Flexibility and quick reaction are key elements for modern and efficient IoT networks. Depending on infrastructure conditions and network coverage, one technology is not enough to run an IoT network efficiently. So, another solution is needed! Within a multi-stack, several communication technologies are combined for wireless data transmission. In this way, stacks can be selected to suit the use case. Once set up, the various protocols can be individually controlled during operation. 

ARCHITECTURE AND CHIP DESIGN 

A multi-stack is not much different from a single stack in terms of architecture. However, as the name suggests, multiple protocols can be operated in parallel. Depending on the technologies, data is sent and received uni- or bidirectionally via previously defined parameters.  

The integration of a multi-stack can be done via a one-chip as well as a two-chip design. All STACKFORCE stacks – not only multi-stacks but also single stacks – are flexible in this respect and can be adapted to individual requirements. If we look at the ongoing chip shortage, integrating a stack using a one-chip design can be a decisive advantage. In this way, valuable resources are saved with the use of only one controller. Only the issue of memory capacity should be dealt with in advance. By using several protocols within a multi-stack, the chip requires somewhat more memory overall.

HIGHEST FLEXIBILITY WITH A WELL-DESIGNED API

When developing our multi-stacks, we focus on the common protocols LoRaWAN®, mioty®, Sigfox and wM-Bus. The protocols available within a multi-stack can not only be controlled individually, but operation as a stand-alone stack is also supported. The following combinations of a multi-stack are basically possible:  

The multi-stacks support the simultaneous operation of multiple protocols on one MCU through a well-designed API (Application Programming Interface), as well as seamless switching between the stacks to ensure maximum flexibility for the user at all times. Basically, the multi-stacks are delivered with predefined parameters, but it is up to the user which strategy of switching between the stacks is used. This allows a user-defined protocol priority to be set for each possible state of a system, a stack to be managed and latency to be minimized.

At the application level, this means that a given network state is maintained even if communication with another network occurs in the meantime. While the strategy for switching between stacks is up to the user, it is possible for the stack to reject a request to switch to another stack if a protocol-specific communication sequence is in progress that must not be interrupted. This may be the case, for example, if a bidirectional LoRaWAN® communication is running and the stack expects a response from the network server or similar.

If a STACKFORCE single stack is already in use and is to be replaced by a multi-stack, the changeover is extremely simple and hardly involves any new programming for the previously used single stack. The single stack library is simply replaced by the multi-stack library and the application is extended to control the newly added stack. Thanks to the intelligent multi-stack API, which works across the individual stacks and provides a constant “look-and-feel”, all settings of the previously used single stack can be transferred to the multi-stack operation. Only the stack that is newly added has to be configured according to its own requirements. 

Conversely, the flexibility via the STACKFORCE API means that a (temporarily) unused stack of a multi-stack can be easily removed from the chip and the device can thus be optimized.   

WHY COMBINE DIFFERENT RADIO PROTOCOLS IN ONE STACK?

In a nutshell: 

• better network coverage
• more capabilities
• higher efficiency

The advantages of using a multi-stack are obvious. Not every radio network is available at every location. In order to achieve the best possible network coverage, many devices that are to be equipped with modern wireless technology require a great deal of effort to determine which device will be equipped with which technology. With the multi-stack, one opts for maximum flexibility, as it is possible to select individually between the available technologies during runtime. The overall network coverage is increased, and several use cases can be served with only one device. 

Use case: Smart Metering

Let's take a look at the Smart Metering use case. Here, for example, the use of a multi-stack leads to more efficient planning of personnel. Wireless M-Bus is the most suitable technology for reading out devices via "walk-by" or "drive-by". Data is sent regularly at short intervals and can be read out by an employee as they walk or drive past. If a multi-stack is used instead of a Wireless M-Bus single stack, which is also equipped with LPWAN technology such as LoRaWAN® or mioty®, the data is sent remotely via LPWAN. This generates a significantly higher range, and the data is transmitted digitally without the need for personnel. 

Use case: combined operation – stationary and mobile

If a use case requires the reading of devices in both stationary and mobile operation, the use of a multi-stack with mioty®/LoRaWAN® and Sigfox technologies brings a decisive advantage. Let's take a look at the example of a brewery. The brewery monitors the individual beer barrels via sensors. If the barrel is located at one of the brewery's sites, data on temperature, air pressure, vibrations, etc. are collected and transmitted to the brewery's own mioty®/LoRaWAN® network via LoRaWAN®. If the barrel leaves the brewery premises for a change of location, the public Sigfox network can be accessed in mobile operation to transmit location data via Sigfox. This way, the brewery always has an overview of where individual beer barrels are located. As soon as a barrel arrives back at one of the brewery's premises, all detailed sensor data is again read out via LoRaWAN® and sent over the mioty®/LoRaWAN® network. 

IS A MULTI-STACK ALWAYS RECOMMENDABLE? 

Nothing is changing as much as digitization. In order to plan future-proof and to ensure the necessary flexibility, it is advisable to decide directly for a multi-stack. Overall, you opt for better network coverage and the sum of the advantages of the individual technologies! However, if you are looking for a very small application that requires little memory space, you will need to determine on a case-by-case basis whether a multi-stack is the right option. We will be happy to advise you on your personal use case.