I have a small doubt. Suppose I transmit just 2 square pulse with frequency of 100 MHz over a wireless channel, will it spread in the time domain when received by a wireless receiver. In other words, a 100 MHz square pulse will have a High for 5ns, and then low for next 5ns and then again a High for 5ns. At the receiver, I receive the same pulse attenuated and which looks like a guassian distribution. But will the difference between the 2 peaks be still 5ns or it may change?
Spreading of a pulse in time domain
communicationdigital modulationdigital-communicationsspread-spectrum
Related Solutions
Your question seems to be contradictory -- you seem to be saying you want to "create a circuit" without actually "designing a circuit".
I'm going to interpret that as saying you want to "build a complete system, including designing a high-level protocol and laying out a few circuit boards and soldering integrated circuits to the boards and plugging sub-assembly modules into those boards", but you'd rather not "design and fab a full-custom ASIC from scratch" or "design something from dozens of discrete transistors instead of a chip" or "design and do EM simulations and construct a full-custom antenna system and get FCC approval".
I've heard that, at least for low data rates, that UWB can be produced using simple circuits using off-the-shelf chips that were common long before anyone ever heard of UWB.
Alas, I don't know any specific chips that you could use for the data rate you want, much less if there exist off-the-shelf modules using those chips, but I hear that such chips exist. Let me give you some links that might lead to those chips.
My understanding is that there is currently only one UWB standard -- WiMedia’s Multiband OFDM, standardized as ECMA-368 and ECMA-369. My understanding is that "Certified wireless USB" and a potential future version of "Bluetooth" and a potential future version of "Zigbee" are higher-level layers on top of WiMedia's UWB standard.
My understanding is that there are several chip manufacturers producing chips that comply with this standard. a b
I hear that several other chip manufacturers are producing non-ECMA-compliant chips, including Pulse~LINK, DecaWave, IMEC, WiLinx, Wisair. Presumably those chip use some other proposed standard or proprietary UWB techniques.
If you can't find an off-the-shelf module, and you find yourself looking for individual chips, I suspect that many of the chips developed for HomePlug might be usable as part of a UWB system.
Your gut starts good, it is the leading edge of the pulse that upsets Bob. You will not, or should not, be surprised to learn the trailing edge gives his receive filters a similar but inverted rattle as well.
Now there are several ways to look at what happens with these two events he sees. First a simple hand-wavy power ratio approach.
With a longer pulse, there's more total energy in it. However the energy in the leading and trailing edges stays the same. So the ratio of adjacent channel interference to transmitted power will fall.
Now a more detailed 'what about the zero power in the sinc spectrum'?
You will notice that your sinc function crosses the zero axis, so that at some frequencies there is zero power. These frequencies are offset from the centre frequency by a function of the length of the pulse. At these pulse lengths, the leading and trailing event are so timed in his receive filter that the second one cancels out the first. At the peaks of the sinc function, the second event reinforces the first for a bigger filter output.
So, you might be asking, how can two events which cancel each other out in his receive filter, one after the other, really be called zero? The problem is you don't really know what you have in the frequency domain until you have waited long enough. How long? Several times longer than 1/f, when you are trying to resolve frequency differences of f. It turns out when the leading and trailing interference effects cancel, there is indeed zero power at the cancelling frequency, but there are sidebands above and below which contain the definitely non-zero power. The filter has to be wide enough to accomodate these sidebands as well. If it was narrow enough to reject them, then its response to the first event would be such a slow buildup (narrow filter = long time delay) then by the time the trailing event arrived, it would cancel a signal that was still way below 'full scale', and was actually zero in the limit of a zero-width filter. Of course in communication systems, we need filters to respond in a finite time, so it's not even theoretically possible to use a zero-width filter, let alone not a practical possibility.
Related Topic
- Electronic – Spreading vector
- Quick digital receiver for Manchester encoded data
- Electronic – Is it possible to receive information if the received power is below the noise floor
- Electronic – What does the phase discriminator portion of the Costas Receiver do mathematically
- Electronic – What are the units used in Shannon formula calculation
Best Answer
Simon is right except there is one more assumption required. If the transmitter and receiver are moving toward or away from each other, then Doppler effects will cause the pulses to be closer together or farther apart in time.
One other kind of weird thing to consider. The channel between TX and RX could be time varying. The propagation speed of EM waves depends on the dielectric properties of the space in between. If a large dielectric solid material was somehow inserted between TX and RX after the first pulse, then the second pulse would be substantially delayed due to the slower EM propagation in the dielectric material. I don't think it is possible to do this in the space of 5ns, but since I don't know what your final application is, I thought I would mention it. Other things like humidity or rain or snow can have an effect also, but normally these are not high-speed processes.
I suspect multi-path will be your biggest problem. You will need to look into some kind of correlation detection scheme.
Also, you will have a hard time getting approval from FCC or similar agencies. In other words, have fun experimenting, but don't think you are going to market a product in the developed world based on broadband pulse transmission unless you are willing to go through a lot of trouble.
One last thing. The shape of your received pulse will depend somewhat on the channel bandwidth, which will depend on antenna bandwidth. The more bandwidth your antennas have, the closer the RX pulse will look to the TX pulse.