共查询到20条相似文献,搜索用时 93 毫秒
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为了在多种信道上实现传真通信,对传真存储转发技术进行了设计,给出了一种基于G3类传真的实现方案。介绍了传真存储转发系统的工作原理,详细阐述了利用单片机和传真Modem芯片构成传真存储转发终端设备的硬件实现方案,设计了基于T.30的传真存储转发流程,给出了系统与普通G3传真机的传真发送与接收的软件设计方案流程图。系统具有较强的通用性,可使现有的信道资源得到有效利用,很大地扩展了传真业务的应用领域。 相似文献
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传真存储转发系统及其组网方式邢春花,吕雅军通常的传真机经长途电话网间的通信只是点一点的通信,因而长途电话网的质量问题常常影响通信质量,同时由于传真机的发送电平不易控制,致使长途电话网传输信道过负荷而降低整个电话网的传输质量。另外随着传真机的大量使用,... 相似文献
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随着传真通信的发展,三类传真机得到了广泛应用,传真技术正向着高速化、网络化、保密化和多媒体化等方向发展.文中研究分析了采用V.34建议的高速传真通信规程,阐述了高速传真网关的基本原理.本设计依据系统的具体需求,移植了uC/OS-II实时操作系统,完成了系统的初始化工作以及系统上电自检过程,实现了高速传真网关,满足了系统的开发需求. 相似文献
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There is a plethora of recent research on high performance wireless communications using a cross‐layer approach in that adaptive modulation and coding (AMC) schemes at wireless physical layer are used for combating time varying channel fading and enhance link throughput. However, in a wireless sensor network, transmitting packets over deep fading channel can incur excessive energy consumption due to the usage of stronger forwarding error code (FEC) or more robust modulation mode. To avoid such energy inefficient transmission, a straightforward approach is to temporarily buffer packets when the channel is in deep fading, until the channel quality recovers. Unfortunately, packet buffering may lead to communication latency and buffer overflow, which, in turn, can result in severe degradation in communication performance. Specifically, to improve the buffering approach, we need to address two challenging issues: (1) how long should we buffer the packets? and (2) how to choose the optimum channel transmission threshold above which to transmit the buffered packets? In this paper, by using discrete‐time queuing model, we analyze the effects of Rayleigh fading over AMC‐based communications in a wireless sensor network. We then analytically derive the packet delivery rate and average delay. Guided by these numerical results, we can determine the most energy‐efficient operation modes under different transmission environments. Extensive simulation results have validated the analytical results, and indicates that under these modes, we can achieve as much as 40% reduction in energy dissipation. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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目前对于较低速率的通信线路,最大限度地利用现有带宽变得越发重要。通过数据/语音复用设备可以实现在带宽为64kb/s的线路上实时传输数据、传真、压缩语音的综合业务,这就用到了数据复接技术。关于低速异步数据的复接设备的研究有很好的实用价值。基于实时性高,升级方便,满足实用化要求,文中主要提出了多业务复用器的系统设计方案。 相似文献
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Space-time coding is well understood for high data rate communications over wireless channels with perfect channel state information. On the other hand, channel coding for multiple transmit antennas when channel state information is unknown has only received limited attention. A new signaling scheme, named unitary space-time modulation, has been proposed for the latter case. In this paper, we consider the use of turbo coding together with unitary space-time modulation. We demonstrate that turbo coded space-time modulation systems are well suited to wireless communication systems when there is no channel state information, in the sense that the turbo coding improves the bit error rate (BER) performance of the system considerably. In particular, we observe that the turbo-coded system provides 10-15 dB coding gain at a BER of 10/sup -5/ compared to the unitary space-time modulation for various transmit and receive antenna diversity cases. 相似文献
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Arslan H. Gupta S.C. Bottomley G.E. Chennakeshu S. 《Vehicular Technology, IEEE Transactions on》2000,49(4):1126-1139
The capacity and signal quality of wireless communication systems can be improved by enhancing receiver performance in the presence of adjacent channel interference (ACI), In this paper, maximum-likelihood sequence estimation (MLSE) receivers based on joint demodulation and successive cancellation of adjacent channel signals are developed. The proposed receivers provide significant improvement in performance over a wide range of carrier-to-interference ratios. To provide coherent reception, novel channel estimation techniques are used, exploiting knowledge of the transmit and receive filter responses. Performance is evaluated and compared via simulation for the Global System for Mobile communications (GSM) digital cellular system 相似文献
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有序多重签名体制中阈下信道通信方法的研究 总被引:1,自引:0,他引:1
本文分析了阈下信道技术在数字签名中的应用,并以一种有序多重数字签名方案为例,对其中存在的宽带和窄带阈下信道进行了具体分析.提出了一种有序多重签名体制下的窄带阈下信道通信方案,通过实时性测试确定阈下信息位数,从而满足了传输信息容量与实时性的要求。 相似文献
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据用户投诉,省外往福建泉州电信发传真,经常出现传真不能发送的现象。经过拨打测试,确认了问题症结。介绍固网华为软交换设备在转接传真业务时出现无法正常发送接收传真的原因、原理及处理方法,通过打开CED开关进而保证VMG能切换到数据通道,实现传真的正常收发。 相似文献
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AD9873是用于彬模和模/数转换的芯片,它带有1个D/A和4个A/D通道,用于对各种不同的混合信号进行处理和传输。该芯片可用于电缆调制解调器、数字通信、数据和视频调制解调器等。介绍AD9873的工作特点与性能参数,以及它在数字电视机顶盒中的应用。 相似文献
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Yuli Yang Bingli Jiao 《Communications Letters, IEEE》2008,12(4):225-227
In this letter, we introduce information-guided channel-hopping, a new scheme for high data rate communication over Rayleigh fading channel using multiple transmit antennas. This scheme is proposed based on the fact that the independence character of multi-channel can be used as an additional information transmitting channel, and the maximum likelihood decoding can be achieved in a simple way by decoupling of the signals conveyed by different methods. The analysis results prove that the capacity behavior of this scheme is better than that of the space-time block coding for more than two transmit antennas. 相似文献