Joint Scheduling and Resource Allocation in OFDMA Downlink Systems Via ACK/NAK Feedback

Abstract

In this paper, we consider the problem of joint scheduling and resource allocation in the OFDMA downlink, with the goal of maximizing an expected long-term goodput-based utility subject to an instantaneous sum-power constraint, and where the feedback to the base station consists only of ACK/NAKs from recently scheduled users. We first establish that the optimal solution is a partially observable Markov decision process (POMDP), which is impractical to implement. In response, we propose a greedy approach to joint scheduling and resource allocation that maintains a posterior channel distribution for every user, and has only polynomial complexity. For frequency-selective channels with Markov time-variation, we then outline a recursive method to update the channel posteriors, based on the ACK/NAK feedback, that is made computationally efficient through the use of particle filtering. To gauge the performance of our greedy approach relative to that of the optimal POMDP, we derive a POMDP performance upper-bound. Numerical experiments show that, for slowly fading channels, the performance of our greedy scheme is relatively close to the upper bound, and much better than fixedpower random user scheduling (FP-RUS), despite its relatively low complexity.

Fairness-Adaptive Goodput-Based Resource Allocation in OFDMA Downlink with ARQ

“…Two standard approaches can be applied to solve (20). With the IP solution, for which the same discussion as in Section IV applies, the subchannels assignment matrix B IP represents the solution to (20) directly obtained using branch-and-bound algorithms, and U (B IP ) refers to the corresponding value of the utility function. Nevertheless, this optimal approach still has a high computational cost.…”

“…In their works, Aggarwal et al [18]- [20] have proposed several methods for allocating subcarriers, power, and MCSs to maximize the expected-sum-goodput-based utility. In [18], they exploit the use of acknowledgment/negative acknowledgment (ACK/NAK) feedback.…”

“…In [19], imperfect channel state information (CSI) at the transmitter (CSIT) is assumed, where Aggarwal et al study the continuous (a single resource shared by several users) and discrete cases and show that the continuous case solves the discrete case in some situations, providing a bound for the others. The work in [19] is extended in [20] to the case when ACK/NAK feedback is utilized. Given that the optimal solution is a partially observable Markov decision process, which is impractical for implementation purposes, Aggarwal et al propose a two-step approach that uses first a greedy resource allocation and afterward updates the subcarrier gain probability.…”

On the performance of adaptive HARQ with no channel state information feedback

“…Nevertheless, the optimization algorithm requires accurate channel state information (CSI) to obtain the corresponding packet error rate (PER) from a lookup table and subsequently the system throughput. In practice, maintaining perfect CSI is difficult and introduces additional cost to HARQ systems [17], [18].…”

Network control without CSI using rateless codes for downlink cellular systems

“…We investigate the cross-layer design of downlink cellular systems with imperfect (possibly no) CSI at the transmitter that employ rateless codes to resolve channel uncertainty. Most of the prior work on cross-layer network control with imperfect CSI was centered on fixed-rate codes, e.g., [14], [15], which can achieve Shannon capacity for a certain channel state. However, these schemes suffer from channel outages or inefficient use of available channel rates, since the CSI information is not perfectly known at the transmitter.…”