SubmissionJoe Kwak, InterDigital1 RCPI and PSNI: New PHY Measurements comparative measurements of...

Submission Joe Kwak, InterDigital1

RCPI and PSNI: New PHY Measurements

comparative measurements of receiver input and output to support network management

Joe Kwak

InterDigital Communications Corporation

doc: IEEE 802.11-03/315r0May 2003


doc: IEEE 802.11-03/315r0May 2003

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


doc: IEEE 802.11-03/315r0May 2003 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.


doc: IEEE 802.11-03/315r0May 2003

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.

PHY Measurement Architecture

Radiofront end

A/D FEC Decoder(optional)

Demodulator andtracking loops(PHY specific)

A: Total RF power,RF S/(N+I) from each AP

DCB

A

B: BB S/(N+I) from each AP (BB power constant by AGC)

C&D: Bit Error Rate (BER) @each data rate

from each AP

FrameCheck(CRC)

E

E: Frame Error Rate (FER) @each data rate

from each AP

AGC


doc: IEEE 802.11-03/315r0May 2003

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.

Measure RCPI power at A. Measure PSNI quality in middle, but specify PSNI with FER at E.

GoodSTA

MedSTA

MarginalSTA

A (dBm) E (FER)

-80dbm

10E-2

10E-4

10E-5 GoodSTA

MedSTA

MarginalSTA

A (dBm) E (FER)

10E-5

10E-5

10E-5

Signal at same objective SNR Signal at same subjective SNR

-80dbm

-80dbm

-80dbm

-78dbm

-75dbm


doc: IEEE 802.11-03/315r0May 2003

RCPI and PSNI Relation to SNR in Demodulator Received Channel Power Level

dBm (S + N + I)

Operating Margin Required Min

RSPL Level

Des

ire

d S

ign

al

Po

wer

dB

m

Interference Power at Input

Boltzman’s C (-198dBm/Hz/K)

Antenna Connector: InputPower Level (S+ N + I)

Input Analog

SNIR Ratio

Thermal Input Noise Level (-100dBm)

Theoretical SNRfor required BER

(RCPI at antenna

connector)

NBW = 22MHz = 73.4dB

Temp = 290K = 24.6dB

Channel Impairments (CI) (fading + multipath + etc, = 0 in AWGN))

dBm

Total ModemImplementationLosses (TML)

FEC Decoder Loss, if any

Demodulator Loss

Rx Amp Noise Figure + IM Distortion

dBm

Observed Digital

SNIR Ratio

(PSNI indemodulator)

Input SNR Ratio

Total ChannelConditionLosses

Observed Analog

SNIR Ratio

o


doc: IEEE 802.11-03/315r0May 2003

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.


doc: IEEE 802.11-03/315r0May 2003

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.


doc: IEEE 802.11-03/315r0May 2003

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


doc: IEEE 802.11-03/315r0May 2003

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.


doc: IEEE 802.11-03/315r0May 2003

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:

Data Rate Mode FEC Rate PPDU Length FER PSNI (Mbit/s) (bytes)

1 DSSS no FEC 125 10% +/-0.2% 32 +/- 82 DSSS no FEC 1250 10% +/-0.2% 66 +/- 8

5.5 HRDSSS no FEC 1250 10% +/-0.2% 101 +/- 85.5 HRDSSS 1/2 1250 10% +/-0.2% 58 +/- 86 OFDM 1/2 1250 10% +/-0.2% 61 +/- 89 OFDM 3/4 1250 10% +/-0.2% 83 +/- 8

11 HRDSSS no FEC 1250 10% +/-0.2% 125 +/- 811 HRDSSS 1/2 1250 10% +/-0.2% 82 +/- 812 OFDM 1/2 1250 10% +/-0.2% 85 +/- 818 OFDM 3/4 1250 10% +/-0.2% 107 +/- 824 OFDM 1/2 1250 10% +/-0.2% 141 +/- 836 OFDM 3/4 1250 10% +/-0.2% 163 +/- 848 OFDM 2/3 1250 10% +/-0.2% 206 +/- 854 OFDM 3/4 1250 10% +/-0.2% 213 +/- 8

Theoretical FEC coding gain assumed in FER calculations:R = 1/2, 5.4dB gainR = 2/3, 4.7dB gainR = 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.


doc: IEEE 802.11-03/315r0May 2003

PSNI SCALING (8 bit, 0-256 range)

-12

-10

-8

-6

-4

-2

0

-100 -50 0 50 100 150 200 250 300

PSNI Value (8 units/db)

BE

R (

10-x

)

11 Mbps DSSS 5.5 Mbps DSSS 2 Mbps DSSS

1 Mbps DSSS 12 Mbps OFDM 24 Mbps OFDM

48 Mbps OFDM 54 Mbps OFDM PSNI Range Limit

9 Mbps OFDM 6 Mbps OFDM 18 Mbps OFDM

36 Mbps OFDM 24 Mbps R=1/2 OFDM

PSNI specified on BER/FER curves


doc: IEEE 802.11-03/315r0May 2003

Data Rate/Modulation Adjustments (DRMx) Used to Offset BER Curves

DRMx:FEC data rate modulation Total S/N

data rate (Mbps) mode modulation code rate coded rate (Mbps) adjustment(db) adjustment(db) adjustment(db)1 DSSS BPSK none (SF=11) 1 0 0 02 DSSS QPSK none (SF=11) 2 3 0 3

5.5 DSSS 11b QPSK none (SF=16) 5.5 7.4 0 7.45.5 DSSS 11b QPSK 1/2 (SF=2) 11 7.4 0 7.4

6 OFDM BPSK 1/2 12 7.78 0 7.789 OFDM BPSK 3/4 12 9.54 0 9.54

11 DSSS 11b QPSK 1/2 (SF=1) 11 10.41 0 10.4111 DSSS 11b QPSK none (SF=8) 11 10.41 0 10.4112 OFDM QPSK 1/2 24 10.79 0 10.7918 OFDM QPSK 3/4 24 12.55 0 12.5522 DSSS 11g 8PSK 2/3 (SF=1) 33 13.42 0 13.4224 OFDM 16-QAM 1/2 48 13.8 3.98 17.7833 DSSS 11g 8PSK 2/3 (SF=1) 49.5 15.19 0 15.1936 OFDM 16-QAM 3/4 48 15.56 3.98 19.5448 OFDM 64-QAM 2/3 72 16.81 8.45 25.2654 OFDM 64-QAM 3/4 72 17.32 8.45 25.77

Note: Modulation adjustments from Table 3.1, OFDM for Wireless Multimedia Communications, Van Nee/Prasad, Artech House, 2000

Table 1: DRM Rate/Modulation Adjustments


doc: IEEE 802.11-03/315r0May 2003

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).

Data Rate Eb/No PPDU(Mbps)/FEC (dB) BER Length FER5.5 (none) 9.6 1.00E-05 1250 1.00E-015.5 (R=1/2) 9.6 1.25E-13 1250 1.00E-096 (R=1/2) 9.2 1.25E-12 1250 1.00E-089 (R=3/4) 7.5 6.00E-09 1250 4.80E-0511 (none) 6.6 1.25E-03 10 1.00E-0111 (R=1/2) 6.6 2.00E-09 12 2.00E-0512 (R=1/2) 6.2 2.00E-08 1250 2.00E-0418 (R=3/4) 4.4 1.40E-04 10 1.10E-02


doc: IEEE 802.11-03/315r0May 2003

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.

.


doc: IEEE 802.11-03/315r0May 2003

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 * DRNo * NBW No * NBW


doc: IEEE 802.11-03/315r0May 2003

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.


doc: IEEE 802.11-03/315r0May 2003

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 ___%


doc: IEEE 802.11-03/315r0May 2003

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 ___%

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