Sequence Sets in Wireless Communication Systems: A Survey

Abstract

Sequences and their properties have been studied widely in different research areas because they have useful characteristics which are used in many applications. Correlation functions such as Golay correlation functions are a measure of similarity among sequences and, besides, they are powerful functions used extensively in many research areas. It is known that unitary sequence sets with ideal autocorrelation and cross-correlation functions do not exist, and this represents the main problem to construct orthogonal sequences given that are limited by bounds. In wireless communication systems (WCSs), orthogonal sequences are used as access codes which play a very important role to increase capacity and to provide higher robustness to interference. This survey describes the properties of these sequences and their relationships that make them attractive to be used in communication systems. We consider the correlation properties to classify and describe four main families of sequences: 1) traditional; 2) complementary; 3) interference free window; and 4) complex. Finally, a discussion on their advantages and disadvantages is given considering the WCS scenario, and the discussion leads to some challenges for future applications which offer some ideas to motivate research to improve those properties.