Wireless Sensor Networks for Logistics

Over the past few years, wireless local networks have been rapidly developing, both technically and ergonomically, and have meanwhile become must-have elements of mobile and stationary TCP/IP infrastructures. Less publicity is given to industrial automation and asset management networks, which are, incidentally, called WSNs - Wireless Sensor Networks. Jennic has recently introduced a reference design based on its wireless microcontrollers JN5148, which is an ideal platform for locating and tracking goods within transportation logistics systems.

Reference design for logistics applications

Based on Jennic’s patented Sleeping Beacon Technology, the logistics reference design allows battery-powered, time-synchronized wireless sensor networks in logistic applications. The sensors within the network, connected to the product as so-called “tags”, transmit at regular intervals, in addition to a unique MAC address for identification, environmental data such as temperature or humidity to a central controller, which in turn communicates with a back office system, forwarding such data in real time to the logistics provider for the movement of goods, and making it available for auditing.

The reference design consists of two parts: one for evaluation and another for development and customer-specific adjustment. The evaluation package is designed in a way that the special properties of wireless concepts can be quickly implemented, with an extremely low power demand. This requires Jennic's standard evaluation kit and a PC for the back office GUI. The Windows-based GUI represents the information coming from the sensor network in real time, including node temperature, battery voltage and RF channel. In addition, frequency agility within the network can be evaluated through the effects of RF interference and channel blacklisting.

The development kit is supplied as a drop-in application for the Jennic SDK, along with project data and the source code. The provision of the source code ensures developers can directly access the application to perform customizations, typically through the integration of a GPRS/GSM modem link to the back office.

At the heart of the design are, however, Jennic’s third-generation wireless microcontrollers. They operate in the unlicensed 2.4GHz ISM band, providing a global solution as they correspond to the IEEE802.15.4 standard. To enable rapid time to market and savings in certification costs, Jennic offers a range of pre-certified wireless modules that are fully compliant with all existing regulatory RF requirements.

The principle of the sleeping beacon

Jennic's monitoring and tracking platform for the logistics industry utilizes the so-called “Sleeping Beacon” technology to implement a robust solution with maximum battery lifetime for both the tags and the coordinators. The principle of the “sleeping beacon” is an extension of standard IEEE802.15.4 beacons, with improved battery lifetime and better control of network traffic. The term 'beacon' originates in radio navigation, and describes a regularly recurring radio signal. The end devices (tags) receive a beacon, transmit their own data, and then go into low-power mode. Using a sleep timer, they “wake up” at the right time before the next beacon, and can then, again, send their current data. As such periodicity may amount to a few seconds only, and end devices are allowed to ignore beacons at regular intervals (e.g. send data only for every 10th beacon), average power consumption is extremely low, and, consequently, the lifetime of the supply battery is very long.

Wireless microcontroller JN5148

As a key element of the reference design, the JN5148 chip, with the lowest power consumption and highest storage density on the market of wireless single-chip microcontrollers, supplemented with an innovative “time-of-flight” range engine, enables the development of next-generation wireless mesh network components for battery-operated applications with a high data traffic. The chip consumes a mere 0.1 μA in the “deep-sleep” mode, 1.1 μA in the standard sleep mode with an activated wake-on timer or wake-on IO, and 2.5 μA for wake-on X with the simultaneous protection of RAM contents.

Because the chip operates with a minimum supply voltage of 2 volts (max. 3.6 V), it is perfectly suited for operation with a button cell, and can exploit it to a maximum degree. During operation, the JN5148 reaches a power input of 18 mA for the reception and 15 mA for the sending of data, with a power level of +2.5dBm, which is typically 35% less than the consumption of traditional solutions. With 128 kbyte ROM, 128 kbyte RAM and improved code efficiency, the JN5148 has sufficient memory for developers to integrate their embedded applications, along with the protocol stack, in a single chip.

Besides ZigBee PRO, the SoC supports further protocols, with 802.15.4 as a basic protocol of course, 6LoWPAN, and finally the Jennic protocol JenNet. Although WPAN, including 802.15.4, is only specified for a transmission rate of 250 kbit/s, the JN5148 is more powerful here, and the activation of so-called “enhanced data rate modes” (e.g. for audio applications) allows transmission rates of 500 and 667 kbit/s. With a programmable CPU clock speed of 4 .. 32 MHz and the use of five separate feed domains, the JN5148 can be flexibly adapted to the entire palette of applications, from low-power, battery-operated networks to process-intensive systems with a high data throughput. Integrated in the SoC at low additional cost, the new patented “time-of-flight” range engine revolutionizes network localization services by delivering a significantly higher accuracy in comparison with purely field strength-based implementations.