Qicai Shi

Performance Analysis of Cooperative Spectrum Sensing in Suzuki Fading Channels

This paper examines the performance of cooperative spectrum sensing, using energy detection, in Suzuki fading channels. Sub-optimal centralized detection approaches are examined where decisions are made based on identical tests performed at the individual radios. Decisions are performed at a fusion center using a counting rule that encompasses the OR, AND, and majority rules as special cases. Analytical and simulation results are presented for Rayleigh, Log-normal and Suzuki distributions.

Performance analysis of relative location estimation for multihop wireless sensor networks

In this paper, we present new analytical, simulated, and experimental results on the performance of relative location estimation in multihop wireless sensor networks. With relative location, node locations are estimated based on the collection of peer-to-peer ranges between nodes and their neighbors using a priori knowledge of the location of a small subset of nodes, called reference nodes. This paper establishes that when applying relative location to multihop networks the resulting location accuracy has a fundamental upper bound that is determined by such system parameters as the number of hops and the number of links to the reference nodes. This is in contrast to the case of single-hop or fully connected systems where increasing the node density results in continuously increasing location accuracy. More specifically, in multihop networks for a fixed number of hops, as sensor nodes are added to the network the overall location accuracy improves converging toward a fixed asymptotic value that is determined by the total number of links to the reference nodes, whereas for a fixed number of links to the reference nodes, the location accuracy of a node decreases the greater the number of hops from the reference nodes. Analytical expressions are derived from one-dimensional networks for these fundamental relationships that are also validated in two-dimensional and three-dimensional networks with simulation and UWB measurement results.

Link Maintenance Protocol for Cognitive Radio System with OFDM PHY

For secondary usage of spectrum in a cognitive radio system, in order to maintain reliable continuous communication among secondary users, secondary radios need to make contact, communicate and switch to an open RF channel simultaneously when the current channel is reclaimed by a primary user. In this paper, we describe a link maintenance protocol aimed at solving this issue. The communication channel is monitored and dynamically updated based on spectrum availability. Spectral sensing is employed at the receivers to monitor the spectrum and assist in RF channel synchronization between transmitter and receiver. Simulation results characterizing the performance of this protocol are provided. A prototype system with a pair of cognitive radios featuring this protocol is also introduced.

A new chip-level differential detection system for DS-CDMA

In this paper we mathematically prove that if the original spreading Pseudo-Noise (PN) code is an m-sequence or a Gold-sequence, then the chip-by-chip differential decoding (CBCDD) sequence of the original PN code is a cyclic shift version of the original PN sequence. By utilizing this property, we design a new chip-level differential detection system for DS-CDMA, which does not require any chip-level differential encoding in the transmitter. We demonstrate simplicity of implementation and robust operation in the presence of carrier frequency shift.

Implementing an Experimental Cognitive Radio System for DySPAN

Motorola Labs implemented an experimental cognitive radio system for use at the Dynamic Spectrum Access Networks (DySPAN) Symposium 2007. To exercise a practical communication link in a shared spectrum, the system provided a live video feed via a dynamically-allocatable OFDM physical layer. Each demonstration unit included an RF signal conditioning module for DySPAN channel allocations, a custom RF transceiver IC, digital signal processing, and an embedded Linux operating system. Connected to the units via Ethernet, a PC presented a graphical user interface, including the video feed and visualization of the spectral sensing, signal detection, and frequency allocation that was taking place in the units.

Performance comparision between TOA ranging technologies and rssi ranging technologies for multi-hop wireless networks

This paper investigates the relationship between the number of hops from a source node to a destination node and the range estimation accuracy for multi-hop wireless networks with a focus on RSSI-based and TOA-based systems. Analytical results show a dramatic difference between RSSI based ranging and TOA based ranging. With TOA-based systems, it is found that by fixing the source to destination distance, the more number of hops between the source and the destination, the worse the ranging estimation accuracy. In contrast, with RSSI-based location systems, the more number of hops, the better the ranging estimation accuracy. Simulations and experimental measurements employing prototypical UWB and 802.15.4 devices are used to validate the findings. Keywords-TOA; RSSI; networks; location; ranging.

Performance of chip-level differential detection with phase noise

Chip-level differential encoding/detection of direct-sequence spread-spectrum signals has been shown to improve receiver robustness in the presence of oscillator frequency offsets and fast fading channels. These gains are achieved at the expense of SNR performance in an AWGN channel, with spreading factor governing the tradeoff. This paper explores the performance of chip-level differential detection in the presence of oscillator phase noise. It is shown that phase noise mitigation is an additional benefit of chip-level differential detection, with higher spreading factors permitting the use of lower-cost, noisier oscillators. Simulations of a DS/SS BPSK system illustrate the relationship between phase noise tolerance and spreading factor, and a simple analytical model is derived for efficient evaluation of systems with high spreading factor.

Location estimation in multi-hop wireless networks

We present the analytic and simulation results of the performance of relative location estimation in multi-hop wireless sensor networks. It is found that the location estimation accuracy has a fundamental upper boundary. Location accuracy improves by adding more mobile nodes into the network. However, the resulting accuracy converges towards a fixed asymptotic value that is determined by the total number of links to the reference nodes. It is also established that for multi-hop networks, the location accuracy of a node is highly dependent upon the number of hops it is away from the reference nodes. The further away it is from the reference nodes, the worse the location accuracy.

A new code-timing estimation algorithm for DS-CDMA

A DS-CDMA receiver requires accurate timing information to synchronize the receiver PN code correlator with the received signal. When utilized for position location applications, the DS-CDMA receiver must further provide accurate timing information to the location algorithm. Typically, DS-CDMA timing estimation algorithms require the transmission of a training sequence to establish timing lock. In addition, the carrier frequency drift encountered in many wireless communication applications adversely effects the performance of these algorithms. This paper introduces a new DS-CDMA code-timing estimation algorithm that operates without a training sequence and provides robustness to carrier frequency drift.

Range-Free Location Estimation Algorithms for Wireless Networks

In this paper, we describe a suite of new range-free location estimation algorithms. With these algorithms, a blindfolded node is first located within some probable regions by comparing the measured received signal strength between nodes. Then the location of the blindfolded node is narrowed down by overlapping all the probable regions. Finally the geographic center of the overlapped region is calculated as the location estimate of the blindfolded node. Location estimation accuracy can be further improved when a blindfolded node that has already been located serves as additional reference node to determine the positions of other blindfolded nodes within its communication range. When compared with other range-free algorithms, results show improved location estimation accuracy with similar or less computation complexity.