6 research outputs found
Multiple Access Outerbounds and the Inseparability of Parallel Interference Channels
It is known that the capacity of parallel (multi-carrier) Gaussian
point-to-point, multiple access and broadcast channels can be achieved by
separate encoding for each subchannel (carrier) subject to a power allocation
across carriers. In this paper we show that such a separation does not apply to
parallel Gaussian interference channels in general. A counter-example is
provided in the form of a 3 user interference channel where separate encoding
can only achieve a sum capacity of per carrier
while the actual capacity, achieved only by joint-encoding across carriers, is
per carrier. As a byproduct of our analysis,
we propose a class of multiple-access-outerbounds on the capacity of the 3 user
interference channel
Delay-rate tradeoff for ergodic interference alignment in the Gaussian case
In interference alignment, users sharing a wireless channel are each able to
achieve data rates of up to half of the non-interfering channel capacity, no
matter the number of users. In an ergodic setting, this is achieved by pairing
complementary channel realizations in order to amplify signals and cancel
interference. However, this scheme has the possibility for large delays in
decoding message symbols. We show that delay can be mitigated by using outputs
from potentially more than two channel realizations, although data rate may be
reduced. We further demonstrate the tradeoff between rate and delay via a
time-sharing strategy. Our analysis considers Gaussian channels; an extension
to finite field channels is also possible.Comment: 7 pages, 2 figures, presented at 48th Allerton Conference on
Communication Control and Computing, 2010. Includes appendix detailing Markov
chain analysi