As LTE defends itself against LPWA, convergence is on the cards

Ericsson has been announcing a string of contracts to support smart meter networks, the latest with Skagerak Nett, a utility in Norway. With 180,000 meters, such a deployment is small fry compared to the smartphone networks the Swedish vendor rolls out, but it has good reason to boast of its conquests with the energy providers. The move by many countries to initiate smart meter programs has been a significant catalyst for the LPWA (low power wide area) networks market, which is now becoming a hotbed of competition between different connectivity technologies. With specialized offerings like LoRa, Sigfox and Weightless all engaged in standards activity and heading towards licensed spectrum, Ericsson is on a mission to prove that cellular solutions – from GSM to the emerging LTE-MTC standards – remain the best choice for smart city applications.
These applications range from metering to lighting to traffic management, and many others. To qualify as true smart city projects, they need to be integrated into a common data platform (as in the pilot being run in Bristol, UK). In most cases, each application remains quite separate, but even where a city hasn’t progressed much beyond metering, there is still a spotlight on the element these services have in common – the need for a very low cost, very low power wireless network which can cover a whole city easily.

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).

Specialized options have leapt to the challenge, and to the opportunity afforded by the future growth of smart cities and the wide area internet of things (IoT). Most of these have gained a quick route to market by implementing their networks in licence-exempt bands, primarily the ISM spectrum (915 MHz in the US, 868 MHz in Europe). The unlicensed airwaves mean their customers can deploy at low cost, although much of the early commercial business of firms like Semtech and Telensa has come from private networks, often in licensed bands, even while they push an ISM solution as the way to achieve significant scale and a broad ecosystem.

There are various technical approaches – Sigfox and Plextek’s Telensa are based on UltraNarrowBand (UNB) principles; Semtech (whose technology underpins the LoRa would-be standard) on DSSS (direct sequence spread spectrum) 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.

On one hand, to date, they have succeeded in keeping their power efficiency and range well ahead of the cellular alternatives, creating a dilemma for mobile operators which want to get into smart city services. Some are even harnessing these LPWA technologies, whether 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 LPWA 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 key services.

In Ericsson’s world, the answer is simply cellular – GSM, broadband LTE and LTE-MTC providing the full range of IoT functionality. But there is a logic to the idea that cellular and LPWA technologies should converge, to harness the advantages of both – the extreme efficiency and wide range of LPWA 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. Weightless originally targeted the TV white spaces spectrum, but has just released its specifications for the ISM band, under the label  Weightless-N. In the meantime, however, its only silicon provider (and major IPR holder), seems to be at the heart of a Huawei initiative which could make the LPWA candidates redundant. Called Cellular IoT, the Chinese company refers to it as a ‘4.5G’ technology, which appears to harness Neul chips and some LPWA functions while running them in cellular bands, and with a convergence path to LTE-MTC.

Vodafone has come out in support of Cellular IoT, which is likely to be commercialized next year as well as becoming part of the 3GPP standards. An interesting outcome – considered quite possible by some stakeholders – is for this effort to converge with that of the LoRa Alliance, which is also seeking to push its technology into 3GPP Release 13 via a licensed-band implementation. This mainly targets operators’ existing GSM spectrum, in which some channels can be freed up as 2G services are turned off or reduced in capacity. Future options for licensed-band M2M may include dedicated frequencies in the guard bands within the 700 MHz LTE spectrum (an outcome being heavily backed by Qualcomm and some carriers ahead of the ITU World Radio Conference this year). With or without the dedicated channels, the 700 MHz ‘second digital dividend’ is expected to be heavily used for M2M applications in Europe, because of its strong propagation qualities – even better than ISM – and because much of the low frequency LTE broadband work has already been done, in the 800 MHz spectrum.

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 LPWA platform, helping to broaden the ecosystem and improve the economics of their approach.

Meanwhile, Weightless claims that it already is a standard  – if 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.

This intense activity among groups promising alternatives to cellular explains why Ericsson is so keen to talk up its successes in smart metering, the most important deployed application to date in the smart city. 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 LPWA alternatives would be a flash in the pan until secure, licensed-band LTE-MTC emerged.

Ericsson said its trials in Germany had shown that LTE base stations could support transmissions between meters and IT systems within the required time of 100ms, even with heavy traffic, because of LTE’s quality of service features. Fiona Williams, research director at Ericsson, said: “We were happy to see that the QoS features of LTE fully met the communication requirements for power network automation, which are far more stringent than other requirements specifications for smart meter measurement acquisition.”

The Swedish firm says LTE Release 13 will improve latency and power efficiency further and provide a path to 5G, in which the IoT will be a key focus.  “We see the trial results as confirmation that public LTE networks, such as Telefonica Germany’s, offer a reliable and cost effective communications option to utilities companies deploying smart meters,” said Sven Koltermann, head of energy sales at the operator.

However, there are other powerful players eyeing the smart energy and smart city opportunities, and the start-ups behind the specialized LPWA technologies need to get their support. While Sigfox and LoRa may be riding on the favors of MNOs for now, the cellcos will always have a natural tendency to use LTE because they drive that ecosystem.

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’.

Source: Rethinkresearch