Modeling the indoor MIMO wireless channel

This paper demonstrates the ability of a physically based statistical multipath propagation model to match capacity statistics and pairwise magnitude and phase distributions of measured 4 × 4 and 10 × 10 narrow-band multiple-input multiple-output data (MIMO) at 2.4 GHz. The model is compared to simpler statistical models based on the multivariate complex normal distribution with either complex envelope or power correlation. The comparison is facilitated by computing channel element covariance matrices for fixed sets of multipath statistics. Multipolarization data is used to demonstrate a simple method for modeling dual-polarization arrays     

Frequency domain characterization of LoS nonfading indoor wireless LAN channel employing frequency and polarization diversity in the 63.4-65.4 GHz band

This paper presents results of frequency domain measurements conducted to characterize the distortionless transmission bandwidth (DTB) of indoor nonfading channels employing vertically and horizontally polarized antennas in the frequency band 63.4-65.4 GHz. The mean delay spread (/spl tau//sub mean/), root mean square (rms) delay spread (/spl tau//sub rms/), and the DTB of the channel are also presented as functions of distance between terminals and are compared for both polarizations. The dependence of DTB on the separation between terminals d is modeled as DTB=kd/sup -n/ where k is a constant. /spl tau//sub mean/ increases linearly with d, and its relationship with DTB is characterized as DTB=(1//spl alpha//spl tau//sub mean//sup n/)+c, where /spl alpha/ and c are constants. The effectiveness of frequency and polarization diversity in mitigating the effects of multipath fading in indoor channels has also been evaluated. The performance of both diversity techniques when modulated signals with high data rates for multimedia applications are utilized is presented for maximum selection combining. The performance of frequency diversity is also shown as a function of frequency separation between diversity branch signals to determine whether an optimal frequency separation exists.     

Temporal variations of the indoor wireless millimeter-wave channel

This paper reports experiments conducted near 30 GHz to characterize human-induced variations of an indoor radio channel for which both terminals are stationary. The dependence of envelope characteristics on various parameters (degree and localization of movement, terminal configuration, and spatial short-range fading level) is examined. In particular, it is found that the received envelopes may be considered realizations of only locally stationary processes, even when movement in the propagation environment is homogeneous. The results presented may be used in the design of broad-band wireless LANs and serve as a basis for the development of a theoretical model capable of predicting channel temporal variation characteristics under a variety of conditions     

室内MIMO系统采用极化分集时的信道容量

典型的室内传播信道为莱斯衰落信道,可将其分解为LOS传播信道和散射信道.本文假设散射信道为瑞利衰落信道,并根据天线的极化特性,给出了存在极化分集时的LOS传播信道.基于此,本文提出了室内MIMO系统采用极化分集时的信道模型.研究表明:极化分集可以有效提高MIMO信道容量.     

Statistical AR models for the frequency selective indoor radio channel

A statistical model of the indoor radio channel is proposed that is derived from a second order autoregressive process representation of the channel frequency response. The accuracy of the statistical model is examined by comparing the cumulative distribution functions of the RMS delay spread and the 3 dB width of the frequency correlation function computed from the regenerated data with that of the measurements performed in two indoor radio propagation studies in the 0.9-1.1 GHz band.<>     

A characterization of indoor space and frequency diversity byray-tracing modeling

The performance of space and frequency diversity techniques at 1800 MHz in an indoor environment are investigated. Three linear signal combining techniques are considered: signal selection (SEL), maximal ratio combining (MRC), and equal gain combining (EGC). The computations of received fading envelopes are performed by means of an analytical model, based on a three-dimensional ray-tracing (RT)/uniform theory of diffraction (UTD) technique; the reliability of the adopted approach is confirmed by comparison with some test measurements. The electromagnetic field components are adequately processed to obtain the single branch and combined signal envelope. The results show the very significant benefits that can be achieved both in terms of diversity gain and diversity advantage for both diversity techniques. Antenna spacings of about 0.75-1λ are nearly sufficient for achieving optimum performance, whereas frequency separation on the order of 10 MHz is needed for sufficiently decorrelated transmission on the two carriers     

Millimeter-wave channel measurements with space diversity forindoor wireless communications

Indoor wireless communication systems experience deep multipath fading due to the presence of people, antenna movement, and other environmental factors. The objective of this paper is to present results concerning envelope fading and large-scale attenuation properties of the signal based on narrowband measurements carried out at 21.6 and 37.2 GHz with and without antenna diversity. By using various transmitter-receiver arrangements in measurements which were taken over one floor of a university building, envelope statistics of received signal are produced with and without antenna diversity. It is shown that the statistical distributions follow the Rayleigh curve and hence a diversity gain close to 10 dB can be obtained for an availability of 99%. Power law exponents and wall loss factors are also calculated to assist in the design of future indoor radio systems in the millimeter frequency range     

Performance evaluation of baseband OOK for wireless indoor infraredLAN's operating at 100 Mb/s

We investigate 100 Mb/s wireless nondirectional infrared communication in the indoor environment using baseband nonreturn-to-zero (NRZ) on-off keying (OOK) modulation. We show that intersymbol interference induced by multipath propagation impairs detection efficiency. Analytical and simulation results on specific channels demonstrate that an adaptive decision-feedback equalizer adapted according to the least-mean-squares algorithm recovers most of the performance degradation. We also evaluate the performance of a timing-recovery phase-locked loop operating independent of the adaptive equalizer; showing that it quickly and accurately determines the sampling phase with negligible performance degradation. We discuss effective methods of mitigating low-frequency noise induced by fluorescent lighting. We present a packet-based communication method and describe its features and performance. Our results support the feasibility of communication at 100 Mb/s over the infrared channel     

A channel detection technique based on Max-Log-MAP algorithm for wireless indoor system

This study introduces a new low complexity Max-Log-MAP based channel estimation technique operating in a multi-path band limited channel. The proposed estimation technique is based on an iterative procedure derived through the maximum a posteriori probability approach. Wireless communication channels often undergo frequency selective fading that leads to inter-symbol interference, which limits the performance of wireless indoor systems. Performance of the algorithms is assessed by combined analysis and simulation. Results are presented and compared against the performance of conventional Log-MAP algorithm. The obtained results show that the required bit-error-rate performance can be achieved with a lower number of iterations using the proposed low complexity algorithm compared to using the conventional Log-MAP algorithm.     

Performance analysis of space time block coding techniques for indoor optical wireless systems

Indoor optical wireless systems provide an attractive alternative for realizing next generation Wireless Local Area Networks (WLANs). In this paper, the performance of diffuse optical wireless systems, employing Space Time Block Coding (STBC) techniques, is numerically investigated, accurately taking into account, the indoor channel impulse response and the characteristics of ambient light and thermal noises at the receiver. Discrete Multitone modulation (DMT) is used to mitigate the effect of intersymbol interference due to the channel?s impulse response. The performance of STBC systems, employing two transmit elements, is compared against Single Input/ Single Output (SISO) and Maximum Ratio Combining (MRC) systems operating with the same total optical transmitter power. It is shown that STBC techniques can be used to increase the capacity of diffuse optical wireless systems, improve their coverage and decrease the required optical power at the transmitter. These results demonstrate the usefulness of Multiple Input Multiple Output (MIMO) techniques in the realization of optical WLANs.     

色/频/空三维资源复用的室内可见光非直流偏置OFDM系统性能研究

提出一种新的室内可见光非直流偏置正交频分（Non-DC-Biased Orthogonal Frequency Division Multiplexing, NDC-OFDM）复用系统,该系统采用多个颜色LEDs作为光源,在保证高传输可靠性的同时可以维持环境光的稳定。将空间调制和同色异谱调制结合并应用到室内可见光OFDM通信系统中得到一种新的适用于室内可见光通信系统的NDC-OFDM传输方案,该方案具有OFDM、空间调制和同色异谱调制的优势,适用于高速室内白光通信系统。仿真结果表明所提出的NDC-OFDM室内可见光传输系统与传统的直流偏置光OFDM （DC-biased Optical OFDM）和非对称限幅光OFDM （Asymmetrically Clipped Optical OFDM）相比具有更好的优势,并且与其它NDC-OFDM室内可见光传输方案相比,对于OFDM信号高峰均功率比引起的光信号非线性畸变问题,本文提出的多色LEDs NDC-OFDM室内可见光传输方案除了具有更好的鲁棒性外,还不会产生光强度波动。     

SIMO channel performance evaluation on indoor environment at 2.4 GHz

This work presents an experimental study of single-input multiple-output (SIMO) channel performance in the indoor radio propagation environment. Indoor channel measurements at the 2.4-GHz ISM frequency band have been conducted using a versatile channel sounder test-bed platform. A single transmitting antenna, four receiving antennas with two proposed geometries and a four-branch receiver circuitry were used in order to achieve channel sounder measurements exploiting baseband signal-processing techniques. In-depth investigation of SIMO wireless channel performance was realised through three types of metrics: signal strength, gain coefficient and capacity. Performance results indicate SIMO channel capacity enhancement and illustrate differences between the two proposed geometries.     

室内走廊环境高频段宽带无线信道测量与建模

为了验证在高频段进行宽带无线通信的可行性,介绍了针对室内走廊环境进行的14 GHz宽带无线信道测量和所获取的信道特征。基于频域信道冲激响应测量方法,设计搭建了宽带无线信道测量平台,较好地克服了高频段电波传播能量实时测量采集的难度。基于实测数据提取信道参数化模型,获取了高频段电波传播特性参数统计分析结果,包括路径损耗与阴影衰落、时延扩展、角度扩展。测试与分析结果表明:高频段电波传播时延小、方向性强,适用于宽带互联通信。     

Gigabit/s indoor wireless systems with directional antennas

The design of a high speed (>150 Mb/s) wireless local area network (WLAN), requires that many factors be considered, including technical, economic, and regulatory. A major technical factor is the channel response behavior (multipath) in the indoor environment as a function of the frequency band, building type and radio system architecture. The consequences of designing indoor wireless systems with directional antennas at one or both ends of a line-of-sight (LOS) link are investigated. We determine how narrow the beamwidth must be so that the maximum data rate is not limited by multipath effects. For such beamwidths, simple unequalized two-level frequency shift keying (FSK) or phase shift keying (PSK) modems can be used in place of the more costly and complex “anti-multipath” modems, and data rates above 1 Gb/s may be achieved. The channel impulse response in an empty room is estimated using geometrical optics, observing that with directional antennas, multipath rays must arrive from the same direction as the LOS ray. The link outage probability is then estimated as a function of the antenna beamwidth, and guidelines are established for the selection of the frequency band and antenna placement. Experiments using a 19-GHz 622-Mb/s binary phase shift keying (BPSK) link and 15° beamwidth horn antennas in an office building with plaster walls and large metallized windows have demonstrated error-free performance on both LOS and non-LOS (NLOS) links     

Performance evaluation of preemptive polling schemes and ARQtechniques for indoor wireless networks

This paper examines a radio-based indoor communication network with a single radio channel shared by several data terminals. By enabling the terminals to communicate with each other and access the resources of a wired network, the system is a potential provider of in-building LAN-like services. In this indoor fading environment, a base-station approach is assumed. In the analysis, a two-state Markov chain model is used to model the nonstationary transmission channel. Two preemptive polling multiple-access schemes combine with ARQ error-control schemes to counteract the effects of a nonstationary transmission channel. The main idea devised is that of making the service interruption dependent on the propagation conditions of the transmission channel by monitoring the outcomes of the data packet transmission attempts. A performance comparison reveals the superiority of the preemptive polling systems with respect to a classical TDMA scheme     

一种宽带多输入多输出双向信道的频域辨识方法

提出一种基于空间交换最大期望(SAGE)算法的信道频域辨识方法。该方法能够有效地估计收发联合宽带多输入多输出(MIMO)双向信道的三维离开角、到达角、极化等特征参数。仿真的结果表明:该方法能准确地估计MIMO双向信道的参数,适合MIMO信道建模的需求。     

Experimental analysis of wireless data transmission systems in space platforms

This paper presents an experimental analysis of the use of wireless data-transmission systems in manned space platforms. Previous studies have analyzed the general advantages of substituting radio systems for some of the harnesses in the platforms. This paper presents a detailed experimental characterization of the radio channel in the environment of a space platform at frequency bands of 2.5 GHz and 17 GHz. For this purpose, a mockup, based on the Columbus Space Laboratory, was built. The probability distribution functions of the fading have been obtained for narrow-band as well as wideband parameters, such as the mean square delay and the coherence bandwidth of the channel. Moreover, a study of the operating mode of a commercial wireless system, based on the IEEE 802.11b standard, has been performed, by monitoring the bit-error rate. The error rates of the IEEE 802.11b system in the typical environment of a small or medium-sized office are compared with those of a space-platform environment. The results and conclusions can be extended to other environments that present geometrical and structural characteristics similar to those of a space platform, such as ships and submarines.     

无线信道中OFDM系统时频同步新算法

OFDM系统中频偏和定时误差的存在,对系统性能有很大的影响。本文根据设计的特殊导颁符号,通过伪随机序列的自相关特性得到定时误差;然后通过导频符号之间的相关性,估计出频率偏离。为了提高估计器的精度,采用了过采样技术。同时可以证明该算法能有效地对抗无线信道中的码间干扰。仿真结果表明,该算法能获得很好的性能,逼近改进的Cramer-Rao下界。     

Experimental characterization of the MIMO wireless channel: data acquisition and analysis

Detailed performance assessment of space-time coding algorithms in realistic channels is critically dependent upon accurate knowledge of the wireless channel spatial characteristics. This paper presents an experimental measurement platform capable of providing the narrowband channel transfer matrix for wireless communications scenarios. The system is used to directly measure key multiple-input-multiple-output parameters in an indoor environment at 2.45 GHz. Linear antenna arrays of different sizes and construction with up to ten elements at transmit and receive are utilized in the measurement campaign. This data is analyzed to reveal channel properties such as transfer matrix element statistical distributions and temporal and spatial correlation. Additionally, the impact of parameters such as antenna element polarization, directivity, and array size on channel capacity are highlighted. The paper concludes with a discussion of the relationship between multipath richness and path loss, as well as their joint role in determining channel capacity.     

移动通信室内外空间几何信道模型的分析与比较

针对频率非选择性无线多径衰落信道,基于室外通信环境下的空心圆模型,提出了一种改进的适应于室内通信环境的空心圆模型。通过推导接收信号的空时联合分布以及边缘分布概率密度函数,分析和比较了两种空心圆几何信道模型的空时统计特性。通过空心圆的空心率以及收发机间距的信道参数变化,仿真结果阐明了空心圆模型在圆盘模型和圆环模型之间过渡的变化机理,以及不同无线通信环境下的信道信息。