0

The definition of bandwidth is frequency range and it seems to be correct to say that higher bandwidth guarantees higher data rate.

However, i do not understand why it does

Data rate depends on modulation scheme and nowdays QAM,which is combination of ASK and PSK, is most widely used scheme

I have understood that FSK needs more frequency so it needs more bandwidth but i do not understand why ASK and PSK need more bandwidth (If QAM did not need more bandwidth, QAM could be used in small bandwidth and it would mean that bandwidth has nothing to do with data rate)

As i understand, ASK does not need more bandwidth. If transmission power in transmitter is bigger, the amplitude of wave will be bigger. In that sense, ASK can be achieved by transmission power control.

Furthermore, PSK will be constructed if signal is delayed. As i know, the angle of phase is decided by delay of wave (timewise)

If what i explained is correct, why does high bandwidth guarantee high data rate?

장영록
  • 65
  • 1
  • 3

2 Answers2

1

In communications engineering, bandwidth is the measure of the width of a range of frequencies, measured in Hertz.

Rate is the number of transmitted bits per time unit, usually seconds, so it's measured in bit/second. Equivalently, it can be given in symbols/time unit.

The rate is proportional to the system bandwidth. The Shannon Capacity is one theoretical way to see this relation, as it provides the maximum number of bits transmitted for a given system bandwidth in the presence of noise.

So If We can consider the bandwidth as the diameter of the water pipe. A larger pipe can carry a larger volume of water, and hence more water can be delivered between two points with larger pipe. How large is the pipe (bandwidth) determines maximum quantity of water (data) flows at a particular time. So more the bandwidth more data can be transferred between two nodes. So increasing bandwidth can increase data transfer rate. Data transfer rate can vary due to distance between two nodes, efficiency of medium used etc. So higher bandwidth does not always guarantee higher data transfer rate. So fundamentally they are not related to each other. Data transfer can be considered as consumption of bandwidth

SHASHI BHUSAN
  • 612
  • 6
  • 12
0

You might want to check out the Nyquist-Shannon Sampling Theorem. In a nutshell it says that the bandwidth limits how much "data" can be transmitted. Further the Shannon–Hartley theorem states how much "data" can be transmitted using a given bandwidth (because of noise).

For example in (A)DSL using QAM64:4000Baud/Channel, 6Bit per Baud, 62 Upstream Channels yields: 6*4000*62 = 1,488 Mbit/s

Hope this helps ^^

Lord_PedantenStein
  • 495
  • 4
  • 9