Support for Femtocell Document Number: IEEE C802.16m-08/1089 Date Submitted: Source: Guang Han, Hua XuVoice: , Motorola Inc. Venue: SDD; in response to the TGm Call for Contributions and Comments m-08/003r4 for Session 57 Base Contribution: Purpose: For review and adapt. Notice: This document does not represent the agreed views of the IEEE Working Group or any of its subgroups. It represents only the views of the participants listed in the “Source(s)” field above. It is offered as a basis for discussion. It is not binding on the contributor(s), who reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE Patent Policy: The contributor is familiar with the IEEE-SA Patent Policy and Procedures: and. Further information is located at and.

Outline Motivation Major technical challenges –Mobility –Interference –Synchronization –Self-organization Conclusions and recommendations

Why Femtocell? Problem: –Poor indoor coverage for high data rate applications due to large penetration loss. –Most mobile data usage is from indoors. Alternate solution is costly: –Adding more outdoor base stations is not an economically desirable solution. Femtocell benefits: –Femtocells will improve indoor coverage for high data rate applications. –Femtocells will reduce network infrastructure cost. –By using existing broadband connection as backhaul, Femtocells will significantly increase network capacity and reduce network operation cost. Additional notes: –SPWG is preparing Wimax Femtocell requirements document. (Current version 0.2.0) –3GPP has been discussing Femtocell topics from early 2007.

Major technical challenges I: Mobility The density of Femtocells can be significantly larger than that of macro cells. In urban area, a passenger on the street may detect hundreds of Femtocells in a short period of time. –Handover The upper limit of the size of the neighbor list is far below the number of potential Femtocell neighbors of a macro cell. Thus the passenger may not be able to perform handover even if an accessible Femtocell is nearby. –Control signal pollution Assume the neighbor list is properly enhanced to support handover Since Femtocells can have closed access such that only very few end users can access a Femtocell, most camping/handover requests by the passenger will be rejected. Such frequent futile camping/handover attempts will increase network signaling load and impact end user mobility performance.

Major technical challenges II: Interference Neighboring Femtocells in the same apartment building will cause large interference to each other. When Femtocells use the same frequency as outdoor cells, they will also cause large interference to nearby Macro cell users. –First scenario: Macro users in the close proximity (E.g. in the same room) of a Femtocell will not be able to detect MAPs of the Macro BS, thus they are completed blocked from the Macro cell. –Second scenario: Macro users relatively farther away from a Femtocell will still be able to receive Macro cell service at the expense of lower data rate and/or more Macro cell resource.

Major technical challenges III: Synchronization GPS receiver may not work well indoors. Also a GPS receiver can be too expensive for a Femtocell. Using high accuracy crystal oscillator (E.g. OCXO) for each femtocell is not a economically viable solution either. IEEE 1588 requires symmetric delay and very small jitter over the backhaul connection. Existing broadband connection (cable/DSL) can hardly meet these requirements.

Major technical challenges IV: Self organization Similar to WiFi access points, A Femtocell is supposed to be installed by its owner. Thus pre-planning is not feasible. –Self configuration A Femtocell needs to automatically acquire its working parameters (frequency, transmission power, neighbor list, cell ID, etc) from the network before serving its users. –Self optimization A Femtocell adaptively adjust its parameters with respect to external environment (RF, network, etc) variation in order to optimize its performance.

Conclusions and recommendations Conclusions: –Femtocell will bring significant benefits to the operators, such as solving indoor coverage problem, increasing network capacity, reducing network infrastructure and operation cost, etc. –But we need to overcome many technical challenges to enable successful Femtocell deployment. Those technical challenges need to be addressed in IEEE m context. Recommendations: –Femtocell has many special characteristics, making it hard to directly reuse solutions for macro cells. We recommend allocating a standalone section in SDD for Femtocell.