ALOHA with Cooperative Diversity

Cooperative transmissions emulate multi-antenna systems and can improve the quality of signal reception. In this paper, we propose and analyze a cross layer random access scheme, C-ALOHA, that enables cooperative transmissions in the context of ALOHA system. Our analysis shows that over a fading channel C-ALOHA can improve the throughput by 30%, as compared to standard ALOHA protocol.

Cooperative MAC Protocol with Distributed Relay Actuation

Cooperative transmissions emulate multi-antenna systems utilizing merely nodes equipped with single-antenna and the degree of performance enhancement is dependent upon the relay selection and actuation mechanism employed. An essential part in the realization of cooperative wireless networks is the design of efficient adaptive MAC protocols that empower distributed selection and actuation of the best relays in the network. In this paper, we propose and analyze a distributed relay selection and actuation scheme based on random access. Our method relies on slotted ALOHA based relay advertisements, and unlike the other protocols in the literature, it supports cooperation with multiple relays. We provide the analysis of the throughput gain provided by the proposed scheme and obtain the optimum channel access probability for the relays to announce their availability for cooperation. The proposed scheme renders simple distributed operation, which makes it suitable especially for densely deployed wireless sensor networks. Via simulations, we verify the validity of optimum cooperation probability solution and we show that the proposed actuation scheme can provide significant throughput enhancements and energy savings over direct transmission.

IPTVhome networking via 802.11 wireless mesh networks: an implementation experience

Wireless multimedia home servers are the next generation of home entertainment systems. From a single broadband connection entering home, multimedia data is transmitted to TV and other peripherals using only wireless links. The provision of hiqh quality time-critical multimedia services in indoor environment is very challenging due to high attenuation and multi-path fading caused by the walls and the contention in the shared wireless channel. In this paper, we demonstrate that mesh networking can help improve the service quality of both multimedia and data users, when the video packets are relayed with EDCA priorities based on their importance. Our results on a real wireless mesh network implementation using the new high definition video streaming standard, H.264 verify our hypothesis, where we observe almost no degradation video quality, and very low packet delay and loss rate in the presence of high amount of competing data traffic.

Opportunistic Scheduling with Frame Aggregation for Next Generation Wireless LANs

The multiuser diversity phenomenon is exploited via opportunistic scheduling for increasing system throughput in wireless networks. Another method to enhance system throughput is through frame aggregation, which increases MAC efficiency. We consider opportunistic scheduling jointly with frame aggregation. In this paper, we argue that existing opportunistic schemes are not optimal when frame aggregation is used. We propose new scheduling approaches that combine channel states with queue states. Through detailed simulations, we show that our new algorithms offer significant improvement in network throughput over non-opportunistic and greedy schedulers. Our algorithms also provide a good compromise between throughput and fairness.