In a wireless communication scenario,
in order to design a good Dynamic Channel Assignment scheme,
one should consider each channel state,
Is there a relationship between frequency band and channel state?
and if so, how do you formulate that relationship?
Thank you.
Yes, the frequency band will definitely be a factor. Noise, interference, signal attenuation, and the type of fading incurred, will be heavily dependent on frequency band. For example, you can expect a lot more interference in the 2.4 GHz band, than in the 5 GHz band, just because there are more devices which use the lower band, and it propagates further. On the other hand, the higher frequencies may have less interference, but will experience more attenuation due to obstacles in the path, including rain, more scattering, potentially more multipath.
Channel state can be determined dynamically. In two-way communications, but also in one-way broadcast, using so-called "training sequences." Or in OFDM, also by making use of the multiple active pilots in the channel (full power pilots distributed throughout the bandwidth, at various subchannel frequencies). This allows the receiver to determine fading characteristics, and to dynamically adjust its equalizer taps.
Another technique, in channels which use short symbol duration with good randomization of symbols, is to adjust the feedback equalizers of receivers to achieve the flattest frequency response. The assumption is that in a short time window, the intended frequency spectrum of the rapid symbols should very flat. This technique accommodates rapidly changing fading characteristics, because the data symbol rate is always going to be a lot higher than the rate of transmission of the training symbols. Not unlike monitoring the shape of the full power pilots of OFDM. So dynamic adjustment of equalizers will be that much more accurate.
The relationship you ask about can be formulated in vague general terms, of course, but in practice, it has to be determined dynamically and continuously.
There are two problems that typically occur with Dynamic Channel Allocation (DCA) based systems.
- First, DCA methods typically have a degree of randomness associated with them and this leads to the fact that frequency reuse is often not maximized unlike the case for FCA systems in which cells using the same channel are separated by the minimum reuse distance.
- Secondly, DCA methods often involve complex algorithms for deciding which available channel is most efficient. These algorithms can be very computationally intensive and may require large computing resources in order to be real-time.
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