Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
1999-08-31
2004-06-22
Corrielus, Jean B. (Department: 2631)
Pulse or digital communications
Spread spectrum
Direct sequence
C375S343000, C370S335000, C370S342000
Reexamination Certificate
active
06754256
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to searchers for Code Division Multiple Access (CDMA) receiver apparatuses, and more particularly to a searcher which searches for a synchronizing timing with respect to a spreading code sequence within a received signal in a CDMA receiver apparatus.
When a CDMA system such as a Direct Sequence Code Division Multiple Access (DS-CDMA) system is applied to a mobile communication, it is essential to provide in a receiver apparatus a searcher function for detecting a timing of a despreading code by carrying out a path detection. In order to realize this searcher function, there are demands to reduce the number of bits of correlation value information which is obtained from a correlator output, and to provide substantially the same dynamic range or an improved dynamic range as compared to the conventional dynamic range.
2. Description of the Related Art
FIG. 1
is a system block diagram for explaining the operating principle of the CDMA system which is employed in a mobile communication or the like. As shown in
FIG. 1
, a transmitting end uses a modulator
81
to modulate information data having a rate of 10 kbps, for example, into a spreading code sequence having a rate of 1 Mcps, for example, so as to carry out a spectrum spreading, and a radio transmission is made from a transmitter
82
. At a receiving end, a spectrum spread radio wave is received by a receiver
85
, and a spreading code sequence having the same pattern as that used at the transmitting end is generated by a spreading code generator
87
. This spreading code sequence is multiplied to the received wave by a demodulator
86
, so as to carry out a despreading and obtain the original information data. When carrying out this despreading, an input timing of the spreading code sequence within the received wave is detected by a searcher
88
, in order to synchronize the spreading code sequence generated by the spreading code generator
87
and the spreading code sequence within the received wave. The searcher
88
instructs a generation timing of the spreading code generator
87
based on the detected input timing, so that the spreading code sequence generated by the spreading code generator
87
is synchronized to the spreading code sequence within the received wave.
FIG. 2
is a system block diagram showing an example of the construction of the searcher
88
. For example, a 8-bit parallel input signal is input to a correlator
90
. The correlator
90
includes a multi-stage shift register
91
successively input with the input signal, a memory
92
storing a part of the spreading code sequence, such as a pilot signal, multipliers
93
, and an adder
94
. Each multiplier
93
compares corresponding bits of the output sequence of the shift register
91
and the output sequence of the memory
92
, and outputs a high-level signal when the corresponding bits of the compared output sequences match. More particularly, each multiplier
93
carries out an exclusive-OR operation on the corresponding bits of the two output sequences. The adder
94
adds outputs of each of the multipliers
93
. According to the correlator
90
, a maximum amplitude is output when the spreading code sequence within the received wave which is successively input matches the part of the spreading code sequence set in the memory
92
. The input timing of the spreading code sequence within the received wave can be detected based on this maximum amplitude output.
For example, a 10-bit output value from the correlator
90
is squared in a multiplier
95
and is converted into a 20-bit power value, for example. This 20-bit power value is stored in a delay profile memory
97
via an adder
96
, as a delay profile data. This delay profile data is generated by the adder
96
which carries out a cyclic integration of the power values which are successively input and a cumulative addition thereof.
According to the conventional searcher
88
, the antilogarithms (true values) of the data are processed subsequent to the output of the correlator
90
. For this reason, when a 10-bit correlation value is converted into a power value by obtaining the square of the correlation value, the data width of the power value is enlarged to 20 bits. As a result, the scale of the circuit which carries out the operation becomes large, and the operation speed becomes slow. In addition, a memory capacity required to store the delay profile data becomes large.
Consequently, the data width of the power value is reduced by deleting the lower 10 bits of the 20-bit power value, for example. But when only the upper 10 bits of the power value are processed, there is a problem in that a dynamic range of the data inevitably becomes small.
In addition, even in the case of the power value having the data width of 20 bits, the dynamic range of the data is only 60 dB, for example, and there are demands to further improve the dynamic range of the data.
On the other hand, the problems described above not only occurs when converting the correlator output value into the power value, but similar problems also occur when a search operation is carried out by using the correlator output value as it is. Hence, there are demands to carry out the search operation by utilizing a correlator output value which has a small data width but has a large dynamic range.
SUMMARY OF THE INVENTION
Accordingly, it is a general object of the present invention to provide a novel and useful searcher for a CDMA receiver apparatus, in which the problems described above are eliminated and the demands described above are satisfied.
Another and more specific object of the present invention is to provide a searcher for a CDMA receiver apparatus, wherein information related to a correlation value which is used or a search operation is subjected to a non-linear processing, so as to reduce the number of bits of the correlation value while enlarging a dynamic range of the correlation value, so that the dynamic range becomes equivalent to or larger than a dynamic range which would be obtained when processing antilogarithms of the data.
Still another object of the present invention is to provide a searcher for a CDMA receiver apparatus, comprising a correlator obtaining a correlation value between a spreading code sequence and a spreading code sequence within a received signal, and a non-linear processor carrying out a non-linear conversion to convert one of the correlation value and a predetermined value indicative of the correlation value into correlation value information which has a data width smaller than that of the one of the correlation value and the predetermined value, where the correlation value information is used to carry out a search process to search for a synchronizing timing with respect to the spreading code sequence within the received signal. According to the searcher of the present invention, it is possible to reduce the data width (number of bits) while enlarging the dynamic range to a range equivalent to or greater than the dynamic range which is obtained when the data is treated in the form of the antilogarithm. Furthermore, it is possible to reduce the scale of the circuit and improve the operation speed of the searcher by carrying out the search operation using such data having the reduced data width.
A further object of the present invention is to provide a searcher for a CDMA receiver apparatus, comprising a correlator obtaining a correlation value between a spreading code sequence and a spreading code sequence within a received signal, a non-linear processor carrying out a non-linear conversion to convert the correlation value into a value which has a data width smaller than that of the correlation value, and a power value converter converting the value obtained from the non-linear processor into a power value and outputting the power value as correlation value information, where the correlation value information is used to carry out a search process to search for a synchronizing timing with respect to the spre
Asano Yoshihiko
Kawaguchi Noriyuki
Kubo Tokuro
Matsuyama Koji
Minowa Morihiko
Corrielus Jean B.
Fujitsu Limited
Ghulamali Qutub
Katten Muchin Zavis & Rosenman
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