For small values of k f , the frequency deviation is small and the spectrum of FM signal has a narrow band. Hence, it is called as the narrow band FM. For large values of modulation index m f , the FM wave ideally contains the carrier and an infinite number of sidebands located symmetrically around the carrier. Such a FM wave has infinite bandwidth and hence called as wideband FM.
The maximum permissible deviation is 75 kHz and it is used in the entertainment broadcasting applications such as FM radio, TV etc. The expression for the wideband FM is complex since it is sine of sine function. As far as mobile radio systems are concerned, the resources are the channels, or, in a more general sense, bandwidth.
Depending on how the available spectrum is utilized, the system can be broadly classified into narrowband and wideband. Most of the wireless protocols are known as wideband, but narrowband also has its place, especially for LPWAN. Narrowband refers to radio communications whose signal bandwidth is within the coherence band of a frequency channel.
This means the bandwidth of the signal does not significantly exceed the coherent bandwidth of the frequency channel. Narrowband systems divide the total frequency spectrum into several narrowband channels.
Wideband refers to broadband communications that uses a relatively wide range of frequencies. It refers to radio channels whose operational bandwidth may significantly exceed the coherence bandwidth of the channel. Unlike the narrowband architecture, the whole or a significant amount of the spectrum is available to all the users in wideband systems.
In narrowband communications, the signal bandwidth is far less than the channel coherent bandwidth which means the bandwidth of the signal does not significantly exceed the channel coherent bandwidth. Wideband, on the other hand, refers to a broader frequency communication channel that uses a relatively wide range of frequencies. In wideband communications, the signal bandwidth significantly exceeds the channel coherent bandwidth. Narrowband systems typically have lower data rate transmissions, whereas the wideband systems support relatively higher data rate transmissions.
Wideband signals are generally greater than 1 MHz in bandwidth. More bandwidth translated into higher data rates, in terms of transmitted and received signal information. Each channel is comprises of a set of two carrier frequencies used for two-way communication: reverse channels frequencies for the uplink and forward channels frequencies for the downlink. A wideband signal is one that does not fit into the coherence bandwidth and therefore experiences frequency selective fading. An OFDM symbol is broken down into separate narrowband channels and since they are just single discrete frequencies, they experience a single discrete level of fading each, which can be calculated by using a training symbol and equalised.
Each frequency within the symbol has a specific frequency response for a certain amplitude at that frequency, and there is one amplitude for that frequency per symbol, this takes into account the self interference from the multipath images of that amplitude. This does not however anticipate interference from another symbol, which cannot be equalised because it is dependent on the previous symbol and not directly ascertianable from just the current symbol and the channel frequency response.
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Asked 3 years, 9 months ago. Active 4 months ago. Viewed 3k times. Mayank Mehra Mayank Mehra 50 1 1 silver badge 7 7 bronze badges. Are you asking about the relationship between the bandwidth of an electronic signal to the coherence bandwidth of its channel?
Activity points 1, Pls give a reason. Any book and paper and link will be appreciated. IanP Advanced Member level 5. Wideband FM has a large number theoretically infinite number of sidebands. Narrowband FM has only a single pair of significant sidebands. Click to expand It occupies bandwidth somewhat similar to AM. Regards Z. You need consider the carrier frequency and the base band signal's amplitude, too. The frequency control was poor in the past and so wide signals widely spaced were used.
As spectrum became scarce and frequency control became better both were cut down. There is a lower limit on the FM modulation index. The signal can be no narrower than twice the highest modulating frequency.
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