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This paper studies the impact of a femto-cell underlay deployment that shares radio frequency resources with urban macro-cells. Femto-cells promise substantial gains in spectral efficiency due to an enhanced reuse of radio resources. However, owing to their random and uncoordinated deployment, they potentially cause destructive interference to macro-cells and viceversa. In order to maintain reliable service of macro-cells, it is most important to mitigate destructive femto to macro-cell interference. In the downlink, this can be achieved by dynamic resource partitioning, in the way that femto base stations (BSs) are denied access to resources that are assigned to nearby macro mobile stations (MSs). By doing so, interference to the macro-cells is effectively controlled, at the expense of a modest degradation in femto-cell capacity. The necessary signalling is conveyed through the wired backbone, using the downlink high interference indicator (DL-HII).

When simulating a wireless network, users/nodes are usually assumed to be distributed uniformly in space. Path losses between nodes in a simulated network are generally calculated by determining the distance between every pair of nodes and applying a suitable path loss model as a function of this distance (power of distance with an environment-specific path loss exponent) and adding a random component to represent the log-normal shadowing. A network with nodes consists of path loss values. In order to generate statistically significant results for system-level simulations, Monte Carlo simulations must be performed where the nodes are randomly distributed at the start of every run. This is a time-consuming operation which need not be carried out if the distribution of path losses between the nodes is known. The probability density function (pdf) of the path loss between the centre of a circle and a node distributed uniformly within a the circle is derived in this work.

In this paper, a distributed and autonomous technique for resource and power allocation in orthogonal frequency division multiple access (OFDMA) femto-cellular networks is presented. Here, resource blocks (RBs) and their corresponding transmit powers are assigned to the user(s) in each cell individually without explicit coordination between femto-base stations (FBSs). The "allocatability" of each resource is determined utilising only locally available information of the following quantities:• the required rate of the user;• the quality (i.e., strength) of the desired signal;• the level of interference incident on each RB; and• the frequency-selective fading on each RB.Using a fuzzy logic system, the time-averaged values of each of these inputs are combined to determine which RBs are most suitable to be allocated in a particular cell, i.e., which resources can be assigned such that the user requested rate(s) in that cell are satisfied. Furthermore, link adaptation (LA) is included, enabling users to adjust to varying channel conditions. A comprehensive study in a femto-cell environment is performed, yielding system performance improvements in terms of throughput, energy efficiency and coverage over state-of-the-art inter-cell interference coordination (ICIC) techniques. Index Termsautonomous resource allocation, distributed ICIC, fuzzy logic, OFDMA, femto-cellular networks. I. INTRODUCTIONFuture wireless networks are moving towards heterogeneous architectures, where in each cell a user may have over four different types of access points (APs) (e.g., macro-, pico-, femtocells, relays and/or remote radio heads) [1]. Intuitively, this has many positive effects for a September 14, 2018 DRAFT 2 mobile station (MS), which can now choose from several base stations (BSs) to find the most suitable. However, pico-and femto-cellular overlays also imbue many difficulties, e.g., cellorganisation/optimisation, resource assignment to users, and especially interference coordination between APs within the same and neighbouring cells. Standard inter-cell interference coordination (ICIC) techniques based on network architectures [2, 3] only go so far in dealing with these challenges, and hence a new approach is necessary. A. Challenges in Heterogeneous Networks (HetNets)Through the various types, locations and dense deployment of APs, and the different transmissions powers/ranges associated with them, numerous technical challenges are posed by femto/picocell overlays [1,4,5]. These mainly fall into the following areas:• Network self-organisation -Self-configuration and -optimisation are required of all cells.In cellular networks, such organisation can be performed via optimisation techniques [6], however these tasks become increasingly difficult given the additional APs and network parameters to be considered, motivating a distributed configuration approach [7].• Backhauling -Connecting the different BSs to the core-network necessitates extra infrastructure [1]. In the femto-cell case, the long delay of connection via wired backhaul...

One of the key challenges for future orthogonal frequency division multiple access-based networks is inter-cell interference coordination. With full frequency reuse and small inter-site distances, coping with co-channel interference (CCI) in such networks has become increasingly important. In this article, an uplink interference protection (ULIP) technique to combat CCI is introduced and investigated. The level of uplink interference originating from neighbouring cells (affecting co-channel mobile stations (MSs) in the cell of interest) can be effectively controlled by reducing the transmit power of the interfering MSs. This is done based on the target signal-to-noise-plus-interference ratio (SINR) and tolerable interference of the vulnerable link. Bands are prioritised in order to differentiate those (vulnerable/victim) MSs that are to be protected from interference and those (aggressor/interfering MSs) that are required to sacrifice transmission power to facilitate the protection. Furthermore, MSs are scheduled such that those users with poorer transmission conditions receive the highest interference protection, thus balancing the areal SINR distribution and creating a fairer allocation of the available resources. In addition to interference protection, the individual power reductions also serve to decrease the total system uplink power, resulting in a greener system. It is shown through analytic derivation that the introduction of ULIP guarantees an increase in energy efficiency for all MSs, with the added benefit that gains in overall system throughput are also achievable. Extensive system level simulations validate these findings.

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