Emerging smart city or government platforms need a very low cost, very low power wireless network which can cover a whole city easily and be easily integrated into a common data platform. In the past, these long range machine-to-machine services were usually handled by GSM, where they existed at all, but as the range and criticality of such services grows, the ageing standard is seen as too limited in functionality and power efficiency to be a long term solution (though there is a body of opinion, and R&D, which contends that ‘GSM-Advanced’ would be a more suitable network for wide area M2M than LTE-MTC).
Consequently, specialized options have leapt to the challenge, with IoT protocols such as Sigfox, LoRa and now Weightless coming to the fore – with the latter finally unveiling v1.0 of its ISM band implementation this week. These three have secured a quick route to market by implementing their networks in license-exempt bands, primarily the ISM spectrum (915 MHz in the US, 868 MHz in Europe).
There are various technical approaches – Sigfox and Plextek’s Telensa are based on ultra-narrow-band (UNB) principles; Semtech’s LoRa uses DSSS CDMA; Weightless uses DBPSK modulation; and another solution, from On-Ramp Wireless, is based on RPMA (random phase multiple access).
All these come with pros and cons – CDMA-based schemes have higher overhead than pure UNB, for instance, but greater flexibility to avoid interference by moving between channels. But they all have key elements in common.
All these options are currently well ahead of cellular in terms of power consumption, which has encouraged some MNOs to begin adopting these LPWAN technologies. Whether this is as a complement or stopgap to LTE remains to be seen (Bouygues and KPN are using LoRa, Telefonica invests in Sigfox).
On the other hand, while the LPWAN technologies may have the headstart – M2M-optimized LTE-MTC will not be finalized for at least another year, and even then may not achieve the same efficiencies as its rivals – they will soon run out of steam if they cannot support mission-critical city apps such as public security and smart grid. This will require new spectrum options – as the ISM band becomes congested, it will remain a low cost option suited to applications that only need best effort performance, but cities and carriers will look to more reliable places to deploy their mission-critical services.
Ericsson’s LTE ambitions vs LPWAN:
In Ericsson’s world, the answer is simply cellular – with GSM, broadband LTE and LTE-MTC providing the full range of IoT functionality. But there is a logic to the idea that cellular and LPWAN technologies should converge, to harness the advantages of both – the extreme efficiency and wide range of LPWAN with the huge ecosystem and licensed spectrum of LTE.
An effort of this kind is already seen at Huawei since it acquired Neul, the chip designer which originally designed the Weightless technology. The Weightless SIG and Neul originally targeted the TV white spaces (TVWS, the gaps between broadcast frequencies) spectrum, but has just released its v1.0 specifications for the ISM band, under the label Weightless-N.
After TVWS progress stalled due to issues with global frequency standardization, Huawei moved on to its own Cellular IoT initiative, while the Weightless SIG pushed ahead with the new ISM implementation – almost solely based on Nwave’s contributions, which explains the speed of its publication. Often referring to it as 4.5G, the Huawei tech looks to be LPWAN in nature but running in cellular bands – with a path to converging with LTE-MTC eventually.
Vodafone has come out in support of Cellular IoT, and it is likely to become part of the 3GPP standards next year. Seeing as this is a common goal with LoRa, some stakeholders are calling for cooperation between Huawei and the LPWAN players.
While LoRa is engaged with the 3GPP, the two main UNB proponents, Sigfox and Telensa (a spin-off from Plextek), are cooperating on specifications which they hope ETSI will adopt for a common LPWAN platform, helping to broaden the ecosystem and improve the economics of their approach.
Meanwhile, Weightless claims that it already is a standard – if, admittedly, one without a commercial deployer or obvious source of silicon at this stage. But it does offer its technology royalty-free to any company wanting to develop base stations or terminals and says the former carries a bill of materials of under $3,000, while a device can be made for $2.
William Webb, CEO of the Weightless SIG, said on the launch of Weightless-N: “Open standards are simply better for developers – they minimize cost, increase choice, mitigate risk, encourage innovation and are sustainable.”
Weightless-N is designed around a DBPSK (differential binary phase shift keying) modulation scheme, which transmits in narrow bands and mitigates interference by hopping between frequencies. Like LoRa, it also supports encryption of all transmissions. It also supports mobility with the network automatically routing terminal messages to the correct destination, even when multiple operators’ networks are present in the same place.
But back to Ericsson:
With this intense activity among groups promising alternatives to cellular, Ericsson is keen to talk up its successes in smart metering. Recently it partnered with Telefonica O2 Germany and the E.ON Research Center at Aachen University to convince the world that LTE really was suitable to smart meter networks – and, implicitly, that LPWAN alternatives (with their lack of QoS, unlike cellular) would be a flash in the pan until secure, licensed-band LTE-MTC emerged.
But utilities, security operators, site owners and other companies in the complex smart city value chain may want a technology they can control themselves – hence UK infrastructure supplier Arqiva’s decision to deploy Sigfox, as well as winning part of the country’s smart metering roll-out contract, with specialized communications technology from Sensus (the rest will be supported on cellular connections by O2).
That UK example shows the complexity of the current smart city situation, and the way it is being carved up between LPWA and cellular contenders. The LPWA firms need to get powerful infrastructure or M2M services companies behind them, with the weight to turn their systems into de facto standards – or alternatively, as LoRa’s and Sigfox’s 3GPP activity may imply, they could seek an integrated role within the emerging cellular standards, which would guarantee their innovations a place within ‘5G’.