Abstract
The combination of multicarrier code-division multiple access (MC-CDMA) with multiple-input multiple-output technology is attractive for broadband wireless communications. However, the large values of the peak-to-average power ratio (PAPR) of the signals transmitted on different antennas can lead to nonlinear distortion and a subsequent degradation of the system performance. In this article, we propose a PAPR reduction scheme for space-frequency block coding MC-CDMA downlink transmissions that does not require any processing at the receiver side because it is based on the addition of signals employing the spreading codes of inactive users. As the minimization of the PAPR leads to a second-order cone programming problem that can be too cumbersome for a practical implementation, some strategies to mitigate the complexity of the proposed method are also explored.
Highlights
Several approaches to combine multicarrier modulation with code-division multiple access (CDMA) techniques have been proposed with the aim of bringing the best of both worlds to wireless communications [1]
The need of reducing the peak-to-average power ratio (PAPR) in multicarrier systems has spurred the publication of a number of PAPR mitigation schemes in orthogonal frequency division multiplexing (OFDM), such as clipping and filtering [7], block coding [8], partial transmit sequences [9,10], selected mapping [11,12], and tone reservation (TR) [13]; most of these methods are applicable with minor modifications to multi-carrier CDMA (MC-CDMA) systems [14,15]
MC-CDMA with space-frequency block coding (SFBC) In the subsections, we describe the architecture of an SFBC multiple-input multipleoutput (MIMO) MC-CDMA transmitter, and define the basic terms related to the PAPR of the involved signals
Summary
Several approaches to combine multicarrier modulation with code-division multiple access (CDMA) techniques have been proposed with the aim of bringing the best of both worlds to wireless communications [1]. Multi-carrier CDMA (MC-CDMA), known as orthogonal frequency division multiplexing CDMA (OFDM-CDMA), offers several key advantages such as immunity against narrowband interference and robustness in frequency-selective fading channels [2]. Such desirable properties make MC-CDMA an attractive choice for the present and future radio-communication systems; among these, we have satellite communications [3], high-frequency band modems [4], and systems based on the concept of cognitive radio [5]. In spite of its advantages, MC-CDMA shares with other multicarrier modulations a common problem: the usually high values of the peak-to-average power ratio (PAPR) of the transmitted signals. In general, reducing the PAPR is always done either at the expense of distorting the transmitted signals, increasing the bit error rate (BER) at the receiver, or by reducing the information data rate, usually because high PAPR signals are somehow discarded and replaced by others with lower PAPR before being transmitted [20]
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