Delay-spread sensor and detection switching circuit using the sa

Details Delay-spread sensor and detection switching circuit using the sa Delay-spread sensor and detection switching circuit using the sa

1995-01-18

1997-02-11

Wieder, Kenneth A.

Electricity: measuring and testing

Impedance, admittance or other quantities representative of...

Distributive type parameters

329316, H03D 300

Patent

active

056024843

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a delay-spread sensor for measuring a delay spread which is caused by multipath propagation in digital transmission for mobile communications, and a detection switching circuit using the sensor.
In digital radio transmission system such as mobile radio communication systems, it is necessary to overcome deterioration of the transmission characteristic caused by fading resulting from multipath propagation. Conventionally, a demodulating scheme employs a differential detector which is resistant to level and phase variations. With the speeding up of the digital signal or its transmission over a wide area, a delay spread by a delay time difference in the multipath propagation increases, and an adaptive equalizer is needed to overcome a received signal waveform distortion. However, the amount of signal processing required of the adaptive equalizer becomes tens of times larger than that of the delay detector--this inevitably leads to a sharp increase in power consumption. With the spread of mobile communication services, portable-type mobile stations are on the increase; hence, simplification of the algorithm used and development of low power dissipation ICs are needed to reduce the power consumption of the adaptive equalizer.
With the goal of low power dissipation, hardware development is proceeding but also studies are given an algorithm for optimum switching between the adaptive equalizer and the delay detector. To implement such an algorithm, a delay-spread sensor is required to detect the delay spread. An equivalent to the delay-spread sensor is disclosed in, for example, Mutsumi Serizawa and Minoru Ikukata, "Adaptive Automatic Equalizer Operation Control Circuit for Digital Mobile Communication", '90 IECEJ Autumn National Meeting, B-281, November, 1990, or Kazuhiko Fukawa and Hiroshi Suzuki, "Adaptive Control Method for Delay Detection and Adaptive Maximum Likelihood Sequence Estimation", 1992 IECEJ Autumn National Meeting, B-258, 1992.
FIG. 1A is a prior art example of a mobile station receiving unit. For instance, a PSK-modulated radio frequency signal received by an antenna 8 is converted by a radio-frequency receiving part 9 to an intermediate-frequency signal S.sub.IF, which is limiter-amplified by a limiter amplifier (a nonlinear amplifier) 11 and then differentially detected by a differential detector 12, by which a code sequence is reconstructed. As is well-known in the art, the differential detector 12 has such a construction as depicted in FIG. 1B, in which the limiter-amplified input intermediate-frequency signal S.sub.IF and a reference carrier signal, obtained by delaying S.sub.IF for a one symbol duration T by a delay element 12D1, are multiplied by a multiplier 12M1, then the phase of the output from the delay element 12D1 is delayed .pi./2 by a delay element 12D2 and the delayed output is provided to a multiplier 12M2 for multiplication by the intermediate-frequency signal S.sub.IF. The multiplied outputs from these multipliers 12M1 and 12M2 are provided to a decision circuit 12C via low-pass filters 12F1 and 12F2, respectively, which compares them with threshold values to make a decision on their levels and provides the decision outputs as an in-phase component I(t) and a quadrature component Q(t).
On the other hand, the intermediate-frequency signal S.sub.IF is also applied to an AGC linear amplifier 13 for linear amplification and the amplified output is provided to an IQ detector (quasi-synchronous detector) 14, wherein its in-phase component (an I component) and quadrature component (a Q component) are detected. The code sequence is reconstructed by an adaptive equalizer 15 from these I and Q components. As is well-known in the art, the adaptive equalizer 15 is formed as an adaptive prediction circuit which is composed of a subtractor 15S, a channel parameter estimation part 15P, a code sequence estimation part 15E, a modulation part 15M and a transversal filter 15T, as shown in FIG. 1C, for instance. The output r(t) from the IQ detector

REFERENCES:
patent: 4253184 (1981-02-01), Gitlin et al.
patent: 4849996 (1989-07-01), Kamerman
patent: 5020078 (1991-05-01), Crespo
patent: 5134464 (1992-07-01), Basile et al.
patent: 5159282 (1992-10-01), Serizawa et al.

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