2,444 research outputs found
An asymptotic approximation of the ISI channel capacity
An asymptotic method to calculate the information rate of an ISI channel is presented in this work. The method is based on an integral representation of the mutual information, which is then calculated by using a saddlepoint approximation along with an asymptotic expansion stemming from the Hubbard-Stratonovich transform. This asymptotic result is evaluated repeatedly to generate a large number of samples required for the Monte-Carlo approximation of the final result. The proposed method has the advantage of being manageable even when the channel memory becomes very large since the complexity grows with polynomial order in the memory length
Amplify-and-Forward in Wireless Relay Networks
A general class of wireless relay networks with a single source-destination
pair is considered. Intermediate nodes in the network employ an
amplify-and-forward scheme to relay their input signals. In this case the
overall input-output channel from the source via the relays to the destination
effectively behaves as an intersymbol interference channel with colored noise.
Unlike previous work we formulate the problem of the maximum achievable rate in
this setting as an optimization problem with no assumption on the network size,
topology, and received signal-to-noise ratio. Previous work considered only
scenarios wherein relays use all their power to amplify their received signals.
We demonstrate that this may not always maximize the maximal achievable rate in
amplify-and-forward relay networks. The proposed formulation allows us to not
only recover known results on the performance of the amplify-and-forward
schemes for some simple relay networks but also characterize the performance of
more complex amplify-and-forward relay networks which cannot be addressed in a
straightforward manner using existing approaches.
Using cut-set arguments, we derive simple upper bounds on the capacity of
general wireless relay networks. Through various examples, we show that a large
class of amplify-and-forward relay networks can achieve rates within a constant
factor of these upper bounds asymptotically in network parameters.Comment: Minor revision: fixed a typo in eqn. reference, changed the
formatting. 30 pages, 8 figure
Noncoherent Capacity of Underspread Fading Channels
We derive bounds on the noncoherent capacity of wide-sense stationary
uncorrelated scattering (WSSUS) channels that are selective both in time and
frequency, and are underspread, i.e., the product of the channel's delay spread
and Doppler spread is small. For input signals that are peak constrained in
time and frequency, we obtain upper and lower bounds on capacity that are
explicit in the channel's scattering function, are accurate for a large range
of bandwidth and allow to coarsely identify the capacity-optimal bandwidth as a
function of the peak power and the channel's scattering function. We also
obtain a closed-form expression for the first-order Taylor series expansion of
capacity in the limit of large bandwidth, and show that our bounds are tight in
the wideband regime. For input signals that are peak constrained in time only
(and, hence, allowed to be peaky in frequency), we provide upper and lower
bounds on the infinite-bandwidth capacity and find cases when the bounds
coincide and the infinite-bandwidth capacity is characterized exactly. Our
lower bound is closely related to a result by Viterbi (1967).
The analysis in this paper is based on a discrete-time discrete-frequency
approximation of WSSUS time- and frequency-selective channels. This
discretization explicitly takes into account the underspread property, which is
satisfied by virtually all wireless communication channels.Comment: Submitted to the IEEE Transactions on Information Theor
A Unifying Model for External Noise Sources and ISI in Diffusive Molecular Communication
This paper considers the impact of external noise sources, including
interfering transmitters, on a diffusive molecular communication system, where
the impact is measured as the number of noise molecules expected to be observed
at a passive receiver. A unifying model for noise, multiuser interference, and
intersymbol interference is presented, where, under certain circumstances,
interference can be approximated as a noise source that is emitting
continuously. The model includes the presence of advection and molecule
degradation. The time-varying and asymptotic impact is derived for a series of
special cases, some of which facilitate closed-form solutions. Simulation
results show the accuracy of the expressions derived for the impact of a
continuously-emitting noise source, and show how approximating intersymbol
interference as a noise source can simplify the calculation of the expected bit
error probability of a weighted sum detector.Comment: 14 pages, 7 figures, 4 tables, 1 appendix. To appear in IEEE Journal
on Selected Areas in Communications (JSAC). Submitted October 21, 2013,
revised April 21, 2014, accepted June 3, 201
Energy-Efficient Power Control in Multipath CDMA Channels via Large System Analysis
This paper is focused on the design and analysis of power control procedures
for the uplink of multipath code-division-multiple-access (CDMA) channels based
on the large system analysis (LSA). Using the tools of LSA, a new decentralized
power control algorithm aimed at energy efficiency maximization and requiring
very little prior information on the interference background is proposed;
moreover, it is also shown that LSA can be used to predict with good accuracy
the performance and operational conditions of a large network operating at the
equilibrium over a multipath channel, i.e. the power,
signal-to-interference-plus-noise ratio (SINR) and utility profiles across
users, wherein the utility is defined as the number of bits reliably delivered
to the receiver for each energy-unit used for transmission. Additionally, an
LSA-based performance comparison among linear receivers is carried out in terms
of achieved energy efficiency at the equilibrium. Finally, the problem of the
choice of the utility-maximizing training length is also considered. Numerical
results show a very satisfactory agreement of the theoretical analysis with
simulation results obtained with reference to systems with finite (and not so
large) numbers of users.Comment: Proceedings of the IEEE International Symposium on Personal, Indoor
and Mobile Radio Communications, Cannes, France, September 15-18, 200
Beyond Massive-MIMO: The Potential of Data-Transmission with Large Intelligent Surfaces
In this paper, we consider the potential of data-transmission in a system
with a massive number of radiating and sensing elements, thought of as a
contiguous surface of electromagnetically active material. We refer to this as
a large intelligent surface (LIS). The "LIS" is a newly proposed concept, which
conceptually goes beyond contemporary massive MIMO technology, that arises from
our vision of a future where man-made structures are electronically active with
integrated electronics and wireless communication making the entire environment
"intelligent".
We consider capacities of single-antenna autonomous terminals communicating
to the LIS where the entire surface is used as a receiving antenna array. Under
the condition that the surface-area is sufficiently large, the received signal
after a matched-filtering (MF) operation can be closely approximated by a
sinc-function-like intersymbol interference (ISI) channel. We analyze the
capacity per square meter (m^2) deployed surface, \hat{C}, that is achievable
for a fixed transmit power per volume-unit, \hat{P}. Moreover, we also show
that the number of independent signal dimensions per m deployed surface is
2/\lambda for one-dimensional terminal-deployment, and \pi/\lambda^2 per m^2
for two and three dimensional terminal-deployments. Lastly, we consider
implementations of the LIS in the form of a grid of conventional antenna
elements and show that, the sampling lattice that minimizes the surface-area of
the LIS and simultaneously obtains one signal space dimension for every spent
antenna is the hexagonal lattice. We extensively discuss the design of the
state-of-the-art low-complexity channel shortening (CS) demodulator for
data-transmission with the LIS.Comment: Submitted to IEEE Trans. on Signal Process., 30 pages, 12 figure
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