Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
1998-11-13
2001-11-13
Bocure, Tesfaldet (Department: 2731)
Pulse or digital communications
Spread spectrum
Direct sequence
Reexamination Certificate
active
06317454
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a rake receiver which rakes reception results of multipaths, and a mobile unit and a base station for a portable telephone system which use such a rake receiver, and more particularly to a reduction of a circuit scale.
In recent years, a portable telephone of the CDMA system in which different PN (pseudo-noise) codes are allocated to users is rapidly developed. Recently, a system in which a PNW code consisting of a combination of short and long codes is used as the PN code has been studied. A short code is defined for each cell. A spread code is generated by multiplying the short code with a long code which is allocated to each user. When a short code has four chips, the chip number of a PNW code is four times that of a PN code constituting a long code.
In the case where such a code is used, even when any short code is selected in a base station, the communication channel of a cell never coincides with that of another cell.
In the CDMA system, multipaths can be separated from each other in processes of spread and despread. The reception quality can be enhanced by raking reception results of the separated paths. When a PNW code is used, chips are spread in a higher degree, and hence the performance of the rake reception is further improved.
A CDMA portable telephone which performs a rake reception has a plurality of finger circuits which perform demodulation. The finger circuits demodulate received data of different paths, and the demodulated data are raked.
In the CDMA system, furthermore, a pilot symbol is periodically inserted into a transmitted frame. On the reception side, the pilot symbol is detected so as to acquire synchronization, and the acquired synchronization is tracked.
As shown in
FIG. 5
, a finger circuit of a conventional CDMA portable telephone comprises: a decimating unit
40
which decimates received signals RxI and RxQ in accordance with the acquired synchronization; a despreading unit
42
which despreads OnTimeI and OnTimeQ that are decimated in the decimating unit
40
, by using PNW to demodulate the received data; a data path demodulating unit
45
which receives demodulated data DataOnTimeI and DataOnTimeQ that are obtained as a result of the despread, and which decodes the data; a despreading unit
43
which despreads OnTimeI and OnTimeQ by using a long code PN and demodulates pilot data; a pilot carrier tracking unit
46
which receives pilot data PilotOnTimeI and PilotOnTimeQ that are obtained as a result of the despread, and which performs synchronous tracking; a decimating unit
41
which decimates the received signals RxI and RxQ at various timings in order to perform synchronous acquisition; a despreading unit
44
which despreads ELI and ELQ that are decimated in the decimating unit
41
, by using a long code PN; and a time tracking unit
47
which acquires synchronization by using PilotELI and PilotELQ that are obtained as a result of the despread.
In the finger circuit, as shown in
FIG. 10
, the decimating unit
41
decimates the received signals RxI and RxQ after the timing of ELCLK, and outputs ELI and ELQ, and the despreading unit
44
despreads the PN codes of PnI and PnQ into the ELI and ELQ.
In the time tracking unit
47
, when a pilot data cannot be detected from the outputs PilotELI and PilotELQ of the despreading unit
44
, ELCLK is shifted by one clock. When ELCLK is sequentially shifted by one clock in this way, it is possible to acquire a synchronized clock which enables a pilot data to be detected.
When synchronous acquisition is attained, the clock is input as OnTimeCLK into the decimating unit
40
, and the decimating unit
40
decimates the received signals RxI and RxQ from OnTimeCLK to output OnTimeI and OnTimeQ.
The despreading unit
42
despreads OnTimeI and OnTimeQ by using PNW codes of PnWI and PnWQ, and demodulates the received data DATaOnTimeI and DataOnTimeQ. The demodulated data are supplied to the data path demodulating unit
45
.
The despreading unit
43
despreads OnTimeI and OnTimeQ with the PN codes of PnI and PnQ and demodulates pilot data PilotOnTimeI and PilotOnTimeQ. The demodulated data are supplied to the pilot carrier tracking unit
46
. The pilot carrier tracking unit
46
performs synchronous tracking while adjusting OnTimeCLK supplied to the decimating unit
40
, so that the pilot data can be always detected from the outputs PilotOnTimeI and PilotOnTimeQ of the despreading unit
43
.
In order to enhance the performance of rake reception, it is required to increase the number of finger circuits and that of paths which are to be subjected to demodulation in the finger circuits. Each finger circuit employed in a rake receiver of the prior art has despreading units which are respectively used for a data path demodulating unit, a pilot carrier tracking unit, and a time tracking unit. As the number of finger circuits is larger, therefore, the number of despreading units is increased, thereby producing a problem in that the circuit scale of the whole of a rake receiver is extremely enlarged.
SUMMARY OF THE INVENTION
The invention has been conducted in order to solve the problem of the prior art. It is an object of the invention to provide a rake receiver in which the number of despreading units is reduced so as to suppress expansion of the circuit scale, and also to provide a mobile unit and a base station for a portable telephone system which use such a receiver.
In the rake receiver of the invention, selecting means for switching a spread code which is to be supplied to despreading means, and/or selecting means for switching received signals which are to be supplied to despreading means are disposed, whereby despreading means for supplying data to a data path demodulating unit, a pilot carrier tracking unit, and a time tracking unit can be commonly used, so that the number of the despreading means is reduced to two or one.
Consequently, the circuit scale of the rake receiver can be reduced.
When the configuration of the rake receiver is applied to a mobile unit or a base station for a portable telephone system, the circuit scale of the mobile unit or the base station can be reduced.
According to the first aspect of the present invention, a rake receiver comprises: first decimating means for extracting received signals in order to perform synchronous acquisition; and second decimating means for extracting received signals from a synchronously acquired clock, and in which the received signals extracted by the first decimating means are despread with a PN code and then supplied to time tracking means, the received signals extracted by the second decimating means are despread with a PN code, obtained pilot data are supplied to pilot carrier tracking means, the received signals extracted by the second decimating means are despread with a wideband PN code, and obtained data are supplied to data path demodulating means, and the rake receiver further comprises: despreading means for despreading the received signals extracted by the second decimating means; and selecting means for switchingly outputting the PN code and the wideband PN code to the despreading means, the data which are to be supplied to the pilot carrier tracking means and the data path demodulating means are despread by using the despreading means which is common to these means. The number of the despreading means can be reduced to two.
According to the second aspect of the present invention, a rake receiver comprises: selecting means for switchingly outputting the received signals extracted by the first decimating means and the received signals extracted by the second decimating means; and despreading means for despreading an output of the selecting means with a PN code, and the data which are to be supplied to the pilot carrier tracking means and the time tracking means are despread by using the despreading means which is common to these means. The number of the despreading means can be reduced to two.
Further, according to the third aspect of the present invention, a rake receiver comp
Bocure Tesfaldet
Matsushita Electric - Industrial Co., Ltd.
Pearne & Gordon LLP
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