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

Carrier Interferometry (CI) provides wideband transmission protocols with frequency-band selectivity to improve interference rejection, reduce multipath fading, and enable operation across non-continuous frequency bands. Direct-sequence protocols, such as DS-CDMA, are provided with CI to greatly improve performance and reduce transceiver complexity. CI introduces families of orthogonal polyphase codes that can be used for channel coding, spreading, and/or multiple access. Unlike conventional DS-CDMA, CI coding is not necessary for energy spreading because a set of CI carriers has an inherently wide aggregate bandwidth. Instead, CI codes are used for channelization, energy smoothing in the frequency domain, and interference suppression. CI-based ultra-wideband protocols are implemented via frequency-domain processing to reduce synchronization problems, transceiver complexity, and poor multipath performance of conventional ultra-wideband systems. CI allows wideband protocols to be implemented with space-frequency processing and other array-processing techniques to provide either or both diversity combining and sub-space processing. CI also enables spatial processing without antenna arrays. Even the bandwidth efficiency of multicarrier protocols is greatly enhanced with CI. CI-based wavelets avoid time and frequency resolution trade-offs associated with conventional wavelet processing. CI-based Fourier transforms eliminate all multiplications, which greatly simplifies multi-frequency processing. The quantum-wave principles of CI improve all types of baseband and radio processing.

Multicarrier sub-layer for direct sequence channel and multiple-access coding

This chapter contains sections titled: Introduction Overview of Multicarrier CDMA Systems Channel Model Performance of MC-CDMA System Performance of Overlapping Multicarrier DS-CDMA Systems Performance of Multicarrier DS-CDMA-I Systems Performance of AMC DS-CDMA Systems Performance of SFH/MC DS-CDMA Systems Chapter Summary and Conclusion 
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Overview of Multicarrier CDMA

In recent years single carrier modulation (SCM) has again become an interesting and complementary alternative to multicarrier modulations such as orthogonal frequency division multiplexing (OFDM). This has been largely due to the use of nonlinear equalizer structures implemented in part in the frequency domain by means of fast Fourier transforms, bringing the complexity close to that of OFDM. Here a nonlinear equalizer is formed with a linear filter to remove part of intersymbol interference, followed by a canceler of remaining interference by using previous detected data. Moreover, the capacity of SCM is similar to that of OFDM in highly dispersive channels only if a nonlinear equalizer is adopted at the receiver. Indeed, the study of efficient nonlinear frequency domain equalization techniques has further pushed the adoption of SCM in various standards. This tutorial paper aims at providing an overview of nonlinear equalization methods as a key ingredient in receivers of SCM for wideband transmission. We review both hybrid (with filters implemented both in time and frequency domain) and all-frequency-domain iterative structures. Application of nonlinear frequency domain equalizers to a multiple input multiple output scenario is also investigated, with a comparison of two architectures for interference reduction. We also present methods for channel estimation and alternatives for pilot insertion. The impact on SCM transmission of impairments such as phase noise, frequency offset and saturation due to high power amplifiers is also assessed. The comparison among the considered frequency domain equalization techniques is based both on complexity and performance, in terms of bit error rate or throughput.

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Single Carrier Modulation With Nonlinear Frequency Domain Equalization: An Idea Whose Time Has Come—Again

An adaptation to Carrier Interferometry synthesis and analysis provides for complex coding and decoding in a sliding window transform Coding and decoding functionality can be extended to spatial processing in systems employing multiple transceiver elements Poly-amplitude codes permit successive interference cancellation in spatial and frequency-domain processing Handoffs in cellular systems are facilitated by selecting spectral/base station combinations that optimize link performance

Orthogonal superposition coding for direct-sequence communications

The paper introduces to orthogonal frequency-division multiplexing (OFDM) systems a novel pseudo-orthogonal carrier interferometry spreading code which spreads each parallel data stream over all the OFDM carriers. Pseudo-orthogonal carrier interferometry (PO-CI) spreading codes are carefully selected to introduce the following benefits to OFDM: up to 2N parallel data streams can be coded onto N carriers, with little degradation in performance; when rate 1/2 channel coding is applied in addition to PO-CI spreading codes, the resulting binary phase-shift keying OFDM systems demonstrate the performance of coded OFDM and the throughput of uncoded OFDM; PO-CI codes are carefully selected to spread in a manner which eliminates the peak-to-average power ratio problems characteristic of traditional OFDM.

High-throughput, high-performance OFDM via pseudo-orthogonal carrier interferometry spreading codes

OFDM (orthogonal frequency division multiplexing) is susceptible to high peak-to-average power due to an unstable envelope. Many solutions have been utilized in order to decrease the high peaks that are possible, but in these cases complexity is also added to the system architecture. In our earlier work, we introduced CI codes as a powerful tool to increase OFDM performance. This paper shows how carrier interferometry phase coding eliminates peaks in the signal envelope and in effect the problems associated with large PAPR.

Overcoming peak-to-average power ratio issues in OFDM via carrier-interferometry codes

Multi-carrier technologies have emerged as important instruments in telecommunications. OFDM is in the forefront, with its adoption by the IEEE 802.11 standards committee and the European HYPERLAN standards group. Following OFDM, MC-CDMA is also demonstrating considerable promise when compared to competing technologies. According to the authors, these technologies are just the beginning in the coming multi-carrier revolution. In Multi-Carrier Technologies for Wireless Communication, the authors explain how a common multi-carrier platform is being designed for DS-CDMA, TDMA, OFDM and MC-CDMA systems. Findings are presented which show how this multi-carrier platform enhances network capacity and probability of error performance.Specific results include (1) innovation in multi-carrier technologies that are enabling them to become an integral part of TDMA and DS-CDMA systems; and (2) the design of multi-carrier systems to overcome PAPR problems (in, e.g., OFDM). Multi-Carrier Technologies for Wireless Communication is an important book for engineers who work with DS-CDMA, TDMA, OFDM, or MC-CDMA systems, and are seeking new ways of exploiting the wireless medium based on a "smarter" signal processing.

Multi-Carrier Technologies for Wireless Communication

OFDM (orthogonal frequency division multiplexing) is susceptible to poor probability of error performance in fading channels. To enhance OFDM's performance, many architectures utilize channel coding. The addition of coding, adds both redundancy and frequency diversity, but comes at a cost of reduced overall throughput (typically by a factor of 2). This paper introduces a novel carrier interferometry phase coding to enhance the performance in OFDM systems without bandwidth expansion or decreased throughput. It is shown that at a bit error rate of 10/sup 3/, this method gains 14 dB over OFDM, equaling the performance of COFDM. A system is now available demonstrating the benefits of coded OFDM, which maintains the throughput of OFDM. The cost is one of increased receiver complexity.

High-throughput, high-performance OFDM via pseudo-orthogonal carrier interferometry coding

Orthogonal frequency division multiplexing (OFDM) demonstrates symbol-by-symbol fluctuations in peak-to-average power ratio (PAPR), a direct consequence of independently modulated carriers. This, in turn, leads to inefficient operation of the transmit power amplifier, and/or in-band and out-of-band distortion due to power amplifier saturation. This paper extends our previous work, which explains how carrier interferometry (CI) spreading codes may be applied to OFDM (creating CI/OFDM) to eliminate PAPR fluctuations. Specifically, we analyze the PAPR benefits of CI codes in higher-order constellation OFDM systems (QPSK, 16-QAM, and 64-QAM OFDM). This work confirms that the proposed technique (of spreading the data symbols onto all carriers) ensures the elimination of high peaks in the signal envelope (thereby eliminating the PAPR problem): It is further shown that the choice of constellation size does little to change the PAPR benefits of the CI spreading technique.

D.A. Wiegandt

Papers

High-throughput, high-performance OFDM via pseudo-orthogonal carrier interferometry spreading codes

Overcoming peak-to-average power ratio issues in OFDM via carrier-interferometry codes

Multi-Carrier Technologies for Wireless Communication

High-throughput, high-performance OFDM via pseudo-orthogonal carrier interferometry coding

The elimination of peak-to-average power ratio concerns in OFDM via carrier interferometry spreading codes: a multiple constellation analysis