DVB-T2 Transmitter

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drmpeg
Posts: 62
Joined: Fri Mar 01, 2013 3:58 am
Location: Silicon Valley
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DVB-T2 Transmitter

Post by drmpeg » Sat Jan 03, 2015 4:57 pm

I've completed a DVB-T2 transmitter for GnuRadio and bladeRF. It's been fully tested with a PCTV 292e USB receiver.

https://github.com/drmpeg/gr-dvbt2

Features of interest:

1) T2-Lite mode. The T2-Lite mode allows both 1/3 and 2/5 code rates. With QPSK modulation, very low receive S/N ratios of just a few dB are possible.

2) 1.7 MHz bandwidth mode. The 1.7 MHz bandwidth mode is supported by DVB-T2 demodulators (including the Si2168 in the PCTV 292e). This mode is intended as a DAB replacement in L band.

3) PAPR reduction. A very useful feature since high PAPR seems to be the major complaint about OFDM. DVB-T2 provides two algorithms for PAPR reduction, Active Constellation Extension (ACE) and Tone Reservation (TR). The tone reservation method is fully implemented in gr-dvbt2. Unfortunately, it is very floating point intensive, and heavy reduction is not possible (in real-time) with the current implementation. However, it does work well with lighter levels of reduction. A perfect candidate for a GPU based heterogeneous computing setup.

4) MISO (Multiple Input Single Output) mode. Pretty advanced stuff, but can be implemented with a MISO/MIMO capable SDR like the Ettus B210 or a pair of slaved bladeRF's. One approach would be to use horizontal polarization for one transmitter output and vertical polarization for the other transmitter output. Implemented in gr-dvbt2, but would need a little more work to synchronize the two transmitters. All DVT-T2 receivers support MISO.

5) More capacity. The 256QAM mode provides high bitrates for those interested in HDTV. With the 32K/256QAM 2/3 rate mode in use by the BBC, the bitrates for each channel size are:

8 MHz = 40.2 Mbps
7 MHz = 35.2 Mbps
6 MHz = 30.1 Mbps

Up to 50 Mbps is possible in an 8 MHz channel with 5/6 code rate.

Here's the flow for Ofcom Mode 6 (44.8 Mbps in an 8 MHz channel) in gnuradio-companion.

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MISO flow.

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Spectrum at 7 MHz channel size.

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Ron

drmpeg
Posts: 62
Joined: Fri Mar 01, 2013 3:58 am
Location: Silicon Valley
Contact:

Re: DVB-T2 Transmitter

Post by drmpeg » Fri Feb 06, 2015 3:31 am

After being clued in by bpadalino about DAC zero-order hold distortion, I've added sin(x)/x equalization to gr-dvbt2.

http://www.maximintegrated.com/en/app-n ... vp/id/3853

The transmitted spectrum response is essentially flat now.

Image

Ron

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