30 research outputs found
Resolving Entanglements in Topological Interference Management with Alternating Connectivity
The sum-capacity of a three user interference wired network for time-varying
channels is considered. Due to the channel variations, it is assumed that the
transmitters are only able to track the connectivity between the individual
nodes, thus only the (alternating) state of the network is known. By
considering a special subset of all possible states, we show that state
splitting combined with joint encoding over the alternating states is required
to achieve the sum-capacity. Regarding upper bounds, we use a genie aided
approach to show the optimality of this scheme. This highlights that more
involved transmit strategies are required for characterizing the degrees of
freedom even if the transmitters have heavily restricted channel state
information
Two-Hop Interference Channels: Impact of Linear Time-Varying Schemes
We consider the two-hop interference channel (IC) with constant real channel
coefficients, which consists of two source-destination pairs, separated by two
relays. We analyze the achievable degrees of freedom (DoF) of such network when
relays are restricted to perform scalar amplify-forward (AF) operations, with
possibly time-varying coefficients. We show that, somewhat surprisingly, by
providing the flexibility of choosing time-varying AF coefficients at the
relays, it is possible to achieve 4/3 sum-DoF. We also develop a novel outer
bound that matches our achievability, hence characterizing the sum-DoF of
two-hop interference channels with time-varying AF relaying strategies.Comment: To appear in Proc. of ISIT 2013 (proof of lemma added
Communication Through Collisions: Opportunistic Utilization of Past Receptions
When several wireless users are sharing the spectrum, packet collision is a
simple, yet widely used model for interference. Under this model, when
transmitters cause interference at any of the receivers, their collided packets
are discarded and need to be retransmitted. However, in reality, that receiver
can still store its analog received signal and utilize it for decoding the
packets in the future (for example, by successive interference cancellation
techniques). In this work, we propose a physical layer model for wireless
packet networks that allows for such flexibility at the receivers. We assume
that the transmitters will be aware of the state of the channel (i.e. when and
where collisions occur, or an unintended receiver overhears the signal) with
some delay, and propose several coding opportunities that can be utilized by
the transmitters to exploit the available signal at the receivers for
interference management (as opposed to discarding them). We analyze the
achievable throughput of our strategy in a canonical interference channel with
two transmitter-receiver pairs, and demonstrate the gain over conventional
schemes. By deriving an outer-bound, we also prove the optimality of our scheme
for the corresponding model.Comment: Accepted to IEEE INFOCOM 2014. arXiv admin note: text overlap with
arXiv:1301.530