EP3956999A1

EP3956999A1 - Low complexity multichannel gnss and dsss receiver

Info

Publication number: EP3956999A1
Application number: EP20717708.0A
Authority: EP
Inventors: Markus Landmann; Johannes Rossouw Van Der Merwe; Christopher Schirmer; Matthias Overbeck; Alexander Popugaev; Alexander RÜGAMER
Original assignee: Fraunhofer Gesellschaft zur Foerderung der Angewandten Forschung eV
Current assignee: Fraunhofer Gesellschaft zur Foerderung der Angewandten Forschung eV
Priority date: 2019-04-18
Filing date: 2020-04-16
Publication date: 2022-02-23
Also published as: WO2020212529A1

Abstract

A receiver comprises an analog beamforming and nullsteering network connected to one or more antennas from receiving RF signals and configured to preprocess the RF signals in order to mitigate interferences within the RF signals; and a digital stage connected to the analog beamforming and nullsteering network and configured to further process the preprocessed RF signals.

Description

Low Complexity Multichannel GNSS and DSSS Receiver

Description

Embodiments of the present invention refer to a receiver, e.g. a DSSS receiver (Direct Sequence Spread Spectrum Receiver) for GNSS (Global Navigation Satellite Systems). A further embodiment refers to a digital pre- and post-beamforming architecture, e.g. of a receiver. Further embodiments refer to the corresponding methods and to corresponding computer programs.

DSSS systems use Code Division Multiple Access (CDMA) to spread a signal over a larger bandwidth through the use of an appropriate de-spreading code (also referred to as a pseudo random noise (PRN) code). As a result the signal is often below the noise floor for a potential receiver. Through correlation of the signal with the spreading code at the receiver (processing gain), the signal can be extracted from the noise.

As CDMA is used, all signals of the systems are transmitted in the same operational band. As a result, the isolation between different signals and the signal quality is limited by the correlation properties of the code family that is used (spreading codes), the number of present signals, the transmitter-receiver geometries, multipath effects, and propagation losses. Therefore, an array of receiver antennas can be used to steer a beam in the direction of the signal to be received and to steer a null in the direction of interference from other signals and multipath signals, to improve system performance. This results in a considerable system improvement. In the case of GNSS, an improvement of Position, Velocity and Time (PVT) is achieved by the reduction of multipath distortion and interference of the signal.

To achieve beamforming, the Direction of Arrival (DOA) of the signal relative to the antenna array has to be known, such that the appropriate beamforming coefficients can be generated. In many systems this is unknown and can be estimated. The problem with DSSS signals is that the signals are typically below the noise floor. As a result, it is considered more reliable to estimate the DOA of the signals after the signal has been de-spread (correlated with the spreading sequence) because of the improvement against the noise. This requires a correlation to be done for each signal, for each antenna at each time and frequency offset of the signal, and is therefore considered processing intensive. The estimation accuracy however, is superior.

To implement beamforming in a DSSS receiver, it can either be done before or after tracking (fine acquisition). Tracking performs the correlation of the signal with the spreading code for the correct time and frequency offset by tracking the time difference and Doppler offset between the transmitter and receiver.

The advantage of implementing beamforming before tracking is that only a single tracking channel is required, and the interferences are removed before processing. Thereby, smaller word-lengths in processing can be used in tracking. Overall, this achieves a significant reduction in the required processing resources. On the other hand more processing is needed per signal source to calculate the beam-steering dynamically before the tracking channel.

The advantage of implementing beamforming-after-tracking is that the coefficient calculation and the beamforming can be done in a single step, whereby additional structures are eliminated. The other benefit is that the correct time and frequency offset is solely used for the beamforming coefficients. The disadvantage is that tracking is done with desired signals and the interfering signals at the same time. This leads to a severe reduction of the tracking performance of each channel. Furthermore, as interferences are present, higher bit depth of the ADC or longer

are required in order to guarantee that no clipping or signal loss is perceived due to the limited dynamic range.

As a summary, beamforming-on-receive can be used to significantly improve the receiver performance for a DSSS system. However, both pre- and post-tracking methods have major disadvantages in terms of processing resource requirements.

Therefore, there is the need for an improved approach.

It is therefore an objective of the present application to provide an improved concept enabling to overcome the drawbacks of the prior art.

This objective is solved by the subject-matter of the independent claims. A basic embodiment according to a first aspect provides a receiver which comprises an adjustable analog beamforming and/or nuilsteering network and a digital stage. The adjustable analog beamforming and/or nullsteering network is connected to one or more antennas that receive signals, like RF signals, over the air and configured to preprocess the signals in order to mitigate interferences within the signals. The digital stage comprises one or more analog digital converters and it may also include one or more power sensors (e.g. by means of an AGC control circuit or additional power sensors per input signal) which are connected to the analog beamforming and/or nullsteering network and configured to further process the analog preprocessed signals.

As indicated above, the signals may be RF signals. According to embodiments, the interferences to be mitigated are within the signals at RF level or at IF level (i.e. after down conversion) or at low IF level (after down conversion) or at analog baseband level (after down conversion).

Embodiments of the present aspect are based on the finding that an analog beamforming and/or nullsteering network, preferable an adjustable analog beamforming and/or nullsteering network, can be used to suppress strong interferers by means of nullsteering to reduce the complexity especially in the digital part of the receiver. For example, the analog beamforming and/or nullsteering network may be controlled or adjusted by the digital stage that may also include one or more power sensors (e.g. by use of beamforming and/or nullsteering coefficients and/or by the minimization of the input power per signal). This approach enables that still the digital analysis of the signals may be the basis for the determination of the interferer which are then mitigated in the analog front end. According to embodiments, the digital stage may comprise a digital beamforming and/or nullsteering entity. Due to this combination, a hybrid analog digital nullsteering and beamforming network is formed. A receiver design having such a hybrid analog digital nullsteering and beamforming network (BFN) has beneficially low complexity and low power consumption.

According to an embodiment, the analog beamforming and/or nullsteering network may be controlled by the digital stage, e.g. by use of beamforming and/or nullsteering coefficients. These coefficients define/adjust the behavior of the adjustable analog beamforming and/or nullsteering network. For example, the coefficient may identify the frequency to which the nullsteering should be performed by the beamforming and/or nullsteering network or other parameters, like filter parameters. Consequently, the analog beamforming and/or nullsteering network may - according to embodiments - be adaptively configured to perform nullsteering in order to suppress time variant or time invariant interferences within the signals.

In another embodiment an analog only control loop adjust the analog beam forming and/or nullsteering network based on the measurement of one or more power sensors to mitigate the interference before connecting to ADC(s).

Regarding the beamforming and/or nullsteering network, it should be mentioned that same may comprise a plurality of inputs and/or a plurality of outputs. Here, the number of the outputs may be equal, smaller or larger to the number of inputs. According to embodiments, said inputs and outputs are fully matched or partially matched. This means that the analog beamforming and/or nullsteering network may be implanted as fully matched or partially matched network.

Further regarding the beamforming and/or nullsteering network, it should be mentioned that same may comprise a plurality of output groups each covering e.g. different frequency band and/or used for example as monitoring outputs that could be also connected to one or more power sensor(s) e.g. connected to an analog control loop of the analog BFN.

Regarding the implementation of the beamforming and/or nullsteering network, it should be noted that same may comprise one or more analog amplifiers or adjustable amplifiers (for (adjustably) amplifying the signals or portion of same). Alternatively or additionally, same can comprise one or more (adjustable) attenuators (for (adjustably) attenuating the signals or a portion of same). Note that according to embodiments all this components (amplifier, attenuator, ..) of a BFN used at RF level can be adjustable to vary the value of the amplification, attenuation and phase w.r.t. to changes over time. According to a further or additional implementation, the network may comprise one or more phase shifters (for (adjustably) delaying the signals or portion of same) or for applying a LO phase shifting of the signals or portion of same in each path of the adjustable analog beamforming and/or nullsteering network so as to perform phase shifting and down conversion in one step. A possible implementation is given by https://ieeexplore.ieee.org/abstract/document/1393205. To sum up, the network may comprise amplifiers (fixed or adjustable), attenuators (fixed or adjustable) and/or phase shifters (preferably adjustable). Note that even if some components of the network may perform a down conversion, according to a further embodiment, the receiver may comprise an antenna interface for one or more antennas. This interface may comprise a down converter configured to down convert the received signals and forward their converted signals to the network. According to a further implementation, the down conversion may be performed within the network, namely by a harmonic-rejection down converting mixer comprised by the network. A possible implementation of such a harmonic-rejection down converting mixer is described by C. Kim, S. Joshi, C.M. Thomas, S. Ha., L.E. Larson and G. Cauwenberghs (A 1.3 mW 48 MHz 4 Channel MIMO Baseband Receiver With 65 dB Harmonic Rejection and 48.5 dB Spatial Signal Separation). To sum up, it should be noted that the phase shifting may be performed by conventional phase shifters (attenuators, amplifiers, etc.) or by the above-mentioned down-converting mixers. Note that processing is typically applied in analog base band or at high IF or at low IF.

Regarding the implementation of the beamforming and/or nullsteering network, it should be noted that it may be fully or partially meshed, e.g. a branch between all inputs and outputs or branches between selected inputs and outputs respectively.

According to embodiments, the receiver is configured to perform beamforming in order to separate signals belonging to different channels and/or separate signals received from different directions. This beamforming, for example, may be performed within the analog beamforming and/or nullsteering network or by the digital stage.

Regarding the digital stage, it should be noted that same may, for example, comprise an analog-to-digital converter. According to a preferred variant, the analog beamforming and/or nullsteering network is configured to reduce the dynamic range (e.g. between the interferer and the wanted signal) of the signal output to the digital stage of the analog-to-digital converter. According to an embodiment, the receiver is configured to perform a combination of analog beamforming and/or nullsteering by use of the network and digital beamforming and/or nullsteering performed by use of the digital stage to suppress strong interferences so as to cope with a interferer-to-signal ratio that is beyond the dynamic range of the applied analog-to-digital converter(s). This approach is called hybrid beamforming network. From a narrow point of view, this means that the digital stage may comprise one or more digital beamforming and/or nullsteering network(s)/entity(ies). This entity is used for at least one channel, wherein the stage may - according to embodiments - comprise further parallel channels. According to an embodiment, the digital beamforming and/or nullsteering entity is controlled using beamforming and/or nullsteering coefficients or using updated beamforming and/or nullsteering coefficients. The coefficients may, for example, be updated for spreading code sequentially over all possible spreading codes or for all groups of spreading codes sequentially over possible groups of spreading codes. According to further embodiments, the coefficients are calculated by use of a beamforming and/or nullsteering coefficient calculator which is connected to at least one tracking path and configured to estimate the beamforming and/or nullsteering coefficients. This calculator is part of a digital stage. According to a further implementation of same, the beamforming and/or nullsteering coefficient calculator may be connected to a plurality of tracking paths. These tracking paths are part of the digital stage, namely of a so-called group-wise switched module, each configured to track one channel included in the signal(s). According to a further embodiment, for each tracking path\channel an own calculator may be used.

According to an embodiment, each tracking entity of the respective tracking path is controlled by a so-called tracking control loop (for example one for the entire group-wise switched module). This tracking control loop which is configured to calculate time offset and/or frequency offset may be part of the digital stage or may be an external entity connected to the digital stage. The tracking control loop provides the calculated time offset and frequency offset of the plurality of tracking paths and/or to other entities of the digital stage. Background thereof is that the above-discussed tracking paths and the beamforming and/or nullsteering calculator forms together with a beamforming and/or nullsteering entity a so-called pre-beamforming architecture. Additionally - according to embodiments - a post-beamforming architecture, i.e. a post-beamforming tracking path connected to the digital beamforming and/or nullsteering entity may be used. This post-beamforming tracking path may also use time offset and/or frequency offset calculated by the tracking loop. Note that time offset is synonymous to code phase, while frequency offset is synonymous to carrier offset. It should be noted that according to embodiments, each tracking path and/or tracking entity performs a tracking by use of the spreading code as present in the signals.

According to embodiments, the above-discussed entities, especially the plurality of beamforming and/or nullsteering entities may be provided for a plurality of channels. Here, according to a first variant, the beamforming and/or nullsteering entity, the tracking control loop as well as the post-tracking entity may be present for several times (at least two times) within the digital stage, while all channels use the same pre-beamforming entity. According to a further embodiment, a plurality of tracking channels (including beamforming and nullsteering entity, tracking control loop as well as the post-tracking entity) may be combined with a plurality of pre-beamforming modules (each comprising one or more tracking paths together with the beamforming and/or nullsteering calculator). When one pre-beamforming tracking and calculating entity is shared, each of the plurality of digital beamforming and/or nullsteering entities may be connected by use of a switch, such that the beamforming and/or nullsteering coefficients are provided by the one calculator in a switched manner. If a plurality of calculators belonging to a plurality of prebeamforming tracking and calculating entities are used in combination with a plurality of beamforming and/or nullsteering entities, there might be a direct connection for providing the coefficients.

In case a plurality of post-tracking channels (comprising a beamforming and/or nullsteering entity, a tracking entity as well as a tracking control loop) are used, another switch connecting the plurality of tracking control loops with the respective tracking paths of the pre-beamforming tracking/calculating entity may be used so as to provide the time offset and/or frequency offset in a switched manner.

Regarding the beamforming and/or nullsteering coefficients, it should be noted that same may be used for controlling the digital beamforming and/or nullsteering entity as well as the analog beamforming and/or nullsteering network. Therefore, there might be a back channel or control channel from the digital stage to the analog beamforming and/or nullsteering network.

According to an embodiment belonging to a second aspect of the invention, a digital pre- and post-beamforming architecture is provided. Same is implemented in the above- discussed digital stage which comprises a digital beamforming and/or nullsteering entity for at least one channel, a group-wise switched module, a post-beamforming tracking path and a tracking control loop. The digital beamforming and/or nullsteering entity is controlled using beamforming and/or nullsteering coefficients or updated beamforming and/or nullsteering coefficients. These are estimated by tracking paths in combination with a beamforming and/or nullsteering parameter calculator comprised by the group-wise switched module. Each tracking path is configured to track one channel of the RF signal, wherein the calculator is connected to the respective tracking paths and configured to estimate the beamforming and/or nullsteering coefficients. The post-beamforming tracking path is connected to the digital beamforming and/or nullsteering entity. The post-beamforming tracking path as well as the tracking path (pre-beamforming tracking path) use time offset and/or frequency offset calculated by the tracking control loop. It should be noted that within the description of aspect 1 of the invention, this digital pre- and post-beamforming architecture was included by one of the optional embodiments, since this architecture can beneficially be combined with the analog beamforming and/or nullsteering network.

Embodiments of this aspect are based on the finding that due to the group-wise switched module (cf. plurality of tracking paths in combination with the calculators) method to estimate the beamforming coefficients for each channel in a multi-signal receiver system after code de-spreading (correlation with the spreading code at the receiver) the complexity in the digital part can be reduced. These beamforming coefficients can be used to spatially filter each the signals before tracking (fine acquisition) is implemented (cf. prebeamforming). Due to the tracking control loop, the group-wise switched module is synchronized with each tracking channel, such that the de-spreading of the code is only done for the correct time- and Doppler offset. This results in an efficient multi-channel beamforming system, e.g. for DSSS signals.

As discussed above, the beamforming and/or nuilsteering coefficients are updated for spreading code sequentially over all possible spreading codes and/or updated for groups of spreading codes sequentially over possible groups of spreading codes. This enables, for example, that each tracking path and/or tracking entity performs a tracking by use of the spreading code as present in the signals.

According to another embodiment, the correlation is performed using a plurality of spreading codes, e.g. x spreading codes (which must not necessarily be the spreading codes found within the received signal, e.g. in case of searching further signals having different codes). According to an embodiment, the tracking entity performs a prioritizing of the spreading codes out of the plurality of spreading codes, which have been marked as relevant. This marking may be performed by analyzing the received plurality of spreading codes over the time. The prioritized spreading codes are, for example, updated/tracked more often than compared to the others.

Above, it has been discussed that the digital part may, for example, comprise a plurality of digital beamforming and/or nullsteering entities for a plurality of channels. This approach may be applied also with respect to the isolated pre- and post-beamforming architecture. Here, the plurality of digital beamforming and/or nullsteering entities may be controlled by coefficients which are directly provided by a plurality of coefficient calculators or which are provided by use of a switch in a switched manner by a beamforming and/or nullsteering calculator. It should be noted that according to embodiments, each beamforming and/or nullsteering entity may comprise an own tracking control loop. In this case, the plurality of tracking control loops are connected to the plurality of tracking paths of the group-wise switched module via a switch.

A further embodiment provides a GNSS or DSSS receiver comprising a receiver according to one of the above-discussed implementations, i.e. according to aspect 1. According to a further embodiment, the GNSS or DSSS receiver may additionally or alternatively comprise a digital pre- and/or post-beamforming architecture as discussed with respect to aspect 2.

A further embodiment provides a method for receiving signals by use of one or more antennas, comprising the basic steps of preprocessing the signals by use of an analog beamforming and/or nullsteering network in order to mitigate interferences within the signals (at RF level, at IF level, at low IF level or at ABB level) and of further processing the preprocessed signals by use of a digital stage connected to the analog beamforming and/or nullsteering network.

According to a further embodiment, a method for pre- and post-beamforming is provided. The method comprises the steps of controlling a digital beamforming and/or nullsteering entity for at least one channel using beamforming and/or nullsteering coefficients or using updated beamforming and/or nullsteering coefficients; pre-tracking a plurality of beamforming channels of the signals by use of group-wise switched module comprising a plurality of tracking paths, and estimating the beamforming and/or nullsteering coefficients based on the tracked channels; post-tracking a single channel of the signals; and calculating a time offset and/or frequency offset and providing the calculated time offset and frequency offset to the pre- and post-tracking.

All methods may be computer implemented.

Further details are defined by the dependent claims. Below, embodiments of the present invention will subsequently be discussed referring to the enclosed figures, wherein

Fig. 1 a shows schematically a basic implementation of a receiver according to a hybrid nullsteering/beamforming approach according to an embodiment of the first aspect; Fig. 1 b-c show enhanced implementations of a receiver according to a hybrid nullsteering/beamforming approach according to further embodiments of the first aspect;

Fig. 2 shows schematically a beamforming coefficient calculation and implementation according to an embodiment;

Fig. 3 shows a schematic representation of a switching between different tracking channels where n is one channel out of N according to an embodiment;

Fig. 4 shows a schematic representation of a pre- and post-beamforming architecture according to an embodiment belonging to aspect 2; and

Fig. 5 shows schematically an example using a group of switched modules for a large number of channels.

Below, embodiments of the present invention will subsequently be discussed referring to the enclosed figures, wherein identical reference numerals are provided to objects/function entities having identical or similar function so that the description thereof is mutually applicable and interchangeable.

Fig. 1 a shows a receiver 10 which is connected to a plurality of antennas marked by the reference numeral 12. The receiver 10 comprises in the basic implementation an analog beamforming and/or nullsteering network 14 and a digital stage 16. According to a preferred variant, the analog beamforming and/or nullsteering network may be controlled by the digital stage as illustrated by the control line 18.

The analog beamforming and/or nullsteering network is arranged between the antennas 12 and the digital stage 16 so that same receives the A analog signals, e.g. RF signals 21 , processes same, e.g. by filtering and/or down conversion, and forwards the B signals to the digital stage 16, cf. reference numeral 23. Note 21 and 23 may both comprise a plurality of signals, namely A input signals and B output signals, wherein A is in the range of 1 to r (r= any arbitrary number) and B is in the range of B=1... s (s= any arbitrary number), Note s may according to embodiments be equal to A. For example, multiple outputs for different frequency bands may be used or the BFN 14 reduces from A to a smaller number B of outputs.

The analog beamforming and/or nullsteering network 14 has the purpose to perform a nullsteering in order to mitigate interferences within the signals. This preprocessing of the signals 21 is performed in the analog domain. According to embodiments, the analog beamforming and nullsteering network may comprise a down conversion so as to down convert the RF signal 21 to a signal at IF, LIF or ABB for the signal 23. Expressed in other words, this means that the analog beamforming and nullsteering network 14 can be realized at radio frequency (RF), low intermediate frequency (LIF), intermediate frequency (IF) or in the analog base band (ABB).

Regarding the implementation of the network 14, it should be noted that same can, for example, comprise analog amplifiers, attenuators and/or phase shifters. Note that the antenna block 12 with a number of A ports can be integrated with the second block 14 including the analog beamforming and nullsteering network and the down conversion to IF/LIF/ABB.

The advantage of the usage of the analog beamforming and nullsteering network 14 is that due to the mitigation of interfering signals in the analog domain, the required dynamic range of one or more of the following ADCs of the digital stage 16 (connected to the digital part of the multi-channel receiver (ADCs and digital processor) can be reduced.

Consequently, a lower bit depth for the ADCs is needed due to the lower dynamic range required. The digital processor sets the ABFN via the ABFN control line. In the digital part beamforming is applied to focus the beam onto the desired spatial signal incidence angle as well as remaining interferer power is null steered (suppressed).

The hybrid analog digital nullsteering and beamforming architecture enables in contrast to the state of the art nullsteering and beamforming architectures operating solely in the digital domain that high bit-depth ADC converters are not required anymore due to the reduced dynamic range of the GNSS signal. This leads to lower power consumption of the ADCs as well as lower processing capabilities which are needed.

According to embodiments the receiver 10 can be applied to different scenarios, so following signal conversions can be performed by same: 1. RF signal 21 -> processed by the BFN 14 at RF (for analog beamforming and\or nullsteering) -> down converted (e.g. by 14) to obtain 23 -> ADC -> processing of the digital signal

2. RF signal 21 -> processed by the BFN 14 including down-conversion (e.g. phase shifting performed by LO shifting) -> to obtain 23 -> ADC -> processing of the digital signal

3. RF signal 21 -> down converted -> analog multiplication at analog base band or at IF\Low IF (for analog beamforming and\or nullsteering) by use of 14 to obtain 23 -> ADC -> processing of the digital signal

4. RF signal 21 -> down converted -> processing (phase shifting and/or attenuating and/or amplifying) by use of the BFN 14 to obtain 23 -> ADC -> processing of the digital signal

Note that for performing the phase shifting and/or attenuating and/or amplifying the BFN 14 may comprise an attenuator, phase shifter and/or amplifier, e.g. an integrated controllable LNAs (integrated in the BFN).

Fig. 1 b shows another receiver 10’. This substantially complies to the receiver 10 of Fig. 1 a, wherein the digital stage 16a additionally comprises to the one or more ADCs in the digital processor one or more power sensors. These may have the purpose to perform an AGC control (automatic gain control) and\or additionally have the purpose to sense the power of the input signal(s) after the ABFN.

As illustrated by Fig. 1 c, this\these power sensor\sensors as well as the controlling portion for the analog beamforming and/or null steering network 14 can be separated from the digital stage. Fig. 1c shows such an implementation. Here, a parallel entity 18b is arranged in parallel to the digital stage 16 (comprising one or more ACDs and/or a digital processor). Both, the digital stage 16 as well as the control entity 18b receives the B signals 23/23a. As illustrated, the entity 18b controls the analog beamforming and/or null steering network 14 via the ABFN control line 18a. Fig. 2 exemplarily shows entities of the digital stage 16 having switched modules 26, a digital beamforming and/or nullsteering entity 28 as well as an optional additional entity/tracking entity 30.

The switched module comprises a plurality of tracking paths 26a, 26b, 26c, 26N, etc. and a beamforming and nullsteering calculator 27. Each tracking path receives from one of the plurality of antennas a respective signal, e.g. a down converted and/or digitized signal 1 , signal 2, signal A. Each signal may comprise l/Q data. The switched module 26 correlates the sampled input signals of the A number of receive antennas sequentially with the different spreading codes (or any other reference symbol) for a number of channels 1 to N. Here, the time offset (code delay) and frequency offset (Doppler) is provided by an appropriate tracking channel which is marked by the reference numeral 29. This tracking channel 29 uses the same spreading code as 26a, 26b ... 26c. The module 26 calculates the phase and the amplitude for each antenna channel signal 1 , signal 2 to signal A. These values are then used to calculate beamforming coefficients, wherein the calculation is performed by the calculator 27 for the channel\spreading code n out of N. The coefficients enable to steer a beam in the direction of the signal and to minimize interferences and multi-path components from other directions. Here, it should be noted that these values may be used to calculate the control values transmitted via the control line 18 (cf. Fig. 1 a) to the analog beamforming and nullsteering network 14. Furthermore, these coefficients are used for the digital beamforming and/or nullsteering entity 28 which has a control input connected to the entity 27.

The signal path following the beamforming and nullsteering network 28 comprises the posttracking entity 31 as well as an optional symbol decoder 31 and a pseudo-range calculator 32. The post-tracking entity uses the same time offset/frequency offset as calculated by the tracking control loop 29 and outputs its signal to the tracking control loop 29. This means that same can be used for the fine acquisitioned signals and for calculating the delay and Doppler (this information is provides to the entities 26a...26c and 30). The output of the symbol decoding entity 31 is a symbol stream which is also used by the pseudo-range calculation 32. This pseudo-range calculation has another input for the delay and the Doppler calculated by the tracking control loop 29. It is configured to output a pseude-range.

Below, the calculation of the beamforming and/or nullsteering coefficients will be discussed in detail. The calculated beamforming/nullsteering coefficients are used to combine the receiver channels to a single tracking channel. The beamforming/nullsteering coefficients are then updated each time the switched module re-evaluates the parameters for the single specified tracking channel. The beamforming/nullsteering coefficients are then stored in a buffer for each channel. The module will then switch to the next spreading code, using the new appropriate time and frequency offsets of the next tracking channel thus the beamforming is calculated sequentially for N different channels.

Since the proposed architecture of the digital processor has been discussed for a single channel n out of N with respect to Fig. 2, Figs. 3 and 4 exemplarily illustrate a switched operation. Fig. 3 comprises a switched module 26’ comprising a plurality of tracking paths 26a, 26b and 26c as well as the beamforming and/or nullsteering calculator 27. Furthermore, the digital stage of the receiver comprises N channels 35a’, 35b’ to 35N’. Each channel comprises a beamforming and/or nullsteering entity 28a', 28b’ and 28N’. Each beamforming and/or nullsteering entity 28a’, 28b’ and 28N’ receive, analogously to the beamforming and/or nullsteering entity 27 of Fig. 2, all signals signal 1 , signal 2 to signal A in order to perform the beamforming for all N channels. The respective data are output as l/Q data to the tracking paths 30 of the single channels 35a’, 35b’ and 35N’. Each of the channels 35a’, 35b’ to 35N’ comprises a tracking control loop 29 which outputs an information regarding the code delay and Doppler to the tracking paths 26a, 26b, 26c. Regarding the tracking control loop, it should be noted that same may, for example, perform scalar tracking or vector tracking. In order to assign the correct data to the correct tracking path, a switch 26s 1 is used to deliver the correct delay and Doppler to the respective tracking paths 26a to 26c. Vice versa, in order to deliver the correct beamforming and/or nullsteering coefficients to the respective beamforming and/or nullsteering entities 28a', 28b’ to 28N’, the beamforming and nullsteering calculator 27 is connected to same using a second switch 26s2’.

Fig. 4 shows another implementation. Here, two exemplary channels 35a’ and 35N’ are shown. Each channel comprising the tracking control loop 29, the tracking entity 30, the symbol decoder 31 as well as the beamforming and nullsteering entity 28a’/28N’. Furthermore, a plurality of switched beamforming modules 26a’ and 26m’ are shown. Each beamforming module 26a’ and 26m’ may be comparable to the beamforming module 26’ (i.e. has the same entities 26a, 26b, to 26c and 27) as well as the switches 26s T and 26s2’. Furthermore, the beamforming module 26a’ as well as the beamforming module 26m’ are both connected to the input of the digital stage in order to receive the signals 1 to A (analogously to the tracking channels 35a’ and 35N’). As discussed in context of Fig. 3, the switch 26s T connects the tracking paths 26a, 26b and to 26c to the control loops 29 of the plurality of tracking channels 35a’, 35N’. The switch 26s2’ connects the beamforming and/or nullsteering calculators 22 of the different beamforming modules 26a’, 26m’ with the beamforming and/or nullsteering entities 28a’ and 28N’.

As already indicated by the m and the n, it should be noted that the digital stage may have more than the two shown tracking channels 35a’ and 35N’ as well as more than the shown beamforming modules 26a’ and 26m’.

The multiple switched (M) modules 26a’ and 26m’ can be used to increase the update rate of the tracking channels. This means instead of just processing the beamforming and nullsteering weights for one channel n at the time (cf. Fig. 3) M channels out of N are processed at the time. E.g. the grouping for M=2 could be group 1 : channel 1 & 2, group 2: channel 4 & 6, group 3: channel 3 & 5, and so on. This increases the system complexity, but greatly increases the response time of the adaptive beamforming and nullsteering. Compared to a conventional receiver where all channels N at each time are processed, it would still decrease the system complexity. Furthermore, the groups could be sorted by signal power and more relevant (better signal top noise ratio C/N) groups may be updated more frequently.

The above-described architecture (cf. Figs. 3 and 4) enables a pre- and post-beamforming architecture. With respect to Fig. 5, the architecture 50 may be illustrated in a simplified manner. Fig. 5 shows an architecture comprising a pre-beamforming 52 as well as a postbeamforming 54. The pre-beamforming entity 52 is coupled in parallel to the beamforming and nullsteering modules 28a’, 28b’ and 28N’ with the antenna ports 12. The prebeamforming entity 52 comprises a plurality of tracking loops 26a to 26N for tracking the different channels and outputting data regarding the amplitude, the phase and the PRN to a calculator 27 for calculating (weights calculation) the coefficients for beamforming and interferer nullsteering. These coefficients are used by the beamforming and nullsteering entities 28a to 28N. Each of the beamforming and nullsteering entity 28a and 28N (belonging to a respective channel) outputs its signal to the post-beamforming entity 54 which comprises for each channel an own tracking unit 30a’ to 30p’.

Expressed in other words, this means that the only difference between Fig. 3 and Fig. 5 is that in Fig. 5 the channel n is switched in increasing order from 1 to N/P, wherein in Fig. 3, the n over the time can be chosen arbitrary. According to a preferred variant, the pre- and post-beamforming approach is combined with the hybrid analog digital nullsteering and/or beamforming architecture (cf. Fig. 1 a\Fig. 1 b, Fig 1 c). By applying a hybrid analog digital nullsteering and beamforming architecture and a hybrid pre- and post-beamforming architecture in the digital domain, a significant reduction of the complexity of the receiver, especially in the digital domain, is achieved.

Another embodiment provides a low complexity hybrid analog digital GNSS, DSSS receiver architecture, e.g. comprising the hybrid beamforming/nullsteering approach and/or the pre- and post-beamforming approach.

According to a further embodiment, the receiver uses the analog beamforming network to suppress strong interferers.

According to a further embodiment, the receiver uses the analog beamforming network to decrease the needed dynamic range for the analog-to-digital converters (of the digital domain).

According to a further embodiment, the receiver applies an analog beamforming network in combination with a digital beamforming network to suppress interferers.

According to a further embodiment, the receiver updates the digital beamforming network per spread code sequentially over all possible spreading codes.

According to a further embodiment, the receiver updates a digital beamforming network for groups of spreading code sequentially over all possible groups of spreading codes.

According to a further embodiment, a method for receiving a signal is provided. The method comprises the steps of preprocessing the signals by use of the analog beamforming/nullsteering network and further processing the preprocessed signals by use of the digital stage.

Another embodiment provides a pre- and post-beamforming. Here, the main steps of pretracking a plurality of beamforming channels of the signal by use of a group-wise switched module and post-tracking a single channel is performed. Although some aspects have been described in the context of an apparatus, it is clear that these aspects also represent a description of the corresponding method, where a block or device corresponds to a method step or a feature of a method step. Analogously, aspects described in the context of a method step also represent a description of a corresponding block or item or feature of a corresponding apparatus. Some or all of the method steps may be executed by (or using) a hardware apparatus, like for example, a microprocessor, a programmable computer or an electronic circuit. In some embodiments, some one or more of the most important method steps may be executed by such an apparatus.

Depending on certain implementation requirements, embodiments of the invention can be implemented in hardware or in software. The implementation can be performed using a digital storage medium, for example a floppy disk, a DVD, a Blu-Ray, a CD, a ROM, a PROM, an EPROM, an EEPROM or a FLASH memory, having electronically readable control signals stored thereon, which cooperate (or are capable of cooperating) with a programmable computer system such that the respective method is performed. Therefore, the digital storage medium may be computer readable.

Some embodiments according to the invention comprise a data carrier having electronically readable control signals, which are capable of cooperating with a programmable computer system, such that one of the methods described herein is performed.

Generally, embodiments of the present invention can be implemented as a computer program product with a program code, the program code being operative for performing one of the methods when the computer program product runs on a computer. The program code may for example be stored on a machine readable carrier.

Other embodiments comprise the computer program for performing one of the methods described herein, stored on a machine readable carrier.

In other words, an embodiment of the inventive method is, therefore, a computer program having a program code for performing one of the methods described herein, when the computer program runs on a computer.

A further embodiment of the inventive methods is, therefore, a data carrier (or a digital storage medium, or a computer-readable medium) comprising, recorded thereon, the computer program for performing one of the methods described herein. The data carrier, the digital storage medium or the recorded medium are typically tangible and/or nontransitionary.

A further embodiment of the inventive method is, therefore, a data stream or a sequence of signals representing the computer program for performing one of the methods described herein. The data stream or the sequence of signals may for example be configured to be transferred via a data communication connection, for example via the Internet.

A further embodiment comprises a processing means, for example a computer, or a programmable logic device, configured to or adapted to perform one of the methods described herein.

A further embodiment comprises a computer having installed thereon the computer program for performing one of the methods described herein.

A further embodiment according to the invention comprises an apparatus or a system configured to transfer (for example, electronically or optically) a computer program for performing one of the methods described herein to a receiver. The receiver may, for example, be a computer, a mobile device, a memory device or the like. The apparatus or system may, for example, comprise a file server for transferring the computer program to the receiver .

In some embodiments, a programmable logic device (for example a field programmable gate array) may be used to perform some or all of the functionalities of the methods described herein. In some embodiments, a field programmable gate array may cooperate with a microprocessor in order to perform one of the methods described herein. Generally, the methods are preferably performed by any hardware apparatus.

The above described embodiments are merely illustrative for the principles of the present invention. It is understood that modifications and variations of the arrangements and the details described herein will be apparent to others skilled in the art. It is the intent, therefore, to be limited only by the scope of the impending patent claims and not by the specific details presented by way of description and explanation of the embodiments herein. List of Reference Numerals

10 Receiver

14 Analog beamforming and/or nullsteering network

12 Antennas

16 Digital stage

21 , 23 Signals

28 Digital beamforming and/or nullsteering entity

26a, 26b, 26c, 26N Tracking path

27 Calculator

30 Tracking entity

29 Tracking control loop

26 Group-wise switched module

54 Post-beamforming tracking path

Claims

1. A receiver (10) comprising: an adjustable analog beamforming and/or null steering network (14) connecting to one or more antennas (12) that receive signal (21 , 23) over the air and configured to preprocess the signal (21 , 23) in order to mitigate interferences within the signal (21 , 23); and a digital stage (16) comprising one or more analog to digital converter, connected to the analog beamforming and/or null steering network (14) and configured to further process the analog preprocessed signal (21 , 23).

2. The receiver (10) according to one of the previous claims, wherein the signal (21 , 23) are RF signal; and/or wherein the interferences are mitigated within the signal (21 , 23) at RF level or after down conversion at IF level or after down conversion at low IF level or after down conversion at analog baseband level.

3. The receiver (10) according to one of the previous claims, wherein the analog beamforming and/or null steering network (14) is controlled by the digital stage (16); or wherein the analog beamforming and/or null steering network (14) is controlled by the digital stage (16) by use of beamforming and/or null steering coefficients.

4 The receiver (10) according to one of the previous claims, wherein the analog beamforming and/or null steering network (14) is adaptively configured to perform null steering in order to suppress time variant or time invariant interferences within the signal (21 , 23).

5. The receiver (10) according to one of the previous claims, wherein the receiver is configured to perform beamforming in order to separate signal (21 , 23) belonging to different channels and/or to separate signal (21 , 23) received from different directions.

6. The receiver (10) according to one of the previous claims, wherein the analog beamforming and/or null steering network (14) comprises a plurality of inputs and a plurality of outputs or wherein the analog beamforming and/or null steering network (14) comprises a plurality of inputs and a plurality, where the number of outputs is equal or larger than the number of inputs; and/or wherein the analog beamforming and/or null steering network (14) comprises a plurality of inputs and a plurality of outputs, said inputs and outputs are fully meshed or partially meshed or wherein the analog beamforming and/or null steering network (14) is implanted as fully meshed or partially meshed network.

7. The receiver (10) according to one of the previous claims, wherein the analog beamforming and/or null steering network (14) comprises one or more analog amplifiers for amplifying the signal (21 , 23) and/or a portion of the signal (21 , 23) and/or one or more adjustable analog amplifiers for adjustably amplifying the signal (21 , 23) and/or a portion of the signal (21 , 23) and/or one or more attenuators for attenuating the signal (21 , 23) and/or a portion of the signal (21 , 23) one or more adjustable attenuators for adjustably attenuating the signal (21 , 23) and/or a portion of the signal (21 , 23).

8. The receiver (10) according to one of the previous claims, wherein the analog beamforming and/or null steering network (14) comprises one or more phase shifters for delaying the signal (21 , 23) and/or a portion of the signal (21 , 23) and/or one or more adjustable phase shifters for adjustably delaying the signal (21 , 23) and/or a portion of the signal (21 , 23) and/ one or more phase shifters applying a LO phase shifting of the signal (21 , 23) and/or a portion of the signal (21 , 23) in each path of the adjustable analog beamforming and/or null steering network (14) so as to perform phase shifting and down conversion is one step.

9. The receiver (10) according to one of the previous claims, wherein the receiver comprises an antenna interface for the one or more antennas (12), wherein the igital stage (16) interface comprises a down converter configured to down convert the received signal and forwarding the converted signal to the analog beamforming and/or null steering network (14); and/or wherein the beamforming and/or nullsteering network comprises an harmonic- rejection down converting mixer.

10. The receiver (10) according to one of the previous claims, wherein the beamforming and/or nullsteering performed by the adjustable analog beamforming and/or null steering network (14) is applied in analog baseband or at IF or at low IF.

1 1. The receiver (10) according to one of the previous claims, wherein the digital stage (16) comprises at least one analog to digital converter.

12. The receiver (10) according to one of the previous claims, wherein the analog beamforming and/or null steering network (14) is configured to reduce the dynamic range of the signal (21 , 23) output to the digital stage and/or to the analog to a digital converter of the digital stage (16).

13. The receiver (10) according to one of the previous claims, wherein the digital stage (16) comprises one or more power sensors which are connected to the analog beamforming and/or nullsteering network and their measurement results may be applied from the digital stage to adjust the analog beamforming and/or nullsteering network via an ABFN control line to as an example to mitigate interference.

14. The receiver (10) according to one of the previous claims, wherein the receiver comprises an analog only control loop configured to adjust the analog beam forming and/or nullsteering network based on the measurement of one or more power sensors of the analog only control loop to mitigate the interference and/or confgured to control the analog beam forming and/or nullsteering network.

15. The receiver (10) according to one of the previous claims, wherein the beamforming and/or nullsteering network comprises an output having a plurality of output groups each or a plurality of output groups each covering different frequency band and/or used as monitoring outputs or a plurality of output groups each used as monitoring outputs which are connected to one or more power sensors.

16. The receiver (10) according to one of the previous claims, wherein the receiver is configured to use a combination of the beamforming and/or null steering network and a digital beamforming and/or or null steering network of the digital stage (16) to suppress strong interferes wherein the interferer to wanted signal ratio is beyond the dynamic range of the applied analog to a digital converters.

17. The receiver (10) according to one of the previous claims, wherein the digital stage (16) comprises a digital beamforming and/or null steering entity (28) for at least one channel.

18. The receiver (10) according to claim 17, wherein the digital beamforming and/or null steering entity (28) is controlled using beamforming and/or null steering coefficients or wherein the digital beamforming and/or null steering entity (28) is controlled using updated beamforming and/or null steering coefficients.

19. The receiver (10) according to claim 18, wherein the beamforming and/or null steering coefficients are updated for spreading code sequentially over all possible spreading codes and/or wherein the beamforming and/or null steering coefficients are updated for groups of spreading codes sequentially over all possible groups of spreading codes.

20. The receiver (10) according to one of claims 17 to 19, wherein the digital stage (16) comprises a beamforming and/or null steering coefficient calculator (28) connected to at least one tracking path (26a, 26b, 26c, 26N) and configured to estimate the beamforming and/or null steering coefficients; and/or wherein the digital stage (16) comprises a group-wise switch module comprising a plurality of tracking paths (26a, 26b, 26c, 26N), each configured to track one beamforming channel of the signal (21 , 23), and a beamforming and/or null steering coefficient calculator (28) connected to the plurality of tracking paths and configured to estimate the beamforming and/or null steering coefficients.

21. The receiver (10) according to claim 20, wherein the group wise switch module comprises a plurality of beamforming and/or null steering coefficient calculators (28) each connected to a plurality of tracking paths (26a, 26b, 26c, 26N).

22. The receiver (10) according to claim 20 or 21 , wherein the digital stage (16) is connected to an external tracking control loop (29) or comprises a tracking control loop (29) configured to calculate a time offset and/or a frequency offset and provide the calculated time offset and frequency offset to the plurality of tracking paths (26a, 26b, 26c, 26N) and/or to a post beamforming tracking path (26a, 26b, 26c, 26N) connected to the digital beamforming and/or null steering entity (28).

23. The receiver (10) according to one of claims 27 to 22, wherein the digital beamforming null steering entity is connected to a tracking entity (30) at its output configured for post-tracking.

24. The receiver (10) according to one of the claims 17 to 23, wherein each tracking path (26a, 26b, 26c, 26N) and/or tracking entity (30) performs the tracking by use of the spreading code as present in the signal (21 , 23).

25. The receiver (10) according to one of the claims 17 to 24, wherein each tracking path (26a, 26b, 26c, 26N) and/or tracking entity (30) is configured to perform the tracking for a plurality of spreading codes and to prioritize spreading codes out of the plurality of spreading codes and/or to track the prioritized spreading codes in a prioritized manner.

26. The receiver (10) according to one of claims 17 to 25, wherein the digital stage (16) comprises a plurality of digital beamforming and/or null steering entities for a plurality of channels.

27. The receiver (10) according to claim 26, wherein each of the plurality of digital beamforming and/or null steering entities is controlled by beamforming and/or null steering coefficients which are directly provided by one of a plurality of beamforming and/or null steering coefficient calculators (28) or which are provided by a switch in a switched manner by a beamforming and/or null steering calculator (28).

28. The receiver (10) according to claim 26 or 27, wherein each beamforming and/or null steering entity comprises a tracking control loop (29) or an interface to an eternal tracking control loop (29).

29. The receiver (10) according to ciaim 28, wherein the digital stage (16) comprises a switch between the plurality of tracking control loops (29) and the plurality of tracking paths (26a, 26b, 26c, 26N) of the group-wise switched module.

30. The receiver (10) according to one of claims 18 to 29, wherein the beamforming and/or null steering coefficients are used to control the analog beamforming and/or null steering network (14).

31. The receiver (10) according to claim 30, wherein the receiver comprises a back or control channel from the digital stage (16) to the analog beamforming and/or null steering network (14).

32. A digital pre- and post-beamforming architecture (50) comprising: a digital stage (16) comprising: a digital beamforming and/or null steering entity (28) for at least one channel; wherein the digital beamforming and/or null steering entity (28) is controlled using beamforming and/or null steering coefficients or wherein the digital beamforming and/or null steering entity (28) is controlled using updated beamforming and/or null steering coefficients; a group wise switch module comprising a plurality of tracking paths (26a, 26b, 26c, 26N), each configured to track one beamforming channel of the signal (21 , 23), and a beamforming and/or null steering coefficient calculator (28) connected to the plurality of tracking paths (26a, 26b, 26c, 26N) and configured to estimate the beamforming and/or null steering coefficients; a post beamforming tracking path (54) connected to the digital beamforming and/or null steering entity (28); and a tracking control loop (29) configured to calculate a time offset and/or a frequency offset and provide the calculated time offset and frequency offset to the plurality of tracking paths (26a, 26b, 26c, 26N) and/or to the post beamforming tracking path.

33. The architecture (50) according to claim 32, wherein the beamforming and/or null steering coefficients are updated for spreading code sequentially over all possible spreading codes and/or wherein the beamforming and/or null steering coefficients are updated for groups of spreading codes sequentially over all possible groups of spreading codes.

34. The architecture (50) according to claim 32 or 33, wherein each tracking path (26a, 26b, 26c, 26N) and/or tracking entity (30) performs the tracking by use of the spreading code as present in the signal (21 , 23).

35. The architecture (50) according to one of claims 32 to 34, wherein the digital stage (16) comprises a plurality of digital beamforming and/or null steering entities for a plurality of channels.

36. The architecture according to claim 35, wherein each of the plurality of digital beamforming and/or null steering entities is controlled by beamforming and/or null steering coefficients which are directly provided by one of a plurality of beamforming and/or null steering coefficient calculators (28) or which are provided by a switch in a switched manner by a beamforming and/or null steering calculator (28).

37. The architecture (50) according to one of claims 35 to 36, wherein each beamforming and/or null steering entity comprises a tracking control loop (29).

38. The architecture (50) according to one of the claims 35 to 37, wherein the digital stage (16) comprises a switch between the plurality of tracking control loops (29) and the plurality of tracking paths (26a, 26b, 26c, 26N) of the group wise switched module.

39. A GNSS or DSSS receiver comprising a receiver (10) according to one of the claims 1 to 31 or a digital pre- and post-beamforming architecture (50) according to one of claims 32 to 38.

40. A method for receiving signal (21 , 23) by use of one or more antennas (12), comprising the following steps: preprocessing the signal (21 , 23) by use of an analog beamforming and/or null steering network (14) in order to mitigate interferences within the signal (21 , 23); and further processing the preprocessed signal (21 , 23) by use of a digital stage (16) connected to the analog beamforming and/or null steering network (14) network.

41. A method for pre- and post-beamforming, comprising the following steps: controlling a digital beamforming and/or null steering entity (28) for at least one channel using beamforming and/or null steering coefficients or using updated beamforming and/or null steering coefficients; pre tracking a plurality of beamforming channels of the signal (21 , 23) by use of a group-wise switch module comprising a plurality of tracking paths (26a, 26b, 26c, 26N), and estimating the beamforming and/or null steering coefficients based on the tracked beamforming channels; post tracking a single channel of the signal (21 , 23); and calculating a time offset and/or a frequency offset and providing the calculated time offset and frequency offset for the pre- and post- tracking.

42. A computer program for performing, when running a computer, one of the method steps according to the method as defined by claim 40 or 41 , when running on a computer.