LAS VEGAS — China digital radio broadcasting in
FM band, commonly referred to as CDR, is a digital radio broadcasting standard
that operates in the FM band (87 MHz to 108 MHz). CDR is a type of In-Band
On-Channel system that works in the FM band.
IBOC is a hybrid method for
simultaneously broadcasting digital radio and analog radio in the same
frequency band by placing additional digital subcarriers in the sidebands of
the AM or FM channel.
chart highlights the key characteristics of FM,
Radio, DRM+ and DAB+.
on the Image to
Current IBOC systems include HD Radio, FMeXtra, CAM-D
The CDR standard, operational since November 2013, is
labeled as GY/T 268.1-2013 and was published by the authority State
Administration of Press, Publication, Radio, Film and Television of the People’s
Republic of China (SAPPRFT).
At the spring NAB Show SAPPRFT’s Director of the
Academy of Broadcasting Science, Peng Gao, held a session focusing on the
background of the CDR Project and the general state of digital radio
broadcasting in China.
Gao explained that in 2011,
the Chinese Academy of Broadcasting Science, TiMi Tech and various broadcasters
began working on the CDR research project, carrying out lab and field tests and
drafting the standard.
of the Academy of
Science at SAPPRFT, speaks
the spring NAB Show.
CDR’s key features include flexible spectrum
utilization modes and the capability to fit both FM and AM broadcasts. As
regards to error-correction, CDR developers decided to use LDPC algorithms as
main FEC. This, says Gao,
proves more powerful than other FEC system currently used in other digital
radio standards. Audio compression is based on the Chinese DRA coding scheme.
In the FM band, CDR transmission modes are based on
100 kHz sub-bands, and a single broadcast can span over 200 to 800 kHz. The
simulcasting of analog FM and digital signals requires a 400 kHz channel.
Digital-only broadcasts require a minimum of 200 kHz to 800 kHz.
The CDR system makes use of the OFDM modulation and
includes QPSK, 16-QAM and 64-QAM modulation levels along with four LDPC code rates
— 1/4, 1/3, 1/2 and 3/4.
CDR defines three possible OFDM transmission modes:
Mode 1 for large area SFN operation; Mode 2 for high-speed mobility; and Mode 3
for higher data rates at the expense of a shorter cyclic prefix, suitable for
Depending on the LDPC code
rate and the adopted transmission mode, net bitrate ranges from 36 to 356.4
kbps per each 100 kHz sub-band, with a maximum spectrum efficiency of 3.56
bit/Hertz. A single 200 kHz channel can then carry a useful bit rate ranging
from 72 to 712.8 kbps.
Guidelines of the China Digital Radio standard.
“According to our studies, CDR
requests a minimum C/N ratio, which is about 2 dB lower than the C/N required
by DRM systems under comparable receiving conditions,” said Gao.
“This is also due to the efficiency
of LDPC error correction algorithms,” he specified. Gao illustrated how under
typical AWGN conditions CDR (FM) requires a minimum C/N equal to -0,57 dB,
while DRM requires 1.3. In SFN operation, CDR minimum C/N is equal to 3.66,
while DRM 5.4.
Audio compression in CDR adopts the latest version of
the Chinese-built DRA+ codec, recently enhanced with Spectral Band Replication
and parametric stereo technologies, thus matching the AAC+ v2 codec in terms of
Gao unveiled how, according to their experience, DRA+
at 24 kbps features a sound quality “near FM,” while at 48 kbps sound quality
is “better than FM” and at 64 kbps with 22 kHz bandwidth sound quality is “comparable to MP3 128 kbps.”
China Digital Radio coverage in Beijing along main roadways.
“Three trial networks are presently on air in
Beijing, Guangzhou and Shenzhen,” Gao said. “And by the end of 2016, CDR
broadcasts will be available in more than 560 cities.” The expected coverage at
that time will span from the southern to eastern regions of China.
The Academy of Broadcasting Science ran comprehensive
test and measurement sessions on the three networks, both static and “en
roulant,” which Gao said confirmed the standard’s “excellent” QoS.
On the receiver side, Gao presented the latest
generation of silicon chipset, with a footprint comparable to the smallest coin
available in China, and commercial receivers are now available on the market
from leading manufacturers. Portable receivers feature a single-board layout,
with onboard SoC chipset, SD card reader and USB ports. The form factor is
comparable to same-class analog receivers
With a potential market of more than 1 billion people,
and a substantial commitment by Chinese authorities toward digital radio, the
country may soon boast the highest number of digital radio listeners worldwide,
thanks to its own “home-grown” CDR digital solution.
Davide Moro reports on the industry for Radio World
from Bergamo, Italy.