P-order metric UWB receiver structures with superior performance

The generalized Gaussian probability density function is shown to better approximate the probability density function of the multiple access interference in ultra-wide bandwidth systems than the Gaussian approximation and the Laplacian density approximation. Two ultra-wide bandwidth receiver structures based on this new approximation using a p-order metric receiver decision statistic are investigated for the detection of time-hopping ultra-wide bandwidth wireless signals in multiple access interference channels. The first receiver outperforms both the conventional matched filter ultra-wide bandwidth receiver and the soft-limiting ultra-wide bandwidth receiver when only multiple access interference is present in UWB channels. The second new receiver with adaptive limiting threshold outperforms the conventional matched filter ultra-wide bandwidth receiver, the soft-limiting ultra-wide bandwidth receiver, and the adaptive threshold soft limiting ultra-wide bandwidth receiver in all multiple access interference-plus-noise environments. In multipath channels, a new Rake receiver based on the p-order metric receiver is proposed for signal detection. Mathematical analysis and numerical results show that this new Rake receiver can achieve larger signal-to-interference-plus-noise ratio than the standard matched filter Rake receiver when multipath components are resolvable in UWB channels.     

A channelized digital ultrawideband receiver

A channelized digital ultrawideband (UWB) receiver that efficiently samples the UWB signal at a fraction of the chip frequency is proposed. The received signal is channelized in the frequency domain by employing a bank of mixers and low-pass filters. After sampling at a much reduced frequency, digital synthesis filters optimally estimate the transmitted signals. The signal-to-noise ratio (SNR) of the proposed receiver has been solved and compared against an ideal conventional receiver, which is defined as a receiver that samples at the signal Nyquist rate. When finite resolution analog-to-digital converters (ADC) are employed in the presence of a large narrowband interferer, the proposed receiver significantly outperforms the ideal conventional receiver. For example, the SNR of the proposed receiver is as much as 20 dB higher than the ideal conventional receiver when a 4-bit ADC is used in the presence of a 50 dB (relative to the noise floor) brickwall narrowband interferer with a bandwidth of 15% of the chip frequency.     

On the performance of a rapid synchronization algorithm for IR‐UWB receivers

Because of the very low signal duty cycles, synchronization is the most critical issue in ultra wideband (UWB) impulse radio (IR) systems. Some effective synchronization schemes like a symbol‐differential (SD) IR‐UWB receiver have been proposed to synchronize received signals rapidly. Yet, SD IR‐UWB receiver is unsuitable for operation in multi‐user environment because of multiple access interference (MAI). By taking advantage of frame‐differential IR‐UWB receivers, we propose a parallel frame‐differential (PFD) IR‐UWB receiver to do so. Our proposed PFD IR‐UWB receiver manifests better immunity against message passing interface and MAI than the SD IR‐UWB. Based on this PFD IR‐UWB receiver, uncertain (search) regions are limited to one frame duration without any symbol‐level synchronization process. Performance of PFD and SD receivers are compared by computer simulations, showing that the proposed PFD receiver not only achieves significant bit error rate performance but also better and more robust results than the SD receiver in this literature. Copyright © 2012 John Wiley & Sons, Ltd.     

A Framework for the Analysis of UWB Receivers in Sparse Multipath Channels with Intra?Pulse Interference via Pad′e Expansion

In this letter, we propose a framework for analyzing the performance of ultra wide band (UWB) receiver architectures in sparse multipath channels with overlapped multipath components (MPCs). The proposed methodology is based on approximating the moment generating function (MGF) of the received signal-to-noise ratio (SNR) via Pade expansion. The method can be applied to any fading scenarios and to any UWB receiver architectures, provided that the MGF of the SNR can be characterized in terms of a convergent Pade expansion. By comparing the results obtained from the analysis with those obtained from simulations in selected reference scenarios, it can be observed that the proposed approximation is very accurate.     

Performance analysis of an over-sampling multi-channel equalization for a multi-band uwb system

This paper proposes an over-sampling multi-channel equalizer per sub-band for multi-band ultra-wideband (UWB) system and compares its performance with conventional RAKE receiver when operating in practical UWB channel models. Three transmission modes have been considered, and inter-symbol interference (ISI) is found to be inherent to certain transmission modes due to the large UWB channel delay spreads. Through detailed analytical and simulation studies, the proposed over-sampled minimum mean square error (MMSE) equalizer is shown to be able to handle ISI under any channel conditions or transmission modes, with an acceptable BER. In addition, the rich multipath diversity of the UWB channels is harnessed by the over-sampling scheme, for output SNR improvement. Over-sampling is done in the expense of an increase in system complexity     

Low-noise amplifier design for ultrawideband radio

A new theoretical approach for designing a low-noise amplifier (LNA) for the ultra-wideband (UWB) radio is presented. Unlike narrow-band systems, the use of the noise figure (NF) performance metric becomes problematic in UWB systems because of the difficulty in defining the signal-to-noise ratio (SNR). By defining the SNR as the matched filter bound (MFB), the NF measures the degree of degradation caused by the LNA in the achievable receiver performance after the digital decoding process. The optimum noise matching network that minimizes the NF as defined above has been solved. When the narrow-band LNA assumption is made, the proposed optimum matching network simplifies to the published optimum narrow-band matching network, and the corresponding NF value also becomes equivalent. Since realizing the optimum matching network is in general difficult, an approach for designing a practical but suboptimum matching network is also presented.     

Bit Error Rate of TH-BPSK UWB Receivers in Multiuser Interference

It is well known that the Gaussian distribution is not an accurate model for approximating the probability density function (PDF) of the multiple access interference (MAI) in time-hopping UWB (TH-UWB) systems. An exact theoretical model which explains the key features of the PDF of the MAI in TH-UWB systems is discussed. These features, which can be precisely anticipated by the proposed model include impulses, singularities, and the tail behaviour in the distribution of the MAI. The model reveals in quantitative terms why a Gaussian approximation for the MAI in TH-UWB systems is highly imprecise even in an environment with a large number of independent interferers. Based on the model obtained for the PDF of the MAI and exploiting the maximum a posteriori (MAP) receiver design rule, the optimal attainable BER performance of binary TH-UWB receivers in additive white Gaussian noise channels is numerically determined. The performances of some recently proposed UWB receivers are benchmarked against the optimal performance showing that some of them achieve near-optimal performance.     

An adaptive CMMSE receiver for space-time block-coded CDMA systems in frequency-selective fading channels

A technique that can suppress multiple-access interference (MAI) in space-time block-coded (STBC) multiple-input-multiple-output (MIMO) code-division multiple-access (CDMA) systems is developed. The proposed scheme, called a constrained minimum mean square error (CMMSE) receiver, is an extension of the CMMSE receiver for a single-input-single-output system to MIMO systems. It is shown that the complexity of the proposed CMMSE receiver is almost independent of the number of transmitter antennas. The advantage of the proposed receiver over the existing receivers for STBC CDMA systems is demonstrated by comparing the closed-form expressions of the signal-to-interference plus noise ratio and simulated bit error rates. The results indicate that the proposed CMMSE receiver can provide a significant performance improvement over the conventional receivers and that the gain achieved by suppressing the MAI can be larger than that from increasing the transmitter or receiver diversity.     

一种新的基于特征向量合并的超宽带系统分集方案

针对超宽带系统在室内环境中面临严重的多径衰落问题,通常在接收端需使用RAKE接收机来收集多径能量改善性能。该文提出了一种新的分集方案,在发送端信号进行预处理,在接收端使用RAKE合并收集多径能量,同时给出了基于信道矩阵特征值估计的最佳合并权重和时延参数估计算法。理论分析和仿真结果都表明,该算法得到的输出信噪比总是大于传统的RAKE接收机输出信噪比。     

Iterative multiuser detection for turbo-coded FHMA communications

An iterative receiver structure Is proposed for turbo-coded frequency-hop multiple access (FHMA) systems. In FHMA systems, the adjacent channel interference (ACI) is the major contributor of multiple access interference (MAI) if orthogonal hopping patterns are used. The ACI is a function of the tone spacings of the adjacent subchannels and the rolloff factor of the pulse-shaping filter. The calculation of the ACI for a square-root raised-cosine pulse-shaping filter in an FHMA system is presented in this paper. In addition, a low complexity iterative multiuser detector is developed to mitigate the degradation caused by ACI in the FHMA systems. The iterative receiver structure is based on a modified turbo decoding algorithm which makes use of the a posteriori log-likelihood ratio (LLR) information of the systematic bits to obtain the a posteriori information of the turbo-encoded parity bits. Iterations of the receiver/decoder are used as the mechanism to estimate and mitigate the MAI in the FHMA system. The properties of both soft and hard interference suppressors based on the modified turbo decoding algorithm are examined and an efficient recursive implementation is derived. Compared to maximum-likelihood multiuser detection, the proposed system is more practical and its complexity is only a linear function of the number of users. Simulation results show that the proposed iterative receiver structure offers significant performance gain in bandwidth efficiency and the required signal-to-noise ratio (SNR) for a target bit-error rate (BER) over the noniterative receiver structure. Moreover, the single user performance can be achieved when imperfect power control exists     

Smart UWB System Based on STC and TR Techniques for BER Performance Enhancement and Interference Rejection

In this research, a novel smart UWB system is introduced. The proposed system is based on using an adaptive maximum ratio combining (MRC) Rake receiver. The proposed adaptive Rake receiver uses Genetic algorithm (GA) to adaptively select the delays of the fingers of the Rake receiver depending on the channel impulse response. It adaptively selects the delays that will allow the Rake receiver to capture most of the energy in the multipath components with minimum complexity. This adaptive Rake receiver is referred to as a GA Rake. The adaptive GA Rake is applied to a single-input single-output and space time coding (STC) multi-input single-output UWB systems. The performance of those systems using a GA Rake is compared to their performance when using a conventional MRC-Rake receiver and showed a great enhancement in performance with less receiver complexity. Also, in this paper, the smart UWB system using STC is modified by using the time reversal (TR) pre-coding technique. The modified system is referred to as a TR smart UWB system. This modification leads to more enhancements in performance and more reduction in receiver complexity over the smart UWB system. Moreover, this paper also shows the ability a TR smart UWB system in combating interference from other UWB systems.     

Energy Detector in Ultra Wideband Systems Using Phase Compensation Technique

Energy detectors have the advantage of simple structure and inexpensive price. Due to the low signal to noise ratio (SNR) of the received signal in ultra-wideBand (UWB) system, these desirable advantages can be achieved at the expense of non-trivial performance degradation. This paper presents a phase compensation (PC) technique to improve the performance of energy detector in UWB systems. In PC-UWB, the frequency dependent phase of the system response at the transmitter is extracted and its opposite spectral phase is used as prefilter. Because of Low complexity, cost and energy consumption of energy detectors, PC techniques has extensive potential for future of UWB communication systems. Measurement results show that the use of PC-UWB leads to signal power concentration at the receiver, which reduces the number of RAKE fingers required in coherent detection as well as achieves a higher data rate with less intersymbol interference. However time reversal UWB can achieve secure data transmission, but its performance is worse than PC-UWB. Simulation results show that phase compensation reduces the inter symbol interference impacts. Therefore it is possible to use a simple receiver with insignificant performance degradation. It is also shown that PC-UWB considerably outperforms TR-UWB and has satisfying performance in SNR greater than 13 dB.     

An uplink DS-CDMA receiver using a robust post-correlation Kalman structure

Kalman filtering has been proposed in the literature for wireless channel estimation, however, it is not sufficiently robust to uncertainties in the channel auto-correlation model as well as to multiple access interference (MAI). This paper presents a receiver structure for direct-sequence code-division multiple-access (DS-CDMA) systems by using robust Kalman estimation and post-correlation (i.e., symbol rate) processing for channel estimation. The proposed structure is also generalized to incorporate multiple-antenna combining and interference cancellation techniques. The resulting receiver outperforms earlier structures in the presence of channel modeling uncertainties, MAI, and low-received signal-to-noise ratio. The enhancement in performance is achieved at the same order of complexity as a standard Kalman-based receiver.     

CCK demodulation via symbol decision feedback equalizer

A symbol decision feedback equalization (DFE) technique is developed for demodulating complementary code keying (CCK) signals. The efficacy of the proposed receiver is demonstrated on the physical layer (PHY) specified in the IEEE 802.11b wireless local area network (WLAN) standard. Packet error rate (PER) performance is compared with that of the conventional RAKE receiver. The proposed receiver structure and its low complexity variations demonstrate significant performance advantages over the RAKE receiver, especially in severe multipath channels. While a large delay spread can limit the performance of two low-complexity variations discussed here, performance of the optimal symbol DFE receiver is not limited by delay spread as long as the channel signal-to-noise ratio (SNR) is sufficiently high.     

基于SOA的超宽带脉冲测距系统

提出了一种采用超宽带（UWB）高斯脉冲的测距系统,利用搜索者优化算法（SOA）搜索本地信号和接收信号之间相关的峰值,计算检测距离。分析了给定信噪比下接收机的相关结果、采用SOA的搜索过程以及搜索结果的概率分布。同时,在各信噪比下,与现有的步进相关法及门限判别法进行比较,仿真结果表明,信噪比在15 dB以上的系统测距测量误差达到3 cm,其性能优于门限判别法,而与步进相关检测法相当,但运算量较之减少84%左右。因此,该系统在高精度测距中极具实用价值。     

Time hopped transmitted reference with multiple autocorrelation sampling for ultra wideband radio

Transmitted reference (TR) schemes for ultra wideband (UWB) eliminate the need for channel estimation, reducing receiver complexity at the cost of reduced performance. This letter proposes a transmitted reference (TR) scheme with multiple autocorrelation sampling detection. The proposed receiver captures the energy in the received signal's autocorrelation side lobes, outperforming the traditional TR scheme for the operational range of signal to noise ratio (SNR) values. Time hoping, as well as the use of bandwidth efficient signaling with favorable spectral characteristics, facilitate significant improvement in system capacity in comparison to a similar scheme using orthogonal chirp signals in multipath spread channels.     

Pilot-Channel-Assisted Log-Likelihood-Ratio Selective Rake Combining for Low-Rate Ultra-Wideband Communications

For ultra-wideband (UWB) communications with signal energy dispersed by a large number of multipath components, the design of a Rake receiver that can provide a desirable output signal-to-noise ratio (SNR) using only a moderate number of fingers becomes an important issue. In this paper, we propose a pilot-channel-assisted log-likelihood-ratio selective combining (PCA-LLR-SC) scheme for UWB Rake receivers to be used in long-range low-rate UWB communications envisioned by the IEEE 802.15.4a PHY specification. The pilot and data channels are constructed using quadrature sinusoidal bursts that have the same Gaussian envelope. The system parameters are optimized through jointly minimizing the channel estimation mean square error and maximizing the receiver output SNR. Extensive simulations confirm that the proposed PCA-LLR-SC scheme is capable of providing robust low-rate UWB communications in fast-fading multipath channels and in the presence of multi-user interference.     

A differential receiver for uwb systems

We consider a UWB communication system operating in a typical indoor environment and we propose a novel differential receiver in which encoding is performed symbol-by-symbol rather than frame-by-frame, as is normally done. The detector structure is derived in a single-user scenario using a generalized likelihood ratio test approach. Its performance is assessed by simulation in the presence of multiple-access interference. The proposed receiver has a simple structure and outperforms other differential schemes of comparable complexity     

多重信号广义似然接收机的设计及性能分析

提出并设计了一类通用的多重信号广义似然接收机.设计时只要求各重信号中高斯噪声是独立和零均值的,而允许是有色的或者非平稳的.推导结果表明,针对各重未知信号的最好情况(高信噪比,且各重信号幅度相等)、最不利情况(信噪比很低,且各重信号幅度独立)和适中情况(信噪比不太高也不太低,且各重信号幅度独立),所设计的接收机结构都是一致的,只是某些具体参数和模块不同. 本文还针对此接收机给出了性能分析的一个比较通用的方法.仿真结果与推导的理论性能相当吻合.     

Ultra-Wideband Communications using Hybrid Matched Filter Correlation Receivers

Transmitted-reference (TR) schemes for time-hopping impulse radio (TH-IR) ultra-wideband (UWB) communications allow the use of simple receiver structures that are able to combine energy from different multipath components without channel estimation. A conventional TR receiver consists of a simple delay-and-multiply operation combined with an integrator. On the downside, it shows a performance loss due to non-linear operations on noise terms (generation of noise-noise cross-terms) when forming the decision variable. This paper describes a hybrid receiver structure for UWB communications that reduces these noise-noise cross-terms by first performing a "matched filtering" operation matched to the time-hopping sequence of pulses. The receiver retains most of the simplicity of the conventional TR receiver, but requires an analog correlator for the time-hopping sequence of pulses. The performance the proposed receiver is analyzed in both AWGN and multipath channels. For the AWGN case, the exact expression for the bit error probability is obtained, which takes into account the nonGaussian nature of the noise-noise cross-terms arising in the correlators. For the multipath case, both inter-frame interference and multipath interference from the reference pulse to the data pulse are considered, and approximate closed-form expressions are derived based on the assumption of a large integration interval. Also approximate criteria for optimal integration interval are obtained for the best receiver performance. Simulation studies are presented to analyze the performance of the proposed receiver structure and to confirm the theoretical analysis