Transmission power control of a random access channel

BACKGROUND OF THE INVENTION

1. Field of the Invention

0001The present invention relates to a mobile communication terminal, and more particularly a mobile communication terminal transmitting a random access channel (RACH) signal and a method thereof.

2. Description of the Related Art

0002Generally, each base station in a cell in a mobile communication network broadcasts a broadcast control channel signal to the mobile communication terminals by means of a broadcast control channel (BCCH). The BCCH is a downlink channel transmitted in a single direction in a point-to-multi point method and is a channel used for notifying the mobile communication terminals of general cell information. All mobile communication terminals are required to receive a BCCH signal before connecting to a mobile communication network. Conventional mobile communication terminals synchronize with the strongest BCCH signal received from base stations in each cell. Then, when a user makes a request for a network connection such as communication or data downloading, the conventional mobile communication terminals originate RACH signals and perform a call allocation request. The RACH is an uplink channel transmitted in a single direction and is a channel used for transmitting a message such as a response message to a call allocation request or question from a network.

0003When originating the RACH signals as described above, the conventional mobile communication terminals have always originated the RACH signals at the maximum power level regardless of their own positions. However, since the mobile communication terminals originate the RACH signals at the maximum power level, the power of terminals is unnecessarily consumed and the interference effect occurs in a mobile communication network.

0004<patcit id="pcit0001" dnum="US5564075A"><text>US-A-5 564 075</text></patcit> refers to a method and system for controlling the power at which an access packet is sent by a mobile in a mobile radio system. A method is described in a situation when a mobile, MS, enters a cell managed by a base transceiver station, BTS. In the case of a GSM system, the BTS can be connected to a base station controller, BSC, by a digital link L which can be of the ABIS,type. A broadcast channel, BCCH, is transmitted at all times at a constant power level set by a system operator. An additional message TPo(BTS) is broadcast on this channel indicating the carrier transmit power to which a corrective term can be added. The MS can therefore determine the attenuation of the messages reaching it by comparing the power at which the messages are received with the power with which they were transmitted. It can then transmit on the Random Access Channel, RACH, an access packet which is received and processed by the BTS. An optimal transmit power TPo(MS) depends on a number of system parameters which can be either fixed or transmitted by the BTS on the broadcast channel BCCH. The optimal transmit power for the access packet is determined on the basis of an estimated propagation loss and parameters of the mobile radio system.

0005<patcit id="pcit0002" dnum="WO0128126A"><text>WO 01/28126 A</text></patcit> refers to a determination of a transmit power value P_RACH for a connection request message, RACH, from a mobile user equipment unit to a telecommunications network by using a target ratio of received energy to an interference value and a modification factor. The modification factor allows for the calculation of the transmit power for the connection request message to be adaptive with respect to a change in characteristic of the mobile user equipment unit.

0006<patcit id="pcit0003" dnum="WO0056103A"><text>WO 00/56103 A</text></patcit> refers to a subscriber unit and method of cell selection for a cellular communication system. In many cases, a subscriber unit can potentially be served by one or more base stations out of a set of base stations. Each of the base stations transmits a downlink pilot signal. The subscriber unit can receive the downlink pilot signal from all potentially serving base stations. As well as transmitting the downlink pilot signal, the base stations also transmit broadcast information. This broadcast information includes uplink characteristics information which informs the subscriber units of certain characteristics of the uplink conditions. Specifically, the uplink characteristics information includes information of the uplink interference level, the uplink congestion, and the downlink transmit power. The uplink interference level has impact on how much transmit power the subscriber unit needs in order to be received at the base stations. A specific example of a congestion indicator is the number of RACH attempts directed at a base station. The subscriber unit is capable of estimating the path loss to each of the base stations by making use of the receive level of the downlink pilot, which it measures, and the transmit level of the pilot, which it can read on the broadcast channel. This is an estimate of the downlink path loss. Based on the assumption that the path losses in an uplink and a downlink is identical or very close, the downlink transmit power level is an indirect indication of characteristics related to the uplink. From its knowledge of the path losses to each base station in a target set and also of uplink interference floors at each of these base stations, the subscriber unit can calculate the required transmit power for the access message.

SUMMARY OF THE INVENTION

0007Accordingly, the present invention has been made to solve at least the abovementioned problems occurring in the prior art.

0008It is the object of the present invention to provide an improved mobile communication terminal and an improved method, by which an optimized transmission power level of a RACH signal is calculated.

0009This object is solved by the subject matter of the independent claims.

0010Preferred embodiments are defined by the dependent claims.

0011According to an aspect of the present invention, there is provided a mobile communication terminal and a method, by which a proper transmission power level of a RACH signal is calculated according to a position of the mobile communication terminal in a cell, and the RACH signal is transmitted at the calculated transmission power level instead of at a maximum power level.

0012In order to accomplish the aforementioned object, according to one aspect of the present invention, there is provided a mobile communication terminal including a radio unit for receiving a broadcast control channel signal including cell information and transmitting a random access channel signal for a call allocation request to a corresponding cell; a reception power level measurement unit for measuring reception power levels of the broadcast control channel signal received in the radio unit; a transmission power level calculation unit for calculating a transmission power level of the random access channel signal by means of the measured reception power levels and the cell information contained in the broadcast control channel signal; a key input unit for outputting a signal corresponding to a network connection request by a user; and a controller for acquiring system information of the corresponding cell after synchronizing with a strongest broadcast control channel signal according to the measured reception power level, and controlling the random access channel signal for a call allocation request to be transmitted at the calculated transmission power level when the signal corresponding to the network connection request is input.

0013In order to accomplish the aforementioned object, according to one aspect of the present invention, there is provided a method for transmitting a random access signal at various transmission power levels by a mobile communication terminal, the method including the steps of receiving broadcast control channel signals and measuring reception power levels of the broadcast control channel signals; synchronizing with a broadcast control channel signal having a highest power level from among the measured reception power levels; acquiring system information related to a corresponding cell from the synchronized broadcast control channel signal; calculating a transmission power level value of the random access channel signal for a call allocation request based on the measured reception power levels and the acquired cell information when a the mobile communication terminal requests a network connection; and transmitting the random access channel signal at the calculated transmission power level.

BRIEF DESCRIPTION OF THE DRAWINGS

0014The above object and other aspects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: <ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">FIG. 1</figref> is a block diagram of a mobile communication terminal according to an embodiment of the present invention; and</li><li><figref idref="f0002">FIG. 2</figref> is a flowchart illustrating an originating process of an RACH signal by a mobile communication terminal according to an embodiment of the present invention.</li></ul>

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

0015Hereinafter, a preferred embodiment according to the present invention will be described with reference to the accompanying drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may obscure the subject matter of the present invention.

0016<figref idref="f0001">FIG. 1</figref> is a block diagram of a mobile communication terminal according to an embodiment of the present invention. Referring to <figref idref="f0001">FIG. 1</figref>, the mobile communication terminal according to the embodiment of the present invention includes a controller 102, a radio unit 104, a reception power level measurement unit 106, a renewing unit 108, a transmission power level calculation unit 110, a memory unit 112, and a key input unit 114.

0017The controller 102 performs a general control operation for the mobile communication terminal. When the mobile communication terminal is powered on, the controller 102 measures reception power levels of a BCCH signal, synchronizes with the strongest BCCH signal, and acquires system information of a corresponding cell. Also, when a network connection request signal for communication or data downloading is input to the mobile communication terminal, the controller 102 calculates an RACH transmission power level based on the reception power levels of the BCCH signal and reception characteristic information of the cell contained in the system information, and performs a control operation necessary for transmitting a RACH signal having the calculated transmission power level.

0018The radio unit 104 receives the BCCH signal broadcast from an external base station and transmits the RACH signal for a call allocation request to a base station in a corresponding cell.

0019The reception power level measurement unit 106 measures the power levels of the BCCH signal received in the radio unit 104. The renewing unit 108 may include a timer, etc., and instructs the reception power level measurement unit 106 to measure the power levels of the BCCH signal, received in the radio unit 104, after each predetermined time period (e.g., 5 seconds).

0020The transmission power level calculation unit 110 receives the power levels of the BCCH signal measured by the reception power level measurement unit 106, receives the reception characteristic information contained in the system information, and calculates the transmission power level of the RACH signal for the call allocation request.

0021The memory unit 112 stores the calculated transmission power level of the RACH signal.

0022The key input unit 114 includes keys to enable entry of to a request for communication or data downloading and outputs a network connection request signal when a user presses the key corresponding to the request for communication or data downloading.

0023<figref idref="f0002">FIG. 2</figref> is a flowchart illustrating an originating process of an RACH signal by a mobile communication terminal according to an embodiment of the present invention. The originating process of the RACH signal by the mobile communication terminal will be described in detail with reference to <figref idref="f0001">FIGs. 1</figref> and <figref idref="f0002">2</figref>.

0024When the mobile communication terminal is powered on in step 202, step 204 is performed. Even when the mobile communication terminal moves into a certain cell, step 204 may be performed. In step 204, the mobile communication terminal measures the reception power levels of a BCCH signal received through the radio unit 104. Then, in step 206, the mobile communication terminal synchronizes with the BCCH signal corresponding to the strongest power level from among the measured reception power levels of the BCCH signal. Then, in step 208, the mobile communication terminal acquires the system information of a corresponding cell from the BCCH signal with which the mobile communication terminal has synchronized. The system information includes reception characteristic information of the corresponding cell.

0025As described above, after the power levels of the BCCH signal and the reception characteristic information the corresponding cell are obtained, the mobile communication terminal determines whether a network connection request exists or not in step 210 and if a network connection request exists, step 220 is performed and if not, the mobile communication terminal waits for the network connection request. For instance, when a user requests a communication link or a data downloading process, step 212 is performed. The mobile communication terminal calculates the transmission power level of a RACH signal, which is to be transmitted for a call allocation request, by means of the reception power levels of the BCCH signal and the reception characteristic information of the cell contained in the system information.

0026For example, the mobile communication terminal calculates the transmission power level of the RACH signal by means of the following Equation (1). <maths id="math0001" num="(1)"><math display="block"><mi>RACH transmission power level</mi><mspace width="1em" /><mfenced><mi>Ptx</mi></mfenced><mo mathvariant="normal">=</mo><mi>min</mi><mfenced open="{" close="}"><mi>ra</mi><mo mathvariant="normal">-</mo><mi>rb</mi><mo mathvariant="normal">-</mo><mfenced><mi mathvariant="normal">C</mi><mo mathvariant="normal">+</mo><mn mathvariant="normal">48</mn></mfenced><mo mathvariant="normal">,</mo><mi>PMAX</mi></mfenced></math><img file="EP1555765B1_D0001.tif" /></maths>

0027This equation is disclosed in an output power section (10.2.1) of a mobile communication terminal of a GPRS (General Packet Radio Service) 505.08 series.

0028In this equation, ra is a maximum transmission power level of the mobile communication terminal. In the case of a mobile communication terminal employing a GSM400 (Global System for Mobile communications), a GSM900, or a GSM850 method in a GPRS specification, ra is defined to have a value of 39 dBm. In the case of a mobile communication terminal employing a DCS 1800 (Digital Cellular Service) or a DCS 1900 method, ra is defined to have a value of 36 dBm.

0029rb is the reception characteristic level of the cell contained in the system information of the acquired corresponding cell, is defmed in the GPRS specification 04.60, and has a value between 0 dBm and 62 dBm. An example of the rb value used herein is 40 dBm which is an experimental value.

0030C is the reception power level of the BCCH signal of a main cell measured in the mobile communication terminal. For example, C has a value of -50 dBm to -110 dBm. PMAX is a permissible maximum output power level of the cell shown in a GSM specification. Accordingly, the GSM has a value of 33 dBm and the DCS has a value of 30 dBm.

0031When solving the aforementioned equation in detail by means of the values as described above, in the case of the GSM, Ptx becomes min {39-40-(C+48), 33}, that is, (-C-49, 33). Further, in the case of the DCS, Ptx becomes min {36-40-(C+48), 30}, that is, (-C-52, 30).

0032In this way, the mobile communication terminal calculates the transmission power level of the RACH signal. Then, in step 214, the mobile communication terminal transmits the RACH signal at the calculated transmission power level. Accordingly, a mobile communication terminal according to the present invention does not transmit a RACH signal for a call allocation request at a maximum power level. Instead, the mobile communication terminal can transmit the RACH signal at a proper power level according to the position of the terminal in a cell.

0033A mobile communication terminal according to the present invention calculates a proper transmission power level of a RACH signal according to its own position in a cell, and transmits the RACH signal at the calculated transmission power level instead of a maximum power level. Accordingly, according to the present invention, when a RACH signal is transmitted, the power consumption of the terminal can be reduced and the interference effect of a mobile communication network can be prevented.