Chi-Cheng Lin, Winona State University CS 313 Introduction to Computer Networking & Telecommunication CDMA

2 Code Division Multiple Access (CDMA) l In FDMA, the bandwidth is divided into channels. l In TDMA, the bandwidth is just one channel that is timeshared. l In CDMA, one channel carries all transmissions simultaneously.

3 CDMA l Each bit time is divided into m short intervals  chips  Typically 64 or 128 chips per bit l To transmit  Bit 1: send chip sequence  Bit 0: send negation of chip sequene l Example:  If station A’s chip sequence = ( )  To transmit bit 1, ( ) is sent  To transmit bit 0, ( ) is sent l All chip sequences must be pairwise orthogonal!  Normalized inner product of any two distinct chip sequences S and T is 0, i.e., S  T = 0  Normalized inner product of the same chip sequence S, i.e., S  S = 1

Code Division Multiplexing Access (a) Chip sequences for four stations (b)Signals the sequences represent (c) Six examples of transmissions (d) Recovery of station C’s Computer Networks, Fifth Edition by Andrew Tanenbaum and David Wetherall, © Pearson Education-Prentice Hall, 2011