IL263128B - Techniques for reducing quantization errors in electronically steerable antenna - Google Patents
Techniques for reducing quantization errors in electronically steerable antennaInfo
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- IL263128B IL263128B IL263128A IL26312818A IL263128B IL 263128 B IL263128 B IL 263128B IL 263128 A IL263128 A IL 263128A IL 26312818 A IL26312818 A IL 26312818A IL 263128 B IL263128 B IL 263128B
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
- H03M1/00—Analogue/digital conversion; Digital/analogue conversion
- H03M1/06—Continuously compensating for, or preventing, undesired influence of physical parameters
- H03M1/0617—Continuously compensating for, or preventing, undesired influence of physical parameters characterised by the use of methods or means not specific to a particular type of detrimental influence
- H03M1/0634—Continuously compensating for, or preventing, undesired influence of physical parameters characterised by the use of methods or means not specific to a particular type of detrimental influence by averaging out the errors, e.g. using sliding scale
- H03M1/0636—Continuously compensating for, or preventing, undesired influence of physical parameters characterised by the use of methods or means not specific to a particular type of detrimental influence by averaging out the errors, e.g. using sliding scale in the amplitude domain
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
- H03M1/00—Analogue/digital conversion; Digital/analogue conversion
- H03M1/06—Continuously compensating for, or preventing, undesired influence of physical parameters
- H03M1/0617—Continuously compensating for, or preventing, undesired influence of physical parameters characterised by the use of methods or means not specific to a particular type of detrimental influence
- H03M1/0634—Continuously compensating for, or preventing, undesired influence of physical parameters characterised by the use of methods or means not specific to a particular type of detrimental influence by averaging out the errors, e.g. using sliding scale
- H03M1/0636—Continuously compensating for, or preventing, undesired influence of physical parameters characterised by the use of methods or means not specific to a particular type of detrimental influence by averaging out the errors, e.g. using sliding scale in the amplitude domain
- H03M1/0639—Continuously compensating for, or preventing, undesired influence of physical parameters characterised by the use of methods or means not specific to a particular type of detrimental influence by averaging out the errors, e.g. using sliding scale in the amplitude domain using dither, e.g. using triangular or sawtooth waveforms
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Description
TECHNIQUES FOR REDUCING QUANTIZATION ERRORS IN ELECTRONICALLY STEERABLE ANTENNA TECHNOLOGICAL FIELD The present invention is generally in the field of digital beamforming systems, and particularly of suppressing quantization errors in such systems.
BACKGROUNDElectronically Steerable Antenna (ESA) systems offer many advantages including electronic beam steering and scanning, optimized beam pattern with reduced sidelobes, and reduced power consumption and weight. True-time-delay (TTD) steering techniques are typically required for controlling operation of multiple antenna elements in the ESA system, while keeping the broad bandwidth of the antenna radiation and allowing large scan angle, so that efficient elemental vector summation (in the receive mode) or distribution (in the transmit mode) can be obtained, that is independent of frequency or angle of the transmitted or received signals. Typical implementations of electronically steerable antennas are based on analog (RF) phase shifting. Hence the term Phased Array Antenna (PAA) is commonly used to describe ESA systems. In the following description the terms ESA and PAA are used interchangeably. Analog ESA implementations suffer from several drawbacks, such as: • due to implementation difficulties of the ESA systems TTD is almost never achieved in such analog implementations; • analog phase shift units are typically non-accurate due to production variations; • multi beam is very difficult to implement due to RF summation/splitting losses; and • large antennas are difficult to implement due to the need of an accurate and low loss-routing. Digital implementations of ESA systems don’t have the above drawbacks. However, digital implementations require a digital-to-analog converter (DAC) in the transmit path/channel of every antenna element of the array (and similarly an ADC in each receive path/channel). The DAC used in each transmit channel of the ESA system introduces quantization noise into the signal transmitted from the respective antenna element of the array. The analog signals generated by the DACs are transmitted simultaneously from the antenna elements of the array, and the quantization noise of all antenna elements coherently summated over the transmission medium (i.e., over the air), which produces out of band emission, deteriorates the signal-to-noise ratio (SNR) at the receiver, and can cause quantization errors at the receiving end. The effect of the quantization noise on SNR degradation becomes more problematic when the sampling resolution is low. It should be noted that the antenna array gain does not substantially influence the out of band quantization noise level at the receiver antenna output since the quantization noises from the DACs of the transmit channels are highly correlated at that point. Some solutions from the patent literature are briefly described below. US 5,103,232 describes means of decorrelating phase quantization errors in a phased array radar antenna using digital randomization at each of the array elements to reduce peak steering errors and to reduce peak sidelobe levels of the antenna. A random phase adjust term is provided to each of the array's antenna elements which comprises a distributed controller (DC) co-located with a digital phase shifter. The distributed controllers are each programmed with a random phase adjust term which represents a phase shift adjustment statistically independent from element to element. The random phase adjust term is stored in a memory located in each distributed controller. The distributed controller drives each element's digitally controlled phase shifter in response to a beam steering command received over a serial line. US 2015/365151 describes an antenna arrangement configured for digital beam-forming of a transmit signal comprising; a number N>1 of DACs, each of the N DACs being arranged to receive one respective digital transmit signal component, and to convert and output an analog transmit signal component, each of the N DACs having a respective resolution below a resolution required to fulfill a regulatory radio requirement in an interchangeable antenna arrangement arranged for transmission by a single antenna element connected to a single DAC; and N antenna elements, each of the N antenna elements being configured to receive one respective analog transmit signal component and to transmit the analog transmit signal component as part of the digitally beam-formed transmit signal. Reference to any prior art in the specification is not an acknowledgment or suggestion that this prior art forms part of the common general knowledge in any jurisdiction or that this prior art could reasonably be expected to be understood, regarded as relevant, and/or combined with other pieces of prior art by a skilled person in the art.
GENERAL DESCRIPTIONThe present application provides techniques, and corresponding implementations, for substantially reducing/suppressing correlation of quantization noise signals in ESA systems utilizing digital beamforming. Digital beamforming provides various advantages in ESA systems, particularly due to the accuracy and flexibility obtained using TTD to implement the beam steering and scanning. However, digital beamforming is more susceptible to quantization errors, since each transmit channel of the ESA/phased array antenna system requires at least one DAC to convert the digital signals generated by the digital beamforming process into corresponding analog signals for RF transmission via the antenna elements (and similarly each receive channel requires at least one ADC). In the transmit stage, for example, the quantization errors occur due to the high correlation between the quantization noise signals introduced by the DACs of the transmit channels of ESA systems, resulting in constructive interference of the quantization noise signals when the analog signals produced by the DACs are transmitted by the ESA, and therefore causing high out of band power emission. There are many advantages for operating ESA systems at low sampling resolutions (e.g., efficiency, simplified design, improved thermal properties, etc.), but on the other hand, as the bit length/depth of the DACs in the ESA system is reduced the maximal transmitted SNR becomes the quantization SNR (SNR Q) of a single antenna element, which does not benefit from the array gain. In the transmit path, quantization errors can be reduced/suppressed by introducing randomness to the signals to be transmitted by the ESA system, for example, by adding random low level noise signals to the signals supplied to each antenna element. Such solutions may require additional hardware means and generation of noise signals in each transmit channel of the ESA system and may decrease the SNR at the receiver. The present application provides in some embodiments digital beamforming techniques configured to manipulate the signals digitally processed therein and introduce some level of variance between the digital signals prepared by the different transmit channels, and thereby cause for substantial decorrelation of the quantization noise signals introduced by the DACs of the ESA system i.e., without requiring generation of random noise signals. The de-correlation of the quantization noise signals induced by the transmit channels improves performance of the ESA system, since the beam-formed signal can be transmitted with uncorrelated distortion components, with zero mean value and without bias, to thereby substantially diminish error vector aggregation at the receiving end. One important effect of this approach is that out-of-band noise introduced by the ESA system is reduced, and thus the complexity and the cost of filtering this out-of-band noise is reduced. Some of the digital beamforming techniques disclosed herein employ properties of elements utilized in digital beamforming processes to introduce the variance between the signals digitally processed by the different transmit channels of the ESA system, such that DACs of each transmit channel are fed by different variants of the signals, thereby reducing/suppressing correlation of the quantization noise from the DACs. This is achieved in some embodiments by utilizing delta-sigma ( ∆Ʃ ) modulation unit(s) in each transmit channel, and configuring each of the transmit channels to cause permutations in time to data generated by its respective ∆Ʃ modulation unit(s). In some embodiments each transmit channel is configured to arrange the stream of data samples generated by its respective ∆Ʃ modulation process in a form of words, each word comprising one or more sequences of the data samples of predefined bit lengths i.e., each word of samples containing a predefined number of data samples bits outputted by the respective ∆Ʃ modulation process, and perform sample time permutations in at least one segment of each of the constructed words, to thereby affect permutation in time domain of the data outputted by the ∆Ʃ modulation process (also referred to herein as time permutation or sample time permutation). The digital beamforming process can be further configured to dynamically change for each transmit channel the permutation scheme(s) to be applied in one or more of the transmit channels. Optionally, the bit length of a segment in at least one transmit channel is a single bit, or greater than one bit. For example, and without being limiting, at least one pseudo-random crossbar network can be generated for one or more of the transmit channels, and implemented in its beamforming process such that the digitally processed samples therein undergo the sample time permutations defined by the respective crossbar network before converted by the respective DAC into a corresponding analog signal. In some embodiment the digital beamforming process can utilize at least one delta-sigma ( ∆Ʃ ) modulator in each transmit channel to oversample digital beamformed data, and/or reduce samples bit-depth, and/or for noise shaping. The samples generated by each ∆Ʃ modulator can be used to construct data words of a predefined length, and at least one segment of each word can be then permuted in time domain by the respective at least one pseudo-random crossbar network, before the data word is converted by the respective DAC into analog signals. In some embodiments the ∆Ʃ modulator of each transmit channel can be configured to implement loop filter having a slightly different transfer function of its filter unit. Optionally, but in some embodiments preferably, the ∆Ʃ modulator of one or more of the transmit channels is operated with one or more initial conditions different from the initial conditions used in the ∆Ʃ modulator of the other transmit channels. Alternatively, or additionally, one or more ∆Ʃ modulators of certain transmit channels are initialized to operate with determined initial conditions at different point in time e.g., each ∆Ʃ modulator is initialized with same, or different, initial condition values, at a different time. Optionally, but in some embodiments preferably, at least one of the ∆Ʃ modulators is configured to exhibit chaotic behavior (e.g., complying with the Devaney definition of chaos). In this way, a desirable level of variance between the data supplied to the DACs of the transmit channels can be maintained throughout operation of the ESA system. The term deterministic modification used herein to refer to manipulation of digital data that modify the data in a known, and optionally controlled, manner, without uncertainty about the modified data obtained i.e., the modified data obtained is generated by system components not involving randomness. Some of the deterministic modifications used in embodiments disclosed herein utilize samples time permutation schemes and/or delta-sigma processes. However, in some embodiments one or more of the parameters used for the deterministic modifications are parameters that can be generated utilizing random/pseudo-random number generation processes e.g., initial conditions, filter coefficients, permutation schemes, and suchlike. The use of such deterministic manipulations is utilized some embodiments to alter digital data processed in transmit channels of ESA systems in a controlled and adjustable manner for introducing a suitable/predefined level of variance between the transmit channels without corrupting the data signals to be thereby transmitted. One inventive aspect of the subject matter disclosed herein relates to a beamforming method comprising receiving digital data to be transmitted by a plurality of transmit channels of a ESA system, performing digital beamforming in each of the transmit channels to adapt the digital data for transmission thereof via a respective antenna element of the transmit channel, manipulating the adapted digital data for causing a different deterministic modification of at least a portion of the adapted digital data in each of the plurality of transmit channels, thereby introducing variance between the digital data produced by the transmit channels, and converting the manipulated data of each transmit channel to a corresponding analog domain signal for transmission thereof via the respective antenna element. The different deterministic modification is configured to cause de-correlation of quantization noise signals introduced into the transmission by the conversion into the analog domain, and thereby substantially reduce out of band quantization noise and errors at a receiver of the transmitted signals. Optionally, but in some embodiments preferably, the manipulating of the adapted digital data comprises applying a delta-sigma modulation process. The delta-sigma modulation process performed in each transmit channel can be configured for at least partially causing the different modification and the variance associated therewith. The method comprises in some embodiments defining a different transfer function for at least one, or for each, of the filter units of the delta-sigma modulation processes, to thereby at least partially cause the variance between the data supplied to the DACs of the transmit channels. Optionally, but in some embodiments preferably, the transfer function of the filter units is of a second order, or of a higher order. The method optionally comprises defining at least one different parameter of a transfer function of a filter unit for at least one of the delta-sigma modulation processes to thereby cause the variance between the digital signals of the different transmit channels. Optionally, but in some embodiments preferably, a different noise transfer function is defined for at least one of the delta-sigma modulation processes of the transmit channels, to thereby cause the variance between the digital data of the transmit channels. For this purpose the method comprises in some embodiments determining at least one different parameter to at least one of the noise transfer functions.
The method comprises in some embodiments defining a same transfer function for the filter unit of each of the delta-sigma modulation processes, and defining at least one different parameter of the same transfer function of the filter unit in each of the transmission channels, to thereby at least partially cause the variance between the digital data of the transmit channels. The method can comprise defining for each of the delta- sigma modulation processes poles causing a band stop at a different frequency in each of the transmission channels. Optionally, but in some embodiments preferably, a different phase θ value (e.g., as defined in the two equations below) is defined for a noise transfer function of at least one of the delta-sigma modulation processes, to at least partially cause the variance between the digital data of the transmit channels. The noise transfer function of the delta-sigma modulation processes is characterized in some embodiments by the expression - (1-z-1)(eiθ-z-1)e-iθ. Alternatively, the noise transfer function of the delta-sigma modulation processes is characterized by the expression - 1-(1+2cosθ)z-1+(1+2cosθ)z-2- z-3. The method comprises in some embodiments defining at least one of the delta-sigma modulation processes to exhibit chaotic behavior. Initial conditions can be determined for at least one of the delta-sigma ( ∆Ʃ ) modulation processes. The term initial conditions used herein to refer to initial values of dynamic variables (also referred to as state variables) of a transfer function of the ∆Ʃ modulation process that affect their values and state at future times. In some embodiments each ∆Ʃ modulation process comprises at least one memory unit for storing state variables of a transfer function thereof, and the method comprises an initialization step, performed during system startup or after the system is reset, in which a specific sequence of input samples/values written into the memory cause the ∆Ʃ modulation to enter a certain modulator state. Optionally, the initial conditions are applied by resetting the memory of a filter of each ∆Ʃ modulation process, and then inputting thereinto specific input samples/values that will cause the required state of the ∆Ʃ modulation process, or alternatively by directly writing the input sample/values into the memories of the filters. Alternatively, the method comprises defining the delta-sigma modulation processes to exhibit similar, or same, chaotic behavior/properties. In this alternative the method can comprise determining different initial conditions for each of the delta-sigma modulation processes. In another variant the method comprises defining the delta-sigma modulation processes to exhibit similar, or same, chaotic behavior, and initializing each the delta-sigma modulation processes with the same initial conditions at a different point in time. The initialization of at least one, or all, of the delta-sigma modulation processes with the determined initial conditions can be carried out periodically according to a defined initialization frequency of the system, or intermittently e.g., if instability of at least one delta-sigma modulation process is identified. Optionally, the method comprises monitoring a state of at least one of the delta-sigma modulation processes, and adjusting the at least one delta-sigma modulation process whenever identifying that it is becoming unstable. For example, and without being limiting, if at least one chaotic ∆Ʃ modulator becomes unstable it is adjusted by the system to restore stability thereof. The adjusting can comprise at least one of the following: defining a different transfer function of a filter unit for the at least one delta-sigma modulation process, defining a different noise transfer function for the at least one delta-sigma modulation process, determining at least one different parameter for the noise transfer function of the at least one delta-sigma modulation process, defining a different phase θ value of the noise transfer function of the at least one delta-sigma modulation processes, determining different initial conditions for the at least one delta-sigma modulation process, and/or initializing the at least one delta-sigma modulation process with newly or previously determined initial conditions. The method comprises in some embodiments determining for each of the transmit channels a size of the portion of the adapted digital data to be manipulated. Optionally, but in some embodiments preferably, the different deterministic modification comprises applying in each transmit channel a different sample permutation in time domain to the at least a portion of the data to be transmitted. The method can thus comprise determining for each of the transmit channels a different time domain permutation scheme. Applying of the sample permutation may comprise constructing from the output of each delta-sigma modulation process a data word of a predefined size, partitioning each of the constructed words into a predetermined number of segments, and performing the sample order permutation in at least one of said segments of each word. Optionally, but in some embodiments preferably, a different sample order permutation scheme is applied to at least one of the following: the partitioned segments; and the constructed words. Applying of the sample order permutation comprises in some embodiments constructing from a sample stream from each delta-sigma modulation process a predetermined number of sub-streams, partitioning each sub-steam into a predefined number of segments, applying a defined permutation scheme to each of the segments, and constructing from the permuted segments a permuted output sample stream. The size of the portion of the adapted digital data to be manipulated can be determined based on at least one of: SNR conditions of the ESA system, an over sampling ratio of the system, and /or error correction capabilities of a receiver of the transmission. Another inventive aspect of the subject matter disclosed herein relates to a beamforming system configured to process digital data for transmission by a ESA system and reduce quantization noise in signals thereby transmitted. The system comprises in some embodiments a plurality of transmit channels, each transmit channel associated with an antenna element of the ESA system and comprises a digital beamforming unit configured to process digital data to be transmitted by the ESA system for affecting a phase shift (relative to the signals of the other transmit channels) and/or change/adjust signal amplitude and/or apply time delay thereto, a data manipulation unit adapted to apply a different deterministic modification to at least a portion of the digital data processed by the digital beamforming unit and thereby introduce variance between the digital data produced by the transmit channels, and a digital to analog converter for converting the digital data modified by the data manipulation unit to a corresponding analog signal for transmission by the antenna element. Optionally, but in some embodiments preferably, the data manipulation unit comprises a delta-sigma modulator. The delta-sigma modulator can define an oversampling ratio of the transmit channel. The delta-sigma modulator used in each transmit channel can be configured for at least partially causing the different deterministic modification. The system comprises in some embodiments a control unit configured and operable to control operation of at least one of the data manipulation units. The control unit can be configured to determine an oversampling ratio for the plurality of transmit channels. The control unit can be also configured to determine the size of the portion of the adapted digital data to be manipulated in the at least one of the plurality of transmit channels based on the determined oversampling ratio. The control unit comprises in some embodiment a delta-sigma setup module configured and operable to determine a different transfer function of a filter unit of each of the delta-sigma modulators and thereby at least partially cause the variance between the data of the transmit channels. Optionally, the delta-sigma setup module is configured and operable to determine at least one different parameter of a transfer function of a filter unit of at least one of the delta-sigma modulators, and thereby at least partially cause the variance between the data of the transmit channels. In some possible embodiments the delta-sigma setup module is configured and operable to determine a different noise transfer function for at least one of the delta-sigma modulation processes, and thereby at least partially cause the variance between the data of the transmit channels. The delta-sigma setup module can be further configured to determine at least one different parameter of at least one of the noise transfer functions. In some embodiments the delta-sigma setup module is configured and operable to determine a same transfer function for each of the delta-sigma modulators, and to determine at least one different parameter for at least one of the transfer functions, and thereby at least partially cause the variance between the data of the transmit channels. For this purpose the delta-sigma setup module can be configured to determine for each of the delta-sigma modulators poles causing a band stop at a different frequency i.e., to affect a different band-stop frequency in each delta-sigma setup module. In some embodiments the delta-sigma setup module is configured to determine a different phase θ value of a noise transfer function of at least one of the delta-sigma modulators. Optionally, but in some embodiments preferably, at least one of the delta-sigma modulators is implemented as a chaotic delta-sigma modulator. The delta-sigma setup module can be configured and operable to determine initial conditions for at least one of the delta-sigma modulation processes. In some possible embodiments all of the delta-sigma modulators are implemented as chaotic delta-sigma modulators. The delta-sigma setup module can be thus configured and operable to determine different initial conditions for each of the delta-sigma modulators.
In another variant all of the delta-sigma modulators are implemented as chaotic delta-sigma modulators exhibiting similar, or same, chaotic behavior, and the delta-sigma setup module is configured and operable to initialize each of the delta-sigma modulators with the same initial conditions at a different point in time. Optionally, the control unit and/or the delta-sigma setup module, configured and operable to periodically or intermittently initialize at least one of the delta-sigma modulators with the determined initial conditions. In some embodiments the control unit is configured and operable to monitor a state of at least one of the delta-sigma modulators and adjust the at least one delta-sigma modulator whenever identifying that it is becoming unstable. The control unit can be configured and operable to carry out at least one of the following when identifying that the at least one of the delta-sigma modulators is becoming unstable: define a different transfer function of a filter unit of the at least one delta-sigma modulator, define at least one different parameter of a transfer function of the filter unit of the at least one delta-sigma modulator, define a different noise transfer function for the at least one delta- sigma modulator, determine at least one different parameter for the noise transfer function of the at least one delta-sigma modulator, define a different phase θ value of the noise transfer function of the at least one delta-sigma modulator, determine different initial conditions for the at least one delta-sigma modulator, and/or initialize the at least one delta-sigma modulator with newly or previously determined initial conditions. The data manipulation unit in at least one of the transmit channels can comprise a permutation unit configured and operable to apply a defined time domain samples permutation to the at least a portion of the digital data, and thereby at least partially cause the variance between the data of the transmit channels. Optionally, but in some embodiments preferably, the size of the data/samples permuted by the manipulation unit is determined based on the oversampling ratio defined by the delta-sigma modulator. Alternatively, the data manipulation unit in each of the transmit channels comprises a permutation unit configured to apply a different time domain samples permutation scheme to the at least a portion of the digital data. The data manipulation unit in each transmit channel can be configured to construct from the output of its respective delta-sigma modulator a data word of a predefined size, partition the constructed word into a predetermined number of segments, and the manipulation unit can be configured to perform the sample time permutation to at least one of the segments. Optionally, but in some embodiments preferably, the manipulation unit is configured to perform a different sample time permutation in each of the segments. The data manipulation unit is configured in some embodiments to construct from a sample stream from each delta-sigma modulator a predetermined number of sub-streams, partition each sub-steam into a predefined number of segments, apply a different sample time permutation scheme to each of the segments, and construct from the permuted segments a permuted output sample stream. The control unit comprises in some embodiments a permutation setup module configured and operable to determine for each of the transmit channels the portion size of the digital data to be modified by its respective data manipulation unit. The permutation setup module can be configured and operable to determine for each of the transmit channels the different permutation scheme used therein. Optionally, the permutation setup module is configured and operable to determine the portion size of the processed digital data to be manipulated based on at least one of: SNR conditions of the ESA system, an oversampling ratio of the system/transmit channel, and/or error correction capabilities of a receiver of the transmission. Any of the preferable features described herein may be applied to any aspect of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings. Features shown in the drawings are meant to be illustrative of only some embodiments of the invention, unless otherwise implicitly indicated. In the drawings like reference numerals are used to indicate corresponding parts, and in which: Fig. 1 is a block diagram schematically illustrating an array antenna / electrical scanning antenna (ESA) implementation according to some possible embodiments; Figs. 2A to 2C are block diagrams schematically illustrating use of delta-sigma (∆Ʃ) modulation in transmit paths of a ESA system according to some possible embodiments, where Fig. 2A shows the ESA transmit paths, Fig. 2B shows a possible implementation of a ∆Ʃ modulator, and Fig. 2C illustrates possible elements of a delta-sigma setup module of the control unit; Figs. 3Ato 3Dare block diagrams schematically illustrating use of delta-sigma (∆Ʃ) modulation and samples permutations in transmit paths of a ESA system according to some possible embodiments, where Fig. 3A shows the ESA transmit paths, Fig. 3B and 3C show a possible sample-stream segmentation and permutation schemes, and Fig. 3D exemplifies carrying out permutation to sub-streams of samples from the delta-sigma (∆Ʃ) modulatior; and Fig. 4 is a flowchart schematically illustrating a beamforming process according to some possible embodiments.
Claims (48)
1. A beamforming method comprising:receiving digital data to be transmitted by a plurality of transmit channels of the ESA system, whereby each transmit channel of said plurality of transmit channels is associated with a respective antenna element of the ESA system;performing digital beamforming in each transmit channel of said plurality of transmit channels to adapt said digital data for transmission via the respective antenna element of the transmit channel and thereby form adapted digital data of the transmit channel;applying different modifications to at least portions of the adapted digital data of said plurality of transmit channels to thereby introduce variance between the adapted digital data produced by the plurality of transmit channels, whereby applying said different modifications comprises applying, in each one of said plurality of transmit channels, a respective delta-sigma modulation process for manipulating said adapted digital data converting the manipulated data of each transmit channel to an analog signal, thereby forming by the plurality of transmit channel a plurality of corresponding analog signals for transmission via respective antenna elements of the ESA,whereby said different modification caused by said respective delta-sigma modulation process is causing de-correlation of quantization noise signals introduced to said plurality of corresponding analog signals by said converting, thereby enabling reduction in constructive interference of the quantization noise at a receiving end of the transmitted digital data.
2. The method of claim 1 wherein the size of the portion of the adapted digital datato be manipulated in the at least one of the plurality of transmit channels is determined based on an oversampling ratio.
3. The method of any one of the preceding claims comprising defining a differenttransfer function for at least one filter, or for each filter, of the respective plurality deltasigma modulation processes.
4. The method of claim 3 wherein the transfer function is of a second order, or of ahigher order. 263128/3 - 30 -
5. The method of any one of the preceding claims comprising defining at least onedifferent parameter of a transfer function for at least one of the respective plurality of delta-sigma modulation processes.
6. The method of any one of the preceding claims comprising defining a differentnoise transfer function for at least one of the respective plurality of delta-sigma modulation processes.
7. The method of claim 6 comprising determining at least one different parameterfor at least one of the noise transfer functions.
8. The method of any one of the preceding claims comprising defining for each ofthe respective plurality of delta-sigma modulation processes poles causing a band stop at a different frequency in each of the plurality of transmission channels.
9. The method of any one of the preceding claims comprising defining a differentphase θ value of a noise transfer function of at least one of the respective plurality of delta-sigma modulation processes.
10. The method of any one of the preceding claims comprising defining a second order delta-sigma modulation processes for each of the respective plurality of sigma-delta modulation processes, a transfer function of said second order delta-sigma modulation process having one zero at 1 and another zero at eiθ, on the 'Z'-plane.
11. The method of any one of claims 9 or 10 wherein the noise transfer function of the respective plurality of delta-sigma modulation processes is characterized by the expression – (1-z-1)(eiθ-z-1)e-iθ.
12. The method of claim 9 wherein a noise transfer function of the respective plurality of delta-sigma modulation processes is characterized by the expression 1-(1+2cosθ)z-1+(1+2cosθ)z-2-z-3 .
13. The method of any one of the preceding claims comprising defining at least one of the respective plurality of delta-sigma modulation process to exhibit a chaotic behavior. 263128/3 - 31 -
14. The method of claim 13 comprising determining initial conditions for at least one of the respective plurality of delta-sigma modulation processes.
15. The method of claim 13 comprising defining all of the respective plurality of delta-sigma modulation processes to exhibit a similar chaotic behavior and determining different initial conditions for each of the respective plurality of delta-sigma modulation processes.
16. The method of claim 13 comprising defining all of the respective plurality of delta-sigma modulation processes to exhibit a similar chaotic behavior and initializing each of the respective plurality of delta-sigma modulation processes with the same initial conditions at a different time.
17. The method of any one of claims 15 and 16 comprising periodically carrying out initialization of at least one of the respective plurality of delta-sigma modulation processes.
18. The method of any one of the preceding claims comprising monitoring at least one of the respective plurality of delta-sigma modulation processes, and adjusting said at least one delta-sigma modulation process whenever identifying that it is becoming unstable.
19. The method of claim 18 wherein the adjusting comprises at least one of the following: defining a different transfer function for the filter of at least one of the respective plurality of delta-sigma modulation process, defining at least one different parameter of a transfer function of the filter of at least one of the respective plurality of delta-sigma modulation process, defining a different noise transfer function for the at least one of the respective plurality of delta-sigma modulation process, determining at least one different parameter for the noise transfer functions of the at least one of the respective plurality of delta-sigma modulation process, defining a different phase θ value of the noise transfer function of the at least one of the respective plurality of delta-sigma modulation processes, determining different initial conditions for the at least one of the respective plurality of delta-sigma modulation process, and/or initializing the at least one of the respective plurality of delta-sigma modulation processes with newly or previously determined initial conditions. 263128/3 - 32 -
20. The method of claim of any one of the preceding claims comprising determining for each of the plurality of transmit channels a size of the portion of the adapted digital data to be manipulated.
21. The method of any one of the preceding claims wherein the different modification comprises applying in each of the plurality of the transmit channels a different sample order permutation to the at least a portion of the data to be transmitted.
22. The method of claim 21 wherein the applying of the sample order permutation comprises constructing from the output of each of the respective plurality of delta-sigma modulation processes a data word of a predefined size, partitioning each of the constructed words into a predetermined number of segments and performing the sample order permutation in at least one of said segments of each data word.
23. The method of claim 22 comprising applying a different sample order permutation scheme in at least one of the partitioned segments of the constructed data words.
24. The method of claim 21 wherein the applying of the sample order permutation comprises constructing from a sample stream from each one of the respective plurality of delta-sigma modulation processes a predetermined number of sub-streams, partitioning each sub-steam into a predefined number of segments, applying a defined permutation scheme to each of said predefined number of segments, and constructing from the permuted segments a permuted output sample stream.
25. The method of any one of claims 20 to 24 wherein the size of the portion of the adapted digital data to be manipulated is determined based on at least one of the following: SNR conditions of the ESA system, an oversampling ratio of the transmit channel, and error correction capabilities of a receiver that receives the transmission.
26. A beamforming system configured to process digital data for transmission by an ESA system, the beamforming system comprises a plurality of transmit channels, whereby each transmit channel of said plurality of transmit channels is associated with a respective antenna element of said ESA system; and wherein said plurality of transmit channels comprise:respective beamforming units of the plurality transmit channels configured to process digital data to be transmitted by the respective antenna elements of the ESA 263128/3 - 33 - system; each beamforming unit is adapted for affecting a phase difference and/or amplitude adjustment and/or time delay to the digital data for forming adapted digital data transmission by the respective antenna element associated with the transmit channel of the beamforming unit;respective data manipulation units of the plurality transmit channels comprising delta-sigma modulators; said data manipulation units are adapted to apply different respective modifications to at least portions of the processed digital data from said respective digital beamforming units and thereby introduce variance between the adapted digital data produced by the plurality of transmit channels to form modified digital data with said variance introduced; anda respective digital to analog converter for converting the modified digital data from said respective data manipulation units of the transmit channels into corresponding analog signals for transmission by said respective antenna elements of the ESA system;whereby said different respective modifications by the data manipulation units yield de-correlation of quantization noise signals introduced to said plurality of corresponding analog signals by said converting, thereby enabling reduction in constructive interference of the quantization noise at a receiving end of the transmitted digital data.
27. The system of claim 26 comprising a control unit configured and operable to control operation of at least one of the plurality of transmit channels.
28. The system of claim 27 wherein the control unit is configured and operable to determine the size of the portion of the adapted digital data to be manipulated in the at least one of the plurality of transmit channels based on an oversampling ratio.
29. The system of any one of claims 27 and 28 wherein the control unit comprises a delta-sigma setup module configured and operable to determine a different transfer function for a filter unit of each one of the respective plurality of delta-sigma modulators and thereby at least partially cause the variance between the data of the plurality of transmit channels.
30. The system of claim 29 wherein the delta-sigma setup module is configured and operable to determine at least one different parameter of a transfer function of the filter unit for at least one of the respective plurality of delta-sigma modulators. 263128/3 - 34 -
31. The system of any one of claims 29 and 30 wherein the delta-sigma setup module is configured and operable to determine a different noise transfer function for at least one of the respective plurality of delta-sigma modulators.
32. The system of claim 31 wherein the delta-sigma setup module is configured and operable to determine at least one different parameter to at least one of the noise transfer functions.
33. The system of any one of claims 30 to 32 wherein the delta-sigma setup module is configured and operable to determine for the noise transfer function of each one of the respective plurality of the delta-sigma modulators poles causing a band stop at a different frequency.
34. The system of claim 33 wherein the delta-sigma setup module is configured and operable to determine a different phase θ value of the noise transfer function of at least one of the respective plurality of delta-sigma modulators.
35. The system of any one of claims 26 to 34 wherein at least one of the respective plurality of delta-sigma modulators is implemented as a chaotic delta-sigma modulator.
36. The system of any one of claims 29 and 35 wherein the delta-sigma setup module is configured and operable to determine initial conditions for at least one of the respective plurality of delta-sigma modulators.
37. The system of claim 36 wherein all of the respective plurality of delta-sigma modulators are implemented as chaotic delta-sigma modulators exhibiting similar chaotic behavior, and wherein the delta-sigma setup module is configured and operable to determine different initial conditions for each one of the respective plurality delta-sigma modulators.
38. The system of claim 37 wherein all of the delta-sigma modulators are implemented as chaotic delta-sigma modulators exhibiting similar chaotic behavior, and wherein the delta-sigma setup module is configured and operable to initialize each of the respective plurality of delta-sigma modulators with the same initial conditions at a different point in time. 263128/3 - 35 -
39. The system of any one of claims 37 and 38 wherein the control unit is configured and operable to periodically or intermittently initialize at least one of the respective plurality of delta-sigma modulators with the determined initial conditions.
40. The system of any one of claims 37 to 39 wherein the control unit is configured and operable to monitor a state of at least one of the respective plurality of delta-sigma modulators and identify if it is becoming unstable.
41. The system of claim 40 wherein the control unit is configured and operable to carry out at least one of the following when identifying that the at least one of the respective plurality of delta-sigma modulators is becoming unstable: define a different transfer function of a filter unit for the at least one of the respective plurality of deltasigma modulation process; define at least one different parameter of a transfer function of the filter unit of the at least one of the respective plurality of delta-sigma modulation process; define a different noise transfer function for the at least one of the respective plurality of delta-sigma modulation process; determine at least one different parameter for the noise transfer function of the at least one of the respective plurality of delta-sigma modulation process; define a different phase θ value of the noise transfer function of the at least one of the respective plurality of delta-sigma modulation process; determine different initial conditions for the at least one of the respective plurality of delta-sigma modulation process; and/or initialize the at least one of the respective plurality of deltasigma modulation processes with newly or previously determined initial conditions.
42. The system of any one of claims 26 to 41 wherein the data manipulation unit in at least one of the plurality of transmit channels comprises a permutation unit configured to apply a defined sample time permutation to the at least a portion of the digital data.
43. The system of any one of claims 26 and 42 wherein the respective data manipulation unit in each one of the plurality of transmit channels comprises a permutation unit configured to apply a different sample time permutation scheme to the at least a portion of the digital data.
44. The system of claim 43 wherein the respective data manipulation unit in each of the plurality of transmit channels is configured to construct from the output of its respective delta-sigma modulator a data word of a predefined size, partition the constructed word into a predetermined number of segments, and wherein the 263128/3 - 36 - manipulation unit is configured to perform a different sample time permutation to each of said segments.
45. The system of claim 43 wherein the respective data manipulation unit is configured to construct from a sample stream from its respective delta-sigma modulator a predetermined number of sub-streams, partition each of said predetermined number of sub-steams into a predefined number of segments, apply a different sample time permutation scheme to of the segments, and construct from the permuted segments a permuted output sample stream.
46. The system of claims 27 and 45 wherein the control unit comprises a permutation setup module configured and operable to determine for each of the plurality of transmit channels a size of the portion of the digital data to be modified by its respective data manipulation unit.
47. The system of claim 46 wherein the permutation setup module is configured and operable to determine for each of the plurality of transmit channels the different permutation scheme used therein.
48. The system of claim 47 wherein the permutation setup module is configured and operable to determine the size of the portion of the processed digital data to be manipulated based on at least one of the following: SNR conditions of the ESA system; an oversampling ratio of the transmit channel; and/or error correction capabilities of a receiver that receives the transmission.
Priority Applications (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| IL263128A IL263128B (en) | 2018-11-19 | 2018-11-19 | Techniques for reducing quantization errors in electronically steerable antenna |
| PCT/IL2019/051258 WO2020105040A1 (en) | 2018-11-19 | 2019-11-18 | Techniques for reducing quantization errors in electronically steerable antenna |
| EP19818283.4A EP3884589A1 (en) | 2018-11-19 | 2019-11-18 | Techniques for reducing quantization errors in electronically steerable antenna |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| IL263128A IL263128B (en) | 2018-11-19 | 2018-11-19 | Techniques for reducing quantization errors in electronically steerable antenna |
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| IL263128A IL263128A (en) | 2020-05-31 |
| IL263128B true IL263128B (en) | 2022-09-01 |
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| US20060119493A1 (en) * | 2004-12-08 | 2006-06-08 | Texas Instruments Incorporated | Transmitter for wireless applications incorporation spectral emission shaping sigma delta modulator |
| US20140314178A1 (en) * | 2013-04-22 | 2014-10-23 | Sang-Ho Seo | Digital wireless transmitter having parallel structure and wireless communication system including the same |
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| US20170179969A1 (en) * | 2015-12-17 | 2017-06-22 | Analog Devices Global | Adaptive digital quantization noise cancellation filters for mash adcs |
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| US20060119493A1 (en) * | 2004-12-08 | 2006-06-08 | Texas Instruments Incorporated | Transmitter for wireless applications incorporation spectral emission shaping sigma delta modulator |
| US20140314178A1 (en) * | 2013-04-22 | 2014-10-23 | Sang-Ho Seo | Digital wireless transmitter having parallel structure and wireless communication system including the same |
| US20150244387A1 (en) * | 2014-02-26 | 2015-08-27 | Elta Systems Ltd. | System and method for enhancing dynamic range of a beamforming multi-channel digital receiver |
| US20150365151A1 (en) * | 2014-06-11 | 2015-12-17 | Telefonaktiebolaget L M Ericsson (Publ) | Apparatus and Method For Digital Beam-Forming With Low-Resolution Quantization |
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| IL263128A (en) | 2020-05-31 |
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