A key feature of the packet scheduler in LTE system is that it can allocate resources both in the time and frequency domain. Furthermore, the scheduler is acquainted with channel state information periodically reported by user equipments either in an aggregate form for the whole downlink channel, or distinguished for each available subchannel. This mechanism allows for wide discretion in resource allocation, thus promoting the flourishing of several scheduling algorithms, with different purposes. It is therefore of great interest to compare the performance of such algorithms in different scenarios. A very common simulation tool that can be used for this purpose is ns-3, which already supports a set of well known scheduling algorithms for LTE downlink, though it still lacks schedulers that provide throughput guarantees. In this work we contribute to fill this gap by implementing a scheduling algorithm that provides long-term throughput guarantees to the different users, while opportunistically exploiting the instantaneous channel fluctuations to increase the cell capacity. We then perform a thorough performance analysis of the different scheduling algorithms by means of extensive ns-3 simulations, both for saturated UDP and TCP traffic sources. The analysis makes it possible to appreciate the difference among the scheduling algorithms, and to assess the performance gain, both in terms of cell capacity and packet service time, obtained by allowing the schedulers to work on the frequency domain.
Performance analysis of downlink scheduler can be carried out either at the MAC layer or at the transport layer where in the latter the effect on transmission control protocol (TCP) is of high importance. While the MAC throughput analysis has its own benefits, a huge fraction of today's data is carried via HTTP @cite_11 which uses TCP because it is reliable, well understood, and can be conveniently managed by firewalls and security systems. However, it is not alway straightforward to infer TCP throughput from MAC performance for a given scheduling algorithm. It is therefore essential to investigate the performance of the scheduling algorithms when they handle TCP traffic as well.
@cite_11
2132454267
TCP is widely used in commercial multimedia streaming systems, with recent measurement studies indicating that a significant fraction of Internet streaming media is currently delivered over HTTP TCP. These observations motivate us to develop analytic performance models to systematically investigate the performance of TCP for both live and stored-media streaming. We validate our models via ns simulations and experiments conducted over the Internet. Our models provide guidelines indicating the circumstances under which TCP streaming leads to satisfactory performance, showing, for example, that TCP generally provides good streaming performance when the achievable TCP throughput is roughly twice the media bitrate, with only a few seconds of startup delay.