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One of the causes of intersymbol interference is multipath propagation in which a wireless signal from a transmitter reaches the receiver via multiple paths. The causes of this include reflection (for instance, the signal may bounce off buildings), refraction (such as through the foliage of a tree) and atmospheric effects such as atmospheric ducting and ionospheric reflection.
A tutorial on the significance of Cyclic Prefix (CP) in OFDM Systems Archived 2023-10-05 at the Wayback Machine. Siemens demos 360 Mbit/s wireless; An Introduction to Orthogonal Frequency-Division Multiplex Technology; Short Introduction to OFDM – Tutorial written by Prof. Debbah, head of the Alcatel-Lucent Chair on flexible radio.
It provides a guard interval to eliminate intersymbol interference from the previous symbol. It repeats the end of the symbol so the linear convolution of a frequency-selective multipath channel can be modeled as circular convolution , which in turn may transform to the frequency domain via a discrete Fourier transform .
In MSK the difference between the higher and lower frequency is identical to half the bit rate. Consequently, the waveforms used to represent a 0 and a 1 bit differ by exactly half a carrier period. Thus, the maximum frequency deviation is δ = 0.5 f m where f m is the maximum modulating frequency. As a result, the modulation index m is 0.5.
Other approximations to scattering by a single sphere include: Debye series, ray tracing (geometrical optics), ray tracing including the effects of interference between rays, Airy theory, Rayleigh scattering, diffraction approximation. There are many phenomena related to light scattering by spherical particles such as resonances, surface waves ...
Since most such codes correct only bit-flips, but not bit-insertions or bit-deletions, the Hamming distance metric is the appropriate way to measure the number of bit errors. Many FEC coders also continuously measure the current BER. A more general way of measuring the number of bit errors is the Levenshtein distance.
Phase-shift keying (PSK) is a digital modulation process which conveys data by changing (modulating) the phase of a constant frequency carrier wave.The modulation is accomplished by varying the sine and cosine inputs at a precise time.
The latter is a data detection technique for communication channels that exhibit intersymbol interference (ISI) with finite memory. Reliable operation of the process is achieved by using hypothesized decisions associated with the branches of the trellis on which the Viterbi algorithm operates as well as tentative decisions corresponding to the ...