Wireless M-Bus Technology Overview
Wireless M-Bus in Industrial Wireless Sensor Networks
Wireless M-Bus was originally defined for Smart Metering (i.e., Meter-Bus), but it’s also the ideal solution for Industrial Wireless Sensor Networks (IWSNs). That’s because Wireless M-Bus has been developed and proven over many years for Smart Metering applications — applications that share many of the fundamental challenges faced by IWSNs.
Benefits of Wireless M-Bus
Using Wirelss M-Bus for your network can be a simple task, or a complex mission, depending on what features you intend to use. Note that also non complex set-up will take benefit of the build in robustness, power efficiency and security in the protocol.
Radiocrafts has developed a document that serves as a simple way of designing and setting up the network, without having a deep understanding of all the features and option that comes with the standard.
This is Wireless M-Bus
Wireless M-Bus is designed to be a robust, power efficient, long range wireless communication solution that operates in the license-free ISM bands. The Wireless M-Bus standard was first published in 2003 and has since been improved based on feedback from several thousands of field installations in very harsh environments — after all, many water and gas meters are located below ground level, in remote basements, sheds, or culverts.
The dialects (see below) and modes used in automatic meter reading (AMR) applications are set by the utility company and driven by their requirements. An AMR device manufacturer needs to understand what has been mandated by the utility so they can design products that will be compatible to the utility’s network needs.
For industrial WSN applications that are proprietary in nature, the dialect and mode can be chosen based on achieving optimum performance, while leveraging the built-in effectiveness, robustness, and security of the Wireless M-Bus standard. Radiocrafts can provide recommendations on what to choose based on the desired performance.
Wireless M-Bus Protocol description
- Star network configuration with optional repeaters
- Lightweight protocol for low cost and low power dissipation
- Support for uni-directional or bi-directional communication
- 868MHZ, 433MHz or 169MHz frequency options
- Support for AES-128 encryption and authentication
- Operating on license-free ISM bands
- Provision for indication alarms and faults
- Data rate from 2.4 kbps up to 100 kbps depending on the mode and frequency (see table below)
- Practical range of 500 m @ 868MHz and 2000 m at 169 MHz (simulation from Marche Polytechnical University, Ancona, Italy ) (see table below)
- Supports long battery life, 15-20 years in field-proven applications
- Physical and MAC layer plus framework for the application layer defined by the EN 13757 standard (more details below)
- Application layer details defined by the OMS (Open Metering Systems Group) for mainstream uses (more details below)
- Two optional dialects for special use cases: GrDF and CIG (more details below)
The Wireless M-Bus standard application layer provides for sending any sensor data, not just metering data, from the device to the collector using the descriptor DIF and VIF and the actual data in encrypted format.
The Wireless M-Bus standard & the rise of “dialects”
CEN/TC (Technical Committee) 294 is responsible for developing and publishing the European EN 13757 standard, which describes the complete M-Bus protocol. EN 13757 has six parts, including EN 13757-4 which includes the Wireless M-Bus specifications for radio-based communications between utility meters and concentrators or smart meter gateways:
- EN 13757-1: Basic data communication between meters and collectors
- EN 13757-2: Physical layer requirements for wired M-Bus
- EN 13757-3: Application Layer
- EN 13757-4: Physical and Data Link layers for the Wireless M-Bus
- EN 13757-5: Relaying and routing for range enhancements.
- EN 13757-6: Local Wireless M-Bus for short distance wired links
EN 13757 is a very flexible and open specification, where some parts are not described in detail or left for future implementation. This has lead to the need to develop further definitions which, in turn, drives the need for “dialects” to have a full specification to ensure compatibility between devices from different suppliers.
The full, current EN 13757 standards are available on-line from http://shop.bsigroup.com/SearchResults/?q=EN13757
Radiocrafts supports common Wireless M-Bus dialects & sensor integration
Radiocrafts Wireless M-Bus modules support the commonly used dialects and modes as described above, operating as complete modems, both on the device and collector side. Radiocrafts also has Wireless M-Bus modules with integrated sensor interfaces to further speed sensor integration and lower the costs for the customer. The modules comply to the OMS specification and the regional requirements in France (GrDF), Italy (CIG), and Holland (DSMR).
Radiocrafts Wireless M-Bus Module Series
- RC11xx – MBUS3, Supports 433/865/868/915 MHz in a Low Cost (10dBm) version
- RC17xx – MBUS4, Supports N-mode 169 MHz in a High Power (27dBm) and a Very High Power (30dBm) version
- RC1xxx- MPC, includes an integrated pulse counter
- RC1xxx-MSM, includes sensor interfaces
The Wireless M-Bus modes & their uses
The Wireless M-Bus defines a number of modes that are targeted for various uses. The most used modes today are the S, T, C and N modes, which are shown below. Also defined in the EN 13757 standard are the R, Q, P and F modes, but they are rarely or never used, so they are not within the scope of this summary. The defined frequencies are 868MHz and 169MHz, as well as 433MHz which is intended for markets where 868MHz is not allowed.
|Mode||Frequency||Uni-/ bidirectional||Description of Use|
|S1, Stationary||868.3 MHz
|Uni||Send data a few times per day. Optimized for battery operation and stationary operation. 32.7 kbps|
|S1-m, Stationary?||868.3 MHz
|Uni||Same as S1, but optimized for mobile receiver|
|S2, Stationary||868.3 MHz
|Bi||Same as S1, but bidirectional communication|
|T1, Frequent transmit||868.95 MHz
|Uni||Send data every few seconds. Configurable interval. 100 kbps
|T2, Frequent transmit||868.95 MHz
|Bi||Same as T2 (T1?), but bidirectional operation|
|C1, Compact||868.95 MHz
|Uni||Unidirectional communication using NRZ coding. Similar to T1 but higher data-rate, 50 kbps. Stationary operation|
|C2, Compact||868.95 MHz
|Bi||Same as C1, but bidirectional operation|
|N1a-f, Narrowband||169 MHz @12.5 kHz||Uni||Unidirectional, 4.8 kbps, stationary operation|
|N2a-f, Narrowband||169 MHz @12.5 kHz||Bi||Same as N1a-f, but bidirectional operation|
|N1g, Narrowband||169 MHz @50 kHz||Uni||Unidirectional, 19.2 kbps, stationary operation|
|N2g, Narrowband||169 MHz @50 kHz||Bi||Same as N1g, but bidirectional operation|
The Data rates for wireless M-Bus modes
|Configuration||Frequency||Device (meter) node Tx||Collector node Tx||Uplink||Downlink|
|Device S1, S2 / Collector S1,S2||868/433||32.7 kbps Manch code||32.7 kbps Manch code||32.7 kbps||32.7 kbps|
|Device T1, T2 / Collector T1,T2||868/433||100 kbps, 3 out of 6||32.7 kbps Manch code||67 kbps||32.7 kbps|
|Device T1, T2 / Collector C1, C2||868/433||100 kbps, 3 out of 6||32.7 kbps Manch code||67 kbps||32.7 kbps|
|Device C1, C2 / Collector C1, C2||868/433||100 kbps, NRZ||50 kbps NRZ||100 kbps||50 kbps|
|Nc mode (Collector and device)||169||2.4 kbps, NRZ||2.4 kbps, NRZ||2.4 kbps||2.4 kbps|
|Na mode (Collector and device)||169||4.8 kbps, NRZ||4.8 kbps, NRZ||4.8 kbps||4.8 kbps|
|Ng mode (Collector and device)||169||19.2 kbps, NRZ||19.2 kbps, NRZ||19.2 kbps||19.2 kbps|
The Wireless M-Bus protocol stack
The EN 13757 protocol stack itself has three different layers: Application layer, Datalink layer and Physical layer. The relative simplicity of the stack makes it very energy and code efficient.
|Traditional OSI model||Wireless M-Bus stack|
|Application Layer||Application Layer|
|Transport Layer||Optionally used for advanced security|
|Data Link Layer||Data Link Layer|
|Physical Layer||Physical Layer|
The Wireless M-Bus dialects for specific requirements
Even if Wireless M-Bus is a standard, there is room for “dialects” of the standard. Dialects have been developed, or are being developed, to meet various regional requirements. If you’re designing a device that needs to be compatible with devices from other suppliers, then understanding the dialects is important. If you are designing an industrial WSN that will not communicate with devices from other suppliers, then you can view the dialects as best practices that can be used or not used as you decide.
The dialects can be classified in three different groups.
1. Adoption or restriction of the Application layer.
Examples of this is the work done by Open Metering Systems Group (OMS) http://oms-group.org and the Dutch Smart Metering Requirements (DSMR). Also, other application layers, not defined in the EN 13757-3, can be integrated, such as the Device Language Message Specification (DLMS) http://www.dlms.com/index2.php
2. The specification of all layers can be adapted.
3. Extension might be added for privacy and security.
This is the case for the work done by the German Federal Office for Information security (Bundesamt fur Sicherheit in der Informationstechnik, BSI) https://www.bsi.bund.de/DE/Home/home_node.html. The BSI has designed a protection Profile (PP) and a Technical Directive (TR) which partially refers to the secure LMN specification of the OMS group.