Analysis of error performance on Turbo coded FDPIM

Due to variable symbol length of digital pulse interval modulation（DPIM）, it is difficult to analyze the error performances of Turbo coded DPIM. To solve this problem, a fixed-length digital pulse interval modulation（FDPIM） method is provided. The FDPIM modulation structure is introduced. The packet error rates of uncoded FDPIM are analyzed and compared with that of DPIM. Bit error rates of Turbo coded FDPIM are simulated based on three kinds of analytical models under weak turbulence channel. The results show that packet error rate of uncoded FDPIM is inferior to that of uncoded DPIM. However, FDPIM is easy to be implemented and easy to be combined, with Turbo code for soft-decision because of its fixed length. Besides, the introduction of Turbo code in this modulation can decrease the average power about 10 dBm, which means that it can improve the error performance of the system effectively.     

Turbo码在INMARSAT-M4系统中的应用

研究JPEG图像通过INMARSAT-M4系统的高速数据线路传输时,Turbo码和16QAM的应用对该系统的性能影响情况.通过计算机仿真,给出了M4系统采用Turbo码作为前向纠错码时,在不同迭代次数下恢复的图像和误比特率曲线,并与M4系统采用卷积码的情况进行比较.仿真结果表明,Turbo码和16QAM的结合不仅提高了通信系统的可靠性和有效性,还节省了系统发射功率.     

基于LDPC码的自适应视频水印算法研究

根据视频水印系统和数字通信系统相似的特性,提出了一种基于LDPC码的自适应视频水印算法。水印信息经随机置换与LDPC编码,对经过二次整数变换之后的直流分量进行修改实现水印的嵌入。为了兼顾水印的不可见性与鲁棒性的要求,算法根据水印长度和变换之后系数的大小自适应地选择嵌入水印的组及系数的改变强度。实验结果表明:该算法能够保证很好的视频质量,较之基于DCT变换的水印算法嵌入速度更快,并实现了水印的盲提取。对于常见的视频攻击有较强的鲁棒性,在码率高于汉明界推导出的下限的情况下,算法鲁棒性随着码率的减小而增强。      

改进的TurbO码算法的FPGA实现

本文提出一种使用ＦＰＧＡ实现改进的Ｔｕｒｂｏ码算法的方法。在选用改进的最优周期交织序列的交织器和ＳＩＳＯ(软输入软输出)译码器的Ｍａｘ－Ｌｏｇ－ＭＡＰ译码算法的硬件实现过程中,采用“自上而下” 和“自下而上”相结合的设计方法。在采用并行算法的同时巧妙地改变前向矢量的计算顺序,减少了占用的硬件资源。整个设计在ＭＡＸ＋ＰＬＵＳⅡ软件环境下仿真的结果表明,本设计实现的改进的Ｔｕｒｂｏ码编码/译码器具有良好的误码性能和较高的实用价值。     

基于(n,ω,λa,λc)OOC的红外OPPM-CDMA系统分析

考虑系统存在多用户干扰、背景光干扰、接收机散粒噪声、暗电流和热噪声的情况下，使用概率的并集界以及有两个判决量度相等也发生判决错误的悲观估计法，推导任意λa，λc下红外OPPM—CDMA系统的相关接收机、单光硬限幅器相关接收机和双光硬限幅器相关接收机的误比特率上限．最后通过计算机仿真对该3种接收机的误码特性进行分析和比较．     

Pairs of codes with prescribed Hamming distances and coincidences

The main problem of coding theory is to construct codes with large Hamming-distances between the code-words. In this work we describe a fast algorithm for generating pairs of q-ary codes with prescribed pairwise Hamming-distances and coincidences (for a letter s ∈ {0,1,...,q − 1}, the number of s-coincidences between codewords a and b is the number of letters s in the same positions both in a and b). The method is a generalization of a method for constructing set-systems with prescribed intersection sizes (Grolmusz (2002) Constructing set-systems with prescribed intersection sizes. J Algorithms 44:321–337), where only the case q = 2 and s = 1 was examined. As an application, we show that the modular version of the classical Delsarte-inequality does not hold for odd, non-prime power composite moduli.      

Codes over and and Hermitian lattices over imaginary quadratic fields

We introduce a family of bi-dimensional theta functions which give uniformly explicit formulae for the theta series of hermitian lattices over imaginary quadratic fields constructed from codes over and , and give an interesting geometric characterization of the theta series that arise in terms of the basic strongly modular lattice . We identify some of the hermitian lattices constructed and observe an interesting pair of nonisomorphic 3/2 dimensional codes over that give rise to isomorphic hermitian lattices when constructed at the lowest level 7 but nonisomorphic lattices at higher levels. The results show that the two alphabets and are complementary and raise the natural question as to whether there are other such complementary alphabets for codes.

     

alternant码的最小距离

对于具有生成多项式(?)(x)的二元Goppa码,令G(x)是能被G(x)整除的最低次数完全平方多项式,则这个Goppa码的最小距离d≥deg(?)(x)+1。本文把这一结果推广到Alternant码上去。     

Synthesis of Synchronous Finite State Machines for All-Optical Implementations

In this paper an efficient method to synthesize all-optical synchronous digital finite state machines is suggested. The synthesis is based on the design of purely combinational circuits composed of a cascade of iterative cells that perform the same logical functions of the corresponding synchronous Finite State Machine (FSM). This allows high bit rates and a high degree of modularity, so an easy integration of the circuit is possible. These characteristics make the method suitable to be adopted in a photonic environment in which clocked digital memory elements are still a critical aspect.     

Iterative Soft-Kalman Filter-based Data Detection and Channel Estimation for Turbo Coded MIMO–OFDM Systems

MIMO channels are often assumed to be constant over a block or packet. This assumption of block stationarity is valid for many fixed wireless scenarios. However, for communications in a mobile environment, the stationarity assumption will result in considerable performance degradation. In this paper, we focus on a new channel estimation technique for Turbo coded MIMO systems using OFDM. In the proposed MIMO–OFDM system, pilots are placed on selected subcarriers and used by a pair of Kalman filter (KF) channel estimators at the receiver. The KF channel estimates are then utilized by a MIMO–OFDM soft data detector based on the computationally efficient QRD-M algorithm. The soft detector output is fed back to the Kalman filters to iteratively improve the channel estimates. The extrinsic information generated by the Turbo decoder is also used as a priori information for the soft data detector. The overall receiver thus combines MIMO data detection, KF-based channel estimation, and Turbo decoding in a joint iterative structure yielding computational efficiency and improved bit-error rate (BER) performance. Parts of this paper were presented at ICC’2005, Seoul, Korea. This work was supported in part by NSF Grant No. CCF-0429596. This work was done when he was with the Nokia Research Center in Dallas, USA.