You have a point in terms of reliability, but one of the problems however is the current level of clutter in the RF spectrum, there simply aren't that many uncluttered bands which could be licensed, even then the cost would be huge. Consequently, one of the main thrusts in wireless these days is spectral efficiency (getting the highest data rate per unit frequency consumed), and improved architectures and algorithms (e.g. mimo and turbo codes) are coming out steadily. Regulation, on the other hand, does not promote spectral efficiency, e.g. FM radio is one of the worst culprits as each station consumes 200kHz of spectrum to provide a simple FM voice signal. My point is that from a research perspective the long term benefits of experimental systems operating in unlicensed bands should not be ignored for the sake of doing things by classical, less efficient methods.
-"A lot of FHSS devices are used in warehouses and the like, as FHSS is fairly immune to noise, but had a much lower limit on it's speed (2 Mbps or slightly more if you go vendor specific)."
Uhmm, no. Frequency hopping (FH) is no more immune to noise than any other technique. This is because noise power tends to be spread equally over all frequencies (white noise) so there is no benefit in hopping from one frequency to another. It is however more immune to interference since this (sometimes) tends to be unequally distributed over frequency.
-"That's not to say it's not possible though, and many FHSS networks have very poor security (as they haven't gone further than WEP with 128 bit keys)."
This is misleading. If there's security issues then they may be due to the choice of protocol, encryption, hop codes, etc, but not to the use of FH itself. In fact, with proper choice of hop codes, security is considered to be one the strengths of FH. This is one reason for its common usage in military communication systems (difficult to intercept a signal transmitted at a frequency which is varied over time in an 'apparently' unpredictable manner).
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You have a point in terms of reliability, but one of the problems however is the current level of clutter in the RF spectrum, there simply aren't that many uncluttered bands which could be licensed, even then the cost would be huge. Consequently, one of the main thrusts in wireless these days is spectral efficiency (getting the highest data rate per unit frequency consumed), and improved architectures and algorithms (e.g. mimo and turbo codes) are coming out steadily. Regulation, on the other hand, does not promote spectral efficiency, e.g. FM radio is one of the worst culprits as each station consumes 200kHz of spectrum to provide a simple FM voice signal. My point is that from a research perspective the long term benefits of experimental systems operating in unlicensed bands should not be ignored for the sake of doing things by classical, less efficient methods.
-"A lot of FHSS devices are used in warehouses and the like, as FHSS is fairly immune to noise, but had a much lower limit on it's speed (2 Mbps or slightly more if you go vendor specific)." Uhmm, no. Frequency hopping (FH) is no more immune to noise than any other technique. This is because noise power tends to be spread equally over all frequencies (white noise) so there is no benefit in hopping from one frequency to another. It is however more immune to interference since this (sometimes) tends to be unequally distributed over frequency. -"That's not to say it's not possible though, and many FHSS networks have very poor security (as they haven't gone further than WEP with 128 bit keys)." This is misleading. If there's security issues then they may be due to the choice of protocol, encryption, hop codes, etc, but not to the use of FH itself. In fact, with proper choice of hop codes, security is considered to be one the strengths of FH. This is one reason for its common usage in military communication systems (difficult to intercept a signal transmitted at a frequency which is varied over time in an 'apparently' unpredictable manner).