Konstantinos Dimou

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.

Blind null-space tracking for MIMO underlay cognitive radio networks

Blind Null Space Learning (BNSL) has recently been proposed for fast and accurate learning of the null-space associated with the channel matrix between a secondary transmitter and a primary receiver. In this paper we propose a channel tracking enhancement of the algorithm, namely the Blind Null Space Tracking (BNST) algorithm that allows transmission of information to the Secondary Receiver (SR) while simultaneously learning the null-space of the time-varying target channel. Specifically, the enhanced algorithm initially performs a BNSL sweep in order to acquire the null space. Then, it performs modified Jacobi rotations such that the induced interference to the primary receiver is kept lower than a given threshold

Future wireless access small cells and heterogeneous deployments

P_{Th}

On the Use of Uplink Received Signal Strength Measurements for Handover

with probability

Method and apparatus for radio link failure recovery in a telecommunication system

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Speed-dependent adaptation of mobility parameters with dual speed measurement

while information is transmitted to the SR simultaneously. We present simulation results indicating that the proposed approach has strictly better performance over the BNSL algorithm for channels with independent Rayleigh fading with a small Doppler frequency.

Dynamic resource selection to reduce interference that results from direct device to device communications

Network densification and heterogeneous deployments are key tools to satisfy future traffic-volume and end-user service-level demands. LTE release 10/11 introduced several features to enhance LTE operation in heterogeneous deployments. This will continue as part of the work on small-cell enhancements in LTE Release 12. Especially, different forms of dual-connectivity are being considered to improve overall system performance and enhance end-user experience.

Handover robustness in cellular radio communications

In most cellular systems, handover decisions are based on measurements of the downlink signal strength. When the average path gain in downlink and uplink is similar, such principles yield good performance in both directions of transmission. In cases with systematic imbalances between downlink and uplink however, it is not evident that the uplink performance is optimized. In this paper, a handover scheme based on a combination of downlink and uplink path gain measurements is outlined, and its performance is evaluated in a system with systematic downlink and uplink imbalances. As a reference, a downlink-based only mechanism is used. Results indicate that the combined scheme yields an insignificant gain in uplink signal to interference ratio (SINR). This gain is considerably lower than the corresponding loss in the SINR of users in the downlink. The reason for the low uplink gain is that uplink interference is higher in the cells with higher uplink/downlink imbalance ratio than in adjacent cells in equally loaded cells. As a result, users which are connected to cells with better uplink/downlink imbalance ratio than their adjacent cells also experience higher interference levels, which results in a limited gain in signal-to-interference ratio.