JPH07297806A - Code division multiple access demodulation method for spread spectrum communication - Google Patents

Abstract

PURPOSE:To reduce the reception bit error rate at the time of make before break (MBK) in the demodulator of a CDMA cell telephone system which is conducted with many cells prepared. CONSTITUTION:Base station parts 102 corresponding to many cell site parts 101 receive the signal of a mobile terminal part 103, and a general station 104 which compares signals of the mobile terminal part 103 received by base stations 102 to designate the base stations 102 being in the MBK state, and interference signals from a cell site itself and stations of other cell sites in the MBK state are removed by estimating reception base band data of respective stations from base band reception signals of spread spectrum signals of demodulators of base stations 102 by sequential interation, thereby reducing the bit error rate of the demodulation signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to code division multiple access (C
DMA) communication, especially personal communication system (PCS)
And CDM in mobile communications such as digital cellular
The present invention relates to a CDMA demodulation method, which is used for A communication and reduces the influence of interference from other stations.

[0002]

2. Description of the Related Art A demodulator for CDMA communication is shown in the following document, for example.

Reference 1: Young C. Yoon, Ryuji Kohno a
nd Hideki Imai: "A Spread-Spectrum Multiaccess
System with Cochannel Interference Cancellation for
Multipath Fading Channels ", IEEE Journal on Selec
tedAreas in Communications, Vol.11, No.7, Septenbe
r Published in 1993 Document 2: Allen Salmasi and Klein S. Gilhousen
Written: "On the system design aspects of Code Division
Multiple Access (CDMA) applied to Digital Cellular
and Personal Communications Networks ", pp.57-61, 4
1st IEEE Vehicular Technology Conference, May 19-2
2 Published in 1991 Document 1 eliminates interference from other transmission stations in CDMA communication. On the transmission side of this document, spread modulation is performed with a spreading code with a transmitting station using a Gold code having an extremely small cross-correlation value for transmission data +1 and -1, converted into a spread signal, and then modulated with a carrier wave. By doing so, the signal is converted into an RF band signal.

The signals converted to the RF band at all transmitting stations are added with the signals affected by multipath,
At the same time, white noise is added and transmitted to the receiver.

The received signals in the RF band received by the receiver are distributed to the registers for storing the received signals received from the antennas by the number of all transmitting stations.

First, a carrier for each station is multiplied by a code peculiar to the transmitting station to perform a correlation operation, and a hard decision operation is used to estimate +1 or -1 which is the transmission estimation data of the i station.

The data estimated for each station is again multiplied by a carrier and a code peculiar to the transmitting station and modulated into an RF band signal,
For multipath data estimated to be data synchronized for each station, the data delayed by the time due to the multipath is multiplied by the amplitude estimation value corresponding to the propagation path based on the Rayleigh distribution.

To re-estimate the transmission data of a certain i station, the received signal in the RF band that has undergone the multipath of the i station and i
Value obtained by adding the received signals in the RF band of all stations considering multipath other than the station to the output of the register file that stores the received signal value in the RF band received from the receiving antenna synchronized with this Using, the correlation calculation is performed by multiplying the carrier wave by the code unique to the transmitting station, and a hard decision is made to estimate +1 or −1 which is the transmission estimation data of the i station.

[0009] Again, the data estimated for each station is multiplied by a carrier and a code unique to the transmitting station to modulate into a signal in the RF band, and the multipath time estimated for the data synchronized for each station The delayed data is multiplied by the amplitude estimation value corresponding to the propagation path based on the Rayleigh distribution. Then, the value obtained by adding the received signal in the RF band that has received the multipath of the i station and the received signal in the RF band of all the stations other than the i station is the received signal value of the RF band received from the receiving antenna synchronized with this. The value subtracted from the output of the saved register file is used to multiply the carrier and the code unique to the transmitting station to perform a correlation operation, and a hard decision is made to estimate the transmission data of the i station, +1 or -1.
To estimate. This estimation method uses a parallel processing configuration for all stations for a total of 3
Repeat to remove interference from other stations.

In Reference 2, a CDMA cell in which a mobile terminal communicates with one of a plurality of divided cells, each cell site is controlled by one central station, and this terminal can communicate with another cell site. In the telephone system, when a terminal decides to transfer a cell site and sends a handoff request for identifying the transfer destination cell site, in response to this handoff request, both the transfer destination cell site and the pre-transfer cell site terminals and the partner Make before break (make before break) that communicates with the terminal at the same time and notifies the terminal of the response to disconnect the call between the pre-transition cell site and the terminal in response to the handoff request.
break: MBK) method, the terminal avoids the momentary interruption of the call due to the transition of the cell site transition, and synthesizes the demodulated data of the current cell site and another cell site,
The demodulation error rate is reduced by the diversity effect.

[0011]

However, in the above-mentioned Document 1, CDMA is performed by preparing a large number of cells.
In a cell phone system, when a mobile terminal avoids a momentary interruption of a call due to a cell site transition using the MBK method, in addition to a station currently providing communication service in the cell, Although it is necessary to service signals that have not been provided with the communication service, the MBK method is not considered. Therefore, the signal increased by the MBK method, which has not been provided in the cell until now, cannot be serviced and remains as an interference signal, which causes an error during data demodulation and increases the error rate.

Further, in the above-mentioned document 2, in a CDMA cell telephone system which prepares a large number of cells, in addition to the signal which is currently providing communication service in the cell, communication service is currently provided in the cell. The number of signals to be serviced increases because it is necessary to service the signals that have not been delivered. Therefore, when each transmitting station asynchronously uses a non-orthogonal code such as a pseudo-random code as a spreading code, a signal transmitted by one station is added to the received data as interference for other stations, and at the same time as other signals. Since the communication signal from the cell is mixed in the cell of the own station, the interference increases. Therefore, when the number of transmitting stations increases, the amount of interference increases, the diversity effect becomes difficult to obtain, and an error occurs in the received data. Therefore, it is necessary to reduce the communication quality or reduce the number of signals to be serviced.

Therefore, an object of the present invention is to reduce data errors due to interference of other stations during MBK execution.

[0014]

According to the present invention, in order to solve the above-mentioned problems, CDMA is performed by preparing a large number of cells.
In the cell phone system, MBK is sent from the control station to the receiving side.
The information of the mobile terminal in the state is received, the interference signal which is the other station is detected from the mobile terminal currently receiving in the cell site and the mobile terminal in the MBK state of the other cell site,
The present invention relates to a method of removing this and obtaining demodulated data by correlation detection.

In the present invention, the control station that controls the receiving side determines the reception level of the mobile terminal that is providing each service, which is obtained from the base station of each cell site, so that the base station that requires MBK. It has a control means for notifying the receiving side of the station of the information of the mobile terminal which is about to move from another cell site.

[0016] Further, spread of received signals and data coming from the mobile terminal currently receiving in the cell site and the mobile terminal in the MBK state of the other cell site in the MBK state controlled by the controlling station. Correlation with the code is performed at the time matched to the multipath, the received signal is generated by combining the multipaths using the amplitude and phase of the multipath, and the estimated interference signal re-spread according to the multipath is again generated. It has a signal estimating means for generating.

Further, it has an interference removing means for removing the estimated interference signal obtained from the signal estimating means from the received signal for each transmitting station.

The reception data from which the interference signal has been removed by the interference removal means has correlation detection calculation means, and the above-mentioned means demodulates the received data.

[0019]

[Operation] In FIG. 1, the CDM service is provided over a wide area.
A: A large number of cell site units are provided to provide mobile band wireless communication services.

At the cell site, a base station is arranged at a position where a signal transmitted from a mobile terminal can be sufficiently received by a call. Further, the mobile terminal on the transmitting side spreads using a spreading code specific to the transmitting station, transmits this as a baseband transmission signal via a wireless line, and is on the receiving side.
It is assumed that a base station at a certain cell site receives the transmission data.

When the mobile terminal is moving from the cell site currently transmitting / receiving to the other cell site, the control means moves away from the base station currently transmitting / receiving, so that the reception signal of the mobile terminal is received. The level will drop. At this time, the base station sends information to the control station that controls the cell site that the mobile terminal is in the situation of moving to another cell site.

Then, the controlling station sends the information of the mobile terminal to the base station of the cell site which is located around the base station by the mobile terminal, and the base station of the cell site which is located around the mobile station receives the information from the controlling station. The received signal level is measured based on the terminal information, and the measured value is sent to the control station.

The control station compares the reception levels of the mobile terminals obtained from the base stations of the cell sites arranged in the vicinity, selects the base station having the highest signal level, and selects the base station for the selected base station. Set to MBK state.

The receiving side M selected by the controlling station
In the state of BK, in the base station,
Obtain information on mobile terminals that need the K state.

The signal estimating means uses the MKs of other cell sites as well as the mobile terminal currently serving based on the information of the mobile terminal obtained from the control station by the base station which needs the MBK state.
The received signal arriving from the mobile terminal in the BK state and the spread code for data are correlated with each other in a time matched with the multipath, and demodulated by combining the multipaths using the amplitude and phase of the multipath, By re-spreading in accordance with multipath again, baseband demodulation data, which becomes an interference signal for other stations, is generated.

The removing means is obtained from the previous signal estimating means,
The re-spread baseband demodulated data obtained from each mobile terminal is used as an interference signal to remove interference signals from other stations from the received signal.

When the respread baseband demodulated data obtained from each mobile terminal is removed as an interference signal, the interference signal from another station is estimated and removed from the received signal, so that an estimation error occurs and Signals from other stations cannot be accurately removed by the removal. Especially, when the number of transmitting stations is large, the estimation error becomes large. This problem is solved by connecting the interference cancellers in cascade.
That is, a demodulated signal with less errors than in the first stage can be obtained by demodulating the signal in which the interference is removed to some extent in the first stage again. By spreading this demodulated signal again, an interference signal with less estimation error than the first stage is generated, and is removed from the received signal again. The same applies to the subsequent stages.

The correlation calculation means demodulates the received signal, which has been subjected to the interference elimination of the Kth stage, which is the final stage, by the signal estimation means and the interference elimination means by correlation detection, and outputs data. Since interference signals from other stations have been removed, demodulated data with a smaller error rate can be obtained as compared with a demodulation method that does not use interference removal.

Therefore, from the above, make indicating from the control station that the make-before-break (MBK) state is in effect
-By using the before-break control signal, the receiving side detects the interference signal from the mobile terminal currently receiving in the cell site and the mobile terminal in another cell site in the MBK state controlled by the controlling station. A method for removing this and obtaining demodulated data by correlation detection is realized.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION CDMA in which the present invention is prepared by preparing a large number of cells
An embodiment applied at the time of MBK in the cell phone system will be described with reference to the drawings.

FIG. 1 shows a schematic overall view of a CDMA cell phone system.

101-1 to 101-19 are cell site parts, and 102
-1 to 7 are base station units, 103 is a mobile terminal unit, and 104 is a control station. Here, although no base station is described in the cell site units 101-8 to 19, it is assumed that there is actually one base station for each cell site.

Next, referring to the flow chart of FIG.
The operation of will be described.

In FIG. 1, the service is provided over a wide area as C.
A large number of cell site units 101-1 to 101-19 are arranged in order to provide service by the DMA mobile band wireless communication.

In advance, base stations (not shown) used for the base stations 102-1 to 10-7 and the cell site units 101-8 to 19 are arranged at positions where cell calls can be sufficiently received in the cell site units 101-1 to 10-19.

It is also assumed that the mobile terminal 103 first transmits and receives at the cell site unit 101-1.

Next, the mobile terminal 103 makes the cell site unit 10
While moving from 1-1 to the cell site unit 101-2, the mobile terminal 103 moves away from the base station 102-1 and the received signal level of the mobile terminal 103 decreases (FIG. 2).
Step ST1).

At this time, the cell site unit 101-1 sends information that the mobile terminal 103 is in the situation of moving to another cell site to the control station 104 which controls the cell site units 101-1 to 10-19 (see FIG. 2). Step ST2).

In the control station 104, the mobile terminal 103 is connected to the base stations 102-2 to 102-7 of the cell sites 101-2 to 7 and the base stations of the cell sites 102-8 to 19 adjacent to the cell site 102-1. Information is sent (step ST3 in FIG. 2).

The base stations 102-2 to 102-7 of the adjacent cell sites 101-2 to 7 and the base stations of the cell sites 102-8 to 19 receive the received signal level based on the information of the mobile terminal 103 obtained from the control station 104. To measure.

Base stations 102-2 to 102 and cell site 10
The base stations 2-8 to 19 send the received signal level of the mobile terminal 103 to the control station 104 (step ST4 in FIG. 2).

The control station 104 compares the reception levels of the mobile terminals 103 obtained from the base stations of the base stations 102-2 to 7-2 and the cell sites 102-8 to 19 and selects the base station having the highest signal level. (Here, it is assumed that the base station 102-2 is selected.) The central station 104 is the cell site 101-
MBs for the base stations 102-1 and 102-2 arranged in 1 and 2
The state of K is set (step ST5 of FIG. 2).

FIG. 3 shows the structure of the receiving section. 301 is a receiving antenna, 302 is a wireless demodulation unit, 303-1 to N are cell-site signal estimation unit first stage, 304 is an interference cancellation unit first stage,
305-1 to N are the second stage of the cell site signal estimation unit, 306
Is the interference canceller second stage, 307-1 to N are the cell site signal estimator Kth stage, 308 is the interference canceller Kth stage, 303-1
~ N is a cell site correlation calculation unit (here, MBK
The base station 102-2 in the state will be described. ). Here, 303-1 to N are the first stage of the cell site signal estimating unit, and 305-1 to N are the second stage of the cell site signal estimating unit.
, 307-1 to N are the cell site signal estimator Kth stages,
M, which is the transmission signal component coming from each cell site
It is configured to have a signal estimator for the station. Also, cell site signal estimation sections 303-1 to N, 305-1 to N, 307
-1 to N allow only the mobile terminals that have received the MBK information from the central station to receive, except for the mobile terminals that have been transmitting and receiving up to now at their cell sites.

Next, referring to the flow chart of FIG.
The operation of will be described.

In FIG. 3, the reception signal input from the reception antenna 301 is converted by the reception radio section 302 into two orthogonal baseband signals. This baseband signal is output with the position and phase of the transmission side and the path different from each other due to the position and phase change of the path by the multipath transmission path. Also, the phase differs depending on the transmitting station. These signals are output to the cell site signal estimator first stage 303-1 to 30-N.

Cell site signal estimator first stage 303-1 to 303-1
N, the baseband signal is subjected to correlation calculation using the spread signal used for the transmission signal according to the position of the path through the multipath transmission line, and demodulation data is obtained from the reception signal by diversity combining.

Since the demodulated data becomes an interference signal when viewed from another station, in order to restore the demodulated data to the baseband signal again, respreading is performed using the spread signal used for the transmission signal, Band demodulation data is generated (step ST6 in FIG. 2). Interference removal unit first stage 304
Removes the interference signal by dividing the signal of another station based on the baseband received data of each of the cell site signal estimator first stages 303-1 to 30-N (step ST7 in FIG. 2). This configuration is shown in FIG.

FIG. 4 shows the structure of the interference removing unit shown in FIG. 401-1 to 5, 402-1 to 5, 403-1
~ 5, 404-1 to 5, 405-1 to 5, 406-1 to
5 is a division unit.

The division calculation units 401-1 to 40-5 receive the received signals from the first cell site 2 station by the M station of the cell site 2, the 1st station of the cell site 1, the M station of the cell site 1 and the 1st station of the cell site N. ,
The interference from other stations is removed by subtracting from the received signal prepared to estimate the cell site N Mth station.

Similarly, the division calculators 402-1 to 40-5, the division calculators 403-1 to 40-5, the division calculators 404-1 to 40-5, the division calculators 405-1 to 40-5, and the division calculators 406-1 to 40-5.
Removes interference from other stations from the received data.

Returning to FIG. 3 again, cell site signal estimator second stage 305-1 to M, cell site signal estimator K stage 30
7-1 to M, the interference canceller second stage 306, and the interference canceller Kth stage 308 are the cell site signal estimator first stage 30.
3-1 to M and an operation similar to that of the interference canceller first stage 304,
That is, the baseband of the received data of each station is estimated, the interference signal of the other station is removed based on the data, and the cell site signal estimation section first stage 303-1 to M and the interference removal section first stage 306. Removes interference signals that could not be removed by the combination with the first stage of the interference removing unit 304 (step ST8 in FIG. 2).

The cell site correlation calculation units 309-1 to 309-N are
The reception baseband signals from which the signals of other stations have been removed by the interference removing unit 308 perform correlation calculation using the spread signal used as the transmission signal according to the position of the path by the multipath transmission path, and demodulate by diversity combining. A signal is output (step ST9 in FIG. 2).

[0053]

As described in detail above, when the code division multiple access method according to the present invention is used, a base station that needs the MBK state is currently serving based on the information of the mobile terminal obtained from the controlling station. Similar to the mobile terminal currently in use, the correlation between the received signal coming from the mobile terminal in the MBK state of the other cell site and the spreading code for data is performed at the time matched with the multipath to determine the amplitude of the multipath. By combining and demodulating multipath using phases, respreading according to multipath again, generating an estimated interference signal, and removing the estimated interference signal from the received signal By performing demodulation by correlation detection and demodulating received data, the amount of interference can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic overview of a CDMA cell phone system.

FIG. 2 is a flowchart for explaining the operation of FIGS. 1 and 3.

FIG. 3 is a block diagram of a receiver.

FIG. 4 is a block diagram of an interference removing unit.

[Explanation of symbols]

 101-1 to 19-19 Cell site section 102-1 to 7 Base station section 103 Mobile terminal section 104 Integrated section 201 Receive antenna 202 Radio demodulation section 203-1 to M Cell site signal estimation section 1st stage 204 Interference removal section 1st stage 205 -1 to M cell site signal estimator second stage 206 interference canceller second stage 207-1 to M cell site signal estimator K stage 208 interference canceller K stage

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Takuro Sato 1-7-12 Toranomon, Minato-ku, Tokyo Oki Electric Industry Co., Ltd.

Claims (1)

[Claims] 1. A large number of cells are prepared and transmission data is
In a code division multiple access cell phone system that spreads using a spreading code unique to the transmitting station and transmits this as a baseband transmission signal via a wireless line, a mobile terminal using the make-before-break method. Is a method of avoiding a momentary interruption of a call due to cell site migration, receiving the reception level of a mobile terminal obtained from receiving stations arranged in a number of cell sites, and comparing the reception level of the mobile terminal, In a make-before-break state,
The receiving unit at the cell site that is about to move is informed of the mobile terminal information, and the receiving station that has received the signal in the make-before-break state from the informing unit is currently receiving the mobile. Make Before of other stations and other cell sites
A signal estimation unit that detects an interference signal from another station in a break state, an interference removal unit that removes the interference signal, and a plurality of times of executing the signal estimation unit and the interference signal removal unit to remove the interference signal. A code division multiple access demodulation method comprising: a correlation calculation unit that obtains demodulation data by correlation detection of a signal removed from the received signal.