JP2000197107A - CDMA cellular radio base station - Google Patents

Abstract

(57) [Summary] [Problem] C by base station antenna diversity scheme
The DMA cellular radio base station accommodates in one sector by controlling the transmission power according to the traffic situation in the sector while maintaining the effect of improving the communication quality against fading without providing a reception diversity means in the mobile station. Avoid reducing the number of mobile stations possible. A plurality of antennas are installed, a service area is divided into a plurality of sectors, and at least two of the plurality of antennas are arranged so as to cover the same sector among the plurality of sectors. A CDMA cellular radio base station of a station antenna diversity system, wherein at least one of at least two antennas covering the same sector is transmitted from the base station to the mobile station according to the traffic situation of the sector covered by the antenna. The transmission power of the communication to the communication is time-variably controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a CDMA (Code Division Multiplexing) cellular radio base station, and more particularly to a CDMA cellular radio base station employing base station antenna diversity.

[0002]

2. Description of the Related Art When a plurality of receiving antennas are prepared as an antenna system of a communication system and the intervals between the plurality of receiving antennas are set to be equal to or longer than the wavelength of a used frequency, a correlation between received signal strengths is reduced. Become. Therefore, fading resistance can be enhanced by comparing the received signal levels of a plurality of receiving antennas on the receiver side and using the larger one on the receiver side. Such a scheme is
It is called receive antenna diversity and is widely used.

[0003] Similar to the reception antenna diversity, the same effect can be obtained even if a plurality of transmission antennas are prepared on the transmitter side. In such transmission antenna diversity, a plurality of prepared transmission antennas are switched. However, the reception signal levels before and after the switching of the transmission antennas are compared on the receiver side, and any one of the transmission signal antennas having the higher signal level is transmitted. A control signal for switching the transmitting antenna is sent from the receiver to the transmitter so that the subsequent transmission is performed.

According to the transmission antenna diversity, since only one antenna is required on the receiver side, it is effective in downsizing the receiver.

[0005] In recent years, mobile communication terminals have been desired to be reduced in size and weight, as well as to improve communication quality, and also to have reduced power consumption so that they can be used for a long time with a battery power supply. I have. For this reason, in the mobile communication system, it is preferable that the above-mentioned transmission antenna diversity is adopted on the base station side, and the reception antenna and the receiver of the mobile terminal can be unified.

When the above-mentioned transmission antenna diversity is adopted, a control signal for switching the transmission antenna must be transmitted from the mobile station on the receiver side to the base station side. Therefore, although the apparatus can be reduced in size and weight while improving the communication quality of the receiver by increasing the fading resistance, there is a problem that the fading characteristic is deteriorated due to the time delay accompanying the transmission and reception of the control signal for switching the transmitting antenna. . In addition, a mechanism for switching antennas on the base station side and a new configuration for transmitting control signals on the mobile device side are required.

In a CDMA cellular radio base station,
In order to solve such a problem, the service area of the base station is divided into a plurality of sectors covered by any one of the plurality of antennas, a signal wirelessly transmitted from the plurality of antennas, A method in which a mobile station is modulated so that radio signals transmitted from the plurality of antennas can be simultaneously received and demodulated, and at least two of the plurality of antennas are installed so as to cover the same sector among a plurality of sectors. There is. FIG. 4 is a diagram illustrating a configuration of a cellular radio base station that does not require a new mechanism on the mobile station side configured as described above.

In FIG. 4, a cellular radio base station is provided with two antennas, a first antenna 101a and a second antenna 101b, corresponding to a sector 102, and these antennas are also used for transmission and reception of the cellular radio base station. You.
The same frequency carrier in which the same information is modulated with different codes is supplied from the first transmitting section 103a and the second transmitting section 103b to the first antenna 101a and the second antenna 101b, respectively. Further, the first antenna 101a and the second antenna 1
The signal from each mobile station received at 01b is distributed and input to the first receiving unit 104a and the second receiving unit 104b.

[0009] The sector 102 includes a sector 102a covered by the first antenna 101a and a second antenna 10a.
1b so that their areas are substantially equal.
a, the 2nd antenna 101b is comprised. Although not shown, this cellular radio base station has a service area (cell) divided into a plurality of sectors, one of which is a sector 102. That is, in this cellular system, in order to realize transmission antenna diversity and reception antenna diversity, one sector 1
02 is associated with a plurality of antennas 101a and 101b.

Using a CDMA cellular radio base station based on the base station antenna diversity scheme, in a communication line (hereinafter referred to as a downlink) from the cellular radio base station to the mobile station 105, transmission information is transmitted to a first transmission section 103a.
Are spread-modulated using the first spreading code, and transmitted to the mobile station 105 located in the sector 102 by the first antenna 101a. At this time, the same transmission information is spread-modulated by the second transmitter 103b using a second spreading code different from the first spreading code, and the second antenna 101b
Is also sent to the mobile station 105 located in the sector 102.

By the way, in the CDMA cellular radio communication system, when a mobile station moves between sectors, the same frequency carrier is separately transmitted from each antenna for each sector to a predetermined spreading code so that a soft handoff function can be realized. , And one receiver having a plurality of despreaders can simultaneously receive and demodulate a plurality of sets of transmission signals from each antenna for each sector.

By utilizing such a reception demodulation function in the CDMA cellular radio communication system, the first spreading code and the second spreading code may be determined from completely different code sequences, or may be the same code sequence. And the code phase may be different, but in any case, the mobile station 105 is connected to the first antenna 101a and the second antenna 10a.
One that can simultaneously receive and demodulate the signal transmitted from 1b is selected. This allows the mobile station 105 to perform reception demodulation processing on signals transmitted from the first antenna 101a and the second antenna 101b as if the signals were transmitted from antennas corresponding to different sectors.

Therefore, the mobile station 105 is configured to include a RAKE receiver (one receiver having a plurality of sets of despreaders and receiving a plurality of sets of signals simultaneously) in the same manner as a generally used CDMA receiver. By doing so, the signal from the first antenna 101a and the signal from the second antenna 101b can be weighted and combined at the mobile station, so that even if the signal from either one is interrupted by fading, Signals can be received, and transmission diversity in the downlink is realized. In addition,
The mobile station 105 may use a RAKE receiver to selectively receive a signal from one of the antennas 101a and 101b in accordance with the signal level instead of weighting and combining the signals.

The communication from the mobile station 105 to the base station via a communication line (hereinafter referred to as an uplink) is performed by the mobile station 10.
5 are received by the first antenna 101a and the second antenna 101b together. Usually, mobile station 1
05 are transmitted from sectors 102a and 102b.
Or a code unique to the mobile station 105, and is spread by the first receiving device 104a and the second receiving device 104a.
The receiving device 104b despreads the signals received by the first antenna 101a and the second antenna 101b with their codes and demodulates them. Then, reception antenna diversity is realized by weighting and combining these demodulated signals or selectively using one of the signals.

[0015]

In general, in a CDMA system, ideally, a P code whose cross-correlation function is always zero is ideal.
When a combination of N sequences is used, there is no interference from other sources, and an infinite transmission path capacity is obtained.
However, since there is no PN sequence combination in which the cross-correlation function is always zero, CDMA always receives some interference from other sets of signals. When the number of multiplexes is large, interference from other sources is statistically replaced by Gaussian noise having the same power, and approximately evaluated, but the ratio of signal power to interference power of the mobile station, so-called S / N ratio Thus, the maximum number of mobile stations that can be accommodated in one sector is determined.

Referring to the conventional base station antenna diversity system described with reference to FIG. 4, in a sector 102 formed by two antennas 101a and 101b having a transmission diversity effect, this sector 10
2 for a number of mobile stations existing in
a and 101b transmit signals having different codes at the same frequency (hereinafter, signals including signals having different code phases are used), and each mobile station receives these signals.

A particular mobile station, for example mobile station 105 of FIG.
In this example, two signals modulated by a code to be received by the mobile station are respectively received and demodulated. At the same time, a signal component modulated by a code to be received by another mobile station and a signal on the other side to be received by itself are The power will be generated as interference power. Therefore, the ratio of the signal power to the interference power of each of the received and demodulated signals at the mobile station 105 in FIG. 4 is almost half as compared with the case where the conventional base station antenna diversity scheme is not performed. This situation is the same because even if the signals received from both antennas are weighted and combined by an optimal method, the interference power component is similarly combined.

In addition, each mobile station has a channel for synchronizing for reception, and necessary information is broadcast using this channel. In need.

Therefore, when the base station antenna diversity system is used, the mobile station can be accommodated in one sector due to an increase in interference power, although the communication quality against fading is improved without providing the mobile station with reception diversity means. A problem has arisen in that the practical maximum of the number is reduced.

Accordingly, the present invention provides a base station antenna diversity system which does not provide a mobile station with a reception diversity means and maintains the effect of improving the communication quality against fading while reducing the transmission power according to the traffic situation in the sector. It is an object of the present invention to provide a CDMA cellular radio base station that can control the number of mobile stations that can be accommodated in one sector and thereby reduce the number of mobile stations.

[0021]

A CDMA cellular radio base station according to claim 1 is provided with a plurality of antennas, a service area is divided into a plurality of sectors, and at least two of the plurality of antennas are the same. A base station antenna diversity CDMA cellular radio base station arranged to cover the same sector among a plurality of sectors, wherein at least one of at least two antennas covering the same sector is the same as the CDMA cellular radio base station. The transmission power of communication from the base station to the mobile station is time-variably changed and controlled according to the traffic situation of the sector covered by the antenna.

According to this configuration, in the CDMA cellular radio base station of the base station antenna diversity system,
If there is sufficient traffic in each sector, the transmission power from the antenna is increased to increase the signal power to interference power ratio of the mobile station, thereby improving the communication quality. Also, when traffic increases in each sector, the transmission power from one antenna is reduced, and although the diversity effect is partially reduced, a necessary communication path is secured and the mobile station can accommodate one sector. Substantially reduce the number of stations

According to a second aspect of the present invention, there is provided the CDMA cellular radio base station according to the first aspect, wherein the mobile station in the same sector handover state allocates transmission power between antennas covering the same sector. The number is controlled so as to be within a certain upper and lower limit value.

According to this configuration, the same effect as in the first aspect is obtained, and the number of mobile stations in the same sector in the handover state is monitored, so that the transmission power distribution between the two antennas can be distributed. It can be varied to approach the optimal power distribution and avoid transmission at unnecessarily high transmission power.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is a diagram illustrating the configuration of a cellular radio base station according to an embodiment of the present invention. 4 is different from FIG. 4 in that the first transmitting unit 103a and the second transmitting unit 1
Transmission power control unit 108 for controlling transmission power from the transmission power control unit 03b, a traffic detection unit 106 and a handover detection unit 107 for giving commands to the transmission power control unit 108.
The other points are the same as those in FIG. 4, and the same components are denoted by the same reference numerals.

Generally, a CDMA cellular radio base station has a channel for broadcasting information from the base station, a channel for calling a mobile station, and a channel for performing one-to-one mutual communication with the mobile station. In each of these channels, the signal is transmitted with a transmission power enough to reach the entire area to be served by the base station.

This means that the CDMA cellular radio base station of the base station antenna diversity system to which the present invention is applied, that is, the service area of the base station is covered by any one of the plurality of antennas. Signals are wirelessly transmitted from a plurality of antennas, and are modulated so that the mobile station can simultaneously receive and demodulate wireless signals transmitted from the plurality of antennas. At least two of the plurality of antennas Is a CDM that is installed to cover the same sector among multiple sectors
The same applies to the A cellular radio base station, and the signal is transmitted with transmission power enough to reach all the sectors to be served by the base station.

According to the present invention, when the base station antenna diversity system is performed, the traffic situation of the sector is monitored, and the base station transmits the traffic with enough transmission power to reach all the sectors to be serviced while transmitting the traffic situation. Accordingly, the transmission power is controlled so that the substantial maximum value of the number of mobile stations that can be accommodated in one sector does not decrease due to an increase in interference power or the like.

In FIG. 1, the traffic detector 106
Is configured to detect a traffic amount between a mobile station and a base station in the sector 102 and to give a command to the transmission power control circuit 108. In this embodiment, the transmission power from the first antenna 101a is set to a constant power enough for the signal to reach all the sectors to be served by the base station, and the transmission power from the second antenna 101b depends on the traffic. This will be described below.

When the traffic detection circuit 106 detects that the total number of mobile stations existing in the sector 102 is small and the traffic is not too high, this state is instructed to the transmission power control circuit 108 and the transmission power control circuit 108
Controls the second transmission unit 103b to increase the transmission power. Thereby, the transmission signal power from the second antenna 101b is increased. The control for increasing the transmission power is gradually performed stepwise in order to minimize the influence on the current communication state.

As a result, in each mobile station, the signal power is increased, while the increase in the interference power is small, and the improvement of the communication quality is improved in combination with the diversity effect. In addition, when the traffic is not so high, the interference power due to the interference wave in the sector is inevitably small, and there is no limitation on the mobile stations that can be accommodated in the sector due to the interference power.

Conversely, when the number of mobile stations in the sector 102 increases and the traffic in the sector 102 increases to a certain value or more, this state is determined by the traffic detection circuit 106.
And gives a command to the transmission power control circuit 108 to
The transmission power of the transmission unit 103b is reduced. This allows
The transmission signal power from the second antenna 101b is reduced, and the interference power of each mobile station in the sector 102 is reduced. Also in this case, the reduction control of the transmission power is performed gradually in stages in order to minimize the influence on the current communication state.

As a result, a communication path between a new mobile station and a base station can be secured in the sector 102, and a new communication request can be satisfied.

As described above, when the transmission signal power from the second antenna 101b is reduced with an increase in traffic in the sector 102, the diversity effect is partially reduced, but the first antenna 101a is reduced. Since the signal is transmitted with constant power enough for the signal to reach all the sectors to be served by the base station, communication between each mobile station and the base station is secured.

Next, in the CDMA cellular system which is generally used, when a mobile station is communicating with a base station in a certain sector, a fault existing on a propagation path between the base station and the mobile body is generated. Due to the influence of an object, there is a case where the received power from another sector is constantly large. This state is
It can be recognized by the reception level of the information broadcast channel that is constantly transmitted. In this case, the mobile station requests a handoff to another sector. The base station determines whether or not to permit handoff based on the handoff request. If so, the base station transmits a required signal and starts communication with the mobile station in another sector. In addition, the base station has a function of detecting that there is some difference in the average signal level reaching the mobile station from the antenna of the base station in response to the handoff request.

In the present invention, using this function, the base station moves between sector 102a covered by first antenna 101a and sector 102b covered by second antenna 101b in the same sector 102. In response to a handover request from the station, a handover process is performed to determine whether or not to permit handoff, and if so, transmit a required signal to the mobile station and start communication with the mobile station. Handover detector 107
Detects the number of mobile stations in the handover state among all the mobile stations in the sector 102. Then, the transmission power control circuit 1 is controlled so that the number of mobile stations in the handover state detected by the handover detection unit 107 falls within a certain value.
08, and the transmission power control circuit 1
08 controls the transmission power of the second transmission unit 103b.

As a result, the transmission power distribution between the first antenna 101a and the second antenna 101b covering the same sector 102 depends on the first antenna 101a of the same sector 102.
Sector 102a covered by the second antenna 1
The number of mobile stations in a handover state with the sector 102b covered by 01b is controlled within a certain value. Further, when the number of mobile stations in the handover state detected by the handover detection unit 107 becomes equal to or smaller than another predetermined value, the power distribution is controlled to be changed in a manner opposite to the above case, whereby the handover state is changed. The number of mobile stations is controlled so as to be within a certain upper and lower limit.

Thus, the sector 102a covered by the first antenna 101a in the same sector 102,
Sector 102 covered by second antenna 101b
b) controlling the number of mobile stations in a handover state between the two antennas to be within a certain upper and lower limit, thereby changing the transmission power distribution between the two antennas and approaching the optimum power distribution. And transmission at an unnecessarily large transmission power can be avoided.

FIGS. 2 and 3 are flowcharts showing an example of transmission power control according to the embodiment of the present invention. In these flowcharts, as in the above description, the first antenna 1
From 01a, a signal is transmitted with constant power enough for the signal to reach all sectors to be served by the base station, and transmission power control is to be performed for the second antenna 101b.

First, referring to FIG. 2, in step S1, transmission power control of second antenna 101b is started.
The start operation of the transmission power control in step S1 is performed at predetermined time intervals once started. Therefore, even during the processing of the subsequent steps S2 to S13, the flow control is newly started every time the transmission power control starts in step S1.

In step S2, it is determined whether the current traffic in the sector 102, that is, the communication capacity has a margin. If the communication capacity is not enough (No),
Return to the original. The operation in this case will be described with reference to FIG. If there is enough communication capacity (Yes), the process proceeds to step S3.

In step S3, the second antenna 101b
Starts transmission with a code different from other codes already used. The transmission power at the start of the transmission starts from a small value.

In step S4, the second antenna 101b
Is gradually increased over time.

In step S5, the first antenna 101a and the second antenna 101b from the mobile stations in the sector 102
The mobile station monitors the number of mobile stations issuing a simultaneous communication request (handover request) with the mobile station, and performs a handover process in response to the handover request.

In step S6, it is determined whether the number of mobile stations in the handover state performing transmission / reception with the two antennas 101a and 101b in the sector 102 has reached the first specified number n1 with respect to the total number N of service mobile stations. Judge.
When the number of mobile stations in the handover state has not reached the first specified number n1 (No), the process returns to step S4, and the transmission power from the second antenna 101b is increased. Steps S4 to S6 are repeated until the number of mobile stations in the handover state reaches the first specified value n1. When the number of mobile stations in the handover state has reached the first specified number n1 (Yes), it means that the transmission power from the second antenna 101b has been increased to a predetermined value, and Proceed to S7.

In step S7, the second antenna 101b
Is stopped, and the process proceeds to step S8.

In step S8, it is determined whether or not the number of mobile stations in the handover state within the sector 102 has reached the second prescribed number n2 (where n2> n1) with respect to the total number N of mobile stations serviced. When the number of mobile stations in the handover state has not reached the second specified number n2 (No),
It returns to step S5. In this case, the number of mobile stations in the handover state is between the upper limit value n2 and the lower limit value n1, and the control target is attained.
Steps S5 to S8 are repeated. When the number of mobile stations in the handover state has reached the second prescribed number n2 (Yes), it means that the transmission power from the second antenna 101b has exceeded a predetermined value. The process proceeds to step S9.

In step S9, the second antenna 101b
Is gradually reduced over time, and the process returns to step S5.

As described above, steps S4 to S9
By this operation, the transmission power of the first antenna 101b is controlled such that the number of mobile stations in the handover state is settled between the upper limit value n2 and the lower limit value n1.

Referring to FIG. 3, transmission power control of second antenna 101b is started in step S1, and it is determined in step S2 whether the communication capacity in sector 102 has room. Steps S1 and S2 are the same as steps S1 and S2 in FIG.

If it is determined in step S2 that the communication capacity is not enough (No), the process proceeds to step S10.

In step S10, the second antenna 101
The transmission power from b is gradually reduced over time, and the process proceeds to step S11.

In step S11, the first antenna 101 from the mobile station in the handover state within the sector 102
The number of mobile stations issuing a call request only by a is monitored, and handover termination processing is performed.

In step S12, it is determined whether or not all the mobile stations in the sector 102 have completed the handover. If all the mobile stations have not completed the handover (No), the process returns to step S10. Also, when all the mobile stations have completed the handover (Yes)
Proceeds to step S13.

In step S13, the second antenna 101
Stop transmission from b.

As can be seen from the flow charts of FIGS. 2 and 3, when there is room in the communication capacity with the mobile station existing in the sector 102, the transmission power from the second antenna 101b is increased, and If there is not enough capacity,
Since the transmission power from the antenna 101b is reduced, when the base station antenna diversity scheme is performed, the traffic condition of the sector 102, that is, the communication capacity is monitored.
While the base station transmits at a transmission power enough to reach all of the sectors 102 to be serviced by the base station, the maximum number of mobile stations that can be accommodated in one sector due to an increase in interference power or the like depending on the traffic situation. The transmission power can be controlled so that the value does not decrease.

The number of mobile stations in a handover state between the sector 102a covered by the first antenna 101a and the sector 102b covered by the second antenna 101b in the same sector 102 is defined as an upper limit n2 and a lower limit n2. Since the control is performed so as to be within the value n1, the transmission power distribution between the two antennas can be made closer to the optimum power distribution, and transmission at an unnecessarily large transmission power can be avoided.

[0059]

According to the configuration of the first aspect, in a CDMA cellular radio base station of a base station antenna diversity system, when there is room in traffic in each sector, the mobile station increases the transmission power from the antenna and moves. It is possible to increase the signal power to interference power ratio of the station and improve the communication quality. Also, if the traffic increases in each sector, reduce the transmission power from one antenna,
Although the diversity effect is partially reduced, it is possible to secure a necessary communication path and avoid a decrease in the number of mobile stations that can be accommodated in one sector.

According to the configuration of claim 2, the same effect as in claim 1 can be obtained, and the number of mobile stations in a handover state within the same sector can be monitored, so that the transmission power between the two antennas can be improved. Can be changed so as to approach the optimum power distribution, and transmission with unnecessary large transmission power can be avoided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a CDMA cellular radio base station according to an embodiment of the present invention.

FIG. 2 is a flowchart showing an example of transmission power control according to the embodiment of the present invention.

FIG. 3 is a flowchart illustrating an example of transmission power control according to the embodiment of the present invention.

FIG. 4 is a configuration diagram of a conventional CDMA cellular radio base station.

[Explanation of symbols]

 101a, 101b First and second antennas 102 Sectors 103a, 103b First and second transmitters 104a, 104b First and second receivers 105 Mobile station 106 Traffic detector 107 Handover detector 108 Transmission power controller

Claims (2)

[Claims] 1. A plurality of antennas are installed, a service area is divided into a plurality of sectors, and at least two of the plurality of antennas are arranged so as to cover the same sector among the plurality of sectors. Base station antenna diversity CDMA cellular radio base station, wherein at least one of at least two antennas covering the same sector is a base station according to a traffic situation of a sector covered by the antenna. CDMA cellular radio base station characterized in that the transmission power of communication from a mobile station to a mobile station is time-variably controlled. 2. The CDMA cellular radio base station according to claim 1, wherein the transmission power distribution between antennas covering the same sector is set such that the number of mobile stations in the same sector handover state is within a certain upper and lower limit. A CDMA cellular radio base station.