JPH104580A - Hand-off communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hand-off communication system in which voice quality nearly equal to that of a conventional software hand-off even when the hardware hand-off with a simple system configuration is adopted. SOLUTION: A base station 10 is provided with a silence period detection means 11 detecting a silence period of the base station, a silence code data generating means 12 generating silence code data by the detection of the silence period, and a transmission data selection means 14 selecting the silence code data in place of voice data at the head of the silence period and giving the data to a transmitter 15, and a mobile station 20 is provided with a hand-off condition relax means 23 by which the hand-off condition is realized by decreasing the threshold level of reception signal power required for the switching of the base station in this hand-off communication system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a handoff communication system for performing bidirectional communication between a mobile station and one base station selected from among a plurality of base stations.

[0002]

2. Description of the Related Art A base station for relaying a communication from a mobile station includes:
Handoff and voice detection discontinuous transmission control (hereinafter referred to as VAD / DTX control) for switching and connecting based on the magnitude of the received power from the base station in a plurality of cells arranged at different positions in accordance with the movement of the mobile station The U.S. standard system is described in, for example, the following document. Literature:
“Mobile Staion-Base Station Compatibility Standar
d for Dual-Mode Wideband Spread Spectrum Cellular
System, TIA / EIA / IS-95, July 1993, U.
SA, pp. 6-20-6-23, 6-30-6-41 "
The above-mentioned document shows a switching procedure regarding handoff of a mobile station.

FIG. 5 is an explanatory diagram of a conventional hard handoff system according to the above-mentioned document. In FIG. 5, the mobile station 101 initially communicates via the base station 102, but from a cell which is an area where effective communication with the base station 102 which is communicating at some point is possible, When switching to the base station 103 of the next cell, those base stations 1
This is a cell switching system in which only one of the base stations 102 and 103 is connected by a switch operation of the mobile communication switching center 104 located above 02 and 103, and this is called hard handoff. In the case of hard handoff, the communication between the mobile station 101 and the base station 102 or 103 may be momentarily interrupted, and the instantaneous interruption greatly deteriorates the voice quality.

FIG. 6 is an explanatory diagram of a conventional soft handoff system according to the above-mentioned document. In FIG. 6, mobile station 2
01 communicates with its own communication destination only through the base station 202 and the mobile communication switching center 204 at first, but if the movement of the own station causes a decrease in the received power from the base station 202 or the like, the switching is performed. To prevent loss of communication data during the transition period,
From a certain point in time, communication is performed simultaneously via both the base station 202 up to that point and the next selected base station 203 to eliminate the instantaneous interruption of the call voice to the mobile communication switching center 204. , Improving call quality. Further, a VAD / DTX control device is used for transmission from the mobile station 201 to the base station, a silent section of voice data is detected, and the transmission power of the silent section is set to zero or reduced to perform communication. I have. With this control, it is possible to reduce the power consumption on the transmitting side and reduce the amount of interference with other stations in communication on the receiving side.

[0005]

However, in the conventional device according to the standard system of the above-mentioned document, in order to execute soft handoff, a call control protocol of a mobile communication switching center located on a higher network side than a base station is complicated. Had a complicated system configuration. Further, the mobile station and the base station require a plurality of transmission / reception devices per communication, and the mobile station also needs a mechanism for searching for a candidate base station to be switched to next, so that hardware becomes complicated and the device cost increases. There was a problem of becoming.

[0006]

SUMMARY OF THE INVENTION A handoff communication system according to the present invention performs bidirectional communication between a mobile station and one base station selected from among a plurality of base stations. In the base station, a silent section detecting means for detecting a silent section of voice data transmitted by the base station to the mobile station, and a silent signal indicating that the base station is in a silent state by a detection signal of the silent section detecting means. Silence code data generating means for generating code data, and as data to be transmitted from the base station to the mobile station, at the head section of the silence section detected by the silence section detection means, the silence code data generation means instead of voice data. Transmission data selecting means for selecting silence code data to be generated, and selecting original voice data after the end of the silence code data generation time, When receiving the silent code data transmitted by the base station and recognizing that the base station is in a silent state, the hand-off condition for lowering the threshold of the received signal power required for switching the base station to ease the hand-off condition It is provided with mitigation means. As a result, the ratio of performing handoff at the timing when the voice communication becomes silent increases, so even if a hard handoff with a simple system configuration is adopted, it does not hinder the call, and it is almost equivalent to the conventional soft handoff. Voice quality can be obtained.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. FIG. 1 is a configuration diagram of a handoff communication system according to Embodiment 1 of the present invention. In FIG. 1, reference numeral 10 denotes a base station and reference numeral 20 denotes a mobile station. In FIG. 1, only a downlink from the base station 10 to the mobile station 20 related to the present invention is shown. There is also an uplink to the base station 10, and the system is capable of bidirectional communication. On the base station 10 side in FIG. 1, reference numeral 11 denotes a silent section detecting means for detecting a silent section of voice data transmitted from the base station 10 to the mobile station 20, and 12 denotes a base station based on a detection signal of the silent section detecting means 11. Silence code data generation means for generating silence code data (details will be described later) indicating that the voice to be transmitted is in a silence state, and transmission data selection means 14 as data to be transmitted by the base station 10 to the mobile station 20 , One of the voice data and the silence code data is selectively output in accordance with the switching control signal output by the silence section detection means 11. Reference numeral 15 denotes a transmitter, and 16 denotes a transmission antenna on the base station side.

In the mobile station 20 shown in FIG. 1, reference numeral 21 denotes a receiving antenna, 22 denotes a receiver, and 23 denotes a handoff condition mitigation means. The silence code transmitted by the base station 10 from the received data output from the receiver 22 Detect data and
In addition to relaxing the handoff condition for the second stage, the handoff condition for the second stage is also relaxed based on a signal that the mobile station itself detects that the voice transmitted is silent. Reference numeral 24 denotes a hand-off condition setting means, in which initial settings for the hand-off condition are initially performed.
At the handoff transition time, relaxation from the initial setting is performed by the handoff condition relaxing means 23 (the details thereof will be described later with reference to FIGS. 2 and 3).

In the handoff communication system according to the present embodiment, the codec (CODEC, codec / decoder) has Ad
aptive Differential Pulse Code Modulation COM
101 (hereinafter referred to as ADPCM COM 101) will be described. The ADPCM COM 101 decodes a 4-bit unit as one numerical information. Especially the first bit (MSB) of the 4-bit unit
Are treated as sign bits. Therefore "000
"0" and "1000" are treated as the same information of 0 and have redundancy.If this "0000" or "1000" is continued for a certain number of times or more, FIG.
The silent section detecting means 11 detects that a voice non-transmitting section (hereinafter referred to as a silent section) has started from that point. The silence code data generating means 12 receives the silence code data, for example, “000”, based on the detection signal of the silence section detection means 11.
"00000000" which is a bit sequence in which "0" is repeated three times
000 "is generated as silence code data indicating that the base station is in a silence section. Since the communication speed of voice data is defined by the ADPCM COM 101, the silence code data is also synchronized with this communication speed. 1
Since two bits are generated, the generation time of silence code data is also constant.

The silence section detection means 11 supplies a switching control signal to the transmission data selection means 14 for a time obtained by adding some margin time before and after the silence code data generation time,
Only during the period in which the switching control signal is supplied, control is performed so that the data supplied by the transmission data selector 14 to the transmitter 15 is switched from normal voice data to silent code data output from the silent code data generator 12. . In this way, silent code data is transmitted from the transmitter 15 to the mobile station 20 via the antenna 16 instead of the voice data in the head section of the silent section on the base station side. Receiver 2 of mobile station 20
2 receives the transmission data from the base station 10 via the antenna 21 and supplies the received data to the handoff condition easing means 23.

As data to be observed for determining execution of handoff, received power used for communication and the like are used. The mobile station monitors the received power from the currently connected base station and the received power from another base station that is adjacent to or near the base station. A method for the mobile station itself to determine a handoff destination based on the observed received power,
Alternatively, various handoff methods such as a method in which the received power observed by the mobile station is transmitted to the base station using the control channel and a handoff destination is determined in a mobile communication switching station above the base station, Since the present invention can be applied to any of the methods, the method does not matter. The mobile station switches the connection to one of the corresponding base stations when there is a base station whose received power is higher than the received power of the currently connected base station by H [dB] or more. Here, the parameter H is referred to as hysteresis and has a function of preventing connection switching from occurring frequently due to fluctuations in received power. In this embodiment, H is set to 3.0 [dB]. Then, 3.0 [dB] of the hysteresis H is initially set in the handoff condition setting means 24 of FIG.

FIG. 2 is a diagram showing a first example of a handoff condition relaxing sequence 1 according to the present embodiment. In FIG. 2, the hysteresis H is relaxed in two stages by detecting a silent state of both the base station and the mobile station. Is shown. The numerical value following S in the figure indicates a step number. When the base station 10 detects a silent section of audio data transmitted by the base station (S in FIG. 2).
31), silence code data (in this example, the "00"
00000000 ") to the mobile station 20 (S
32). The mobile station 20 communicates with the base station 10 during voice communication.
(S3)
3), the hand-off condition relieving means 23 detects the silence code data from the received data, and when recognizing that the base station is in the silence state, the hand-off condition hysteresis H is set to 0.5 for the first stage. [DB] and the initially set hysteresis H is increased from 3.0 [dB] to 2.
It is reduced to 5 [dB] (see S34). The handoff becomes slightly easier due to the relaxation of 0.5 [dB] for the first stage.

Thereafter, when the mobile station itself becomes silent,
The handoff condition relaxing means 23 further relaxes the hysteresis H by 0.5 [dB] of the second stage based on the signal detecting the silent state of the own station (see S35), and reduces the hysteresis H by 2.5 [dB]. ] To 2.0 [dB] (see S36). As described above, when one communication becomes silent, 0.5 [dB] is reached, and when both uplink and downlink communications become silent, 1.0 [dB] hysteresis H is relaxed. A hard handoff protocol is performed between the base stations (see S37 and S38).

FIG. 3 is a diagram showing a second example of the handoff condition relaxing sequence according to the present embodiment.
0 indicates that the first-stage hysteresis is alleviated by detecting the silent state of the own station, and then the second-stage hysteresis is alleviated by recognizing the silent state of the base station. First, the mobile station 20 detects a silent state of the mobile station during voice communication (see S41), and the hand-off condition relaxing unit 23 relaxes the hysteresis H by 0.5 [dB] of the first stage, and 3 From 0.0 [dB] to 2.5 [dB] (S4
2). Next, in this state, the base station 10 detects a silent state of its own station (see S43) and transmits silent code data (see S44). When the mobile station 20 receives the silence code data transmitted from the base station (see S45), the handoff condition mitigation means 23 further reduces the hysteresis H by 0.5 [dB] of the second stage,
It is reduced from 2.5 [dB] to 2.0 [dB] (see S46). When handoff is required, a hard handoff protocol is performed between the mobile station and the base station (S47, S48).
See).

According to the above, the ratio of performing the handoff at the timing when the two-way communication is silenced increases, so that the hard handoff process can be performed. That is, even if an instantaneous interruption of the communication link occurs due to hard handoff, this occurs during a silent state of two-way communication (that is, a timing that does not hinder the use of the user). Can be.

Embodiment 2 FIG. 4 is a configuration diagram of the handoff communication system according to Embodiment 2 of the present invention. 4, 12, 15, 16 and 20 to 24 are the same as those in FIG. 10A is a base station according to the second embodiment, 11A
Is a silent section detection unit according to the second embodiment, 13 is a voice output control unit according to the second embodiment, and 14A is a transmission data selection unit according to the second embodiment. Except for the above 11A, 13 and 14A, the same operations as those in FIG. 1 are performed, and the description of those operations will be omitted.

The silent section detecting means 11A of FIG. 4 detects a silent section of voice data transmitted from the base station 10A to the mobile station 20 as in the case of FIG. Then, the silent section detection signal is supplied to the silent code data generating means 12 and the voice output control means 13, and a selection control signal is supplied to the transmission data selecting means 14A. And silent section detecting means 11
The selection control signal that A supplies to the transmission data selection means 14A is three of voice data, silence code data, and silence data.
The difference from the switching control signal for switching between the two types of data in FIG. 1 is that the control signal is used to select any one of the types of data.

The voice output control means 13 controls the voice data in the voiceless section to zero output or low output voice data based on the voiceless section detection signal supplied from the voiceless section detection means 11A and outputs the data. Transmission data selection means 1
4A selects any one of the three input data and outputs it to the transmitter 15 based on the selection control signal supplied from the silent section detecting means 11A.
In this embodiment, the selection control signal output by the silent section detecting means 11A selects normal voice data during a period in which the silent section detection signal is not obtained, and when the silent section detection signal is obtained, The silence code data output by the silence code data generation means 12 is selected in the head section, and the zero output or low output silence data output by the voice output control means 13 is selected in the silence section after the end of the silence code data generation time. Is to select.

Therefore, during the voice communication, the transmitter 15 of the base station sends three pieces of data in the order of normal voice data, the first silent code data of the silent section, the remaining silent section of the silent section, and the voice data after the end of the silent section. The type of data will be transmitted. The handoff condition mitigation processing on the mobile station side described in FIGS. 2 and 3 can be applied to the second embodiment in FIG. 4 as in the case of the first embodiment in FIG. 1, but since the operation is the same, Description is omitted.

[0020]

As described above, according to the present invention, there is provided a handoff communication system for performing bidirectional communication between a mobile station and one base station selected for handoff among a plurality of base stations. The base station has a silent section detecting means for detecting a silent section of voice data transmitted from the base station to the mobile station, and silent code data indicating that the base station is in a silent state by a detection signal of the silent section detecting means. The generated silent code data generating means, and the data generated by the silent code data generating means instead of voice data in the head section of the silent section detected by the silent section detecting means as data to be transmitted from the base station to the mobile station. Transmission data selecting means for selecting silence code data and selecting original voice data after the end of the silence code data generation time, wherein the base station transmits to the mobile station. When the base station recognizes that the base station is in a silence state by receiving the silence code data, the threshold value of the received signal power required for switching the base station is reduced, and the handoff condition mitigation means is provided to alleviate the handoff condition. However, the ratio of handoff at the timing when the voice communication becomes silent will increase, and even if a hard handoff with a simple system configuration is adopted, there is little hindrance to the call, and it is almost the same as that of the conventional soft handoff. Voice quality can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a handoff communication system according to a first embodiment of the present invention.

FIG. 2 illustrates a handoff condition relaxation order example 1 according to the present embodiment.
FIG.

FIG. 3 is a handoff condition relaxation order example 2 according to the embodiment;
FIG.

FIG. 4 is a configuration diagram of a handoff communication system according to Embodiment 2 of the present invention.

FIG. 5 is an explanatory diagram of a conventional hard handoff system.

FIG. 6 is an explanatory diagram of a conventional soft handoff system.

[Explanation of symbols]

 10, 10A base station 11, 11A silent section detecting means 12 silent code data generating means 13 voice output controlling means 14, 14A transmitting data selecting means 15 transmitter 16 antenna 20 mobile station 21 antenna 22 receiver 23 handoff condition relaxing means 24 handoff Condition setting means

Claims (6)

[Claims] 1. A handoff communication system for performing bidirectional communication between a mobile station and one base station selected for handoff from a plurality of base stations, wherein the base station includes a base station. A silent section detecting means for detecting a silent section of voice data to be transmitted to the base station; a silent code data generating section for generating silent code data indicating that the base station is in a silent state based on a detection signal of the silent section detecting means; As data to be transmitted by the station to the mobile station, in the head section of the silent section detected by the silent section detecting means, the silent code data generated by the silent code data generating means is selected instead of the voice data, and the silent code data is selected. Transmission data selection means for selecting original voice data after the end of the generation time, wherein the mobile station receives the silent code data transmitted by the base station. A handoff communication system, comprising: a handoff condition mitigation unit that reduces a threshold value of a received signal power required for switching between base stations when the base station recognizes that the base station is in a silent state, thereby relaxing handoff conditions. 2. The handoff condition mitigation means provided in the mobile station, first, when receiving silence code data transmitted by the base station, lowers the threshold value of the received signal power by the first step, and then the mobile station itself 2. The handoff communication system according to claim 1, wherein when a silence state is detected, the threshold value of the received signal power is further reduced by a second step to reduce the handoff condition to two steps. 3. The handoff condition mitigation means provided in the mobile station, first, when the mobile station itself detects a silent state, lowers the threshold value of the received signal power by the first step, and then reduces the silent state transmitted by the base station. 2. The handoff communication system according to claim 1, wherein when code data is received, the handoff condition is relaxed to two levels by further lowering the threshold value of the received signal power by a second level. 4. A handoff communication system for performing bidirectional communication between a mobile station and one base station selected for handoff from a plurality of base stations, wherein the base station includes a base station. A silent section detecting means for detecting a silent section of voice data to be transmitted to; a silent code data generating means for generating silent code data indicating that the base station is in a silent state by a detection signal of the silent section detecting means; Voice output control means for controlling voice data in a voiceless section detected by the voiceless section detection means to zero-output or low-output voiceless data; and voicelessness detected by the voiceless section detection means as data transmitted from a base station to a mobile station. In the first section of the section, select silence code data generated by the silence code data generation means,
In the silent section after the end of the silent code data generation time, zero output or low output silent data controlled by the audio output control means is selected, and normal audio data is selected in sections other than the silent section. When the mobile station receives the silent code data transmitted by the base station and recognizes that the base station is in a silent state, the mobile station receives the silent signal power required for switching the base station. A handoff communication system comprising: a handoff condition easing means for lowering a threshold to ease a handoff condition. 5. The handoff condition mitigation means provided in the mobile station, first, when receiving the silent code data transmitted by the base station, lowers the threshold value of the received signal power by the first step, and then the mobile station itself 5. The handoff communication system according to claim 4, wherein when a silent state is detected, the handoff condition is reduced to two levels by further lowering the threshold value of the received signal power by a second level. 6. The handoff condition mitigation means provided in the mobile station, first, when the mobile station itself detects a silence state, lowers the threshold value of the received signal power by the first stage, and then reduces the silence transmitted by the base station. 5. The handoff communication system according to claim 4, wherein when code data is received, the handoff condition is relaxed to two steps by further lowering the threshold value of the received signal power by a second step.