WO2000064069A2

WO2000064069A2 - Method for adjusting the transmitter power in radiocommunications systems

Info

Publication number: WO2000064069A2
Application number: PCT/DE2000/001009
Authority: WO
Inventors: Stefan Oestreich
Original assignee: Siemens Aktiengesellschaft
Priority date: 1999-04-15
Filing date: 2000-04-03
Publication date: 2000-10-26
Also published as: DE19917061A1; WO2000064069A3

Abstract

According to the inventive method for adjusting transmitter power, radio stations are interlinked via a radio interface, which is organised according to a TDD transmission method with several time slots per frame. Said time slots can be allocated to different connections. Emissions from a first radio station are received by a second radio station in a control loop-type arrangement, correction values are determined based on the emissions received and the correction values are conveyed to the first radio station where they are taken into account in adjusting the transmitter power for subsequent emissions. The invention also provides that the first radio station receives emissions from the second radio station in at least two time slots of the frame, that the at least two emissions are compared with each other and that the result of this comparison is taken into account in adjusting the transmitter power.

Description

description

Procedure for setting the transmission power in radio grain communication systems

The invention relates to a method and a radio station for setting the transmission power in radio communication systems, in particular in mobile radio systems with a TDD radio interface.

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), in which 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 transmission power setting is desirable, but requires that both transmission and reception are permanent.

In a mode of radio communication systems known from IMT-2000 Study Committee, Air-Interface WG, SWG2, "Specifications of Air-Interface for 3G Mobile System", from November 18, 1998, the radio interface is based on a TDD transmission Process organized, this means that a frame is divided into time slots and in a frequency band, the up and down direction are only separated in time. So it can only be either received or sent in the frequency band at a time. This results in errors in the transmission power setting, which arise, among other things, from the time delay between the power measurement and the transmission or implementation of the corresponding correction value.

In IMT-2000 Study Committee, Air-Interface WG, SWG2, "Specifications of Air-Interface for 3G Mobile System", from November 18. 1998, pp. 152-154, it is proposed to carry out measurements in addition to the control loop with correction values that are also taken into account for the setting of the transmission power. For this purpose, a special channel (perch channel) with known constant transmission power is measured and the path attenuation is determined (TBTS-RM _S ) • However, the special channel is only available in the downward direction and in a few time slots and can therefore only be used to a limited extent.

The invention has for its object to further improve the transmission power setting for any direction of transmission. The object is achieved by the method with the features of claim 1 and the radio station with the features of claim 18. Advantageous developments of the invention can be found in the subclaims.

In the method according to the invention for setting the transmission power, radio stations are connected to one another via a radio interface, the radio interface being organized according to a TDD transmission method with several time slots which can be assigned to different connections per frame. According to an additional option of the method according to the invention, transmissions from a first radio station are received in the sense of a control loop from a second radio station, correction values from the received transmissions determined, transmit the correction values to the first radio station and take them into account there for the transmission power setting of the following transmissions.

In the upward direction, it is possible to transmit power of the mobile station only with an open control loop, i.e. H. without correction value from the base station. This is done e.g. with the help of a control channel transmitted by the base station with known power. In addition, the invention provides that the mobile station receives transmissions from the base station in at least two additional time slots of the block, the at least two transmissions are compared with one another and the comparison result is taken into account when setting the transmission power.

The method according to the invention does not depend on a special channel in which transmission must take place with a fixed reference power. It can be used both in an upward and downward direction and in an open or in addition to a closed control loop. Since measurements are made more than once per block, the tendency of the received power can be read and the transmitted power can be set more precisely. The transmission power is not changed within a transmission block, so that e.g. based on the difference in the reception performance of both transmissions within one

Blocks the following transmission power is adapted to the current development with less time delay.

According to an advantageous development of the invention, the two transmissions of the second radio station in the transmission block are as far apart in time as possible. From this, the tendency can be read more precisely. For example, the two transmissions of the second radio station are carried out in the first and last time slot of the respective block for the respective transmission direction. A possible extrapolation is also improved in that the second radio station in the largest possible number of time slots of the block sends. The more measurements there are, the more accurate the comparison.

It is advantageous if two separate control loops are used: the determination and transmission of the correction values is a closed control loop, which is based on measurements from the opposite side, and when the comparison result is taken into account, an open control loop from the radio station's own measurements . The closed control loop specifies the basis of the transmission power setting, but is somewhat slower. The open control loop according to the invention is fast and complements the transmission power setting. Only the open control loop can be used for the upward direction.

The transmission power setting is improved without loss of capacity if the transmissions of the second radio station are transmitted in traffic connections. The traffic data, codes or means sent for one connection (for both transmission directions) and beyond for other connections (for the downlink direction) can also be used.

The measurements relating to the transmissions of the second radio station advantageously relate to channel measurement sequences, e.g. Middle Ages. This means that it is not necessary to send complete radio blocks in the time slots, but only channel measurement sequences if necessary. These can still be reduced by a predefined amount in terms of performance, since only their reception performance has to be measured. This reduces the interference and allows the transmission power to be set in the sense of the invention if temporarily no data is to be transmitted.

Further refinements of the invention provide that the comparison of the at least two transmissions includes an extrapolation for a future transmission power and / or that an offset value is also taken into account when setting the transmission power. The extrapolation can be related to the time slot or frame in which the first radio station will transmit again within the connection next time. The offset value represents a further correction that results from the specific radio transmission. For example, the offset value results from the ratio of the time slots in the upward and downward direction, from the parameter of the transmission quality, from the speed of a radio station's movement, from empirical values obtained in active operation, or from a calculation during test operation.

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

Show

1 shows a radio communication system,

2 shows a radio interface with TDD transmission methods, FIG. 3.4 shows a division of the time slots over several base stations, FIG. 5 shows a transmission power setting for a base station and a subscriber station, and FIG. 6 shows a schematic structure of a radio 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 devices RNC in turn enables a connection to at least one base station BS. Such a base station BS can use a radio interface to connect to a subscriber station, for example mobile stations MS or other mobile and stationary stations. build end devices. At least one radio cell is formed by each base station BS.

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 a control channel BCH as a point-to-multipoint connection from the Base station BS to the subscriber stations MS shown.

An operations and maintenance center OMC implements control and maintenance functions for the mobile radio system or for parts thereof. The functionality of this structure can be transferred to other radio communication systems in which the invention can be used, in particular for subscriber access networks with a wireless subscriber connection and for base stations and subscriber stations operated in the unlicensed frequency range.

The frame structure of a TDD radio transmission (Time Division Duplex) is shown in FIG. 2. Within a broadband frequency range, for example the bandwidth B = 5 MHz, a division into several time slots ts of the same duration, for example 16 time slots ts 1 to, takes place according to a TDMA component (Time Division Multiple Access)

16 per frame for instead. Several frames for form a multi-frame, etc. This creates a channel structure. It can also be provided that the time slots ts of a frame are not only used by a base station BS, but each time slot ts of a frame is allocated to a base station BS1 to BS3 according to FIGS. 3 and 4. In any case, some of the time slots ts are used in the downward direction DL and some of the time slots in the upward direction UL. The transmission direction can also change several times per frame, see FIG. 5. In this TDD transmission method, the frequency band for the upward direction UL corresponds to the frequency band for the downward direction DL. The same is repeated for other carrier frequencies. Through the variable allocation of the time slots ts for upward or downward direction UL, DL, a variety of asymmetrical resource allocations can be made and through the arbitrary allocation of the time slots ts to the base stations BS1 to BS3, a load-dependent adaptation of the radio resources allocated to a base station BS can be carried out.

The time slots ts are allocated in the device RNC for the allocation of radio resources, in the case of adjacent base stations and time clustering, a time slot ts is only allocated to one base station BS1 to BS3. The time slots ts allocated to a base station BS1 are signaled to this by the device RNC.

Information of several connections is transmitted in radio blocks within the time slots ts. The data is spread individually for each connection with a fine structure, a spreading code c, so that, for example, n connections can be separated at the receiving end by this CDMA component (code division multiple access). The CDMA component created a variable capacity expansion of the radio interface by setting spreading factors or by assigning a variable number of spreading codes. There are short protection times - the difference between the radio block length and the length of a time slot ts - which serve as a tolerance for the time synchronization. Within the radio blocks, midambles m are transmitted, which are embedded in the data-carrying signal components or sent alone.

The transmission power setting is explained on the basis of FIG. 5, method steps 1 to 12 roughly following the chronological order of the individual radio stations involved, the base station BS and the mobile station MSI. feeding process steps. The frame fr comprises only 16 time slots, all of which are used by a base station BS, the blocks frdl and frul each having four time slots in the downward and upward direction DL, UL. 5 shows the transmission power setting for both transmission directions DL, UL of only one connection. The base station BS is usually involved in several connections, so that the same procedure is repeated for the other connections.

In step 1, the base station BS transmits in the downward direction DL in the control channel BCH, the transmission power of the signals in the control channel BCH being constant over time and known to the subscriber stations MS. In the other time slots of the downward direction DL of the frame fr, the base station BS sends traffic and signaling information ni, si to the respective subscriber stations MS of the connections in traffic channels TCH, to which a spreading code c is assigned in the time slots ts. In the last time slot of the downlink DL, the base station BS sends, for example, data to a specific subscriber station MSI in step 2.

In step 3, the subscriber station MSI measures the transmissions from the base station BS in step 2 and determines a correction value PC _ßT Sr which, for example, indicates the deviation of the received power from a target power.

In the upward direction UL, four time slots are available for different connections from different subscriber stations MS to the base station BS. A time slot is provided for a channel RÄCH with random access, the remaining time slots contain traffic channels TCH.

For example, the subscriber station MSI considered here is assigned a channel TCH in the first of the four time slots, in which it transmits itself in step 4. In addition to useful information, a correction value PCBT _{S is used} for the base tion-side transmission power setting transmitted to the base station BS. In addition, the subscriber station MSI also sends useful information or a midamble in step 5. Alternatively, the subscriber station MSI can also send an individual midamble in all time slots, regardless of whether and in how many time slots their traffic channels are assigned.

In step 6, the base station BS receives the transmissions from the subscriber station MSI and evaluates them. From the correction value PCBT _S , it can see the necessary change in the transmission power step (PC _BTS ) m compared to step 2 from the point of view of the subscriber station MSI. In addition, the base station BS can derive a tendency by comparing the reception powers of the outside fertilizers from steps 4 and 5 (see equation 1) as to how the reception power of the transmissions from the subscriber station MSI develops. The function according to equation 1 can be a simple difference formation or an extrapolation for the following block or frame for or even a specific time slot ts in this frame for. The transmission powers used by the radio stations MS, BS in the traffic channels TCH are constant within a connection during a frame fr, so that the tendency is not falsified. In addition to determining the tendency from the transmissions of the traffic channels TCH, the control channel BCH can also be measured for the downward direction DL. This results in a larger number of measured values, the measured values having to be standardized before a comparison due to the different transmission powers of BCH and TCH.

Since the transmission channel in the TDD transmission method between base station BS and subscriber station MS (provided the same antenna devices are used for transmitting and receiving) is reciprocal, the measurements of the closed and open control loop can be carried out for different transmission directions DL, UL. The tendency gives the possibility to readjust the transmission power of the base station BS the next time the station station MSI is sent (see equation 2). The constant K can either have been determined in the test mode, can be set depending on the cell according to the topographical conditions or can depend on variant conditions such as the ratio of time slots ts of the up and down direction, the transmission conditions (bit error rate) or the speed of the subscriber station MSI. It can also be determined automatically by the base station from empirical values during operation.

In step 7, the base station BS in turn sends the control information in the control channel BCH with known performance. In steps 8 and 9, either only one channel measurement sequence or, if present, also useful information is sent. In step 10, the subscriber station MSI can in turn carry out several measurements of the reception power of the signals from the base station BS over time. It is not significant here (unless connection-specific directional diagrams are used) to which subscriber station MS the transmissions are directed. The transmission power of the base station in steps 8 and 9 is the same or different by a predefined amount. However, it must not fall below a minimum output to ensure secure reception. This minimum power can be the lowest power used for another code on the same time slot.

In step 11, the subscriber station MSI receives the correction value PC _S from the base station. In step 12, the subscriber station MSI sends to the base station BS, with both the received power RX (BCH) of the control channel BCH sent by the base station with known power TX (BCH) together with the received power RBTS required at the BTS and the one in step 10 being used for setting the transmit power certain Tendency of the reception power are taken into account (see equation 4).

Alternatively, the correction value PC _MS for the transmission power of the subscriber station MSI can also be transmitted in step 9 within the connection to the subscriber station MSI. This correction value PC _M s is received by the subscriber station in step 11 and used for power setting in step 12 in accordance with equation (5)

Equations:

Trend MS = (RX _M s (5), RX _M s (4)) (1)

TX _B τs (8) = TX _B τs (2) + step (PCBTS) + tendency _M s + K (2)

Trend TTS = (RXBTS (8), RX _B τs (9)) (3) TXM _S (H) = TX (BCH) - RX (BCH) + R _BTS + Trend _B τs + K (4)

TX _MS (11) = TX _M s (4) + step (PC _M s) + tendency TS + K (5)

In FIG. 5 below, it is also shown that with some asymmetry conditions from up to down direction, the transmission power setting for a transmission direction can change greatly to the disadvantage (transmission power setting of the base station BS becomes imprecise due to a long opening of the control loop). Here, the improvement of the transmission power setting according to the invention with the aid of the open readjustment according to the invention is particularly important.

The radio station, designed as a base station BS - however, the same applies to the subscriber station MS; according to FIG. 6, it receives the reception signals of all connections via an antenna device AE. The received signals are amplified in a HF part, filtered and fed to a receiving device RXE, in which digitization and further signal evaluation take place.

A control device SE takes the correction values PCBT _S from the signals and also determines the tendency with respect to the received power from the respective to a subscriber station Receive signals belonging to MSI. Furthermore, the control device SE determines the correction values PCM _S for the subscriber stations MS and initiates the transmission of the correction values PCM _S via the transmission device TXE and the antenna device AE. Selection and coding of the correction values PC can be found in ETSI SMG2 UMTS Ll # 8, Tdoc SMG2 UMTS Ll 549/98, Siemens AG, dated November 9, 1998.

Claims

claims

1. Method for setting the transmission power in radio communication systems, in which radio stations (BS, MS) are connected to one another via a radio interface, the radio interface organizing time slots (ts) per frame (fr) according to a TDD transmission method with multiple, different connections characterized in that a first radio station (BS, MS) receives transmissions from a second radio station (MS, BS) in at least two time slots (ts) of the frame (fr),

- and that the at least two transmissions received by the second radio station are compared with one another and the comparison result is taken into account when setting the transmission power of the first radio station.

2. The method according to claim 1, characterized in that

- transmissions from a first radio station (BS, MS) are received by the second radio station (MS, BS), correction values (PC) for a transmission power of the first radio station (BS, MS) are determined from the received transmissions,

- the correction values (PC) are transmitted to the first radio station (BS, MS),

-. the correction values (PC) in the first radio station (BS, MS) for the transmission power setting of the following transmissions are taken into account.

3. The method according to claim 1, characterized in that the correction values (PC) for the transmission power setting from transmissions of a control channel (BCH) are determined.

4. The method according to any one of the preceding claims, characterized in that the two transmissions of the second Radio station (MS, BS) in the block (frdl, frul) are as far apart in time as possible.

5. The method according to any one of the preceding claims, characterized in that the two transmissions of the second radio station (MS, BS) in the first and last time slot (ts) of the respective block (frdl, frul) for the respective transmission direction (UL, DL) become.

6. The method according to any one of the preceding claims, characterized in that it is a closed control loop in the determination and transmission of the correction values (PC) and an open control loop when considering the comparison result.

7. The method according to any one of the preceding claims, characterized in that the second radio station (MS, BS) in the largest possible number of time slots (ts) of the frame (fr) sends.

8. The method according to any one of the preceding claims, characterized in that the transmissions of the second radio station (MS, BS) are transmitted in traffic channels (TCH).

9. The method according to any one of the preceding claims, characterized in that the transmissions of the second radio station (MS, BS) at least partially contain only channel measurement sequences.

10. The method according to claim 9, characterized in that the channel measurement sequences are designed as middle tambours.

11. The method according to claim 9, characterized in that the channel measurement sequences in the downward direction as transmissions to a plurality of subscriber stations are formed with a previously defined individual code (c).

12. The method according to claim 9, characterized in that the channel measurement sequences are sent with the same power or with a previously defined power difference.

13. The method according to any one of the preceding claims, characterized in that the comparison of the at least two transmissions includes an extrapolation for a future transmission power.

14. The method according to any one of the preceding claims, characterized in that an offset value (K) is further taken into account in the transmission power setting.

15. The method according to claim 14, characterized in that the offset value (K) is derived from the ratio of the

Time slots (ts) in the up and down direction, from the parameter of the transmission quality, from the speed of a radio station (MS) movement, from empirical values during active operation or from a calculation during a test operation.

16. The method according to any one of the preceding claims, characterized in that the first radio station is a base station (BS) and the second radio station is a subscriber station (MS).

17. The method according to any one of claims 1 to 15, characterized in that the first radio station is a subscriber station (MS) and the second radio station is a base station (BS).

18. Radio station (BS, MS) for a radio communication system, with a transmitter (TX) for transmitting signals via a radio interface to a further radio station (MS, BS) - the radio interface using a TDD transmission method with several, different connections assignable time slots (ts) per frame (fr) is organized with a receiving device (RXE) for receiving signals from the further radio station (MS, BS), the signals containing correction values (PC) which the further radio station (MS , BS) from the received transmissions from the radio station (BS, MS), with a control device (SE) for setting the transmission power, which corrects the values (PC) and a comparison result from the other radio station (MS, BS) in at least two time slots ( ts) of a frame (fr) received transmissions taken into account when setting the transmission power.