**2. xDSL characterization**

138 Mobile Networks

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

Less than 150 ms round-trip delay (more than 200 ms will not be practical for two ways

 A general packet loss of 3% or less is acceptable; however, packet loss is typically "bursty" by nature, and, as such, average rates below 0.25% should be maintained; At least 1 Mbps in downlink, i.e. from the broadband IP provider network to the FAP

 At least 256 kbps in uplink, i.e. from the FAP GW to the broadband IP provider network. 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

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,

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

performance of:

GW;

conversation); Less than 40 ms jitter;

which need to take into account the backhaul quality.

video surveillance for home monitoring, etc).

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 to the other access technologies including fiber.

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 downstream frequency around 2.2 MHz.

Femtocell Performance Over Non-SLA xDSL Access Network 141

Based on those information, cable model were constructed based on the following

NEXT reference value (@ 1 MHz) is considered the value @ 1% of the estimated

FEXT reference value (@ 1 MHz and 1 km) is assumed as in standard (Recommendation

Present broadband systems: 95% ADSL2/2+ (over POTS), 5% SHDSL, no regeneration

 Medium Term Broadband Services penetration assumed for performance estimation: 30% Long Term Broadband Services penetration assumed for performance estimation: 50%


Physical layer setting for ADSL2/2+ ; Internet access services: NM=6dB, Channel Mode

Based on above data and the xDSL modeling, the performance of ADSL2/ADSL2+ and

 Physical layer setting for VDSL2, IPTV services: NM=9dB, INP=2, Max Delay=8ms ADSL2/2+ performance curves refer to systems implementing extended framing.

Based on the xDSL modeling, the simulation can provide the following results:


Attenuation: as of CT 1341 Italian cable, polyethylene insulated quad cable

First level of aggregation:

Reference cable binder:


statistical distribution

ITU-T G996.1, ETSI 101 524)

Noise mix follows the assumption;

allowed in access network

Frequency Plan for VDSL2: 998 Hz

ADSL2/ADSL2+ Performance in FTTE

VDSL2 can be seen in Figure 2 and Figure 3.

ADSL2/ADSL2+/VDSL2 Performance in FTTC


Noise mix composition for scenario (FTTC):

xDSL Physical layer setting for performance evaluation follows

FAST ; IPTV services: NM=9dB, INP=2, Max Delay=8ms

 Number of boxes per access binder: 3 Number of drops per building cable: 4

Crosstalk model is based on following assumptions:

Crosstalk (statistical value @ 99% of confidence):

parameter:

 For cables up to 100 cp: Unit, consists of 5 quad (10 cp) For cables with 200 cp or more: Super Unit of 25 quad (50 cp)


Diameter of conductors: 0.6mm (worst case)

ADSL and ADSL+ are deployed using the existing PSTN infrastructure. The DSLAM node is located in the central office and defined as aggregation nodes. The existing copper cable is used so that the broadband service can be evenly distributed from Local Exchange, Street Cabinet and household's area. The size of access network zone is determined by the maximum copper cable length [5]. At DSLAM side, traffic is multiplexed and transmitted over fiber based transmission to the IP backbone.

An ISP may implement xDSL technology using different approach including DSLAM in the local exchange (fiber to the exchange, FTTE), DSLAM/MSAN in the cabinet (fiber to the cabinet, FTTC) and DSLAM/MSAN in the building/house (fiber to the house/building, FTTH/FTTB). For this study, we focus on FTTE and FTTC deployment where MSANs are located in the central exchange (FTTE) and street cabinet respectively to reach customer residential with the cable length less than 4 km.
