Reflection on wireless usability in Feature/TV

  • 20 June 2018

Wireless Solution recently participated at the Cinegear Expo, a fair dedicated to motion picture and TV manufacturers, from lighting, grip, sound, special effects, and many others. W-DMX™ exhibited with TMB, their exclusive partner in the United States.

It has been acknowledged that Wireless Solution has a modest presence in this industry, due to the proximity of successful wireless champions with manufacturers located in Burbank. However, it has presence that has existed nonetheless since W-DMX’s very beginnings, through the early adoption by Hollywood’s A-list gaffers like Joshua Thatcher and Jason McKinnon, along with trendsetting investments from companies like MACCAM and Cinelease.

As wireless technology improved and increased in every market, the motion picture sector has been suffering the most due to its exponential adoption by the many departments on a film set: from sound, with wireless intercoms, to video – with devices like Teradek video transmitters, and lighting, with companies like ARRI and KINO FLO adopting Wireless DMX receivers built-in their own fixtures. And without coordination between departments, this means that devices have to fight between themselves to allocate a channel in the busy spectrum.

On the first day of Cinegear, this all came clear to our team, who hear about these problems every other week. There were countless companies exhibiting products with some sort of wireless technology: from HD video transmitters, follow focus devices, intercoms, wireless interfaces for iPad control, and so on.

But first, let’s recap how wireless works: there are 13 channels in the 2.4 GHz spectrum – typically, Wi-Fi uses channels 1, 6 and 11, because these channels do not overlap:

non overlapping

 

You can easily identity these channels after doing a spectrum analysis:

Screen Shot 2018-06-26 at 08.30.59

We decided to take a Metageek Wi-Spy analyser – a tool we frequently use to measure the wireless usage in different venues – and read out spectrum around wireless manufacturer’s stands. This test was done in both 2.4 GHz and 5 GHz between 15:50 and 18:00 during the first day of the show (Friday), with a 5dBi omni-directional antenna plugged to the Wi-Spy device. There was an error during two of the readings, where the software was not updating its data correctly, and unfortunately that was only spotted after the show had come to an end. Those errors will be reported ahead.

The first reading was taken at TMB’s booth, in the b-tank, where some 20 manufacturers were exhibiting inside the marquee. We should highlight that no W-DMX™ device was on any point of the show.

Image 1

The picture above (a measurement on 2.4 GHz) shows what you would expect from an environment with several wi-fi networks: there is a great amount of traffic on channels 1, 6 and 11, but there seems to be space available in the adjacent channels.

However, we were next to CINEGEARS’ Ghosteye, who seems to be transmitting around 5.2 GHz. When we asked them which specific frequency there were using, no one seemed to be able to tell more than “5 Gig”. We asked for a more specific answer, but they weren’t able to give one:

Image 2

There was also a spike between 5.3 and 5.4 GHz, and some intermittent signal in 5.8 GHz. As we approached their booth with the laptop, the above started happening:

Image 4

After measuring next to Astera, we concluded that the company was clearly (and rightly so!) masking most channels and selecting their transmission on channels 9 and 13 – this clearly benefited them, as the spectrum, in b-tank, was clearly very busy in the normal wi-fi channels:

Image 1

Our next visit was to Ratpac and ARRI, two stands that were side-by-side, with several wireless devices co-existing in the same frequency spectrum. This was the analysis right between ARRI, LiteGear and RAPTAC’s booths:

Image 5

The 5 GHz analysis was quite interesting too – bearing in mind that ARRI now produces video transmitters embedded in their cameras, we could easily read out frequencies in that same spectrum. In the same hall (Stage 18), there were also companies exhibiting with video transmitters, such as DJI, Atomos, and perhaps Sony and Panasonic.

Image 6

As we got closer to DJI, we got a clearer idea of what frequencies in the 5 GHz spectrum were being used. Unfortunately, it was at this point where we failed to refresh the readings in 2.4 GHz, so the screenshot that we got in that frequency was the same than the previous reading. Nevertheless, we got a better idea of the frequency usage in the higher band:

Image 7

At the time of writing of this article, the DJI Mavic Air drone claims to transmit of both 2.4 and 5.8 GHz – the reading above with fair utilisation of 5.8 GHz may be related to that.

In Stage 17, where companies like RED Digital Cinema, ETC, Cineo, A.C. Lighting, Ikan and others were, we had mixed measurements depending of the area of the building. Once again, our measurement in 2.4 GHz was stuck in a similar fashion than before:

Image 9

However, the readings in 5 GHz were mixed. Here’s next to RED Digital Cinema:

Image 8

RED doesn’t actually have a video transmitter, but they were using a third-party device.

And next to IKAN:

Image 10

Now – this is where this were getting interesting! As we walked towards New York Street exhibits (where all the booths are outdoor, in the iconic Paramount NY St lot), we found Teradek, Swit Electronics and Crystal Video (CVW) [all manufacturers of video transmitters]. After having done an analysis right next to Teradek on 5 GHz, this was the result:

Image 11

And right next to CVW:

Image 12

And next to Boxx TV (video transmitters again!):

Image 13

We also visited Kino Flo – they were also in NY St, but inside one of the ‘buildings’ – it was a ‘shop’ used as a film set, it’s worth mentioning that,  because it’s indoors, it’s likely to have less noise from other wireless devices, but at the same time subject to a lot of reflections from the waves bouncing off the walls. The result was more positive than expected, however, for a small room with only one manufacturer with wireless, the noise level was very high:

Image 15

For those who like cool and unusual camera rigs, the next one was interesting to read. We went next to DEFY (or Defy Products), a wire suspended camera right controlled wirelessly. The reading was also only done on 5 GHz:

Image 16

Back to B-Tank, but outside the tent, we got next to CINEGEARS’ Ghosteye again:

Image 17

Finally, we measured Transvideo’s equipment (more video transmitters), on both 2.4 GHz and 5 GHz. It is to note that the measurement may be high on some frequencies in 2.4 GHz due to the venue’s Wi-Fi devices, but also traces of what looks like follow focus devices. None of the manufacturers gave specific indication of what frequencies they use:

Image 18

Here, still next to Transvideo, we can see an increase of signal strength between 5.3 and 5.4 GHz. If you compare with the reading of CINEGEARS’ transmitter, it looks that the previous works on 5.1/5.2 GHz, whereas this one is between 5.3/5.4 GHz:

Image 19

In conclusion – as the need for wireless devices increases, it’s important to understand exactly what frequencies are being used by each equipment – no matter how good the frequency/cognitive hopping may be, if you have several devices compete for the same frequency usage, no device will work properly.

The advantage of W-DMX™ G5 is the possibility to use three different frequencies – 2.4, 5.2 and 5.8 GHz. No matter how many devices there are on set, you always have the possibility to change to a higher frequency in less than 20 seconds. As shown above, manufacturers of video transmitters tend to keep information regarding their specific frequencies, as they are also not compatible with each other, just like in the Wireless DMX world. The different here is that W-DMX™ uses the entire frequency spectrum (per frequency band), unless you create a frequency mask with our Co-Existence dongle: masking is advantageous if you know your environment, and know that is not subject to change. If it’s a volatile environment like an open-air event like a festival or a temporary, large-scale corporate event, then you should leave the Adaptive Frequency Hopping feature find its best transmission channel.

Furthermore, as noticed above, we’re more likely to have available space on the 5 GHz spectrum, rather than on 2.4 GHz – this is because most wireless devices co-exist in the free 2.4 GHz. For manufacturers, it’s cheaper to create a wireless device on the 2.4 GHz instead of any other band – meaning that *anything* can come up in that frequency spectrum – examples of that are Wi-Fi devices, Intercom systems, follow focus, wireless dimmers, battery-lights, among many others.

For more information about frequency masking and solutions for your specific project, you can reach out to us at helpdesk@wirelessdmx.com.