France’s technology institute, LETI, worked with South Korean organizations under a project called 5G Champion, which created a 5G prototype for demonstrations running on a bus in the Olympic campus. This was driving at 60 kilometres per hour, receiving data at 5Gbps to allow users to view two sports event broadcasts simultaneously.
LETI is one of the European institutes that is focused on key aspects of future 5G, such as new waveforms and dynamic spectrum. For instance, one of its recent projects was an outdoor ‘super Wi-Fi’ technology, which uses dynamic spectrum access (DSA) to create a flexible solution for broadband access, based on a patented scalable waveform for next generation wireless, which could be adapted for 5G.
New waveforms, optimised for different 5G use cases such as massively dense IoT, have also been important areas of study for the UK’s 5G Innovation Centre (an academic research centre at the University of Surrey) and universities including King’s College London and Glasgow, as well as research centres around Europe. The waveforms that will be adopted in Release 16 are a central aspect of 5G R&D, although that doesn't mean that all would-be players are on, as it were, the same wavelength.
LETI’s design uses a new BF-OFDM (block-filtered OFDM) multicarrier waveform for the air interface, addressing a wide range of requirements with a unified physical layer in the same system bandwidth. This is backwards compatible with OFDM waveforms currently in use in LTE and Wi-Fi, so that the same terminals can be used, but LETI says it overcomes the shortcomings of those implementations.
This fits in with several attempts to develop new waveforms for 5G, based on enhanced OFDM implementations or on new approaches. Many of these are being tested first for fixed wireless and backhaul applications.
For instance, start-up Cohere Technologies (described on its website as “one of the leading pioneers in the global wireless connectivity industry”) submitted its Orthogonal Time Frequency and Space (OTFS) technology for inclusion in Release 15, 3GPP’s first 5G standards. 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.
Some mobile stakeholders were frustrated that the first wave of 5G standards, 3GPP Release 15, stuck with OFDM in the air interface, rather than adopting a more radical modulation technology. The 3GPP NR Release 15 study item agreed to support CP-OFDM (Cyclic Prefix OFDM) for the downlink in enhanced mobile broadband applications, with the complementary technology, DFT-Spread OFDM, working alongside CP-OFDM on the eMBB uplink. This has some continuity with LTE, which uses OFDM in the downlink and DFT-S OFDM in the uplink, but increases the importance of CP-OFDM.
According to Qualcomm, DFT-S OFDM provides link budget benefits while CP-OFDM supports MIMO spatial multiplexing advantages. It believes there are advantages to using both technologies on the uplink, which can adaptively switch between them to get the best of both worlds.
However, additional standards are likely to creep into Release 16 next year, providing renewed opportunities for new approaches from various players – ranging from giants like Huawei to start-ups like Cohere Technologies.
Telefónica has conducted fixed wireless tests using Cohere’s 5G implementation, turboConnect FWA, which was unveiled at Mobile World Congress in February. While the company waits and hopes for acceptance in mobile and IoT standards, it aims to take advantage of the recent burst of interest in FWA, especially in 5G mmWave spectrum, to push OTFS into the mainstream.
Other operators have shown an interest in OTFS, while further ‘flavours’ of OFDM are also being promoted in a scenario that is getting, to say the least, interesting.