Wpan/wlan/wwan multi-Radio Coexistence Authors



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WPAN/WLAN/WWAN Multi-Radio Coexistence


Authors



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.



Agenda

  • motivation

  • state of the art

  • media independent time sharing

  • conclusion





Comparison of Wi-Fi / WiMAX / Bluetooth*



Multi-Radio Concurrent Usages



Coexistence Challenges (1): Inter-Radio Interference



Coexistence Challenges (2): Multi-Radio Integration



Coexistence-related IEEE Standards





Case Study: 802.11/802.15.1 Time Sharing Coexistence Mechanisms



What is the Problem with Time Sharing (TS)?

  • 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


Today’s OTA Techniques for Time Sharing Coexistence



Limitations of UAPSD



PER Performance with UAPSD

  • Two .11g Links: VoIP (54Mbps)+ Data (Variable)

    • Interference Period: 6 Bluetooth Slots
  • High (up to 40%) downlink PER due to varied channel access time



Limitations of 802.16e Sleep Mode

  • 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)


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



Media Independent Description of Radio Activity



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.
  • Goal: Media Access Control with multiple constraints

    • QoS, channel condition, traffic arrival, multi-radio coexistence, …


Time Sharing of 802.16 / 802.11 / 802.15.1 Activities



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


  • 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



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


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


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


Thank You



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