Orthogonal frequency-division multiplexing

About: Orthogonal frequency-division multiplexing is a research topic. Over the lifetime, 50541 publications have been published within this topic receiving 682648 citations. The topic is also known as: Ορθογώνια Πολύπλεξη Διαίρεσης Συχνότητας & OFDM.

The effects of phase noise on 26 Mb/s OFDMA broadband radio in the local loop systems

Abstract: The effects of phase noise on broadband radio in the local loop (BRITL) systems employing orthogonal frequency division multiple access (OFDMA) are assessed analytically and numerically. Phase noise causes a common phase error (CPE) and inter-carrier interferences (ICI). The former is easy to estimate and equalize, since it identically affects all subcarriers. It is shown that neither a significant degradation of the symbol error rate (SER) due to CPE nor a detrimental error floor due to ICI is introduced provided the constant range of the phase noise power spectral density (PSD) of the stabilized oscillator does not exceed 20 kHz. Above that limit, the SER performance is dominated by a prohibitive error floor caused by ICI.

Totally blind APP channel estimation for mobile OFDM systems

Abstract: A new two-dimensional blind channel estimation scheme for coherent detection of orthogonal frequency-division multiplexing (OFDM) signals in a mobile environment is presented. The channel estimation is based on the a posteriori probability (APP) calculation algorithm. The time-variant channel transfer function is completely recovered without phase ambiguity with no need for any pilot or reference symbols, thus maximizing the spectral efficiency of the underlying OFDM system. The phase ambiguity problem is solved by using a 4-QAM (quadrature amplitude modulation) scheme with asymmetrical arrangement. The results clearly indicate that totally blind channel estimation is possible for virtually any realistic time-variant mobile channel.

Frame selection algorithm with adaptive FFT input for OFDM systems

Abstract: Orthogonal frequency division multiplexing (OFDM) systems transmit a cyclic prefix, called a guard-interval, which is inserted in front of the effective symbol period along with signals copied from some of the last parts in the effective symbol period. This guard-interval is then used to reduce distortions which are due to multipath conditions. However, conventional OFDM systems produce intersymbol interference (ISI) under severe multipath or pre-ghost channel conditions even though they accurately estimate the effective symbol period. Accordingly, the current paper proposes a frame selection algorithm for a fast Fourier transform (FFT) operation in the OFDM receiver to remove the ISI produced in conventional OFDM systems under multipath conditions. The proposed algorithm replaces some of the rear parts of the effective symbol period with some of the guard-interval as an FFT input frame. The replaced period for the FFT input frame is changed according to the multipath environment. Four estimation methods for determining the replaced period are also presented. The proposed algorithm can increase the receiver performance by more than 3 dB under multipath conditions in a terrestrial digital video broadcasting (DVB-T) system without changing the equalization method.

Adaptive multiple input multiple output (mimo) optical orthogonal frequency division multiplexing (o-ofdm) based visible light communication

Abstract: Systems and methods for adaptive MIMO O-OFDM VLC are disclosed to involve adaptively choosing modulation type, modulation order, MIMO configuration, and MIMO type. A receiver estimates channel information, and based on the channel information, an adaptive controller makes a selection of transmission mode and provides feedback to a transmitter, which uses a set of transmission parameters indicated in the transmission mode feedback. MIMO O-OFDM VLC provides diversity gain (i.e., higher link reliability or better coverage range) and/or multiplexing gain (i.e., higher data rate).

Method and system for multi-protocol transmissions

Abstract: Methods and systems for multi-protocol transmissions in shared spectrum are disclosed. According to principles described herein, a wireless transmitter is configured to generate subcarriers or symbol information from one OFDM technology using subcarriers of another OFDM technology. With this approach, a wireless transmitter configured to transmit OFDM symbols using subcarriers and a subcarrier frequency spacing associated with one OFDM protocol can also be configured to transmit OFDM symbols associated with another OFDM protocol which normally uses different subcarriers and a different subcarrier frequency spacing. In one application, an LTE transmitter uses LTE subcarriers to generate 802.11 (e.g. Wi-Fi) subcarrier or symbol information that can be understood by Wi-Fi receivers, for example to reserve the channel for a certain duration, to indicate a transmission time associated with an on-going and/or upcoming symbol transmission or to create a carrier sense indication, for example, to cause Wi-Fi receivers and other radio technologies to consider the channel as busy.