WO2000057573A1 - Initial regulation of transmission power for the downlink direction of w-cdma radio communication systems - Google Patents

Abstract

The invention relates to a method for regulating the transmission power in a radio communication system, in which base stations and subscriber stations are connected by a radio interface. A subscriber station receives transmissions from a base station and determines a measured value therefrom for regulating the transmission power. According to the invention, the subscriber station links a service-dependent transmission power value to the measured value to obtain a regulating value and transmits said regulating value to the base station. The base station uses the regulating value to regulate the transmission power. The invention is characterised in that a reference to the desired service is immediately established, thus allowing the base station to calculate and regulate the necessary transmission power for the subsequent transmissions without further requests.

Description

description

Initial transmit power setting for the downward direction of W-CDMA radio communication systems

The invention relates to a method and a subscriber station which are designed for setting the transmission power for a base station. The invention relates in particular to the initial transmission power setting of the base station for a connection to the subscriber station within a W-CDMA radio communication system.

In radio communication systems, messages (for example voice, image information or other data) are transmitted as signals with the aid of electromagnetic waves via a radio interface. The radio interface relates to a connection between a base station and subscriber stations, it being possible for the subscriber stations to be mobile stations or fixed radio stations. The electromagnetic waves are emitted at carrier frequencies that lie in the frequency band provided for the respective system. For future radio communication systems, for example the UMTS (Universal Mobile Telecommunication System) or other 3rd generation systems, frequencies in the frequency band of approx. 2000 MHz are provided.

The 3rd generation radio communication systems are to use a subscriber separation method known as CDMA (Code Division Multiple Access). If the frequency band used is broadband, the radio interface is organized as a W-CDMA (wideband CDMA) radio interface. In all radio communication systems, but especially in those with a CDMA radio interface, a transmission power setting is necessary in order to keep the interference low and to compensate for fading effects in the reception power. A quick and accurate setting of the transmission power is desirable. worth, but assumes that the transmission power control has already settled.

From ARIB Specification: "Specification of Air-Interface for 3G Mobile System", Vol. 3, dated 14.1.99, p.94, it is known that after the subscriber station has received the reception power of transmissions from the base station within the established connection, uses a transmission power control in a closed loop. Depending on the quality of the reception power measurement, the closed loop regulates more or less quickly to the setpoint of the transmission power of the base station.

ARIB Specification: "Specification of Air-Interface for 3G Mobile System", Vol. 3, dated January 14, 1999, does not contain any information about the initial transmission power, i.e. before the closed loop in the connection regulates the transmission power. The problems that result from a too high initial transmission power, unnecessary interference, or from a transmission power that is too low, reduced transmission quality, have been neglected.

The invention is therefore based on the object of specifying a method and a subscriber station which result in an improved transmission power setting for the initial phase of a connection. The object is achieved by the method with the features of claim 1 and the subscriber station with the features of claim 10. Advantageous developments of the invention can be found in the subclaims.

In the method for setting the transmission power in a radio communication system, base stations and subscriber stations are connected to one another via a radio interface. A subscriber station receives transmissions from a base station and uses this to determine a measured value for the transmission power setting. According to the invention, the partial subscriber station a service-dependent transmission power value with the measured value to a control value and transmits this control value to the base station, which uses the control value for the transmission power ^setting . Because a connection to the desired service is immediately established, the base station can calculate and set the necessary transmission power for the next transmissions to the subscriber station without further inquiries.

The transmission power setting is particularly fast if the control value is transmitted in an RACH channel. The RACH channel (Random Access Channel) is used to establish a connection and to transmit short packet data in the upward direction. The correct transmission power value can thus already be established for the first, the initial transmission of a connection.

Further advantageous developments of the invention provide that measurement and transmission power values are related to reception powers or to signal / noise ratios. These values can be easily determined in the subscriber station and give one

Reference, which allows the transmission power of the connection to be set correctly in relation to the transmission power in an organizational channel that was previously measured by the subscriber station.

If the radio interface is organized according to a CDMA transmission method, which enables flexible capacity distribution by setting a spreading factor, the control value advantageously also takes into account a ratio of spreading factors between the received, measured transmissions and the desired service. The ratio can be set for the service by separate information or a previously signaled or defined spreading factor.

According to advantageous embodiments of the invention, the control value is based on a difference in the transmission powers or sig- nal / Rauschverhaltnisse the base station m gen a control channel and a channel for the desired service bezo ^¬. In this case, the base station from the control value, and for example, the transmission power in the control channel used before, the benotigte transmission power itself quickly calculate. Alternatively, the subscriber station can carry out the calculation if the transmission power in the organization channel is known, so that the control value is directly related to the transmission power of the base station for the desired service.

In a further development of the invention it is provided that the control value is related to a value which compares the measured value with a minimum value. The minimum value is, for example, the minimum required reception power or the minimum required signal / noise ratio for a service. The value range of the control value is reduced by reference to a minimum value, so that the control value can be encoded with a few bits. This ties up less transmission capacity.

An exemplary embodiment of the invention is explained in more detail with reference to the accompanying drawings.

1 shows a radio communication system,

2 shows a procedure for setting the transmission power of a base station, and FIG. 3 shows a schematic structure of a subscriber station.

The mobile radio system shown in FIG. 1 as an example of a radio communication system consists of a multiplicity of mobile switching centers MSC which are networked with one another or which provide access to a fixed network PSTN. Furthermore, these mobile switching centers MSC are each connected to at least one device RNC for controlling the base stations BS and for allocating radio resources, ie a radio resource manager. Each of these RNC facilities in turn enables a connection to at least one base station BS. Such a base station BS can establish a connection to a subscriber station, for example mobile stations MS or other mobile and stationary terminals, via a radio interface. At least one radio cell is formed by each base station BS. According to DE 198 34 210, the radio interface is designed as a broadband radio interface, B = 5 MHz, with CDMA subscriber separation (Code Division Multiple Access).

1 shows, by way of example, connections VI, V2, V3 for the transmission of useful information ni and signaling information si as point-to-point connections between mobile stations MS and a base station BS and an organization channel BCCH as point-to-multipoint connection from the base station BS to the subscriber stations MS.

An operation and maintenance center OMC implements control and maintenance functions for the mobile radio system or for parts thereof. The functionality of this structure is different

Radio communication systems can be transmitted, in which the invention can be used, in particular for subscriber access networks with a wireless subscriber connection.

According to FIG. 2, base station BS m send the organization channel BCCH with a constant and known transmission power. The subscriber station MS receives the transmissions from the base stations BS and determines a measured value w in each case. For establishing a connection, the base station BS is selected for which the best transmission conditions exist (e.g. lowest attenuation or best signal / noise ratio).

In a memory device SP, see FIG. 3, the subscriber station MS also stores a service-dependent transmission power value sw, which is linked by the subscriber station MS to the measured value mw. The service-dependent transmission power value sw is for a voice service or for agreed packet data services differently and takes into account individual quality of service.

A control value delta is determined from both values mw, sw, which is transmitted to the base station BS in a channel with random access RÄCH, RACH channel (Random Access Channel). This transmission also contains, for example, a request for resource allocation or short data packets for a packet data transmission.

The base station BS receives the control value delta, determines the transmission power P desired by the subscriber station MS and sets this already in the next transmission to this subscriber station MS in a channel FACH (Forward Access Channel) of the connection.

Different variants are possible for the measurement, transmission power and control values mw, sw, delta:

Measured value mw:

Receive power RMS, BCCH of the transmissions of the base station BS in the BCCH at the subscriber station MS - signal-to-noise ratio SIRMS, BCCH of the transmissions of the base station BS in the BCCH at the subscriber station MS

Transmission power value sw: for the desired service (service) required receiving power RMS, _S ervice of emissions of the base station BS at the subscriber station MS - for the desired service (service) required signal / noise ratio SIR ^ S, _S of the transmissions ervice the base station BS at the subscriber station MS

The values are connected to each other using the following equation:

SE

^ ~ - 'BS.Sennce ~ BS, BCCH ~ ^ MS .Service ~ ^ MS.BCCH ~ ^^ MS.Semce ~~ ^^ MS.BCCH ⁺ * ^' ° S ^{} 1} service P _{BS, BCCH} is the transmission power of the base station BS in the organization channel BCCH, and PB _S, Se _r vice desired Sen ^¬ deleistung the base station BS for the service (Service).

This results in different forms of representation for the control value delta to be transmitted, e.g .:

1) delta = PßS, service

2) delta = Δ 3) delta = SIR _{MS BCCH}

4) delta = SIR _{MS BCCH} - SIR _{MS BCCH mm}

The final calculation of the transmission power of the base station BS is carried out at 2) to 4) by the base station BS. At 1) the calculation has already been carried out by the subscriber station MS.

If reference is made to the signal-to-noise ratio SIR, the selected spreading factors SF in the organization channel BCCH and in the channel FACH of the connection must be taken into account. The spreading factor SFB _CCH is fixed and known. The spreading factor SFservice to be selected for the transmission from the base station BS to the subscriber station MS of the service can either be set permanently, during the establishment of the connection context or can be signaled in the transmission of the subscriber station MS to the base station BS in the RACH channel. When using the signal-to-noise ratio SIR is therefore a

SF

Correction term lOloe— ^{S ££} I taken into account.

^{L} Λ} F service

Variant 4) offers particular advantages, since the received signal / noise ratio SIR _{MS BCCH is compared} with a minimum value mw in, which relates to a minimum signal / noise ratio SIR _{MS BCCH of} the organization channel BCCH for the service. Particularly high-rate data services can only be received in a radio cell at a short distance from the base station BS, since otherwise the transmission power of the base station Station BS had to be too big. The minimum value thus specifies a service-dependent threshold value for reception. The difference according to 4) can be coded with just a few bits, since the range of values is much smaller than when the received signal / noise ratio is signaled

^^ MS BCCH ^•

An example for the calculation according to the above equation results in a measured signal / noise ratio in the BCCH SIR _{MS BCCH} of -3 dB, a desired signal / noise ratio of the service SIR _{MS Semce} of 0.7 db (language m downward direction at

Vehicle speeds) and spreading factors SF = 128 for the service and SF = 256 in the BCCH a transmission power of the base station BS, which should be 6.7 dB above the transmission power in the BCCH.

A subscriber station MS according to FIG. 3 receives the transmissions from the base station BS of the organization channel BCCH as received signals via an antenna device AE. The received signals are amplified in a HF part HF-T, filtered and fed to a receiving device RXE, which is digitized and further signal evaluated.

An evaluation device AU determines a measured value mw for setting the transmission power from the transmissions of the base station BS and carries out a calculation of the control value delta, the service-dependent transmission power value sw being taken into account. The service-dependent transmission power value sw is stored in a memory device SP and can be called up by the evaluation device AU. Furthermore, the evaluation device AU initiates the transmission of the control value delta via a transmission device TXE and the antenna device AE to the base station BS.

Claims

claims 1. Method for setting the transmission power in a radio communication system in which - base stations (BS) and subscriber stations (MS) are connected to one another via a radio interface, - a subscriber station (MS) receives transmissions from a base station (BS) and uses this to determine a measured value (mw) for the transmission power setting, and - the measured value (mw) influences later transmission power settings of the base station (BS), characterized in that the subscriber station (MS) links a service-dependent transmission power value (sw) with the measured value (mw) to a control value (delta), transmits this control value (delta) to the base station (BS), and - The control value (delta) is used for setting the transmission power of the base station (BS). 2. The method according to claim 1, characterized in that the transmission of the control value (delta) takes place in a RACH channel. 3. The method according to any one of the preceding claims, characterized in that the transmission power setting of the base station (BS) already takes place for the initial transmissions of a connection to the subscriber station (MS). 4. The method according to any one of the preceding claims, characterized in that measurement and transmission power values (sw, mw) are based on reception powers. 5. The method according to any one of claims 1 to 3, characterized in that measurement and transmission power values (sw, mw) are based on signal / noise ratios. 6. The method according to claim 5, characterized in that the radio interface is organized according to a CDMA transmission method and the control value (delta) additionally takes into account a ratio of spreading factors (SF) between the received transmissions from the base station (BS) and the desired service . 7. The method according to any one of the preceding claims, characterized in that the control value (delta) on a difference of the transmission powers or the signal / noise ratios of the base station (BS) in an organizational channel (BCCH) and a channel (FACH) for the desired Service related. 8. The method according to any one of claims 1 to 6, characterized in that the control value (delta) is based on the transmission power of the base station (BS) for the desired service. 9. The method according to any one of the preceding claims, characterized in that the control value (delta) is related to a value which compares the measured value (mw) with a minimum value (mwmin) for the measured value (mw). 10. subscriber station (MS) for a radio communication system, which is connected via a radio interface to a base station (BS), with a receiving device (RXE) for receiving transmissions from the base station (BS), with a storage device (SP) for storing a service-dependent transmission power value (sw), with an evaluation device (AU) for determining a measured value (mw) from the transmissions of the base station (BS) and for linking the service-dependent transmission power value (sw) with the measured value (mw) to form a control value (delta) for transmission - Power setting, with a transmitter (TXE) for transmitting the control value (delta) to the base station (BS).