WO2002093764A1

WO2002093764A1 - Device and method for processing cdma-data packets

Info

Publication number: WO2002093764A1
Application number: PCT/DE2001/001864
Authority: WO
Inventors: Reinhold Braam; Ulf Niemeyer
Original assignee: Siemens Aktiengesellschaft
Priority date: 2001-05-16
Filing date: 2001-05-16
Publication date: 2002-11-21

Abstract

The invention relates to a device for the treatment of CDMA-data packets ('Code Division Multiple Access'), which comprises a RAKE-receiver (10) with a plurality of processing paths (#1,, #8) and a combiner (22), wherein signals from the processing paths (#1,, #8) are combined. Said inventive device is characterised in that the processing paths (#1,, #8) are associated with means (18) for the multiplication of data with characteristic coefficients for the processing path (#1,, #8) and the processing paths (#1,, #8) are associated with means (14) for scaling data. Preferably, means for limiting the data values to a maximum level are provided. The invention also relates to a method for processing CDMA-data packets.

Description

description

DEVICE AND METHOD FOR PROCESSING CDMA DATA PACKAGES

The invention relates to a device for processing CDMA data packets ("Code Division Multiple Access"), which has a receiver, in particular a RAKE receiver, with a plurality of processing paths and a combiner in which signals from the processing paths are combined, the processing paths Means for multiplying data with a coefficient characteristic of the processing path are assigned.

The invention further relates to a method for processing CDMA data packets using a receiver, in particular a RAKE receiver, with a plurality of processing paths and a combiner, in which signals from the processing paths are combined, with data in the processing paths having a coefficient which is characteristic of the processing path be multiplied.

The CDMA method is a method that enables multiple users to access a 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 you replace a bit with a bit combination of, for example, 10 bits, you achieve a spread by a factor of 10. Although a higher transmission bandwidth is required, the transmission channel can be used simultaneously for several user channels. The data of the individual users must be clearly separated from one another in the transmission channel. divorce. A major advantage of the CDMA method, for example over the known TDMA method ("Time Division Multiple Access"), is the better utilization of the available transmission bandwidth.

In principle, 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 to say 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.

However, the problem with such devices and methods that use a RAKE receiver is that depending on the spreading factors used and the received signal strength at the output of a RAKE receiver, very different values are obtained for the partial symbols assigned to the respective RAKE fingers. One is therefore forced to work in all processing stages with large bit widths in order to take their signal dynamics and the different spreading factors into account. This results in a considerable amount of hardware. The present invention is based on the task _. e is based on further developing the generic device and the generic method in such a way that the implementation effort is reduced.

The object is achieved with the features of claims 1 and 8.

Advantageous embodiments and developments of the invention are specified in the dependent claims.

The invention builds on the generic device in that means for scaling data are assigned to the processing paths. Depending on the spreading factor and the signal strength received, there are generally very different values for the partial symbols of the individual RAKE fingers at the output of the RAKE receiver. The RAKE fingers are assigned to the individual processing methods. However, since only certain bits of the individual received partial symbols are information carriers - which bits are involved depends on the signal strength and the respective spreading factor - a scaling of the data can reduce the bit width. Downstream processing stages can thus work with a smaller bit width, ultimately the implementation effort is thus reduced.

The device according to the invention is particularly advantageously developed in that means for supplying scaling values to the means for scaling data are provided. The means for scaling data can thus be supplied with values from outside which determine the extent of the scaling. The scaling is carried out in a simple manner by shifting the data word by a number of digits, which is specified by the scaling value supplied from the outside. The scaling values are adapted to the signal conditions so that in as many cases as possible the complete information is retained despite scaling of the data.

It is particularly preferred to design the device according to the invention in such a way that the means for supplying scaling values supply the same processing values to the different processing paths. By using the same scaling values for the various RAKE fingers, it is ensured that no other measures are to be taken in principle for further processing than for devices of the prior art

Technology. The relevant information is retained in the respective RAKE fingers and matches the information of the other RAKE fingers in a known manner. Subsequent processing can therefore be designed in a conventional manner.

The device is developed in a particularly advantageous manner in that the processing paths are assigned means for limiting the data values to a maximum value. Due to the advantageous scaling of the data values, which is carried out in the context of the present invention, only smaller bit widths are available for the different signals. Therefore, overflows can occur despite careful selection of the scaling. These overflows are counteracted by means of limiting the data values to a maximum value. A limitation to such a maximum value has a lesser influence with regard to the quality of the received signal than, for example, allowing overflows. This can be illustrated in such a way that an overflow often results from a large noise signal value which is also superimposed on a large signal value. It is very likely that the signal value, which is limited to the maximum value, will be in the range of this maximum value anyway.

It is particularly advantageous if the means for multiplying data are used for weighting. Such Weighting promotes good signal quality, since it makes it possible to take signal components with a high intensity into account, even with a high weighting. Signal components with a lower intensity, however, are suppressed in comparison to the more intensive signal components.

Furthermore, the device is further developed in an advantageous manner in that in-phase data and quadrature data are processed in the processing paths and that the in-phase data and the quadrature data of the processing paths are thus used with the means for multiplying data can be adjusted so that in the combiner in-phase parts are combined with in-phase parts and quadrature parts with quadrature parts. The channel coefficients with which the data are changed in the multiplication means thus serve on the one hand to weight the individual RAKE fingers and on the other hand to correct the in-phase components and the quadrature components of the signals.

The device is particularly advantageous when 8-bit dynamics are made available. Such 8-bit dynamics can be guaranteed regardless of the spreading factor and the performance of their individual sub-symbols of the RAKE fingers. Such 8-bit dynamics are sufficient in particular for a satisfactory signal quality if short-term changes in the symbol energies, which would in themselves lead to overflows, are limited to a maximum value by a limiter logic.

The invention builds on the generic method in that data is scaled in the processing paths. In this way, the advantages of the device according to the invention are realized in the context of a method.

The method according to the invention is particularly advantageous in that scaling values are supplied for scaling data become. Such scaling can reduce the bit widths of the data passed on.

In a further advantageous embodiment of the method according to the invention, it is developed in such a way that the same processing values are supplied to the different processing paths. This ensures that the data can be further processed in the individual RAKE fingers in a known manner.

In a particularly preferred embodiment, the method according to the present invention is to be carried out in such a way that the data values are limited to a maximum value. This prevents overflows. Such overflows could otherwise lead to the creation of two's complement. Limiting the data values to a maximum value therefore serves to promote the signal quality.

In the method according to the invention, weighting is advantageously carried out by multiplying data. The weighting makes it possible to take signal components with high intensities into account, even with a high weighting. Signal components with a low intensity, however, are less considered.

It is also particularly advantageous if the method according to the invention is developed in such a way that in-phase data and quadrature data are processed in the processing paths, and that when data is multiplied, the in-phase data and the quadrature data of the Processing paths are adjusted in such a way that in the combiner in-phase parts are combined with in-phase parts and quadrature parts with quadrature parts. The multiplication of the data by channel coefficients thus serves not only to weight but also to rotate an image signal vector in the complex I / Q plane. In the method according to the present invention, an 8-bit dynamic range is preferably made available. An 8-bit dynamic provides a satisfactory signal quality in numerous applications.

The invention is based on the finding that the complexity of the combiner of a RAKE receiver can be greatly reduced by scaling and preferably by limiting the data to a maximum value.

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

It shows:

Figure 1 is a schematic block diagram of a device according to the invention.

FIG. 1 shows a schematic block diagram which illustrates a device according to the invention. A part of a RAKE receiver 10 can be seen, which in the present case has eight processing paths in an exemplary manner. Of these eight processing paths, only the first processing path (# 1) and the eighth processing path (# 8) are shown. For example, the remaining processing paths can be designed in the same way. In general, n processing paths # 1 to #n are provided, where n is a natural number.

Each of the processing paths includes a RAKE finger 12 which, for example, outputs two data words with a respective width of 21 bits. The two data words are in-phase data or quadrature data.

In the subsequent unit 14 there is a scaling and a limitation of the given data values instead. The scaling value is input to the unit 14 from a scaling value transmitter 16. The data values are shifted in the unit 14, so that ultimately the information-carrying points of the data words are filtered out. The output of the unit 14 thus comprises, for example, two 8-bit data words. So there has been a significant reduction in the bit width. Since there is a greater probability of overflows due to the reduction in the bit width, even if the scaling value which is output by the scaling value generator 16 is carefully selected, the unit 14 is also equipped with a limiter. This limits ("clipping") the value output by the unit 14 to a maximum value. This prevents the data from overflowing.

The data output by the unit 14 are input to a multiplier 18, where they are multiplied by a channel coefficient which is output by the unit 20. This multiplication in the multiplier 18, on the one hand, results in a weighting of the data assigned to the different RAKE fingers 12. On the other hand, the in-phase components and the quadrature components of the data are influenced in such a way that a subsequent combination of the respective components with the data of the other RAKE fingers 12 is possible.

A combination of the data then takes place in the combiner 22. This is entered, for example, two data words, each 7 bits long, from each processing path.

The output of the combiner 22 can then be reduced to an even smaller bit width. For example, a bit width of two 4 bits can be made available to a decoder 24, this being sufficient for a satisfactory result of the decoding. 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 RAKE receivers

12 RAKE fingers 14 scalers and delimiter logic

16 scaling encoder

18 multipliers

20 channel coefficient transmitter

22 combiners 24 decoders

Claims

claims

1. Device for processing CDMA data packets ("Code Division Multiple Access"), which has a receiver, in particular a RAKE receiver, (10) with several processing paths (# 1, ..., # 8) and a combiner (22), in which signals from the processing paths (# 1, ..., # 8) are combined, the processing paths (# 1, ..., # 8) having means (18) for multiplying data by one for the processing path (# 1, ..., # 8) are assigned characteristic coefficients, characterized in that means (14) for scaling data are assigned to the processing paths (# 1, ..., # 8).

2. Device according to claim 1, so that means (16) for supplying scaling values to the means (14) for scaling data are provided.

3. Apparatus according to claim 1 or 2, so that the means (16) for supplying scaling values supply the same processing values (# 1, ..., # 8) with the same processing values.

4. Device according to one of the preceding claims, that the processing paths (# 1, ..., # 8) are assigned means (14) for limiting the data values to a maximum value.

5. Device according to one of the preceding claims, characterized in that the means (18) for multiplying data are weighted.

6. Device according to one of the preceding claims, characterized in that in the processing paths (# 1, ..., # 8) in-phase data and quadrature data are processed and - that with the means (18) for multiplying data the in-phase data and the quadrature data of the processing paths (# 1, ..., # 8) are adjusted such that in the combiner (22) in-phase components with in-phase components and quadrature components can be combined with quadrature parts.

7. Device according to 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 an 8-bit dynamic is provided.

8. Method for processing CDMA data packets using a receiver, in particular a RAKE receiver

(10), with several processing paths (# 1, ..., # 8) and - a combiner (22) in which signals from the processing paths (# 1, ..., # 8) are combined, whereby in the processing paths ( # 1, ..., # 8) data are multiplied by a coefficient which is characteristic of the processing path (# 1, ..., # 8), characterized in that in the processing paths (# 1, ..., # 8) data be scaled.

9. The method according to claim 8, d a d u r c h g e k e n n z e i c h n e t that scaling values are supplied to scale data.

10. The method according to claim 8 or 9, characterized in that the different processing paths (# 1, ..., # 8) are supplied with the same scaling values.

11. The method according to any one of claims 8 to 10, d a d u r c h g e k e n n z e i c h n e t that the data values are limited to a maximum value.

12. The method according to any one of claims 8 to 11, that a weighting is carried out by multiplying data.

13. The method according to any one of claims 8 to 12, characterized in that in the processing paths (# 1, ..., # 8) in-phase data and quadrature data are processed and that when multiplying data, the in-phase Data and the quadrature data of the processing paths (# 1, ..., # 8) are adapted so that in-phase components are combined with in-phase components and quadrature components with quadrature components in the combiner (22).

14. The method according to any one of claims 8 to 13, d a d u r c h g e k e n n z e i c h n e t that an 8-bit dynamic is provided.