Channel Selection Support in TVWS

1. Channel Selection Support in TVWS Date: 2010-07-14 Authors: Notice:This document has been prepared to assist IEEE 802.19. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Alex Reznik, et. al. (InterDigital)

2. Abstract • TVWS Network has flexibility in selecting both operating channels and operating bandwidth • Network must use only unoccupied channels • Can group adjacent unoccupied channels to create a single wider BW channel • This creates a coexistence problem • Channel selection process may make it easier – or harder – for other networks to gain access to higher BW channels • Coexistence algorithms for channel selection/re-selection can alleviate this problem • Demonstrate how this is done using a typical architecture Alex Reznik, et. al. (InterDigital)

3. Channel Selection Problem • Example of Initial Channel Selection Problem • 8 TV channels create 48 MHz of available TVWS frequency • An 802.11 (with af) system selects the middle 4 channel and initiates 20 MHz operation • No other 20 MHz operation is possible (Channel Wastage) • This problem may also occur if a network manager (AP, BS, etc) vacates a channel, potentially creating an unusable fragment (illustrated in a later slide) Alex Reznik, et. al. (InterDigital)

4. Solution Outline • Basic Idea • Select a center frequency as close to the edge (as far from center) of a continuous frequency band as possible as shown below: • For the example considered, this opens up enough spectrum for another network operating on 20MHz bandwidth • When ? • Initial Channel Selection • After becoming aware of the “channel wastage” problem anytime during the operation • Make necessary allowances for adjacent TV broadcasts Alex Reznik, et. al. (InterDigital)

5. Example Architecture Alex Reznik, et. al. (InterDigital)

6. Selection Procedure • Available TV Channels • Query the TV White Space (TVWS) Database to get the list of available channels • The network manager (AP, BS etc) will select the bandwidth from the list • The operating bandwidth should be selected such that spectrum is not wasted as shown in slide 4. • To optimize the spectrum, the network manager needs to collect information about other networks that are present in TVWS and their operating channel • Network Manager may find/acquire information about other networks through: • Sensing (if available) • Checking the CDIS for nearby TVBDs • Polling other CMs Alex Reznik, et. al. (InterDigital)

7. What is an “Available” Channel • Channel is available within a requested area IF • Channel is cleared for use by the Regulatory TVWS DB (at the desired power) for all points within the requested area • Channel is currently known to have acceptable “interference levels:” • Transmission from neighboring devices will not cause harmful interference to any receiver within this area • Transmission at desired power from transmitters anywhere within this area will not cause harmful interference to any known neighboring receiver • Sensed interference sources do not cause harmful interference to any receiver within this area • What is a “requested area” • Location • Resolution/radius • Available channel is defined only w.r.t a specific “requested area” Alex Reznik, et. al. (InterDigital)

8. Channel Assignment Process • The coexistence manager (CM) will manage the channel assignment • CM will make sure that the channels are assigned such that the bandwidth is optimized • Interface B3 might be used by the CM to learn about the operating channels of APs/BSs under other CM’s • This will help all the CMs to obtain a complete picture of the TV white space spectrum and optimize the spectrum if the “channel wastage” problem occurs • Example on the following slide Alex Reznik, et. al. (InterDigital)

9. Example of operation • 3 network managers (APs) operating as shown in the figure • Suppose AP2 ceases to operate • Creates the “wastage problem” • Solution: • CM 1 informs CM 2 via interface B3 • CM 2 sends channel change request to AP3 • AP3 replies back with channel change response • Message exchange is shown in the figure: • 1 : Wastage indication • 2 : Channel change request • 3 : Channel change response • 4: Channel change indication Alex Reznik, et. al. (InterDigital)

10. Adjacent TV Channel Constraint • Some devices might not be able to move to the edge of the White Space spectrum due to the transmit limit when operating adjacent to a TV Broadcast Channel • In this case the network should try to leave some vacant space (if possible) for some low transmit power network and then establish its network e.g. should establish its network after leaving an open spectrum for 20MHz Alex Reznik, et. al. (InterDigital)

11. B2/3 Interfaces Protocol Messaging • Major questions • How is channel availability information disseminated? • How does CM request that others change channels if needed • A possible approach • CM/CDIS broadcast what they know about channel availability • CMs can subscribe to such broadcasts and/or request specific reports • CMs can request that a channel be freed up • Response is simply an updated channel usage report back to CM • Protocol success/failure • Assumes no ability to force all networks to move • Add-on of “move commands” is helpful, but does not completely solve the problem as the command would only apply to 802.19.1 compliant networks • THEREFORE – whether a Free-Up request generated a fully successful response from all involved is best established by measurement – does a channel appear free after a request Alex Reznik, et. al. (InterDigital)

12. Conclusions and Next Steps • Introduced channel selection and assignment as an important coexistence mechanism • Defined the notion of “available” channels • Defined an algorithm for selecting a channel from among the available channels • Open items • Need to address the possibility of sharing channels that are not available but are “lightly loaded” • Next steps • Discussion by the group and agreement on the need and specifics of the proposed mechanism • Work out the details and develop normative text Alex Reznik, et. al. (InterDigital)