Some thoughts on Lorawan

It cropped up on my news feed here on WordPress an article regarding three major flaws on the Lorawan protocol. Since I’m following the Lorawan topic I was interested to see what those “Major” flaws where, and found it rather interesting, that the text, also derived from a commercial vendor, looked like the conundrum story like if a glass is half full or half empty.

First there is an huge misconception regarding low power communications protocols (LPWAN), being either Lorawan, Sigfox or anything else. The key is power, and lower power usage, the less the better. Asking for LPWAN protocols to do the same that other high energy, higher bandwidth protocols can do, is mixing apples with oranges.

Anyway the “flaws”, if we can call then that, are as follow:

– All uplink messages are unacknowledged.
This not true. Lorawan supports three classes of devices. Class A, the less power hungry of them, opens two receive windows for downlink messages from the server, that can be used for acknowledging the uplink message. If it makes sense to have acknowledge, it depends on the business case… If it is required probably LoraWan neither Sigfox or other LPWAN protocols are adequate to be used…

Also any protocols that use the ISM radio bands must obey the defined rules by the government bodies that control the radio spectrum. These rules apply to any protocol on those bands, so it’s not a flaw specific to any protocol. The 1% duty cycle applies to Lorawan and SigFox. In fact Sigfox will enforce the 1% duty cycle by refusing messages that exceed that percentage, and the LoraWan backend provider The Things Network will do the same.

Also there is some confusion regarding the medium access protocol, in this case the radio spectrum. The medium is shared by anyone, so collisions and interference will happen. Sigfox adds some resilience to this this by transmitting each message three times in three different ISM band frequencies, for example. As Lorawan it also doesn’t check for the medium before transmitting but only transmits once, since the physical modulation CSS (Chirp Spread Spectrum) has more resilience to interference. Also due to the availability of what is called Spread Factor, several transmissions can happen at the same time at the same frequency, and successfully be decoded at the other end.

On radio protocols checking for medium occupancy before transmitting only makes sense for non constrained devices, since the process of checking the medium before transmitting will consume power (a lot by having the radio on) and without any sort of guarantee that interference will not start right away or the interferance is happening not at the node side, but on the gateway side. So since one of the engineering requirements for LPWAN is low power, then the exchange between power and medium access control is made, which means ALOHA and let’s transmit!. So now we can have devices that have batteries that last years.

– All gateways in range see all uplink traffic which is not safe
I find this one rather funny since, turning on my radio can catch any available radio broadcasters, or any radio scanner can receive anything. Just check out Web SDR for hours of amusement.

The fact that all gateways see all traffic is a direct consequence of the radio medium, not an issue with the protocol. Any protocol that uses radio has the same “flaw” and it applies to Lorawan, SigFox, UNB, Weightless, 3G, LTE, you name it.

To solve this, encryption is used and at least in Lorawan there are several encryption keys and ways of providing them.
Lorawan can use fixed provided keys (ABP – Activation by personalisation) or variable keys through OTAA (over the air activation).

Anyway the gateways can receive any Lorawan packets, but without at least the 128 bit Network key and 128 bit application key, can’t do anything with the data. Gateways only forward data to network backend servers, and there, if they have the correct keys, decryption can be done and data forward to the correct application servers.

Check out this for more information.

– LoRaWAN requires an enormous amount of bandwidth
Well, yes, it is a SPREAD spectrum technology and it makes part of the holy war between Narrow band supporters vs Wide band supporters. Ones say that UNB is better, others don’t, and so on. Spread spectrum technology exists since a long time ago. Lorawan bandwidth can be 150Khz, 250Khz and 500Khz vs the 200Hz of Sigfox.

While SST can be used and detected below the noise floor level and accepts variations on the frequencies (reflections, Doppler effects), UNB is, on the receiver side way more complicated since it requires very precise crystals for frequency reference and higher power levels on the spectrum.

So in the article that I read it seems that Lorawan SST is just bad, without any consideration of the advantages vs UNB, which by itself is a discussion on different technologies which have advantages and disadvantages each.

Conclusion:
Nothing is perfect in engineering. Trade offs need to be made to achieve the requested requirements, and then based on the initial implementations, improve on it. So Lorawan, as Sigfox, solve the same issues by different means with the associated advantages and disadvantages.

So the above flaws, are just engineering trade offs that can be applied to any protocol.

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