Constant Amplitude (CA), Zero Auto Correlation (ZAC) sequences (or CAZAC sequences, aka perfect sequences) have numerous applications. We generalize the CAZAC notion to what we term as CASAC by permitting small autocorrelations (SAC). We extend Björck’s classification result of two-valued CAZAC sequences by providing a complete classification of all almost 2-valued (i.e., two-valued except for the first position which uses a third value) CASAC sequences. While Björck’s original work dealt only with primes p, we extend his ideas to any abelian group of order$v\equiv 1\pmod {4}$, as opposed to restricting just to the prime fields GF(p). Björck sequences have better ambiguity function than Zadoff-Chu sequences, making them suitable for radar and communications applications in the presence of high Doppler shifts. In fact, the discrete narrow band ambiguity function has an optimal bound in case of Björck sequences (as opposed to Gauss sequences). A one-parameter infinite family of CASAC we construct would have applications in Multiple-Input Multiple-Output (MIMO) areas. Toward MIMO applications, we introduce a performance measure we term as cross merit factor to study cross correlation behavior, generalizing the well-known notion of Golay Merit Factor (GMF).

In this paper, we present some construction methods for punctured binary array/sequence pairs (PBAPs/PBSPs) with ideal/optimal correlation constant using their algebraic counterparts punctured difference set pairs in Abelian groups. In addition, we provide new construction techniques of PBAPs/PBSPs via geometry and also using the embeddable sequence pairs of smaller lengths to obtain larger ones. PBAPs/PBSPs find a plethora of applications in radar systems, cryptography, frame synchronization, mismatched filtering, and various other engineering fields.

We give a new existence criterion for p-ary sequences which have ideal two-level autocorrelation; and we use it to obtain four general families of such sequences: one for p=2, one for general odd primes p and two special ones for p=3. The binary family turns out to be equivalent to that discovered by Dillon and Dobbertin and published in 2004. The general p-ary family is equivalent to that discovered by Gong and Helleseth, by Dillon and, when p=3, by Helleseth, Kumar, and Martinsen. All of these p-ary results were published in 2001 and 2002. The special ternary families are new and give as special cases the sequences conjectured by Alfred Lin in his 1998 Ph.D. thesis as well as most of those conjectured in 2001 by Ludkovski and Gong. Our sequences may also be used to construct (relative) difference sets, their corresponding block designs and generalized weighing matrices.

A pair of binary sequences is generalized from the concept of a two-level autocorrelation function of a single binary sequence. In this paper, new families of binary sequence pairs with period N = np, where gcd(n,p) = 1, and optimal correlation values -1 are constructed, as well as new families of binary sequence pairs with three-level correlation and period N≡0(mod 4). For the new binary sequence pairs with optimal correlation values, their corresponding new difference set pairs and almost difference set pairs are also derived.

Previously, self-dual codes ternary have been constructed from conference matrices. In this paper, we present codes constructed from negacirculant conference matrices. A necessary condition for these codes to be self-dual is given, and examples are given for lengths up to 108. The equivalence with the Pless symmetry codes is established

Almost difference sets have interesting applications in cryptography and coding theory. We give a well-rounded treatment of known families of almost difference sets, establish relations between some difference sets and some almost difference sets, and determine the numerical multiplier group of some families of almost difference sets. We also construct six new classes of almost difference sets, and four classes of binary sequences of period n/spl equiv/0 (mod 4) with optimal autocorrelation. We have also obtained two classes of relative difference sets and four classes of divisible difference sets (DDSs). We also point out that a result due to Jungnickel (1982) can be used to construct almost difference sets and sequences of period 4l with optimal autocorrelation.

Previously, self-dual codes have been constructed from Hadamard matrices. In this correspondence, codes constructed from weighing matrices, and in particular conference matrices are presented. A necessary condition for these codes to be self-dual is given, and examples are given for lengths up to 40. Codes constructed from all weighing matrices of order n/spl les/13 are also considered.

We study two-dimensional (2-D) arrays of fourth roots of unity which have all out-of-phase periodic autocorrelations equal to zero. Generalizing the concept of a perfect binary array, we call these arrays perfect quaternary arrays. We establish connections with combinatorial design theory and exhibit large families of such arrays. Increasing the alphabet from size two to size four greatly increases the flexibility one has in choosing the dimensions for 2-D arrays with perfect periodic autocorrelation. For example, we show that the number of entries in a 2-D perfect quaternary array may be divisible by any Mersenne prime and indeed by many other primes, whereas 2-D perfect binary arrays are only known to exist with size equal to a power of two times a power of three.