LED可见光模拟通信实验系统的设计

基于可见光通信原理设计了LED可见光模拟通信实验系统,该系统实现了短距离无线传输模拟信号。系统包括三个主要模块,分别为电源、发射端、接收端。实验系统的发射端采用大功率10W LED灯作为信号源,接收端采用高精度TDA2030音频专用功率放大器和20000HZ低通滤波器,用以提升该实验系统的传输距离和效果,经测试该系统可传输300—15000HZ的模拟信号,传输距离可达5m以上,接收到的信号强度大且无明显失真。     

Precoded Modulo-Precanceling Systems for Simulcasting Analog FM and Digital Data

We present techniques for simulcasting low-power digital data and analog FM over fading channels. Our methods have strong connections to what are referred to as dirty paper coding techniques in that a low-power digital data signal is modulo-added to the host analog FM signal. Due to the low power levels of the digital data and the suppression capability of analog FM, a standard analog FM receiver can be used to reliably recover the analog audio signal. We develop digital receivers that work reliably over fading channels given imperfect channel state information. Spreadresponse precoding is exploited to not only provide rate-1 temporal diversity benefits, but also to simplify the design of the modulo-precanceler and the receiver. Our theoretical and simulation-based performance analysis of the digital receivers and our MSE-based analog FM distortion analysis suggest that precoded modulo-precanceling schemes provide substantially higher data rates than existing precanceling strategies at the cost of transmission delay and transmitter and receiver complexity. The systems we present are also readily compatible with conventional channel coding techniques as well as with analog FM postcancelers, which can improve the digital receiver bit-error-rate performance at the expense of receiver complexity.     

基于移动Agent平台的多媒体无线情景仿真

在无线多媒体通信系统中,视频信源在发送端按照一定的编码方式进行编码,形成视频帧,然后在网络层和传输层封装成IP数据包,经过无线信道传输到达接收端,在接收端进行解包和恢复,得到视频帧,再形成重建后的视频流。在此过程中,无线信道的传输特性会影响到视频的传输质量。文中在利用Agent平台的基础上,综合NS2仿真工具,建立研究多媒体信息在无线网络中的传输平台。仿真结果表明,由于无线信道特性的不理想,在接收端恢复视频信息与视频信源相比较,会出现一定的失真     

Fully integrated W-CDMA IF receiver and IF transmitter including IFsynthesizer and on-chip VCO for UMTS mobiles

A fully integrated, dual intermediate frequency (IF) receiver and an IF transmitter, each with on-chip IF synthesizer, for use in third-generation wide-band code division multiple access (W-CDMA) mobiles has been implemented in a standard, high-frequency, Si-bipolar process with an f_T of 25 GHz. The IF receiver (318 MHz) and IF transmitter (285 MHz) include a complete phase-locked loop (PLL) and on-chip voltage-controlled oscillator (VCO) with integrated varactors and transformers. The VCOs are used for on-chip local oscillator (LO) generation and operate at four times IF, 1272 MHz and 1140 MHz, for Rx and Tx, respectively. Fully integrated, active, analog base-band filters further increase functionality and integration level. In the receiver, a channel select filter, composed of a fifth-order Chebyshev lowpass filter and a first-order all-pass filter, is implemented. In the transmitter, a fifth-order Butterworth low-pass filter functions as a reconstruction filter. Both devices operate on 2.7-3.3-V supply. The designs comply with ARIB W-CDMA and UMTS standards. Each chip is mounted in a small outline, 32-pin, leadless surface mount package     

Frequency-Division Bidirectional Communication Over Chip-to-Chip Channels

Frequency division multiple access is applied to bidirectional communication over chip-to-chip links. Frequency division is implemented by dividing the spectrum into low-frequency (dc) and high-frequency (ac) bands using a simple LC filter. The nonidealities that this filter introduces are compensated for with a transmitter/receiver pair that can recover signals in both bands. The receiver uses a dual-path topology that includes hysteresis to recover data from a signal with no dc content. The transmitter is a 6-tap (FIR) pre-emphasis equalizer with variable tap spacing. In simulation, the transmitter and receiver simultaneously communicate error-free at 8 Gb/s over the ac channel and at 500 Mb/s over the dc channel. Measurements shows that the ac and dc signals can be individually recovered and that the two signals occupy distinct frequency bands.      

神经信号遥测模块及电路的设计与实现

介绍了一种可用于植入式中枢神经恢复系统遥测模块的设计与实现.模块由信号发射电路和接收电路组成,发射电路完成信号的多路选择、模/数转换、编码、调制和功率放大;接收电路完成放大、解调、解码、数/模转换和滤波等功能.电路工作于3.3 V,正常工作时发送端功耗小于110 mW,接收端功耗小于100 mW,有效传输距离大于30 m.根据神经信号的特点,采样率为50 kHz,数据传输速率为1 Mbit/s.收发电路采用印刷电路板(PCB)实现,工作于2.45 GHz的ISM频段.测试结果表明,该模块能够很好的实现神经信号的遥测功能.     

Improved auxiliary particle filter‐based synchronization of chaotic Colpitts circuit and its application to secure communication

In this paper, we propose a synchronization scheme based on an improved auxiliary particle filter (IAPF) for chaotic Colpitts circuit and conduct an experimental study on the synchronization performance with application to secure communications. Specifically, with the synchronization scheme, when the chaotic signals generated by an analog Colpitts circuit are transmitted through a nonideal channel, the distorted signals are processed digitally by the novelly designed IAPF at the receiver, in order to obtain the synchronized signals of the transmitter circuit. Experimental results indicate that synchronization can be achieved over both the additive white Gaussian noise channel and the multipath fading channel with low signal‐to‐noise ratio, even if there exist severe circuit parameter mismatches between the transmitter and the receiver. Furthermore, a chaos‐masking secure communication system is constructed and verified over both the additive white Gaussian noise channel and the multipath fading channel, and the bit error rate is evaluated versus different signal‐to‐noise ratios and symbol periods. It is shown that the achievable bit error rate can reach the order of magnitude of 10 ^{− 4} without error correction coding techniques. In addition, security analysis demonstrates that the proposed chaotic secure communication system is resistant to the brute‐force attack. Copyright © 2013 John Wiley & Sons, Ltd.     

Video coding for OFDM systems with imperfect CSI: A hybrid digital–analog approach

Performance of an orthogonal frequency division multiplexing (OFDM) system is greatest when the exact channel state information (CSI) is used for transmitter rate control and power allocation. However, in real systems CSI can only be approximately known. Moreover, in video communication, it can be difficult to use any CSI for rate control of a video codec if the channel changes significantly during a group of pictures coded jointly, such as when the receiver is moving. We address this issue through a hybrid digital–analog (HDA) coding system where a standard video codec is used to generate a fixed-rate base layer upon which the analog quantization error is superimposed as a refinement layer. The system adapts to channel variations by proper transmit-power allocation between digital and analog components and across OFDM subcarriers, based on CSI. We present a power allocation scheme for this system which explicitly takes into account the imprecise nature of the available CSI. Experimental results obtained with simulated OFDM channel traces show that proposed scheme is able to achieve a much better quality-vs-reliability trade-off in video transmission, compared to the best known digital-only and analog-only alternatives.     

A data broadcasting system expanding the information capacity of existing analog communication systems

This paper presents the physical layer functions powering a new wireless data broadcasting system over analog television signals, referred to as dNTSC system (for data over National Television System Committee (NTSC) standard). Novel data insertion techniques at the transmitter and data extraction techniques at the receiver allow data rates of 1-4 Mbps that coexist with existing analog transmission but do not adversely affect normal television reception. Novel digital signal processing (DSP) techniques include a video abatement system that reduces data-to-video crosstalk for unimpaired analog television reception, adaptive nonlinear amplifier compensation, and advanced video cancellation and adaptive data equalization methods in the receiver. An analysis of the dNTSC system through noisy, multipath channels reveals the subtleties of the dNTSC system, compared to a conventional, dedicated digital communication link.     

A Single-Chip Dual-Band CDMA2000 Transceiver in 0.13 μm CMOS

A single-chip, dual-band transceiver for CDMA2000 is presented. The design supporting the North American cellular and PCS bands features a complete zero-IF receiver, a direct-conversion transmitter and two fully integrated synthesizers with VCOs. The analog receiver front-end comprises two self-matched wideband LNAs, a highly linear demodulator and a third-order baseband filter. In a test version I/Q ADCs and a digital front-end (DFE) to provide channel and matched filtering are included to demonstrate the performance of a fully integrated analog/digital line-up. Measured maximum SNR values of 23 dB and 25 dB for PCS and Cell bands, respectively, are achieved. The transmitter comprises baseband buffers and filters, an I/Q-modulator and separate output drivers for each band. An analog gain control (AGC) for realization of a dynamic range is implemented and a maximum output power of at a total CDG4 urban current of 34 mA is achieved for the PCS band. Measured ACPR1 and values are and 0.998 for the Cell band and and 0.995 for the PCS band, respectively. The chip is fabricated in a 0.13 RF-CMOS process, occupies a die size of 8.4 and operates with a 2.5 V supply.     

WaveVideo – An integrated approach to adaptive wireless video

The transmission of wireless video in acceptable quality is only possible by following an end-to-end approach. WaveVideo is an integrated, adaptive video coding architecture designed for heterogeneous wireless networks. It includes basic video compression algorithms based on wavelet transformations, an efficient channel coding, a filter architecture for receiver-based media scaling, and error-control methods to adapt video transmissions to the wireless environment. Using a joint source/channel coding approach, WaveVideo offers a high degree of error tolerance on noisy channels, still being competitive in terms of compression. Adaptation to channel conditions and user requirements is implemented on three levels. The coding itself features spatial and temporal measures to conceal transmission errors. Additionally, the amount of introduced error-control information is controlled by feedback. The video stream coding, applied to multicast capable networks, can serve different user's needs efficiently at the same time by scaling the video stream in the network according to receivers' quality requirements. The WaveVideo architecture is unique in terms of its capability to use QoS mapping and adaptation functions across all network nodes providing the same uniform interface.     

Postcanceling techniques for simultaneous broadcasting of analog FM and digital data

We consider simultaneous broadcasting of low-power digital data and analog FM and present reliable receivers for the digital data. Due to the relatively low power level of the digital data and the interference suppression capability of analog FM, standard analog FM receivers can reliably recover the analog FM audio signal. To recover the digital data, an extended Kalman filter front end is developed that exploits the capture capability of analog FM to reconstruct and postcancel the analog FM component from the received composite signal. Simulations are conducted with artificial analog FM signals, suggesting that postcanceling schemes can provide higher data rates than their precanceling counterparts, at a lower transmission delay penalty but higher digital receiver complexity. For analog FM to digital signal power level ratios in the range of 30-50 dB, the postcanceler digital signal recovery appears fairly robust, providing digital signal-to-noise ratios of 2-7.5 dB. The corresponding uncoded bit error rates strongly depend on the power level difference between the host analog FM and the digital data signal. In particular, at 260 kb/s and E/sub b//N/sub o/=10 dB they range between 1% to about 15%, and can be reduced to acceptable levels using standard channel coding techniques.     

Approaching MIMO-OFDM Capacity with Per-Antenna Power and Rate Feedback

This paper presents power-efficient transmission schemes for the multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) block-fading channel under the assumption that the channel during each fading block is known perfectly at the receiver, but is unavailable at the transmitter. Based on the well-known vertical Bell Labs layered space-time (V-BLAST) architecture that employs independent encoding for each transmit antenna and successive decoding at the receiver, this paper presents a per-antenna-based power and rate feedback scheme, termed the "closed-loop" V- BLAST, for which the receiver jointly optimizes the power and rate assignments for all transmit antennas, and then returns them to the transmitter via a low-rate feedback channel. The power and rate optimization minimizes the total transmit power for support of an aggregate transmission rate during each fading block. Convex optimization techniques are used to design efficient algorithms for optimal power and rate allocation. The proposed algorithms are also modified to incorporate practical system constraints on feedback complexity and on modulation and coding. Furthermore, this paper shows that the per-antenna-based power and rate control can be readily modified to combine with the conventional linear MIMO transmit preceding technique as an efficient and capacity-approaching partial-channel-feedback scheme. Simulation results show that the closed-loop V-BLAST is able to approach closely the MIMO-OFDM channel capacity assuming availability of perfect channel knowledge at both the transmitter and the receiver.     

A Technique of Modulating Pulsed Semiconductor Lasers

This paper gives details of the pulse-position modulation technique as applied in the case of a pulsed room-temperature-operated GaAs laser diode for communication purposes. The input analog signal is converted into a digital format and information transmission takes place through the laser pulses occurring at different positions in time. Special care is taken to synchronize the receiver with the transmitter. At the receiver the analog information is reconstructed. The technique can be incorporated in the development of a short-haul point-point-to-point voice communication system using the laser diode.     

Simultaneous broadcasting of analog FM and digital audio signals bymeans of adaptive precanceling techniques

A method for broadcasting digital audio simultaneously with existing analog frequency modulation (FM) radio is presented. The method is based on precomputing the response of the host analog FM signal at the digital receiver and precanceling it at the transmitter. As a result, the digital transmission is free from interference from analog FM. We select the rate and power level of the digital transmission in a manner that the interference the digital data incur on the analog FM signal remains at acceptably low levels. The digital transmission is based on adaptive orthogonal frequency-division multiplexing (OFDM) (adaptive multicarrier). The frequencies and number of carriers of the digital multicarrier modem are judiciously selected in a time-varying fashion so as to cause a negligible distortion in a standard receiver for analog FM. Simulations based on conservative nonoptimized signal design indicate that data rates up to about 130 kb/s inside the 200-kHz FM channel are achievable for acoustic test signals. We present a number of numerical examples where the average digital data use up to 50% of the 200-kHz power spectrum with digital signal power levels 25-35 dB below the analog signal. Due to the resulting variable-rate digital transmission, a control channel is required. A method of precanceling with multiple orthogonal direct-sequence spread-spectrum schemes is also presented     

Broadband MIMO-OFDM wireless communications

Orthogonal frequency division multiplexing (OFDM) is a popular method for high data rate wireless transmission. OFDM may be combined with antenna arrays at the transmitter and receiver to increase the diversity gain and/or to enhance the system capacity on time-varying and frequency-selective channels, resulting in a multiple-input multiple-output (MIMO) configuration. The paper explores various physical layer research challenges in MIMO-OFDM system design, including physical channel measurements and modeling, analog beam forming techniques using adaptive antenna arrays, space-time techniques for MIMO-OFDM, error control coding techniques, OFDM preamble and packet design, and signal processing algorithms used to perform time and frequency synchronization, channel estimation, and channel tracking in MIMO-OFDM systems. Finally, the paper considers a software radio implementation of MIMO-OFDM.     

DTV repeater emission mask analysis

Terrestrial digital television (DTV) requires careful planning in the allocation of RF channels, especially during the transition period when intermixing both analog and digital signals in the same coverage area. One important issue to consider is adjacent channel interference, which limits the number of RF channels utilized in any given area. This issue is important in the deployment of not only full service stations, but also of secondary stations such as translators, on-channel repeaters, and low power television stations. Full service stations have FCC rules that limit the amount of adjacent channel splatter by requiring the splatter energy to remain below a rigid emission mask. Currently there are no FCC rules for translators and low power television stations. The paper discusses typical DTV transmitter splatter sidebands and their causes, as well as specific methods for interference analysis from adjacent channel DTV splatter into adjacent NTSC or DTV signals. Two rigid emission masks ("simple" and "stringent") are proposed and evaluated. Several filter designs are computer simulated and analyzed for minimizing adjacent channel splatter interference as well as in-band DTV signal degradation. Linear pre-correction techniques are analyzed for various length (15-tap and 31-tap) transversal filter equalizers. The simulation is verified by measuring and evaluating DTV system performance for two hardware band-pass filters individually placed at the output of a low power (30 W average) transmitter.     

Robust image transmission over energy-constrained time-varyingchannels using multiresolution joint source-channel coding

We explore joint source-channel coding (JSCC) for time-varying channels using a multiresolution framework for both source coding and transmission via novel multiresolution modulation constellations. We consider the problem of still image transmission over time-varying channels with the channel state information (CSI) available at (1) receiver only and (2) both transmitter and receiver being informed about the state of the channel, and we quantify the effect of CSI availability on the performance. Our source model is based on the wavelet image decomposition, which generates a collection of subbands modeled by the family of generalized Gaussian distributions. We describe an algorithm that jointly optimizes the design of the multiresolution source codebook, the multiresolution constellation, and the decoding strategy of optimally matching the source resolution and signal constellation resolution “trees” in accordance with the time-varying channel and show how this leads to improved performance over existing methods. The real-time operation needs only table lookups. Our results based on a wavelet image representation show that our multiresolution-based optimized system attains gains on the order of 2 dB in the reconstructed image quality over single-resolution systems using channel optimized source coding     

Mixed BB-IF predistortion of OFDM signals in non-linear channels

It is well known that power amplifier induced non-linear distortions produce a signal spectral regrowth at the IF transmitter output of digital radio communication systems. This effect is responsible for both adjacent channel interference and BER degradation. Signal predistortion is a technique that counteracts such phenomena. Technological advances in the last decade, renewing the interest in this technique, led to the realization of digital baseband (BB) predistorters that overcome the performance of the existing analog IF (intermediate frequency) ones. However, the substitution of an analog IF predistorter with a digital BB one forces one to partially redesign the system architecture. An alternative approach is proposed in this paper, based on digital and analog techniques, which combines the precision of the digital BB solution with the practicality of an IF architecture. This solution is particularly interesting to substitute an old analog IF predistorter simply plugging-in the new digital one, without further changes in the transmitter architecture. Critical aspects, predistortion algorithms and simulation performance are presented with respect to a digital video broadcasting system which is based on an OFDM modulation and is very sensitive to non-linear distortions because of the adopted multicarrier modulation