Non‐linear Chirp UWB Ranging System with Narrowband Interference Suppression Abilities

In this letter, we analyze an ultra‐wideband ranging system based on non‐linear chirp waveforms with the ability of narrowband interference suppression. A number of non‐linear chirp waveforms are proposed and evaluated by simulation. The results verify that the proposed schemes can suppress the Narrowband interference to a certain degree.     

M‐ary Bi‐orthogonal Modulation UWB with Narrowband Interference Suppression Capability

An M‐ary bi‐orthogonal modulation scheme for ultra‐wideband (UWB) systems capable of narrowband interference (NBI) suppression is proposed in this letter. We utilize a set of bi‐orthogonal pulse series to achieve NBI suppression. Through analysis and simulation, we verify that the proposed scheme can suppress NBIs effectively.     

Non‐linear chirp based UWB waveform design for suppression of NBI

In order to alleviate the narrowband interference (NBI) to ultra wideband (UWB) systems, we propose two non‐linear UWB chirp waveforms based on the arctrigonometric and archyperbolic function in this paper. The proposed UWB pulses can obtain good performance in NBI suppression. Both of the two chirp pulses require only the time domain processing because of the inherent relationship between the frequency domain and the time domain. Theoretical analysis and simulation results show that the direct sequence pulse binary amplitude modulation (DS‐BPAM) UWB systems with the proposed chirp waveforms can achieve excellent NBI suppression performance and outperform the linear chirp waveform based UWB system significantly. Copyright © 2010 John Wiley & Sons, Ltd.     

Direct Blind Adaptive MOE Receiver for PAM Modulated Time-Hopping UWB System Over Frequency-Selective Fading Channel

Ultra wideband impulse radio systems have attracted great attention for their promised applications in high-speed short-range indoor wireless communication systems. Among the various modulation and multiple access schemes, this paper deals with time-hopping (TH) antipodal pulse amplitude modulation operating in the presence of a multipath fading downlink channel. We first employ a constrained optimization technique to design a batch mode blind (without exploiting training sequences and undesired users’ time-hopping (TH) codes) mobile station receiver. To reduce the computational complexity, we propose a blind adaptive receiver that is based on the criterion of maximizing the receiver’s minimum possible output energy. The algorithm jointly and iteratively optimizes the weight vector and channel impulse response to improve system performance. Simulation results show that the proposed adaptive receiver converges to the optimum batch mode receiver. Moreover, the algorithms are shown to be robust to multi-user interference and near-far problems.     

Performance of DS‐UWB in MB‐OFDM and multi‐user interference over Nakagami‐m fading channels

The mutual interference between the two ultra wideband (UWB) technologies, which use the same frequency spectrum, will be a matter of concern in the near future. In this context, we present a performance analysis of direct‐sequence (DS) UWB communication in the presence of multiband orthogonal frequency division multiplexing (MB‐OFDM) UWB interfering transmissions. The channel fading is modeled according to Nakagami‐m distribution, and multi‐user interference is taken into account. The DS‐UWB system performance is evaluated in terms of bit error rate (BER). Specifically, using the characteristic function approach, an analytical expression for the average BER is derived conditioned on the channel impulse response. Numerical and simulation results are provided and compared for different coexistence scenarios. Copyright © 2011 John Wiley & Sons, Ltd.     

Multiple Access <Emphasis Type="Italic">M</Emphasis>-ary Modulation UWB System Based on Code-Selected Direct Sequence Bipolar PAM

This work presents an M-ary multiple access code-selected direct sequence (DS) ultra wideband (UWB) communication system. A high data rate multiple access UWB system can be obtained by a code selection mechanism. In the proposed system, each user is assigned a DS code set with M/2 DS code sequence and a particular DS code sequence can be selected by the log₂ (M/2) bits from the DS code set. More importantly for this M-ary UWB communication system, with the increase of the modulation level M, it allows to reduce the required transmitter power maintaining the number of users, the data transmission rate and the multiple access performance. In this paper, we also introduce the detailed algorithm to compute the bit error rate (BER) over the AWGN channel and correlation receivers.

Chirp‐Based Cognitive Ultra‐wideband Radio

In this letter, we propose a cognitive ultra‐wideband radio scheme which is based on a modified chirp waveform. Therefore, it requires only time domain processing in the cognitive radio systems and reduces system complexity and power consumption.     

An Ordered Successive Interference Cancellation Scheme in UWB MIMO Systems

In this letter, an ordered successive interference cancellation (OSIC) scheme is applied for multiple‐input multiple‐output (MIMO) detection in ultra‐wideband (UWB) communication systems. The error rate expression of an OSIC receiver on a log‐normal multipath fading channel is theoretically derived in a closed form solution. Its bit error rate performance is analytically compared with that of a zero forcing receiver in the UWB MIMO detection scheme followed by RAKE combining.     

Application of SVD on Suppression of IEEE 802.11a Interference in TH‐PAM UWB Systems

Interference from IEEE 802.11a systems affects ultra‐wideband (UWB) systems significantly. In this letter, we suggest a novel narrow‐band interference (NBI) suppression technique based on the singular value decomposition (SVD) algorithm in time‐hopping pulse amplitude modulation (TH‐PAM) UWB systems. The SVD algorithm is used to approximate the interference which then is subtracted from the received signals. In contrast to the conventional notch filter and rake receiver, our method is more effective and the receiver complexity can be greatly reduced.     

Non‐Data‐Aided Weighted Non‐Coherent Receiver for IR‐UWB PPM Signals

This letter proposes an energy‐detection‐based non‐data‐aided weighted non‐coherent receiver (NDA‐WNCR) scheme for impulse radio ultra‐wideband (IR‐UWB) pulse‐position modulated signals. Compared to the conventional WNCR, the optimal weights of the proposed NDA‐WNCR are tremendously simplified as the maximum eigenvector of the IR‐UWB signal energy sample autocorrelation matrix. The NDA‐WNCR serves to blindly obtain the optimal weights and entirely circumvent the transmission of training symbols or channel estimation in practice. Analysis and simulation results verify that the bit error rate (BER) performance of the NDA‐WNCR closely approaches the ideal BER of the conventional WNCRs.     

On the Degradation of a UWB System Due to a Realistic TX‐RX Antenna System

The ultra‐wideband (UWB) signal radiation process in an antenna is different from that of a narrowband signal. In this paper, we study the degradation of the desired signal component according to the antenna structure and location of a receiver in a bipolar time‐hopping UWB system. And we propose a receiver structure with an adaptive template waveform generator to compensate for the degradation caused by a realistic TX‐RX antenna system.     

Improved Delay‐Locked Loop in a UWB Impulse Radio Time‐Hopping Spread‐Spectrum System

As ultra‐wideband impulse radio (UWB‐IR) uses short‐duration impulse signals of nanoseconds, even a small number of timing errors can cause a detrimental effect on system performance. A delay‐locked loop (DLL) is proposed to synchronize and reduce timing errors. The design of the DLL is vital for UWB systems. In this paper, an improved DLL is introduced to a UWB‐IR time‐hopping spread‐spectrum system. Instead of using only two central correlator branches as in a conventional DLL, the proposed system uses two additional correlator branches with different delay parameters and different weight parameters. The performance of the proposed schemes with the optimal parameters is compared with that of traditional schemes through simulation: the proposed four‐branch DLLs achieves less tracking jitter or a longer mean time to lose lock (MTLL) than the conventional two‐branch DLLs if proper parameters are chosen.     

Polarization filtering for narrowband interference suppression in ultra‐wideband communications

To suppress narrowband interference (NBI) in an ultra‐wideband (UWB) communications environment, a null phase‐shift polarization (NPSP) filter is proposed. The proposed NPSP filter is a combination of a linear polarization‐vector transformer (PVT), a conventional single notch polarization (SNP) filter, and an amplitude and phase compensator (APC). The NBI, which has polarized states different from those of the UWB, can be suppressed completely and the UWB signal can be recovered without distortion if the polarized states can be estimated exactly. Analytical and simulation results indicate that the signal‐to‐interference ratio (SIR) can be improved effectively after NPSP filtering. The proposed NPSP filter can be implemented in a time‐hopping spread spectrum (TH‐SS) or a direct‐sequence spread spectrum (DS‐SS) UWB system. Copyright © 2007 John Wiley & Sons, Ltd.     

A Novel M‐ary Code‐Selected Direct Sequence BPAM UWB Communication System

In this letter, a novel M‐ary code‐selected direct sequence (DS) ultra‐wideband (UWB) communication system is presented. Our purpose is to achieve a high data rate by an M‐ary code‐selected direct sequence bipolar pulse amplitude modulation (MCSDS‐BPAM) scheme. In this system, a particular DS code sequence is selected by the log₂M/2 bits from the DS gold code set. This scheme can accomplish both a high data rate without increasing the system bandwidth or changing the pulse shape and improve the BER with an increase of modulation level M even at a lower signal‐to‐noise ratio (SNR). The receiver signal processing algorithm is given for an MCSDS‐BPAM UWB system over an ideal AWGN channel and correlation receivers.     

Design of an Internal Antenna with Near‐Omnidirectional H‐Plane Radiation Pattern over Ultra‐wide Bandwidth

In this paper, an ultra‐wideband internal antenna for use in mobile applications is proposed. The proposed antenna has symmetrical bi‐arm structures printed on the top and bottom of the substrate, and it occupies a compact area of 10 mm × 10 mm × 1 mm. The designed antenna has an impedance bandwidth from 3 GHz to 12 GHz and near omnidirectional radiation patterns over the frequency band of interest. The group delay between two antennas fabricated using the proposed design is less than 0.8 ns, and the maximum gain variation is about 3.16 dB.     

一种提高超宽带无线系统干扰容限的方法

超宽带无线电系统常常因窄带干扰强度超出其干扰容限而无法正常工作,自适应陷波技术可大幅度提升其干扰容限.但在超宽带接收机中,实现高阶陷波非常困难,常规方法复杂度高、稳定性差、难于收敛.本文提出一种时分复用并行高阶自适应陷波方法,能同时快速跟踪并有效滤除一个或多个窄带强干扰,使系统干扰容限大幅度提升,且稳定性好、收敛快、对有用信号损伤小.理论分析与仿真结果验证了其优越性,且具有重要应用价值.     

A Low‐Complexity 128‐Point Mixed‐Radix FFT Processor for MB‐OFDM UWB Systems

In this paper, we present a fast Fourier transform (FFT) processor with four parallel data paths for multiband orthogonal frequency‐division multiplexing ultra‐wideband systems. The proposed 128‐point FFT processor employs both a modified radix‐2⁴ algorithm and a radix‐2³ algorithm to significantly reduce the numbers of complex constant multipliers and complex booth multipliers. It also employs substructure‐sharing multiplication units instead of constant multipliers to efficiently conduct multiplication operations with only addition and shift operations. The proposed FFT processor is implemented and tested using 0.18 µm CMOS technology with a supply voltage of 1.8 V. The hardware‐ efficient 128‐point FFT processor with four data streams can support a data processing rate of up to 1 Gsample/s while consuming 112 mW. The implementation results show that the proposed 128‐point mixed‐radix FFT architecture significantly reduces the hardware cost and power consumption in comparison to existing 128‐point FFT architectures.     

Support vector machine‐based equalisation for direct‐sequence ultra wideband systems

We proposed the support vector machine (SVM)‐based equalisation schemes for direct‐sequence ultra wideband (UWB) systems. The severe intersymbol interference caused by the UWB channel was formulated as a pattern classification problem in the SVM‐based equaliser, which operates in two main modes: training and detection. We also applied the least squares support vector classifiers (LS‐SVCs) to reduce the training complexity and sparse LS‐SVCs to reduce the detection complexity, with little performance loss compared to SVCs. Simulation results confirm the outperformance of the proposed equalisers over the conventional rake receiver with the same order of complexity for detection, especially when no channel information is known at the receiver. Also, the SVM‐based equalisers in the line‐of‐sight scenario provide a performance close to the case with additive white Gaussian noise only. Copyright © 2011 John Wiley & Sons, Ltd.     

Cross‐level PRC transmitter for TH‐PAM UWB systems

A cross‐level pre‐RAKE combining (PRC) scheme for time hopping pulse amplitude modulation ultra wideband (TH‐PAM UWB) transmitter is studied in this paper. A two‐stage cross‐level PRC (CL‐PRC) scheme is proposed. The conventional PRC schemes suppress all the chip‐wise interference. However, the proposed scheme suppresses only the specific frame‐wise inter‐symbol interference (ISI) by exploiting the characteristic that the information bits are transmitted only at ultra short time slots. This results in a low complexity pre‐equalizer without bit error rate (BER) performance degradation. Furthermore, an order selection rule is presented to achieve the tradeoff between signal‐to‐interference ratio (SIR) and computational complexity. Simulation results illustrate the superior SIR and BER performance of our proposal. Copyright © 2009 John Wiley & Sons, Ltd.     

基于自适应调制技术的MIMO UWB无线通信系统的研究

在对多输入多输出(MIMO)技术和超宽带(UWB)无线通信研究的基础上提出了一种基于自适应调制技术的时变多进制MIMO UWB系统。通过采用奇异值分解理论和速率分阶的方法对系统性能进行了分析,推导出了速率离散分阶情况下的功率和速率的分配公式,提出了相邻时隙平均功率控制(JTAPC)算法,并且对系统的性能进行了仿真。研究结果表明,功率控制算法的使用很大程度上提高了采用速率分阶的系统的性能,并且降低了系统实现的复杂度。