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In cooperative wireless communications, beamforming at relays can be employed to increase the signal-to-noise ratio (SNR). Since beamforming at relays requires that channel state information (CSI) be exchanged, an efficient CSI feedback scheme is proposed to reduce the feedback overhead incorporating an optimization of the combining and beamforming weights. With 802.16e OFDMA time-division duplexing...
This paper considers a large multi-user time-division duplex (TDD) system, where the base station (BS) acquires channel state information via pilot signaling from the users. In the downlink the BS employs zero-forcing (ZF) and regularized zero-forcing (RZF) precoding. We derive the optimal sum rate maximizing amount of channel training using sum rate approximations from the large system analysis of...
How to achieve the closed-loop processing gain is an important issue for frequency division duplexing (FDD) based multi-input multi-output (MIMO) systems, since the channel state information (CSI) is not available by reciprocity as time division duplexing (TDD). Current technique mainly uses the codebook based precoding, where the receiver feeds back the precoding matrix index (PMI) of the codebooks...
In this paper, we study the impact of imperfect channel state information at the transmitter and receiver (CSITR) on the diversity-multiplexing tradeoff in single-input multi-output (SIMO)/multi- input single-output (MISO) fading channels with two- way training. We consider two two-way training strategies: 1) the destination initiates the training, and 2) the source initiates the training. We show...
The communication between a multiple-antenna transmitter and multiple receivers (users) with either a single or multiple-antenna each can be significantly enhanced by providing the channel state information at the transmitter (CSIT) of the users, as this allows for scheduling, beamforming and multiuser multiplexing gains. The traditional view on how to enable CSIT has been as follows so far: In time-division...
Coordinated linear transmit-receive processing with beam selection is a method to utilize all degrees of freedom available in multiuser multiple-input multiple-output (MIMO) cellular systems in order to increase system capacity. By applying channel state information in the transmitter (CSIT), the base station (BS) is able to spatially multiplex downlink data streams for different users. In the time...
Recently research has been focused on techniques that simplify the mobile receiver structure in CDMA systems by means of precoding. 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...
In a communication network, it is often impractical for each node to learn the global channel knowledge (network connectivity and channel state information of each link). In this paper, we address distributed rate optimization for Time-Division Duplex (TDD) Multiple-Input Multiple-Output (MIMO) networks when part of the local channel knowledge is learned via message passing between each transmitter...
The absolute gain of multi-user diversity in the context of a downlink channel is the focus of this contribution. Enjoying multi-user diversity gain first requires the channel information availability at the transmitter (CSIT) in a normal downlink (DL) system. Although multi-user diversity gains have been specified well, but the burden of exchange of information required is not rigorously accounted...
Two distinct models of feedback, suited for FDD (frequency division duplex) and TDD (time division duplex) systems respectively, have been widely studied in the literature. In this paper, we compare these two models of feedback in terms of the diversity multiplexing tradeoff for varying amount of channel state information at the terminals. We find that, when all imperfections are accounted for, the...
We present linear precoding methods for downlink transmission in multi-user multiple-input multiple-output (MIMO) systems where channel state information (CSI) can be obtained through training. In this paper, channel training overhead and estimation error are rigorously accounted for while determining the net system throughput. First, we consider the case with training on the reverse link only. We...
In future time division duplex (TDD)-based broadband wireless systems, it will be possible to exploit the channel reciprocity to implement channel state information (CSI)-based multi user multiple input multiple output (MU-MIMO) techniques, which will ensure highly efficient spectrum usage. To increase the cell coverage while ensuring the quality of service (QoS) for all UEs across the cell area,...
We analyze a broadcast channel with no initial assumption of channel state information neither at the base station (BS) nor at the users' side. For the case when there is no possibility of feedback to the BS and it remains oblivious of the channel state information throughout the transmission, it is shown that the capacity region is bounded by the capacity of a point-to-point MISO link and hence the...
Recent work on wireless beamforming has focused on multi-user diversity effects, where terminals are chosen opportunistically based on their responses to test beams. Orthogonality between the test beams is typically chosen to aid subsequent interference-free transmission to the corresponding terminals. However, much of this work assumes that: (i) the pool of terminals on a given frequency-band is...
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