应用空时编码的正交多载波直接序列扩频CDMA系统

本文把空时编码(STC)技术应用于正交多载波直接序列扩频CDMA(MC—DS—CDMA)系统，给出了空时编码MC—DS—CDMA系统的发射机和接收机方案。计算机仿真给出了应用空时编码的MC—DS—CDMA系统性能，和普通MC—DS—CDMA以及应用空时编码的多载波CDMA(MC—CDMA)系统的性能比较也由计算机仿真给出。     

Bit error rate performance of multicarrier CDMA system with application to image transmission

In this paper, we proposed and analyzed a multicarrier CDMA system with application to image signal transmission over wireless communication channels. Instead of the conventional method of transmitting signal with one carrier frequency, the image signal is partitioned into subsets and a different subband carrier modulates each subset. By so doing, the probability that all the subcarrier will simultaneously fade and be in error is minimized. The performance of the proposed system is evaluated in terms of the average bit error rate in the presence of multipath fading and thermal noise and as a function of data rate, bandwidth, delay range, and space diversity. The effectiveness of multicarrier modulation in resisting fading is demonstrated for a maximal ratio combining space diversity system. Results reveal considerable performance improvement using multicarrier modulation, compared to single carrier modulation.     

A kind of PAPR reduction method based on pruning WPM and PTS technology

Wavelet packet multicarrier system gains widespread concern because of its better resistance performance to Inter-Symbol Interference (ISI) and Inter-Carrier Interference (ICI), as well as the higher spectrum efficiency. However, multicarrier system has a high Peak to Average Power Ratio (PAPR), which will lead to many problems such as lower system performance. In order to solve the problem, a kind of PAPR reduction method based on pruning Wavelet Packet Modulation (WPM) and Partial Transmit Sequences (PTS) technology is proposed in this paper, through proper pruning of the full-tree structure of wavelet packet modulation in the PTS technology to reduce the number of nodes in the system, and finally improve the reduction effect of PAPR. Simulation results show that when Complementary Cumulative Distribution Function (CCDF) is 10^?3, PTS based on pruning WPM compared with PTS technique and pruning technique has improved about 1 dB and 1.5 dB, which will not affect the system’s Bit Error Rate (BER) performance in the wavelet packet multicarrier system.     

MC-CDMA调制在散射通信信道下的性能分析

为提高对流层散射通信系统容量和抗干扰能力,对散射信道下的多载波扩频方案进行研究.基于所建立的Rayleigh 分布对流层散射信道模型,分析了频域扩频多载波技术MC-CDMA的系统性能,对典型散射信道下的系统误码率进行了分析与仿真.结果表明:MC-CDMA可有效提升散射通信系统容量,单用户时系统误码率性能较好,随着用户数和散射信道多普勒频移的增大,系统误码率随之增大,需采用多址干扰控制和子载波干扰消除技术来改善系统误码率性能.     

配合智能电表趋势的安森美半导体PLC技术及解决方案

本文介绍了安森美半导体电力线载波(PLC)调制解调器的技术特点及优势,以及最新多载波PLC调制解调器的最新产品。     

Alternatives for on-board digital multicarrier demodulation

In this paper alternatives for digital multicarrier demodulators (MCD) suitable for advanced digital satellite communications systems are presented. The MCD permits the direct on-board interfacing of FDMA and TDM communication links by digital signal processing techniques. Two main functions are implemented by a MCD: demultiplexing (DEMUX) and demodulation (DEMOD). We focus here only on a digital implementation of the MCD, looking at its advantages, flexibility, better performance and VLSI integrability. The DEMUX may be implemented in a number of ways: the analytic signal method, fast Fourier transform with polyphase network technique, or multistage methods. For all the implementation methods considered it is shown that a certain degree of integration of DEMUX and DEMOD functions is possible. To this end, in the proposed MCD schemes the receiver pulse-shaping filter has been integrated in the DEMUX structure, reducing the overall implementation complexity. It is shown that, for the per-channel structure based on the analytic signal method, a highly modular and flexible implementation can also be achieved. Coherent demodulation is used to reduce the signal-to-noise ratio required to achieve a specified bit error rate. The coherent demodulation is carried out by using the maximum likelihood (ML) estimation method. Two different approaches to receiver synchronization have been studied. For the first, the carrier phase and symbol timing estimates are independently derived by suitable techniques. The second approach makes use of the maximum a posteriori probability method to estimate both the carrier phase and symbol timing of the receivied signal. In particular, for this technique it is shown that, by a suitable choice of the architecture of the digital coherent receiver, the ML demodulator can be integrated in the joint carrier and clock recovery circuit, with no increase in the overall system complexity. The digital architecture of the proposed MCD can be adapted to different digital modulation techniques. However, here we consider only the application for QPSK signals, as this modulation scheme is the most promising for digital satellite communications. A theoretical analysis and computer simulation have been used to evaluate the performance degradation of the proposed MCD, including finite-arithmetic implementation effects.     

Low-Complexity PAPR Reduction of MC-SS Signals in PAN

A peak-to-average power ratio (PAPR) reduction scheme with low complexity is proposed for the multicarrier spread spectrum (MC-SS) system in personal area network (PAN). Traditional clipping and filtering scheme requires a high oversampling rate to meet the emission mask requirements. This would cause high power consumption for mobile PAN devices in personal network. To solve the problem, upsampling is introduced between clipping and filtering in this paper to reduce the oversampling rate. A simplified implementation structure is also derived for the proposed scheme. Simulation results show that its complexity is about 65% of the conventional scheme while achieving satisfying performance.

The Performance of Multicarrier CDMA for the Correlated Rayleigh Fading Channel

We present an new method for the analytical calculation of the error probability in a Rayleigh fading channel with correlated fading amplitudes. Even though the method can be applied for more general problems, we restrict ourselves on the investigation of a multicarrier CDMA transmission. The frequency correlation between the fading amplitudes of the carriers is given by the delay power spectrum of the channel. We generalize the well-known analytical expressions for the pairwise error probability of the uncorrelated Rayleigh channel to this case of correlated fading. This probability can be expressed in a closed form by an integral over a finite interval which can be easily evaluated numerically. We present some examples to show how much of the diversity of a code remains useful if the transmission channel does not provide an arbitrary degree of diversity.     

一种新的基于判决反馈的OFDM频率跟踪算法

该文提出了一种新的用于多径信道的基于判决反馈的OFDM载波频率跟踪算法。该算法具有精度高,计算量小,实现简单的优点。基于该算法的特点同时提出了根据信道特性加权的改进方法,加强了对抗频率选择性衰落信道的能力,进一步提高了在低信噪比下的跟踪性能。     

时隙ALOHA DS/CDMA系统与多载波时隙ALOHA系统吞吐性能的比较研究

该文对同样带宽下时隙 ALOHA DS/CDMA系统和多载波时隙 ALOHA系统的吞吐量进行了理论计算、比较和仿真。结果表明,在总负载较大时,采用高纠错能力的时隙 ALOHA DS/CDMA系统可以在吞吐量上有更好的性能。但若网络负载过重,时隙ALOHA DS/CDMA系统的吞吐性能较多载波时隙ALOHA的系统下降快;码字总数受限会带来码字选择的冲突,从而降低系统的吞吐性能。