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Joe Kwak InterDigital Communications Corporation

May 2003. doc: IEEE 802.11-03/315r0. RCPI and PSNI: New PHY Measurements comparative measurements of receiver input and output to support network management. Joe Kwak InterDigital Communications Corporation. Outline. Need for new PHY measurements

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Joe Kwak InterDigital Communications Corporation

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  1. May 2003 doc: IEEE 802.11-03/315r0 RCPI and PSNI: New PHY Measurementscomparative measurements of receiver input and output to support network management Joe Kwak InterDigital Communications Corporation Joe Kwak, InterDigital

  2. Outline • Need for new PHY measurements • RCPI and PSNI Relation to SNR in Demodulator • Received Channel Power Indicator (RCPI) Definition • Perceived Signal-to-Noise-plus-interference Indicator (PSNI) Definition • PSNI Analysis: Relation to EbNo, SNR and BER • Motions to incorporate RCPI and PSNI Joe Kwak, InterDigital

  3. Need for New PHY Measurements • RSSI is defined at antenna input connector but is not fully specified: no unit definitions, no performance requirements (accuracy, 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/PHYs 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 handoff or load balancing. RSSI from one STA does not relate to RSSI from any other STA. • In high interference environments, RSSI is not an adequate indicator of desired signal quality, since it indicates the sum of desired signal + noise + interference powers. • Proposed RCPI provides quantized, objective input power measure (S+N+I). • Proposed PSNI provides quantized, comparative measure of received signal quality [observed S/(N+I)] for all channels/rates and among all PHYs and between all STAs. Joe Kwak, InterDigital

  4. PHY Measurement Architecture • RCPI measures total RF Power at antenna input connector A. • PSNI measures observed S/(N+I) within demodulator but normalizes measurement for FER at E. AGC B C D Demodulator and tracking loops (PHY specific) E Radio front end FEC Decoder (optional) Frame Check (CRC) A/D A A: Total RF power, RF S/(N+I) from each AP C&D: Bit Error Rate (BER) @each data rate from each AP B: BB S/(N+I) from each AP (BB power constant by AGC) E: Frame Error Rate (FER) @each data rate from each AP Joe Kwak, InterDigital

  5. Measure PHY Demod Input (power) and Output (QOS) • Accurate S/(N+I) 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 quality measure, 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 10E-5 -80dbm Good STA 10E-5 -80dbm E (FER) A (dBm) E (FER) A (dBm) Med STA 10E-5 Med STA 10E-4 -78dbm -80dbm Marginal STA Marginal STA 10E-5 10E-2 -75dbm -80dbm Signal at same objective SNR Signal at same subjective SNR Measure RCPI power at A. Measure PSNI quality in middle, but specify PSNI with FER at E. Joe Kwak, InterDigital

  6. Received Channel Power Level dBm (S + N + I) Operating Margin Observed Digital SNIR Ratio (PSNI in demodulator) Required Min RSPL Level (RCPI at antenna connector) Theoretical SNR for required BER Observed Analog SNIR Ratio Desired Signal Power dBm FEC Decoder Loss, if any Total Modem Implementation Losses (TML) Input Analog SNIR Ratio Input SNR Ratio Demodulator Loss Rx Amp Noise Figure + IM Distortion Channel Impairments (CI) (fading + multipath + etc, = 0 in AWGN) Total Channel Condition Losses o dBm Antenna Connector: Input Power Level (S+ N + I) Interference Power at Input dBm Thermal Input Noise Level (-100dBm) Temp = 290K = 24.6dB NBW = 22MHz = 73.4dB Boltzman’s C (-198dBm/Hz/K) RCPI and PSNI Relation to SNR in Demodulator Joe Kwak, InterDigital

  7. RCPI Concept: Measure Input Power • Specified like RSSI: 8-bit unsigned value, monotonically increasing with increasing signal strength. • RCPI shall be logarithmically scaled in dB to measure total received power within defined channel bandwidth at the antenna connector. Includes power from desired signal, noise, and interference. • RCPI values shall be quantified in dBm and accuracy shall be specified across entire RCPI range. • The 221 RCPI levels shall range from -110 dBm to 0 dBm with 2 units per dB. • RCPI accuracy shall be +/- 5dB across the defined range, equivalent to accuracy specified by TGH for RPI histogram. • RCPI may be used wherever RSSI is specified. Joe Kwak, InterDigital

  8. RCPI Normative Specification Text • The RCPI indicator is a measure of the received RF power in the selected channel, measured at the antenna connector. This parameter shall be a measure by the PHY sublayer of the received RF power in the channel measured over the PLCP preamble and over the entire received frame. RCPI shall be a monotonically increasing, logarithmic function of the received power level defined in dBm. The allowed values for the Received Channel Power Indicator (RCPI) parameter shall be an 8 bit value in the range from 0 through 220, with indicated values rounded to the nearest 0.5 dB as follows: • 0: Power < -110 dBm • 1: Power = -109.5 dBm • 2: Power = -109.0 dBm and so on • 220: Power > -0 dBm • 221-255: reserved • Accuracy for each measurement shall be +/- 5dB. The measurement shall assume a receiver noise equivalent bandwidth of 22 MHz. Joe Kwak, InterDigital

  9. PSNI: Demodulator-specific, Post-processing Estimator of Observed S/(N+I) and BER/FER. • 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 and received Error Vector Magnitude (EVM) • 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 S/(N+I) are available at all data rates. • Demodulator internal metrics may be calibrated with respect to actual FER performance to accurately indicate perceived or observed S/(N+I) in controlled environment with AWGN. • 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 PSNI indicator relates to S/(N+I) and FER Joe Kwak, InterDigital

  10. PSNI Concept: Measure Output Signal Quality • 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 value for each data rate using FER points: first point to “anchor” indicator, additional points to quantize and scale indicator slope and range of values. • Specify accuracy of PSNI in AWGN to be +/- 1dB for all FER points. • PSNI range shall span the lower 32 dB portion of the operating range of S/(N+I) to cover high FERs at data rates from 1 to 54 Mbps. Joe Kwak, InterDigital

  11. PSNI Normative Specification Text • 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 the PLCP preamble and over the entire received frame. PSNI is intended to be used in a relative manner, and it shall be a monotonically increasing, logarithmic function of the observed S/(N+I). PSNI accuracy and range shall be specified in AWGN at given FERs for each data rate as follows: Theoretical FEC coding gain assumed in FER calculations: R = 1/2, 5.4dB gain R = 2/3, 4.7dB gain R = 3/4, 4.4dB gain PSNI SPECIAL VALUE: “0” shall indicate inability to measure PSNI When PSNI exceeds high end of measurable range for a given data rate, maximum PSNI for that rate shall be reported. Joe Kwak, InterDigital

  12. PSNI specified on BER/FER curves Joe Kwak, InterDigital

  13. Data Rate/Modulation Adjustments (DRMx) Used to Offset BER Curves Table 1: DRM Rate/Modulation Adjustments Joe Kwak, InterDigital

  14. Example: PSNI = 101 • BERs vary based on FEC coding used at each data rate. FERs vary based on BER and PPDU length. • Note: in any STA, PSNI will vary only as a result of changing Channel Conditions or changing received Desired Signal Power Level. • Note: for efficiency, all STAs should operate at highest data rate possible while maintaining acceptable FER (QOS). Joe Kwak, InterDigital

  15. PSNI Analysis: Relation to Observed Eb/No • PSNI = 0 is selected for a post-processing, Observed Eb/No (OEbNo) equal to 4.4dB, for BPSK at 1Mbit/s data rate. • 8 units (steps) per dB is selected to provide 32 dB range in 8 bit PSNI value. • So for 1 Mbit/s BPSK operation, PSNI = 8*[OEbNo - 4.4dB]. • In general for all other data rates and modulations, PSNI = 8*[OEbNo - 4.4dB + DRMx - CFy] , where DRMx is an S/N adjustment unique for each data rate/demodulation combination. DRMx values are calculated in Table 1 , as shown on page 11, and where CFy is a hardware-specific factor used to account for implementation variances in each FEC decoder in the STA. CFy = CGtheo - CGact = actual FEC decoder loss, for each decoder at each specified FER point. CGtheo values are listed on page 11. When no FEC decoder is used CFy = 0. • This relation is the foundation of the PSNI measurement. . Joe Kwak, InterDigital

  16. PSNI Analysis: Relation to Input SNIR (ISNIR) • SNR = C / N, where Eb = C * Tb, N = No * NBW (noise BW) and DR = 1 / Tb • So SNR = -------------- = -------------- = EbNo * DR / NBW • In db: SNR = EbNo + DR - NBW , where EbNo is shorthand for Eb/No in dB. • For DR = 1 Mbit/s and NBW + = 22 MHz, SNR = EbNo + 60dB - 73.4dB = EbNo -13.4dB • In general, SNR = EbNo -13.4dB + DRMx, with DRMx from Table 1. and so EbNo = SNR + 13.4dB - DRMx, and OEbNo = OSNIR + 13.4dB - DRMx • From page 15 we have: PSNI = 8*[OEbNo - 4.4dB + DRMx - CFy], and substituting for OEbNo, PSNI = 8*[(OSNIR + 13.4dB - DRMx) - 4.4dB + DRMx - CFy], and PSNI = 8*[OSNIR + 9.0dB - CFy] • Since ISNIR = OSNIR + TML + CI, where TML is the modem implementation loss and CI is the sum of all channel impairments, we have PSNI = 8*[(ISNIR-TML-CI) + 9.0dB - CFy] Eb / Tb Eb * DR No * NBW No * NBW Joe Kwak, InterDigital

  17. PSNI Analysis: Relation to BER/FER • PSNI is a direct measure of observed SNIR considering all channel impairments and implementation losses measured at the demodulator. • PSNI is specified with respect to output FER, which considers all implementation losses including any FEC decoder implementation loss. • Each STA will measure PSNI using a correction factor Cfy to account for the actual coding gain (CGact) of each FEC decoder. • Any STA measuring PSNI on a frame using FEC will use CFy so that the reported PSNI from all STAs is normalised and assumes a theoretical coding gain. CFy = CGtheo - CGact = actual FEC decoder loss • Reported PSNI value may be used to estimate OEbNo and BER/FER (QOS) for the reporting STA for each data rate. OEbNo = (PSNI/8) + 4.4dB - DRMx : • For data rates without FEC decoder, OEbNo is used with the theoretical PSK EbNo curve to estimate BER. • For data rates with FEC decoder, OEbNo is used with the theoretical FEC EbNo curve for PSK to estimate BER. • Note: PSNI relation to BER is specified only for AWGN. Since the net effect of channel impairments is to degrade OEbNo in the same way as AWGN, PSNI should be an adequate estimator of BER in all channel conditions. Joe Kwak, InterDigital

  18. Motion for RCPI normative text • Move to instruct the editor to incorporate text from document 11-03-xxxr__-K-RCPI_NormText.doc into TGk draft specification document • Moved by Joe Kwak • Seconded by: _______________ • Vote YEA _______ • Vote NEA _______ • ABSTAIN _______ • Motion Passes/Fails at ___% Joe Kwak, InterDigital

  19. Motion for PSNI normative text • Move to instruct the editor to incorporate text from document 11-03-xxxr__-K-PSNI_NormText.doc into TGk draft specification document • Moved by Joe Kwak • Seconded by: _______________ • Vote YEA _______ • Vote NEA _______ • ABSTAIN _______ • Motion Passes/Fails at ___% Joe Kwak, InterDigital

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