Understanding CDMA Technologies — Lesson 3

This lesson covers the fundamentals of Code Division Multiple Access (CDMA) technologies. It delves into the process of CDMA signal generation, the types of codes used in CDMA, and the forward and reverse link code channels. The lesson also explains the CDMA call processing and the importance of error control codes in wireless standards. It further compares the error control codes used for GSM and CDMA technologies. For instance, the lesson illustrates how CDMA uses codes to convert between analog voice signals and digital signals, and to separate voice and control data into data streams called channels.

Video Highlights

01:19 - Introduction to the lecture on wireless communications and focus on CDMA technologies
03:09 - Explanation of the process of generating a CDMA signal and the five essential steps involved
06:44 - Explanation of how CDMA systems take advantage of pauses in speech activity by using a variable rate vocoder
09:09 - Explanation of the encoding and interleaving process in CDMA systems to build redundancy into the signal
13:58 - Discussion on the process of channelizing in CDMA systems and the use of Walsh and PN codes for channelization
22:16 - Explanation of the final stage in generating a CDMA signal, the digital to RF conversion
31:09-Explanation of the different types of reverse link channels used in CDMA systems, including access and traffic channels
42:45 - Discussion on the use of error control codes in GSM and CDMA systems
53:10 - Conclusion of the lecture on GSM and CDMA technologies

Key Takeaways

- CDMA uses codes to convert between analog voice signals and digital signals and to separate voice and control data into data streams called channels.
- CDMA signal generation involves five essential steps: analog to digital conversion, voice coding, encoding and interleaving, channelizing of the signals, and conversion of the digital signals into RF signals.
- CDMA uses two types of codes for channelizing users: Walsh codes and pseudorandom noise (PN) codes.
- CDMA systems use strong burst error correcting techniques and sophisticated error control schemes for channel errors.
- CDMA systems use a variable rate vocoder that varies the compression of the voice signal based on the rate of the user’s speech activity.
- CDMA systems use different types of channels to transmit voice and control data to the mobile, including pilot, sync, paging, and traffic channels.