Abstract
We propose a new non-coherent multicarrier spread-spectrum system that combines orthogonal chaotic vector shift keying (OCVSK) and orthogonal frequency-division multiplexing (OFDM). The system enhances OCVSK by sending multiple groups of information sequences with the same orthogonal chaotic vector reference sequences over the selected subcarriers. Each group carries M information bits and is separated from other groups by orthogonal chaotic reference signals. We derive the information rate enhancement (IRE) and the energy saving enhancement (ESE) factors as well as the bit error rate theory of OFDM-OCVSK under additive white Gaussian noise and multipath Rayleigh fading channels and compare the results with conventional OCVSK systems. For large group numbers, the results show that the IRE and ESE factors approach M×100% and M/(M+1)×100%, respectively, and thus outperform OCVSK systems. The complexity analysis of the proposed scheme as compared with OFDM-DCSK shows a significant reduction in the number of complex multiplications required.
Highlights
Over the past decade, chaos-based wireless digital communication systems have attracted increasing research interest [1]
The need to introduce a delay component for synchronization was solved with code-shifted differential chaos shift keying (DCSK) (CS-DCSK) [17] and code-shifted quadrature chaos shift keying (QCSK) (CS-QCSK) [18] using Walsh codes that allow both the reference and information-bearing signal to be transported in the same time slot
The derivation of the information rate, the energy-saving enhancements and the dataenergy-to-bit-energy ratio (DBR) factors compared with orthogonal chaotic vector shift keying (OCVSK) systems was presented
Summary
Chaos-based wireless digital communication systems have attracted increasing research interest [1]. The mth orthogonal chaotic vectors of the jth frame xmj,k can be expressed as [37], [38] These orthogonal chaotic signals are used as reference sequences that have the total length M · β. The complexity of the GS algorithm in terms of multiplication, addition and division operations for transmitted M × N bits of data is easy to calculate, only requiring M chaotic vectors, each with lengths of β samples. By substituting (3) and (19) in (9), the complex output correlation of the mth transmitted bits in the nth group at the receiver side can be expressed as (20), as shown at the top of the page, where xm,k−τl , is the delay version of the mth orthogonal chaotic vector, ηk+(m−1)β and ηk+Mβ+(n−1)β are the AWGN vectors added for each corresponding reference and information signal respectively and (.)∗ is the conjugate function. The BER of the OFDM-OCVSK system under AWGN only is derived from (28) by setting as BERAWGN
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