Haowei Bai

Error modeling schemes for fading channels in wireless communications: A survey

Network system designers need to understand the error performance of wireless mobile channels in order to improve the quality of communications by deploying better modulation and coding schemes, and better network architectures. It is also desirable to have an accurate and thoroughly reproducible error model, which would allow network designers to evaluate a protocol or algorithm and its variations in a controlled and repeatable way. However, the physical properties of radio propagation, and the diversities of error environments in a wireless medium, lead to complexity in modeling the error performance of wireless channels. This article surveys the error modeling methods of fading channels in wireless communications, and provides a novel user-requirement (researchers and designers) based approach to classify the existing wireless error models.

Wireless sensor network for aircraft health monitoring

Wireless sensor networks is an emerging paradigm of computing and networking where a node may be selfpowered, and have sensing, computing, and communication capabilities. They have been proposed for use in a wide variety of applications. The objective of this article is to describe a wireless sensor network for monitoring of the health of aircraft engines. We describe the architecture of the wireless sensor network along with how it fits into the general area of wireless sensor networks.

The applicability of adaptive control theory to QoS design: limitations and solutions

Due to the increasing complexity, the behavior of large-scale distributed systems becomes difficult to predict. The ability of online identification and auto-tuning of adaptive control systems has made the adaptive control theoretical design an attractive approach for quality of service (QoS) guarantee. However, there is an inherent constraint in adaptive control systems, i.e. a conflict between asymptotically good control and asymptotically good parameter estimates. This paper addresses these limitations via sensitivity analysis. The simulation study demonstrates that the adaptive control theoretical design depends on the excitation signal, environment uncertainty, and a priori knowledge on the system. In addition, this paper proposes an adaptive dual control framework for mitigating these constraints in QoS design. By incorporating the existing uncertainty of the online prediction into the control strategy, the dual adaptive control framework optimizes the tradeoff between the control goal and the uncertainty.

Applying speculative technique to improve TCP throughput over lossy links

The throughput degradation of transport control protocol (TCP) over lossy links due to the coexistence of congestion losses and link corruption losses is very similar to the degradation of processor performance due to control hazards in CPU design. First, two types of loss events in networks with lossy links can be considered as two possibilities of a branching result (correct speculation vs. incorrect speculation) in a CPU. Secondly, both problems result in performance degradations in their application environments, i.e., penalties (in clock cycles) in a processor, and throughput degradation (in bit per second) in TCP networks. This has motivated us to apply speculative techniques (i.e., speculating on the outcome of branch predictions), used to overcome control dependencies in a processor, to TCP improvements when lossy links are involved in TCP connections. The objective of this paper is to propose a protocol-level speculation based TCP modification to improve its throughput over lossy links. Simulation results show that, compared to other prior research, our proposed algorithm significantly improves TCP throughput in a network with satellite links

Improving TCP throughput over lossy links using protocol-level speculations

The degradation of transport control protocol (TCP) throughput in networks with lossy links is mainly due to the coexistence of two types of losses, congestion losses and link corruption losses. This is very similar to processor performance degradation due to control hazards in CPU design. First, two types of loss events in networks with lossy links can be considered as two possibilities of a branching result (correct speculation vs. incorrect speculation) in a CPU. Secondly, both the problems result in performance degradations in their application environments, i.e., penalties (in clock cycles) in a processor, and throughput degradation (in bit per second) in TCP networks. This has motivated us to apply speculative techniques (e.g., speculating on the outcome of branch predictions), used to overcome control dependencies in a processor, to TCP algorithm design when lossy links are involved in TCP connections. The objective of this paper is to propose a protocol-level speculation based TCP modification to improve its throughput performance over lossy links. Simulation results show that our proposed algorithm significantly improves TCP throughput in a network with satellite links.

Enhancing TCP throughput over lossy links using ECN-capable RED gateways

Explicit congestion notification (ECN), when used with random early detection (RED) gateways, reduces packet losses and delays of transport control protocol (TCP) based applications. However, choosing the buffer size and optimum parameter values of RED buffers are still open research issues. In this paper, we first present a model to determine the optimal value of REDs maximum threshold to achieve zero packet loss at RED gateways. Secondly, as an application of our model, we propose a new TCP algorithm, called differentiation capable TCP (Diff-C-TCP) to improve the TCP performance over lossy satellite links. Since most of network congestion losses can be eliminated by our zero loss model, Diff-C-TCP assumes packet losses to be indicators of link corruption, and uses ECN to explicitly indicate network congestion. We have shown that our zero packet loss analytical model matches simulation results very well, and our proposed Diff-C-TCP algorithm significantly improve TCP throughput.

Cross-layer speculative architecture for end systems and gateways in computer networks with lossy links

The throughput degradation of Transport Control Protocol (TCP)/Internet Protocol (IP) networks over lossy links due to the coexistence of congestion losses and link corruption losses is very similar to the degradation of processor performance (i.e., cycle per instruction) due to control hazards in computer design. First, two types of loss events in networks with lossy links are analogous to two possibilities of a branching result in computers (taken vs. not taken). Secondly, both problems result in performance degradations in their applications, i.e., penalties (in clock cycles) in a processor, and throughput degradation (in bits per second) in a TCP/IP network. This has motivated us to apply speculative techniques (i.e., speculating on the outcome of branch predictions), used to overcome control dependencies in a processor, for throughput improvements when lossy links are involved in TCP/IP connections. The objective of this paper is to propose a cross-layer network architecture to improve the network throughput over lossy links. The system consists of protocol-level speculation based algorithms at transport layer, and protocol enhancements at middleware and network layers that provide control and performance parameters to transport layer functions. Simulation results show that, compared with prior research, our proposed system is effective in improving network throughput over lossy links, capable of handling incorrect speculations, fair for other competing flows, backward compatible with legacy networks, and relatively easy to implement.

QoS Support in ARINC 664 P8 Data Networks: ATN Applications Over TCP/IP Ground-to-Ground Subnetworks ∗

Aeronautical Telecommunication Network (ATN) has been developed by International Civil Aviation Organization (ICAO) to integrate air-ground and ground-ground data communications for aeronautical applications into a single network serving air traffic control and aeronautical operational communications. The current ICAO ATN model specifies a standalone network with its own protocols, which requires building an expensive separate network for air-ground and ground-ground communications. However, the cost of building ATN can be reduced if it can use existing networks wherever possible, such as the Internet.ARINC 664 Part 8 committee has been developing an approach for inter-operation of ATN applications over the commercial TCP/IP networks. To carry time critical information required for aeronautical applications,ATN provides different Quality of Services (QoS) to applications. Although the current Internet does not provide QoS, Internet Engineering Task Force (IETF) developed the Differentiated Services (DiffServ) network to provide differential QoS to users of next generation data networks. The objective of this paper is to investigate the possibility and conduct a proof-of-concept evaluation of providing QoS to ATN applications over the DiffServ network in the next generation Internet. Our results show that the QoS requirements ofATN applications for ground-to-ground communications can be successfully satisfied when ATN is run over a DiffServ backbone.

Achieving QoS for aeronautical telecommunication networks over differentiated services

Aeronautical Telecommunication Network (ATN) has been developed by the International Civil Aviation Organization to integrate Air-Ground and Ground-Ground data communication for aeronautical applications into a single network serving Air Traffic Control and Aeronautical Operational Communications. To carry time critical information required for aeronautical applications, ATN provides different Quality of Services (QoS) to applications. ATN has been designed as a standalone network with its own protocols which requires building an expensive separate network for ATN. However, the cost of building ATN can be reduced if it can run over a public network such as the Internet. Although the current Internet does not provide QoS, Internet Engineering Task Force (IETF) is standardizing the Differentiated Services (DiffServ) network to provide differential QoS to users of next generation data networks. The objective of this paper is to investigate the possibility of providing QoS to ATN applications when it runs over the DiffServ network in the next generation Internet. Our results show that the QoS requirements of ATN applications can be successfully provided when they run over a DiffServ backbone in the next generation Internet.

Layered view of QoS issues in IP-based mobile wireless networks

SUMMARY With the convergence of wireless communication and IP-based networking technologies, future IP-based wireless networks are expected to support real-time multimedia. IP services over wireless networks (e.g. wireless access to Internet) enhance the mobility and flexibility of traditional IP network users. Wireless networks extend the current IP service infrastructure to a mix of transmission media, bandwidth, costs, coverage, and service agreements, requiring enhancements to the IP protocol layers in wireless networks. Furthermore, QoS provisioning is required at various layers of the IP protocol stack to guarantee different types of service requests, giving rise to issues related to cross-layer design methodology. This paper reviews issues and prevailing solutions to performance enhancements and QoS provisioning for IP services over mobile wireless networks from a layered view. Copyright # 2006 John Wiley & Sons, Ltd.