19 research outputs found
Degrees of freedom region for an interference network with general message demands
We consider a single hop interference network with transmitters and
receivers, all having antennas. Each transmitter emits an independent
message and each receiver requests an arbitrary subset of the messages. This
generalizes the well-known -user -antenna interference channel, where
each message is requested by a unique receiver. For our setup, we derive the
degrees of freedom (DoF) region. The achievability scheme generalizes the
interference alignment schemes proposed by Cadambe and Jafar. In particular, we
achieve general points in the DoF region by using multiple base vectors and
aligning all interferers at a given receiver to the interferer with the largest
DoF. As a byproduct, we obtain the DoF region for the original interference
channel. We also discuss extensions of our approach where the same region can
be achieved by considering a reduced set of interference alignment constraints,
thus reducing the time-expansion duration needed. The DoF region for the
considered system depends only on a subset of receivers whose demands meet
certain characteristics. The geometric shape of the DoF region is also
discussed.Comment: 26 pages, 5 figures, revised version, submitted to IEEE Transactions
on Information Theor
Multiple-Antenna Interference Channel with Receive Antenna Joint Processing and Real Interference Alignment
We consider a constant -user Gaussian interference channel with
antennas at each transmitter and antennas at each receiver, denoted as a
channel. Relying on a result on simultaneous Diophantine
approximation, a real interference alignment scheme with joint receive antenna
processing is developed. The scheme is used to provide new proofs for two
previously known results, namely 1) the total degrees of freedom (DoF) of a
channel is ; and 2) the total DoF of a channel is
at least . We also derive the DoF region of the channel,
and an inner bound on the DoF region of the channel
Degrees of Freedom of Full-Duplex Multiantenna Cellular Networks
We study the degrees of freedom (DoF) of cellular networks in which a full
duplex (FD) base station (BS) equipped with multiple transmit and receive
antennas communicates with multiple mobile users. We consider two different
scenarios. In the first scenario, we study the case when half duplex (HD)
users, partitioned to either the uplink (UL) set or the downlink (DL) set,
simultaneously communicate with the FD BS. In the second scenario, we study the
case when FD users simultaneously communicate UL and DL data with the FD BS.
Unlike conventional HD only systems, inter-user interference (within the cell)
may severely limit the DoF, and must be carefully taken into account. With the
goal of providing theoretical guidelines for designing such FD systems, we
completely characterize the sum DoF of each of the two different FD cellular
networks by developing an achievable scheme and obtaining a matching upper
bound. The key idea of the proposed scheme is to carefully allocate UL and DL
information streams using interference alignment and beamforming techniques. By
comparing the DoFs of the considered FD systems with those of the conventional
HD systems, we establish the DoF gain by enabling FD operation in various
configurations. As a consequence of the result, we show that the DoF can
approach the two-fold gain over the HD systems when the number of users becomes
large enough as compared to the number of antennas at the BS.Comment: 21 pages, 16 figures, a shorter version of this paper has been
submitted to the IEEE International Symposium on Information Theory (ISIT)
201
Degrees of Freedom of Uplink-Downlink Multiantenna Cellular Networks
An uplink-downlink two-cell cellular network is studied in which the first
base station (BS) with antennas receives independent messages from its
serving users, while the second BS with antennas transmits
independent messages to its serving users. That is, the first and second
cells operate as uplink and downlink, respectively. Each user is assumed to
have a single antenna. Under this uplink-downlink setting, the sum degrees of
freedom (DoF) is completely characterized as the minimum of
,
, , and , where denotes
. The result demonstrates that, for a broad class of network
configurations, operating one of the two cells as uplink and the other cell as
downlink can strictly improve the sum DoF compared to the conventional uplink
or downlink operation, in which both cells operate as either uplink or
downlink. The DoF gain from such uplink-downlink operation is further shown to
be achievable for heterogeneous cellular networks having hotspots and with
delayed channel state information.Comment: 22 pages, 11 figures, in revision for IEEE Transactions on
Information Theor
Ergodic Interference Alignment
This paper develops a new communication strategy, ergodic interference
alignment, for the K-user interference channel with time-varying fading. At any
particular time, each receiver will see a superposition of the transmitted
signals plus noise. The standard approach to such a scenario results in each
transmitter-receiver pair achieving a rate proportional to 1/K its
interference-free ergodic capacity. However, given two well-chosen time
indices, the channel coefficients from interfering users can be made to exactly
cancel. By adding up these two observations, each receiver can obtain its
desired signal without any interference. If the channel gains have independent,
uniform phases, this technique allows each user to achieve at least 1/2 its
interference-free ergodic capacity at any signal-to-noise ratio. Prior
interference alignment techniques were only able to attain this performance as
the signal-to-noise ratio tended to infinity. Extensions are given for the case
where each receiver wants a message from more than one transmitter as well as
the "X channel" case (with two receivers) where each transmitter has an
independent message for each receiver. Finally, it is shown how to generalize
this strategy beyond Gaussian channel models. For a class of finite field
interference channels, this approach yields the ergodic capacity region.Comment: 16 pages, 6 figure, To appear in IEEE Transactions on Information
Theor