Interference Management for TVWS Networks

1. Interference Management for TVWS Networks Date: July 15, 2011 Authors:

2. Contents • Abstract • Comments • Discussion • The Interference Management Problem • Over-the-DS Signaling to enable Coexistence • RLSS for Interference Management • Summary

3. Abstract • There are many comments asking to specify the coexistence mechanisms to avoid interference between overlapping BSS in TVWS band. This presentation discusses the problems and proposed solutions for the following CIDs on coexistence: • CIDs: 8, 13, 270, 500, 733, 753, 797, 811 and 973.

4. Comments

5. Comments ..

6. Comments ..

7. Discussion • The larger cell coverage in TVWS band exacerbates the problem of overlapping BSS with hidden node STAs. In order to improve the utilization of limited available spectrum in TVWS band, enhanced coexistence mechanisms are required • There are many possible scenarios for which, the legacy mechanisms currently available in 802.11 (e.g. CSMA/CA, RTS/CTS etc) are not sufficient • Interference avoidance among overlapping WLAN networks from same or different operator’s service area becomes important • How high-power BSS and low-power BSS can operate in same area? • How to manage different channel widths in overlapping BSS ? • Two solutions are discussed in this presentation: • Over-the-DS message exchange with remote request broker (RRB) for coexistence • Interference management among multiple APs connected to a common RLSS

8. The Interference Management Problem • There are two main problems: • When the transmit power levels in two overlapping BSS are significantly different (4 W Fixed vs 100 mW/40 mW Personal/Portable operation), the conventional RTS/CTS protection can not solve the interference from a hidden STA. • The larger coverage range in TVWS makes it more difficult problem than in the legacy WLAN bands (limited channels but increased interference area)

9. The Interference Management Problem .. • Overlapping BSS with different channel bandwidths will be common due to limited TV channels in many locations. • One BSS with 5 MHz bandwidth may be adjacent with another which uses 10 MHz channel overlapping to it. However, OBSS scanning and coexistence notifications like in 802.11n can not work due to non-interoperable preambles

10. Over-the-DS message exchange for coexistence • To effectively manage overlapping networks, stations in two overlapping BSS should be able to exchange coexistence messages • 802.11r has fast BSS transition (FT) protocol already specified which utilizes over-the-DS message exchange using the remote request broker (RRB) function

11. Over-the-DS message exchange .. • The RRB mechanisms can be extended for coexistence purposes. Another possible use of RRB is for establishing communication link from a Fixed/Mode II device not having its direct internet connection to another Fixed/Mode II • The RRB function of AP allows message passing between two BSS • The STA of BSS-A transmits FT action frame to its AP • The AP of BSS-A generates a Remote Request message with the payload containing a FT action frame and forwards it to neighbouring AP of BSS-B. • The message payload inside Remote Request/Response is delivered with encapsulation (Ethertype 89-0d). • Two new FT action frame types are proposed to support remote coexistence request/response transmissions over the DS: • Request can be for aligning the operational channel widths (for Problem 2) • Request to switch the operating channel (for Problem 1 or 2) • Request for sharing the medium time (for Problem 1)

12. Over-the-DS message exchange .. • Example- low power/high power overlap: • A STA in LP_BSS notifies its AP to indicate presence of signal from HP_BSS (frames from STA Type = Fixed, or identifying signal from Fixed device), and HP_OBSS_Present flag is set • A STA in LP_BSS transmits FT action frame for Remote Coexistence Request to be forwarded to the AP of HP_BSS. The request could be for: • Request to switch the operating channel • or change the channel width, • or Request for a medium time for its use • The AP of HP_BSS responds with the Remote Coexistence Response action frame with indication of result (success or denied). For the case of medium request, the AP transmits a CTS_to_Self frame with NAV set to the requested period, and transmits FT action frame in the remote response to the AP of the LP_BSS.

13. Over-the-DS message exchange .. • What is required? • FT Action frames for Remote Coexistence Request and Response • Remote Coexistence Request Frame • Remote Coexistence Response Frame

14. Network Coexistence Support through RLSS • A registered location secure server (RLSS) entity has been specified in current 802.11af specification: • RLSS is an advertisement server to support RLQP using inter-working capability of 802.11u. RLSS can be implemented inside an AP or can reside outside • It can provide the following functions for white space operation: • proxy to external geo-location database • a network management service node that facilitates the operational controls • In many deployments, networks of different coverage range and capacity (e.g. low data rate coverage for parking lots/campus, and high-data rate indoor service) may be managed through a common RLSS • How the RLSS can provide interference management (IM) service? • Additional information about neighbourhood during network initiation by an AP • Notification of any changes in operational environment (changes in frequency channel, bandwidth, power, mobility)

15. Coexistence Support through RLSS .. • Once an AP (Mode II or Fixed) obtains the list of authorized frequencies and transmit power levels for the network initiation, additional information about other networks around its area becomes important for choosing its actual operational parameters (e.g. channel, bandwidth, power) • Assumption: multiple APs or master mode capable devices are served by the same RLSS within one operator’s (i.e., service provider’s) domain

16. Coexistence Support through RLSS .. • For setting up a network, an AP first obtains list of available channels at its location by performing channel availability query. It can then request additional IM information from the RLSS for other networks in its neighbourhood served by the same RLSS • IM Information Request from a Master mode capable TVBD to RLSS: • Device ID, geo-location, device class (max. transmit power, spectrum mask etc.) • Request Type: • 0 for Neighbourhood information only • 1 for Request for operational parameters (for actively managed nodes) • Optionally indicate the radius of its influence • IM Information Response from RLSS: • The response message contains current operational parameters of potentially interfering networks (BSSID, used frequency channels, used channel bandwidths, used transmit power levels, relative distances, device classes) • Recommended operational parameters if Request Type is 1

17. Coexistence Support through RLSS .. • How RLSS can provide the relevant information? • From the known information on geo-location and device class of each TVBD, RLSS internally identifies the possible interfering networks within its service zone within a proximity region • An exclusion zone may be calculated based on possible overlapping in list of available channels, and propagation ranges of other BSS based on types of devices and their current transmit power levels • Actual algorithm for deriving the information could be implementation specific • After receiving the IM Information Response from RLSS, the AP can select its operating frequency, bandwidth and transmit power to minimize interference to itself, as well as, possible interference to its neighbouring networks • What is needed in the specification? • RLQP element for IM Information Request and Response for use by the master capable devices • The RLQP element can be transmitted over the air using GAS frames for devices not having direct connection to Internet • For master devices connected to RLSS, only the message content/format is defined

18. Summary • The interference management among multiple BSS is more challenging in TVWS band due to larger coverage range • Message exchange through remote request broker mechanism among neighbouring APs can provide coexistence support between networks of dissimilar power levels or bandwidths • RLSS can also provide additional information and control mechanisms for coexistence among multiple BSS operated by same service provider

19. Straw-polls • Do you support the use of RRB communication mechanism to exchange coexistence information in neighbouring BSS? • Yes: • No: • Abstain: • Do you support the need of RLQP element for interference management request/response through RLSS to allow exchange of neighbourhood knowledge? • Yes: • No: • Abstain: