共查询到19条相似文献,搜索用时 531 毫秒
1.
2.
3.
4.
针对对流层散射信号的时域衰落特点给出了一种适用于单天线、单发通道和单收通道轻便散射站的新型信号时间分集方法,即将待发送信息符号按等时间间隔多次延迟后重组为一个新的发送序列并共享带宽发出,在接收端对各冗余发送信息进行合并从而获得分集增益。分析了该体制的扩谱隐频率分集作用以及与各种前向纠错编码方法的兼容特性。实测结果表明,在平坦衰落与频率选择性衰落信道中信号的平滑能力均与传统的多天线空间分集体制相当。 相似文献
5.
在3GPP2 AIE的框架标准中同时要求采用频率复用和宏分集,但是现有的频率复用方法是无法支持宏分集策略的.鉴于此,在软分数频率复用方法的基础上,基于可拓集合思想,通过建立可用频段与研究区域之间的物元模型,得到了一种能够在小区边缘支持宏分集的软分数频率复用方法.研究表明该频率复用方法在有效降低小区干扰的同时提高了频率利用率,同时小区边缘用户由于小区间干扰的协调以及宏分集策略带来的增益,性能得到了较大提高.仿真结果表明该方法有效地提高了小区边缘的平均容量。 相似文献
6.
文章主要讨论了提高W-CDMA通信系统容量采取的技术,包括:小区间异步操作和3步快速小区搜索、引导符号辅助相干信道估计、基于信干功率比的快速发射功率控制、位置分集、前向链路的发射分集,以及干扰抵消和自适应天线阵列分集接收和发射。 相似文献
7.
分布式天线系统中宏分集的性能分析 总被引:1,自引:0,他引:1
分布式天线系统中普遍采用宏分集技术,通过对相关阴影衰落下瑞利及莱斯信道中选择性宏分集的研究,得出合并器输出的瞬时接收功率分布的闭式表达式。通过不同条件下的性能比较,看出阴影相关系数及宏分集选择范围等参数对宏分集的性能有明显影响。 相似文献
8.
为了满足中等速率对流层散射设备的性能提升需求,从原理上对失真自适应和自适应均衡2种散射信号处理方法在抗失真能力与隐分集效果两方面进行分析与对比,同时建立采用前向纠错编码(FEC)的散射系统模型,分析了不同分集条件下FEC的误码性能以及编码增益;进而给出一种中等速率散射传输波形优化设计方案,对信号处理方式以及FEC进行优化设计,并在硬件系统测试平台上对优化设计波形进行误码性能实测。测试结果表明,该优化设计波形易于实现,误码性能优越。 相似文献
9.
10.
给出一种多层空时分组码设计方法,对原始L维信号向量首先进行线性变换,然后重新分组进行空时编码。在块衰落信道下,多层空时分组码可同时获得时间分集和空间分集。容量分析及仿真结果表明,多层空时分组码提供的遍历信道容量略高于文献【1,2】中给出的对角空时分组码。 相似文献
11.
Space-time processing for wireless communications 总被引:3,自引:0,他引:3
Space-time processing can improve network capacity, coverage, and quality by reducing co-channel interference (CCI) while enhancing diversity and array gain. This article focuses largely on the receive (mobile-to-base station) time-division multiple access (TDMA) (nonspread modulation) application for high-mobility networks. We describe a large (macro) cell propagation channel and discuss different physical effects such as path loss, fading delay spread, angle spread, and Doppler spread. We also develop a signal model incorporating channel effects. Both forward-link (transmit) and reverse-link (receive) channels are considered and the relationship between the two is discussed. Single- and multiuser models are treated for four important space-time processing problems, and the underlying spatial and temporal structure are discussed as are different algorithmic approaches to reverse link space-time professing with blind and nonblind methods for single- and multiple-user cases. We cover forward-link space-time algorithms and we outline methods for estimation of multipath parameters. We also discuss applications of space-time processing to CDMA, applications of space-time techniques to current cellular systems, and industry trends 相似文献
12.
Wan Choi Jin Young Kim 《Vehicular Technology, IEEE Transactions on》2001,50(3):737-749
Some studies have been done on capacity of a code division multiple access (CDMA) system with mixed multirate sources. However, a vast majority of these studies have concentrated on the reverse-link. This trend comes from the fact that the capacity of a CDMA system is reverse-link limited. However, the forward-link can be a limiting link because emerging data services are likely to require higher data rates in the forward-link than in the reverse-link. In this paper, we analyze and simulate the forward-link capacity of a CDMA system with mixed multirate sources in a multipath fading channel. The outage probability of the forward-link is derived for a CDMA system with mixed multirate sources. By introducing a forward-link power factor, the forward-link Erlang capacity is obtained in a closed form. The forward-link capacity is analyzed in terms of the number of multipaths, the number of RAKE fingers in a mobile station, closed-loop power control, and impact of soft handoff. The results in this paper can be applied to overall system design of a CDMA system with multimedia services in future mobile communication systems 相似文献
13.
Capacity analysis in CDMA distributed antenna systems 总被引:3,自引:0,他引:3
Lin Dai Shidong Zhou Yan Yao 《Wireless Communications, IEEE Transactions on》2005,4(6):2613-2620
In this letter, the effect of maximal ratio combining (MRC)-based macrodiversity on the reverse-link and forward-link capacity in code division multiple access (CDMA)-distributed antenna systems is analyzed. The concept of virtual cell is illustrated, and the analytical outage probability expressions are derived. The present investigation shows that on the reverse link, the interference can be suppressed greatly with macrodiversity, which leads to a significant increase in capacity. However, on the forward-link, it is proven that if simulcasting is used in CDMA-distributed antenna systems, the forward-link capacity cannot increase with macrodiversity whatever power allocation scheme is adopted. Based on the analysis of the cause of capacity loss, a new transmission scheme is further presented and the optimal power allocation scheme is derived. It is shown that, in this case, the forward-link capacity increases rapidly with the number of involved distributed antennas. 相似文献
14.
Kuehner R. Todd T.D. Shad F. Kezys V. 《Vehicular Technology, IEEE Transactions on》2001,50(4):1024-1038
We consider a base station, which communicates to a set of portable stations using a smart antenna operating in multibeam, packet-switched, space division multiple access (SDMA) mode. We assume that the system operates using time division duplexing (TDD) and focus on the problem of access to the stations by the base station in the forward-link direction. A polling protocol is used which permits efficient access in this type of system. The operation of the protocol is unique in that it permits dynamic slot allocation and accommodates variations in channel time coherence. In the protocol, dynamic slot assignment is integrated into the forward-link beam scheduling. This allows us to explore the value of dynamic station slot assignment when constructing the SDMA/TDMA frames. The results show the improvements in capacity, which are possible in such systems and give insight into the degradation in protocol performance that occurs when channel coherence times decrease. We find that very large improvements in capacity are possible using dynamic slot allocation, especially under harsh channel conditions. We also investigate various base station queueing issues in this type of system. It is shown that care must be taken in how buffering is performed so that blocking effects do not unnecessarily degrade the forward-link capacity 相似文献
15.
Handoff is the process during which a mobile node (MN) needs to change its connectivity point to the wireless internetwork from one access node (AN) to another during an ongoing communication. If MNs are allowed to have two or more simultaneous connections to the internetwork through different ANs, then the handoff is said to be soft; otherwise, it is said to be hard. Traditionally, during forward-link soft handoff, multiple identical copies of each packet are simultaneously transmitted to the MN through the associated ANs. At the MN's physical-layer, the received signals are combined on a bit-by-bit basis resulting in improving the bit-error rate. However, this approach requires tight synchronization of the ANs involved in the soft handoff. In addition, as shown in the literature, the capacity often decreases due to the increase of the number of channels used by MNs during soft handoff. In this paper, we propose, analyze, simulate, and implement a soft handoff scheme called soft handoff over IP (SHIP) for forward-link that 1) overcomes the need for synchronization and 2) increases the capacity of the network. Through both analytic and simulation studies, we show that SHIP achieves significant performance improvements. We derive analytic expressions of the power-capacity relationship for two-dimensional (2-D) and one-dimensional (1-D) cell models. By comparing our scheme with the hard handoff, we empirically show that the capacity increases by about 30% and 20%, respectively, for the 2-D and 1-D cell models. Further, the simulation results show that SHIP saves up to 30% of the total power consumed by the ANs. 相似文献
16.
Effect of soft and softer handoffs on CDMA system capacity 总被引:11,自引:0,他引:11
The effect of soft and softer handoffs on code-division multiple-access (CDMA) system capacity is evaluated for unsectorized and sectorized hexagonal cells according to an average bit energy-to-interference power spectral density, which corresponds to a bit-error rate (BER) of 10-3. The effect of imperfect sectorization on sectorization efficiency is also considered. On the reverse link, there is no capacity loss as no extra channels are needed to perform soft handoff, while the macrodiversity provided by soft handoff can improve the reverse-link quality and extend the cell coverage. On the forward link, when soft handoff is employed in unsectorized cells, the capacity loss due to two traffic channels assigned to a user in the handoff zone is 0.2% or 1.1% for a voice activity factor of 3/8 or 1/2, respectively. As the forward-link capacity is higher than that of the reverse link, this small capacity loss does not affect the system capacity. For sectorized cells having three sectors per cell, there are overlapping coverage areas between sectors, where mobiles in these areas are subjected to an increase in cochannel interference. For an overlapping angle of 5°, the sectorization efficiency is 0.96 and 0.7 for the reverse-link and forward-link systems, respectively. When soft and softer handoffs are employed, the forward-link sectorization efficiency is improved to 0.97. We find the application of soft and softer handoff improves not only the forward-link capacity, but also the signal-to-interference ratio (SIR) for mobiles near the cell and sector boundaries 相似文献
17.
Youngoo Yang Jeonghyeon Cha Bumjae Shin Bumman Kim 《Microwave and Wireless Components Letters, IEEE》2003,13(9):370-372
In this letter, we demonstrate a microwave Doherty amplifier employing an input signal envelope tracking technique. In the amplifier, the gate bias of the peaking amplifier is controlled according to the magnitude of the envelope. A 2.14-GHz Doherty amplifier is implemented using 4-W PEP LDMOSFETs, and an adaptive controlled gate bias circuit is constructed and the control shape is optimized experimentally. The performance of the microwave Doherty amplifier is compared with that of a class AB amplifier using one-tone, two-tone, and forward-link wideband code-division multiple access (WCDMA) signals. For a forward-link WCDMA signal, the measured power added efficiency (PAE) of the microwave Doherty amplifier is 39.4% at -30 dBc adjacent channel leakage ratio (ACLR), while that of the comparable class AB amplifier is 24.2% at the same ACLR level. 相似文献
18.
19.
Ildu Kim Jeonghyeon Cha Hong S. Bumman Kim Young Yun Woo Cheon Seok Park 《Microwave and Wireless Components Letters, IEEE》2006,16(4):176-178
We have demonstrated a high linear three-way Doherty amplifier by applying uneven power drive and optimizing the peaking biases and load impedances. The amplifier has been implemented at 2.14GHz using 190-W peak envelope power laterally diffused metal-oxide-semiconductor field-effect transistors. For comparison, a class AB biased amplifier is tested as it's counterpart. The two-tone signal and forward-link wideband code-division multiple access (WCDMA) signal have been selected as test signals. At 42dBm (12.5-dB backed-off output power), there are large improvements in the third- and fifth-order intermodulation distortions. For the forward-link four-carrier WCDMA signal, the adjacent channel leakage ratio (ACLR) performances at 5-MHz and 10-MHz offsets are -52.5dBc and -53.4dBc, respectively, and satisfy the generally medium high power amplifier linearity target without using any other linearization circuits. In comparison with the class AB amplifier, the three-way Doherty amplifier with uneven power drive has 9.8-dB lower ACLR at 5-MHz offset while maintaining a comparable drain efficiency of 10.2%. 相似文献