1. EVM vs PER Plot Not Promising for PSNI
Month 2002
doc.: IEEE /xxxr0
July 2003
EVM vs PER Plot Not Promising for PSNI
Brian Hart, David Skellern (Cisco Systems)
TGk July 2003
Hart/Skellern Cisco
John Doe, His Company

2. Background
July 2003
IEEE /218r2 (file r2-K-PSNI_Measurement_V2.ppt) proposed the use of a measure named PSNI to quantify the quality of the signal that is able to be recovered by a particular receiver
In document IEEE /531r0 we suggested that a new measure was not needed because an appropriate measurement of output signal quality was already available in EVM which:
works for all digital modulations
has the desired properties specified on slides 9 & 10 of doc: IEEE /218r2
can provide a direct indication of observed S/(N+I) considering all channel impairments and implementation losses when measured at the demodulator
is defined already in the standard as a signal quality measure
can be measured with commercially available test equipment
Hart/Skellern Cisco

3. Background cont.
July 2003
However, discussion in TGk at the May 2003 concluded that
Simulations and/or measurements were needed to verify the validity of EVM as an output signal quality measure
Even if EVM was a valid measure, it was a measure that needed to be extended to take into account the implementation characteristics of the receiver from the demodulator to the output (principally the FEC block)
This submission is about the validity of EVM and reports on an investigation of the relationship between EVM and PER across different channels and practical systems.
Hart/Skellern Cisco

4. Investigation of EVM validity
July 2003
Investigation of EVM validity
We thought that if any useful standardized PSNI measure existed it would be based on EVM because it captures all the degradations present on a communications link
in proportion to the impact they have
at a point where the cumulative degradation is easy to estimate
includes: quantisation, non-ideal converters, clock frequency offsets and phase noise, carrier frequency offsets and phase noise, power-amplifier distortions, multipath, co-channel interference, adjacent channel interference, other interference, thermal noise, and poor receiver algorithms.
We therefore expected that if we plotted average EVM vs average PER for an IEEE a link operating at a given rate over a range of practical implementations and typical channels we would find a useful relationship between EVM and PER.
Hart/Skellern Cisco

5. Investigation of EVM validity
July 2003
Investigation of EVM validity
We generated results using a Matlab a modeling framework
with a range of channels, from AWGN to Rayleigh, that we believe from our channel measurements to be representative of the indoor office environment
with a range of practical hardware settings and implementations, including ADC resolutions, datapath widths, Viterbi algorithm details, synchronization options, channel tracking methods and AGC strategies
“practical hardware settings and implementations” = workable designs, many of which are in current manufacturers’ implementations
Simulation set-up
there are over 250 plotted simulation points
generally the simulations wait for byte packets in error or 750 packets, whichever comes first
a few points (<< 5%) at high PER are based on fewer packets
Hart/Skellern Cisco

6. EVM vs PER results for 6 Mbit/s
July 2003
EVM vs PER results for 6 Mbit/s
Genie-aided EVM is EVM calculated using the known transmitted constellation point.
Hart/Skellern Cisco

7. July 2003
Conclusion
These results show no useful relationship between EVM and PER across different channels and practical systems.
While further study is needed, we conclude that obtaining an output data quality measure that would be useful across different designs and implementations (manufacturers) is unlikely in the short term – and not in any timeframe commensurate with timely completion of an 11k draft.
We therefore propose that text related to PSNI not be included in the draft.
Hart/Skellern Cisco