Shahzada B. Rasool

A Distributed Joint Channel-Assignment, Scheduling and Routing Algorithm for Multi-Channel Ad-hoc Wireless Networks

The capacity of ad hoc wireless networks can be substantially increased by equipping each network node with multiple radio interfaces that can operate on multiple non-overlapping channels. However, new scheduling, channel-assignment, and routing algorithms are required to fully utilize the increased bandwidth in multi-channel multi-radio ad hoc networks. In this paper, we develop a fully distributed algorithm that jointly solves the channel-assignment, scheduling and routing problem. Our algorithm is an online algorithm, i.e., it does not require prior information on the offered load to the network, and can adapt automatically to the changes in the network topology and offered load. We show that our algorithm is provably efficient. That is, even compared with the optimal centralized and offline algorithm, our proposed distributed algorithm can achieve a provable fraction of the maximum system capacity. Further, the achievable fraction that we can guarantee is larger than that of some other comparable algorithms in the literature.

Constant-Time Distributed Scheduling Policies for Ad Hoc Wireless Networks

We propose two new distributed scheduling policies for ad hoc wireless networks that can achieve provable capacity regions. Known scheduling policies that guarantee comparable capacity regions are either centralized or need computation time that increases with the size of the network. In contrast, the unique feature of the proposed distributed scheduling policies is that they are constant-time policies, i.e., the time needed for computing a schedule is independent of the network size. Hence, they can be easily deployed in large networks.

Distributed and provably efficient algorithms for joint channel-assignment, scheduling, and routing in multichannel ad hoc wireless networks

The capacity of ad hoc wireless networks can be substantially increased by equipping each network node with multiple radio interfaces that can operate on multiple nonoverlapping channels. However, new scheduling, channel-assignment, and routing algorithms are required to fully utilize the increased bandwidth in multichannel multiradio ad hoc networks. In this paper, we develop fully distributed algorithms that jointly solve the channel-assignment, scheduling, and routing problem. Our algorithms are online algorithms, i.e., they do not require prior information on the offered load to the network, and can adapt automatically to the changes in the network topology and offered load. We show that our algorithms are provably efficient. That is, even compared with the optimal centralized and offline algorithm, our proposed distributed algorithms can achieve a provable fraction of the maximum system capacity. Furthermore, the achievable fraction that we can guarantee is larger than that of some other comparable algorithms in the literature.

An Approximate Analysis of Buffered S-ALOHA in Fading Channels Using Tagged User Analysis

Tagged user analysis (TUA) is a generic approximate method of analyzing random access protocols for finite-user finite-buffer systems. This technique decouples the channel contention behavior from the user queuing behavior and allows the use of classical queuing theory results to be directly applicable to the analysis of finite-user finite-buffer random access methods. In this paper, we extend TUA to analyze finite buffer S-ALOHA operating over flat fading radio channels and derive expressions for system performance indices like throughput, average packet delay, blocking probability and queue length. It is shown that for a moderate number of active users, the simulation and analytical results fit closely

Biologically Inspired Processing of Radar Waveforms for Enhanced Delay-Doppler Resolution

In this paper, we study an approach to the processing of radar signals motivated by the neural processing of echolocation waveforms by certain species of bats. We propose a transmission strategy and a corresponding family of processing algorithms and study the resulting delay-Doppler resolution characteristics. We investigate both the improvement in delay-Doppler resolution and the generation of artifacts in the delay-Doppler maps generated by this approach. Because the resulting schemes are not optimal for detection, we investigate the degradation in detection performance when compared to the matched filter. The contribution of the proposed scheme is a significant improvement in delay-Doppler resolution without a significant increase in system or computational complexity or a significant degradation in detection performance.

Increasing delay-Doppler resolution using chirp diversity and nonlinear processing

In this paper, we study the resolution properties of linear FM pulses (chirps). Based on the ambiguity surface properties of chirp pulses, we propose a transmission strategy and a processing algorithm that has better delay-Doppler resolution than traditional matched filtering. It is shown that the improvement in resolution is accompanied by a small degradation in detection performance.

Efficient pulse-Doppler processing and ambiguity functions of nonuniform coherent pulse trains

We propose a DFT based pulse Doppler processing receiver for staggered pulse trains. The proposed receiver is a simple extension of traditional DFT based coherent pulse train processing. We show that P DFT processors are required to process the staggered train of pulses as a coherent signal, where P is the number of available pulse positions in each pulse repetition interval (PRI). Thus the complexity of the processing hardware only increases linearly with the number of available positions. We also look at the distribution of ambiguity volume around the delay-Doppler map by varying the pulse positions and the selection of pulse shapes.

Novel waveform and processing techniques for monostatic and bistatic radar

In this paper, we study the resolution properties of linear FM pulses (chirps). Based on the ambiguity surface properties of chirp pulses, we propose a transmission strategy and a processing algorithm that has better delay-Doppler resolution than traditional matched filtering. It is shown that the improvement in resolution is accompanied by a small degradation in detection performance. We also discuss the general requirements on the signal set that will result in improved resolution properties when using the proposed form of processing. Our results also show that we can change resolution performance for detection performance under certain conditions. The contribution of our proposed scheme is a significant increase in delay-Doppler resolution without a significant increase in system or computational complexity or a significant degradation in detection performance. We also extend the results to a simple bistatic radar configuration and evaluate the performance for orthogonal and near-orthogonal transmitted signals under varying conditions.