Definition of CDMA :
Detailed information :
- CDMA is very different from the time and frequency multiplexing, It is digital cellular technology that uses spread spectrum techniques.
- In this technology, many users share the same carrier frequency. This frequency also multiplexed with the spreading signal of larger bandwidth. This spreading signal is a pseudo-noise code sequence has a higher chip rate than the data rate of the message signal.
- CDMA is commonly used in an ultra-high-frequency cellular telephone system, band ranging between the 800 Mhz and 1.9 GHz.
- The main advantage of CDMA, when compared to another multiple access method, is a reduced level of interference. As each user is allocated an individual pseudo-random codeword is orthogonal to the code words of the other users at the receiver end. Receiver tunes at the receiver end receive the intended signal of the user.
- Power control is essential to minimize the near-far problem in these systems. Power control is implemented at the base station by sampling the radio signal strength indicator level of each mobile and then a power change command over the forward radio link.
Features of CDMA :
- Soft capacity limit.
- Higher user capacity
- CDMA is an interference-limited system.
- Higher frequency reuse.
- Share the same frequency
- As the number of users increases, system performance decreases.
- The near-far problem arises at the receiver end.
- Multipath fading can be reduced as the signal is spread over a large spectrum.
For detailed information :
Application of CDMA :
- Used for the cellular system.
- Most important for the GPS system.
- Used for subscriber access control.
- Used for personal communication service.
- Used for over the air activation.
- Used for short message service.
- The US-based Qualcomm standard marketed as CDMAOne.
- Used by UMTS 3G mobile phone standard.
- Used in the OmniTRACS satellite system for transportation logistics.
For detailed information :
Read more >> CDMA applications