In this article, the first general constructions of fast-decodable, more specifically (conditionally) g-group decodable, space-time block codes for the nonorthogonal amplify and forward (NAF) multiple-input multiple-output (MIMO) relay channel under the half-duplex constraint are proposed. In this scenario, the source and the intermediate relays used for data amplification are allowed to employ multiple antennas for data transmission and reception. The worst-case decoding complexity of the obtained codes is reduced by up to 75%. In addition to being fast-decodable, the proposed codes achieve full-diversity and have nonvanishing determinants, which has been shown to be useful for achieving the optimal diversity-multiplexing tradeoff (DMT) of the NAF channel. Furthermore, it is shown that the same techniques as in the cooperative scenario can be utilized to achieve fast-decodability for K-user MIMO multiple-access channel (MAC) space-time block codes. The resulting codes in addition exhibit the conditional nonvanishing determinant property which, for its part, has been shown to be useful for achieving the optimal MAC-DMT.

We study fast lattice decodability of space-time block codes for n transmit and receive antennas, written very generally as a linear combination Σi=12lsiAi, where the si are real information symbols and the Aiare n×n ℝ-linearly independent complex-valued matrices. We show that the mutual orthogonality condition AiAj* + AjAi* = 0 for distinct basis matrices is not only sufficient but also necessary for fast decodability. We build on this to show that for full-rate (l = n2) transmission, the decoding complexity can be no better than |S|(n2+1), where |S| is the size of the effective real signal constellation. We also show that for full-rate transmission, g-group decodability, as defined by Jithamithra and Rajan, is impossible for any g ≥ 2. We then use the theory of Azumaya algebras to derive bounds on the maximum number of groups into which the basis matrices can be partitioned so that the matrices in different groups are mutually orthogonal-a key measure of fast decodability. We show that in general, this maximum number is of the order of only the 2-adic value of n. In the case where the matrices Aiarise from a division algebra, which is most desirable for diversity, we show that the maximum number of groups is only 4. As a result, the decoding complexity for this case is no better than |S|⌈l/2⌉ for any rate l.

We study fast decodability for general rate space-time block codes. We derive bounds on the number of generators that can be in mutually orthogonal groups and use these to show that that the ML decoding complexity of a full-rate n × n space-time block code is unfortunately quite high: at least of the order of |S|n2+1, where S is the effective real constellation. We also show that g-group decodability is not possible for full-rate codes.

We propose a full-rate iterative space-time code construction, which uses an algebraic space-time code in order to design a new space-time code of double the code rank. We give a condition for determining whether the resulting codes satisfy the full diversity property, and study their maximum likelihood decoding complexity with respect to sphere decoding. Particular emphasis is given to the asymmetric multiple input double output codes. In the process, we derive an interesting way of obtaining division algebras, and study their centers and maximal subfields.

In this paper, fast-decodable lattice code constructions are designed for the nonorthogonal amplify-and-forward (NAF) multiple-input multiple-output (MIMO) channel. The constructions are based on different types of algebraic structures, e.g. quaternion division algebras. When satisfying certain properties, these algebras provide us with codes whose structure naturally reduces the decoding complexity. The complexity can be further reduced by shortening the block length, i.e., by considering rectangular codes called less than minimum delay (LMD) codes.

We present an iterative construction of algebraic space-time codes. Starting from a division algebra D, we show how to embed it into a larger ring A = A(D) and give conditions for A to be a new division algebra. Starting from a quaternion division algebra D1, we thus obtain a sequence D1⊂ D2⊂... of division algebras where Di= A(Di-1). Each of the Dican be used as an underlying structure to build a space-time Ci. Furthermore, the iteration step is done such that fast-decodability of the original code is preserved. We illustrate our technique by creating an iterative version of the Silver code.

In the context of space-time block codes (STBCs), the theory of generalized quaternion and biquaternion algebras (i.e., tensor products of two quaternion algebras) over arbitrary base fields is presented, as well as quadratic form theoretic criteria to check if such algebras are division algebras. For base fields relevant to STBCs, these criteria are exploited, via Springer's theorem, to construct several explicit infinite families of (bi-)quaternion division algebras. These are used to obtain new 2 × 2 and 4 × 4 STBCs.

In this paper we compute the Fourier spectra of some recently discovered binomial almost perfect nonlinear (APN) functions. One consequence of this is the determination of the nonlinearity of the functions, which measures their resistance to linear cryptanalysis. Another consequence is that certain error-correcting codes related to these functions have the same weight distribution as the 2-error-correcting Bose–Chaudury–Hocquenghem (BCH) code. Furthermore, for field extensions of $\mathbb{F}_2$ of odd degree, our results provide an alternative proof of the APN property of the functions.

The authors give a construction of multiblock space-time block codes from cyclic division algebras with a givennth root of unity as the nonnorm element. The construction uses local class field theory. Multiblock codes withMblocks can achieve anM-fold increase in diversity.