Support for Deferral Management in 802.11v

1. doc: IEEE 802.11-05/xxx2r0 May 2005 Support for Deferral Management in 802.11v Joe Kwak, Marian Rudolf (InterDigital) Kwak, Rudolf

2. Motivation • CSMA is meant to prevent two nodes in the same vicinity from transmitting simultaneously by having one defer to the other • This limits the level of interference perceived by receivers but it also limits the level of simultaneous channel reuse in the system thus limiting the capacity • The two key parameters involved in carrier-sensing and deferral are: • The transmission power used by the transmitter • The energy detection threshold (EDT) used by the receiver • Both parameters can be controlled to allow for higher channel reuse and higher system capacity • We refer to this as deferral management Kwak, Rudolf

3. Example Noise floor at Rx = -94 dBm 107 dB 104 dB 104 dB 101 dB 70 dB 70 dB STA 2 STA 1 AP 2 AP 1 BSS 2 Capacity BSS 1 Capacity Tx = 20 dBm EDT= -90 dBm S=-50dBm Imax=-81 dBm SNR=44 dB SIR=  Tx = 20 dBm EDT= -90 dBm S=-50dBm Imax=-84 dBm SNR=44 dB SIR=  Tx = 20 dBm EDT= -90 dBm S=-50dBm Imax=-81 dBm SNR=44 dB SIR=  Tx = 20 dBm EDT= -90 dBm S=-50dBm Imax=-84 dBm SNR=44 dB SIR=  C/2 C/2 Tx = 20 dBm EDT= -80 dBm S=-50dBm Imax=-81 dBm SNR=44 dB SIR= 31 dB Tx = 20 dBm EDT= -80 dBm S=-50dBm Imax=-84 dBm SNR=44 dB SIR= 34 dB Tx = 20 dBm EDT= -80 dBm S=-50dBm Imax=-81 dBm SNR=44 dB SIR= 31 dB Tx = 20 dBm EDT= -80 dBm S=-50dBm Imax=-84 dBm SNR=44 dB SIR= 34 dB C EDT control C Tx = 10 dBm EDT= -90 dBm S=-60dBm Imax=-91 dBm SNR=34 dB SIR= 31 dB Tx = 10 dBm EDT= -90 dBm S=-60dBm Imax=-94 dBm SNR=34 dB SIR= 34 dB Tx = 10 dBm EDT= -90 dBm S=-60dBm Imax=-91 dBm SNR=34 dB SIR= 31 dB Tx = 10 dBm EDT= -90 dBm S=-60dBm Imax=-94 dBm SNR=34 dB SIR=34 dB C Power control C Kwak, Rudolf

4. Need for standardization? • Without standardization, the AP can only control its own deferral management settings • Restricting deferral management to the APs leads to the following issues: • In the case of EDT control • The STA will not capitalize on the potential increase in channel reuse • In the case of Power Control • The increase in channel reuse not be achieved when STA transmit • STA ACKs can collide with packets in other BSSs. • For Deferral Management to reach its full potential, it has do be done in a coherent and a cohesive manner amongst the AP and its STAs Kwak, Rudolf

5. Challenges of Deferral Management • Potential impact on transmission rates • Elevating the EDT of WLAN nodes tends to elevate the level of co-channel interference in the system => decrease of SIR • Lowering the power of WLAN nodes tends to decrease the SNR • In general, a decrease of SIR and/or SNR can translate into transmission rate reductions • Power and/or EDT have to be controlled such that capacity gains due to increase of channel reuse are not offset by the decrease of SNR/SIR Kwak, Rudolf

6. Power control vs. EDT control • EDT control • Less interactions with rate control • Offers battery savings from the Rx side • Less dynamic range than Power Control • Most direct consequence of elevating the EDT within a BSS is more Tx opportunity in that BSS • Power Control • More interactions with rate control • More dynamic range • Offers battery savings from both Rx and Tx side • Most direct consequence of reducing the power within a BSS is more Tx opportunity in other BSSs • 802.11v should support both Kwak, Rudolf

7. Why TPC from 802.11h is not enough • The TPC feature of 802.11h is a good start but geared towards regulatory requirements; not Radio Resource Management • Does not provide the means to control EDT of STA • Does not provide the means to control the transmission power of STA on an individual basis Kwak, Rudolf

8. Proposed control mechanisms • Direct control from AP • Centralized approach where the AP determines the STA deferral management parameters • AP sends management/action frame to associated STAs that dictates a certain: • Tx power and/or EDT value and/or CCA mode to use • This control could done on a per-STA basis • This implies some mechanisms to measure/report inter-STA RPI/pathlosses • Indirect control from AP • Distributed approach where the determination of the settings is done at the STA • Less signaling overhead and can react faster to changes in environments • AP sends rules that STAs need to follow to determine the power/EDT settings • Examples of rule: • STA have to set their EDT/DT at the highest value that still makes them defer to a list of nodes provided by the AP • STA that have the required link margin have to set their power at the smallest value possible that ensures that they are heard by a list of nodes. MAC address and EDT of the nodes would be provided by the AP Kwak, Rudolf

9. Element ID Length Control Mode Controlled parameter Parameter Value Rule Node list Category Action Deferral Management set command Proposed signaling • New Deferral management IE’s • Deferral management capability • Supported CCA modes, Max/Min Tx power, Max/Min EDT • Deferral management reports and requests • CCA mode, EDT, Tx Power operational settings (or range) • Deferral management set command • Single IE could be used for both direct and indirect control modes • Similar to 802.11h TPC or DFS, Deferral management can use Beacon/Probe Response frames and/or new dedicated action frames • New Deferral management action frames • Deferral management request + reports • Deferral management set command Kwak, Rudolf

10. Other Support features • STA reporting to AP inter-STA path losses • Periodic loud packets would enhance this • EDT/CCA parameters to be used during measurement periods Kwak, Rudolf