Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Reexamination Certificate
1997-07-17
2001-02-13
Olms, Douglas W. (Department: 2732)
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
C370S310000
Reexamination Certificate
active
06188682
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a receiving method and apparatus which performs a visited cell search and a neighbor cell search in radio communications using a CDMA radio access system.
With a conventional receiving apparatus in the CDMA radio communication system, a mobile station uses what is called a dedicated searcher whereby, at turn-on or during the standby state, a decision is made about the cell where the mobile station ought to stay or a search is conducted for surrounding cells or a multi-path that the mobile station receives.
In
FIG. 1A
there is shown in block form an example of the configuration of the receiver of the mobile station for the conventional CDMA radio communication. A signal received by an antenna
11
is demodulated by a radio part
12
into a base band signal, which is converted by an A-D converter
13
to a digital signal. Code generators
14
1
to
14
4
are each given spreading code information and frame timing detected by a multi-path searcher
15
, and hence they generate codes synchronized with spreading codes used at the sending side. In correlators
16
1
to
16
4
the base band signal from the A-D converter
13
is despread through multiplication by the spreading codes from the code generators
14
1
to
14
4
, by which the original signal can be detected. Thereafter, these despread signals are detected by detectors
17
1
to
17
4
and the detected outputs are combined by a RAKE combiner
18
, whose combined output is fed to a signal processing part
19
. Since signals from different transmission or propagation paths (a multi-path), contained in the received signal, can be separated by the despread processing in the correlators
14
1
to
14
4
, this processing is a RAKE reception that has a diversity effect.
The mobile station receiver of the prior art configuration is provided with receiving fingers Fn
i
each composed of the code generator
14
i
, the correlator
16
i
and the detector
17
i
for despreading and detecting the received signal and the multi-path searcher
15
provided independently of the receiving finger Fn
i
to search for the multi-path in the receiving channel. A brief explanation will be given of the start-up operation of the mobile station at its turn-on, that is, an operation from a decision about its visited cell to the start of signal reception. When power is turned on, the mobile station accepts the base band signal from the A-D converter
13
by the multi-path searcher
15
and searches for the cell where the mobile station ought to stay. The multi-path searcher
15
has such a configuration as shown in
FIG. 1B. A
code number designator
23
reads out of a memory
24
a candidate for the spreading code of the base station and indicates to a code generator
25
a spreading code to be generated. The code generator
25
generates the designated spreading code, which is fed to a multiplier
26
for multiplication by the input signal from the A-D converter
13
. A correlation value calculator
27
uses the multiplied output to calculate the value of correlation between the input signal and the spreading code generated by the code generator
25
. A check is made to see if the thus computed correlation value is larger than a predetermined threshold value, thereby specifying the spreading code of the input signal and choosing the cell where the mobile station is staying. The spreading codes that are used to discriminate the cell usually have very long repetition periods. Hence, much time is spent in making a decision about the spreading code of the visited cell by examining the correlation between every long-period spreading code (also referred to simply as a long code) and the input signal.
In the conventional receiver configuration, the receiving fingers Fn
1
to Fn
4
are not equipped with a function of searching for the timing at which the correlation reaches its peak, and since the searcher
15
is provided separately of them to perform the cell search and the multi-path search, no fast searches can be expected. Additionally, a plurality of searchers must be prepared to implement fast searches.
In the CDMA radio communication system communications are performed using the same carrier frequency and the cell identification needs to be made after establishment of synchronization between the spreading code and the received signal. In a system that makes the cell identification on the basis of the kind or phase of the long-period spreading code (IS-95, for instance), the cell search requires a very large number of candidates for the long-period spreading codes. Besides, the repetition period of each long-period spreading code is so long that much time is needed to make a decision about the spreading code.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a receiving scheme which permits a fast cell search using long codes without a substantial increase in the circuit scale.
To attain the above objective, no dedicated searcher is provided but a plurality of receiving fingers of the same configuration are each adapted to function as a searcher or RAKE receiving finger according to the circumstances.
According to the present invention, the method for reception by CDMA radio communication receiving equipment, which has a plurality of receiving fingers for extracting received data resulting from despreading the received signal by a plurality of spreading codes from code generating means, is characterized by a step of using at least one of the plurality of receiving fingers to make a cell search.
In the above method, all the receiving fingers may simultaneously conduct the cell search with different spreading codes set therein at the start-up of the receiver.
In the above method, while in a standby mode of the receiver, the receiving fingers may each perform the cell search and the control channel reception alternately.
In the above method, while in standby mode and communication mode of the receiver, at least one of the receiving fingers may be used for a communication channel reception and the remaining receiving fingers for the cell search.
In the above method, while in the standby mode, the number of receiving fingers used for the control channel reception and the number of receiving fingers for the cell search may be changed complementarily according to the control channel receiving level.
In the above method, while in the standby mode, it is possible to detect a multi-path in the control channel and change the control channel receiving timing with variations in the detected multi-path.
In the above method, it is possible to employ a scheme in which the spreading code in the control channel and new timing at which the multi-path receiving level is higher than a threshold value are set in one receiving finger not used for the control channel reception, then this receiving finger is caused to begin the control channel reception and the control channel receiving finger of the lowest receiving level is stopped from receiving the control channel.
In the above method, the numbers of receiving fingers used for the communication channel reception and for the cell search may be changed complementarily with the maximum communication channel receiving level while in the communication mode.
In the above method, while in the communication mode, it is possible to detect a multi-path in the communication channel and change the communication channel receiving timing with variations in the detected multi-path.
In the above method, it is possible to employ a scheme in which the spreading code in the communication channel and new timing at which the multi-path receiving level is higher than a threshold value are set in one receiving finger not used for the communication channel reception, then this receiving finger is caused to begin the communication channel for reception and the communication channel the receiving finger of the lowest receiving level is stopped from the reception of the communication channel.
The CDMA radio receiver according to the present invention
Higashi Akihiro
Takagi Hirofumi
NTT Mobile Communication Networks, Inc.
Olms Douglas W.
Pizarro Ricardo M.
Pollock, Vande Sande & Amernick, R.L.L.P.
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