Research Proposal: Performance of Femtocell

A femtocell is a device that essentially functions as a repeater by improving cellular reception in an office building or at home. As a wireless access point, it communicates with a cell phone and changes voice calls into voice over IP packets. To ensure efficient functioning, a femtocell has to exist in harmony with nearby users and other femtocells. This is made possible because a femtocell can sense the spectrum and other femtocells. Typically, a femtocell only uses the frequency band it has been allocated and due to its short range and intelligence, it is able to adjust transmission power down or up based on the location of the users and their extent of use.

Due to advantages such as enhanced link quality, higher spatial reuse, and better use of spectrum resources, a hierarchical network comprising of macro and femtocell tiers is a cost effective way of enhancing the performance of cellular systems. However, the Co-Channel Interference created by individual femtocells poses a significant threat to the communication between the tiers. Since Femto Base Stations are deployed randomly by end-users, they do not have a definite infrastructure. In addition, standalone femtocells operate in an uncoordinated manner because they are not networked. Therefore. It is important to solve the challenge posed by interference to increase the viability of a network.

In this regard, this work aims at determining the best arrangement for femtocells in a building to increase their performance. The experiment will apply several models including the practical network deployment model, coordination mechanism, analytical framework, and performance metrics. This paper will provide various femtocell location plans in an office scenario with the design procedure described later in the paper.

The Analysis Setup

The figure below shows the layout of the proposed scenario which covers an area of 3 by 2.6km which is served by trisectorized macrocells (black hexagons). An office building (represented by blue square) is included in one of the microcell about 500m away from the microcellular site. A wrap around technique will be used to create several replicas to eliminate border effects. We assume the building comprises of five floors of 50m by 50m each with each floor having four symmetrical offices. As a constraint of the femtocell plan, one femtocell will be put in every office hence 4 femtocells per floor.

The figure below represents the floor layout. Lines drawn indicate walls and blue circles represent femtocell positions.

The experiment will apply propagation models proposed by Kyosti et al. (2017). Various models are utilized in accordance with the receiver and transmitter environments (indoor-indoor, indoor-outdoor, outdoor-outdoor, outdoor-indoor cases) and their line of sight or non-line of sight conditions. However, in all scenarios, PL is determined as shown below.

PL [dB] = Alog (d [m])+B+Clog f [GHz]/5 +X ,

Where the values of A, B, and C depend on the propagation environment while X takes into account the attenuation effect of diffraction and walls. The table below shows the WINNER II progation models hBS is microcell station height and hMS is mobile station height. nf represents the number of floors between the receiver and the transmitter and FL represents the attenuation caused by propagation in various floors.

Since the primary objective is to come up with an explanation of how the system will operate, the system model is applied. Here, we describe assumptions, network deployments, and the system models for the communication channel.

Theory 1 of a Tagged Receiver. A receiver that is perceived as the benchmark to determine the statistics of the aggregate CCI is represented by tagged receiver. The receiver can be a Femtocell User (FU)or a Macrocell User (MU) based on the tier studied. In coordination procedures, a victim user will indicate a tagged user that causes the CMs after sensing the CCI interfering femtocells beyond the set limit.

Theory 2 of observation region. An Observation OMU will be an annular region that is centered at the MU tagged receiver, and delimited by maximum and minimum radius. Similarly, such a region in the FU tagged receiver will be known as femtocell observation region.

Network Deployment Model

we will assess the DL of two-tier networks whereby Macro Base Stations ((MBSs) are used together with standalone Femtocell Base Stations. The underlaid tier will be composed of FBS that will be scattered uniformly all over the area of network deployment. We will focus on a single reference macro base station to address the overlaid tier. Since each femtocell schedules a femtocell user in every interval of transmission while at the same time the serving microcell schedules a microcell user, we assume that only one microcell user will be active for every microcell in each transmission interval.

Coordination Mechanisms

To carry out the experiment, a coordination procedure based on reservation busy tones will be used. The procedure will protect the persistent resource allocation of the tagged receiver. In the experiment, we will focus on stochastic modelling and analysis of such procedures. Packet loss and packet delay will be used as triggering criteria for the coordination mechanisms. While analyzing the system performance, we will assume that the coordination procedure was triggered by the tagged receiver hence allowing us to focus on the interactions invoked.

References

Kyosti, P., Meinila, J., Hentila, L., Zhao, X., Jamsa, T., Schneider, C., ... & Holappa, V. (2007). WINNER II channel models part II radio channel measurement and analysis results. Tech. Rep., isT-4-027756 WINNER II.