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Multiple Access Part 3. FDMA, TDMA, CDMA, OFDMA & SDMA Division Multiple Access for Multiple Users.

Multiple Access playlist. Watch these video to understand more on Multiple Access.    • Multiple Access Part 1. Simplex (Radi...   How we can allocate multiple users sharing the same resource like spectrum. Multiple Access. Understand what is Multiple Access. Multiple Access techniques for wireless communication. The five most common Multiple Access. 1) Frequency Division Multiple Access (FDMA), 2) Time Division Multiple Access (TDMA), 3) Code Division Multiple Access (CDMA), 4) Orthogonal Frequency Division Multiple Access (OFDMA), and 5) Spatial Division Multiple Access (SDMA). MULTIPLE ACCESS - FDMA/TDMA/CDMA/OFDMA/SDMA The different types of Division Multiple Access (DMA) techniques enable multiple users or signals to share the same communication channel or bandwidth. Here’s a breakdown of each: 1. Frequency Division Multiple Access (FDMA) How it works: FDMA divides the available frequency band into separate channels, each assigned to a different user or device. Usage: Traditional analog cellular systems, satellite communications. Advantage: Simple to implement and provides continuous access for each user. Limitation: Limited by the number of frequency bands, inefficient in handling dynamic user loads. 2. Time Division Multiple Access (TDMA) How it works: TDMA assigns users to specific time slots within a single frequency band. Multiple users can share the same frequency by using it at different times. Usage: 2G (GSM) cellular networks. Advantage: Efficient use of bandwidth and no interference between time slots. Limitation: Time synchronization is crucial, and it may be less efficient for high data-rate applications. 3. Code Division Multiple Access (CDMA) How it works: CDMA assigns a unique code to each user, spreading the signal over a broad frequency range. All users transmit simultaneously, but the unique codes allow the receiver to distinguish each user’s signal. Usage: 3G cellular networks, GPS. Advantage: High security and resilience to interference, can support multiple users on the same frequency band. Limitation: Complex decoding process, susceptible to the “near-far” problem where stronger signals may overpower weaker ones. 4. Orthogonal Frequency Division Multiple Access (OFDMA) How it works: OFDMA divides the frequency band into many narrow sub-bands (subcarriers) and assigns subsets of these subcarriers to different users. This enables simultaneous data transmission by multiple users across various frequencies. Usage: 4G (LTE), Wi-Fi 6 (802.11ax). Advantage: High spectral efficiency, reduces interference, and can dynamically allocate resources. Limitation: Sensitive to frequency offset and Doppler shifts, complex processing required. 5. Space Division Multiple Access (SDMA) How it works: SDMA uses spatial separation to allow multiple users to use the same frequency and time, but in different physical locations. Techniques like beamforming direct the signal to specific users. Usage: MIMO (Multiple Input Multiple Output) systems in 4G/5G networks, satellite systems. Advantage: Increased capacity by reusing frequencies in different spatial locations. Limitation: Requires complex antenna systems and precise control over beam direction and user location.