WPAN/WLAN/WWAN Multi-Radio
Coexistence
IEEE 802 Plenary, Atlanta
Tuesday, November 13 2007, 9:00 PM
Presenters:
Jari Jokela (Nokia)
Floyd Simpson (Motorola)
Artur Zaks (Texas Instruments)
Jing Zhu (Intel)
Sponsored by Stuart J. Kerry (802.11 WG Chair) with
support from Roger B. Marks (802.16 WG Chair)
1
Authors
Name
Company
Jari Jokela
Nokia
Floyd Simpson
Artur Zaks
Jing Zhu
Address
Visiokatu 3, Tampere,
Finland
Motorola
8000 W. Sunrise Blvd
Plantation, FL 33322,
USA
Texas Instruments 26 Zarchin St,
Raanana, Israel
Intel
2111, NE 25th Ave.,
Hillsboro, OR 97124
Phone
email
+358504860445 Jari.jokela@nokia.co
m
1-954-723-5269 floyd.simpson@motor
ola.com
+9729 7476853
+1 (503)
2647073
2
Arturz@ti.com
jing.z.zhu@intel.com
Abstract
This presentation gives an overview on multi-radio coexistence
with radios operating on adjacent and overlapping unlicensed
or licensed frequency bands, covering use cases, problem
analysis, and possible directions for solution. It shows that
coexistence has to consider both proximity and collocation.
Collocation imposes big challenges due to limited isolation and
various interference sources. Need for cost-effective solution
leads to approach where antennas are shared by multiple
radios thus introducing the requirement for multi-radio time
resource coordination. Today’s solutions are neither effective,
nor scalable with number of radios and number of vendors.
Standardization efforts are needed to provide information
service, command, and air-interface support necessary for
addressing coexistence issues.
3
Agenda
 motivation
 state of the art
 media independent time sharing
 conclusion
4
Motivation
Many Radios with Limited Spectrum and
Limited Space
Wi-Fi
A,B,G,N
Near Field
Communication
WiMAX
3G
UWB
Bluetooth
GPS
TV- DVB
5
60GHz
FM
Motivation
Comparison of Wi-Fi / WiMAX / Bluetooth*
Wi-Fi
(802.11g)
WiMAX
(802.16e)
Bluetooth
Range
100m
1000m
3m
Bandwidth
20MHz
10MHz
1MHz
Media Access
CSMA
OFDMA
TDMA
Peek Data Rate
54Mbps
64Mbps (2x2)
3Mbps
QoS Support
Low
High
Medium
Spectrum
Unlicensed
Licensed /
Unlicensed
Unlicensed
TX Power
20dBm
24dBm
0dBm
Wireless technologies have different sweet spots of
operation in terms of coverage, QoS, power,
throughput, etc.
*Other names and brands may be claimed as the property of others.
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Motivation
Multi-Radio Concurrent Usages
WiMAX Coverage
Bluetooth Coverage
Bluetooth Coverage
Wireless Gateway
on the road
Wi-Fi Coverage
in home / office
Seamless Handover
7
Coexistence Challenges (1):
Inter-Radio Interference
Interferer
Victim
WiMax
Wi-Fi
GSM 800
CDMA18
00
BT
Motivation
UWB
WiMax
Wi-Fi
GSM 800
CDMA
1800
BT
UWB
GPS
Isolation
Requirements
Severe
>55db
Moderate
40-55db
Cautious No-problem
25-40db
<25db
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Motivation
Coexistence Challenges (2):
Multi-Radio Integration
Wi-Fi
A,B,G,N
Near Field
Communication
WiMAX
3G
UWB
Bluetooth
TV- DVB
GPS
FM
60GHz
• Antenna sharing is more and more commonly being used for
multi-radio integration due to limited space on small formfactor device.
•Wi-Fi & Bluetooth Integrated Solution
• What is next? Reconfigurable / Software Defined Radio
• Multi-radio usage and performance should not be sacrificed
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State of the Art
Coexistence-related IEEE Standards
Standard
Year of
Publication
Scope
802.16.2
2001
2004 (revision)
recommended practice for coexistence of fixed
broadband wireless access systems
802.15.2
2003
recommended practice for coexistence of WPAN with
other wireless devices operating in unlicensed
frequency bands
802.11h
2003
amendment for spectrum and transmission power
management extensions in the 5GHz band in Europe
802.16h
ongoing
amendment for improved mechanisms, policies and
medium access control enhancements, to enable
coexistence among license-exempt 802.16 systems,
and to facilitate the coexistence of such systems with
primary users
802.19
ongoing
recommended practice for metrics and methods for
assessing coexistence of IEEE 802 wireless networks
P1900.2
ongoing
technical guidelines for analyzing the potential for
coexistence or in contrast interference between radio
systems operating in the same frequency band or
between different frequency bands.
Lack of coexistence support in air-interface for emerging WPAN/WLAN/WWAN
multi-radio device
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State of the Art
Overview of Coexistence Solutions
Techniques
True
Concurrency
Issues

spectrum partition /
mask
 insufficient with limited isolation (<
30dB) and wideband interference

antenna isolation

adaptive frequency
hopping
 may sacrifice performance (e.g. filter
reduces dynamic range)

transmission power
control

dynamic frequency
selection

notch filtering

time sharing / MAC
coordination with
various time
granularity
Perceived
Concurrency
–
–
–
connection (e.g. sec.)
period (e.g. ms)
packet (e.g. us)
• media dependent, vendor-specific,
component-specific and often not
interoperable
• additional cost and size
not scalable, and not support
component sharing
• best-effort
• solutions may not exist if wireless
stacks is not aware of coexistence
needs (e.g. being active 100% of time)
media independent, and potentially
scalable, but needs air-interface support
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State of the Art
Case Study: 802.11/802.15.1 Time
Sharing Coexistence Mechanisms
Basic Ideas
• per-packet authorization of all
transmissions
• arbitrate the radio activity by priority
when collision happens
Over-The-Air (OTA) Requirements
• maintain radio duty cycles at
friendly/low level
• provide flexibility to (re)schedule
radio activity
• forecast schedule for other radios to
react
Compressibility
Selectivity
Predictability
[IEEE 802.15.2, 2003]
Table: IEEE 802.15.1 packet types
SCO-HV1
SCO-HV2
SCO-HV3
ACL
TX Duty Cycle
50%
25%
16.5%
Varied
RX Duty Cycle
50%
25%
16.5%
Varied
Total Duty Cycle
100%
50%
33%
Varied
Schedulable
No
No
No
Yes
Difficult to support TS
coexistence
Commonly used in
cellular headset
PTA: Packet Traffic Arbitration, AWMA: Alternating Wireless Medium Access
SCO: Synchronous Connection-Oriented, ACL: Asynchronous Connection-Less, HV: High Quality Voice
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Most friendly to TS
coexistence
State of the Art
What is the Problem with Time Sharing (TS)?
Device A
Device C
Inter-Radio
Interference
Wireless
Network 1
(Multi-Radio)
Device B
TX
TX
Wireless
Network 2
RX
RX
 Radio activities may not always be locally controllable
– 802.11: frame may arrive at any time due to random access
– 802.16: base station to schedule all the activities of a mobile
station
– 802.15.1: master to schedule but usually power constrained
 Challenging to provide desirable performance on each of the
coexisting radios
– the performance on one radio is usually protected at the cost of
the other radio’s performance
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State of the Art
Today’s OTA Techniques for Time
Sharing Coexistence
Techniques
Retransmission
802.11
UAPSD / Power Save
CTS-to-self
Quiet
Sleep Mode
802.16
Scan
802.15.1
Retransmission
(eSCO & ACL)
Issues
ill-guided link adaptation
unpredictable response time
not applicable to AP and IBSS
silence the whole channel
coarse granularity
silence the whole BSS
little guarantee
may conflict with its intended usage
coarse granularity
master role
low efficiency due to low data rate
Common Problems
•Inexplicit, after-thought and case-specific, and difficult to be applied to new usages
•Low reliability and low efficiency due to lack of explicit / reliable support in air-interface
UAPSD: unscheduled automatic power save delivery, CTS: Clear-To-Send, eSCO: extended SCO
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State of the Art
Limitations of UAPSD
(3.75mSec for HV3)
BT Inactivity period
(2.5mSec for HV3)
BT_Active
Trigger Frame
or PS-POLL
STA
T2
T1
T4
AP
T3 ACK
DL Data
Frame
Difficult to predict T4 due
to Access Point
implementation specifics,
varied channel access time
and transmission time
ACK
•Unpredictable AP response time for downlink traffic
•Not applicable to AP experiencing jamming co-located interferences
•wireless residential gateway
•Not efficient to use with asymmetric or heavy traffic (e.g. data,
video, etc.)
•video streaming
•additional overhead due to trigger frame / PS poll
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State of the Art
PER Performance with UAPSD
0.45
0.45
Interference Burst Length= 0
Interference Burst Length= 0
0.4
Interference Burst Length= 1 BT Slot
Interference Burst Length= 2 BT Slots
0.35
0.3
0.3
0.25
0.25
0.2
Interference Burst Length = 1 BT Slot
0.35
PER
PER
0.4
Interference Burst Length = 2 BT Slots
0.2
0.15
0.15
0.1
0.1
0.05
0.05
0
0
6 Mbps
9 Mbps 12 Mbps 18 Mbps 24 Mbps 36 Mbps 48 Mbps 54 Mbps
6 Mbps
9 Mbps
12 Mbps 18 Mbps 24 Mbps 36 Mbps 48 Mbps 54 Mbps
Background Data Rate
Background Data Rate
a) Uplink Trigger
b) Downlink Data
 Two .11g Links: VoIP (54Mbps)+ Data (Variable)
– Interference Period: 6 Bluetooth Slots
 High (up to 40%) downlink PER due to varied channel access time
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State of the Art
Limitations of 802.16e Sleep Mode
Class A
Listening
Sleep
Class B
Sleep Mode
Coexistence
Inactive
Active
 Not applicable to multiple interferences reports with different pattern
 Coarse granularity: frame duration (5ms)
– Bluetooth Slot: 625 us
– inefficient when only a small portion is interfered
 Little flexibility
– Rx and Tx may be treated differently in coexistence
 Little reliability & Best-Effort
– coexistence is about avoiding interference and protecting radio activities
– reliability is important, and time info needs to be respected
 Other limitations
– Not applicable to other states (e.g. network entry)
– may be intended for other usage (scanning)
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Media Independent TS
Recap: Why Time Sharing?
 Power / Frequency control is ineffective in mitigating
wideband co-located interference
– further limited by other network factors, e.g. channel, link
budget, etc.
– not support component sharing due to integration
 Low duty-cycle radio activity is possible
– broadband / MIMO techniques  more bits/s
– 802.11: 20MHz  40MHz
– 802.16: 5MHz  10MHz  20MHz
– MIMO: 1x2  2x2  4x4
 Media independent description of radio activity is possible
•High Data Rate
•Coverage
•QoS
Design Considerations
of Support
•Security
an Air-Interface
•Low Power
•Mobility
•Multi-Radio Coexistence
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Media Independent TS
Media Independent Description of
Radio Activity
t
Type 1: Duty Cycle
Active
Inactive
T
P
Type 2: Bitmap
B
1
0
0
0
1
1
0
0
0
1
1
0
0
•t: starting time of an activity cycle
•T: duration of each activity burst (Type 1)
•B: bitmap (Type 2)
•x: time unit
•P: burst period – i.e., interval between bursts
 both type 1 and type 2 descriptions can be periodic, and P indicate
the duration for one period
•N: number of bursts
•s: type of activity: TX, RX, or both
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Media Independent TS
Explicit Coexistence Support
 Explicit Coexistence Feedback
– heterogeneous time granularity
– Bluetooth slot = 625us, 802.11 Time Unit = 1024us, 802.16
symbol = 102.9us, 802.16 frame = 5ms
Requirement 1: scalable time unit
– synchronization
– clock drift
– period mismatch
Requirement 2: information update & feedback control
 Explicit Coexistence Protection
– reliable and beyond best-effort
– link adaptation, scheduling, etc.
Requirement 3: reliable protection
Goal: Media Access Control with multiple constraints
– QoS, channel condition, traffic arrival, multi-radio coexistence, …
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Media Independent TS
Time Sharing of 802.16 / 802.11 / 802.15.1
Activities
3.75ms
625us
802.15.1 HV3
(33%)
M
S
5ms
802.16 frame
Structure
DL
UL
802.11 Activity (20%)
DL
UL
DL
UL
802.16 Activity (58%)
15ms
Explicit coexistence support enables seamless time sharing
of radio activates, reduces the collisions, and ensures
desirable performance on individual radio
Note: the pattern may change over time if radios are not in sync
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Media Independent TS
What is the benefit?
 Better User Experience
– support more multi-radio concurrent usages
– cheaper / smaller device without sacrificing functionality
& performance
 More efficient usage of wireless medium and
spectrum
– prevent ill-guided air-interface behavior
– reduce frame loss and improve reliability
– seamless interaction among radios
 Easier and lower cost integration of multiple
wireless technologies
– unified interface / signaling
– scale to number of radios and number of vendors
22
Media Independent TS
802.11v – Co-located Interference
Reporting
 Simple protocol enables terminal
to indicate it is using several
radios simultaneously and
performance of WLAN RX is
degraded
 Report allows terminal to
indicate interference time
characteristics, level, and other
information
 Automatic reporting is
supported, i.e., whenever STA
realize co-located interference is
changed it can send Report to
AP
 AP can use reported information
several ways, 1) it can schedule
DL transmissions not to collide
with interference slots and 2) it
can use information to adjust
e.g., rate adaptation and
retransmission logics
STA
AP
Co-located Interference Request
Other radio
operation is
started
causing
performance
degradation
Co-located Interference Report
Other radio
operation is
stopped
Co-located Interference Report
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Media Independent TS
Beyond IEEE
 Wi-Fi Alliance Converged Wireless Group (CWG) is working to
extend CWG RF Test Plan to cover Bluetooth / Wi-Fi / Cellular
coexistence testing
 Bluetooth SIG is defining feature requirements for coexistence
with broadband wireless access technologies, and Telephony
Working Group (TWG) is currently working towards publishing
a whitepaper to address Bluetooth/WiMAX coexistence
 WiMAX Forum Coexistence Ad-Hoc has reviewed contributions
for WiMAX-BT and WiMAX-Wi-Fi coexistence from Motorola,
Altair-Semiconductor, Nextwave and others.
– Coexistence based on the ‘perceived concurrency’ approach
– Key enabler is power save mode of WiMAX/Wi-Fi for time sharing
and BT MAC retransmission capability
– Currently working on harmonizing on the key WiMAX system
requirements to support time sharing at MAC level
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Conclusion
Summary
 Multi-radio concurrent usage is becoming the
norm, and coexistence is the limiting factor
• Existing approaches are ineffective
• limited true concurrency (due to cost, size, etc.)
• best-effort perceived concurrency
• Media independent time-sharing is promising,
but coexistence-awareness in air interface is the
must
• explicit coexistence feedback / protection
Is a more coordinated approach to support coexistence
in wireless necessary, or even possible?
http://www.youtube.com/watch?v=Rh0awIw7PNY
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Conclusion
Call to Action
 Develop standard-based, scalable, and reliable
coexistence solutions, considering the following
issues
– heterogeneous time granularity
– synchronization
– reliable protection
 Add explicit coexistence support to individual air
interface to enable
– Predictability: forecast activity for other radios to react
– Compressibility: maintain radio duty cycles at friendly level
– Selectivity: provide flexibility to (re) schedule activity
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Thank You
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