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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.
This paper explores the potential to use accurate but outdated channel estimates for adaptive modulation. The work is novel in that the research is conditioned on block by block adaptation. First, we define a new quantity, the Tolerable Average Use Delay (TAUD), which can indicate the ability of an adaptation scheme to tolerate the delay of channel estimation results. We find that for the variable-power schemes, TAUD is a constant and dependent on the target Bit Error Rate (BER), average power and Doppler frequency; while for the constant-power schemes, it depends on the adaptation block length as well. At last, we investigate the relation between the delay tolerating performance and the spectral efficiency and give the system design criterion. The delay tolerating performance is improved at the price of lower data rate.  相似文献   
6.
杨玉丽  马猛  焦秉立 《电子学报》2007,35(9):1660-1664
 本文提出了一种分段限速的传输方式、用以改善频率选择性块衰落信道中导频辅助调制OFDM系统的频谱效率,具体设计为:发射机将一个OFDM数据块分为若干组、每组的传输速率限定为它能够达到的输入与输出之间互信息的下界;接收机将当前组的符号判决后用作下一组附加的导频符号,附加导频符号的增多将提高信道估计质量,并最终改善系统频谱效率.理论上讲,在每组信息符号足够多的情况下,只要传输速率不大于互信息下界,信道编码可以保证该组误符号率的极限为零.文中以这一极限为前提,推导了分段限速设计能够达到的频谱效率.理论分析及其数值结果表明:与传统导频辅助调制OFDM系统相比,分段限速设计能够实现更高的频谱效率.  相似文献   
7.
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   
8.
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   
9.
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   
10.
在已知精确信道状态信息的情况下,使用自适应调制等技术能改善OFDM系统的性能。然而,反馈信息传输延时导致的信道估计噪声和多普勒频移,使得实际的时变快衰落信道条件中不可能获得完全精确的信道状态信息。本文利用多个“过期的”信道估计值,使用扩展自相似过程模型来修正当前的信道估计值。仿真分析表明,在快衰落信道条件下,新方法能有效地改善自适应OFDM系统平均频谱效率。  相似文献   
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