Apparatus and methods for modulation and demodulation of data

DETAILED DESCRIPTION The present invention seeks to provide improved methods and apparatus for modulating and demodulating data.
One object of a preferred embodiment of the present invention is to provide a modulation/demodulation scheme with improved bandwidth efficiency, sharp ingress rejection, robustness to time and phase errors and low latency, which is therefore suitable for reliable continuous transmission of packets in multi-point systems such as HFC (hybrid fiber coax).
According to a preferred embodiment of the present invention, a modem is provided which is generally insensitive to timing and phase impairments because it employs signals which overlap in frequency and in time but maintain orthogonality.
Also, unlike SQAM, each signal preferably includes an in-phase component and a quadrature component which is a Hilbert transformation of the in-phase component, rather than employing signals which include staggered in-phase and quadrature phase components as in prior art systems.
There is thus provided, in accordance with a preferred embodiment of the present invention, a signal modulation method including receiving at least first and second synchronized incoming streams of complex symbols, thereby to define a plurality of incoming vectors each including at least first and second synchronized complex symbols, mapping each complex symbol into a signal component including a linear combination of an in-phase signal and a quadrature signal, the quadrature signal including a Hilbert transform of the in-phase signal, wherein all of the signal components are substantially mutually orthogonal, and wherein the frequency spectrums of all signal components mapped from a single incoming stream are centered around a common frequency location which is unique to the single incoming stream and wherein the frequency spectrums of signal components mapped from different incoming streams having adjacent common frequency locations are partially overlapping, and wherein signal components mapped from sequential incoming symbols partially overlap in time, and combining all of the signal components into a representation of an output signal