CDMA: Exploring Bandwidth Allocation & Capacity

[netizen]

Hi!

I've been reading up on FDMA and CDMA and wondering why is it that in CDMA, each message is spread over the entire bandwidth allotted instead of using a single range of frequencies (say, alloted to one user in FDMA), for several users (by assigning a unique code to each of them)?

Why is it that the entire bandwidth is utilised by all users instead of many ranges accomodating several users each? Is the restriction imposed by capacity?

This probably sounds very childish but I'm a greenhorn and would really appreciate some clarification. Thanks in advance...

 

[mgb_phys]

Why is it that the entire bandwidth is utilised by all users instead of many ranges accomodating several users each?

Because then you would have to implement all the hardware for both systems FDMA and CMDA.

Really they aren't all that different if you think of them in Fourier terms - but that gets a bit mathematically complex

 

[netizen]

Yeah I get that you would then have to implement hardware for both technologies. But won't it be compensated by the fact that the number of users can now be increased manifold?

 

[mgb_phys]

CDMA let's you use the entire bandwidth (all frequenices) by mixing the signals from all the users with a code and then decoding them, FDMA let's you use the entire bandwidth by giving each user a different frequency.
They both fill the available bandwidth, so other than signal-noise and practical engineering considerations they are equivalent.

 

[alphy]

Hi there,

First of all, it's great that you are exploring different techniques for bandwidth allocation and capacity in communication systems. To answer your question, let's start by understanding the basic differences between FDMA and CDMA.

FDMA (Frequency Division Multiple Access) is a technique where the available bandwidth is divided into smaller frequency ranges and each user is assigned a different range of frequencies to transmit their data. This means that each user has exclusive access to a specific frequency range, and the rest of the bandwidth remains unused.

On the other hand, CDMA (Code Division Multiple Access) allows multiple users to share the same bandwidth by using unique codes to differentiate their data transmissions. This means that all users can transmit their data simultaneously over the entire bandwidth, but their data is spread out using different codes. This is why CDMA is also known as a spread spectrum technique.

Now, to answer your question, the reason why CDMA uses the entire bandwidth for all users instead of dividing it into smaller ranges is because it allows for more efficient use of the available bandwidth. In FDMA, the unused frequency ranges for each user result in wasted bandwidth, while in CDMA, the entire bandwidth is utilized by all users. This leads to higher capacity and better spectral efficiency.

Additionally, CDMA also offers better resistance to interference and noise compared to FDMA. This is because the unique codes used in CDMA can be designed to cancel out any interference that may occur, making the system more robust.

So to summarize, the use of the entire bandwidth in CDMA is not a restriction imposed by capacity, but rather a deliberate design choice to maximize efficiency and improve overall performance in communication systems.

I hope this helps clarify your doubts. Keep exploring and learning more about different communication techniques! Best of luck.