JPH04167720A - Method for hand-off of mobile communication system and mobile receiver - Google Patents

Abstract

PURPOSE:To enhance the quality of hand-off by installing plural radio circuits simultaneously and applying diversity reception. CONSTITUTION:Base stations 11, 12 send a signal to a mobile terminal equipment 15 in frequencies F1, F2 amidst the hand-off. The mobile terminal equipment 15 receive the signals in a way of diversity to receive a stable signal. A signal of a frequency f1 is sent from the mobile terminal equipment 15 and received respectively by the base stations 11, 12, the signals are subject to diversity synthesis by an exchange station 13 and the result is outputted to a wire network from a terminal 10. Thus, even when a reception level is rapidly fluctuated, the hand-off not giving effect on the talking quality is executed.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is applicable to handoff applications in mobile communication systems that provide a continuous communication path even when a mobile terminal moves between multiple base stations, such as a car telephone system. The present invention relates to a base station switching method and a mobile receiver that implements the method.

(Prior art) In so-called cellular mobile communication systems, such as automated telephone systems, where multiple base stations cover different service areas, communication with mobile terminals is necessary as the mobile terminal moves during a call. The realization of handoff technology that allows calls to continue by switching base stations has become an extremely important issue. Conventional handoff is controlled so that communication is performed with the base station that receives the strongest signal from the mobile terminal, and if the level of the received signal from the mobile terminal decreases at the base station during the call, the communication is performed with the base station that receives the strongest signal from the mobile terminal. The received signal level was measured at the base station, and communication with the mobile terminal was switched to the base station that received the strongest signal. This handoff method is described in detail on pages 197 to 200 of the book "Car Telephone" published by the Institute of Electronics and Communication Engineers in 1985.

(Problem to be solved by the invention) However, with the conventional handoff method, it takes time to actually switch base stations after the received signal level changes, so mobile terminals such as cars may be behind buildings. If the received signal level suddenly fluctuates, for example, the optimum base station cannot be selected, resulting in a drop in sound quality or the line being disconnected.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a handoff method that does not affect speech quality even if the received signal level fluctuates rapidly, and to provide a mobile receiver that implements the handoff.

(Means for Solving the Problems) A handoff method for a mobile communication system of the present invention is a mobile communication system that continuously provides a communication path by sequentially changing a communication path to a mobile terminal moving between a plurality of base stations. A handoff method for a system in which, when a mobile terminal is in a position where it can communicate with multiple base stations, each of the base stations with which it can communicate transmits the same signal to the mobile terminal on a different frequency, and Each communicable base station is characterized in that it simultaneously receives signals from the mobile terminal and combines them with diversity.

Furthermore, the mobile receiver of the present invention is a mobile receiver used in a mobile terminal, and includes a plurality of antennas, a plurality of frequency converters that convert the received signals of the plurality of antennas to the same frequency, and a plurality of demodulators that demodulate respective output signals of the plurality of frequency converters; a combining circuit that combines the respective output signals of the plurality of demodulators; and a plurality of demodulators when the mobile receiver is in a handoff state. The reception frequencies of the plurality of frequency converters are set to different values so that the mobile receiver receives signals from different base stations, and when the mobile receiver is not in a handoff state, the reception frequencies of the plurality of frequency converters are set to different values so that the mobile receiver receives signals from different base stations. and a control circuit that sets the frequencies to the same value.

(Function) Methods for improving the quality of handoff include a method of shortening the time required for handoff, and a method of connecting multiple wireless circuits at the same time to perform tie-versus reception. The present invention adopts the latter method.

In the handoff method for a mobile communication system of the present invention, handoff is started when a mobile terminal approaches a base station boundary, that is, a cell boundary. At this time 1. Set up a line with a new base station while maintaining the line with the base station you were previously communicating with. When transmitting signals from multiple base stations to the same mobile terminal at the same time, each base station uses a different frequency since using the same frequency will cause interference. The signal transmitted from the mobile terminal has a single frequency, and the signals of the same frequency may be simultaneously received by a plurality of base stations. In this way, when the mobile terminal can communicate with the new base station with sufficiently high quality, it switches the transmission frequency. For a while thereafter, the base station with which the base station was communicating continues to transmit, and at the same time receives a signal on the new frequency from the switched mobile terminal. When multiple base stations are receiving signals from the same mobile terminal, diversity combining is performed at the switching center. By doing this, even if one base station is hidden behind a building, it can continue communicating with the other base station, making it possible to achieve extremely high quality handoff.

The mobile receiver of the present invention includes a plurality of signal receiving sections each including an antenna, a frequency converter, and a demodulator, a combining circuit, and a control circuit, and the mobile receiver has a plurality of signal receiving sections each including an antenna, a frequency converter, and a demodulator, a combining circuit, and a control circuit. A high-quality handoff is realized by changing the frequency of the signal received by the signal receiving section using the control circuit and performing diversity combining using the combining circuit.

(Example) Next, the present invention will be explained 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. The situation in FIG. 1 is just in the middle of a handoff, and base station 11 and base station 12 are transmitting signals to mobile terminal 15 on frequencies Fl and F2, respectively. The mobile terminal 15 can receive stable signals by receiving these signals in diversity.

The signal is transmitted from the mobile terminal 15 at frequency f1, received by the base stations 11 and 12, diversity-combined by the switching center 13, and output from the terminal 10 to the wired network.

FIG. 2 shows the detailed operation of the embodiment shown in FIG.

Consider a case where a mobile terminal 15 currently located at point X where base station 11 is located moves to point Y, t where base station 12 is located. From point X to point A, the base station 11 is close enough to receive no signal from the base station 12, so the mobile terminal 15 transmits frequency 1, and the base station 11 transmits frequency F1, allowing normal communication. It is being said. When the mobile terminal 15 passes point A, signals from the base station 12 also begin to be received, so a line is also set up between the base station 12 and the mobile terminal 15. At this time, the base station 12 transmits a signal at frequency F2. The mobile terminal 15 can maintain stable reception quality by receiving frequencies F1 and F2 and performing diversity combination. The base station 12 receives the signal f1 from the mobile terminal 15. Signals from the mobile terminals 15 received by the base stations 11 and 12 are sent to a switching center 13 as shown in FIG. 1, where they are diversity-combined. When the mobile terminal 15 passes point B, the signal from the base station 12 is received more strongly, and the mobile terminal 15 switches the frequency of the transmission signal to F2. At this time, base station 11
continues to receive frequency f2 and transmit frequency Fk without cutting off communication with mobile terminal 15. In this way, diversity combining still continues at both the base station 11.12 and the mobile terminal 15. When the mobile terminal 15 passes point C, the signal from the base station 11 becomes weaker, so the line between the base station 11 and the mobile terminal 15 is disconnected, the base station 11 stops transmitting and receiving, and the mobile terminal 15 communicates only with the base station 12. Continue.

By doing this, you can
Even in section C, the mobile i-terminal 15 can continue to communicate stably, and handoff without quality deterioration can be achieved. Note that the diversity combination and points A and B described in this embodiment.

The present invention does not define handoff processing for C1, and any method may be used.

FIG. 3 is a diagram showing an embodiment of the mobile receiver of the present invention. Signals received by antennas 30.31 are each converted to a desired frequency by frequency converters 32.33 and sent to demodulators 34.35.

Here, each of the frequency converters 32 and 33 is composed of a variable frequency oscillator and a multiplier, and can independently control the reception frequency using a control signal from the control circuit 37. The demodulators 34 and 35 demodulate the received signals and output them to the combining circuit 36, and the combined output is sent to the terminal 4.
Output from 0.

Information indicating what handoff state the mobile terminal is currently in is input from the terminal 41, and the control circuit 37 uses the same frequency f1 when the mobile terminal is not in the handoff state, as shown in X-A in FIG. Frequency converters 32 and 33 are set to perform normal diversity reception. On the other hand, when the mobile terminal is in a handoff state as shown in A-B in FIG. 2, the control circuit 37 sets the frequency converter 32 to fl and the frequency converter 33 to F2. receives signals of different frequencies and performs diversity combining. By doing this, it is possible to realize a mobile receiver that receives signals from different base stations during handoff to create a diversity effect, and that normally receives signals from the same base station in a diversity manner to improve communication quality. . Note that any method may be adopted as the diversity combining method in the present invention.

(Effects of the Invention) As described in detail below, 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 that implements the method.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of a handoff method for a mobile communication system according to the present invention, FIG. 2 is a diagram explaining details of the operation of the embodiment of FIG. 1, and FIG. 3 is a diagram showing a mobile receiver according to the present invention. It is a figure showing one example of this. 11.12...Base station, 13...Switching center, 15...
・Mobile terminal, 30.31...Antenna, 32.33・
...Frequency converter, 34.35...Demodulator, 36...
-Synthesis circuit, 37...control circuit.

Claims (2)

[Claims] (1) A handoff method for a mobile communication system that continuously provides a communication path by sequentially changing the communication path for a mobile terminal moving between multiple base stations, in which the mobile terminal communicates with multiple base stations. When located at a possible location, each of the base stations with which it can communicate transmits the same signal to the mobile terminal on different frequencies, and each of the base stations with which it can communicate simultaneously receives signals from the mobile terminal. A handoff method for a mobile communication system, which is characterized by combining diversity. (2) A mobile receiver used in a mobile terminal, which includes a plurality of antennas and a plurality of frequency converters that frequency convert the received signals of each of the plurality of antennas to the same frequency;
a plurality of demodulators that demodulate respective output signals of the plurality of frequency converters; a combining circuit that combines the respective output signals of the plurality of demodulators; and a combination circuit that combines the respective output signals of the plurality of demodulators; The reception frequencies of the plurality of frequency converters are set to different values so that the demodulators receive signals from different base stations, and when the mobile receiver is not in a handoff state, the reception frequencies of the plurality of frequency converters are set to different values so that the demodulators receive signals from different base stations. A mobile receiver comprising: a control circuit that sets reception frequencies to the same value.