33,351 research outputs found
On Constant Gaps for the Two-way Gaussian Interference Channel
We introduce the two-way Gaussian interference channel in which there are
four nodes with four independent messages: two-messages to be transmitted over
a Gaussian interference channel in the direction, simultaneously
with two-messages to be transmitted over an interference channel (in-band,
full-duplex) in the direction. In such a two-way network, all
nodes are transmitters and receivers of messages, allowing them to adapt
current channel inputs to previously received channel outputs. We propose two
new outer bounds on the symmetric sum-rate for the two-way Gaussian
interference channel with complex channel gains: one under full adaptation (all
4 nodes are permitted to adapt inputs to previous outputs), and one under
partial adaptation (only 2 nodes are permitted to adapt, the other 2 are
restricted). We show that simple non-adaptive schemes such as the Han and
Kobayashi scheme, where inputs are functions of messages only and not past
outputs, utilized in each direction are sufficient to achieve within a constant
gap of these fully or partially adaptive outer bounds for all channel regimes.Comment: presented at 50th Annual Allerton Conference on Communication,
Control, and Computing, Monticello, IL, October 201
Divide-and-conquer: Approaching the capacity of the two-pair bidirectional Gaussian relay network
The capacity region of multi-pair bidirectional relay networks, in which a
relay node facilitates the communication between multiple pairs of users, is
studied. This problem is first examined in the context of the linear shift
deterministic channel model. The capacity region of this network when the relay
is operating at either full-duplex mode or half-duplex mode for arbitrary
number of pairs is characterized. It is shown that the cut-set upper-bound is
tight and the capacity region is achieved by a so called divide-and-conquer
relaying strategy. The insights gained from the deterministic network are then
used for the Gaussian bidirectional relay network. The strategy in the
deterministic channel translates to a specific superposition of lattice codes
and random Gaussian codes at the source nodes and successive interference
cancelation at the receiving nodes for the Gaussian network. The achievable
rate of this scheme with two pairs is analyzed and it is shown that for all
channel gains it achieves to within 3 bits/sec/Hz per user of the cut-set
upper-bound. Hence, the capacity region of the two-pair bidirectional Gaussian
relay network to within 3 bits/sec/Hz per user is characterized.Comment: IEEE Trans. on Information Theory, accepte
Enabling the Multi-User Generalized Degrees of Freedom in the Gaussian Cellular Channel
There has been major progress over the last decade in understanding the
classical interference channel (IC). Recent key results show that constant bit
gap capacity results can be obtained from linear deterministic models (LDMs).
However, it is widely unrecognized that the time-invariant, frequency-flat
cellular channel, which contains the IC as a special case, possesses some
additional generalized degrees of freedom (GDoF) due to multi-user operation.
This was proved for the LDM cellular channel very recently but is an open
question for the corresponding Gaussian counterpart. In this paper, we close
this gap and provide an achievable sum-rate for the Gaussian cellular channel
which is within a constant bit gap of the LDM sum capacity. We show that the
additional GDoFs from the LDM cellular channel carry over. This is enabled by
signal scale alignment. In particular, the multi-user gain reduces the
interference by half in the 2-user per cell case compared to the IC.Comment: 5 pages, to appear in IEEE ITW 2014, Hobart, Australi
Information Transmission using the Nonlinear Fourier Transform, Part III: Spectrum Modulation
Motivated by the looming "capacity crunch" in fiber-optic networks,
information transmission over such systems is revisited. Among numerous
distortions, inter-channel interference in multiuser wavelength-division
multiplexing (WDM) is identified as the seemingly intractable factor limiting
the achievable rate at high launch power. However, this distortion and similar
ones arising from nonlinearity are primarily due to the use of methods suited
for linear systems, namely WDM and linear pulse-train transmission, for the
nonlinear optical channel. Exploiting the integrability of the nonlinear
Schr\"odinger (NLS) equation, a nonlinear frequency-division multiplexing
(NFDM) scheme is presented, which directly modulates non-interacting signal
degrees-of-freedom under NLS propagation. The main distinction between this and
previous methods is that NFDM is able to cope with the nonlinearity, and thus,
as the the signal power or transmission distance is increased, the new method
does not suffer from the deterministic cross-talk between signal components
which has degraded the performance of previous approaches. In this paper,
emphasis is placed on modulation of the discrete component of the nonlinear
Fourier transform of the signal and some simple examples of achievable spectral
efficiencies are provided.Comment: Updated version of IEEE Transactions on Information Theory, vol. 60,
no. 7, pp. 4346--4369, July, 201
- …