131 research outputs found
Opportunistic Scheduling for Full-Duplex Uplink-Downlink Networks
We study opportunistic scheduling and the sum capacity of cellular networks
with a full-duplex multi-antenna base station and a large number of
single-antenna half-duplex users. Simultaneous uplink and downlink over the
same band results in uplink-to-downlink interference, degrading performance. We
present a simple opportunistic joint uplink-downlink scheduling algorithm that
exploits multiuser diversity and treats interference as noise. We show that in
homogeneous networks, our algorithm achieves the same sum capacity as what
would have been achieved if there was no uplink-to-downlink interference,
asymptotically in the number of users. The algorithm does not require
interference CSI at the base station or uplink users. It is also shown that for
a simple class of heterogeneous networks without sufficient channel diversity,
it is not possible to achieve the corresponding interference-free system
capacity. We discuss the potential for using device-to-device side-channels to
overcome this limitation in heterogeneous networks.Comment: 10 pages, 2 figures, to appear at IEEE International Symposium on
Information Theory (ISIT) '1
Random Access for Massive MIMO Systems with Intra-Cell Pilot Contamination
Massive MIMO systems, where the base stations are equipped with hundreds of
antenna elements, are an attractive way to attain unprecedented spectral
efficiency in future wireless networks. In the "classical" massive MIMO
setting, the terminals are assumed fully loaded and a main impairment to the
performance comes from the inter-cell pilot contamination, i.e., interference
from terminals in neighboring cells using the same pilots as in the home cell.
However, when the terminals are active intermittently, it is viable to avoid
inter-cell contamination by pre-allocation of pilots, while same-cell terminals
use random access to select the allocated pilot sequences. This leads to the
problem of intra-cell pilot contamination. We propose a framework for random
access in massive MIMO networks and derive new uplink sum rate expressions that
take intra-cell pilot collisions, intermittent terminal activity, and
interference into account. We use these expressions to optimize the terminal
activation probability and pilot length
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