title: Analysis of data-aided channel tracking for hybrid massive MIMO systems in millimeter wave communications
Creators: name: Pang, Xiaolin
Publisher: name: Memorial University of Newfoundland
Year: 2023

description: As the data traffic in future wireless communications will explosively grow up to 1000 folds by the deployment of 5G, several technologies are emerging to satisfy this demand, including massive multiple-input multiple-output (MIMO), millimeter wave(mmWave) communications, Non-Orthogonal Multiple Access (NOMA), etc. The combination of millimeter wave communication and massive MIMO is a promising solution since it can provide tens of GHz bandwidth by fundamentally exploring higher unoccupied spectrum resources. As the wavelength of higher frequency shrinks, it is possible to design more compact antenna array with a very large number of antennas. However, this will cause enormous hardware cost, energy consumption and computation complexity of decent RF(Radio Frequency) chains. To this end, spatial sparsity is widely explored to enable hybrid mmWave massive MIMO systems with limited RF chains to achieve high spectral and energy efficiency. On the other hand, channel estimation problem for systems with limited RF chains is quite challenging due to the unaffordable overhead. To be specific, the conventional pilot-based channel estimation requires to repeatedly transmit the same pilot because only a limited number of antennas will be activated for each time slot. Therefore, it consumes a huge amount of temporal and spectral resources. To overcome this problem, channel estimation for mmWave massive MIMO systems is still an on-going research area. Among plenty of candidates, channel tracking is the most promising one. To achieve the extremely low cost and complexity, which is also the greatest motivation of this thesis, data-aided channel tracking method is thoroughly investigated with closed-form CRLB(Cram´er-Rao lower bound). In this thesis, data-aided channel tracking systems with different types of antenna, including ULA(Uniform Linear Antenna array), DLA(Discrete Lens Antenna ar ray) and UPA(Uniform Planar Antenna array), are comprehensively studied and proposed, and the closed-form expressions of the corresponding CRLBs are carefully derived. The numerical results of the simulations for each case are shown respectively, and they reveal that the performance of the proposed data-aided channel tracking system approaches the CRLB very well. In addition, to further explore the data-aided channel tracking system, the multi-user scenario is investigated in this thesis. This is motivated by the highway and high-speed railway application, where overtaking operation happens frequently. In this case, the users in the same beam suffer from high channel interference, thus degrading the channel estimation performance or even causing outage. To deal with this issue, we proposed an estimated SER(Symbol Error Rate) metric to indicate if a scheduling operation is necessary to be taken place and restart of the whole channel tracking system is required. This metric is included as the Update phase in the proposed channel tracking method for multiuser scenario with DLA. The theoretical SER closed-form expression is also derived for multi-user data detection. The numerical results of the simulations verified the theoretical SER expression, and the scheduling metric based on the estimated SER performance is also discussed.