1. Consideration on Neighbor Discovery
January 2015
Consideration on Neighbor Discovery
Date:
Authors:
Hyunduk Kang et al, ETRI
Steve Shellhammer, Qualcomm

2. Interference vs. Neighbor discovery
January 2015
Interference vs. Neighbor discovery
Interference among wireless systems is caused by wireless systems located nearby each other
A first step on interference mitigation might be which wireless systems are interfering me on which channel
Interference on the same operating channel
Interference on the adjacent channel (due to partial channel overlap)
Hyunduk Kang et al, ETRI

3. Case Study: Interference vs. Neighbor Discovery among WLANs
January 2015
Case Study: Interference vs. Neighbor Discovery among WLANs
Inter-BSS Interference (IBI) is interference among multiple basic service sets (BSSs), located nearby each other
There are three types of inter-BSS interference
AP-AP IBI
AP-STA IBI
STA-STA IBI
Hyunduk Kang et al, ETRI

4. Inter-BSS Interference: AP-AP
January 2015
Inter-BSS Interference: AP-AP
It occurs when a AP receiving data from its associated STA is interfered by a neighbor AP transmitting data to its associated STA, and vice versa.
Hyunduk Kang et al, ETRI

5. Inter-BSS Interference: AP-STA
January 2015
Inter-BSS Interference: AP-STA
It occurs when a AP receiving data from its associated STA is interfered by a neighbor AP transmitting data to its associated STA, and vice versa.
Hyunduk Kang et al, ETRI

6. Inter-BSS Interference: STA-STA
January 2015
Inter-BSS Interference: STA-STA
It occurs when a STA receiving data from its associated AP is interfered by a neighbor STA transmitting data to its associated AP, and vice versa.
Hyunduk Kang et al, ETRI

7. Overlapping Geography
January 2015
Overlapping Geography
It is possible to categorize overlapping geography based on IBI classification
Types of overlapping
AP-AP overlapping
BSS-BSS overlapping
STA-STA overlapping
Hyunduk Kang et al, ETRI

8. AP-AP Overlapping AP1 and AP2 directly can hear each other
January 2015
AP-AP Overlapping
AP1 and AP2 directly can hear each other
APs and STAs might suffer from
AP-AP IBI
AP-STA IBI
STA-STA IBI
Hyunduk Kang et al, ETRI

9. BSS-BSS Overlapping AP1 and AP2 directly can NOT hear each other
January 2015
BSS-BSS Overlapping
AP1 and AP2 directly can NOT hear each other
APs and STAs might suffer from
AP-STA IBI
STA-STA IBI
Hyunduk Kang et al, ETRI

10. STA-STA Overlapping AP1 and AP2 directly can NOT hear each other
January 2015
STA-STA Overlapping
AP1 and AP2 directly can NOT hear each other
STAs might suffer from
STA-STA IBI
Hyunduk Kang et al, ETRI

11. No Overlapping: BSS-BSS Separation
January 2015
No Overlapping: BSS-BSS Separation
There is no interference between BSSs
Ideal spatial reuse is possible
Hyunduk Kang et al, ETRI

12. Comparison among Types of Overlap
January 2015
Comparison among Types of Overlap
AP-AP could get lot of co-channel interference. However, it might be favorable to mitigate interference since AP can hear each other directly
BSS-BSS seems to difficult to mitigate co-channel interference since APs are blinded each other
Type of overlapping
Inter-BSS interference: AP-AP
Inter-BSS interference: AP-STA
Inter-BSS interference: STA-STA
Amount of Inter-BSS interference
Hidden neighbor AP
AP-AP
YES
Heavy -
BSS-BSS
Medium
STA-STA
Light No
Hyunduk Kang et al, ETRI

13. Existing Mechanisms for Neighbor Discovery on WLANs
January 2015
Existing Mechanisms for Neighbor Discovery on WLANs
Spectrum sensing
CCA-ED (for other wireless system)
CCA-SD (for WLANs, preamble detection is possible)
Passive scanning
Beacon listening
Active scanning
Probe request/response
Virtual carrier sensing
RTS/CTS
BSS color: ah-D2.0
Neighbor report
Reduced neighbor report: af-2012
Radio measurement
Hyunduk Kang et al, ETRI

14. Possible Mechanisms for Neighbor Discovery among Wireless Systems
January 2015
Possible Mechanisms for Neighbor Discovery among Wireless Systems
Spectrum sensing (or radio measurement)
Each wireless systems perform it by itself
In general, two methods are
Energy detection (to reveal existence of wireless systems)
Feature detection (to identity type of wireless systems)
Message exchanging (directly or indirectly)
Neighbor information could be exchanged
Via wireless channel
Via wired channel
Neighbor information could be obtained by combinations of
Results of spectrum sensing (or radio measurement) by each wireless systems
Geo-location information if available
Hyunduk Kang et al, ETRI

15. Intuition on Interference Mitigation for Coexistence
January 2015
Intuition on Interference Mitigation for Coexistence
Which system is interfering on which channel? (Seen/Hidden)
How to identify neighbor systems which interfere my system
“Stay on the channel” or “Switch to new channel”
Determination based on what grounds?
What is useful information for decision?
Stay on the channel with which channel sharing method?
Existing methods, e.g., LBT, are enough or we need a new one?
Select to new channel with which channel allocation method?
Existing methods, e.g., DFS, are enough or we need a new one?
Hyunduk Kang et al, ETRI

16. January 2015
Concluding Remarks
Neighbor discovery is the very first step for interference mitigation for better coexistence among wireless systems
Neighbor discovery among dissimilar wireless systems might be more difficult than that among similar wireless systems
Just to reveal existence of neighbor is not enough for interference mitigation.
The more information on neighbor, the better coexistence among neighbor
Neighbor discovery without geo-location information would be a challenging issue on unlicensed frequency bands
Hyunduk Kang et al, ETRI