14,962 research outputs found
Matched Metrics and Channels
The most common decision criteria for decoding are maximum likelihood
decoding and nearest neighbor decoding. It is well-known that maximum
likelihood decoding coincides with nearest neighbor decoding with respect to
the Hamming metric on the binary symmetric channel. In this work we study
channels and metrics for which those two criteria do and do not coincide for
general codes
Gaussian Broadcast Channels with an Orthogonal and Bidirectional Cooperation Link
This paper considers a system where one transmitter broadcasts a single
common message to two receivers linked by a bidirectional cooperation channel,
which is assumed to be orthogonal to the downlink channel. Assuming a
simplified setup where, in particular, scalar relaying protocols are used and
channel coding is not exploited, we want to provide elements of response to
several questions of practical interest. Here are the main underlying issues:
1. The way of recombining the signals at the receivers; 2. The optimal number
of cooperation rounds; 3. The way of cooperating (symmetrically or
asymmetrically; which receiver should start cooperating in the latter case); 4.
The influence of spectral resources. These issues are considered by studying
the performance of the assumed system through analytical results when they are
derivable and through simulation results. For the particular choices we made,
the results sometimes do not coincide with those available for the discrete
counterpart of the studied channel
Construction of Capacity-Achieving Lattice Codes: Polar Lattices
In this paper, we propose a new class of lattices constructed from polar
codes, namely polar lattices, to achieve the capacity \frac{1}{2}\log(1+\SNR)
of the additive white Gaussian-noise (AWGN) channel. Our construction follows
the multilevel approach of Forney \textit{et al.}, where we construct a
capacity-achieving polar code on each level. The component polar codes are
shown to be naturally nested, thereby fulfilling the requirement of the
multilevel lattice construction. We prove that polar lattices are
\emph{AWGN-good}. Furthermore, using the technique of source polarization, we
propose discrete Gaussian shaping over the polar lattice to satisfy the power
constraint. Both the construction and shaping are explicit, and the overall
complexity of encoding and decoding is for any fixed target error
probability.Comment: full version of the paper to appear in IEEE Trans. Communication
Accessible Capacity of Secondary Users
A new problem formulation is presented for the Gaussian interference channels
(GIFC) with two pairs of users, which are distinguished as primary users and
secondary users, respectively. The primary users employ a pair of encoder and
decoder that were originally designed to satisfy a given error performance
requirement under the assumption that no interference exists from other users.
In the scenario when the secondary users attempt to access the same medium, we
are interested in the maximum transmission rate (defined as {\em accessible
capacity}) at which secondary users can communicate reliably without affecting
the error performance requirement by the primary users under the constraint
that the primary encoder (not the decoder) is kept unchanged. By modeling the
primary encoder as a generalized trellis code (GTC), we are then able to treat
the secondary link and the cross link from the secondary transmitter to the
primary receiver as finite state channels (FSCs). Based on this, upper and
lower bounds on the accessible capacity are derived. The impact of the error
performance requirement by the primary users on the accessible capacity is
analyzed by using the concept of interference margin. In the case of
non-trivial interference margin, the secondary message is split into common and
private parts and then encoded by superposition coding, which delivers a lower
bound on the accessible capacity. For some special cases, these bounds can be
computed numerically by using the BCJR algorithm. Numerical results are also
provided to gain insight into the impacts of the GTC and the error performance
requirement on the accessible capacity.Comment: 42 pages, 12 figures, 2 tables; Submitted to IEEE Transactions on
Information Theory on December, 2010, Revised on November, 201
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