Claims Analysis
Total Claims: 6
Claim 1
Independent Claim
177 words
FIXED CELLULAR TERMINAL for access to a mobile communications network and provision of telecommunications services to a telephone terminal (TT) connected to it by means of a two-wire line, this fixed cellular terminal having an interface that includes a two-wire conversion circuit (H) connected between the transmit (TP) and receive (RP) paths and the subscriber line pair (SL) to which the telephone terminal (TT) is connected, to perform in this way a four-to-two wire conversion; this interface being characterised in that it also incorporates an echo suppressor (ES) in the four-wire part of the link and prior to the two-wire conversion circuit (H), which includes two signal attenuators (ATT1, ATT2), one for the transmit path and the other for the receive path, in the four-wire part of the link, whereby at least one of the two voice band electrical signals is attenuated, one travelling towards the telephone terminal (TT) and the other coming from it, in order to reduce substantially the echo signals produced mainly in the two-wire conversion circuit (H) and in the telephone terminal (TT).
Claim 2
Dependent Claim
84 words
TERMINAL according to claim 1, characterised in that the echo suppressor (ES) also includes an attenuation control circuit (ATTC) that receives a speech indicator signal (SP) coming from the silence descriptor frame detector (SIDFD) present in all GSM terminals, in order to decide when the received frames correspond to speech or to silence, and in this way attenuate the signals present on the transmit path (TP) in the four-wire part of the link in the event that the received frames are carrying speech information.
Claim 3
Dependent Claim
71 words
TERMINAL according to claim 2, characterised in that the attenuation control circuit (ATTC) receives a speech detection signal coming from the voice activity detector (VAD) that is present in all GSM terminals in order to attenuate the signal present in the transmit path (TP) and receive path (RP) at the four-wire interface, in the event that voice activity is detected in the terminal and also the received frames contain speech information.
Claim 4
Dependent Claim
33 words
TERMINAL according to claim 3, characterised in that the sum of the attenuations in the transmit path (TP) and receive path (RP) remains approximately constant, independently of the voice activity in both directions.
Claim 5
Dependent Claim
72 words
TERMINAL according to claim 3, characterised in that the variations in the value of the attenuation produced in the receive path (RP) and transmit path (TP), when changes in voice activity occur in either of the two directions, progress in a gradual manner from their previous value to their new value, avoiding thereby the noise that would be produced as a consequence of the switching action of the signal attenuators (ATT1, ATT2).
Claim 6
Dependent Claim
93 words
TERMINAL according to claim 1, characterised in that at the four-wire interface and prior to the two-wire conversion circuit (H) the signals that are being handled are digital, there being for this reason a digital-to-analogue converter (DAC) in the receive path (RP) and an analogue-to-digital converter (ADC) in the transmit path (TP), and in that the attenuators are both formed by a shift register in which the bits at their input are shifted by a whole number so as to divide the encoded value by a number that is the power of two.