Jeffrey M. Capone

Smart antenna system analysis, integration and performance for mobile ad-hoc networks (MANETs)

This paper focuses on the interaction and integration of several critical components of a mobile ad-hoc network (MANET) using smart antenna systems. A MANET is a wireless network where the communicating nodes are mobile and the network topology is continuously changing. One of the central motivations for this work comes from the observed dependence of the overall network throughput on the design of the adaptive antenna system and its underlying signal processing algorithms. In fact, a major objective of this work is to study and document the overall efficiency of the network in terms of the antenna pattern and the length of the training sequence used by the beamforming algorithms. This study also considers in sufficient detail problems dealing with the choice of direction of arrival algorithm and the performance of the adaptive beamformer in the presence of antenna coupling effects. Furthermore, the paper presents strategies and algorithms to combat the effects of fading channels on the overall system.

Integrating data traffic into a CDMA cellular voice system

Part one of this paper analyzes the effects of data traffic integration into a CDMA cellular voice system. The figure of merit used for the quality of service seen by the voice users is measured by the probability of blocking. The CDMA system under consideration is a power controlled, cellular architecture in which blocking occurs when the total interference level exceeds the background noise level by 10 dB [1]. It is shown that the introduction of data can be done at little or no increase in the probability of blocking on the voice users. In part two we propose and analyze a protocol which achieves the efficient integration of data by maximizing the utilization of the resources and minimizing the delay experienced by the voice users. The proposed protocol admits data traffic into the CDMA cellular system based on the current aggregate voice interference level, and allows for the efficient integration of voice and data without degrading the quality of service for the delay-critical voice traffic. A Markovian model for this protocol is developed, evaluated and compared to computer simulation results.

Delivering QoS requirements to traffic with diverse delay tolerances in a TDMA environment

The focus of this paper is on determining the call admission region and scheduling policies for a time-division multiple-access (wireless) system supporting heterogeneous real-time variable bit rate applications with distinct quality of service (QoS) requirements and traffic characteristics. The QoS is defined in terms of a maximum tolerable packet delay and dropping probability. A packet is dropped if it experiences excess delay. The call admission region is established for policies that are work-conserving (WC) and that satisfy the earliest due date (EDD) service criterion (WC-EDD policies). Such policies are known to optimize the overall system performance. In addition to the determination of the call admission region, this study leads also to the construction of scheduling policies that deliver any performance in the region established for WC-EDD policies. Finally, an upper bound on the call admission region that can be achieved under any policy (not limited to the WC-EDD policies) is determined.

Delivering diverse delay/dropping QoS requirements in a TDMA environment

In this paper, the problem of sharing resources (slots of an up-link TDMA frame) among real-time heterogeneous variable bit rate (VBR) applications with diverse quality of service (&OS) requirements is addressed. The QoS requirements for each application is defined in terms of a maximum tolerable packet delay and dropping probability; a packet is dropped if it experiences excess delay. The region of achievable QoS vectors which is central to the call admission problem is established for policies that are work-conserving and satisfy the earliest due date (EDD) service criterion (WC-EDD policies); such policies are known to optimize the overall system performance. In addition to the determination of the region of achievable QoS vectors, this study leads also to the construction of scheduling policies which deliver any performance in the region established for WC-EDD policies. Finally, an upper bound on the region of QoS vectors that can be achieved under any policy (not limited to the WCEDD policies) is determined.

Achievable QoS and scheduling policies for integrated services wireless networks

In Integrated Services Wireless Networks transmission resources are shared among geographically disperse applications with diverse Quality of Service (QoS) requirements and traffic characteristics. To provide QoS guarantees and use the bandwidth efficiently, call admission and scheduling functions are necessary. These functions should ensure the delivery of the target QoS to the supported applications while achieving statistical multiplexing gains, without explicit and continuous exchange of information between sources and scheduler. In this dissertation, call admission and transmission scheduling policies are studied for a TDMA system. Variable bit rate (VBR) applications with distinct QoS requirements and traffic characteristics are considered. In this environment, packets which cannot be transmitted over the frame following their arrival may be dropped (due to delay violations) or may be delayed to compete for service in the next frame, depending on the QoS requirements. The focus of the research is to determine the region of achievable multi-dimensional (non-degenerate) QoS vectors for heterogeneous VBR applications in this shared resource environment. Determining the region of achievable QoS is central to the admission control problem. For example, if with the addition of the new source, the new multi-dimensional target QoS vector is in the region of achievable QoS, then the call can be admitted. The problem of determining the region of achievable QoS vectors is formulated in a manner that makes it possible to investigate by employing polytope/convex space and game theory. As a result, the region of achievable QoS for heterogeneous applications in a interference/resource-limited wireless network is precisely described. In addition, it is possible to identify simple policies which deliver any given QoS vector within the region, by proving properties associated with the extreme points of the region. Together, call admission and scheduling are shown to ensure that the target QoS is delivered to each application. Finally, the impact that channel quality has on the region of achievable QoS is studied. In a wireless environment, packets are dropped not only due to the competition for the transmission resources, but also due to channel induced errors (interference). Thus, the physical channel can affect the region of achievable QoS as well. As a consequence, the region of achievable QoS vectors is shaped by the packet discarding process at both the transmitter and the receiver due to resource and interference limitations, respectively.

Achievable QoS in an interference/resource limited shared wireless channel

In this work, the region of achievable quality-of-service (QoS) is precisely described for a system of real-time heterogeneous variable bit rate (VBR) sources competing for slots (packet transmission times) of a time division multiple access (TDMA) frame. The QoS for each application is defined in terms of a maximum tolerable packet-dropping probability. Packets may be dropped due to delay violations and channel induced errors. The region of achievable QoS is precisely described for an interference/resource limited network by considering the underlying TDMA-multiple access control (TDMA-MAC) structure and the physical channel. A simple QoS-sensitive error-control protocol that combats the effects of the wireless channel while satisfying the real-time requirements is proposed and its impact on the region of achievable QoS is evaluated. The results presented here clearly illustrate the negative impact of a poor channel and the positive impact of the employed error-control protocol on the achievable QoS. The region of achievable QoS vectors is central to the call admission problem, and in this work, it is used to identify a class of scheduling policies capable of delivering any achievable performance.

Scheduling in packet radio networks-a new approach

In the broadcast schedule construction problem in a radio network, a frame of minimum length provides every transceiver an opportunity for transmission after least amount delay. However, such a frame does not necessarily maximize the network throughput. The network throughput can be increased by choosing a frame of suboptimal length, although in this situation the throughput of some of the individual transceivers might decrease. We present a schedule construction scheme that takes into account the interests of the network as well as the individual transceivers and finds a balance between the two conflicting interests. The objective of this scheme is to maximize the network throughput without a significant adverse impact on the performance of individual transceivers. This scheme guarantees a network throughput that is at least as large as in the traditional scheduling schemes using the minimum length frame.

Impact of smart antenna designs on network throughput and BER

The demand for increased capacity in wireless networks motivated recent research toward wireless systems that exploit space selectivity. The paper presents a comprehensive effort on smart antennas that examines and integrates antenna array designs and beamforming, and the impact of these designs on the network throughput. Fading and coding channel modeling are also examined to improve the system BER. The antenna design that has been chosen is a planar array of rectangular microstrip elements, The frequency of operation is 20 GHz, and both 4/spl times/4 and 8/spl times/8 designs are examined. Tchebyscheff and adaptively beamformed designs are considered, and their impact on network throughput and system BER is examined. From the results, it is possible to provide guidelines for the design of smart antenna systems for optimum capacity in mobile ad hoc networks.

A framework for analysis of VBR traffic over CDMA

With emerging multi-media wireless applications, there is a need for next-generation W-CDMA to be designed to support variable rate traffic. Several schemes have previously been proposed to support variable rate transmission, namely, variable spreading gain (VSG), multicode transmissions and fixed spreading gain (FSG). In this paper, a universal framework to evaluate and compare the various variable rate transmission schemes in terms of bit error rate (BER), power and required bandwidth is proposed. The framework also provides for the synthesis of the power assignment that delivers a specified BER to heterogeneous variable rate sources under each scheme.

Equalization for a page-oriented optical memory system

In this work, a method of decision-feedback equalization is developed for a digital holographic channel that experiences moderate-to-severe imaging errors. Decision feedback is utilized, not only where the channel is well-behaved, but also near the edges of the camera grid that are subject to a high degree of imaging error. In addition to these effects, the channel is worsened by typical problems of holographic channels, including non-uniform illumination, dropouts, and stuck bits. The approach described in this paper builds on established methods for performing trained and blind equalization on time-varying channels. The approach is tested on experimental data sets. On most of these data sets, the method of equalization described in this work delivers at least an order of magnitude improvement in bit-error rate (BER) before error-correction coding (ECC). When ECC is introduced, the approach is able to recover stored data with no errors for many of the tested data sets. Furthermore, a low BER was maintained even over a range of small alignment perturbations in the system. It is believed that this equalization method can allow cost reductions to be made in page-memory systems, by allowing for a larger image area per page or less complex imaging components, without sacrificing the low BER required by data storage applications.