Sunday 21 August 2016

China Goes For Its Own Digital Radio Standard

New digital radio standard CDR soon available in 560 cities in China
China digital radio broadcasting in FM band - CDR - is a standard for terrestrial radio that operates in the FM band (87 MHz to 108 MHz).  CDR is operational since November 2013 by the authority of State Administration of Press, Publication, Radio, Film and Television of the People’s Republic of China (SAPPRFT). Three trial networks are presently on air in Beijing, Guangzhou and Shenzhen, By the end of 2016, CDR broadcasts will be available in more than 560 cities.

CDR is a type of In-Band On-Channel (IBOC) 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. Current IBOC systems include HD Radio, FMeXtra, CAM-D and DRM. But it is not convertable with DAB.

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.

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 the main FEC. According to SAPPRFT this 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 key characteristics of FM, HD Radio, China Digital Radio, DRM+, DAB+ and DVB-T2 Lite
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. 

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 nominal features.

According to Chinese 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.” 

According to SAPPRFT 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.

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