It is shown that, particularly for terrestrial cellular telephony, the interference-suppression feature of CDMA (code division multiple access) can result in a many-fold increase in capacity over analog and even over competing digital techniques. A single-cell system, such as a hubbed satellite network, is addressed, and the basic expression for capacity is developed. The corresponding expressions for a multiple-cell system are derived. and the distribution on the number of users supportable per cell is determined. It is concluded that properly augmented and power-controlled multiple-cell CDMA promises a quantum increase in current cellular capacity. >

On the capacity of a cellular CDMA system

Relying on basic tools such as eigensignals of linear time-invariant systems, linear and circular block convolution, and fast Fourier transforms (FFTs), this article develops a systematic discrete-time framework and designs novel systems for single- and multiuser wireless multicarrier communications-a field rich in signal processing challenges that holds great potential in various applications including audio/video broadcasting, cable television, modem design, multimedia services, mobile local area networks, and future-generation wideband cellular systems. Wireless multicarrier (MC) communication systems utilize multiple complex exponentials as information-bearing carriers. MC transmissions thus retain their shape and orthogonality when propagating through linear time-dispersive media, precisely as eigensignals do when they pass through linear time-invariant (LTI) systems.

Wireless multicarrier communications

This paper focuses on a CDMA design study for future third-generation mobile and personal communication systems such as FPLMTS and UMTS. In the design study, a rigorous top down approach is adopted starting from the most essential objectives and requirements of universal third-generation mobile systems. Emphasis is laid on high flexibility with respect to the implementation of a wide range of services and service bit rates including variable rate and packet services. Flexibility in frequency and radio resource management, system and service deployment, and easy operation in mixed-cell and multioperator scenarios are further important design goals. The system concept under investigation is centered around an open and flexible radio interface architecture based on asynchronous direct-sequence CDMA with three different chip rates of approximately 1,5, and 20 Mchip/s

Design study for a CDMA-based third-generation mobile radio system

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Quadrature Amplitude Modulation: From Basics to Adaptive Trellis-Coded, Turbo-Equalised and Space-Time Coded OFDM, CDMA and MC-CDMA Systems

Adaptive Wireless Transceivers provides the reader with a broad overview of near-instantaneously adaptive transceivers in the context of TDMA, CDMA and OFDM systems The adaptive transceivers examined employ powerful turbo codecs, turbo equalisers and space-time codecs, equipping the reader with a future-proof technological road map It demonstrates that adaptive transceivers are capable of mitigating the channel quality fluctuations of the wireless channel as a lower-complexity alternative to space-time coding By contrast, if the higher complexity of multiple transmitters and multiple receiver-assisted systems is deemed acceptable, the advantages of adaptability erode • Provides an in-depth introduction to channel equalisers and Kalman filtering and discusses the associated complexity versus performance trade-offs • Introduces wideband near-instantaneously adaptive transceivers and studies their performance both with and without turbo channel coding • Describes how to optimise adaptive modulation mode switching and highlights a range of practical considerations • Introduces neural network based channel equalisers and discusses Radial Basis Function (RBF) assisted equalisers embedded into adaptive modems supported by turbo channel coding and turbo channel equalisation • Employs the above adaptive principles also in the context of CDMA and OFDM transceivers and discusses the pros and cons of space-time coding versus adaptive modulation Researchers, advanced students and practising development engineers working in wireless communications will all find this valuable text an informative read

Adaptive Wireless Transceivers: Turbo-Coded, Turbo-Equalized and Space-Time Coded TDMA, CDMA and OFDM Systems

Analyses a successive interference cancellation (IC) scheme for M-ary QAM modulation in direct sequence code division multiple access (DS/CDMA) systems. The performance under Rayleigh fading is analysed for single modulation systems and systems employing either of two different methods, mixed modulation or parallel channels, for handling multiple data rates. The authors show that the successive IC scheme for higher modulation together with mixed modulation or parallel channels give a considerable increase in performance and flexibility compared to single modulation systems employing a conventional detector.

Successive interference cancellation in multiple data rate DS/CDMA systems

This paper investigates interference cancellation (IC) in direct-sequence code-division multiple access (DS-CDMA) systems that support multiple data rates. Two methods for implementing multiple data rates are considered. One is the use of mixed modulation and the other is the use of multicodes. We introduce and analyze a new approach that combines these multiple data rate systems with IC. The cancellation in the receiver is performed successively on each user, starting with the user received with the highest power. This procedure can in turn be iterated, forming a multistage scheme, with the number of iterations set as a design parameter. Our analysis employs a Gaussian approximation for the distribution of the interference, and it includes both the AWGN and the flat Rayleigh fading channel. The systems are also evaluated via computer simulations. Our analysis and simulations indicate that the IC schemes used in mixed modulation or multicode systems yield a performance close to the single BPSK user bound and, consequently, give a prospect of a considerable improvement in performance compared to systems employing matched filter detectors.

On Multirate DS-CDMA Schemes with Interference Cancellation

A novel hybrid interference cancellation (IC) scheme is proposed for the uplink of multirate direct-sequence code division multiple access (DS/CDMA) systems communicating over mobile radio channels. The hybrid IC scheme includes both non-decision directed and decision directed IC, joined together with a modified RAKE combiner for utilization of the diversity. The performance is evaluated via computer simulations for two multiple data rate schemes, mixed modulation and parallel channels, in a multipath environment. Both the case of known channel parameters and channel estimation using pilot symbols are considered. An analytical performance assessment is also given using a Gaussian approximation.

Multistage interference cancellation in multirate DS/CDMA on a mobile radio channel

In this paper we propose successive interference cancellers (IC) for a variable data rate environment. Firstly, a successive interference cancellation (IC) scheme for M-level rectangular QAM in DS/CDMA systems is analysed. Secondly, the performance under Rayleigh fading is analysed for single modulation systems and different systems for handling multiple data rates. One alternative for handling multi-rate systems is to use mixed modulation, which imply that each user chooses modulation format according to need. Another alternative is to use parallel channels, where each user transmits over one or several synchronous channels. We show that the successive IC, for mixed modulation or parallel channel systems, has a performance close to the single BPSK user bound and, consequently, it gives a considerable increase in performance and flexibility compared to both single modulation systems and mixed modulation or parallel channel systems employing a conventional detector.

Ann-Louise Johansson

Papers

Successive interference cancellation in multiple data rate DS/CDMA systems

On Multirate DS-CDMA Schemes with Interference Cancellation

Multistage interference cancellation in multirate DS/CDMA on a mobile radio channel

Successive interference cancellation schemes in multi-rate DS/CDMA systems

Successive interference cancellation schemes in multi-rate DS/CDMA systems