During the propagation, we mixed the signals of all users, but by that you use the same code as the code that was used at the time of sending the receiving side. The following figure shows the technicality of the CDMA system. Conversely, when signals are received from several mobile stations, the base station is capable of isolating each as they have different orthogonal spreading codes. Using different orthogonal codes, interference between the signals is minimal. In fact, many different "signals" baseband with different spreading codes can be modulated on the same carrier to allow many different users to be supported. Operational limits and quality issues will reduce the maximum number of calls somewhat lower than this value. There are 64 Walsh codes available to differentiate between calls and theoretical limits. How Does CDMA Work?ĬDMA allows up to 61 concurrent users in a 1.2288 MHz channel by processing each voice packet with two PN codes. Using a group of codes, which are orthogonal to each other, it is possible to select a signal with a given code in the presence of many other signals with different orthogonal codes.
A code called spreading code is used to perform this action. Here, a signal is generated which extends over a wide bandwidth. Techniques generally used are direct sequence spread spectrum modulation (DS-CDMA), frequency hopping or mixed CDMA detection (JDCDMA). The basic principle is that different CDMA codes are used to distinguish among the different users. In this system, a user has access to the whole bandwidth for the entire duration. CDMA OverviewĬode Division Multiple Access system is very different from time and frequency multiplexing. The technology is commonly used in ultra-high-frequency (UHF) cellular telephone systems, bands ranging between the 800-MHz and 1.9-GHz. It optimizes the use of available bandwidth.
Code Division Multiple Access (CDMA) is a sort of multiplexing that facilitates various signals to occupy a single transmission channel.
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