Patent Description:
The Third Generation Partnership Project (3GPP) has developed and is developing standards for Fourth Generation (<NUM>) (also referred to as Long Term Evolution (LTE)) and Fifth Generation (<NUM>) (also referred to as New Radio (NR)) wireless communication systems. Such systems provide, among other features, broadband communication between network nodes, such as base stations, and mobile wireless devices (WD), as well as communication between network nodes and between WDs. Sixth Generation (<NUM>) wireless communication systems are also under development.

Wireless communication systems according to the 3GPP may include one or more of the following channels:.

Fifth generation (<NUM>) wireless systems introduced massive multiple input multiple output (MIMO) technology to further improve the spectral efficiency of mobile communication networks. Base station architectures have fundamentally been impacted as the number of antenna increased approximately by one order of magnitude together with the associated number of transceiver chains. This paradigm shift introduced some challenges to the design of radio products. As a result, radio size and power consumption are of concern to network equipment vendors.

Full digital beamforming offers flexibility since every subcarrier can potentially be beamformed using a unique set of weights in both the vertical and the horizontal dimensions. <FIG> illustrates an example of a <NUM> radio processing chain using full digital beamforming. For every subcarrier, the K MIMO layers are mapped to the N antennas using a digital beamformer. The total number of antennas is N = N<NUM> × N<NUM>, where N<NUM> is the number of horizontal antennas and N<NUM> is the number of vertical antennas.

Following the frequency-domain (FD) digital beamformer, N parallel processing chains are needed to upconvert the signal to the RF frequencies. The digital radio processing includes operations that are computationally intensive such as the inverse Fast Fourier transformation (IFFT), channel filtering, sample rate up-conversion (↑N), Crest Factor Reduction (CFR), digital predistortion (DPD), digital to analog conversion (DAC), analog processing, and band filtering.

To mitigate the hardware complexity challenge, hybrid beamforming methods such as constrained digital beamforming may be utilized to reduce the amount of digital processing. For example, some digital time-domain (TD) beamforming (BF) weights can be applied later in the processing chain as illustrated in the example of <FIG>. In <FIG>, the time-domain beamforming weights are applied by the time domain beam former <NUM> positioned electrically in series between the CFR circuits <NUM> and the Digital Pre-Distortion (DPD) modules <NUM>, thus reducing the number of processing chains from N to M between the FD beamformer <NUM> and the TD beamformer <NUM>. In some embodiments, M is configured to correspond to N<NUM>, the number of horizontal antenna ports.

Typically, the beamforming weights are updated on a symbol or on a slot basis, an example of which is illustrated in <FIG>. When the beam weights are applied in the time-domain, the sudden coefficient change at the symbol or slot boundary creates a discontinuity which causes some spectral regrowth, as shown in the example of <FIG>. In <FIG>, trace A is the power spectral density (PSD) before time domain beam forming. Trace B is the PSD after symbol-based time domain beam forming. Trace C is the PSD after slot-based time domain beam forming. The dashed line D is a mask requirement of the United Stated Federal Communication Commission (FCC).

The distortion shown in <FIG> that is close to the carrier cannot be removed as the channel filter is located upstream of the TD beamformer. This may lead to unsatisfactory radio performance that fails to meet the regulatory operating band unwanted emission (OBUE) requirement masks, such as those from the 3GPP or regulatory agencies.

To alleviate this problem, one approach includes providing circuitry <NUM> to insert zeros within the cyclic prefix prior to the channel filter, as illustrated in the example of <FIG>. The baseband zero insertion may be done by smoothly ramping the signal down, or by simply zeroing the signal using a step function. The baseband zero insertion method does help improve the spectrum. <FIG> shows an example of the spectrum before and after applying the time-domain beamforming using known methods for a NR <NUM> carrier. The beamforming coefficients are updated at a symbol-level rate.

In <FIG>, the trace A shows the spectrum when zeros replace <NUM>% of the cyclic prefix. While this arrangement may meet the U. Federal Communication Commission (FCC) requirement mask (with little margin), this arrangement fails to meet other requirements such as the Korean B42 spurious emission mask. The trace B shows the spectrum when zeroing <NUM>% of the cyclic prefix. In this example, both the U. FCC and Korean requirement masks are met, but there is very little margin left for random variations or other sources of impairment. In addition, such a long zeroing length will impact the link-level performance, especially when the channel delay spread is large.

<CIT> discusses a power efficient and simple structure for linearizing the output of power amplifiers in multi-antenna beamforming systems. Beamforming factors are obtained for controlling transmission beams of the antennas in an analogue/hybrid beamforming system. At least one power amplifier model is determined on the basis of the output of the power amplifiers and the beamforming factors. Predistortion parameters, for feeding a predistorted signal to power amplifiers for linearizing the outputs of the power amplifiers, are determined such that after the operating parameters of the power amplifiers have been adjusted, errors in the outputs of the power amplifiers are reduced.

Some embodiments advantageously provide a method and system for forward distortion correction (FDC) for time-domain beamforming. Some embodiments mitigate the spectral regrowth that is produced by time-domain beam switching activity.

In some FDC methods disclosed herein, non-linear distortion may be isolated using fast transition band digital filters and then subtracted from the signal such that the emission masks are met with sufficient margins, even when using symbol-based switching, for the narrower carrier bandwidths, and with high power spectral density (PSD).

Some embodiments may have at least one of the following advantages:.

According to the present disclosure, a method and a network node according to the independent claims are provided. Developments are set forth in the dependent claims.

According to one aspect, a method in a network node configured to communicate with a wireless device is provided. The method includes filtering each signal output by a time domain beamformer by a band stop filter, the band stop filter including a stop band overlapping a pass band of the signal output by the time domain beamformer. The method also includes filtering each signal output by the time domain beamformer by a group delay filter in electrical parallel with a band stop filter, the group delay filter providing a group delay to the signal output by the time domain beamformer. The method further includes subtracting an output of each band stop filter from an output of a corresponding group delay filter.

According to this aspect, in some embodiments, the method further includes inserting zeros to a signal that is processed to be input to the time domain beamformer to achieve a specified level of suppression of out-of-band emissions using a band stop filter that is of lower order than a band stop filter that achieves the specified level of suppression of out-of-band emission when no zeros are inserted to the signal. In some embodiments, each band stop filter includes an infinite impulse response, IIR, band stop filter electrically in series with a phase equalizer. In some embodiments, transfer function poles and transfer function zeros of both the IIR band stop filter and the phase equalizer are combined to provide a phase linear IIR filter. In some embodiments, the phase equalizer is an all pass phase equalizer. In some embodiments, the all pass phase equalizer is configured as a sum of two all pass filters using a Hilbert transform. In some embodiments, each band stop filter includes an infinite impulse response, IIR, band stop filter implemented using zero-phase IIR filtering, thereby doubling the filter order and providing zero phase distortion. In some embodiments, each band stop filter includes a cascade of band stop filters. In some embodiments, each band stop filter is an infinite impulse response, IIR, filter having quantized poles inside a unit circle centered at the origin of a complex plane. In some embodiments, each band stop filter is a finite impulse response, FIR, filter. In some embodiments, each band stop filter is a finite impulse response, FIR, filter, implemented in the frequency domain using a cascade of a Fast Fourier Transform, FFT, and an inverse FFT, following one of an overlap and save method and an overlap and add method. In some embodiments, portions of the signal output by the time domain beamformer in a vicinity of time domain beam weight transitions are filtered to improve the signal Error Vector Magnitude (EVM).

According to another aspect, a network node is configured to communicate with a wireless device. The network node is configured to implement a time domain beamformer, and includes circuitry configured to filter each signal output by the time domain beamformer by a band stop filter, the band stop filter including a stop band overlapping a pass band of the signal output by the time domain beamformer. The network node also includes circuitry configured to filter each signal output the time domain beamformer by a group delay filter in electrical parallel with a band stop filter, the group delay filter providing a group delay to the signal output by the time domain beamformer. The network node further includes circuitry to subtract an output of each band stop filter from an output of a corresponding group delay filter.

According to this aspect, in some embodiments, the circuitry is further configured to insert zeros to a signal that is processed to be input to the time domain beamformer to achieve a specified level of suppression of out-of-band emissions using a band stop filter that is of lower order than a band stop filter that achieves the specified level of suppression of out-of-band emission when no zeros are inserted to the signal. In some embodiments, each band stop filter includes an infinite impulse response, IIR, band stop filter in electrical series with a phase equalizer. In some embodiments, transfer function poles and transfer function zeros of both the IIR band stop filter and the phase equalizer are combined to provide a phase linear IIR filter. In some embodiments, the phase equalizer is an all pass phase equalizer. In some embodiments, the all pass phase equalizer is configured as a sum of two all pass filters using a Hilbert transform. In some embodiments, each band stop filter includes a cascade of band stop filters. In some embodiments, each band stop filter is an infinite impulse response, IIR, filter having quantized poles inside a unit circle centered at the origin of a complex plane. In some embodiments, each band stop filter is a finite impulse response, FIR, filter. In some embodiments, each stop band filter is a finite impulse response, FIR, filter, implemented in the frequency domain using a cascade of a Fast Fourier Transform, FFT, and an inverse FFT.

According to another aspect, a network node is configured to communicate with a wireless device. The network node includes: a time domain beamformer configured to beam-form a plurality of signals to produce a plurality of time domain beamformer output signals; a plurality of band stop filters, each band stop filter of the plurality of band stop filter being configured to receive an output signal of the time domain beamformer; a plurality of group delay filters, each group delay filter of the plurality of group delay filters receiving an output signal of the time domain beamformer and being in electrical parallel with a band stop filter of the plurality of band stop filters; and a plurality of summation circuits, each summation circuit configured to subtract an output of a band stop filter of the plurality of band stop filters from an output of a corresponding group delay filter of the plurality of group delay filters.

According to this aspect, in some embodiments, the network node also includes circuitry to insert zeros to a signal that is processed to be input to the time domain beamformer to produce an output of the summation circuits that achieves a specified level of suppression of out-of-band emissions using a band stop filter that is of lower order than a band stop filter that achieves the specified level of suppression of out-of-band emission when no zeros are inserted to the signal. In some embodiments, each band stop filter of the plurality of band stop filters includes an infinite impulse response, IIR, band stop filter in electrical series with an all pass phase equalizer. In some embodiments, a stop band of a band stop filter of the plurality of band stop filters is configured to encompass a pass band of a time domain beamformer output signal that is input to the band stop filter.

According to yet another aspect, a method in a network node configured to communicate with a wireless device is provided. The method includes: beamforming a plurality of signals to produce a plurality of time domain beamformer output signals; filtering each signal of the plurality of signals by a band stop filter, each band stop filter being configured to receive an output signal of the time domain beamformer; group delay-filtering each signal of the plurality of signals by a of group delay filter, each group delay filter being configured to receive an output signal of the time domain beamformer and being in electrical parallel with a band stop filter; and for each band stop filter, subtracting an output of a band stop filter from an output of a corresponding group delay filter.

According to this aspect, in some embodiments, the method also includes inserting zeros to a signal that is processed to be input to the time domain beamformer to produce an output of the subtracting that achieves a specified level of suppression of out-of-band emissions using a band stop filter that is of lower order than a band stop filter that achieves the specified level of suppression of out-of-band emission when no zeros are inserted to the signal. In some embodiments, each band stop filter includes an infinite impulse response, IIR, band stop filter in electrical series with an all pass phase equalizer. In some embodiments, a stop band of a band stop filter is configured to encompass a pass band of a time domain beamformer output signal that is input to the band stop filter.

Before describing in detail example embodiments, it is noted that the embodiments reside primarily in combinations of apparatus components and processing steps related to forward distortion correction (FDC) for time-domain beamforming. Accordingly, components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

The term "network node" used herein can be any kind of network node comprised in a radio network which may further comprise any of base station (BS), radio base station, base transceiver station (BTS), base station controller (BSC), radio network controller (RNC), g Node B (gNB), evolved Node B (eNB or eNodeB), Node B, multi-standard radio (MSR) radio node such as MSR BS, multi-cell/multicast coordination entity (MCE), relay node, donor node controlling relay, radio access point (AP), transmission points, transmission nodes, Remote Radio Unit (RRU) Remote Radio Head (RRH), a core network node (e.g., mobile management entity (MME), self-organizing network (SON) node, a coordinating node, positioning node, MDT node, etc.), an external node (e.g., 3rd party node, a node external to the current network), nodes in distributed antenna system (DAS), a spectrum access system (SAS) node, an element management system (EMS), etc. The network node may also comprise test equipment. The term "radio node" used herein may be used to also denote a wireless device (WD) such as a wireless device (WD) or a radio network node.

It can be any kind of a radio network node which may comprise any of base station, radio base station, base transceiver station, base station controller, network controller, RNC, evolved Node B (eNB), Node B, gNB, Multi-cell/multicast Coordination Entity (MCE), relay node, access point, radio access point, Remote Radio Unit (RRU) Remote Radio Head (RRH).

Referring again to the drawing figures, in which like elements are referred to by like reference numerals, there is shown in <FIG> a schematic diagram of a communication system <NUM>, according to an embodiment, such as a 3GPP-type cellular network that may support standards such as LTE and/or NR (<NUM>), which comprises an access network <NUM>, such as a radio access network, and a core network <NUM>. The access network <NUM> comprises a plurality of network nodes 16a, 16b, 16c (referred to collectively as network nodes <NUM>), such as NBs, eNBs, gNBs or other types of wireless access points, each defining a corresponding coverage area 18a, 18b, 18c (referred to collectively as coverage areas <NUM>). Each network node 16a, 16b, 16c is connectable to the core network <NUM> over a wired or wireless connection <NUM>. A first wireless device (WD) 22a located in coverage area 18a is configured to wirelessly connect to, or be paged by, the corresponding network node 16a. A second WD 22b in coverage area 18b is wirelessly connectable to the corresponding network node 16b. While a plurality of WDs 22a, 22b (collectively referred to as wireless devices <NUM>) are illustrated in this example, the disclosed embodiments are equally applicable to a situation where a sole WD is in the coverage area or where a sole WD is connecting to the corresponding network node <NUM>. Note that although only two WDs <NUM> and three network nodes <NUM> are shown for convenience, the communication system may include many more WDs <NUM> and network nodes <NUM>.

A network node <NUM> (eNB or gNB) is configured to include a NN filter unit <NUM> which is configured to filter each signal output by a time domain beamformer by a group delay filter in electrical parallel with a band stop filter, the group delay filter providing a group delay to the signal output by the time domain beamformer.

Example implementations, in accordance with an embodiment, of the WD <NUM> and network node <NUM> discussed in the preceding paragraphs will now be described with reference to <FIG>.

The communication system <NUM> includes a network node <NUM> provided in a communication system <NUM> and including hardware <NUM> enabling it to communicate with the WD <NUM>. The hardware <NUM> may include a radio interface <NUM> for setting up and maintaining at least a wireless connection <NUM> with a WD <NUM> located in a coverage area <NUM> served by the network node <NUM>. The radio interface <NUM> includes an array of antennas <NUM> to radiate and receive signal(s) carrying electromagnetic waves and also includes the network node filter unit <NUM>.

Thus, the network node <NUM> further has software <NUM> stored internally in, for example, memory <NUM>, or stored in external memory (e.g., database, storage array, network storage device, etc.) accessible by the network node <NUM> via an external connection. The processing circuitry <NUM> may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by network node <NUM>. Processor <NUM> corresponds to one or more processors <NUM> for performing network node <NUM> functions described herein. The memory <NUM> is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software <NUM> may include instructions that, when executed by the processor <NUM> and/or processing circuitry <NUM>, causes the processor <NUM> and/or processing circuitry <NUM> to perform the processes described herein with respect to network node <NUM>. For example, processing circuitry <NUM> of the network node <NUM> may include a NN filter unit <NUM> which is configured to filter each signal output by a time domain beamformer by a group delay filter in electrical parallel with a band stop filter, the group delay filter providing a group delay to the signal output by the time domain beamformer.

The radio interface <NUM> includes an array of antennas <NUM> to radiate and receive signal(s) carrying electromagnetic waves, and also include the WD filter unit <NUM>.

The client application <NUM> may be operable to provide a service to a human or non-human user via the WD <NUM>.

The processing circuitry <NUM> may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by WD <NUM>. The processor <NUM> corresponds to one or more processors <NUM> for performing WD <NUM> functions described herein. The WD <NUM> includes memory <NUM> that is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software <NUM> and/or the client application <NUM> may include instructions that, when executed by the processor <NUM> and/or processing circuitry <NUM>, causes the processor <NUM> and/or processing circuitry <NUM> to perform the processes described herein with respect to WD <NUM>.

In some embodiments, the inner workings of the network node <NUM> and WD <NUM> may be as shown in <FIG> and independently, the surrounding network topology may be that of <FIG>.

More precisely, the teachings of some of these embodiments may improve the data rate, latency, and/or power consumption and thereby provide benefits such as reduced user waiting time, relaxed restriction on file size, better responsiveness, extended battery lifetime, etc. In some embodiments, a measurement procedure may be provided for the purpose of monitoring data rate, latency and other factors on which the one or more embodiments improve.

Although <FIG> and <FIG> show various "units" such as filter unit <NUM> as being within a respective processor, it is contemplated that these units may be implemented such that a portion of the unit is stored in a corresponding memory within the processing circuitry. In other words, the units may be implemented in hardware or in a combination of hardware and software within the processing circuitry.

<FIG> is a flowchart of an example process in a network node <NUM> for forward distortion correction for time-domain beamforming. One or more blocks described herein may be performed by one or more elements of network node <NUM> such as by one or more of processing circuitry <NUM> (including the filter unit <NUM>), processor <NUM>, and/or radio interface <NUM>. Network node <NUM> such as via processing circuitry <NUM> and/or processor <NUM> and/or radio interface <NUM> is configured to filter each signal output by a time domain beamformer by a band stop filter, the band stop filter including a stop band overlapping a pass band of the signal output by the time domain beamformer (Block S10). The process also includes filtering each signal output by the time domain beamformer by a group delay filter in electrical parallel with a band stop filter, the group delay filter providing a group delay to the signal output by the time domain beamformer (Block S12). The process further includes subtracting an output of each band stop filter from an output of a corresponding group delay filter (Block S14).

<FIG> is a flowchart of another example process in a network node <NUM> according to some embodiments of the present disclosure. One or more blocks described herein may be performed by one or more elements of network node <NUM> such as by one or more of processing circuitry <NUM>, processor <NUM>, and/or radio interface <NUM> (including the filter unit <NUM>). The network node <NUM> such as via processing circuitry <NUM> and/or processor <NUM> and/or radio interface <NUM> is configured to beamform a plurality of signals to produce a plurality of time domain beamformer output signals (Block S16). The process also includes filtering each signal of the plurality of signals by a band stop filter, each band stop filter being configured to receive an output signal of the time domain beamformer (Block S18). The process also includes group delay-filtering each signal of the plurality of signals by a of group delay filter, each group delay filter being configured to receive an output signal of the time domain beamformer and being in electrical parallel with a band stop filter (Block S20). The process also includes for each band stop filter, subtracting an output of a band stop filter from an output of a corresponding group delay filter (Block S22).

Having described the general process flow of arrangements of the disclosure and having provided examples of hardware and software arrangements for implementing the processes and functions of the disclosure, the sections below provide details and examples of arrangements for forward distortion correction for time-domain beamforming.

Some embodiments for forward distortion correction (FDC) provide a digital distortion mitigation approach that can be used to limit the spectral regrowth caused by time-domain beamforming switching activity. Some digital filters with very sharp transition bands isolate the operating band unwanted emissions (OBUE), which is then subtracted from the distorted signal as shown in the example of <FIG>. This processing may take place immediately after the time-domain beamformer.

<FIG> shows an example schematic diagram of a plurality of parallel processing chains <NUM> for processing signals from a frequency domain digital beam former <NUM>. The processing chain may be the same as the processing chain of <FIG> with the addition of the filter unit <NUM> after each time domain beamformer <NUM> and before the corresponding DPD <NUM>. The filter unit <NUM> may include a band stop filter <NUM> in electrical parallel with a group delay filter <NUM>. The band stop filter <NUM> may have a sharp transition band and a stop band overlapping a pass band of a signal output by the time domain beamformer <NUM>. The group delay filter <NUM> may be configured to provide a group delay to the signal output by the time domain beamformer <NUM>. The outputs of the band stop filter <NUM> and the group delay filter <NUM> may be subtracted by the summation circuit <NUM> to produce a signal that is at least partially compensated for switching spectra.

The FDC method described below eliminates or shortens the length of baseband zero insertion required to meet the OBUE requirement masks. This baseband zero insertion may be implemented by the circuitry <NUM>, which may be a multiplexer such as a baseband zero insertion multiplexer. There is a trade-off between the link-level performance, filter complexity and the desired safety of margin with respect to the OBUE requirement masks. This tradeoff may be achieved by introduction of the band stop filter <NUM> which may be implemented as a Finite Impulse Response (FIR) filter or an Infinite Impulse Response (IIR) filter. The higher the order of the band stop filter <NUM>, the lower the percentage of zeros to be input to the baseband zero insertion multiplexer circuitry <NUM> in order to meet mask requirements.

FIR filters have a stable behavior with predictable group delays. However, they require more filter taps to achieve the required steep transition bands at the potentially high-sampling rate in the time-domain. Long impulse response FIR filters can alternatively be implemented in the frequency domain with fewer multiplication operations using the well-known "overlap and save" or "overlap and add" methods. In these techniques, the signal is converted to the frequency domain by Fast-Fourier Transform (FFT) on a block-by-block basis. Each frequency domain signal block is then multiplied by the frequency domain FIR filter response, thus achieving a block-wise circular convolution between the signal and the filter response. The output from the block-wise circular convolution is then converted back to the time domain using an Inverse Fast Fourier Transform (IFFT) operation. Proper overlapping may be provided between the consecutive block-wise circular convolution outputs in order to generate the full convolution. The reduced number of multiplications in the overlap and save and the overlap and add methods is done at the expense of an increased latency and a reduced signal to quantization noise ratio (SQNR) due to the FFT and IFFT operations.

The IIR filters can achieve sharp transition bands with much lower filter order. However, IIR filters can be unstable if not properly designed. The IIR stability issue can be addressed by ensuring that the (quantized) filter poles are located inside the unit circle centered at the origin of a complex plane.

The IIR group delay may also widely vary over frequency, especially around the transition band. This can be fixed by cascading an all-pass phase equalizer <NUM> in electrical series with the band stop filter <NUM>, as illustrated in the example of <FIG>.

In some embodiments, all-pass phase equalizers <NUM> may be designed following known algorithms. In accordance with other embodiments, all-pass phase equalizers <NUM> can be implemented as the sum of two all-pass filters using a Hilbert transform. A benefit of this approach is reduced coefficient quantization sensitivity. Since the all-pass phase equalizer <NUM> may also be implemented as an IIR filter, the poles and the zeros from both the band stop filter <NUM> and the all-pass phase equalizer <NUM> may be combined into a single impulse response filter <NUM>, thereby yielding the architecture illustrated in the example diagram of <FIG>. Another benefit of IIR filters is that they can be used to implement multiband filters, which is useful for handling signals containing multiple carrier components.

In some embodiments, the IIR band stop filter <NUM> of <FIG> is implemented using zero-phase IIR filtering, by first processing the signal through the filter in the forward direction, and then in the reverse direction. This effectively doubles the filter order but eliminates the need for the all-pass phase equalizer <NUM> as the signal does not have any phase distortion. Zero-phase IIR filtering can be performed on streaming data at the cost of increased latency using the overlap and save or the overlap and add method.

In some embodiments, limited signal portions are filtered around the time domain beamforming weight transitions instead of filtering the entire data stream to improve the signal Error Vector Magnitude (EVM).

<FIG> shows an example of the spectrum of a NR <NUM> carrier after the filter unit <NUM>, using a cascade of two 6th order elliptic IIR filters using zero-phase IIR filtering to form the band stop filter <NUM>. In <FIG>, the trace A is an example of the FDC spectrum without baseband zero insertion. Both requirement masks are met with good margin. However, a small bump appears at around <NUM>. This can be fixed by either slightly increasing the IIR filter order or by using a short baseband zero insertion window. Trace B shows the FDC spectrum when zeroing <NUM>% of the cyclic prefix. In this case, both requirement masks are met with some healthy margins. For comparison, the trace C displays the spectrum of the prior art using a baseband zero insertion length corresponding to <NUM>% of the cyclic prefix. Lines D and E are the FCC and Korea mask requirements, respectively.

The methods described herein may be implemented in edge computing or in the cloud. The methods described herein may also apply to ORAN radios.

According to one aspect, a method in a network node <NUM> configured to communicate with a wireless device <NUM> is provided. The method includes filtering each signal output by a time domain beamformer <NUM> by a band stop filter <NUM>, the band stop filter <NUM> including a stop band overlapping a pass band of the signal output by the time domain beamformer <NUM>. The method also includes filtering each signal output by the time domain beamformer <NUM> by a group delay filter <NUM> in electrical parallel with a band stop filter <NUM>, the group delay filter <NUM> providing a group delay to the signal output by the time domain beamformer <NUM>. The method further includes subtracting an output of each band stop filter <NUM> from an output of a corresponding group delay filter <NUM>.

According to this aspect, in some embodiments, the method further includes inserting zeros to a signal that is processed to be input to the time domain beamformer <NUM> to achieve a specified level of suppression of out-of-band emissions using a band stop filter <NUM> that is of lower order than a band stop filter <NUM> that achieves the specified level of suppression of out-of-band emission when no zeros are inserted to the signal. In some embodiments, each band stop filter <NUM> includes an infinite impulse response, IIR, band stop filter <NUM> electrically in series with a phase equalizer <NUM>. In some embodiments, transfer function poles and transfer function zeros of both the IIR band stop filter <NUM> and the phase equalizer <NUM> are combined to provide a phase linear IIR filter. In some embodiments, the phase equalizer <NUM> is an all pass phase equalizer <NUM>. In some embodiments, the all pass phase equalizer <NUM> is configured as a sum of two all pass filters using a Hilbert transform. In some embodiments, each band stop filter <NUM> includes an infinite impulse response, IIR, band stop filter <NUM> implemented using zero-phase IIR filtering, thereby doubling the filter order and providing zero phase distortion. In some embodiments, each band stop filter <NUM> includes a cascade of band stop filters. In some embodiments, each band stop filter <NUM> is an infinite impulse response, IIR, filter having quantized poles inside a unit circle centered at the origin of a complex plane. In some embodiments, each band stop filter <NUM> is a finite impulse response, FIR, filter. In some embodiments, each band stop filter <NUM> is a finite impulse response, FIR, filter, implemented in the frequency domain using a cascade of a Fast Fourier Transform, FFT, and an inverse FFT, following one of an overlap and save method and an overlap and add method. In some embodiments, portions of the signal output by the time domain beamformer <NUM> in a vicinity of time domain beam weight transitions are filtered to improve the signal Error Vector Magnitude (EVM).

According to another aspect, a network node <NUM> is configured to communicate with a wireless device <NUM>. The network node <NUM> is configured to implement a time domain beamformer <NUM>, and includes filter unit <NUM> configured to filter each signal output by the time domain beamformer <NUM> by a band stop filter <NUM>, the band stop filter <NUM> including a stop band overlapping a pass band of the signal output by the time domain beamformer <NUM>. Filter unit <NUM> is also configured to filter each signal output the time domain beamformer <NUM> by a group delay filter <NUM> in electrical parallel with the band stop filter <NUM>, the group delay filter <NUM> providing a group delay to the signal output by the time domain beamformer <NUM>. Filter unit <NUM> also include summation circuit <NUM> configured to subtract an output of each band stop filter <NUM> from an output of a corresponding group delay filter <NUM>.

According to this aspect, in some embodiments, circuitry <NUM>, e.g., baseband zero insertion multiplexer, is configured to insert zeros to a signal that is processed to be input to the time domain beamformer <NUM> to achieve a specified level of suppression of out-of-band emissions using a band stop filter <NUM> that is of lower order than a band stop filter that achieves the specified level of suppression of out-of-band emission when no zeros are inserted to the signal. In some embodiments, each band stop filter <NUM> includes an infinite impulse response, IIR, band stop filter <NUM> in electrical series with a phase equalizer <NUM>. In some embodiments, transfer function poles and transfer function zeros of both the IIR band stop filter <NUM> and the phase equalizer <NUM> are combined to provide a phase linear IIR filter. In some embodiments, the all pass phase equalizer <NUM> is an all pass phase equalizer. In some embodiments, the all pass phase equalizer <NUM> is configured as a sum of two all pass filters using a Hilbert transform. In some embodiments, each band stop filter <NUM> includes a cascade of band stop filters <NUM>. In some embodiments, each band stop filter <NUM> is an infinite impulse response, IIR, filter having quantized poles inside a unit circle centered at the origin of a complex plane. In some embodiments, each band stop filter <NUM> is a finite impulse response, FIR, filter. In some embodiments, each band stop filter <NUM> is a finite impulse response, FIR, filter, implemented in the frequency domain using a cascade of a Fast Fourier Transform, FFT, and an inverse FFT.

According to another aspect, a network node <NUM> is configured to communicate with a wireless device. The network node <NUM> includes: a time domain beamformer <NUM> configured to beam-form a plurality of signals to produce a plurality of time domain beamformer output signals; a plurality of band stop filters <NUM>, each band stop filter <NUM> of the plurality of band stop filters <NUM> being configured to receive an output signal of the time domain beamformer <NUM>; a plurality of group delay filters <NUM>, each group delay filter <NUM> of the plurality of group delay filters <NUM> receiving an output signal of the time domain beamformer <NUM> and being in electrical parallel with a band stop filter <NUM> of the plurality of band stop filters <NUM>; and a plurality of summation circuits <NUM>, each summation circuit <NUM> configured to subtract an output of a band stop filter <NUM> of the plurality of band stop filters <NUM> from an output of a corresponding group delay filter <NUM> of the plurality of group delay filters <NUM>.

According to this aspect, in some embodiments, the network node <NUM> also includes circuitry <NUM>, e.g., baseband zero insertion multiplexer, to insert zeros to a signal that is processed to be input to the time domain beamformer <NUM> to produce an output of the summation circuits that achieves a specified level of suppression of out-of-band emissions using a band stop filter <NUM> that is of lower order than a band stop filter <NUM> that achieves the specified level of suppression of out-of-band emission when no zeros are inserted to the signal. In some embodiments, each band stop filter <NUM> of the plurality of band stop filters includes an infinite impulse response, IIR, band stop filter <NUM> in electrical series with an all pass phase equalizer <NUM>. In some embodiments, a stop band of a band stop filter <NUM> of the plurality of band stop filters is configured to encompass a pass band of a time domain beamformer output signal that is input to the band stop filter <NUM>.

According to yet another aspect, a method in a network node <NUM> configured to communicate with a wireless device is provided. The method includes: beamforming a plurality of signals to produce a plurality of time domain beamformer output signals; filtering each signal of the plurality of signals by a band stop filter <NUM>, each band stop filter <NUM> being configured to receive an output signal of the time domain beamformer <NUM>; group delay-filtering each signal of the plurality of signals by a of group delay filter <NUM>, each group delay filter <NUM> being configured to receive an output signal of the time domain beamformer <NUM> and being in electrical parallel with a band stop filter <NUM>; and for each band stop filter <NUM>, subtracting an output of a band stop filter <NUM> from an output of a corresponding group delay filter <NUM>.

According to this aspect, in some embodiments, the method also includes inserting zeros to a signal that is processed to be input to the time domain beamformer <NUM> to produce an output of the subtracting that achieves a specified level of suppression of out-of-band emissions using a band stop filter <NUM> that is of lower order than a band stop filter <NUM> that achieves the specified level of suppression of out-of-band emission when no zeros are inserted to the signal. In some embodiments, each band stop filter <NUM> includes an infinite impulse response, IIR, band stop filter <NUM> in electrical series with an all pass phase equalizer <NUM>. In some embodiments, a stop band of a band stop filter <NUM> is configured to encompass a pass band of a time domain beamformer output signal that is input to the band stop filter <NUM>.

Some abbreviations that may be used herein are defined as follows:.

Accordingly, all embodiments can be combined in any way and/or combination, and the present specification, including the drawings, shall be construed to constitute a complete written description of all combinations and subcombinations of the embodiments described herein, and of the manner and process of making and using them.

Claim 1:
A method in a network node (<NUM>) configured to communicate with a wireless device, the network node (<NUM>) comprising a time domain beamformer (<NUM>), the method comprising:
filtering (S10) each signal output by the time domain beamformer (<NUM>) by a band stop filter (<NUM>), the band stop filter (<NUM>) including a stop band overlapping a pass band of the signal output by the time domain beamformer (<NUM>);
filtering (S12) each signal output by the time domain beamformer (<NUM>) by a group delay filter (<NUM>) in electrical parallel with the band stop filter (<NUM>), the group delay filter (<NUM>) providing a group delay to the signal output by the time domain beamformer (<NUM>); and
subtracting (S14) an output of each band stop filter (<NUM>) from an output of a corresponding group delay filter (<NUM>).