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.

     

An embedded transmission scheme using PPM signaling with symmetric error-correcting codes for optical CDMA

An embedded transmission (ET) scheme is proposed to easily apply error-correcting codes into optical code-division multiple-access (CDMA) systems for immunity from multiple-access interference (MAI). The ET scheme offers high transmission capability over the traditional scheme using pulse position modulation (PPM) signaling, because a 2/sup J/-ary symbol of each user is embedded in the signature sequence with 2/sup J/ weighted positions. Furthermore, the ET scheme with 2/sup J/-ary PPM signaling makes the optical CDMA system J parallel transmission systems, because J bits consisting of 2/sup J/-ary symbol are separately decided. Since such a separate decision is a comparison decision, the effect of MAI added in the optical channel is converted to symmetric errors in the individual parallel transmission systems. Using the symmetric error-correcting (SEC) code immunizes the individual parallel transmission systems against MAI more easily than the embedded-modulation scheme described in because the ET scheme avoids using the asymmetric error correcting code, which is difficult to implement. We analyze the bit error rate under Poisson photon counting channel and show that the ET scheme has an advantage of good energy efficiency over the traditional scheme in applying SEC codes.     

Performance comparison of dual‐hop hybrid decode‐or‐amplify‐forward relay schemes for M‐ary quadrature amplitude modulation burst transmission over Rayleigh fading channels

This paper shows the analytical performance expressions of M‐ary quadrature amplitude modulation burst symbol transmission for hybrid decode‐or‐amplify‐forward (HDAF) relay schemes over quasi‐static Rayleigh‐fading channels. First, we derive the probability density function of the received instantaneous signal‐to‐noise ratio as the simplified form, which is related to all the possible occurrence probabilities of error‐events for M‐ary quadrature amplitude modulation burst transmission. On the basis of the derived probability density function, we express average bit error probability, average symbol error probability, and average burst error rate as closed forms, which can be also applied to both amplify‐and‐forward and adaptive decode‐and‐forward (ADF) schemes. The analysis and simulation results show that HDAF scheme for burst transmission can achieve the performance of ADF scheme with symbol‐by‐symbol transmission, which is the achievable lower bound. Furthermore, the outage probability, the normalized channel capacity, and the goodput performance are also derived as closed forms. The analysis shows the superiority of HDAF scheme to ADF scheme. Comparison with simulations confirms that the derived analytical expressions are accurate over all signal‐to‐noise ratio regions and for different numbers of relays and modulation orders.     

Multistage detection in asynchronous code-division multiple-accesscommunications

A multiuser detection strategy for coherent demodulation in an asynchronous code-division multiple-access system is proposed and analyzed. The resulting detectors process the sufficient statistics by means of a multistage algorithm based on a scheme for annihilating successive multiple-access interference. An efficient real-time implementation of the multistage algorithm with a fixed decoding delay is obtained and shown to require a computational complexity per symbol which is linear in the number of users K. Hence, the multistage detector contrasts with the optimum demodulator, which is based on a dynamic programming algorithm, has a variable decoding delay, and has a software complexity per symbol that is exponential in K. An exact expression is obtained and used to compute the probability of error is obtained for the two-stage detector, showing that the two-stage receiver is particularly well suited for near-far situations, approaching performance of single-user communications as the interfering signals become stronger. The near-far problem is therefore alleviated. Significant performance gains over the conventional receiver are obtained even for relatively high-bandwidth-efficiency situations     

A Novel Wavelet Packet Division Multiplexing Based on Maximum Likelihood Algorithm and Optimum Pilot Symbol Assisted Modulation for Rayleigh Fading Channels

Wavelet packet division multiplexing (WPDM) is a high-capacity, flexible, and robust multiple-signal transmission technique. In this paper, a novel WPDM system based on optimum pilot symbol assisted modulation (OPSAM) and a maximum likelihood (ML) algorithm is studied for Rayleigh fading channels. The ML detecting algorithm and the new discrete wavelet packet transform structure, which is based on pilot symbol assisted modulation (PSAM) using a least mean squares algorithm, are two novel aspects of the presented system. An expression for the bit error rate of the WPDM scheme on quadrature phase-shift keying (QPSK) is derived in the presence of flat fading and Gaussian noise. It is demonstrated by simulation results that the OPSAM WPDM scheme can provide greater immunity to flat fading channels and Gaussian noise than the OPSAM orthogonal frequency division multiplexing scheme, the differential QPSK WPDM scheme, and the normal PSAM WPDM scheme.     

On generalized two-dimensional cross constellations and the opportunistic secondary channel

An optimum bits-to-symbol mapping for square constellations is introduced which allows a simple detection in narrow-sense quadrature amplitude modulation (qam) systems. Then, a family of two-dimensional generalized cross constellations is presented as well as upper and lower bounds on the symbol error probability over an ideal band-limited channel which generalize those previously known for conventional qam. The application of this scheme to the opportunistic secondary channel is analysed and it is shown how fractional rates (in bits per 2-dimensional signal) can be supported on 2D generalized qam systems. These signaling schemes are compared with multidimensional generalized constellations recently proposed by Forney and Wei.     

一种利用约束Viterbi算法改进IS95协议信道编码的方法

IS95具有两个速率集,在同一个速率集中,不同的速率其数据帧的长度不同,为了使进入正交调制的数据帧的长度相同,其采用了信号重复器.信号重复器进行简单的重复作用,使得带宽不能充分利用.文中提出的方法利用一个信号发生器,产生已知的信号进入卷积编码,卷积编码后的数据帧长度同样符合要求,而信号发生器产生的已知信号在译码端可以作为译码时的约束条件进行约束Viterbi译码.在BSC信道模型的仿真结果证明,其在较高误码率的情况下具有较好的性能.     

DVB-T接收端同步系统设计与仿真

提出了一种DVB-T接收端的同步方案,包括符号粗同步-精载波频偏联合同步、符号精同步-采样钟相位联合估计、粗载波频偏估计3个部分,完成DVB-T接收端同步,并给出了该同步方案在高斯信道、莱斯信道下的仿真结果.     

Timing recovery for OFDM transmission

Orthogonal frequency division multiplexing (OFDM) is an effective modulation technique for high-rate and high-speed transmission over frequency selective fading channels. However, OFDM systems can be extremely sensitive and vulnerable to synchronization errors. In this paper, we present a scheme for performing timing recovery that includes symbol synchronization and sampling clock synchronization in OFDM systems. The scheme is based on pilot subcarriers. In the scheme, we use a path time delay estimation method to improve the accuracy of the correlation-based symbol synchronization methods, and use a delay-locked loop (DLL) to do the sampling clock synchronization. It is shown that by using this scheme, the mean square values of the symbol timing estimation error can be decreased by several orders of magnitude compared to the common correlation methods in both the AWGN and multipath fading channels. In addition, the scheme can track the symbol timing drift caused by the sampling clock frequency offsets     

Adaptive Minimum Symbol Error Rate Beamforming Assisted Detection for Quadrature Amplitude Modulation

We consider beamforming assisted detection for multiple antenna aided multiuser systems that employ the bandwidth efficient quadrature amplitude modulation scheme. A minimum symbol error rate (MSER) design is proposed for the beamforming assisted receiver, and it is shown that this MSER design provides significant performance enhancement, in terms of achievable symbol error rate, over the standard minimum mean square error (MMSE) design. A sample-by-sample adaptive algorithm, referred to as the least symbol error rate, is derived for adaptive implementation of the MSER beamforming solution. The proposed adaptive MSER scheme is evaluated in simulation using Rayleigh fading channels, in comparison with the adaptive MMSE benchmarker.     

Optimization for faster-than-Nyquist signaling based combining under multi-path channel

We propose a faster-than-Nyquist (FTN) signaling based combining scheme to increase the achievable rate for the single-input-single-output (SISO) system and the single-carrier system under the multi-path channel, where the combining scheme aims to combine the signals received at all symbol periods during the channel length for each transmitted symbol. An important feature of the FTN signaling based combining scheme is that the transmitter ceases the transmission for b symbol periods after transmitting each symbol. By proposing the optimization algorithm for finding the optimum b that maximizes the achievable (information) rate, we propose in this paper the optimal FTN signaling based combining scheme. We first establish the optimization problem and then present a theorem for proving the existence of the optimum b that maximizes the lower bound of the average achievable (information) rate. On the basis of this theorem, we present the steps of the proposed optimization algorithm. Numerical results are provided, and they confirm that the proposed optimization algorithm can find the optimum b.     

Data-Derived Symbol Synchronization of MASK and QASK Signals

Much has been said in the literature with regard to the problem of establishing symbol synchronization in binary baseband digital communication systems. By comparison, the literature contains little information relating to the extraction of symbol sync from multilevel baseband data. With the recent interest in multilevel amplitude-shift keying (MASK) and quadrature amplitude-shift keying (QASK) as signaling techniques for multilevel digital communications systems, the problem of providing symbol synchronization in the receivers of such systems becomes paramount. This paper presents a technique for extracting symbol sync from an MASK or QASK signal which has been transmitted over an infinite bandwidth white Gaussian noise channel. The scheme is essentially a generalization of the data transition tracking loop (DTTL) which has heretofore been used in PSK systems. The performance of the loop is analyzed in terms of its mean-squared symbol sync jitter and its effects on the data detection process in MASK and QASK systems.     

Doppler-corrected differential detection of MPSK

An open-loop technique is presented for estimating and correcting Doppler frequency shift in an M-ary differential phase-shift-keyed (MDPSK) receiver. The novelty of the scheme is based on the observation that whereas the change in phase of the received signal over a full symbol contains the sum of the data (phase) and the Doppler-induced phase shift, the same change in phase over half a symbol (within a given symbol interval) contains only the Doppler-induced phase shift. Thus, by proper processing, the latter can be estimated and removed from the former. Analytical and simulation results are given for the variance of the above estimator, and the error probability performance of the MDPSK receiver is evaluated in the presence of the Doppler correction. Next, the practical considerations associated with the application of this technique on bandlimited Nyquist channels are discussed and incorporated into the final design. It is shown that the receiver can, in the absence of timing jitter, be designed to allow combined Doppler correction and data detection with no penalty due to intersymbol interference (ISI). The effects of ISI due to timing jitter are assessed by computer simulation     

Image transmission in an OFDM VLC system using symbol scrambling and chaotic Walsh-Hadamard precoding

Abstract- An image secure transmission scheme combining symbol scrambling and chaotic Wahsh-Hardmard precoding is proposed in orthogonal frequency division multiplexing (OFDM)-based visible light communication (VLC) system. In the proposed scheme, a two-dimensional (2D) logistic-sine-coupling map (LSCM) is employed to generate two chaotic sequences. One is used to scramble the 16 quadrature amplitude modulation (QAM) symbols, and the other is used to scramble the rows of standard Walsh-Hadamard transform (WHT). The simulation results show that the proposed scheme can not only reduce the peak-average-power ratio (PAPR) but also achieve the image secure transmission over OFDM-based VLC systems.     

Joint resource allocation,routing and CAC for uplink OFDMA networks with cooperative relaying

In this paper, we propose a joint resource allocation, routing, and connection admission control (CAC) scheme for uplink transmission in orthogonal frequency division multiple access (OFDMA) relay networks with cooperative relaying. For cooperative relaying, relay station can relay uplink data from mobile station (MS) to base station with cooperation of the MS using transmit diversity. Transmit diversity can be achieved by virtual MISO via distributed space–time coding. The proposed scheme jointly allocates OFDMA resources and selects path for each user with CAC to maximize the upink throughput of cooperative OFDMA relay networks. The basic OFDMA resource unit is considered as a resource element which is one subcarrier over one OFDMA symbol. An efficient multi-choice multi-dimensional knapsack (MMKP) algorithm is presented for the proposed scheme. The proposed MMKP algorithm provides a unified framework which is applicable to OFDMA networks with and without cooperative relaying. We evaluate the performance of the proposed scheme with and without cooperative relaying in a hilly terrain with heavy tree density by using OPNET-based simulation. We show that the cooperative relaying improve the uplink system throughput compared with non-cooperative relaying, and the proposed scheme outperforms the conventional link quality-based scheme in both cooperative and non-cooperative relay networks.     

频率选择性信道下Turbo码和SC-FDE的联合方案

针对频率选择性信道下宽带数据传输存在符号间干扰(ISI),提出了一种频率选择性信道下联合Turbo码和单载波频域均衡(SC-FDE)的宽带传输方案.通过改进传统SC-FDE结构,设计了一种SC-FDE软信息提取方法,提高了进入Turbo码译码器先验信息的精确性,从而改善了系统整体性能.仿真结果表明,相比较于硬信息输出,采用SC-FDE软信息输出能够改善输出信噪比,提高系统性能.     

The performance of trellis-coded MDPSK with multiple symboldetection

The idea of using a multiple (more than two) symbol observation interval to improve error probability performance is applied to differential detection of trellis-coded multiple phase-shift keying (MPSK) over an additive white Gaussian noise (AWGN) channels. An equivalent Euclidean distance measure per trellis branch is determined for this detection scheme. This is used to define an augmented (larger multiplicity) trellis code whose distance measure is the conventional squared Euclidean distance typical of conventional trellis-coded modulation on the AWGN. Such an augmented multiple trellis code is a convenient mathematical tool for simplifying the analysis. Results are obtained by a combination of analysis and computer simulation. It is shown that only a slight increase (e.g. one symbol) in the length of the observation interval will provide a significant improvement in bit error probability performance     

空时分组编码多载波码分多址系统的直接解码

针对宏蜂窝小区中基站使用均匀线阵空时分组编码多载波码分多址系统的上行物理链路,该文提出了一种无需信道估计,直接对多个用户的发射符号和波达方向进行盲估计的算法。该算法通过构筑蕴涵用户编码符号序列和波达方向的辅助矩阵,对其进行特征分解,得到了每个用户波达方向的闭式解。进而,利用空时分组码的正交结构以及发射符号的有限码集特性给出了所有活动用户原始符号序列的闭式估计。计算机仿真实验验证了该算法的有效性。     

Data detection of MPSK in the presence of rapidly changing carrierphase

We present a novel method for data detection of M-ary phase shift keying (MPSK) in the presence of unknown carrier phase and additive white Gaussian noise. Here, the unknown carrier phase is rapidly changing and random. That is, the unknown phase changes from symbol to symbol in a nondeterministic manner. The rate of phase change is such that phase change over two symbol intervals is negligible, but it is not necessarily negligible over a longer interval. Our proposed system outperforms traditional differential phase shift keying (DPSK) by 1.5 dB at error probabilities of 10^-3 and 10^-4. We also compare the performance of our scheme with that of multiple symbol differential detection (MSDD). Except under very slow phase change conditions, our scheme outperforms MSDD. Our decoder is well suited to mobile communication systems. Here, receivers usually move with different speeds at different times     

正交空时分组码性能估计的一种方法

本文给出并证明了采用正交空时分组码传输的衰落信道条件下,接收机输出瞬时信噪比的一般表达形式,分析了瑞利衰落信道条件下接收机输出符号差错性能.给出了正交空时分组码的符号差错概率的最小距离球界,由此可以得到空时分组码关于发送天线数量的"地板效应".