Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
2000-01-18
2003-04-29
Vo, Don N. (Department: 2631)
Pulse or digital communications
Spread spectrum
Direct sequence
C375S150000
Reexamination Certificate
active
06556620
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a synchronization acquisition device and a method of performing synchronization acquisition in a spread spectrum communication system for performing synchronization acquisition in a receiver that employs the spread spectrum communication method.
2. Description of the Related Art
In recent years, the spread spectrum communication system, which is effective against interference and disturbances, has received increased attention as a communication system for use in mobile communication systems. A spread spectrum communication system is a communication system in which, on the transmitting side, a spreading code is used to spread an information signal that is to be transmitted, and on the receiving side, a spreading code that is the same as this spreading code is used to carry out despreading and obtain the original information signal.
The information signal that is transferred as information is called a symbol, and the unit of data constituting the spreading code for spreading these symbols is called a chip.
In such a spread spectrum communication system, a plurality of transmitting sides each carries out spreading using different spreading codes having orthogonality, and each communication can be designated on the receiver side by selecting the spreading code used when carrying out despreading. As a result, Code Division Multiple Access (CDMA) can be realized in which a plurality of communications use the same frequency band.
In a transmitting/receiving system according to this spread spectrum communication system, however, despreading cannot be properly achieved if the spreading timing, which is the timing at which spreading is carried out on the transmitting side, is not accurately obtained on the receiving side. If this spreading timing is shifted by just one chip, for example, none of the signals transmitted from the transmitting side can be received on the receiving side. A synchronization acquisition device for obtaining the spreading timing is therefore provided in receivers of the spread spectrum communication system. Synchronization acquisition refers to receiving from a transmitter reception data in which data of a specific timing are spread by a specific spreading code, and using this specific spreading code to obtain the specific timing.
In this way, an example of data in which data of a specific timing are spread by a specific spreading code is explained using a W-CDMA (Wide-band CDMA) system, which is one type of CDMA communication system. A W-CDMA system is one spread spectrum communication system that has been applied to mobile communication systems.
In the W-CDMA system that is described here, a mobile station can obtain base station information, such as the spreading code and spreading timing that the base station uses when carrying out spreading of logical symbols, by receiving a perch channel transmitted from the base station.
The spreading codes in this W-CDMA system include a long code (long-period spreading code) and a short code (short-period spreading code), and logical symbols in a W-CDMA system are spread twice by this long code and short code. A long code is a code of an extremely long period corresponding to the length of several tens or several hundreds of symbols, and short code is a code of short period corresponding to the length of one symbol.
Referring now to
FIG. 1
, the data structure of a perch channel is explained. In a W-CDMA system, data to be transmitted are transmitted in units of superframes of 640 msec. Perch channel
30
is one of these superframes and is composed of 64 radio frames
31
1
-
31
64
for transferring information of each receiver. Radio frame
31
1
is in turn composed of 16 time slots
32
1
-
32
16
, and time slot
32
1
is composed of pilot symbol
33
, BCCH (Broadcast Control CHannel) symbol
34
, and long code mask symbol
35
.
Since the case explained here regards a W-CDMA system in which the spreading code length of the short code is 256 chips, a one-bit logical symbol is spread to 256 chips.
Long-code mask symbol
35
is a signal in which a particular one-bit logical symbol is spread by only the short code and not spread by the long code. All logical symbols other than long-code mask symbol
35
are spread by both long-code and short-code spreading codes. As a result, if signals that are demodulated by RF unit
1
are subjected to despreading by only the short code, only long-code mask symbol
35
appears as the original symbol. A synchronization acquisition device takes advantage of this fact to detect the spreading timing.
FIG. 2
shows one example of the composition of a receiver in a spread spectrum communication system that is provided with this type of synchronization acquisition device. The receiver in this spread spectrum communication system includes RF unit
1
, A/D converter
2
, and synchronization acquisition device
13
.
RF unit
1
modulates signals received from a transmitter and converts the signals to baseband signals. A/D converter
2
carries out A/D conversion of the baseband signals that were demodulated by RF unit
1
to convert the signals to digital signals. Synchronization acquisition device
13
performs synchronization acquisition by using digital data that were converted by A/D converter
2
.
FIG. 3
shows the configuration of this synchronization acquisition device
13
. Synchronization acquisition device
13
is composed of correlator
4
, adder
20
, correlation value storage unit
21
, and peak detector
22
.
Correlator
4
calculates correlation values between digital data outputted from A/D converter
2
and preset spreading codes. As for the actual constitution of correlator
4
, matched filters may be used that hold digital data the length of the spreading code and simultaneously calculate correlation values with the spreading code, or a correlator bank may be used that sequentially calculates correlation values between the spreading code and digital data and accumulates these correlation values.
In this case, correlation values are calculated as electrical values in a W-CDMA system, quadruple over-sampling normally being carried out when calculating electrical values. If the spreading length of short code in this case is 256 chips and the number of symbols in one time slot is 10, the timing number, which is the number of data items in one slot interval, is:
4 (quadruple sampling)×256 (chips)×10 (symbols)=10,240.
FIG. 4
shows an example of the correlation values for each timing obtained by correlator
4
. In
FIG. 4
, the correlation values of the 10240 timings of one slot interval have been artificially produced and represented as a graph for the purpose of explaining actual data. Here, cases in which the correlation values exhibit high values are cases in which digital data and short code match. The occurrence of a plurality of these timings in this graph indicates that this mobile station is receiving radio waves from a plurality of base stations.
Data of correlation values in a one-slot interval are shown. In a mobile communication system made up of a mobile station and a plurality of base stations, the mobile station communicates with base stations while moving, and the obtained correlation values therefore fluctuate widely due to the influence of such factors as fading. The obtained correlation values in some cases may drop sharply when fading is high, giving the perception that no radio waves at all are being received from the base station.
To solve this type of problem, a slot averaging process is carried out to prevent malfunctions due to loss of data caused by fading whereby, rather than detecting spreading timing based on the correlation value data at a single time, an average of the correlation value data is calculated for each slot interval.
Adder
20
adds correlation values found in correlator
4
and correlation values read from correlation value storage unit
21
.
Correlation value storage unit
21
stores the accumulated correlation values obtained by adde
Foley & Lardner
NEC Electronics Corporation
Vo Don N.
LandOfFree
Synchronization acquisition device for both preventing... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Synchronization acquisition device for both preventing..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Synchronization acquisition device for both preventing... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3014391