Hanbing Shen

Modified Chirp Waveforms in Cognitive UWB System

In this paper we propose a method to modify chirp waveforms in cognitive ultra wideband (UWB) system. By utilizing the time-frequency relationship of the chirp waveform, we can avoid the spectrum authorized to other existing systems. After estimating other applications in the electromagnetic environment, the adaptive waveform generation is adopted which adapts to the changing wireless environment and synthesizes chirp waveform features in the time domain. Therefore, coexistence with other applications can be accomplished. Furthermore, the proposed scheme can avoid the frequency-time transform that can increase the system complexity. Computer simulations with additive white Gaussian noise successfully demonstrate an increase in performance with the proposed system as compared to traditional linear chirp systems for cognitive UWB systems.

The modified chirp UWB ranging system for vehicular applications

In this paper we propose a modified pulse compression method in the chirp ultra wideband (UWB) ranging system for vehicular applications. Chirp signals are categorized as spread spectrum signals and have good advantages in interference rejection. Because the chirp waveform has limited length for one signal, when the matched filter is adopted on the receiver side, the output of the filter has high-level side lobes. If there exists narrowband interference (NBI) in the radio environments, the ranging performance degrade much. Therefore, a series of window functions are proposed to reduce the level of side lobes and obtain high ranging resolutions. Simulation results verify that our proposed improved scheme outperforms the traditional ones.

Pulse Series Based UWB CR System

Ultra-wideband (UWB) based cognitive radio (CR) system combines the advantages of these two spectrum sharing techniques and is considered as one of the candidates of the next generation short range wireless communication technology. We propose narrow band interference (NBI) suppression method which can be adopted in ultra-wideband (UWB) based cognitive radio (CR) system in this paper. The proposed scheme is based on a series of pulse waveforms and can reduce the system complexity to some degree. We evaluate the performance of the proposed scheme and compare it with a conventional UWB scheme. The evaluation results verify that the proposed scheme can suppress the NBls effectively.

A novel UWB modulation method based on time-frequency energy distribution

In this paper, the time-frequency characteristics of IR-UWB signal is analyzed and concluded by using short-time Fourier transform (STFT). According to the time-frequency characteristic of IR-UWB signal, a novel UWB modulation and demodulation method based on the time-frequency energy distribution is presented. This novel modulation method has very good antinoise performance in AWGN environment.

A novel timing jitter resist method in UWB systems

Ultra wideband (UWB) is a kind of wireless communication system which can perform high data rate with nano-second pulses of baseband, and has recently received much attention for short-range applications. Thus a high sensitivity of timing synchronization between modulation and demodulation is required. Timing synchronization error named timing jitter between transmitter and receiver has been introduced and their properties have been analyzed in some papers. However, there are not many methods brought forward to improve the system performance in the scenarios that deteriorated jitter existents. We consider this problem and offer a method to resist the adverse effect by timing jitter to the whole system by adopting a new designed correlator reference signal in UWB receiver. This reference signal is formed corresponding to the timing jitter distribution of the received pulses waveforms to increase the jitter robust performance. From the simulation results of different UWB modulation systems, better performance can be achieved by adopting this reference signal in the receiver than the conventional schemes.

Cognitive Implementation of Chirp Waveform in UWB System

Cognitive Radios (CR) can recognize the communication environment and switch its communication scheme to more efficiently and flexibly utilize the radio spectrum. The performance of ultra wideband (UWB) degrades if interference is not suppressed properly. We propose here a series of adaptive chirp waveforms in UWB systems. By designing waveform shaping of both linear chirp and non-linear cases, we avoid the estimated spectrum of the on-going applications without the necessity of notch filters, and thus reduce the system complexity. We evaluate system performance of the proposed scheme by simulations and verify that the proposed scheme is a candidate for cognitive UWB systems.

A Novel NBI Suppression Scheme in UWB Ranging Systems

Due to the ultra low power spectral desity of the ultra-wide band (UWB), narrow band interference (NBI) with high-level emission power will degrade the accuracy of UWB ranging system. We propose a novel waveform to suppress the accuracy degradation by NBI with a given frequency. In addition, we compare the ranging error ratio (RER) of the proposed scheme with the traditional one with Gaussian monocycle in this letter.

Design of Delay-Locked Loop (DLL) with Low Jitter and High Lose Lock Time in UWB-IR System

Ultra-wide band impulse radio (UWB-IR) transmits data using sub-nanosecond baseband pulses with very low duty cycle. It is a promising candidate for short-range communications. However, due to the short duration of the impulse signal, very precise synchronization control is vital for the whole system. In this paper, an improved delay-locked loop (DLL) is introduced to the UWB-IR system with time hopping/spread spectrum (TH/SS). Instead of using only two central correlator branches in the DLL, more correlator branches with different delay parameters and different weight parameters are added to the conventional DLL. Lower tracking jitter and higher mean time to lose lock (MTLL) than the conventional systems can be achieved from proposed ones. Performance of several different combinations of correlator parameters are evaluated in this paper and some of them perform superior to that of the conventional DLLs

A new multiple access protocol for time-hopping UWB ad-hoc wireless networks

Ultra-wide bandwidth (UWB) is a prospective radio technology for wireless networks. As being approval by FCC, UWB radio has received much attention. In this paper, we propose a new multiple access protocol for time-hopping UWB ad-hoc network. As UWB system is a carrier-less impulse radio system, it is cumbersome to implement the carrier sensing capability needed in popular approaches such as carrier-sense, multiple access with collision avoidance (CSMA/CA) MAC protocols. The novel multiple access scheme to detect the busy medium and reduce the probability of collisions in TH UWB ad-hoc network is given out and evaluated. In UWB TH modulation, the spreading codes for target node are used. In our scheme, another binary PN sequence according to the destination node is also added to the modulation scheme to sense the busy medium before transmission. Communications outside the definition of directly transmission region (DTR) have to relay over intermediate nodes.

Jitter Distribution Evaluation and Suppression Method in UWB Systems

For the extreme short duration of the baseband Impulse Radio (IR) Ultra-Wideband (UWB) transmission waveforms, even small amounts of timing jitter can bring out considerable system performance degradation. Thus jitter performance evaluation and corresponding suppression methods are very important for UWB high rate transceiver. We analyzed the jitter distribution function in UWB systems, also a jitter suppression method is proposed by modification of template waveforms. Performance of our proposed waveforms and traditional template waveforms are compared by analysis and simulation, and the results verify our jitter suppression method works.