Wireless: How does FreeSpeak II work and what is the basic technology

Can you provide the following general information and technical data (non-commercial sensitive) about:
- Definition of an DECT RF Space / coverage. When discussing number of antennas/BPs in an RF space are we referring to a basestation being an RF space or a number of antennas in range of one another being an RF space?
- Number of antennas and belt packs in a single RF Space.
- The structure of the RF architecture, beyond the information on bases having separate System IDs:
- How does FreeSpeak II manage its frequency hopping within the system range on a single system
- How does FreeSpeak II manage synchronization when multiple DECT systems are being used.
Please read reply below along with the Clear-Com white paper on our FSII 2.4 system 

Some basics to begin with DECT: is just like all other RF systems. For example you can have a radio station transmitting on 100MHz in London-UK and a totally different radio station transmitting on 100MHz in Bristol-UK and another one transmitting on 100MHz in Dublin-Ireland all 3 playing different music channels but not interfering with each other.  The most common application for DECT is your home digital cordless phone. However because DECT provides license free operation worldwide in most countries, nowadays most intercom manufacturers have a DECT wireless system that is part of their intercom system.

Timeslots and Channels

DECT generally operators in the 1.9GHz spectrum and is license free worldwide. There are 30 discrete RF channels allocated for DECT worldwide and depending on the region you are in you will either use 10 channels (EU, Australia, NZ, ME), 6 channels (JAP) or 5 channels (Americas).  Europe / UK uses 10 RF channels and each channel has 24 timeslots. These timeslots are allocated as 10 Transmit and 10 Receive with 4 time slots reserved for hand-overs. Each timeslot handles 1 audio connection. Therefore in theory you could have  10 x 10 = 100 DECT audio connections to devices in use at the same time in the same place in Europe.

 

For Clear-Com FSII we use 1 timeslot in each direction for the FreeSpeak II 1.9 BPs, therefore we use 10 x 10 = 100 BPs in use at the same time in the same place with a 7KHz audio codec using IP antennas (IPTs).

For the older Clear-Com FSBP or Cellcom or those based on the E1 Transceivers we use 2 timeslots for our 1.9 BPs, therefore we use 10 x 5 = 50 BPs in use at the same time in the same place with a 7KHz audio codec using the older E1 Antenna (E-Que or E-IPA E1 or FSII-BASE-II)

 

For RTS/Telex they claim to be able to use 1 or 2 timeslots for their BPs, 2 slots allows them to use a 7KHz audio codec , 1 slot allows them to use a 3KHz audio codec (giving them 50/100 users in the same place depending on codec selected)

For Riedel they claim to use 1 timeslot for their BPs, whilst using a 7KHz audio codec giving them 100 users in the same place. They use a similar codec as we use in our FSII 2.4 BPs

Note: For Clear-Com we can mix both 1.9 and 2.4 BPs on the same system allowing us to reach the same if not higher system densities in the RF zone.

 

RF Zone: Each antenna/ transceiver has a set RF Zone /coverage pattern and it can connect using any of the 10 channels with 10x timeslots. Therefore if you place 10 antenna/ transceivers  into the same area you could in theory connect 100 FS II beltpacks but this will use up all of your possible RF space. If you take into account possible system losses and co-channel interference you get a reduction in the theoretical limits and you will mostly have a real working system of approx. 90 BP roaming connections if using 1 timeslot system (FreeSpeak II and IP transceivers) or 40-45 BP roaming connections if using a 2 timeslot system (FSII and E1 Transceivers). Static (non-roaming) BP systems will use the full 100 or 50 beltpack capacities.

Note: All manufacturers are limited to using 10 antennas / transceivers in the same RF space. Having more antennas in the same RF space will not add to the real world number of BPs that can connect.

  1. It is very important to only use the real world figures of approx. 90/40 users max per RF zone when quoting / designing a ROAMING system.

  2. When testing a system try to hear how the system actually deals with handovers between the antennas/ transceivers are they silent and seamless or do you hear a pop (or some audio artefact) every time the BP switches RF channels or slots? See #3 below.

  3. For high capacity IPT systems to work it is essential to have a very stable and precise PTP clock. The Trilogy Mentor RG is a good choice here.

Clear-Com antennas/transceivers use a proprietary channel allocation protocol to allow for clean, silent and seamless handovers.

Now if we go back to the 3 radio stations all transmitting at 100MHz then we know that as long as there is a RF dead space between them, they will not interfere with each other and you can re-use the same 10 RF channels again and again. Same principle for DECT systems. If you max ;out the RF capacity of 100 BP connections then you will need a dead space between the next RF zone and your last RF zone.  

What happens if you have different DECT manufacturers in the same place? Different DECT systems are built to co-exist quite happily together. As long as there is room in the (10x RF channel) * (10x timeslot) grid for a connection to be made then you can have as many systems as possible working in the same area without having to frequency co-ordinate them. Again, like any other RF system if two transmitters transmit at the same time on the same frequency then you will get an RF clash. DECT is no different but the system will quickly recover and the customer may not hear any audio artefacts. With larger systems that employ multiple antennas, the antennas/ transceivers will drift over time in terms of when they start to transmit on the timeslot boundary. You can make them all drift at the same rate by using a DECT sync pulse. The use of the sync pulse will then allow the antennas/ transceivers to drift at the same rate and minimize RF clash. Clear-Com provides an external DECT in/out sync connector on our products to help synchronization of the DECT timeslots when used in the same RF zone as other manufacturer’s systems.

System Capacities

FreeSpeak II Base II (standalone basestation)
o  10 x E1 Antennas
o  25 Users

Arcadia Central Station

  • up to 16 IP Transceivers antennas per Arcadia

  • Or up to 10 E1 Transceivers per Arcadia

  • up to 40 Beltpacks per Arcadia.

  • up to 100 Beltpacks per single RF zone (using multiple Arcadias or mixing with other systems)

 

Eclipse-HX Matrix @ HX 12.2 or later

  • Using IP Transceiver Antennas:

  • up to 64 antennas per IPA card

  • up to 200 Beltpacks per matrix frame.

  • up to 100 Beltpacks per single RF zone

  • up to 200 active users per matrix assuming there are a number of separated RF zones created by the system.

 

Eclipse-HX Matrix @ HX 12.2 or later

  • Using E-IPA card in E1 mode or using legacy E-QUE card

  • 40 Antennas per matrix (10 per E-Que card)

  • 50 Users (in a single RF Space),

  • 200 across the whole matrix assuming there are a number of RF zones created by the system.  



 

 

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