A system for the digital conversion of a time division multiplex signal into a frequency division multiplex signal wherein the signals of the individual time multiplex channels are filtered by means of bandpass filters, their sampling rates are increased by the factor N to fA and the output signals of these bandpass filters are combined, by means of a summing member, into the frequency multiplex signal, and/or a system for the digital conversion of a frequency multiplex signal into a time division multiplex signal, wherein the digitalized frequency multiplex signal is divided by means of respective bandpass filters into the signals of the individual frequency multiplex channels and their sampling rate fA is reduced by the factor N. The individual bandpass filters (BP) are designed as recursive filters having the transfer function where U1(z) and U2(z) represent the filter input and filter output spectra respectively, z=e.sup.j2.pi.f/fA, and f is the signal frequency.
A data interpolating filter is disclosed, in which a wave digital filter is used for processing two-channel data with one data path. A sample and hold part samples and holds data, and selectively provides the sampled and held data for at least two different channels. An adapter filters the sampled and held data from the sample and hold part to produce interpolated data. The adapter filters the sampled and held data using a selectable one of at least two different filter coefficients, and a filtering signal delaying part delays the interpolated data in response to selecting signals.
An RF communications system that can determine when a requesting subscriber unit comprises a TDM capable unit, and when it doesn't. Channel assignments are based upon this determination. The system also includes repeaters that can translate communications in a TDM format as transmitted by a TDM capable unit into non-TDM format for subsequent transmission to a non-TDM capable unit, and vice versa.
A device is described which utilizes an addressing circuit to output, from a memory device, stored digital samples of an analog sinusoid, in logarithmic form, to a level control circuit, which modifies the digital level by means of adding a logarithmic scaler, and subsequently is encoded into a standard format, either linear, North American u-255 Law, or CCITT A-Law, and, after multiplexing with the respective bit rate. The addressing circuit has the capability to give an output with apparent frequencies in integer multiples of 8000/3989 Hz. Unused channels may be filled by a variety of digital signals, through use of a programmable memory device. Signalling control for the channels under interest is separate from the unused channels to aid in impulse noise testing. The signalling option can also be disabled. A device which demultiplexes digital samples from a time division multiplex frame, encoded in linear, u-255 Law North American, or CCITT A-Law format, decodes the samples into 16 bit linear form via a memory device, and reconstructs the waveform into analog form via a digital to analog converter. The appropriate signalling information is also demultiplexed. Programmable gain is available digitally at the 16 bit linear decoding stage by utilizing a separate "page" of the memory device (up to 60.2 DB of gain).
Apparatus for converting a frequency division multiplex (fdm) signal to a time domain multiplex (tdm) signal in which a voltage control oscillator whose output is a staircase of reference frequencies is mixed by a mixer with a received fdm signal. Each received frequency is output in turn at a common intermediate frequency from a bandpass filter thereby forming a tdm signal after passing through a demodulator and low pass filter. The conversion may take place in the optical domain by mixing optical reference frequencies with an optical fdm signal in, for example, a coherent heterodyne optical receiver.
An FDMA (Frequency-Division Multiple Access) transmitter-receiver for use in an FDMA communication system which is capable of changing a bandwidth of a channel as required. The FDMA transmitter-receiver includes: a plurality of trans-demultiplexers which are different in the number of channel multiplexings from each other and each of which serves to convert the received FDMA signal into a TDMA signal; a communication signal demultiplexing/multiplexing circuit for subjecting the output communication channel signals from the trans-demultiplexers to demultiplex and channel-reassignable multiplex them; a plurality of trans-multiplexers which are provided in correspondence to the plurality of trans-demultiplexers and each of which serves to convert the output channel signal after demultiplexing and remultiplexing from the associated communication signal demultiplexing/multiplexing circuit into an FDMA signal; an adder for adding the FDMA signals outputted from the trans-multiplexers; and a transmission circuit connected to an output of the adder for transmitting therefrom the signal which has been obtained by adding the FDMA signals. The bandwidth per channel of each of the trans-demultiplexers and the trans-multiplexers is different in correspondence to the number of channel multiplexing.
