Difference Between FDMA, TDMA, and CDMA

FDMA Vs. TDMA Vs. CDMA: Find Out the Difference Between FDMA, TDMA, and CDMA

All of these are modes of data transmission and communication. They are very effective but used in different aspects due to their varying characteristics and features. Read ahead to know the difference between FDMA, TDMA, and CDMA in detail. Let us know why we use them in the first place.

When establishing a connection among the users sharing a similar radio spectrum, a traditional method of analog modulation may limit the data conveyed within any given channel (such methods include FM and AM). In this case, every channel can host only one conversation at a given time. It thus needs a pair of users- one receiving and one transmitting.

Since a finite number of users would be able to occupy a spectrum of AM (Analog Modulation), it does not go well with the ever-expanding needs of today. Digital radio fixes this issue with a variety of modulation schemes that let the conveyance of more information on a channel. The digital radio ultimately came up with several ways in which it could accommodate more than a single conversation (multiplex it) inside one physical RF channel. It majorly uses three common ways to achieve it:

FDMA
TDMA
CDMA

What is FDMA?

The term FDMA is an acronym for Frequency Division Multiple Access. It splits its available radio frequency (RF) channel into multiple sub-channels (smaller). For instance, an FM channel that’s 13 kHz wide in narrowband that carried just one conversation previously gets split into two 6.5 kHz sub-channels, both able to carry separate conversations. This technique is not very new, and it works for both- digital radios and analog signals. One can also establish a telephone-style conversation if they use one channel for receiving and one channel for transmitting signals.

One major drawback of this method is that when you try to fit in more sub-channels in the original channel, the users will start suffering from the call interference. It happens because the decreased channel spacing makes the filtration of one intended sub-channel very difficult while simultaneously rejecting all the others at the receiver’s end. This way, it becomes impractical to consequently divide a single narrowband of channel frequency of 13 kHz into two or more sub-channels.

What is TDMA?

The term TDMA is an acronym for Time Division Multiple Access. The TDMA doesn’t split its primary RF channel into two or more sub-channels- but splits it into two time slots instead. Each slot carries an identical RF frequency- but they hold the capacity of carrying separate conversations in each of them. For instance, if the primary channel splits into four time slots, then each of them will take a quarter of the original time to transmit the intended data and information.

Digital technology makes this type of speech compression possible. But eventually, it also possesses practical far/near limits. These put a limit on the number of blocks that a single RF channel could accommodate before the neighboring slots slowly began to overlap at the intended Base Station. Again, TDMA also helps in setting up a telephone-style conversation– if it uses certain slots for receiving and the others for transmitting.

What is CDMA?

The term CDMA is an acronym for Code Division Multiple Access. The CDMA doesn’t split the original RF channel into two or more time slots or sub-channels but assigns a unique code to each of them. Unlike the FDMA method, CDMA has the very same frequency of transmission in every slot. Also, unlike the TDMA method, CDMA transmits individual slots simultaneously.

Let’s take a case where CDMA splits the primary RF channel into four code slots. Here, each slot can carry separate conversations. It is because the receiver is only capable of reconstructing info sets from a transmitter that has the very same code. This method, however, does create an issue. The receiver does receive and decode the transmissions with different codes and a similar frequency- but they start reappearing as noise. It means that an increase in the total number of users will also make the noise level higher on any given system. In turn, it affects the overall coverage.

Near/far issues also occur whenever a transmitter transmits a very strong signal to the intended receiver- thus blocking it from receiving any weak signals. Such near/far issues also require dynamic power control in the case of a CDMA system to ensure that every signal arrives at almost the same level at the Base Station. It ensures that none of the signals get lost while transmitting from a distant transmitter.