Message waiting time performance for meteor-burst communicationsystems

The performance is investigated of the meteor-burst channel in terms of the waiting time required to reliably transmit a message of length N bits. Two modulation techniques are considered. The first is the traditional fixed-rate modulation scheme where the modem operates at a constant bit rate whenever the channel is available for message traffic. The second is an adaptive modulation method where the channel symbol rate varies continuously to match the time-varying signal-to-noise ratio at the receiver. Upper and lower bounds on waiting time for the general case are derived using probabilistic arguments. Novel closed-form expressions for waiting time and optimal bit rate are derived for the fixed-rate modem. Bounds on mean waiting time are derived for the adaptive-symbol-rate modem. It is shown that for fixed-rate modems operating at the optimal bit rate and for adaptive modems operating at a minimum bit rate equal to this rate, the improvement in mean waiting time can never exceed a factor of two     

Impact of hardware impairments on large-scale MIMO systems over composite RG fading channels

In this paper, we analyze the impact of receiver hardware impairments on the achievable sum rate of multiple-input multiple-output (MIMO) systems, where the channel follows composite Rician-Gamma (RG) distribution and may be correlated at the transmitters. More specifically, we derive the analytical expressions on the lower bound for the achievable sum rate of regular and large-scale MIMO systems with zero-forcing (ZF) receivers. In order to obtain deeper insights, the asymptotic analysis for the achievable sum rate of regular MIMO systems at high signal-to-noise ratio (SNR) regime is explored. It explicitly reveals that there is a finite rate ceiling on the achievable sum rate for regular MIMO systems at high SNRs, which is irrespective of the transmit power. Additionally, for large antenna configuration, three representative cases are considered insightfully by deriving in closed-form expressions for the asymptotic achievable sum rate. It demonstrates that the finite rate ceiling vanishes for large-scale MIMO limits, which means that large-scale MIMO systems are robust to hardware impairments.     

Data transparent reconfigurable optical interconnections based onpolarization-switching VCSELs and polarization-selective diffractiveoptical elements

A polarization-switching VCSEL is combined with an anisotropic diffractive optical element to demonstrate, for the first time, reconfigurable free-space optical interconnects at a rate of 30 MHz. The same set of components is also used in a proof-of-principle demonstrator for data transparent reconfigurable optical interconnects at a bit rate of 1 MHz and a reconfiguration rate of 40 kHz     

Strategies for Weather-Dependent Data Acquisition

A strategy for data acquisition from a very distant spacecraft is presented, when the system performance can be severely degraded by the earth's weather due to the high microwave frequency being used. Two cases are considered, one in which there is a certain minimum data rate to be maintained and one in which there is not. The goal is to maximize expected data return, where we assume that there are always new data, or a backlog of old data, that can be sent if conditions are favorable. When there is no minimum rate to be maintained, the optimum strategy is typically the greedy strategy, which always transmits at that single rate which maximizes the expected data returned. If there is a minimum data rate which we strive to maintain even in adverse conditions, the optimum strategy transmits simultaneously at the minimum or base data rate and typically at a bonus data rate. We use a coding system designed for the bandwidthconstrained degraded broadcast channel. The optimum version of this system can, under realistic assumptions, save on the order of 5 dB over the conservative strategy of just transmitting at a single lower data rate.     

两种OFDM调制实现方法的性能分析

将基于FFT变换和基于正交小波变换的OFDM调制系统都归结于用滤波器组来实现，分析了两种调制方法实现准确重建OFDM信号的充分条件；并在Raleigh频率选择衰落信道模型上对两种方法的误码率进行了MATLAB仿真。仿真结果表明：小信噪比时，正交小波变换误码率性能要优于FFT变换；而大信噪比时，FFT变换的误码率性能要优于正交小波变换。     

Exponential error bounds for incoherent orthogonal signals (Corresp.)

It is well known that arbitrarily small error probabilities can be obtained at any source rate less than capacity for the band-infinite Gaussian channel by block coding binary digits into either coherent or incoherent orthogonal signals. In this correspondence it is shown that the exponential rate at which the error probability approaches zero with increasing block length is the same for the coherent and incoherent orthogonal signals for any source rate less than channel capacity.     

Backscatter and attenuation by falling snow and rain at 96, 140,and 225 GHz

The results of measurements are presented for backscatter cross section per unit volume and attenuation for falling snow and rain at 96, 140, and 225 GHz. The attenuation due to rain is almost independent of the measurement frequency, but for snow the attenuation is considerably greater at 225 GHz than at 96 GHz. The rain attenuation generally varies with the rain accumulation rate in accordance with an aR^b relationship for a Laws and Parsons drop-size distribution where R is the rain rate and a and b are constants. The attenuation at all three frequencies is about 3 dB/km for a rain rate of 4 mm/h. The attenuation due to snow varies with airborne snow-mass concentration, with the average rates of increase being 0.9, 2.5, and 8.7 (dB/km)(g/m³) at 96, 140, and 225 GHz, respectively. Generally the attenuation for snow is lower than that for rain. The backscatter cross section per unit volume for rain at 96 GHz is about -35 dB m²/m³ for a rain rate of 4 mm/h. The backscatter from snow at 96 GHz is much lower than that from rain under equivalent accumulation rates or airborne mass concentrations. Snow backscatter at 140 GHz is comparable but higher than that at 96 GHz     

Measurements of rainfall attenuation at 8 and 15 GHz

Measurements of attenuation at frequencies of 8 and 15 GHz, and their correlation with rainfall rate, along a 15.78 km path near Ottawa, are described. Empirical expressions which relate the observed attenuation to the measured rainfall rate are derived and compared with similar expressions obtained on the basis of earlier theoretical studies of the problem. It is concluded that while the theoretical predictions of attenuation in rain are reasonably satisfactory, at least for rains observed at Ottawa, there is a definite tendency for observed attenuations at low rainfall rates to be somewhat higher than the expected values. The cumulative distribution of rainfall attenuation over a six-month period is compared with the attenuation predicted on the basis of average rainfall data obtained during the last five years. Although the agreement between observation and prediction, using the theoretical relation between rainfall rate and attenuation, is good for path attenuations greater than 2 dB, it can be greatly improved if the empirical expression relating rainfall rate to attenuation is used.     

基于伪随机码置乱的分布式视频残差编码端码率控制算法

提出一种基于伪随机码置乱的分布式视频残差编码端码率控制算法,利用伪随机码对残差视频帧的像素进行置乱处理,将信源图像与其边信息图像之间的差别均匀化,实现帧级别上的码率估计,即每一帧用同一码率发送。如果收端译码失败,利用提出的一种量化序号估计算法能显著提高译码成功率,解决码率低估问题。同时发端视频残差帧的特性能近似表示收发两端信号之间的相关性,因此,发端无需产生一个预测的边信息。仿真结果表明,该算法发端复杂度低、译码成功率高、系统延迟小、率失真性能良好。     

Rationale for a Modified Duane Model

The Duane model for reliability growth involves a rate function which is an inverse power law and has an ``infinite' value at t = 0. The model is usually motivated entirely empirically. Here a probabilistic rationale is proposed via a reliability growth model involving the removal of design faults. This rationale results in a modified power law rate, finite at the origin. A wider class of rate functions should be investigated for NHPP models of reliability growth.     

细胞培养用品光透射规律的研究

应用紫外分光光度计对细胞培养板盖及培养液的光透射规律进行了初步观察。结果显示，200－280nm波长范围的光很难透过培养板盖（透射率仅2％－10％），对400－800nm波长范围光的透过率达84％左右，含小牛血清和未含小牛血清的PRMI细胞培养液对600－800nm波长范围的光透过较高（透射率分别为78％左右，81％左右），对小于600nm波长的光透过较弱。     

Slepian-Wolf Coded Nested Lattice Quantization for Wyner-Ziv Coding: High-Rate Performance Analysis and Code Design

Nested lattice quantization provides a practical scheme for Wyner-Ziv coding. This paper examines the high-rate performance of nested lattice quantizers and gives the theoretical performance for general continuous sources. In the quadratic Gaussian case, as the rate increases, we observe an increasing gap between the performance of finite-dimensional nested lattice quantizers and the Wyner-Ziv distortion-rate function. We argue that this is because the boundary gain decreases as the rate of the nested lattice quantizers increases. To increase the boundary gain and ultimately boost the overall performance, a new practical Wyner-Ziv coding scheme called Slepian-Wolf coded nested lattice quantization (SWC-NQ) is proposed, where Slepian-Wolf coding is applied to the quantization indices of the source for the purpose of compression with side information at the decoder. Theoretical analysis shows that for the quadratic Gaussian case and at high rate, SWC-NQ performs the same as conventional entropy-coded lattice quantization with the side information available at both the encoder and the decoder. Furthermore, a nonlinear minimum mean-square error (MSE) estimator is introduced at the decoder, which is theoretically proven to degenerate to the linear minimum MSE estimator at high rate and experimentally shown to outperform the linear estimator at low rate. Practical designs of one- and two-dimensional nested lattice quantizers together with multilevel low-density parity-check (LDPC) codes for Slepian-Wolf coding give performance close to the theoretical limits of SWC-NQ     

Approaching MIMO-OFDM Capacity with Per-Antenna Power and Rate Feedback

This paper presents power-efficient transmission schemes for the multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) block-fading channel under the assumption that the channel during each fading block is known perfectly at the receiver, but is unavailable at the transmitter. Based on the well-known vertical Bell Labs layered space-time (V-BLAST) architecture that employs independent encoding for each transmit antenna and successive decoding at the receiver, this paper presents a per-antenna-based power and rate feedback scheme, termed the "closed-loop" V- BLAST, for which the receiver jointly optimizes the power and rate assignments for all transmit antennas, and then returns them to the transmitter via a low-rate feedback channel. The power and rate optimization minimizes the total transmit power for support of an aggregate transmission rate during each fading block. Convex optimization techniques are used to design efficient algorithms for optimal power and rate allocation. The proposed algorithms are also modified to incorporate practical system constraints on feedback complexity and on modulation and coding. Furthermore, this paper shows that the per-antenna-based power and rate control can be readily modified to combine with the conventional linear MIMO transmit preceding technique as an efficient and capacity-approaching partial-channel-feedback scheme. Simulation results show that the closed-loop V-BLAST is able to approach closely the MIMO-OFDM channel capacity assuming availability of perfect channel knowledge at both the transmitter and the receiver.     

A Code Set for a Robust 8.25 Mb/s Data Rate for IEEE 802.11b WLANs

In this paper, a code set for an 8.25-Mb/s data rate is proposed for the Institute of Electrical and Electronics Engineers 802.11b system, which can act as a better fallback option than a 5.5-Mb/s data rate when an 11-Mb/s data rate is not sustainable in a large delay-spread channel environment. We present a systematic procedure for the design of the code set. The proposed code set works at significantly higher path loss when compared to an 11-Mb/s data rate in moderate to large delay-spread channel environment. We also discuss the resource requirement for including the proposed data rate in the existing 802.11b transceiver and note that the additional hardware is minimal. Since the current WIreless FIdelity chipsets are enabled with the 802.11g option, we investigated the performance of the proposed data rate and the 6and 9-Mb/s data rates provided by 802.11g, and the results show that the 8.25-Mb/s data rate is a reliable fallback option compared to the 9-Mb/s rate when the 11-Mb/s data rate is not sustainable. The 8.25-Mb/s data rate is shown to work at 1.7 dB higher path loss when compared to the 9-Mb/s rate in a frequently occurring moderate delay-spread channel     

Methods of Controlling the Word Rate of Recorded Speech

Six methods for increasing speech rate are presented. They are as follows. 1. Speech at a rate that is faster than normal may be obtained by pacing an oral reader at a rate that is faster than his normal reading rate. 2. The word rate of recorded speech may be increased by reproducing a tape or record at a speed that is faster than the speed used during recording. 3. The word rate of recorded speech may be increased by an electromechanical device that reproduces consecutive samples of a recorded tape. 4. Consecutive sampling may also be accomplished by a computer. 5. The word rate of synthesized speech may be manipulated by instructions in the program followed by a speech synthesizer. 6. The harmonic compressor increases word rate by a method of frequency division without temporal alteration, and frequency restoration with temporal alteration.     

The dynamics of rain-induced fades

The dynamics of rain-induced fades on radio links is studied by evaluating the rate at which the first Fresnel zone volume fills with rain. The amount of water in this volume determines the fade depth, and the rate at which it fills establishes the fade slope. A compact expression for fade slope on a terrestrial path is derived. This expression shows that once the rain rate is specified, fade slope is very sensitive to differences in rain velocity. Thus, there is no unique relationship between fade slope and rain rate     

Optimal design of partially accelerated life tests for theexponential distribution under type-I censoring

Optimal designs for two partially accelerated life tests (PALTs) in which items are run at both accelerated and use conditions until a predetermined time are considered. The step PALT allows the test to be changed from use to accelerated condition at a specified time; the constant PALT runs each item at either use or accelerated condition only. For items having constant hazard (failure) rate, maximum-likelihood estimators (MLEs) of the hazard rate at use condition and the acceleration factor, the ratio of the hazard rate at accelerated condition to that at use condition, are obtained. The change time for the step PALT or the sample proportion allocated to accelerated condition for the constant PALT is determined to minimize either the generalize asymptotic variance of MLEs of the acceleration factor and the hazard rate at use condition or the asymptotic variance of MLE of the acceleration factor     

Variable rate data transmission with blind rate detection forcoherent DS-CDMA mobile radio

A variable rate data transmission scheme with blind rate detection is described for pilot-symbol-assisted coherent DS-CDMA mobile radio. Cyclic redundancy check (CRC) coding and decoding is used for blind rate detection. Computer simulations of eight-rate variable rate data transmission demonstrate that when 16 bit CRC is used, the loss in required total E_b/N₀ at a frame error rate of 10 ^-2 under two-path Rayleigh fading, is only ~0.1 dB from the known rate case     

RAINFALL RATE CONVERSION IN SOUTHEAST ASIA COUNTRIES

The knowledge of 1-minute rainfall rate distribution is very important in order for the prediction of rainfall attenuation at any location. Due to the availability of 1-minute rainfall rate data is limited, conversion of rainfall rate distribution over a long integration time into the distribution for 1-minute is needed. Therefore several rainfall rate conversion methods were proposed.     

UWB Echo Signal Detection With Ultra-Low Rate Sampling Based on Compressed Sensing

A major challenge in ultra-wide-band (UWB) signal processing is the requirement for very high sampling rate. The recently emerging compressed sensing (CS) theory makes processing UWB signal at a low sampling rate possible if the signal has a sparse representation in a certain space. Based on the CS theory, a system for sampling UWB echo signal at a rate much lower than Nyquist rate and performing signal detection is proposed in this paper. First, an approach of constructing basis functions according to matching rules is proposed to achieve sparse signal representation because the sparse representation of signal is the most important precondition for the use of CS theory. Second, based on the matching basis functions and using analog-to-information converter, a UWB signal detection system is designed in the framework of the CS theory. With this system, a UWB signal, such as a linear frequency-modulated signal in radar system, can be sampled at about 10% of Nyquist rate, but still can be reconstructed and detected with overwhelming probability. The simulation results show that the proposed method is effective for sampling and detecting UWB signal directly even without a very high-frequency analog-to-digital converter.