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1.
Using the enhanced data rates for GSM evolution (EDGE) system with cyclic frequency hopping as an example, we apply a Kalman-filter power control method based on interference tracking to packet voice service in wireless networks. Our results show that the power-control method significantly improves the spectral efficiency by enabling the 1/3 frequency reuse while maintaining a stringent requirement of 2% packet loss probability for voice service. Specifically, for allocated spectrum of 1.8, 3.6 and 5.4 MHz, the 1/3 reuse with the Kalman power control can yield 102.5%, 49.5% and 32.5% improvement in spectral efficiency, respectively, over the 3/9 reuse (regardless of whether or not power control is used). We also compare the performance of the Kalman method with a traditional Signal-to-interference-ratio method and a control method that is based on the last interference measurement. We find that appropriate selection of power for the first packet of each talk spurt and the filtering function for noisy measurements are crucial in providing high system capacity for packet voice service. For the EDGE system, we also identify a need for shortening the power update period, which is 480 ms in the specifications.  相似文献   
2.
The design of 4th Generation Cellular Communication Systems will face manychallenges, including the need to achieve very high spectrum efficiency whencompared to 3rd Generation cellular systems. In this paper, we investigate thefundamental limits of DSSS-CDMA versus TDMA for achieving high spectrumefficiency by presenting the capacity regions for each including the effectsof multiple transmit and receive antennas. To assess the channel capacityregion for local area and wide area coverage, a channel model based uponuncorrelated Rayleigh fading and model with a strong spatial correlation andRicean component are evaluated. For multiple transmit and receive antennas,both open loop and closed loop capacity regions are assessed, where the closedloop capacity assumes channel state information at the transmitter and optimumpower allocation. Conclusions from the work include an assessment of whatapproaches hold the best promise for achieving high spectrum efficiency forfuture cellular communication systems. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
3.
In this paper transmitter antenna diversity for the downlink of a cellular system is proposed in conjunction with optimum anti-fading diversity. In spectrally efficienttransmitter antenna, frequency and time diversity schemes the information bit stream is divided into sub-streams and each sub-stream is transmitted over a different antenna, a different frequency, or a different time slot.The present work provides a fading resistant transmission scheme where a base station uses M1 antennas and M2 time slotsM=M1+M2. These transmissions are coordinated tomitigate the effects of multi-path Rayleigh fading and the mobilereceiver can recover the entire M-dimensional transmitted vector as longas the signal energy of at least one coordinate is large enough. TheSelective Transmitter Antenna Diversity (space diversity) scheme iscoordinated with new Orthonormal Complex Rotation Matrices(time diversity) to get the highest BER performance for low and medium signaltonoise ratio. Orthonormal Complex Rotation Matrices with variable and maximum peak toaverage amplitude ratio (PAR) are presented. The modulations considered in this workareQPSK, 8PSK and 16QAM.  相似文献   
4.
In this paper, we propose a new adaptive transmission scheme for wirelesscommunication systems utilizing frequency diversity combining technique. Thecapacity of Rayleigh fading chanels under the proposed adaptive transmissionscheme is analytically evaluated and compared with the capacity under theconventional adaptive transmission scheme. The results show that the channelcapacity under the new adaptive scheme exceeds that under the conventionalone, and this capacity increment becomes more apparent especially for loweraverage carrier-to-noise ratio (CNR) and larger number of diversity branches.Also, the capacity with the new scheme isshown to exceed even the capacity ofAWGN channels for some small values of CNR and large number of diversitybranches.  相似文献   
5.
无线通信新技术展望   总被引:1,自引:0,他引:1  
文章对在未来无线通信领域有望得到重要应用的新技术进行描述,包括无线局域网、码分多址、高频谱效率(正交频分复用、超宽带调制和空时处理)、自组网络和网络跨层优化。这些技术和方法有许多优越之处,同时有许多问题尚待解决。  相似文献   
6.
从理论上分析比较了FDMA,TDMA与CDMA蜂窝网系统的频谱效率,指出了其频谱效率的限制因素和提高方法,计算了Q-CDMA,GSM与TACS三种实用蜂窝网系统的频谱效率,得出了几点有用结论。  相似文献   
7.
Adaptive Modulation over Nakagami Fading Channels   总被引:25,自引:1,他引:24  
We first study the capacity of Nakagami multipath fading (NMF) channels with an average power constraint for three power and rate adaptation policies. We obtain closed-form solutions for NMF channel capacity for each power and rate adaptation strategy. Results show that rate adaptation is the key to increasing link spectral efficiency. We then analyze the performance of practical constant-power variable-rate M-QAM schemes over NMF channels. We obtain closed-form expressions for the outage probability, spectral efficiency and average bit-error-rate (BER) assuming perfect channel estimation and negligible time delay between channel estimation and signal set adaptation. We also analyze the impact of time delay on the BER of adaptive M-QAM.  相似文献   
8.
提出了一种基于虚拟实时服务的协议构架,可有效发掘用户提出通信请求之前的“负时间轴”上的空闲时频资源或可再生能源,将用户可能感兴趣的内容以多播的方式预先推送到终端的存储器中,从而以非实时的通信提供虚拟实时服务,在确保服务质量的前提下大幅度提升频谱和能量效率.对终端缓存内容的选择算法进行了标准化,从而允许基站在本地预测用户已缓存的内容,并判断当前是否应发起推送和推送哪条内容;提出了虚拟实时服务涉及的若干关键算法,也给出了虚拟实时服务的演进途径及主要开放问题,旨在为相关新兴产业的技术发展提供参考.  相似文献   
9.
朱近康  邓 娜  赵 明 《通信学报》2015,(1):2015002-2015002
提出一种在蜂窝小区边缘同频嵌入垂直覆盖的新型混合小区网络结构,具有抑制小区间干扰和提高边缘信干比等优点。该网络结构是以不改变目前蜂窝网络“水平覆盖”结构的前提下,在小区边缘干扰区域同频嵌入天线波束为垂直向下的微小基站,称作“垂直覆盖”,因此易于实际操作和实现。首先分析了蜂窝小区水平覆盖的干扰深度,垂直覆盖基站的干扰特性,及各自的频谱效率。随后,针对提出的蜂窝小区边缘同频嵌入垂直覆盖的网络结构,分别研究了混合小区的水平覆盖中心区域和垂直覆盖小区边缘区域的频谱效率。结果表明,提出的新型混合小区网络结构,能有效抑制蜂窝小区间干扰,改善小区边缘性能,实现更高的频谱效率。  相似文献   
10.
超高速超大容量超长距离(3U)光传输作为一种新型光通信模式,推动了下一代互联网和宽带移动通信网的发展和技术进步,已成为国际高科技知识产权竞争的焦点和制高点.从3U光传输研究的背景与意义出发,给出了3U光传输的3个科学问题,并介绍了3U光传输的体系架构、研究的基础理论与关键技术,最后介绍了3U光传输的实验验证平台和在该平台上完成的重要实验以及产学研结合创新成果的产业化应用范例.  相似文献   
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