How to add the right radio communications solution to your product design

Radio communications and wireless technology significantly boost IoT performance and functionality because they allow IoT devices to be placed in locations inaccessible to cables or wires.

This is critical for mobile applications from smart watches and phones, through warehouse robots, to vehicles of all types, but it equally allows IoT solutions for a wider range of fixed applications, including remote monitoring and control systems.

However, adding wireless connectivity to an OEM product is not straightforward, because there are so many factors involved. Although the situation can be mitigated by buying in ready-to-use radio modules and antennas, decisions must still be made about the radio technology to be used, and assembling a matched configuration of modules, antennas, software and firmware – as well as on choosing the supplier that can best integrate all these components into an efficient, reliable, and adequately certified solution.

This article shows how Würth Elektronik has developed an ecosphere of radio modules with support products and services, which allows engineers to rapidly add radio capability to their products, or change to a different radio protocol, using a simple plug ‘n’ play approach.

We start with a brief overview of radio communications fundamentals, and then of practical considerations, including modular approach advantages, range estimation, and meeting global certification requirements.

Then we review some of the most popular radio protocols, and the Würth Elektronik radio module solutions available for each.

Fundamentals of radio communication

There are five main key facts for consideration:

1. Signal Transmission
2. Link Budget
3. Duty Cycle
4. Access
5. Integration of Radio Technology

• Signal transmission: For transmission, the signal modulates either the amplitude or the frequency of a (mostly) sinusoidal, constant amplitude carrier wave. The modulated wave is radiated by an antenna and detected by a receiving antenna. The signal can be extracted by demodulation in the receiver.

• Link budget: A link budget is an account of all the power gains and losses that a communication signal experiences in a telecommunication system; from a transmitter, through a medium (free space, cable, waveguide, fibre, etc.) to the receiver. It is an equation giving the received power from the transmitter power, after the attenuation of the transmitted signal due to propagation, as well as the antenna gains and feedline and other losses and amplifications of the signal in the receiver or any repeaters it passes through.

  

  Figure 1: Link budget illustration

• Duty cycle: A duty cycle or power cycle is the fraction of one period in which a signal or system is active. Duty cycle is commonly expressed as a percentage or ratio.

• Polite Spectrum Access - listen before talking: When an application uses polite spectrum access, the duty cycle restrictions are relaxed. Polite spectrum access encompasses two aspects: Listen Before Talking (LBT) and Adaptive Frequency Agility (AFA).

• Integration of Radio Technology: Certification is one of the last steps before a product with integrated wireless technology can be launched on the market. Manufacturers of products with integrated RF-technology may only market these with the necessary certification. Fig.2 shows the three options available for integrating wireless technology.

Figure 2: Three options for integrating wireless technology

Practical solutions for adding radio capability to an OEM product

Figure 2 shows the three options available for integrating wireless technology into an OEM product. We now look at some practical considerations for achieving technically and commercially successful integration, including:

• Why using a radio module is the best approach.
• How to estimate range
• Certification and conformity considerations

Why use a radio module?

To fully appreciate the advantages of using Würth Elektronik modules, it is important to understand that they comprise complete hardware, firmware and software solutions.

The ready-to-use hardware modules are based on powerful RF-chips and support for integrated or external antenna. The firmware comprises the WE-ProWare Radio Stack (described later) and conformity certifications for Europe, North America, Japan and, in some cases, China.

The software element includes Plug & Play PC-Software for easy evaluation, testing and updating, and mobile apps for easy evaluation and testing. Design libraries are available for fast Altium and Eagle PCB design. A Software Development Kit (C-Files) is provided for comfortable coding of the HOST-controller system.

The availability of these components as an integrated solution will have a significant impact on reducing development and certification cost, time, risk, resource and expertise requirements. Above all, the radio modules allow users to bring their products to market months earlier than would otherwise be possible – or switch rapidly to a different radio protocol on demand.

Range estimation

Engineers who have elected to base their designs on radio modules can use Würth Elektronik eiSos’s free Range Estimator, available at http://www.we-online.com/redexpert. With this tool, modules can be sorted and selected by their attributes. While simplified equations only yield approximate results, experience shows that these results provide reliable estimates of transmission range, if applied correctly.

Below is a path loss calculation that estimates the range of a radio link in a free space environment, using the Friis Transmission for Free Space model. A two-ray ground reflection model is also available.

This model assumes that the emitted power is radiated equally in every direction (isotropic) and calculates the power loss only allowing for the decreasing power density of the wavefront with increasing distance to the origin, without any reflection, absorption or attenuation.

Range calculation using Friis transmission for free space model

Figure 3: Free space model

To determine the maximum range of a Würth Elektronik eiSos RF-module, the path losses of the transmission are equalled to the ratio of the received power to the emitted power:

Figure 4: Path losses for different frequencies

Certification and conformity

A product that is to be launched globally must meet the certification or conformity criteria of each country where it is marketed. This is to prove that the product complies with regulations, laws, norms, standards, and other requirements. There is no worldwide certification applicable to all countries.

For example, the CE mark is required in Europe, and FCC certification in North America.

All Würth Elektronik radio modules are either certified and/or declared for conformity. This simplifies their approval process within the end-application significantly.

Radio technologies

A large number of radio technologies and protocols are available for a wide range of applications. Below, we look a some of the most popular:

Cellular

LTE (Long Term Evolution) is a cellular communication standard, which operates in licensed spectrum. LTE is also referred to as fourth generation (“4G”) cellular communication technology. The standards for LTE are defined by 3rd Generation Partnership Project (3GPP). 3GPP is a worldwide standards organisation that develops protocols/standards for cellular telecommunications.

LPWAN cellular technologies are for low-power, low transmitting speeds, low-cost module and devices with low data usage per month, and wide area coverage. Existing cellular technologies were not designed to handle low power applications, hence cellular LPWAN technologies cover scenarios where existing mobile network technology is not suitable. These cellular LPWANs refer to low power wide area networks (LPWAN) in licensed spectra. 3GPP specified LTE-M (LTE-MTC) and NB-IoT (Narrow-Band IoT) to address the fast-expanding market for low power wide area network (LPWAN) connectivity.

Multiple IoT connectivity options are available, which can be broadly categorised into two types:

• Short range wireless connectivity solutions in unlicensed spectrum
• Long range wireless connectivity solutions in licensed spectrum

Würth Elektronik solution: Cellular module

The Adastrea-I is a dual-mode LTE-M/NB-IoT cellular module, which supports international multi-regional coverage. The module will select NB-IoT where LTE-M coverage is not available, and vice versa. Fig.5 shows the module’s key features.

Figure 5: Adrastea-l LTE-M/NB-IoT cellular module

An integrated ARM Cortex-M4 MCU is provided exclusively for customer application firmware; this reduces cost, size, and power consumption. The integrated MCU also enables positioning, through GPS and GLONASS satellite systems. This allows GNSS positioning for asset management applications where infrequent position updates are required.

Bluetooth

Bluetooth Classic was released in 1998; from Release 4.0 in 2010, Bluetooth Low Energy (BLE) was added. Key differences between Classic and BLE include:

• Classic Bluetooth operates on 79 frequency channels, whereas BLE uses only 40.
• Classic Bluetooth has a higher throughput and can send larger data files than BLE, but it also consumes more energy.
• Classic Bluetooth can only connect to seven other devices, while BLE has no theoretical limit.
• BLE stays in sleep mode until users initiate a connection, and hops between frequencies at a different rate, helping save more power.

Industrial and IoT applications need easy connections between field devices and mobile phones or tablets. As the field devices do not need displays, significant cost savings are possible. Typical BLE applications include door control, service interface, light, roller shutter, and heart rate monitor. Bluetooth Mesh was release in 2017.

Würth Elektronik offers their Proteus modules for Bluetooth 5.1; the Proteus-e Slim-version and their fastest, Proteus-lll/ Proteus-lll SPI.

Figure 6: Proteus-e slim-version BLE 5.1 module

Figure 7: Proteus-lll/ Proteus-lll SPI BLE 5.1 module

Wi-Fi

Wi-Fi (wireless fidelity) is a specification for ensuring interoperability, based on the IEEE 802.11 family of standards, which are commonly used for local area device networking and Internet access.

Wi-Fi‘s wavebands have relatively high absorption and work best in line-of-sight use. Many common obstructions such as walls, pillars, home appliances, etc. may greatly reduce range, but this also helps minimise interference between different networks in crowded environments. An access point (or hotspot) often has a range of about 20 metres indoors while some modern access points claim up to a 150-metre range outdoors.

Wi-Fi networks can operate in two modes. In the infrastructure mode, an access point acts as a central entity serving several connected clients. To connect to such a Wi-Fi network, a user typically needs the network name (the SSID) and a password. The password is used to encrypt Wi-Fi packets to block eavesdroppers.

The Wi-Fi direct mode offers a point-to-point connection without the need for a dedicated central entity.

Würth Elektronik offers their Calypso fully-featured standalone Wi-Fi IEEE 802.11 b/g/n 2.4 GHz module as shown in Fig. 8.

Figure 8: Calypso IEEE 802.11 b/g/n 2.4GHz Wi-Fi module

The module provides a good basis for secure end applications, with secure boot and secure storage for user data. Other features include low power operation, smart antenna selection, firmware over the air update (FOTA) and provisioning.

Connectivity possibilities include HTTP, Multicast DNS, SSL and TL51.2 support, and MQTT client on module.

Proprietary radio as BLE alternative

There are several advantages to using Proprietary Radio as a BLE alternative:

• Connection only with manufacturer-authorised devices
• Security aspect as a benefit for end customers
• Closed communication is “invisible “for Smart devices
• Higher throughput possible – no effort with large Bluetooth overhead
• Saving Bluetooth Listing costs
• Business model to build the whole chain as user experience
• Binding the end customer to the product with additional accessories using the same communications

All Wireless Connectivity RF Modules have the WE-ProWare radio stack pre-loaded: Würth Elektronik modules’ added value is the fully included WE-ProWare operating system. Communication functions are configured with simple AT commands. Designers can easily swap between radio channels and protocols to simplify new market entry.

WE-ProWare can connect to external peripherals using numerous interfaces, such as UART or digital and analogue I/O. Network topologies it supports include:

• Point to Point
• Point to Multipoint
• Peer to Peer
• Mesh
• Multi-hop

Würth Elektronik’s strongest proprietary 868 MHz modules are the Tarvos-lll and Thebe-ll, as shown in Fig. 9.

Figure 9: Tarvos-lll and Thebe-ll proprietary 868 MHz modules

Figure 10: Thyone-I proprietary 2.4 GHz module

Combined proprietary 2.4 GHz and Bluetooth Low Energy 5.1

The Würth Elektronik Setebos-I combines Bluetooth® Low Energy 5.1 Standard and a Proprietary 2.4 GHz radio module. It contains both the Thyone-l and Proteus-lll modules.

Figure 11: Setebos-l combined proprietary 2.4 GHz and Bluetooth Low Energy 5.1 module

Mesh

A Mesh is a network of multiple interconnected devices. All nodes interconnect directly with no need of a master controller. In general, there are more connection paths between the source and the target. The information is passed from one node to another. Bluetooth Mesh and Wirepas Mesh are two established protocols.

Bluetooth Mesh: Bluetooth released a Mesh Version in 2017. It is not strictly part of the Bluetooth standard. It uses Bluetooth Low Energy link layer and radio and prefers Bluetooth 5.0 or newer due to long advertising packets. As a flooding Mesh it includes time to live (TTL) in the messages. Security is approved by application key and network key.

Wirepas Mesh is a connectivity protocol for radio modules, optimised for large scale and energy efficient 2.4 GHz wireless mesh networks. This innovative technology can be used to create large IoT networks, for example using battery-powered sensors, in which each node also functions as a router.

An asynchronous flooding mesh is integrated into Würth Elektronik Thyone-I, Tarvos-III, Thebe-II, Thelesto-III, Themisto-I & Setebos-I modules. These are suited for applications using small/medium size mesh networks (much traffic due to flooding technique), or where current consumption does not play a role (always on RX or TX).

Würth Elektronik also offers their Thetis-l 2.4 GHz Radio Module with Wirepas Mesh protocol. The Wirepas Mesh grows organically and has automated interference avoidance, so one network can handle multiple use cases and thousands of assets.

Figure 12: Thetis-1 Wirepas Mesh module

Wireless M-Bus

Wireless Meter Bus (wM-Bus) is the extension of the Meter Bus (M-Bus) with a wireless protocol and role scheme for handling communication over a standardised wireless communication interface between meters and data loggers – so called smart meter gateways (SMGW). This scheme is specified by the European standard EN 13757 and its sub-standards. This standard was introduced to allow automated measuring and processing of data, track resource usage, and optimise provisioning to create an “Advanced Metering Infrastructure” (AMI).

The Würth Elektronik Wireless M-Bus Analyzer is a tool for receiving and parsing wireless M-Bus telegrams that comply with EN 13757-4:2013 transmitted by “meter” or “other” devices. It is excellent for analysing errors and M-Bus devices’ RF range. Thanks to the simplified representation and an integrated logging function, data can also be analysed at a later time.

Available modules include Mimas-l, Metis-l, and Metis-ll.

Build your own firmware (BYOFw)

With Würth Elektronik’s portfolio of BYOFw modules like Ophelia-I, customers can receive a radio module in a hardware-only version, allowing them to develop and flash their own firmware for the transceiver chipset.

GNSS

GNSS (Global Navigation Satellite System) provides positioning and time synchronisation capabilities to unlimited numbers of users worldwide. The system is based on signals from the following four satellite constellations – see Fig.13.

Figure 13: GNSS frequency bands and satellite constellations

Fig. 14 shows Würth Elektronik’s range of GNSS radio modules, and Fig.15 shows the external antennas available.

Figure 14: Choice of GNSS radio modules

Figure 15: External antenna for GNSS modules

Conclusion

Committing today to tomorrow’s wireless technology seems impossible. Würth Elektronik offers freedom to use one radio module footprint for multiple radio modules to expand applications with different radio protocols at any time without any layout changes. It is a single quality-proven hardware base that eliminates enormous future re-design costs today. Explore more about Wurth Elektronik Wireless Connectivity & Sensors, click here.