Scheduling Policies in Time and Frequency Domains for LTE Downlink Channel: A Performance Comparison

A key feature of the Long-Term Evolution (LTE) system is that the packet scheduler can make use of the channel quality information (CQI), which is periodically reported by user equipment 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 under different scenarios. Here, we carry out a thorough performance analysis of different scheduling algorithms for saturated User Datagram Protocol (UDP) and Transmission Control Protocol (TCP) traffic sources, as well as consider both the time- and frequency-domain versions of the schedulers and for both flat and frequency-selective channels. The analysis makes it possible to appreciate the difference among the scheduling algorithms and to assess the performance gain, in terms of cell capacity, users' fairness, and packet service time, obtained by exploiting the richer, but heavier, information carried by subchannel CQI. An important part of this analysis is a throughput guarantee scheduler, which we propose in this paper. The analysis reveals that the proposed scheduler provides a good tradeoff between cell capacity and fairness both for TCP and UDP traffic sources

State Modulated Traffic Models for Machine Type Communications

Machine-to-machine (M2M) traffic is variegate and finding a traffic model which can cover a wide range of M2M sources is challenging. In this paper we address this challenge by proposing an extension of legacy renewal processes for modeling of M2M traffic sources. To this end, we first describe the model and derive some performance parameters, as the overall packet arrival distribution and its moments. We then discuss the packetgeneration process and consider the counting variable in atime interval, and give the mean and the Laplace transformof the z-transform for this variable. Successively, we present the asymptotic expansion for the variance and the Index of Dispersion of Counts (IDC). We derive the expression of the two first coefficients of this expansion in the general case, while more explicit expressions are provided for some special cases. More specifically, for the special case of a source model with two states, geometric distribution of the numbers of arrivals in each state, and exponential inter-arrival times, we solve for the modelparameters in terms of mean, variance and two IDCs. The model is then applied to real M2M traces obtained from an operational network. Albeit the match is not perfect, yet the proposed model captures the main features of the traces, in particular the large burstiness in the packet arrival process

Service differentiation for improved cell capacity in LTE networks

The wide flexibility of LTE resource allocation scheme has led to the definition of various schedulers that attempt to maximize the quality of the service offered to the different users, depending on their channel conditions. Unfortunately, providing service guarantees in dynamic channel conditions typically requires a cost in terms of spectral efficiency of the transmission resource allocation. In this work, we investigate this tradeoff and propose a resource allocation scheme that adapts the service level guarantees to the average channel conditions of the users, in order to provide fair resource allocation among users with homogeneous channel conditions, while improving the cell spectral efficiency. A performance analysis is carried out by comparing the proposed scheduler with other well known schedulers. Results show that the proposed method can improve the cell capacity, while guaranteeing long-term throughput fairness among users of the same class. In addition, we analyze the short-term throughput provided by the proposed scheduler and provide a semi-analytical model to assess the gap with respect to the long-term performance

A performance comparison of LTE downlink scheduling algorithms in time and frequency domains

A number of scheduling algorithms for LTE downlink have been proposed and evaluated leveraging the flexibility of the resource allocation in both the time and the frequency domain. However, the existing literature falls short when it comes to schedulers that provide throughput guarantees. In this paper, 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 perform a thorough performance analysis comparing this algorithm with the other well known 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 in the frequency domain