WO2002091609A1 - Method and system for regulating the frequency of a rake receiver - Google Patents

Abstract

The invention relates to a method for regulating the frequency of a RAKE receiver. According to said method, the phase difference of signals received at different moments is measured and the phase difference is used as a regulating variable. The temporal position of a sampled signal is detected and the temporal position is used as a regulating variable. The invention also relates to a system for regulating the frequency of a RAKE receiver.

Description

description

Method and system for regulating the frequency of a RAKE receiver

The invention relates to a method for regulating the frequency of a RAKE receiver, comprising the steps of: detecting the phase difference of signals received at different times and using the phase difference as a controlled variable. The invention further relates to a system for regulating the frequency of a RAKE receiver with means for detecting the phase difference of signals received at different points in time, the phase difference being usable as a controlled variable.

Generic methods and generic systems are used in particular in connection with CDMA technology (CDMA: "Code Division Multiple Access"). CDMA technology enables multiple users to access one transmission channel. In this method, which is used, for example, in mobile radio systems, several users occupy the same frequency range, but the useful signal is coded differently for each user. A different code is used for the transmission of the bits for a first user than for a second user. The coding is based on a spread of the user data channel. The individual bits of a narrowband useful signal are replaced by longer bit combinations. If a bit is replaced by a bit combination of, for example, 10 bits, then a spread by a factor of 10 is achieved. Although a higher transmission bandwidth is required, the transmission channel can be used simultaneously for several user channels. The data of the individual users can be clearly distinguished from one another in the transmission channel. A major advantage of the CDMA method, for example over the known TDMA method ("Time Division Multiple Access ") is to make better use of the available transmission bandwidth.

Basically, data packets travel from the sender to the receiver on different transmission paths. For example, a direct transmission path is conceivable; another transmission path for the signal can sometimes contain several reflection points. The existence of such different transmission paths and the associated different delays in the data packets entail disadvantages in most transmission methods, for example in the TDMA method. With the CDMA method, however, you can take advantage of the existence of several transmission paths. This is done using a RAKE receiver. Such a RAKE receiver has several RAKE fingers, that is, several

Processing paths for data packets which have come from the transmitter to the receiver on different signal paths and which therefore generally have different delay times. By suitable processing of the data packets in the different RAKE fingers, the data can be processed so that they can ultimately be combined in a combiner. Only this combined signal is decoded and a high quality signal is obtained.

It is necessary that the communicating with each other

Stations work with great accuracy at the same frequencies. This applies, for example, to the mobile station and the base station of a mobile communication system. In order to ensure that the frequencies match during the operation of the stations, automatic frequency control (AFC: "Automatic Frequency Control") is generally used. High demands are placed on such an automatic frequency control. The 3GPP ("3rd Generation Partnership Project") standardization requires a frequency accuracy of 0.1 ppm in "loked mode". It is known to detect the phases of signals received at different times and to use the phase difference as a control variable for the automatic frequency control. In general, efforts will be made to coordinate the successive phases, which, for example, belong to different timeslots, so that the phase difference is zero.

However, such a regulation, which is based on the phase difference of the symbols received, does not always work reliably. For example, inaccuracies in the calculations result in phase errors, which are very small but can add up over a longer period of time. This leads to temporal shifts in the sampled signals, so that they are removed from the match filter window of the

RAKE receiver can run out. This leads to an undesirable reduction in the overall intensity of the signal. Furthermore, automatic frequency control based on the phase difference is problematic, especially in the initial synchronization phase. During this initial

Synchronization phase, the frequency differences between, for example, a mobile station and a base station are very large in most cases. This often leads to phase differences above 180 ° between adjacent slots. In these situations, the automatic frequency control is no longer able to determine the direction of the deviation based on the phase difference.

The invention is based on the object of specifying a method and a system in which, in particular, the problems of phase difference control mentioned are eliminated.

This problem is solved with the features of the independent claims. Advantageous embodiments and developments of the invention are specified in the dependent claims.

The invention builds on the generic method in that the temporal position of a sampled signal is recorded and that the temporal position is used as a controlled variable. The control based on the temporal position of a sampled signal is able to correct the inaccuracy of the angle control. Furthermore, the control mechanism can be used as a separate operating state of the automatic frequency control due to the position in time, so that a further control mechanism is available in phases for which the phase difference control does not provide reliable results.

In this context, it is particularly advantageous that the temporal position of the sampled signal is used as a controlled variable during an initial synchronization phase between two transmitting and / or receiving stations. Due to the possible phase deviation of more than 180 ° during the initial synchronization, regulation based on the phase difference can often not be used during this operating state. Only position control can then be used during this phase.

The method according to the invention is particularly advantageously further developed in that the phase difference of signals received that are too different is used as a controlled variable during the ongoing synchronization between two transmitting and / or receiving stations. When the frequency is relatively stable, the automatic frequency control is switched to control based on the phase difference. With this control on the basis of the phase difference (angle control) it is possible to precisely determine and correct very rapid phase deviations. It can also be useful if the temporal position of the sampled signal and the phase difference are used simultaneously as a controlled variable. This operating state is particularly suitable during the continuous operation of the communication system, since during this phase the phase difference control very quickly determines and regulates phase deviations. The position control then serves to correct the phase difference control.

The method according to the invention is developed in a particularly advantageous manner in that the phase difference Δφ, the time target position P _so ιι and the time actual position Pi _st are linked according to the following relationship to a controlled variable x:

x = Δφ + k »(P _S oiι - Pist),

where k is a predetermined factor that determines the proportion of the controlled variables, temporal position and phase difference in the controlled variable x, and that the controlled variable x is used as the controlled variable. In this way it is in your hand to combine the various control variables in a suitable manner. In the initial synchronization phase, k can be set to a very large value, for example, so that the position control plays the decisive role.

During the subsequent continuous synchronization, k can be chosen small, so that the phase difference control is crucial. The position control then only serves to correct the phase difference control.

It is particularly preferable if the phase difference is regulated to zero. A constant phase, for example over a large number of successive timeslots, ensures a good match of the frequencies.

It can be advantageous if the temporal position is used as a controlled variable by referring to the position of a time window is matched. The match filter window of the RAKE receiver can be used as this time window. It is desirable that the individual sampled signals be within the match filter window.

One possible concept in this context is that the position in time of the strongest RAKE finger is used as the control variable. Since the strongest RAKE finger also provides a large proportion of the total signal intensity, it makes sense to ensure that this RAKE finger lies within the match filter window.

It can be advantageous for the time position to be regulated in the middle of a time window. This regulation to the middle of the time window is one of several

Possibilities for determining the target position P _so ιι On the frame of the position control.

It is particularly useful if the time position is regulated to maximize the signal energy. In this way, a high signal power is made available, in particular already at the beginning of the synchronization phase.

The invention builds on the generic system in that means are provided for detecting the time position of a sampled signal and in that the time position can be used as a controlled variable. A system is therefore available in which a position control is available as a correction option or alternatively for the angle control.

It is particularly advantageous that the temporal position of the sampled signal can be used as a control variable during an initial synchronization phase between two transmitting and / or receiving stations. In particular during the initial synchronization, there may be a phase deviation of more than 180 ° between successive symbols. During this phase it is then possible to use position control only.

The system according to the invention is advantageously further developed in that the phase difference of signals received at different points in time can be used as a control variable during a continuous synchronization between two transmitting and / or receiving stations. The regulation based on the phase difference offers the possibility of precisely determining and correcting very rapid phase deviations. Therefore, it is preferable that the control based on the phase difference is used during the continuous synchronization.

It is also particularly useful in this context if the temporal position of the sampled signal and the phase difference can be used simultaneously as a controlled variable. In particular, the position control can have a corrective effect on the angle control during the continuous synchronization.

The invention is further developed in an advantageous manner in that the phase difference Δφ, the temporal target position Psoii and the temporal actual position Pi _{st are combined in} accordance with the following relationship to form a controlled variable x:

x = Δφ + k «(P _S oiι - Pist),

where k is a predetermined factor that determines the proportion of the control variables, temporal position and phase difference, in the control variable x, and that the control variable x can be used as a control variable. The size k can be viewed as a weighting factor for the proportions of the individual control variables, so that the control variable x can be adapted to the current requirements by suitable selection of the size k. It is particularly advantageous if the phase difference can be regulated to zero. A phase difference of zero, for example in the case of successive timeslots, is a reliable criterion for good frequency synchronization.

It is also particularly useful if the temporal position can be used as a controlled variable by adjusting it to the position of a time window. Basically, it is desirable that the individual sampled signals are within the match filter window.

The system according to the invention can be designed such that the temporal position of the strongest RAKE finger can be used as a controlled variable. This is a possible concept of control in order to generate the greatest possible total signal intensity.

It can also be provided that the temporal position can be regulated to the middle of a time window. This is also one of several options for determining the target position as part of the position control. It is then very likely that a certain number of RAKE fingers will be within the time window.

It is usefully provided that the time position can be regulated in order to maximize the signal energy. This means that high signal power is made available even at the beginning of the synchronization phase.

The invention is based on the knowledge that the two different control principles "angle control" and "position control" can complement one another well. On the one hand, the position control during the initial synchronization phase can replace the angle control, which is sometimes not possible during this phase. On the other hand, the position control can correct the results of the angle control. The angle control compensates during continuous operation in particular errors that are based on the Doppler effect and errors that are caused by the drift of the local reference oscillator.

The invention will now be explained by way of example with reference to the accompanying drawings using preferred embodiments.

It shows:

1 shows a schematic diagram with functional blocks to illustrate the present invention;

FIG. 2 shows a diagram for explaining an automatic frequency control on the basis of a determined phase difference;

Figure 3 is a diagram for explaining a position control; and

Figure 4 is a diagram illustrating the improvement in the bit error rate based on the present invention.

FIG. 1 shows a schematic diagram with functional blocks to illustrate the present invention. The received signals 10 are sampled by means of a scanner 12. The sampling rate is determined by a reference oscillator 14. The sampled signals are divided into several RAKE fingers 16 _x , 16 ₂ , 16 ₃ , ..., 16 _k . After processing the signals in the RAKE fingers 16 _x , 16 ₂ , 16 ₃ , ..., 16, these are fed to a combiner 18. The output signal 20 of the combiner is processed further. The output signal 20 is also fed to a phase difference detection 22 and a position detection 24. The information resulting from the phase difference detection 22 and the position detection 24 becomes selective or simultaneous used to change the frequency of the reference oscillator 14. For example, at the beginning of the synchronization phase, it is possible to use only the information from the position detection 24 in order to regulate the frequency of the reference oscillator 14. The information of the phase difference detection 22 can then be transferred later during the continuous synchronization. The information from the position detection 24 can continue to be used.

Figure 2 shows a diagram for explaining an automatic frequency control based on a determined phase difference. The illustration shows an in-phase / quadrature diagram, so that the phases of the signals received, for example, in adjacent slots can be represented as vectors AI and A2. The phase difference Δφ then results directly from this representation. In a preferred embodiment of the present invention, the angle between the vectors AI and A2 is now regulated to zero, the regulation preferably being used during the continuous synchronization.

Figure 3 shows a diagram for explaining a position control. Here, sampled signal intensities B, B 'are shown as a function of time t. The signal B can represent the actual position Pi _{Ξt of} a sampled signal, while the signal B 'drawn with a broken line characterizes the desired position. Both signals lie within the match filter window 26 of the RAKE receiver. In order to prevent a signal from running out of the match filter window, a control is set to the middle of the

Match filter window made. In other words, efforts are made to shift signal B to the position of signal B 'with the desired position. For example, the control can work in such a way that the signal B shown is the strongest RAKE finger. However, other control options are also available which generally serve to maximize the signal power. Figure 4 shows a diagram illustrating the improvement in the bit error rate based on the present invention. Here are two measurement curves of bit error rate measurements (BER measurements) in a moving channel

("Moving Channel"; 3GPP standard) depending on the size E _t , - N ₀ shown. The square measuring points show a measurement in which an angle control and a position control were used. The round measuring points show a measurement in which only position control was used. It can be seen that the measuring points for a combined angle and position control have a significantly improved characteristic. In the case of an increased signal-to-noise ratio in particular, the bit error rate drops sharply in the case of the combined angle and position control, with only a slightly decreasing course being evident in the pure position control.

The features of the invention disclosed in the above description, in the drawing and in the claims can be essential for realizing the invention both individually and in any combination.

LIST OF REFERENCE NUMBERS

10 received signals

12 scanner 14 reference oscillator

16ι RAKE fingers

18 combiners

20 output signal

22 Phase difference detection 24 Position detection

26 Match filter window

Claims

claims 1. A method for regulating the frequency of a RAKE receiver with the steps: - Detecting the phase difference of signals received at different times and using the phase difference as a control variable, characterized in that the time position of a sampled signal is recorded and that the time position as a control variable is used. 2. The method according to claim 1, so that the time position of the sampled signal is used as a controlled variable during an initial synchronization phase between two transmitting and / or receiving stations. 3. The method of claim 1 or 2, so that the phase difference of signals received at different times is used as a control variable during a continuous synchronization between two transmitting and / or receiving stations. 4. The method according to any one of the preceding claims, that the time position of the sampled signal and the phase difference are used simultaneously as a controlled variable. 5. The method according to any one of the preceding claims, characterized in that the phase difference Δφ, the desired time position Psoii and the actual time position Pι _s t are linked according to the following relationship to a controlled variable x: x = Δφ + k «(Psoii - Pist), where k is a predetermined factor that is the proportion of Control variables determine the temporal position P and phase difference Δφ on the control variable x, and that the control variable x is used as the control variable. 6. The method according to any one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that the phase difference is regulated to zero. 7. The method according to any one of the preceding claims, that the time position is used as a controlled variable by being matched to the position of a time window (26). 8. The method according to any one of the preceding claims, that the time position of the strongest RAKE finger is used as a control variable. 9. The method according to any one of the preceding claims, that the time position is regulated to the center of a time window (26). 10. The method according to any one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that the temporal position is regulated to maximize the signal energy. 11. System for regulating the frequency of a RAKE receiver with means (22) for: Detect the phase difference from too different Signals received at times and - using the phase difference as a controlled variable, characterized in that that means are provided for detecting the temporal position of a sampled signal, and that the temporal position can be used as a controlled variable. 12. System according to claim 11, so that the time position of the sampled signal can be used as a controlled variable during an initial synchronization phase between two transmitting and / or receiving stations. 13. System according to claim 11 or 12, so that the phase difference of signals received at different times can be used as a controlled variable during a continuous synchronization between two transmitting and / or receiving stations. 14. System according to one of claims 11 to 13, that the time position of the sampled signal and the phase difference can be used simultaneously as a controlled variable. 15. System according to one of claims 11 to 14, characterized in that the phase difference Δφ, the desired time position Psoii and the actual time position Pi _s are linked according to the following relationship to a controlled variable x: x = Δφ + k »(P _S oiι - Pist), - where k is a predetermined factor which determines the proportion of the controlled variables, temporal position P and phase difference Δφ in the controlled variable x, and that the controlled variable x can be used as a controlled variable. 16. System according to any one of claims 11 to 15, characterized in that the phase difference can be regulated to zero. 17. The system as claimed in one of claims 11 to 16, that the time position can be used as a controlled variable by being matched to the position of a time window (26). 18. System according to one of claims 11 to 17, so that the time position of the strongest RAKE finger can be used as a control variable. 19. System according to one of claims 11 to 18, that the position in the middle of a time window (26) is adjustable. 20. System according to one of claims 11 to 19, so that the time position can be regulated in order to maximize the signal energy.