IoT Needs Good Neighbours - Cognitive Radio Turns Enemies into Friends

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IoT Needs Good Neighbours Cognitive Radio Turns Enemies into Friends

Steve Clarke, Technical Director

Presentation for Embedded World

25 February 2016


Founded in 2009 in Cambridge,

AMHIO Technology designs and

develops intelligent wireless

communications for smart meters and

IoT applications and networks,

including S/W stacks, hardware IP and

embedded modules.

Formerly a senior engineer at the BBC

and lecturer at Salford University,

Steve Clarke has designed systems

from bus telematics to multi-award

winning AV processors. He is

Technical Director and co-founder of

AMIHO Technology.

About the Author and Amiho


An explosion of connected devices and applications is

occurring in machine communications that makes up the

Internet of Things

Industrial, Scientific and Medical (ISM) radio spectrum is

used for the majority of these communications

Users are searching for reliable communications, which

is encouraging selfish behaviour

Sub 1GHz ISM bands are under threat

Cognitive radio makes better use of shared spectrum

To cope with the increase of users, we need these

radio devices to be Good Neighbours

The Everything-Connected World


The Future is Rosy Noisy

The New World of Connected Devices

50bndevices

That’s more than

100k! devices / km2

Inner London

population density

> 10,000/ km2

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systems

Remote

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Wir

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Th

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Doorbells

Barrier control

Traffic light

priority

Baby monitors

RFID


ISM – Industrial, Scientific and Medical

Used by Short Range Devices, divided into 2 bands:

Sub- GHz used for longer-range and older applications,

characterised by:

Shared spectrum, with many unrelated users / uses

Often just pairs of devices

Often unidirectional

Often fairly dumb devices

Transmit any time (Aloha) and accept collisions

Lack of standards

> 1GHz – occupied by WiFi, Bluetooth and others

Typically shorter range, higher data rate

Unlicensed Spectrum – ISM Bands


Simple ISM band systems expect lightly used channels

so as to allow data to be received reliably

Defence against noise is usually through the use of

multiple transmissions of the same message

Classical communications theory shows that transmit-

at-will (Aloha) protocol gives low channel capacity

Increasing the number of users exponentially reduces

reliability of communications

Fixed frequency systems are susceptible to jamming:

Frequency hopping and spread-spectrum are 2

techniques to reduce the effect of this

Deficiencies of Simple Systems

Example - a simple ISM

transmitter may send a

message with probability of

correct reception of 0.9.

If we send the message 3

times, we get overall failure

probability of 0.13

i.e. 1 in a 1000

If the noise level doubles, the

probability of each message

failing is 0.2, giving an overall

failure rate of 0.23

i.e. 1 in 125


Large-scale networks have appeared in the sub-1GHz ISM bands

– they represent a major nuisance for existing users. These

include both public and private networks:

Smart Metering – private utility networks, predominantly

using the Wireless Meter-Bus protocol

Sigfox – subscription-based public networks, using ultra

narrow-band transmissions

LoRa – both public and private networks, using spread-

spectrum transmissions

All of these are set to use large amounts of ISM spectrum

The New, High Volume ISM Users


Both designed for low data-rate applications, typical 3-30

transmissions / day, to cover medium distances (several km) in a

single hop.

Both use aggressive techniques to maintain the network.

Sigfox uses ultra narrow-band transmissions to increase the

sensitivity of the receiver, with frequency agility to prevent

transmissions being continually blocked.

Channels are a few-hundred Hz wide, ultimately allowing more

energy to be put into the ISM band by a large number of devices

with narrow channels

Sigfox is only available for subscription networks

Sigfox and LoRa Basics (1)


LoRa uses CSSS (Chirp Sequence Spread Spectrum) modulation

to spread the data through a wide channel.

Bits are represented with codes that are sequences from 64 to

4096 symbols.

This redundancy improves sensitivity by up to 20dB

The redundancy comes at price – bit rates range from 37.5 kb/s

to 18 bits / sec

Transmissions with different code sequences can occupy the

same band and still be discriminated from each other

LoRaWAN is a proprietary network protocol used by the

LoRa Alliance. It can be implemented both as a subscription and a

private network.

Sigfox and LoRa Basics (2)


600M meters in Europe are being replaced.

Radio communications used for almost all gas and water

meters

The majority of radio communications uses Wireless Meter-

Bus, a sub 1GHz simple transmission protocol.

The system was designed for the frequent transmission of

short messages every 10-15 seconds

Most devices are unidirectional and communicate at full

power

Hard-to-reach ‘dark meters’ represent a major problem

that is being solved through the use of high power

transmissions and lower frequency (169 MHz)

communications

Smart Meter Networks


What do we mean by ‘Cognitive’?

‘Cognition is a black-box of what we colloquially call memory, attention, language/communication and decision making’

Dr KMJ Diederen, Neuroscientist, University of Cambridge

What is Cognitive Radio?


The term Cognitive Radio was first used in 1989 by J Mitola, to

describe a radio that senses its environment and adapts its

behaviour to best suit that environment.

In radio terms, this might include:

The frequency spectrum and division of channels within it

Intelligent sensing of channel occupancy and of the channels to

use

Power levels needed

Modulation or coding schemes

It was envisaged to allow devices to use then relatively lightly-used

spectrum without interfering with existing users.

True cognitive radio, by its nature, is cooperative.

What is Cognitive Radio (2)


Much of the effort goes into choosing the channel to be

used

Try to send messages in a way that is least likely to cause

collisions

Sensing can (and should) be done at both ends of the

communication link.

Devices build up a map of how spectrum is used, such as

a database of the most frequently used channels

Features such as power control are ‘self-interested’

techniques that save energy and coincidentally minimise

interference

How Clever Does it Need to be?


2.4 GHz standard, developed for short range (<10m) small networks at data rates from 100kbps – 2Mbps

Adaptive power control

Adaptive channel – the next channel used depends on clear-channel assessment at both ends

Error correction in packets is added adaptively according to error rates

Data rate has back-off to achieve shortest possible packets

Modulation scheme, and thus the bits/symbol, is selected according to background noise

Phasing of packet slots in multi-device networks is chosen to minimise collisions from timing drifts

Cognitive Examples - Bluetooth


Wireless Meter-Bus has added higher layers for some systems – notably the Italian gas (CiG) specification UN/TS11291, using 169 MHz

CiG specifies listen-before-talk and power control

LoRaWAN implements

adaptive data rate

adaptive channel hopping

power control

Its intelligence lies mainly in the gateway

LoRaWAN does not implement listen-before talk

Semi-Cognitive Examples


Some networks – such as metering – are infrastructure and

could (as in the UK) use dedicated frequencies

New ISM band applications will have to consider the large

amount of noise generated by other users

All users of shared spectrum should strive to minimise the

interference they generate

Just shouting louder will not work – networks need to be

cooperative

Cognitive Radio makes better, less selfish use of

spectrum and is better able to cope with interference

Making ISM Bands Work


www.amihotechnology.com | +44 1223 422345

Steve Clarke

Technical Director

[email protected]

http://www.amihotechnology.com/