摘要:
A block adaptive quantisation device processes blocks of sample pairs to determine an aggregate or average value at 18. The average or aggregate value is applied to each of a number of exponent look up tables 22 to 26, which output an exponent value (E) dependent on the extent of compression required. The exponent value is split by an exponent splitter into a remainder value (R) and a shift value (S). The remainder value is used to select one of a number of divide look up tables to which the unsigned data sample is applied, and the shift value is used to apply a variable bit shift to the data sample (either before or after the division operation). The divide code tables are grouped, and within each group the code tables are spaced logarithmically, as are the groups themselves. This arrangement considerably reduces the number of look up tables required for a given processor, reducing memory requirement and increasing speed.
摘要:
Digital signal processing apparatus for frequency demultiplexing a wideband channel digitised at 1 converts the data stream into parallel branches by means of serial-to-parallel converter 6, and the demultiplexing operation which consists of a low pass and high pass fine filtering stage 3a, 3b and a coarse filtering stage 4a, 4b is split among processors 3a, 3b, 4a, 4b across the parallel branches. Wideband signals can be processed without expensive processors because of the slower rate in the parallel channels. The invention may also be used for the inverse function of multiplexing.
摘要:
A block adaptive quantisation device processes blocks of sample pairs to determine an aggregate or average value at 18. The average or aggregate value is applied to each of a number of exponent look up tables 22 to 26, which output and exponent value (E) dependent on the extent of compression required. The exponent value is split by an exponent splitter into a remainder value (R) and a shift value (S). The remainder value is used to select one of a number of divide look up tables to which the unsigned data sample is applied, and the shift value is used to apply a variable bit shift to the data sample (either before or after the division operation). Each divide look up table 42 to 48 comprises the same group of divide look up tables. The combination of the four look up tables in the group, together with the variable bit shift defines a series of code tables made up of a group of divide look up tables repeated at six dB intervals. The remainder value selects one of the code tables within the group, and the bit shift operation determines the selected one of the repeated groups. The code tables within the group are spaced logarithmically, as are the groups themselves. This arrangement considerably reduces the number of look up tables required for a given processor, reducing memory requirement and increasing speed.
摘要:
A tachograph 20 determines and records the location of a vehicle with time as well as other information relating to the operation of the vehicle. Access is restricted to an electronic storage means 73, in which the information is recorded, preventing tampering with that information.
摘要:
Apparatus for and a method of digital signal processing utilises a technique known as sub-band decomposition and reconstruction. A plurality of input channels are provided each of which is mixed with a vernier frequency correction. In a multiplexer implementation, an FFT weighted overlap-add demultiplexer (c) is provided for decomposing each input channel into sub-bands. The sub-band outputs are decimated by a factor (d) to the common input sampling rate of a multiplexer, the sub-bands from each channel then being passed into the appropriate ports of an FFT weighted overlap-add multiplexer (f) by means of a switch matrix (e). The multiplexer (f) reconstructs the individual channels, interpolates each channel up to the output sampling rate of the FDT signal, mixes each channel up to its assigned carrier frequency in the FDM and multiplexes the channels. This provides a computationally efficient architecture with the flexibility to accommodate channels of differing bandwidths.