Define FDMA, TDMA and CDMA.

16. Define FDMA, TDMA and CDMA.

FDMA, TDMA, and CDMA are all multiple access techniques used in telecommunications to allow multiple users to share the same frequency spectrum. Here are their definitions:

1. FDMA (Frequency Division Multiple Access):

    FDMA is a multiple access technique where the available frequency spectrum is divided into multiple non-overlapping frequency bands. Each user is assigned a unique frequency band, and the user's communication signals are transmitted simultaneously but in different frequency channels. FDMA allows multiple users to access the network concurrently by allocating separate frequency bands to each user. It is commonly used in analog cellular systems like the first-generation (1G) cellular networks.

2. TDMA (Time Division Multiple Access):

    TDMA is a multiple access technique where the available frequency spectrum is divided into time slots. Each user is allocated one or more time slots during which they can transmit their signals. Time slots are allocated in a sequential manner, and users take turns transmitting within their assigned time slots. TDMA allows multiple users to share the same frequency channel by dividing the transmission time into discrete intervals. It is commonly used in digital cellular systems such as the second-generation (2G) GSM (Global System for Mobile Communications) networks.

3. CDMA (Code Division Multiple Access):

    CDMA is a multiple access technique where each user is assigned a unique code or spreading sequence to differentiate their signals. Instead of dividing the frequency spectrum into separate bands or time slots, CDMA allows all users to transmit simultaneously on the same frequency channel. User signals are spread using different codes, and they are then combined at the receiver using the same codes to extract the desired signal. CDMA uses the property of orthogonal codes or sequences to achieve user separation and interference mitigation. It is commonly used in digital cellular systems like the third-generation (3G) CDMA2000 and the fourth-generation (4G) LTE (Long-Term Evolution) networks.

Each of these multiple access techniques offers advantages and disadvantages in terms of capacity, spectral efficiency, and resilience to interference. The choice of FDMA, TDMA, or CDMA depends on the specific requirements of the communication system and the technology being used.