1D-Bernoulli Chaos Sequences Based Collaborative-CDMA: A Novel Secure High Capacity CDMA Scheme

Abstract

Collaborative multi-user transmission and detection is a contemporary technique used for the up-link of code-division multiple access (CDMA). CDMA has contributed much to the field of wireless communication and still addresses many of the capacity and security requirements. The collaborative multi-user technique achieves an increase in capacity by sharing the spreading sequences among the users. In such grouped CDMA schemes, the sum of large numbers of statistically uncorrelated pseudo-random (PN) sequences results in multiple access interference. This restricts the number of PN sequences available for spreading, thereby limiting the total number of full rate users. Furthermore, PN sequences can be detected by their bit timings and consequently the security of the users' data is a matter of concern. To solve this problem, a novel high-capacity and secure system, called the 1D-Bernoulli-chaotic-collaborative-CDMA (BCC-CDMA), is proposed. In the BCC-CDMA, a set of specific `initial-conditions' are used, and identified for the 1D-Bernoulli Map, that generates row elements of an N × N matrix of mutually orthogonal chaotic sequences,. The ith row of this matrix acts as the spreading sequence for the ith group of collaborating users in BCC-CDMA. The proposed scheme eliminates the constraints in security and user capacity outperforming the existing multi-user detection schemes. Simulations show the bit-error-rate performance of BCC-CDMA supporting 120 full-rate users compared to the almost 90 and 30 users offered by conventional schemes.