Self-orthogonal codes have attracted considerable attention owing to their applications in quantum error-correcting codes, linear complementary dual codes, and a variety of other fields. In this paper, we construct new families of self-orthogonal codes and self-orthogonal minimal codes by establishing criteria that characterize the self-orthogonality of certain linear codes. To this end, we first establish several new criteria for linear codes arising from the defining-set construction to be self-orthogonal. More specifically, for
q>3, we show that the code
CD is self-orthogonal whenever the defining set
D is
G-invariant, where
G⊆Fq∗ and
∣G∣>2. For
q=2,3, we characterize the self-orthogonality of
CD using certain character sums. By combining these criteria with partial difference sets, we construct several new families of self-orthogonal codes, which lead to optimal or almost optimal quantum codes. Secondly, via the action of a multiplicative subgroup
G⊆Fq∗ with
∣G∣>2 on the columns of a projective linear code, we construct self-orthogonal codes with flexible parameters. From their augmented codes, we derive quantum codes. By choosing suitable projective codes, we obtain optimal quantum codes with high parametric flexibility. Thirdly, we employ the characteristic function method to construct linear codes and establish criterion for their self-orthogonality. Based on this, we construct several classes of self-orthogonal minimal codes that violate the Ashikhmin-Barg condition, using vectorial dual-bent functions and
s-plateaued functions.
After the pioneering work of Shor and Steane, we are able to establish links between quantum codes and classical codes with certain self-orthogonality. Therefore, constructing classical self-orthogonal codes with small dimension and large dual distance becomes our centre point due to the interesting application to quantum codes. \n \n \n \nOne of the most interesting and useful families of classical codes are MDS codes. We will show a systematic construction for classical Hermitian self-orthogonal MDS codes through generalized Reed-Solomn codes. Afterwards, new families of quantum MDS codes can be produced. \n \n \n \nClassical BCH codes would be another good choice for self-orthogonal codes. We show the dual containment through polynomial evaluations, simply by choosing suitable cyclotomic cosets. As a result, quantum codes with good parameters can be derived. \n \n \n \nAnother good candidate of classical codes to investigate for dual containment comes from the class of \n \nalgebraic geometry codes. Instead of testing for dual containment directly, this thesis explores an equivalent condition for the existence of self-orthogonal AG codes. \n \n \n \nAfter various constructions for quantum codes, this thesis ends with a study on bounds for estimating the parameters of codes.
Multiweight optical codes are one of the alternative designs for differentiated quality-of-service (QoS) in multimedia optical CDMA (OCDMA) networks. In this paper, we address the design of reconfigurable multiweight wavelength-time optical codes that lead to secure multimedia transmission in OCDMA networks. The proposed multiweight wavelength-time optical codes are constructed based on quasigroups (QGs) for wavelength hopping and one-dimensional multiweight optical orthogonal codes (MWOOCs) for time spreading, then called QG/MWOOCs. Both QGs and MWOOCs are randomly generated by computer search. As a result, the proposed QG/MWOOCs have many different code set groups which differ in both time and wavelengths positions. Furthermore, a secure network is suggested by employing reconfigurable encoders/decoders array waveguide gratings (AWGs)-based, which allow the users to change their codewords patterns to protect against eavesdropping. Finally, the degree of security which may provide by the proposed scheme is analyzed. The results show that the proposed scheme offers both differentiated QoS and differentiated quality-of-security (QoSec) in multimedia OCDMA networks.
The finite Euclidean and Projective geometry codes are the most known among One-Step Majority-Logic Decodable codes that are Low-Density Parity-Check codes as well. Unfortunately, these codes are rare, and we do not have a great diversity when designing communication systems with a fixed code-length and code rate. Regarding the non-binary Euclidian and projective geometric Codes, each code is restricted to a unique alphabet. To offer a bigger range of possible alphabets for each code, we propose new construction by redefining the incidence vector of the lines of Euclidean and projective geometries over finite fields. This approach leads to an enrichment of the class of EG and PG codes. An error performance study of some new codes has been carried out and shows good results.
Based on the characteristics of optical orthogonal codes,a new algorithm for constructing quasi-cyclic LDPC codes is proposed.Firstly,based on optical orthogonal codes,we can get an initial matrix which meets the parameter request,then under the proposed formula and the characteristics of quasi-cyclic LDPC codes to determine the shift parameter matrix.Finally,using all-zero matrix and the circlet permutation matrix to fill the shift parameter matrix,we can get a check matrix without cycles with length of 4 and 6.Simulations show that,under the AWGN channel and the BP decoding algorithm,the new quasi-cyclic LDPC codes are better than Mackay's codes in the bit error rate and they are more proper for hardware implementation.
In this paper, we construct new families of classical convolutional codes (CCC's) and new families of quantum convolutional codes (QCC's). The CCC's are derived from (block) algebraic geometry (AG) codes. Furthermore, new families of CCC's are constructed by applying the techniques of puncturing, extending, expanding, and by the direct product code construction applied to AG codes. In addition, utilizing the new CCC's constructed here, we obtain new families of QCC's. The parameters of these new codes are good. More precisely, in the classical case, a family of almost near maximum distance separable (MDS) codes is presented; in the quantum case, we construct a family of MDS (optimal) quantum convolutional codes.