This paper considers imperfect channel state information (CSI) in the downlink precoding of cellular multi-user large-scale distributed antenna system (DAS). Specifically, the uncertainty of channel estimation is main...
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ISBN:
(纸本)9781509016983
This paper considers imperfect channel state information (CSI) in the downlink precoding of cellular multi-user large-scale distributed antenna system (DAS). Specifically, the uncertainty of channel estimation is mainly caused by the pilot reuse among users in adjacent cells. The phenomenon is termed as pilot contamination in a multi antenna system. Since the large-scale fading may vary from antenna to antenna, it's not easy to jointly estimate the channels from all antennas to a certain user. Instead, this paper only jointly estimates the downlink channels of the antennas at the same site, therefore with the same large scale fading. Consequently, the channel estimation is executed in a distributed manner while the subsequent precoding is done in a centralized way. Based on the analysis of the properties of the DAS channel estimations, a multi-cell MMSE precoding scheme is proposed which aims to minimize the sum of intra-cell interference and the interference the cell pours to other cells. An approximation of the multi-cell MMSE precoding is further derived to reduce the computational complexity. Simulation results show significant performance gains over traditional singlecell precoding schemes.
This paper considers imperfect channel state information (CSI) in the downlink precoding of cellular multi-user large-scale distributed antenna system (DAS). Specifically, the uncertainty of channel estimation is main...
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ISBN:
(纸本)9781509016990
This paper considers imperfect channel state information (CSI) in the downlink precoding of cellular multi-user large-scale distributed antenna system (DAS). Specifically, the uncertainty of channel estimation is mainly caused by the pilot reuse among users in adjacent cells. The phenomenon is termed as pilot contamination in a multi antenna system. Since the large-scale fading may vary from antenna to antenna, it's not easy to jointly estimate the channels from all antennas to a certain user. Instead, this paper only jointly estimates the downlink channels of the antennas at the same site, therefore with the same large scale fading. Consequently, the channel estimation is executed in a distributed manner while the subsequent precoding is done in a centralized way. Based on the analysis of the properties of the DAS channel estimations, a multi-cell MMSE precoding scheme is proposed which aims to minimize the sum of intra-cell interference and the interference the cell pours to other cells. An approximation of the multi-cell MMSE precoding is further derived to reduce the computational complexity. Simulation results show significant performance gains over traditional single-cell precoding schemes.
We propose an improved Joint Spatial Division and Multiplexing (JSDM) method which can be applied under the SCM model. The performance of basic JSDM under the SCM model is analyzed, and the problem of overlapping scat...
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ISBN:
(纸本)9784902339314
We propose an improved Joint Spatial Division and Multiplexing (JSDM) method which can be applied under the SCM model. The performance of basic JSDM under the SCM model is analyzed, and the problem of overlapping scattering angles is solved by adopting beamforming at user terminals (UTs). Simulations show that the idea of JSDM can be transplanted to the SCM model and the proposed method can greatly reduce the overhead of downlink training and uplink feedback for CSIT acquisition.
Large-scale MIMO （multiple-input multiple-output） systems with numerous low-power antennas can provide better performance in terms of spectrum efficiency, power saving and link reliability than conventional MIMO. Fo...
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Large-scale MIMO （multiple-input multiple-output） systems with numerous low-power antennas can provide better performance in terms of spectrum efficiency, power saving and link reliability than conventional MIMO. For large-scale MIMO, there are several technical issues that need to be practically addressed （e.g., pilot pattern design and low-power transmission design） and theoretically addressed （e.g., capacity bound, channel estimation, and power allocation strategies）. In this paper, we analyze the sum rate upper bound of large-scale MIMO, investigate its key technologies including channel estimation, downlink precoding, and uplink detection. We also present some perspectives concerning new channel modeling approaches, advanced user scheduling algorithms, etc.
In this paper, we consider the downlink of a multiuser wireless communication system with multiple antennas at the base station and users each with a single receive antenna. It is known that when channel state informa...
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In this paper, we consider the downlink of a multiuser wireless communication system with multiple antennas at the base station and users each with a single receive antenna. It is known that when channel state information (CSI) is available at the transmitter a large performance gain can be achieved. In a system employing time-division duplexing (TDD), CSI can be obtained at the base station if there is reciprocity between the forward and reverse channels. CSI can also be conveyed from the users to the base station via a limited-rate feedback channel in a frequency-division duplexing (FDD) system. In any case, channel estimation errors are inevitable due to the presence of background noise in the estimated signal and due to the finite number of feedback bits used in a limited-rate feedback system model. In this paper, we first consider the general case when partial CSI is available at the transmitter. We derive an MMSE based precoding technique that considers channel estimation errors as an integral part of the system design. Using rate-distortion theory and the generalized Lloyd vector quantization algorithm, we then specialize our results for the more practical limited-rate feedback system model. Compared to previously proposed precoding techniques such as channel inversion and regularized channel inversion, it is shown that the proposed precoding technique significantly improves the average bit error rate (BER) in the system. Furthermore, the performance of the proposed technique is investigated in the high signal-to-noise ratio (SNR) regime, and similar to [1], [2], it is shown that the proposed technique suffers from a ceiling effect that asymptotically limits the system performance.
In this paper, we study the downlink of cooperative Direct-Sequence Code Division Multiple Access (DS-CDMA) systems, where a set of Mobile Terminals (MT) cooperate with the purpose of improving their downlink communic...
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ISBN:
(纸本)9781424451234
In this paper, we study the downlink of cooperative Direct-Sequence Code Division Multiple Access (DS-CDMA) systems, where a set of Mobile Terminals (MT) cooperate with the purpose of improving their downlink communications reliability with the Base Station (BS). For combating Multiple-Access Interference (MAI) as well as transferring complexity and spatial processing from the mobile terminals to the transmitter of BS, multiuser transmitter precoding is considered. In addition to multiuser precoding based on Minimum Mean-Square Error (MMSE) criterion for mitigating MAI, the proper transmission power control strategy under a fixed total power constraint is proposed and analyzed. Compared with equal transmission power assigning where BS and cooperative terminals transmit with the same power, the proposed power allocation scheme enables significant performance gain at the destination. Finally, simulation results demonstrate acceptable performance of the proposed algorithms in synchronous DS-CDMA systems.
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