In a Viterbi decoder, there are two known memory organization techniques for the storage of survivor sequences from which the decoded information sequence is retrieved, namely register exchange method and traceback method. This paper extends previously known traceback approaches describes two new traceback algorithms, and compares various traceback methods with each other. Memory size, latency and implementational complexity of the survivor sequence management are analyzed for both uniprocessor and multiprocessor realizations of Viterbi decoders. A new one-pointer traceback method is shown to be better than other known traceback methods.
Polar codes are the latest breakthrough in coding theory, as they are the
first family of codes with explicit construction that provably achieve the
symmetric capacity of discrete memoryless channels. Ar{\i}kan's polar encoder
and successive cancellation decoder have complexities of $N \log N$, for code
length $N$. Although, the complexity bound of $N \log N$ is asymptotically
favorable, we report in this work methods to further reduce the encoding and
decoding complexities of polar coding. The crux is to relax the polarization of
certain bit-channels without performance degradation. We consider schemes for
relaxing the polarization of both \emph{very good} and \emph{very bad}
bit-channels, in the process of channel polarization. Relaxed polar codes are
proved to preserve the capacity achieving property of polar codes. Analytical
bounds on the asymptotic and finite-length complexity reduction attainable by
relaxed polarization are derived.
For binary erasure channels, we show that the computation complexity can be
reduced by a factor of 6, while preserving the rate and error performance. We
also show that relaxed polar codes can be decoded with significantly reduced
latency. For AWGN channels with medium code lengths, we show that relaxed polar
codes can have lower error probabilities than conventional polar codes, while
having reduced encoding and decoding computation complexities.Comment: Conference version,Relaxed Channel Polarization for Reduced
Complexity Polar Coding, accepted for presentation at IEEE Wireless
Communications and Networking Conference WCNC 201
We propose a least-mean square based gain calibration technique of an RF digitally controlled oscillator (DCO) in an all-digital phase-locked loop (ADPLL). The DCO gain of about 12-kHz/least significant bit is subject to process, voltage and temperature variations, but is tracked and compensated in real time. Precise setting of the inverse DCO gain in the ADPLL modulating path allows direct wide-band frequency modulation that is independent from the ADPLL loop bandwidth. The technique is part of a single-chip fully compliant Global System for Mobile Communications (GSM)/EDGE transceiver in 90-nm digital CMOS.
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