Get Here about CDMA technology and How CDMA Works, CDMA Solution and CDMA RF Optimization.
This graphically demonstrates why interleaving data improves error correction performance of data transmission systems. In the top Image, data is sequentially read out of a buffer than goes by rows. No interleaving is employed. The data is read and transmitted in numerical order. During transmission, data blocks 5 through 8 are corrupted by some interference. … Read more
Time diversity is a technique common to most digital transmission systems. The Rake Receiver is used to find and demodulate multipath signals that are time delayed from the main signal. Rake Receiver to Find and Demodulate Multipath Signals. Data is Interleaved : Spreads Adjacent Data in time to Improve Error Correction Efficiency Convolutional Encoding : … Read more
Correlation Is a Measure of How Well a Given Signal Matches a Desired Code, The Desired Code is Compared to the Given Signal at Various Test times. Correlation is key enabling concept for direct sequence CDMA systems. Correlation is a measure of how well a given signal spread with a digital code matches a desired … Read more
Frequency diversity is inherent in a spread spectrum system. A fade of the entire signal is less likely than with narrow band systems. Combats Fading, Caused by Multipath Fading Acts like Notch Filter to a Wide Spectrum Signal May Notch only Part of Signal Fading is caused by reflected images of an RF signal arriving … Read more
CDMA extends the idea of diversity reception with the concept of soft handoff. In the slide, a mobile CDMA phone has established a call with base station one. As the mobile moves away from base station one and approaches base station two, a device in the phone known as the searcher identifies base station one … Read more
Diversity Reception: Multiple Antennas at Base Station Each Antenna is Affected by Multipath Differently Due to Their Different Location Allows Selection of the Signal Least Affected by Multipath Fading If Diversity Antennas are Good, Why Not Use Base Stations as a Diversity Network? – Soft Handoff The concept of diversity reception has been well known … Read more
Rake Receiver Instead of trying to overpower or correct multipath problems, CDMA takes advantage of the multipath to improve reception quality in fading conditions. CDMA does this by using multiple correlating receivers and assigning them to the strongest signals. This is possible because the CDMA mobile is synchronized to the serving base station. The mobile’s … Read more
Vocoders Human voice is made up of a combination of voiced and unvoiced sounds Vocoders exploit these properties of speech production mechanism Vocoders do not respond to music, non-human sounds and tones from voice band modems PCM vs VOCODERS CDMA VOCODERS 8 kbps variable rate coder Rate 1 Rate 1/2 Rate 1/4 Rate 1/8 Cdma … Read more
Why Power Control Essential in CDMA ? Power control is essential for the smooth operation of a cdma system. Because all users share the same rf band through the use of pn codes Each user looks like random noise to other users. The power of each individual user therefore, must be carefully controlled so that no … Read more
There are Four channel in Forward direction in cdma. PILOT CHANNEL (1) SYNC CHANNEL (1) FORWARD TRAFFIC + PAGING CHANNELS (62) PAGING CHANNELS ( MAXIMUM 7) PILOT CHANNEL PILOT SIGNALS ARE TRANSMITTED BY EACH CELL SITE TO ASSIST MOBILE RADIO IN ACQUIRING AND TRACKING THE CELL SITE DOWNLINK SIGNAL PILOT CHANNEL IS ASSIGNED CODE CHANNEL … Read more