10,877 research outputs found
On Capacity of the Dirty Paper Channel with Fading Dirt in the Strong Fading Regime
The classical writing on dirty paper capacity result establishes that full
interference pre-cancellation can be attained in Gelfand-Pinsker problem with
additive state and additive white Gaussian noise. This result holds under the
idealized assumption that perfect channel knowledge is available at both
transmitter and receiver. While channel knowledge at the receiver can be
obtained through pilot tones, transmitter channel knowledge is harder to
acquire. For this reason, we are interested in characterizing the capacity
under the more realistic assumption that only partial channel knowledge is
available at the transmitter. We study, more specifically, the dirty paper
channel in which the interference sequence in multiplied by fading value
unknown to the transmitter but known at the receiver. For this model, we
establish an approximate characterization of capacity for the case in which
fading values vary greatly in between channel realizations. In this regime,
which we term the strong fading regime, the capacity pre-log factor is equal to
the inverse of the number of possible fading realizations
Interference Alignment for the Multi-Antenna Compound Wiretap Channel
We study a wiretap channel model where the sender has transmit antennas
and there are two groups consisting of and receivers respectively.
Each receiver has a single antenna. We consider two scenarios. First we
consider the compound wiretap model -- group 1 constitutes the set of
legitimate receivers, all interested in a common message, whereas group 2 is
the set of eavesdroppers. We establish new lower and upper bounds on the secure
degrees of freedom. Our lower bound is based on the recently proposed
\emph{real interference alignment} scheme. The upper bound provides the first
known example which illustrates that the \emph{pairwise upper bound} used in
earlier works is not tight.
The second scenario we study is the compound private broadcast channel. Each
group is interested in a message that must be protected from the other group.
Upper and lower bounds on the degrees of freedom are developed by extending the
results on the compound wiretap channel.Comment: Minor edits. Submitted to IEEE Trans. Inf. Theor
Elements of Cellular Blind Interference Alignment --- Aligned Frequency Reuse, Wireless Index Coding and Interference Diversity
We explore degrees of freedom (DoF) characterizations of partially connected
wireless networks, especially cellular networks, with no channel state
information at the transmitters. Specifically, we introduce three fundamental
elements --- aligned frequency reuse, wireless index coding and interference
diversity --- through a series of examples, focusing first on infinite regular
arrays, then on finite clusters with arbitrary connectivity and message sets,
and finally on heterogeneous settings with asymmetric multiple antenna
configurations. Aligned frequency reuse refers to the optimality of orthogonal
resource allocations in many cases, but according to unconventional reuse
patterns that are guided by interference alignment principles. Wireless index
coding highlights both the intimate connection between the index coding problem
and cellular blind interference alignment, as well as the added complexity
inherent to wireless settings. Interference diversity refers to the observation
that in a wireless network each receiver experiences a different set of
interferers, and depending on the actions of its own set of interferers, the
interference-free signal space at each receiver fluctuates differently from
other receivers, creating opportunities for robust applications of blind
interference alignment principles
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