Multi-tier Topologies in Future Wireless Broadband Networks IEEE 802.16 Presentation Submission Template (Rev. 9) Document Number: IEEE C802.16-10/0004 Date Submitted: 2010-01-10 Source: Kerstin Johnsson, Shilpa Talwar, Nageen Himayat, S. Yeh E-mail: kerstin.johnsson@intel.com Intel Corporation Venue: San Diego, CA, USA Base Contribution: None Purpose: For discussion in the Project Planning Adhoc Notice: This document does not represent the agreed views of the IEEE 802.16 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 802.16. Patent Policy: The contributor is familiar with the IEEE-SA Patent Policy and Procedures: <http://standards.ieee.org/guides/bylaws/sect6-7.html#6> and <http://standards.ieee.org/guides/opman/sect6.html#6.3>. Further information is located at <http://standards.ieee.org/board/pat/pat-material.html> and <http://standards.ieee.org/board/pat >.

Trend towards personal and mobile devices Device Perspective Macro- BS (1km) Micro- BS (500m) Pico-BS (300m) Communications evolution lags computing Femto-AP (100m) Soft-AP (WiFi/ WiMax) MID (Mobile Hotspot/ Mobile PAN) Personalization Mobility Mainframe We started this process by looking at this area through the view of the 2010 user – here is the question we decided that user would face - As a likely technology use leader you may well already seeing the beginnings of this Laptop Netbook Desktop Trend towards personal and mobile devices

Multi-tier Networks Spectrum Utilization Overlay multiple tiers of cells, macro/pico/femto, potentially sharing common spectrum Client can be viewed as center of additional tier (see client co-op) Tiers can be heterogeneous (WiFi) WiFi-AP (Offload macro-BS) Macro-BS Femto-AP (Indoor coverage & offload macro-BS) Pico-BS (Areal capacity) Client Cooperation Wired backhaul Relay Wireless backhaul Coverage Hole

Advantages of Multi-tier Networks Significant gains in Areal Capacity through aggressive spectrum reuse and use of unlicensed bands Cost structure of smaller cells (Pico & Femto) is more favorable Indoor coverage is improved through low cost femto-cell Small Cell Scenario Areal capacity gain* from spectral efficiency improvement and increase spatial reuse Sparse FAP deployment Dense FAP deployment Public Private FAP Tx Power 0 dBm 34 152 10 dBm 36 38 144 154 20 dBm 35 39 135 Capacity gain comes from: Spectral Efficiency Improvement Spatial reuse of frequency Ex: 150x ~ 1.5(average SE gain) x 100 FAP’s *Areal capacity gain = (System Capacity with Femto-APs deployed) / (System Capacity without Femto-APs) Source: Johansson at al, ‘A Methodology for Estimating Cost and Performance of Heterogeneous Wireless Access Networks’, PIMRC’07. Significant savings in Cost per Bit from Multi-tier Networks

Challenge: Inter-tier Interference Need to protect control & data signals from inter-tier interference Femto-cells cause significant INT to macro-users and other femto-cells Power control improves interference only slightly Macro and femto on diff carriers prevents INT, but lowers throughput and significantly decreases trunking efficiency and RRM flexibility Simple FFR on macro & femto reduces INT; but more sophisticated FFR and/or Femto-Free Zones (FFZ) required to fully protect macro-users Tx Scheme Max FAP Tx Pwr Outdoor Outage (%) Indoor Outage (%) 50% Outdoor rate (Mbps) 50% Indoor rate (Mbps) No FAP 25 31.8 0.06 0.05 Co-channel (10MHz) -10dBm 38.2 8.6 6.4 0dBm 61.9 2.2 14.3 Tx Scheme Outdoor Outage (%) Indoor Outage (%) 50% Outdoor rate (Mbps) 50% Indoor rate (Mbps) FFR + NO FAP on 10 MHz 3.0 17.0 0.07 0.03 FFR Macro on 5 MHz, Femto on diff 5 MHz 0.2 0.06 10.7 FFR + FFZ + 0dBm FAP power on 10 MHz 0.5 11.3 Interference reduction for Control Signals remains unresolved

Challenge: Mobility Handovers across small cells can be highly inefficient Intelligent handover mechanisms required to determine when intra- or inter-tier handover is beneficial Example 1: If a macro-user moves into the coverage area of a high data rate femto-cell, the first instinct is to handover. However, the benefit/cost of handover depends on the user’s mobility. Example 2: Although a femto-user may have better channel quality to the macro-ABS, it may benefit from remaining associated to the femto-ABS if the femto load is significantly less. handoff

Challenge: Network Management Scalability is key feature in multi-tier networks Self-organization and management across tiers will be crucial to maintaining low OPEX and quick network response May facilitate network management to merge network elements Need to consider new network elements Example: what is the optimum middle ground between consumer owned & deployed private femto-AP (low cost) versus operator owned & deployed public pico-BS?

Summary & Recommendations Multi-tier networks promise significant improvements in total network, average user, and indoor user throughput However, to realize these gains, next generation 802.16 standard should develop protocols to control interference across network tiers, perform handover intelligently, and manage network elements efficiently.