JPH06326653A - Handing off method during conversation and mobile machine for spread spectrum mobile communication - Google Patents

Abstract

PURPOSE:To realize hand off during conversation without providing the receivers of two systems, and besides, without making a signal burst-like. CONSTITUTION:The radio frequencies of a number corresponding to zone traffic of radio zones are allocated to the radio zones 2a to 2d, and one frequency f1 among these frequencies is allocated in common to all the zones, and as for the same frequency, spreading codes different for every zone are allocated. A mobile machine is provided with two correlators 15, 16 in, e.g. the zone 2a to communicate by the frequency f2, and when speech quality is deteriorated, the mobile machine executes once switching to the common frequency f1, and continues communication by one side of the correlators 15, 16, and simultaneously, scans spreading codes by the other side, and measures the receiving level of a down signal, and determines a hand off destination radio zone. When the determined zone is 2a, for instance, the communication is continued by switching the communication to the communication by the frequency f2 or f3 other than the common frequency f1. In the zone other than the zone 2d to which only f1 is allocated, the common frequency f1 is used only for the switching of channel during conversation and line setting, etc., at the time of the origination and the termination of a call.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a channel switching method during communication in a cellular mobile communication system using a spread spectrum system and a mobile device for spread spectrum mobile communication.

[0002]

2. Description of the Related Art Cellular mobile communication systems are currently in practical use as digital car telephone systems. That is, in the digital car telephone system, the service area 1 is divided into a plurality of wireless zones 2a, 2b, 2c ... As shown in FIG. 2A, and individual frequency control for each of these wireless zones 2a, 2b, 2c. Channels 3a, 3b, 3c ... Are assigned respectively, and control channels 3a, 3b, 3c ... Are respectively transmitted from the radio base stations 4a, 4b, 4c ... Installed in the respective radio zones 2a, 2b, 2c. . When the mobile device switches channels during communication, the control channel 3 of the individual frequency provided for each of the wireless zones is used by using the empty slot I of TDMA as shown in FIG. 2B.
The reception levels of a, 3b, 3c ... Are sequentially measured, and the reception levels are compared to determine the switching destination wireless zone to switch the communication channel.

On the other hand, in a mobile communication system using spread spectrum, only one radio frequency common to all radio zones is prepared, different spread codes are assigned to each radio zone, and when performing channel switching during communication. , One of the correlators in the mobile device scans the spread code, measures the reception level of each wireless zone and compares it to determine the wireless zone of the switching destination, thereby performing the channel switching during communication. Conceivable. However, in this spread spectrum mobile communication system, when there is traffic imbalance in each radio zone, it is necessary to prepare a wideband radio channel in order to enable use of a large number of spreading codes in accordance with the radio zone having the maximum traffic. Therefore, it is over-designed for wireless zones with low traffic.

In order to avoid this, a radio channel having a band corresponding to a certain traffic is prepared, only one radio channel is assigned to a radio zone with little traffic, and the radio channel is assigned to a radio zone with a lot of traffic. A configuration in which multiple allocations are made is possible. That is, FIG.
As shown in A, generally, there is a lot of traffic in the center of the city, and it tends to decrease as it goes to the suburbs. In this case, the number of wireless channels required to handle traffic is also large in the central part of the city as shown in FIG. However, when switching channels during communication with such a configuration, the mobile device determines the switching destination wireless zone by using a wireless channel common to all wireless zones, and multiple wireless channels are allocated. In order to determine the switching destination wireless zone during a call on a wireless channel other than the common wireless channel in the wireless zone, it is necessary to switch to the common wireless channel and measure the reception level so that the call is not disconnected It is not suitable for downsizing a mobile device because it requires two reception systems.

In order to avoid this, as used in the digital car telephone system, in the spread spectrum mobile communication as well, a radio channel is constructed by TDMA, and a switching destination radio zone is used by utilizing an empty slot of TDMA. There is a problem that the electromagnetic environment problem (EMC) needs to be taken into consideration due to the signal becoming bursty and that the guard bit / synchronization bit is required and the channel use efficiency is impaired. .

[0006]

SUMMARY OF THE INVENTION The object of the present invention is not to overdesign in a radio zone with little traffic, it is not necessary to prepare two receiving systems, there is no fear of causing an electromagnetic environment problem, and there is no communication channel. An object of the present invention is to provide a communication channel switching method for spread spectrum mobile communication that enables switching.

[0007]

According to the present invention, a radio frequency common to all radio zones in a service area is provided, and a different control spreading code is assigned to the common radio frequency for each radio zone. Two correlators are prepared for the machine, and when switching channels during communication, one correlator scans the spreading code and measures the reception level to determine the switching destination wireless zone and Communication continues with the correlator.

[0008]

FIG. 1A shows an example of radio frequency allocation to radio zones in the method of the present invention. The number of radio frequencies according to the number of traffics is assigned to each of the radio zones 2a to 2d. Assign the three frequencies f _1, f _2, f ₃ and most traffic in Figure 1A many radio zone 2b, then assign traffic often radio zone 2a, two each of the 2c the frequencies f _1, f _2, One frequency f ₁ is assigned to the wireless zone 2d with the least traffic. For the same frequency, different spreading codes are assigned to each radio zone in the area where there is a risk of interference.

In the present invention, a common radio frequency is assigned to all radio zones in the service area. Allocates a common radio frequency f ₁ to the radio zone 2a~2d in Figure 1A, to the radio frequency f _1, the radio zone 2a~2
A different spreading code for control is assigned to each d. Also in this case, the same spreading code, code 1 in this example, is repeatedly used in the wireless zones such as the wireless zones 2a and 2d which are separated by a distance that does not affect the interference.

Control spreading codes 2 and 3 are assigned to the common frequency f _{1 in the} radio zones 2b and 2c, respectively. In the method of the invention of claim 1, the mobile device of the invention of claim 2 is used. As shown in FIG. 1B, for example, the mobile device includes an antenna 11 connected to a duplexer 12, and a high frequency reception amplifier 13 and a high frequency transmission amplifier 14 connected to the duplexer 12. In the present invention, two correlators 15 and 16 are connected to the output side of the high frequency receiving amplifier 13, and a modulation / demodulation unit 17 is connected to the output side of the correlators 15 and 16, and the modulation signal is supplied from the modulation / demodulation unit 17 to the transmission amplifier 14. To be done. Received signals that match the spreading codes respectively set in the correlators 15 and 16 are selected, demodulated in the modulation / demodulation unit 17, spectrum despread in the spread despreading processing unit 18, and further processed in the signal processing unit 19. The handset 22 is decoded as a voice signal by the voice codec 21.
Is supplied to. The voice signal transmitted from the handset 22 is coded by the voice codec 21, signal-processed by the signal processing unit 19, spread-spectrum processed by the spread despreading processing unit 19, the carrier wave is modulated by the modulation / demodulation unit 17, and the modulated output thereof. Are supplied to the transmission amplifier 14. The control unit 23 performs incoming / outgoing call processing, channel switching during a call, and the like.

A code indicating a common frequency f ₁ is set in advance in the mobile device, and when the mobile device makes a call, both the correlators 15 and 16 are used to make a downlink common frequency from each radio base station. The nearest wireless zone is determined by measuring the signal reception level, and the connection is made using the code of the wireless zone. This wireless zone determination is performed by the correlator 1
Alternatively, one of the steps 5 and 16 may be used.

Now, when the mobile station is in the wireless zone 2a of FIG. 1A, the mobile station makes a call connection at the frequency of f ₂ after making an outgoing connection with the control spreading code 1 at the frequency of f _1. To do. The designation of the communication channel, that is, the designation of the frequency and the spreading code is designated by the control station through the base station, as in the normal mobile communication. When the reception level decreases during a call or the call quality deteriorates due to interference or the like, the mobile device once switches the frequency to the common frequency f ₁ and continues communication with one of the correlators 15 and 16 and another one. The switching destination wireless zone is determined by scanning the spreading code with the correlator and measuring the reception level of the downlink signal. For example, if the wireless zone 2b is the switching destination wireless zone, the spreading of the wireless frequency f ₂ is performed. The communication is continued by switching to the code 2 channel or the spread code 1 channel of the radio frequency f ₃ . The designation of this frequency and spread code is received from the control station.

As described above, since the channel of the radio frequency f ₁ common to all the radio zones is frequently used when switching the channel during communication, when there is only one radio frequency that can be used in the radio zone or when the radio zone is used. Even if multiple radio frequencies are assigned to the zone, use it only when there is no room to assign the radio frequency other than f ₁ , and normally leave it for switching channels during communication, and set the line when sending and receiving. Used as a control channel for

[0014]

As described above, according to the present invention, in the cellular mobile communication system using spread spectrum, a radio frequency common to all radio zones is provided, and two correlators are provided in the mobile device. , The mobile station switches to this common radio frequency when switching channels during communication, and continues communication with one of the two correlators, while the other correlator determines the switching destination wireless zone. It is not necessary to have two receivers in the mobile device, TDM
There is an effect that the wireless channel does not have to be configured in A.

According to the second aspect of the present invention, since a plurality of correlators are provided, while using one of the correlators to continue communication, another correlator is used to determine the switching destination zone. And the determination of the zone in which the call originates
By simultaneously scanning the spread codes with these plural correlators, it is possible to perform the processing in a short time.

[Brief description of drawings]

FIG. 1A is a diagram showing an example of allocation of radio frequencies and spreading codes to radio zones to which the invention of claim 1 is applied;
B is a block diagram showing a configuration example of a mobile device according to the invention of claim 2 used in the invention of claim 1.

FIG. 2A is a diagram showing an example of a zone configuration of a cellular mobile communication system, and B is a diagram showing reception level measurement using an empty slot in the TDMA system.

3A is a diagram showing a traffic distribution by region, and FIG. 3B is a diagram showing allocation of radio channels corresponding to this distribution.

Claims (2)

[Claims] 1. A method of switching a channel during communication of a cellular mobile communication system using a spread spectrum system, wherein one or more radio frequencies are allocated to each radio zone, and a radio common to all radio zones in a service area. A frequency is provided, different control spreading codes are assigned to the common radio frequencies for each radio zone, two correlators are prepared for the mobile device, and when the channel is switched during communication, the mobile device is communicating. From the radio frequency of the radio frequency to the radio frequency common to all the radio zones, the spread code is scanned by one correlator to measure the reception level, and the radio zone to switch to is determined, and communication is performed by other correlators. A method for switching a channel during communication of spread spectrum mobile communication, characterized by continuing the above. 2. A mobile device for detecting a channel divided by a spread code by taking a correlation between a received spread spectrum signal and a local spread code by a correlator, wherein a plurality of the correlators are provided, and the correlators are provided. A mobile device for spread spectrum mobile communication characterized by being operated independently.