WO2000052846A2

WO2000052846A2 - Method for regulating the transmission power of radio stations in a cdma radio communications system

Info

Publication number: WO2000052846A2
Application number: PCT/DE2000/000631
Authority: WO
Inventors: Markus Dillinger; Martin Haardt; Egon Schulz
Original assignee: Siemens Aktiengesellschaft
Priority date: 1999-03-03
Filing date: 2000-03-01
Publication date: 2000-09-08
Also published as: DE19909299A1; WO2000052846A3

Abstract

The invention relates to a method for regulating the transmission power of radio stations in a W-CDMA radio communications system, whereby an averaging of the quality evaluation is carried out on the receive side which guarantees a more precise criterion for the quality of the transmission conditions. A temporal variance of the received signal is determined on the receive side and an adjustment which is inversely proportional to the variance of the received signal is made to the averaging time for the mean value. If the averaging time has not been predetermined in a fixed manner, but follows the changes in the ratios of the radio interface, the regulation of the transmission power can be individually improved for each connection.

Description

description

Method for setting the transmission power of radio stations in a CDMA radio communication system

The invention relates to a method for setting the transmission power of radio stations in a CDMA radio communication system and a receiving device, on the basis of whose evaluation the necessary control instructions are generated.

In radio communication systems, messages (for example voice, image information or other data) are transmitted 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.

Two modes are provided for the third mobile radio generation, one mode being FDD operation (frequency division duplex), see ETSI STC SMG2 UMTS-Ll, Tdoc SMG2 UMTS-Ll 221/98, dated August 25, 1998, and the other mode is a TDD Operation (time division duplex). In the FDD mode, in which in a broadband frequency band, e.g. 5 MHz, a W-CDMA

Subscriber separation procedure (W-CDMA wideband code division multiple access) is to be used, an exact transmission power setting is a prerequisite for a good use of the radio resources. Especially for the upward direction of the transmission from the mobile stations to the base station, only a qualitatively good transmission power setting can solve the so-called near / far problem. From ETSI SMG2 UMTS Ll, Tdoc SMG2 UMTS Ll to "Slotted ode lm studies provements for FDD", Siemens AG, 14.10.1998, it is known be ^¬ that Sendeleistungsemstellung after an interruption of the continuous transmission in itself due to the "slotted mode "Modify operations. For this, the step size for an increase or decrease of the transmission power is briefly increased ^¬ time. The Sendeleistungsemstellung However, for all connections tion equal and by the lack of differentiation ^¬ suboptimal.

Also from ETSI SMG2 UMTS Ll # 8, Tdoc SMG2 UMTS Ll 549/98, Sie ^¬ mens AG, dated November 9, 1998, there are known tips for designing the step size with which the transmission power is to be adjusted within a control loop. For the control, the signal / noise ratio is evaluated as a quality assessment, the delay in the setting being 0.625 ms.

The object of the invention is to adapt the transmission power generation to different conditions of the radio interface. The object is achieved by the method with the features of claim 1 and the receiving device with the features of claim 16. Advantageous developments of the invention can be found in the subclaims.

In the method according to the invention for generating the transmission power of radio stations in a CDMA radio communication system, an averaging of the quality evaluation is carried out on the receiving side, which guarantees a more precise criterion for the quality of the transmission conditions. A more precise assessment reduces the likelihood of an increase in the transmission power (thus unnecessary interference) or an inadequate transmission power (thus poor transmission quality).

After a further development of the invention, a temporal variance of the received signal is determined and the averaging time adapted for the mean inversely proportional to the variance of the received signal. If the averaging time is not fixed, but follows the changes in the conditions of the radio interface, the transmission power can be improved individually for each connection. In the case of slow changes, the averaging time is long in order to obtain the most accurate estimate possible. With rapid changes a short averaging time is before ^¬ Trains t to be able to follow the changes in accordance quickly.

The quality assessment can be the result of channel estimation or data detection. In channel estimation, symbols known to the receiving device are compared with the received signal. The comparison result indicates the transmission conditions very well, but an error rate is only related to a few symbols. The data detection, on the other hand, evaluates a much larger number of symbols and thus offers greater statistical security. So-called "soft decision" information about the good to be detected can also be taken into account in order to better estimate the error rate. From J.G. Proakis, "Digital Communications", Mc-Graw-Hill, New York, 1995, pp. 483-489, the application of a "soft decoding" decoding m Viterbi decoders is explained.

3 shows suggestions for the length of the averaging tents at different speeds of mobile radio stations MS. The speed of the mobile stations only serves as a reference for the temporal variance of the transmission conditions of the radio interface. The changes in the transmission conditions naturally also depend on other influences, e.g. Development of the radio cell, type of interference, indoor or outdoor radio coverage, etc.

According to advantageous embodiments of the invention, the variance is determined by evaluating pilot symbols of the received signal, with, for example, a correlation of the received signals The performance of the pilot symbols is used from time slot to time slot. This is done for example in a RAKE receiver, either correlations between the signal ^¬ components of individual delay paths of the RAKE receiver with approximately the same delay to the variance determination ^¬ miteinan be compared, one for employee turnover of the signals of individual delay paths of the RAKE receiver to determine the Va ^¬ Rianz is used or the number of newly discovered or disappeared powerful delay path of the received signal per measurement period is used as a measure of the variance. This information can be generated in receiving devices without major additional effort, so that the method according to the invention can be easily implemented in existing receiver structures.

The bit error rate BER is particularly suitable for quality assessment. However, the block or frame error rate (BLER, FER) can also be used as measured variables.

The method is advantageously carried out with a second, e.g. The internal control combines that a second setpoint for a second signal quality evaluation is subjected to the adaptation value, a signal quality value determined from the received signal is compared with the second setpoint, and depending on the comparison result, a control instruction for increasing or reducing the transmission power to the transmitting radio station is transmitted. The adjustment value thus influences the internal regulation.

The signal quality value of the second signal quality assessment is advantageously determined from a signal / noise ratio or from another quickly and easily ascertainable measurement variable of the received signal. The adaptation value of the external regulation can take several sizes and can be set depending on the strength of the temporal variance. Larger steps should be allowed for rapid changes than for slow changes. An embodiment of the invention will be explained in more detail with reference to the beilie ^¬ constricting drawings.

Show

1 shows a radio communication system,

2 e ne schematic representation of two control loops for a transmission power setting,

3 is a table of the relationship between mobile station speed and averaging time;

4 shows a channel structure of the W-CDMA transmission, and

Fig. 5 e ne schematic representation of a receiving device.

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 provided with at least one device RNC for controlling the base stations BS and for allocating radio resources, i.e. a radio resource manager. Each of these RNC devices 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, e.g. Set up mobile stations MS or other mobile and stationary devices. At least one radio cell is formed by each base station BS.

Connections VI, V2, V3 for the transmission of useful information ni and signaling information si are shown as examples in FIG. 1 as point-to-point connections between mobile stations MS and a base station BS.

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 transferable, m which the dung ^¬ OF INVENTION can be used, in particular for Teilnehmerzu- access networks with wireless subscriber terminal and for censored in the frequency range unli- powered base stations and subscriber stations.

According to Figure 2, a reception signal is pre-filtered through a fitted at ^¬ filter, a RAKE m Kombmierer (RAKE receiver) processes. The RAKE Kombmierer contains several Verzogerungspfade representing branches that are tailored to individual spreading codes, and thus extract a ge to a compound ^¬ sound proof signal from the composite signal of the reception signal. A Viterbi decoder can thus carry out a connection-specific decoding of the signals obtained by the RAKE combiner. Viterbi decoding corresponds to data detection. At the same time, the signal / noise ratio can be measured for each of the signals.

An external control loop wins from the Viterbi

Decoder with a first quality evaluation a bit error rate BER or equivalent values such as block error rate BLER or frame error rate FER. An average value is determined from several of these determined bit error rates BER of a connection. The averaging is running (movmg average), i.e. a window with several bit error rates BER is shifted by one value with each new determination. For the size of the window, i.e. the averaging times are discussed below.

After each new determination, the mean value is compared with a target value for the bit error rate BER and a difference value is determined. This difference value is compared with a threshold value decoder with a threshold value. If the difference value is less than the threshold value, the is

Output value 0 otherwise the output value is 1. This means that the difference values have an amount greater than that Is threshold value, after a multiplication by a step size ^¬ (step) an increase or decrease a quality ^¬ setting (adjustment value) will solve for the inner control loop out ^¬. This adjustment value is subtracted from the delayed adjustment value of the previous calculation, so that the solution ANPAS ^¬ a second target value (target value SIR) for the internal control of the transmission power is carried out for a subsequent period.

The inner, fast control loop is based on a measurement of the signal-to-noise ratio SIR for a connection which is obtained from the RAKE combiner. The current signal-to-noise ratio SIR as the second signal quality evaluation is compared with the second setpoint and a difference value is generated. This difference value is fed to a threshold value separator, which is one for larger differences

Control instruction (TPC) to increase or decrease transmission power generated. This control instruction is transmitted in band to the transmitting radio station and is taken into account there in a subsequent transmission.

It is further assumed that the transmission power of the mobile station MS is set. The sending radio station is therefore the mobile station MS. The evaluation of the received signals and the generation of the control instruction for increasing or decreasing the transmission power is carried out in a receiving device of the base station BS. However, the method can also be used for the opposite transmission path.

It can be seen from FIG. 3 that the averaging time for the concurrent averaging is not designed to be constant, but rather is dependent on a temporal variance of the received signals. With a large variance, which corresponds to a high speed of the mobile station (250 km / h), the averaging time is short, for example 0.3 s. The averaging time is increased for smaller variances; e.g. 0.6 or 6 s. The decorrelation distance specifies the distance between two points whose slow with fading (signal fluctuations) are uncorrelated. The center ^¬ averaging time is based on the time required at a given speed Ge ^¬ to pass to this distance between the two points.

The step size (step) of the adjustment value is also provided a ^¬ dependent on the temporal variance of the received signal. With a small variance, the step size is smaller than with a large variance.

According to the exemplary embodiment, the temporal variance is determined by evaluating pilot symbols according to FIG. 4. Within a continuous signal, which is denoted by an individual spreading code, a distinction can be made between a pilot with symbols known to the receiver and a data part with useful or signaling information ni, si. The pilot is 8 or 16 bits depending on the transmission conditions.

Within a frame of length 635 ms that fills a time slot, the receiving device EE, according to FIG. 5, the receiving base station BS can use known symbols to estimate the transmission ratios with quality assessments.

The first quality rating is based on data detection and the second quality rating is based on channel estimation. In contrast to the prior art, the quality assessment is used to optimize the specifications for the transmission power setting individually for the connection.

5 receives the received signals of all connections via an antenna device AE. The received signals are amplified, filtered and digitized in an RF section. A data detector DT, which combines the functions of the RAKE receiver and the Viterbi decoder, evaluates the received signal and carries out the described quality assessments.

An evaluation device AU evaluates the quality assessments and determines a temporal variance of the received signal. The variance is determined consecutive by evaluating the correlation of the performance of the pilot symbols Empfangsmo ^¬ ments. The correlation shows the differences in the transmission conditions from the comparison of the pilot symbols of successive time slots.

In a RAKE receiver nger several Verzogerungspfade are provided a ^¬ on each reception signal with an individual spreading code for each an individual delay time is set. The delay paths are correlators, the output signals of which are superimposed after the evaluation. This corresponds to the temporal spread of the signal due to the multipath propagation.

According to the exemplary embodiment, the temporal variance is determined based on the correlations between the signal components of individual delay paths of the RAKE receiver with approximately the same delay. Alternatively, a fluctuation (power changes over time) of the signals of individual delay paths of the RAKE receiver to determine the variance or the number of newly discovered or disappeared powerful delay paths of the received signal per measurement period can be used as a measure of the variance. The averaging time and step size are derived from the variance and set by a control device ST by reading from a table.

The evaluation device AU determines an average value from several quality evaluations, compares the average value with the setpoint value and, in the event of a deviation between the mean value and the setpoint value, calculates the adaptation value, which further influences the instruction for setting the transmission power. A signaling device SIG generates an instruction for the transmission power control for the mobile station MS based on the quality evaluations of the inner and outer regulation. The instruction contains at least three options: increase, maintain or reduce the transmission power. The instruction is transmitted to the mobile station MS via the HF part HF-T and the antenna device AE. The selection and coding of the control instructions 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 of radio stations (MS, BS) in a CDMA radio communication system, in which

- a signal transmitted over a radio interface from a transmitting radio ^¬ station (MS) receiving signal is received,

an average value is determined on the reception side from a plurality of quality evaluations of the reception signal which follow one another and which is compared with a setpoint value in order to calculate an adaptation value,

- And the adjustment value for transmitting power control for the transmitting radio station (MS) is used.

2. The method according to claim 1, wherein

a temporal variance of the received signal is determined,

- The averaging time for the mean value is adjusted inversely proportional to the variance of the received signal.

3. The method according to any one of the preceding claims, wherein a channel estimate of the received signal is carried out, the quality assessment is carried out based on the channel estimate.

4. The method according to any one of the preceding claims, in which a data detection of the received signal is carried out, the quality evaluation is carried out based on the data detection.

5. The method according to any one of claims 2 to 4, wherein the variance is determined by evaluating pilot symbols of the received signal.

6. The method according to claim 5, wherein the variance takes place from a correlation of the powers of the received signals of the pilot symbols in different time slots.

7. The method according to claim 6, wherein the variance is determined in a RAKE receiver.

8. The method according to claim 7, wherein

Correlations of the signals humor found to be about the same delay, a ^¬ of individual delay paths of the RAKE receiver to Varianzbe ^¬.

9. The method according to claim 7 or 8, in which a fluctuation of the signals of individual delay paths of the RAKE receiver is used to determine the variance.

10. The method of claim 7 or 8, wherein the number of newly discovered or disappeared powerful delay paths of the received signal per measurement period is used as a measure of the variance.

11. The method according to any one of the preceding claims, in which a bit error rate is determined for quality evaluation.

12. The method according to any one of the preceding claims, in which a second setpoint for a second signal quality evaluation is acted upon by the adaptation value, a signal quality value determined from the received signal is compared with the second setpoint, depending on the comparison result, a control instruction for increasing or reducing the transmission power to the transmitting radio station is transmitted.

13. The method according to claim 12, wherein the signal quality value of the second signal quality evaluation is determined from a signal / noise ratio of the received signal.

14 is set _V out to one of the preceding claims, in which he _d adaptation value can assume a plurality of sizes, and ⁱ Abhäng- g of the _S TRENGTH of the time variance.

15. The method of claim 12, wherein an inner closed-loop control for the second signal quality ^¬ tätsbewertung and an external control for the first Quali ^¬ used tätsbewertung.

16. receiving device (EE) for a radio station (MS, BS) of a W-CDMA radio communication system, with a signal estimator (DT) which evaluates a received signal sent via a radio interface by a transmitting radio station (MS, BS) and carries out quality assessments, with an evaluation device (AU) that determines an average value from several quality assessments, compares the average value with a target value and calculates an adaptation value in the event of a deviation from the mean value and target value, with a signaling device (SIG) that provides instructions for transmitting power control for a transmitting party Radio station (MS) generated, which relates to the adaptation value.

17. Receiving device (EE) according to claim 16, characterized in that the evaluation device (AU) is designed to determine a temporal variance of the received signal, and a control device (ST) adjusts the averaging time for the mean value inversely proportional to the variance of the received signal.