Abstract
The use of massive multiple-input multiple-output (MIMO) techniques for communication at millimeter-Wave (mmW) frequency bands has become a key enabler to meet the data rate demands of the upcoming fifth generation (5G) cellular systems. In particular, analog and hybrid beamforming solutions are receiving increasing attention as less expensive and more power efficient alternatives to fully digital precoding schemes. Despite their proven good performance in simple setups, their suitability for realistic cellular systems with many interfering base stations and users is still unclear. Furthermore, the performance of massive MIMO beamforming and precoding methods are in practice also affected by practical limitations and hardware constraints. In this sense, this paper assesses the performance of digital precoding and analog beamforming in an urban cellular system with an accurate mmW channel model under both ideal and realistic assumptions. The results show that analog beamforming can reach the performance of fully digital maximum ratio transmission under line of sight conditions and with a sufficient number of parallel radio-frequency (RF) chains, especially when the practical limitations of outdated channel information and per antenna power constraints are considered. This work also shows the impact of the phase shifter errors and combiner losses introduced by real phase shifter and combiner implementations over analog beamforming, where the former ones have minor impact on the performance, while the latter ones determine the optimum number of RF chains to be used in practice.
Highlights
Nowadays, one of the most active research areas in the wireless communication field is the design of communication techniques for fifth generation (5G) cellular systems
In digital precoding non frequency selective (DP NFS), all frequency blocks (FB) are allocated to a single set of UEs per subframe, while, in digital precoding frequency selective (DP FS), the allocation is optimized per resource block (RB), thereby allowing different sets of UEs to be scheduled per subframe in different FBs
This model is based on real measurements taken in New York City. It is consistent with the 3rd Generation Partnership Project (3GPP) ray-based modeling methodology, and includes characterization of the channel in azimuth, elevation and polarization. This model takes into account channel variability in the frequency and time domains, considering the actual correlation between antennas depending on the geometry of the antenna array deployment
Summary
One of the most active research areas in the wireless communication field is the design of communication techniques for fifth generation (5G) cellular systems. Many ABF and HBF approaches have been proposed in the last years, both for single-user (SU) [8,9] and multi-user (MU) transmissions [10,11], all of them using a substantially reduced number of RF chains with respect to the number of antennas The potential of these schemes is well-known; to the best of the authors’ knowledge, there is not yet a clear view on the performance of the different beamforming alternatives in a complete system with multiple transmission and reception points and a realistic channel model. Motivated by the lack of concluding results on the mmW multi-cell performance of ABF, this paper provides a thorough assessment of ABF schemes for MU single-stream transmission under realistic channel conditions in the lower edge of the mmW frequency band.
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