Khaled Fazel

Multi-Carrier and Spread Spectrum Systems

From the Publisher: Frequency spectrum is a limited and valuable resource for wireless communications. A good example can be observed among network operators in Europe for the prices to pay for UMTS-frequency bands. Therefore, the first goal when designing future wireless communication systems (e.g. 4G - fourth generation) has to be the increase in spectral efficiency. The development in digital communications in the past years has enabled efficient modulation and coding techniques for robust and spectral efficient data, speech, audio and video transmission. These are the multi-carrier modulation (e.g. OFDM) and the spread spectrum technique (e.g. DS-CDMA), where OFDM was chosen for broadcast applications (DVB, DAB) as well as for broadband wireless indoor standards (ETSI HIPERLAN-II, IEEE-802.11) and the DS-CDMA was selected in mobile communications (IS-95, third generation mobile radio systems world wide, UMTS/IMT 2000). Since 1993 various combinations of multi-carrier (MC) modulation and the spread spectrum (SS) technique have been introduced and the field of MC-SS communications has become an independent and important research topic with increasing activities. New application fields have been proposed such as high rate cellular mobile, high rate wireless indoor and LMDS. It has been shown that MC-SS offers the high spectral efficiency, robustness and flexibility that is required for the next generation systems. Meanwhile, different alternative hybrid schemes such as OFDM/OFDMA, MC-TDMA, etc. have been deeply analysed and adopted in different international standards (ETSI-BRAN, IEEE-802 & MMAC). Multi-Carrier & Spread-Spectrum: Analysis of Hybrid Air Interfaces draws together all ofthe above mentioned hybrid schemes therefore providing a greatly needed resource for system engineers, telecommunication designers and researchers in order to enable them to develop, build and deploy several schemes based on MC-transmission for the next generation systems (which will be an integration of broadband multimedia services covering both 4G mobile and fixed wireless systems). Offers a complete treatment of multi-carrier, spread-spectrum (SS) and time division multiplexing (TDM) techniquesProvides an in-depth insight into hybrid multiple access techniques based on multi-carrier (MC) transmissionPresents numerous hybrid multiple access and air interface architectures including OFDM/CDMA, MC-CDMA, MC-DS-CDMA and MT-CDMACovers new techniques such as space-time coding and software radio Telecommunications engineers, hardware & software system designers and researchers as well as students, lecturers and technicians will all find this an invaluable addition to their bookshelf.

A Flexible and High Performance Cellular Mobile Communications System Based on Orthogonal Multi-Carrier SSMA

The conventional Direct-Sequence Spread-Spectrum-Multiple-Access (DS-SSMA) system with RAKE-receiver is an interesting approach in mobile communications in order to combat the frequency selectivity of the channel. The main advantages of DS-SSMA are well known, but its capacity is limited by other-user interference. Another interesting SSMA technique that combats the frequency selectivity of the channel and achieves high spectral efficiency is based on Orthogonal-Frequency-Division-Multiplexing (OFDM). This new SSMA technique combines the principles of DS-SSMA with OFDM and is called Multi-Carrier Spread-Spectrum-Multiple-Access (MC-SSMA). By providing high frequency diversity, this combination enables the possibility to perform a maximum-likelihood detection (MLD) resulting in high performance/capacity, to use the spectrum in an efficient way and to retain many advantages of the conventional DS-SSMA system. In addition, it allows both simple cell-separation by using frequency hopping and simple hardware realization. An example for the downlink of a mobile communications system, i.e. the transmission from the base station to a mobile station, using MC-SSMA with Walsh-Hadamard code spreading is studied. Different coherent detection algorithms such as conventional detection, MLD, and iterative detection are analyzed. The analytical performance of MLD is evaluated. It is also shown analytically, and by simulations that the MC-SSMA system with MLD outperforms the DS-SSMA system with RAKE-receiver. Up to 64 active users can be transmitted in a 1.25 MHz bandwidth. Each user has a rate of 16.0 kbit/s by using BPSK modulation. At a signal to noise ratio (SNR) of 13 dB a bit error probability ofPb=10−3 can be guaranteed without channel coding. This results in a spectral efficiency of about 0.8 bit/s/Hz. Under the same conditions the conventional DS-SSMA system results in a spectral efficiency of about 0.15 bit/s/Hz. Hence, using MC-SSMA for the downlink of a cellular mobile communications system is a promising approach.

Multi-Carrier Spread-Spectrum & Related Topics

Multi-Carrier Spread-Spectrum has been deeply studied and new alternative solutions have been proposed. This book edits the newest contributions and research results in this new field presented at the Third International Workshop on MC-SS & Related Topics, held in Oberpfaffenhofen, Germany.

Comparison of Error Concealment Techniques for an MPEG-2 Video Decoder in Terrestrial TV-Broadcasting

In terrestrial broadcasting the received power fluctuation might be in the order of 10 dB, where a non-hierarchical TV-transmission scheme may fail at bad reception conditions. A two layer hierarchical transmission system, also specified by the European digital terrestrial TV-broadcasting standard, may help to have better reception conditions especially for fixed receivers. However, the portable/mobile receiver that only needs the base layer of this hierarchical signal may risk a total loss of picture. Since no time interleaving is foreseen in the standard, the situation is more critical in the case of shadowing, high Doppler (mobile reception), or impulsive noise, whereas even for fixed receivers with two hierarchical levels a good quality of service cannot be guaranteed. Therefore, in order to assume a continuous service with higher quality, some post-processing techniques such as error concealment at the receiver side will be desirable. These techniques, for instance even in the case of hierarchical transmission, may offer better results by concealing the errors instead of using only the most robust stream. The aim of this article is to study different error concealment techniques for the European digital terrestrial TV-broadcasting standard where the source coding is based on MPEG-2. These techniques are based on temporal, spatial and frequency error concealment techniques and on the combination of them. Simulations showed that motion compensated temporal error concealment provides best results for P- and B-pictures, whereas a combination of temporal error concealment and re-synchronization or the use of shorter slices provides best results for I-pictures.

On the performance of the DVB-T system in mobile environments

Mobile multimedia services may become an important feature of terrestrial networks for many applications. One possible scenario to offer digital TV services for mobile and portable receivers is to use the DVB-T specifications that may allow high data rate transmission in an 8 MHz UHF channel. Although this specification was designed for fixed reception, some of its robust modes might allow mobile reception of TV-services. By means of theoretical investigations, simulations, laboratory tests and field trials, we analyse the behaviour and limits of the DVB-T standard in mobile environments. It seems that the Doppler shift is not necessarily the limitation. Rather, it is the lack of time interleaving that might pose problems.

On the Performance of the DVB-T System in Mobile Environments

Mobile multimedia services may become an important feature of terrestrial networks for many applications. One possible scenario to offer digital TV services for mobile and portable receivers is to use the DVB-T specifications that may allow high data rate transmission in an 8 MHz UHF channel. Although this specification was designed for fixed reception, some of its robust modes might allow mobile reception of TV-services. By means of theoretical investigations, simulations, laboratory tests and field trials, we analyse the behaviour and limits of the DVB-T standard in mobile environments. It seems that the Doppler shift is not necessarily the limitation. Rather, it is the lack of time interleaving that might pose problems.

Multi-Carrier Systems & Solutions 2009

The wireless standards 3GPP Long Term Evolution (LTE), WiMAX, IEEE 802.11a/n, and DxB have in common that they apply the spectrally efficient multi-carrier modulation in order to achieve very high rate data transmission. This trend is expected to continue in the future with the development of the next generation of mobile wireless communications under the IMT-Advanced standardization activities. Additional measures like advanced coding, spreading, and MIMO are combined with multi-carrier transmission to further enhance the efficiency of future systems. The aim of Multi-Carrier Systems & Solutions 2009 is to edit the ensemble of the newest contributions and research results in this field that have been presented during the 7th International Workshop on Multi-Carrier Systems & Solutions (MC-SS 2009), held in Herrsching, Germany.

ETT Special Issue LTE/LTE Advanced

The needs for traditional mobile communications, that is, ‘voice-only’ communications, are recently heavily decreasing, even in third-world countries. The number of data-centric wireless terminals (so-called smart phone, tablet PC, e-book, etc.) and hence the amount of data traffic per mobile user have been increasing drastically over the last 5 years. This trend is still to continue. Therefore, the third-world countries together with Europe, USA and Japan are still huge markets for future data-centric network operators and especially for the ‘smart phone’ manufacturers, which offer new devices supporting simple mixed-voice and data-centric service operations.

Performance Tradeoffs in Asynchronous Spread Spectrum Multi-Carrier Multiple Access

The paper presents simple detection algorithms to mitigate interference due to asynchronism in the uplink of a mobile radio system using spread spectrum multi-carrier multiple access (SS-MC-MA). The effects of a pilot-symbol-aided uplink channel estimation are taken into account in the analysis. The presented system allows some intersymbol interference (ISI) and intersubchannel interference (ICI) in the uplink but in return reduces the loss in bandwidth efficiency due to a shortened guard interval and avoids the complexity of a dedicated uplink synchronization scheme.

A System Design for a Wireless Home Multi-Media LAN

In this paper we describe and specify the design of a radio interface and Data Link Layer for a wireless indoor multimedia communications system. A radio frequency link operating in the 2.4/5.8 GHz ISM-band is considered as the transmission medium, where the maximum data rate using 16-QAM modulation can be up to 26.8 Mbit/s. The general concept of the system, which is based on a decentralised, i.e. ad-hoc, topology is illustrated. The radio interface is based on a combination of TDMA and FDMA with single carrier modulation. The system supports variable rate transmission and is flexible, since it can provide stream and packet services. We discuss the Data Link Layer of the system, as well as some physical layer receiver issues (synchronisation, equalisation, and antenna diversity), as well as providing simulation results.