Paper of Jinal MIMO BC Nov06Edit

Multiple transmit antennas in a downlink channel can provide tremendous capacity (i.e., multiplexing) gains, even when receivers have only single antenna. However, receiver and transmitter channel status information is generally required. In this correspondence, a system where each receiver has perfect channel knowledge, but the transmitter only receives quantized information regarding the channel instantiation is analyzed. The well-known zero-forcing transmission technique is considered and simple expressions for the throughput degradation due to finite-rate feedback are derived. A key finding is that the feedback rate per mobile must be increased linearly with the signal-to-noise ratio (SNR) (in decibels) in order to achieve the full multiplexing gain. This is in sharp contrast to point-to-point multiple-input multiple-output (MIMO) systems, in which it is not necessary to increase the feedback rate as a function of the SNR.

My Comments Edit

This paper shows the number of feedback bits to achieve the optimal multiplexing gain. The optimal number of feedback bits should be proportional to the average SNR of the downlink channel, as follows:

$ B = (M-1) \log_2(P) $

where $ M $ is the number of transmit antennas and $P$ is the average SNR. This paper does not consider the feedback resource point of view. Although the number of feedback bits increases, the feedback resource can not be increased if the capacity of the feedback link increases according to the average SNR. Notice that as the average SNR depends on the distance between the transmitter and the receiver, the average SNRs of the downlink and the uplink usually closely related.


The subject of this paper is the long-standing open problem of developing a general capacity theory for wireless networks, particularly a theory capable of describing the fundamental performance limits of mobile ad hoc networks (MANETs). A MANET is a peer-to-peer network with no pre-existing infrastructure. MANET's the most general wireless networks, with single-hop, relay, interference, mesh, and start networks comprising special cases. The lack of a MANET capacity theory has stunted the developement and commercialization of many types of wireless networks, including emergency, military, sensor, and community mesh networks. Information theory, which as been vital for links and ceteralized networks, has not been sucessfullly applied to decentralized wireless networks. Even if this was accomplished, for such a theory to truly chracterize the limits of deployed MANETs it must overcome three key roadblocks. First, most current capacity results rely on the allowance of unbounded delay and reliability. Second, sptial and timescale decompositions have not yet been developed for optimally modeling the spatial and temporal dynamics of wireless networks. Third, a useful network capacity theory must integrate rather than ignore the important role of overhead messaging and feedback. This paper describes some of the shifts in thinking that may be needed to overcome these roadblocks and develop a more general theory that we refer to as non-equilibrium information theory.


Tags: cooperation, relay, compress-and-forward

In this paper, we investigate the capacity of Compress-and-Forward (C&F) cooperative relaying scheme when the C&F relay operates in Time Division Duplex (TDD). In our evaluation, we consider MIMO-OFDM transmission. An achievable rate was previously dereived in [6] assuming sclar channel. We extend this Wyner-Ziv bound to MIMO-OFDM, by applying results from Bayesian vector estimation and rate-distortion coding theory. Then we derive the mutual information of a sub-optimum relaying scheme in which the relay applies K-L transform to the signal received from the source before quantizing it and forwarding it to the destination as a new codeword. Finally, we illustrate by simulations (in an environment similar to IEEE802.16) the fact that for some scenarios, the C&F approach other known relaying techniques. This remains true even if the C&F sub-optimal scheme is considered.


This paper studies upper bounds and lower bounds on the outage capacity and ergodic capacity of a three-node wireless relay channel in a Rayleigh fading environment. We also take into account practical constraints on the transmission duplexing at the relay node and on the synchronization between the source node and the relay node. We find that the gap between the upper bounds and lower bounds is typically negligible. Compared to direct transmission and traditional multihop protocols, out results reveal that optimum relay channel signaling can significantly outperform multi-hop protocols, and that power allocation has a significant impact on performance.

Paper: Trivellato and Huang's paper Edit

Abstract: We consider a MIMO [[[broadcast channel]] where both the transmitter and receivers are equipped with multiple antenns. Channel state information at the transmitter (CSIT) is obtained through [limited feedback|limited (i.e., finite-bandwidth) feedback] from the receivers that index a set of precoding vectors contained in the predefined codebook. We propose a novel transceiver architecture based on zero-forcing beamforming and liner receiver combining. The receiver combining and quantization for CSIT feedback are jointly designed in order to maximize the expected SINR for each user. We provide analytic characterization of the achievable throughput in the case of many users and show how the additional receiver antennas or higher multiuser diversity can reduce the required feedback rate to achieve a target throughput. We also propose a design methodology for generating codebooks tailored for arbitrary spatial correlation statistics. The resulting codebooks have a tree structure that can be utilized in time-correlated MIMO channels to significantly reduce feedback overhead. Simulation results shows the effectiveness of the overall transceiver design strategy and codebook design methodology compared to prior techniques in a variety of correlation environments.

Comments on the paper Edit

This paper proposes a new approach which feeds back the codebook index maximizing expected SINR (ESINR) and the associate ESINR.


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