July 2010
doc.: IEEE 802.19-10/0104r0
Channel Selection Support in TVWS
Date: 2010-07-14
Authors:
Name
Company Address
Alex Reznik
InterDigital
Joe Kwak
InterDigital
Saad Ahmad
InterDigital
Rocco Di
Girolamo
Jean-Louis
Gauvreau
InterDigital
781 3rd Ave.,
King of Prussia, PA
19406
Phone
E-mail
610-878-5784
[email protected]
InterDigital
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.
Submission
Slide 1
Alex Reznik, et. al. (InterDigital)
July 2010
doc.: IEEE 802.19-10/0104r0
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/reselection can alleviate this problem
– Demonstrate how this is done using a typical architecture
Submission
Slide 2
Alex Reznik, et. al. (InterDigital)
July 2010
doc.: IEEE 802.19-10/0104r0
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)
Submission
Slide 3
Alex Reznik, et. al. (InterDigital)
July 2010
doc.: IEEE 802.19-10/0104r0
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
Submission
Slide 4
Alex Reznik, et. al. (InterDigital)
July 2010
doc.: IEEE 802.19-10/0104r0
Example Architecture
Submission
Slide 5
Alex Reznik, et. al. (InterDigital)
July 2010
doc.: IEEE 802.19-10/0104r0
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
Submission
Slide 6
Alex Reznik, et. al. (InterDigital)
July 2010
doc.: IEEE 802.19-10/0104r0
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”
Submission
Slide 7
Alex Reznik, et. al. (InterDigital)
July 2010
doc.: IEEE 802.19-10/0104r0
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
Submission
Slide 8
Alex Reznik, et. al. (InterDigital)
July 2010
doc.: IEEE 802.19-10/0104r0
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:
–
–
–
–
Submission
1 : Wastage indication
2 : Channel change request
3 : Channel change response
4: Channel change indication
Slide 9
Alex Reznik, et. al. (InterDigital)
July 2010
doc.: IEEE 802.19-10/0104r0
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
Submission
Slide 10
Alex Reznik, et. al. (InterDigital)
July 2010
doc.: IEEE 802.19-10/0104r0
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
Submission
Slide 11
Alex Reznik, et. al. (InterDigital)
July 2010
doc.: IEEE 802.19-10/0104r0
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
Submission
Slide 12
Alex Reznik, et. al. (InterDigital)