共查询到20条相似文献,搜索用时 125 毫秒
1.
Vali Noor Mohammed Narayanappa Srinatha Partha Sharathi Mallick Lakshmanan Nithyanandan 《Radioelectronics and Communications Systems》2017,60(11):485-494
Multi Carrier Code Division Multiple Access (MC-CDMA) is attractive technique for high speed data transmission in multipath fading channel. MC-CDMA system cannot handle the sudden time variations of the channel which cause the subcarriers to lose their orthogonality. The loss of orthogonality between the subcarriers of a user or unwanted correlation between the spreading codes of different user can lead to increase in Multiple Access Interference (MAI). Space Time Block Code (STBC) based MC-CDMA system is chosen to achieve full diversity and transmission rate without the knowledge of Channel State Information (CSI) at the transmitter. Thus, in the paper STBC is introduced at the transmitter to improve the quality of the receiver. Space Time Block Code-Parallel Interference Cancellation (STBC-PIC) receiver has been proposed for MC-CDMA system. In the proposed STBC-PIC receiver, at each interference cancellation stage, weighted signal of the other user is subtracted from signal of the desired user, thereby reducing the MAI and improving the BER performance. From the simulation results, it is observed that the proposed receiver outperforms STBC-Orthogonal Complete Complementary Code (STBC-OCCC), STBC-Minimum Mean Square Error (STBC-MMSE) and STBC-Zero Forcing (STBC-ZF) receivers for MAI reduction. 相似文献
2.
为分析离散傅里叶变换(DFT)与离散正弦变换(DST)对单载波频分多址(SC-FDMA)系统某些性能的影响,提出了一种基于离散正弦变换的单载波频分多址系统。给出了基于DST的SC-FD-MA系统的结构框图,接着重点推导和分析了DST IFDMA和DSTLFDMA信号的时域表达式,最后讨论了系统的峰值平均功率比(PAPR)和不同脉冲成形滤波器的冲激响应。仿真结果表明,基于DST的SC-FDMA系统比传统的基于DFT的SC-FDMA系统和正交频分多址接入(OFDMA)系统有更好的比特误码率。此外,DST SC-FDMA信号的PAPR性能接近于DFT SC-FDMA且优于OFDMA。 相似文献
3.
This paper addresses the problem of interference mitigation in cooperative Space Time Block Coded Orthogonal Frequency Division
Multiplexing (STBC-OFDM) systems in the presence of asynchronism. This scheme first preprocesses the received ST codewords
to convert the equivalent fading matrix into a suboptimal ordering upper triangular form based on low complexity permutation
QR decomposition, and then suppresses the InterCarrier Interference (ICI) and InterSymbol Interference (ISI) by exploiting
Successive Interference Cancellation (SIC) technique. Simulation results show that the performance of the proposed algorithm
slightly outmatches or asymptotically approaches to that of the existing Minimum Mean Square Error (MMSE) detector depending
on the magnitude of the Carrier Frequency Offsets (CFOs) but with less complexity. 相似文献
4.
Gunther M.A. Sessler Ralf Machauer Friedrich K. Jondral 《AEUE-International Journal of Electronics and Communications》2002,56(6):421-425
The family of international standards for mobile communications IMT-2000 includes amongst others the UMTS Terrestrial Radio Access (UTRA) proposal, which consists of two modes: Frequency Division Duplex (FDD) and Time Division Duplex (TDD). Both are wideband CDMA systems. CDMA systems are Multiple Access Interference (MAI) limited. Conventional detectors like the RAKE receiver do not decrease the MAI, this leads to a limited Bit Error Rate (BER) performance. For further improvement of system capacity Multiuser Detectors (MUD) should be applied. In this paper a non-linear approach employing Radial Basis Functions (RBF) is shown. The adaption of this algorithm to UTRA, its complexity and the BER-performance is discussed. 相似文献
5.
S. Sasipriya C.S. Ravichandran 《AEUE-International Journal of Electronics and Communications》2012,66(9):721-726
A novel method of Hybrid Parallel/Successive Interference Cancellation (HIC) for Overloaded Direct Sequence Code Division Multiple Access (OCDMA) system involving two groups of users is proposed in this paper. The impact of timing synchronization error on acceptable channel load in a synchronous binary spread CDMA system is studied by mitigating the effect of multi-access interference (MAI). A small timing synchronization error is introduced in the DS-CDMA system under study to disturb the orthogonality of group-1 users and group-2 users. This orthogonality loss leads to Multi User Interference (MUI) in group-1 users and it is cancelled using Parallel Interference Cancellation (PIC). The interference of group-2 users on group-1 users is cancelled using Successive Interference Cancellation (SIC). The analytical expressions of the Bit Error Rate (BER) are derived. The simulation results prove that the BER performance of the proposed HIC method is better than the conventional PIC and SIC. 相似文献
6.
Hao Lu Tao Xu Homayoun Nikookar Leo P. Ligthart 《Wireless Personal Communications》2013,68(3):587-608
In this paper, we investigate the diversity, capacity and complexity issues of cooperative Zero-Padding (ZP)-Orthogonal Frequency Division Multiplexing (OFDM) communication. We consider cooperative ZP-OFDM communication over a multipath Rayleigh channel and with multiple Carrier Frequency Offsets (CFOs) existing at different relays. We use a cooperative tall Toeplitz scheme to achieve full cooperative and multipath diversity, while simultaneously combat the CFOs. Importantly, this full diversity scheme only requires Linear Equalizers (LEs), such as Zero-Forcing (ZF) and Minimum Mean Square Error (MMSE) equalizers, an issue which reduces the system complexity when compared to a Maximum-Likelihood Equalizer (MLE) or other near-MLEs. Theoretical analysis of the proposed cooperative tall Toeplitz scheme is provided on the basis of the analytical upper bound of the channel orthogonality deficiency derived in this paper. Utilizing only low-complexity linear equalizers, theoretical analysis and simulation results show that the proposed Toeplitz scheme achieves the full cooperative, multipath and outage diversity. 相似文献
7.
ZhouLerong GuoJinghong WeiGang 《电子科学学刊(英文版)》2004,21(4):332-336
This letter derives the Equivalent M-band Discrete Wavelet(EMDW) transmission mode of Orthogonal Frequency Division Multiplexing(OFDM) transmission systems, and presents a new Quadrature M-band Discrete Wavelet(QMDW) based OFDM-CDMA(Code Division Multiple Access) communication systems for high speed Power Line Communication (PLC) channels,This system gives much better robustness to Inter-Channel Interference (ICI), Multi-User Interference (MUI) and noise interference, which is verified by simulation. 相似文献
8.
空频分组码(SFBC)可以为MIMO系统带来发射分集增益,而单载波频分多址(SC-FDMA)系统的发送信号具有低峰均比(PAPR),但直接传输正交SFBC(OSFBC)会出现PAPR过大的问题。为此,本文以四发射天线为例针对OSFBC提出了一种基于DFT扩频的低PAPR传输方案,通过设置多个并行DFT单元并将得到的多组频域数据等间隔交叉排列映射到子载波上,根据频域循环移位和内插的性质使时域信号等效为多条单载波信号的叠加,PAPR与同点数SC-FDMA信号大致相当。同时,本文方案未带来误码率性能的下降,能够取得的分集增益与正交空时分组码(OSTBC)相同。 相似文献
9.
Multi Carrier Code Division Multiple Access (MC-CDMA) is an appropriate modulation technique for high data rates. In this modulation scheme, employing of combining techniques are unavoidable for restoring orthogonality between different user signals. In this paper, the combining techniques of a MC-CDMA based on wavelet transform are studied. The partial combining of the wavelet based MC-CDMA system is suggested and its performance is compared with the maximum ratio combining (MRC), equal gain combining (EGC), orthogonality restoring combining (ORC) and the minimum mean square error (MMSE) techniques. Orthogonal filter banks of the wavelet transforms provide orthogonality between the wavelets and scaling functions, subcarriers and spreading sequences. Therefore, they provide new dimensions in combatting multipath fading, inter carrier interference (ICI) and narrowband interference in MC-CDMA systems. Furthermore, analysis of partial combining shows that coefficients of this technique can be computed in a simple manner. Simulations results indicate that the bit error rate (BER) performance of the proposed scheme is almost comparable with the MMSE combining scheme and the proposed system has a proper performance in terms of BER versus the signal to noise ratio (SNR) in frequency selective fading channels. 相似文献
10.
Fan Da Cao Zhigang 《电子科学学刊(英文版)》2007,24(4):433-438
This paper investigates Carrier Frequency Offset (CFO), estimation in the uplink of the Orthogonal Frequency-Division Multiple Access (OFDMA) systems with the interleaved subcarrier assignment. CFOs between the transmitters and the uplink receiver will destroy orthogonality among different subcarriers, hence resulting in inter-carrier interference and multiuser interference. A two-stage frequency offset estimation algorithm based on subspace processing is proposed. The main advantage of the proposed method is that it can obtain the CFOs of all users simultaneously using only one OFDMA block. Compared with the previously known methods, it not only has a relatively low implementation complexity but is also suitable for random subchannel assignment. 相似文献
11.
Ju Meiyan Feng Guangzeng 《电子科学学刊(英文版)》2006,23(6):848-852
This paper proposes Steepest Decreasing Constant Modulus Algorithm (SDCMA) detection in frequency dornain for MultiCarrier Direct Sequence-Code Division Multiple Access (MC DS-CDMA) systems. The proposed algorithm is used to equalize independent ladings of all subcarriers. At the same time we compare the SDCMA blind detection with subspace-based Minimum Mean-Squared Error (MMSE) detection. The simulation results show that the pertbrmance of SDCMA blind detection is superior to that of subspace-based MMSE detection and the complexity of the former is much lower than that of the latter. 相似文献
12.
Yang Wei Chen Junshi Tan Zhenhui Cheng Shixin 《电子科学学刊(英文版)》2007,24(5):607-612
Code-Division Multiple-Access (CDMA) systems are interference limited,and therefore efficient interference management is necessary to enhance the performance of a CDMA system.In this paper,a successive beamforming (spatial filtering),linear decorrelating MultiUser Detection (MUD, temporal filtering) and diversity reception structure for uplink multicarrier Direct Sequence CDMA (DS-CDMA) system with antenna array are proposed.By beamforming,the antenna array suppresses interference according to the distinct array signature.Subsequently,linear decorrelating MUD is ap- plied to separate the signals of different users and eliminate Multiple Access Interference (MAI).Finally, the decorrelated signals at different subcarriers that belong to the same user are combined to achieve frequency diversity.Simulation results show that the proposed structure offers significant Bit Error Rate (BER) performance improvement by successively exploiting the space-time-frequency processing. 相似文献
13.
14.
LiKe ShiXinhua ZhangEryang 《电子科学学刊(英文版)》2004,21(4):289-295
Multiple Access Interference(MAI) is the major factor that degrades the performance of a CDMA system. In this paper, a novel transform domain algorithm combined with parameter estimation for MAI suppression is proposed. Compared with the method that combines an adaptive array antenna with parameter estimation for interference suppression, it converges faster with the same Bit Error Rate(BER) performance. 相似文献
15.
一种OFDM系统中的同频干扰消除算法 总被引:3,自引:1,他引:3
该文研究正交频分复用(OFDM)系统中的同频干扰(CCI)问题。基于正弦信号模型,该文提出一种基于最小均方误差(MMSE)准则的干扰时域估计与消除算法,并进行仿真验证。仿真结果表明:与现有算法相比,该文提出的方法可以更为有效地抑制单频模型的CCI。同时,该文提出的方法对干扰进行时域估计与消除,减小了时频变换后的干扰能量泄漏,并具有不依赖于信道估计,避免直接清零造成的有用信息损失等优点。 相似文献
16.
Optimal resource allocation in uplink SC-FDMA systems 总被引:1,自引:0,他引:1
We present algorithms for resource allocation in Single Carrier Frequency Division Multiple Access (SC-FDMA) systems, which is the uplink multiple access scheme considered in the Third Generation Partnership Project-Long Term Evolution (3GPP-LTE) standard. Unlike the well-studied problem of Orthogonal Frequency Division Multiple Access (OFDMA) resource allocation, the "subchannel adjacency" restriction, whereby users can only be assigned multiple subchannels that are adjacent to each other, makes the problem much harder to solve. We present a novel reformulation of this problem as a pure binary-integer program called the set partitioning problem, which is a well studied problem in operations research. We also present a greedy heuristic algorithm that approaches the optimal performance in cases of practical interest. We present simulation results for 3GPP-LTE uplink scenarios. 相似文献
17.
18.
Sheng-Wei Hou Chi Chung Ko 《Vehicular Technology, IEEE Transactions on》2008,57(1):194-205
In this paper, the issue of multiple-access interference (MAI) suppression for the uplink in an interleaved orthogonal frequency-division multiple-access (OFDMA) system is investigated. In such a system, a carrier frequency offset (CFO) disrupts the orthogonality between the subcarriers and gives rise to MAI among users. Based on the signature vector formulated for each user, we propose a novel detector that performs MAI suppression before CFO compensation and fast Fourier transform (FFT) demodulation. Subspace zero-forcing and minimum mean square error (MMSE) techniques are then developed to suppress MAI. The proposed scheme is shown to become almost MAI free, provided that the CFO estimation is accurate enough. From the obtained simulation results, the proposed scheme is also found to be able to enhance the system performance at low complexity. 相似文献
19.
单载波频分多址( SC-FDMA)系统由于其低峰均比特性,广泛受到人们的关注.为了有效的增加发射分集但又不破坏其低峰均比特性,一种新型的空频编码方案即单载波空频块编码( SC-SFBC)被发现.针对单载波空频块编码系统中,发射机与接收机之间存在载波频偏( CFO)降低链路传输可靠性问题,建立接收信号模型,提出一种迭代载波频偏补偿方法.提出的算法通过分离子载波间干扰( ICI)并迭代消除,同时每个子载波独立进行频偏补偿与均衡,降低算法复杂度.仿真结果表明这种算法能显著提高存在载波频偏时的SC-SFBC系统性能. 相似文献
20.
为了提高单载波频分多址接入(SC-FDMA)系统的性能,一种简单且有效的基于探测参考信号(SRS)的噪声估计算法是必要的.针对传统基于离散傅里叶变换(DFT)算法的缺陷,提出了一种改进的基于DFT的算法.另外,在该改进的基于DFT的算法的基础上,又通过增加汉宁窗进行修正,减小了高信噪比下信号能量的泄露.仿真结果表明,在低信噪比下,改进的基于DFT的算法的性能相比传统的算法性能上有4 dB的改善.但是,在高信噪比下,改进的基于DFT的算法的性能逐渐变差,而通过添加汉宁窗却能修正这一缺陷,使其性能得到至少4 dB的改善. 相似文献