How to receive DVB-S digital video transmissions from the International Space Station with a bit of hardware and a lot of software.

2. Objectives One goal of the present project is to significantly reduce costs and other barriers to entry. [IZ8YRR] already showed that interesting experiments can be performed with a small 12 dB fixed antenna. Another goal is to explore the benefits of software-defined radio (SDR). Many DATV experiments are already conducted with software-defined DVB modulators, but the receive side usually consists of black-box demodulators embedded in PCI cards, USB dongles or standalone set-top-boxes ([N6GHZ]). Open-source software-defined receivers are a good introduction to modern signal processing techniques, offer more flexibility in demodulation strategies, and achieve independence from the product life cycle of specific off-the-shelf components.

6. Real-time software demodulation Textbook DVB-S demodulation techniques, as implemented in gr-dvb, are CPU-intensive. I wrote a simpler demodulator which trades sensitivity for real-time performance on low-power hardware: see [LEANDVB].

7. Off-the-shelf DVB-S demodulators The high latency and/or power requirements of software-defined demodulators make them unsuitable for some applications. Therefore, I also investigated dedicated DVB-S receivers. The evaluation criteria are: Support for low symbol rates (down to 1.3 Msymbols/s)

Ability to tolerate large frequency offsets from low-cost downconverters

Behaviour at low SNR

Ability to parse the Transport Stream of the ISS (which is not formatted exactly like mainstream DVB-S broadcasts). Since the ISS is in direct line of sight for only a few minutes per day, it would have been impractical to experiment with the live signal. Instead, I connected the devices under test to a USRP with RFX2400 daughter board, and I played back a 4 MS/s recording on 2395 MHz. I also connected the RTL-SDR dongle in parallel for troubleshooting. This confirmed that the L.O. of the 3650 MHz downconverter is not very reliable. 7.1. STV6110A / STV0903B These chips are found in the TechnoTrend S2 1600, a PCI DVB-S receiver that is popular in the DATV community (at least on Windows). With custom programming, this card can reportedly tune up to 2600 MHz, i.e. it should be able to receive DATV from the ISS without a downconverter, assuming an antenna with sufficient gain. 7.2. STB6100 / STB0899 These chips are found in the TechnoTrend S2 3200, another popular PCI receiver for DATV. According to the manufacturer they are being EOL'ed. 7.3. M88TS2022 / M88DS3103



DVBSky S960



DVBSky S960



DVBSky S960

Affiliate links These chips are found in low-cost USB receivers. I tested the DVBSky S960DVBSky S960DVBSky S960DVBSky S960. Create iss.conf with a virtual transponder at 11.255 GHz: [ISS] SERVICE_ID = 2395 VIDEO_PID = 256 AUDIO_PID = 257 DELIVERY_SYSTEM = DVBS FREQUENCY = 11255000 SYMBOL_RATE = 2000000 INNER_FEC = 1/2 POLARIZATION = VERTICAL MODULATION = QPSK INVERSION = AUTO Tell dvbv5-scan we have a "standard" LNB, which implies a L.O. of 10.000 GHz. The dongle will actually tune to 1255 MHz, which is 2395 MHz downconverted by the BT-480. # dvbv5-scan -l STANDARD -v -T 100 iss.conf ERROR command BANDWIDTH_HZ (5) not found during retrieve ERROR command MODULATION (4) not found during store ... (0x00) Signal= 100.00% C/N= 0.00% postBER= 0 (0x00) Signal= 100.00% C/N= 0.00% postBER= 0 (0x00) Signal= 100.00% C/N= 0.13% postBER= 0 (0x00) Signal= 100.00% C/N= 0.11% postBER= 0 Lock (0x1f) Signal= 100.00% C/N= 0.12% postBER= 0 A signal is detected but the channel scan fails because the ISS stream does not contain Program Map Tables, unlike commercial satellite TV broadcasts. Since we specified the PIDs manually we can retrieve the MPEG Transport Stream anyway: # dvbv5-zap -l STANDARD -c iss.conf ISS -r using demux '/dev/dvb/adapter0/demux0' reading channels from file 'iss.chan' ERROR command MODULATION (4) not found during store tuning to 11255000 Hz video pid 256 dvb_set_pesfilter 256 audio pid 257 dvb_set_pesfilter 257 ... (0x00) Signal= 100.00% C/N= 0.22% postBER= 0 (0x00) Signal= 100.00% C/N= 0.13% postBER= 0 (0x00) Signal= 100.00% C/N= 0.15% postBER= 0 DVR interface '/dev/dvb/adapter0/dvr0' can now be opened # hexdump -C /dev/dvb/adapter0/dvr0

8. Manual antenna pointing As an intermediate step between fixed antennas and fully-automated Az/El rotators, it is possible to point a dish manually by equipping it with a smartphone running an "augmented reality sky" app. These apps use the GPS, magnetic and inertial sensors found in modern smartphones, together with orbital parameters downloaded from online sources, to visually guide the user toward any satellite. See [HAMPADS]. Figure 7. Shoulder-mounted dish and tracker



10. Miscellaneous notes Recent digital satellite television standards, such as DVB-S2 and H.264, can transmit HD video. By contrast, ISS DATV uses DVB-S and MPEG-2 (which were designed around 1995) and a low bitrate. On the one hand, video quality might turn out to be disappointing (lower than DVD quality). On the other hand, all relevant patents have expired or will expire shortly in most countries.

11. Acknowledgements Thanks to Edmund Tse for publishing the source code and technical report for his DVB project. Anyone who has implemented ETSI standards from scratch can appreciate the effort that went into it. Tonino Giagnacovo IZ8YRR and Fabrice Bellard helped validate the receive chain.