Don’t forget the machines!
- using radio to connect the Internet of Things
John Haine
Cellular Technology Innovation
u-blox Melbourn Ltd.
locate, communicate, accelerate
I’m full!
Fire!
I’m fit!
10 cubic metres!
I’m Here!
Water me!
I’m empty!
Slide 2
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There’s lots of things!
They don’t say a lot!
They need talking to as well
They get in some very inconvenient
places…
And stay there a long time!
Slide 3
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WANTED “Direct to Cloud” Connectivity
- one hop to the Internet
Slide 4
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Keeping it going on batteries
X
•
?
LiPo
•
•
•
•
3V - high capacity
High peak current – “C”
~3%/month leakage
Needs charging
Zn/MnO2
•
•
Li/MnO2
3V – good energy
density
Limited peak
current, <20 mA
Slide 5
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•
•
•
•
•
•
•
•
•
1.5 V, wide voltage range
High internal resistance
Poor at low temperature
•
3.6 V – high energy
density, 9 Wh
Peak current ~250
mA
Good at low
temperature
Potential safety
issues
3.6 V – high energy
density, 60 Wh
Peak current ~400 mA
Good at low
temperature
Potential safety issues
How much transmit power?
33 dBm
23 dBm
0.15
1.5
0.02
10 dBm
AMPS DC
Battery limits peak transmit power – keep it low!
Slide 6
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Example:
30% devices indoors
20% indoors with “extreme loss”
50% outdoor
3 km cell
How much signal?
“PATH
LOSS”
L = 120.9 + 37.6log10(R) dB
BUILDING
CLUTTER
Log-normal, 8 dB SD
BASE
STATION
Slide 7
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BUILDING
LOSS
15 dB
Log-normal
10 dB SD
EXTREME
LOSS
e.g. 30 dB
15 dB S.D.
100%
90%
80%
%age < abscissa
70%
60%
50%
CDF
40%
30%
20%
10%
0%
100
110
120
130
140
150
160
170
180
Coupling loss - dB
GSM max coupling loss = 144 dB
Target max coupling loss = 164 dB (20 dB improvement)
Slide 8
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190
200
Bucking the trend…
From analogue through GSM to 3G, HSPA, to LTE & 5G, cellular standards
have used wider radio channels and higher symbol rate
• Statistical multiplexing efficiency
• Minimising nodeB RF complexity
• Minimising latency
• Out-of-band noise levels increasing
• Worse battery life
Is this always the best approach?
• For many IoT applications, latency is not a key factor
• Radio “reach” and maximum battery life are critical
• Low cost is also important
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Some gentle information theory…
• Shannon’s Law:
𝑹𝒆𝒇 = 𝑹𝒔𝒚𝒎 𝒍𝒐𝒈𝟐 𝟏 +
• For low SNR approximately:
𝑹𝒆𝒇 = 𝟏. 𝟒𝟒 ∙
𝑷𝒄
𝑷𝒄
𝑭𝑵𝑹𝒔𝒚𝒎
𝑭𝑵
F = 3 dB; N = -174 dBm/Hz; Coupling loss = 164 dB
Slide 10
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Tx Power dBm
Rx Power,
dBm
Limiting bitrate
kbit/s
33
-131
14.4
23
-141
1.44
13
-151
0.144
• 180 kHz resource
block divided into
variable number of
carriers
• Tx power is per
carrier
Aggregate error-free rate, kbit/s
• 164 dB coupling loss
1000
100
10
23 dBm
1
13 dBm
3 dBm
0.1
0.01
1
10
No. of sub-carriers
Use narrow-band carriers for highest total throughput in coverage limited
system
Slide 11
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Possible channel arrangement for coverage-limited
Paired resource blocks, consuming 1 GSM channel
system
45 MHz duplex spacing (900 MHz band)
Example channel pair for a UE
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Uplink sub-channels of different widths within resource block
5 kHz channel
10 kHz channel
20 kHz channel
Use higher-rate modulation and wider channels for devices in good
coverage
Slide 13
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What about spectrum?
• 868 MHz? 900MHz? 433 MHz? White-Space? 169 MHz?
Licensed/licence exempt?
• Friis’ formula:
𝑃𝑡
𝑃𝑟 = 𝐺𝑡 𝐺𝑟
𝜆
4𝜋𝑅
2
= 𝐺𝑡 𝐺𝑟
𝑐
4𝜋𝐹𝑅
2
• Path “loss” is proportional to the inverse-square of frequency
•
Low frequency = lower “loss” but longer antennas
• Balance between antenna efficiency and propagation
• EMI is higher at VHF especially in and around buildings
• “Quiet” spectrum preferred to maximise radio reach
•
Licensed rather than licence exempt
•
Advantages to having a dedicated band
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• Antennas need to be embedded in “things”
(otherwise they get broken)
• At VHF embedded antennas are very
inefficient
• VHF spectrum is therefore unattractive for
embedded communications
130 mm
~90 cm @ 169 MHz
Slide 15
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Wireless m-Bus
antenna design for
169 MHz
95 x 63 mm
Efficiency: ~7%
i.e. 11.5 dB loss
“Things” are different, and need a different approach to communication
standards design
The need to work for years on small batteries imposes new constraints,
especially on maximum transmit power
Coverage is critical – systems need much better link budget than
conventional cellular
Latency tolerant applications permit different design trade-offs
Ideal spectrum is <1000 MHz (building penetration) but higher than 500
MHz (antenna size)
If the Internet of Things is so important, why aren’t we allocating it
dedicated spectrum?
Slide 16
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New standards emerging in 3GPP…
Narrow-Band M2M demonstration at MWC’15
Slide 17
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