Finding scale with mmWave in 5G

17 NOV 2017

PhilMarshall-113NEW ANALYSIS: It’s exhausting. The repetitive drum of 5G and its three-prong strategy for ultra-broadband, massively connected or ultra-reliable services. PowerPoint presentations make it look so easy. But it isn’t. Ultra-broadband can only be achieved with lots of spectrum, or revolutionary solutions that combine mmWave technology with intelligent antennas.

Current 5G proposals for massive connectivity and ultra-reliability lack compelling business cases to drive large-scale 5G deployments and will be constrained to local implementations for the foreseeable future. It is not to say that 5G is a folly, but to be successful it must align with opportunities that provide sufficient market scale.

Market scale for 5G will initially come from solutions that complement existing mobile operator services and business models. This aligns 5G most closely with ultra-broadband. As operators advance their 4G networks, it is inevitable there will come a time when it makes economic sense to deploy 5G in the existing and new (sub-6GHz) spectrum bands. However, as this occurs, it is unclear what the “ultra” in ultra-broadband really means.

From a pure spectrum efficiency standpoint, we believe 5G will be between 130 per cent and 150 per cent more efficient than 4G, depending on the level of spectrum aggregation. In reality, the ultra-broadband performance touted for 5G generally depends on services that operate in mmWave spectrum with intelligent antenna technology. It is in this realm that uncertainty emerges.

Mobile networks generally operate at frequencies below 3GHz – a far cry from mmWave which are upwards of 20GHz to 30GHz. The laws of physics tell us that as the operating frequency of a radio signal increases, its wavelength decreases, and its energy disperses more rapidly with distance. These laws also tell us that path obstructions with physical dimensions comparable or larger than the wavelength of a radio signal generally cause significant signal attenuation.

On this basis, mmWave coverage is pathetic without highly directional antenna technology. This has enabled mmWave usage for fixed transmission links and short-range indoor coverage under strict line-of-sight (LOS) conditions. In recent years, researchers have observed that mmWave signals can be received under non-LOS conditions in reflective environments, using intelligent antenna systems to track to the orientation of the reflected signals. These same tracking capabilities also enable nomadic and mobile wireless access in cases where adequate signals can be received.

Still immature
The coverage performance of mmWave is hotly debated, particularly in the context of 5G mobile. This is a testament to the immaturity of mmWave technology and the intelligent antennas needed for it to function. Although numerous field trials have been conducted, it is too early to establish a consistent view of mmWave performance. Some field trial results indicate that mmWave will only function under LOS conditions for mobile services. Other results, including those conducted by researchers and New York University (NYU), and by Qualcomm, tell a different story.

NYU has conducted extensive field measurements, which suggest it is reasonably likely for mmWave to achieve small cell like coverage in urban environments. Qualcomm has also conducted field trials with comparable results to NYU and has combined its field results with mmWave propagation models developed by the 3GPP (which are less optimistic than NYU).

Qualcomm predicts mmWave could commonly achieve 40 per cent to 70 per cent of outdoor network coverage in urban environments when deployed on existing macro and small cell network infrastructure. Qualcomm is so confident in its findings that it has invested heavily in semiconductor technology and developed smartphone device prototypes with mmWave capabilities.

As the mmWave debate rages on, we believe that irrespective of the outcome several key tenets should dictate the short- to medium-term strategies for operators. In particular, operators cannot afford to ignore 5G mmWave and its potential to enable massive network capacity gains. Some operators are already applying mmWave to niche applications such as fixed-wireless. However, we do not believe that fixed-wireless offers meaningful scale. Instead, the long-term success of mmWave depends on its role in 5G mobile.

Although the coverage expectations for mmWave are inconclusive, there is general agreement that network-wide coverage will be patchy. On this basis, mmWave is most likely best suited for local and campus orientated applications, or as a capacity offload solution. The capacity offload approach fails to deliver the promise of “ultra-broadband” in wide area networks, but ensures service consistency rather than having users “fall-off-a-cliff” every time they move out of mmWave coverage.

Even though 5G promises to address an enormous variety of use cases, mobile operators must take a measured approach towards the use cases they enable. Even if some use cases are risky and speculative, it is important that they are supported by basic broadband solutions which align with existing operator business models and are positioned to drive market scale.

By Phil Marshall, chief research officer at Tolaga Research

The editorial views expressed in this article are solely those of the author and will not necessarily reflect the views of the GSMA, its Members or Associate Members.