JP3313595B2 - Pilot channel transmission method in CDMA mobile communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a code division multiple access (hereinafter abbreviated as CDMA) mobile communication system in which a plurality of cells are provided with base stations, and each base station is assigned differently. The present invention relates to a pilot channel transmission method in a CDMA mobile communication system in which a mobile station transmits a pilot channel spread with a spreading code, and a mobile station determines a serving cell by receiving the pilot channel.

[0002]

2. Description of the Related Art In a downlink radio channel in a CDMA mobile communication system, all downlink radio channels transmitted to a plurality of other mobile stations in the same cell in all mobile stations generally become interference power, and the reception quality is reduced. Deterioration or deterioration of the radio channel capacity.

In a cellular mobile communication system, each base station transmits a channel for identifying a base station, called a pilot channel. The mobile station determines the serving cell by measuring the received power of the pilot channel. Further, the pilot channel can be used for selecting an optimal path for path diversity reception, and can also be used for transmitting pilot symbols for synchronous detection of a communication channel.

[0004] In order to solve the near-far problem which is a problem peculiar to CDMA, the communication channel is controlled in transmission power so as to have a minimum required transmission power. Thereby, the transmission power differs for each user and changes with time. On the other hand, the pilot channel needs to be able to be constantly received by all mobile stations, including mobile stations located in adjacent cells, in order to use the mobile station in determining the serving cell of the mobile station. If the spreading factor is the same, it is necessary to transmit at a constant transmission power relatively larger than the communication channel. Here, the spreading factor is “the ratio of the spreading chip rate to the information bit rate”.

FIG. 3 shows a conventional pilot channel transmission method. Conventionally, one of a plurality of spreading codes is assigned as a spreading code for a pilot channel, the pilot channel is always transmitted with this spreading code, and the other spreading codes are used for a communication channel. Also, the spreading factors of the pilot channel and the communication channel were the same. In this method, a pilot channel is transmitted with a relatively larger transmission power than a communication channel so that a mobile station located in an adjacent cell can receive its own pilot channel in order to determine a cell in which the mobile station is located. Needed.

[0006]

In a CDMA mobile communication system, the radio channel capacity is determined by the interference power. In the conventional method, as described above, it was necessary to transmit a pilot channel with relatively higher transmission power than a communication channel. For this reason, there is a problem that a large interference is given to the own cell and other cells, and the capacity is deteriorated.

In order to solve this problem, a method of intermittently transmitting a pilot channel as shown in FIG. 4 can be considered. According to this method, the influence of interference of the pilot channel on its own cell and other cells can be reduced as compared with the conventional method of continuously transmitting pilot channels shown in FIG. However, when using this method, the mobile station accurately grasps the timing at which the pilot channel is transmitted, receives the pilot channel during a short transmission time, and determines the serving cell and selects the optimal path for path diversity reception. In addition, pilot symbols must be extracted for synchronous detection, and the accuracy may be lower than when pilot channels are continuously transmitted. Further, in order to guarantee the accuracy, accumulation processing and high-speed processing are required, and as a result, there is a problem that the device configuration becomes complicated.

[0008] The present invention has been made in view of the above,
The purpose is to reduce the transmission power by increasing the spreading factor of the pilot channel, reduce the interference power to other cells and the own cell, and continuously transmit the pilot channel to keep the mobile station It is an object of the present invention to provide a pilot channel transmission method in a CDMA mobile communication system that can perform a serving cell determination, optimal path selection, pilot symbol extraction, and the like with a simple configuration.

[0009]

In order to achieve the above object, according to the present invention, a base station is provided in each of a plurality of cells, and each base station uses a spreading code assigned differently. A pilot channel transmission method in a CDMA mobile communication system, in which a spread pilot channel is transmitted, and a mobile station determines a serving cell by receiving the pilot channel, wherein the spreading factor of the pilot channel is determined by spreading a communication channel. The gist is to make the ratio larger than the ratio and to reduce the transmission power.

According to a second aspect of the present invention, a base station is provided in each of a plurality of cells, each base station transmits a pilot channel spread with a differently assigned spreading code, and the mobile station transmits the pilot channel. A pilot channel transmission method in a CDMA mobile communication system for determining a serving cell by receiving a pilot channel, wherein a spreading factor of the pilot channel is set to a maximum spreading factor usable as a system, and transmission power is reduced. Is the gist.

According to a third aspect of the present invention, a base station is provided in each of a plurality of cells, each base station transmits a pilot channel spread with a differently assigned spreading code, and the mobile station transmits the pilot channel. A pilot channel transmission method in a CDMA mobile communication system in which a serving cell is determined by receiving a pilot channel, wherein a spreading factor of the pilot channel is made larger than an average value of a spreading factor that can be used as a system, and transmission power is increased. Is to be reduced.

According to a fourth aspect of the present invention, in the first, second or third aspect, the pilot channel is continuously transmitted.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating an example of a pilot channel allocation method for implementing a pilot channel transmission method in a CDMA mobile communication system according to an embodiment of the present invention. In the example of FIG. 1, the downlink radio channel is composed of X spreading codes (1 to X), spreading code 1 is allocated as a pilot channel, and the other codes are allocated as communication channels. The pilot channel has a larger spreading factor than the communication channel.

The transmission power of the communication channel is controlled so as to have a minimum necessary transmission power in order to solve the near-far problem which is a problem unique to CDMA. Thereby, the transmission power differs for each user and changes with time. On the other hand, the pilot channel needs to be able to be constantly received by all mobile stations, including mobile stations located in adjacent cells, in order to use the mobile station in determining the serving cell of the mobile station. If the spreading factor is the same, it is necessary to transmit at a constant transmission power relatively larger than the communication channel.

According to the present invention, since the pilot channel has a higher spreading factor than the communication channel, the number of spreading chips constituting one symbol increases, and if the occupied frequency bandwidth is constant (spread chip rate is constant), One symbol time is also increased. For example, assume that the original one symbol time is T and the received power is P. At this time, in the demodulation of the digital signal, the energy of the signal per symbol that affects the reception quality is T × P. Here, if the spreading factor is increased by N times, one symbol time becomes NT, so that the reception power may be P / N to obtain the same signal energy per one symbol. Therefore, according to the present invention, since the pilot channel has a higher spreading factor than the communication channel, the transmission power can be made smaller than the value required when the spreading factor is the same as that of the communication channel. For this reason, the interference power that the pilot channel gives to other cells and its own cell is also reduced, and the effect of capacity degradation can be reduced.

FIG. 2 shows an example of the configuration of a base station apparatus for implementing the present invention. The base station transmitter 1 shown in FIG. 2 includes a plurality of encoders 11a for encoding the broadcast information (information rate is low), control information, user information 1, user information 2,... 11b, ..., 11n,
A spread / modulator 13a (large spreading factor), a spread / modulator 13b, which spreads and modulates each of the encoded information,
, 13n and an amplifier 1 for amplifying each of these signals
, 15n, a multiplexer 17 for multiplexing these signals (indicated as MUX in the figure), and an antenna. In this configuration, the broadcast information transmitted on the pilot channel has a feature that the information amount is relatively small and is transmitted periodically, and is transmitted at a lower speed compared to other control information and user information of the communication channel. be able to. For this reason, the pilot channel can have a larger spreading factor than the other channels, and can transmit with reduced transmission power for the reasons described below.

Further, according to the present invention, since the transmission power of the pilot channel is relatively small, even if the transmission is performed continuously, the influence of interference on other cells or its own cell is small. For this reason, the mobile station can always receive the pilot channel continuously transmitted for cell selection, optimal path selection for path diversity, and pilot symbol extraction, thereby simplifying the device configuration.

Although the above description is for a case where only one spreading factor can be used as a system except for the pilot channel, a system in which the spreading factor differs for each channel is also conceivable. In the present invention, it is effective to increase the spreading factor of the pilot channel, but there is a system limit to the spreading factor of the pilot channel. As an example of giving a limit, if the spreading factor of the pilot channel is too large, the period of the spreading code becomes longer, and it takes time to pull in the synchronization when the power of the mobile station is turned on. The increase in the synchronization pull-in time lengthens the time from when the mobile device is turned on until the mobile device becomes usable, which adversely affects the serviceability to the user. In such a case, by maximizing the spreading factor of the pilot channel within the limits of this system,
A certain effect of the present invention can be obtained. Also, by setting the spreading factor of the pilot channel to a spreading factor larger than the average value of the spreading factors that can be used as a system, the same effect can be obtained.

[0019]

As described above, according to the present invention,
By making the spreading factor of the pilot channel larger than that of the communication channel, transmission power can be reduced.
By this means, it is possible to reduce interference that the pilot channel gives to other cells and its own cell.

Further, according to the present invention, since a large amount of interference is not given to the own cell and other cells with relatively small transmission power, the pilot channel can be continuously transmitted. A pilot channel can be received to select an optimal path necessary for cell selection and path diversity and to extract pilot symbols, thereby simplifying the device configuration.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a pilot channel allocation method for implementing a pilot channel transmission method in a CDMA mobile communication system according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a base station device in the CDMA mobile communication system shown in FIG.

FIG. 3 is a diagram for explaining a conventional pilot channel transmission method.

FIG. 4 is a diagram for explaining another conventional pilot channel transmission method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Base station transmitter 11 Encoder 13 Spreading / modulator 15 Amplifier 17 Multiplexer

────────────────────────────────────────────────── (5) References JP-A-9-327060 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04Q 7/34 H04Q 7/38

Claims (4)

(57) [Claims] 1. A base station is provided in each of a plurality of cells,
Each base station transmits a pilot channel spread with a differently assigned spreading code, and the mobile station receives the pilot channel to determine a serving cell, thereby providing a pilot channel transmission method in a CDMA mobile communication system. A method of transmitting a pilot channel in a CDMA mobile communication system, wherein a spreading factor of the pilot channel is made larger than a spreading factor of a communication channel and transmission power is reduced. 2. A base station is provided in each of the plurality of cells,
Each base station transmits a pilot channel spread with a differently assigned spreading code, and the mobile station receives the pilot channel to determine a serving cell, thereby providing a pilot channel transmission method in a CDMA mobile communication system. A pilot channel transmitting method in a CDMA mobile communication system, wherein the spreading factor of the pilot channel is set to a maximum spreading factor that can be used as a system, and transmission power is reduced. 3. A base station is provided in each of the plurality of cells,
Each base station transmits a pilot channel spread with a differently assigned spreading code, and the mobile station receives the pilot channel to determine a serving cell, thereby providing a pilot channel transmission method in a CDMA mobile communication system. A pilot channel transmission method in a CDMA mobile communication system, characterized in that a spreading factor of the pilot channel is made larger than an average value of a spreading factor that can be used as a system, and transmission power is reduced. 4. The method of transmitting a pilot channel in a CDMA mobile communication system according to claim 1, wherein the pilot channel is continuously transmitted.