Joe Kwak, InterDigital 1 Submission PSNI: New PHY Measurement a subjective, comparative measurement to support network management Joe Kwak InterDigital Communications Corporation doc: IEEE /100r3January 2003

doc: IEEE /100r3January 2003 Submission Joe Kwak, InterDigital 2 Outline Need for new PHY measurement Difficulties with objective measurements RSSI Limitations Perceived Post-Processing S/(N+I) Indicator (PSNI) PSNI Specification details Tasks for next meeting

doc: IEEE /100r3January 2003 Submission Joe Kwak, InterDigital K PHY Measurements TGK is tasked with providing interfaces, measurements, and mechanisms to support higher layer functions for efficient network management currently has several PHY measurements, none of which seem suitable for handoff or network management purposes. RSSI: reportable parameter for each received frame, but unquantized and not fully specified. Can be used to compare frames from different AP sources. SQ: another unquantized indicator of code sync, but applicable only to DSSS PHY. RPI histogram: quantized and specified, but measures channel power from all sources: x, radars, and other interferers. Cannot target measurement on any AP using particular PHY.

doc: IEEE /100r3January 2003 Submission Joe Kwak, InterDigital 4 Network Management Needs Comparative PHY (sects. 15, 17, 18, 19) Measurement 1. To compare AP signals on same channel, same PHY, in same STA 2. To compare AP signals on same channel, same PHY, in different STAs 3. To compare AP signals on different channels, same PHY, in same STA 4. To compare AP signals on different channels, same PHY, in different STAs 5. To compare AP signals on different PHYs in different STAs 6. To compare AP signals on different PHYs in same STA Comparative measurements are crucial to QOS and handoff decisions for Network Management, as discussed at Tutorial at last meeting. Comparative measurements are important for load management and interference mitigation. RSSI, as currently defined, only addresses needs #1 and #3.

doc: IEEE /100r3January 2003 Submission Joe Kwak, InterDigital 5 RSSI definitions in PMD_RSSI.indicate(RSSI): The RSSI shall be a measure of the RF energy received by the DSSS PHY. RSSI indications of up to 8 bits (256 levels) are supported RXVECTOR RSSI: The allowed values for the receive signal strength indicator (RSSI) parameter are in the range from 0 through RSSI maximum. This parameter is a measure by the PHY sublayer of the energy observed at the antenna used to receive the current PPDU. RSSI shall be measured during the reception of the PLCP preamble. RSSI is intended to be used in a relative manner, and it shall be a monotonically increasing function of the received power PMD_RSSI.indicate: This primitive shall provide the following parameters: PMD_RSSI.indicate(RSSI) The RSSI shall be a measure of the RF energy received by the OFDM PHY. RSSI indications of up to eight bits (256 levels) are supported PMD_RSSI.indicate: This primitive provides RSSI parameter as 0–8 bits of RSSI. The RSSI is a measure of the RF energy received by the High Rate PHY RSSI: The RSSI is a measure of the RF energy received by the ERP. The value depends on the value of the MODULATION parameter: CCK, ER-PBCC: the 8 bit value of RSSI as described in ERP-OFDM, DSSS-OFDM, the 8 bit value is in the range of 0 to RSSI maximum as described in

doc: IEEE /100r3January 2003 Submission Joe Kwak, InterDigital 6 RSSI Limitations RSSI is a monotonic, relative indicator of power at the antenna connector, which indicates the sum of desired signal + noise + interference powers. In high interference environments, RSSI is not an adequate indicator of desired signal quality. RSSI is not fully specified: no unit definitions, no performance requirements (accuracy, fidelity, testability). Since so little about RSSI is specified, it must be assumed that widely variant implementations already exist. It is not possible to compare RSSIs from different STAs and perhaps not even from different channels/bands within same STA. RSSI may have limited use for evaluating AP options within a STA and within a given PHY, but not between PHYs. RSSI is rescaled between DSSS and OFDM PHYs. RSSI is clearly not useable by network management for load balancing or load shifting. RSSI from one STA does not relate to RSSI from any other STA.

doc: IEEE /100r3January 2003 Submission Joe Kwak, InterDigital 7 Desired Signal RF Power level and resulting Signal-to-Noise ratio (S/N+I) at antenna input are both directly proportional to FER at output. Options for PHY measurements Radio front end A/D FEC Decoder (optional) Demodulator and tracking loops (PHY specific) A: RF power, RF S/(N+I) from each AP DC B A B: BB S/(N+I) from each AP, (BB power constant by AGC) C&D: Bit Error Rate data rate Frame Check (CRC) E E: Frame Error Rate data rate AGC

doc: IEEE /100r3January 2003 Submission Joe Kwak, InterDigital 8 Best Choice for K PHYs? Accurate S/N+I (or RSSI power) measurement at A is interesting but because RF/demod implementations vary widely, it cannot be used comparatively between STAs to evaluate delivered signal quality. Accurate FER measurement at E is ideal, but cannot be measured frame by frame. FER can only be accurately measured over 100s-1000s of frames. Also, FERs are comparable only at same frame size and data rate. Good STA Med STA Marginal STA AE 10db 10E-2 10E-4 10E-5 Good STA Med STA Marginal STA AE 10db 12db 15db10E-5 Signal at same objective S/N Signal at same subjective S/N Best choice is somewhere in the middle.

doc: IEEE /100r3January 2003 Submission Joe Kwak, InterDigital 9 Proposal: Use a demodulator-specific, subjective estimator of S/(N+I) to provide quantized FER indication. All digital demodulators use tracking loops and complex post-processing to demodulate received symbols. Many internal demodulator metrics are proportional to perceived S/(N+I). Examples: PSK: baseband phase jitter DSSS: spreading code correlation quality OFDM: frequency tracking and channel tracking stability Demodulator internal metrics are available on a frame-by-frame basis. Demodulator metrics proportional to analog S/(N+I) are available at all data rates. Metric may be rate dependant or not. Demodulator internal metrics may be calibrated with respect to actual FER performance (at any specified data rate/coding rate) in controlled environment to accurately indicate perceived or delivered S/(N+I). Such demodulator internal metrics are fast estimators of S/(N+I) in both interference environments and interference-free (noise only) environments. TGK need not specify which demodulator metrics to use, but needs only to specify how the quantized indicator relates to S/(N+I) and FER

doc: IEEE /100r3January 2003 Submission Joe Kwak, InterDigital 10 Perceived Signal to Noise Indication (PSNI) Specified like RSSI: 8-bit unsigned value, monotonically increasing with increasing S/(N+I). PSNI shall be logarithmically scaled to perceived S/(N+I) which relates directly to FER performance. Specify PSNI output indication value at two FER points: first point to anchor indicator, second point to quantize and scale indicator range of values. Specify accuracy of output indicator for the selected two FER points. PSNI range shall span the lower 40 db portion of the operating range of S/(N+I) to cover high FERs at data rates from 1 to 54 Mbps.

doc: IEEE /100r3January 2003 Submission Joe Kwak, InterDigital 11 First Draft Spec Wording for PSNI PSNI: The PSNI indicator is a measure of the perceived, post-processing signal-to-noise- plus-interference (S/N+I) ratio in the demodulator. The allowed values for the Perceived Signal to Noise Indicator (PSNI) parameter shall be an 8 bit value in the range from 0 through 255. This parameter shall be a measure by the PHY sublayer of the perceived signal quality observed after RF downconversion and is derived from internal digital signal processing metrics of the demodulator used to receive the current frame. PSNI shall be measured over an entire received frame. PSNI is intended to be used in a relative manner, and it shall be a monotonically increasing, logarithmic function of the perceived S/(N+I). PSNI accuracy and range shall be specified at two different FER operating conditions for each PHY: For DSSS PHYs at 1, 2, 5.5, and 11Mpbs: 1. At an FER of 10% for 1000 octet frames received at an uncoded data rate of 11Mbps, PSNI shall indicate 128 +/ At an FER of 10% for 100 octet frames received at an uncoded data rate of 11Mbps, PSNI shall indicate 121 +/- 7. For OFDM PHYs at 6, 9, 12, 18, 24, 36, and 54Mpbs: 1. At an FER of 10% for 1000 octet frames received at a data rate of 12Mbps using R=1/2 coding, PSNI shall indicate TBD. 2. At an FER of 10% for 100 octet frames received at a data rate of 12Mbps using R=1/2 coding, PSNI shall indicate TBD.

doc: IEEE /100r3January 2003 Submission Joe Kwak, InterDigital 12 PSNI Supercedes RSSI in Existing Specs The definition of PSNI meets the requirements for RSSI: 8-bit unsigned value (for DSSS PHYs) Proportional to received signal power TGK can specify that for STAs which comply with K, STAs shall report PSNI in any data field calling for RSSI. This makes the PSNI indicator broadly applicable as a frame quality measurement useful for all PHYs and STAs. RSSI(PSNI) elements and reporting/posting may further be mandated in the MIB by K to make the PSNI improvements available to higher layers.

doc: IEEE /100r3January 2003 Submission Joe Kwak, InterDigital 13 PSNI specified on BER/FER curves For 11 Mbps For 5.5 Mbps For 2 Mbps For 1 Mbps PSNI Two specified points on logarithmic scale: STA front-end losses, antenna configs, or demod losses do not affect PSNI measure.

doc: IEEE /100r3January 2003 Submission Joe Kwak, InterDigital 14 Partial DSSS PSNI table

doc: IEEE /100r3January 2003 Submission Joe Kwak, InterDigital 15 Need to place OFDM curves on PSNI scale Figure 3: BER Curves for Coded and Uncoded OFDM

doc: IEEE /100r3January 2003 Submission Joe Kwak, InterDigital 16 Tasks for Next Meeting Complete OFDM mapping onto PSNI scale. Complete PSNI table for OFDM Verify PSNI scale range. Discuss ease of implementation with modem manufacturers. Discuss PSNI accuracy spec: +/- 7 units == +/- 1.1 dB. Discuss PSNI accuracy, for full range of log scale, when specified at only two points. Consider feedback, criticism and alternate approaches.