Functional scheme of DTS TS with direct coding

Figure 3.2 – Functional scheme of DTS TS with direct coding

The hybrid system № 1 serves for transition from 2 wire VBC termination to a 4 wire termination. Also prevents VBC generation with a 2-wire termination.

A LPF-3,4 (№ 2) in a transmission path serves for a limiting of frequency band of an input signal before a sampling for possibility of use of a Kotelnikov theorem.

The electronic key (№ 3) carries out sampling of a signal with limited spectrum (it is the PAM modulator). Working frequency of this key (sampling frequency) is defined by Kotelnikov theorem. Generation equipment (GE) in the transmission path closes a key on very short time (considerably less period of short circuit). The given key carries out functions of the pulse-amplitude modulator (PAM).

The sampling of an initial analogue signal is carried out for TDM realization. Empty intervals between samples of one channel are filled by samples of other channels and in a result is formed a group PAM signal. On reception return transformation is carried out. The key № 4 in the receiving path separates samples of one channel from multichannel PAM signal (it is the PAM demodulator). The LPF-3,4 (№ 5) restores a continuous signal from an individual PAM signal.

The listed blocks № 2 - №5 forms individual channel signals by TDM method at the transmission and their demultiplexing at the receiving. The TDM is a simple method-, however PAM signal has a low noise stability to noises and distortions. Linear distortions (the nonlinearity the amplitude-frequency and phase-frequency characteristic) lead to a long transient process and intersymbol interference (ISI) in the result.

The group PAM signal converted to a digital binary signal by means of PCM coder (№ 6) for increasing of noise stability in this MTS. Return transformation is carried out by means of PCM decoder (№ 7). Sometimes the coder and the decoder are called as the codec (COder + DECoder). The coder can be group (see figure 1.1 above) qr individual type.

For correct DTS work is necessary to transmit a such type of service signals:

- frame alignment signal (FAS);

- command and interaction signal (CIS);

- signal of the discrete information (DI), service communication (SC) and others.

The frame alignment signal transmitter (FAStr) № 8 forms a frame alignment signal for synchronization of receiver and transmitter. The CIS transmitter № 9 carried out a CIS transformation (coding). The multiplexing device (MD) № 10 forms a cycle of the analogue-digital equipment (ADE). Return transformation carries out the demultiplexing device (DD) №11, CIS receiver № 12 and the frame alignment signal receiver (FASrec) № 13. Signal from the output of this device comes to a (GErec) for synchronous reception of channel signals. The converter of a transmission code (CTCod) №14 serves for transformation of a binary signal from MD output to a signal convenient for transmission on physical circuit. On reception the converter of a reception code (CRCod) №15 carries out the return transformation.

The block of line path terminal equipment (LPTE) consist of:

1. Forming device (FD) № 16. It serves for forming of pulses with demanded amplitude and duration.

2. Station regenerator (SR) № 17. It serves for restoration of the distorted impulses in the physical circuit.

3. Line transformers (№ 18, 19). They serve for connection of terminal station to cable pairs.

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