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  • Low Power Wide Area Networks (LPWAN)

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    Tim Kannegieter

    Low Power Wide Area Networks (LPWAN) are a key technology underpinning the growth and broader adoption of the Internet of Things. They provide secure, low data rate, low energy and low cost connectivity over a wide geographic area which is precisely what the majority of IoT applications need. Low energy is required because many IoT devices need to operate of batteries with very long life. High data rates are not usually required for IoT applications so there is no need to pay the cost of high bandwidth internet connections typically associated with 3G and 4G cellular connections.

    LPWANs can be deployed independently to support a specific application and increasingly, it is possible to subscribe to publicly operated LPWAN networks. This has led to LPWAN powered IoT applications such as smart metering of water utilities, which has been limited by power and penetration of other communications technologies. Compared to other internet connectivity options, there is a quality of service trade-off against cost, capacity and energy requirements. Key elements of LPWAN technologies are:

    • Support low power/energy requirements
    • Long battery life of devices (10-15 years)
    • Small message payloads (typically tens of bytes)
    • Infrequent message transmission (typically <100 messages/day/Thing)
    • Better penetration of buildings
    • Wider coverage between base stations (~20km to 100km)
    • Low cost per bit of data conveyed (dollars per year per Thing)
    • Low hardware cost (target <$10) to make wide-scale deployment feasible.

    A significant caveat of LPWAN technologies is they generally do not provide guaranteed message delivery. The networks that are available are either unidirectional or provide limited back link connectivity, so that messages sent via things are not acknowledged and so we don't have a guaranteed message delivery capability. This significantly impacts the sort of applications that one can consider using these networks for.

    There is also a significant difference in the way that the data is conveyed to the user, in that the operator of the network would typically operate their own server which would provide data communications to and from the deployed things. The user would access this data via direct connection from their server into the server of the system operator.

    The other key point is that LPWANs facilitate the deployment of isolated things, so significant numbers of things that are not necessarily clustered, so that the connectivity is directly from the network to the thing, and not via a local area network.

    There are a range of commercial technologies competing in the LPWAN space. The main LPWAN technologies active in Australia or scheduled to be available include:

    The best supported technologies in terms of range of vendors and network availability in Australia are Sigfox, LoRaWAN, Taggle and NBIoT. There are also a growing number of practitioners with experience and knowledge of how to implement LPWAN solutions using these technologies. Each of the LPWAN technologies have their advantages and disadvantages. The following tables compare a variety of relevant attributes.

    Image: Curtesy Dr Boyd Murray of Murray Wireless

    Image curtesy Dr Boyd Murray of Murray Wireless

    They main telecom operators in Australia have been trialing the LTE technologies and are beginning to roll them out commercially (still in soft launch mode at the end of 2017). At this point, deployment of LPWAN technologies are likely to experience rapid growth in IoT solutions. Other technologies include:

    • DASH-7
    • Greenwaves
    • IEEE802.15.4k LECIM
    • IEEE802.15.4g (Wi-SUN)
    • LTE-M
    • LTE Cat-0
    • NB-Fi (WAVIoT)
    • Nwave
    • Weightless –w –n –p

    Design considerations:

    Following are some of the main design considerations when choosing the most appropriate LPWAN:

    • Duplex: Consideration needs to be given as to whether communication needs to be bi-directional. Bi-direction allows ability to control the device and do firmware updates but often this is not required and it introduces complications.
    • Security: Does the link allow eavesdropping? Can the nodes be hacked or can they be spoofed, or can they be hacked? Generally speaking the nodes can only be hacked if they receive data, in other words, in the downlink. If they only have an uplink, it's very difficult to hack them.

    • Capacity: Consideration should be given to how many nodes and transmissions per day are required in a gateway. What happens if you have multiple nodes transmitting at the same time and you get dropped packets? Is there provision for retransmits or some other form of redundancy.

    • Standards and chip sources: For commercial and operational reasons, some designers may want open standards and multiple sources for the chipsets used in their IoT solutions, while others are happy with proprietary solutions. Some solutions involve communication protocol using open standards with a proprietary chip set, while others are proprietary communication protocols with multiple chip sources. 
    • Technology approach: LoRaWAN uses spread spectrum modulation technology which allows it to operate below the noise floor, while most other LPWANS use narrow-band technologies that pick up the signal in a very narrow slice of spectrum usually operating 8dB to 10dB above the noise floor.
    • Spectrum: Another consideration is whether to use a technology that employs licenced or unlicensed spectrum. If it's class licenced or unlicensed, how much interference are you going to get from other users who are using that? For example, WiFi is using 2.4 GHz ISM band, many other users using the 915 MHz ISM band. The other users in the urban regions can actually increase the noise floor by up to 20 Db.
    • Global roaming: Some IoT applications need to be able to track objects from one country to another. Various countries operate on different frequencies so it in this case it would be important to choose a technology that can cope with this.
    • Deployment and Operational costs: A key consideration is the cost of installing and maintaining a network. Some solutions allow you to deploy your own network but all the nodes but you would have to maintain them. With other solutions you dont own the network so this is not a consideration but you might then have to pay for SIMs and the network connection.

    Sources: The information on this paged was sourced primarily from the following sources:

    Links

     

    Edited by Tim Kannegieter



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