262,226 research outputs found
MMSE Pre-Filtering techniques for Downlink MC-CDMA transmissions
No full textWe discuss signal pre-filtering in the downlink of a multi-carrier code-division-multiple-access (MC-CDMA) network operating in a time-division-duplex (TDD) mode. The base station (BS) is equipped with multiple antennas and channel state information (CSI) is available at the transmit side due to the channel reciprocity between uplink and downlink transmissions. The pre-filtering coefficients are designed so as to minimize the sum of mean square errors at all mobile terminals (MTs). The resulting scheme mitigates the detrimental effects of multiple access interference (MAI) and multipath propagation, thereby allowing the use of simple and power efficient single-user detection (SUD) techniques at the MTs. Simulation results are given to highlight the effectiveness of the proposed method with respect to other existing pre-filtering schemes
On the peak-to-average power ratio of pre-equalized multi-carrier code-division multiple-access transmissions
No full textRecently, pre-equalization for multi-carrier code-division multiple-access (MC-CDMA) systems has attained increased interest. In addition, combined-equalization has been proposed to further enhance the error rate performance of conventional MC-CDMA systems. However, an important issue, peak-to-average power ratio (PAPR), has not been addressed within such systems in the literature. The purpose of this paper is to fill this gap. In particular, we focus on uplink MC-CD MA with pre- or combined-equalization and analyze its PAPR. A general expression for the PAPR of uplink MC-CDMA is derived and some analytical properties are provided. It turns out that PAPR significantly depends on applied pre-equalization technique. Thus, we show how pre-equalization coefficients could be designed in order to reduce PAPR
OFDM synchronization in an uncoordinated spectrum sharing scenario
No full textIn this paper synchronization of uncoordinated OFDM spectrum sharing systems that operate in the presence of narrowband interference (NBI) is analyzed. Conventional synchronization algorithms based on correlation of synchronization preamble in time domain suffer from considerable performance degradation when NBI is present. To overcome this degradation we propose and analyze a method to detect NBI presence and to suppress its influence on synchronization before estimation of synchronization parameters is performed at the OFDM receiver. We focus on an OFDM WLAN system operating in license-exempt band and analyze synchronization performance when NBI is active. The proposed method does not introduce any additional preamble overhead with respect to existing WLAN preamble and requires only slightly higher computational complexity at the receiver. To illustrate effectiveness of the proposed method, several numerical examples are provided
Channel Estimation for MC-CDMA Uplink Transmissions with Combined Equalization
No full textCombined equalization has recently been proposed to enhance the error rate performance of conventional multicarrier code-division multiple-access (MC-CDMA) systems. This technique applies pre-equalization at the transmitter in conjunction with post-equalization at the receiver, thereby splitting the overall equalization process into two separate parts. In this way, efficient power allocation over the available subcarriers is possible at the transmitter, while leaving the interference cancellation task at the receiver. In this paper, we consider the uplink of an MC-CDMA system employing combined equalization. As the users transmit from different locations, the uplink signals arrive at the base station after passing through different multipath channels and the goal is to estimate the pre-equalized channel frequency response of each user. This is pursued following two different approaches. The first operates in the frequency-domain and treats the channel gains over adjacent subcarriers as independent unknown parameters. The second operates in the time-domain and achieves better performance by reducing the number of unknown parameters. Both schemes are based on maximum-likelihood reasoning and require knowledge of the transmitted symbols. Numerical examples are given to highlight the effectiveness of the proposed methods
On the Performance of Cancellation Carrier-Based Schemes for Sidelobe Suppression in OFDM Networks
No full textAn efficient scheme for limiting the inherent high out-of-band radiation of the orthogonal frequency-division multiplexing signal has been studied by Brandes el al.. The scheme achieves sidelobe suppression by using few subcarriers, referred to as cancellation carriers (CCs), positioned at the edges of the spectrum and modulated by data-dependent complex-valued symbols that are designed so as to minimize the out-of-band radiation. Unfortunately, its performance has been investigated at the input of the power amplifier (PA) without considering the spectral re-growth induced by PA's non-linear region. Motivated by the above consideration, in this work we return to the aforementioned scheme and investigate its performance at the output of the PA. In addition, since reducing the time-domain signal peaks may alleviate the problem of spectral re-growth, we also adopt two well-known tone reservation (TR)-based peak reduction algorithms
RECEIVER APPARATUS FOR DETECTING NARROWBAND INTERFERENCE IN A MULTI-CARRIER RECEIVE SIGNAL
No full textReceiver apparatus, transmitter apparatus and communication system for detecting a narrowband interference in a multi-carrier receiver signal
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