三维空间非平稳车载几何信道模型的研究分析

本文提出一种新型的三维空间非平稳车载几何信道模型.我们采用圆柱体描述发射端（Mobile Transmitter,MT）以及接收端（Mobile receiver,MR）附近运动的车辆,而采用椭圆柱描述路边静止的建筑物.由于发射端和接收端的相对运动而使得本文提出的模型呈现时变非平稳几何特性.针对提出的三维空间信道模型,作者深入研究其统计特性,比如时域相关特性以及多普勒功率谱分布.仿真结果和过去研究结果进行比较,进而验证本文提出的信道模型能够很好地描述车载无线通信环境.     

Frequency domain analysis of robust signal estimators

This paper addresses the problem of robust linear estimations of systems perturbed by noise with a wide sense stationary (WSS) process, with its spectral density known only to be in a neighborhood of some specified spectral density. The asymptotic efficiency of the least-square (LS) estimator relative to the best linear unbiased estimator (BLUE) is known to depend upon the degree of the variance of the spread of the noise spectral density at the frequencies where the spectral mass of the system's impulse response function is concentrated. A signal estimator in the frequency domain is considered and it is demonstrated that where the Fourier transform is applied to the observed data, robust estimation occurs.     

Continuous Phase Modulation--Part II: Partial Response Signaling

An analysis of constant envelope digital partial response continuous Phase modulation (CPM) systems is reported. Coherent detection is assumed and the channel is Gaussian. The receiver observes the received signal over more than one symbol interval to make use of the correlative properties of the transmitted signal. The Systems areM-ary, and baseband pulse shaping over several symbol intervals is considered. An optimum receiver based on the Viterbi algorithm is presented. Constant envelope digital modulation schemes with excellent spectral tail properties are given. The spectra have extremely low sidelobes. It is concluded that partial response CPM systems have spectrum compaction properties. Furthermore, at equal or even smaller bandwidth than minimum shift keying (MSK), a considerable gain in transmitter power can be obtained. This gain increases withM. Receiver and transmitter configurations are presented.     

Capacity limits of cognitive radio with distributed and dynamic spectral activity

We investigate the capacity of opportunistic communication in the presence of dynamic and distributed spectral activity, i.e., when the time varying spectral holes sensed by the cognitive transmitter are correlated but not identical to those sensed by the cognitive receiver. We develop a two switch model that captures the localized spectral activity estimates at the transmitter and receiver. The information theoretic framework of communication with side information is employed to characterize the capacity of the cognitive link with both causal and non-causal side information at the transmitter and/or the receiver. These capacity results are used to determine the benefits of any feedforward and feedback information. We find that cognitive radio capacity is robust to the uncertainties arising out of distributed and dynamic spectral environments, even when the communication occurs in bursts of only 3-5 symbols. The capacity depends strongly on the correlation of the local spectral environment at the cognitive transmitter and receiver     

On the second order statistics of non-isotropic Nakagami Hoyt mobile to mobile fading channel

This paper presents second order statistical properties of the mobile to mobile Nakagami Hoyt channel model under non-isotropic condition. The spatial-time correlation function, the power spectral density (PSD), level crossing rate (LCR) and the average duration of fade (ADF) of the Nakagami Hoyt channel have been derived under the assumption that both the transmitter and receiver are non-stationary having non-omnidirectional antennas. Design of simulator using the Inverse Fast Fourier Transform (IFFT) based computation method has been applied for this model. The simulator and analytical results have been corroborated.     

一种TD-SCDMA上行链路发送和接收方案

为了在TD-SCDMA上行链路传输中获得更高的频谱利用率,提出了一种上行链路的发送和接收方案。发送端采用准同步CDMA加QAM调制,扩频序列采用优选相位的Gold序列,该序列在一定时延范围内具有良好的互相关性。接收端采用串行干扰抵消的方法去除或抑制很严重的多用户干扰,该方法实现简单,适合瑞利衰落信道。仿真结果说明采用这种发送和接收方案后,在应用智能天线抑制多径后,只要用户间的时延控制在3／8个chip之内,误符号率(SER)性能就几乎与单用户界(SUB)一致,频谱利用率可以达到4 bit／s／Hz。     

基于数字化插值的频偏抑制因子的计算

组建通信网时,为确保通信正常,需要对系统的电磁兼容性进行分析预测.频偏抑制因子衡量接收机选择性曲线对干扰发射机发射频谱的抑制程度,是对干扰信号定量分析的重要影响指标.针对这一问题,结合受扰接收机与干扰发射机的收发频率间隔、干扰信号功率谱密度及接收机选择特性,对频偏抑制因子进行分析研究,采用数字化插值计算并进行误差分析及仿真验证,结果显示该算法精度高、复杂度低,适用于工程运算.     

Compensation of non-reciprocal interference in adaptive MIMO-OFDM cellular systems

In a time-division-duplex communication system, the channel knowledge can be obtained at the transmitter side due to channel reciprocity and it can be used to increase the spectral efficiency of a multiple-input multiple-output (MIMO) communications. However, the interference structure between transmission directions does not necessarily correlate. The obtained quality of service at the receiver may differ significantly from the desired one if the transmission parameters are assigned based on the reverse link measurements only. In this paper, the performance of an orthogonal frequency division multiplexing (OFDM) cellular system with adaptive MIMO transmission is studied in the presence of non-reciprocal inter-cell interference when the downlink interference structure is known at the receiver and only limited feedback information about the interference is available at the transmitter. The results are compared to those with perfectly known interference structure per each sub-carrier. The system level impact of realistic interference non-reciprocity scenarios is studied via network simulations. Linear minimum mean squared error (MMSE) filter is applied at the receiver to suppress the impact of structured inter-cell interference together with a simple and bandwidth efficient closed-loop compensation algorithm. Both link and system level simulation results show that the proposed compensation algorithm with a simple scalar power offset feedback combined with interference suppression at the receiver results in nearly the same performance as the ideal case     

High-Bit-Rate Dense SS-WDM PON Using SOA-Based Noise Reduction With a Novel Balanced Detection

The major drawback of incoherent broadband sources (BBSs) is their inherent intensity noise. Semiconductor optical amplifiers (SOAs) can be exploited at the transmitter to mitigate this noise. Optical filtering at the receiver, however, leads to the return of most of suppressed noise. Wider filtering at the receiver is the best known strategy to maintain performance gains, at the price of reduced spectral efficiency due to the tradeoff between noise cleaning and adjacent channel crosstalk. We introduce a novel balanced receiver for wavelength division multiplexing (WDM) systems that maintains greater noise cleaning and leaves spectral efficiency unchanged. Unlike standard receivers, our balanced scheme does not filter the desired signal. In this paper, we first demonstrate that the newly proposed receiver is equivalent to standard WDM receivers when no SOA for noise cleaning is present at the transmitter. Although a 2.9-dB power penalty is incurred, network capacity is unchanged, i.e., bit error rate (BER) floors due to intensity noise are the same. When SOAs are employed to mitigate severe intensity noise, we show that our receiver outperforms the wide filtering strategy by two orders of magnitude. Dense WDM capacity is demonstrated up to 10 Gb/s using a thermal source, a saturated SOA, and the balanced detection scheme. A BER of 10^-6 is achieved at 10 Gb/s; further improvement is possible using low overhead forward error correction or a better SOA design. This demonstrates the ability of spectrum-sliced wavelength division multiplexing (SS-WDM) passive optical networks (PONs) to operate at 10 Gb/s at good spectral efficiency. Error performance better than 10^-9 is achieved up to 8 Gb/s with 30-GHz optical channel bandwidth and 100-GHz spacing.     

A filterbank approach to window designs for multicarrier systems

Windowing is often applied to multicarrier systems to improve frequency separation among the subcarriers. At the transmitter side better frequency separation leads to a smaller out-of-band spectral leakage and also less interference to radio frequency transmission. At the receiver side better separation gives more suppression of radio frequency interference. As these are frequency based characteristics, a filterbank representation presents a natural and useful framework for formulating the problem. In this work, we propose a unified filterbank approach to the design of windows for multicarrier systems. The filterbank viewpoint provides an additional insight into the transmitter design for spectral leakage reduction as well as to the receiver design for interference suppression. A better frequency separation among the subchannels can be achieved     

超结构光纤光栅的正交波分复用系统实现方案及接收机串扰分析

解释了超结构光纤光栅(SSFBG)作为脉冲成型滤波器的特性,说明SSFBG能够产生规则的时域矩形光脉冲,在频域上功率谱密度表现为sinc函数的形式.当光波道的频率间隔为码元速率的整数倍时,相邻波长的功率谱零点位于信号波长的中心频率处,频谱正交交叠.研究了一种基于SSFBG的正交波分复用(OWDM)系统,发送端用SSFBG进行脉冲整形,接收端采用窄带滤波器.给出基于理想窄带滤波器和高斯窄带滤波器两种接收机的串扰噪声模型,并得出了仿真结果.结果显示,两种窄带滤波器均可抑制严重的信道串扰,当接收机窄带滤波器通带足够窄时,接收机串扰比信道串扰降低约10 dB;理想窄带滤波器优于高斯窄带滤波器2～5 dB.     

Frequency-Division Bidirectional Communication Over Chip-to-Chip Channels

Frequency division multiple access is applied to bidirectional communication over chip-to-chip links. Frequency division is implemented by dividing the spectrum into low-frequency (dc) and high-frequency (ac) bands using a simple LC filter. The nonidealities that this filter introduces are compensated for with a transmitter/receiver pair that can recover signals in both bands. The receiver uses a dual-path topology that includes hysteresis to recover data from a signal with no dc content. The transmitter is a 6-tap (FIR) pre-emphasis equalizer with variable tap spacing. In simulation, the transmitter and receiver simultaneously communicate error-free at 8 Gb/s over the ac channel and at 500 Mb/s over the dc channel. Measurements shows that the ac and dc signals can be individually recovered and that the two signals occupy distinct frequency bands.      

非视线光散射通信的大气传输模型

利用大气对光的散射作用可以实现非视线通信.在单次散射假定下,研究了非视线光散射通信系统的大气传输模型.利用该模型分析了光源发散角、接收视场和收发仰角等系统几何参数与接收散射光能量之间的关系;重点讨论了大气分子散射和气溶胶散射各自对接收散射光能量的贡献.结果表明当系统的收发仰角较大时,接收光能量主要来自大气分子散射;反之,气溶胶散射则成为接收光能量的主要部分.对于工作在日盲紫外光谱区的非视线通信系统,增加接收视场可以有效地增大系统的信噪比.发现在两种典型的收发仰角情况下,接收散射光能量随光源发散角的变化趋势是相反的,这说明光源发散角要根据实际的应用场合设计确定.     

Performance analysis of a rate-adaptive dual-branch switched diversity system

In this letter, a performance analysis of a dualbranch switched diversity system operating on statistically independent and identically distributed Nakagami-m flat-fading channels is presented. An adaptive coded modulation (ACM) scheme is employed to increase the spectral efficiency of the system. The ACM scheme consists of a set of multidimensional trellis codes originally designed for additive white Gaussian noise channels, where the codes are based on quadrature amplitude modulation (QAM) signal constellations of varying size. The performance is evaluated by assuming perfect channel knowledge at both transmitter and receiver and instantaneous feedback of channel state information, conveyed from the receiver to the transmitter on an error-free feedback channel. The optimal switching threshold of the switched diversity combiner, maximizing the average spectral efficiency, is identified for spatially uncorrelated antenna branches.     

Wireless smart sensor with small spiral antenna on Si-substrate

This paper presents a wireless smart sensor (WSS) with a thermoelectric sensor, a wireless transmitter and a small spiral antenna on a single package. To transmit a sensor signal, the wireless transmitter was designed to consist of an amplifier, a modulator, an oscillator, a buffer stage and an antenna. The wireless transmitter used dual pulse position modulation for low-power transmission. The fabricated transmitter has a sampling frequency of 2.6 kHz and an output carrier wave frequency of 300 MHz band due to the higher far field radiation of the transmitted signals from inside the body. The small size spiral antenna on the chip was fabricated for the transmission of carrier waves. The antenna has a bandwidth of 270-360 MHz for VSWR<2 and a gain of −40 dBi. The fabricated sensor, transmitter and spiral antenna were packaged with bond-wire on a single package. The WSS consumed a power of about 16.9 mW at the supply power of 5 V. The electric field strength of the WSS was measured to be 64.6 dB μV/m at a distance of 3 m. The wireless operation of the fabricated WSS was confirmed by demonstrating that the sensor signal was modulated by the transmitter and that the modulated sensor data was transmitted through the small size spiral antenna.     

Environmental issues for MIMO capacity

Wireless communication using multiple-input multiple-output (MIMO) systems enables increased spectral efficiency for a given total transmit power. Increased capacity is achieved by introducing additional spatial channels that are exploited using space-time coding. In this paper, the environmental factors that affect MIMO capacity are surveyed. These factors include channel complexity, external interference, and channel estimation error. The maximum spectral efficiency of MIMO systems in which both transmitter and receiver know the channel (using channel estimate feedback) is compared with MIMO systems in which only the receiver knows the channel. Channel complexity is studied using both simple stochastic physical scattering and asymptotic large random matrix models. Both uncooperative (worst-case) and cooperative (amenable to multiuser detection) interference are considered. An analysis for capacity loss associated with channel estimation error at the transmitter is introduced.     

Capacity of a mobile multiple-antenna communication link inRayleigh flat fading

We analyze a mobile wireless link comprising M transmitter and N receiver antennas operating in a Rayleigh flat-fading environment. The propagation coefficients between pairs of transmitter and receiver antennas are statistically independent and unknown; they remain constant for a coherence interval of T symbol periods, after which they change to new independent values which they maintain for another T symbol periods, and so on. Computing the link capacity, associated with channel coding over multiple fading intervals, requires an optimization over the joint density of T·M complex transmitted signals. We prove that there is no point in making the number of transmitter antennas greater than the length of the coherence interval: the capacity for M>T is equal to the capacity for M=T. Capacity is achieved when the T×M transmitted signal matrix is equal to the product of two statistically independent matrices: a T×T isotropically distributed unitary matrix times a certain T×M random matrix that is diagonal, real, and nonnegative. This result enables us to determine capacity for many interesting cases. We conclude that, for a fixed number of antennas, as the length of the coherence interval increases, the capacity approaches the capacity obtained as if the receiver knew the propagation coefficients     

Ultimate limits of subcarrier multiplexed lightwave transmission

An analysis of the fundamental limits in SCM lightwave transmission is presented. The system studied comprises an ideal overmodulated laser transmitter with nonsymmetrical threshold clipping and a shot-noise limited receiver. The power spectral density of the nonlinear distortion noise is evaluated and the optimum modulation index m/sub opt/ is determined. Results are given for the ultimate requirements for VSB-AM and FM SCM modulation formats.<>     

Multiple antennas in cellular CDMA systems: transmission,detection, and spectral efficiency

Providing wireless high-speed packet data services for Web browsing and streaming multimedia applications will be a key feature in future code-division multiple-access (CDMA) systems. We study down-link CDMA schemes for providing such services using multiple antennas at the transmitter and receiver. We propose a generalization of the point-to-point narrowband Bell Labs layered space-time (BLAST) system to a wideband multiple access system which simultaneously supports multiple users through code spreading. We discuss transmission options for achieving transmit diversity and spatial separation and introduce a generalization of the vertical BLAST detector for CDMA signals. Using link level simulations, we determine the bit-error rates versus signal-to-interference ratio of the various transmitter options. We then describe a novel technique for determining the system spectral efficiency (measured in bits per second per Hertz per cell sector) by incorporating the link level results with system level outage simulations. Using four antennas at the transmitter and eight antennas at each receiver, the system can support multiple receivers at 16 times the voice rate, resulting in a system spectral efficiency an order magnitude higher than a conventional single-antenna voice system     

High-speed power-efficient indoor wireless infrared communication using code combining .II

For pt.I see ibid., vol.50, no.7, p.1098-1109 (2002). We examine an infrared link composed of a multibeam transmitter and a direction-diversity receiver, employing code combining. The latter represents an added dimension to the conventional diversity concepts, which are limited to combining the individual received symbols. Rate-compatible punctured convolutional codes are used to encode intensity-modulated on-off keying (OOK) optical power, to create an adaptive environment for efficient utilization of channel spectral bandwidth, to provide a means for accurate channel estimation, and to maintain a guaranteed bit error rate (BER) performance at all receiver positions. It is shown that a BER not exceeding 10/sup -9/ with 99% probability can be achieved at bit rates up to a few hundreds of megabits per second, at very low transmitted power levels.