2.3 time division multiple access
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TDMA divides the radio spectrum into time slots and allows only one user to transmit or receive data during each time slot. It uses a buffer-and-burst transmission method, making it well-suited for digital systems. TDMA systems employ TDMA/TDD or TDMA/FDD for duplexing and multiple access. A TDMA frame includes a preamble for identification and synchronization, and multiple time slots containing user data, trail bits, and guard bits between slots. TDMA provides high transmission rates, simpler handoff, and is more cost-effective than FDMA, though it requires minimum guard times between slots to avoid interference.
2.3 time division multiple access
- 2. Lecture Videos are available for this slides at www.youtube.com/gurukula Support by Subscribing to my Channel
- 3. Frequency Division Multiple Access - FDMA USER 1 USER 3 USER 2 GUARD BANDS To avoid interference
- 4. Time Division Multiple Access - TDMA USER 1 USER 3 USER 2
- 5. Time Division Multiple Access - TDMA TDMA divides the entire radio spectrum in to time slots, and in each slot only one user is allowed to either transmit or receive. Each user occupies a cyclically repeating time slot TDMA System transmits data in Buffer and Burst method, This makes the transmission a discontinuous one. Hence this makes the TDMA Systems more suitable for Digital Systems. Systems use TDMA/TDD or TDMA/FDD methods for Duplexing and Multiple Accessing. In TDMA/TDD – The Single Frame will be used as forward link for half of the duration and as reverse link on another half period. In TDMA/FDD – 2 Different Frames will be used for Forward and Reverse Link but the carrier frequency will be different.
- 6. Understanding TDMA Frame Structure
- 7. Time Division Multiple Access - TDMA Preamble: Consists of Address and Synchronisation bits which is used by base stations subscribers to identify each others. Information Message: Contains multiple slots of user information Each slot will have Trail Bits Sync Bits Information Guard Bits Trail Bits
- 8. Features of TDMA 1.In case of TDMA a single carrier frequency is shared among several users. The time slots used by the users depends on several factors such as modulation techniques and the available bandwidth. 2.The Handoff process is much simpler in the case of TDMA because of its discontinuity and it is able to listen to the other base stations during its idle slot time. 3.The Transmission rates are very high in the case of TDMA as compared to the FDMA because of the Adaptive Equalization which is necessary in the case of TDMA. 4.The guard time present in the case of TDMA should be minimum. 5.The main advantage of TDMA is that it is very cost-effective. 6.TDMA technology is used to separate users in time and ensure that there will not be any interference which is presented from any other simultaneous transmissions.
- 9. Efficiency in TDMA • Calculation of Efficiency becomes trivial as TDMA uses high Overhead than compared to FDMA. • The efficiency of TDMA System is a measure of the percentage of transmitted data that contains information as opposed to providing overhead for the scheme. Frame Efficiency (η 𝑓 ) is calculated by η 𝑓 = 1 − 𝑏 𝑂𝐻 𝑏 𝑇 X 100% 𝑏 𝑂𝐻 = Nr Br + Nt Bp + Nt Bg + Nr Bg Nr – Number of reference burst per frame Br – Number of overhead bits per reference burst Nt – Number of Traffic Burst per Frame Bp – Number of Overhead bits per Preamble in each slot Bg – Number of Equalent bits in each guard time interval 𝑏 𝑇 = Tf R Tf – Frame Duration R – Channel Bit Rate 𝑏 𝑂𝐻 - Number of overhead bits per frame 𝑏𝑇 – Total Number of Bits per Frame
- 10. Number of Channels in TDMA Systems • The number of TDMA Channels slots that can be provided in a TDMA system is found by multiplying the number of TDMA slots per channel by the number of channels available. 𝑵 = 𝒎(𝑩 𝒕𝒐𝒕 − 𝟐𝑩 𝒈𝒖𝒂𝒓𝒅) 𝑩 𝒄 m – maximum number of TDMA users supported in channel It is also important to note that the 2 Guard Bands , one at the lower end and other at the higher end of the allotted frequency are required to ensure the users at the edge do not “bleed over” into an adjacent radio channels
- 11. Summary • Recap of FDMA • Concepts and Working of TDMA • Frame Structure of TDMA • Features of TDMA • Efficiency of TDMA Systems • Capacity of TDMA Systems ***---***