Selective repeating and duty-cycle lock
May 16, 2014
EnOcean products for use in the European Union are certified according to the Radio and Telecommunications Terminal Equipment Directive (usually referred to as RTTE) which specifies applicable standards for radio devices. These applicable standards in turn define the required functional parameters of radio devices intended for use in the European Union.
Examples of such parameters include radiated output power, duty cycle and spurious emissions produced by radio transmitters. In the case of devices operating in the 868MHz band (e.g. EnOcean products for the European market) the duty cycle is limited to 1% based on a 60 minute rolling interval. Compliance with this requirement means that the total transmission time of an individual radio device may not exceed 36 seconds within any given 60 minute interval.
This duty cycle limitation is ensured by design and/or use case for all EnOcean sensors and switches.
For products such as gateways and repeaters however, the responsibility of ensuring compliance with this duty cycle limit rests with the customer. This is because the nature of the data traffic was specific for each customer and application and therefore unknown to EnOcean (e.g. a repeater will repeat only as much traffic there is, a gateway will only transmit so much data as it is commanded).
EnOcean was contacted by several customers that they would like EnOcean to provide a solution and help them fulfill the regulatories so they do not have to worry and track the radio load in their applications, which is also a challenging task when using a transparent gateway (e.g. TCM 310).
EnOcean developed a duty-cycle watcher in the Dolphin API. This watcher limits the transmission of telegrams beyond the defined 1 % boundary. It is also incorporated into standard product of Gateway Controller (aka TCM 310) and TCM 300 / TCM 320. Additionally customers can choose in project that they develop with the Dolphin API not to use the lock if they wish so.
Duty cycle watcher available in:
Dolphin API 18.104.22.168 upwards - only 868 MHz
Gateway Controller 22.214.171.124 and higher - only 868 MHz
TCM 300 126.96.36.199 - only 868 MHz
The EnOcean Duty cycle watcher implementation works as follows, the 60 minute regulatory interval is divided into n time slots of equal length. For each of these time slots, the total transmission time is then recorded. In addition to that, the transmission time in the current time slot is also recorded. New telegrams will only be transmitted if the total transmission time in the previous n time slots (representing a full 60 minute interval), the transmission time in the current time slot and the transmission time of the current telegram combined do not exceed the regulatory limit. For details how transmission time is counted please visit this page.
In the actual implementation, ten time slots per hour where chosen (n=10). This choice provides a good compromise between memory requirements and estimation accuracy. Compliance with the duty cycle limit of 1% will be guaranteed under all conditions by this implementation.
The required change will have two consequences:
- Functional changes due to ensured duty cycle compliance
For devices operating near or above the maximum permissible duty cycle, functional behavior will change since transmit packets will have to be dropped (= not transmitted). In all other cases there won’t be a functional difference. If transmission request is drooped an specif return code will inform the application about this fact.
- Change in the amount of available application memory.
The implementation of the required duty cycle supervision feature will require an additional 400 Bytes of program memory (Flash) and 30 Bytes of data memory (SRAM) for the firmware which won’t be available for applications anymore.
Repeaters are devices that do range extensions and are also obliged to fulfill the duty cycle regulation. If they reach the limit in working installation and stop repeating then there might be unpleased effects for the end customer. Therefore EnOcean would like to enable selective repeating to choose what telegrams are repeated and to decrease the amount of telegrams repeated and make the repeater more predictable on radio communication.
Selective repeating is enabled in the DolphinAPI by extending the existing filter interface. You can add filters and they will be applied during repeating. You can do selective repeating based on:
- Sender ID
- Destination ID
- dBm value
Similar to the existing filter interface a white list (e.g. select Sender IDs that are repeated, all others are NOT) or an black list (e.g. select Sender IDs that are NOT repeated, all others are) can be defined. With the current filter interface you can have separate list that applies for the get telegram interface and the repeater interface.
Selective repeating is also supported in the Gateway Controller firmware (aka TCM 310, USB 300). Please visit this page to get more information (repeating, filtering)
Selective repeating available in:
Dolphin API 188.8.131.52 upwards
Gateway Controller 184.108.40.206 and higher
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