Performance of turbo trellis coded/continuous phase modulation over MIMO channels

Bit error performance of turbo trellis coded/continuous phase modulation (TTC/CPM) is investigated for multiple input multiple output (MIMO) channels. The performance of TTC/CPM for 16-continuous phase frequency shift keying (CPFSK) over AWGN and Rician channels (for Rician channel parameter K=10 and 4 dB) is given for 1Tx-1Rx, 2Tx-1Rx and 2Tx-2Rx antenna combinations. Channel capacities of TTC-16CPFSK signals are obtained for these antenna configurations. TTC/CPM over MIMO fading channels is found to be very good, especially for low power applications     

Space?frequency coded cooperation in OFDM multiple-access wireless networks

A cooperative space-frequency (SF) coded orthogonal frequency division multiplexing system is considered and its performance over quasi-static frequency-selective Rayleigh fading channels is evaluated. An expression for exact outage error probability is derived and its tight closed-form lower bound is presented. The tightness of the lower bound is demonstrated through Monte Carlo simulation. Asymptotic analysis indicates that the proposed protocol achieves full spatial and frequency diversities available in the cooperative communication system. The theoretical analysis of the proposed SF coded cooperation protocol is further confirmed by computer simulation using a previously introduced SF block code that is capable of achieving full spatial and frequency diversities.     

基于循环延迟分集的差分空时频编码方案

结合正交空时码的分集优势,将正交空时码应用到差分空频系统中,提出了一种基于循环延迟分集的多流差分空时频编码新方法,在差分系统中同时获得了空间和频率分集.该差分编码方法在满足信道的时间和频率选择性前提下,只需要发送很少的参考矩阵用于非相干检测.仿真结果表明,正交空时码的引入,可以有效提高整个系统的分集增益,从而在很大程度上改善整个差分MIMO-OFDM系统的误码性能.     

一种新的水声MIMO空时频编码技术

基于贝尔实验室垂直分层空时编码（Vertical Bell Labs Layered Space-Time,VBLAST）的水声多输入多输出（Multiple-Input Multiple-Output,MIMO）通信技术,通过充分开发空间资源,可在不增加系统带宽的条件下成倍提高数据传输速率,是一种极具潜力的高速水下通信技术。但由于其接收信号中同时含有同频干扰及多径干扰,当信道多径扩展严重时,其性能下降严重。为此,提出一种新的空时频编码技术,该技术通过将各层信号调制到彼此正交的子载波上,不但可在接收端完全消除同频干扰,同时还能获得频率分集增益,从而使水声MIMO通信系统的性能获得极大改善。仿真及湖试结果证明了其有效性。     

Pilot overhead reduction in turbo coded OFDM systems employing an iterative channel estimation under low signal-to-noise ratio environments

The authors evaluate the improved energy and spectral efficiency by pilot overhead reduction of turbo coded orthogonal frequency division multiplexing (OFDM) systems employing an iterative phase estimation algorithm. Developed from the recently proposed iterative phase estimation schemes, the phase estimation and compensation process is embedded into the basic iterative turbo decoding process for the application to OFDM systems with just a slight complexity overhead. At each decoding iteration, sub-carrier phase rotations are estimated from the extrinsic information arranged in each sub-carrier and are compensated for the next decoding iteration. This enables the iterative phase estimation algorithm to successfully work under very low signal-to-noise ratios even without pilot symbols. The pilot symbols are just very rarely inserted only for breaking the erroneous phase estimation propagation frame to frame in case of large residual phase offset beyond reliable decoding range. Simulation results show that the iterative phase estimation algorithm drastically reduces the pilot insertion overhead and thus, it achieves improved spectral efficiency as well as bit error rate (BER) performance by saving pilot energy compared to the conventional method.     

Linearly coded profilometry

A new optical profilometry-linearly coded profilometry (LCP)-is presented. It uses a sawtoothlike linear light structure to code the surface to be measured and a phase-shifting technique to decode the profile. Two kinds of coding-light structure, one with right-angle triangle teeth and the other with isosceles triangle teeth, are proposed. For coding with light with right-angle triangle teeth, a general decoding method is given. In addition, an optimum sampling manner and the measurement error are discussed with respect to a special case. For coding with light with isosceles triangle teeth, a decoding method with three samples is given. In our laboratory, an experimental system was established, and experiments that verified the reliability of the proposed methods were performed. Experimental results typical of those obtained are given. We find that LCP is similar to the widely used phase-measuring profilometry but has a faster measuring speed.     

A fourier-transforming coded aperture

A Fourier-transforming coded aperture can be synthesized with a pair of two-dimensional detector arrays, each preceded by a properly designed sequence of two Gabor-zone plates. The coded image falling on one of the arrays corresponds to the cosine transform of the object. The coded image falling on the other array corresponds to the sine transform. Thus the Fourier transform of the object can be formed by using the first coded image as the real part, and the second coded image as the imaginary part, of the Fourier transform. Fourier-transforming coded apertures of this type are capable of producing better resolution than spatial-domain apertures. Although the system described in this article is specifically applied to a gamma-ray camera, such a system is generally applicable to a wide varioty of noncoherent imagers.©1993 John Wiley & Sons Inc     

Sensitivity of coded mask telescopes

Simple formulas are often used to estimate the sensitivity of coded mask x-ray or gamma-ray telescopes, but these are strictly applicable only if a number of basic assumptions are met. Complications arise, for example, if a grid structure is used to support the mask elements, if the detector spatial resolution is not good enough to completely resolve all the detail in the shadow of the mask, or if any of a number of other simplifying conditions are not fulfilled. We derive more general expressions for the Poisson-noise-limited sensitivity of astronomical telescopes using the coded mask technique, noting explicitly in what circumstances they are applicable. The emphasis is on using nomenclature and techniques that result in simple and revealing results. Where no convenient expression is available a procedure is given that allows the calculation of the sensitivity. We consider certain aspects of the optimization of the design of a coded mask telescope and show that when the detector spatial resolution and the mask to detector separation are fixed, the best source location accuracy is obtained when the mask elements are equal in size to the detector pixels.     

Upper bounds on the error probability of coded space?time block coded systems with diversity reception

New union bounds are derived for space-time block coded systems over Rayleigh fading channels. Both maximal ratio combining and generalised selection combining are considered as combining schemes at the receiver. The union bounds are easy to be evaluated using the transfer function of the code. Furthermore, the bounds are general to any coding scheme with a known weight distribution. Results show that the proposed union bounds are tight to simulation results for wide ranges of diversity orders and signal-to-noise ratio values.     

宏/子脉冲编码光子计数激光雷达

光子计数激光雷达因其极高的探测灵敏度在远距离目标探测领域有着非常重要的作用。针对远距离、高速度的目标,普通的光子计数激光雷达无法简单通过统计直方图获得有用的回波信息。为了解决这一问题,本文提出了一种基于宏/子脉冲编码的光子计数激光雷达,利用时移脉冲累加的方法提取子脉冲的飞行时间进而在一个宏脉冲内获得目标距离信息。建立了宏/子脉冲编码光子计数激光雷达的理论模型,对虚警概率和探测概率的影响进行了分析,并通过蒙特卡洛仿真和实验验证了其对远距离高速径向运动目标探测的有效性。

     

High frequency coded imaging system with RF

Coded transmission is an approach to solve the inherent compromise between penetration and resolution required in ultrasound imaging. Our goal was to examine the applicability of the coded excitation to HF (20-35 MHz) ultrasound imaging. A novel real-time imaging system for research and evaluation of the coded transmission was developed. The digital programmable coder- digitizer module based on the field programmable gate array (FPGA) chip supports arbitrary waveform coded transmission and RF echo sampling up to 200 megasamples per second, as well as real-time streaming of digitized RF data via a high-speed USB interface to the PC. All RF and image data processing were implemented in the software. A novel balanced software architecture supports real-time processing and display at rates up to 30 frames/sec. The system was used to acquire quantitative data for sine burst and 16-bit Golay code excitation at 20 MHz fundamental frequency. SNR gain close to 14 dB was obtained. The example of the skin scan clearly shows the extended penetration and improved contrast when a 35-MHz Golay code is used. The system presented is a practical and low-cost implementation of a coded excitation technique in HF ultrasound imaging that can be used as a research tool as well as to be introduced into production.     

Trellis coded modulation based distributed channel coding

A novel technique is described for distributed channel coding in wireless communication networks. The protocol is based on a block fading model of the multi-user uplink channel and on adapting multidimensional trellis coded modulation techniques to a coding theorem derived for the block fading channel. The coded modulation (CM) protocol is designed to optimise code performance, especially at high spectral efficiencies. The CM protocol is very simple to implement at the cooperating users. Complexity is completely transferred to the destination. The latency of the protocol is only one symbol. The CM protocol achieves full diversity order equal to the number of cooperating users and maximises coding gains by designing the code for the specific modulation used. We derive analytical results and present simulation results showing the benefits of CM protocol over other comparable schemes.     

Iterative reduced-state decoding for coded partial-response channels

The conventional iterative decoding based on the Bahl-Cocke-Jelinek-Raviv (BCJR) algorithm rises exponentially in terms of channel memory length. In this paper, we propose a low-complexity soft-input/soft-output (SISO) channel detector based on tentative hard estimates fed back from the outer decoder in the previous iteration. The computational complexity of the proposed detector is polynomial in terms of the channel memory length. To demonstrate the performance/complexity tradeoff of the proposed detector, we present simulation results for 9-tap, 11-tap, and 12-tap channels. We show that the proposed detector significantly reduces the computational complexity with only slight performance degradation compared to the full-complexity BCJR algorithm.     

High-resolution ultrasound displacement measurement using coded excitations

Resolution of displacement measurements based on ultrasound pulse-echo techniques is limited by the center frequency of the transmitted wave, echo sampling rate, quantization errors, and electronic noises in the measurement system. We developed a new method utilizing the clutter signal in coded excitations to determine the displacement of an object or a desired region of an object with much improved resolution. The method includes transmitting a pair of Golay complementary sequences, receiving echoes from the object or a region of the object, compressing the pulse, eliminating the main lobe, and determining the object displacement between the two transmissions from the residual clutter signal around the main lobe of the compressed pulse. Results of computer simulations showed that the new method improved the resolution by several orders of magnitude and was more robust to noise than traditional pulse-echo methods. The new method was also evaluated using an experimental ultrasound system (10 MHz center frequency, 100 MHz sampling rate, and 8-bit sampling precision). A high precision in the displacement measurement was achieved with a measurement error of ?5.76 nm ±36.27 nm (mean ± standard deviation). The method has the potential to be applied in biomedical and industrial measurements of distance, displacement, and thickness.