Application and Uses for Orthogonal Signals

Application and Uses for Orthogonal Signals

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Orthogonal signals are used extensively in communications because they can be received and demodulated as separate data streams with very little interference between the orthogonal signals. Quadrature demodulation is used to eliminate the ambiguity of the phase of the incoming signal, but also is used to provide a means of either sending more data or providing two separate data streams that can be demodulated separately. Antenna polarization is used to allow two channels to operate on the same frequency in quadrature. This can be either horizontal/vertical or LHCP/RHCP GSOs can be used to reduce the effects of jamming signals. The jammer and the signal are forced to be orthogonal so that the jammer can be eliminated and the signal be detected. GSOs are based on the inner product of orthogonal signals being equal to zero. Therefore, if they are orthogonal and the inner product is zero, then the desired signal can be easily detected in the presence of an unwanted signal or jammer. This approach assumes that the jammer signal level is much higher than the desired signal level. The basic GSO uses two inputs: one of the inputs contains more signal than jammer. This applies to having two antennas with one directed towards the signal providing higher power. The error signal for feedback in updating the weight value is produced by subtracting the weighted reference input signal from the received signal which contains the higher level of desired signal. When the weight has converged, the jamming signal is suppressed. OFDM is a method used in many communication applications where high-speed data or multiple users are desired. OFDM provides an optimal, spectrally efficient system for use with multiple users or the combination of parallel frequency channels for overall high data rates used for broadband communications and home networking.

Chapter Contents:

  • 4.1 Quadrature Sine/Cosine Signals
  • 4.2 Orthogonalizer Techniques
  • 4.3 Orthogonal Frequency Division Multiplexing (OFDM)
  • 4.4 Summary
  • 4.5 References

Inspec keywords: jamming; OFDM modulation; demodulation; quadrature amplitude modulation

Other keywords: horizontal-vertical GSO; orthogonal signals; left hand circular polarized/right hand circular polarized technique; LHCP-RHCP GSO; antenna polarization; data streams; OFDM; jamming signals; broadband communications; Gram-Schmidt orthogonalizer; home networking; parallel frequency channels; quadrature demodulation

Subjects: Electromagnetic compatibility and interference; Modulation and coding methods

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