| 摘要 |
In order to reduce the effect of noise on information signals transmitted over a communications link (such as television signals in a DBS link), encoding-decoding apparatus is provided which treats the signals as a series of samples (S) each composed of a base-level component (BLS) having a limited number of possible values and represented by the whole or part of a coarsely quantised signal (termed a Q symbol), and a difference component (DS) providing a fine measure of the difference between the actual sample level and the value of the base-level component (BLS), this difference component (DS) being represented by a high-resolution signal (termed an A symbol). The Q and A symbols are simultaneously or sequentially impressed on a carrier signal as first and second modulations respectively, the Q-symbol first modulations having a limited number of values while the A-symbol second modulations being analog in nature. The first and second modulations may be of the same or different types though the use of phase modulation for both is preferred. Due to this arrangement the base-level component (BLS) of each sample (S) is generally received error free so that the effect of noise on the received signal is kept to a low level. |
