Method for polar diagram shaping in a radio communications system

This application is based on and hereby claims priority to German Application No. 10137580.8 filed on Aug. 1, 2001 and European Application No. 01118546.9 filed on Aug. 1, 2001, the contents of which are hereby incorporated by reference.

The invention relates to a method for polar diagram forming in a connection between a subscriber and a base station with adaptive antenna arrangement in a radio communications system using multiple access methods.

Various concepts are known for improving the reception for connections between a subscriber and a base station in radio communications systems, in particular mobile radio systems.

By way of example, a first concept for this purpose uses a phased array antenna arrangement as the antenna arrangement at the base station for receiving subscriber signals in an uplink connection, with the antenna arrangement having a number of individual antennas and a number of polar diagrams. Each individual one of the polar diagrams is in this case currently aligned with a three-dimensional area, in order to supply this area. A subscriber signal which is sent by an individual subscriber is received as antenna signals via the individual antennas and depending on the number of the individual antennas, and these antenna signals are passed, with the aid of a common beam forming unit, as weighted sum signals to outputs of the beam forming unit. In this case, each output of the beam forming unit has one, and only one, associated polar diagram.

The weighted sum signals are passed to a user-specific polar diagram selection circuit, which is connected downstream of the beam forming unit, for further processing, the output from which once again contains not only the signal from a desired subscriber but also a subset of signals from further subscribers who are physically associated with the same polar diagram as the desired subscriber.

Thus, in this first concept, common polar diagram forming is carried out for all the subscribers, and for their subscriber signals, at the base station. Depending on their respective location, the individual subscriber signals are effectively amplified or attenuated on reception by the polar diagrams and by their polar diagram characteristic, with each individual polar diagram once again being associated with one, and only one, of the outputs of the beam forming unit.

The implementation of the first concept, which can be carried out in a very robust manner, makes it possible to improve both the supply and the system capacity of the radio communications system. Furthermore, it is possible to suppress disturbing interference signals from subscribers who are located, in comparison to a first subscriber, in a physical area which is associated with an adjacent polar diagram. It is impossible to suppress disturbing interference signals from subscribers who are supplied jointly using the same polar diagram.

The three-dimensional resolution is reduced by selecting a limited number of preformed polar diagrams.

In a second concept, an antenna arrangement with individual antennas is used for receiving subscriber signals at the base station. However, there is no longer rigid association between fixed polar diagrams or physical areas and the subscribers, and the antenna signals which are received by the individual antennas are instead of this processed directly and on a user-specific basis, that is to say the individual antenna signals are adaptively combined with one another. In radio communications systems using CDMA multiple access methods, this is done, by way of example, using an “eigen beam former”.

This second concept is characterized by the radio communications system having a full adaptation capability to the respective transmission and interference situation. Good capabilities to suppress disturbing interference signals are obtained by technically proven algorithms and user-specific, adaptive calculation of any desired polar diagrams (beams). This makes it possible to optimize a received signal in terms of noise and interference, and this is done using a signal-to-noise and interference ratio value (SINR).

However, this involves a high level of complexity and increased computation complexity owing to the user-specific processing of the subscriber signals, for example by the eigen beam former, and this is particularly true when processing spread spectrum received signals.

One aspect of the invention is based on the object of using a user-specific adaptive evaluation to optimize the reception of subscriber signals in terms of a signal-to-noise and interference ratio value for a connection within a radio communications system, while at the same time reducing the complexity which this results in.

A reception situation is matched to a predetermined SINR value by the combination, of the common beam forming network, with whose aid signal preprocessing and polar diagram preselection are carried out on the one hand, and of the user-specific beam forming unit on the other hand.

Compared with the exclusive user-specific processing of the antenna or subscriber signals, the combination makes it possible, with an essentially constant SINR value, to achieve a reduction in the complexity and a reduction in the computation effort with only a small amount of additional hardware and software, and to achieve a reduction in the data rate.

The user-specific selection of a subset of polar diagrams, which is advantageously carried out with the aid of a selector, and further processing with the aid of, for example, an eigen beam former, allow energy concentration. Three-dimensional preprocessing is provided by the common beam forming network. The selector is used to select those input signals to the beam forming unit which form an optimum ratio between the respective subscriber useful signal and the disturbing interference signals and noise, or whose-specific weighting combination forms an optimum ratio between the respective subscriber useful signal and the disturbing interference signals and noise.

Use of the common beam forming network and optimized user-specific algorithms in the beam forming unit make it possible to achieve an adaptable tradeoff between the complexity on the one hand and the system capacity on the other hand. Compared with the individual concepts, the combination of the first concept and the second concept allows the tradeoff to be made essentially without any restrictions or disadvantages. For example, viewed from a theoretical standpoint, the individual antennas and the individual polar diagrams (transformed domain) are the same as one another if all Kb outputs of the common beam forming network are selected by the selector for further processing in the user-specific beam forming unit.

The advantage of three-dimensional preprocessing with the aid of the common beam forming network is that it is possible to set up suitable signal relationships (energy concentrations) which allow the adaptive, user-specific algorithms to be designed in a simpler manner, or allow their dimensions to be reduced.

These and other objects and advantages of the present invention will become more apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1 shows a method for joint polar diagram forming according to the related art,

FIG. 2 shows a method for user-specific polar diagram forming according to the related art,

FIG. 3 shows a circuit example relating to the implementation of the method according to one aspect of the invention, and

FIG. 4 shows a circuit example relating to the implementation of the user-specific beam forming unit in a circuit as shown in FIG. 3 .

Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout.

FIG. 1 shows a method for joint polar diagram forming according to the related art.

A signal Tx 1 which is sent by a first subscriber TN 1 is received by an adaptive antenna arrangement ANT. The antenna arrangement is, by way of example, in the form of a phased array antenna arrangement and has a total of Kb polar diagrams, which are arranged horizontally offset with respect to one another, so that each individual polar diagram provides fixed coverage of a respective three-dimensional area of the radio communications system.

In order to produce the Kb polar diagrams, the antenna arrangement ANT has a total of Ka individual antennas ANT 1 , ANT 2 , . . . , ANTa, via which subscriber signals are received from a total of Ku subscribers. The individual antennas ANT 1 to ANTa receive the signal Tx 1 which has been sent by the first subscriber TN 1 as Ka antenna signals Rx 1 , Rx 2 , . . . , Rxa, which are passed as input signals to a common network for polar diagram forming, the beam forming network CBF 1 , which thus has Ka inputs E 1 , E 2 , . . . , Ea for receiving the Ka antenna signals Rx 1 to Rxa, and has a total of Kb outputs A 1 , A 2 , . . . , Ab. In this case, each individual one of the Kb outputs A 1 to Ab is permanently associated with one, and only one, of the Kb polar diagrams.

The common beam forming network CBF 1 is used to combine the Ka antenna signals Rx 1 , Rx 2 , . . . , Rxa from the first subscriber TN 1 to form Kb weighted sum signals RXS 1 , RXS 2 , . . . , RXSb, which are passed to the individual Kb outputs A 1 to Ab of the common beam forming network CBF 1 . Each individual sum signal RXS 1 to RXSb can thus be associated with one, and only one, of the Kb polar diagrams, depending on the respective output A 1 to Ab. Its sum signals are of different intensity, and thus have different weightings, depending on the position of the subscriber TN 1 in the radio communications system.

This association process is carried out jointly for all Ku subscribers, with the sum signals RXS 1 to RXSb which are formed in this way for an individual subscriber being passed together with those from all the other subscribers as overall signals RS 1 , RS 2 , . . . , RSb via the respectively associated outputs A 1 , A 2 , . . . , Ab of the common beam forming network CBF 1 as input signals to Kb inputs EE 1 , EE 2 , . . . , Eeb of a user-specific polar diagram selection circuit USS 1 for further processing. This is used to produce an output signal for each individual subscriber, which output signal contains not only the signal from a desired subscriber but also a subset of signals from those subscribers who are physically associated with the same polar diagram. By way of example, the output signal for the desired subscriber TN 1 also contains signal components from a subscriber TN 2 .

The common beam forming network CBF 1 may in this case contain a Butler matrix, with an N×N Butler matrix, in each case having the same number of inputs and outputs, preferably being used. The respective sum signal is in this case formed on a carrier-frequency basis, is then converted to baseband and is then converted from analog to digital form, and is not illustrated here, while user-specific further processing is then carried out in baseband. In the same sense, it is also possible to first of all convert the individual antenna signals to baseband, with the sum signal formation and user-specific further processing being carried out subsequently.

The method described here is characterized by the low level of complexity in the radio communications system, which is achieved by the common beam forming network CBF 1 and the subsequent user-specific selection of each individual one of the Ku subscriber signals.

The selection of a limited number of preformed polar diagrams reduces the three-dimensional resolution. Furthermore, with this method, it is impossible to suppress interference signals which are physically associated with the same polar diagram.

FIG. 2 shows a method for user-specific polar diagram forming according to the related art. In comparison with FIG. 1 , a subscriber signal which is received with the aid of the antenna arrangement ANT, or a subscriber signal which is received by the Ka individual antennas ANT 1 , ANT 2 , . . . , ANTa, from a subscriber TN 1 is passed as Ka antenna signals Rx 1 , Rx 2 , . . . , Rxa to a total of Ka inputs of a user-specific, adaptive beam forming unit ABF 1 , which is used to calculate user-specific polar diagrams.

The user-specific, adaptive beam forming unit ABF 1 may be in the form of an eigen beam former, for example in radio communications system using CDMA access methods.

The user-specific adaptive method described here is characterized by the capability to deliberately mask out disturbing interference signals on a user-specific basis, and by a full adaptation capability of the polar diagrams which are in each case calculated for each of the Ku subscribers. However, this involves a high level of complexity in the radio communications system. For example, the polar diagrams are in this case used to separate and mask out disturbing interference signals TX 2 and TX 3 from subscribers TN 2 and TN 3 deliberately from a useful signal TX 1 from a subscriber TN 1 .

FIG. 3 shows a circuit example relating to the implementation of the method according to one aspect of the invention. In comparison with FIG. 1 and FIG. 2 , the common polar diagram forming is combined with the user-specific polar diagram forming.

The Ka antenna signals Rx 1 to Rxa, which are received by the Ka individual antennas ANT 1 to ANTa, from a subscriber TN 1 who has sent a subscriber signal TX 1 , are passed as Ka input signals to a common beam forming network CBF 1 , which has a total of Ka inputs E 1 , E 2 , . . . , Ea for receiving the Ka antenna signals Rx 1 to Rxa. The common beam forming network CBF 1 uses this to form Kb sum signals RXS 1 , RXS 2 , . . . , RXSb, which are passed to a total of Kb outputs A 1 , A 2 , . . . , Ab of the common beam forming network. Each individual one of the Kb outputs A 1 , A 2 , . . . , Ab is in this case associated in a fixed manner with in each case one of Kb polar diagrams.

This association process is carried out jointly for all Ku subscribers, with the sum signals RXS 1 to RXSb which are formed in this way for an individual subscriber being passed together with those from all the other subscribers as overall signals RS 1 , RS 2 , . . . , RSb via the respectively associated outputs A 1 , A 2 , . . . , Ab of the common beam forming network CBF 1 as input signals to Kb inputs EI 1 , EI 2 , . . . , Eib of a user-specific beam forming unit ABF 1 , which is used to carry out a user-specific selection of a subset of polar diagrams, and for user-specific processing of this subset.

This combination combines the advantages of the two methods described in FIG. 1 and FIG. 2 , in particular the full adaptation capability and the suppression of disturbing interference signals, while at the same time reducing the complexity, with this being achieved by the common beam forming network CBF 1 in combination with the user-specific selection process.

FIG. 4 shows a circuit example relating to the implementation of the user-specific beam forming unit ABF 1 in a circuit as shown in FIG. 3 .

By way of example, this is based on a radio communications system using CDMA access methods.

The overall signals RS 1 , RS 2 , . . . , RSb from all Ku subscribers are passed as input signals to the Kb inputs EI 1 , EI 2 , . . . , Eib of the user-specific beam forming unit ABF 1 , which has an eigen beam former EBF and a selector S. The selector S is used to carry out a user-specific selection of a subset Kc from the Kb overall signals from the total of Ku subscribers. This selected subset Kc is supplied as input signals to the eigen beam former EBF.

The eigen beam former EBF uses the signals from the subset Kc and with the aid of an interference covariance estimation device IKS which is arranged there to form an interference covariance matrix, and with the aid of a signal covariance estimation device SKS which is likewise arranged there, to form a signal covariance matrix from the respectively supplied signals in the subset Kc.

Weights, which are passed to a combiner CB, are calculated in each case adaptively and on a user-specific basis by a weighting device GEW, using eigenvalue decompositions with the aid of the signal covariance matrix and the interference covariance matrix.

The signals in the subset Kc are passed as output signals for the selector to a despreading device ENT, with whose aid they are likewise passed, as despread input signals, to the combiner CB. The combiner is used to weight and to add up the Kc output signals from the selector. These user-specific sum signals are then processed further.

Thus, in summary, the common beam forming network CBF 1 can be used to associate polar diagrams with the antenna signals. A selector S selects a subset Kc, which is less than or equal to the number of polar diagrams Kb of the antenna arrangement, on a user-specific basis from the overall signals RS 1 to RSb. This is done for each individual one of the total of Ku subscribers. An eigen polar diagram forming algorithm is carried out by the beam forming unit ABF 1 on the signals from the subset Kc.

Both despreading and estimation of the covariance matrix as well as eigen value decomposition are simplified by the preselection of polar diagrams using the common beam forming network CBF 1 , and the overall complexity is reduced.

In this case, the selector S allows a smooth transition between pure common polar diagram forming and pure user-specific polar diagram forming. This transition is set by the respective subset Kc selected from the overall signals. If Kc is allocated the value 1, then one of the Kb inputs EI 1 to Eib is considered, and this corresponds to common polar diagram forming. If Kb is used as the subset Kc, then this corresponds to pure user-specific polar diagram forming.

The invention has been described in detail with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.