Simulcast packet transmission in ad hoc networks

In previous work, unequal error-protection techniques have been applied to improve the throughput of a wireless communication system in which a transmission is received by several radios with different capabilities. For instance, these capabilities may correspond to differences in path loss, fading, or interference. By taking advantage of the broadcast nature of the channel, additional messages for the more-capable receivers can be included on transmissions to the less-capable receivers at very little cost (in terms of required energy at the transmitter or error probabilities at the receivers). This technique has been termed simulcasting or multicast signaling. In this paper, we consider the use of these techniques in an ad hoc network. These techniques impact the link throughput, end-to-end throughput, and network connectivity. We investigate how the choice of parameters for the simulcasting technique affects these network performance metrics. The results indicate that a properly chosen simulcasting technique can improve the link and end-to-end throughput in wireless ad hoc networks with only a slight degradation in other metrics, such as network connectivity.     

语音信号光纤发射机的设计

使用光纤发射机进行语音通信可以开发具有极高抗干扰能力的新产品。介绍了语音光纤发射机的结构设计原理,提出了设计的方法,并给出了以语音编码芯片AD74111和发光器件HFBR-1414为核心芯片的电路设计过程。设计实例适合用于工作环境复杂的语音通信系统。     

On the outage probability in single frequency networks for digitalbroadcasting

The new digital modulation schemes (OFDM) proposed for broadcasting of sound and television allow for the use of simulcasting, i.e., letting all transmitters in a radio network transmit on the same frequency. Such single-frequency networks (SFNs) have the potential of providing good coverage and very good frequency economy in wide-area (nationwide) applications. An OFDM-based SFN is analyzed with respect to its coverage properties. The network performance is measured by the outage probability and frequency economy. Both wide and local area systems are considered. Results show that in wide-area networks, very low outage probabilities may be achieved with very modest transmitter powers. The main reason for this is the inherent diversity, the efficiency is of which is primarily dependent on the transmitter density. However, in local area systems with only a few transmitters in each region, the performance is shown to drop drastically, mainly due to the low degree of diversity. This work implies that good network planning results in low-power, closely spaced transmitters     

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.     

Performance Analysis of a Sectorized Distributed Antenna System with Reduced Co-Channel Interference

1IntroductionThe next generation mobile communication systemissupposedto provide high data rate services such as Inter-net access and multi media applications whichare morelikelyto be affected by Inter-Symbol-Interference(ISI)inwireless multi-path fading …     

Quadrature Amplitude Modulated Microwave Signal Generation Using a Single Electro-Optic Nd:YVO $_{4}$ Solid-State Laser

In this communication a new optical scheme is described that is able to generate quadrature amplitude modulation RF signals, with exceptional flexibility and tunability. The device readily implements a channel-adaptive transmitter for wireless communications with multiple modulation formats and radio bands. Due to the optical generation, the transmitter is particularly ideal for radio over fiber applications.     

Transmission of block turbo coded digital audio over FM-SCA

In this paper, an efficient coded scheme for transmitting digital audio over the existing FM channel, by multiplexing it with the baseband FM signal, is described. Transmission of multiplexed signals in the FM baseband called FM-SCA (subsidiary communications authorization) has been previously used for low quality analog content and some low rate digital content. The investigated scheme opens up the possibility of achieving CD quality audio over FM-SCA by enabling high bitrate transmission using MPEG-I layer 3 and MPEG-AAC audio coding for the digital audio. These schemes provide CD quality audio at or below 128 kbps, MPEG-AAC being able to do so at rates as low as 96 kbps. Block turbo codes (BTC), which offer near Shannon's limit performance with relatively low hardware complexity requirements, provide the error protection. Block turbo codes have been shown to be particularly effective for high coding rates. The system uses OFDM in conjunction with 8PSK/16PSK to modulate the digital bitstream and fit it in the 44 kHz (54 to 98 kHz) band available in the FM baseband. Simulation results show an optimal system configuration for digital audio transmission in FM-SCA.     

电台发射台改进设计

针对电台发射台搬迁对发射台的建立做出了改进设计,发射台播出体系由拉线塔、中波发射机、音频切换和监控、光缆、数字微波、UPS、发电机组、综合布线和安全监控、测试仪器、卫星地面站、调频发射塔、调频发射机、天馈系统、应急直播室等14部分组成.     

Methodology and computer tools to semi-automate assessments of shortwave broadcast coverage resulting from multiple transmissions

A computer-assisted methodology, developed for using a point-to-point ionospheric propagation and communications system performance model to assess shortwave broadcast coverage, is presented. The listening area is approximated by a set of geographic coordinates (test points), and the required power gain (RPRG) for the link from each transmitter site to each test point is computed using the IONCAP ionospheric communications analysis and prediction program. The broadcasts may originate simultaneously from a single site or from multiple-transmitter sites (i.e., multicast). Figures of merit are assigned in terms of the RPG values, and area coverage statistics are computed for the simulated broadcasts. Three interactive computer programs were developed to permit a semi-automated multicast broadcast coverage analysis using IONCAP and a computerized equipment database. They are: propagation parameter set-up program; transmission plan set-up program; and multicast analysis program.<>     

即时通信系统中的音视频处理技术

围绕即时通信系统中的音视频处理技术,以Gstreamer/Farsight框架和Jingle/XMPP通信协议为重点,阐述了即时通信中多媒体音视频通信框架及相关协议.最后以Pidgin软件为例介绍音视频处理框架在即时通信客户端中的实现方法,为即时通信系统中音视频处理功能的开发提供了有效的解决方案.     

中波同步广播的回顾及同步技术的探讨

本文回顾了实施中波同步广播的经历，分析了目前运行中的同步网所存在的问题。笔者根据１０余年参与同步广播运行管理，科研的体会，论述了实施良好同步广播的措施。就同步广播的发展：标频传送，同步激励的性及同步网的管理三个关键方面的，提出了探讨性的建议和意见。     

一种基于参差QAM的全数字HDTV传输调制技术的研究

数字HDTV地面传输技术中的一个基本要求是能与现有模拟电视同播。本文提出一类新的数字HDTV调制方式。计算机模拟和分析表明，此方式较适于与现有电视同播，且其抗干扰性能优于QAM和VSB方式。硬件实现也较简单。     

Joint transmitter-receiver optimization in synchronous multiusercommunications over multipath channels

Transmitter optimization, in addition to receiver optimization, contributes significantly to efficient interference suppression in multiple access and multipath channels. The system design is based on the joint optimization of the transmitter and the receiver in a synchronous multiuser channel characterized by multipath propagation. Joint optimization is represented by a linear transformation of the transmitted signals at the transmitter and a linear transformation of received signals at each receiving site that minimize the effect of multiple access and multipath interference. The minimum mean squared error between the true bit value and its estimate at the output of the receiver is taken as the cost function, subject to average and peak transmit power constraints. It is shown that joint transmitter-receiver optimization outperforms significantly either transmitter optimization or receiver-based techniques. The crucial assumption, in the case of multipath channels, is that the transmitter knows the multipath characteristics of all channels and that the channel dynamics are sufficiently slow so that multipath profiles remain essentially constant over a block of preceded bits. The practical applications can be found in indoor and cellular communications, satellite communications, or military communications where nonorthogonal signature waveforms are employed     

基于DSP和DDS的数字立体声调频发射系统

介绍了计算机控制的数字立体声调频发射机的设计。该系统利用DSP实现数字立体声调制,并通过AD9852DDS芯片将数字信号转换成射频信号。系统采用计算机控制,接收S／PDIF接口的数字音频输出,适合校园数字调频广播和外语听力训练。     

A POMDP‐based long‐term transmission rate maximization for cognitive radio networks with wireless‐powered ambient backscatter

Wireless energy harvesting enables wireless‐powered communications to accommodate data services in a self‐sustainable manner over a long operational time. Along with energy harvesting, an ambient backscatter technique helps a secondary transmitter reflect existing radio frequency (RF) signal sources to communicate with a secondary receiver when the primary channel (PC) is utilized. However, secondary system performance is significantly affected by factors such as the availability of the primary channel, imperfect spectrum sensing, and energy‐constrained problems. Therefore, we propose a novel approach for wireless‐powered cognitive radio networks (CRNs) to improve the transmission performance of secondary systems. To reduce the dependence of the secondary system on RF sources, in the paper, we provide a new paradigm by integrating ambient backscattering with both RF and non‐RF wireless‐powered communications to facilitate secondary communications. On the basis of the sensing result in a time slot, the secondary transmitter can dynamically select the operational action: (a) backscattering, (b) harvesting, or (c) transmitting to maximize the long‐term achievable data transmission rate at the secondary receiver. In addition, the optimal action set for CRNs with wireless‐powered ambient backscatter is selected by the partially observable Markov decision process (POMDP), which maximizes an expected transmission rate calculated over a number of subsequent time slots. The proposed scheme aims to improve long‐term transmission rate of CRNs with wireless‐powered ambient backscatter in comparison with conventional schemes where an action is taken only to maximize the immediate reward in every single time slot.     

小型调频广播发射机的工作原理与系统建设

主要以300W调频广播发射为例,阐述了发射机、音频处理器、发射机自动监测仪、音频幅度监测仪、监听系统和稳压电源的工作原理。并介绍了调频发射机的发射系统方案与建设。     

The Washington University broadband terminal

The requirements of broadband asynchronous transfer mode (ATM) audio/video (A/V) transmission systems and the approach used to implement the Washington University broadband terminal (BBT) are discussed. The goal of the project was the development of a system with real-time audio and video capability that fully utilized the capability of the Washington University ATM network. The BBT transmits standard NTSC color video and audio over the local ATM network, using a novel approach. A composite analog A/V signal is digitized at three times the video color burst frequency at the transmitter; at the receiver, a unique frame buffer scheme is used to regenerate the transmitted audio and video signals     

双音频在高清安防监控系统中的应用

介绍了HDMI数字音频和传统模拟音频两种音频格式在高清安防系统中的应用。当系统输出的视频格式为HDMI高清视频时,音频通道自动将音频数据发送给HDMI发送芯片,HDMI发送芯片将音频数据复合到视频流,并最终将音视频复合流输出到HDMI接收设备。而当系统当前输出的视频格式为VGA视频输出时,音频通道自动将音频数据发送给音频D/A芯片作数模转换,转换后得到的模拟音频信号最后输出到模拟音频接收设备。利用此方法,可以在实现HDMI数字音频输出的同时很好地兼容原有的模拟音频输出,并实现双音频流的自动选择与自由切换。     

A single-frequency communications system

In those radio communications applications where area coverage is not desired, a series of repeaters, each operating at low power, can be used to extend the radio over long distances. Microwave relay systems operate on this principle with each node representing a point of potential local distribution. Where it is desirable to have the nodes closely spaced, such as along a highway, it becomes desirable to utilize a single frequency for all transmissions in one direction in the interest of conserving spectrum. This paper covers such a system operating in the 935-MHz band. The system described provides both the "backbone" communications system which employs single-frequency repeaters and the "roadside" communications from the repeater node points to users in their vehicles. The functioning of the repeaters is described, and the relationship between signal levels, isolation, external noise levels, and thresholds is presented. Both analog and digital modulations are employed, and it is shown how each repeater is remotely switched between "backbone" and "roadside" communications modes. Extensions from current single-channel to multiple-channel operation is described in terms of the application to a variety of highway-related uses. The results of propagation experiments both along the "backbone" and on the "roadside" are described and related to theoretical models. From these data, conclusions can be drawn about the relationship between repeater spacing, height, and power level, as well as their relationship to user antenna height, output power, and receiver sensitivity.     

Technique of enhancing the noise immunity of broadband communications systems

A technique is considered for enhancing the noise immunity of broadband communications systems with repetition. This technique is based on generating a broadband noise-like signal in the transmitting circuit of the system and adaptive compensation of broadband localized interferences in the receiver. In this case, an adaptive variation of transmitter carriers is conducted in each of the channels. The gain in noise immunity provided by the technique proposed was calculated in comparison with other known techniques.