US 5,465,271 AGranted

Post detection weighted vector combining diversity receivers using phase metrics for mobile and indoor radio channels

AssigneeGeneral Electric Company

InventorsStephen M. Hladik, Sandeep Chennakeshu

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Abstract

A digital radio communications system employs a digital information source for providing digital information such as message bits, a transmitter for transmitting encoded digital information into data symbols in a radio-frequency (RF) signal to a plurality of antennae which sense the transmitted RF signal. A post detection measure of signal quality, the signal-to-impairment ratio, (SIR), is utilized by the receiver to perform post detection combining of signals received by a plurality of antennae. The antennae are coupled to a receiver which for each received signal: digitizes the signal, determines phase angles of the digitized signal, converts the signal to unit vectors, determines a signal-to-impairment ratio (SIR) estimates .gamma..sup.j of the digitized signals. The SIR estimate .gamma..sup.j is weighted by combining weight computation element and multiplied by each unit vector to provide an in-phase is component and a quadrature component for each signal. The in-phase components are combined into a in-phase composite signal I.sub.c (n). The quadrature-phase components are combined into a quadrature-phase composite signal Q.sub.c (n). The composite signal (I.sub.c (n), Q.sub.c (n) is then decoded into phase angles which are reversed mapped to message bits which are utilized by an output device resulting in a radio communication system exhibiting improved performance during radio "fade" periods.

Claims11

Dependent claims

A fade-resistant method of communicating digital information comprising the steps of:

a) transmitting encoded message bits in a radio-frequency (RF) signal;
b) sensing the transmitted RF signal with a plurality of N antennae;
c) for each sensed RF signal j where j indicates the receiving antenna, and j=1,2,3, . . N:
i. down converting the sensed signal to a sampled baseband signal r.sub.j (n);
ii. detecting a phase .phi..sub.j (n) for each sample r.sub.j (n),
iii. estimating a signal to impairment (SIR) ratio .gamma..sup.j from each detected phase .phi..sub.j (n),
iv. calculating a weighting factor F(.gamma..sup.j) for post detection maximal ratio combining as a predetermined function of the jth signals estimated SIR .gamma..sup.j,
v. determining the rectangular coordinates (cartesian coordinates) of a unit magnitude vector resulting in a cosine and sine of detected phase .phi..sub.j (n),
vi. weighting both the sine and cosine of detected phase .phi..sub.j (n) by the weighting factor F(.gamma..sup.j) to result in an in-phase component I.sub.j (n), and a quadrature-phase component Q.sub.j (n) for the signal sensed from antenna j;
d) summing in-phase components I.sub.j (n) for all antennae j into a composite in-phase coefficient I.sub.c (n);
e) summing quadrature-phase components Q.sub.j (n) for all antennae j into a composite quadrature-phase coefficient Q.sub.c (n);
f) determining a composite phase .phi..sub.c (n) according to:
##EQU11## g) estimating the most likely message bits corresponding to the observed composite phase .phi..sub.c (n);
and
h) providing the estimated message bits to an output device capable of utilizing the digital information.

12 more elements

A simplified fade-resistant digital communications system comprising:

a) a digital information source adapted for providing a stream of message bits;
b) a transmitter means adapted for encoding and transmitting the message bits in a radio-frequency (RF) signal;
c) a plurality of N receiver branches each adapted for receiving the transmitted RF signal wherein each receiver branch comprises:
i. an antenna adapted for sensing the transmitted RF signal;
ii. a front end unit coupled to the antenna for down converting each sensed signal to a sampled baseband signal, r.sub.j (n),
iii. a phase detector coupled to the front end unit for detecting a phase .phi..sub.j (n) for each sample r.sub.j (n),
iv. signal-to-impairment ratio (SIR) estimator coupled to the phase detector for estimating an SIR .gamma..sup.j from each detected phase .phi..sub.j (n),
v. a combining weight computation element coupled to the SIR ratio estimator adapted for weighting each SIR .gamma..sup.j by a predetermined amount to result in a weighting factor F(.gamma..sup.j),
vi. vector converter coupled to the phase detector adapted for determining a unit magnitude vector having components defined as the cosine and sine of detected phase .phi..sub.j (n),
vii. a first signal multiplier coupled to the vector converter for weighting the sine component of detected phase .phi..sub.j (n) by the weighting factor F(.gamma..sup.j) to result in an in-phase component I.sub.j (n), and
viii. a second signal multiplier coupled to the vector convertor for weighting the cosine component of detected phase .phi..sub.j (n) by the weighting factor F(.gamma..sup.j) to result in a quadrature phase component Q.sub.j (n) for the signal sensed from antenna j;
d) an in-phase summer adapted for combining all in-phase components I.sub.j (n) for all antennae j into a composite in phase coefficient I.sub.c (n);
e) a quadrature phase summer adapted for combining all quadrature-phase components Q.sub.j (n) for all antennae j into a composite quadruture-phase coefficient Q.sub.c (n);
f) an inverse tangent unit coupled to the summers for determining a composite phase .phi..sub.c (n) according to:
##EQU18## g) a decision device coupled to the inverse tangent unit for converting .phi..sub.c (n) into message bits;
and
h) an output device coupled to the decision device for utilizing the message bits.

14 more elements

Dependencies are inferred from the claim text.