How Low Power is NB-IoT?

nb-iot

NB-IoT is considered a licensed low power wide area networks (LPWANs) technology supported by your local telecom operator. That means each device requires a SIM card and monthly or annual payments to your operator just like your cell phone. The benefit is that you don’t need to manage the infrastructure; you do not need to install your own base stations.

The key advantage of NB-IoT is the protocol is synchronous and designed to optimize the spectral usage and throughput of the network. This optimization for spectral utilization comes at the cost of compromised battery life and recurring costs (monthly or yearly).

Unlicensed LPWANs, such as LoRaWAN® and Weightless™ are optimal for longer battery lifetime. If sensor data is small and infrequent (one or twice a day), LoRaWAN could be the optimal choice being an asynchronous protocol. If data is larger and data transmissions must be acknowledged then Weightless stands alone as the option for a synchronous protocol for private networks.

The effect of asynchronous versus synchronous protocols has significant impact on the battery lifetime of sensors.

Semtech conducted a comparison using the T-Mobile NB-IoT network available in the U.S. The NB-IoT sensor consistently took more than 20 seconds of active time to negotiate a slot to communicate an 11-byte packet. The average current consumption over this 20 second period was 40mA. In comparison, sending the same 11-byte packet over LoRaWAN required an active time of only 1.6 seconds, with an average active current consumption of 6.4mA. This translates into greater than 50 times advantage in battery lifetime for LoRaWAN.

Take an example application: wireless, battery powered, pushbutton. A LoRaWAN-enabled pushbutton and an NB-IoT pushbutton each were equipped with a 600 maH battery. The LoRaWAN device could support roughly 70,000 button presses on a single battery,  while the NB-IoT button could handle only about 2,000 button presses on a single battery. The difference is quite drastic.

When choosing a LPWAN technology, be sure to thoroughly review the application requirements. One size does not fit all.

 

 

The 3 Major Flaws of LoRaWAN

LoRaWAN has three undeniable flaws

  1. Nearly all uplink messages are unacknowledged (you won’t know if the message was ever successfully delivered)
  2. All gateways in range see all uplink traffic (not safe)
  3. LoRaWAN requires an enormous amount of bandwidth (tough to scale, culprit for ISM band traffic, subject to interference from other LoRaWAN gateways)

 

1. Nearly all uplink messages are unacknowledged

LoRaWAN has 1% Duty Cycle Limit for both end devices and the gateway (A duty cycle is the fraction of one period in which a signal or system is active. A period is the time it takes for a signal to complete an on-and-off cycle) In order to support the 1% duty cycle limitation for the gateway, all uplink messages are unacknowledged and uncoordinated, LoRaWAN is considered a “pure-aloha” scheme.

What is pure-aloha: “The idea is applicable to systems in which uncoordinated users are competing for a single channel (shared resource). ALOHA permits users to transmit any time they feel like. Collisions will occur and therefore colliding frames will be destroyed. However, if feedback is available on the destruction, then users will be made aware of their frames have not been transmitted (received) successfully  (1)

“Such a network has about 18% efficiency. This means that 82% of packets are lost when a LoRaWAN network is fully utilized. Since most messages are unacknowledged, the end node does not know its message was missed”(2). The Things Network also confirms this statement by stating “the capacity for downlink messages is even lower than for uplink messages, so don’t waste it.”

2. All gateways in range see all uplink traffic (not safe)

No explanation required.

3. LoRaWAN requires an enormous amount of bandwidth

see my previous post: LORA vs. Sigfox vs. Weightless-P

Sources:

1: Notes on the efficiency of ALOHA: http://www.csee.umbc.edu/~chettri/cs481/notes/NotesOnTheEfficiencyOfALOHA.pdf

2.Link Labs Blog: https://www.link-labs.com/use-cases-and-considerations-for-lorawan/

3. https://iotee.wordpress.com/2015/12/08/lpwan-technology-comparison/