DE19930747C2 - Method and device for regulating the transmission power of radio stations in a radio communication system - Google Patents

Description

The invention relates to a method and a device for Control of the transmission power of radio stations in a radio Communication system, with a radio transmission according to a CDMA (Code Division Multiple Access) procedure.

The mobile radio system shown in Fig. 1 as an example of a radio communication system consists of mobile switching devices MSC / SGSN, which are networked with each other and access to analog and digital fixed networks PSTN, ISDN and data networks, such as. B. secure an IP network. They are each connected to at least one radio network controller RNC for the allocation of radio resources. Each radio network controller RNC enables a connection via an interface Iub to at least one base radio station Node B, each of which in turn communicates with a plurality of subscriber radio stations UE via the radio interface in the downward direction DL (downlink) and upward direction UL (uplink). At least one radio cell Z is formed by each base radio station Node B. In the case of sectoring or hierarchical cell structures, a respective base radio station Node B can also be used to supply several radio cells Z. The above structure of a cellular Mobilfunksy stems is transferable to other radio communication systems in which the invention can be used, the designations and the functionality of the interfaces, radio stations and other devices for controlling and managing a network can also vary.

In a radio communication system, data between egg a variety of mobile or stationary subscriber stations UE and the stationary base radio stations Node B after one Multiple access method separated and in the upward direction UL to the base radio station Node B and / or in the downlink DL to the subscriber station UE on channels via the radio interface place transferred.

A well-known multiple access method is the code multiple access procedure CDMA (Code Division Multiple Access), at which the transmission of a narrowband radio signal in one wide frequency spectrum takes place, the narrow band Signal by a suitable coding regulation on a wide bandy signal is spread.

For the future digital mobile radio system of the third genes UMTS (Universal Mobile Telecommunication System) two basic transmission modes are provided - the FDD (Fre quency division duplex) mode and TDD (Time Division Du plex) mode. FDD mode is a broadband CDMA (W-CDMA) process, characterized by the Frei degrees of frequency and spreading code, and in TDD mode by one TD-CDMA process, characterized by the degrees of freedom Frequency, time slot and spreading code. In the latter the Multiple access through a broadband FDMA / TDMA (Frequency Di vision multiple access / time division multiple access) system realized, in certain time slots of a time slot frame also multiple access according to the CDMA Procedure is allowed.

The FDD mode allows both packet- and circuit-switched services with multiple connections, so-called bearers, per session. When establishing a connection, it is not necessary to first search for a free time slot or a free frequency and the change in the transmission rate is relatively simple. Frequency planning does not have to be carried out in this system either, since neighboring radio cells can only be distinguished by an individual additional code. The same frequencies can be used again in neighboring cells (reuse factor 1 ). A reuse factor of 3 is provided for the TDD mode. In the event of a channel change as a result of a transition to an adjacent radio cell, the connection to two base radio stations is set up in parallel for the duration of the switchover time to prevent data loss (soft handover).

In contrast to an FDMA / TDMA system, where due to the dis continuous structure of the transmission only a small mutual influence of connections operated in parallel different participants, there is a continuous reaction This CDMA system is very sensitive to fluctuations in the signal pe gel-to-interference level ratio, since in principle all Subscriber stations have the same carrier frequency with one band width of z. B. use 5 MHz and therefore as annoying Make interference noticeable to other subscriber stations. In practice, deviations from this are different lightest combinations of access methods and special Specifications, such as frequency hopping, to be used to meet.

The use of the same carrier frequency requires fast response control of the transmission power (PC = Power Control) with high control accuracy. Otherwise there is a so-called "near-far" effect, which means that subscriber stations that are close to a base radio station transmit and receive with a much higher transmission power than is actually necessary. In this way, for example, a base radio station Node B receives a transmission signal from a nearby subscriber station UE1 more strongly than the more distant subscriber stations UE2, UE3, as a result of which the signal-to-noise ratio within this radio cell Z deteriorates (see FIG. 1). For the separation of the individual connections on the reception side, this then leads to reception problems as soon as the interference signals become larger than the correlation signals sought. This significantly influences both the quality of service (QoS) and the transmission capacity of the system. Each additional subscriber station in the radio cell Z generates additional interference, so that there is a gradual deterioration of all other connections.

Both for the uplink and for the downlink therefore a transmission power control via dedicated channels provided that both on an "open" and thus feedback smooth control (OLPC = Open Loop PC) as well as on one "closed" control CLPC (Closed Loop PC) with feedback based. The first control provides the initial worth for the closed control loop. The open regulation is based on an assumed reciprocity of the transfer properties in the up and down direction. For the brisk The radio stations receive the control loop (Subscriber station, base radio station) each other in very short intervals (e.g. every 0.625 ms) signals to their sen power in small steps (e.g. +/- 1 dB) dynamic adapt.

Such a realization of the transmission power regulation can be found, inter alia, in the document "Japan's Proposal for Candidate Radio Transmission Technology on IMT-2000: W-CDMA", ARIB IMT-2000 Study Committee, June 1998 , Japan, pages 39 to 42.

From the publication "ETSI STC SMG2 UMTS-L1, Tdoc SMG2 UMTS-L1 221/98: UTRA Physical Layer Description FDD parts (v0.4, 1998-06-25), Turin, 1998, pp. 29-30" is one Transmission power control in a mobile radio system according to the CDMA process be known. For this purpose, the transmission power is controlled in a first inner loop such that the signal level to Interfe ence level value (SIR) reaches a certain set value (SIR _soll) accepts. In an outer loop, the target value (SIR _soll) adapted to estimate the connection quality. In order to achieve a high accuracy of the estimate, it is necessary to monitor the connection over a relatively long time. Since, on the other hand, due to the rapidly changing transmission conditions, a fast regulation is sought, such a solution is only inadequate.

The closed control is in an internal control loop (Inner Loop PC) and an outer control loop (Outer Loop PC) divided. The internal regulation influences the transmission power. If a currently measured signal level to interference level Ratio (signal to interference ratio) less than a be is a correct threshold value, a command becomes a transmitter performance increase to the transmitting radio station (Node B or UE) signals. On the other hand, if the current signal level to Interference level ratio the determined threshold ü a command to reduce the transmission power is exceeded signaled to the transmitting radio station. Could as well a more sophisticated algorithm can also be used. This function is for the upward stretch in the Base radio station and for the downlink in the participant merstation.

This type of transmission power regulation is only for one Connections permanently assigned to subscriber stations, so-called dedicated channels, and for a so-called shared channel applied in the downward direction.

The external regulation affects the perceived by the participant quality of service and adapts the specified signal level to interference level ratio threshold such that a specified quality of service value with the conditions bit error rate (BER = Bit Error Rate), block error rate (BLER = Block Error rate) or frame error rate (FER = frame error rate) can be supported. Ver different algorithms are applied. This function be is found for the upward stretch due to a possible  Soft handovers in the radio network control, which the different which combines up-received signals with each other, and for the downlink in the subscriber station. For this Basically, the quality of service description and the thresholds value in the uplink via the Iub interface between between the base radio station and the radio network controller be. The base radio station is for the inner rule loop responsible, whereas the outer control loop in the radio network controller is arranged.

A significant problem of the external regulation is the compromise between the accuracy of the estimation of the quality of service perceived by the subscriber and the reaction time of the external regulation to changes in the transmission conditions. The quality of service perceived by the subscriber is defined by the frame error rate or block error rate, which can be estimated on the basis of the checksums from a cyclic redundancy check CRC (Cyclic Redundancy Check) within the base radio station. A reliable estimate of relatively small frame error rates or block error rates in the range from 10 ^-2 to 10 ^-4 requires a long measuring time, which corresponds to a transmission time of more than 10 ² to 10 ⁴ frames or blocks. This stands in the way of a fast reaction time to changing influences as a result of a change in the speed of a moving subscriber station, a change from a connection without visual contact to a connection with visual contact, corner effects and others. For this reason, a compromise must be made between the response time and the accuracy of the external control.

An alternative solution is to use the uncorrected bit error rate upstream of the channel decoder (raw BER) or the soft output metric of the channel decoder, which allows the threshold value to be changed more quickly. On the other hand, these quality measures are not directly related to the quality of service perceived by the subscriber, i.e. there may be an environmental-dependent deviation between the quality measurement (uncorrected bit error rate, soft output metric, etc.) and the CRC error rate perceived by the subscriber. give. This deviation depends on the signal statistics, in particular on the interrelation between bit error rates and frame error rates, and leads to a systematic error in the quality control. Due to the correlation of the bit errors, for example in a real system a frame error rate of 10 ^{-2 is achieved} with a bit error rate of 10 ^-3 , while the frame error rate would be 0.47 if the bit errors occur uncorrelated. For this reason, precise regulation of the quality of service perceived by the subscriber should be based on the values of the frame error rate and / or block error rate.

The invention has for its object a method and a device for regulating the transmission power of Funksta tions (subscriber stations, base radio stations) in one Radio communication system, especially a mobile radio system stem, to reflect the changing radio conditions and thus an improvement in the quality of service and / or Increase in the transmission capacity in the system The technical effort and the effort should No or only insignificant signaling compared to previously known solutions are increasing.

The object is achieved by the in the claims 1 and 13 specified features solved. Advantageous form conditions indicate the dependent claims.  

According to the invention, it is proposed to divide the external control (Ou ter Loop PC) within the closed control loop (CLPC = Closed Loop PC) into two control steps, namely into a primary external control (Primary Outer Loop PC), which provides a desired signal level Interference level value SIR _is to _be adapted to a quality indicator QI, which _is measured according to a further development, for example, at the output of a channel decoder of the radio station, and in a secondary external control (secondary outer loop PC), which is a target value for the quality indicator QI _should adapt to an error rate.

The invention is illustrated below with the aid of an embodiment be explained in more detail. In the accompanying drawing demonstrate

FIG. 1 shows the general appearance already described ei nes radio communication system, especially a mobile radio system,

FIG. 2 shows a block diagram of an exemplary live implementation of transmission power control according to the invention, and

Fig. 3: a special design of a control loop.

Fig. 2 shows a highly schematic of a transmitter 1 of a subscriber station UE according to FIG. 1. On the opposite side, a receiver 2 of a base radio station Node B according to FIG. 1 is Darge. A so-called rake receiver 3 is connected to the receiver 2 of the base radio station. This enables a further significant gain by using reusable signals that arrive at the receiving antenna with different delay times. This rake receiver 3 can alternatively be replaced by a known joint detection receiver. A deinterleaver (deinterleaver) 4 is connected to the rake receiver 3 . This has the task of bringing the time-spread symbols of a data block back into the original chronological order in order to avoid bundle errors on the radio interface in a block interleaver (interleaver) on the opposite side. In the rake receiver 3 are integrated or between the rake receiver 3 and the deinterleaver 4 is a member for loading vote of the current signal-to-interference ratio SIR _is arranged. The data blocks or frames, which are channel-coded for the purpose of error detection and elimination, are then decoded again in a channel decoder 5 and corrected if necessary. Finally, a checksum check is carried out in a CRC element 6 , which is obtained from the cyclic redundancy check method (CRC) and serves to determine whether all the data has been transmitted completely and without errors. The result of the CRC check CRC _is (good / bad) is signaled using a bit to the outer control loop. Between the channel decoder 5 and the CRC element 6 or alternatively integrated in the channel decoder 5 there is another element for detecting the current quality of the connection by means of a quality indicator QI _ist (QI = Quality Indicator). The quality of a connection is assessed, for example, on the basis of the uncorrected bit error rate (raw BER) or the soft output metric of the channel decoder 5 .

In addition, this quality indicator QI can be designed with the aid of an appropriate coding rule so that the outer control loop can be deactivated. This is deviated at play then of benefit if the currently measured SIR value SIR _is clearly _intended from the predetermined target value SIR. Thus can be advantageously prevented that due to the limited dynamics of the inner loop a continuous increase or decrease of the target value SIR _to the inner control loop occurs if the maximum or minimum transmit power is reached. For example, with a large path loss (path loss) in the signal transmission via the radio interface between the subscriber station and the base radio station, the maximum possible transmission power is reached, which is why the setpoint SIR _should not be able to reach the inner control loop. Therefore, the transmission quality is over permanently bad and the outer control loop would be a steady increase in the target value SIR _to causes. This must be prevented so that when the signal loss is subsequently reduced, the internal control loop is not sent with a transmission power that is much too great due to a target value that is much too large. The semi the outer control loop should override the who, when the inner control loop encounters the upper or lower transmit power limit or if significantly differences between the SIR _and SIR _{is to} occur.

In the lower part of FIG. 2, three control loops for the adaptation of the transmission power to the transmission conditions on the radio interface are assigned to the upper block diagram. The inner control loop (inner loop PC) 7 controls the increase or decrease of the transmission power in uplink and downlink Rich processing after the current detected signal level-to-level Interfe ence value _is SIR and SIR of the reference variable _to.

The external control of the closed transmit power control loop is divided into a primary external control (primary outer loop PC) 8 and a secondary external control (secondary outer loop PC) 9 . The primary external control 8 controls the SIR value _should after the output of the Kanaldeko 5 _is the value determined for the quality indicator QI QI and the reference variable _{is intended.} The secondary outer regulation (Se condary Outer Loop PC) 9 ultimately controls the target value of the quality indicator QI _{is to} take into account to a value that _is perceived by the user CRC -Fehlerrate, in the Ba sisfunkstation Node B is calculated.

The measured values for the quality of service CRC _is QI _is transmitted in the uplink direction over the lub interface between the radio base station Node B to the radio network controller RNC (s. Fig. 1), since the outer control 8 tion in the Funknetzsteue RNC located. The measured values are fed to a control algorithm and the calculated result SIR _{should be} transmitted back to the base radio station Node B via the Iub interface.

In one aspect of this implementation, the two outer control loops (primärer- and secondary outer control loop) to form a single outer loop with the example, two input parameters, _namely, for the Qualitätsindi cator QI and the CRC _is -Fehlerrate (BLER FER), be united. Such a control loop is shown schematically in FIG. 3. This configuration allows a more general control algorithm with arbitrary functional dependencies between CRC _is error rate, quality indicator QI _is and SIR _should , that is, SIR _should = f (CRC _is , QI _is ). At the output, SIR _{Soll is available to} the internal control as a reference variable for the transmission power.

The proposal according to the invention has the advantage that a high quality of service over a long period of time with a high Accuracy achieved while changing at short notice  Radio conditions can be reacted to. This enables the procedure minimizes the fluctuations in the transmission performance regulation initiated by the external regulation the. This can advantageously increase the capacity of the network and the quality of service will be increased.

The structure of the transmission power control described can be used for the downlink DL in the subscriber station UE and for the Uplink UL applied in the radio network controller RNC become.

The procedure is also for external regulation in one future radio communication system applicable both in FDD mode as well as in TDD mode, since here too the outer Regulating a quality indicator QI or a quality Estimation and the result of a CRC via the interfaces Iub (between RNC and Node B) and Iur (between two RNC's) receives.

Claims (11)

1. A method for controlling the transmission power of radio stations in a radio communication system comprising a radio communication according to a CDMA method, wherein a closed control loop for controlling the transmission power according to a current signal level to interference level value _(is SIR) at least and a refreshes ellen transmission error rate (CRC _is ) is formed from an inner control loop and an outer control loop, characterized in that the outer control loop is formed from a primary outer control loop and a secondary outer control loop, with a quality indicator (QI _is), which output metric of the channel decoder (5) is determined at the output of a channel decoder (5) by measuring an uncorrected bit error rate (raw BER) or a soft, a nominal signal level to interference level value _is (SIR) governs , and in the secondary outer control loop the current transmission error rate (CRC _ist ) de n target value of the quality tätsindikators (QI _to) controls. 2. The method according to claim 1, characterized in that the quality indicator (QI _is ) at the output of a channel decoder ( 5 ) of a radio station (Node B, UE) of the radio communication system is measured. 3. A method according to any preceding claim, characterized in that the quality indicator _(QI) additionally indicates that the inner loop significantly _(to SIR) from the desired signal level to inter ference level value deviates, so the outer control disabled circular should be. 4. The method according to any preceding claim, characterized in that the quality indicator (QI _is ) additionally indicates that the inner control loop has reached a maximum or a minimum transmission power, which is why the outer control loop should be deactivated. 5. The method according to any preceding claim, characterized in that measured values (QI _is , CRC _is ) with respect to a quality of service (QoS _is ) in an upward direction (UL) from a subscriber station (UE) to the base radio station (Node B) via an Iub - Interface (Iub) are transmitted from the base radio station (Node B) to a radio network controller (RNC) of the radio communication system. 6. The method according to the preceding claim, characterized in that the measured values (QI _is , CRC _is ) for the quality of service (QoS _is ) are supplied to a control algorithm, and the calculated result (SIR _should ) via the Iub interface ( Iub) is transmitted back to the base radio station (Node B). 7. The method according to any preceding claim, characterized, that the primary outer loop and the secondary outer Control loop combined into a single outer control loop be grasped. 8. The method according to any preceding claim, characterized,  that the transmission power control for the downlink (DL) in the subscriber station (UE) and for the uplink (UL) in the base radio station (Node B) regarding the internal rule loop, and in the radio network controller (RNC) regarding the outer loop of the radio communication system leads. 9. The method according to any preceding claim, characterized, that the transmission power control in an FDD mode and / or in a TDD mode of the radio communication system application fin det. 10. The method according to any preceding claim, characterized, that the radio communication system as a mobile radio system o designed as a wireless subscriber line system is. 11. Device for regulating the transmission power of Funksta tion (Node B, UE) in a radio communication system Carrying out a method according to one of the preceding Expectations.