Variable transmission rate digital modem with multi-rate filter bank

A digital sender multiplexer having a band-multiplexing filter bank comprising serially-connected 2-multiplexing filter banks;

• wherein
• a 2-multiplexing filter bank comprises up-samplers for doubling sampling frequencies of each input signal and
• filters for filtering output signals from said up-samplers;
• and
• adders for multiplexing output signals from each filter when there are two types of said filters;
• and
• when said 2-multiplexing filter bank includes four types of filters designated as E, F, G and H in an ascending order in band-pass frequency fs, where fs is a sampling frequency of output signals from each 2-multiplexing filter bank, then
• 2-multiplexing filter banks are connected such that;
• signals output from one 2-multiplexing filter bank having at least a filter E or a filter F are input in another 2-multiplexing filter bank having at least a filter E and a filter G;
• and
• signals output from one 2-multiplexing filter bank having at least a filter G or a filter H are input into another 2-multiplexing filter bank having at least a filter F or filter H.

A digital signal transmitter comprising:

• a serial-parallel conversion circuit for converting serial signals into a plurality of parallel slow speed signals;
• a plurality of modulation circuits for modulating each signal in a plurality of parallel converted signals;
• a channel multiplexing circuit for frequency multiplexing the modulated signals;
• where
• said channel multiplexing circuit comprises not less than one 2-multiplexing filter bank containing:
• up-samplers for doubling sampling frequencies of each signal in two groups of input signals;
• two types of filters having different pass-bands for filtering output signals from said up-sampler;
• and
• an adder for multiplexing output signals from said two types of filters;
• and when two or more 2-multiplexing filter banks are required,
• said channel multiplexing circuit is constructed by serially connecting a plurality of 2-multiplexing filter banks in a multi-stage configuration such that:
• said plurality of modulation circuits are grouped into groups so that each group contains two modulation circuits, and each two output signals from two modulation circuits of the groups are input into one 2-multiplexing filter bank, respectively;
• the 2-multiplexing filter banks are grouped into groups so that each group contains two 2-multiplexing filter banks, and each two output signals from the 2-multiplexing filter banks of the groups are further input into another 2-multiplexing filter bank in a next-stage;
• output signals from two preceding 2-multiplexing filter banks are input into another 2-multiplexing filter bank in a next-stage so that
• signals from the 2-multiplexing filter bank in a final-stage are produced as output signals from said digital signal transmitter.

A digital signal receiver comprising:

• a plurality of channel demultiplexing circuits for separating frequency multiplexed signals into two groups of signals;
• a plurality of demodulation circuits for demodulating output signals from said channel demultiplexing circuits;
• a parallel-serial conversion circuit for receiving output signals from each demodulation circuit;
• wherein
• a channel demultiplexing circuit comprises not less than one 2-demultiplexing filter bank having:
• a circuit for separating input signals into two groups of signals by using two types of filters having different pass-bands;
• and
• a down-sampler for culling sampling frequencies of two separated signals to 1/2;
• and
• channel demultiplexing circuits are connected such that
• when there are two or more 2-demultiplexing filter banks, 2-demultiplexing filter banks are connected serially so that
• output signals from a receiving circuit are input into a 2-demultiplexing filter bank;
• two groups of signals output from the 2-demultiplexing filter bank are input respectively into 2-demultiplexing filter banks in a next-stage,
• two groups of signals output from the 2-demultiplexing filter bank are input respectively into 2-demultiplexing filter banks in a next-stage, and ultimately,
• output signals from the 2-demultiplexing filter banks in a last-stage are input into respective demodulation circuits;
• and
• output signals from demodulation circuits are input into said parallel-serial conversion circuit;
• so that
• signals output from said parallel-serial conversion circuit are produced as digital receiver output signals.