Receiver and an adaptive equalizer method

Details Receiver and an adaptive equalizer method Receiver and an adaptive equalizer method

2001-02-27

2003-05-06

Chin, Stephen (Department: 2634)

Pulse or digital communications

Equalizers

Automatic

Reexamination Certificate

active

06560278

ABSTRACT:

TECHNICAL FIELD
This invention in general relates to a receiver to be used for a mobile phone or the like. More specifically, this invention relates to the receiver and an adaptive equalizer method in the receiver which judges data without utilizing a training sequence for an operation of an adaptive equalizer.
BACKGROUND ART
A conventional receiver and adaptive equalizer method will be explained below. For example, in wireless communication such as a mobile phone, a non-ignorable delay wave is occasionally generated in a data symbol due to multipath propagation. If such a delay wave is generated, interference occurs between code symbols. This phenomenon is called as inter-symbol interference. For this reason, an equalizing technique, for example, exists as a receiving technique which overcomes the inter-symbol interference.
FIG. 20
shows a structure of an adaptive equalizer adopted by a conventional receiver. In
FIG. 20
, legend
1
denotes a received signal input terminal, legend
2
denotes a decision value output terminal, legend
3
denotes an over-sample sampler, legend
100
denotes a symbol rate data output circuit, legend
101
denotes a timing detector utilizing a training sequence, and legend
102
denotes an equalizer utilizing a training sequence.
Operation of this receiver will now be explained.
FIG. 21
is a diagram showing a principle of an over-sample by the receiver. For example,
FIG. 21
shows an example of 8-time over-sample, namely, the case where sampling is performed eight times with 1 symbol cycle. Here, sampling time is represented by integer numbers, and over-sample timing numbers corresponding to the sampling time are represented by eight numbers from ‘0’ to ‘7’. Namely, in a sequence where the over-sample timing number is “1”, data of time ‘9’ are output as symbol data next to time ‘1’. For example, when the equalizer
102
operates based on the double over sampling, data of time ‘5’ are output as over-sample data as symbol data next to time ‘1’ in a sequence where the over-sample timing number is ‘1’. However, a received sequence will be explained as symbol rate data, but over-sample data can be treated by similar concept.
In FIG.
20
and
FIG. 21
, a received signal is first sampled at predetermined timing by the over-sample sampler
3
. Next, the timing detector
101
receives the over-sampled received signal and determines over-sample timing numbers shown in
FIG. 21
by utilizing a training sequence which is a known pattern. Next, the symbol rate data output circuit
100
receives the over-sample timing number, and outputs a received sequence of a symbol rate corresponding to this number. Finally, the equalizer
102
utilizing a training sequence receives the received sequence of the symbol rate, and creates a decision value which is an estimated value of a transmission data sequence so as to output the decision value from the decision value output terminal
2
.
In such a manner, normally, the receiver, which uses the equalizer
102
utilizing a training sequence, once estimates a position of a training sequence in any manner so as to operate.
Meanwhile, in addition to such an adaptive equalizer utilizing a training sequence, an equalizer which does not require a training sequence exists. This is referred to as a blind equalizer (for example, described in “Linear Equalization Theory” written by Yoichi Sato, Maruzen, 1990). Since a blind equalizer operates without utilizing a training sequence, the above-mentioned process utilizing training can be avoided.
FIG. 22
shows a structure of a conventional receiver using a blind equalizer described in “Synchronization Establishing System for Equalizer” written by Masaaki Fujii (Japanese Patent Application Laid-Open No. 6-216810 (1994)) In
FIG. 22
, legend
1
denotes a received signal input terminal, legend
2
denotes a decision value output terminal, legend
3
denotes an over-sample sampler, legend
111
denotes a received signal storage circuit, legend
102
denotes an equalizer utilizing a training sequence, legends
103
A,
103
B and
103
C denote blind equalizers with UW (unique word) detecting function, legend
104
denotes a UW portion error comparing circuit, and legend
105
denotes an optimum phase selecting circuit. Here, in later explanation, a training sequence and an unique word (UW) are treated as equivalent.
FIG. 23
shows an example of the structure of the blind equalizer
103
with UW detecting function shown in FIG.
22
. In
FIG. 23
, legend
7
denotes a UW detector, legend
8
denotes a received sequence input terminal, legend
13
denotes a blind equalizer, legend
107
denotes an error output terminal, and legend
108
denotes a mask circuit.
Operation of the receiver shown in
FIG. 22
will now be explained. At first, a received signal, which is over-sampled by the over-sample sampler
3
, is once stored in the received signal storage circuit
111
. Next, the received signal storage circuit
111
outputs an N-systemic received sequence, shown in
FIG. 21
, where over-sample timing number differs, and N-numbered blind equalizers
103
A,
103
B, . . . ,
103
C with UW detecting function receive received signals respectively.
Detailed operation of the blind equalizers with UW detecting function will now be explained with reference to FIG.
23
. At first, the blind equalizer
13
which received the received sequence outputs a decision value and an error value. The UW detector
7
receives the decision value so as to detect UW and instructs the mask circuit
108
on mask for mask period other than UW detection time. The mask circuit
108
outputs an error value which was received except at mask instructing period.
Next, the UW portion error comparing circuit
104
receives N-numbered pieces of error information from the N-numbered blind equalizers
103
with UW detecting function, and outputs timing corresponding to a received sequence where the error is the smallest. The optimum phase selecting circuit
105
selects a received sequence of a symbol rate from the received signal storage circuit
111
according to the timing instruction from the UW portion error comparing circuit
104
, and outputs the received sequence. Finally, the equalizer
102
receives the received sequence, and performs an adaptive equalizer process utilizing a training sequence so as to output a decision value from the decision value output terminal
2
.
As mentioned above, in the conventional blind equalizers, an error signal to be used for timing selection is generated. As a result, this is equivalent to the case where the timing detector
101
utilizing a training sequence in
FIG. 20
is realized by utilizing the blind equalizers
103
A to
103
C with UW detecting function in FIG.
22
. Namely, decision values of the blind equalizers with UW detecting function are not utilized as a decision value of the adaptive equalizer process.
However, in the conventional receiver described in the above publication, there arises the following problems:
(1) In order that the adaptive equalizer operates, before the adaptive equalizer operates, a position of a training sequence should be known.
(2) Even if the blind equalizers are utilized, the equalizer which has another structure and utilizes a training sequence is required at a later stage.
(3) It is difficult to reproduce stable timing in an environment of inter-symbol interference.
SUMMARY OF THE INVENTION
The present invention is devised in order to solve the above problems. It is an object of the present invention to provide a receiver which is capable of reproducing stable timing even in the environment of inter-symbol interference and outputting a decision value in an adaptive equalizer process only using a blind equalizer without utilizing a training sequence, and relates to an adaptive equalizer method in the receiver.
A receiver of the present invention having an adaptive equalizer which judges a transmission data sequence by means of an adaptive equalizer process comprises a sampling unit which samples a received signal at a speed of not less than a

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