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Joint uplink and downlink optimization of pilot assignment for massive MIMO with power control
Author(s) -
Marinello Filho José Carlos,
Panazio Cristiano Magalhães,
Abrão Taufik
Publication year - 2017
Publication title -
transactions on emerging telecommunications technologies
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.366
H-Index - 47
ISSN - 2161-3915
DOI - 10.1002/ett.3250
Subject(s) - telecommunications link , precoding , computer science , base station , mimo , power control , performance metric , metric (unit) , interference (communication) , mathematical optimization , transmitter power output , power (physics) , optimization problem , algorithm , computer network , mathematics , transmitter , engineering , channel (broadcasting) , physics , operations management , management , quantum mechanics , economics
In this paper, we investigate the effects of pilot assignment (PA) in multicell massive multiple‐input–multiple‐output systems. When deploying linear detection/precoding algorithms and a large number of antennas at base station (BS), it is well‐known that system performance in both uplink (UL) and downlink (DL) is mainly restricted by pilot contamination. Such interference is proper of each pilot sequence, and thus, system performance can be improved by suitably assigning the pilots to the users within a given cell, according to a certain desired metric. We show in this paper that UL and DL performances constitute conflicting metrics, since it is not possible to achieve the best performance in UL and DL concomitantly. Thus, we propose an alternative metric, namely, total capacity, aiming to simultaneously achieve a suitable performance in both directions, ie, UL and DL. Since the PA problem is combinatorial, and the search space grows with the number of pilots in a factorial fashion, we also propose a low‐complexity suboptimal algorithm that achieves promising capacity performance avoiding the exhaustive search. In addition, to fully benefit from the large excess of BS antennas, we combine our proposed PA schemes with an efficient power control algorithm, unveiling the great potential of the proposed schemes to provide improved performance for more users, even with a not‐so‐large number of BS antennas. In a limit condition, for example, our numerical results demonstrate that with 64 BS antennas serving 10 users, our proposed method can assure a 95% likely rate of 4.2 Mbps for both DL and UL, and a symmetric 95% likely rate of 1.4 Mbps when serving 32 users. If a higher number of antennas is allowed at BS, the guaranteed rates can be significantly higher.