Multiple Access Techniques

Multiple access techniques are the methods through which a user is able to access the data information that has been sent from the sender end.

With the passage of time this technique has received a lot of updates from being analog signal to accumulation of the digital signal, from single user support to unlimited user access. The technology of data transfer we are able to enjoy today is derived from these basic principles.


Multiple Access Techniques History

So, let’s understand with some historical context, earlier there were telephone services which used analog signal to transfer the voice signal over the wire cable there was one line reserved for the sender and the same line reserved for the receiver, this was first of all costly because of wires and second there were only two users for one channel.

Then came digital signal world and wireless communication method, here we saw methods such as Amplitude Modulation (AM) and Frequency Modulation (FM) where one channel was allocated to the sender and he was able to broadcast to the all their user, but you have to wait… we are not at the multiple access technique, the technology begins from here.

The major need for two way communication was required through the wireless technology, now came the real technology that was the multiplexing method where we can send and receive the data at the same time with many users with the use of one channel. It’s like four people from hotel have their voice data signal traveling through from their telephone in the room, and then their voice signal come together to each other and travel through one route, and when they have travelled through their route and near the end to the receiver that is the hotel room service people, the voice signal got separated to the respective room service caretaker, now this technological feat may sound simple and easy but it took generation to make it actually happen. In this example we may have talked about the telephone cable line but the same thing is possible with the wireless technology.

There are many ways to make multiple user communication possible like FDMA, TDMA and the CDMA. Each was an improvement one after another.


Frequency Division Multiple Access

Let’s see what is FDMA or Frequency Division Multiple Access. So when you make a call in the FDMA technology one frequency range is reserved completely for the caller and the receiver and one this frequency the communication will take place. When some other person wants to place the call then the same process will repeat and a separate frequency will get reserved for the caller and the receiver over which they can communicate. Let’s assume the mobile tower of that area is permitted to have a bandwidth which can support a hundred such frequency allocation but one more reservation of the caller’s frequency allocation will become problematic and the mobile tower will have to communicate to each other which of them are idle to allocate that additional caller. For example you have 1000 Hz of frequency bandwidth and then your one caller frequency reserves 10 Hz then in total you will be able to make 100 calls in the smart time over one channel at the same time.


Time Division Multiple Access

Now FDMA were good for the voice signals but when the internet came data packets were introduced and to access the internet we required sending and receiving of the data packet. So, when the messages were sent on the emails they were divided into many data packets which had the address of the receiver end and these data packet travels from various routes to reach their receiver and the club together to form the message. Therefore we cannot reserve the frequency for such small data packet as this will only reduce the bandwidth. So, a new system was devised that was TDMA or Time Division Multiple Access. Here to transfer each data packet you have to wait in turn in a line and send when it is your allocated time and as there are more than one data packet you will have to wait in line and wait for the turn to come again to send the remaining data packets. Their were reserved time slots instead of frequency to transfer the data packets at respective turns. This method was great for sending and receiving of messages, gmails, downloading or uploading as it was the voice signals that needed frequency reservations for clear flow of information but small data packets that can trace their own best routes. The TDMA technology was greatly used in combination with FDMA in 2G technology but when the 3G came it was purely based on the CDMA a new intervention to use both the reserved time slots and the frequency slots.


Code Division Multiple Access

The CDMA or the code division multiple access is completely different approach is the multiple access technique. In this technique there are use of the codes that are used to send and receive the data over the channel and when you send the information say in form of bits, the bits is multiplied to the particular code and the generated data is used to send over the channel. Along with the bits from each sender as there are multiple senders in each channel all their data gets added up which where earlier multiplied with the code, and then the signal is sent to the receiver where it is decoded with the same key and distributed to their respective user 


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