MC-CDMA

摘要： 水声通信由于其信道延迟大、带宽窄、干扰多等特点而发展缓慢,为了实现高质量、长距离的水下无线通信,通过对CDMA(码分多址)、OFDM(正交频分复用)等多种通信技术的分析和对比,基于FPGA平台建立了一种比较先进的水声通信调制解调系统.该系统采用MC-CDMA技术,设计了一种基于Gold序列的信号扩频办法,采用FFT/IF-FT模块实现OFDM调制解调,该系统通过了水槽实验环境的测试,运行稳定.

摘要： 多载波码分多址(MC-CDMA)技术结合了正交频分复用(OFDM)技术和码分多址(CDMA)技术的优点,具有数据传输速率高、频谱利用率高、抗干扰能力强和系统容量大的优点,是现阶段备受瞩目的一种无线通信方式.由于该通信系统中的码分多址技术结合了多载波调制技术,所以要求该系统中使用的扩频序列在兼具良好的自相关、互相关特性的同时,还要有较低的峰均比,这对扩频序列的设计提出了较高的要求.为了满足上述要求,设计了一种以Golay码为基础码,以m序列对Golay码进行加扰的扩频序列,该扩频序列具有良好的自相关、互相关特性,且峰均比较低.通过对比仿真验证,证明了本文中设计的扩频序列具有良好的特性,适用于MC-CDMA系统.

摘要： 针对多载波系统信道的稀疏特性，提出一种基于压缩感知（ CS ）的 MC-CDMA 多载波系统信道估计方法。信号自适应匹配追踪（ SAMP ）是一种压缩感知算法，详细研究了该算法的设计原理和实现过程。将该算法与传统信道估计方法及基于压缩感知的 OMP 算法做比较，仿真结果表明， SAMP 算法的信道估计均方误差（ MSE ）和系统误比特率（ BER ）均更小。对于在稀疏度未知的多载波系统信道中，该算法可以获得很好的信道估计性能，降低系统的复杂度。%A novel method of MC-CDMA multicarrier systems channel estimation based on compressed sensing (CS) is proposed in sparse multicarrier systems channel. Signal adaptive matching pursuit (SAMP) is a recovery algorithm. This paper conducts a detailed research on the design principle and realization of this algorithm. Simulated results show that channel estimation mean square error(MSE)and bit error rate(BER) of SAMP algorithm is less than that of traditional channel estimation method and OMP algorithm based on compressed sensing. In multicarrier system channel of unknown sparseness,this algorithm not only can obtain good channel estimation performance, but also can reduce complexity of the system.

摘要： FPGA implementation used of Rotating phase shift (RPS) for peak-to-average power ratio (PAPR) reduction in Multi Carrier Code Division Multiple Access (MC-CDMA) signals. Because, MC-CDMA is still suffering from PAPR which is a major drawback in most of the multi carrier communication systems. In addition, the implementation of the system in an FPGA becomes more flexible and scalable. It eliminates the search for optimum phase factors from a given set, which manifests improved PAPR at reduced computational complexity as compared to conventional PTS and SLM. The amplitude of the signal is reduced by rotating each of the partially transmitted sequence anticlockwise by a π/2 degree and the peak power is reduced by circularly shifting the quadrature component of the partially transmitted sequence after phase rotation. A brief description of PTS, SLM is compared with the RPS, which best reduces PAPR from PTS and SLM. It is also presented that VHDL code of the RPS is designed by Xilinx ISE 14.1 implements of FPGA. The peak-to-average power ratio performance of the proposed method has been investigated.

摘要： This paper proposes a time and frequency domain spread multicarrier direct sequence code division multiple-access(TF/MC DS-CDMA)system supporting parallel transmission,which first takes the data bit from serial to parallel conversion and then employs both time-domain and frequency-domain spreading . In the case of constant transmission data rate and spread spectrum gain,parallel transmission can increase the symbol time and reduce code chip-rate,which can improve the capability of anti-frequency selective fading and achieve low-rate signal processing . Signals are received by invoking chip waveform matched filter . The detection performance of single-user is analyzed and the bit-error rate(BER)expression over additive white Gaussian noise channels is deduced . The research reveals that the serial to parallel conversion ratio is related to the reduction of code chip-rate and the number of subcarrier,but unrelated to BER . There is no interference between different data bits for the same user,and the multiuser interference(MUI)only exists between different data bits for different users transmitted by the same subcarrier and there will exist no MUI when the time-domain spreading codes assigned to different users are orthogonal . BER will rise along with the increase of users number and reduce along with the increase of spread spectrum gain and signal-to-noise ratio(SNR)per bit . In the condition of the limited band-width,the system can be simplified and meet the performance requirements of BER by reasonably setting the se-rial to parallel conversion ratio and the parameters of time-domain and frequency-domain spread spectrum .%　　提出了一种并行传输的时频域扩频多载波DS-CDMA系统，它先将传输数据进行串并转换而后经过时域和频域两次扩频。在不改变传输数据速率和扩频增益的情况下，并行传输可以增大符号时间和降低码片速率，从而提高信号的抗频率选择性衰落的能力和实现低速率信号处理。采用码片匹配滤波的方式对信号进行接收，分析了高斯信道下的单用户检测性能并推导了误比特率表达式。研究表明，在此系统中串并转换比与码片速率的降低和子载波个数成正比，而与误比特率无关；不存在比特间干扰；多用户干扰只存在于同一子载波传输的不同用户的数据比特之间，且可通过采用正交时域扩频码来消除；误比特率随用户数量的增加而增加，而随每比特信噪比和扩频增益的增加而降低；在带宽受限的情况下，可通过合理设置串并装换比、时域和频域扩频增益参数来简化系统实现，满足误比特率的性能需求。

摘要： 统一扩频测控系统是在MC-CDMA为主的多载波通信体制的基础上建立起来的,MC-CDMA等多载波通信体制的基础是正交频分复用(orthogonal frequency division multiplexing,OFDM)技术;相对于传统的单载波系统,采用OFDM技术的统一扩频测控系统对于载波频率偏移和相位噪声的影响尤为敏感,所以在系统设计时必须考虑相噪的跟踪与抑制;文章在分析相位噪声对统一扩频测控系统性能影响的基础上,用有限个正弦波近似的方法建立相噪的频域线性参数模型,并基于该模型提出了加入相噪估计导频来跟踪相噪的方法;由于导频与数据子载波之间有空子载波作为保护间隔,该方法可以估计出相噪的高阶频谱分量,从而达到了很好的相噪抑制效果.

摘要： 本文提出了将ZCZ序列偶应用于准同步MC-CDMA系统的新见解,并用matlab仿真软件对系统性能进行仿真,实验验证了ZCZ序列偶准同步MC-CDMA系统的误码率性能,将ZCZ序列偶,Gold序列和Hardmard序列进行比较,实验结果表明,ZCZ序列偶准同步MC-CDMA通信系统误码率性能十分接近Hardmard序列和Gold序列作为扩频序列的准同步MC-CDMA系统误码率性能.

摘要： 0引言正交频分复用(OFDM)技术在高速水声通信系统中的应用已得到广泛研究。OFDM采用并行多载波,子载波间频谱重叠实现高速传输,循环前缀的加入则可有效对抗ISI[1],然而水声信道中除了相位起伏和多普勒频移造成的解调困难,频率选择性深度幅度衰落往往造成子载波解码错误[2]。

摘要： Automatic Digital Modulation Recognition (ADMR) is becoming an interesting problem with various civil and military applications. In this paper, an ADMR algorithm in Multi-Carrier Code Division Multiple Access (MC-CDMA) systems using Discrete Transforms (DTs) and Mel-Frequency Cepstral Coefficients (MFCCs) is proposed. This algorithm uses various DT techniques such as the Discrete Wavelet Transform (DWT), Discrete Cosine Transform (DCT) and Discrete Sine Transform (DST) with MFCCs to extract features from the modulated signal and a Support Vector Machine (SVM) to classify the modulation orders. The proposed algorithm avoids over fitting and local optimal problems that appear in Artificial Neural Networks (ANNs). Simulation results shows the classifier is capable of recognizing the modulation scheme with high accuracy up to 90% - 100% using DWT, DCT and DST for some modulation schemes over a wide Signal-to-Noise Ratio (SNR) range in the presence of Additive White Gaussian Noise (AWGN) and Rayleigh fading channel, particularly at a low Signal-to-Noise ratios (SNRs).

摘要： In today’s scenario mobile phones are not used only for messaging and talking, now we use mobiles also to access internet. For that we need higher data rates. Mobiles use wireless communication channel, which is very fast varying channel. To increase the data rate we have to utilize the full channel based on the channel condition. For that we have to estimate the channel condition and based on that we have to vary the data rate so that our communication system performance parameters (bit error rate, throughput) do not change beyond the accepted level. To increase the data rate we are also using the multi-carrier CDMA system in conjunction with the above described adaptive modulation. Adaptive modulation, in conjunction with MC-CDMA transmission system is very assuring way to increase data rate. In current scenario demand of very high data rates up to 100 Mbits/s may be achieved with this scheme. In this paper, adaptive modulation based M-ary QAM, M-PSK and M-ary CPM systems applied to a MC-CDMA system in Rayleigh fading channel environment have been investigated and BER performances of all these digital modulation schemes have been compared.

摘要： 自适应子载波分配是提高多载波系统性能的关键技术之一。本文借鉴已有的OFDMA系统自适应子载波分配算法，结合MC-CDMA系统特点，根据各用户在各个子载波上的信道增益情况，并考虑系统用户间的公平性，提出一种基于用户间公平性约束的速率自适应子载波分配算法。通过理论分析和仿真结果表明，该方案提高系统性能的同时显著提高了系统中各用户间的公平性。

摘要： 自适应子载波分配是提高多载波系统性能的关键技术之一。本文借鉴已有的OFDMA系统自适应子载波分配算法，结合MC-CDMA系统特点，根据各用户在各个子载波上的信道增益情况，并考虑系统用户间的公平性，提出一种基于用户间公平性约束的速率自适应子载波分配算法。通过理论分析和仿真结果表明，该方案提高系统性能的同时显著提高了系统中各用户间的公平性。

摘要： 自适应子载波分配是提高多载波系统性能的关键技术之一。本文借鉴已有的OFDMA系统自适应子载波分配算法，结合MC-CDMA系统特点，根据各用户在各个子载波上的信道增益情况，并考虑系统用户间的公平性，提出一种基于用户间公平性约束的速率自适应子载波分配算法。通过理论分析和仿真结果表明，该方案提高系统性能的同时显著提高了系统中各用户间的公平性。

摘要： 自适应子载波分配是提高多载波系统性能的关键技术之一。本文借鉴已有的OFDMA系统自适应子载波分配算法，结合MC-CDMA系统特点，根据各用户在各个子载波上的信道增益情况，并考虑系统用户间的公平性，提出一种基于用户间公平性约束的速率自适应子载波分配算法。通过理论分析和仿真结果表明，该方案提高系统性能的同时显著提高了系统中各用户间的公平性。

摘要： 自适应子载波分配是提高多载波系统性能的关键技术之一。本文借鉴已有的OFDMA系统自适应子载波分配算法，结合MC-CDMA系统特点，根据各用户在各个子载波上的信道增益情况，并考虑系统用户间的公平性，提出一种基于用户间公平性约束的速率自适应子载波分配算法。通过理论分析和仿真结果表明，该方案提高系统性能的同时显著提高了系统中各用户间的公平性。

摘要： MC-CDMA系统利用多个子载波传输数据,它对系统同步错误非常敏感.本文简单介绍了MC-CDMA系统,重点描述了一种新的定时同步算法.该算法利用循环前缀和扩频码的相关性实现定时恢复.本文的循环前缀的构成与以往的不同,但是可以更好的实现帧同步,由于扩频码的引入,可以很好的实现MC-CDMA帧中的符号同步.仿真结果表明这种新的同步算法能更好的实现定时恢复.

摘要： MC-CDMA系统利用多个子载波传输数据,它对系统同步错误非常敏感.本文简单介绍了MC-CDMA系统,重点描述了一种新的定时同步算法.该算法利用循环前缀和扩频码的相关性实现定时恢复.本文的循环前缀的构成与以往的不同,但是可以更好的实现帧同步,由于扩频码的引入,可以很好的实现MC-CDMA帧中的符号同步.仿真结果表明这种新的同步算法能更好的实现定时恢复.

摘要： MC-CDMA系统利用多个子载波传输数据,它对系统同步错误非常敏感.本文简单介绍了MC-CDMA系统,重点描述了一种新的定时同步算法.该算法利用循环前缀和扩频码的相关性实现定时恢复.本文的循环前缀的构成与以往的不同,但是可以更好的实现帧同步,由于扩频码的引入,可以很好的实现MC-CDMA帧中的符号同步.仿真结果表明这种新的同步算法能更好的实现定时恢复.

摘要： MC-CDMA系统利用多个子载波传输数据,它对系统同步错误非常敏感.本文简单介绍了MC-CDMA系统,重点描述了一种新的定时同步算法.该算法利用循环前缀和扩频码的相关性实现定时恢复.本文的循环前缀的构成与以往的不同,但是可以更好的实现帧同步,由于扩频码的引入,可以很好的实现MC-CDMA帧中的符号同步.仿真结果表明这种新的同步算法能更好的实现定时恢复.

摘要： 由于无线信道的多径性和时变性,造成了接收端MC-CDMA符号子载波间的干扰,为了能够准确地解调MC-CDMA信号,就必须对接收到的信号进行信道估计.利用导频符号的辅助信道估计方法是MC-CDMA系统信道估计的一个有效方案.本文对MC-CDMA系统导频信道估计进行了系统描述,并分析了几种插值算法,仿真结果显示基于离散傅立叶变换(DFT)估计算法能够获得较好的估计性能.