- Overview:
- FDMA is a channel access method used in telecommunications. It allows multiple users to share a common communication medium by dividing the available frequency bandwidth into smaller sub-channels.
- Each sub-channel is allocated to a specific user or device, ensuring that they can transmit data simultaneously without interfering with each other.
- How FDMA Works:
- Frequency Division: The total available frequency spectrum is divided into non-overlapping frequency channels.
- Allocation to Users: Each user or station is assigned one or more of these frequency channels for their exclusive use.
- Reserved Bands: Once allocated, a specific frequency band remains reserved for a particular station at all times.
- Fixed Bandwidth: The bandwidth assigned to each user remains constant, ensuring predictable communication.
- Two Main Techniques within FDMA:
- Multi-Channel-Per-Carrier (MCPC) Transmission:
- In satellite communication, analog multiplexing is initially used at earth stations.
- Telephone channels are combined into a single baseband signal, which is then modulated onto a single RF carrier.
- Up to 1800 telephone channels can be multiplexed using Frequency Division Multiplexing (FDM), resulting in a wide baseband occupying an 8 MHz bandwidth.
- Different RF carriers are used for frequency modulation, and a common transponder is shared among various earth stations.
- This technique is known as FDM-FM-FDMA.
- Single-Channel-Per-Carrier (SCPC) Transmission:
- When a single signal is transmitted via an earth station, it’s referred to as SCPC transmission.
- SCPC-FDMA systems are used in scenarios with many small earth stations (e.g., mobile phones) accessing a single transponder.
- These systems can be reconfigured based on traffic conditions, making them compatible with demand assignment systems.
- Only the carrier for the active SCPS (Single Channel Per Station) channel is transmitted, reducing transponder power consumption.
- Multi-Channel-Per-Carrier (MCPC) Transmission:
- Comparison with Other Multiple Access Schemes:
- FDMA vs. TDMA (Time Division Multiple Access):
- FDMA allocates frequency bands, while TDMA divides time into slots.
- In FDMA, each user has a dedicated frequency band, whereas in TDMA, users share the same frequency but transmit in different time slots.
- FDMA vs. CDMA (Code Division Multiple Access):
- CDMA uses unique codes to differentiate users, allowing simultaneous transmission over the same frequency.
- FDMA, on the other hand, assigns separate frequency bands to each user.
- FDMA vs. TDMA (Time Division Multiple Access):
What is FDMA (Frequency-Division Multiple Access)
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