TABLE OF CONTENTS The key to CDMA high capacity is the use of noise-like carrier waves. Instead of assigning frequency or time slots, different users are assigned different nearly orthogonal instances of the noise carrier. This alters the system sensitivity to interference, from having to design a system based on the worst-case interference to the average interference. Traditional time or frequency slotted systems must be designed with a reuse ratio that satisfies the worst-case interference scenario, which is experienced by only a small fraction of users. Use of pseudonoise carriers, with all users occupying the same spectrum, makes the effective noise the sum of all other-user signals. The CDMA receiver correlates its input with the desired noise carrier, enhancing the signal-to-noise ratio at the detector and overcoming the summed noise enough to provide an adequate SNR at the detector. Because the interference is summed, the system is sensitive to the average interference instead of the worst-case interference. Frequency reuse is universal, that is, multiple users use the same CDMA carrier frequency. Capacity is determined by the balance between the required SNR for each user, and the spread spectrum processing gain, defined as the ratio between the carrier chip rate to the user s data rate. The figure of merit of a well-designed digital receiver is the dimensionless E b /N t , defined as
The noise part of E b /N t , in a spread spectrum system is the sum of thermal...
