Multiple access techniques TDMA, FDMA, CDMA, OFDMA

The multiple access techniques used in telecommunications:

1. TDMA (Time Division Multiple Access): divides the available frequency spectrum into time slots, with various users transmitting in turn within their assigned time periods.

2. FDMA (Frequency Division numerous Access): divides the available frequency spectrum into numerous frequency channels for communication, with each user assigned to a distinct channel.

3. CDMA (Code Division several Access): Allows several users to transmit signals over the same frequency spectrum at the same time by utilizing unique codes to distinguish their transmissions.

4. OFDMA (Orthogonal Frequency Division Multiple Access): Like FDMA, except it divides the frequency channels into smaller sub-channels for more efficient data transfer.

Depending on the communication system's individual requirements, each approach has advantages and use cases.

Let's take a closer look at each of the various access methods:

1. Time Division Multiple Access (TDMA): 

  - TDMA is commonly utilized in cellular systems like 2G and 3G networks. It makes the best use of available bandwidth by allocating time periods to individual users, letting several users to share the same frequency channel without interfering.

   - Each user is given a set of time intervals during which they can transmit data. In a frame structure, time windows are often brief and recurrent.

2. FDMA (Frequency Division Multiple Access):

  - FDMA is widely used in analog communication systems and older cellular networks such as 1G. It divides the available frequency range into distinct channels and assigns one to each user.

   - Each user runs on its own frequency, ensuring that signals from different users do not cross and therefore preventing interference.

3. CDMA (Code Division Multiple Access):

 - CDMA technology is widely employed in modern cellular networks such as 3G, 4G (LTE), and 5G. It uses unique codes to distinguish different user signals, allowing numerous users to transmit over the same frequency range at the same time.

   - CDMA systems can segregate user signals even when their frequencies overlap, resulting in efficient spectrum utilization.

4. OFDMA (Orthogonal Frequency Division Multiple Access):

   - OFDMA is an important technology in both 4G (LTE) and 5G networks. It extends the ideas of FDMA by further subdividing frequency channels into smaller subchannels known as subcarriers.

   - Each user is assigned a set of subcarriers, and many users can broadcast across various sets of subcarriers within the same frequency range at the same time.

   - OFDMA enables flexible and effective resource usage by dynamically allocating subcarriers to users based on their bandwidth requirements.

These various access approaches are critical in current wireless networks for maximizing spectrum utilization, boosting network capacity, and addressing the growing need for data transfer.