doc IEEE 802 11 130890 r 0 July

doc. : IEEE 802. 11 -13/0890 r 0 July 2014 WLAN-3 GPP Interworking Metric Authors: Submission Date: 2014 -07 -15 Slide 1 Youhan Kim, Qualcomm

doc. : IEEE 802. 11 -13/0890 r 0 July 2014 Background • 3 GPP TSG RAN WG 2 (RAN 2) is developing a mechanism for interworking (IW) between 3 GPP RATs (UMTS and LTE) and WLAN – 3 GPP had sent a liaison statement to IEEE 802. 11 in April 2014 (11 -14/0519 r 0) – IEEE 802. 11 responded as in 11 -14/0658 r 6 • See next slide • Discouraged use of RCPI and RSNI Submission Slide 2 Youhan Kim, Qualcomm

doc. : IEEE 802. 11 -13/0890 r 0 July 2014 Previous Liaisons Questions in liaison statement from 3 GPP (11 -14/0519 r 0) Response from IEEE 802. 11 to 3 GPP (11 -14/0658 r 6) Question 1: Does IEEE 802. 11 WG consider WLAN RCPI a suitable metric of WLAN signal strength such that it can be compared to thresholds as in the above described mechanism? We consider the RCPI value as defined in IEEE 802. 11™-2012 a metric for signal strength. Question 2: Does IEEE 802. 11 WG consider WLAN RSNI a suitable metric of WLAN signal quality such that it can be compared to thresholds as in the above described mechanism? We consider the RSNI value as defined in IEEE 802. 11™-2012 a metric for signal quality in downlink direction. Submission Slide 3 Youhan Kim, Qualcomm

doc. : IEEE 802. 11 -13/0890 r 0 July 2014 Previous Liaisons (Cont’d) Questions in liaison Response from IEEE 802. 11 to 3 GPP (11 -14/0658 r 6) statement from 3 GPP • 3 GPP TSG RAN WG 2 (RAN 2) is developing a (11 -14/0519 r 0) mechanism for inter-working between 3 GPP RATs Question 3: Does IEEE 802. 11 Understanding that the objective of the mechanism is to select WG(UMTS and LTE) and WLAN consider any other WLAN the network that provides the best match to the Qo. S and/or signal metric more suitable for throughput requirements of the system, the consideration of – 3 GPP had sent a liaison. RNSI/RCPI statementistonot IEEE 802. 11 in April the above described sufficient on[1] its own to efficiently estimate 2014, to which the IEEE responded in Qo. S [2] that will be experienced in the mechanism? the 802. 11 available throughputasand IEEE 802. 11 WLAN. Other metrics should be taken into account, especially channel bandwidth, operating band, number of spatial streams, BSS load, and WAN metrics, see also the attached Table 1. Comparing only the RSNI/RCPI, as is, to thresholds presents some risks of poor decisions. Ideally, a single parameter, such as estimated available throughput, which combines all of the above parameters, would be determined inside of the WLAN modem and then delivered to the upper layers. Submission Slide 4 Youhan Kim, Qualcomm

doc. : IEEE 802. 11 -13/0890 r 0 July 2014 Further Background • 3 GPP RAN 2 is still using RCPI and RSNI as the PHY metrics for WLAN-3 GPP IW – – • ftp: //ftp. 3 gpp. org/tsg_ran/WG 2_RL 2/TSGR 2_86/Docs/R 2 -142955. zip ftp: //ftp. 3 gpp. org/TSG_RAN/TSGR_64/Docs/RP-140556. zip ftp: //ftp. 3 gpp. org/TSG_RAN/TSGR_64/Docs/RP-141010. zip ftp: //ftp. 3 gpp. org/TSG_RAN/TSGR_64/Docs/RP-141011. zip 3 GPP RAN 2 had requested 3 GPP SA 2 to include RCPI and RSNI in the requirements documents – RAN 2 is the PHY standards group – SA 2 is the Architecture requirements group • During discussion in 3 GPP SA 2, additional issues were found for RCPI and RSNI – ftp: //ftp. 3 gpp. org/tsg_sa/WG 2_Arch/TSGS 2_104_Dublin/Docs/S 2 -142942. zip • This contribution describes additional issues with using RCPI and RSNI for WLAN-3 GPP IW, and proposes way forward for WLAN 3 GPP IW Submission Slide 5 Youhan Kim, Qualcomm

doc. : IEEE 802. 11 -13/0890 r 0 July 2014 RSNI Submission Slide 6 Youhan Kim, Qualcomm

doc. : IEEE 802. 11 -13/0890 r 0 Definition of RSNI in IEEE 802. 11 • IEEE P 802. 11 -REVmc/D 3. 0 • P. 24 • P. 40 Submission

doc. : IEEE 802. 11 -13/0890 r 0 Definition of RSNI in IEEE 802. 11 (Cont’d) • IEEE P 802. 11 -REVmc/D 3. 0 • 10. 11. 9. 4. Noise Histogram report: P 1646 -1647 Submission

doc. : IEEE 802. 11 -13/0890 r 0 Example • STA 1 is DUT • BSS 1 and BSS 2 have partially overlapping channel – Also, AP 2 close to STA 1 – But BSS 2 is lightly loaded. So, channel is clear for BSS 1 most of the time. • Good candidate for 3 GPP WLAN roaming for STA 1 • Assume noise floor of -96 d. Bm/20 MHz at STA 1 RX 80 MHz AP 1 BSS 1: VHT 80 5210 MHz STA 2 AP 2 STA 1 Submission BSS 2: VHT 40 5230 MHz BSS 2 40 MHz

doc. : IEEE 802. 11 -13/0890 r 0 Example Over what period should ANPI be measured? ? Not clearly defined in the standard Frequency [MHz] 5250 AP 2 STA 2 -40 d. Bm 5230 5210 BSS 1 Primary 20 5190 AP 1 STA 1 -65 d. Bm AP 1 STA 1 -60 d. Bm 5170 Submission Time

doc. : IEEE 802. 11 -13/0890 r 0 Example • Case 1 ANPI measured here (no interference) Submission

doc. : IEEE 802. 11 -13/0890 r 0 • Case 2 Submission Example ANPI measurement duration includes interference packet. STA 1 cannot RX this packet (does not use Primary 20 of BSS 1). Thus, this should be included in ANPI. Note that this is not a ‘corner case’ scenario

doc. : IEEE 802. 11 -13/0890 r 0 Example ANPI measurement • Case 3 What should be the ANPI used for this packet? ? • Before receiving the first green packet, STA 1 RX likely listening to the entire 80 MHz – – • Don’t know the BW of the next packet coming in. Need to perform CCA on 80 MHz Then, should be ANPI for the first green packet be over 20 MHz or 80 MHz? – – Submission Of course, a ‘logical’ answer is that it should be over 20 MHz (-96 d. Bm), not 80 MHz (-90 d. Bm) But the point here is that the standard does not define this clearly – yet another example of potential pitfall.

doc. : IEEE 802. 11 -13/0890 r 0 Other Notes • What if DUT has multiple RX antennas? – How is ANPI defined? • Average over RX chains? Summed over RX chains? – Not defined clearly in the IEEE standard Interop issue expected w/o further clarification • RSNI measurement is optional • RSNI is NOT RSRQ in 3 GPP – RSRQ = Reference Signal Received Quality • Roughly speaking, SINR – RSNI does not measure the interference ‘present’ in the packet – Rather, the interference is measured during ‘idle’ time some time before the packet arrives • That interference may or may not be present in the packets the DUT is receiving Submission

doc. : IEEE 802. 11 -13/0890 r 0 Summary – RSNI • RSNI is currently broken – RSNI definition fails (numerically cannot be computed) in some cases – Many ambiguities exists • WLAN-3 GPP IW should not be based on a metric which is broken • RSNI is not RSRQ Submission

doc. : IEEE 802. 11 -13/0890 r 0 July 2014 RCPI AND RSSI Submission Slide 16 Youhan Kim, Qualcomm

doc. : IEEE 802. 11 -13/0890 r 0 RCPI vs. RSSI • RCPI and RSSI are similar in nature – RCPI is the power measured during the data portion of the packet – RSSI is the power measured during the preamble portion of the packet • HT/VHT preamble in case of HT/VHT PPDUs – Signal power between preamble and data are the same – There is minor difference in noise bandwidth • RCPI assumes noise equivalent BW 1. 1 times greater than the channel BW • No noise equivalent BW specified for RSSI • Difference should be small • Measurement accuracy – Dominated by analog gain inaccuracy, not digital power measurement inaccuracy • RCPI and RSSI should be able to achieve similar accuracy • Accuracy requirement in IEEE 802. 11 – RCPI has a ± 5 d. B (95% confidence interval) accuracy requirement, while RSSI does not. • But as mentioned above, there is no reason why RSSI cannot achieve similar accuracy as RCPI Submission

doc. : IEEE 802. 11 -13/0890 r 0 RSSI is Mandatory • RCPI is optional • RSSI, on the other hand, is mandatory – Used for CCA • CCA is key functionality of CSMA, which all WLAN devices have to implement – IEEE P 802. 11 REVmc/D 3. 0: P 2674 Submission

doc. : IEEE 802. 11 -13/0890 r 0 RSSI Unit • RSSI unit in IEEE 802. 11 is a ‘relative’ d. B, not an ‘absolute’ d. Bm • But since RSSI is used for CCA – CCA is in absolute d. Bm – Thus, RSSI in absolute d. Bm is implicitly available Submission

doc. : IEEE 802. 11 -13/0890 r 0 Other Ambiguities • Multiple RX chains – RCPI for DSSS/CCK and NON_HT OFDM PPDUs does not specify how to deal w/ multiple RX chains • E. g. Average over RX chains? Summed over RX chains? • HT/VHT PPDUs specify that the RCPI is averaged over RX chains – RSSI also does not specify how to deal w/ multiple RX chains Submission

doc. : IEEE 802. 11 -13/0890 r 0 Summary – RSSI vs. RCPI • RSSI and RCPI convey essentially the same information – RCPI is optional – RSSI is mandatory • Both RSSI and RCPI has some ambiguities to be clarified Submission

doc. : IEEE 802. 11 -13/0890 r 0 July 2014 BEACON VS. DATA Submission Slide 22 Youhan Kim, Qualcomm

doc. : IEEE 802. 11 -13/0890 r 0 What Packet Should be Used? • Before WLAN has associated w/ an AP – There is no traffic. Only Beacon RSSI is available. • When performing active scan, Probe Response RSSI would be available instead of Beacon RSSI • But typically, Probe Response and Beacon are both sent in the lowest supported rate • After WLAN has associated w/ an AP – If device is using 3 GPP link as the main data pipe, then WLAN will not have much traffic • WLAN will likely be in DTIM mode to save power – Again, only beacon RSSI is available • Even if data traffic is available – Devices often change TX power as a function of MCS • Several d. B of TX power difference between the lowest rate and the highest rate is not uncommon – Hence, for the same path loss, data packet RSSI could vary considerably just because of TX power • Receiver has no information on what the TX power was – Hence, data packet RSSI is not suitable for link quality assessment Submission

doc. : IEEE 802. 11 -13/0890 r 0 July 2014 Beacon RSSI • P 802. 11 REVmc D 3. 0 – P 513 L 54 Submission Slide 24 Youhan Kim, Qualcomm

doc. : IEEE 802. 11 -13/0890 r 0 Summary – Beacon vs. Data RSSI • Beacon RSSI is always available – Before association – After association, w/ and w/o traffic • Data packet RSSI is not as reliable for link quality accessment – Function of TX power, which is implementation specific (i. e. can change drastically) Submission

doc. : IEEE 802. 11 -13/0890 r 0 July 2014 SUGGESTED WAY FORWARD Submission Slide 26 Youhan Kim, Qualcomm

doc. : IEEE 802. 11 -13/0890 r 0 July 2014 Suggested Way Forward • Communicate the following to 3 GPP – Do not use RSNI for IW • Fixing RSNI would take some effort • Besides, RSNI does not necessarily reflect interference present in the packet. Hence, benefit for WLAN-3 GPP IW is not clear – Replace RCPI w/ Beacon RSSI • Need some clarifications in the IEEE 802. 11 – Please see 11 -14/0921 for details of the proposed changes Submission Slide 27 Youhan Kim, Qualcomm