Ylva Timner

Handover within 3GPP LTE: Design Principles and Performance

The 3GPP LTE system has been designed to offer significantly higher data rates, higher system throughput, and lower latency for delay critical services. This improved performance has to be provided and guaranteed under various mobility conditions. Hence, handover (HO) and its performance are of high importance. This paper investigates the performance of the handover procedure within 3GPP LTE in terms of HO failure rate and the delay of the whole procedure. System level simulations within a typical urban propagation environment, with different User Equipment (UE) speeds, cell radii and traffic loads per cell have been performed. The entire layer 3 signalling exchanged via air interface is considered in the simulations. In addition, errors at the Layer 1 (L1) control channels are taken into account. Simulation results show that the handover procedure within 3GPP satisfies the goal of high performance mobility. Namely for cell radii up to 1 km and for UE speeds up to 120 km/h, the HO failure rate lies within the range of 0-2.2% even in high loaded systems. For medium and low loads even at speeds of 250 km/h, HO failure is below 1.3 %. In addition, simulation results show that the handover procedure is robust against L1 control channel errors.

Estimating the inter cell dependency matrix in a GSM network

Cellular network planning is often based on propagation prediction or manual measurements. Both these methods have disadvantages. An alternative approach is suggested here, where mobile station measurements are utilized to collect system data. This information can be used to tune or re-plan the frequency plan. The data acquisition part of this method is investigated by means of simulations in a realistic simulation environment, using a commercial urban network as a template. The results are compared to true values from the simulator, and high correlation was found.

Efficient QoS over LTE — A scheduler centric approach

With increasing use of smart phones and mobile broadband, efficient differentiation of traffic is essential for system stability and user satisfaction. In this paper we propose a scheduler centric approach to traffic differentiation (called QoS in this paper) over LTE, in which the scheduler acts as a core entity assisted with congestion control and admission control. The scheduler is responsible for enforcing the wanted differentiation; it guarantees that high priority bearers, which are in danger of not fulfilling their QoS contract, receive necessary resources. The bearer based congestion control reacts on scheduling decisions and removes bearers with insufficient resources. The admission control algorithm takes decisions using load measurements from the scheduler. Simulation results with a mixed traffic scenario show that applying the proposed approach guarantees GBR bearers sufficient resources efficiently in the order of set priorities while background bearers utilize the remaining resources.

Control Signaling Robustness in LTE

In LTE, the control signaling required for scheduling and HARQ on the MAC layer is partly protected by cyclic redundancy checks (CRC) but no ARQ, or other error recovery mechanisms, are used. Therefore, errors occur with a certain probability and may or may not be detected. Errors in HARQ feedback and scheduling grants could cause underutilization of resources, longer delays, redundant retransmissions, collisions, and HARQ failures. In this study, the frequency of these effects, and the influence of control channel quality, data channel block error rate (BLER), and ACK/NACK detection thresholds are investigated. It is shown that the effects are acceptable small when the control channel performance is within the 3GPP target requirements. Keywords-LTE, 3GPP, control, signaling, HARQ, error

Optimization of Fairness for HTTP Adaptive Streaming with Network Assistance in LTE Mobile Systems

HTTP adaptive streaming is becoming dominant for commercial video streaming services. It is typically the client that chooses the rate based on estimation of the available network bandwidth in order to avoid the client buffer to be underrun or overrun. However, the unfairness among the clients and between the clients and other competing traffic has been identified as one of major issues that lead to degraded user service quality and system capacity. Therefore, this paper proposes a network assisted rate adaptation method for HTTP streaming in the radio access network. The simulation results show that the network rate assistance is able to guarantee a fair share of the network resources. As a result, the system capacity and the user service quality can be improved.

Network assisted rate adaptation for conversational video over LTE, concept and performance evaluation

This work investigates rate adaptation of conversational video in a mobile system using Long Term Evolution, LTE, and where the adaptation is assisted by the radio network. The conventional way to do rate adaptation is through adaptation in the end-points where the transmission rate is selected based on measurements of received packets. This study investigates two network-based algorithms for rate adaptation, a rate fair algorithm that assigns the same rate to all conversational video users in a cell, and a resource fair algorithm that aims to give all users in the cell a fair amount of resources. Both algorithms are combined with delay based scheduling. Both network-based algorithms perform excellently. The delay stays low even when the resource utilization is close to 100%, and the video rate is adapted to the system load. As could be expected, the average user rates are higher with the resource fair algorithm. An end-point based adaptation algorithm is investigated as well, but it cannot keep a low delay at high load.