JP3386586B2 - Mobile communication method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile communication method such as a digital cellular telephone system.

[0002]

2. Description of the Related Art The multiple access system is a line connection system in which a plurality of stations simultaneously communicate in the same band. TDMA (Time Division Multiple Access)
Time-division multiple access that divides radio frequency into time
In this method, a user is assigned a specific time zone and communication is performed in the assigned time zone. In addition, CDMA (Co
de Division Multiple Access) is code division multiple access, and is a technique for performing multiple access by spread spectrum communication in which the spectrum of an information signal is spread over a band sufficiently wider than the original information bandwidth for transmission. CDMA
In the above, the direct spread method is a method in which a spread sequence code is directly multiplied by an information signal in spread. FDD (Freq
uency Division Duplex) is a method of performing communication by assigning different radio frequencies to each of transmission and reception. In addition, TDD (Time Division Duplex) is a transmission / reception same-band system, and is a system for performing communication by time-dividing the same radio frequency into transmission / reception.

Among these, the TDMA / TDD system in which TDMA and TDD are combined is a PHP (Personal H) which is a next-generation digital cordless telephone system in Japan.
andyPhone) system as well as DECT under development in Europe
Used in the system.

On the other hand, the CDMA system, as shown in "Spread spectrum communication system" (Mitsuo Yokoyama: Science and Technology Publishing Co.), can achieve higher frequency efficiency than TDMA in the cellular system, and can be used by more users. It is attracting attention as a system that can be accommodated. In the direct sequence CDMA system, when the desired transmitting station is far from the receiver and the non-desiring transmitting station is near, the received signal from the desired station is
There is a "far-and-far problem" in which the received signal of the interfering station has a larger received power, the cross-correlation between the spreading codes cannot be suppressed only by the processing gain (spreading gain), and communication with the desired station becomes impossible. . For this reason, in the cellular system, control of transmission power (power control) according to the state of each transmission line is indispensable in the line (uplink) from the mobile terminal to the base station side. 4-502284
The power control as shown in Japanese Patent No. 1 is performed to deal with the near-far problem.

[0005]

However, in the above-mentioned conventional uplink transmission power control in the CDMA system using direct spread, the other movement due to the processing delay from the estimation of the propagation loss to the actual change of the transmission power. The increase in the amount of interference with the terminal poses a problem. Especially in microcellular systems, deterioration of communication quality due to shadowing is an important issue. For example, as shown in FIG.
The power from the mobile station 11 reaching the base station 10 becomes weaker as the mobile station 11 that has been under the transmission power control of 1 moves away from the base station 10. The base station 10 controls the transmission power of the mobile station 11 to increase the transmission power amount of the mobile station 11. Propagation loss between the base station 12 and the mobile station 11, which was not under the control of the transmission power of the mobile station 11, is drastically improved by the influence of the building 13, which is an obstacle to radio wave propagation, and the transmission power of the mobile station 11 is It affects the communication between the base station 12 and all mobile stations connected to the base station 12 as interference. In order to prevent this, it is considered that the mobile station 11 sharply reduces the transmission power by itself, but as a result, the communication quality of the mobile station 11 is deteriorated.

[0006] The present invention solves such a conventional problem, and an object of the present invention is to provide an excellent mobile communication method capable of reducing deterioration of communication quality due to shadowing.

[0007]

In order to achieve the above-mentioned object, the present invention is directed to a cellular mobile communication system in which a plurality of base stations and a plurality of mobile stations communicate with each other, as a multiple access method, direct spreading in a cell. CDMA
CDMA-TDMA (Time Division) which uses a (Code Division Multiple Access) method and divides time into slots and allocates time slots for communication to each cell.
Division Multiple Access) method, further using a common uplink frequency and downlink frequency between cells, and using different frequencies for the uplink and downlink, a FDD (Frequency Division Duplex) method , Or when using the same frequency for the uplink and downlink
TDD (Time Division Dupl) that divides communication between
ex) method, each base station is
The mutual interference of the two is measured and the result is used
Musslots are set autonomously and mutual interference is large.
Different time slots between different base stations
Therefore, a time slot is set between base stations with little mutual interference.
This is set arbitrarily for each cell .

[0008]

Therefore, according to the present invention, even when the propagation loss between a mobile station and a base station which is not under the transmission power control by the mobile station is sharply improved by the shadowing, the mobile station is Is different from the time slot assigned to the base station in communication, since the time slot assigned to the base station with improved propagation loss is different, the transmission signal of the mobile station is with the base station with improved propagation loss. The quality of all mobile stations in a call is not deteriorated, and since the mobile station does not need to reduce the transmission power, the communication quality of the mobile station itself is not deteriorated. In addition,
Appropriate time slot allocation for each cell according to sudden changes
High-quality communication that can be applied without interference from other cells
Can be realized.

[0009]

【Example】

(Embodiment 1) Hereinafter, a first embodiment of the present invention will be described with reference to FIG.
Will be described with reference to. The present embodiment uses a direct spread CDMA system in a cell as a multiple access system, divides time into slots, and allocates time slots for communication to each cell CDMA-TDM.
The A method is used, and further, the CDMA-TDMA / FDD method that uses different frequencies for the uplink and the downlink is used.

In the CDMA-TDMA / FDD system of this embodiment, communication between a base station and a mobile station connected to the base station is multiplexed by using a spreading code, and as shown in FIG. Between the cells, a common uplink carrier frequency of a certain frequency and a common downlink carrier frequency of another frequency are used, and a fixed time period (frame) is divided into a number of time intervals (time slots). In the assigned time slot, the line is set up with a plurality of users by code division multiple access.

According to the above method, a common carrier frequency having different frequencies is used in the uplink and the downlink between the cells, and a time slot is assigned to each cell. Since other cells cannot communicate, high quality communication without interference from other cells can be performed.

(Embodiment 2) In the second embodiment of the present invention, instead of the FDD in the first embodiment, communication is performed by dividing the time by using the same frequency for the uplink and the downlink. The CDMA-TDMA / TDD method is used. In the CDMA-TDMA / TDD system of this embodiment, communication between a base station and a mobile station connected to the base station is multiplexed by using a spread code, and as shown in FIG. The carrier frequency is used to divide a fixed time period (frame) into a number of time intervals (time slots), and each cell is assigned time slots to perform line setting with multiple users by code division multiple access.

According to the above method, the same carrier frequency is used for each cell and a time slot is assigned to each cell, so that while one cell is communicating in the time slot, the other cell cannot communicate. It is possible to perform high-quality communication without interference from.

Further, in the TDD system, since the carrier frequencies used in the uplink and the downlink are the same, transmission and reception can be performed by the modulator corresponding to one carrier frequency, and there is an advantage that the scale of the mobile station can be small. is there.

(Embodiment 3) In the third embodiment of the present invention, in the CDMA-TDMA / FDD system of the first embodiment, different time slots are allocated between base stations which have large mutual interference, and The time slot is arbitrarily set for each cell between base stations with less interference.

For example, as shown in FIG. 3, cells A, B,
In cells such as C and D and cells E, F, and G where mutual interference is large, different time slots # 1, # 2, and # are used.
3, # 4 and # 1, # 3, # 4 are assigned, and in cells I and H where mutual interference is small, an arbitrary time slot is set for each cell. In this case, the same # 4 is set, but since there is no mutual interference in cells I and H, there is no inconvenience even if the same time slot is used.

According to the above method, by changing the time slot allocation depending on the frequency of mutual interference, even if the common carrier frequency is used, the influence of interference between cells does not affect each other, and the user does not Two methods can be switched and used in a system with one synthesizer.

(Fourth Embodiment) In the fourth embodiment of the present invention, in the CDMA-TDMA / TDD system of the second embodiment, different time slots are allocated between base stations having large mutual interference, and The time slot is arbitrarily set for each cell between base stations with less interference.

For example, as shown in FIG. 3, cells A, B,
In cells such as C and D and cells E, F, and G where mutual interference is large, different time slots # 1, # 2, and # are used.
3, # 4 and # 1, # 3, # 4 are assigned, and in cells I and H where mutual interference is small, an arbitrary time slot is set for each cell. In this case, the same # 4 is set, but since there is no mutual interference in cells I and H, there is no inconvenience even if the same time slot is used.

According to the above method, by changing the time slot assignment depending on the amount of mutual interference, even if the same carrier frequency is used, the influence of interference between cells does not affect each other, and the user can Two methods can be switched and used in a system with one synthesizer.

Further, in the TDD system, since the carrier frequencies used in the uplink and the downlink are the same, transmission and reception can be performed by a modulator corresponding to one carrier frequency, and there is an advantage that the scale of the mobile station can be small. is there.

(Embodiment 5) In the fifth embodiment of the present invention,
In the third embodiment, instead of allocating time slots in advance according to the amount of mutual interference, mutual interference with surrounding base stations is measured, and the time slot to be used is determined from the measurement result. The allocation is done autonomously.

For example, as shown in FIG. 4, when the received power measuring means of the mobile station detects a sudden increase in the received power amount (step 1), the sudden increase in the received power amount of the mobile station belongs to the mobile station. If it is not due to the transmission power control of the base station in the cell but due to the sudden change of the propagation path condition with the base station belonging to another cell (step 2), the identification of the base station of the other cell for which the power amount is rapidly increased The numbers are stored (step 3), and the stored numbers are used for future time slot allocation (step 4), and time slots are allocated so that mutual interference is reduced.

By using this method, appropriate time slot allocation can be performed for each cell according to a sudden change in the propagation path, and high quality communication without interference from other cells can be realized.

(Embodiment 6) In the sixth embodiment of the present invention,
In the fourth embodiment, instead of allocating time slots in advance according to the frequency of mutual interference, mutual interference with surrounding base stations is measured, and the time slot to be used is determined from the measurement result. The allocation is done autonomously.

For example, as shown in FIG. 4, when the received power measuring means of the mobile station detects a sudden increase in the received power amount (step 1), the sudden increase in the received power amount of the mobile station belongs to the mobile station. If it is not due to the transmission power control of the base station in the cell but due to the sudden change of the propagation path condition with the base station belonging to another cell (step 2), the identification of the base station of the other cell for which the power amount is rapidly increased The numbers are stored (step 3), and the stored numbers are used for future time slot allocation (step 4), and time slots are allocated so that mutual interference is reduced.

By using this method, appropriate time slot allocation can be performed for each cell according to a sudden change in the propagation path, and high-quality communication without interference from other cells can be realized.

Further, in the TDD system, since the carrier frequencies used in the uplink and the downlink are the same, it is possible to perform transmission / reception with the modulator corresponding to one carrier frequency 8, which has the advantage that the scale of the mobile station can be small. is there.

(Seventh Embodiment) In the seventh embodiment of the present invention, in the sixth embodiment, the time slot allocation to be used is autonomously assigned based on the measurement result of the mutual interference with the surrounding base stations. Instead, each base station directly receives the downlink signals of the surrounding base stations, detects the reception level, and measures the mutual interference using the reception level to allocate time slots. Is to be performed autonomously.

For example, as shown in FIG. 5, cell A and cell B
Assume that the mutual interference amount is large. When the time slot T _A is assigned to the cell A, the communication in the cell B is not performed while the cell A is communicating using the time slot T _A. The station can directly receive the downlink signal from the base station located in the cell assigned to the time slot T _A , know the assignment of the time slot, and measure the interference amount. The base station in the cell B can autonomously set the time slot T _B used by the cell B using the measurement result.

In the TDD system, since the carrier frequency used in the uplink and the carrier frequency used in the downlink are the same, transmission and reception can be performed by the modulator corresponding to one carrier frequency. This has an advantage that it is easy to monitor a time slot other than the time slot assigned to each cell in a system of the same scale as the conventional system.

[0032]

As is apparent from the above embodiment, the present invention assigns time slots between cells in transmission / reception between a base station and a mobile station, and performs code division multiple access in the time slots assigned by each cell. I will do so with the mobile station,
Even if the propagation loss with a base station that is not under the transmission power control of the mobile station is drastically improved, it affects the communication quality of all other mobile stations connected to the base station. This phenomenon disappears and high quality mobile communication can be realized. In addition, according to one embodiment of the present invention, a time interval is set between cells.
After allocating lots, a common upstream for each cell
In addition to using the line frequency and the downlink frequency,
FDD method using different frequencies for line and downlink
ing. In another aspect, the common
The reverse line frequency and the down line frequency are used, and
The same frequency is used for the line and downlink to divide the time and communicate.
It uses the TDD method of communicating. This makes the same
Time slots are not used between adjacent base stations
Since it is possible to change the
A mobile station under the control of the transmission power of the base station suddenly appeared
Even if the sudden movement due to time division
Shadow communication is not possible because the communication timing with the station does not match.
Problem can be prevented. Also
For the base station, it is unacceptable during transmission power control operation.
Move to a different time slot if a conflict is detected
The effect of being able to (escape) is obtained.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a mobile communication method according to a first embodiment of the present invention.

FIG. 2 is a conceptual diagram of a mobile communication method according to a second embodiment of the present invention.

FIG. 3 is a conceptual diagram of a mobile communication method in third and fourth embodiments of the present invention.

FIG. 4 is a flow chart of inter-cell time slot allocation in the mobile communication method in fifth and sixth embodiments of the present invention.

FIG. 5 is a conceptual diagram of a mobile communication method in a seventh embodiment of the present invention.

FIG. 6 is a schematic diagram illustrating shadowing in a CDMA system.

[Explanation of symbols]

10 base stations 11 mobile stations 12 base stations 13 Buildings that become obstacles to radio wave propagation

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Osamu Kato 4-3-1, Tsunashima-higashi, Kohoku-ku, Yokohama-shi, Kanagawa Matsushita Communication Industrial Co., Ltd. (56) Reference JP-A-5-145470 (JP, A) ) JP-A-6-104865 (JP, A) JP-A-6-104820 (JP, A) JP-A-7-284149 (JP, A) Actually open flat 2-64250 (JP, U) (58) Field (Int.Cl. ⁷ , DB name) H04B 7/26

Claims (3)

(57) [Claims] 1. In a cellular mobile communication system in which communication is performed by a plurality of base stations and a plurality of mobile stations, direct-spread CDMA is used in a cell as a multiple access method.
CDMA-TDMA (Time Division) which uses a (Code Division Multiple Access) method and divides time into slots and allocates time slots for communication to each cell.
Division multiple access) system, further using an up-link frequency and a down-link frequency common to each cell, and an FDD (Frequency Division Duplex) system using different frequencies for the up-link and the down-link, and each base station However, the
The time slot used to measure the interference and use the results.
Base stations that set each other autonomously and have large mutual interference.
Assign different time slots to each other
Time slots are assigned to each cell between base stations with less interference.
A mobile communication method characterized by being arbitrarily set . 2. In a cellular mobile communication system in which communication is performed by a plurality of base stations and a plurality of mobile stations, direct spread CDMA is performed in the cell as a multiple access method.
CDMA-TDMA (Time Division) which uses a (Code Division Multiple Access) method and divides time into slots and allocates time slots for communication to each cell.
Division Multiple Access) method, a common uplink frequency and downlink frequency are used in each cell, and the same frequency is used for the uplink and downlink to divide the time and perform communication.
ision duplex) method , each base station is
Measuring the mutual interference with the base station, and using the result.
Set the time slot to be used autonomously
Different time slots between base stations with large interference
Is assigned to the base stations to reduce the time
A mobile communication method characterized in that a lot is arbitrarily set for each cell . 3. The base station directly receives a downlink signal of a base station existing around it, detects the reception level thereof, and measures mutual interference using the reception level. 2. The mobile communication method described in 2 .