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.

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Multi-Carrier and Spread Spectrum Systems

A method and apparatus for allocating subcarriers in an orthogonal frequency division multiple access (OFDMA) system is described. In one embodiment, the method comprises allocating at least one diversity cluster of subcarriers to a first subscriber and allocating at least one coherence cluster to a second subscriber.

Multi-carrier communications with adaptive cluster configuration and switching

We analyze the effects of Doppler spread in mobile channels on orthogonal frequency division multiplex (OFDM) systems. This is important, since channel variations during one OFDM symbol cause inter sub-carrier interference (ICI) in OFDM systems, which degrades the performance, since ICI can be seen as additional near-Gaussian noise. The analysis is outlined, and closed-form results given for numerous important practical Doppler spread encountered in mobile channels. We also show that for the case of asymmetrical Doppler spreads, the frequency correction of the receiver can be adjusted so as to minimize the ICI. To extend our work to OFDM(A) mobile radio systems in the uplink case where many users' contributions to the ICI overlap, we have introduced the concept of an equivalent single-user which causes the total ICI, in order to use the same analytical framework. For some channel examples, we simulated the Doppler spread of this equivalent user. Simulation results confirm our analysis and show the importance of the analytical tool to perform realistic system analysis without having to resort to time consuming time-domain simulations.

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The effects of Doppler spreads in OFDM(A) mobile radio systems

Multicarrier spread spectrum transmission methods based on orthogonal frequency division multiplexing employ a linear transform to spread energy of transmitted symbols over statistically independent Rayleigh fading subcarriers, in order to enable a diversity gain at the receiver. We jointly treat the mapping from bits into transmit symbols and the spreading transform as a code in Euclidean space. We describe criteria to identify good and bad spreading transforms, in terms of the asymptotic bit-error probability (BEP) at high signal-to-noise ratio. Upper and lower bounds on the BEP are derived. It is shown that the BEP performance of the commonly used Hadamard transform is asymptotically bad. Alternative orthogonal transforms with better asymptotic performance are proposed. Simulation results are given for the example of 2-phase-shift keying, block length 8.

Diversity comparison of spreading transforms for multicarrier spread spectrum transmission

The paper quantifies the significant effects of Doppler spread in a time variant mobile radio channel on the performance of OFDM multi-carrier systems. A suitable model for OFDM is introduced and serves as the basis for the derivation of the inter-carrier interference (ICI) due to the loss of sub-carrier orthogonality. Several Doppler spectra are analyzed and compared, such as the classical and uniform distributions, as well as the case of two distinct values for the Doppler frequency. We can thus employ the computed variance of the ICI process, together with the channel noise, in system analyses and designs, and avoid lengthy time-domain simulations. We also analyze optimal receiver frequency synchronisation in the case of Doppler spreads.

Analysis of the loss of orthogonality through Doppler spread in OFDM systems

The multi-carrier (MC) multiple access schemes MC-FDMA, MC-TDMA, MC-CDMA and the previously proposed SS-MC-MA scheme are investigated and compared for the suitability in the uplink and the downlink of a mobile radio system. By presenting a bandwidth efficiency plan for the different MC multiple access schemes in fading channels, the influence of the channel code rate, the system load, and the spreading code length is presented. Moreover, results with oneand two-dimensional pilot symbol aided channel estimation are shown for the various MC multiple access schemes considering typical multipath propagation scenarios in the uplink and the downlink.

S. Kaiser

Papers

MC-FDMA and MC-TDMA versus MC-CDMA and SS-MC-MA: performance evaluation for fading channels