Constrained sequence codes are widely used to meet constraints imposed by digital communication systems. This study presents methods to evaluate the capacity of constrained codes that have multiple independently or dependently constrained signalling dimensions. The authors outline a straightforward analysis technique when the signalling dimensions are independent, and demonstrate how the capacity can be evaluated, estimated or upper bounded when the signalling dimensions are dependent. Their motivation for this work is capacity analysis of DC‐free codes with complex‐valued symbols, and they present results for these types of codes throughout the study.

The use of spectral shaping constrained codes is commonplace in baseband digital communication systems. In this study, the authors consider the use of constrained codes in bandpass systems through the design of DC‐free codes for the complex baseband representations of commonly used signalling constellations including quaternary phase shift keying, eight‐phase shift keying and sixteen quadrature amplitude modulation. The authors construct DC‐free codes for these signalling alphabets and present their spectral performance. They show that, similar to DC‐free codes for baseband systems, the variance of the running digital sum remains a good indicator of spectral performance and that Justesen's relationship between the sum variance and cut‐off frequency holds.

Constrained sequence codes are widely used to meet constraints imposed by digital storage and communication systems. This paper develops an algorithm for the construction of constrained codes that admit state-independent decoding. By partitioning the code into a group of alphabets, one for each state, a codebook is developed using this algorithm that will allow the code to be decoded at the receiver without the need for state information. Finally, we use this algorithm to construct DC-free runlength-limited (RLL) codes, and we present two highly efficient state-independent decodable DC-free RLL codes.

This paper proposes an extension of Knuthpsilas complementation method for constructing balanced codewords. By placing the encoding process in the context of a multimode code, we propose generating a number of alternative balanced words using Knuthpsilas method to represent each source word, and selecting the word with minimum squared weight (MSW) as the codeword in order to achieve improved spectral performance. Spectral results, which demonstrate increased suppression of low frequency components by up to 3 dB through the use of this approach, are presented.

This paper proposes a new method for peak-to-average power ratio (PAPR) reduction in orthogonal frequency division multiplexing (OFDM) systems using forward error correction (FEC). The scheme combines the intentional insertion of correctable errors into the data stream with a specialized bit mapping. The latter deviates from traditional Gray encoding of bits into modulation symbols in order to maximize the benefits of FEC-based PAPR reduction. Using the code redundancy, the proposed scheme achieves significant reduction in PAPR and satisfactory bit error rate (BER) performance at the expense of acceptable computational complexity. Specifically, the complementary cumulative distribution function (CCDF) of the coded signal shows about a 5dB improvement over the original OFDM signal. In addition, BER performance in an additive white Gaussian noise demonstrates trade-offs between reduction in PAPR and remaining error correction capability of the deployed codes.