Study and modelling of the propagation and RF impairments at frequencies above 90 GHz aims at:
- Implementing realistic link- and system-level simulators.
- Designing the new air interface based on well-understood physical constraints.
- Evaluating and demonstrating B5G scenarios.
Most of the propagation and the model characteristics established for 5G mmW bands are expected to remain valid above 90 GHz, however the current models are not yet fulﬁlling all requirements, and (as always) adjustments will be mandatory.
The radio propagation research and modeling above 100 GHz are gaining interest. Some indoor results highlight that the predominance of the LoS still increases compared to sub-100GHz spectrum. However, the most powerful multi-paths remain quite similar (in terms of delay and angle) at 26 or 28 GHz and 140 GHz. Moreover, channel properties and models have been recently proposed in the range 245–350 GHz for the deﬁnition of future THz IEEE P802.15 WPAN standard. Concerning the transceiver, mmW systems are critically impacted by the radio frequency (RF) impairments, such as non-linearities, IQ imbalance and phase noise. For high frequency broadband systems, the nonlinearity of analogue components used in RF front ends gives increased challenges in the modeling of circuits and in anticipating the compensation measures required for performance improvements.The RF front end is composed of all components between the antenna and the digital baseband system of a transceiver, namely mixer or modulator, phase shifter, and power ampliﬁer (PA). At higher frequency, especially for Complementary Metal Oxide Semiconductor (CMOS) implementation, the PA efﬁciency and achievable output power decreases . Therefore, it is important to reduce the required power back-off of the PA by considering near-constant envelope modulation or by implementing PAPR reduction schemes at baseband level. Mixers and oscillators are also sources of impairments, especially at high frequencies. Mixing the RF signal with the local oscillator (LO) realizes frequency conversion within the RF transceivers. The phase of the LO can be non-stationary or time varying. Ideally, the LO generates a single tone. However, due to impermanent, the tone is modulated and phase noise is introduced. Phase noise causes signiﬁcant degradation in the performance. Therefore, design of low phase noise oscillators has been a popular research topic for decades, by exploring new semiconductor technologies and circuits design topologies. From the physical layer perspective, this has motivated extensive work on phase noise estimation and compensation . Last but not least, digitalization constraints are also a bottleneck. Data converters designed for high-end instrumentation have large bandwidth and resolution requirements. However the power constraint, integration as well as cost requirements are relaxed. One can imagine for certain scenario such as backhaul infrastructure high end equipment’s without integration and power constraints. However for consumer applications, at the device (mobile equipment) side, digitalize a large amount of bandwidth with power and integration constraints is still a research topic. The digitalization of sub band of a few GHz, seems to be a consensus. Depending on the capacity of a mobile one or more sub channel could be acquired in parallel. The interference management in that case could limit the performance of the transceiver.