EURASIP Journal on Applied Signal Processing
Volume 2004 (2004), Issue 5, Pages 591-604
doi:10.1155/S1110865704312072
PhantomNet: Exploring Optimal Multicellular Multiple Antenna Systems
1Electrical Engineering and Computer Science, University of California, Irvine, Irvine 92697-2625, CA, USA
2Bell Laboratories, Lucent Technologies, 791 Holmdel-Keyport Road, Holmdel 07733, NJ, USA
3Wireless Systems Laboratory, Stanford University, Stanford, 94305-9505, CA, USA
Received 20 December 2002; Revised 11 August 2003
Copyright © 2004 Syed A. Jafar et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
We present a network framework for evaluating the
theoretical performance limits of wireless data communication. We
address the problem of providing the best possible service to new
users joining the system without affecting existing users. Since,
interference-wise, new users are required to be invisible to
existing users, the network is dubbed PhantomNet. The novelty is
the generality obtained in this context. Namely, we can deal with
multiple users, multiple antennas, and multiple cells on both the
uplink and the downlink. The solution for the uplink is
effectively the same as for a single cell system since all the
base stations (BSs) simply amount to one composite BS with
centralized processing. The optimum strategy, following directly
from known results, is successive decoding (SD), where the new
user is decoded before the existing users so that the new users'
signal can be subtracted out to meet its invisibility
requirement. Only the BS needs to modify its decoding scheme in
the handling of new users, since existing users continue to
transmit their data exactly as they did before the new arrivals.
The downlink, even with the BSs operating as one composite BS, is
more problematic. With multiple antennas at each BS site, the
optimal coding scheme and the capacity region for this channel
are unsolved problems. SD and dirty paper (DP) are two schemes
previously reported to achieve capacity in special cases. For
PhantomNet, we show that DP coding at the BS is equal to or better
than SD. The new user is encoded before the existing users so
that the interference caused by his signal to existing users is
known to the transmitter. Thus the BS modifies its encoding
scheme to accommodate new users so that existing users continue
to operate as before: they achieve the same rates as before and
they decode their signal in precisely the same way as before. The
solutions for the uplink and the downlink are particularly
interesting in the way they exhibit a remarkable simplicity and
an unmistakable, near-perfect, up-down symmetry.