BER analysis for MPAM signal constellations in the presence of fading and ADC quantization noise

In this letter, closed-form expressions for the bit error rate of M-ary pulse amplitude modulated signal constellations as a function of the analog-to-digital converter word length, the signal-to-noise ratio and the fading distribution, are derived. These results allow for a rapid and accurate evaluation of the system performance when the analog-to-digital converter resolution is limited, as is generally the case in high sampling rate communication systems, and thus provide a useful tool for system design, analysis and optimization.     

BER sensitivity to mistiming in ultra-wideband impulse radios - part II: fading channels

We investigate timing tolerances of ultra-wideband (UWB) impulse radios. We quantify the bit-error rate (BER) sensitivity to epoch timing offset under different operating conditions, including frequency-flat fading channels, dense multipath fading channels, multiple access with time hopping, and various receiver types including sliding correlators and RAKE combiners. For a general correlation-based detector, we derived in Part I unifying expressions for the decision statistics as well as BER formulas under mistiming, given fixed channel realizations. In Part II, we provide a systematic approach to BER analysis under mistiming for fading channels. The BER is expressed in terms of the receiver's energy capture capability, which we quantify under various radio operating conditions. We also develop the optimal demodulator in the presence of timing offset and show a proper design of the correlation-template that is robust to mistiming. Through analyses and simulations, we illustrate that the reception quality of a UWB impulse radio is highly sensitive to both timing acquisition and tracking errors.     

Propagation model for simulating shadowing and multipath fading inland-mobile satellite channel

A land-mobile satellite propagation model which includes multipath fading and shadowing effects using five-state Markov transitions between fade states and nonfade states is proposed. This generates a time-series of the fading, very closely matching statistical characteristics such as fade duration, nonfade duration and fade depth obtained from measured data     

抗MMDS信号衰落的有效方法

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Rate control for wideband radios

We show a technique to control the data rate emitted by wideband radio terminals. This technique is designed for adapting terminals to channel capacity variations. The proposal is based on notifying the application layer of the channel status. This information is generated by the packet scheduler, which is designed for guaranteeing appropriate channel sharing to the traffic components. Results show the effectiveness of the control in most of the analyzed situations     

Software radios for airborne platforms

Defense contributions to the Programmable Modular Communications System (PMCS) Integrated Product Team (IPT) included designs for an RF module based on software radio configurations useful in airborne systems. Several configurations were examined, analyzers were consolidated, and concepts of operation (CONOPS) were evaluated. Geographic separation of platforms and on-board separation of radio modules have consequences for the remote control of reconfigurable radios. This paper identifies organizational roles in software radio development, characterizes the need for software radios in airborne applications, and highlights those configurations found to be attractive. The methodology, CONOPS, and conclusions are summarized     

Energy spreading transform based iterative signal detection for mimo fading channels

Multiple transmit and receive antenna arrays can be used to form multiple input and multiple output (MIMO) systems for diversity and multiplexing in wireless communications. In this paper, we develop iterative signal-detection schemes based on energy spreading transform (EST) (T. Hwang and Y. Li) for MIMO channels. The EST in a MIMO system improves signal-detection performance by spreading the symbol energy over the space and time domain. It also enables iterative signal detection without employing channel coding. Analytical and simulation results demonstrate that the performance of the proposed schemes is very close to that of the genie-aided receiver when there are a sufficiently large number of receive antennas and signal-to-noise ratio (SNR) is above a threshold     

Efficient signal processing techniques for exploiting transmitantenna diversity on fading channels

A class of powerful and computationally efficient strategies for exploiting transmit antenna diversity on fading channels is developed. These strategies, which require simple linear processing at the transmitter and receiver, have attractive asymptotic characteristics. In particular, given a sufficient number of transmit antennas, these techniques effectively transform a nonselective Rayleigh fading channel into a nonfading, simple white marginally Gaussian noise channel with no intersymbol interference. These strategies, which we refer to as linear antenna precoding, can be efficiently combined with trellis coding and other popular error-correcting codes for bandwidth-constrained Gaussian channels. Linear antenna precoding requires no additional power or bandwidth and is attractive in terms of robustness and delay considerations. The resulting schemes have powerful and convenient interpretations in terms of transforming nonselective fading channels into frequency- and time-selective ones     

Input-polarisation scanning technique for overcomingpolarisation-induced signal fading in interferometric fibre sensors

Results of theoretical and experimental studies are presented, which show that polarisation-induced signal fading, caused by random polarisation fluctuations in an interferometric sensor, can be overcome by interrogating the sensor at three pre-defined input SOPs     

Broad-band fading channels: signal burstiness and capacity

Medard and Gallager (2002) showed that very large bandwidths on certain fading channels cannot be effectively used by direct sequence or related spread-spectrum systems. This paper complements the work of Medard and Gallager. First, it is shown that a key information-theoretic inequality of Medard and Gallager can be directly derived using the theory of capacity per unit cost, for a certain fourth-order cost function, called fourthegy. This provides insight into the tightness of the bound. Secondly, the bound is explored for a wide-sense-stationary uncorrelated scattering (WSSUS) fading channel, which entails mathematically defining such a channel. In this context, the fourthegy can be expressed using the ambiguity function of the input signal. Finally, numerical data and conclusions are presented for direct-sequence type input signals     

Analysis of observed Doppler fading signal in low-VHF band

Short-term amplitude variations of a tropospheric radio signal are presented and discussed. Radio wave transmissions from Newbury on 46.95 MHz were received at the University of Hull. These fluctuating signals were recorded, edited and finally analysed using time-frequency and regression techniques     

Optimal periodic training signal for frequency offset estimation in frequency-selective fading channels

This paper addresses an optimal periodic training signal design for frequency offset estimation in frequency-selective multipath Rayleigh fading channels. For a fixed transmitted training signal energy within a fixed-length block, the optimal periodic training signal structure (the optimal locations of identical training subblocks) and the optimal training subblock signal are presented. The optimality is based on the minimum Cramer-Rao bound (CRB) criterion. Based on the CRB for joint estimation of frequency offset and channel, the optimal periodic training structure (optimality only in frequency offset estimation, not necessarily in joint frequency offset and channel estimation) is derived. The optimal training subblock signal is obtained by using the average CRB (averaged over the channel fading) and the received training signal statistics. A robust training structure design is also presented in order to reduce the occurrence of outliers at low signal-to-noise ratio values. The proposed training structures and subblock signals achieve substantial performance improvement.     

Combating/eliminating dispersion-induced fading using suppressed carrier link for OFDM signal

We investigate the performance of 20-GHz radio over fibre (RoF) system having orthogonal frequency division multiplexed (OFDM) as radio signal using two modulation techniques – balanced detection for intensity modulation direct detection (IMDD) and coherent heterodyne detection suppressed carrier (SC) modulation. Dispersion-induced power fading is seen in conventional IMDD links due to the dependence of dispersion over frequency-dependent refractive index of the fibre. SC link is seen to compensate the power fading by terminating the direct current and even-order harmonics with the suppression of carrier along with balanced detection.     

A modified model for the fading signal at a mobile radio channel

A generalization of an existing model for the fading signal at a mobile radio antenna has been made. The generalization lies in letting the scattering waves not necessarily be traveling horizontally. The effects of this generalization are investigated concerning probability density function (pdf), correlational properties, and power spectra of the phase and envelope. The pdf is not affected, but the power spectrum of the envelope is significantly affected. This generalized spectrum is smoother than the original and always finite, which the latter is not. Thus it is assumed that the generalized model is more consistent with measured spectra, especially in urban environments.     

First-order statistics of a non-Rayleigh fading signal and its detection

The first-order statistics of the vecter sum of a complex Gaussian variable and N complex exponentials with constant amplitudes but random independent phases are used to model a non-Rayleigh fading signal. Envelope detection, optimal for detecting Rayleigh (N = 0) and Rician (N = 1) signals, is also shown to be optimal for the considered non-Rayleigh signals in additive white Gaussian noise. However, the signal-to-noise ratio required to detect the latter signal for N = 2 may be substantially higher than for the former cases. Possible applications of this fading model to studies of multipath fading, non-Rayleigh sea echoes, microwave or laser radar detection and tracking are discussed.     

Closed-form generalized power correlation coefficient of the Hoyt fading signal

Exact, closed-form and general expressions of the marginal and joint moments as well as-of the correlation coefficient of the instantaneous powers of two Hoyt (Nakagami-q) signals are derived. All provided statistics are expressed as finite sums of simple functions of the model parameters. The model allows for environments where the variances of the quadrature components of a signal are different from their counterparts of the other signal. Some numerical results illustrate the generalized power correlation coefficient provided in this work, simulations support the theoretical results, and an approximation to the envelope correlation coefficient of the Hoyt Model is proposed.     

Nakagami衰落信道下的蜂窝系统性能分析

文中考虑多小区蜂窝系统中小区边缘用户受到来自其他小区间同信道干扰,分析了在Nakagami-m衰落信道下,用户和基站均为单天线时的多小区蜂窝系统性能,以获得干扰信号衰落参数m和干扰基站发射功率对系统性能的影响。采用概率密度函数（PDF）分析法推导了系统中断概率和平均误符号率（ASER）的闭合表达式,并进一步通过数值仿真来分析同信道干扰对系统性能的影响。仿真结果表明,系统的中断概率和ASER的解析曲线均与仿真结果一致,系统性能随着干扰信号衰落参数m和干扰功率的增加而降低。     

A formula for an FM signal under Rayleigh fading [mobile radio]

A simple formula for the baseband signal-to-noise ratio of an FM signal under Rayleigh fading is derived. The formula automatically includes the noise component due to modulation. Calculated values of the average signal-to-noise ratio for FM and AM signals under Rayleigh fading are given. The results show that the FM signal with a modulation index of one or greater, outperforms an AM signal under identical fading conditions     

High-resolution background calibrated ADCs for software-defined radios

Next-generation transceivers operating with different standards require the existence of a wide bandwidth and highly linear analog-to-digital converters (ADCs) to enable software-defined radios (SDR). Several methods dealing with the design and implementation of high-resolution and high-speed ADCs to provide the stringent requirements of the wide-bandwidth transceivers are presented. A special focus is made on pipelined ADC for its superior performance in terms of speed and resolution. A digital background calibration technique to compensate for the capacitors mismatch, and the finite opamps gain is presented. Low overhead digitally oriented technique to increase the speed of the ADC beyond the technological limits by overcoming the problems of the conventional time-interleaving is also presented. Simulation results prove the effectiveness of these techniques.     

Orthogonally-spread block transmissions for ultra-wideband impulse radios

Differential, transmitted reference (TR) and energy detection (ED) based ultra-wideband impulse radios (UWBIR) can collect the rich multipath energy offered by UWB channels with a low-complexity receiver. However, they perform satisfactorily only when the channel induced inter-pulse interference (IPI) is negligible. This can be achieved by appending a guard interval with duration greater than or equal to the channel's delay spread to each frame ? an operation limiting the maximum achievable data rate. As a remedy, this Letter advocates block transmissions in conjunction with orthogonal spreading sequences to remove the introduced IPI. The resultant scheme requires no channel knowledge besides timing offset and incurs slightly more complexity than non-block alternatives, while it increases the data rate at no cost in error performance. Given a fixed data rate of 25Mbps, the novel block scheme exhibits about 1.8 dB gain relative to its non-block counterpart in single-user simulated tests.