Fractional frequency reuse (FFR) is an interference management technique well-suited to OFDMA-based cellular networks wherein the bandwidth of the cells is partitioned into regions with different frequency reuse factors. To date, FFR techniques have been typically been evaluated through system-level simulations using a hexagonal grid for the base station locations. This paper instead focuses on analytically evaluating the two main types of FFR deployments-Strict FFR and Soft Frequency Reuse (SFR)-using a Poisson point process to model the base station locations. The results are compared with the standard grid model and an actual urban deployment. Under reasonable special cases for modern cellular networks, our results reduce to simple closed-form expressions, which provide insight into system design guidelines and the relative merits of Strict FFR, SFR, universal reuse, and fixed frequency reuse. Finally, a SINR-proportional resource allocation strategy is proposed based on the analytical expressions and we observe that FFR provides an increase in the sum-rate as well as the well-known benefit of improved coverage for cell-edge users. © 2011 IEEE.

Radha Krishna Ganti

Department of Electrical Engineering

Analytical evaluation

Analytical expressions

BASE STATION LOCATION

Cellular network

Closed-form expression

Different frequency

Fixed frequency

Fractional Frequency Reuse

GRID MODEL

HEXAGONAL GRID

INTER-CELL INTERFERENCE COORDINATION (ICIC) TECHNIQUES

Interference management

POISSON POINT PROCESS

RESOURCE ALLOCATION STRATEGIES

SOFT FREQUENCY REUSE

Sum-rate

System level simulation

base stations

Cellular neural networks

Frequency division multiple access

Systems analysis

Orthogonal frequency division multiplexing

Fulltext

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IIT Madras

IEEE Transactions on Wireless Communications

The κ-μ shadowed fading model is a very general fading model as it includes both κ-μ and η-μ as special cases. In this paper, we derive the expression for outage probability when the signal-of-interest (SoI) and interferers both experience κ-μ shadowed fading in an interference limited scenario. The derived expression is valid for arbitrary SoI parameters, arbitrary κ, and μ parameters for all interferers and any value of the parameter m for the interferers excepting the limiting value of m → ∞. The expression can be expressed in terms of Pochhammer integral, where the integrands of integral only contains elementary functions. The outage probability expression is then simplified for various special cases, especially when SoI experiences η-μ or κ-μ fading. Furthermore, the rate expression is derived when the SoI experiences κ-μ shadowed fading with the integer values of μ, and the interferers experience κ-μ shadowed fading with arbitrary parameters. The rate expression can be expressed in terms of sum of Lauricella's function of the fourth kind. The utility of our results is demonstrated by using the derived expression to study and compare fractional frequency reuse and soft frequency reuse in the presence of κ-μ shadowed fading. Extensive simulation results are provided and these further validate our theoretical results. © 2017 IEEE.

Outage probability and rate for κ-μ shadowed fading in interference limited scenario

The coverage probability (CP) and the average rate expressions when fractional frequency reuse (FFR) or soft frequency reuse (SFR) schemes are employed in single-input-multiple-output (SIMO) network are derived when the interferers undergo correlated Rayleigh fading. It is analytically shown that both the CP and the rate are higher in the presence of the correlated interferers (when the interferers are positively correlated) when compared with the case where the interferers are independent. It is also shown that the impact of correlation on SFR is more when compared with FFR, and it decreases with an increase in the power control factor. We show that the average rate achieved by FFR is higher when compared with the SFR in SISO networks for both the independent and correlated cases. However, the situation is reversed for SIMO networks. The impact of large-scale fading has also been briefly studied. © 2015 IEEE.

IEEE Transactions on Vehicular Technology

Impact of correlated interferers on coverage and rate of FFR and SFR schemes

In this paper, we analytically study the impact of spectrum-Allocation scheme in picocells on the coverage probability (CP) of the pico user (PU) when the macro base stations (MBSs) employ either fractional frequency reuse (FFR) or soft frequency reuse (SFR). Assuming a fixed size for the picocell, the CP expression is derived for a PU present in either a FFR-or a SFR-based deployment and when the PU uses either the center or the edge frequency resources. Based on these expressions, we propose two possible frequency-Allocation schemes for the picocell when FFR is employed by the macrocell. The CP and the average rate expressions for both schemes are derived, and it is shown that these schemes outperform the conventional scheme where no intercell interference coordination is assumed. The impact of both schemes on the macro-user performance is also analyzed. When SFR is used by the MBS, it is shown that the CP is maximized when the PU uses the same frequency resources as used by the center region. © 1967-2012 IEEE.

Spectrum Allocation for ICIC-Based Picocell

Expressions are derived for the coverage probability and average rate of both multi-user multiple input multiple output (MU-MIMO) and single input multiple output (SIMO) systems in the context of a fractional frequency reuse (FFR) scheme. In particular, given a reuse region of 1/3 (FR3) and a reuse region of 1 (FR1) as well as a signal-to-interference-plus-noise-ratio (SINR) threshold Sth, which decides the user assignment to either the FR1 or FR3 regions, we theoretically show that: 1) the optimal choice of Sth which maximizes the coverage probability is Sth = T, where T is the target SINR required for ensuring adequate coverage, and 2) the optimal choice of Sth which maximizes the average rate is given by Sth = T′, where T′ is a function of the path loss exponent, the number of antennas and of the fading parameters. The impact of frequency domain correlation amongst the OFDM sub-bands allocated to the FR1 and FR3 cell-regions is analysed and it is shown that the presence of correlation reduces both the coverage probability and the average throughput of the FFR network. Furthermore, the performance of our FFR-aided MU-MIMO and SIMO systems is compared. Our analysis shows that the (2 x 2) MU-MIMO system achieves 22.5% higher rate than the (1 x 3) SIMO system and for lower target SINRs, the coverage probability of a (2 x 2) MU-MIMO system is comparable to a (1 x 3) SIMO system. Hence the former one may be preferred over the latter. Our simulation results closely match the analytical results. © 2015 IEEE.

IEEE Transactions on Communications

Coverage probability and achievable rate analysis of FFR-aided multi-user OFDM-based MIMO and SIMO systems

In this work, the authors derive the optimal signal-to-interference-ratio (SIR) thresholds S<inf>t</inf> which maximise coverage probability for both fractional frequency reuse (FFR) and soft frequency reuse (SFR) networks with base station locations modelled using Poisson point process. It is analytically shown that for both FFR and SFR, the optimal SIR threshold is equal to the target SIR T, i.e, S<inf>t</inf> = T. The authors also show that at the optimal SIR threshold, FFR achieves a higher coverage than frequency reuse (1/δ). Furthermore, for the cases when S<inf>t</inf> > T and S<inf>t</inf> < T, FFR achieves a higher coverage than reuse (1/δ) and reuse 1, respectively. On the other hand, SFR coverage can be higher or lower than reuse (1/δ) coverage, even when S<inf>t</inf> = T. However, when S<inf>t</inf> > T, SFR achieves a higher coverage than reuse 1, and when S<inf>t</inf> < T, the SFR coverage can be lower than reuse 1 coverage. The FFR and SFR coverages are also compared for a given δ, and it is shown that FFR achieves a higher coverage than SFR at the optimal value of S<inf>t</inf>. © The Institution of Engineering and Technology 2015.

IET Communications

Optimal design parameters for coverage probability in fractional frequency reuse and soft frequency reuse

Wiley Series in Probability and Statistics

Stochastic Geometry and its Applications

2011 IEEE International Conference on Communications (ICC)

A New Way of Computing Rate in Cellular Networks

2010 IEEE Global Telecommunications Conference GLOBECOM 2010

Comparison of Fractional Frequency Reuse Approaches in the OFDMA Cellular Downlink

2010 48th Annual Allerton Conference on Communication, Control, and Computing (Allerton)

A new tractable model for cellular coverage

21st Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications

Interference constrained soft frequency reuse for uplink ICIC in LTE networks

Analytical evaluation of fractional frequency reuse for OFDMA cellular networks

Journal	IEEE Transactions on Wireless Communications
ISSN	15361276
Open Access	Yes