MulteFire brings first release to market

Standalone LTE gets first "end-to-end" system and architecture release to sound starting gun on private LTE networks in unlicensed spectrum. Question of whether MulteFire could yet join 3GPP family "still open".

The MulteFire Alliance expects to see vendor trials of MulteFire technology by late 2017, after it published today the first release of specifications for the technology that enables LTE networks to operate in unlicensed spectrum without a licensed spectrum “anchor”.

The Alliance’s President Mazen Chmaytelli said the specifications would enable any vendor to build an end to end MulteFire deliverable. “It’s a complete release, from the system architecture to radio interface, to various deployment architectures,” he said. The release will be made available at first only to Alliance members, and then later to the wider ecosystem. He expected some MulteFire-capable devices to be available by mid-2017, and then full vendor trials by late 2017. (Qualcomm, which is a the key proponent of MulteFire, is already a leading supplier of LAA chipsets to the market.)

Chmaytelli said that the specification had been produced in very quick time, with a host of meetings that kicked off in December 2015. Clearly from an ecosystem point of view, the desire is to keep specifications as close as possible to LAA and with LAA as the existing framework, most of the technical work focussed on those areas where MulteFire is necessarily different from LAA.

That meant defining a “robust anchor” in unlicensed spectrum – ie replacing the method of control and authentication within LAA operation with enhancements to LAA’s Discovery Reference Signals (DRS). The design provisions for increased reliability of acquisition for each instance of the DRS compared to LTE as well as reliable transmission of system information.

The specifications also added a flexible frame structure to enable support for any combination of traffic on the uplink and downlink. Additionally, the specifications outline interworking between MulteFire and licensed spectrum LTE.

There was also work to be done on defining SIM or non-SIM authentication, with the latter enabling IoT devices to be deployed within MulteFire networks. As LAA and MulteFire are necessarily small cell (or perhaps edge C-RAN) technologies because of their very tight synch and timing requirements, they could lend themselves well to providing connectivity to clusters of IoT devices.

From an architecture standpoint, the specifications also model two different operational models: a neutral host mode that connects to local IP networks or the internet, and a mode that connects the MulteFire RAN to a 3GPP MNO core as an additional Radio Access Network.

MulteFire is based on 3GPP’s LAA – as specified in R13 last year and the upcoming R14. LAA (Licensed Assisted Access) is a technology that lets LTE cells aggregate unlicensed spectrum channels with licensed spectrum bands to create higher capacities and throughputs. To do this, LAA-equipped cells “listen” to channel signals, and utilise the unlicensed spectrum when it is available. This is known as Listen Before Talk (LBT). LAA technology and its less polite precursor LTE-U have been controversial with some in the WiFi industry because they said it could interfere with the operation of WiFi networks in the same unlicensed spectrum that LAA cells are accessing.

The WiFi camp also objected to LTE-U and LAA on commercial grounds. Some felt it unfairly favoured the owners and operators of licensed spectrum by requiring an LAA cell to have a licensed spectrum anchor to enable the carrier aggregation facility. There was a push to include a standalone mode of LAA within 3GPP specs – something that 3GPP decided not to progress.

So MulteFire is, in essence, standalone LAA by another name – in that it allows LTE small cells to operate in unlicensed and shared spectrum  even without requiring the LTE cell to also have a licensed spectrum anchor. That opens up the potential for enterprise and building owners, as well as to cable operators and “neutral host” operators to deploy LTE networks.

For the major vendors signed up to the alliance, all of whom are also producing 3GPP LAA equipment, MulteFire offers the chance to address new purchasers of LTE network equipment. Nor is MulteFire necessarily bad news for licensed operators: it also gives those same operators the ability to extend coverage, whilst remaining connected to the EPC (existing packet core network) via the S1 interface.

In time, it is possible 3GPP will re-engage with MulteFire, adopting the technology within its own specifications. Chmaytelli said MulteFire’s potential status within 3GPP is “still an open question”.

“Most members have the same teams in both (MF Alliance and 3GPP) and the reason for the Alliance was to move fast and come up with the specifications in one year. But it’s the same methodology in standards and IPR declarations and all that, so it tracks well with 3GPP. The question – if [3GPP] inherits or we do it ourselves – will be more interesting as we start stepping into 5G as well and see the concept progressing,” he added.