1,104 research outputs found
Active Attack on User Load Achieving Pilot Design in Massive MIMO Networks
In this paper, we propose an active attacking strategy on a massive
multiple-input multiple-output (MIMO) network, where the pilot sequences are
obtained using the user load-achieving pilot sequence design. The user
load-achieving design ensures that the signal-to-interference-plus-noise ratio
(SINR) requirements of all the users in the massive MIMO networks are
guaranteed even in the presence of pilot contamination. However, this design
has some vulnerabilities, such as one known pilot sequence and the correlation
among the pilot sequences, that may be exploited by active attackers. In this
work, we first identify the potential vulnerabilities in the user
load-achieving pilot sequence design and then, accordingly, develop an active
attacking strategy on the network. In the proposed attacking strategy, the
active attackers transmit known pilot sequences in the uplink training and
artificial noise in the downlink data transmission. Our examination
demonstrates that the per-cell user load region is significantly reduced by the
proposed attacking strategy. As a result of the reduced per-cell user load
region, the SINR requirements of all the users are no longer guaranteed in the
presence of the active attackers. Specifically, for the worst affected users
the SINR requirements may not be ensured even with infinite antennas at the
base station.Comment: Accepted in IEEE GlobeCOM 201
Harmonized Cellular and Distributed Massive MIMO: Load Balancing and Scheduling
Multi-tier networks with large-array base stations (BSs) that are able to
operate in the "massive MIMO" regime are envisioned to play a key role in
meeting the exploding wireless traffic demands. Operated over small cells with
reciprocity-based training, massive MIMO promises large spectral efficiencies
per unit area with low overheads. Also, near-optimal user-BS association and
resource allocation are possible in cellular massive MIMO HetNets using simple
admission control mechanisms and rudimentary BS schedulers, since scheduled
user rates can be predicted a priori with massive MIMO.
Reciprocity-based training naturally enables coordinated multi-point
transmission (CoMP), as each uplink pilot inherently trains antenna arrays at
all nearby BSs. In this paper we consider a distributed-MIMO form of CoMP,
which improves cell-edge performance without requiring channel state
information exchanges among cooperating BSs. We present methods for harmonized
operation of distributed and cellular massive MIMO in the downlink that
optimize resource allocation at a coarser time scale across the network. We
also present scheduling policies at the resource block level which target
approaching the optimal allocations. Simulations reveal that the proposed
methods can significantly outperform the network-optimized cellular-only
massive MIMO operation (i.e., operation without CoMP), especially at the cell
edge
Group-blind detection with very large antenna arrays in the presence of pilot contamination
Massive MIMO is, in general, severely affected by pilot contamination. As
opposed to traditional detectors, we propose a group-blind detector that takes
into account the presence of pilot contamination. While sticking to the
traditional structure of the training phase, where orthogonal pilot sequences
are reused, we use the excess antennas at each base station to partially remove
interference during the uplink data transmission phase. We analytically derive
the asymptotic SINR achievable with group-blind detection, and confirm our
findings by simulations. We show, in particular, that in an
interference-limited scenario with one dominant interfering cell, the SINR can
be doubled compared to non-group-blind detection.Comment: 5 pages, 4 figure
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