**1. Introduction**

26 Will-be-set-by-IN-TECH

136 Mobile Networks

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Femtocells are low-power wireless access points; operate in licensed spectrum and use residential or office DSL, cable or other broadband connections. Most mobile network operators (MNOs) offer femtocell access point (FAP) to retain their customers by improving indoor coverage and capacity. However in order to leverage massive femtocells deployment and generate new revenue, there should be business cases beyond the connectivity. Offering various femto services are crucial to strengthen customer value preposition and create new revenue generator for operators. Each service certainly requires a specific amount of bandwidth and QoS treatment. Therefore the study of bandwidth and QoS requirement for different traffic types are important, in order to design an optimum backhaul requirement for femtocell.

Heavy Reading in its report [1] stated that the cost of leased line for macrocell backhaul counted 25% of total MNO's capex. The need of small cells are paramount important in delivering high speed wireless broadband data. However the cost of new carrier-grade backhaul to support indoor base stations (IBSs) may increase depend on the new IBSs numbers and availability of leased lines. Femtocells utilize the existing broadband connection in the customer side. By this approach, the cost of backhaul can be reduced with the trade off fluctuation on the backhaul quality; if there is no specific service level agreement (SLA) setup between MNO and internet service provider (ISP).

Bear in-mind that femtocell is a CPE with self configure capabilities, so that it will impose less interaction with mobile operators. For residential users, they may buy the femtocell from the mobile operator or electronic store and instantly plug it to the existing broadband connection at home. The users may not be aware of how the fixed-wireline operator will treat the femto traffic compared to other best-effort internet traffic. They may not be alert to that other broadband traffic traversed via the same home gateway will affect femtocell service performance. Bottleneck may occur anywhere in the network and affect femtocell performance.

A comprehensive femtocell deployment guideline considering backhaul quality for 3G femtocell was addressed in [2]. The guideline describes the quality issue of VoIP services over 3G femtocell networks. VoIP services were observed as representation of real time

Femtocell Performance Over Non-SLA xDSL Access Network 139

may cope with the performance degradation but with the cost of adding more bandwidth to the existing broadband line. We also give some comments to the FREEDOM study outcome; how femtocell performance in non-SLA network can be improve by implementing backhaul

xDSL technology offers fix broadband services over the existing copper twisted pair infrastructure. According to Organisation for Economic Co-operation and Development (OECD) as shown in Figure 1, the xDSL access technology has more subscribers compared

Fig. 1. OECD Fixed (wired) broadband subscriptions, by technology, Dec. 2010

The end user gets a dedicated link from xDSL modem to aggregation node called DSLAM (Digital Subscriber Line Access Multiplexer) or MSAN (Multi Switch Access network). There are several standards of xDSL which mostly asymmetric such as ADSL, ADSL2 and ADSL2+. The DSL also support symmetrical upstream and downstream ratio as in SDSL, SHDSL; however in terms of commercial penetration rate, asymmetrical DSL is higher compared to the symmetrical one, hence this paper pay more focus on asymmetrical DSL. The ADSL2 standard, a recent version of ADSL, adopts enhanced modulation to reduce noise effect on the signals for higher coding gain and higher rate of the line. The ADSL2 system works at 50 K faster than the ADSL system and transmits signals 200 m farther, amounting to 6% more coverage. The newer version of ADSL is ADSL2. This standard issued in 2003 which referred to ITU-T G.992.5 standard. According to this standard, an ADSL2+ system shall work at up to 24 Mbps or a higher rate on downstream with

aware scheduling and admission control [4].

to the other access technologies including fiber.

downstream frequency around 2.2 MHz.

**2. xDSL characterization** 

traffic. It was assumed that the users may complain to the cellular operator (instead of broadband IP provider) when they experience delay or poor Mean Opinion Score (MOS) during a voice call. As in 3G cases, users may wait for FTP data transfer or surfing the internet web site. In the latter case, higher latency or packet loss will not create a question from users than if the same situation experienced by users use VoIP or video services.

According to [2] and [3], most femtocell technologies provide good quality voice calls and sufficient support to data services when the broadband IP link provides a minimum performance of:


This chapter describes the femtocell performance over xDSL access network as the backhaul. This work has been conducted as part of TELKOM contribution to FREEDOM Project (www.ict-freedom.eu) which consists of two phases of measurements and analysis. The first phase addressed the performance of ADSL2, ADSL2+ as a function of distance. It also observes the population of user's density enjoying certain attainable rate or less. Furthermore it also addresses transmission delay of xDSL over different bandwidth profiles. DSL backhaul quality model is derived in order to address different qualities of backhaul. The model can be used in elaboration of RRM, scheduling and system level simulation which need to take into account the backhaul quality.

While in the first phase characterization, the measurement was conducted without femtocell, in the second phase we observed femtocell bandwidth requirement to support various basic services including HTTP, FTP, voice and video streaming. We limit the study for residential case where xDSL access network is used. In this case mobile network operator and xDSL provider do not have agreement to maintain end-to-end QoS, hence non-SLA terminology is used. It should be understood that the bottleneck is not always occurred in the low speed backhaul, but it may occur event in high speed backhaul link; if the wireline broadband service requires a huge amount of bandwidth (for example high definition IPTV, video surveillance for home monitoring, etc).

The study of femtocell bandwidth requirement aims to observe the individual bandwidth consumption according to basic communication traffic types including HTTP, voice, video and FTP. For this purpose, we measured the bandwidth for 4-unit FAP and calculate bandwidth requirement for higher capacity FAP types such as 8-unit FAP which may be used in apartment deployment case. The bandwidth requirement study will give some insight to customer as well as operator, who deal with limited backhaul bandwidth, in order to understand how far their backhaul is capable of delivering basic communication services.

Based on the measurement result reported in FREEDOM, we will show the effect of background traffic in xDSL modem to the femtocell performance. Increasing the bandwidth may cope with the performance degradation but with the cost of adding more bandwidth to the existing broadband line. We also give some comments to the FREEDOM study outcome; how femtocell performance in non-SLA network can be improve by implementing backhaul aware scheduling and admission control [4].
