WPAN/WLAN/WWAN Multi-Radio Coexistence

1
WPAN/WLAN/WWAN Multi-Radio Coexistence
IEEE 802 Plenary, Atlanta Tuesday, November 13
2007, 900 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)
2
Authors
3
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. Todays 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.

4
Agenda

• motivation
• state of the art
• media independent time sharing
• conclusion

5
Motivation
Many Radios with Limited Spectrum and Limited
Space
FM
6
Comparison of Wi-Fi / WiMAX / Bluetooth
Motivation
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.
7
Multi-Radio Concurrent Usages
Motivation
WiMAX Coverage
Bluetooth Coverage
Bluetooth Coverage
Wireless Gateway
on the road
Wi-Fi Coverage
Seamless Handover
in home / office
8
Coexistence Challenges (1) Inter-Radio
Interference
Motivation
Interferer
Victim
Isolation Requirements
Severe Moderate Cautious No-problem gt55db
40-55db 25-40db lt25db
9
Coexistence Challenges (2) Multi-Radio
Integration
Motivation
FM

• Antenna sharing is more and more commonly being
  used for multi-radio integration due to limited
  space on small form-factor device.
• Wi-Fi Bluetooth Integrated Solution
• What is next? Reconfigurable / Software Defined
  Radio
• Multi-radio usage and performance should not be
  sacrificed

10
Coexistence-related IEEE Standards
State of the Art
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
11
State of the Art
Overview of Coexistence Solutions
Techniques Techniques Issues
True Concurrency spectrum partition / mask antenna isolation adaptive frequency hopping transmission power control dynamic frequency selection notch filtering insufficient with limited isolation (lt 30dB) and wideband interference may sacrifice performance (e.g. filter reduces dynamic range) media dependent, vendor-specific, component-specific and often not interoperable additional cost and size
Perceived Concurrency time sharing / MAC coordination with various time granularity connection (e.g. sec.) period (e.g. ms) packet (e.g. us) best-effort solutions may not exist if wireless stacks is not aware of coexistence needs (e.g. being active 100 of time)
not scalable, and not support component sharing
media independent, and potentially scalable, but
needs air-interface support
12
Case Study 802.11/802.15.1 Time Sharing
Coexistence Mechanisms
State of the Art

• 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
Commonly used in cellular headset
Difficult to support TS coexistence
Most friendly to TS coexistence
PTA Packet Traffic Arbitration, AWMA
Alternating Wireless Medium Access SCO
Synchronous Connection-Oriented, ACL
Asynchronous Connection-Less, HV High Quality
Voice
13
What is the Problem with Time Sharing (TS)?
State of the Art
Device C
Device A
Inter-Radio Interference
Wireless Network 1
Wireless Network 2
TX
TX
(Multi-Radio) Device B
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 radios performance

14
Todays OTA Techniques for Time Sharing
Coexistence
State of the Art
Techniques Issues
802.11 Retransmission ill-guided link adaptation
802.11 UAPSD / Power Save unpredictable response time not applicable to AP and IBSS
802.11 CTS-to-self silence the whole channel
802.11 Quiet coarse granularity silence the whole BSS
802.16 Sleep Mode little guarantee may conflict with its intended usage coarse granularity
802.16 Scan little guarantee may conflict with its intended usage coarse granularity
802.15.1 Retransmission (eSCO ACL) 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
15
Limitations of UAPSD
State of the Art
Difficult to predict T4 due to Access Point
implementation specifics, varied channel access
time and transmission time

• 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

16
PER Performance with UAPSD
State of the Art
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

17
Limitations of 802.16e Sleep Mode
State of the Art
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)

18
Recap Why Time Sharing?
Media Independent TS

• 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 Support
• Security
• Low Power
• Mobility
• Multi-Radio Coexistence

Design Considerations of an Air-Interface
19
Media Independent Description of Radio Activity
Media Independent TS
t
Active
Inactive
Type 1 Duty Cycle
T
P
Type 2 Bitmap
1
0
0
0
1
1
0
0
0
1
1
0
0
B

• 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

20
Explicit Coexistence Support
Media Independent TS

• 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,

21
Time Sharing of 802.16 / 802.11 / 802.15.1
Activities
Media Independent TS
3.75ms
625us
M
S
802.15.1 HV3 (33)
5ms
802.16 frame Structure
DL
UL
DL
UL
DL
UL


802.16 Activity (58)
802.11 Activity (20)
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
22
What is the benefit?
Media Independent TS

• 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

23

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
24
Beyond IEEE
Media Independent TS

• 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

25
Summary
Conclusion

• 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?vRh0awIw7
PNY
26
Call to Action
Conclusion

• 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

27
Thank You