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
Intel Corporation
Venue:
San Diego, CA, USA
Base Contribution:
None
Purpose:
For discussion in the Project Planning Adhoc
Notice:
E-mail: kerstin.johnsson@intel.com
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Device Perspective
Communications evolution lags computing
Micro- BS
(500m)
Pico-BS
(300m)
Femto-AP
Personalization
(1km)
Soft-AP
(100m)
Mobility
Macro- BS
(WiFi/ WiMax)
MID
(Mobile Hotspot/
Mobile PAN)
Netbook
Laptop
Desktop
Mainframe
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 Public Private
0 dBm
34
34
152
152
FAP
10 dBm
Tx
Power 20 dBm
36
38
144
154
35
39
135
152
*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
Tx Scheme
Max FAP
Tx Pwr
Outdoor Outage
(%)
Indoor Outage
(%)
50% Outdoor rate
(Mbps)
50% Indoor rate
(Mbps)
25
31.8
0.06
0.05
-10dBm
38.2
8.6
0.06
6.4
0dBm
61.9
2.2
0
14.3
No FAP
Co-channel
(10MHz)
•
•
•
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
Outdoor
Outage (%)
Indoor
50% Outdoor 50% Indoor
Outage (%) rate (Mbps) 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 intraor 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 macroABS, it may benefit from remaining associated to the femto-ABS if the femto load
is significantly less.
handoff
handoff
handoff
handoff
handoff
handoff
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.