Further analytical results on the joint detection of cochannel signals using diversity arrays

We derive a fully analytical expression for the union bound on symbol-error rate for the joint detection of several cochannel fading signals using a diversity antenna array, putting numerical results previously published on a firm analytical base. We prove that with pilot-based multiuser channel estimation, any number of users can enjoy diversity order equal to the number of antennas, and we quantify the performance penalty relative to single-user binary phase-shift keying as a function of number of users, constellation density, and number of antennas. We also demonstrate the interdependence of all users participating in the detection process.     

Performance enhancement of CDMA cellular systems with augmentedantenna arrays

The use of base station adaptive antenna arrays is an attractive way to increase the capacity of code division multiple access cellular systems. In this paper, a system with an adaptive minimum redundancy array (MRA) at the base stations is proposed. This system uses the high-resolution signal angle of the arrival estimation algorithm, ESPRIT, in conjunction with array augmentation techniques, and linear least squares adaptation. For the MRA, we propose to use virtual array elements at the locations where there is no sensor element. All real and virtual sensor outputs are weighted and combined to extract the desired signal components and suppress interference. To simplify the evaluation of the interference from adjacent cells, the concentric circle cell geometry is employed in place of the common hexagonal cell geometry. The performance of the proposed system is quantified by comparison with the omnidirectional antenna, and the adaptive uniform linear array (ULA) with the same number of elements and same array aperture, using realistic simulations. It is shown that, for a four-element array, there is about a 4- and a 1-dB improvement in the despread output signal-to-interference-plus-noise ratio of the proposed system over the omnidirectional antenna and the conventional ULA, respectively     

Performance limits of coded diversity methods for transmitterantenna arrays

Several aspects of the design and optimization of coded multiple-antenna transmission diversity methods for slowly time-varying channels are explored from an information-theoretic perspective. Both optimized vector-coded systems, which can achieve the maximum possible performance, and suboptimal scalar-coded systems, which reduce complexity by exploiting suitably designed linear precoding, are investigated. The achievable rates and associated outage characteristics of these spatial diversity schemes are evaluated and compared, both for the case when temporal diversity is being jointly exploited and for the case when it is not. Complexity and implementation issues more generally are also discussed     

Capacity enhancement using adaptive arrays in an AMPS system

Adaptive arrays for an advanced mobile phone service (AMPS) system can significantly increase cell capacity, improve signal quality, and reduce transmitter power requirements. In this paper, we investigate the capacity improvement that can potentially be achieved using adaptive arrays at the base station of an AMPS system. For the analysis, we use two types of spatial filters at the base station: an ideal and flat-top beamformer. An ideal beamformer has a flat main lobe and no side lobes, while a flat-top beamformer has flat main and side lobes. Analysis includes calculation of outage probability when a beamformer is used at the base station, and then we calculate the capacity increase that can be offered by practical antenna arrays. In this paper, we show that spatial-division multiple access (SDMA), i.e., all the users in a cell occupying the same frequency, is impossible to achieve in an AMPS system. A cell-reuse factor of four can be easily achieved with a five-element uniform linear array (ULA) with λ/2 spacings, but to achieve a reuse factor of three, a ULA with eight elements is required     

Performance analysis of joint switched diversity and adaptive modulation

In this paper, a simple and practical system based on a switched diversity scheme with adaptive modulation is presented. This system provides a reduced number of channel estimation while offering the optimum spectral efficiency given by a selection diversity system. In addition, the switching threshold is easily manipulated so as to make an efficient use of the tradeoff between spectral efficiency and channel estimation overhead. An extension of switched diversity into a multiuser scheduling is later also considered. This switch-based multiuser access scheme results in a lower average feedback load than that for the optimal selection-based multiuser scheme. Numerical results show that we can obtain a trade-off between spectral efficiency and the feedback load by choosing the switching threshold appropriately.     

Sensitivity enhancement using coherent heterodyne detection

This paper focuses on some heretofore overlooked advantages of coherent detection (CD) over direct detection (DD) in optical fiber communication systems. The basis for these sensitivity improvements is the fact that the local laser in coherent fiber optic systems adds a large number of photons to the net received optical signal. Under these conditions, the Bohr correspondence principle enables us to treat the photodiode output signal classically. Specifically, the usual CD environment yields a photodiode output that can be regarded as a classical signal disturbed by Gaussian noise (central limit theorem). This detection process has been studied extensively, and there exist many powerful signal processing techniques that may be used to enhance system sensitivity. In particular, we utilize a sum of digitally modulated subcarriers to frequency modulate an optical carrier along with the aid of coherent detection to achieve 11.1 photons/b sensitivity as determined by computer simulation     

Performance enhancement of BPSK-SIM- and DPSK-SIM-based FSO downlink over atmospheric turbulence using aperture averaging and receiver diversity

In this paper, we evaluate the bit error rate (BER) performance of a free-space optical satellite downlink by considering the atmospheric turbulence effects using binary shift keying subcarrier intensity modulation and differential phase shift keying subcarrier intensity modulation (DPSK-SIM). The performance of the link is enhanced using aperture averaging and receiver diversity. The closed form mathematical expressions of BER for BPSK-SIM and DPSK-SIM schemes are derived and analyzed. It is observed that on varying the turbulence level, the performance of the link degrades when the turbulence level increases. The improved BER of 10^?12 and 10^?10 at signal-to-noise ratio of 30 dB of the link for both BPSK-SIM and DPSK-SIM is obtained by using aperture averaging (aperture diameter, D?=?10 cm) and receiver diversity with optimal combining.

     

Capacity enhancement of secondary links through spatial diversity in spectrum sharing

Previous investigations on capacity of secondary users in spectrum-sharing environments have determined the capacity of a secondary link based on the interference power threshold set at the primary receiver. In contrast to these previous works, we show that the capacity of a secondary link is determined based on a geographical relationship expressed as the ratio of the distance between the primary receiver and secondary transmitter to the distance between the secondary transmitter and receiver. Proceeding from that and in an effort, to enhance the capacity of the secondary user, which is limited by this distance-ratio, we adopt a secondary transmitter with Μ antennas. Furthermore, we analyze the capacity achieved using a simple antenna selection process.     

Performance of a cellular hybrid C/TDMA mobile radio systemapplying joint detection and coherent receiver antenna diversity

For future mobile radio systems, an appropriately chosen multiple access technique is a critical issue. Multiple access techniques presently under discussion are code division multiple access (CDMA), time division multiple access (TDMA), and hybrids of both. In the paper, a hybrid C/TDMA system using joint detection (JD-C/TDMA) with coherent receiver antenna diversity (CRAD) at the base station (BS) receiver is proposed. Some attractive features of the JD-C/TDMA system are the possibility to flexibly offer voice and data services with different bit rates, soft capacity, inherent frequency and interferer diversity, and high system capacity due to JD. Furthermore, due to JD, a cluster size equal to 1 can be realized without needing soft handover. The single cell E_b/N₀ performance and the interference situation in a cellular environment of the uplink of a JD-C/TDMA mobile radio system with CRAD is investigated in detail. It is shown that the cellular spectrum efficiency is remarkably high, taking values up to 0.2 bit/s/Hz/BS in the uplink, depending on the actual transmission conditions     

Performance analysis of narrow-band adaptive arrays using projectedperturbation sequences

When signals on the elements of an array are not accessible, algorithms for adjusting the weights of an adaptive array may employ perturbation techniques to obtain a gradient estimate for weight adaptation. To reduce the amount of noise introduced into the receiver by perturbation of the weights and to maintain constant gain in the signal direction during adaptation, the application of projected orthogonal perturbation sequences to adaptive beamforming is required. An analysis of the performance of projected orthogonal perturbation sequences is presented, and the performance of two specific sequences is investigated. Two methods of performance analysis are presented. They confirm that, in general, the projected perturbation sequences generate smaller variance in the gradient estimate and hence lower misadjustment than conventional perturbation techniques. Results of computer studies of the performance of the new sequences are presented     

Field-emission enhancement of Mo-tip field-emitted arrays fabricated by using a redox method

This work has improved the emission characteristics for Mo-tips of field-emitter array (FEA) through a reduction-oxidation (redox) process. The maximum emission current of the 1600 tips array significantly increased from 23.2 /spl mu/A to 2.36 mA with the turn-on voltage decreasing from 70 V to 48 V after the redox treatment. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicate that the main factor improving electron field emission characteristics for the Mo-tips is the increase in enhancement factor (/spl beta/) and, possibly, number of emission sites of Mo films.     

Elderly-falling detection using distributed direction-sensitive pyroelectric infrared sensor arrays

This paper presents a new distributed direction-sensitive infrared sensing approach for fall detection in elderly healthcare applications. Pyroelectric infrared (PIR) sensors are employed in sensing human activities. For capturing the characteristics of human normal and abnormal activities, three modules of a direction-sensitive PIR sensor are organized using a distributed sensing structure. The advantage of using the distributed sensing paradigm is that the synergistic motion patterns of head, upper-limb and lower-limb can be efficiently encoded and thus the more discriminative features can be captured. This is the new consideration of using PIR sensors in building a full detection system. In addition, a two-layer hidden Markov model is developed for recognizing a fall event based on the multidimensional signals of the distributed infrared sensing system. Experimental studies are conducted to validate the proposed method.     

分集技术下频谱感知的性能分析

研究了在普适的相关非同分布Nakagami-m衰落模型情况下,次用户采用能量检测和等增益合并技术进行频谱感知的性能.给出了检测概率的闭式表达式,并通过分析漏检概率的渐进曲线斜率说明分集技术对频谱感知性能带来了提升.利用数值结果和Monte-Carlo仿真验证了理论推导的准确性.最后通过Monte-Carlo仿真观察了等增益合并分集技术下信道相关性对检测概率的影响.     

Performance enhancement of SC-FDMA systems using a companding technique

In this paper, a companding technique is proposed to effectively reduce the peak-to-average power ratio (PAPR) in single-carrier frequency division multiple access (SC-FDMA) systems. By companding the samples with large amplitudes, while enhancing those with small amplitudes, a significant reduction in the PAPR can be achieved. The performance of the proposed SC-FDMA with companding system is studied and compared with that of the standard SC-FDMA system. Simulation results show that the SC-FDMA with companding system has a lower PAPR when compared with the conventional SC-FDMA system, while the complexity of the system slightly increases. Results also reveal that the companding coefficient must be chosen carefully in order to limit the PAPR without introducing degradations into the bit error rate performance.     

Iterative multiuser detection using antenna arrays and FEC onmultipath channels

This paper investigates a multiple-access communication receiver system that receives coded data modulated using either direct-sequence code division multiple access or narrowband binary phase shift keying, with an antenna array in a multipath propagation environment. We describe an iterative receiver that improves the initial estimates from the antenna array, and therefore reduces the multiple access interference. Simulation results show that the bit error rate performance approaches that obtained when only one user's signal is incident on the array. This occurs even with a large number of users in comparison to the product of the spreading gain and array size     

基于天线阵列的一种预处理LCLSCM多用户检测算法

给出了一种天线阵列信号的预处理方法,并将线性受限条件和判决反馈用于最小二乘,提出了一种基于天线阵列的预处理线性受限判决反馈最小二乘恒模多用户检测算法,称为PLC-DFB-LSCMA算法,并与判决反馈最小二乘恒模算法(DFB-LSCMA)及传统的最小二乘恒模算法(LSCMA)进行了仿真比较,仿真结果表明,PLC-DFB-LSCMA算法的信干比性能及误码性能仍优于后二者。     

The yield enhancement of field-programmable gate arrays

The fine granularity and reconfigurable nature of field-programmable gate arrays (FPGA's) suggest that defect-tolerant methods can be readily applied to these devices in order to increase their maximum economic sizes, through increased yield. This paper identifies the inability to contain faults within single cells and the need for fast reconfiguration as the key obstacles to obtaining a significant increase in yield. Monte Carlo defect modeling of the photolithographic layers of VLSI FPGA's is used as a foundation for the yield modeling of various defect-tolerant architectures. Results suggest that a medium-grain architecture is the best solution, offering a substantial increase in size without significant side effects. This architecture is shown to produce greater gate densities than the alternative approach of realizing ultralarge scale FPGA's-multichip modules     

Saliency detection using contrast enhancement and texture smoothing operations

An effective framework to improve the saliency maps in complex (low-contrast, small object, and similar background etc.) images is proposed. In proposed scheme, firstly weighted approximated histogram equalization is used to enhance image contrast. Secondly, edge-preserving guided filter is used to minimize the unwanted details (texture) while maintaining the edges and semantics. Afterward, iterative rolling guidance filter is also applied to perform scale-aware local operations for image abstraction. Cellular automata is then used to obtain and optimize saliency cues by exploiting local similarity. Visual and quantitative analysis with state-of-the-art existing techniques shows the significance of proposed technique.     

Postdetection diversity using differential phase detection forM-ary DPSK

Postdetection diversity that uses L differential phase detector outputs for data decision is described for M-ary differential phase shift keying (M-ary DPSK. Data decision is based on minimising the weighted sum of the errors of L DPD detector outputs. The squared geometric mean of the two consecutively received signal envelope samples is used as the branch weight. The simulation results on average bit error rate (BER) performances due to additive white Gaussian noise (AWGN), multipath Doppler spread, and delay spread of π/4-shift 4DPSK are reported     

Improved iterative joint detection and estimation through variational Bayesian inference

We propose an improved variational Bayesian (VB) receiver for orthogonal frequency-division multiplexing (OFDM) systems over frequency-selective block-fading channels. Conventional VB receivers provide distribution-estimates for the channel and information symbols iteratively and jointly. The proposed scheme is different from conventional VB inference in that the VB iterative receiver also exploits the hard channel estimate extracted from previous iterations to update the channel and symbol distributions. In this way, we reduce the impact of channel uncertainty on the decoder performance by means of a modified formulation of the VB formalism. The adequacy of the proposed approach compared to classically used VB receivers is demonstrated by simulations.