owadays, the demand for high rate data transmission in wireless environment increases rapidly. One of the best techniques in this environment is multi carrier modulations (MCM). The orthogonal frequency division multiplexing (OFDM) is one of the most important justify; TEXT-INDENT: 21.3pt; MARGIN: 0cm 0cm 0pt; unicode-bidi: embed; DIRECTION: ltr; mso-layout-grid-align: none" which the signal occupies a bandwidth in excess of the minimum necessity to send the information. Chirp spread spectrum (CSS) is one way to increase the frequency spectra that multiplies signal with chirp. Several techniques of chirp spread spectrum and IEEE 802.15.4a standard with CSS physical layer are explained in this thesis. The main limitation of CSS techniques is multiple access interference (MAI). Multiple access was designed for simultaneously accessing the common channel by many users. The MAI occurs because of high cross correlation between two user chirps and this limitation can be waived by using FrFT. In this thesis, we have proposed the chirp spread spectrum system that uses FrFT in both transmitter and receiver. This method has less complexity, easier implementation and more flexibility. Additive white Gaussian noise (AWGN) is considered as a channel noise for evaluation of performance. Bit error rate (BER) is taken as a measure ment of performance with different signal to noise ratio and the results of the novel system are presented and discussed. Keywords: Multi-Carrier Modulation, Fractional Fourier Transform (FrFT), Orthogonal Frequency Division Multiplexing (OFDM), Inter-Carrier Interference (ICI), Chirp Spread Spectrum (CSS), IEEE802.15.4a standard
