Analytical Model of Proportional Fair Scheduling in Interference-limited OFDMA/LTE Networks

Various system tasks like interference coordination, handover decisions, admission control etc. in upcoming cellular networks require precise mid-term (spanning over a few seconds) performance models. Due to channel-dependent scheduling at the base station, these performance models are not simple to obtain. Furthermore, upcoming cellular systems will be interference-limited, hence, the way interference is modeled is crucial for the accuracy. In this paper we present an analytical model for the SINR distribution of the \textit{scheduled} subcarriers of an OFDMA system with proportional fair scheduling. The model takes the precise SINR distribution into account. We furthermore refine our model with respect to uniform modulation and coding, as applied in LTE networks. The derived models are validated by means of simulations. In additon, we show that our models are approximate estimators for the performance of rate-based proportional fair scheduling, while they outperform some simpler prediction models from related work significantly.Comment: 7 pages, 6 figures. This work has been submitted to the IEEE for possible publication. Copyright may be transferred without notice, after which this version may no longer be accessibl

On the Interference As Noise Approximation in OFDMA/LTE Networks

In this paper we generalize analytical performance models for proportional fair scheduling in OFDMA/LTE networks. We address the issue of modelling multiple fading interferers present in practical deployments. Specifically, we elaborate on the stochastic modelling of SINR-distribution for which we derive the rate expectation of instantaneously scheduled resources. The resulting analytical performance model is validated by means of simulations considering realistic network deployments. Compared with related work, our model demonstrates a significantly higher accuracy for long-term rate estimation. We illustrate the utility of such high-precision models by studying the impact on terminal assignment in fractional frequency reuse. Simply by using a suitable estimation model, cell-edge throughput can be improved up to 50%.QC 20150123</p

Rate Selection Analysis under Semi-Persistent Scheduling in LTE Networks

Upcoming LTE networks have basically two different modes for scheduling data in the down-link by the base station. Dynamic scheduling brings the advantage of exploiting instantaneous channel state information while it puts on the other hand a significant burden on the system in terms of overhead and computation requirements. Especially for small packets that show up periodically, the overhead is typically too high. Therefore, the base station can serve such packet flows by the semi-persistent scheduling mode. In this mode, a certain resource allocation is fixed to a periodic schedule. While this does not allow any longer to exploit instantaneous channel states, it requires much less overhead. In this paper, we address the problem of selecting a modulation and coding scheme for such semi-persistent scheduling grants. The problem lies here in the stochastic characterization of the resource blocks over the next few seconds while on the other hand estimating based on such a characterization the blok error rate (and hence the average goodput). We provide a novel scheme, which outperforms all previously presented schemes significantly. The underlying model that we provide can also be used for any other long-term decision in an LTE system with semi-persistent scheduling such as interference coordination, handover decision etc.QC 20131212</p

Registration & Continental Breakfast

In this paper we generalize analytical performance models for proportional fair scheduling in OFDMA/LTE networks. We address the issue of modelling multiple fading interferers present in practical deployments. Specifically, we elaborate on the stochastic modelling of SINR-distribution for which we derive the rate expectation of instantaneously scheduled resources. The resulting analytical performance model is validated by means of simulations considering realistic network deployments. Compared with related work, our model demonstrates a significantly higher accuracy for long-term rate estimation. We illustrate the utility of such high-precision models by studying the impact on terminal assignment in fractional frequency reuse. Simply by using a suitable estimation model, cell-edge throughput can be improved up to 50%.QC 20150123</p

Semi-Static Interference Coordination in OFDMA/LTE Networks : Evaluation of Practical Aspects

To minimize interference in LTE networks, several inter-cell interference coordination (ICIC) techniques have been introduced. Among them, semi-static ICIC offers a balanced trade-off between applicability and system performance. The power allocation per resource block and cell is adapted in the range of seconds according to the load in the system. An open issue in the literature is the question how fast the adaptation should be performed. This leads basically to a trade-off between system performance and feasible computation times of the associated power allocation problems. In this work, we close this open issue by studying the impact that different durations of update times of semi-static ICIC have on the system performance. We conduct our study on realistic scenarios considering also the mobility of mobile terminals. Secondly, we also consider the implementation aspects of a semi-static ICIC. We introduce a very efficient implementation on general purpose graphic processing units, harnessing the parallel computing capability of such devices. We show that the update periods have a significant impact on the performance of cell edge terminals. Additionally, we present a graphic processing unit (GPU) based implementation which speeds up existing implementations up to a factor of 92x.QC 20150123</p

On Semi-Static Interference Coordination under Proportional Fair Scheduling in LTE Systems

In this paper we consider the design of semi-static inter-cell interference coordination schemes for LTE networks. In this approach, base stations coordinate the power settings per resource block over long time spans such as seconds. In order to optimize the power settings, one needs to employ models which predict the rate of terminals over the next coordination period under the usage of a given power setting. However, these models are typically quite simple and neglect the impact from fading as well as from dynamic resource allocation performed at the base stations on a millisecond basis. Ignoring such properties of OFDMA networks leads therefore to suboptimal transmit power settings. In this paper, we study the impact from a precise rate prediction model that accurately accounts for fading and dynamic resource allocation. On the down-side, this more precise model leads to a much more involved optimization problem to be solved once per coordination period. We propose two different heuristic methods to deal with this problem. Especially the usage of genetic algorithm results to be promising to counteract the complexity increase. We then study the overall system performance and find precise rate prediction models to be essential for semi-static interference coordination as they provide significant performance improvements in comparison to approaches with simpler models.QC 20130830</p

From Radio Design to System Evaluations for Ultra-Reliable and Low-Latency Communication

Ultra-reliable and low-latency communication is the enabler for many new use cases, including wireless industrial automation. Fulfilling varying requirements of these use cases demands a flexible radio design. To address this, a holistic approach needs to be adopted. Therefore, this paper presents the radio access concepts affecting the communication reliability and latency, and comprehensively evaluates link and system level considerations through simulations. In particular, we describe the choice of suitable modulation and coding schemes, and discuss the impact of different numerologies and waveform candidates. We also point out the key principles for radio frame design to reduce the end-to-end latency. The presented concepts are then used to evaluate the performance at system level for an industrial scenario. It is shown that by an appropriate design of the radio interface for 5G system, the required low-latency and high reliability for industrial applications and many other use cases can be achieved.QC 20170919</p