Abstract
Performance evaluation and comparison of multi-carrier code division multiple access (MC -CDMA) system model for usually used spreading sequences (Golay, Zadof-Chu, Gold) with chaotic sequences (generated by improved logistic map, by chaotic map with different slopes and by tent function) at the presence of Saleh and Rapp model of high power amplifier (HPA) is investigated. Rayleigh channel model and AWGN channel model is used in this simulation. Nonlinear amplification of HPA introduces degradation of bit error performance and destroys the orthogonality among subcarriers. In order to avoid performance degradation without requiring extremely large backoffs in the transmitter amplifier, it becomes convenient to use nonlinear multi-user detection techniques at the receiver side for all spreading sequences. To illustrate this fact, microstatistic multi-user receiver (MSF-MUD) and conventional minimum mean square error receiver (MMSE-MUD) are considered and mutually compared. The results of analyses are based on computer simulations. The best performance for Rayleigh channel model we can obtain when we used the Golay or Chaotic sequences in combination with MSF-MUD or MMSE-MUD, with using 8 –PSK modulation type.
Highlights
One major difference between chaotic sequences and another type of Pseudorandom Number (PN) sequences is that chaotic sequences are not binary
Generation of chaos is described in [22, 23, 25], Direct Sequence Spread Spectrum (DSSS) CDMA with chaotic sequences is described for example in [14], Direct Sequence (DS) CDMA is described in [15,16,17,18,19,20,21] and MC/DS CDMA is described in [4]
This paper is dealing with chaotic sequences in MC CDMA system
Summary
Spread spectrum techniques have been used in wire and wireless communication [14]. Sequences derived from chaotic phenomena are actively being considered for spread-spectrum communications [15]. Random-like process found in non-linear dynamical system, which is non-periodical, non-converging and bounded. It has a very sensitive dependence upon its initial condition and parameters. The pseudo-noise sequences such as Gold, Golay, Zadoff-Chu and Walsh Hadamard are the most popular spreading sequences that have good correlation properties. Generators of these pseudorandom sequences can generate the finite number of states for several users. Can be used as spread-spectrum sequence in place of PN sequence in conventional Direct-Sequence, SpreadSpectrum and Multi-carrier (DS/SS/MC) CDMA communication systems. Chaotic sequences are uncorrelated when their initial values are different, so in chaotic spread-spectrum systems, each user has the different initial value
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