A key feature of the packet scheduler in LTE system is that it can allocateresources both in the time and frequency domain. Furthermore, the scheduler isacquainted with channel state information periodically reported by userequipments either in an aggregate form for the whole downlink channel, ordistinguished for each available subchannel. This mechanism allows for widediscretion in resource allocation, thus promoting the flourishing of severalscheduling algorithms, with different purposes. It is therefore of greatinterest 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, whichalready supports a set of well known scheduling algorithms for LTE downlink,though it still lacks schedulers that provide throughput guarantees. In thiswork we contribute to fill this gap by implementing a scheduling algorithm thatprovides long-term throughput guarantees to the different users, whileopportunistically exploiting the instantaneous channel fluctuations to increasethe cell capacity. We then perform a thorough performance analysis of thedifferent scheduling algorithms by means of extensive ns-3 simulations, bothfor saturated UDP and TCP traffic sources. The analysis makes it possible toappreciate the difference among the scheduling algorithms, and to assess theperformance gain, both in terms of cell capacity and packet service time,obtained by allowing the schedulers to work on the frequency domain.
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