OCC-CDMA system design for wireless communications

by Rajatasereekul, Thunyawat

In modern telecommunication applications, the need for high-reliability and

high data rate is important because of factors such as a higher demand in

multimedia capability of mobile devices and the exponentially increasing number of

subscribers. Wireless communications in today’s technology have many limitations

due to channel imperfections, which result in less than satisfactory speed of

transmission and less reliability. Moreover, bandwidth, one of the most the precious

resources of all communication schemes, has been reaching the limit established

either by the spectrum governing bodies such as the FCC in the U.S. or by

technological shortcomings. This means that increasing the number of users is

extremely difficult. Researchers have been inventing and developing many

techniques to overcome such limitations. Good examples are real-time channel

estimation and compensation, new modulation techniques, efficient coding

algorithms and novel multiple-access techniques.

This thesis presents a new CDMA modem (modulator-demodulator) which

achieves a higher bandwidth efficiency in a multiple user scenario than conventional

CDMA-based systems and attains low BER performance through the application of

orthogonal-complementary coded CDMA (OCC-CDMA) and non-conventional QAM.

The OCC-CDMA itself has the advantages of less multiple access interference (MAI) and capability of transmitting the maximum of 1 bit per spreading chip, which

is impossible to achieve with conventional CDMA. By utilizing such unique

properties of OCC-CDMA, high information transmission rates with acceptable BER

performance can be achieved.