SubmissionJoe Kwak, InterDigital1 BSS Load: AP Loading Metric for QOS Joe Kwak InterDigital doc: IEEE /0079r0January 2005

doc: IEEE /0079r0January 2005 Submission Joe Kwak, InterDigital 2 TGe Load Metric: QBSS Load Actually provides three elements all relating to load: Station Count Field, unsigned 16 bit integer indicating total number of STAs associated Channel Utilization, 8 bit percentage of time the QBSS detects the medium as busy Available Admission Capacity, 16 bit integer representing amount of medium time (32usec units) available via explicit admission control

doc: IEEE /0079r0January 2005 Submission Joe Kwak, InterDigital 3 Problems with TGe Metrics Three metric components make comparative loading evaluations difficult/impossible. No agreed way to combine the three variables into a summary metric for comparison purposes. Simulation results show how AP Service Load metric relates to Channel Utilization, number of STAs associated and traffic asymmetry. New AP Service load metric permits AP loads to be compared between APs operating under different conditions.

doc: IEEE /0079r0January 2005 Submission Joe Kwak, InterDigital 4 New Metric Definition The Medium Access Delay (MAD) metric is defined as the average delay incurred from the time that any DCF packet is ready for transmission (i.e. begins CSMA/CA access) to the actual packet transmission start time. Since DCF packets are lower priority than PCF or HCF packets, the DCF access delay values are sensitive to all PCF, HCF and DCF channel loads. While channel is busy for PCF or HCF, DCF backoff counting is suspended while access delay timing continues.

doc: IEEE /0079r0January 2005 Submission Joe Kwak, InterDigital 5 MAD is sensitive to DCF, PCF and HCF Loads DCF PCF HCF DCF with 5 users at rate A DCF with 20 users at rate A DCF with 10 users at rate A % 75% Each beacon interval example yields same MAD result 3msec Access Delay

doc: IEEE /0079r0January 2005 Submission Joe Kwak, InterDigital 6 MAD Timing in Packet Transmission PduRequest to Protocol Control Process TxRequest to Transmission Process CSMA/CA Transmit Access Delay == MAD, optionally contains RTS/CTS. MAD Timer or timestamps used to measure CSMA/CA duration. Packet Transmission Time Optional ACK PduRequest for next Packet

doc: IEEE /0079r0January 2005 Submission Joe Kwak, InterDigital 7 MAD Timing Examples Normal PDU Transmission TxRequest MAD Timer TxOut(Pdu) RxIn(ACK) PduRequest PduConfirm AC C B3 B2 B1 3 Fragment PDU Transmission Normal PDU with Retransmission TxRequest Stops Timer PduRequest Starts Timer

doc: IEEE /0079r0January 2005 Submission Joe Kwak, InterDigital 8 Simulation Results 1

doc: IEEE /0079r0January 2005 Submission Joe Kwak, InterDigital 9 Simulation Results 2

doc: IEEE /0079r0January 2005 Submission Joe Kwak, InterDigital 10 Simulation Results 3

doc: IEEE /0079r0January 2005 Submission Joe Kwak, InterDigital 11 New BSS Load IE Similar to TGe QBSS Load but modified for Radio Measurement capable APs Three component elements: Station Count Field, same as TGe Channel Utilization, same as TGe New AP Service Load (total load metric for AP) New Access Category Service Load (loads for each of 4 ACs) Included in Beacons and Probe Response, like TGe Conditional inclusion of Station Count and Channel Utilization in Beacon and Probe Response to prevent redundant information Included as new Statistics Group in Statistics Report to provide upper layer MIB interface and radio interface

doc: IEEE /0079r0January 2005 Submission Joe Kwak, InterDigital 12 New AP Service Load Properties Quantized to 8 bits like RSSI & RCPI Based on MAD measurements in AP downlink during contention periods. logarithmic scaling over meaningful range Scaled so min value 1 represents 50usec (DIFS), and max value 253 represents 5.5msec covering a 20.4 db range Special values: 0 = All capacity available (no STAs associated) 254 = no capacity available (not accepting new associations) 255 = AP Service Load not available AP measures MAD over thirty second window; accuracy of +/-200 usec specified with minimum of 200 packets in average Combines AP loading effects of #STAs, Channel Utilization (PCF, HCF and DCF) and traffic assymetry into SINGLE metric to compare BSS relative loading.

doc: IEEE /0079r0January 2005 Submission Joe Kwak, InterDigital 13 New AP Service Load Definition "The AP Service Load shall be a scalar indication of the relative level of service loading at an AP. A low value shall indicate more available service capacity than a higher value. The value 0 shall indicate that this AP is not currently serving any STA. The values between 0 and 254 shall be a logarithmically scaled representation of the average medium access delay for DCF transmitted packets measured from the time the DCF packet is ready for transmission (i.e. begins CSMA/CA access) until the actual packet transmission start time. Value 1 represents 50 usec, value 253 represents 5.5 msec or any delay greater than 5.5 ms. The value 254 shall indicate no additional AP service capacity is available. The value 255 shall indicate that the AP Service Load is not available. The AP shall measure and average the medium access delay for all transmit packets using DCF mechanism over a continuous thirty second measurement window. The accuracy for the average medium access delay shall be +/- 200 usec or better when averaged over at least 200 packets.”