2011 IEEE Conference on Open Systems (ICOS2011), September 25 - 28, 2011, Langkawi, Malaysia
An Investigation of Femtocell Network Synchronization Mohammad Kamrul Hasan, R. A. Saeed, Aisha-Hassan Abdalla, Shayla Islam,Omer Mahmoud, Othman Khalifah, Shihab A. Hameed, Ahmad Fadzil Ismail Electrical and Computer Engineering Department, Kullyyiah of Engineering, International Islamic University Malaysia (IIUM), Kuala Lumpur, Malaysia
[email protected] (ADSL). Since a public network is used to establish the connectivity between the femtocell and core network elements that presents a set of problems for operators. Due to huge number of possible target femtocell candidates for macrocell to femtocell handover need a large neighbor list and communication with many femtocells for the pre-handover procedure. The femtocell architecture is much more different than existing cellular networks. Fig. 1 represents that femtocells provide excellent 3G coverage and capacity in the home which are connected to the public broadband IP service, femtocells are integrated into core network by a concentrator (RAN Gateway) and femtocells are manageable by remotely the fundamental entities of femtocell network.
Abstract— Currently, Femtocell technology emerged for cellular wireless networks, which has rapidly engrossed cellular industry. The principle of femtocell to the mobile operators is to reduce cost and improve 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 network i.e. ADSL. Femtocell access point (FAP) or home base station (HBS) intends to serve small number of users i.e. 4 users and covers about 30 meter square similar to existing WiFi access points. However, femtocell introduces new challenges to the telecom industries in terms of handoff between femto and macrocells, interference management, localization and synchronization. Among all of these challenges, synchronization is considered corner stone for proper working for femtocell. The problematic issue in femtocell synchronization is that all the data and control traffics travel through IP broadband network. The IP broadband network is usually owned and managed by third party and not by the mobile operator, which is complicated the synchronization. Unsynchronized FAPs may cause harm interferences and wrong handover dictions. In this study we investigate and overview the current femtocell synchronization techniques and compare between them. Possible improvements and recommendation for each method is identified. Proposed schemes and indicated future research areas are also discussed. Keywords- Femto Access Point (FAP); Synchronization; Frequency Division Multiple Access (OFDMA).
I.
INTRODUCTION
Cognitive Nowadays, mobile operator’s principal thinking is to save the cost by reducing the macro cell traffic load and offloading it over public broadband connections to the core network. Potentially this technology reduces the cost and complexity of having to deploy higher-capacity links to the macrocell. The femtocell extends network coverage and delivers high-quality mobile services inside residential and business buildings with the better cellular network coverage, and has triggered the design and development of new structured cellular standards such as WiMAX (802.16e), the Third Generation Partnership Project’s (3GPP’s) High Speed Packet Access (HSPA) and LTE standards, and 3GPP2’s EVDO and UMB standards. The communication link of the Femtocell may be one of Wide Area Network (WAN) technologies such as Asymmetric Digital Subscriber Line
978-1-61284-931-7/11/$26.00 ©2011 IEEE
Fig. 1 Femtocell network’s fundamental entities
In absence of time synchronization among femtocells motivates the generation of the interference due to the uplink or downlink transmissions. Considering the adoption of distributed techniques for time synchronization at frame level and will evaluate how the synchronization is related with the generated interfering power. When a Base Station (BS) operates with time division duplex mode (TDD), synchronization of the transmission time at the BS is important to avoid inter-slot interference with adjacent BSs. Since femto BSs are generally located indoor, they may not receive the global positioning system (GPS) signal which is used to
196
2011 IEEE Conference on Open Systems (ICOS2011), September 25 - 28, 2011, Langkawi, Malaysia
with high capacity. It is necessary to define femto deployment environment and requirements to ultimately replace wireless local area network (WLAN) environment. Interference and synchronization problems are considered as critical issues for this purpose. For time division duplex (TDD) systems, synchronization between adjacent cells should be maintained to avoid inter-slot interference. Especially, since femto BSs can be installed in unplanned and uncoordinated way by users, femto BSs can be located near to each other and cause severe interference to each other due to imperfect synchronization. Furthermore, various interference mitigation schemes such as femto BS cooperation, soft frequency reuse schemes etc., need synchronization of femto BSs. A range of scenarios were discussed in [4] to compare femtocell open and closed access. This shows that with adaptive open access, the interference in two-tier networks is mitigated and the deployment of cochannel femtocells becomes feasible. However, since femtocells are installed and paid for by their owners, it is necessary to evaluate their loss of femtocell resources in open access. It is important that the benefits of mitigated interference are not undermined by the loss of femtocell resources, such as over-the-air (OTA) and backhaul capacity.
synchronize the wireless cellular network. Today, it is strongly considered a practical solution required to secure both the seamless indoor coverage and the high network capacity. The emerging IMT-advanced candidate systems including 3GPP LTE-advanced and IEEE 802.16m also feature this femtocell technology [1-2]. The rest of the paper is organized as follows. Section II presents femtocell network infrastructure. Section III investigates analysis of related works. Section IV investigates of femtocell synchronization technical challenges, and indicates the future research. Proposed the possible solution discussed in section V. In section VI summarizes the paper. II.
FEMTOCELL NETWORK INFRASTUCTURE
As Micro cellular networks infrastructure is expensive. A recent development is femtocells, also called home base stations, which are small size short-range low-cost lowpower(
