Percorrer por autor "Silva, Henrique J.A. da"
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- M-Ary Mutually Orthogonal Complementary Gold CodesPublication . Pereira, João; Silva, Henrique J.A. daA method to obtain large sets of periodic conjugate symmetric sequences with perfect periodic autocorrelation functions is presented. Each of these perfect sequences can be transformed into two real sequences which are perfectly orthogonal for any cyclic shift. In this way, mutually orthogonal complementary (MOC) sequences derived from bipolar Gold codes can be transformed into M-ary MOC Gold codes. Ternary MOC Gold codes are the simpler implementation case and exist in large number. These Ternary MOC Gold codes provide a greater immunity to multi-path interferences than other codes, like Hadamard codes, Orthogonal Gold codes, Gold codes, and Complementary Golay codes, when a periodic or aperiodic autocorrelation function is used for asynchronous bit detection.
- Optimal design of perfect DFT sequencesPublication . Pereira, João S.; Silva, Henrique J.A. daIn this paper, we propose a novel scheme to construct a large set with N(N + 1) perfect sequences of length N, derived from an Inverse Discrete Fourier Transform (IDFT) of Chu and maximum-length sequences. This optimum set of perfect periodic autocorrelation sequences has a maximum absolute value of periodic cross-correlation strictly lower than N and close to the well known lower bound SQRT(N). Moreover, we present a method to transform these perfect sequences into orthogonal sequences. A similar method is also proposed to obtain optimum bipolar codes derived from an alternative set of N2 perfect sequences. In the design of perfect sequences, the difficulty is to achieve both low cross-correlation and low peak-to-average power ratio (PAPR). Many of the proposed perfect DFT sequences should have low PAPR and thus can be applied in an OFDM–CDMA (Orthogonal Frequency-Division Multiplexing–Code Division Multiple Access) communication system or in a simple CDMA communication system. Alternatively, the proposed perfect DFT sequences may be useful for pre-coded mapping in OFDM communication systems or for the design of radar waveform diversity sets.