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 © u-blox AG 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 © u-blox AG WANTED “Direct to Cloud” Connectivity - one hop to the Internet Slide 4 © u-blox AG 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 © u-blox AG • • • • • • • • • 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 © u-blox AG 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 © u-blox AG 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 © u-blox AG 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 Slide 9 © u-blox AG 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 © u-blox AG 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 © u-blox AG 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 Slide 12 © u-blox AG 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 © u-blox AG 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 Slide 14 © u-blox AG • 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 © u-blox AG 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 © u-blox AG New standards emerging in 3GPP… Narrow-Band M2M demonstration at MWC’15 Slide 17 © u-blox AG
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