Electronics Project:CDMA

  Simulation of CDMA transmitter and receiver:

Code division multiple access (CDMA) is a channel access method used by various radio communication technologies. One of the concepts in data communication is the idea of allowing several transmitters to send information simultaneously over a single communication channel. This allows several users to share a band of frequencies. This concept is called multiple access. CDMA employs spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code) to allow multiple users to be multiplexed over the same physical channel. By contrast, time division multiple access (TDMA) divides access by time, while frequency-division multiple access (FDMA) divides it by frequency. CDMA is a form of spread-spectrum signaling, since the modulated coded signal has a much higher data bandwidth than the data being communicated.

An analogy to the problem of multiple access is a room (channel) in which people wish to talk to each other simultaneously. To avoid confusion, people could take turns speaking (time division), speak at different pitches (frequency division), or speak in different languages (code division). CDMA is analogous to the last example where people speaking the same language can understand each other, but other languages are perceived as noise and rejected. Similarly, in radio CDMA, each group of users is given a shared code. Many codes occupy the same channel, but only users associated with a particular code can communicate.

Uses:

• One of the early applications for code division multiplexing is in GPS. This predates and is distinct from its use in mobile phones.

• The Qualcomm standard IS-95, marketed as cdmaOne.

• The Qualcomm standard IS-2000, known as CDMA2000. This standard is used by several mobile phone companies, including the Globalstar satellite phone network.

• The UMTS 3G mobile phone standard, which uses W-CDMA.

• CDMA has been used in the OmniTRACS satellite system for transportation logistics.

This project builds the simulations model of CDMA transmitter and receiver with different parameter settings.