multiple access techniques used in wireless communication
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This document discusses multiple access techniques for wireless communication. It describes frequency division duplexing (FDD) and time division duplexing (TDD) for sharing radio spectrum. The main multiple access techniques are described as frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA). FDMA allocates different frequency bands to each user, TDMA divides the available time into time slots and allocates one slot per user, and CDMA uses pseudo-random codes to distinguish users transmitting simultaneously on the same frequency. Common cellular systems like AMPS, GSM, and IS-95 are cited as examples.
multiple access techniques used in wireless communication
- 1. MULTIPLE ACCESS TECHNIQUES FOR WIRELESS COMMUNICATION
- 2. Presented To: Dr Imran Presented By : Syed Sajid Ali Reg No: 11-MDTLC-0513 Class No: 37
- 3. INTRODUCTION • Multiple access schemes are used to allow many users to share simultaneously a finite amount of radio spectrum resources. • For high quality communication this sharing of spectrum should not degrade performance of the system high performance duplexing generally required frequency domain time domain
- 4. DUPLEXING What is Duplexing? to talk and listen simultaneously is called duplexing. Classification of communication systems according to their connectivity. Simplex Half-duplex Duplex A B A B A B
- 5. Duplexing may be done using frequency domain technique time domain technique
- 6. Frequency division duplexing (FDD) two bands of frequencies for every user forward band ( for traffic from Base station to mobile unit) reverse band (for traffic from mobile unit to Base station) • frequency separation between forward band and reverse band is constant throughout the system
- 7. Time division duplexing (TDD) uses different time slots for forward and reverse link forward time slot reverse time slot Communication is not full-duplex
- 8. TYPES OF MULTIPLE ACCESS Frequency division multiple access (FDMA) Time division multiple access (TDMA) Code division multiple access (CDMA)
- 9. Frequency division multiple access FDMA one phone circuit per channel idle time causes wasting of resources simultaneously and continuously transmitting usually implemented in narrowband systems Complexity of FDMA mobile systems is lower compared to TDMA FDMA uses duplexers for example: AMPS is a FDMA system with bandwidth of 30 kHz
- 10. FDMA power Example: Advanced Mobile Phone System
- 11. Time Division Multiple Access Time slots one user per slot Buffer and burst method Non-continuous transmission Advantage: Total bandwidth is utilized Disadvantage: Strict Burst Timing is required at the earth station
- 12. TDMA power Example: Global System for Mobile (GSM)
- 13. Code division multiple access (CDMA) Narrowband signals is multiplied by a very large bandwidth signal called the spreading signal. The spreading signal is pseudo noise code sequence that has a chip rate which is orders of magnitudes greater than data rate of the message All users use the same carrier frequency and transmit simultaneously Each user has its own pseudo random code word which is approximately orthogonal to other codewords.
- 14. Receiver performs time co-relation All other codewords appear as noise Receiver needs to know the code word used by transmitter
- 15. CDMA power
- 16. Multiple Access Techniques in use Cellular System Multiple Access technique used Advanced Mobile Phone System (AMPS) FDMA/FDD Global System for Mobile (GSM TDMA/FDD US Digital Cellular (USDC) TDMA/FDD Digital European Cordless Telephone (DECT) FDMA/FDD US Narrowband Spread Spectrum (IS-95) CDMA/FDD
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