TAILIEUCHUNG - Multiple Access Techniques for Wireless Communications

Enable many mobile users to share simultaneously radio spectrum. Provide for the sharing of channel capacity between a number of transmitters at different locations. Aim to share a channel between two or more signals in such way that each signal can be received without interference from another. | Multiple Access Techniques for Wireless Communications 2005/07/06 Weng Chien-Erh Table of Contents(1) Introduction FDMA TDMA CDMA SS (Spread Spectrum) FHSS DSSS Hybrid Packet Radio Pure ALOHA Slotted ALOHA CSMA Reservation Protocol Reservation-ALOHA PRMA NC-PRMA Table of Contents(2) Introduction (1) Multiple Access: Enable many mobile users to share simultaneously radio spectrum. Provide for the sharing of channel capacity between a number of transmitters at different locations. Aim to share a channel between two or more signals in such way that each signal can be received without interference from another. Introduction (2) Introduction (3) In conventional telephone systems, it is possible to talk and listen simultaneously, called duplexing. Duplexing Allow the possibility of talking and listening simultaneously. Frequency Division Duplex (FDD) Provides two distinct bands of frequencies for every user Time Division Duplex (TDD) Multiple users share a signal channel by taking turns in time domain Each duplexing channel has both a forward time slot and a reverse time slot to facilitate bidirectional communication. Introduction (4) Each transmitter is allocated a channel with a particular bandwidth. All transmitters are able to transmit simultaneously. Frequency Division Multiple Access (FDMA) (1) Frequency Division Multiple Access (FDMA) (2) Allocation of separate channels to FDMA signals Time-frequency characteristic of FDMA Frequency Division Multiple Access (FDMA) (3) Features of FDMA If an FDMA channel is not in sue, then it sits idle and can’t be used by other users. Transmit simultaneously and continuously. FDMA is usually implemented in narrowband systems. Its symbol time is large as compared to the average delay spread. Frequency Division Multiple Access (FDMA) (4) Features of FDMA (Cont.) For continuous transmission, fewer bits are needed for overhead purposes (such as synchronization and framing bits) as compared to TDMA. FDMA uses duplexers since both TX .

• Kĩ thuật Viễn thông
• simultaneously radio spectrum
• channel capacity
• different locations
• channel between
• received without
• conventional telephone