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Putting the IBOC Quality Metric to the Test

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Putting the IBOC Quality Metric to the Test Powered By Docstoc
					Putting the IBOC Quality
Metric to the Test
Achieving Optimal HD RadioTM Coverage

Philipp Schmid               April, 2010
Overview
•Motivation to define IBOC Quality
•IBOC Signaling and Demodulation
•Standard Modulation Error Ratio
•Basic IBOC Receiver Concepts
   – Fractional sample delays
   – IBOC Symbol, Delay and Frequency Synchronization
•IBOC Quality Metric Components
•Defining Acceptable IBOC Quality
•Factors impacting IBOC Quality
   – FM Over-modulation, clock stability, peak reduction
•Measuring Nautel HD Power Boost technology
   – IBOC Quality versus increased power output
Motivation
             • Spectral analysis until now has been the
               accepted metric for good IBOC transmission
                –Enforces emission mask compliance
                –Spectral re-growth shows transmitter linearity
                –Identifies gain variation
             • Spectral analysis provides little in-band
               information
                –How clean are the carriers in-band?
                –How do reference carriers compare to data carriers?
                –How much error correction is lost in the transmitter?
             • IBOC Quality Metric is a crucial component in
               the design and validation of new peak reduction
               algorithms
IBOC Signaling




                 data carriers   QPSK
                 ref carriers    BPSK
               Basic IBOC Demodulation
                                                                  Cyclic prefix removal
                                                                  • apply pulse shape 2x
                                                                  • add last 112 samples to
                                                                  front

                                                                  2048 point FFT
                                                                  • complex carrier
                                                                  constellation points
       +
    Sin(x)                                               Cos(x)
                                                                         IBOC receivers
                Cyclic                     Fast
                                                                         operate on each
                Prefix                   Fourier
                                                                         sideband
               Removal                  Transform                        independently
2160 samples             2048 samples               2048 carriers
744187.5 Hz              time domain                frequency domain
Modulation Error Ratio (MER)
                   Requires IBOC demodulation

                   Modulation Error Ratio:




                   Error Vector Magnitude:
Fractional Sample Delays
                      Signal capture and sample
                      rate conversion may cause
                      fractional sample delays

                      delay error  phase error
Step 1: Symbol Synchronization
                          Autocorrelation on
                          cyclic prefix

                          Pulse shaping
                          function emerges
                          over iterations

                          Provides sample
                          rate error estimate
Step 2: Delay and Frequency Tracking
                Delay tracking fine tunes sub-
                sample delays by linear phase
                adjustments.

                Frequency tracking is needed if
                capturing IBOC signals with an
                independent reference oscillator.
                • can measure transmitter clock stability
                • max frequency error of up to ±2.5 ppm
                • slope of phase adjustment changes with
                  each symbol
Gain, Group Delay and
Reference Carrier Level
                                          Metric measures the power level
                                          of reference carriers compared to
                                          data carriers
                                          • ensures they are evenly matched
                                              – specified limit: -1.0 dB to +0.5 dB
                                          • a 0.5 dB lower reference level is typical
                                          • can be observed on spectrum
 1   2    3   4   5   6   7   8    9 10

                                          Gain and group delay require lots of
                                          averaging
         10 frequency partitions
                                          • measured on demodulated carriers
                                          • max ±0.5 dB gain variation
                                          • max 600ns group delay
Modified Data Carrier MER
                Reference carriers are measured using
                standard MER

                Peak reduction performs “intelligent” carrier
                placement and correction
                • peak canceling carriers are boosted
                • carriers close to decision region are corrected

                MER is modified to only measure the
                component toward the decision region
    Defining Acceptable Quality


                                  additive
MER=17.5 dB  69 dB-Hz   +        channel =                 56 dB-Hz


                                  noise

                             -10 log10(10-56/10-10-69/10)
                             = 56.22 dB-Hz
                             0.22 dB loss in coverage
    Defining Acceptable Quality
                             Average   Coverage
10 dB IBOC       possible    MERdata   Reduction
power increase   coverage
                               18 dB    0.22 dB    Exgine output
                 reduction
                               16 dB    0.31 dB
                               14 dB    0.48 dB    Specified limit

                               12 dB    0.74 dB
                               10 dB    1.13 dB
                                8 dB    1.73 dB
Impact of FM Modulation
                          Innermost frequency
                          partitions are affected

                          Occasional over-
                          modulation may not be
                          detected in spectrum,
                          but can be measured
                          in MER metric

                          Severely affected
                          partitions need to be
                          filtered out for
                          synchronization
Exciter Clock Stability
                 Exciter is intentionally offset by 0.5 ppm
                 and slews transmit clock based on
                 Ethernet based reference clock.

                 Fast clock causes clockwise rotation,
                 slow clock causes counter clockwise
                 rotation.

                 Reference carrier MER:
                       20.8 dB => 15.5 dB
                 Data carrier MER:
                       17.7 dB => 13.7 dB
Impact of Peak Reduction
                         IBOC injection:           -10 dBc
                         Transmitter:              20 kW
                         Output Power:             12.8 kW
                         Peak to Average (PAPR):   3.6 dB
                         DC-RF Efficiency:         56.8%
                         Data MER:                 24.5 dB
                         Coverage Reduction:       ~0.1 dB

                         Compared to exgine signal:
                         • exceeds MER by 6 dB
 Nautel HD Power Boost
                         • PAPR slightly better
 soft peak reduction
Impact of Peak Reduction
                          IBOC injection:           -10 dBc
                          Transmitter:              20 kW
                          Output Power:             13.8 kW
                          Peak to Average (PAPR):   3.1 dB
                          DC-RF Efficiency:         58.7%
                          Data MER:                 19.1 dB
                          Coverage Reduction:       0.2 dB

                          Compared to exgine signal:
                          • slightly better MER
 Nautel HD Power Boost
 typical peak reduction   • almost 1 dB better PAPR
Impact of Peak Reduction
                         IBOC injection:           -10 dBc
                         Transmitter:              20 kW
                         Output Power:             15.0 kW
                         Peak to Average (PAPR):   2.7 dB
                         DC-RF Efficiency:         60.9%
                         Data MER:                 16.4 dB
                         Coverage Reduction:        0.28 dB

                         Compared to exgine signal:
                         • slightly lower MER
 Nautel HD Power Boost
                         • 1.3 dB better PAPR (30% more power)
 hard peak reduction
  Summary
•IBOC quality metric has been detailed
•All constellation plots shown were measured on real transmitters
   – signal captured with real time spectrum analyzer
   – IBOC quality computed in Matlab®
•Acceptable IBOC quality limits have been defined
   – impact on coverage is not significant with currently broadcast signals
•IBOC Quality can be affected by
   –FM overmodulation, clock stability, peak reduction
•Nautel’s HD Power Boost technology has been demonstrated to meet
 the setout IBOC quality standard
   –HD Power Boost can create signals with 6 dB better IBOC quality
   –HD Power Boost can create signals with 1.3 dB lower peaks
Thank You

				
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posted:2/22/2011
language:English
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