Transmit power and bits/channel use adaption in competitive cognitive radio networks

In this paper, we propose an optimization framework to determine the distribution of power and bits/channel use to secondary users in a competitive cognitive radio networks. The objectives of the optimization framework are to minimize total transmission power, maximize total bits/channel use and also to maintain quality of service. An upper bound on probability of bit error and lower bound on bits/channel use requirement of secondary users are considered as quality of service. The optimization problem is also constrained by total power budget across channels for a user. Simulating the framework in a centralized manner shows that more transmit power is required to allocate in a channel with higher noise power. However, allocation of bits/channel use is directly proportional to signal to interference plus noise power ratio. The proposed framework is more capable of supporting high bits/channel use requirement than existing resource allocation framework. We also develop the game theoretic user based distributed approach of the proposed framework. We see that user based distributed solution also follows centralized solution.     

Quantum Dialogue Based on Hypertanglement Against Collective Noise

The major problem faced by photons propagating through a physical channel is that of collective noise. This collective noise has the ability to reduce the number of quantum bits that are transmitted, thereby reduces the message fidelity. The traditional method of noise immunity is the use of entanglement purification, which consumes a lot of quantum resources in accomplishing the joint probability of noise immunity but does not guarantee accurate quantum dialog. In this paper, we investigate a new approach to quantum dialogue in which quantum information can be faithfully transmitted via a noisy channel. we constructs corresponding Decoherence Free Subspace(DFS), the quantum state after the change is in the maximally entangled state, so as to realize the fidelity of quantum dialogue model that can ensure the accuracy and noise resistance, and secret information exchange.     

时变信道下的被动时间反转扩频水声通信

本文研究了时变信道条件下采用被动时间反转的直接序列扩频水声通信方案。多通道被动时间反转可通过对信道多径进行时间、空间聚焦实现信道匹配,但低信噪比、时变特性造成的信道特性失配对被动时间反转处理的性能造成严重影响。在垂直阵接收的基础上,本文采用码片级信道估计获取水声信道特性并进行周期性更新,并采用已判决码元产生的扩频码片作为信道估计训练序列,结合应用稀疏信道估计算法抑制零值抽头上的估计噪声,从而可有效改善时变、低信噪比条件下的被动时间反转处理的时、空多径聚焦效果,提高扩频通信性能。通过湖试实验比较了采用稀疏信道估计、传统信道估计算法的时反扩频接收机,以及经典直扩接收机的通信性能,实验结果表明：本文方案可在低信噪比获得较好的性能,并有效抑制时变信道对时反扩频通信性能的影响。     

离散空间上的最小能量框架及其在矩形脉冲信号去噪中的应用研究

最小能量(小波)框架在信号处理领域有着广泛的应用前景,但目前只能应用在连续信号上.为解决这一问题,给出了离散信号空间上的最小能量框架的定义,并证明了它所具备的一些优良性质.在实际应用中,针对通信领域中的受加性高斯白噪声污染的二进制矩形脉冲信号提出一个新的去噪算法,利用离散空间上一个最小能量框架对接收波形的抽样离散数列进行去噪工作,获得了较好的处理效果.仿真结果表明,如果利用该算法对接收波形进行去噪预处理,则接收机可以降低误码率,在信噪比4 dB 处获得了3.4 dB的性能增益. 关键词： 离散信号空间 最小能量(小波)框架 二进制矩形脉冲信号 去噪     

基于开关电容阵列ASIC芯片的多通道波形数字化系统设计

基于开关电容阵列（SCA）技术可以实现超高速的波形数字化。本研究是基于实验室设计完成的FEL_SCA芯片进行8通道2 Gsps的波形数字化模块的设计,电路的配置和读出控制功能集成在单个FPGA中完成,此外该模块还包含SDRAM缓存及USB接口。目前已在实验室环境下对其进行了直流电压测试、瞬态波形测试和带宽测试,测试结果表明,在FEL_SCA芯片的输入动态范围100 mV~1 V之间,本波形数字化模块的INL好于1%,通道的RMS噪声约为1.76 mV,带宽约为450 MHz,达到设计目标。Switched Capacitor Arrays (SCAs) can be employed to achieve high speed waveform digitization. In this paper, we designed an 8-channel 2 Gsps waveform digitization module using four SCA chips named FEL_SCA which was designed in our laboratory. In this module, we used a FPGA device for data readout and circuit configuration. Besides, a 128 Mb SDRAM and USB interface were integrated in this module. We have also conducted DC voltage tests, transient tests and bandwidth tests on this module. The results indicate that in the signal voltage range 100 mV~1 V, the INL is better than 1%, the RMS noise is about 1.76 mV and the -3 dB input bandwidth is 450 MHz.     

Noise immunity of a combined hydroacoustic receiver

A statistical analysis of the noise immunity of a combined receiver is performed for the observation of a fluctuating tone signal against the background of underwater dynamic noise. The analysis is based on the experimental data obtained in deep ocean with the use of two four-component combined hydroacoustic receivers positioned at depths of 150 and 300 m. Theoretical expressions are obtained for the signal-to-noise ratio of a combined receiver, for reciprocal spectral levels of the signal and noise in both narrow and wide frequency bands. The definition of the combined receiver gain is introduced in terms of the functions of a common single-point coherence for the acoustic pressure and the particle velocity in an acoustic wave. According to the experimental data obtained, in the case of multiplicative processing, the maximal gain in the signal-to-noise ratio of a combined receiver, as compared to a hydrophone-based square-law detector, can reach 15–16 dB for the horizontal channel and 30 dB for the vertical channel of the combined receiver in the case of the compensation of opposing flows of the signal and noise energy.     

Estimation of the detection range of a hydroacoustic system based on the acoustic power flux receiver

Approaches to estimating the detection range of systems based on vector receivers are considered. The approaches rely on a detailed analysis of the process of signal’s acoustic power flux formation in the presence of ambient sea noise and uncover the signal information parameters at the receiver output that provide the required statistically confident range of weak signal detection under these conditions. Based on the sonar equations and the known fundamental relationships between the outputs of a pressure receiver and a vector receiver for signal and noise, estimates of the maximum possible gain in the detection range of an acoustic power flux receiver are considered as a function of anisotropy of the ambient noise field in the area.     

Limitations Due to Er-Doped Optical Amplifier Noise and Stimulated Raman Scattering in Optic-Frequency Division Multiplexed Communications

In this paper, system limitations of an optic-frequency division multiplexed commu nication link are evaluated due to stimulated Raman scattering and noise in erbium-doped optical fiber amplifiers. It is shown that the product of the number of optical amplifiers and the gain (i.e., total gain) are limited by a factor that depends upon the number of channels, channel spacing and required signal-to-noise ratio (bit-error-rate), etc. Thus an indefinite increase in the number of amplifiers and or amplifier gain may not extend the repeaterless distance significantly while keeping the bit-error-rate above a minimum level. Numerical results show that appropriate choice of optical amplifier gain can improve the bit-error-rate of the worst effected channel without adding significant requirements on the receiver. However, large changes in the amplifier gain cannot be allowed if the receiver dynamic range is to be kept small.     

Gain Characterization of All-Optical Gain-Clamped PDFFA for WDM Networks Using the Feedback Theory

Using feedback theory, we analyze the gain of an all-optical gain-clamped praseodymium-doped fluoride fiber amplifier (AOGC PDFFA) for eight-channel multiwavelength operation. We demonstrate by numerical simulation that gain stabilization is achieved when the open-loop gain is higher than the feedback path attenuation. If this condition is fulfilled, the gain stabilizes to a value equal to the feedback path attenuation and is not influenced by the pump power, input signal power, number of channels, doped fiber length, or any other doped fiber parameter. In our setup the AOGC PDFFA noise figure is 0.12 dB lower than the open-loop PDFFA noise figure.     

A CMOS Low-Power Optical Front-End for 5 Gbps Applications

In this paper, a new low-power optical receiver front-end is proposed in 90 nm CMOS technology for 5 Gb/s AApplications. However, to improve the gain-bandwidth trade-off, the proposed Trans-Impedance Amplifier (TIA) uses an active modified inverter-based topology followed by a common-source amplifier, which uses active inductive peaking technique to enhance the frequency bandwidth in an increased gain level for a reasonable power consumption value. The proposed TIA is analyzed and simulated in HSPICE using 90 nm CMOS technology parameters. Simulation results show a 53.5dBΩ trans-impedance gain, 3.5 GHz frequency bandwidth, 16.8pA/√Hz input referred noise, and 1.28 mW of power consumption at 1V supply voltage. The Optical receiver is completed using three stages of differential limiting amplifiers (LAs), which provide 27 dB voltage gain while consume 3.1 mW of power. Finally, the whole optical receiver front-end consumes only 5.6 mW of power at 1 V supply and amplifies the input signal by 80 dB, while providing 3.7 GHz of frequency bandwidth. Finally, the simulation results indicate that the proposed optical receiver is a proper candidate to be used in a low-power 5 Gbps optical communication system.     

Improved Resolution and Signal-to-Noise Ratio in MRI via Enhanced Signal Digitization

The high frequencyk-space data in magnetic resonance imaging is often poorly reproduced due to the finite dynamic range of an analog-to-digital converter. The magnitude of this digitization error can equal and even exceed the magnitude of the thermal noise. Under such conditions, attempts to increase image signal-to-noise ratio via signal averaging meet with diminishing success. Because the relative size of the digitization error increases at higher spatial frequencies, a reduction in image resolution is incurred as well. By adjusting the level of the analog signal sampled by the analog-to-digital converter during the course of an imaging experiment, the magnitude of the digitization artifact can be greatly reduced. The results of simulations and imaging experiments are presented which demonstrate that this strategy improves both the signal-to-noise ratio and resolution of magnetic resonance images.     

Chaotic digital communication by encoding initial conditions

We investigate the possibility to improve the noise performance of a chaotic digital communication scheme by utilizing further dynamical information. We show that by encoding the initial information of the chaotic carrier according to the transmitting bits, extra redundance can be introduced into the segments of chaotic signals corresponding to the consecutive bits. Such redundant information can be exploited effectively at the receiver end to improve the noise performance of the system. Compared to other methods (e.g., differential chaos shift keying), straightforward application of the proposed modulation/demodulation scheme already provides significant performance gain in the low signal-to-noise ratio (SNR) region. Furthermore, maximum likelihood precleaning procedure based on the Viterbi algorithm can be applied before the demodulation step to overcome the performance degradation in the high SNR region. The study indicates that it is possible to improve the noise performance of the chaotic digital communication scheme if further dynamics information is added to the system.     

Noise statistics in optically preamplified differential phase-shift keying receivers with Mach-Zehnder interferometer demodulation

We report an analysis of the noise statistics for an optically preamplified differential phase-shift keying (DPSK) receiver with balanced and single-port detections. It is found that identical signal-amplified spontaneous emission beating noise exists for bits 1 and 0 in DPSK balanced detection. It is also revealed that the bit error ratio (BER) of a DPSK receiver with balanced detection has no direct relation to the conventional Q factor. Moreover, an analytic BER expression for the DPSK balanced detection receiver is presented.     

A New Type of Digital Compensatory Millimeter Wave Radiometer

System gain and receiver noise are two main impact factors of total power millimeter wave (MMW) radiometer output. In this paper, a new method of using software to compensate system gain and receiver noise fluctuation is introduced. This method can keep the long-term stability and accuracy of the radiometer. At the same time, only one matching load is used as the reference source, which can prevent the trouble caused by using two cold and hot calibration sources in ground-based or airborne radiometer. The preliminary experiment proves the efficiency of the method.     

一种铷原子频标频率综合器新方案的设计与实现

数字化和小型化是铷原子频标（RAFS）发展的重要方向．在传统铷原子频标电路中,6 840 MHz微波信号与频率综合器产生的5.312 5 MHz信号进行混频,得到用于激励铷原子跃迁的6 834.687 5 MHz微波探寻信号．早期铷频标的频率综合器大量使用了分立的模拟器件,数字化程度低、参数优化工作繁杂、电路体积较大．目前常用直接数字频率合成器（DDS）方案直接产生5.312 5 MHz信号,但这种数字电路方案通常需要对10 MHz信号进行倍频,它存在频谱纯度较低、相位噪声高等缺点．本文介绍一种产生5.312 5 MHz信号的频率综合器解决方案,这种设计方案在应用DDS器件时无需使用10 MHz倍频电路,它具有频谱纯度较高、相位噪声低、输出频率和相位可调等优点．     

Effective noise estimation and filtering from correlated multiple-coil MR data

Modern magnetic resonance (MR) imaging protocols based on multiple-coil acquisitions have carried on a new attention to noise and signal statistical modeling, as long as most of the existing techniques for data processing are model based. In particular, nonaccelerated multiple-coil and GeneRalized Autocalibrated Partially Parallel Acquisitions (GRAPPA) have brought noncentral-χ (nc-χ) statistics into stake as a suitable substitute for traditional Rician distributions. However, this model is only valid when the signals received by each coil are roughly uncorrelated. The recent literature on this topic suggests that this is often not the case, so nc-χ statistics are in principle not adequate. Fortunately, such model can be adapted through the definition of a set of effective parameters, namely, an effective noise power (greater than the actual power of thermal noise in the Radio Frequency receiver) and an effective number of coils (smaller than the actual number of RF receiving coils in the system). The implications of these artifacts in practical algorithms have not been discussed elsewhere. In the present paper, we aim to study their actual impact and suggest practical rules to cope with them. We define the main noise parameters in this context, introducing a new expression for the effective variance of noise which is of capital importance for the two image processing problems studied: first, we propose a new method to estimate the effective variance of noise from the composite magnitude signal of MR data when correlations are assumed. Second, we adapt several model-based image denoising techniques to the correlated case using the noise estimation techniques proposed. We show, through a number of experiments with synthetic, phantom, and in vivo data, that neglecting the correlated nature of noise in multiple-coil systems implies important errors even in the simplest cases. At the same time, the proper statistical characterization of noise through effective parameters drives to improved accuracy (both qualitatively and quantitatively) for both of the problems studied.     

The impact of ADC nonlinearity in a mixed-signal compressive sensing system for frequency-domain sparse signals

Compressive sensing (CS) holds new promises for the digitization of wideband frequency-domain sparse signals at sub-Nyquist rate sampling without compromising the reconstruction quality. In this paper, the impact of ADC nonlinearity in a CS receiver for frequency-domain sparse signals is investigated. In a mixed-signal CS system, signals are randomized before sampling. The signal spectrum at each building block in the mixed-signal CS system is analyzed and compared to a conventional Nyquist-rate sampling system. It is shown that the signal randomization in a mixed-signal CS system is able to spread the spurious energy due to ADC nonlinearity along the signal bandwidth, rather than the concentration of harmonic distortion on a few frequencies as it is the case for a conventional ADC. As a result, this paper shows that a significant ADC SFDR (Spurious Free Dynamic Range) improvement is achieved in a CS receiver when processing sparse signals. Simulation results are reported which are in good agreement with the qualitative analysis.     

A novel multilevel coding technique for high speed optical fiber communication systems

This paper delineates a novel coding technique, a combination of coding and multiplexing technique, known as mapping multiplexing technique (MMT). A mapping algorithm is used to multiplex four channels, each of which running at 10 Gbit/s. Up to four bits per symbol at a symbol rate of 10 Gboud was successfully transmitted over a single wavelength. Compare to the conventional return to zero (RZ) and none-return to zero (NRZ)-time division multiplexing (TDM) more than 75% and 50% reduction in the spectral width are achieved, respectively. Calculated chromatic dispersion tolerance of ±130 ps/nm is achieved for the 40 Gbit/s MMT transmission system at the expense of ∼2 dB degradation in the receiver sensitivity (compared to NRZ) due to an increase in the number of levels and in the signal dependency of signal-spontaneous beat noise. In comparison with conventional 4-ary system, the proposed system depicts ∼6.5 dB improvement in terms of receiver sensitivity.     

Advanced coupled PHY and MAC scheduling in IEEE 802.16e WiMAX systems

In this paper we address some issues related to the mutual influence between the PHY layer building blocks (FEC blocks) and the MAC level allocations in IEEE 802.16e /WiMAX systems, in order to increase the overall PHY and MAC combined efficiency. In these systems transmissions are carried in physical Bursts, both on the Uplink and Downlink channels. Bursts are composed of slots, which are grouped into FEC blocks. The number of slots in a Burst determines the length and number of the FEC blocks. The FEC blocks have a direct influence on the probability that bits are received successfully, and thus on the Burst Goodput, which is defined as the ratio between the average number of bits in the Burst that arrive successfully at the receiver, to the Burst length. In this paper we address a new coupled PHY and MAC scheduling methodology by investigating the relationship between the Burst length and its Goodput in different Modulation/Coding schemes, and investigate, given a Burst, the most efficient such scheme. The outcomes of the paper are twofold: first we show that the Goodput of a Burst is almost not dependent on its length. Second, we show that in most cases, the most efficient Modulation/Coding scheme is the one that enables us to transmit the largest number of bits in a Burst. However, there are a few cases where this is not the case. We show these cases in the paper.     

Fundamental limit to linear one-dimensional slow light structures

Using a new general approach to limits in optical structures that counts orthogonal waves generated by scattering, we derive an upper limit to the number of bits of delay possible in one-dimensional slow light structures that are based on linear optical response to the signal field. The limit is essentially the product of the length of the structure in wavelengths and the largest relative change in dielectric constant anywhere in the structure at any frequency of interest. It holds for refractive index, absorption, or gain variations with arbitrary spectral or spatial form. It is otherwise completely independent of the details of the structure's design, and does not rely on concepts of group velocity or group delay.