At Real Wireless, we tend to assume that our expertise will be called upon by a number of industry players as 5G throws up new challenges and competing ways of solving problems. However, even though most activity is still only at the trial stage, there’s no doubt that 5G waveforms are already inspiring some diverse approaches that our clients will want us to assess. Here’s why.
There have been several attempts to develop new waveforms for 5G, based on enhanced OFDM implementations or on new approaches. For example, start-up Cohere Technologies (described as one of the leading pioneers in the global wireless connectivity industry) submitted its Orthogonal Time Frequency Space (OTFS) technology for inclusion in 3GPP’s first 5G standards, Release 15. It failed, but continues in trials with operators such as Telefónica, and has hopes of success in Release 16. OTFS sits on top of OFDM and claims significantly lower susceptibility to fading, which boosts data rates and reliability.
Netherlands-based multinational telecoms company Altice and Australian telecommunications and media company Telstra are among the start-up’s investors, and it has conducted commercial trials with both those companies, as well as Charter Communications, C-Spire and Deutsche Telekom, all in fixed wireless. Cohere says several more operators are scheduled for FWA trials in the early part of this year.
Cohere stresses that its technology can coexist with OFDM to support smooth migration from current networks, or coexistence between different 5G flavours. That integration could be critical to win acceptance for a technology from a small player. Many observers believe OFDM will be the most efficient option for sub-6 GHz spectrum and mobile broadband use cases, but that alternatives will be needed to optimize performance in millimetre wave bands, or for emerging IoT and ultra-low latency applications.
Larger companies are also hoping to get their favoured air interface technologies into the standards in Release 16. For the mmWave bands, China Mobile has validated Huawei’s Filtered OFDM and ZTE’s FB-OFDM in its high frequency tests, but has provided no details of the results as yet. In 2016, Huawei described a ‘unified’ air interface which draws on several approaches at once and allows different sub-bands, within the baseband, to be configured individually for different purposes.
Its design is based on three key concepts – Filtered OFDM (fOFDM), Sparse Code Multiple Access (SCMA) and polar code. Each has a contribution to make to a standard which can be adaptable without compromising on the performance requirements, says Huawei.
Qualcomm’s pitch for IoT applications has been non-orthogonal RSMA (resource spread multiple access) technology, plus a new multiplexing technique which would allow traffic requiring very low latency to take priority automatically and to use RSMA. This technology uses time and frequency spreading and overlaps users in a way that aims to improve network efficiency and power consumption. It can support mobility and downlink meshing, as well as network-assisted mesh on the uplink.
Release 16 is due at the end of next year, though even then it’s by no means clear that the waveform debate will be brought to an end. In the event, we expect to be employing our expertise in technology, standards and regulation to deal with a lot of 5G waveform-related enquiries well beyond that date…