Multi-Cell Multiuser Massive MIMO Networks: User Capacity Analysis and Pilot Design

Abstract

Abstract-We propose a novel pilot sequence design to mitigate pilot contamination in multi-cell multiuser massive multiple-input multiple-output networks. Our proposed design generates pilot sequences in the multi-cell network and devises power allocation at base stations (BSs) for downlink transmission. The pilot sequences together with the power allocation ensure that the user capacity of the network is achieved and the pre-defined signalto-interference-plus-noise ratio (SINR) requirements of all users are met. To realize our design, we first derive new closed-form expressions for the user capacity and the user capacity region. Built upon these expressions, we then develop a new algorithm to obtain the required pilot sequences and power allocation. We further determine the minimum number of antennas required at BSs to achieve certain SINR requirements of all users. Numerical results are presented to corroborate our analysis and to examine the impact of key parameters, such as the pilot sequence length and the total number of users, on the network performance. A pivotal conclusion is reached that our design achieves a larger user capacity region than the existing designs and needs less antennas at the BS to fulfill the pre-defined SINR requirements of all users in the network than the existing designs.

On the Pilot Contamination Attack in Multi-Cell Multiuser Massive MIMO Networks

“…Specifically, the correlation between pilot sequences assigned to Bob ij and Bob lk is given by ρ ijlk = s T lk s ij . Afterwards, Alice l obtains the least-square (LS) channel estimate of the channel from Bob lk to Alice l by multiplying (1) with the pilot sequence matrix S ij as [4], [11], [13].…”

“…PC stems from the reuse of pilot sequences in the massive MIMO network. Consequently, the pilot sequences assigned to different users in the network are non-orthogonal [11], [12]. We highlight that the nextgeneration wireless networks are required to support a large number of high-mobility users.…”

“…However, this assumption may not be practical in realistic massive MIMO networks. Fortunately, pilot sequence design methods relax the assumption of strict orthogonality between the pilot sequence set [11]- [13]. As such, the pilot sequences set is non-orthogonal and every pilot sequence has a non-zero cross-correlation with other pilot sequences.…”

“…In this paper, we analyze the user capacity-achieving pilot sequence design from the perspective of an active attacker. We highlight that the user capacity-achieving pilot sequence design method composes correlated pilots for all the users in the network [11]- [13]. The user capacity-achieving pilot sequence design determines the user capacity region of the network under PC, where the user capacity-region signifies the range for the SINR requirements that can be satisfied by using the user capacity-achieving pilot sequence design.…”

“…• We analyze and identify the limitations of using correlated pilots in a multiuser massive MIMO network where the correlated pilots are designed using the user capacityachieving pilot sequence design [11]- [13]. To this end, we first derive analytical expressions to demonstrate the reduction in the user capacity region in a massive MIMO network under PC attack.…”