JP3179091B2 - Handoff method for mobile communication system and mobile terminal - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a handoff of a mobile communication system such as an automobile telephone system which continuously provides a communication path even when a mobile terminal moves between a plurality of base stations. The present invention relates to a (base station switching) method and a mobile receiver for realizing the method.

(Prior Art) In a so-called cellular mobile communication system in which a plurality of base stations cover different service areas, such as an automobile telephone system, a base for communicating with a mobile terminal in order for the mobile terminal to move during a call. The realization of a hand-off technique for switching stations to continue a call has become a very important issue. In the conventional handoff, communication is performed with a base station that receives a signal from a mobile terminal most strongly. When a received signal level from the mobile terminal is reduced in a base station during a call, a nearby base station is controlled. , The received signal level is measured, and the communication with the mobile terminal is switched to the base station that receives the strongest signal. This handoff method is described in detail in the book "Car Phone" published by the Institute of Electronics, Communication and Communication in 1985, pp. 197-200.

(Problems to be Solved by the Invention) However, in the conventional hand-off method, it takes time from the change of the received signal level to the actual switching of the base station, so that a mobile terminal such as a car is behind a building. For example, when the received signal level fluctuates rapidly, it is not possible to select an optimal base station, resulting in a decrease in sound quality and a disconnection of the line.

Therefore, an object of the present invention is to provide a handoff method that does not affect the communication quality even if the received signal level fluctuates rapidly, and to provide a mobile receiver that realizes the handoff.

(Means for Solving the Problems) A handoff method according to the present invention is provided in a mobile communication system that sequentially changes a communication path for a mobile terminal that moves between a plurality of base stations and continuously provides a communication path. At least one frequency is commonly assigned to the first and second base stations, and when the mobile terminal performs a handoff from the first base station to the second base station, the mobile terminal communicates with the first and second base stations. The first and second base stations are located in a place where communication is possible and before the reception level of a signal from the second base station becomes higher than the reception level of a signal from the first base station, The mobile station starts receiving a signal transmitted from the mobile terminal using the commonly assigned frequency, and the upper station starts diversity combining of the signals received by the first and second base stations. .

In addition, the handoff method of the present invention is a mobile communication system that sequentially provides a communication path by sequentially changing a communication path for a mobile terminal that moves between a plurality of base stations. And a mobile terminal communicating with the first base station using the commonly allocated frequency, where the mobile terminal can communicate with the first and second base stations. And before the reception level of the signal from the second base station becomes higher than the reception level of the signal from the first base station, while maintaining communication with the first base station, The communication with the second base station is started using the allocated frequency.

Further, the handoff method of the present invention further comprises the first step.
After the reception level of the signal from the base station becomes lower than the reception level of the second signal,
The communication with the base station is terminated.

In addition, the handoff method of the present invention is a mobile communication system that sequentially provides a communication path by sequentially changing a communication path for a mobile terminal that moves between a plurality of base stations. And the second base station are commonly assigned to each other, and the mobile terminal is located at a place where it can communicate with the first and second base stations, and the reception level of the signal from the first base station is the second base station. When the reception level of the signal from the station is higher and lower, the first and second base stations receive the signal transmitted from the mobile terminal using the commonly assigned frequency, and the upper station 1st and 2nd
Is characterized in that signals received by the base stations are diversity-combined.

In addition, the mobile terminal of the present invention continuously provides a communication path by sequentially changing a communication path for a mobile terminal moving between a plurality of base stations, and at least one frequency is shared by adjacent base stations. Allocated, when the mobile terminal is in a position capable of communicating with a plurality of base stations, transmits a signal using a commonly allocated frequency, each base station receives a signal from the mobile terminal, A mobile station in a mobile communication system that diversity-combines signals received by respective base stations. When the mobile terminal performs handoff from a first base station to a second base station, the first and second base stations Using the commonly assigned frequency before the reception level of the signal from the second base station becomes higher than the reception level of the signal from the first base station. Signal It is characterized by comprising means for starting transmission.

In addition, the mobile terminal of the present invention continuously provides a communication path by sequentially changing a communication path for a mobile terminal moving between a plurality of base stations, and at least one frequency is shared by adjacent base stations. Allocated, when the mobile terminal is in a position capable of communicating with a plurality of base stations, transmits a signal using a commonly allocated frequency, each base station receives a signal from the mobile terminal, The station is a mobile terminal in a mobile communication system that diversity-combines signals received by the respective base stations, and is located at a place where it can communicate with the first and second base stations during communication with the first base station; Before the reception level of the signal from the second base station becomes higher than the reception level of the signal from the first base station, the communication with the first base station is performed using the commonly assigned frequency. While maintaining 2
And means for starting communication with the base station.

Further, the mobile terminal of the present invention further terminates communication with the first base station after the reception level of the signal from the first base station becomes lower than the reception level of the second signal. It is characterized by comprising means for performing.

In addition, the mobile terminal of the present invention continuously provides a communication path by sequentially changing a communication path for a mobile terminal moving between a plurality of base stations, and at least one frequency is shared by adjacent base stations. Allocated, when the mobile terminal is in a position capable of communicating with a plurality of base stations, transmits a signal using a commonly allocated frequency, each base station receives a signal from the mobile terminal, A station is a mobile terminal in a mobile communication system that diversity-combines signals received by respective base stations. The mobile terminal is located at a location where the mobile terminal can communicate with the first and second base stations, and a signal from the first base station is transmitted. Reception level is 2nd
When the reception level of the signal from the base station is higher than or lower than the reception level, the first
And a means for performing communication with the second base station while maintaining communication with the second base station.

(Operation) As methods for improving the quality of handoff, there are a method of shortening the time required for handoff, and a method of simultaneously extending a plurality of radio circuits and receiving diversity. In the present invention, the latter method is adopted.

In the handoff method for a mobile communication system according to the present invention, handoff starts when a mobile terminal approaches a boundary of a base station, that is, a cell boundary. At this time, a line with a new base station is set while maintaining a line with the base station with which communication has been performed. When signals are transmitted from a plurality of base stations to the same mobile terminal at the same time, interference occurs if the same frequency is used, so that each base station uses a different frequency. A signal transmitted from a mobile terminal has a single frequency, and a signal having the same frequency may be received by a plurality of base stations simultaneously. The mobile terminal switches the transmission frequency when communication with the new base station becomes possible with sufficient quality. For a while thereafter, the base station with which it has been communicating continues to transmit and at the same time receives a signal of a new frequency from the switched mobile terminal. When a plurality of base stations are receiving signals from the same mobile terminal, diversity combining is performed at the exchange. In this way, even if one base station is hidden behind a building, communication with the other base station can be continued, and extremely high quality handoff can be realized.

The mobile receiver of the present invention includes a plurality of signal receiving units including an antenna, a frequency converter, and a demodulator, a combining circuit, and a control circuit, and according to a handoff state of the mobile receiver. The frequency of a signal received by the signal receiving unit is changed by the control circuit, and diversity combining is performed by the combining circuit, thereby realizing high-quality handoff.

(Example) Next, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of a handoff method for a mobile communication system according to the present invention. In the situation shown in FIG. 1, the base station 11 and the base station 12 are each in the midst of handoff,
Signals are transmitted to the mobile terminal 15 at F ₁ and F ₂ . The mobile terminal 15 can receive stable signals by diversity receiving these signals. Mobile terminal 15
Sent in the frequency f ₁ from its signals are received respectively by the base station 11 and base station 12 is output at the switching center 13 and the diversity combining has been the terminal 10 to a wired network.

FIG. 2 shows the detailed operation of the embodiment shown in FIG. Consider a case where the mobile terminal 15 at the point X where the base station 11 is present moves to the point Y where the base station 12 is present. From the point X to the point A mobile terminal 15 because are not of the signal received from the well near the base station 12 to the base station 11 transmits the frequency f _1, the base station 11 is normal communication by sending frequencies F ₁ Is being done. When the mobile terminal 15 passes through the point A, a signal from the base station 12 also starts to be received, so that a line is set between the base station 12 and the mobile terminal 15. At this time, the frequency F ₂
To send the signal. Mobile terminal 15 by diversity combining by receiving frequency F ₁ and F _2, it is possible to maintain the stable reception quality. In the base station 12 receives the signal f ₁ from the mobile terminal 15. Signals from the mobile terminal 15 received by the base station 11 and the base station 12 are transmitted to the exchange 13 as shown in FIG.
, Where the diversity is synthesized. Mobile terminal 15
After passing the point B, the signal from the base station 12 is received more strongly, and the mobile terminal 15 changes the frequency of the transmission signal.
It switched to f _2. In this case the base station 11 continues to transmit the frequencies F ₁ which receives the frequency f ₂ without cutting the communication with the mobile terminal 15. In this way, diversity combining is still continued at both base stations 11, 12 and mobile terminal 15. Mobile terminal 1
When the point 5 passes the point C, the signal from the base station 11 becomes weak, so that the line between the base station 11 and the mobile terminal 15 is cut off.
Stops transmission and reception, and the mobile terminal 15 continues to communicate only with the base station 12. By doing so, the mobile terminal 15 can continue communication stably even in the section A-C around the cell where the line is unstable, and can realize a handoff without quality deterioration. Note that diversity synthesis described in the present embodiment,
The handoff process at the points A, B, and C is not defined in the present invention, and any method may be used.

FIG. 3 is a diagram showing one embodiment of the mobile receiver of the present invention. Signals received by antennas 30 and 31 are converted to desired frequencies by frequency converters 32 and 33, respectively, and demodulated by demodulators 34 and 35, respectively.
Sent to Here, the frequency converters 32 and 33 each include a variable frequency oscillator and a multiplier, and can independently control the reception frequency by a control signal from the control circuit 37. The demodulators 34 and 35 demodulate the received signals and output the demodulated signals to the combining circuit 36.
Output from Information indicating the state of the mobile terminal in the handoff state is input from the terminal 41, and the control circuit 37 indicates that the mobile terminal is not in the handoff state.
Frequency of the same frequency f ₁ when like -A converter 32,3
Set to 3 to perform normal diversity reception. On the other hand, when the mobile terminal is in a handoff state as shown by AB in FIG.
_1, performs a diversity combining receives signals different frequencies by setting f ₂ respectively to the frequency converter 33. In this way, a mobile receiver that receives signals from different base stations during the handoff to have a diversity effect, and that normally receives signals from the same base station with diversity to improve communication quality can be realized. . In addition, any method may be adopted as the diversity combining method in the present invention.

(Effects of the Invention) As described in detail above, according to the present invention, it is possible to provide a handoff method for a mobile communication system with extremely good communication quality and a mobile receiver realizing the method.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a handoff method for a mobile communication system of the present invention, FIG. 2 is a diagram for explaining details of the operation of the embodiment of FIG. 1, and FIG. 3 is a mobile receiver of the present invention. FIG. 3 is a diagram showing an example of the embodiment. 11,12 …… Base station, 13 …… Exchange station, 15 …… Mobile terminal, 30,3
1 ... antenna, 32, 33 ... frequency converter, 34, 35 ... demodulator, 36 ... synthesis circuit, 37 ... control circuit.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masanori Takeji 5-7-1 Shiba, Minato-ku, Tokyo Within NEC Corporation (72) Kojiro Hamana 5-7-1 Shiba, Minato-ku, Tokyo No. 1 NEC Corporation

Claims (8)

(57) [Claims] 1. A mobile communication system for continuously providing a communication path by sequentially changing a communication path for a mobile terminal moving between a plurality of base stations, wherein at least one frequency has a first and a second frequency. A mobile station that is commonly assigned to a base station, is located at a location where it can communicate with the first and second base stations when the mobile terminal performs handoff from the first base station to the second base station, and Before the reception level of the signal from the base station becomes higher than the reception level of the signal from the first base station, the first and second base stations use the common allocated frequency to Starting the reception of the signal transmitted from the base station, and the upper station starts diversity combining of the signals received by the first and second base stations. 2. A mobile communication system for continuously providing a communication path by sequentially changing a communication path for a mobile terminal moving between a plurality of base stations, wherein at least one frequency has a first and a second frequency. A mobile terminal that is commonly assigned to the base station and that is communicating with the first base station using the commonly assigned frequency is located at a place where it can communicate with the first and second base stations, And before the reception level of the signal from the second base station becomes higher than the reception level of the signal from the first base station, while maintaining communication with the first base station, while maintaining the communication with the first base station. Starting a communication with a second base station using the communication method. 3. The mobile terminal terminates communication with the first base station after a reception level of a signal from the first base station becomes lower than a reception level of the second signal. The handoff method according to claim 1 or 2, wherein: 4. A mobile communication system for continuously providing a communication path by sequentially changing a communication path for a mobile terminal moving between a plurality of base stations, wherein at least one frequency has a first and a second frequency. The mobile terminal is allocated to a common base station and is located at a location where the mobile terminal can communicate with the first and second base stations, and the reception level of the signal from the first base station is the signal from the second base station. When the reception level is higher than or lower than the reception level, the first and second base stations receive the signal transmitted from the mobile terminal using the commonly assigned frequency, and the higher-level station receives the first and second signals. A diversity combining of signals received by the base station. 5. A mobile terminal moving between a plurality of base stations, the communication path being sequentially changed to provide a continuous communication path, and at least one frequency is commonly assigned to an adjacent base station; When the mobile terminal is in a position where it can communicate with a plurality of base stations, the mobile terminal transmits a signal using the commonly assigned frequency, each base station receives a signal from the mobile terminal, and the upper station receives each signal. A mobile terminal in a mobile communication system that diversity-combines a signal received by a base station, wherein the mobile terminal can communicate with the first and second base stations when handing off from the first base station to the second base station. And transmitting the signal using the common allocated frequency before the reception level of the signal from the second base station is higher than the reception level of the signal from the first base station. Start A mobile terminal in a mobile communication system, characterized by comprising means. 6. The communication path is sequentially changed for mobile terminals moving between a plurality of base stations to provide a continuous communication path, and at least one frequency is commonly assigned to an adjacent base station. When the mobile terminal is in a position where it can communicate with a plurality of base stations, the mobile terminal transmits a signal using the commonly assigned frequency, each base station receives a signal from the mobile terminal, and the upper station receives each signal. A mobile terminal in a mobile communication system that diversity-combines a signal received by a base station, wherein the mobile terminal is located at a location where communication with the first and second base stations is possible during communication with the first base station, and Before the reception level of the signal from the base station becomes higher than the reception level of the signal from the first base station, while maintaining communication with the first base station using the commonly assigned frequency, With two base stations A mobile terminal in a mobile communication system, characterized by including means for starting communication. 7. A communication system comprising means for terminating communication with the first base station after a reception level of a signal from the first base station becomes lower than a reception level of the second signal. The mobile terminal in the mobile communication system according to claim 5, wherein 8. A mobile terminal moving between a plurality of base stations, the communication path being changed successively to provide a continuous communication path, and at least one frequency is commonly assigned to an adjacent base station; When the mobile terminal is in a position where it can communicate with a plurality of base stations, the mobile terminal transmits a signal using the commonly assigned frequency, each base station receives a signal from the mobile terminal, and the upper station receives each signal. A mobile terminal in a mobile communication system that diversity-combines a signal received by a base station, wherein the mobile terminal is located at a location where it can communicate with the first and second base stations, and the reception level of the signal from the first base station is When the reception level of the signal from the second base station is higher and lower, the communication with the second base station is performed while maintaining the communication with the first base station using the commonly assigned frequency. Means to do A mobile terminal in a mobile communication system, comprising: