Zhiguo Lai

Performance of UWB systems in the presence of severe multipath and narrowband interference

This paper is a companion to D. Gupta et al. (2008). The primary objective is to motivate the need for interference rejection by analyzing the bit-error-rate performance of the frequency-shifted reference UWB system by D. Goeckel (2007) in the presence of a single sinusoidal interferer. Numerical simulations are then carried out to validate the interference rejection mechanism proposed by D. Gupta et al (2008).

A unified framework for reference-based ultra-wideband signaling

One application area of significant interest for ultra-wideband (UWB) technology is in localization and low-to-moderate data rate communication. Due to implementation complexity concerns, many recently proposed systems have been based around transmitted reference (TR) or pulse-position modulation (PPM) architectures. In response to the difficulty in implementing the delay line in small integrated receivers for the original TR system, frequency-shifted reference (FSR) UWB systems were developed, which in turn motivated recent code-shift (CS)-UWB and code-multiplexed (CM)-UWB systems. Here, we update our recent framework for reference-based UWB systems to encompass these recently-proposed systems and use recent experience on a UWB commercialization project for radio frequency identification (RFID) applications to provide perspective on the evaluation of systems within the framework. Performance is considered under both average and peak energy constraints. Under the latter constraint, it is important to consider methods of peak mitigation, so an extension of the tone reservation method employed in orthogonal frequency division multiplexing (OFDM) systems is applied to systems within the framework, often without the cost in bandwidth efficiency observed in standard OFDM systems. Differences across the class, as measured in terms of peak power, can often be larger than those measured versus average power. Operating conditions where such is significant (or not) are reviewed.

Optimization of frequency-shifted reference ultrawideband systems

Recently, there has been significant interest in developing ultrawideband (UWB) radio techniques. A transmitted reference (TR)-UWB technique is often considered for low-to-moderate data rate applications. However, the TR-UWB technique is limited by the difficulty in building the required highly accurate wideband analog delay line in the receiver. Frequency-shifted reference (FSR)-UWB avoids this analog delay by shifting the reference signal from the data signal in frequency, and FSR-UWB has been shown to outperform the standard TR-UWB scheme. The performance of the FSR-UWB system has been further improved in succeeding work by sending multiple data signals that share a common reference carrier, referred to as multi-differential (MD) FSR, but this comes with a significant increase in the peak-to-average power (PAPR) of the pulses. In this paper, three improvements are proposed for the FSR-UWB system: the front-end filter and the integration time at the receiver are optimized, and a PAPR minimization scheme for the MD-FSR scheme is introduced. After describing and characterizing these approaches, simulation results are provided to consider the varying degrees of improvement offered through the proposed techniques.

Indoor transmission of multi-gigabit-per-second data rates using millimeter waves

Demands for high data rate communication in an indoor environment require innovations on high speed and energy efficient channel equalizer designs. In this paper, we propose a ‘semi-analog’ channel equalizer with high power efficiency and fast processing speed for 60 GHz channels. The proposed system consists of a channel estimator and a multipath canceler. The channel estimator uses a prolate spheroidal wave function (PSWF) with low peak-to-average power ratio (PAPR) to provide an accurate estimation of channel parameters, based on which the multipath canceler removes reflected signals due to multipath. We evaluate its performance in terms of bit error rate (BER) considering a real indoor propagation environment at 60 GHz.