Opportunistic Feedback Protocol Research Articles

Improved opportunistic feedback with multiuser diversity for wireless systems with finite queue

A contention-based opportunistic feedback protocol has been proposed in the literature, to achieve multiuser diversity for the downlink transmission of a multiuser wireless system, with the assumption that the incoming data for the active users are infinitely backlogged. However, this assumption is not valid if the authors consider the finite-length queuing effect in practical systems. By taking not only the channel states, but also the queuing states into account, the authors propose an improved opportunistic feedback protocol with multiuser diversity, and analyse its performance with adaptive modulation and coding. Additionally, instead of solving a system of equations directly, a simple iterative method is proposed to obtain the stationary distribution of the system, where the system behaviour is modelled by a two-dimensional finite-state Markov chain. Numerical results demonstrate that the authors proposed protocol is superior to the protocol in the literature in terms of the average throughput, the average spectral efficiency and the average packet delay, when considering the queuing dynamics.

Throughput Analysis of Opportunistic Feedback for Downlink Multiuser Diversity with Capture Effect

An opportunistic feedback protocol has been proposed in the literature to achieve multiuser diversity for the downlink transmission of a multiuser wireless system. In this letter, through theoretical analysis and extensive simulations, it is shown that the capture effect can have a significant impact on system throughput. It is also shown that, to achieve optimal throughput, the number of minislots used for opportunistically finding a user in the protocol should not be too large due to the overhead induced by the control packets.

Capacity and Fairness Trade-off in an Outage Situation over Multiuser Diversity Systems

Without an appropriate scheduling scheme for subscriber stations (SSs) in an outage situation, the opportunistic feedback protocol degrades the system performance and it does not achieve the desired capacity and fairness trade-off. In this paper, we propose a new downlink multiuser scheduling scheme to balance a trade-off between capacity and fairness with one-bit information. In particular, we propose a high successful-feedback SS selection (HSSS) scheme using one-bit information to provide the flexible trade-off in an outage situation. As a result, the proposed scheme not only reduces a significant feedback overload but also considers scheduling in the outage situation. Simulation results show that the proposed scheme achieves the flexible trade-off between capacity and fairness in the outage situation.

Multiuser Diversity in a MIMO System With Opportunistic Feedback

An opportunistic feedback protocol with multiple thresholds and multiple access probabilities is proposed for multiuser diversity in multiple-input-multiple-output (MIMO) broadcast channels. Users compete to report the channel state information (CSI) via contention-based feedback channels if their scheduling metric exceeds a threshold. The users are divided into two classes according to their scheduling metric. For each class, the users have different random access probabilities and different chances to access feedback minislots. The performance of the proposed feedback protocol is evaluated in a MIMO system with zero-forcing (ZF) receivers in terms of the sum-rate capacity, the feedback load, and fairness. The simulation results show that the proposed feedback protocol significantly reduces the feedback load without sacrificing the sum-rate capacity too much. The proposed feedback protocol can be operated with existing scheduling algorithms without modification.

Opportunistic feedback with multiple classes in wireless systems

An opportunistic feedback protocol with multiple access probabilities is proposed, where users are divided into several classes according to their measured channel state. Different random access probabilities are assigned to each class. All users compete to send a feedback message through random access if their scheduling metric exceeds a threshold. An analytical model is developed for evaluating the proposed feedback protocol in terms of the sum-rate capacity and the feedback load. The proposed feedback protocol achieves an asymptotic sum-rate capacity with a minimal amount of feedback information.

Capacity and Fairness in Multiuser Diversity Systems with Opportunistic Feedback

An opportunistic feedback protocol is proposed for multiuser diversity systems with proportional fair scheduling and maximum-throughput scheduling. The uplink feedback period is divided into two subperiods and users randomly access the feedback minislots according to their scheduling metric. An integrated analytical model is developed for evaluating the proposed feedback protocol.

Opportunistic Feedback for Multiuser MIMO Systems With Linear Receivers

A novel multiuser scheduling and feedback strategy for the multiple-input multiple-output (MIMO) downlink is proposed in this paper. It achieves multiuser diversity gain without substantial feedback requirements. The proposed strategy uses per-antenna scheduling at the base station, which maps each transmit antenna at the base station (equivalently, a spatial channel) to a user. Each user has a number of receive antennas that is greater than or equal to the number of transmit antennas at the base station. Zero-forcing receivers are deployed by each user to decode the transmitted data streams. In this system, the base station requires users' channel quality on each spatial channel for scheduling. An opportunistic feedback protocol is proposed to reduce the feedback requirements. The proposed protocol uses a contention channel that consists of a fixed number of feedback minislots to convey channel state information. Feedback control parameters including the channel quality threshold and the random access feedback probability are jointly adjusted to maximize the average throughput performance of this system. Multiple receive antennas at the base station are used on the feedback channel to allow decoding multiple feedback messages sent simultaneously by different users. This further reduces the bandwidth of the feedback channel. Iterative search algorithms are proposed to solve the optimization for selection of these parameters under both scenarios that the cumulative distribution functions of users are known or unknown to the base station