| 51. |
- Khan, Zain Ahmed, 1987-, et al.
(författare)
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Multitone design for third order MIMO volterra kernels
- 2017
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Ingår i: 2017 IEEE MTT-S International Microwave Symposium (IMS). - : IEEE conference proceedings. - 9781509063604 ; , s. 1553-1556
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Konferensbidrag (refereegranskat)abstract
- This paper proposes a technique for designing multitone signals that can separate the third order multiple input multiple output (MIMO) Volterra kernels. Multitone signals fed to a MIMO Volterra system yield a spectrum that is a permutation of the sums of the input signal tones. This a priori knowledge is used to design multitone signals such that the output from the MIMO Volterra kernels does not overlap in the frequency domain, hence making it possible to separate these kernels from the output of the MIMO Volterra system. The proposed technique is applied to a 2×2 RF MIMO transmitter to determine its dominant hardware impairments. For input crosstalk, the proposed method reveals the dominant self and cross kernels whereas for output crosstalk, the proposed method reveals that only the self kernels are dominant.
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| 52. |
- Khan, Zain Ahmed, et al.
(författare)
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Study of the Power Amplifier transfer function symmetry and its relation to dynamic effects
- 2015
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Ingår i: 2015 IEEE 16th Annual Wireless and Microwave Technology Conference (WAMICON). - : IEEE conference proceedings. - 9781479975211 ; , s. 1-6
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Konferensbidrag (refereegranskat)abstract
- Future wireless networks will employ unprecedentedly high number of transmitters along-with larger bandwidth signals. Therefore, complexity efficient Power Amplifier (PA) modelling methods with the ability to quantify memory effects are required. This paper presents a low complexity method to quantify memory effects by studying the symmetry in the PA transfer functions estimated with the density estimation method. It is shown that the symmetry helps in reducing the method complexity by more than two orders of magnitude. Further, it is verified that the symmetry can be used as a non-model based metric for quantifying memory effects in PAs.
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| 53. |
- Landin, Per, 1983-
(författare)
-
Digital Baseband Modeling and Correction of Radio Frequency Power Amplifiers
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Aspects related to behavioral modeling and correction of distortions for radio frequency (RF) power amplifiers (PAs) are treated in the thesis. When evaluating the performance of a behavioral model it is important to, first of all, use an evaluation criterion, and second, make sure that the criterion actually tells something about the behavior one wishes to describe. This is used in the weighted error spectral power ratio (WESPR) criterion by means of a frequency dependent weighting function. When the parameters of the models are estimated a suitable error criterion should likewise be used. The frequency weighting function in the WESPR is used in the extraction of the parameters. It is shown on two types of PAs that the model performance measured as WESPR can be improved while the model complexity is reduced compared to the standard frequency neutral criterion. When building a model of a system it is advantageous to take account of the physical structure and incorporate this knowledge into the model. It can improve model performance and possibly reduce the number of parameters. By starting from a physically motivated nonlinear model of a RF PA, the commonly used memory polynomial (MP) models are derived. Additionally, three novel MP model structures are derived. Using data measured on a PA it is found that two of these model structures have lower model errors while using fewer parameters than models previously published in the literature. Methods to increase the power efficiency and the linearity of RF PAs have been investigated. One of these methods is digital predistortion (DPD) which improves the linearity, thus facilitating operation at higher power levels which improves power efficiency. The other method is a signal shaping method that makes the signal more favorable to the PA by reducing the highest peaks to lower values. It is experimentally shown that the combination of DPD and signal shaping results in an increase of power efficiency in the order of 2-4 times. An instability in the feedback loop that updates the parameters of the DPD was also identified and two solutions were proposed. One solution changes the parameters of the DPD in such a way that the instability is avoided and the other changes the signal to avoid high amplitudes. The nonlinear effects of class-D outphasing amplifiers are considered. Four model structures are proposed and evaluated on data measured from two amplifiers. In order to reduce the distortions in the output signal from the amplifiers an algorithm using constant envelope amplitude (purely phase-modulated) signals is proposed. The DPD is evaluated and found to reduce the distortions in a state-of-the-art 32 dBm class-D outphasing PA to make it fulfill the linearity requirements for downlink signals used in the universal mobile telecommunications system (UMTS).
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| 54. |
- Landin, Per N., et al.
(författare)
-
Comparison of Evaluation Criteria for Power Amplifier Behavioral Modeling
- 2008
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Ingår i: 2008 IEEE MTT-S INTERNATIONAL MICROWAVE SYMPOSIUM DIGEST. - New York : IEEE. - 9781424417803 ; , s. 1441-1444
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Konferensbidrag (refereegranskat)abstract
- In this paper different evaluation criteria for power amplifier behavioral modeling are studied and evaluated using measuremed data. The figure-of-merits are calculated from complex-envelope data of a sampled power amplifier intended for 3G. Both time- and frequency domain methods are included in the study. It is found that a model evaluation criterion should have ability to capture both the linear and nonlinear distortion as well as the memory effects in the power amplifier. The normalized mean square error (NMSE) and the weighted error-to-signal power ratio (WESPR) are found to be the strongest candidates for capturing the in-band and the out-of-band errors, respectively. Both are also independent of power amplifier technology and stimuli input.
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| 55. |
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| 56. |
- Landin, Per N.
(författare)
-
On Radio Frequency Behavioral Modeling : Measurement Techniques, Devices and Validation Aspects
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Effektförstärkare för radiofrekvensapplikationer utgör fortfarande ett av de största problemen i trådlösa kommunikationssystem. Detta beror på att dessa förstärkare är ickelinjära, har låg energieffektivitet och ger mycket distortioner. Bättre verktyg för att förstå och korrigera dessa beteenden är nödvändiga. Ett sådant verktyg är beteendemodellering. En beteendemodell kan ses som en svart låda med insignal(er) och utsignal(er). In detta fall är dessa signaler samplade basbandssignaler och den svarta lådan är en matematisk relation mellan en insignal och en utsignal. Avhandlingen behandlar några krav för beteendemodellering av nämnda system genom att presentera metoder för utvärdering och förbättring av modellernas prestanda. Detta åstadkoms genom att betrakta ett frekvensviktat felkriterium. Ett högpresterande mätsystem är också nödvändigt för experimenten. Prestandan hos det tillgängliga systemet jämförs med prestandan hos ett allmänt erkänt mätsystem, en s.k. storsignalsnätverksanalysator, genom att betrakta prestandan hos beteendemodellerna som extraheras och valideras med data från respektive mätsystem. Resultatet visar att det existerande mätsystemet har god prestanda. Ett stort problem vid beteendemodellering är att kunna sampla med tillräckligt hög hastighet. Genom att använda Zhu-Franks generaliserade samplingsteorem vid beteendemodellering kan en del av detta problem undvikas. Teoremet medför att man kan sampla med en väsentligt lägre samlingsfrekvens än vad Nyquistteoremet säger. Modeller extraheras och prestandan utvärderas genom att använda kriteriet normalized mean square error (NMSE). För stabil prediktion och korrektion av utsignalen måste robustheten hos de använda modellerna verifieras. En sådan studie som berör robustheten mot variationer i lastimpedansen har genomförts. Prestandan på direkta modeller försämras med 7 dB mätt som adjacent channel error power ratio (ACEPR). Prestanda på inversmodellen, implementerad som digital predistortion, försämras med upp till 13 dB mätt som adjacent channel power ratio (ACPR).
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| 57. |
- Landin, Per N., 1983-, et al.
(författare)
-
Parameter Extraction and Performance Evaluation Method for Increased Performance in RF Power Amplifier Behavioral Modeling
- 2010
-
Ingår i: International Journal of RF and Microwave Computer-Aided Engineering. - : Hindawi Limited. - 1096-4290 .- 1099-047X. ; 20:2, s. 200-208
-
Tidskriftsartikel (refereegranskat)abstract
- A frequency-weighted parameter extraction method based on the performance evaluation criterion weighted error spectral power ratio (WESPR) is proposed. Performance of models extracted using the normalized mean square error (NMSE) are compared to the performances of models extracted using the WESPR. The results show an increase in performance with a decrease in model complexity.
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| 58. |
- Landin, Per N., et al.
(författare)
-
Peak-power controlled digital predistorters for RF power amplifiers
- 2012
-
Ingår i: IEEE transactions on microwave theory and techniques. - 0018-9480 .- 1557-9670. ; 60:11, s. 3582-3590
-
Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the issue of predistorter blow-up, i.e., uncontrolled peak expansion caused by the predistorter. To control the peak expansion, an extension of the multistep indirect learning architecture (MS-ILA) is proposed by adding a constraint that describes the allowed peak power of the predistortion signal. The resulting optimization problem is shown to be convex and an optimization method is formulated to solve it.
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| 59. |
- Landin, Per N., et al.
(författare)
-
Two novel memory polynomial models for modeling of RF power amplifiers
- 2015
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Ingår i: International journal of microwave and wireless technologies. - 1759-0795 .- 1759-0787. ; 7:1, s. 19-29
-
Tidskriftsartikel (refereegranskat)abstract
- Two novel memory polynomial models are derived based on physical knowledge of a general power amplifier (PA). The derivations are given in detail to facilitate derivations of other model structures. The model error in terms of normalized mean square error (NMSE) and adjacent channel error power ratio (ACEPR) of the novel model structures are compared to that of established models based on the number of parameters using data measured on two different amplifiers, one high-power base-station PA and one low-power general purpose amplifier. The novel models show both lower NMSE and ACEPR for any chosen number of parameters compared to the established models. The low model errors make the novel models suitable candidates for both modeling and digital predistortion.
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| 60. |
- Landin, Per Niklas, et al.
(författare)
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Wideband Characterization of Power Amplifiers Using Undersampling
- 2009
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Ingår i: 2009 IEEE MTT-S International Microwave Symposium Digest. - Boston : IEEE MTT. - 9781424428038 ; , s. 1365-1368
-
Konferensbidrag (refereegranskat)abstract
- In this paper a radio frequency power amplifier is measured and characterized by the use of undersampling based on the generalized Zhu-Frank sampling theorem. A test system has been designed allowing the bandwidth of the stimuli signal to be 100 MHz in the characterization process. That would not be possible with any vector signal analyzer on the market. One of the more challenging problem within the proposed concept is the model validation process. Here, two different techniques for model validation are proposed, the multitone and the spectrum scan validation methods.
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