NAB Engineers Focus on Asymmetric Sideband Report
recent technical study about asymmetric sideband technology is the subject of
discussion by NAB’s Radio TechCheck newsletter.
The study was about lab tests at iBiquity Digital, done with
funding from the NAB FASTROAD technology advocacy program. It was sent to the
FCC by iBiquity in support of a proposal toauthorize use of asymmetric sidebands.
FCC rules require equal-power sidebands; proponents would like the commission
to allow stations to hike power “unequally,” to improve coverage without
hurting first-adjacent signals on one side or the other.
As summarized by NAB, iBiquity wrote
about improvements in the peak-to-average power ratio reduction (PAPR)
algorithms involved in this approach, and discussed the results of a lab
evaluation of the expected improvement in digital signal-to-noise ratio. The
summary explains that the tests were performed using typical automotive HD
Radio receivers with HD Radio chipsets made by ST Micro, NXP and Texas
“Briefly, these tests established the
bit error rate (BER) performance of the receivers under test as a function of
digital SNR for various digital sideband configurations, both symmetric and
asymmetric,” NAB wrote.
It continued: “Shown in the table is
the increase in total digital power for various sideband configurations
compared to the legacy configuration (equal power sidebands, total digital
power of –20 dBc). Ideally, the improvement in digital SNR should track this
increase in digital power so that, for example, in the case where the LSB and
USB powers are set to –23 and –17 dBc, respectively (first row in table), and
the total increased digital power is 3.96 dB, the expected improvement in
digital SNR would also be 3.96 dB.”
An example of lab test
results is shown, for a case with no interfering adjacent channel. “Each group
of columns in the figure corresponds to one of the configurations shown in the
table. The measured values indicate the improvement in digital SNR (in dB above
the –20 dBc symmetric reference case) at which a BER of 5x10was achieved.”
NAB wrote that in the
symmetric cases (–17/–17 and –13/–13), the expected performance, shown in black
columns, and observed performance are virtually identical, as was also true
with a 4 dB asymmetry (–17/–13).
“However, the cases
with greater asymmetry demonstrate a shortfall over the expected performance.
For the first case (–23 /–17), the expected digital SNR improvement is 3.96 dB,
however the measured improvement for each receiver was only about 3 dB (a 1 dB
shortfall), and similarly for the third case (–23 / –13) where a 2 dB shortfall
is measured.” IBiquity, NAB summarized, believes that this shortfall is due to
coding losses that are brought about by the extreme asymmetry in these received
The full report is available at www.nabfastroad.org