Ultra wide bandwidth spread-spectrum communications system
View Patent ↗An ultra wide bandwidth, high speed, spread spectrum communications system uses short wavelets of electromagnetic energy to transmit information through objects such as walls or earth. The communication system uses baseband codes formed from time shifted and inverted wavelets to encode data on a RF signal. The combination of short duration wavelets and encoding techniques are used to spread the signal energy over an ultra wide frequency band such that the energy is not concentrated in any particular narrow band and is not detected by conventional narrow band receivers so it does not interfere with those communication systems. The use of pulse codes composed of time shifted and inverted wavelets gives the system according to the present invention a spatial resolution on the order of 1 foot which is sufficient to minimize the negative effects of multipath interference and permit time domain rake processing.
1. A data communications method, comprising:
receiving a stream of digital data that are mapped such that a first data value corresponds to a positive value and a second data value corresponds to a negative data value;
repetitively generating a codeword to produce a digital code signal;
modulating the codeword digital code signal by either the positive value or the negative value in accord with the digital data, to generate a modulated code signal;
generating a modulated ultrawideband impulse signal by modulating the modulated code signal with a pulse shape; and
outputting the modulated ultrawideband impulse signal.
2. The method of claim 1 , wherein in the operation of generating a modulated ultrawideband impulse signal, each bit of the modulated code signal is modulated individually onto the pulse shape.
3. The method of claim 2 , wherein: the generating of the modulated ultrawideband impulse signal comprises:
generating a first pulse having a first predetermined shape,
generating second pulse having a second predetermined shape that is an inverse of the first pulse shape; and
selecting between the first pulse and the second pulse in response to a value of each bit of the modulated code signal.
4. The method of claim 1 , wherein the pulse shape corresponds to a pulse wavelet having a duration between 100 and 1000 picoseconds.
5. The method of claim 1 , wherein the codeword comprises a Barker code.
6. The method of claim 1 , further comprising processing the stream of digital data prior to the modulating of the codeword digital code signal in accord with the digital data.
7. The method of claim 6 , wherein the processing of the stream of digital data comprises one or more of: forward error correction (FEC) encoding, differential encoding, and modulating a separate code signal comprising a repeating codeword.
8. The method of claim 6 , wherein the outputting of the modulated ultrawideband impulse signal comprises transmitting the modulated ultrawideband impulse signal as a carrierless baseband signal.
9. The method of claim 6 , further comprising:
receiving the modulated ultrawideband impulse signal;
compressing code modulated groups of pulses in the received modulated ultrawideband impulse signal, to form a received modulated sequence of pulses; and
demodulating the received modulated sequence of pulses, to recover the stream of digital data.