The debate about LTE in unlicensed spectrum, and whether it will interfere with WiFi, is a heated and topical one and has certainly been a key discussion point during this spring’s conference season. But while the WiFi and 3GPP communities hurl their respective arguments, test results and even insults, many companies are actually still focusing on bringing the two technologies harmoniously together across the licensed/unlicensed divide.
One is Korea’s KT, which is demonstrating what the elusive heterogeneous network could really do, delivering gigabit speeds to smartphones over a combined LTE/WiFi network.
Working with Samsung, the operator has developed a hybrid platform it calls Giga LTE, which can be accessed with a firmware upgrade to Galaxy S6 or S6 Edge handsets. The technology leverages KT’s own network of about 140,000 WiFi hotspots nationwide, and its 200,000 LTE base stations.
Further devices, and wider coverage, will be added during the rest of this year, and will see KT upping the ante against the largest mobile operator, SKT. The two carriers are always locked in combat to deliver ever-faster speeds to mobile broadband-hungry consumers, a race which has driven them to be among the world’s most advanced deployers – and developers – of cutting edge mobile technology.
Both have made extensive use of small cells and have shown the way towards the HetNet before most of their peers round the world have got much beyond WiFi offload. They have also been developing architectures for Cloud-RAN and contributing to the 5G R&D efforts.
For now, KT has stolen a march on its rival, since Giga LTE can achieve peak end user speeds which, at 1.17Gbps, are four times faster than those of SKT’s top end LTE-only service. The latter is enabled by technical wizardry of its own, namely triband LTE-Advanced carrier aggregation.
But KT may not keep its lead for long. SKT is reported to be working with Samsung rival LG on its own hybrid WiFi/LTE platform.
The Korean one-upmanship comes against a broader backdrop of R&D into new ways to harness WiFi and cellular networks in parallel – a feature of planned 4G HetNets and a likely hallmark of 5G. These approaches may rely on convergence at OSS/BSS, packet core, RAN or even small cell chip level.
One recent development was Alcatel-Lucent’s launch of WiFi Boost, which uses cellular connections for uplink traffic only, and WiFi for downlink only, to deliver an overall boost of 70% on the latter, and even more on the former. A later version will allow the two networks to combine their download signals, ALU said at this year’s Mobile World Congress.
Another is Qualcomm’s latest disruptive contribution to the LTE-Unlicensed debate, MuLTEfire. Having pushed heavily to use LTE in the 5 GHz band only to provide supplemental capacity for a licensed-spectrum anchor network, it has now announced MuLTEfire, which enables LTE to run standalone in 5 GHz – potentially making it a WiFi-like weapon for non-licence owners, such as cable operators, to create competitors to the cellcos’ services.
Introduced in a blog post by Qualcomm technical marketing manager Matt Branda (and also in its filing with the FCC as part of the LTE-U comment process), MuLTEfire claims to provide “LTE-like performance benefits to more deployment scenarios with WiFi-like simplicity – a leaner, self-contained network architecture that is suitable for neutral deployments where any deployment can service any device.”
Qualcomm also said MuLTEfire would “create expanded opportunities for small cell deployments, especially in hyper-dense environments and indoor locations”, by providing complementary capacity and coverage options for MNOs.
Meanwhile, no fewer than 36 companies have filed comments to the FCC as part of its process of evaluating LTE-Unlicensed. Most of the comments have acknowledged some benefits of LTE-U, such as spectral efficiency, high speeds and, for MNOs, a cost effective way to add capacity. But most have also expressed concerns over interference and potential weakening of operators’ existing WiFi investments.
- AT&T echoed many reactions to the FCC’s original request for comment, which said the regulator was going beyond its remit in addressing specific technologies’ pros and cons. The carrier reiterated that the FCC must make any decision on LTE-U from a technology neutral standpoint, and said any interference issues must be resolved by standards bodies, not regulators.
- Verizon and T-Mobile USA have been vocal supporters of LTE in 5 GHz and have promised to deploy it – the former’s filing suggested that date could be soon, since in the US, there is no need to wait for the listen before talk features of LAA. If the FCC approves, they could deploy existing LTE-U, for supplemental downlink only (LAA will also support uplink in future), almost at once.
- Google, unsurprisingly, was more negative about LTE-U, though the search giant might well be expected to leap on a non-anchored implementation of 4G in the 5 GHz band, as another way to disrupt the established carrier business model and provide alternatives to the MNOs’ services. It noted the potential for interference with WiFi and commented: “The Commission should be vigilant in ensuring that deployments of LTE-U and LAA in unlicensed spectrum will not systematically exclude unlicensed-only technologies.”
- Other WiFi supporters went a lot further, including Ruckus, which said pre-standard implementations, or LTE-U systems without listen before talk, would have “a potentially devastating effect on 802.11-based WiFi networks, especially for services such as voice and video over WiFi.”
- And Cablevision, one of the most aggressive US cablecos in deploying WiFi as an alternative to cellular, wrote in a lengthy filing that “LTE-U/LAA proponents have distorted the historical, healthy dynamics of the unlicensed bands, using their FCC licences to unjustly and unreasonably exploit unlicensed spectrum, harm consumers and undermine an essential input for their competitors.” It demanded that the FCC “step up” to protect consumers and competition.
- Ericsson used its filing to deny any prospect of pre-standard implementations coming to the US. It wrote that LTE-U specifications are already complete, since it is included in Release 12, not in R13 like LTE-LAA. R12 has multiple coexistence mechanisms for fair, shared usage with WiFi, it insisted, pointing to “extensive coordination between 3GPP and IEEE 802.11 on appropriate sharing characteristics to ensure coexistence between LTE-U/LAA and 802.11/WiFi.”
- However, another filing, by Paul Nikolich, chair of the IEEE 802 LAN/MAN standards committee, claimed: “There has been no coordination between IEEE 802 and any standards body associated with LTE-U, because LTE-U was not developed by a standards body.” He wrote that he believed LTE-U to be a proprietary solution which does not use appropriate sharing mechanisms to ensure coexistence with IEEE 802.11 standards, and that there had been no coordination with the 3GPP beyond some presentations.
- The WiFi Alliance said there was, at this stage, insufficient information about how LTE-U and LAA will coexist with WiFi and urged the FCC to continue monitoring developments to ensure there is sufficient attention to fair sharing. It also claimed LTE-U was a proprietary system developed by a few companies, because it used a technology (CSAT or carrier sensing adaptive transmission) which was not under consideration by 3GPP. “This lack of industry standard implementation of CSAT means that its impact on other users of shared spectrum will be variable and unpredictable,” it added.
- On a similar theme, Broadcom wrote that LTE-U was unlikely to be a good neighbor to WiFi for various reasons – the coexistence algorithms are proprietary, there are variations in equipment, and coexistence is controlled at time of operation, among other reasons. It added to the claims that LTE-U is not a proper standard, since its LTE-U Forum is restricted in participation, and its sharing algorithms are proprietary. The company wrote: “The standards-setting process should evaluate coexistence with WiFi as it is currently deployed in the market: it should recognize that WiFi devices can operate using 20 to 160 MHz channels, incorporate MIMO technology, and use explicit transmit beamforming (TxBF).”