Femtocells: The HOMESNET vision

This paper addresses the problem of allocating frequencies in a GSM-based home base station (HBS) system. A novel solution called total frequency hopping (TFH) is presented in order to overcome the frequency allocation and the inter-HBS synchronisation problems. The HBS system will use the same frequency band as the overlaying GSM network and thus creates more interference to it. The simulation results reveal that the negative impact of the underlying HBS system on the GSM network performance is minimal provided that the HBS transmission (TX) power is reasonable low. The TX power cannot be arbitrarily low, however, since the HBS system must be able to function in the presence of the interference from the overlaying high power GSM network. When the power ratio between GSM base station and HBS is around 40 dB, the both networks can co-exist at the same frequency band.

One of the major challenges of Cellular network based localization techniques is lack of hearability between mobile terminals (MTs) and base stations (BSs), thus the number of available anchors is limited. In order to solve the hearability problem, previous work assume some of the MTs have their location information via Global Positioning System (GPS). These located MT can be utilized to find the location of an un-located MT without GPS receiver. However, its performance is still limited by the number of available located MTs for cooperation. This paper consider a practical scenario that hearability is only possible between a MT and its home BS. Only one located MT together with the home BS are utilized to find the location of the un-located MT. A hybrid cooperative localization approach is proposed to combine time-of-arrival and received signal strength based fingerprinting techniques. It is shown in simulations that the proposed hybrid approach outperform the stand-alone time-of-arrival techniques or received signal strength based fingerprinting techniques in the considered scenario. It is also found that the proposed approach offer better accuracy with larger distance between the located MT and the home BS.

MIMO downlink with base station coordination in a cellular network is considered. In centralized coordinated transmission from a cluster of base stations, the channel state information (CSI) of users needs to be sent to a central processor for precoding and resource allocation. Real time CSI feedback from the users to their home base station and from the base stations to the central processor is a serious challenge from a practical point of view. CSI feedback schemes based on user channel strength and distance of a user to its home base station are proposed that reduce feedback overhead while having not much affect on system throughput. Numerical results show the effectiveness of the proposed schemes.

In this paper an algorithm has been proposed based on Hata model that employs an improved procedure in detecting the mobile location in three dimensional environment using received signal strength (RSS). This technique considers path loss and shadowing effect for the channel to compute the distance between the mobile phone and its home base station and neighboring base stations using Hata model. Considering the distance from the mobile phone to the base station (including its home base station) as the radius of the sphere (i.e., shape produced by signal propagation from Omni directional antenna) to find out an intersection point of all these spheres that denotes the location of the mobile phone. An intersection point of all these spheres is computed that denotes the location of the mobile phone. The algorithm has been simulated and the result has been found to be accurate.

In this paper, the throughput performance of uplink Base Station (BS) cooperation in a realistic multi-cell MIMO system is evaluated. We choose LTE Release 8 as our baseline, and propose a whole implementation scheme for uplink BS cooperation. First we propose a dynamic cooperative BS selection algorithm, in which each cell-edge user will be assigned a potential cooperative BS by comparing the reception powers between its home BS and neighbor interference BSs. Next, an efficient multi-cell scheduling algorithm is proposed to explore the system throughput gain with low complexity. Finally, since scheduling results can be shared between different cells, we can use this information to recalculate each sector's Signal to Interference plus Noise Ratio so that more accurate Modulation and Coding Scheme can be set for each UE. System level simulation results show that the great performance gain that uplink Base Station cooperation can achieve. Moreover, the impacts of multiuser MIMO and power control are analyzed.

ABSTRACTThe multiple‐input multiple‐output (MIMO) downlink with transmitter coordination in a cellular network is considered. The transmitters are assumed to be either neighbouring base stations (homogeneous) or a base station with a number of remote radio heads that form picocells in its coverage area (heterogeneous). In centralized coordinated transmission from a cluster of nodes, the channel state information (CSI) of users needs to be sent to a central processor for precoding and resource allocation. Real‐time CSI feedback from the users to their home base station and from the base stations to the central processor is a serious challenge from a practical point of view. In this work, efficient location‐assisted limited‐feedback schemes for homogeneous and heterogeneous cellular networks are proposed. First, a hybrid mode transmission scheme with reduced feedback requirement is proposed for a homogeneous network, in which on the basis of the location of users, some are served using a single‐cell multiuser MIMO approach and some using a network MIMO approach. Next, for a heterogeneous network, a location‐assisted clustering and scheduling scheme is proposed for the case of joint reference signals, in which multiple transmission nodes that share the reference signals cannot be distinguished from each other. We evaluate the performance of our schemes with a series of simulations. In the homogeneous scenario, we compare with the case of full CSI, and in the heterogeneous scenario, we compare with joint transmission from all nodes in a cell. Copyright © 2012 John Wiley & Sons, Ltd.

The optimization of the channel capacity in the new fourth generation (4G) wireless networks became a key issue during the last decade. In this work, the co-existence of macrocell Base Stations (MBSs) and Femtocell Access Points (FAPs) or home base stations (HBS) with shared and dedicated carrier frequency allocations is considered. The simulation framework for analysis of channel capacity improvement in complex urban environment is introduced. The analysis of heterogeneous network consisting of dedicated femtocells for home coverage in a presence of traditional macrocell pattern is presented. The advantages and drawbacks for different deployment strategies are investigated using the proposed simulation framework.

An error existed in the distance-difference is the major problem for stationary signal-strength-difference (SSSD) positioning method in wireless communications. The error primarily is caused by the two impairment factors: one factor that is the SSSD measurement error and one factor that is a detection error in the reference distance between the mobile caller and the home base station (BS). This paper presents the analysis of the detection and SSSD measurement errors and proposes a correction method in the least square (LS) sense. Theoretical findings are validated with the measurements in a commercial wireless cellular 900 MHz communication network. According to numerical results, we show that the proposed correction method is an attractive solution to mitigate the larger error met initially.

Long Term Evolution (LTE) is a new technology that becomes an important part of everyday life and for the future which is consists of heterogeneous networks. LTE is the new standard recently specified by the Third Generation Partnership Program (3GPP) on the way towards fourth-generation mobile. The deployment of femtocell (HeNB) which act as home base station can give seamless handoff in LTE network. In order to satisfy the seamless handoff in LTE, the femtocell was deployed with the existing networks to act as backhaul connectivity which can fulfill the upcoming demand of high data rate in a wireless communication system and also can extend the coverage area. This research is to analyze the performance of Receive Signal Strength (RSS) between Macrocell/Femtocell when the UE is inside or outside the house. The simulation results show a better performance of using our proposed adaptive RSS in initiating a handoff when the speeds varies.

In cellular networks, it is estimated that more than 50% calls and over 70% of data services occur indoors. Femtocells, also known as home base station, are cellular network access points that connect standard mobile devices to a mobile operator's network using residential Digital Subscriber Line (DSL), cable broadband connections, optical fibres or wireless last-mile technologies. This femtocell antenna is designed to work at frequency 2.3–2.4 GHz for VSWR <2 and have 100 MHz Impedance bandwidth. From measurement of S11 parameter shows that the single element antenna has 320 MHZ impedance bandwidth which covers frequency 2.12–2.47 GHz.

Presently, femtocell technology is emerging for cellular wireless networks, which have rapidly engrossed the cellular industry. The main advantage of femtocell to the mobile operators is a reduction of cost and an improvement of the signal quality in indoor coverage, which is also considered a possible path to the Fixed–Mobile Convergence (FMC) goal. Femtocell extends network coverage and delivers high-quality mobile services inside residential and business buildings through broadband networks (i.e. ADSL). Femtocell Access Points (FAP) or Home Base Stations (HBS) are intended to serve small number of users (i.e. 4 users) and cover about 30-square meters, similar to existing WiFi access points. However, femtocell introduces new challenges to the telecom industries in terms of handoff between femto and microcells, interference management, localization, and synchronization. Among all of these challenges, synchronization is considered as the cornerstone for the femtocells to function properly. The problematic issue in femtocell synchronization is that all the data and control traffic travels through an IP broadband network. The IP broadband network is usually owned and managed by a third party and not by the mobile operator which can complicate the synchronization. Unsynchronized FAPs may cause harmful interference and wrong handover dictions. In this chapter, the authors investigate and overview the current femtocell synchronization techniques and make comparisons between them. Possible improvements and recommendations for each method have been identified. Future research areas and open issues are also discussed.

Recently much attention has been devoted to the potential of femtocell to improve indoor cellular coverage and high speed wireless communications. Femtocell networks use home base station and existing digital subscriber line (DSL) or other cable line as backhaul connectivity constructing a hierarchical cell structure (HCS) networks operating with macrocells which cover wider service areas. This paper investigates the effect of interference on system performances of femtocell embedded HCS networks adopting detailed radio propagation models while most of works evaluate system performance using simple radio propagation models. Considering various environmental factors such as wall structure, number of walls, and distance between femtocell and users, this paper evaluates not only the overall outage probability and the dynamic range of spectral efficiency achieved by overall femtocells in HCS networks, but also separation distances from macrocell required to femtocell for provision of the minimum required spectral efficiency. Our evaluation includes outage probability of 2~40%, spectral efficiency dynamics of around 250%, 50~200m of required separation from macrocell with various wall structures, which could be useful for femtocell embedded HCS network planning.

Chapter 21 - Mobile health monitoring for senior citizens using femtolet-based fog network

This paper presents a numerical analysis of reverse link capacity by obtaining a closed form of ICI (InterCell Interference) over OFDM (Orthogonal Frequency Division Multiplexing)-based broadband wireless networks. In the analysis, shadowing factors are taken into account for determining the home BS (Base Station) of each MS (Mobile Station) over multicell environments. Under the consideration, a more accurate analysis of link capacity can be performed compared to Gilhousen's approximation. In the numerical results, it turns out that the actual interference is lower than Gilhousen's approximation with a decrease of around 20% in the interference.

A Femtocell (FMC) is a low power cellular home base station, which is low in cost and operating in licensed spectrum.Nowadays, because of the requirement for high data rate and large area coverage indoors, FMC provides the solution to these requirements.FMC is deployed mainly indoors and sometimes outdoors at the cell edge to increase the area of coverage, capacity and in order to enhance the received signal in the user's premises.In this paper, a novel technique and a Monte Carlo simulation is implemented to calculate the interference, the SINR and the probability of connection at the downlink for a varied number of FMCs based on LTE and WiMAX OFDMA range.Moreover, a novel Monte Carlo simulation is used to carry out the comparison of interference, SINR and probability of connection for three different numbers of FMCs.Furthermore, a novel comparison of FMCs at various SINR threshold values is presented.The downlink interference occurs from neighbouring FMCs to the target user equipment (UE) when the signal transmits from the serving FMC to the target UE and the signals which are transmitted from the neighbouring FMCs would have the same subchannels during the downlink transmission.This paper will explore the appropriate number of FMCs that could serve a specific indoor area and the proper number of UEs in the specified area.