Opportunistic Feedback Scheme Research Articles

Reducing feedback load for OFDM-based wireless system

In this paper, the feedback load reduction problem in wireless systems based on orthogonal frequency division multiplexing (OFDM) is investigated and an opportunistic feedback scheme (OFS) is proposed. The key idea behind OFS is that only the key channel gains which can significantly affect the system throughput are fed back to the BS. Firstly, the key channel gains are proved to belong to a channel gain interval. Secondly, a statistical method is proposed to estimate the channel gain interval. Thirdly, the opportunistic feedback scheme is formulated and the feedback load of OFS is analyzed. The advantage of OFS is threefold: the first is OFS can work in both OFDM-based multicast system and OFDM-based unicast system. The second is the channel fading type of the BS-user link is not required, which is more realistic. The third is OFS can get better feedback load performance compared with other schemes, while achieving almost the same throughput performance compared with that of full feedback scheme.

Opportunistic Two-Stage Feedback and Scheduling for MIMO Downlink Systems

We propose an opportunistic two-stage feedback and scheduling algorithm that is based upon zero-forcing beamforming with semi-orthogonal user selection (ZFBF-SUS) to reduce its feedback load. In an SUS algorithm, a base station schedules semi-orthogonal users using the feedback of all users' channel information. However, such feedback overhead significantly increases with the number of users. To reduce the feedback load of ZFBF-SUS systems, the proposed two-stage feedback scheme opportunistically and separately exploits the signal-to-interference-plus-noise ratio and orthogonality in each stage such that only a fraction of users feed back their channel information. Based on this opportunistic feedback scheme, we decouple the entire process of the SUS into two sub-processes. The proposed two-stage feedback and scheduling scheme effectively exclude the inappropriate users for ZFBF transmission in both feedback and scheduling periods, and thus save the scarce resources consumed for the feedback process. We derive an analytical expression for the average number of feedback bits of the proposed system and optimize it in an averaged sense. Further, the sum-rate of the proposed system is theoretically investigated. Both analytical and simulation results show that the proposed algorithm achieves the performance of conventional ZFBF-SUS systems with a significantly reduced number of feedback bits.

Opportunistic Feedback and Scheduling to Reduce Packet Delays in Heterogeneous Wireless Systems

We consider an opportunistic feedback and scheduling scheme for multiuser wireless systems. In opportunistic feedback schemes, a set of thresholds is assigned to the users, and only users with channel quality above the threshold transmit the feedback on channel state information (CSI) to the base station. We propose an opportunistic feedback scheme that combines techniques from queue/weight-based opportunistic scheduling to improve users' delay performance. A set of queue-based weights designed to slowly track variations in users' backlog is computed; then, each user is assigned a threshold based on the weights. The proposed scheme effectively captures heterogeneity in the offered loads, which is crucial for delay performance. To that end, we formulate a nonconcave maximization problem and propose an approximation algorithm that is numerically shown to have high accuracy. By simulation, we show that our scheme substantially reduces the mean delay, compared with conventional schemes.

Two-Stage Opportunistic Feedback Over Multiuser Diversity Systems

In order to reduce feedback overload, a framework of contention-based feedback was established. However, since a user is randomly chosen, it cannot maximize capacity. Moreover, if a collision occurs, a base station cannot obtain any information to schedule a user; thus, a scheduling outage happens. In this paper, we propose a two-stage opportunistic feedback scheme to maximize capacity with the limited feedback. The proposed scheme guarantees selecting the user with the highest signal-to-noise ratio (SNR) channel state and considers the scheduling outage situation using previous feedback information. In addition, we define the effective capacity to show the relation between the capacity and the feedback overload. Simulation results show that the proposed scheme achieves higher effective capacity with limited feedback than existing contention-based feedback schemes do.

Net Throughput Maximization of Per-Chunk User Scheduling for MIMO-OFDM Downlink

Per-chunk user scheduling for multiple-input-multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) downlink is considered. By grouping adjacent subcarriers into chunks, the amount of required channel state information feedback is reduced. Based on the net throughput criterion, which accounts for the reduction in sum rate due to the feedback overhead, it is shown that there exists an optimal chunk size that maximizes the net throughput. To reduce the feedback requirement even further, an opportunistic feedback scheme is proposed, and a close approximation for its net throughput is derived. The net throughput of per-chunk user scheduling with optimized chunk size is compared to various other limited-feedback MIMO-OFDM downlink strategies. The results show that increasing the total number of users in the system results in the net throughput of most existing MIMO-OFDM downlink schemes decreasing to zero for moderate-size user pools, whereas the net throughput of per-chunk user scheduling with opportunistic feedback increases with the total number of users, even when that number is very large(>; 1000).

Comments on "Partial channel feedback schemes maximizing overall efficiency in wireless networks" [Apr 08 1306-1314

The proof of Proposition 2 in the above-mentioned paper was incorrect due to some flaws in the prerequisite analysis of the proposed hybrid feedback scheme. We fix the flaws and correct the proof in this comment. From the corrected proof, we arrive at a new observation that the hybrid feedback scheme has exactly the same feedback overhead as the pure opportunistic feedback scheme if the threshold is adaptively set for a target utilization. Simulation results demonstrate the correctness of our analysis.