Tiered Transmit Power Control, 01/215r1 May 2001 doc.: IEEE 802.11-00/215r1a May 2001 Tiered Transmit Power Control, 01/215r1 Peter Larsson Ericsson Research Torshamnsgatan 23, Kista 164 80 Stockholm, Sweden peter.larsson@era.ericsson.se Peter Larsson, Ericsson Radio Systems AB Peter Larsson, Ericsson Radio Systems AB

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

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 802.11. 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

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 802.11. 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

TPC design Philosophy - Tiered TPC May 2001 doc.: IEEE 802.11-00/215r1a 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

TTPC Main Features Distributed operation DCF Integrated May 2001 doc.: IEEE 802.11-00/215r1a 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

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

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

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

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

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

(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

(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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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 802.11a. Peter Larsson, Ericsson Radio Systems AB