11,648 research outputs found
Study of EEPN mitigation using modified RF pilot and Viterbi-Viterbi based phase noise compensation
We propose - as a modification of the optical (RF) pilot scheme -a balanced phase modulation between two polarizations of the optical signal in order to generate correlated equalization enhanced phase noise (EEPN) contributions in the two polarizations. The method is applicable for n-level PSK system. The EEPN can be compensated, the carrier phase extracted and the nPSK signal regenerated by complex conjugation and multiplication in the receiver. The method is tested by system simulations in a single channel QPSK system at 56 Gb/s system rate. It is found that the conjugation and multiplication scheme in the Rx can mitigate the EEPN to within 1/2 orders of magnitude. Results are compared to using the Viterbi-Viterbi algorithm to mitigate the EEPN. The latter method improves the sensitivity more than two orders of magnitude. Important novel insight into the statistical properties of EEPN is identified and discussed in the paper
The effect of familiarity with the response category labels on item response to likert
Surveys in the social sciences often employ rating scales anchored by response category labels such as “strongly (dis)agree” or “completely (dis)agree.” Although these labels may exert a systematic influence on responses since they are common to all items, academic research on the effect of different labels is surprisingly scarce. In order to help researchers choose appropriate category labels, we contrast the intensity hypothesis (which posits that response categories are endorsed less frequently if the labels are more extreme) with the familiarity hypothesis (which states that response categories are endorsed more frequently if the labels are more common in day-to-day language). In a series of studies we find consistent support for the familiarity hypothesis. Our results have important implications for the appropriate use of category labels in multilingual surveys, and we propose a procedure based on Internet search engine hits to equate labels in different languages in terms of familiarity
An Investigation into the Implementation and Performance of Spectrally Shaped Orthogonal Frequency Division Multiplex
Orthogonal Frequency Division Multiplex (OFDM) is a flexible, robust multi-carrier
modulation scheme. The orthogonal spectral shaping and spacing of OFDM sub-carriers
ensure that their spectra can be over-lapped without leading to undesirable inter-carrier
interference. Conventional OFDM systems have non-band limited Sinc(x) shaped subcarrier
spectra. An alternative form of OFDM, referred to hereafter as Spectrally Shaped
OFDM, employs band limited Nyquist shaped sub-carrier spectra. The research described
in this thesis investigates the strengths and weaknesses of Spectrally Shaped OFDM as a
potential modulation scheme for future mobile radio applications.
From this research a novel Digital Signal Processing architecture for modulating and
demodulating Spectrally Shaped OFDM sub-carriers has been derived which exploits the
combination of a complex Discrete Fourier Transform (DFT) and PolyPhase Network
(PPN) filter. This architecture is shown to significantly reduce the minimum number of
computations required per symbol compared to previous designs.
Using a custom coded computer simulation, the effects of varying the key parameters of
the novel architecture's PolyPhase Filter (PPN) filter an the overall system complexity,
spectral performance and system signal-to-distortion have been extensively studied. From
these studies it is shown that compared to similar conventional OFDM systems, Spectrally
Shaped OFDM systems possess superior out-of-band spectral qualities but significantly
worse Peak-to-Average-Power-Ratio (PAPR) envelope performance. lt is also shown that
the absolute value of the end PPN filter coefficients (dependent on the roll-off factor of the
sub-carrier spectral shaping) dictate the system signal-to-distortion ratio when no time-domain
windowing of the PPN filter coefficients is applied. Finally the effects of a both time
and frequency selective fast fading channels on the modulation scheme's uncoded Bit
Error Rate (BER) versus Signal-to-Noise (SNR) performance are simulated. The results
obtained indicate that Spectrally Shaped OFDM is more robust (lower BER) to
frequency-selective fading than time-selective fading
Pilot embedding for channel estimation and tracking in OFDM systems
Journal ArticleAbstract-We consider the problem of channel estimation and tracking in OFDM systems and explore the idea of adding pilot symbols to the data symbols as a means to conserve bandwidth. The term pilot embedding (PE) is used to refer to this scheme. Compared to the pilot insertion (PI) scheme, i.e., the conventional pilot symbol assisted modulation (PSAM), PE is more bandwidth efficient since no separate subcarriers/timeslots are allocated to pilots. We formalize this by evaluating the capacity of the two schemes and showing that PE indeed has the potential to transmit at a higher rate. The problem of channel tracking using a decision directed approach is reviewed and found to be unreliable, in the sense that the channel estimator fails to track the channel variations after some iterations because of unavoidable decision errors. We propose an ad hoc channel estimation algorithm that uses the embedded pilots along with the past decisions of data for reliable tracking of the channel
LTE SFBC MIMO Transmitter Modelling and Performance Evaluation
High data rates are one of the most prevalent requirements in current mobile
communications. To cover this and other high standards regarding performance,
increasing coverage, capacity, and reliability, numerous works have proposed
the development of systems employing the combination of several techniques such
as Multiple Input Multiple Output (MIMO) wireless technologies with Orthogonal
Frequency Division Multiplexing (OFDM) in the evolving 4G wireless
communications. Our proposed system is based on the 2x2 MIMO antenna technique,
which is defined to enhance the performance of radio communication systems in
terms of capacity and spectral efficiency, and the OFDM technique, which can be
implemented using two types of sub-carrier mapping modes: Space-Time Block
Coding and Space Frequency Block Code. SFBC has been considered in our
developed model. The main advantage of SFBC over STBC is that SFBC encodes two
modulated symbols over two subcarriers of the same OFDM symbol, whereas STBC
encodes two modulated symbols over two subcarriers of the same OFDM symbol;
thus, the coding is performed in the frequency domain. Our solution aims to
demonstrate the performance analysis of the Space Frequency Block Codes scheme,
increasing the Signal Noise Ratio (SNR) at the receiver and decreasing the Bit
Error Rate (BER) through the use of 4 QAM, 16 QAM and 64QAM modulation over a
2x2 MIMO channel for an LTE downlink transmission, in different channel radio
environments. In this work, an analytical tool to evaluate the performance of
SFBC - Orthogonal Frequency Division Multiplexing, using two transmit antennas
and two receive antennas has been implemented, and the analysis using the
average SNR has been considered as a sufficient statistic to describe the
performance of SFBC in the 3GPP Long Term Evolution system over Multiple Input
Multiple Output channels.Comment: 11 pages, 20 figures, 5 table
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