Congestion in the unlicensed 2.4 GHz space causes integration firms headaches as more and more services are competing for wireless spectrum, Chris Fitzsimmons explores the possible solutions in the congress market.
The 2.4 GHz band has long been the bane of the installers existence. First of all it was the source of microphone RF interference. Mobile devices created that well known, but thankfully almost extinct buzzing sound. The microphone vendors overcame that problem with shielding technologies, and phone makers got better at making their electronics less noisy.
Then, congress system manufacturers sought to embrace the technology themselves, abandoning traditional infrared techniques to create a new generation of wireless enabled conference solutions. Compared with their IR based-brethren, they were capable of serving multiple rooms, didn’t need infrared line of sight from relays and were immune to interference from such evils as plasma displays, fluorescent lighting or even plain old fashioned daylight.
For the rental business this was a boon – it enabled them to build bigger systems wirelessly, with all the flexibility inherent in that technology. It also reduced SKU inventory requirements. But now, things are getting sticky again. The very thing that makes 2.4 GHz so attractive – its license free availability, means that everyone else wants to play there and the playground is getting crowded.
The proliferation of WiFi connections on devices such as laptops, tablet computers and mobile phones means that every hotel, conference venue and corporate facility in the region now boasts numerous wireless networks. There are networks for guests, for staff, for security systems, for individual boardrooms and the control system. And those are just in the customer’s building.
What happens if your proposed location is in a city centre, and shares a building with four other businesses all of whom have their own wireless networks in the adjacent floors? One integrator I recently spoke to remarked that the first piece of equipment out of his bag when performing a site survey these days is his mobile phone with a piece of wireless sniffing software on it.
What it usually tells him is that virtually all the WiFi channels (of which there are 13 available in Europe) are already occupied by something. The results of wireless congestion are as follows.
If two or more networks share the same WiFi channel, then they will be forced to share the available bandwidth, and generally the one with the most powerful transmitters wins the lions share.
This can therefore go one of two ways. Either your congress system suffers quality degradation due to interference from other sources or it causes degradation in other systems. Neither is an acceptable outcome for the client, so what’s the answer?
According to some vendors the problem has been over stated. James Wang, manager of the Gonsin’s foreign trade department says : “Sometimes the 2.4GHz congestion / interference problems may be overstated by suppliers. This might be because they are unable to offer wireless systems, or represent a manufacturer that only offers infrared technology.
“Gonsin chose to use Direct Sequence Spread Spectrum technology (DSSS) in the development of its new products.”
DSSS is an innovative solution to the problem of WiFi congestion, and is actually contained within the 802.11b specification, as well as being used by satellite navigation systems. A detailed explanation of how it works can easily be found on
wikipedia, but essentially the signal is scrambled into white noise by a particular factor, and then de-scrambled at the other end. The clever part is that the factor is unique to the signal so any other signals don’t interfere.
Beyerdynamic’s Matthias Holz believes the solution lies in better management of WLANs in general.
“As long as the set up is organised properly via frequency management, just like in a multi-channel wireless microphone system, there should be no problem with coexistence. In order to give additional reliability in wireless operation, we will definitely have to be aware of the proliferation of wireless frequency ranges in the future. The European Government will legislate to give different RF frequency ranges for different applications and manufacturers in different industries will have to evaluate which will be the best solution for their application.”
Brähler’s patented radio protocol APRON (intelligent Adaptive Proprietary Narrow Band Protocol) including FHSS (Frequency Hopping, Spread Spectrum) for Digimic wireless, ensures that transmission is even more robust to interference than that used by DSSS technology, says the company’s Gerhard Bauer.
Digimic wireless continuously checks the received data packets for transmission errors and avoids the exact frequency ranges where transmission errors occur.
Due to the different operation methods of APRON and DSSS for Digimic it is not directly possible to identify an existing Wi-Fi network and bypass. It does however indirectly determine the potential interference with WLAN and then bypasses the WLAN-range.
WLANs always use a fixed broadband channel. If this radio channel is known, DIGIMIC will skip that channel-area and use its own narrowband channel, instead the of using adaptive learning curves described above.
This more robust radio transmission method was chosen because an audio application like Digimic must always transmit the signals in real time.
Bosch offers the Next Generation wireless solution, which includes several features to alleviate the problem, according to the company’s Murat Keskinkilinc, product marketing manager for conference systems:
“First of all we don't use the full 2.4 Ghz frequency range, but we have three non overlapping carriers in DCN Wireless. This makes it possible for the installer to look at which wireless networks channels are not used (or are weak) in that area and choose one carrier in DCN that operates in that frequency range. Furthermore we have the possibility in DCN Wireless to increase the level of redundancy, which means that data packages are resent multiple times decreasing the chance that a package gets lost due to interference.”
Televic produce the Confidea system which is able to operate in both the 2.4 GHz and 5 GHz bands. The company’s Kristoff Henry commented:
“There is a huge difference in using 2.4 GHz to transfer data or using it to transport conference audio. When during data transmission the band gets congested during a transmission burst of several devices (WLAN, Bluetooth, …) a device will simply resend the lost IP packets and the user of the device will hardly notice anything. In audio conferencing any lost IP packet, or delayed packet immediately translates in disturbances in the audio. Buffering isn’t a solution either as this introduces inevitably a noticeable delay in the audio.
“You need to have at least some free space in the RF spectrum to set up a reliable connection. The required bandwidth for an audio conferencing system also means that in the 2.4Ghz band at most three systems can coexist: a problem when rooms are adjacent and there are already two wireless LAN’s in the air.
“In short: the 2.4GHz band should actually be avoided for conference systems. Our Confidea system is dual band and also uses the 5 GHz band. This band offers a lot more possibilities to ‘position’ a conference system (theoretically 22 additional channels in Europe).”
The other solution is not to use 2.4 GHz at all. Despite the drawbacks stated above, IR technology does offer some significant advantages. The most obvious is that it isn’t competing with anything that isn’t in the same room. The latest versions are also much more resistant to interference from sources such as plasma displays and lighting, although direct sunlight is still a problem.
Security is also a factor, particularly in government and corporate applications. The fact that IR doesn’t “leak” through walls makes it attractive in these situations. Ultimately, the requirement for wireless isn’t going to go away, far from it. Spaces are required for more than just conference use whether they are in local government, or boardrooms.
The challenge for the integrator is to deliver that flexibility with a technology that fits the bill.