Multi-tier Topologies in Future Wireless Broadband Networks

IEEE 802.16 Presentation Submission Template (Rev. 9) Document Number:

IEEE C802.16-10/0004Date Submitted:

2010-01-10Source:

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

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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)

Per

son

aliz

atio

n

Mo

bili

ty

Communications evolution lags computing

Device Perspective

Multi-tier NetworksSpectrum 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-BSFemto-AP

(Indoor coverage & offload macro-BS)

Pico-BS(Areal capacity)

Relay

WiFi-AP(Offload macro-BS)

Coverage Hole

Client CooperationWired 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’, PIMRC’07.

Small Cell Scenario

Areal capacity gain* from spectral efficiency improvement

and increase spatial reuse

Sparse FAP deployment

Dense FAP deployment

Public Private Public Private

FAP Tx Power

0 dBm 34 34 152 152

10 dBm 36 38 144 154

20 dBm 35 39 135 152

*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 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 0.06 6.4

0dBm 61.9 2.2 0 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 3.0 0.2 0.06 10.7

FFR + FFZ + 0dBm FAP power on 10 MHz 3.0 0.5 0.06 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.

handoffhandoff handoff

handoffhandoff

handoffhandoff

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.