1. Reporting Mechanisms Needed for DFS to Support Regulatory Compliance
January 2002
doc.: IEEE /xxxr0
January 2002
Reporting Mechanisms Needed for DFS to Support Regulatory Compliance
Colin Lanzl
Aware, Inc.
Colin Lanzl, Aware, Inc.
John Doe, His Company

2. January 2002
The Motivation
Regulators insist on DFS mechanisms to ensure protection of primary (licensed) users in a band
Protection needs to be provided for an occupied band when a network starts
Protection needs to be provided for an occupied band when a licensed user start
Protection needs be provided for a mobile primary user
Colin Lanzl, Aware, Inc.

3. Scenarios Illustrating the Problem
January 2002
Scenarios Illustrating the Problem
IEEE a system having one member outside a building and several other members inside a building
The building provides 25dB attenuation of signals traveling through the outer walls
Assumed: regulations require that networks detect energy above -65dBm: if found, the network must vacate that band
Colin Lanzl, Aware, Inc.

4. January 2002
Scenario #1: Network attempts to start in presence of radar. Radar provides enough power in band occupied by network to exceed threshold at STA 1 and also enough to be measurable but not exceed threshold at AP, STA 2 and STA 3
STA 1 can determine that RSSI is above regulatory threshold and that signal does not fit preamble for IEEE a or Hiperlan2
STA 1 must not transmit if it can determine the band is occupied; if the AP chooses the occupied band, the STA needs a mechanism to inform the AP that it sees a potential primary user
Colin Lanzl, Aware, Inc.

5. Scenario 1: needed mechanisms
January 2002
Scenario 1: needed mechanisms
STA 1 needs RSSI measurement to determine band is occupied: this measurement must be based on some absolute level. Broad tolerances can work, but relative measurements must be tied to some absolute value to satisfy regulatory concerns.
STA 1 probably needs to sample the band over some time to ensure that isolated noise spikes or collisions don’t force DFS churn (does not need standardization); but, simple reporting of incident also works
STA 1 can take advantage of whatever signature the licensed user provides in its radio signal to determine that the band is occupied: some time stamp mechanism is necessary in this context
STA 1 must make a decision to avoid this band on its own if the network is an IBSS and so must also have that capability in a BSS.
STA needs some mechanism to inform the network that it needs to change frequencies or avoid a band because it detects primary users in that band
Colin Lanzl, Aware, Inc.

6. Scenario 1: Potential Solution
January 2002
Scenario 1: Potential Solution
In BSS at startup, AP requests information about current channel from all stations. To ensure that collisions don’t masquerade as interference, the AP issues request for information during contention-free period
If AP starts before any STAs, then must request this information periodically in contention-free periods, probably independent of association / authentication mechanisms
STA 2 and STA 3 report channel clear at startup
STA 1 reports channel occupied based on RSSI threshold
AP collates all information, respects STA 1 information, requests STAs to measure alternate channel (selected randomly to support even distribution across frequencies)
STAs all report alternate channel clear, AP chooses and informs, STAs shift to new channel with AP
In IBSS, same sort of mechanism works
Colin Lanzl, Aware, Inc.

7. January 2002
Scenario #2: Radar starts on channel after network successfully starts up. Radar provides enough power in band occupied by network to exceed threshold at STA 1 and also enough to be measurable but not exceed threshold at AP, STA 2 and STA 3
STA 1 can determine that RSSI is above regulatory threshold and that signal does not fit preamble for IEEE a or Hiperlan2
STA 2 and 3 don’t see RSSI above threshold
STA 1 must inform AP that interference exists and that it must cease transmissions in that band
Colin Lanzl, Aware, Inc.

8. Scenario 2: Potential Solution
January 2002
Scenario 2: Potential Solution
In BSS, STA 1 must inform AP (or IBSS) that it must vacate the channel and might inform that primary user interference exists
AP respects STA 1 report; in next contention-free period, requests all STAs to report on status of current channel
STA 2, STA 3 and AP report RSSI measurements that are below regulatory threshold BUT that are periodic (based on time stamp and RSSI measurements) and that signals are unrecognized (no preambles)
AP collates all information, requests STAs to measure alternate channel (selected randomly to support even distribution across frequencies)
STAs all report alternate channel clear, AP chooses and informs
AP updates table of channels to indicate bad channel
Alternately, AP does not respect STA 1 request for channel change: STA 1 notes bad channel to avoid and tries to find other networks on alternate (randomly-chosen) channels
Colin Lanzl, Aware, Inc.

9. Scenario 2: Alternate Solution
January 2002
doc.: IEEE /xxxr0
January 2002
Scenario 2: Alternate Solution
In BSS, AP periodically requests information about current channel from all stations. To ensure that collisions don’t masquerade as interference, the AP issues request for information during contention-free period
STA 1 reports channel occupied based on interference exceeding RSSI threshold and that interference is periodic
STA 2, STA 3 and AP report no RSSI threshold exceeded, but report periodic RSSI readings
AP collates all information, notes correlation of time stamp information between STA1 and STA 2-3, requests STAs to measure alternate channel (selected randomly to support even distribution across frequencies)
STAs all report alternate channel clear, AP chooses and informs, STAs shift to new channel with AP
Colin Lanzl, Aware, Inc.
John Doe, His Company

10. January 2002
Scenario #3: Radar moves past after network successfully starts up. Radar initially does not interfere, then gradually provides enough power in band occupied by network to exceed threshold at STA 1 and also enough to be measurable but not exceed threshold at AP, STA 2 and STA 3
Radar eventually provides enough power that all units see RSSI above threshold
Radar eventually leaves
Colin Lanzl, Aware, Inc.

11. Scenario 3: needed mechanisms
January 2002
Scenario 3: needed mechanisms
All mechanisms provided in Scenarios 1 & 2 can be used here
If STA 1 is ignored at first, eventually STA 2 and STA 3 and AP will see the primary user and must vacate the band
Once the interference is established, either the network can periodically measure all channels or it can measure random channels and maintain tables of “restricted” channels
If tables of “restricted channels” are maintained, probably should age them?
If interference sweeps a group of channels slowly, these mechanisms will work, especially if “restricted channels” mechanism used
If multiple primary users are present, these mechanisms will work
Colin Lanzl, Aware, Inc.

12. Summary of Mechanisms Needed
January 2002
Summary of Mechanisms Needed
Need absolute measurement based on RSSI at both STAs and APs
Can use some sort of integration mechanism to prevent false alarms
Need some sort of time stamp mechanism
Need Inform / Request / Report mechanism for primary users
Need constant interference measurements made (preferably in contention-free periods): this can be periodic, commanded by AP or essentially random, based on RSSI threshold being exceeded at any one unit (STA or AP)
Can provide tables of occupied frequencies to be avoided, may want to age those tables
Need mechanism for any unit (AP or STA) to vacate band when interference detected; should consider orphan STA
Colin Lanzl, Aware, Inc.