TBSDTV Community Forum

On May 12, 2024, China's first official satellite 8K UHD TV channel "CCTV-8K UHD" launched for testing.

The channel uses 128 Mbps MPEG-2 TS transmission on ChinaSat 9B (101.4°E), transport carrier is 12170 L 51400, modulation is DVB-S2 5/6 8-PSK.

Video coding is AVS3 HLG, audio coding is 2CH MPEG-1.

Code: Select All Code

  Program 711
    Metadata:
      service_name    : CCTV-8K-S
      service_provider: CCTV
  Stream #0:0[0x200]: Video: avs3 ([212][0][0][0] / 0x00D4), yuv420p10le(bt2020nc/bt2020/arib-std-b67), 7680x4320, 50 fps, 50 tbr, 90k tbn
  Stream #0:1[0x28a](eng): Audio: mp2 ([3][0][0][0] / 0x0003), 48000 Hz, stereo, fltp, 256 kb/s

Since the channel adopts very high bitrates and symbol rates, many satellite receivers and software may not work properly.

This will exceed allowed transfer rate probably on all USB2 devices.
Time to migrate to USB3

DVB Wrote:This will exceed allowed transfer rate probably on all USB2 devices.
Time to migrate to USB3

Your statement is absolutely correct. When TBS5520SE (USB card) is used to receive the channel, the tuner shows that the signal reception is OK, but BDA receiving data rate is less than 100 Mbps (while the channel requires 128 Mbps data bandwidth). And the received portion contains large amount of bit errors. However, TBS6522 (PCI-e card) is fine with this channel.

USB2 supports speeds up to 480 Mbps, but the HW solution of the USB interface TBS (Cypress) is limited to 111.6 Mbps

Unfortunately reaching 480 Mbps on USB2 is never possible, because everything relies on a multiple bottlenecks of the standard, like half duplex, wasted space due to a need to fill up packets with stuffing bits, overheads of protocol and payload sizes.

At the end of the day realistic seems to be 280 Mbps of netto transfer (real data without protocol overheads), but... when dealing with Transport Streams another bottleneck comes out - TS packet size is fixed to 188 bytes. So additional overhead comes out from a need of splicing them and keep in sync. I wouldn't be surprised if that ~120 Mbps limit is not anything related to a faulty implementation, but a result of unavoidable tradeoffs when processing this kind of data... Although I would be happy to hear some specialist comment on this field

Transfer limitation can be seen e.g. on USB3 SSD disks - connecting it to USB2 only controller also won't give 480 Mbps, despite that on USB3 the same device easily exceeds that transfer speed.

Anyhow I also recall discussion (I think) with steven, who pointed out that there's no ready USB3 bridge solution for DVB TS processing (no USB3 DVB card exists, even Dektec having USB3 device is not pushing DVB-TS through it, it's a SDR device type), so this would bring a lot of work to prepare a device basically from the scratch (and later need to probably fix some issues that will originate only from the fact that this would be a completely new implementation, e.g. surely we would like to have i2c access like today to run blindscan etc.). Usage of Cypress EZ-USB FX2 guarantees good TTM.

But I do believe that sooner or later migration to some new USB3 controller will be needed.
E.g. DVB-S2X/64APSK with SR 107140 (like SR used on 15°W) would kill even 480 Mbps

So we had:
TBS5925 - profi
TBS5927 - profi
It's about a time for TBS5929! (with USB3, DVB-S2X up to 256APSK, short frames support, blindscan etc.) I'm buying first one made