Jani Puttonen

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.

Using link layer information for improving vertical handovers

In this paper we present a common triggering mechanism (cross-layer framework) and logic to gather link state and quality related information from the link layers of different access technologies. This information may he utilized by upper layer protocols and applications to react to changes of the link layer. Examples of such a utilization is movement detection, handover decision and application adaptation. The access technology dependent events and parameters, when necessary, are converted into access technology independent triggers and hints. The presented prototype architecture, link information provider (LIP), is currently tested with the VERHO vertical handover controller, which enables intelligent policy-based handover decisions according to several input parameters from the user, application, link layer, etc. Currently, LIP supports certain general link layer parameters, which can he gathered from the operating system and network interface drivers. The system is designed to be easily extended

On LTE performance trade-off between connected and idle states with always-on type applications

In cellular networks it is envisioned an explosion of diverse data applications running in smart phones, which could increase significantly not only user plane but also control plane load in the network. Smart phones and their always-on applications introduce several challenges: From the network perspective, an increased amount of UEs/applications can increase the signaling load due to frequent state transitions and handover signaling. From the UE perspective, challenges of power consumption are evident, since UE would increasingly be in connected state. In this article we study the trade-off between releasing the UE into idle state vs. keeping the UE in connected state, in a LTE system. The results indicate that optimum performance can be achieved using UE specific RRC release timer and DRX configurations by taking advantage of traffic characteristics and UE mobility.

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.

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.

Radio problem detection assisted rescue handover for LTE

In this paper we propose a radio problem detection based rescue handover for 3G Long Term Evolution (LTE). The radio problem detection based handover algorithm takes advantage of already existing Radio Link Failure (RLF) detection mechanism specified in 3GPP for LTE. In coverage limited scenarios as well as challenging interference and mobility conditions, the event triggered handover measurement report may not be even sent to Evolved NodeB at the time of RLF. In proposed algorithm UE shall monitor the downlink quality based on the cell-specific reference signal in order to detect the downlink radio link quality of the serving cell. In case of a detected radio link problem handover process is initiated to a better cell. The proposed handover algorithm is compared to the default UE assisted hard handover process by means of fully dynamic system level simulations. Based on the studies it can be concluded that the radio problem detection assisted handover algorithm decreases the amount of RLFs thereby improving the handover and system performance. Especially the RLFs that occur before the handover process is even started are basically non-existent.