US 4,135,057 A · High density digital transmission system

Abstract

A high density bandlimited digital transmission system with a transmitter and a receiver connected by a radio path with an end-to-end channel transfer function selected to form at the receiver either raised cosine pulses or partial response pulses. The transmitter is partitioned or divided into an active pulse forming network and a passive pulse shaping and bandlimiting network. The active and passive networks are concatenated and in combination provide an optimal transmitter-receiver combination for raised cosine or for partial response signaling. Transmit and receive filters provide optimal signal pulse shaping while meeting specified out-of-band signal suppression. In-phase and quadrature phase carriers (I and Q channels) work with rectangular or half-wave sinusoidal modulating pulses. Further, time-offset or time-coincident pulses on each of the respective I and Q channels are used. Multi-level embodiments are also disclosed. Receivers using time-offset modulation forms allowing coherent detection using VSB and SSB techniques with resulting simplification of the receiver structures. This mode of operation is possible without the use of sideband separation filters at the transmitter. Only the receiver structure is affected. Preferred embodiments are described that closely approach optimal performance and achieve information densities in the range from 1.75 to 4 bits per second per Hertz.

Claims53

Dependent claims

In a band limited high density digital transmission system operating in combination with input and output signal processing means, the combination which comprises:

(a) a transmitter adapted to be connected to said input processing means,
(b) a receiver adapted to be connected to said output processing means,
(c) said transmitter including a modulator having an active pulse forming network and a bandlimiting passive pulse shaping network and said receiver including a detector having a bandlimiting passive pulse shaping network, said networks including means to produce specified output pulse shapes from receiver input pulses, with said receiver input pulse shapes generated by said transmitter passive pulse shaping network operating on specified input pulse shapes generated by said transmitter active pulse shaping network,
(d) the signal channel comprising said transmitter and receiver having a channel function H.sub.c (j.omega.) which is the Fourier transform of the desired output pulse in accordance with the relation
H.sub.c (j.omega.) = H.sub.TX (j.omega.)H.sub.RX (j.omega.),
said bandlimiting passive pulse shaping network of said receiver having the function H.sub.RX which is the complex conjugate of the function H.sub.TX, where
H.sub.TX (j.omega.) = .vertline.H.sub.c (j.omega.).vertline. .sup.1/2 e.sup.j.theta.(.omega.)
and
H.sub.RX (j.omega.) = .vertline.H.sub.c (j.omega.).vertline..sup.1/2 e.sup.-j.theta.(.omega.)
wherein
H.sub.TX (j.omega.) is the product of the transmitter active pulse forming network pulse function, P(j.omega. ), and the transfer function of the passive pulse shaping network, H.sub.T (j.omega.), as
H.sub.TX (j.omega.) = P(j.omega.)H.sub.T (j.omega.)
the transmitter and receiver pulse shaping networks both being specified by network poles and residues and time domain optimized for achieving specified input-to-output pulse shape transformation and minimizing adjacent channel interference where said transmitter and receiver passive pulse shaping networks are integral parts of the system modulation and detection means.

10 more elements

In a transmitter system for use in a high density bandlimited digital transmission system for use with a receiver having a pulse shaping network;

(a) an active pulse shaping network for generating modulated output pulses in response to data input from a precoder and frequency input from a stable frequency source;
(b) a passive pulse shaping network connected to accept input from the said active pulse shaping network and related to said receiver pulse shaping network to assure specified receiver output pulses with controlled intersymbol interference and predetermined suppression of adjacent channel interference;
(c) a transmitter output system accepting input from said passive pulse shaping network and said stable frequency source for producing an output signal for transmission to said receiver where the composite channel function H.sub.c (j.omega.) is the Fourier transform of the desired output pulse and is given by
H.sub.c (j.omega.) = H.sub.TX (j.omega.) H.sub.RX (j.omega.)
matching the receiver filter performance with the receiver filter function being the complex conjugate of the transmitter function
H.sub.TX (j.omega.) = .vertline.H.sub.c (j.omega.).vertline..sup.1/2 e.sup.j.theta. (.omega.)
H.sub.RX (j.omega.) = .vertline.H.sub.c (j.omega.).vertline..sup.1/2 e.sup.- j.theta.(.omega.)
with H.sub.TX (j.omega.) being realized as the product of the transmitter active pulse forming network pulse function, P(j.omega.), and the transfer function of the passive pulse shaping network, H.sub.T (j.omega.), as
H.sub.TX (j.omega.) = P(j.omega.) H.sub.T (j.omega.);
and
where said transmitter passive pulse forming network is specified by the network poles and residues enabling time domain optimization of the end-to-end channel response in achieving the specified input-to-output pulse shape transformation while meeting specified adjacent channel interference attenuation where said transmitter passive pulse shaping filter means thus is an integral part of the system modulation.

8 more elements

In a receiver system for use in high density bandlimited digital transmission from a transmitter having a passive pulse shaping network;

a receiver input system for accepting a received RF input signal and a frequency reference signal from a timing and frequency recovery circuit and for producing an amplifier output signal for further receiver processing;
a receiver pulse shaping network for accepting as input the output from said receiver input system and operating in combination with said transmitter passive pulse shaping network to produce output pulses with controlled intersymbol interference and predetermined suppression of adjacent channel interference, said receiver pulse shaping network also including means for providing inputs to said timing and frequency recovery circuit;
a detection and decoding system for accepting as its input the output from the receive pulse shaping network and including means to sample said output in synchronism with a clock signal supplied from the timing and frequency recovery means producing sample values which are decoded into output data values;
with the composite channel function H.sub.c (j.omega.) being the Fourier transform of the desired output pulse and being given by
H.sub.c (j.omega.) = H.sub.TX (j.omega.) H.sub.RX (j.omega.)
with optimal channel partitioning yielding matched filter receiver performance with the receiver function being the complex conjugate of the transmitter function yielding
H.sub.TX (j.omega.) = .vertline.H.sub.c (j.omega.).vertline..sup.1/2 e.sup. j.theta.(.omega.)
H.sub.RX (j.omega.) = .vertline.H.sub.c (j.omega.).vertline..sup.1/2 e.sup.-j.theta.(.omega.)
with H.sub.TX (j.omega.) being realized as the product of the transmitter active pulse forming network pulse function, P(j.omega.), and the transfer function of the passive pulse shaping network, H.sub.T (j.omega. ), as
H.sub.TX (j.omega.) = P(j.omega.) H.sub.T (j.omega.);
and
transmitter and receiver passive pulse forming network means being specified by the network poles and residues enabling time domain optimization of the end-to-end channel response in achieving the specified input-to-output pulse shape transformation while meeting specified adjacent channel interference attenuation;
said transmitter and receiver passive pulse shaping filter means thus being an integral part of the system modulation and detection means.

10 more elements

Dependencies are inferred from the claim text.

High density digital transmission system

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High density digital transmission system

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Abstract

Claims53