Service-differentiated downlink flow scheduling to support QoS in long term evolution
The growing demand of network services, especially for broadband downlink communication, has triggered the evolution of cellular systems. Recently, 3GPP continuously works out the standard of long term evolution (LTE) in response to the oncoming 4G cellular system. LTE adopts the OFDMA technology for downlink communication, and divides the spectral resource into physical resource blocks (PRBs). However, the LTE flow scheduling problem, which asks how to allocate PRBs to downlink flows for communication, is not well addressed in the standard but has great impact on transmission efficiency. On the other hand, LTE categorizes flows into guaranteed bit rate (GBR) and non-GBR classes, where GBR flows usually have higher priorities and shorter delay constraint than non-GBR flows. Although various solutions have been proposed to the LTE flow scheduling problem, many of them generally aim at maximizing transmission efficiency or keeping fair transmission, which may starve non-GBR flows or cannot well support quality of service (QoS) for GBR flows. Therefore, the paper develops a service-differentiated downlink flow scheduling (S-DFS) algorithm by taking the aforementioned difference between flows into consideration. Except for increasing transmission efficiency, S-DFS has two major goals: (1) satisfying the QoS requirement of GBR flows, and (2) ensuring the data transmission of non-GBR flows. Specifically, S-DFS first deals out PRBs to flows according to their channel conditions and QoS class identifier (QCI) defined in LTE. Then, with the mechanism of resource reallocation, S-DFS can assign a dynamic amount of reallocatable PRBs to the flows whose packets are about to be dropped. Experimental results demonstrate that S-DFS can achieve higher LTE transmission efficiency. Furthermore, it not only reduces both dropping ratio and delay of GBR packets, but also improves data throughput of non-GBR flows.