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Author: Srinivas rao Vaidya Publisher: ISBN: Category : Languages : en Pages : 116
Book Description
[Author's abstract] Transmit diversity technique, like the one in [2], has been found to provide good reliability for a flat fading channel. For CDMA systems there are two popular transmit diversity techniques, which are OTD and STS proposed in [3] [4]. STS scheme outperforms the OTD as, OTD offers temporal diversity, in contrast to spatial diversity offered by STS. For frequency selective channel, performance of the above schemes depends on the correlation properties of the spreading sequence used. Selection of proper spreading sequence with good correlation properties improves the system reliability in presence of MAI. On the other hand coherent detection at the receiver requires the channel knowledge, which is provided by channel estimation at the receiver. But channel estimation for frequency selective channel costs the resources and lowers the data rate due to which differential detection is done which does not require the knowledge of the channel. For the STS scheme which offers spatial diversity by coherent detection, it is not possible to do differential detection, hence channel estimation is necessary. So we propose a new transmit diversity technique which uses a complex spreading sequence called SP [1] sequence, for which coherent as well as differential detection exists. This scheme as the STS offers spatial diversity for both coherent and differential detection.
Author: Srinivas rao Vaidya Publisher: ISBN: Category : Languages : en Pages : 116
Book Description
[Author's abstract] Transmit diversity technique, like the one in [2], has been found to provide good reliability for a flat fading channel. For CDMA systems there are two popular transmit diversity techniques, which are OTD and STS proposed in [3] [4]. STS scheme outperforms the OTD as, OTD offers temporal diversity, in contrast to spatial diversity offered by STS. For frequency selective channel, performance of the above schemes depends on the correlation properties of the spreading sequence used. Selection of proper spreading sequence with good correlation properties improves the system reliability in presence of MAI. On the other hand coherent detection at the receiver requires the channel knowledge, which is provided by channel estimation at the receiver. But channel estimation for frequency selective channel costs the resources and lowers the data rate due to which differential detection is done which does not require the knowledge of the channel. For the STS scheme which offers spatial diversity by coherent detection, it is not possible to do differential detection, hence channel estimation is necessary. So we propose a new transmit diversity technique which uses a complex spreading sequence called SP [1] sequence, for which coherent as well as differential detection exists. This scheme as the STS offers spatial diversity for both coherent and differential detection.
Author: Khaled Fazel Publisher: Springer Science & Business Media ISBN: 1461544637 Category : Technology & Engineering Languages : en Pages : 368
Book Description
Khaled Fazel Stefan Kaiser Digital Microwave Systems German Aerospace Center (DLR) Bosch Telecom GmbH Institute for Communications Technology D-71522 Backnang, Germany D-82234 Wessling, Germany In this last decade of this millennium the technique of multi-carrier transmission for wireless broadband multimedia applications has been receiving wide interests. Its first great success was in 1990 as it was selected in the European Digital Audio Broadcasting (DAB) standard. Its further prominent successes were in 1995 and 1998 as it was selected as modulation scheme in the European Digital Video Broadcasting (DVB-T) and in three broadband wireless indoor standards, namely ETSI-Hiperlan-II, American IEEE-802. 11 and Japanese MMAC, respectively. The benefits and success of multi-carrier (MC) modulation in one side and the flexibility offered by spread spectrum (SS) technique in other hand motivated many researchers to investigate the combination of both techniques, known as multi-carrier spread-spectrum (MC-SS). This combination benefits from the main advantages of both systems and offers high flexibility, high spectral efficiency, simple detection strategies, narrow band interference rejection capability, etc. . The basic principle of this combination is straightforward: The spreading is performed as direct SS (DS-SS) but instead of transmitting the chips over a single sequence carrier, several sub-carriers could be employed. As depicted in Figure 1, after spreading with assigned user specific code of processing gain G the frequency mapping and multi-carrier modulation is applied. In the receiver side after multi-carrier demodulation and frequency de-mapping, the corresponding detection algorithm will be performed.
Author: David Tse Publisher: Cambridge University Press ISBN: 9780521845274 Category : Computers Languages : en Pages : 598
Book Description
This textbook takes a unified view of the fundamentals of wireless communication and explains cutting-edge concepts in a simple and intuitive way. An abundant supply of exercises make it ideal for graduate courses in electrical and computer engineering and it will also be of great interest to practising engineers.
Author: Paulo Silva Publisher: CRC Press ISBN: 1000794156 Category : Science Languages : en Pages : 264
Book Description
Future broadband wireless communication systems are expected to be able to offer new and powerful services enabling fast transmission rates of several tens of Mbit/s. This is an ambitious challenge especially for mobile communication systems since these systems should be able to cope with severely time dispersive channels, associated to the signal multipath propagation. Moreover, these systems should have high spectral and power efficiencies, as well as high capacity and flexibility. Spread spectrum techniques, particularly coded division multiple access (CDMA) techniques allow high capacity and flexibility, continuous transmission requiring low-peak power requirements for the amplifiers, as well as some robustness against fading and time-dispersion effects associated with the multipath propagation. When employed in prefix assisted (PA) block transmission schemes combined with frequency-domain receiver implementations they become especially interesting for broadband wireless systems. In Frequency-Domain Multiuser Detection for CDMA Systems the use of PA block transmission is considered in the context of both DS (Direct Sequence) and MC (Multicarrier) CDMA schemes. The main goal is the study of frequency-domain multiuser detection techniques with iterative signal detection/decoding techniques, also in combination with estimation and cancelation of nonlinear distortion effects. The receiver structures are suitable to scenarios with high interference levels and strongly time-dispersive channels.
Author: Ariel Sacramento Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
With applications such as video conferencing, extensive web browsing and live video streaming, future wireless systems become extremely demanding in terms of high data rates and improved signal quality. In this thesis the performance of a space-time spreading transmit diversity scheme is examined over a frequency-flat Nakagami- m fading channel. The Nakagami- m channel model is considered as it is well known for modeling signal fading conditions ranging from severe to moderate, to light fading or no fading, through its parameter m. We also propose in this thesis a coded transmit diversity scheme which is based on a combination of a convolutional code with a space-time transmit diversity scheme that uses direct-sequence code division multiple access (DS-CDMA) for multiuser access. Our focus will be on the uplink of the communication system. The space-time scheme employs N = 2 and N r antennas at the mobile station (MS) side and at the base station (BS) side respectively. DS-CDMA is used to support many users and a linear decorrelator detector is used to combat the effect of multiuser interference. We study the performance of both the uncoded and coded transmit diversity schemes over slow fading and fast fading channels. In all cases, the investigations start by determining the probability density function (PDF) of the signal to interference and noise ratio at the output of the space-time combiner at the BS receiver side. Using this PDF we derive a closed-form (or an approximation) expression for the bit error rate (BER) of the system under consideration. The accuracy of the PDF and BER expressions are verified when compared to simulation results for different values of the fading figure m and for different combinations of transmit and receive antennas. In the case of the coded space-time transmit diversity scheme, the pairwise error probability and the corresponding BER upper bounds are obtained for fast and slow fading channels. The derived error bounds, when compared to system simulations, are shown to be tight at high signal-to-noise ratios. Furthermore, our analytical results explicitly show the achieved system diversity in terms of the number of transmit and receive antennas and the fading figure m. When the coded space-time scheme is considered, its diversity is shown to be a function of the minimum free distance d free of the convolutional code used. Furthermore we show that the diversity of the different schemes considered is always independent of the system load.
Author: Mohamed Aljerjawi Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
The application of space-time coding in wireless communication systems has shown to improve the quality of the received signal at the mobile user by placing the spatial diversity at the base station. In this thesis, we propose a simple space-time spreading scheme for code-division multiple-access (CDMA) systems over fast-fading channels. The proposed transmit diversity scheme is based on two transmit and M receive antennas and is suitable for Rayleigh fast-fading channels. In this we employ orthogonal spreading codes to exploit the time diversity introduced by the channel, and hence a two-fold of the diversity order obtained using existing spacetime spreading schemes is achieved. Nevertheless, for slowly-fading channels, we show that the proposed coding scheme reduces to existing schemes introduced in the literature with no performance degradation. Then, we examine the effect of using nonorthogonal spreading codes on the receiver performance. Our results show that using a simple adaptive decoder, based on the minimum mean-squared error (MMSE) criterion, the diversity order is still maintained and only a small loss in the signal-to noise ratio (SNR) is incurred relative to the ideal case with orthogonal codes.
Author: Simon Plass Publisher: Springer Science & Business Media ISBN: 1402061293 Category : Technology & Engineering Languages : en Pages : 445
Book Description
This book provides the proceedings of the 6th International Workshop on Multi-Carrier Spread Spectrum (MC-SS 2007), 7-9 May 2007, held in Herrsching, Germany. The book aims to edit the ensemble of the newest contributions and research results in this new field. The book presents comprehensive state-of-the-art articles about multi-carrier spread spectrum techniques, and discusses multi-carrier spread spectrum techniques.
Author: Srinivas rao Vaidya
Author: Srinivas rao Vaidya
Author: Claude D'Amours
Author: Khaled Fazel
Author: 
Author: David Tse
Author: Paulo Silva
Author: Ariel Sacramento
Author: Mohamed Aljerjawi
Author: Simon Plass
Author: