An interesting approach for coping with the delay spread of wireless channels is the use of multi-carrier modulation. It is also called orthogonal frequency division multiplexing (OFDM). In this case the symbol frequency is lowered to be much below the source symbol frequency 1/T, resulting in the fact that the delay spread is a fraction of the symbol duration NT, taking away the need for combatting the delay spread. In addition it is more robust against bursty errors in Rayleigh fading channels.
Major reason for the use of CDMA system is that multiple users to share a common frequency band by using orthogonal access codes. This allows for detecting the different users one-by-one.
In this paper, an Implementation of a transmitter and receiver algorithm for multi-carrier code division multiple access system is described and its performance is analyzed using simulation for a fading Doppler channel. We implement a MC-CDMA modem in real time using the ADSP-21020 digital signal processor(DSP) chip. The modem algorithm is designed based on the principles of OFDM and CDMA. The features implemented include a simple start-up protocol, modulation and demodulation using the discrete Fourier transform(DFT), synchronization, equalization and spreading code using the Walsh code.
We have evaluated the performance of the MC-CDMA modem, and the modem performs successfully.
