Efficient Hybrid Modulation/Demodulation Scheme Using Differential Encoding/Decoding for UWB-IR

An efficient hybrid modulation/demodulation scheme using a short duration pulse in the time-domain for ultra wideband-impulse radio (UWB-IR) systems is proposed. The proposed modulation scheme is pulse position modulation (PPM) of the UWB-IR standard modulation combined with differential encoding, and non-coherent energy detection (ED) adopting differential decoding is proposed for demodulation. Differential encoding makes a pulse that can transfer additive information bit into bits assigned in one symbol without increasing the symbol period. The BER performance is evaluated for 2-PPM, 4-PPM and the proposed HD-2PPM (which has the same symbol duration as BPPM and includes two information bits per symbol). The error performance indicates that the proposed scheme is an outstanding 0.5 dB over existing schemes of UWB-IR, and the data-rate performance shows that the proposed method has higher spectral efficiency than conventional methods that occupy the same duration as the proposed scheme.

     

On the Amplify-and-Forward Cooperative Diversity with Time-Hopping Ultra-Wideband Communications

In this paper, we extend the Amplify-and-Forward cooperative diversity scheme to the context of impulse radio ultra wideband (IR-UWB). In particular, we present the construction of three families of minimal-delay and totally-real distributed algebraic space-time (ST) codes suitable for IR-UWB. The first family encodes adjacent symbols and is based on totally-real cyclic division algebras. The second family encodes the pulses used to transmit one information symbol and permits to achieve high performance levels with lower complexity. Both families of codes achieve full rate, full diversity with non-vanishing determinants for various number of relays. These schemes can be associated with pulse position modulation (PPM), pulse amplitude modulation (PAM) and hybrid pulse position and amplitude modulation (PPM-PAM). The third family of codes is information-lossless and does not require any pulse repetitions. It is specific to M-PPM-M'-PAM with M ges 3 and for all values of M'. Simulations performed over realistic indoor UWB channels are provided to verify the theoretical results.     

On Differential Detection of M-ary DPSK with Intersymbol Interference and Noise Correlation

In this paper we study differential detection ofM-ary differential phase-shift-keyed (DPSK) signals with intersymbol interference and noise correlation. With these impairments there can be a wide variation in the error rate of the individual symbols, with this variation increasing withM. However, by adding a phase shift offset and adjusting the decision boundaries in the detector, this variation can be reduced and the average symbol error rate can be decreased. For example, for quaternary DPSK with a signal to adjacent (from the previous and next symbols) intersymbol interference power ratio of 17 dB, these methods can reduce the variation in symbol error rates by more than two orders of magnitude and decrease the required signal-to-thermal noise ratio for a 10^-6symbol error rate by more than 2 dB.     

低功耗IR-UWB接收机和LNA设计研究

在分析各种超宽带(UWB)接收机系统结构的基础上,提出了一种低功耗IR-UWB接收机结构.该结构基于非相干通信机制,使用自混频技术和脉冲宽度调制方式(PPM).在该结构中,低噪声放大器(LNA)的低功耗优化是系统低功耗实现的关键.综合分析各种宽带LNA结构,提出了一种低功耗LNA设计.该LNA采用65 nmCMOS标准...     

SNR Enhancement Algorithm Using Multiple Chirp Symbols with Clock Drift for Accurate Ranging

A signal‐to‐noise ratio (SNR) enhancement algorithm using multiple chirp symbols with clock drift is proposed for accurate ranging. Improvement of the ranging performance can be achieved by using the multiple chirp symbols according to Cramer‐Rao lower bound; however, distortion caused by clock drift is inevitable practically. The distortion induced by the clock drift is approximated as a linear phase term, caused by carrier frequency offset, sampling time offset, and symbol time offset. SNR of the averaged chirp symbol obtained from the proposed algorithm based on the phase derotation and the symbol averaging is enhanced. Hence, the ranging performance is improved. The mathematical analysis of the SNR enhancement agrees with the simulations.     

Pilot-Symbol-Aided 16PSK and 16QAM for Digital Land Mobile Radio Systems

The paper proposes a novel pilot-symbol-aided (PSA) technique for fading compensation of digital signals in the mobile environments. In a PSA system, the data sequence at the transmitter is divided into frames of data. A pilot symbol from a known pseudoradom-symbol sequence is inserted periodically into a frame of data symbol for transmission. In a conventional PSA-receiver, these pilot symbols are extracted from the received signal and used to estimate the effects of signal distortion introduced in the fading channel. The resultant estimates are then used to correct the distortion effects in the received data frames. In the paper, a novel estimation technique that uses the data symbols as well as the pilot symbols is proposed. The technique has the major advantages of simple implementation and short storage-delay time. Results are presented in a series of computer-simulation tests. These assess the effectiveness of the estimation technique on the BER performances of a 16-ary phase-shift keyed (16PSK) and a 16-ary quadrature-amplitude modulated (16QAM) signals in the frequency-selective and frequency-nonselective Rayleigh fading channels. The channels are corrupted by co-channel interference or additive white Gaussian noise. Results of differential-detected 16PSK and star-16QAM signals are also presented for comparison. It has been shown that, the use of PSA technique can significantly improve the bit-error-rate performances of the systems, relative to those using differential detection.     

无线激光DH-PIM室内通信系统性能分析

研究了加性高斯白噪声和多径码间串扰下采用双头脉冲间隔调制(DH-PIM)的无线激光室内通信系统的性能,对DH-PIM系统的符号结构、带宽、差错率特性等方面进行了分析,并与OOK,PPM和DPIM调制方式做了比较。     

脉冲超宽带测控信号时延精密跟踪方法

脉冲超宽带测控新体制可有效提高测控系统的安全性能,且具有潜在的高精度测距能力.为了实现其高精度测距功能,提出了一种基于延迟锁定环路的脉冲超宽带测控信号时延精密跟踪方法.该方法在传统伪码跟踪环的基础上进行改进,利用基于非相干积分的非线性反馈环路对接收信号的脉冲相位进行精密跟踪.理论分析和仿真结果表明,该延迟锁定环路可以完成对脉冲超宽带测控信号的时延精密跟踪.与直扩测控信号相比,在相同条件下,脉冲超宽带测控信号的时延跟踪相对误差更大,但由于脉冲宽度很窄,在一定载噪比条件下,其测量精度仍可达厘米量级甚至更高.     

Performance of coded modulation employing differential encodingover Rayleigh fading channels

Multilevel coding and bit-interleaved coded modulation employing differential encoding and non-coherent reception over flat fading channels are assessed. To achieve high bandwidth efficiencies mixed amplitude/phase modulation is performed. It is shown that multiple symbol detection only provides gains for multilevel coding as Gray labelling of the differential symbols is not possible     

Performance analysis of b-bit digital receivers for TR-UWB systems with inter-pulse interference

An ultra-wideband (UWB) transmitted reference (TR) system transmits an un-modulated pulse and a delayed modulated pulse pair. Then, a correlation receiver uses the former to demodulate the latter. Because of the long spread of a typical UWB channel, time delay between the two pulses is preferable to be larger than the channel delay spread for reduced noise at the receiver. However, for bandwidth efficiency, that delay should be made small, resulting in inter-pulse interference at the receiver. In this paper, digital receivers are constructed for TR-UWB systems including inter-pulse interference. A typical mean matching technique, appropriate for both PPM and PAM schemes, is implemented digitally to obtain a good template for symbol detection. Joint estimation and detection performance of this family of digital receivers, using finite number of bits in analog-to-digital conversion and finite noisy observations, is analyzed. Closed form results are derived and verified by computer simulations. In addition, the effect of time offset between the reference pulse and information carrying pulse is studied. Overlap of the two pulses does not incur noticeable performance degradation. The proposed analytical framework can be applied to study detection performance of other related digital receivers not covered in this paper     

Performance of non-coherent receiver with UWB PPM signal in multipath channels

Mainly due to its implementation simplicity, the non-coherent Ultra-Wide Band （UWB） receiver is attractive for lower data rate applications, which gains much attention again in recent years. In this paper, a General Likelihood Ratio Test （GLRT） based non-coherent receiver on UWB Pulse-Position-Modulation （PPM） signal in multipath channels is derived, and a novel structure is proposed as well. Subsequently, the closed-form expressions of asymptotic error-rate performance related to the non-coherent receiver are also derived and verified.     

LPI in pulsed laser space communications

A basic low-probability of intercept (LPI) study for a pulsed-laser pulse position modulated (PPM) optical link with a colocated direct detection intercepting receiver is presented. The latter is considered to be a form of optical radiometer using continuous threshold testing to detect the presence of the transmitting laser. The various design alternatives for the coded PPM link, and their effect on the communication and LPI performance, are examined. It is shown that the use of optical pulse power spreading via multiple frame symbol coding is vital for avoiding interception. It can be achieved by transmitting message symbols as repeated PPM symbols using a laser pulse of sufficiently low peak power so that the detected pulse energy is much less than the detected background energy. The possibility of the use of both wideband and narrowband radiometers by the interceptor further limits the communicator's code design choices. Some equations defining effective LIP gain parameters for the communication link are developed     

A Survey on Various Coherent and Non-coherent IR-UWB Receivers

The recent developments in radio technologies, paves its way to impulse radio (IR) ultra-wideband (UWB) communication, which is used for low power, short range and high bandwidth communication, thereby exploiting a large portion of radio spectrum. In this paper, a brief review of the work done by various researchers on coherent and non-coherent IR-UWB receivers has been analysed, based on their bit error rate (BER) performances, as well as pros and cons of using these receivers. An in depth study on the receivers concludes that, non-coherent IR-UWB receiver is preferred over its counterpart coherent IR-UWB receiver even though it comes at the expense of poor BER performance. The simulation results prove that, though the performances are same, the low complexity of energy detector (ED) receivers gives an edge over the autocorrelation receivers. Further, ED receiver suffers from noise, which paves way to using weighted ED (WED) receiver. The superiority of WED receivers over all the other non-coherent UWB receivers is further confirmed by the simulation performed in AWGN and IEEE 802.15.4a UWB channels. It can also be concluded from the review that, some special receivers such as generalized likelihood ratio test, multi-symbol differential detector and decision feedback differential transmitted reference, when clubbed with UWB systems, lead to further improvement in BER performance.     

Channel impulse response insensitive feature for non-coherent signal detection in molecular communication

To solve the inter-symbol interference (ISI) and background noise challenges of molecular communication via diffusion (MCvD),four ISI-resistant signal-features were deployed,and a reliable non-coherent signal detection algorithm,which was insensitive to different types of molecular channel impulse response (CIR),was proposed.Also,an adaptive decision threshold and theoretical bound of bit error rate (BER) were deduced.Simulation results demonstrate a lower BER of the proposed non-coherent scheme compared to the state-of-the-art schemes in the same order of computational complexity,therefore suggesting its potential applications for future nano-scale MC.     

Error rate analysis of MDPSK/CPSK with diversity reception undervery slow Rayleigh fading and cochannel interference

The distribution of the phase noise due to additive white Gaussian noise (AWGN) and cochannel interference (CCI) is analyzed for differential phase detection (DPD) and coherent phase detection (CPD) in a very slow nonfrequency selective Rayleigh fading environment. The effects of modulation timing offset between the desired signal and the CCI and of the overall channel filter response are considered. Simple closed-form expressions are derived for ideal selection diversity reception. The derived phase noise distributions are used for evaluating the bit error rate (BER) performance of 2-16DPSK/CPSK assuming square-root raised cosine Nyquist transmit/receive filters. It is found that the BER performance of CPSK is less sensitive to CCI modulation timing offset than DPSK, and that increasing the filter rolloff factor can improve the BER performance due to CCI. Finally, the accuracy of the BER approximation that uses the symbol error rate is discussed     

紫外分离双脉冲位置调制误码性能分析

基于紫外非视距(NLOS)单次散射信道传输模型,分析了用于无线紫外光通信的分离双脉冲位置调制(SDPPM)方案的误码性能.介绍了SDPPM调制方案的符号结构,将该调制方案与开关键控调制(OOK)、脉冲位置调制(PPM)和双脉冲位置调制(D-PPM)在带宽需求、功率需求方面进行比较.利用光子计数方法,研究了无背景辐射噪声条件下SDPPM的误符率(SER).对PPM、D-PPM和SDPPM紫外通信系统的误码性能进行仿真,分析路径损耗对其影响.结果表明,SDPPM在信源比特分组长度n为5和6 bit时获得了带宽需求与功率需求的较好平衡.当SER达到10-4时,有效通信距离比D-PPM长20 m左右.同时,SDPPM调制方案降低了紫外光散射通信中因多径色散造成的码间串扰(ISI).     

Detection of multiuser orthogonal space-time block coded signals via ordered successive interference cancellation

This paper investigates multiuser orthogonal space-time block coded signal detection within the ordered successive interference cancellation (OSIC) framework. Both the zero-forcing and minimum-mean-square-error ordering criteria are considered. When each user terminal is equipped with no more than four transmit antennas, it is shown that orthogonal transmit redundancy leads to an appealing signal ordering property: in each processing layer the transmitted symbols of an arbitrary user are associated with an identical ordering metric. This guarantees the feasibility of (user based) group-wise symbol recovery through the OSIC mechanism. Analytic bit-error-rate performance is given. Computer simulations and flop count evaluations are also provided for comparing the OSIC based solution with existing multiuser detection schemes reported for the considered system     

MLD and mse algorithms for adaptive detection of digital signals in the presence of interchannel interference

Adaptive mean-square error (mse) and maximum-likelihood detection (MLD) algorithms for a dual-channel digital communication system in the presence of interchannel interference and white Gaussian noise are presented. The mse algorithm forms estimates of the transmitted symbols from a linear combination of received symbols using weights that minimize the mse between transmitted and estimated symbols. The nonlinear MLD algorithm minimizes the probability of symbol error by maximizing the probability of the received signal samples on the two channels over ail possible transmitted symbol pairs. The probability of error is derived for the two algorithms when quadrature phase-shift keying (QPSK) is used as a modulation technique, and is compared with that of a dual-channel QPSK system having no compensation for the crosstalk.     

Iterative detection for multicarrier transmission employing time-frequency concentrated pulses

We consider multicarrier transmission schemes in which the elementary signal pulses relate to the elements of a Weyl-Heisenberg system, i.e., resulting from a prototype function shifted in time and frequency. The overlapping of the information-bearing signal parts at the output of doubly dispersive channels and the resulting interference are confined by utilizing a prototype function whose energy is concentrated in both time and frequency. We derive a symbol detector which first calculates a sufficient statistic for the unknown data symbols from the linearly combined output signals of a filter bank, and second, performs an iterative maximization of the likelihood function. The presented receiver takes full advantage of the confined pulse overlapping to limit the computational effort. An analysis of the computational complexity and bit-error rate performance of the iterative detection scheme is provided for wide-sense stationary uncorrelated scattering channels.     

Closed-form blind symbol estimation in digital communications

We study the blind symbol estimation problem in digital communications and propose a novel algorithm by exploiting a special data structure of an oversampled system output. Unlike most equalization schemes that involve two stages-channel identification and channel equalization/symbol estimation-the proposed approach accomplishes direct symbol estimation without determining the channel characteristics. Based on a deterministic model, the new method can provide a closed-form solution to the symbol estimation using a small set of data samples, which makes it particularly suitable for wireless applications with fast changing environments. Moreover, if the symbols belong to a finite alphabet, e.g., BPSK or QPSK, our approach can be extended to handle the symbol estimation for multiple sources. Computer simulations and field RF experiments were conducted to demonstrate the performance of the proposed method. The results are compared to the Cramer-Rao lower bound of the symbol estimates derived in this paper