User-Centric cell-free massive MIMO networks at millimeter and sub-THz frequencies
Tuesday, 7 June 2022, 14:00-15:30/16:00-17:30, Room A306
Speaker:
- Stefano Buzzi (University of Cassino and Lazio Meridionale, Consorzio Nazionale Interuniversitario per le Telecomunicazioni, IT)
- Carmen D’Andrea (University of Cassino and Lazio Meridionale, Consorzio Nazionale Interuniversitario per le Telecomunicazioni, IT)
Motivation and Context
Cell-free massive MIMO (CF-mMIMO) is unanimously considered as the evolution of Massive MIMO, one of the key technologies of the 5G wireless systems. In CF-mMIMO, the base stations (BSs) are substituted by several access points (APs), having a lower number of antennas and lower complexity. CF-mMIMO overcomes the cell-edge problem typical of cellular systems occurring when the user equipment (UE) is located in between the reference base station (BS) and an interfering BS and experiences a poor signal-to-interference-plus-noise ratio (SINR). Most of the research on CF-mMIMO focuses on sub-6 GHz frequencies, while fewer studies have addressed the challenges posed by the use of such deployments at millimeter-wave (mmWave) frequencies and, to the best of the proposers’ knowledge, no references can be found for the sub-THz spectrum.
The use of mmWave and sub-THz carrier frequencies is one of the key pillars of future wireless systems. The availability of large bandwidths greatly contributes to providing the huge data rates that are requested to implement current and future ultra-broadband mobile services. A distributed network architecture seems to be ideally suited for coping with the blockage effects and large path loss suffered by wireless link and such high frequencies. CF-mMIMO and high-frequencies are thus perfectly matched and will be very popular in future network deployments. We thus believe that this tutorial is extremely timely and fully matched to the EUCNC community interests and expertise.
To the best of proposers’ knowledge, this is the first tutorial focusing on user-centric CF-mMIMO at mmWave and sub-THz carrier frequencies. The main challenges of user-centric CF-mMIMO deployments at mmWave and sub-THz will be discussed, with emphasis on channel estimation, beamforming design, and signal processing techniques, topics of particular interest for the conference attendees.
Structure and Content
Part I – Cell-free Massive MIMO: definition and key features (20min) In the first part of the tutorial, the fundamentals of this technology are discussed with emphasis on the main characteristics and advantages in its original form at sub-6 GHz.
Part II – The mmWave and sub-THz propagation and channel models (30min) The features of the propagation at these frequencies and the well-known clustered channel model are introduced and commented. Emphasis is given to the need to use multiple antennas at the transmitter and receiver to overcome the high path-loss and on the need to use hybrid (analog/digital) beamforming techniques to reduce the complexity of signal processing.
Part III – Transceiver Signal Processing for CF-mMIMO at mmWave and sub-THz (40min) Transceiver design for will be addressed here. Topics such as hybrid analog-digital beamforming, data decoding and channel estimation for CF-mMIMO operating at mmWave will be discussed here.
Break
Part IV – The beam alignment in CF-mMIMO (40min) The challenging task of beam alignment will be discussed in a multi-UE multi-AP setting. After an initial review of the main approaches to beam alignment, the solutions developed in [6]-[8] will be described and commented in detail.
Part V – CF-mMIMO with Mobility (30min) The problem of beam tracking and of handover algorithm design in CF-mMIMO for mmWave and sub-THz carrier frequencies will be addressed here.
Part VI – Challenges and Future research directions (10min)
Part VII – Q&A (10min)
