| 1. |
- Soltani Tehrani, Ali, 1982, et al.
(författare)
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Successive Cancellation of Power Amplifier Distortion for Multiuser Detection
- 2010
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Ingår i: IEEE Vehicular Technology Conference. - 1550-2252. - 9781424435746
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Konferensbidrag (refereegranskat)abstract
- This paper presents an iterative interference suppression technique to cancel power amplifier (PA) distortion at the receiver. The focus is mainly on single carrier frequency division multiple access systems, and on removing the distortion created by adjacent users' power amplifier. It is assumed that the receiver has perfect knowledge of all the users' transmitter power amplifier nonlinearities.By relaxing the requirement on PA linearity at the mobile terminals, the PA power efficiency can be improved. The simulations show that by utilizing the successive interference cancelation technique, the require signal to noise ratio required to achieve 10^-3 symbol error rate is decreased by 3 - 4 dB. By using a clipped communication signal instead of backing off the power in the transmitter PA, we are able to improve the power added efficiency by 8 percentage points.
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| 2. |
- Behravan, Ali, 1971, et al.
(författare)
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A model for bandpass nonlinearities based on Harmonic measurements
- 2003
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Ingår i: Proceedings of the IEEE Radio and Wireless conference, Boston, MA, USA, AUG 10-13. - 0780378296 ; , s. 409-412
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Konferensbidrag (refereegranskat)abstract
- This paper presents a model for a bandpass nonlinearity which is based on measurements on several harmonies of the output. The model has a quadrature structure, with a memoryless nonlinearity and a filter in each branch. structure can describe AM/AM as well as AM/PM conversions. The parameters of the nonlinearity and the filter are jointly optimized to fit the measurements. Analytic expressions for the parameters of the model is found by means of the MMSE optimization. The method is applied to find a model for a 60GHz solid-state power amplifier based on a set of measurements on different harmonics of the output.
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| 3. |
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| 4. |
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| 5. |
- Behravan, Ali, 1971, et al.
(författare)
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Baseband compensation techniques for bandpass nonlinearities
- 2003
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Ingår i: Proceedings of the IEEE Vehicular technology conference fall 2003, Orlando, Florida, USA, OCT 06-09. ; , s. 279-283
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Konferensbidrag (refereegranskat)abstract
- In this paper we present and compare several methods of compensating the nonlinearity of the RF front-end of a wireless system. Two baseband compensation techniques, namely predistortion and postdistortion (equalization) of the baseband signal are discussed and the problems associated with each one is addressed. Furthermore a combination of a predistorter and a nonlinear equalizer and also predistortion of oversampled baseband signal are analyzed. It will be shown that under realistic conditions with a frequently saturated amplifier and ISI channel, the latter two methods are able to compensate the nonlinearity up to a good extent, while the first two methods can only operate under certain assumptions for channel conditions and nonlinearity type.
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| 6. |
- Behravan, Ali, 1971
(författare)
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Evaluation and Compensation of Nonlinear Distortion in Multicarrier Communication Systems
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In modern wireless communication systems with increasing data transfer rateand mobility, designing efficient transceivers is a key issue. Among differentchallenges, nonlinearity of high power amplifiers is a problem that has to beovercome by means of adding extra hardware or using more efficient signalprocessing algorithms. Large signal envelope fluctuations of a multicarriersignal compared to a single carrier is the motivation for extensiveinvestigations in this area.This thesis covers different methods of overcoming the distortion caused by anonlinearity at the transmitter of a multicarrier communication system. Thefocus is mainly on digital baseband compensation methods for multicarriersignals undergoing a nonlinearity at the transmitter front-end. Digital basebandpredistortion and nonlinear equalization are examples of methods for linearizinga nonlinear high power amplifier. Both of these methods are implemented andcompared in this thesis. We also implement a method based on intercarrierinterference cancellation to reduce the distortion at the receiver side by meansof iterative estimation and refining the received signal. Since this method is areceiver side solution, no extra bandwidth or extra power is required, and onlya more complex receiver is needed.Spectral spreading over the neighboring channel is a huge problem, that requiressome means of compensation at the transmitter. The spectral spreading can bereduced by forming signals with less sensitivity to nonlinear amplifications. Weimplement and compare methods of reducing peak-to-average power ratio (PAPR) ofa signal in order to limit the spectral outgrowth and improve the bit error rate(BER) performance of the system. Complexity, bandwidth efficiency and powerefficiency are important factors that have to be considered in selection ofthese method.Except PAPR, other measures of the signal envelope variations can be used toevaluate the susceptibility of signal to nonlinear amplification. We use ameasure related to the variance of the instantaneous power, and try to reducethat, thereby improving the performance of the system.
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| 7. |
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| 8. |
- Behravan, Ali, 1971, et al.
(författare)
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Harmonic-based model for bandpass nonlinearity and its application to RF predistorter design
- 2003
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Ingår i: Proceedings of the 15th international conference on wireless communications, Calgary, Canada.
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Konferensbidrag (refereegranskat)abstract
- Due to their large bandwidth of operation, RF predistorters are suitable for linearizing amplifier nonlinearity in high speed wireless applications. Unlike baseband linearization techniques, RF predistorters generate overtones which contribute to the first zone output of the bandpass high power amplifier. This paper presents a model for a bandpass nonlinearity that is based on measurements on several harmonics of the output. The model matches different harmonics of the output signal fairly well. The model is then used to design an RF predistorter. The advantage of the method compared to a design based on first zone of the output, is that the predistorter minimizes the total distortion power instead of reducing one specific intermodulation product.
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| 9. |
- Behravan, Ali, 1971
(författare)
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Nonlinearity in Broadband Wireless Communication Systems
- 2003
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the implementation of a digital communication system, there often exist imperfections that are not considered in the primary design. One such imperfection is the nonlinearity of the front-end devices. In most cases the physics of the nonlinearity is not completely known, and therefore the analysis of the system is very difficult, if not impossible. In this case models based on the observations from the device behavior has to be built and used in the study of the system.This thesis focuses on modeling and analysis of a system with nonlinearity. The topics covered here are modeling the nonlinearities, the impact of nonlinearity on a digital communication link, compensation of the nonlinearity effects, and measures to evaluate the susceptibility of signals to nonlinearity. In the modeling part, a model for a bandpass nonlinearity which is based on measurements on several harmonics of the output is presented. Unlike linear systems, in nonlinear systems a baseband equivalent does not contain all the information about the bandpass system. In this case the original bandpass model has to be used in some analysis. The model is then used to evaluate the performance of a broadband wireless communication system in the presence of nonlinearity. Two major classes of modulation for broadband wireless transmission are studied and the effect of nonlinearity on them is addressed. We also present and compare several methods of compensating the nonlinearity of the RF front-end of a wireless system. The methods include baseband and RF compensation methods. The design procedure for each one is discussed and the performance of the compensated system is evaluated. Finally we study signal measures related to nonlinearities, such as PAPR (Peak-to-Average-Power-Ratio), with respect to their ability to correctly predict the impact of a nonlinearity on an OFDM (Orthogonal Frequency Division Multiplexing) system. We also propose new measures for signal distortion in nonlinear systems.
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| 10. |
- Behravan, Ali, 1971, et al.
(författare)
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PAPR and other measures for OFDM systems with nonlinearity
- 2002
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Ingår i: Proc of the 5th International Symposium on Wireless Personal Multimedia Communications, OCT 27-30, Honolulu, Hawaii. ; , s. 149-153
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Konferensbidrag (refereegranskat)abstract
- In this paper, we discuss the effects of nonlinearity on the performance in transmission of OFDM signals. Furthermore, we study measures related to nonlinearities, such as PAPR (Peak-to-Average-Power-Ratio), with respect to their ability to correctly predict the effect of a nonlinearity in an OFDM system. We also propose new measures for signal distortion in nonlinear systems. The performance of the measures are studied using several examples.
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