Abstract
We consider a multi-antenna broadcast channel with more single-antenna receivers than transmit antennas and partial channel state information at the transmitter (CSIT). We propose a novel type of CSIT representation for the purpose of user selection, coined as ranking-based feedback. Each user calculates and feeds back the rank, an integer between 1 and W + 1, of its instantaneous channel quality information (CQI) among a set of W past CQI measurements. Apart from reducing significantly the required feedback load, ranking-based feedback enables the transmitter to select users that are on the highest peak (quantile) with respect to their own channel distribution, independently of the distribution of other users. It can also be shown that this feedback metric can restore temporal fairness in heterogeneous networks, in which users' channels are not identically distributed and mobile terminals experience different average signal-to-noise ratio (SNR). The performance of a system that performs user selection using ranking-based CSIT in the context of random opportunistic beamforming is analyzed, and we provide design guidelines on the number of required past CSIT samples and the impact of finite W on average throughput. Simulation results show that feedback reduction of order of 40‐50% can be achieved with negligible decrease in system throughput.
Highlights
Multiple-input multiple-output (MIMO) communication systems have the potential to offer high spectral efficiency as well as link reliability
We provide a bound on the ratio of the empirical distribution observed over W samples by the actual cumulative distribution functions (CDFs) (W→∞) as a means to quantify the throughput reduction using ranking-based channel state information at transmitter (CSIT) calculated over finite
(ii) Scheme II: random beamforming (RBF) in which users are selected based on quantized signal-to-noise ratio (SNR)/signal-to-interference plus noise ratio (SINR) feedback in the scheduling stage
Summary
Multiple-input multiple-output (MIMO) communication systems have the potential to offer high spectral efficiency as well as link reliability. An alternative approach, referred to as selective or threshold-based feedback, allows a user to send back information depending on whether its current channel conditions exceed a certain threshold or not This feedback reduction algorithm was first proposed in [20] for a downlink singleinput, single-output (SISO) system and SNR-dependent thresholds. Similar distribution-based schedulers have been proposed in [29,30,31] as a means to schedule a user whose instantaneous rate is in the highest quantile of its distribution These works were solely focused on scheduling at the transmitter side, and not in the context of feedback reduction nor that of MIMO systems. The performance of the proposed feedback reduction technique is numerically evaluated in Section 7, and, Section 8 concludes the paper
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
