Massive MIMO pilot assignment optimization based on total capacity

  • José Carlos Marinello
  • Cristiano Magalhães Panazio
  • Taufik Abrão


We investigate the effects of pilot assignment in multi-cell massive multiple-input multiple-output systems. When deploying a large number of antennas at base station (BS), and linear detection/precoding algorithms, the system performance in both uplink (UL) and downlink (DL) is mainly limited by pilot contamination. This interference is proper of each pilot, and thus system performance can be improved by suitably assigning the pilot sequences to the users within the cell, according to the desired metric. We show in this paper that UL and DL performances constitute conflicting metrics, in such a way that one cannot achieve the best performance in UL and DL with a single pilot assignment configuration. Thus, we propose an alternative metric, namely total capacity, aiming to simultaneously achieve a suitable performance in both links. 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. Besides, the combination of our proposed PA schemes with an efficient power control algorithm unveils the great potential of the proposed techniques in providing improved performance for a higher number of users. 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.


Massive MIMO Pilot contamination Pilot assignment Joint uplink-downlink optimization Heuristic Power control 



This work was supported in part by the National Council for Scientific and Technological Development (CNPq) of Brazil under Grant 304066/2015-0 and in part by Londrina State University - Paraná State Government (UEL).


  1. 1.
    Marzetta, T. (2010). Noncooperative cellular wireless with unlimited numbers of base station antennas. IEEE Transactions on Wireless Communications, 9(11), 3590–3600.CrossRefGoogle Scholar
  2. 2.
    Marzetta, T., Larsson, E., Yang, H., & Ngo, H. (2016). Fundamentals of Massive MIMO. New York, NY: Cambridge University Press.CrossRefGoogle Scholar
  3. 3.
    Zhu, X., Wang, Z., Dai, L., & Qian, C. (2015). Smart pilot assignment for massive MIMO. IEEE Communications Letters, 19(9), 1644–1647.CrossRefGoogle Scholar
  4. 4.
    Marinello, J. C., & Abrão, T. (2016). Pilot distribution optimization in multi-cellular large scale MIMO systems. AEU - International Journal of Electronics and Communications, 70(8), 1094–1103.CrossRefGoogle Scholar
  5. 5.
    Ngo, H. Q., Ashikhmin, A., Yang, H., Larsson, E. G., & Marzetta, T. L. (2017). Cell-free massive MIMO versus small cells. IEEE Transactions on Wireless Communications, 16(3), 1834–1850.CrossRefGoogle Scholar
  6. 6.
    Zhu, X., Dai, L., Wang, Z., & Wang, X. (2017). Weighted-graph-coloring-based pilot decontamination for multicell massive MIMO systems. IEEE Transactions on Vehicular Technology, 66(3), 2829–2834.CrossRefGoogle Scholar
  7. 7.
    Chen, Z., & Yang, C. (2016). Pilot decontamination in wideband massive MIMO systems by exploiting channel sparsity. IEEE Transactions on Wireless Communications, 15(7), 5087–5100.Google Scholar
  8. 8.
    Zhao, P., Wang, Z., Qian, C., Dai, L., & Chen, S. (2016). Location-aware pilot assignment for massive MIMO systems in heterogeneous networks. IEEE Transactions on Vehicular Technology, 65(8), 6815–6821.CrossRefGoogle Scholar
  9. 9.
    Wang, Z., Zhao, P., Qian, C., & Chen, S. (2016). Location-aware channel estimation enhanced TDD based massive MIMO. IEEE Access, 4, 7828–7840.CrossRefGoogle Scholar
  10. 10.
    Zhang, Q., Jin, S., McKay, M., Morales-Jimenez, D., & Zhu, H. (2015). Power allocation schemes for multicell massive MIMO systems. IEEE Transactions on Wireless Communications, 14(11), 5941–5955.CrossRefGoogle Scholar
  11. 11.
    Zarei, S., Aulin, J., Gerstacker, W., & Schober, R. (2017). Max-min multicell-aware precoding and power allocation for downlink massive MIMO systems. IEEE Signal Processing Letters, 24(10), 1433–1437.CrossRefGoogle Scholar
  12. 12.
    Björnson, E., Larsson, E. G., & Debbah, M. (2016). Massive MIMO for maximal spectral efficiency: How many users and pilots should be allocated? IEEE Transactions on Wireless Communications, 15(2), 1293–1308.CrossRefGoogle Scholar
  13. 13.
    Rasti, M., & Sharafat, A.-R. (2011). Distributed uplink power control with soft removal for wireless networks. IEEE Transactions on Communications, 59(3), 833–843.CrossRefGoogle Scholar
  14. 14.
    Fernandes, F., Ashikhmin, A., & Marzetta, T. (2013). Inter-cell interference in noncooperative TDD large scale antenna systems. IEEE Journal on Selected Areas in Communications, 31(2), 192–201.CrossRefGoogle Scholar

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© Springer Science+Business Media, LLC, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Department of Electrical EngineeringState University of LondrinaLondrinaBrazil
  2. 2.Laboratory of Communications and SignalsPolytechnic School of the University of São PauloSão PauloBrazil

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