New Linear Phase Binary User Codes and Their Performance Comparison with Existing Codes for Direct Sequence Spread Spectrum Communication

Spread spectrum (SS) is a modulation technique in which the signal occupies a bandwidth much larger than the minimum necessary to send the information. A synchronized reception with the code at the receiver is used for despreading the information before data recovery. From a long period, Walsh codes and Gold codes have been used as spread spectrum codes in Code Division Multiple Access(CDMA) communications because of their ease of generation than the efficiency of these codes. Walsh codes are perfectly orthogonal binary user codes that have many popular applications in synchronous multicarrier communications although they perform poorly for asynchronous multiuser communications. Therefore, the nearly orthogonal Gold codes with their superior performance are the preferred user codes in asynchronous CDMA communications with small number of simultaneous users in the system due to their good auto-correlation (intracode correlation) and cross-correlation (intercode) properties. Major drawback of these codes is that they are limited in number and in their lengths. In this thesis paper, we performed Matlab(7.1version) algorithm to obtain some of the new orthogonal sets of binary space for multiuser spread-spectrum communications. We compared their performance with existing codes like Gold and Walsh code families. Our comparisons include their time domain properties like auto and crosscorrelations along with bit error rate (BER) performances in additive white Gaussian noise (AWGN) channels for the synchronous and asynchronous DS-SS communications. It is shown that these new orthogonal binary codes provide a comparable performance with Gold codes in asynchronous DS-SS AWGN channel and are comparable to Walsh codes for synchronous AWGN channel. As a result, these can be used in both cases along with the advantage of their large availability.