Method for transmitting items of speech information

Method for transmitting speech information (si) between a transmission apparatus (S) and a reception apparatus (E) via at least one radio channel (F), in which the transmission quality is increased by determining, in the transmission apparatus (S), speech pauses (sp) within the speech information, producing an item of control information (st) that represents the time position of the speech pauses (sp) within the speech information (si), and sending these suitably with respect to time via the radio channel (F)in addition to the speech information (si), and by evaluating the control information (st) in the terminal apparatus (E) in such a way that the speech pauses (sp) are correctly inserted with respect to time into the speech information (si). The method is particularly suited for the digital transmission of items of speech information (si) in wireless communication systems according to the DECT standard.

BACKGROUND OF THE INVENTION 
The invention concerns a method for transmitting speech information, as 
well as a transmission apparatus and a reception apparatus. 
In mobile communication connections for speech transmission, at least one 
of the parties to the call can be reached only via a radio channel. The 
speech information is standardly transmitted including the pauses in the 
conversation that it contains. The transmission of the speech information 
is exposed to various types of disturbing influences in the radio channel, 
so that disturbances occur at the receiver side that reduce the 
transmission quality. 
In, for example, digital radio transmissions according to the DECT 
standard, these disturbances reach bit error rates of 10.sup.-3 to 
10.sup.-2 in the maximum range region. These bit errors are distributed 
uniformly over the actual speaking time and the speech pauses. For the 
receiving party, the disturbances of the radio transmission manifest 
themselves as unpleasant interference noise. Standard error correction 
methods, such as repeated transmission of the disturbed speech segments, 
are not possible due to the real-time conditions. 
In connection with DECT wireless telephones, a method for speech 
transmission is known from Siemens Components 31, 6 (1993). The 
transmission in the radio channel ensues with digital signals, whereby the 
transmission of the speech information also contains speech pauses. At the 
transmitting apparatus, an A/D conversion of the speech information and a 
forming of the transmission signals takes place, and an evaluation of the 
received transmission signals and a D/A conversion takes place at the 
receiving apparatus. In addition to the speech information, items of 
control information are also transmitted. The method is correspondingly 
also transferrable to mobile radiotelephone transmission systems, and is 
known there. A generalization to analog transmission methods of the speech 
information is also possible; the A/D conversion and D/A conversion are 
thereby omitted. 
The inventive method makes use of the fact that during a transmission of a 
two-party call the actual speaking time of an individual party is on 
average much less than 50% of the duration of the call; thus, the pauses 
in speech contained in the speech information take up a large part of the 
transmitted speech information. A correspondingly large portion of the bit 
errors fall to these pauses in speech. 
From the German laid open print DE 42 36 088 A1, it is known to improve 
speech transmission for wireless telephones according to the DECT standard 
by temporarily suppressing speech transmission when determined error 
boundary values are exceeded. However, it is necessary to determine the 
errors that have occurred, which is possible only at the receiver. 
Furthermore, from Blaesner, W.; "Audioprozessor vereinfacht 
NF-Signalaufbereitung im Mobilfunk," ntz vol. 43, 1990, no. 6, pp. 
446-451, an audio processor is known that determines speech pauses at the 
transmitter and produces a logic signal for switching off the transmission 
final stage. The transmission energy expended and the background noise can 
thereby be reduced. However, the disturbances occurring in the 
transmission channel cannot be corrected during the speech pauses. 
SUMMARY OF THE INVENTION 
The underlying aim of the invention is to develop the known method for 
transmitting speech information such that the quality of the speech 
transmission is improved, and to indicate associated transmission and 
reception apparatuses. The solution of the aim ensues based on the method 
according to the preamble of patent claim 1, by means of the 
characterizing features thereof. Further inventive transmission and 
reception apparatuses are indicated in independent claims. 
In the scope of the inventive method for transmitting speech information, 
the speech information to be transmitted is analyzed in the transmitting 
apparatus for the speech pauses it contains. The speech pauses are 
recognized and items of control information are respectively produced that 
represent the time position of the speech pauses within the speech 
information. In addition to the speech information, the control 
information is sent suitably with respect to time via the radio channel by 
the radio part so that in the reception apparatus the speech pauses 
represented in the control information can be inserted into the speech 
information at the correct time position by the arithmetic logic unit of 
the receiver apparatus after the evaluation. 
If the inserted signals realizing the speech pauses exhibit no 
disturbances, the inventive method reduces the transmission errors by a 
percentage amount that corresponds approximately to the portion of the 
speech information consisting of speech pauses. For the receiving party, 
the disturbing noises fall during the speech pauses of the transmitting 
party, whereby a more pleasing hearing sensation is achieved. The quality 
of the speech transmission is detectably increased. 
An advantageous development of the inventive method introduces a comparison 
of the length of the speech pauses with the length of a frame of a frame 
clock during the determination of the speech pauses. The control 
information is produced only when the speech pause is longer than the 
frame length. It is thereby ensured that the control information is 
produced only given a minimum duration of the speech pauses. The control 
information can thereby be connected with the character generation of the 
frame clock. 
Corresponding to an advantageous development of the invention, the 
insertion of the speech pauses ensues by interrupting the current supply 
of the D/A converter for the time duration of the speech pauses. The 
additional advantage of an energy saving thereby results. In addition to 
the interruption of the current supply of the D/A converter, a noise 
signal generated in a signal generator can be supplied to the 
electroacoustic converter in place of the analog speech information 
produced in the D/A converter. The speech pauses can thereby be organized 
in a way that is pleasant for customary human hearing. 
The inventive method can be used not only for digital transmission methods, 
but is also suited for analog transmission of the speech information in 
the radio channel. 
The method can be constructed in such a way that it is compatible with the 
previous method for transmitting speech information. The control 
information (coding and manner of transmission) is adapted to the 
transmission method of the speech information in such a way that during a 
communication of a transmission apparatus without means for producing the 
control information, or of a reception apparatus without means for 
evaluation of the control information, the speech information, including 
the speech pauses contained therein, are supplied to the electric-acoustic 
transducer of the reception apparatus. The transmission apparatus and the 
reception apparatus can thereby work together independently of whether 
both are provided with means for carrying out the inventive method.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Concerning the construction and the most important modules of a DECT mobile 
station and of a base station, reference is made to Siemens Components 31, 
6(1993), p. 216. A transmission installation and receiver installation are 
integrated into the mobile station. An AF analog circuit (PMB 2920) 
contains an A/D converter and a D/A converter. A digital module (PMB 2720) 
contains the functions of the arithmetic logic unit and the formation or, 
respectively, evaluation. An RF transmitter and an RF receiver essentially 
form a transmitting or, respectively, receiving radio part (PMB 2220, PMB 
2420). 
The transmission apparatus S shown in FIG. 1 is connected with a reception 
apparatus E via at least one radio channel F, in a one-sided communication 
connection. A speech transmission from party A to party B is thereby 
given. For a bidirectional transmission, each of the parties must be 
provided with a transmission apparatus and a reception apparatus. In 
addition, radio channels F must be provided for both directions. 
An acoustic-electric converter M in the transmission apparatus S, e.g. a 
microphone, receives the speech information si of the party A in the form 
of acoustic oscillations, and converts it into an analog electrical item 
of speech information si. An A/D converter AD, in which the analog 
electrical speech information si is converted into digitized form, is 
connected to the microphone M. The digital speech information is supplied 
to a means for forming the transmission signals BS (burst mode logic 
element) and to a means for speech pause recognition ES. In addition, a 
signal containing the length of the frame clock r1 is processed in the 
means ES for speech pause recognition ES. The speech pause recognition 
means ES then produces an item of control information st that represents 
the time position of the speech pauses sp within the speech information 
si, if the speech pause sp completely fills at least one frame length r1. 
The control information st is supplied to the arithmetic logic unit RS by 
the speech pause recognition means ES. Transmission signals containing the 
speech information si and the control information st are formed in the 
means for forming the transmission signals BS, which is connected with the 
A/D converter AD and with the arithmetic logic unit RS. The field 
designated in the DECT standard as the A field for control information of 
a frame clock receives the control information st prepared in the 
arithmetic logic unit RS. The control information st is written to bit 
positions that are not used by the method according to the DECT standard. 
A single bit position in the A field of each transmitted frame determines 
whether the frame is completely filled by a speech pause sp (e.g. the bit 
is logical "1"), or whether the frame at least partly contains spoken 
information (bit is logical "0"). The means for forming the transmission 
signals BS supplies the speech information si and the control information 
st to a radio part FS, which sends the items of information via a radio 
channel F . 
The reception apparatus E receives the speech information si and the 
control information st from the radio channel F via a radio part FE. A 
means for evaluating the received transmission signals BE is connected 
with the radio part FE. An arithmetic logic unit RE takes over the control 
information st from this means for evaluating the received control signals 
BE, and a D/A converter DA takes over the speech information si from this 
means. 
The power supply SV of the D/A converter DA can be switched off via the 
contact K1. The D/A converter DA converts the received digitized speech 
information si into analog items of speech information si, and supplies it 
to an electric-acoustic converter H, e.g. a playback head, via a converter 
K2. The party B receives the speech information si from the 
electric-acoustic transducer H via acoustic oscillations. The converter 
K2, controlled by the arithmetic logic unit RE, selectively connects the 
electric-acoustic transducer H with the D/A converter DA or with a signal 
generator SG. The signal generator SG produces a noise signal. This noise 
signal has a timbre that is pleasing for the receiving party B and that 
represents the speech pauses. 
The arithmetic logic unit RE evaluates the control information st and 
places the speech pauses sp into the speech information si correctly with 
respect to time. For this purpose, the opening of the contact K1, and, at 
the same time, the switching over of the changeover switch K2 from the 
connection with the D/A converter DA to the signal generator SG, is caused 
by the arithmetic logic unit RE. The D/A converter DA is thereby in the 
off position, and the noise signal for a number of frame clocks 
representing the duration of the speech pauses sp is supplied to the 
electric-acoustic transducer H. At the end of the speech pauses sp, the 
contact K1 is again closed, and the changeover switch K2 connects the D/A 
converter DA again with the electric-acoustic transducer H; the speech 
information si, containing no speech pauses sp, is thus again transmitted. 
FIG. 2 shows a further exemplary embodiment of the transmission apparatus 
S. The design differs in principle from the transmission apparatus S shown 
in FIG. 1 only in that the digitized speech information si is already 
supplied to the transmission apparatus S. An acoustic-electric converter M 
and an A/D converter AD can thus be omitted. The digitized speech 
information si is supplied directly to the speech pause recognition means 
ES and to the means for producing the transmission signals BS. This form 
of the transmission apparatus S is suited for base stations in mobile or 
wireless communication systems. 
The invention is not limited to the particular details of the method and 
apparatus depicted and other modifications and applications are 
contemplated. Certain other changes may be made in the above described 
method and apparatus without departing from the true spirit and scope of 
the invention herein involved. It is intended, therefore, that the subject 
matter in the above depiction shall be interpreted as illusrative and not 
in a limiting sense.