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1.
Downlink channel covariance matrix (DCCM) estimation and itsapplications in wireless DS-CDMA systems
The downlink channel covariance matrix (DCCM) is of vital importance in determining downlink beamforming weights for base station (BS) antenna array systems. For the frequency-division-duplex (FDD) mode, DCCM is difficult to obtain due to a lack of direct measurement of downlink channel responses. In this paper, a novel technique is proposed for estimating DCCM using uplink channel responses only, which does not need direction-of-arrival (DOA) estimation and its association. The downlink beamforming scheme is then proposed for wireless DS-CDMA systems, using the obtained DCCM information together with the so-called virtual uplink beamforming and power control technique. Computer simulations show that using the BS antenna array together with this new beamforming technique can provide larger system capacity than traditional DOA-based approaches, which just direct the main beam toward the desired user 相似文献
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无线通信中基于线性预测和参数反馈的下行波束形成方法 总被引:2,自引:0,他引:2
本文基于最大信号噪声比准则(MSNR,Maximum Signal Noise Ratio)提出一种新的下行波束形成方法,即根据天线收发的互易性原理,通过上行波束形成得到的上行天线阵列矢量,变换而得到下行天线阵列矢量,再通过移动端Rake接收机的合作,反馈回每一径的衰落系数,考虑到存在传输和处理时延并且在此时间内信道有明显变化时,反馈的衰落系数存在误差。因此,本文采用了信道预测的方法,估计即时衰落系数,这样求得期望信号的相关矩阵,计算相应的最大广义特征值所对应的特征矢量,进行下行波束形成。 相似文献
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The quality of channel state information (CSI) affects the performance of multiple input multiple output (MIMO) systems which
employ multi-elements antenna arrays at both the transmitter and the receiver. In a time division duplex (TDD) systems, the
CSI for downlink can be obtained from uplink channel using reciprocity principal. However, the performance of a MIMO system
can be degraded due to channel impairments especially in fast fading scenarios when the CSI obtained from uplink is used for
downlink transmission. In this paper, we study performance of autoregressive (AR) modeling based MIMO channel prediction under
varying channel propagation conditions (mobile speed, multipath number and angle spread) and prediction filter order. Our
simulation results show that using the predicted CSI for downlink provides capacity improvement compared to conventional method. 相似文献
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Group-blind multiuser detectors for uplink code-division multiple-access (CDMA) were recently developed by Wang and Host-Madsen. These detectors make use of the spreading sequences of known users to construct a group constraint to suppress the intracell interference. However, such techniques demand the estimation of the multipath channels and the delays of the known users. In this paper, several improved blind linear detectors are developed for CDMA in fading multipath channels. The proposed detectors utilize the correlation information between consecutively received signals to generate the corresponding group constraint. It is shown that by incorporating this group constraint, the proposed detectors can provide different performance gains in both uplink and downlink environments. Compared with the previously reported group-blind detectors, our new methods only need to estimate the multipath channel of the desired user and do not require the channel estimation of other users. Simulation results demonstrate that the proposed detectors outperform the conventional blind linear multiuser detectors. 相似文献
6.
Wei-Chiang Wu 《电子科技学刊:英文版》2020,18(3):266-275
This paper addresses the problem of channel estimation in a multiuser multi-cell wireless communications system in which the base station (BS) is equipped with a very large number of antennas (also referred to as “massive multiple-input multiple-output (MIMO)”). We consider a time-division duplexing (TDD) scheme, in which reciprocity between the uplink and downlink channels can be assumed. Channel estimation is essential for downlink beamforming in massive MIMO, nevertheless, the pilot contamination effect hinders accurate channel estimation, which leads to overall performance degradation. Benefitted from the asymptotic orthogonality between signal and interference subspaces for non-overlapping angle-of arrivals (AOAs) in the large-scale antenna system, we propose a multiple signals classification (MUSIC) based channel estimation algorithm during the uplink transmission. Analytical and numerical results verify complete pilot decontamination and the effectiveness of the proposed channel estimation algorithm in the multiuser multi-cell massive MIMO system. 相似文献
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TD-LTE系统中动态下行波束赋形算法性能分析 总被引:1,自引:0,他引:1
根据加权粒度的差别,介绍了per-RB-MRT算法和full-BW-EBB算法的原理,并对这两种算法的特点以及性能差异进行了理论分析.构建了符合3GPP规范定义的TD-LTE系统上下行仿真平台,对这两种算法在有信道估计误差(包括信道估计精准度和信道信息时延)的情况下的其性能进行了理论分析和仿真研究.仿真结果表明,per-RB-MRT算法在上行信道估计值和下行信道实际值契合较好的情况下能够趋于最佳理论性能,而full-BW-EBB算法由于利用了相对稳定的信道空间相关特性,因而能够在较差的信道环境中保持较高的性能鲁棒性.这些仿真结果对于实际场景中的算法选择提供了重要的参考依据. 相似文献
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TD-LTE系统中的波束成形(Beam Forming)会受到收、发天线不对称性的影响。TD-LTE-Advanced(TD-LTE-A)系统中使用上行多天线发送可以解决天线不对称性的问题,因此需要对其分析以优化Beam Forming的性能。通过对上行多天线的信道状态信息(CSI)做特征值(SVD)分解,指出了Beam Forming对下行信噪比(SNR)的改善。针对Beam Forming模式下SNR和链路质量指示(CQI)的差异,提出了一种优化链路自适应的方法。数值仿真验证了优化后的TD-LTE-A相比TD-LTE的Beam Forming吞吐率最大提高了24%,其结论对商用TD-LTE网升级到TD-LTE-A具有显著价值。 相似文献
12.
徐卫 《中国电子科学研究院学报》2006,1(1):98-101
研究了智能天线在下行链路的应用。利用上行链路接收数据,建立分布式目标信道模型。估计移动用户的发射角、扩展角度和发射功率以及下行信道相关矩阵,确定下行链路的波束形成方法。即对频分复用(FDD)系统进行上行相关矩阵变换,构建下行信道协方差矩阵,利用最大合并比准则获得下行链路权值。计算机仿真证实了这种方法的有效性。 相似文献
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Hsueh-Jyh Li Ta-Yung Liu 《Vehicular Technology, IEEE Transactions on》2003,52(4):752-760
Different beamforming techniques are employed in a wideband code-division multiple-access base station, and their uplink and downlink signal-to-interference-plus-noise ratio (SINR) performances are compared. It is found that the direction of arrival (DOA) method and the complex conjugate method have almost the same uplink SINR performance, but the complex conjugate method shifts the downlink main beam direction slightly due to the difference between the uplink and downlink carrier frequency. However, the degradation in the downlink mean SINR performance is less than 1 dB compared with that obtained by the DOA method. In the downlink, the SINR performances obtained by the single-beam method and multiple-beam beamforming technique are compared. It is found that the single-beam method has a poorer SINR performance in the low SINR region because it is more likely to suffer from deep fading. In the moderate or high SINR regions, the single-beam method has a much better SINR performance because it has a higher gain in the main path direction and a smaller angular coverage of the mainlobe, which results in a stronger signal level and smaller multiple-access interference at the mobile receiver. 相似文献
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大规模MIMO时分双工系统的基站天线互易校准算法 总被引:1,自引:0,他引:1
对于采用大规模MIMO技术的时分双工系统,基站天线的互易误差会破坏上下行基带信道互易特性,大幅降低系统下行传输性能。考虑到大规模MIMO技术所带来的基站天线间的耦合效应,该文设计了基于总体最小二乘估计的基站天线互易校准算法,以实现对基站的天线互易误差的补偿。该算法以增加计算复杂度为代价,以及通过增加信道测量样本,克服了上下行信道估计误差对现有天线互易误差校准算法的影响。同时,该文通过瑞利商迭代求解降低了该算法的复杂度。若忽略用户天线互易误差,计算机仿真结果表明,该算法相对于现有的基站天线互易误差校正算法,具有1.8 dB左右的性能增益。若考虑用户天线互易误差,该算法相对于已有的算法,具有随信道估计误差方差减小而增大的增益。 相似文献
15.
Li Fung Chang Noerpel A.R. Ranade A. 《Selected Areas in Communications, IEEE Journal on》1996,14(4):718-727
The FCC has allocated the band between 1920 MHz and 1930 MHz for unlicensed personal communications services (UPCS) using isochronous or circuit operation. The UPCS spectrum is between the licensed PCS spectrum bands of 1850-1910 MHz and 1930-1990 MHz. Terminal interoperability in both the UPCS spectrum on private indoor wireless systems and the licensed spectrum on public PCS systems is desirable and encouraged by the FCC. This paper presents a port channel assignment process for the personal access communications system-unlicensed B (PACS-UB) which abides by the FCC etiquette for UPCS and discusses the corresponding uplink and downlink performance. Uplink power control is employed to improve the uplink performance. PACS-UB has a high degree of commonality with licensed PACS to permit economical licensed/unlicensed terminals and common network services. The results of our simulation show that, at 1% to 2% blocking probability, 99% of downlink local-mean signal-to-noise plus interference ratio (SINR) values are above 17 dB for a 10 to 20 m port separation. For a three-dimensional office environment, the uplink limits the SINR performance, however, with uplink power control, a 5.5 to 7 dB improvement in the uplink SINR can be achieved even for high traffic load 相似文献
16.
Yanrong Zhao Wenjing Zhao Gongpu Wang Bo Ai Hervin Hidayat Putra Bagus Juliyanto 《中国通信》2020,(3):90-100
Channel estimation is a well-known challenge for wireless orthogonal frequency division multiplexing(OFDM)communication systems with massive antennas on high speed rails(HSRs).This paper investigates this problem and design two practicable uplink and downlink channel estimators for orthogonal frequency division multiplexing(OFDM)communication systems with massive antenna arrays at base station on HSRs.Specifically,we first use pilots to estimate the initial angle of arrival(AoA)and channel gain information of each uplink path through discrete Fourier transform(DFT),and then refine the estimates via the angle rotation technique and suggested pilot design.Based on the uplink angel estimation,we design a new downlink channel estimator for frequency division duplexing(FDD)systems.Additionally,we derive the Cramér-Rao lower bounds(CRLBs)of the AoA and channel gain estimates.Finally,numerical results are provided to corroborate our proposed studies. 相似文献
17.
Shiann‐Shiun Jeng Hsin‐Piao Lin Chen‐Wan Tsung 《International Journal of Communication Systems》2003,16(3):211-223
This paper presents some preliminary results from experimental studies on space‐division‐multiple‐access (SDMA) for wireless communications. A smart antenna system utilizing direction‐of‐arrival (DOA)‐based beamforming techniques can enhance signal quality by reducing co‐channel interference from mobiles located at angles spatially distinct from the base station. Adopting both smart uplink and downlink beamforming, a communication system with an antenna array can increase the cell coverage of a base station and significantly boost capacity compared with conventional antenna systems. However, successful implementation of DOA‐based beamforming techniques depends on the DOA characteristics. This paper presented the feasibility of direction finding and DOA variation with respect to frequency. Furthermore, the angle spread was studied for selected environments. The results demonstrate the feasibility of applying proposed smart antenna system utilizing DOA‐based beamforming algorithm for increasing channel capacity and improving system performance in frequency‐division‐duplex (FDD) wireless communication systems. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
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The outage occurring from beamformer-based smart antennas is analysed for an antenna array deployed in an urban macro-cell environment. Spatio-temporal channel data obtained from a small, urban cell and from within the UTRA frequency allocation has enabled beamforming performance to be determined from the measured uplink and downlink frequency bands. The analysis shows a sub-optimum uplink beamformer performance is observed for 8% of occasions and a 25% downlink beamforming outage for an eight-element uniformly spaced linear array 相似文献
19.
Adapting a downlink array from uplink measurements 总被引:3,自引:0,他引:3
In a frequency division duplex system, a transmitter adaptive antenna array can potentially improve the performance of a wireless downlink, but because the uplink and downlink channels have different wavelengths, and, therefore, different responses, direct downlink adaptation based on channel estimates of the uplink is generally not feasible. Instead, there has been some interest in adaptations that require only the second-order statistics of the uplink and downlink to be similar. These algorithms derive adaptive weights from the covariance of the received signal to apply to a downlink transmitter array. We make two contributions to this area. First, we introduce an array configuration employing M+1 elements with log-periodic spacing that comprises two overlapping subarrays, each with M elements, that are scaled versions of each other, with the scale factor equal to the ratio of the uplink wavelength to the downlink wavelength. This array has identical beampatterns at the two wavelengths, thus helping to fulfill the requirement that the uplink and downlink second-order statistics be the same. Second, we demonstrate that obtaining a good estimate of the uplink covariance matrix is not essential for the successful operation of the adaptive scheme. Even when the mobile is at rest and the uplink information comprises only a single snapshot from the receiver array, an adaptive scheme can improve the SNR 相似文献
20.
The analytical expressions for the average intensity, root mean square (RMS) beam width and angular spread of Gaus- sian Schell-model (GSM) beams propagating under slant atmospheric turbulence are derived, and they are used to study the influence of different propagation paths on the propagation of laser beams in atmospheric turbulence. It is shown that under the same condition, the influence of atmospheric turbulence along a downlink path on the GSM beam propagation is the smallest among the three paths. Therefore, the downlink propagation is more beneficial to the beam propagation through atmospheric turbulence compared with the uplink propagation and horizontal propagation. 相似文献