73 research outputs found
Generalized Degrees of Freedom of the Symmetric Cache-Aided MISO Broadcast Channel with Partial CSIT
We consider the cache-aided MISO broadcast channel (BC) in which a
multi-antenna transmitter serves single-antenna receivers, each equipped
with a cache memory. The transmitter has access to partial knowledge of the
channel state information. For a symmetric setting, in terms of channel
strength levels, partial channel knowledge levels and cache sizes, we
characterize the generalized degrees of freedom (GDoF) up to a constant
multiplicative factor. The achievability scheme exploits the interplay between
spatial multiplexing gains and coded-multicasting gain. On the other hand, a
cut-set-based argument in conjunction with a GDoF outer bound for a parallel
MISO BC under channel uncertainty are used for the converse. We further show
that the characterized order-optimal GDoF is also attained in a decentralized
setting, where no coordination is required for content placement in the caches.Comment: first revisio
Network Coherence Time Matters - Aligned Image Sets and the Degrees of Freedom of Interference Networks with Finite Precision CSIT and Perfect CSIR
This work obtains the first bound that is provably sensitive to network
coherence time, i.e., coherence time in an interference network where all
channels experience the same coherence patterns. This is accomplished by a
novel adaptation of the aligned image sets bound, and settles various open
problems noted previously by Naderi and Avestimehr and by Gou et al. For
example, a necessary and sufficient condition is obtained for the optimality of
1/2 DoF per user in a partially connected interference network where the
channel state information at the receivers (CSIR) is perfect, the channel state
information at the transmitters (CSIT) is instantaneous but limited to finite
precision, and the network coherence time is T_c= 1. The surprising insight
that emerges is that even with perfect CSIR and instantaneous finite precision
CSIT, network coherence time matters, i.e., it has a DoF impact.Comment: 19 pages, 4 figure
Elevated Multiplexing and Signal Space Partitioning in the 2 User MIMO IC with Partial CSIT
The user MIMO interference channel with arbitrary antenna configurations
is studied under arbitrary levels of partial CSIT for each of the channels, to
find the degrees of freedom (DoF) achievable by either user while the other
user achieves his full interference-free DoF. The goal is to gain new insights
due to the inclusion of MIMO (multiple antennas at both transmitters and
receivers) into the signal space partitioning schemes associated with partial
CSIT. An interesting idea that emerges from this study is "elevated
multiplexing" where the signals are split into streams and transmitted from
separate antennas at elevated power levels, which allows these signals to be
jointly decoded at one receiver which has fewer spatial dimensions with lower
interference floors, while another receiver is simultaneously able to
separately decode these signals with a higher interference floor but across a
greater number of spatial dimensions. Remarkably, we find that there is a DoF
benefit from increasing the number of antennas at a transmitter even if that
transmitter already has more antennas than its desired receiver and has no
CSIT.Comment: Submitted as an invited paper to IEEE SPAW
- …