دانلود رایگان مقاله طرح گزارش بازخورد جزئی برای انتقال ویدیو موبایل LTE با تامین کیفیت سرویس

Abstract

Opportunistic frequency-domain scheduling and link adaptation enable the long term evolution (LTE) cellular systems to maximize the throughput. Successful scheduling and link adaptation require perfect channel state information (CSI) at the eNodeB. However, for multi-carriers systems, a huge undesirable amount of signaling overhead is required to report the channel quality indicator (CQI) for the whole bandwidth. On the contrary, reducing the size of CQI overhead detriments the downlink performances and does not guarantee the quality-of-service (QoS) when real-time multimedia services are applied. As a consequence, a tradeoff between CQI overhead and the downlink performances is presented in this paper. Then, an Adaptive Threshold CQI Partial Feedback (ATCPF) scheme is proposed by using multi-objective swarm intelligence to find the optimal feedback threshold. Based on an LTE system-level simulation, significant enhancements of 20% and 38% in throughput and packet loss ratio (PLR) respectively are obtained compared to a fixed threshold feedback. Since video flows are considered, a self-optimized partial feedback (SOPF) is further developed by using cross-layer optimization to guarantee QoS. The results show that the feedback overhead is minimized at low-load network condition while maintaining the PLR below its target. The proposed algorithm provides a high flexibility in responding to certain variations, and it enables the cellular systems to support multimedia services.

7. Summary and conclusion

Reducing the amount of CQI signaling overhead is crucial for saving energy and bandwidth of a UE. However, the reduction in channel feedback information results in downlink performance degradation, and might sacrifice the QoS when real time multimedia services are targeted. In this paper, the relationship between CQI overhead and LTE downlink performances was analyzed. It is revealed that the more signaling overhead to report the channel quality at the uplink, the more throughput can be achieved at the downlink transmission with less outage capacity. Accordingly, the ATCPF algorithm is developed to find the best tradeoff between uplink and downlink performances by using a hybrid of swarm intelligence and SAW. Based on the system level simulation, the ATCPF algorithm has achieved the best FOP compared with the fixed-threshold and subband level feedback schemes, especially when the maximum priority is assigned to the outage capacity (ATOP). Moreover, the SOPF algorithm is proposed to guarantee QoS for video traffic. It is shown that the signaling overhead can be minimized to the lowest possible as long as the video flows are correctly received by UEs. The developed scheme provides a high flexibility in responding to various network conditions without applying complicated modifications. Generalizing the proposed algorithm for real-time applications other than video streaming is possible as long as the QoS parameter is specified. For non-real time traffic, the QoS constraint will be relaxed for the benefit of other system performances. In addition to CQI feedback, the precoding matrix and rank indicators are also required to be incorporated in the future work when MIMO-based LTE systems are investigated.