Signal Space Diversity Augmented Space Time Block Coded Communication System

In this paper we propose the combination of space-time diversity techniques and signal space diversity, in order to improve communication system performance. Specifically, we use prior knowledge of the channel behavior to design a mapping algorithm to generate a two-dimensional constellation with the same number of symbols as MPSK constellations currently used in coherent space time block coding applications, to demonstrate that superior performance can be achieved. This is accomplished by constructing a two-dimensional map that results from the minimization of the estimated symbol error probability when transmission occurs in a fading environment. System performance for each each mapping is assessed in quasi-static Rayleigh fading channels.     

Sparse Approximations of the LMMSE Channel Estimation in OFDM with Transmitter Diversity

The linear minimum mean-squared error (LMMSE) channel estimation for orthogonal frequency-division multiplexing (OFDM) systems requires a large number of complex multiplications. We evaluate a simplified LMMSE channel estimation algorithm in a transmit diversity environment by applying a significant weight catching (SWC) technique to the LMMSE fixed weighting matrix. The SWC technique itself is based on modifying the smoothing matrix by leaving the Γ largest values in each row and turning the rest to zeros. This allows the computational complexity of the full LMMSE processor to be reduced by more than 50%. In the well known LMMSE by singular value decomposition (SVD) technique the sparse approximation is accomplished by zeroing out all but the r largest singular values. LMMSE by SVD is the preferred approximation technique for low delay spread channels. However, in channels with large delay spreads, LMMSE by SWC is a better choice in terms of computational complexity and estimation accuracy Igor Tolochkoreceived his Dipl.-Eng. Degree in Electrical Engineering from Polytechnic Institute, Riga, Latvia in 1987 and PhD from Victoria University, Melbourne, Australia in 2005. He was a senior and later principal design engineer in mobile communications at the Riga Semiconductor Institute Alpha (1988 – 1993). During 1993 – 1998, he was involved in research and development activities in communications with different companies in Riga and Melbourne, Australia. From 1998 to 2002, he was with Ericsson Australia as a senior design engineer. Currently, he works for NEC Australia Pty. Ltd. as a senior design engineer in 3G Mobile Department. His current research interests include digital signal processing, indoor and outdoor wireless communications and error control coding. Michael Faulkner(M'84) received the B.Sc. (Eng) from Queen Mary College, London University, UK, in 1970, the M.E. degree from the University of New South Wales, Australia in 1978, and the PhD from University of Technology Sydney in 1993. From 1972 to 1975 he was with STC (now Alcatel) Australia. From 1975 to 1977 he as with the University of New South Wales, and since then as a lecturer and now professor at Victoria University of Technology, Melbourne, Australia where he is director of the Telecommunications and Micro-electronics research centre. Between 1988 and 2000 he spent four periods at Lund University, Sweden. He was co-recipient of the IEE's 1997 IERE prize for a paper on amplifier linearisation. His current interests are, signal processing, radio technology, radio systems and MIMO/OFDM.     

空时编码在卫星通信系统中的应用

无线数据传输发展迅速,人们对数据服务的要求也越来越广泛。卫星传输信道存在着多径衰落,而且频谱带宽有限,而空时编码(STC)作为对抗多径衰落的有效办法,同时能够趋近多输入多输出(MIMO)信道理论上的容量极限,日益引起人们的重视。探讨了空时编码(STC)在卫星通信系统中的应用,并进行了性能比较,表明空时编码(STC)能够带来更好的效果。     

RELAY ASSISTED TRANSMISSSION WITH BIT-INTERLEAVED CODED MODULATION

We investigate an adaptive cooperative protocol in a Two-Hop-Relay （THR） wireless system that combines the following： （1） adaptive relaying based on repetition coding; （2） single or two transmit antennas and one receive antenna configurations for all nodes, each using high order constellation; （3） Bit-Interleaved Coded Modulation （BICM）. We focus on a simple decoded relaying （i.e. no error correcting at a relay node） and simple signal quality thresholds for relaying. Then the impact of the two simple thresholds on the system performance is studied. Our results suggest that compared with the traditional scheme for direct transmission, the proposed scheme can increase average throughput in high spectral efficiency region with low implementation-cost at the relay.     

SIR Weighting Combining Diversity Using Matched Filter for Personal Communication Systems

We propose a novel SIR weighting postdetection combining diversity scheme with a new accurate SIR estimation method. The SIR is estimated and used as the weighting factor to compensate severe cochannel interference, one of the most important issues for PCS in terms of frequency utilization. Theimprovement offered by the proposal depends on SIR estimation accuracy.The SIR is, in this paper, estimated by a matched filter where theauto-correlation between received signal and unique word is calculated. Computer simulationsconfirm that the SIR of each diversity branch can be estimated easily andaccuratelyby the proposed SIR estimation method. The proposed diversity scheme achievesaperformance very close to that of ideal SINR weighting diversity underRayleighfading with severe cochannel interference. When average SIR = 10 dB and thenumber of branches(L)=4, the proposed diversity scheme lowers the requiredE_b/N₀ by 5 dB at BER = 1×10^-3compared to conventional maximal ratio combining diversity. This paper alsopresentsthe unique word length required to realize adequate performance, i.e.,robustnessagainst high-pitch Rayleigh fading.     

新疆阿拉山口地区鼠类群落物种多样性的初步研究

根据阿拉山品地区环境和鼠类分布的差异将该地区的鼠类划分为５种鼠类群落，（１）红尾沙鼠＋五趾跳鼠群落，（２）五趾跳鼠＋小家鼠群落；（３）红尾沙鼠群落；（４）褐家鼠＋小家鼠群落；（５）小家鼠＋灰仓鼠群落，同时对鼠类群落的多样性－均匀度和相似性等进行了初步分析。     

Opportunistic Multi-Access: Multiuser Diversity, Relay-Aided Opportunistic Scheduling, and Traffic-Aided Smooth Admission Control

We study multi-access control in opportunistic communication systems, and propose two new schemes to address channel asymmetry and throughput-guaranteed admission control, respectively. We first devise a relay-aided opportunistic scheduling (RAOS) scheme, in which a user can choose to communicate with the base station either directly or using multiple hops (relay transmissions). We develop relay/direct link construction algorithms using either a channel-capacity-based criterion or a throughput-based criterion, and devise opportunistic scheduling schemes accordingly. Our results show that in the presence of channel asymmetry across users, the RAOS scheme performs significantly better than Qualcomm's HDR scheme. Next, we propose a traffic-aided smooth admission control (SAC) scheme that aims to guarantee throughput provisioning. Simply put, in the SAC scheme, the admission decision is spread over a trial period, by increasing gradually the amount of the time resource allocated to incoming users. Specifically, using the modified weighted proportional fair (WPF) scheduling, we devise a QoS driven weight adaptation algorithm, and the weights assigned to new users are increased in a guarded manner. Then an admission decision is made based on the measured throughput within a time-out window. A key feature is that we exploit explicitly the traffic information and throughput requirements in devising the back-off time. Our results show that the proposed SAC scheme works well in opportunistic communication systems.     

Boosted leave-many-out cross-validation: the effect of training and test set diversity on PLS statistics

It is becoming increasingly common in quantitative structure/activity relationship (QSAR) analyses to use external test sets to evaluate the likely stability and predictivity of the models obtained. In some cases, such as those involving variable selection, an internal test set – i.e., a cross-validation set – is also used. Care is sometimes taken to ensure that the subsets used exhibit response and/or property distributions similar to those of the data set as a whole, but more often the individual observations are simply assigned `at random.' In the special case of MLR without variable selection, it can be analytically demonstrated that this strategy is inferior to others. Most particularly, D-optimal design performs better if the form of the regression equation is known and the variables involved are well behaved. This report introduces an alternative, non-parametric approach termed `boosted leave-many-out' (boosted LMO) cross-validation. In this method, relatively small training sets are chosen by applying optimizable k-dissimilarity selection (OptiSim) using a small subsample size (k = 4, in this case), with the unselected observations being reserved as a test set for the corresponding reduced model. Predictive errors for the full model are then estimated by aggregating results over several such analyses. The countervailing effects of training and test set size, diversity, and representativeness on PLS model statistics are described for CoMFA analysis of a large data set of COX2 inhibitors.     

A Combined Interleaving Technique for Trellis Coded MPSK Systems in Rayleigh Fading Channels

Freedom of mobility is the latesttrend in the evolution of digital communicationsystems. In these systems bandwidth and powerconstraints limit the mobility of the users. TCM(trellis coded modulation) is a combined coding andmodulation scheme which increases the productivity ofa digital communication system without increasing thetransmitted power or the required bandwidth. A mobilecommunication channel is affected from noise andfading because of the multipath propagation. On aRayleigh fading channel, coding should be used withtechniques which uncorrelate the received energy ofeach consecutive coded symbol. Interleaving is one ofthese techniques and used to make burst errors intorandom errors which can be corrected by errorcorrecting codes. In this paper, the trellis codingsystem which combines a regular convolutional encoder,bit interleaver, coordinate interleaver, and anappropriate decoder is considered. The analytical biterror probability upper bounds are derived for the8-PSK TCM system whose diversity is increased by usinga regular 2/3 rate convolutional code followed bythree bit interleavers and a 8-PSK signal mapperfollowed by two coordinate interleavers. Theanalytical and simulation results show that toincrease the diversity of the trellis coded M-PSKsystems in Rayleigh fading channels is the primary keyfor reliable transmission of high quality voice anddigital data.     

收发信机通道不平对分集系统性能的影响

分析了分集系统收发信机通道增益不一致产生的原因,分2种情况讨论:一是通道增益不一致导致的信噪比不同对系统误码性能的影响,二是通道增益虽然不一致但不影响分集通道信噪比,即仅仅电平不同对系统误码性能的影响。分析结果表明,通道信噪比不一致对系统性能影响较大,在系统设计时应特别注意避免,这一结论对工程设计具有重要的指导作用。