System and apparatus for high data rate wireless communications
A system and apparatus including a wireless network architecture that provides broadband data network coverage over an expandable geographic area. A media access control layer is also provided that facilitates access to the broadband wireless network. A high-frequency wireless modem enables high data rate access to the wireless network in a spectrally-efficient manner using SSB modulation. A wideband millimeter-wave antenna includes a cosecant-squared reflector enabling signal propagation between network elements thereby enabling seamless wireless communications. A millimeter-wave polarizer, and a septum polarizer each convert between linear and circular polarization. A cross-shaped horn antenna adapted for circularly polarized signals can also be used in combination with the septum polarizer. A combined horn antenna is fed using a microstrip patch antenna.
1. A digital communications modem that uses analog signal processing to transform an information signal into a combined encoded signal, the modem comprising:
a pulse-shaping filter receiving the information signal having a baud rate and generating a filtered pulse train having a reduced bandwidth that is less than the baud rate;
an encoder receiving the filtered pulse train and generating an encoded signal having one of two orthogonal relationships;
a combiner receiving two encoded signals having different orthogonal relationships and combining them, the resulting combined encoded signal having a signal bandwidth within the reduced bandwidth.
2. The digital communications modem of claim 1 , further comprising a modulator modulating a carrier signal with the combined encoded signal, the modulated signal having a signal spectrum within a bandwidth of less than half of the baud rate of the received information signal.
3. The digital communications modem of claim 2 , further comprising a frequency translator receiving the modulated signal at a first frequency band and translating it to a different frequency band.
4. The digital communications modem of claim 3 , wherein the frequency translator translates the encoded information signal to a millimeter-wave frequency band.
5. The digital communications modem of claim 4 , wherein the millimeter-wave frequency band is between about 30 GHz and about 300 GHz.
6. The digital communications modem of claim 4 , wherein the millimeter-wave frequency band is between about 50 GHz and about 70 GHz.
7. The digital communications modem of claim 1 , wherein the pulse-shaping filter comprises a raised cosine filter.
8. The digital communications modem of claim 1 , wherein the pulse-shaping filter comprises a part of a matched filter, the other part of the matched filter provided within a remote receiver.
9. The digital communications modem of claim 1 , wherein the encoder comprises a dual-rail binary encoder.
10. The digital communications modem of claim 9 , wherein the dual-rail binary encoder comprises a Hilbert Transformer.
11. The digital communications modem of claim 2 , wherein the modulator comprises a sideband suppressor suppressing one of two sidebands of the modulated signal.
12. The digital communications modem of claim 11 , wherein the sideband suppressor comprises a filter.
13. The digital communications modem of claim 2 , wherein the modulator comprises a single side band (SSB) modulator.
14. The digital communications modem of claim 2 , wherein the modulator comprises a vestigial side band (VSB) modulator.
15. The digital communications modem of claim 1 , further comprising a first pilot signal source combining a first pilot signal with the filtered pulse train, the first pilot signal having a center frequency of about half the baud rate.
16. The digital communications modem of claim 15 , further comprising a second pilot signal source combining a second pilot signal with the filtered pulse train, the second pilot signal having a center frequency corresponding to the inverse of twice the baud period at baseband.
17. The digital communications modem of claim 16 , wherein the second pilot signal is provided with a well-defined power level.
18. The digital communications modem of claim 1 , further comprising a millimeter-wave wireless transmitter, the transmitter transmitting the combined encoded signal wirelessly at a carrier frequency greater than about 30 GHz.