Multi-tier Topologies in Future Wireless Broadband Networks IEEE Presentation Submission Template (Rev. 9) Document Number: IEEE C /0004 Date Submitted: Source: Kerstin Johnsson, Shilpa Talwar, Nageen Himayat, S. Yeh 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 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 IEEEs name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEEs 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.http://standards.ieee.org/guides/bylaws/sect6-7.html#6http://standards.ieee.org/guides/opman/sect6.html#6.3 Further information is located at and.http://standards.ieee.org/board/pat/pat-material.htmlhttp://standards.ieee.org/board/pat
Trend towards personal and mobile devices Macro- BS (1km) Micro- BS (500m) Pico-BS (300m) Femto-AP (100m ) Mainframe Desktop Soft-AP (WiFi/ WiMax) Laptop Netbook MID (Mobile Hotspot/ Mobile PAN) Personalization Mobility Communications evolution lags computing Device Perspective
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) Macro-BS Femto-AP (Indoor coverage & offload macro-BS) Pico-BS (Areal capacity) Relay WiFi-AP (Offload macro-BS) Coverage Hole Client Cooperation Wired backhaul Wireless backhaul
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 Significant savings in Cost per Bit from Multi-tier Networks Source: Johansson at al, A Methodology for Estimating Cost and Performance of Heterogeneous Wireless Access Networks, PIMRC07. Small Cell Scenario Areal capacity gain* from spectral efficiency improvement and increase spatial reuse Sparse FAP deployment Dense FAP deployment PublicPrivatePublicPrivate FAP Tx Power 0 dBm dBm dBm *Areal capacity gain = (System Capacity with Femto-APs deployed) / (System Capacity without Femto-APs)
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 Challenge: Inter-tier Interference Tx SchemeMax FAP Tx Pwr Outdoor Outage (%) Indoor Outage (%) 50% Outdoor rate (Mbps) 50% Indoor rate (Mbps) No FAP Co-channel (10MHz) -10dBm dBm Tx SchemeOutdoor Outage (%) Indoor Outage (%) 50% Outdoor rate (Mbps) 50% Indoor rate (Mbps) FFR + NO FAP on 10 MHz FFR Macro on 5 MHz, Femto on diff 5 MHz FFR + FFZ + 0dBm FAP power on 10 MHz 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 users 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 standard should develop protocols to control interference across network tiers, perform handover intelligently, and manage network elements efficiently.