535 research outputs found
Constellation Shaping for Communication Channels with Quantized Outputs
Channel capacity is an important aspect of every digital communication system. Capacity can be defined as the highest rate of information that can be transmitted over the channel with low error probability. The purpose of this research is to study the effect of the input symbol distribution on the information rate when the signal is transmitted over an Additive White Gaussian Noise (AWGN) channel with a quantized output. The channel was analyzed by transforming it into a Discrete Memoryless Channel (DMC), which is a discrete-input and discrete-output channel. Given the quantizer resolution and Signal-to-Noise Ratio (SNR), this thesis proposes a strategy for achieving the capacity of a certain shaping technique previously proposed by Le Goff, et al. Under the constraints of the modulation, the shaping technique, and the quantizer resolution, the capacity is found by jointly optimizing the input distribution and quantizer spacing. The optimization is implemented by exhaustively searching over all feasible input distributions and a finely-spaced set of candidate quantizer spacings. The constrained capacity for 16-QAM modulation is found using the proposed technique
Modulation Diversity in Fading Channels with Quantized Receiver
In this paper, we address the design of codes which achieve modulation
diversity in block fading single-input single-output (SISO) channels with
signal quantization at receiver and low-complexity decoding. With an
unquantized receiver, coding based on algebraic rotations is known to achieve
modulation coding diversity. On the other hand, with a quantized receiver,
algebraic rotations may not guarantee diversity. Through analysis, we propose
specific rotations which result in the codewords having equidistant
component-wise projections. We show that the proposed coding scheme achieves
maximum modulation diversity with a low-complexity minimum distance decoder and
perfect channel knowledge. Relaxing the perfect channel knowledge assumption we
propose a novel training/estimation and receiver control technique to estimate
the channel. We show that our coding/training/estimation scheme and minimum
distance decoding achieve an error probability performance similar to that
achieved with perfect channel knowledge
Precoded Integer-Forcing Universally Achieves the MIMO Capacity to Within a Constant Gap
An open-loop single-user multiple-input multiple-output communication scheme
is considered where a transmitter, equipped with multiple antennas, encodes the
data into independent streams all taken from the same linear code. The coded
streams are then linearly precoded using the encoding matrix of a perfect
linear dispersion space-time code. At the receiver side, integer-forcing
equalization is applied, followed by standard single-stream decoding. It is
shown that this communication architecture achieves the capacity of any
Gaussian multiple-input multiple-output channel up to a gap that depends only
on the number of transmit antennas.Comment: to appear in the IEEE Transactions on Information Theor
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
Polar codes and polar lattices for independent fading channels
In this paper, we design polar codes and polar lattices for i.i.d. fading channels when the channel state information is only available to the receiver. For the binary input case, we propose a new design of polar codes through single-stage polarization to achieve the ergodic capacity. For the non-binary input case, polar codes are further extended to polar lattices to achieve the egodic Poltyrev capacity, i.e., the capacity without power limit. When the power constraint is taken into consideration, we show that polar lattices with lattice Gaussian shaping achieve the egodic capacity of fading channels. The coding and shaping are both explicit, and the overall complexity of encoding and decoding is O(N log2 N)
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