The present invention relates to a method in a cellular communication system, for avoiding errors in a HARQ process, wherein an NDI flag is used both for indicating either semi-persistent scheduling, SPS activation or SPS retransmissions, and also for indicating, by toggling of the flag, a new transmission in dynamic scheduling mode. The method comprises the steps of receiving, in a scheduling message, an indication that dynamically scheduled transmission will take place; if a semi persistent resource has occurred for the same HARQ process since a previously received indication for dynamically scheduled transmission, then considering the NDI flag to be toggled regardless of the value of the NDI flag. Thus, if the condition is fulfilled, a UE will always regard the NDI flag as indicating or requesting a new data transmission.

Method and Arrangement in a Telecommunication System

In this paper, we present an analytical solution to carry out performance analysis of various frequency reuse schemes in an OFDMA based cellular network. We study the performance in downlink in terms of signal to interference (SIR) ratio and cellular capacity. Analytical models are proposed for integer frequency reuse (IFR), fractional frequency reuse (FFR) and two level power control (TLPC) schemes. These models are based on a fluid model originally proposed for CDMA networks. The modeling key of this approach is to consider the discrete base stations entities as a continuum. To validate our approach, Monte Carlo simulations are carried out. Results of validation study show that results obtained through our analytical method are in conformity with those obtained through simulations. However, compared to time consuming simulations, our model is very time efficient. We also present a comparison between above three frequency reuse scheme.

Analytical evaluation of various frequency reuse schemes in cellular OFDMA networks

Analytical performance evaluation of various frequency reuse and scheduling schemes in cellular OFDMA networks

Long Term Evolution Advanced (LTE-A) technology is considered as the most possible candidate for next generation mobile communications. LTE-A networks offer high capacity and are specified and designed to accommodate small, high performance, power-efficient end-user devices. Similarly to its predecessor LTE, LTE-A incorporates inter-cell interference mitigation methods in order to mitigate interference and to enhance efficiency in bandwidth usage. These methods include power and frequency allocation schemes that allow neighbouring cells and femtocells in heterogeneous networks to co-ordinately share and reuse available spectral resources, in order to avoid performance degradation for interference suffering cell-edge users. In this paper, the authors study the LTE-A multi-cell systems' performance using a simulation framework, which integrates several frequency reuse techniques and provides a user-friendly graphical presentation of the evaluation results. The optimal Fractional Frequency Reuse (FFR) configuration for the user-defined network instance is also determined, based on overall performance and fairness index metrics. Finally, the authors examine FFR techniques in two-tier femtocell/macrocell environments and evaluate them based on the optimization of different metrics, depending on the network operator's needs.

A Simulation Framework for the Evaluation of Frequency Reuse in LTE-A Systems

In the context of long term evolution (LTE) Advanced networks so called coordinated multi point transmission (CoMP) - where transmission is done jointly from several cells to user equipment (UE) - has gained a lot of interest lately. To benefit from CoMP by interference mitigation, UEs have to be served user centric to really leverage potential performance gains like increased capacity or spectral efficiency. This leads to a severe challenge how to assign user groups (UG) to cooperation areas (CA) in a user centric way because UGs must be found with an unique set of strongest cells. Here the so called partial CoMP concept is proposed and analyzed, which allows to serve up to 90% of all UEs in a user centric manner by their 3 strongest cells. The main achievement is to reach the significant performance gains of user centric cooperation for a practical and easy to realize system.

User Centric Coordinated Multi Point Transmission

OFDMA (orthogonal frequency division multiple access) has emerged as a promising physical layer technology for 4G wireless networks. Along with the requirement for higher system capacity, how to improve cell edge performance to provide better QoS (quality of service) support has become a pressing issue. Considering the channel characteristic in wireless communication, new interference avoidance based algorithms, which consider both time domain and frequency domains, are proposed to mitigate the influence of frequency selective channel on cell edge user in MIMO-OFDM system. Meanwhile, in order to further improve the system spectral efficiency, an algorithm that integrates beamforming is put forward. Simulation results show that the proposed algorithms can improve the throughput of cell edge user effectively as well as the overall system throughput.

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Hongmei Sun

Papers

Co-Channel Interference Mitigation in MIMO-OFDM System