Companies wanting to build an M2M (machine-to-machine) solution integrating a WWAN (Wireless Wide Area Network, eg GSM) communication function will typically opt to add a wireless modem to existing equipment. This approach generally yields a dual-processor architecture with a host processor (external microcontroller) and wireless modem (including a processor). The host processor carries out the application execution and interfaces with a set of external peripheral sensors, buses, memory etc, and it communicates with the wireless modem via AT commands.

For long-lasting competitiveness, however, developers of embedded systems need to focus on eliminating duplicate components and optimising software development.

The Wireless CPU

Embedding the GSM and application binaries on the same processor requires specialist expertise. In order to avoid this complex integration work and concentrate resources on company-specific intellectual property generation, developers can adopt a programmable Wireless CPU – a microcontroller with integrated WWAN communications capability, onto which the complete software application of the product can be embedded.

The Wireless CPU controls the external peripherals as well as the cellular communication, and it is no longer necessary to use an additional application processor.

With the addition of an M2M-optimised operating system featuring functionalities such as power management, response to time-critical interrupts, and support for over-the-air upgrades, as well as a set of suitable application development tools, developers have a cost-effective platform that can be programmed relatively easily. Compared to the ‘black box’ approach, this design philosophy aims at creating an inherently wireless solution from the outset.

Example: emergency response network

eCall is an initiative by the European Union to establish a pan-European emergency response network in order to reduce the number of highway fatalities. Response times of the emergency services are of vital importance in the event of road accidents. eCall therefore proposes that location information should be transmitted with the emergency call to a Public Safety Answering Point (PSAP) from which emergency services are dispatched.

The eCall in-vehicle system must:

• Collect data from the vehicle network and sensors, and maintain an up-to-date GPS-fix.
• Automatically detect a crash based on car-sensor information.
• Call a PSAP automatically when a crash is detected (or when the driver presses a dedicated eCall button) to establish voice contact between the car’s occupants and a PSAP operator, and transmit the vehicle’s position.

In order to perform all these functions, the system must integrate GPS, GSM/GPRS, and ideally an in-band modem which enables data transmission over the voice channel.

Previously, each of these functional blocks required its own separate processor, memories and crystal (for clock generation). If we examine this architecture, the following opportunities for cost optimisation appear:

• Merging all CPUs into one, shared by all applications.
• Sharing a single FLASH and a single RAM for all software.
• Avoiding multiple interconnection physical connectors.

A high-performance Wireless CPU can exploit all of the above, using a processor with enough CPU power for all applications and which also includes the GSM radio and communications stack.u

Mathieu Lasne-Villoing is Application Engineering Director, Wavecom, Issy-les-Moulineaux, France. www.wavecom.com