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Polyphase Matrix
In signal processing, a polyphase matrix is a matrix whose elements are filter masks. It represents a filter bank as it is used in sub-band coders alias discrete wavelet transforms. If \scriptstyle h,\, g are two filters, then one level the traditional wavelet transform maps an input signal \scriptstyle a_0 to two output signals \scriptstyle a_1,\, d_1, each of the half length: :\begin a_1 &= (h \cdot a_0) \downarrow 2 \\ d_1 &= (g \cdot a_0) \downarrow 2 \end Note, that the dot means polynomial multiplication; i.e., convolution and \scriptstyle\downarrow means downsampling. If the above formula is implemented directly, you will compute values that are subsequently flushed by the down-sampling. You can avoid their computation by splitting the filters and the signal into even and odd indexed values before the wavelet transformation: :\begin h_\mbox &= h \downarrow 2 & a_ &= a_0 \downarrow 2 \\ h_\mbox &= (h \leftarrow 1) \downarrow 2 & a_ &= (a_0 \lef ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polyphase System
A polyphase system (the term coined by Silvanus Thompson) is a means of distributing alternating-current (AC) electrical power that utilizes more than one AC phase, which refers to the phase offset value (in degrees) between AC in multiple conducting wires; ''phases'' may also refer to the corresponding terminals and conductors, as in color codes. Polyphase systems have two or more energized electrical conductors carrying alternating currents with a defined phase between the voltage waves in each conductor. Early systems used 4 wire two-phase with a 90° phase angle, but modern systems almost universally use three-phase voltage, with a phase angle of 120° (or 2π/3 radians). Polyphase systems are particularly useful for transmitting power to electric motors which rely on alternating current to rotate. Three-phase power is used for industrial applications and for power transmission. Compared to a single-phase, two-wire system, a three-phase three-wire system transmits thr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
