Branislav Popovic

Generalized chirp-like polyphase sequences with optimum correlation properties

A new general class of polyphase sequences with ideal periodic autocorrelation function is presented. The new class of sequences is based on the application of Zadoff-Chu polyphase sequences of length N=sm/sup 2/, where s and m are any positive integers. It is shown that the generalized chirp-like sequences of odd length have the optimum crosscorrelation function under certain conditions. Finally, recently proposed generalized P4 codes are derived as a special case of the generalized chirp-like sequence. >

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. >

Spreading sequences for multicarrier CDMA systems

The paper contains an analysis of the basic criteria for the selection of spreading sequences for the multicarrier CDMA (MC-CDMA) systems with spectrum spreading in the frequency domain. It is shown that the time-domain crosscorrelation function between the spreading sequences is not a proper interference measure for the asynchronous MC-CDMA users. Therefore, the spectral correlation function is introduced and, together with the crest factor and the dynamic range of the corresponding multicarrier waveforms, is used for the evaluation of MC-CDMA sequences. Some well-known classes of sequences, such as Walsh, Gold, orthogonal Gold, and Zadoff-Chu sequences, as well as Legandre and Golay complementary sequences, are evaluated with respect to the aforementioned basic criteria. It is also shown that the crest factors of the multicarrier spread spectrum waveforms based on the multilevel Huffman sequences are very close to or even lower than the crest factor of a single sine wave.

New complex space-time block codes for efficient transmit diversity

The two new methods of complex orthogonal space-time block coding are proposed, which make possible a more efficient transmit diversity with larger number of transmit antennas. The new space-time block codes, based on modulatable orthogonal sequences, have the minimum code length for a given number of antennas, resulting in the minimised complexity of the receiver.

Orthogonal sets of quadriphase sequences with good correlation properties

A general construction for orthogonal sets of quadriphase sequences based on the sequence family A discovered by Sole (1989), Boztas, Hammons, and Kumar (1992) is presented. The sequence family A is equivalent to the S(0) family that belongs to a chain of sequence families S(i),i=0,1,2,..., m with each family in the chain containing the preceding family. Therefore, a number of orthogonal subsets can be generated for an arbitrary family S(m). The algorithm for an efficient implementation of the bank of correlators corresponding to any orthogonal subset of family S(m) is derived as well.

Comments on "Code acquisition for a frequency-hopping system

For the original article see ibid., vol.COM-35, no.5, p.566-8 (1987). It is pointed out that in the paper by I. Vajda and G. Einarsson the proposed sets of frequency-hopping sequences, that permit the correct resynchronization in FH-MFSK (frequency-hopping multiple-frequency-shift-keyed) multiple-access systems, are only the special case of the Reed-Solomon sets of asynchronous frequency-hopping sequences previously derived. For the case when the number of available frequencies is prime, another class of FH-MFSK sequences with good resynchronization and interference properties is presented. >