1. Tiered Transmit Power Control, 01/215r1
May 2001
doc.: IEEE /215r1a
May 2001
Tiered Transmit Power Control, 01/215r1
Peter Larsson
Ericsson Research
Torshamnsgatan 23, Kista
Stockholm, Sweden
Peter Larsson, Ericsson Radio Systems AB
Peter Larsson, Ericsson Radio Systems AB

2. Outline Introduction Functional description Summary & Conclusions
May 2001
Outline
Introduction
Functional description
Illustration of function
Formats and MSCs
Summary & Conclusions
Peter Larsson, Ericsson Radio Systems AB

3. Introduction TGh has as objectives to design TPC and DFS for 802.11.
May 2001
Introduction
TGh has as objectives to design TPC and DFS for
TPC is considered in this proposal
Task: Design a TPC scheme that meet the following basic input
“All requirements …. are to be met by IBSS and infrastructure BSS, during DCF or optional PCF operation…..”. [Functional Requirement 01/071]
Peter Larsson, Ericsson Radio Systems AB

4. May 2001
TPC design Philosophy
Solve the generic IBSS problem. BSS treated as a special case of IBSS.
Build solution on DCF, not PCF or HCF. DCF is widely deployed and it is the legacy access mechanism of
TPC shall integrate well with power saving mechanisms.
TPC inherently interacts with MAC (for all proposals). Therefore, TPC shall integrate well with MAC mechanisms. Hence TPC frames & IEs must be put in a context to test viability. Ensure backward compatibility.
Generate least possible interference and consume least possible energy.
Peter Larsson, Ericsson Radio Systems AB

5. TPC design Philosophy - Tiered TPC
May 2001
doc.: IEEE /215r1a
May 2001
TPC design Philosophy - Tiered TPC
Several TPC mechanisms and settings.
Bulk traffic uses the most accurate TPC. Energy minimization.
Topological constraints exists.
Prevalent sent frames
Minimal transmit power
Occasional sent frames
Moderate transmit power
Transmit range
Rarely sent frames
High transmit power
Peter Larsson, Ericsson Radio Systems AB
Peter Larsson, Ericsson Radio Systems AB

6. TTPC Main Features Distributed operation DCF Integrated
May 2001
doc.: IEEE /215r1a
May 2001
TTPC Main Features
Distributed operation
DCF Integrated
Tiered TPC mechanisms
Fixed TP
Open loop TPC
Closed loop TPC
Peter Larsson, Ericsson Radio Systems AB
Peter Larsson, Ericsson Radio Systems AB

7. Illustration of function
May 2001
Illustration of function
Reason: Important to understand what effects TPC has on channel access.
Start with an example scenario. IBSS with RTS-CTS-DATA-ACK phase.
Peter Larsson, Ericsson Radio Systems AB

8. Open Loop Path Gain Estimation in IBSS
May 2001
Open Loop Path Gain Estimation in IBSS
Beacon
transmit
range
IBSS 1
Beacon
transmit
range
Beacon
transmit
range
Beacon
Legend:
STA
Range
time
Peter Larsson, Ericsson Radio Systems AB

9. Minimum Receive Power PRX_min Estimation in IBSS
May 2001
Minimum Receive Power PRX_min Estimation in IBSS
IBSS 2
IRX
Overheard traffic RSSI other (I)BSS, C
Own (I)BSS RSSI (on certain frames)
IBSS 1
Legend:
STA
Range
External
unidentified
noise
General IRX and noise.
Receivers is responsible to ensure that suitable PRX_min is determined through various inputs such as:
Peter Larsson, Ericsson Radio Systems AB

10. Open Loop TPC estimation
May 2001
Open Loop TPC estimation
OL transmit power = Prx_min - G [dB] G = RSSI - PTX [dB]
Algorithmic Complexity O(N) frames, for N STAs to determine N·(N-1) power levels
Each STA determines N-1 entries
Low complexity compared to a individual request-reply scheme O(N2)
Interacts with power save mode
Peter Larsson, Ericsson Radio Systems AB

11. Open Loop TPC usage (I)BSS Group TPC Unicast setting (optional)
May 2001
Open Loop TPC usage
(I)BSS Group TPC
RTS, CTS, ACK
Single DATA frames shorter than dot11RTSThreshold
Multicast/ Broadcast
Unicast setting (optional)
Last ACK in a frame exchange sequence
Peter Larsson, Ericsson Radio Systems AB

12. (I)BSS Group TPC Philosophy
May 2001
(I)BSS Group TPC Philosophy
The channel is seen as one resource in an (I)BSS
All nodes within the (I)BSS should be reached with both RTS and CTS.
Reason: Physical carrier sense desirable for both RTS and CTS in the whole (I)BSS.
Floor in adjacent (I)BSS should preferably not be acquired unnecessary.
Avoid generating high interference (peaks).
Peter Larsson, Ericsson Radio Systems AB

13. (I)BSS Group TPC Interfered IBSS, PRX_min  Noise floor Single IBSS
May 2001
(I)BSS Group TPC
Interfered IBSS, PRX_min  Noise floor
PRX_min,2
PRX_min,1
PRX_min,3
PRX_min,4
Single IBSS
CTS
RTS
CTS
RTS
Legend:
STA
Range
Peter Larsson, Ericsson Radio Systems AB

14. Comment on Open Loop TPC
May 2001
Comment on Open Loop TPC
The proposed Open loop TPC acquire all knowledge and has all functionality needed for a rudimentary distributed TPC.
Peter Larsson, Ericsson Radio Systems AB

15. Closed loop TPC philosophy & usage
May 2001
Closed loop TPC philosophy & usage
Closed Loop TPC is used as a complement to further refine performance.
Utilize exchanged frames (e.g. RTS-CTS) to perform precise and instantaneous TPC.
Receiver has the best knowledge about reception quality, not the transmitter.
Perform CL-TPC on bulk traffic, i.e. Unicast DATA/ Management frames longer than dot11RTSThreshold
Peter Larsson, Ericsson Radio Systems AB

16. Closed Loop TPC IBSS 1 Legend: STA Range time Power May 2001 ACK RTS
CTS
DATA
RTS
CTS
RTS
DATA
RTS
CTS
This ACK may optionally
be sent with lower
transmit power
Power
Legend:
STA
Range
time
Peter Larsson, Ericsson Radio Systems AB

17. Open & Closed Loop TPC MSC
May 2001
Open & Closed Loop TPC MSC
Source
Destination
CTS informs Source
about relative transmit
power change
TPC setting
RTS
IBSS group TPC setting
CTS
Closed loop TPC setting
DATA
IBSS group TPC setting
or optionally
unicast TPC setting
ACK
NAV setting upon
hearing source STA
NAV setting upon
hearing destination STA
Concern about NAV being reset after detecting RTS but not DATA?
See Next page.
Peter Larsson, Ericsson Radio Systems AB

18. NAV setting issue IBSS IBSS Short distance between
May 2001
NAV setting issue
IBSS
IBSS
Short distance between
source and destination STA
RTS-CTS Overlap
 NAV is not reset
RTS
CTS
DATA
ACK S D
RTS
CTS S D
DATA
ACK
Large distance between
source and destination STA
RTS-DATA overlap
 NAV is not reset
Peter Larsson, Ericsson Radio Systems AB

19. NAV setting issue cont. DATA overlap RTS  NAV is not reset
May 2001
NAV setting issue cont.
DATA overlap RTS
 NAV is not reset
DATA link rate >
RTS link rate
6  54 Mbps require
roughly 15 dB higher C/I
IBSS
RTS
CTS
DATA link rate =
RTS link rate S D
ACK
Peter Larsson, Ericsson Radio Systems AB

20. BSS Open Loop TPC Legend: BSS STA AP Range The AP selects a STA
May 2001
BSS Open Loop TPC
Legend:
The AP selects a STA
Issues a Probe request asking the selected STA to respond with TPC information. Transmit just after the Beacon to align with the wake up phase.
The response is a Probe response containing PTX and PRX_min
Probe response
PTX, PRX_min
The AP selects a STA
Issues a Probe request asking the selected STA to respond with TPC information. Transmit just after the Beacon to align with the wake up phase.
Probe Request
IE Transmit power request
BSS
STA AP
Range
The AP selects a STA
Issues a Probe request asking the selected STA to respond with TPC information. Transmit just after the Beacon to align with the wake up phase.
The response is a Probe response containing PTX and PRX_min
Open loop transmit power is estimated as in the IBSS.
The AP selects a STA.
Peter Larsson, Ericsson Radio Systems AB

21. May 2001
BSS Open Loop TPC
AP determines polling sequence. Implementation specific.
Algorithmic complexity retained = O(N)
Peter Larsson, Ericsson Radio Systems AB

22. New IEs Transmit Power Information Request Element
May 2001
New IEs
Transmit Power Information Request Element
Transmit Power Information Element
Peter Larsson, Ericsson Radio Systems AB

23. IEs are conveyed in Beacon modifications Probe request modifications
May 2001
IEs are conveyed in
Beacon modifications
Probe request modifications
Probe response modifications
Peter Larsson, Ericsson Radio Systems AB

24. May 2001
IE issues
The proposed IE extension is backward compatible to legacy STA, in the sense that they neglect new IE fields.
Peter Larsson, Ericsson Radio Systems AB

25. Frames TPC CTS frame TPC ACK frame PTX_Request 2 2 6 1 4 Frame control
May 2001
Frames 2 2 6 1 4
Frame
control
Duration RA
PTX_Req
FCS
TPC CTS frame
MAC header 2 2 6 1 4
Frame
control
Duration RA
PTX_Req
FCS
TPC ACK frame
MAC header
PTX_Request
Peter Larsson, Ericsson Radio Systems AB

26. May 2001
Frame format issues
PTX_req field incur no extra OH, merely a fuller OFDM symbol for all link rates.
TPC CTS (ACK) is only sent from and to TPC enabled STAs. If one or two legacy STAs are involved, legacy CTS (ACK) are used
TPC CTS (ACK) sets NAV on legacy STA, i.e. backward compatible.
Peter Larsson, Ericsson Radio Systems AB

27. Frame format issues cont.
May 2001
Frame format issues cont.
Legacy CTS (ACK) and TPC CTS (ACK) can coexist
Method 1: Differentiate through PHY length or address information + CTS subtype field
Method 2: Define new subtype for TPC CTS
Peter Larsson, Ericsson Radio Systems AB

28. May 2001
Summary
A Tiered TPC scheme, able to operate in both BSS and IBBS network, on basis of the fundamental DCF channel access scheme has been presented.
TTPC uses fixed TP, OL and CL TPC
Peter Larsson, Ericsson Radio Systems AB

29. May 2001
Summary
It is characterize by low OH, low algorithmic complexity, insurance of backward compatibility, speed and precision
It has also been shown how the interaction between TPC and channel access scheme has been considered in this proposal.
Peter Larsson, Ericsson Radio Systems AB

30. May 2001
Conclusion
It is our belief that this proposal can meet current as well as future requirements on TPC.
It is our recommendation that this proposal shall be considered for TPC in a.
Peter Larsson, Ericsson Radio Systems AB