Synchronous circuit and receiver

Details Synchronous circuit and receiver Synchronous circuit and receiver

2000-01-13

2004-03-16

Vo, Don N. (Department: 2631)

Pulse or digital communications

Spread spectrum

Direct sequence

C375S150000, C375S152000

Reexamination Certificate

active

06707844

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a synchronous circuit and a receiver for performing CDMA communication, which is one type of communication systems of a cellular phone, and the like, particularly to a synchronous circuit and a receiver which can determine a long code for use in communication in a short time, and receive signals.
2. Description of the Related Art
In the communication in which a code divisional multiple access (CDMA) system is employed, in order to reduce the influence of phasing, and meet the request for capacity enhancement, a specification called a wide band CDMA (W-CDMA) is proposed.
There are several codes for use in actual communication. In those codes, there are 512 codes for initial synchronizing in a base station, and the codes are divided into 16 groups. Specifically, 32 types of codes belong to each group.
Furthermore, a group short code indicating each group is allotted.
When power is supplied, a mobile station which performs the communication of the W-CDMA system captures a first perch channel to specify a base station with which the communication is performed.
As shown in FIG.
10
(
c
), the first perch channel has an entire length of ten symbols, and is constituted of four pilot symbols, five logic channel symbols, and a first long code mask symbol with a length of one symbol.
FIG. 10
is an explanatory view showing the signal formal of the W-CDMA system.
Additionally, the pilot symbols and logic channel symbols will generically be referred to as “information symbols” hereinafter. The first long code mask symbol is diffused with an internationally unified short code.
Moreover, as shown in FIG.
10
(
d
), a second perch channel is a channel for transmitting only a second long code mask symbol with a length of one symbol. The second long code mask symbol is diffused with specific one short code among the predetermined 16 types of group short codes.
Here, the first long code mask symbol and the second long code mask symbol are transmitted with the same phase.
Additionally, when the first perch channel is regarded as one unit (one slot time), 16 slot time units are referred to as a radio frame. The long code is repeated with the radio frame unit. Moreover, the unit of 64 radio frames is referred to as a super frame.
Here, the constitution for performing reception of a conventional mobile station will concretely be described.
A circuit (synchronous circuit) for capturing synchronization and receiving signals in the conventional mobile station is, as shown in
FIG. 11
, mainly constituted of a radio unit
1
for converting an incoming signal on an antenna to a base band signal; an A/D converter
2
for converting the signal inputted from the radio unit
1
into a digital signal; a spreading code generator
3
for generating a designated spreading code; a matched filter
4
for despreading the signal successively inputted from the A/D converter
2
with the spreading code inputted from the spreading code generator
3
, and outputting a correlation signal; a profiler unit
5
for outputting a signal indicative of a signal incoming timing (path position timing) based on the correlation signal outputted from the matched filter
4
; a plurality of correlators
6
for despreading the signal inputted from the A/D converter
2
with the spreading code inputted from the spreading code generator
3
over one symbol time from a plurality of path position timings inputted from the profiler unit
5
, and outputting the correlation signals; a RAKE synthesizing unit
7
for RAKE-synthesizing the correlation signals outputted from the plurality of correlators
6
; a decoder
8
for reproducing the original signal from the RAKE-synthesized signal; a voice CODEC
9
for converting the reproduced signal to a voice signal; and a controller
10
for controlling each unit. Additionally, the matched filter
4
, profiler unit
5
, and correlators
6
are collectively referred to as “despreading means” in the following description.
FIG. 11
is a constitution block diagram of a conventional synchronous circuit.
Here, the matched filter
4
is, as shown in
FIG. 12
, basically constituted of a plurality of sample hold circuits
41
, multipliers
42
disposed for the sample hold circuits
41
, and an adder
43
.
FIG. 12
is a constitution block diagram of the matched filter in the conventional mobile station synchronous circuit.
Each component of the matched filter
4
shown in
FIG. 12
will concretely be described. There are, for example, the number of chips per symbol×the number of over-samplings of sample hold circuits
41
, which are connected to multiple stages. A first-stage sample hold circuit
41
holds the CDMA modulated signal inputted from the outside for a time of one chip time/the number of over-samplings, and outputs the signal to the next sample hold circuit
41
.
Moreover, the subsequent sample hold circuit
41
similarly holds the signal inputted from the previous-stage sample hold circuit
41
for the time of one chip time/the number of over-samplings, and outputs the signal to the next sample hold circuit
41
.
The multiplier
42
multiplies the signal held by the corresponding sample hold circuit
41
, and the spreading code inputted from the outside, and transmits an output to the adder
43
.
The adder
43
adds all the signals inputted from the multipliers
42
together, and transmits a correlation output to the outside.
Additionally, the operation performed by the multipliers
42
and the adder
43
will hereinafter be referred to as “product sum operation”.
Specifically, for the matched filter
4
in the conventional mobile station, a plurality of sample hold circuits
41
successively take the CDMA modulated input signals, and hold one symbol of information. The multipliers
42
multiply the separately inputted spreading codes and the signals held by the corresponding sample hold circuits
41
, and the adder
43
adds multiplication results to output the correlation output.
When the controller
10
specifies, for example, the group short code based on the signal of the correlation output inputted from the matched filter
4
, and obtains the long code for use in communication, a processing shown in
FIG. 13
is performed.
FIG. 13
is a flowchart showing the processing in the control unit
10
from when the group short code is specified until the long code is obtained.
As shown in
FIG. 13
, the controller
10
first detects whether it is synchronized with a slot (S
1
). When it is not synchronized (No), processing S
1
is repeated, and is on standby until the synchronization is established.
Moreover, when the synchronization is established in the processing S
1
(Yes), the group short code is successively set to the spreading code generator
3
(S
2
), and the spreading code generator
3
is allowed to generate the set group short code.
Subsequently, the controller
10
is on standby until the long code mask symbol is received (S
3
). When the long code mask symbol is received, the correlation output outputted from the matched filter
4
is checked, and it is judged whether or not correlation is obtained (S
4
).
Then, when no correlation is obtained (No), the processing returns to S
2
, thereby continuing.
Moreover, when the correlation is obtained in the processing S
4
(Yes), the processing shifts to S
5
.
Subsequently, the controller
10
successively sets the code belonging to the group short code specified in the processing S
2
to S
4
to the spreading code generator
3
(S
5
), thereby allowing the spreading code generator
3
to output the code.
The controller
10
is on standby until the pilot symbol is received (S
6
), upon receiving the pilot symbol, checks the correlation output outputted by the matched filter
4
, and judges whether the correlation is obtained (S
7
).
Subsequently, when the correlation is not obtained in the processing S
7
(No), the processing returns to S
5
, thereby continuing. When the correlation is obtained (Yes), the long code indicated by the code having

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