基于PCIe接口的多径信道实时测量设备设计方法

针对当前商用无线多径信道测量设备结构复杂、价格昂贵、灵活性不够的问题,提出了一种基于PCIe接口的软件化无线信道实时测量设备设计方法。该方法利用PCIe接口对接收到扩频测量信号进行获取,并利用多线程方式进行相关处理,具有实时测量的能力,可对无线信道多径特性开展实时测量,具有结构通用性好、测量算法改变灵活、信息存储量内容丰富和实时性较好的特点。给出了一个实际的研制案例,测试结果表明,该设计方法对于较低带宽的测量信号具有良好的适用性。     

IEEE802.16标准中OFDM技术研究

描述了802.16—2004中OFDM和OFDMA的物理层特性．比较了两种固定宽带无线接入系统的空中接口的异同点,就物理层参数设计(如信道带宽和中心频率、调制编码方式)．帧结构子信道分配、距离修正和带宽请求过程进行了详细阐述。     

带限连续波时分复用技术的SystemView与Matlab混合仿真

带限连续波时分复用技术是一种多路带限信号在一连续信道中时分复用的传输技术,其频率利用系数高,设备复杂度低。简要介绍了带限连续波时分复用技术的原理和SystemView与Matlab的动态接口M-Link,并联合SystemView与Matlab进行了相关性能仿真。结果表明带限连续波时分复用技术能有效降低传输过程中的波形失真和邻道间泄漏。     

基于USB接口的对流层散射信道测试设备

为拓展散射通信在各种地域时域环境下,比如在沙漠、海面、春夏秋冬季及不同天气状况下的应用,需对各种地域、季节和天气状态下对流层散射信道的电波传播特性进行测试和统计。基于USB接口的散射信道测试设备,对信道特性-电平衰落、信号多径传输特性、相关带宽及空间相关性进行单项或多项循环测试。用PC机对测试数据进行图形化显示并对数据完成后续处理与分析,具有连接方便、数据传输速率高、可热插拔等优点。     

下一代数字显示接口DisplayPort

介绍了一种新的数字显示接口DisplayPort,讲述了其形成的技术背景和基本技术组成,并与现有接口(DVI,HDMI,LD-VS)的各项性能参数进行了对比.新的数字显示接口能在更少的线数上提供更高的带宽,并具有很好的可扩展性.     

WCDMA接入网传输带宽需求计算

简要介绍了WCDMA网络传输接口,给出了WCDMA接入网各接口带宽计算方法,并根据业务模型实例,详细阐述了不同承载方式下各接口的带宽需求。     

OFDM系统隐藏导频的信道估计与跟踪

传统插入导频的信道估计方法占用固有的带宽,而基于隐藏导频的信道估计的方法不需要占用额外的带宽.基于隐藏导频信道估计理论提出了一种隐藏导频信道跟踪的方法:在叠加最优PAPR序列进行信道估计之后,增加了一个简单的周期冲激序列作为信道跟踪.该方法在节约有效资源的同时,也简化了算法复杂度.     

综合线路倍增设备的设计与实现

综合线路倍增设备是一种利用ATM/AAL2技术增加传输信道容量的设备,它可充分利用线路资源进行话音与数据业务的综合传输,提高传输链路的带宽利用率。给出了综合线路倍增设备的设计原理和相关概念,对该设备的设计与实现进行了论述,最后将其信道倍增增益与STM信道倍增设备进行了对比。     

WCDMA网络基站传输电路的计算方法

分析了WCDMA的网络结构和接口要求,给出了3G业务中电路域业务、分组域业务和互联互通业务的预测模型,以及Node B Iub接口带宽计算公式,通过WCDMA网络Node B上行Iub接口带宽的需求分析,对WCDMA网络传输所需要的总的E1电路数进行了计算。     

基于协方差反馈和空时分组码预编码的自适应QAM调制

基于多天线相关信道协方差反馈,提出一种低复杂度自适应正交幅度调制(QAM)机制以提高系统发送速率。根据最小误比特率(BER)准则,建立了最优空时分组码(STBC)预编码方案。并在保证系统可靠性要求下,针对不同的信道衰落条件选取合适的QAM星座图级别。结果表明所建议机制具有低实现复杂度、低反馈带宽开销和高数据流通率等优点。     

一种利用窄波束成形提高短波信道相干带宽的方法

短波通信信道具有频率选择衰落特性,相干带宽是描述单载波系统平坦衰落信道带宽的重要参数。提高相干带宽有利于系统使用更大的带宽来实现高数据速率传输并且有助于减少接收机的复杂度。该文提出一种利用发射端窄波束成形在空间上将发射能量集中于主路径且抑制其它路径信号来提高短波信道相干带宽的方法,并利用自适应技术来建立及保持点对点之间的窄波束通信。理论研究表明,该方法能有效地提高信道相干带宽。该文以中距离短波通信为例,计算了使用不同发射天线数时的相干带宽值,计算结果证实了该方法的有效性。     

On channel quantization and feedback strategies for multiuser MIMO-OFDM downlink systems

We consider a multiuser MIMO-OFDM downlink system with single antenna mobile terminals (MTs) where channel state information at the base station is provided through limited uplink feedback (FB). In order to reduce the FB rate and signal processing complexity, the available bandwidth is divided into resource blocks (RBs) whose number of subcarriers reflects the coherence bandwidth of the channel. This approach is very common in the standardization of 4th generation wireless communication systems and justifies an independent channel quantization per RB. Within this framework the paper contains two main contributions. Firstly we provide joint conditions on the channel coherence bandwidth and the FB rate per RB that allow for a simpler quantization of the RB channel matrix (space-frequency) by a space vector, causing negligible performance loss in terms of system achievable throughput. This is accomplished after deriving a new metric for codebook design in RB channel quantization that exploits spatial and frequency correlation. As a second contribution we investigate the trade-off between accurate channel knowledge and frequency/multiuser diversity. It is seen that even for a moderate number of MTs in the network, concentrating all the available FB bits in characterizing only one RB provides a significant gain in system throughput over a more classical distributed approach and this result is validated both analytically and by simulations.     

Computationally Efficient Lattice Reduction Aided Detection for MIMO‐OFDM Systems under Correlated Fading Channels

We analyze the relationship between channel coherence bandwidth and two complexity‐reduced lattice reduction aided detection (LRAD) algorithms for multiple‐input multiple‐output (MIMO) orthogonal frequency division multiplexing (OFDM) systems in correlated fading channels. In both the adaptive LR algorithm and the fixed interval LR algorithm, we exploit the inherent feature of unimodular transformation matrix P that remains the same for the adjacent highly correlated subcarriers. Complexity simulations demonstrate that the adaptive LR algorithm could eliminate up to approximately 90 percent of the multiplications and 95 percent of the divisions of the brute‐force LR algorithm with large coherence bandwidth. The results also show that the adaptive algorithm with both optimum and globally suboptimum initial interval settings could significantly reduce the LR complexity, compared with the brute‐force LR and fixed interval LR algorithms, while maintaining the system performance.     

A soft-output bidirectional decision feedback equalizationtechnique for TDMA cellular ratio

Issues encountered in the design of reliable narrowband time-division multiple access (TDMA) digital cellular mobile communication systems are considered. In particular, the problem of compensating for the harsh multipath fading environment in systems whose transmission bandwidth is commensurate with the coherence bandwidth of the fading channel is considered. A TDMA channel characterization parameter, the slot-normalized fade rate, is introduced, and an adaptive bidirectional equalization technique, which estimates the location of a deep fade within a time slot, is proposed. The simulation results show that the carrier-to-noise ratio requirement is only 15.5 dB when this equalization technique is used. This is achieved without diversity, and with low complexity. An equivalent equalized land mobile radio channel model and the analytical solution for the optimal bit likelihood calculation for π/4-shift quadrature differential phase-shift keying (QDPSK) modulation are also derived under certain channel conditions. The results are used as soft decisions for the convolutional decoder     

The off‐grid frequency selective millimeter wave channel estimation

Broadband millimeter wave (mmW) systems are a promising pioneer of cellular communication for next generation which is utilizing the hybrid baseband/analog beamforming structures along with the miniature massive antenna arrays at both sides of the communication link. mmW channel with an available unlicensed spread spectrum is frequency selective because the signal bandwidth can be larger than the coherence bandwidth. Due to the sparse nature of mmW channel, extracting compressive sensing model of the system is preferable. In fact, exploiting the sparse structure will lead to the reduction of the computational complexity, because there is a reduction in the channel training length compared with the conventional methods such as least square estimation. Most of the prior works have considered on‐grid quantized departure/arrival angles in the input/output antennas to obtain a sparse virtual channel model. However, the sparse angles in the physical channel model are continuous where this continuity indicates a mismatch between the physical angles and the on‐grid angles. Such a mismatch will contribute to unwanted components in the virtual channel model. Given these extra components, the conventional compressive sensing tools are unable to recover the channel. In this paper, we propose two solutions for overcoming the problem caused by off‐grid angle selection. The first is based on the vector shaping, and the second one is based on the sparse total least square concepts. Simulation results demonstrate that the proposed methods both could obtain an adequate channel recovery and are preferable regarding computational complexity concerning the newly developed surrogate method.     

Unitary matrix modulation with splitting over the coherence bandwidth for OFDM in a single antenna system

Recently, unitary matrix modulation (UMM) has been investigated in multiple antenna systems which is called unitary space‐time modulation (USTM). In an OFDM, different channel delay profiles and path strengths bring different frequency selective patterns. Therefore, OFDM system can potentially provide a diversity at the frequency selective fading due to the different channel delay profiles. When we consider only the diagonal components of UMM with splitting over the coherence bandwidth, the system can obtain a frequency diversity in a single antenna, since the channel response of the diagonal components of UMM that split over the coherence bandwidth shows to be totally different. In this paper, we propose the diagonal components of UMM/OFDM with splitting over the coherence bandwidth (UMM‐S/OFDM) in a single antenna. The proposed system can obtain the frequency diversity with splitting the diagonal components of UMM/OFDM over the coherence bandwidth. Therefore, the proposed system with a single antenna can obtain good BER performance like the USTM/OFDM with two antennas. Copyright © 2006 John Wiley & Sons, Ltd.     

Measurements and characterization of wideband indoor radio channel at 60 GHz

This paper presents the measurements, the statistical results and channel models extracted by impulse response measurements of an indoor 60 GHz radio channel. The measurements were based on the pulse sounding technique. Multipath parameters that characterize the channel have been extracted and analyzed statistically concerning corridors and offices locations. The mean excess delay is in the range of 3.84 to 8.18 ns for hallways and 3.52 to 14.69 ns for offices. Additionally, rms delay spread varies from 12.34 to 15.04 ns in corridors and from 12.56 to 21.09 ns inside the laboratory. The coherence bandwidth varies between 13.88 and 30.49 MHz in corridors with a mean value of 22.48 MHz. Inside offices the mean coherence bandwidth is 22.80 MHz for LoS locations and drops to 7.05 MHz for NLoS. Small-scale models for all the measured locations were developed using tapped delay lines. The maximum Doppler frequency of the modeled channel remains around 1 Hz, whereas the coherence time is calculated 1.04 s, which indicates that the channel remains, almost stationary, exhibiting very slow fading. Finally, from the models it is derived that the channel preserves WSS and US characteristics giving rise to a WSSUS representation.     

Layered space-time receivers for frequency-selective wirelesschannels

Results in information theory have demonstrated the enormous potential of wireless communication systems with antenna arrays at both the transmitter and receiver. To exploit this potential, a number of layered space-time architectures have been proposed. These layered space-time systems transmit parallel data streams, simultaneously and on the same frequency, in a multiple-input multiple-output fashion. With rich multipath propagation, these different streams can be separated at the receiver because of their distinct spatial signatures. However, the analysis of these techniques presented thus far had mostly been strictly narrowband. In order to enable high-data-rate applications, it might be necessary to utilize signals whose bandwidth exceeds the coherence bandwidth of the channel, which brings in the issue of frequency selectivity. In this paper, we present a class of layered space-time receivers devised for frequency-selective channels. These new receivers, which offer various performance and complexity tradeoffs, are compared and evaluated in the context of a typical urban channel with excellent results     

Estimating channel performance for time invariant channels

It is shown that estimating the coherence bandwidth (/spl beta//sub c/) of a static WLAN channel from frequency domain snapshot measurements using the complex autocorrelation function, commonly reported in the literature, is wrong and meaningless. In such cases the channel is time invariant or non-fading but time variant theories are mistakenly applied. An alternative parameter that estimates the distortionless transmission bandwidth (DTB) of the non-fading channel is proposed and used to characterise a line of sight, indoor microcell, at millimetre waves.     

Data Aided Iterative Channel Estimation in OFDM Systems Using a Controlled Superimposition of Training Sequences

This work pertains to the use of superimposed training for channel estimation in orthogonal frequency division multiplexing (OFDM) based systems. An iterative time domain Least Squares based channel estimator is proposed. The estimator is generalized to provide scope for exploiting the coherence time and the coherence bandwidth of the channel. By exploiting the periodicity of the training sequences in the time domain and inserting zeros instead of data at some of the training sequence subcarrier locations depending on the desired estimation accuracy, a controlled superimposition technique is proposed. This method includes the flexibility to trade off between bandwidth efficiency and performance without any change in the structure of the channel estimator. The mean squared estimation error (MSEE) performance of such a system is mathematically analyzed and a training sequence selection criterion optimizing the same is proposed. The simulation performance of the scheme is presented in terms of the MSEE and also its impact on the bit error rate is shown. Such a scheme is attractive in high data rate scenarios in closed loop OFDM systems.