1. Neighboring Network Information Sharing through RLSS
Month Year
doc.: IEEE yy/xxxxr0
Neighboring Network Information Sharing through RLSS
Date: Sept 12, 2011
Authors:
Name
Company
Address
Phone
Padam Kafle
Nokia
6021 Connection Drive, Irving, TX, 75039
Mika Kasslin
Itämerenkatu 11-13, Helsinki, Finland
Prabodh Varshney
Hiroshi Harada
NICT
John Doe, Some Company

2. Contents Abstract Comments Discussion The OBSS Problem in TVWS
Deployment Scenarios
RLSS for Neighboring Network Information Sharing
Network Coexistence through RLSS with Centralized Decision
Summary

3. doc.: IEEE 802.15-<doc#>
<month year>
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 solution from xxxxr0 to provide resolution for the following CIDs on coexistence:
CIDs: 8, 270, 733, 753 and 811.
>
Page 3

4. Comments > doc.: IEEE 802.15-<doc#> <month year> Page 4
CID
Clause Number(C)
Page(C)
Line(C)
Comment
Proposed Change 8
Need a mechanism for a portable BSS to detect presence of co-channel fixed devices so that it can move into a different channel. This is because there is a 16dB EIRP difference between the fixed and portable. So fixed APs may never detect a portable devices in the co-channel and thereby cause interference to the portable device BSS.
Make transmission of unsolicited TPC report element mandatory for fixed TVWS devices. Also see 11/0265r0 for suggested text.
270
19.1.1 66 61
What is the impact on OBSS operation when there are BSSs with different BW sharing some spectrum? Do slot times line up? Are slot times the same? If either condition is not true, does this increase the rate of inter-BSS collisions? Or are the different modes of operation restricted by regulatory domain so that overlapping BSSs of dissimilar width will not arise in practice?
Clarify.
733
General
there is no specification for how the 5 and 10 MHz mode would coexist in a same TVWS channel, since the preambles cannot interoperate
add detailed coexistence mechanisms
>
Page 4

5. Comments .. > doc.: IEEE 802.15-<doc#> <month year>
CID
Clause Number(C)
Page(C)
Line(C)
Comment
Proposed Change
753 79 38
"The slot time shall follow for 5 GHz and TVWS bands and for 2.4 GHz bands." According to the above sentence, BSSs using different channel width will have different slot times. In the overlapping BSSs case this will have negative impact on the BSS with narrower bandwidth in terms of medium access. For example, when a BSS using 5 MHz wide channel (5 MHz BSS) is overlapping with a BSS using 10 MHz wide channel (10 MHz BSS), the 10 MHz BSS will have more chance to access the medium than the 5 MHz BSS since the slot time of the 10 MHz BSS (13 usec) is much shorter than the slot time of the 5 MHz channel (21 usec). This will result in unfair medium access because contention backoff time will be much shorter for the 10 MHz BSS than the 5 MHz BSS even if both BSSs choose the same backoff counter value.
Provide a coexistence mechanism for overlapping BSSs with different channel bandwidths.
811
General 66 36
802.11af is intended for increased range. However with that comes increased OBSS interference.
Recommend studying interference mitigation schemes between OBSS
>
Page 5

6. doc.: IEEE 802.15-<doc#>
<month year>
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 (e.g. CSMA/CA, RTS/CTS etc) are not sufficient
We had discussed some possible solutions in r1 during SFO meeting. This presentation is built upon the RLSS based approach, which had received good support from the straw poll:
Do you support the use of RLSS to allow exchange of neighbourhood knowledge to address some of coexistence related comments? 7 Yes, 2 No, 5 Abstains
Interference avoidance among multiple networks served by a common RLSS is considered here with two possible options for implementation:
Distributed decision making
Centralized decision making
>
Page 6

7. The OBSS Problem in TVWS
doc.: IEEE <doc#>
<month year>
The OBSS Problem in TVWS
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)
>
Page 7

8. The OBSS Problem in TVWS ..
doc.: IEEE <doc#>
<month year>
The OBSS Problem in TVWS ..
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 using 10 MHz channel overlapping to it (refer to .11af channelization in next slide). However, OBSS scanning and coexistence notifications like in n can not work due to non-interoperable preambles
>
Page 8

9. The OBSS Problem in TVWS ..
doc.: IEEE <doc#>
<month year>
The OBSS Problem in TVWS ..
Current channelization in .11af for US
>
Page 9

10. doc.: IEEE 802.15-<doc#>
<month year>
Deployment Scenarios
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
Assumption: multiple APs are served by the same RLSS within one service provider’s domain, or AP from one SP’s network can request information from another AP with other SP’s network
>
Page 10

11. doc.: IEEE 802.15-<doc#>
<month year>
Deployment Scenarios ..
A registered location secure server (RLSS) entity has been specified in current af specification:
RLSS is an advertisement server to support RLQP using inter-working capability of u. 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
Once an AP (Mode II/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 selection of its actual operational parameters (e.g. channel, bandwidth, power)
How the RLSS can support/manage to avoid OBSS interference?
Provide additional information about neighbouring networks to the APs. The decisions (network initiation or changes during operation) are local to the AP
Control the operating parameters of the APs. The decisions on parameters are centralized to the RLSS
>
Page 11

12. Neighboring Network Information through RLSS
doc.: IEEE <doc#>
<month year>
Neighboring Network Information 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 Neighboring Network Information (NNI) from the RLSS for other networks in its neighbourhood served by the same RLSS
NNI Query from a GDC AP to RLSS:
Device ID, device class (indicates max. transmit power, spectrum mask etc.), estimated coverage radius, geo-location (optional)
Request Type:
0 for Neighboring Network Information Request
values are reserved
NNI Response from RLSS to the requesting AP:
The response message contains current operational parameters of networks which are around the neighbourhood of the requesting STA (BSSID, used frequency channels, used channel widths, used transmit power levels, relative distances, device classes)
>
Page 12

13. Neighboring Network Information through RLSS ..
doc.: IEEE <doc#>
<month year>
Neighboring Network Information through RLSS ..
How RLSS can provide the relevant information?
From the known information about identity, device class and geo-location of each TVBD, RLSS internally determines the possible interfering networks in its service zone
An exclusion zone may be calculated using the knowledge of available channels, and propagation ranges of other BSS from the types of devices and their current transmit power levels
Actual algorithms for deriving the information is implementation specific, and not specified by the standard
After receiving the response for the NNI Query from RLSS, the AP can select its operating frequency, channel width and transmit power to minimize interference to itself, as well as, possible interference to its neighbouring networks
What is required in .11af specification ?
New RLQP elements to allow query and response messages for neighbouring network information
>
Page 13

14. Neighboring Network Information through RLSS ..
doc.: IEEE <doc#>
<month year>
Neighboring Network Information through RLSS ..
Neighboring Network Information Query
RLQP ID
Length
Requester STA Address
Request Type
Device Identification
Device Class
Estimated Coverage Radius
Device Location Information
1 octet
2 octets
6 octets
18 octets
4 octets
18 octets (only if location is changed)
Neighboring Network Information Response
 These fields are repeated as determined by the length field 
RLQP ID
Length
Requester STA Address
Status Code
BSSID
Operating Class
Channel Number
Device Class
Operating Transmit Power
Relative Distance
1 octet
2 octet
6 octet
6 octets
>
Page 14

15. Network Coexistence through RLSS with Centralized Decision
doc.: IEEE <doc#>
<month year>
Network Coexistence through RLSS with Centralized Decision
Once an AP (Mode II or Fixed) obtains the list of authorized frequencies and transmit power levels for the network initiation, it sends an NCC to RLSS to request a set of network channels
The RLSS determines these set of channels based on information of neighboring APs to avoid coexistence problems
Assumption: multiple APs are served by the same RLSS within one service provider’s domain and they use the network channels as determined by the RLSS
Network Channel Control procedure in D1.03 can be already used (with some additional description on the usage)
>
Page 15

16. Network Coexistence through RLSS with Centralized Decision ..
doc.: IEEE <doc#>
<month year>
Network Coexistence through RLSS with Centralized Decision ..
RLQP Network Channel Control (NCC) request and response frame in
The first message sent by the NCC requesting STA asserts identity and requests NCC.
The NCC requesting STA may select its preferred frequencies from the WSM and request usage of the selected frequencies for multiple WLAN network channels usage.
The NCC responding STA may grant permission of using the selected frequencies, or provides its recommended set of frequencies, for multiple WLAN network channels to the NCC requesting STA by using the NCC response frame
The recommendation of the NCC responding STA is based on the effort to minimize coexistence issue. The actual algorithm of deriving the recommended channels, however, will not be specified in af.
>
Page 16

17. doc.: IEEE 802.15-<doc#>
<month year>
Summary
The interference management among multiple BSS is more challenging in TVWS band due to larger coverage range
Neighboring network information query through RLSS allows distributed decision making for APs
RLSS shares the operating parameters of neighbours relevant for the requesting AP
Each AP selects its operating parameters, but the network coexistence can be improved from the additional knowledge about other networks
In addition, RLSS can also be used to enable centralized decision making for network coexistence management
RLSS makes decisions for multiple APs for allocating operating parameters in order to resolve any coexistence problems
Each AP uses NCC to obtain a set network channels as decided by the RLSS, so that all networks linked to the RLSS can coexist
For flexibility in implementations, .11af should enable both of the above options
>
Page 17

18. © 2009 Nokia V1-Filename.ppt / 2H 2010 / P. Kafle
Comments/Questions?
© Nokia V1-Filename.ppt / 2H 2010 / P. Kafle