Call to participate in the 3rd Nokia Ubimedia MindTrek Awards Competition. September 30th – October 2nd, 2009, Tampere, Finland http://www.mindtrek.org/ubimedia. Competition deadline: August 7th. Award Sum: 7.000 Euros.
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Welcome to participate at the Russian Mobile VAS Awards'2009 competition. Entry deadline: October 16, 2009. The Awards winners will be announced at the VI Mobile VAS Conference gala dinner and Awards Ceremony on November 19. Russian Mobile VAS Awards'2009 categories:
For last few decades, Orthogonal Frequency Division Multiplexing has been recognized not only as an efficient modulation format but also as an effective way of supporting multiple access. The orthogonal frequency division multiple access (OFDMA) principle employs assignment of orthogonal sub-carrier sets to a number of the network users and has been adopted in Metropolitan Area Networks (IEEE 802.16.std), Wide Area Networks such as Ultra Mobile Broadband for 3GPP Long Term Evolution.
Whenever an OFDMA operates in a time-frequency dispersive radio channel the link adaptation provides a benefit in terms of any system performance metric by employing time, frequency and multi-user diversities. The aim of the project is elaboration of low complexity (practical) link adaptation algorithms with QoS constraints (such as fairness, delay etc.) for OFDMA.
Contacts
Contact person: Natalia Ermolova
Introduction
High peak-to-average signals play a key role in the modern wireless communications. More over OFDM technology being applied to the initially constant envelope signal like QPSK, makes it distribution Gaussian with theoretically infinite crest factor. Such signals are very sensitive to the nonlinear distortions.
Quadrature (I/Q) modulation is a most popular technique of baseband signal spectrum translation to the radio frequency (RF) bands. From the mathematical point of view this way provides one of two forms of the complex numbers representation as real and imaginary parts. Practical realization of this method is very convenient and therefore widely used both for BPSK, QPSK GMSK and QAM modulation constellations. But among a lot of advantages it has one serious drawback. In the case of non constant amplitude signal modulation schemes (including OFDM technology) it requires high transmitter linearity. As a result power efficiency suffers.
Polar modulation is alternative way of complex envelope forming. In this case angle and amplitude but not real and imaginary variations are applied to the carrier signal. It corresponds to the polar representation of complex envelope. Polar modulation realization allows nonlinear operation of RF transmitter. Even high efficiency switching classes of operation of power amplifiers are appropriated. Amplitude component of signal modulation is introduced at the last stage of power amplifier in this case.
Difficulties of practical realization of such approach quite clear – it is necessary to provide sufficient accuracy of amplitude and angle variations during modulation.
The purpose of the project is practical polar modulation development, hardware prototype elaboration, its experimental research and numerical estimation of the power efficiency improving.
Environment
Experimental set consists of the next blocks:
- bit stream source;
- digital processor (modulator);
- RF transmitter;
- RF receiver;
- digital demodulator;
- BER tester.
Standard measurement equipment is also necessary for a purpose of prototypes tuning and experiments providing:
- vector generator;
- spectrum analyzer;
- digital oscilloscope.
Research Directions
- Amplitude modulation technique at power amplifiers, operating in the different classes, including switched regimes.
- Combined angle and amplitude modulation accuracy and its distortions due to hardware imperfection.
- Development of the polar modulation signals digital processing for a popular communication standards like 802.11, 802.16.
Project Stages
- Literature analysis. Different classes operation of the power amplifiers simulation. Polar modulation technique simulation. Calculation of achievable modulation parameters and limitations.
- Choice of practical realization variants. Electronic components analysis. Development of prototypes and its fabrication. Signal processing special algorithms development.
- Prototypes tuning and parameters measurement. Complete experiments wit different modulation formats. Experimental results summarizing and analysis.
Contacts
Team leader: Vladimir Prikhodko
Orthogonal frequency division multiplexing (OFDM) is an effective modulation technique that is able to support very high rate data transmission under a relatively simple transceiver structure. Due to these features OFDM is adopted as the standard in many wireless applications and being considered as a strong candidate for mobile phone and multimedia communication standards of future generation.
To satisfy the requirements of supporting very high rate and reliable data transmission under limited spectrum availability and constrained transmit power, signal-processing techniques that allow the available signal bandwidth and transmit power to be used more effectively should be applied.
The main factors deteriorating reliability of the OFDM data transmission are nonlinear effects, frequency offset effects and those of deep fading. The aims of the project are:
- Analysis of nonlinear effects, frequency offset effects and those of fading in OFDM-based communication systems ;
- Elaboration of signal-processing algorithms for mitigation of harmful impact of the above factors.
Contacts
Contact person: Natalia Ermolova
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