Performance analysis of impulse-radio ultra-wideband techniques for low-rate communications
Date of Issue2014
School of Electrical and Electronic Engineering
Impulse-radio (IR) ultra-wideband (UWB) has drawn much attention as a promising technology for low-data-rate applications such as ranging, identification and low-rate communication in sensor networks. In this research work, we focus on the communication perspective of the IR-UWB applications. To begin with, we investigate various UWB transmission and reception schemes. With the criteria of low complexity, low power consumption and reliable data transmission, we select two systems for detailed study. They are transmitted reference (TR) signaling with auto-correlation receiver (AcR) and on-off keying (OOK) transmission with energy detection receiver. After studying the systems’ characteristics, we observe that the system performance suffers mainly from two types of interference. They are narrowband interference (NBI) from existing in-band wireless services, and multiple access interference (MAI). TR systems have another source of interference which is interpulse interference (IPI) from the overlapping of reference and data waveforms after passing through the highly dispersive propagation channel. Various suppression schemes have been investigated for all these types of interference. For NBI mitigation, notch filtering is adopted in this work. IPI can be mitigated by applying the statistic averaging concept. Our study shows that with these two techniques, the overall performance of TR systems can be improved significantly. Theoretical analysis is provided to evaluate the lower-bound performance for the single-user case. It shows that the system performance is able to approach that under the additive-white-Gaussian-noise (AWGN) environment. We also observe that OOK can be seen as a special case of TR when the delay between reference and amplitude-modulated data pulses is zero. Inspired by the AcR used for TR signals, we then propose a pseudo-coherent detector for OOK signals which is able to provide significant performance improvement as compared with the conventional energy detector. We also look into implementation issues of the proposed receiver. The high sampling rate required by the digital implementation motivates the investigation on techniques to reduce the sampling rate. We then develop a novel subsampling technique, namely bandpass downsampling (BPDS) technique from the standpoint of signal detection rather than signal reconstruction. Our proposed BPDS is capable of reducing the sampling rate to one tenth of the Nyquist rate with small performance degradation introduced to the receivers. Our analysis work is subsequently extended to multiple access system or multiuser system under quasi-synchronous condition. Extended from OOK signaling for single user system, unipolarWalsh code (UWC) are adopted in our proposed multiuser system to distinguish different users. Over bipolar coding, unipolar coding has the advantages of providing better correlation template, and hence, lower detection error rate for the receiver. BPDS technique is also considered in our multi-user system for the ease of digital implementation with significant reduction in the required sampling rate. Theoretical analysis and numerical results support that our system can provide near-optimal performance under perfect timing acquisition and satisfactory performance with certain amount of timing acquisition error.
DRNTU::Engineering::Electrical and electronic engineering::Wireless communication systems