Tero Henttonen

Dynamic packet scheduling performance in UTRA Long Term Evolution downlink

In this paper we evaluate the performance of dynamic Packet Scheduling (PS) of 3GPP UTRAN Long Term Evolution (LTE) Downlink. Packet scheduling is of utmost importance in 3G LTE, because all traffic types with different Quality of Service requirements are competing of the resources. We present a decoupled time and frequency domain packet scheduling framework for LTE downlink. Simulation results with three basic packet scheduler combinations with different amount of fairness are presented in four different 3GPP macro simulation cases to show the both extremes in tradeoff between fairness and spectral efficiency. In addition, the effect of multiuser diversity on packet scheduling performance is studied. It is shown that by dividing the packet scheduler into a time domain and a frequency domain and utilizing different algorithms in both domains, the throughput fairness between users can be effectively controlled.

Channel Quality Indication Reporting Schemes for UTRAN Long Term Evolution Downlink

In this paper we evaluate the performance of channel quality indicator (CQI) reporting schemes in 3GPP UTRAN long term evolution (LTE) downlink (DL). In LTE, time and frequency dependent CQI is needed for DL packet scheduling (PS) and fast link adaptation (LA). Studies have indicated that frequency domain PS (FD-PS) and LA are essential techniques in improving the LTE performance, giving e.g. both cell throughput and coverage gain of around 40 % over a distributed multiplexing scheme. However, there is a tradeoff with signaling overhead related to the CQI feedback and overall LA and PS performance, which is rather overlooked in the literature. We analyze four different CQI reporting schemes with respect to system spectral efficiency and conclude that the best-M average and threshold based CQI reporting schemes seem to be the most promising in terms of the compromise between system performance and signaling overhead.

Voice-Over-IP Performance in UTRA Long Term Evolution Downlink

In this paper, we study voice-over-IP (VoIP) performance in UTRA long term evolution (LTE) downlink (DL). We have utilized fully dynamic system simulations to study the VoIP adaptive multi-rate (AMR) 12.2 codec capacity in four different 3GPP simulation cases. The effects of link adaptation (LA), packet bundling, control channel capacity and number of HARQ processes on VoIP capacity have also been considered. The results present the absolute VoIP capacity numbers of LTE DL. We also show that LA together with packet bundling provides clear gain on the VoIP capacity, because more VoIP packets can be scheduled in each TTI. Also, the control channel limitations can be effectively compensated by packet bundling.

Impact of Control Channel Limitations on the LTE VoIP Capacity

In this paper, we present a fully dynamic simulative analysis of the Downlink (DL) Voice-over-IP (VoIP) performance in 3G Long Term Evolution (LTE) with both Uplink (UL) and DL control channel constraints. In UL the Physical Uplink Control Channel (PUCCH) capacity affects the Channel Quality Indicator (CQI) resolution and in DL the Physical Downlink Control Channel (PDCCH) capacity has an impact to the amount of multiplexed users per Transmission Time Interval (TTI). The results indicate that with realistic control channel assumptions, semi-persistent packet scheduling outperforms dynamic packet scheduling.

A decentralized cooperative Uplink/Downlink adaptation scheme for TDD Small Cell Networks

This paper presents a cooperative decentralized scheme for adjusting the Uplink (UL)-Downlink (DL) configuration of a Small Cell Network (SCN) with a TDD air interface. The goal of the cooperative decentralized scheme is to make a more efficient use of common wireless resources, selecting convenient TDD-frame configurations to maximize a sum utility function that takes into account both individual traffic demands and actual interference coupling situations. The cooperative decentralized scheme for UL/DL adaptation can be executed locally at each Base Station (BS), and relies solely on the exchange of low-rate signaling information among neighboring cells. Based on observed performance improvements, we conclude that cooperative decentralized schemes are a viable option for flexible-TDD implementation in SCN environments, particularly in presence of cells with strong interference coupling and low-rate signaling capabilities.

On Idle Mode Mobility State Detection in Evolved UTRAN

In this paper we present different idle mode mobility state detection mechanisms targeted for 3GPP Evolved UTRAN. The purpose is to study the reliability of the mobility state detection mechanism specified in 3GPP TS 36.304 for 3GPP Release 8 in varying conditions, such as different re-selection thresholds, UE velocities and inter-site distances. Three mobility states have been defined in TS 36.304 based on occurred cell re-selections in a certain time window. According to small inter-site distance simulations, pedestrian speeds (normal mobility state) can be detected with a quite satisfactory accuracy but distinguishing the medium and high mobility states is quite challenging, since UEs are experiencing quite large variance in number of re-selections with the same UE velocities. Simulations with large inter-site distances show similar results.

Performance of VoIP with Mobility in UTRA Long Term Evolution

In this paper, we study VoIP capacity in UTRA Long Term Evolution downlink under different mobility conditions. Since LTE is designed to be a wide area system supporting very high mobility, VoIP capacity for different mobility conditions is an important measure for the LTE system. We show how the mobility dynamics affect the VoIP capacity, using a dynamic system simulator to model the effects of both Robust Header Compression (ROHC) and handovers. The results indicate that the effect of non-ideal ROHC to VoIP system capacity is minimal, especially when compared to the mobility effects to system capacity.

Effect of measurement bandwidth to the accuracy of inter-frequency RSRP measurements in LTE

In this paper we study the effect of reference signal received power (RSRP) measurement bandwidth on the accuracy of handovers and the UTRAN Long Term Evolution (LTE) system performance. In 3rd Generation Partnership Project (3GPP) it has been agreed that inter-frequency RSRP measurement requirements would be developed assuming 6 middle physical resource blocks measurement bandwidth, which has also been agreed to be used for developing intra-frequency RSRP measurement requirements. Wider handover measurement bandwidth could potentially provide better averaging against fading and thus, reduce the time required for performing inter-frequency handover measurements. These studies are conducted with fully dynamic time-driven system simulator and simulations are done with different RSRP measurement bandwidths and different filters. Based on these studies wider bandwidth provides only minor improvement in measurement accuracy and it does not clearly reduce the time required for performing measurements.

Persistent packet scheduling performance for Voice-over-IP in evolved UTRAN downlink

In this paper we present and analyze different packet scheduling mechanisms for Voice-over-IP (VoIP) in UTRAN Long Term Evolution Downlink. Dynamic packet scheduling provides multi-user and frequency domain scheduling gain, but at the expence of high control channel utilization. VoIP service with high number of simultaneous users and small packets can cause the control channel consumption to be the bottleneck for VoIP performance. Thus several persistent packet scheduling mechanisms have been proposed in 3GPP, such as fully persistent, talk-spurt based persistent and semi-persistent packet scheduling. We analyze the VoIP performance of different packet scheduling mechanisms by using fully dynamic system level simulations. We observe that with dynamic packet scheduling the VoIP capacity is restricted by the control channel capacity, whereas with persistent scheduling the capacity is restricted by the delay budget due to worse PRB SINR and resulting increased number of retransmissions.

Mixed traffic packet scheduling in UTRAN Long Term Evolution Downlink

In this paper we study the packet scheduling of mixed traffic in UTRAN long term evolution downlink. A dynamic packet scheduling (PS) architecture with service classification, queue specific sorting and scheduling algorithms as well as frequency domain PS has been presented to differentiate scheduling of different traffic classes. Simulation results have been provided by using control data, voice-over-IP (VoIP) and best effort (BE) traffic types. The results show that VoIP prioritizing is needed to keep the VoIP UEs satisfied. However, the strict prioritizing decreases the system spectral efficiency to around 70-80% of the pure BE spectral efficiency due to small VoIP packets.