ADVANCED-METERING-INFRASTRUCTRE (AMI) systems have enabled utility companies to more efficiently collect energy, gas, and water-consumption data. Eventually, these systems will allow consumers to monitor and control their own energy consumption in real time. Yet such capabilities will require interoperability between different manufacturers' systems. In Europe, the Wireless M-Bus protocol, which is now detailed in the European normative (EN) standard variant EN 13757-4, is increasingly preferred as the standard for communication between meters. In an eight-page application note titled, "Designing a Wireless Transceiver System to Meet the Wireless M-Bus Standard," Analog Devices' Austin Harney discusses the EN 13757-4 standard and the system requirements when using the firm's ADF7020 transceiver integrated circuit (IC) to design an M-Bus-compatible device.
Wireless M-Bus specifies three modes of operation all of which use subbands G1 and G2 in the ETSI 868.0-to-870.0-MHz general usage band. Stationary mode (Mode S) is intended for communications between stationary or mobile devices, where the data is transmitted only several times a day. In contrast, frequent transmit mode (Mode T) sends out data in chirps every few seconds. Frequent receive mode (Mode R) wakes up frequently to listen for messages from a mobile transceiver. Compared to Mode T, for example, this is typically a higher-power mode because the receiver must be on for a longer time to detect sufficient preamble bits. Although this aspect might make it difficult to design a multiyear battery-powered system, Mode R also is more narrowband. It allows as many as 10 channels for frequency division multiplexing (FDM), which allows the readout of several meters simultaneously.
The discussion of technical considerations for meeting the Wireless M-Bus standard centers on the ADF7020 or ADF7021 sub-gigahertz, low-power radio devices. The ADF7020 is suitable for operation in S, T, and R modes. Despite its relatively narrow bandwidth in R mode, the ADF7021 is a better choice for optimizing adjacent-channelrejection (ACR) performance.
Beyond the radio devices, the appropriate external crystal must be chosen to meet the Sand T-mode data rates of 32.768 and 100 kb/s, respectively. The ETSI emissions mask also must be considered, as M-Bus specifies frequency-shiftkeying (FSK) modulation instead of Gaussian FSK or raised cosine FSK. In doing so, it makes the ETSI modulation-bandwidth requirement more difficult to meet. That modulation bandwidth can be simulated, however, using the free ADI SDR Design Studio tool. The note also delves into frequency and chip-rate tolerance, receiver sensitivity requirements, and deviation tolerance.
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