Security in Multicast Over α-μ Fading Channels with Orthogonal Frequency Division Multiplexing

The orthogonal space-frequency block coding (OSFBC) with orthogonal frequency division multiplexing (OFDM) system reduces complexity in the receiver which improves the system performance significantly. Motivated by these advantages of OSFBC-OFDM system, this paper considers a secure wireless multicasting scenario through multiple-input multiple-output (MIMO) OFDM system employing OSFBC over frequency selective α-μ fading channels. The authors are interested to protect the desired signals from eavesdropping considering the impact of the number of multicast users and eavesdroppers, and the fading parameters α and μ. A mathematical model has been developed based on the closed-form analytical expressions of the probability of non-zero secrecy multicast capacity (PNSMC) and the secure outage probability for multi-casting (SOPM) to ensure the security in the presence of multiple eaves-droppers. The results show that the security in MIMO OSFBC OFDM system over α-μ fading is more sensitive to the magnitude of α and μ and this effect increases in the high signal-to-noise ratio (SNR) region of the main channel.

A Non-orthogonal STFC-OFDM on Frequency-Selective Fading Channels

A new non-orthogonal space-time-frequency code (STFC) was proposed. In conjunction with orthogonal frequency-division multiplexing (OFDM), it is appropriate for the application on frequency-selective fading channels. On the basis of the existing non-orthogonal STC, frequency diversity is studied and a new non-orthogonal STFC is further designed. Monte-Carlo simulations show that the non-orthogonal STFC-OFDM has the advantage of large diversity order, high bandwidth efficiency and better BER performance when compared with the orthogonal STC/STFC-OFDM and non-orthogonal STC-OFDM systems.

Construction of time-frequency codes based on protograph LDPC codes in OFDM communication systems

This paper proposes a scheme to construct time- frequency codes based on protograph low density parity check （LDPC） codes in orthogonal frequency division multiplexing （OFDM） communication systems. This approach synthesizes two techniques： protograph LDPC codes and OFDM. One symbol of encoded information by protograph LDPC codes corresponds to one sub-carrier, namely the length of encoded information equals to the number of sub-carriers. The design of good protograph LDPC codes with short lengths is given, and the proposed proto- graph LDPC codes can be of fast encoding, which can reduce the encoding complexity and simplify encoder hardware implementa- tion. The proposed approach provides a higher coding gain in the Rayleigh fading channel. The simulation results in the Rayleigh fading channel show that the bit error rate （BER） performance of the proposed time-frequency codes is as good as random LDPC- OFDM codes and is better than Tanner LDPC-OFDM codes under the condition of different fading coefficients.

Polar codes based OFDM-PLC systems in the presence of impulsive noise

Power line communication(PLC)has the potential to become the preferred technique for providing broadband communication to homes and offices with advantage of eliminating the need for new wiring infrastructure and reducing the cost.But it suffers from the impulsive noise because it introduces significant time variance into the power line channel.In this paper,a polar codes based orthogonal frequency division multiplexing(OFDM)PLC system is proposed to deal with the impulsive noise and thereby improve the transmission performance.Firstly,the impulsive noise is modelled with a multi-damped sine function by analyzing the time behavior of impulse events.Then the polar codes are used to combat the impulsive noise of PLC channel,and a low complexity bit-flipping decoding method based on CRC-aided successive cancellation list(CA-SCL)decoding algorithm is proposed.Simulations evaluate the proposed decoding algorithm and the results validate the suggested polar codes based OFDM-PLC scheme which can improve the BER performance of PLC with impulsive interference.

FREQUENCY-TIME BLOCK CODE FOR FREQUENCY DIVERSITY IN UWB-OFDM SYSTEMS

The Ultra-WideBand Orthogonal Frequency Division Multiplexing (UWB-OFDM) approach is a promising physical-layer technique for short-range, high data-rate wireless networks. As the occupied band-width increases, however, its implementation becomes more and more difficult. In order to make it easier to achieve a UWB-OFDM system, a complexity-reduced Frequency diversity (F-diversity) scheme, Fre-quency-Time Block Code (FTBC), is presented in this paper. The FTBC halves the sampling rate required by other F-diversity techniques so as to cut down the cost of UWB-OFDM systems with F-diversity to a certain extent.

Symbols detection for frequency-selective V-BLAST OFDM systems

As the combining form of the orthogonal frequency-division multiplexing (OFDM) technique and the vertical Bell Labs layered space-time (V-BLAST) architecture, the V-BLAST OFDM system can better meet the demand of next-generation (NextG) broadband mobile wireless multimedia communications. The symbols detection problem of the V-BLAST OFDM system is investigated under the frequency-selective fading environment. The joint space-frequency demultiplexing operation is proposed in the V-BLAST OFDM system. Successively, one novel half-rate rotational invariance joint space-frequency coding scheme for the V-BLAST OFDM system is proposed. By elegantly exploiting the above rotational invariance property, we derive one direct symbols detection scheme without knowing channels state information (CSI) for the frequency-selective V-BLAST OFDM system. Extensive simulation results demonstrate the validity of the novel half-rate rotational invariance joint space-frequency coding scheme and the performance of the direct symbols detection scheme.

基于优化CCSK调制的低轨卫星通信导航一体化信号设计方法

给出了一种基于优化循环码移键控(cyclic code shift keying,CCSK)方式的通信导航一体化信号设计方法,使通信信号的互相关函数的正值与导航信号自相关函数的峰值一致,从而克服互相关干扰,提高通信速率。通过频分复用的方式划分通信信号和导航信号的频带,基于正交频分复用(orthogonal frequency division multiplexing,OFDM)技术提出连续分配、交替分配和随机分配3种子载波分配方案。对优化CCSK调制和CCSK调制的一体化信号的自相关峰值性能进行仿真和分析,结果表明,在3种子载波分配方案下,采用优化CCSK调制的一体化信号的自相关峰值性能均优于CCSK调制的一体化信号,且采用优化CCSK调制的通信信号的互相关特性对相应的导航信号的自相关峰值有增强作用,可提升通信导航一体化信号体制下导航信号的码相位同步性能。

多OFC-SAW传感器敏感信息同时提取方法

讨论了多正交频率编码声表面波(OFC-SAW)传感器敏感信息同时提取的方法,设计了多OFCSAW传感器敏感信息同时提取系统。通过相同中心频率叠加信号片测量值与每个反射OFC信号的关系方程组计算每个OFC反射信号的幅度和延时,通过反射信号的延时差提取敏感信息。经过仿真分析验证了该方法的正确性和有效性。

DRM技术在中波广播中的应用研究

以数字音频广播(Digital Radio Mondiale,DRM)技术在中波广播中的应用为研究对象,首先介绍DRM技术的发展、关键组成部分、产业现状及其在国内外的应用情况,其次重点分析DRM技术在中波广播中的应用优势和应用实例,最后阐述DRM技术在偏远地区的应用,以期为DRM技术与中波广播的融合提供参考。

多径衰落信道中多OFC-SAW传感器同时读取算法

针对多个正交频率编码声表面波(OFC-SAW)传感器存在同时读取困难的问题,对理想信道中多OFC-SAW传感器反射信号进行了建模分析,通过理论推导实现了对理想信道中多OFC-SAW传感器信息的同时读取。针对实际应用中的多径衰落信道特点,建立了多径衰落信道中阅读器接收到的OFC-SAW传感器反射信号数学模型。对理想信道中阅读器接收到的信号与多传感器反射信号之间的关系模型进行修正,从而得到多径衰落信道中阅读器接收到的信号与多传感器反射信号之间的关系模型。实际应用中通过适时监测信道来估计信道模型参数,从而实现多径衰落信道中多OFC-SAW传感器信息的同时读取。最后经过仿真分析验证了该算法的有效性。

OFDMA中同频干扰的Coded-IRC抑制算法

正交频分多址(Orthogonal Frequency Division Multiple Access,OFDMA)的同频干扰问题一直是蜂窝移动通信系统的研究重点。本文从信号域时延出发,通过分析推导了系统中干扰的表达式,并验证了不同相对时延方差下同频干扰(Co-Channel Interference,CCI)对系统的影响。针对干扰的异步非相关性以及传统干扰抑制合并(Interference Rejection Combining,IRC)算法的局限性,利用卷积码时延小、高编码增益的特点,采用Coded-IRC方法抑制干扰。仿真结果表明,时延导致的CCI在很大程度上降低了系统的误比特率性能,而Coded-IRC算法克服了IRC的局限,使得系统误比特率性能得到提升。

High resolution range profile analysis based on multicarrier phase-coded waveforms of OFDM radar

Orthogonal frequency division multiplexing（OFDM） radar with multicarrier phase-coded waveforms has been recently introduced to achieve high range resolution.The conventional method for obtaining the high resolution range profile（HRRP） is based on matched filters.A method of synthesizing HRRP based on the fast Fourier transform（FFT） and decoding is proposed.The mathematical expressions of HRRP are derived by assuming an elementary scenario of point-scattering targets.Based on the characteristic of OFDM multicarrier signals,it mainly analyzes the influence on HRRP exerted by several factors,such as velocity compensation errors,the sampling frequency offset,and so on.The conclusions are significant for the design of the OFDM imaging radar.Finally,the simulation results demonstrate the validity of the conclusions.

PERFORMANCE EVALUATION OF LOW DENSITY PARITY CHECK CODES FOR DIGITAL RADIO MONDIALE (DRM) SYSTEM

In Digital Radio Mondiale (DRM) system, achieving good audio quality becomes a challenge due to its limited band-width of 9 or 10kHz and the very bad fading channels. Therefore, DRM needs highly efficient channel coding schemes. This paper, proposes the schemes which use the Low-Density Parity-Check (LDPC) coded Bit-Interleaved Coded Modulation (BICM) schemes for the implementation of DRM systems. Simulation results show that the proposed system is more efficient than the Rate Compatible Punctured Con volutional (RCPC) coded DRM system on various broadcast channels, and may be recommended as a coding technology for Digital Amplitude Modulation Broadcasting (DAMB) systems of China.

Turbo Coded OFDM with Large Number of Subcarriers

Wireless communication systems have greatly advanced during the last years. A significant contributor in these systems’ performance has been Orthogonal Frequency Division Multiplexing (OFDM). Since its invention, it is considered to be a technological leap. This leap in splitting an information stream in multiple frequency carriers has been adapted by various scientists working on the development of wireless systems. Moreover, as OFDM presented excellent tolerance of channel fading and noise signals, the evolvement in terms of speed and reliability was consequent, because only a small stream of information is lost due to noise effects. OFDM along with the knowledge that Turbo codes is another excellent scheme of reducing BER, has triggered us to expand our research. So, we experimented in simulation level not only in joining OFDM with Turbo Codes but even in finding a better Turbo scheme compared to a typical PCCC, SCCC and a Convolutional encoder with Viterbi decoder. As the last goal has already been accomplished, in this paper is presented the new OFDM system consisted of our Turbo scheme. The analysis of the previous system took into consideration the effects of an AWGN channel. Also, this noise analysis was conducted using a simulation platform with specific attributes such as transmitting and receiving fixed number of subcarriers (2048 carriers after IFFT block) while using different types of convolutional concatenated codes, such as PCCC (Parallel), SCCC (Serial) and the new PCCC scheme. The results clearly show not only the improvement in the BER performance of the Turbo Coded OFDM systems (compared to others consisted of Viterbi decoders) but the overall superiority of the proposed design.

Reducing Peak-to-Average Power Ratio of a Turbo Coded OFDM

Peak to Average Power Ratio (PAPR) is defined as the instantaneous power (maximum value) to the average power ratio. PAPR is considered to be a major problem in OFDM systems. This problem can cause radical unexpected behavior of the signal fluctuation. This fluctuation is constituted by a large number of power states. The enormous number of these states leads to an additional complexity of ADCs and DACs. This research addresses the previous problem in OFDM systems utilizing Turbo Codes. μLaCP technique is employed for the purpose of decreasing PAPR. Moreover, our OFDM system was simulated in the presence of an AWGN channel with four types of codes (without the presence of ADCs and DACs). These were constituted of PCCC (typical and new), SCCC, and Convolutional Codes. Our Turbo Coded OFDM exhibited unchanged BER performance before and after the use of μLaCP technique. This was accomplished by modifying our previous PAPR reduction technique without sacrificing greatly its attributes.

Optimal transmissions for space-time coded OFDM UWB systems

The emerging ultra-wideband (UWB) system offers a great potential for the design of high-speed short-range communications.Compared with great progress at physical layer,the corresponding medium access control (MAC) layer designs are naturally placed on the schedules.We focus on the optimal power load scheme,which is an integral part of the MAC layer protocol design,for UWB space-time coded (STC) orthogonal frequency-division multiplexing (OFDM) transmissions.Assumed the transmitter has perfect or partial channel stage information (CSI).Based on the optimization criteria of maximizing capacity,three kinds of power load schemes were presented with different tradeoff among performance,complexity and feedback bandwidth overhead.The proposed schemes are verified and compared under the channel prototype proposed by IEEE 802.15.3a Task Group.

A CODE DESIGN CRITERIA FOR NOT FULLY CONNECTED CHANNEL

There are parallel channels which are not fully connected in practice, such as Frequency Division Multiplex (FDM or Orthogonal FDM) systems. Conventional space-time codes can be used for such parallel channels but not the optimal. Based on the derivation of PEP expression for codes transmitted on parallel block fading channels, criteria of codes design for not fully connected channels are proposed and are compared with Tarokh's criteria for fully connected channel. New codes for such channels are provided by systematical and exhaustive search. Simulation results show that these codes offer better performance on parallel FDM channels than other known codes.

A NEW UEP SCHEME FOR ROBUST VIDEO TRANSMISSION IN LDPC CODED MIMO-OFDM SYSTEM

In order to improve the video transmission performance in Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) system,a new scheme,which integrates Multiple Description Coding (MDC),Low Density Parity Check (LDPC) coding and hybrid space time coding,is proposed in this letter. In particular,a hybrid space time coding algorithm is combined with LDPC codes to perform Unequal Error Protection (UEP) of MDC encoded video streams. Comparing with the UEP transmission with only LDPC codes,the proposed scheme achieves more than 1dB gain in terms of Signal to Noise Ratio (SNR) when the Peak Signal to Noise Ratio (PSNR) of reconstructed video is above 30dB.

极化码在水下光通信系统中的应用研究

为了验证不同水质条件对水下光通信的影响,采用蒙特卡罗模拟算法模拟了水下光信道的离散冲激响应。在此基础上结合具有抗衰落优点的正交频分复用技术搭建了水下光通信系统,针对收发端已知信道状态信息前提下,采用16正交幅度调制方式,结合蒙特卡罗构造算法完成极化码的构造,译码端使用基于循环冗余校验辅助的串行抵消译码算法,设计并实现了基于正交频分复用技术的水下光通信系统中的极化码编译码方案。通过实验验证了不同水质条件下码长等参数对极化码性能的影响,证明了在高信噪比时,极化码相比同等码长的低密度奇偶校验码在不同水质下具有0.2 dB~0.6 dB左右的性能增益;随着水质环境越差,其渐进性能优势表现得越明显,且不会出现误码平层的问题。极化码的编码结构更加清晰简单,译码复杂度与低密度奇偶校验码相差不大,且在译码中不需要多次迭代。因此相比于其他编码方案,极化码具有较低的编译码复杂度,在水下光通信场景中具有很强的竞争力和应用潜力。

极化编码调制正交频分复用水声通信中的极化码构造方法

为进一步提高水声通信可靠性和频带利用率,针对极化编码调制的水声通信需求和信道特性,基于蒙特卡洛法提出动态水声信道认知优化统计目标参数、联合译码的判决反馈信道估计两点改进,建立了适用于编码调制水声信道中的极化码构造算法。为验证该算法性能,建立了极化编码调制水声通信的两步应用机制。通过仿真,比对并分析改进前后的极化码构造方法性能、对时变信道的鲁棒性,以及在不同映射规则下的联合比特交织和多级编码的极化编码调制水声通信性能,并与低密度校验(LDPC)编码调制系统进行对比。湖试结果表明,提出的极化编码调制水声通信方案有效保证了信息在浅水水声信道中的可靠传输,在信噪比约为14 dB、通信距离约1 km时,实现无误码传输,性能优于相同条件下的LDPC编码调制系统。