Polyphase Sequences Research Articles

Families of polyphase sequences with near-optimal two-valued autoand crosscorrelation functions

A construction method is proposed for new families of uniform polyphase sequences with near-optimal correlation.

Synthesis of power efficient multitone signals with flat amplitude spectrum

It is shown that, generally, any binary or polyphase sequence belonging to a pair of complementary sequences can be used to construct the initial phases of tones forming a multitone signal with the crest factor less than or equal to 6 dB. The previously proposed Shapiro-Rudin sequences are representatives of a much larger family of binary Golay complementary sequences. Numerical investigations show that the values of the crest factors obtained by applying complementary sequences (binary or polyphase) are between 5 and 6 dB, regardless of the number of tones. >

Complementary sets of chirp-like polyphase sequences

A new construction for the complementary sets of polyphase sequences is presented. The new construction is based on the application of Zadoff—Chu, as well as Ipatov polyphase sequences with ideal periodic autocorrelation function. It is shown that cyclic time shifted versions of either polyphase sequences form the complementary set, if the length of sequences is N = 5. m2 and the corresponding time shifts are different multiples of m, where s and m are any positive integers.

New complementary pairs of sequences

A general method for construction of polyphase complementary pairs of sequences of length 2N is presented. This method is based on the recursive algorithms introduced by Golay for binary sequences and by Sivaswamy for polyphase sequences. A modification of the proposed algorithm can generate multilevel and complex sequences of magnitude different from unity. The proposed sequences are suitable for radar applications where complementary sequences different from the known binary sequences are required.

Progressive deformation structures associated with ductile thrusts in the Moine Nappe, Sutherland, N. Scotland

In the deeper parts of mountain belts, polyphase structural sequences observed at outcrop-scale can arise due either to overprinting of regionally distinct deformation phases (e.g. reworking, changes in orogenic boundary conditions), or to localized controls that bring about transient changes in the patterns of ductile flow. These are unlikely to be mutually exclusive processes, and examples from Scotland demonstrate that, once regionally separate events are delimited using radiometric evidence, it is possible to isolate complex deformation sequences arising due to local controls. In the western Moine Nappe of Sutherland, the dominant structures were formed during Caledonian ductile thrusting towards the WNW, whilst earlier (?Precambrian) phases are relatively minor in importance. Two groups of Caledonian folds and fabrics are recognized in many exposures: main phase ( D 2) structures which are broadly contemporaneous with ductile thrust fabrics, and later secondary phase ( F 3) folds. The latter can be divided into two geometric groups: sheath-fold types which formed initially as WNW-overturned buckles subsequently modified by ductile shearing; and asymmetric types, which are commonly open folds apparently formed with axes close or sub-parallel to the thrust transport direction. Secondary structures show a close spatial association with high strain zones along ductile thrusts, and can be shown to have formed during the later stages of thrusting in certain critical exposures. I propose that they may form due to strain perturbations resulting from variations in the relative rates of ductile flow within the mylonites. Where differential shearing occurs due to flow-normal perturbations, wrench-related asymmetric fold types may form. In contrast, secondary sheath-fold structures may result from localized compression phases caused by flow-parallel perturbations. Local flow-perturbation models may be appropriate in situations where the distribution of later structures is apparently related to spatial variations in strain intensity and/or there is a strong geometric and kinematic similarity between sets of folds and fabrics. If such features are not observed, a regional polyphase sequence is more likely, and it is therefore necessary to obtain radiometric dates (or some other independent source of data) to demonstrate a time separation.

Polyphase Barker sequences

Polyphase sequences are time-discrete complex sequences with constant magnitude and variable phase. In this letter polyphase sequences with aperiodic autocorrelation function (ACF) sidelobcs of values less than or equal to 1 are presented. Such sequences are called Barker sequences. Binary Barker sequences with elements 1 or - 1 are only known up to 13 elements. Now, with an iteration scheme, polyphase Barker sequences are found up to 25 elements, except for 20 elements.

Polyphase complementary codes

Previous work on polyphase complementary codes is reviewed, and a number of new results are presented including additional kernels and lengths. Generating methods from other binary and polyphase sequences are given and negative results of other existence searches reported. Advantages of specialized forms for radar and Loran-C are discussed, including complementary Barker codes. A table of known lengths of pairs, triads and quads of sequences is given.

Polyphase modulation as a solution of certain filtration problems in telecommunication

An important class of filtration problems in telecommunication is associated with frequency changing; it includes the generation and demodulation of single-sideband carrier channels and the elimination of image-frequency interference in heterodyne demodulators, such as the superheterodyne radio receiver or the conventional wave analyser. Filters for these applications are often difficult to design or realize, or may be inconvenient on account of variable tuning, etc. It has been realized recently that polyphase modulation can be used as part of the frequency-changing process with great advantage. It can eliminate the need for difficult or inconvenient filters, although other design problems are introduced which may some times be as difficult to solve. But there is no doubt that the idea of polyphase modulation is of great importance in telecommunication theory and practice. The basis of the advantages given by polyphase working is that polyphase signals possess an identifying property additional to that of frequency, namely sequence. By using circuits which distinguish between signals of the same frequency but opposite sequence, it is possible, without any preliminary filtration, to separate signals which lie in the same frequency band after modulation, and which, therefore, could be separated by normal means only by filters before the modulation stage. The first Section of the paper outlines the main filtration problems which can be tackled by polyphase methods, and then the necessary polyphase theory is given. This is followed by a discussion of circuit design for polyphase modulation and sequence discrimination. The list of references shows that there have been many publications covering some of the separate applications of this work, but the paper is believed to present for the first time a comprehensive theory of polyphase modulation embracing all the known applications.