Pulse or digital communications – Receivers – Particular pulse demodulator or detector
Reexamination Certificate
1998-06-12
2001-04-10
Pham, Chi (Department: 2631)
Pulse or digital communications
Receivers
Particular pulse demodulator or detector
C714S794000
Reexamination Certificate
active
06215832
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a maximum likelihood sequence estimation receiver that estimates a transmission signal from a signal with transmission distortion due to a frequency-selective fading in multiple radio propagation (multipath) such as a radio line in a high-speed digital communications system, for example, a digital mobile telephone system. More particularly, the present invention relates to a maximum likelihood sequence estimation receiver that obtains estimates of transmission signals by selecting an optimum portion among impulse response sequences with transmission distortion. Moreover, the present invention relates to a method of receiving maximum-likelihood sequence estimates.
An example of the technique in which that type of signal estimation is performed by selecting the optimum portion among impulse response sequences with transmission distortion is disclosed in, for example, JP-A-292139/1993 titled as “maximum likelihood sequence estimation receiver”.
FIG. 4
is a block diagram illustrating the configuration of a conventional maximum likelihood sequence estimation receiver. In
FIG. 4
, each of tap coefficients of the matched filter
22
is added based on impulse responses of a received input signal from the transmission line. In this case, the number of taps of the matched filter
22
has to be minimized to reduce the throughput of the status estimator
23
with the largest arithmetic amount. A reduced number of taps allows only a limited region of impulse response sequences to be processed.
Hence, it is needed to judge whether or not what region of impulse response sequences to be processed with a tap coefficient provides the highest estimation capability. The receiver shown in
FIG. 4
implements an estimation region judgment according to the following steps.
FIG. 5
is a diagram explaining impulse response values.
Referring to
FIGS. 4 and 5
, upon receiving a training signal from the transmission side, the signal generator
26
generates the same signal as the training signal. The estimator
25
determines characteristic-line impulse response values. When impulse response values are obtained as shown in
FIG. 5
, the position estimator
27
compares the amplitudes of the impulse response values. This comparison operation numbers the impulse response values in decreasing order. The region where the sum of pulse numbers is smallest among regions containing a pulse with the maximum amplitude is regarded as an optimum signal estimation region. The timing signal representing the optimum signal estimation region is sent to the matched filter
22
and the status estimator
23
to implement the optimum maximum likelihood sequence estimation.
However, the above-mentioned prior art requires to implement a complicated algorithmic operation to determine the optimum estimation region. That is, amplitude values, as shown in
FIG. 5
, need to be numbered in decreasing order. Moreover, the comparison operation must be repeated several times to determine the optimum estimation region by performing arithmetic to compare impulse response values. This results in making the whole algorithm complicated. Particularly, as the number of taps of the matched filter increases, the arithmetic operations to be processed increases.
The optimum estimation region judgment cannot always obtain an optimum estimation region because impulse responses necessarily contain a maximum value pulse.
FIG. 6
is a diagram explaining the status where impulses response values are numbered in a decreasing order of amplitude value in a transmission line. In order to estimate a signal with distortion in a transmission line with impulse responses as shown in
FIG. 6
, the pulses
2
,
3
, and
4
must be selected as optimum estimation regions. In this case, since the pulse
1
with the maximum value is necessarily selected, the optimum estimation region cannot be specified.
SUMMARY OF THE INVENTION
The present invention is made to solve the above-mentioned problems. The objective of the present invention is to provide a maximum likelihood sequence estimation receiver that can certainly and accurately find optimum estimation regions with a simple algorithm, instead of the use of the power arithmetic scheme which requires a large operation capability, when regions which enable optimum signal estimation are determined from transmission line impulse responses.
Another objective of the present invention is to provide a maximum sequence likelihood sequence estimation receiver that can easily realize its low power consumption and its simplified circuit configuration, thus resulting in compactness and lightweight thereof.
Still another objective of the present invention to a method of receiving maximum-likelihood sequence estimates.
The objective of the present invention is achieved by a maximum likelihood sequence estimation receiver that selects an optimum region among impulse response sequences with transmission line distortion to estimate a transmission signal among signals with transmission distortion, comprising decision means for substitutively implementing a power calculation within an estimation region by an absolute value operation and detecting a timing at which a cumulative value of absolute values in said estimation region is maximized and thus deciding an optimum estimation region with a small amount of processes.
According to the present invention, the decision means comprises a transmission line characteristic detector for detecting a transmission line characteristic in a received signal, an absolute value arithmetic section for performing arithmetic on absolute values of amplitude components in the transmission line characteristic detected by the transmission line characteristic detector, an accumulator for accumulating the absolute values of the amplitude components from the absolute value arithmetic section and then outputting an output signal, a maximum value detector for detecting a timing at which the output signal of the accumulator indicates a maximum value, and a maximum likelihood sequence estimator for performing a maximum likelihood estimation of the received signal using the transmission line characteristic from the transmission line characteristic detector and the timing from the maximum value detector.
Moreover, according to the present invention, the absolute value arithmetic section comprises a first absolute value arithmetic section for determining a real part absolute value of a complex signal with a transmission characteristic, a second absolute value arithmetic section for determining an imaginary part absolute value of the complex signal with a transmission characteristic, a comparator for comparing the real part absolute value from the first absolute value arithmetic section with the imaginary part absolute value from the second absolute value arithmetic section and then outputting a comparison signal, a switching section for outputting said real part absolute value and the imaginary part absolute value without any change when said real part absolute value is larger than said imaginary part absolute value and reversely outputting said real part absolute value and the imaginary part absolute value when said real part absolute value is smaller than said imaginary part absolute value, a multiplier for outputting the imaginary part absolute value when the real part absolute value from the switching section is larger than the imaginary part absolute value from the switching section or decreasing the real part absolute value switched by the switching section when the real part absolute value from the switching section is smaller than the imaginary part absolute value from the switching section, and an adder for adding an output signal from the switching section and an output signal from the multiplier and then outputting a resultant signal as an absolute value signal.
Furthermore, according to the present invention, the maximum value detector comprises a first register for storing a maximum value among values of output signals from the accumulato
Bayard Emmanuel
NEC Corporation
Ostrolenk Faber Gerb & Soffen, LLP
Pham Chi
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