采用MSK调制的物理层网络编码信号检测

针对双向中继信道,提出一种采用最小频移键控（MSK）调制的物理层网络编码（PNC）方案,即MSK-PNC。与采用BPSK、QPSK等线性调制技术的物理层网络编码方案相比,MSK-PNC具有更高的频谱效率和功率效率。本文对MSK-PNC方案中的物理层网络编码信号检测进行研究,提出了两种检测方法。第1种方法采用正交解调映射,第2种方法采用最大似然序列检测。分析和仿真结果表明,正交解调映射方案使得MSK-PNC误比特率性能等于QPSK-PNC,最大似然序列检测算法在实现复杂度上相对较高,但是其误比特率性能更优,并且同样适用于检测采用CPFSK调制方式的物理层网络编码信号。      

基于分层调制的物理层网络编码研究

在实际的移动通信环境中,信道的状态复杂多变,该文针对双向中继信道的非对称性,提出采用分层调制方式的物理层网络编码方案。首先构建源节点、中继节点均采用分层(2/4-PSK)调制的双向中继通信系统模型;其次给出了中继节点的物理层网络编码解调及映射规则,推导出加性高斯白噪声下中继误比特率及端到端误比特率理论计算公式;最后仿真验证了理论分析结果。与采用传统QPSK调制技术的物理层网络编码相比,该方案利用分层调制的技术优势,确保较优信道的高速率传输,也兼顾了较差信道的传输可靠性。     

基于连续相位频移键控调制的物理层网络编码检测及性能分析

针对双向中继信道,该文提出一种基于连续相位频移键控(CPFSK)调制的物理层网络编码(PNC)机制,即CPFSK-PNC。与已有的采用BPSK, QPSK等调制方式的物理层网络编码相比,该机制引入CPFSK的技术优势,提高了系统的频谱效率和功率效率。该文对瑞利衰落信道中CPFSK-PNC的物理层网络编码检测进行了研究。首先,利用CPFSK信号的记忆特性,根据最大似然准则设计了中继节点的物理层网络编码检测方案;其次,分析了信号之间最小欧氏距离并给出中继检测的平均误比特率下边界;最后,仿真验证了理论分析结果。     

一种信道编码与物理层网络编码的联合设计

基于正交振幅调制（QAM）设计了一种信道编码与物理层网络编码的联合实施方案,该方案巧妙的引入了一种去噪映射机制,即重新安排QAM调制的星座映射,中继节点对接收数据去噪后直接映射为对应数字比特流的异或。同时,利用卷积码和MAC-XOR网络编码（Network Coding, NC）的线性性质,使得中继节点只需直接估计网络编码的码字,因此中继节点的解调/译码的复杂度减少50%。在此基础上对该方案的误比特率性能进行分析。仿真结果表明了该方案的有效性,即与已有的物理层网络编码方法相比,在没有增加译码复杂度的基础上,该方案的信道容量有了显著提高。      

正交调制器载波I/Q幅相失配对TCM-8PSK性能影响

论文首先介绍了高速调制解调器中正交调制器载波I/Q支路幅相失配的模型,然后在此模型上推导了TCM-8PSK信号误比特率性能公式,最后运用Matlab中的动态仿真工具Simulink仿真验证了推导结果。推导与仿真结果都表明,在载波I/Q幅相失配条件下TCM-8PSK信号的误比特率性能下降了。     

基于无线帧的物理层网络编码同步误差性能

物理层网络编码充分利用无线信道的广播特性,能够有效提高网络吞吐量和带宽利用率。但是物理层网络编码的性能受到载波相位、载波频率、时间、采样钟不同步的影响,因此分析同步误差对物理层网络编码性能影响具有重要的研究意义。基于单载波系统,针对使用BPSK调制的无线通信系统,从理论上分析了一定帧长下,载波相位、载波频率、时间及采样时钟同步误差对系统性能的影响。分析结果表明,在载波相位和时间不同步两种情形下,物理层网络编码性能不受帧长影响;而在载波频率和采样时钟不同步两种情形下,系统性能均随帧长的增加而有所下降,其中采样时钟不同步情形受帧长影响最大。     

乘法运算的模拟网络编码中继方法

当前无线网络编码中继采用异或运算和叠加运算实现,该文提出一种基于乘法运算的网络编码中继方案。该方案中继节点对接收到的两个源节点信号直接相乘,然后放大转发,从而实现网络编码。与异或运算的网络编码相比,该方案采用模拟技术实现,降低了中继节点网络编码的复杂度;同时该方案将接收信号与本地信号相乘实现网络译码,译码算法比叠加运算的方案简单。理论分析表明该方案的分集增益与未经网络编码的中继系统相同;仿真结果表明,该方案与现有的网络编码中继协作方案性能相当。     

基于联合迭代检测译码的多中继RA编码协作系统

为提高协作系统的性能,提出一种RA码多中继编码协作通信系统。首先,在系统的源和中继节点处采用RA编码,推导出与目的节点接收码字对应的多层Tanner图;然后,以多层Tanner图为基础,结合MAP算法给出一种联合迭代检测译码新算法译码,完成目的点的信号检测。理论分析和数值模拟表明,所提出的新方法能够充分实现多中继编码协作所具有的潜在分集和编码增益,随着内外迭代次数的增加,误比特率性能迅速提升,在相同条件下明显优于编码非协作系统。     

Chirp扩频通信系统抗噪声性能研究

Chirp扩频被IEEE 802．15．4A列为物理层可选标准之一,正得到越来越多的关注。文中分析了Chirp信号的特点及Chirp—BOK系统的组成和调制解调方式,提出了一种对Chirp扩频的理论研究方法,在高斯白噪声信道下,分析并得到系统误比特率一信噪比公式。误比特率的仿真结果与理论推导公式相吻合,并证明该扩频机制与其他调制方式比较,抗噪声性能有明显的改善。     

自适应调制编码技术在LTE OFDM系统中的性能分析

文章在给出了自适应LTE OFDM系统模型之后,采用基于SNR的自适应算法,对自适应调制及编码技术在LTE OFDM系统中的误比特率性能进行了分析和仿真验证.仿真结果表明,将基于SNR门限的自适应编码调制技术用于LTE OFDM系统,可提高系统性能,且计算复杂度低.     

Physical‐layer network coding with limited feedback using orthogonal space–time block codes

This paper introduces limited feedback technique into physical‐layer network coding (PLNC) scheme, which is the most spectrally efficient protocol in two‐way relay channels, consisted of one relay and two end nodes (sources). Decode‐and‐forward (DF) and partial‐decode‐and‐forward (PDF) strategies are considered for PLNC, and all nodes are assumed to have two antennas to allow transmission by Alamouti's orthogonal space–time block code to provide diversity. In DF, by limited feedback, one of the sources is informed about instantaneous channel state information (CSI) to increase the bit error rate (BER) performance at relay. The closed‐form upper and lower bounds on the bit error probability are derived for binary phase‐shift keying (BPSK) and quadrature PSK (QPSK) modulations and approved via computer simulations. In PDF strategy, each source has to know CSI between relay and the other source for decoding, which causes extra protocol complexity. Moreover, for the system in which all nodes have two antennas, classical PDF strategy does not satisfy orthogonality at the end nodes. Therefore, in this paper, a modified‐PDF (MPDF) strategy with limited feedback is proposed. In MPDF, for decoding at the end nodes, differential phase information between channel fading coefficients having maximum amplitudes is fed back to the sources by relay. This approach enables single‐symbol decoding, besides full diversity, and sources do not need to know CSI between relay and the other source. It is shown via computer simulations that MPDF strategy provides significantly better BER performance than the classical PDF for BPSK and QPSK modulations.Copyright © 2012 John Wiley & Sons, Ltd.     

协作通信中的自适应分级调制与功率分配

基于分级调制的中继协作技术可以很好地利用无线信道的广播特性和中继节点的位置优势来对抗信道衰落.本文提出一种自适应的协作方法,这种方法根据中继的相对位置,选择最优的分级调制星座图以及源与中继之间的功率分配比例,以使目的节点接收的数据误码率最小.仿真结果表明优化星座图和优化源与目的节点之间的功率分配比例都可以获得可观的性能提升.当中继位于源与目的节点的中点附近时,在消耗相同能量带宽资源的条件下,这种最优化的协作方法比非协作系统有3-4dB的性能增益.     

Multi-user receiver scheme and uplink performance of space–time-coded CDMA system in Rician fading channels

The uplink performance of multi-user space–time-coded code-division multiple access (STC-CDMA) system in Rician fading channel is presented. A simple and effective multi-user receiver scheme is developed for STC-CDMA system. The scheme has linear decoding complexity when compared to the existing scheme with exponential decoding complexity, and thus implements low-complexity decoding. Based on the bit error rate (BER) analysis and moment generation function, theoretical BER expressions are derived for STC-CDMA with orthogonal and quasi-orthogonal spreading code, respectively. It is shown that these expressions have more accuracy. Using these expressions and the approximation of error function, closed-form approximate BER expressions are obtained, which can simplify the calculation of the derived theoretical BER. Simulation results show that the developed low-complexity decoding scheme can achieve almost the same performance as the existing scheme. The theoretical BER are in good agreement with the corresponding simulated values. Moreover, the presented approximate expressions are also close to the simulated values due to the better approximation. Under the same system throughput and concatenation of channel code, the presented full-rate STC-CDMA system has lower BER than the corresponding full-diversity STC-CDMA systems.     

BER of OFDM in Rayleigh fading environments with selective diversity

This paper derives the analytical bit error rate (BER) of orthogonal frequency division multiplexing (OFDM) systems employing selective diversity in Rayleigh fading environments. First, the probability density function (pdf) of inter‐carrier interference (ICI) power in Rayleigh fading environments is derived. Second, the pdf of the signal‐to‐interference ratio (SIR) is then derived. The cumulative distribution function (cdf) and hence pdf of the SIR with selective diversity are then given in the third and fourth steps. Using the BER expressions of binary phase shift keying (BPSK) and differential BPSK (DBPSK) modulation in an added white Gaussian noise (AWGN), the corresponding BER expressions of OFDM systems can then be derived. Detailed discussions are given. Possible future work is also outlined. Copyright © 2009 John Wiley & Sons, Ltd.     

Performance Analysis of Space-Time Coded CDMA System Over Nakagami Fading Channels with Perfect and Imperfect CSI

In this paper, the performance of multiuser CDMA systems with different space time code schemes is investigated over Nakagami fading channel. Low-complexity multiuser receiver schemes are developed for space-time coded CDMA systems with perfect and imperfect channel state information (CSI). The schemes can make full use of the complex orthogonality of space-time coding to obtain the linear decoding complexity, and thus simplify the exponential decoding complexity of the existing scheme greatly. Moreover, it can achieve almost the same performance as the existing scheme. Based on the bit error rate (BER) analysis of the systems, the theoretical calculation expressions of average BER are derived in detail for both perfect CSI and imperfect CSI, respectively. As a result, tight closed-form BER expressions are obtained for space-time coded CDMA with orthogonal spreading code, and approximate closed-form BER expressions are attained for space-time coded CDMA with quasi-orthogonal spreading code. Computer simulation for BER shows that the theoretical analysis and simulation are in good agreement. The results show that the space-time coded CDMA systems have BER performance degradation for imperfect CSI.     

Combined orthogonal physical‐layer network coding over fading two‐way relay channels

This paper proposes a new physical‐layer network coding (PNC) scheme, named combined orthogonal PNC (COPNC), for fading two‐way relay channels. The scheme is based on orthogonal PNC (OPNC). In the scheme, the two source nodes employ orthogonal carriers, and the relay node makes an orthogonal combining of the two information bits rather than exclusive or (XOR), which is employed in most PNC schemes. The paper also analyzes the bit error rate (BER) performance of PNC, OPNC, and COPNC for Rayleigh fading model. Simulation results for Rayleigh and Nakagami‐m fading channels show that COPNC can provide outstanding BER performance compared with PNC and OPNC, especially when the uplink channel conditions are asymmetric. The results in Nakagami‐m channels also imply that COPNC will provide higher BER gain with more severe fading depth. Potential works about COPNC are also presented in this paper. Copyright © 2013 John Wiley & Sons, Ltd.     

Performance of orthogonal frequency division multiplexing based M-ary quadrature amplitude modulation in asymmetrical dual-hop mixed RF-FSO transmission system

This paper investigates the performance of a dual-hop mixed relay system with radio frequency (RF) and free-space optics (FSO) communication under the effect of pointing error (PE) and atmospheric turbulence (AT). This paper considers a system where RF and FSO links are cascaded. The RF link is modeled by Nakagami-m fading, and the FSO link is modeled as gamma–gamma (G-G) fading channel. Both the channel models use orthogonal frequency division multiplexing (OFDM) with M-ary quadrature amplitude modulation (QAM). The expressions for probability density function, cumulative distribution function, signal-to-noise ratio, and ergodic capacity are derived. The moment generating function (MGF) of fading and the bit error rate (BER) of the OFDM-based M-ary QAM scheme is derived in terms of Meijer's G-function. It has been observed that, in fixed gain relay systems, the modulation scheme's BER is dominated by the SNR of the RF link. While in a variable gain relay system, the turbulence conditions of the FSO system affect the SNR and the BER of the modulation method. The feasibility of heterodyne detection and intensity modulation direct detection (IM/DD) is analyzed in terms of outage probability and ergodic capacity. The results can be used to choose the optimal modulation order and relay system for QAM-OFDM-based optical wireless systems.     

Probability of Error Analysis of BPSK OFDM Systems with Random Residual Frequency Offset

In this paper, we derive closed form bit error rate (BER) expressions for orthogonal frequency division multiplexing (OFDM) systems with residual carrier frequency offset (CFO). Most of the published work treats CFO as a nonrandom parameter. But in our study we consider it as a random parameter. The BER performance of binary phase shift keying (BPSK) OFDM system is analyzed in the cases of additive white Gaussian noise (AWGN), frequency-flat and frequency-selective Rayleigh fading channels.We further discuss how these expressions can be related to systems with practical estimators. The simulation results are provided to verify the accuracy of these error rate expressions.     

OFDMA uplink frequency offset estimation via cooperative relaying

Frequency offset estimation for an orthogonal frequency-division multiple access (OFDMA) uplink for amplify-and-forward (AF) relays and a new type of relay (R) called decode-and-compensate-and-forward (DcF) relays are studied. Multiple relays are considered, and the relay with the best S rarr R channel is chosen to perform re-transmission, where S and R represent the source and relay nodes, respectively. Frequency offsets due to the mismatches between the transmitter and receiver oscillators are considered, and without considering the effect of Doppler shift, both S rarr D and S rarr R rarr D links have the same frequency offset, where D represents the destination. Thus, by using these two transmissions, D generates two frequency offset estimates, which are combined to minimize the mean square error (MSE). Power allocation between S and R can be adaptively adjusted to optimize the cooperative scheme in terms of frequency offset error variance. When channel state information (CSI) is available at each mobile node, a scheme where the relays adaptively switch between the cooperative and conventional (no relaying) transmissions is proposed to optimize the frequency offset estimation. Although the frequency offset estimation accuracy in the DcF mode is somewhat worse than the AF mode, both modes outperform the conventional transmission. However, DcF (or decode-and-forward (DF)) relays outperform AF relays in terms of channel capacity and bit error rate (BER).