1. European regulations for RF communications
The relevant norm for Sub-1GHz communications in Europe is the ETSI 300 220-1 V2.3.1 (February 2010). The established 868 and 433 MHz license-free ISM bands for metering applications were expanded with a 75kHz narrowband at 169.400MHz for meter reading applications. The maximum transmit power permitted is +500mW (equals +27dBm), the duty cycle is <=10%. The channel spacing is 50kHz or less; LBT (listen before talk) or AFA (adaptive frequency agility) channel access may be used, but both are not mandatory.
Obviously, having a +27dBm radiated power low-cost RF link at 169MHz will deliver a superior range coverage compared to the existing wM-Bus solutions with +25mW (equals +14dBm) at 868 MHz (see Figure 1
). Note that “old” T-mode and the “new” C-mode each use two different frequencies, one for the meter-to-data-collector direction and a second one for the link from the data-collector to the meter.
Click on image to enlarge.
Figure 1: WMBus modes S, T and C and ETSI 300220v2.3.1 relationship
Data collectors in T-mode transmit at 868.3MHz with maximum +14dBm and in C-mode with up to +27dBm at 869.525MHz.
The range of RF metering solutions is the biggest problem to solve when deploying smart meters in dense populated areas in Europe with multi-storey buildings and unfriendly RF environments with multiple concrete and brick walls between the different RF nodes. This turned out to be the main shortcoming of Zigbee®-based 2.4GHz solutions in the UK, where the existing ZigBee SE1.1 products failed to deliver enough range in urban areas. A new generation of wM-Bus-enabled smart meters at 169MHz is aimed at solving the range issue in countries like Italy or France.
The longer range of the 169MHz RF link simplifies the system architecture and reducing the total cost of the networks by avoiding repeaters and eliminating the repeating functionality in meters. Less functionality means lower Flash and RAM size requirements for the metering nodes as well as shorter product development and certification due to the lower software complexity.