Optimal Thresholds for Coverage and Rate in FFR Schemes for Planned Cellular Networks

Abstract

Fractional frequency reuse (FFR) is an inter-cell interference coordination scheme that is being actively researched for emerging wireless cellular networks. In this work, we consider hexagonal tessellation based planned FFR deployments, and derive expressions for the coverage probability and normalized average rate for the downlink. In particular, given reuse 1 3 (FR3 ) and reuse 1 (FR1) regions, and a Signal-to-Interference-plus-noise-Ratio (SINR) threshold S th which decides the user assignment to either the FR1 or FR3 regions, we theoretically show that: (i) The optimal choice of S th which maximizes the coverage probability is S th = T , where T is the required target SINR (for ensuring coverage), and (ii) The optimal choice of S th which maximizes the normalized average rate is given by the expression S th = max(T, T ′ ), where T ′ is a function of the path loss exponent and the fade parameters. For the optimal choice of S th , we show that FFR gives a higher rate than FR1 and a better coverage probability than FR3. The impact of frequency correlation over the sub-bands allocated to the FR1 and FR3 regions is analysed, and it is shown that correlation decreases the average rate of the FFR network. Numerical results are provided, and these match with the analytical results.[2] is a simple ICIC scheme, and has been proposed for OFDMA based wireless networks which are based on standards such as IEEE WiMAX [3] and 3GPP LTE [4].FFR is a combination of frequency reuse 1 (FR1) and frequency reuse 1 δ (FRδ). FR1 allocates all the frequencies to each cell, leading to a high spatial reuse, but could result in a low coverage due to inter-cell interference. On the other hand, FRδ allocates 1 δ of the frequencies to each cell, and trades-off spatial reuse and rate, for higher coverage. FFR exploits the advantage of both FR1 and FRδ by using FR1 for the cell-centre users (i.e., for those users who experience less interference from other cells and/or are close to their serving base station (BS)) and FRδ for the cell-edge users (i.e., for those users who experience high interference from co-channel signals from neighbouring cells and/or are far from their serving BS). Typically, there are two modes of FFR deployment: static and dynamic FFR [1]. In this paper, we consider the more practical static FFR scheme, where all the parameters are configured and kept fixed over a certain period of time. Fig. 1 depicts a frequency allocation in the FFR scheme for three adjacent cells, where F 1 , F 2 and F 3 each use x% of the total spectrum, and F 0 uses (100 − 3x)% of the spectrum.FFR schemes have been rather well studied using both system level simulations and theoretical analysis [5]- [12]. Blocking probability of reuse partitioning based cellular system for voice traffic, assuming a TDMA system has been derived in [9]. Analysis of the theoretical capacity and outage rate of an OFDMA cellular system assuming FFR and proportional fair scheduling has been presented in [11] where the users are classified as cell-centre users and cell...

Power Control Factor Selection in Uplink OFDMA Cellular Networks

“…The natural extension of this work could be to evaluate the uplink power control factor in presence of inter-cell interference coordination scheme, i.e. fractional frequency reuse [10] and soft frequency reuse [11]…”