1. Simple SNIR for TGk 2005-JULY-21 Authors: Joe Kwak, InterDigital
January 2003
IEEE /100r1
Simple SNIR for TGk
Authors:
2005-JULY-21
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Joe Kwak, InterDigital
Submission

2. January 2003
IEEE /100r1
Introduction
At very inception of TGk, the need for a signal quality metric was identified. Measuring the “goodness” of a STAs communication link with its serving AP and measuring the “goodness” of the links to neighbor APs is crucial to effective roaming.
Erred packet counts at MAC level do not suffice:
most links adapt to operate with minimal or no errors so scaled measurement is not possible. “no errors” or “few errors” is insufficient.
Time delay to get true picture of link quality is too long to be useful; 100’s or 1000’s of errors needed for meaningful measure.
No information is available if “no errors” detected.
TGk needs a fast signal quality metric.
PSNI attempted to define a fast metric to quantify quality of link output data stream. Considered too complex.
A new metric is proposed here as a simple metric to quantify input RF signal quality at a receiving STA.
SMI – Structure of Management Information
ASN.1 – Abstract Syntax Notation 1
Joe Kwak, InterDigital
Submission

3. Receive Signal to Noise Indicator (RSNI)
SIMPLE, based on what we already have: RCPI and Noise Histogram
RCPI measures RF signal (plus noise & interference) at antenna connector.
Noise Histogram measures noise & interference at antenna connector
RSNI is simple ration derived from these two.
Need to define new “average” noise plus interference metric (ANPI) as intermediate product.
Suggest that we attach new ANPI to Noise Histogram Report.
ANPI may be derived as a summary metric from the Noise Histogram by calculating a weighted average of the histogram bin power levels.
Define RSNI at MAC layer:
Add new RSNI to:
Beacon Report
Frame Report
Link Measurement Report
(RCPI - ANPI)
ANPI
Joe Kwak, InterDigital
Submission

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.
RSNI measures RF S/(N+I) at antenna input connector A.
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
RF (N+I) in the channel
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
Submission

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.
-80dbm
Good
STA
10E-5
-80dbm
Good
STA
10E-5
A (dBm)
E (FER)
A (dBm)
E (FER)
Med
STA
10E-4
Med
STA
10E-5
-78dbm
-80dbm
Marginal
STA
Marginal
STA
10E-2
-75dbm
10E-5
-80dbm
Signal at same objective SNR
Signal at same subjective SNR
Measure RCPI power at A. Measure PSNI quality in middle,
Measure Noise power at A. but specify PSNI with FER at E.
Joe Kwak, InterDigital
Submission

6. RCPI and PSNI Relation to SNR in Demodulator
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
Input RF
SNIR Ratio
(RSNI at
antenna conn)
FEC Decoder Loss, if any
Total Modem
Implementation
Losses (TML)
Demodulator Loss
Rx Amp Noise Figure + IM Distortion
Input
RF SNR
Ratio
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)
Joe Kwak, InterDigital
Submission

7. DRAFT Normative Text Changes
"Average Noise Power Indication (ANPI) is the time average of the measured RPI power indicated by the following RPI densities. ANPI indicates the average noise plus interference power at antenna connector during the measurement duration when NAV is equal to 0 (when virtual CS mechanism indicates idle channel). ANPI power is in dbm using the same units as defined for RCPI. This may calculated by a weighted average for the reported RPI densities assuming noise power to be the mid range value for each of the nine defined ranges for the RPI levels. Other measurement techniques are allowed.”
" RSNI (Received Signal to Noise Indicator) is a measurement of received signal to noiseplus interference ratio. RSNI is derived from the RCPI value indicated here and from the most recent ANPI value measured on this channel. RSNI may be calculated by the ratio of the received signal power (RCPI - ANPI) to the noise plus interference power (ANPI) expressed in db (1/2 db steps), where RSNI = [(ratio(dB) + 10) * 2], for ratios in the range -10dB to +118dB. Other measurement techniques are allowed."
Joe Kwak, InterDigital
Submission

8. Conclusions
This SIMPLE new approach which defines RSNI plugs the TGk hole for fast signal quality metric.
RSNI builds upon existing facilities to accomplish this goal in the MAC layer.
Informal discussions indicate some support for this change.
We propose that 11k should modify the draft to incorporate ANPI and RSNI.
STRAW POLL TO ASSESS LEVEL OF SUPPORT
Joe Kwak, InterDigital
Submission

9. ANNEX A
The following charts are excerpts of prior work which attempted to define a SNIR metric for TGk. PSNI was proposed as an SNIR-based metric which measured the quality (PER & BER) of an link. Excerpts which follow are from 03/898r2 and 04/0109r1.
Joe Kwak, InterDigital
Submission

10. 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
Submission

11. 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.
-80dbm
Good
STA
10E-5
-80dbm
Good
STA
10E-5
A (dBm)
E (FER)
A (dBm)
E (FER)
Med
STA
10E-4
Med
STA
10E-5
-78dbm
-80dbm
Marginal
STA
Marginal
STA
10E-2
-75dbm
10E-5
-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
Submission

12. RCPI and PSNI Relation to SNR in Demodulator
Received Channel Power Level
dBm (S + N + I)
Operating
Margin
Required Min
RSPL Level
Desired Signal
Power dBm
Interference Power at Input
Boltzman’s C (-198dBm/Hz/K)
Antenna Connector: Input
Power Level (S+ N + I)
Input
Analog
SNIR Ratio
Thermal Input Noise
Level (-100dBm)
Theoretical SNR
for 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 Modem
Implementation
Losses (TML)
FEC Decoder Loss, if any
Demodulator Loss
Rx Amp Noise Figure + IM Distortion
Observed
Digital
(PSNI in
demodulator)
Input SNR
Ratio
Total
Channel
Condition
Losses o
Joe Kwak, InterDigital
Submission

13. PSNI is Specified for “Black Box”
SET INPUTS
READ OUTPUT
Sig Level
Chan Fade
PSNI
STA RCVR
(at selected rate)
Noise
BER or
throughput
RCVR implementation may use:
-EVM on data symbols
-EVM on pilots
-other FEC decoder metrics
-FEC corrected bit rate
-spreading code correlation quality
-many others possible
Adjust sig, noise, fading for
desired BER or Throughput
for selected rate
Joe Kwak, InterDigital
Submission

14. 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.
PSNI output values reflect output FER and are specified in AWGN and in one representative fading channel.
Specify tabular performance using single PSNI output value for each data rate. Make PSNI performance optional.
Specify accuracy of PSNI in AWGN to be +/- 2.0dB in AWGN and +/- 6.0dB in fading channels with 20 packets/sample.
PSNI range shall span the lower 43 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
Submission

15. PSNI specified on BER/FER curves
PSNI SCALING (8 bit, range)
-10 -8 -6 -4 -2
-50 50
100
150
200
250
300
PSNI Value (6 units/db)
BER (10-x)
1 Mbps DSSS
2 Mbps DSSS
5.5 Mbps R=1/2 DSSS
6 Mbps R=1/2 OFDM
9 Mbps R=3/4 OFDM
11 Mbps R=1/2 DSSS
12 Mbps R=1/2 OFDM
18 Mbps R=3/4 OFDM
24 Mbps R=1/2 OFDM
36 Mbps R=3/4 OFDM
48 Mbps R=2/3 OFDM
54 Mbps R=3/4 OFDM
PSNI Range Limit
43 dB total range
32 dB useful range
11 dB
margin
where OSNIR = (PSNI / 6) - 9dB
Joe Kwak, InterDigital
Submission

16. PSNI Normative Specification Text
The PSNI 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 link quality observed after RF downconversion, demodulation, and FEC decoding and is derived from internal digital signal processing metrics of the demodulator, e.g. Error Vector Magnitude (EVM). 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 link S/(N+I). Specified PSNI performance shall be measured over no less than 20 PPDUs from the same transmitter. PSNI accuracy and range shall be specified in AWGN and fading at given FERs for each data rate as indicated in Table XX. The fading channel model shall be the IEEE exponential ray decay model with 50nsec decay time.
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
Submission

17. PSNI Normative Specification Text (cont)
Since the PHY layer measures PSNI on a packet-by-packet basis, the statistics processing and variance adjustment will be done in the MAC layer.
Additional Specification Text: The MAC layer will process statistics for PSNI measured on multiple packets from the same transmitter. The MAC will collect packet PSNI measurements, received from the PHY layer from the same transmitter, into a measurement set called a PSNI sample. The MAC will calculate the mean and standard deviation for the PSNI sample. The MAC will use the mean and standard deviation of the PSNI sample to calculate a PSNI fading correction. The MAC will add the fading correction to the mean of the PSNI sample to produce the PSNI Value to be reported for the PSNI sample. The calculation of the PSNI fading correction is designed to decrease the mean of the PSNI sample to produce a reported PSNI value which indicates output BER/FER using AWGN demodulation/decoder curves, where SNR = (PSNI / 6) - 9dB.
PSNI 3
PSNI 5
PSNI 4
PSNI 2
PSNI 1
PSNI Mean
PSNI StdDev
Calc
Fade
Correction + -
PSNI Value
Sample Variance
Sample Size
PSNI Sample
Statistics
Reported Results
Adjust for Fading
Joe Kwak, InterDigital
Submission