Generalized Frequency Division Multiplexing in Cognitive Radio
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In today’s scenario, radio spectrum is becoming scarce, and the intelligent use of the available spectrum by cognitive radio (CR) has become an important aspect of research in wireless communication. To cope with this huge demand for spectrum, regulatory bodies (such as FCC in the USA, BNetzA in Germany, and Ofcom in the UK) have recently opened up licensed spectrum for secondary unlicensed access. Unlicensed access in licensed bands should not create interference to incumbent users, and hence, new physical layer (PHY) designs and waveforms are being researched, which can fill in the TV white spaces (TVWS) in an opportunistic manner. One of the strict specifications for CR physical layer modulation design is that the opportunistic signal should have extremely low out-of-band radiation, so that incumbent signals are not disturbed, and co-existence is assured. Moreover, to cope with spectrum fragmentation, the receiver should be able to aggregate several TV white spaces (TVWS) by a single wide band signal. Hence, innovative waveform design with a new multicarrier modulation capable of interference mitigation has emerged as a very important topic of research.
The multiband Generalized Frequency Division Multiplexing (GFDM) is a new idea for designing a multicarrier PHY. GFDM is block based multicarrier transmission scheme derived from filter bank approach where the transmit data of each block is distributed in time and frequency and each subcarrier is pulse shaped with an adjustable pulse shaping filter. GFDM is well suited for cognitive radio, as the choice of pulse shaping filters makes the out-of-band leakage extremely small. Compared to OFDM, which has rectangular pulse shaping, GFDM with a choice of transmit pulse shaping, causes lesser interference to the adjacent incumbent frequency bands.
The thesis introduces the concept of GFDM and extends it towards cognitive radio applications. The basic GFDM transceiver chain is described in detail along with all its intricacies. The thesis analyses the adjacent channel leakage ratio of GFDM and compares them with traditional OFDM and other new waveforms like filter bank multi-carrier (FBMC) and interference avoidance partition frequency technique (IAPFT). The thesis studies the effects of different pulse shaping filters, like raised cosine and root raised cosine filters, to out of band leakage, and also, to the bit error rate performance. The thesis studies the adjacent channel leakage ratio (ACLR) of GFDM and introduces the concept of cancellation carrier insertion to GFDM. This method reduces the out of band leakage to match that of FBMC.
In a cognitive radio application, sensing the opportunistic signal is extremely important. Towards this, the thesis studies the sensing performance of GFDM. Along with theoretical analysis, simulation methods are explained and numerical studies have been performed. The thesis also introduces the idea of sensing opportunistic signals with GFDM sharper filters with a significant gain in performance.
Along with sensing, feature detection of an opportunistic signal is also an interesting and invigorating study. The thesis details the study of cyclostationary properties of GFDM and identifies new correlative properties in the GFDM signals which give rise to additional cyclostationary peaks in the cyclostationary autocorrelation function. The thesis uses these additional peaks of correlative informations to improve the detection performance of a GFDM signal compared to OFDM.
The concept of GFDM data block and flexible pulse shaping filters to reduce the ACLR, however, introduces severe non-orthogonality between the subcarriers. This in-turn produces self interference which degrades the bit error rate (BER) performance of the GFDM system. The thesis implements a successive interference cancellation scheme which cancels out the self interference and matches the GFDM performance to theoretical studies and that of OFDM. The thesis also describes an experimental testbed for GFDM as a cognitive radio waveform in a 4G LTE cellular whitespace. The GFDM waveform is transmitted with SIGNALION SDR testbed, and interference to the legacy LTE signal is calculated. Apart from which, a sensor, which proves the spectral efficiency of sharper GFDM waveform compared to traditional OFDM, has also been implemented. The prototype implementation proves the validity of GFDM as a suitable candidate for CR access beyond doubt.
As a major outcome, the results clearly indicate the suitability of GFDM as an opportunistic waveform for application in fragmented TVWS cognitive radio environments. The thesis studies the applicability of GFDM in cognitive radio not only in respect to its out of band leakage but also to its robust sensing performance. The new results of low ACLR in GFDM and improved sensing performance for GFDM makes it very suitable for CR applications. Additional correlative properties found in its cyclostationary autocorrelative functions improves its detection performance and also hints at ease of synchronization of GFDM in this direction. The results from the thesis highlights the overall applicability and suitability of GFDM as a next generation flexible waveform for cognitive radio application in fragmented spectrum scenarios.
The multiband Generalized Frequency Division Multiplexing (GFDM) is a new idea for designing a multicarrier PHY. GFDM is block based multicarrier transmission scheme derived from filter bank approach where the transmit data of each block is distributed in time and frequency and each subcarrier is pulse shaped with an adjustable pulse shaping filter. GFDM is well suited for cognitive radio, as the choice of pulse shaping filters makes the out-of-band leakage extremely small. Compared to OFDM, which has rectangular pulse shaping, GFDM with a choice of transmit pulse shaping, causes lesser interference to the adjacent incumbent frequency bands.
The thesis introduces the concept of GFDM and extends it towards cognitive radio applications. The basic GFDM transceiver chain is described in detail along with all its intricacies. The thesis analyses the adjacent channel leakage ratio of GFDM and compares them with traditional OFDM and other new waveforms like filter bank multi-carrier (FBMC) and interference avoidance partition frequency technique (IAPFT). The thesis studies the effects of different pulse shaping filters, like raised cosine and root raised cosine filters, to out of band leakage, and also, to the bit error rate performance. The thesis studies the adjacent channel leakage ratio (ACLR) of GFDM and introduces the concept of cancellation carrier insertion to GFDM. This method reduces the out of band leakage to match that of FBMC.
In a cognitive radio application, sensing the opportunistic signal is extremely important. Towards this, the thesis studies the sensing performance of GFDM. Along with theoretical analysis, simulation methods are explained and numerical studies have been performed. The thesis also introduces the idea of sensing opportunistic signals with GFDM sharper filters with a significant gain in performance.
Along with sensing, feature detection of an opportunistic signal is also an interesting and invigorating study. The thesis details the study of cyclostationary properties of GFDM and identifies new correlative properties in the GFDM signals which give rise to additional cyclostationary peaks in the cyclostationary autocorrelation function. The thesis uses these additional peaks of correlative informations to improve the detection performance of a GFDM signal compared to OFDM.
The concept of GFDM data block and flexible pulse shaping filters to reduce the ACLR, however, introduces severe non-orthogonality between the subcarriers. This in-turn produces self interference which degrades the bit error rate (BER) performance of the GFDM system. The thesis implements a successive interference cancellation scheme which cancels out the self interference and matches the GFDM performance to theoretical studies and that of OFDM. The thesis also describes an experimental testbed for GFDM as a cognitive radio waveform in a 4G LTE cellular whitespace. The GFDM waveform is transmitted with SIGNALION SDR testbed, and interference to the legacy LTE signal is calculated. Apart from which, a sensor, which proves the spectral efficiency of sharper GFDM waveform compared to traditional OFDM, has also been implemented. The prototype implementation proves the validity of GFDM as a suitable candidate for CR access beyond doubt.
As a major outcome, the results clearly indicate the suitability of GFDM as an opportunistic waveform for application in fragmented TVWS cognitive radio environments. The thesis studies the applicability of GFDM in cognitive radio not only in respect to its out of band leakage but also to its robust sensing performance. The new results of low ACLR in GFDM and improved sensing performance for GFDM makes it very suitable for CR applications. Additional correlative properties found in its cyclostationary autocorrelative functions improves its detection performance and also hints at ease of synchronization of GFDM in this direction. The results from the thesis highlights the overall applicability and suitability of GFDM as a next generation flexible waveform for cognitive radio application in fragmented spectrum scenarios.
| Erscheint lt. Verlag | 28.11.2014 |
|---|---|
| Sprache | englisch |
| Maße | 148 x 210 mm |
| Gewicht | 200 g |
| Themenwelt | Technik ► Elektrotechnik / Energietechnik |
| Schlagworte | FDMA • Generalized Frequency Division Multiplexing, Cognitive Radio • Mobilfunk |
| ISBN-10 | 3-938860-80-4 / 3938860804 |
| ISBN-13 | 978-3-938860-80-9 / 9783938860809 |
| Zustand | Neuware |
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