FI105758B - Method and arrangement for mobile telephony - Google Patents

Description

1 105758

Method and device for mobile phones

FIELD OF THE INVENTION The present invention relates to a method of telephone transmission systems comprising analog mobile communications, preferably NMT communications. The invention further relates to a telephone transmission system including analog mobile communication, preferably NMT communication. The invention further relates to an analog mobile switching center, preferably a switching center for NMT communication.

. . BACKGROUND OF THE INVENTION 15 · • · · *! In cellular systems, communication via a mobile station (MS; I · I • 1 1

Mobile Station) and a Mobile Exchange (MTX; Mobile Telephony Exchange) via channels known as channels. The channel traffic consists of signaling • · * · '1 20 and the actual voice or voice traffic. In this context, speech is meant to mean sound that is transmitted and • played on the receiver side. The traffic signaling part is used to exchange messages between MTX (also known as a Mobile Switching Center (MSC)) and mobile stations. Signaling Manual- • · ·, · 1 ·. for example, "ordering and deleting calls," "handover", "update", "transmit power switching", etc. · Signaling also transmits various alarms and further handles remote control of base station 30 between MTX and MS. Signaling equipment generally consists of a modem (or modems) and coding equipment. In addition, MTX has a function to compensate for group delay distortion.

2 105758

In analog mobile communication systems, the analog part consists of an air interface between a mobile station and a base station. To enable signaling traffic, the binary position of the signaling is transmitted as a frequency shift signal in accordance with the Fast Frequency Shift Keying (FFSK) method. For example, at a data rate of 1200 bit / s, logical "one" is represented by one period of 1200 Hz and logical "zero" by 1.5 period of 1800 Hz. The transition between "zero" and 10 "one" occurs at the zero transition points of the signal. All signaling is done by frames, which are always the same length and consist of 166 bits in current systems. During reception the first 15. bits can be used to synchronize bits. The transmission of the signal frames • · 15 is performed over the entire transmission channel.

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In current analog communication systems, signaling and voice transmission are transmitted over the same traffic channel.

«·«] ... It is therefore important to split the signal with this

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20 channel before it arrives at the called side part ... the ear. Splitting can be • · !!! also defines voice path muting • · f "* during signaling.

In one prior art solution, sharing is arranged using an MTX ETC (Exchange Terminal Circuit Board) card, which distributes the signal in response to a request from the exchange software. . However, due to the delay in the distribution of the switchgear software, signaling arrives in the ear 30 and instead of signaling, silence is transferred to the PSTN (Public Switched Telephone Network). The ETC delay is estimated to be up to 20 ms.

3, 105758

Summary of the Invention

A disadvantage of prior art arrangements is that due to the delay in the distribution of the signal stream in the communication channel, part 5 of the signaling comes to the user's ear. Thus, part of the signaling is transferred to the headset instead of the central signaling system. In addition, speech is also cut in an unnatural way and it is not very pleasant for the user of the receiving end telephone to listen to it.

The object of the present invention is to overcome the disadvantages of prior art solutions and to provide a new type of solution for splitting a signal stream containing speech and signaling .. in systems containing analog communication.

It is also an object of the present invention to provide a method and an arrangement for minimizing the delay in signaling.

'in silencing the signal stream.

It is also an object of the invention to provide a method and an arrangement for eliminating loud speech cuts and improving the quality of the reproduced voice in systems containing analog communication.

It is also an object of the present invention to provide a method and arrangement for generating meaningful noise in the speech of the receiving side. ..) noise during periods in which the signal stream of the radio transmission is cut in systems containing analogue traffic.

It is an object of the invention to provide a method and arrangement for eliminating the need for a single modem per 4,105,758 for each channel coming from a base station.

It is a further object of the invention to provide a method and arrangement for selectively connecting a modem behind a group switch to an incoming call from any base station connected to the exchange.

Other objects and advantages of the invention will be apparent from the following description taken in conjunction with the accompanying drawings.

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The objects are achieved by a method for distributing signaling stream and speech in a telephone system containing analog mobile communication, wherein the signaling and speech are transmitted over the same communication channel, comprising signaling h! 15 in the frames included in the signal stream. to monitor the signal stream for detecting frames containing signaling bit sequences, the signal stream !. dividing into a signaling portion and a speech portion during signal stream transfer based on said monitoring, the method 20 further comprising evaluating acoustic noise during transmission, and meaningfully generating noise on the truncated areas of the signal stream to fill the truncated areas of the speech portion. : From the signal stream during splitting.

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According to the invention, an arrangement in a telephone system containing an analog mobile communication system in which signaling and speech is transmitted over the same communication channel comprises: at least one base station arranged to communicate with at least one mobile station via an analog air interface, a mobile switching center arranged to communicate with said at least one base station, the arrangement further comprising modem means adapted to monitor a signal stream from a transmitting mobile station for detecting signaling frames containing signaling information in a stream, and distributing speech and signaling in an analog mobile communication stream. means for evaluating acoustic noise during transmission and means for generating meaningful noise in truncated areas of the signal stream based on noise evaluation to replace areas of the speech signal that may have been cut off during splitting.

The mobile switching center according to the invention comprises means for communicating via a base station with a mobile station. . with the mobile station and the base station * _ '. | 15 with an analog air interface • · * · · '; via modem means adapted to monitor the signal stream from the mobile station transmitting the signal stream.

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1 signaling information sig-

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for detecting frame frames and for distributing speech and signaling «« «'20 during signal stream transmission in response to said monitoring, and means for generating meaningful noise in the truncated areas of the signal stream during transmission

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based on the evaluation of the acoustic noise that has occurred to replace the areas of the speech signal that are:: ***; 25 possibly cut off during splitting.

· · • _ «· · • · · ______ 1 /. The invention achieves a number of advantages in that the solution provides a simple method for splitting the signal so as to minimize the delay in splitting and thereby improve the quality of the sound being reproduced. The minimum amount of signaling is lost, that is, routed to the wrong destination, and in practice, no signaling goes to the receiver's headset. Lost parts of speech are replaced by comfort noise Γ 6 105758 and thus the user does not notice any significant cuts in speech. Further, the number of modems in the exchange can be reduced by the invention.

The invention and other objects and advantages thereof will be described in more detail below by way of example only, with reference to the accompanying drawings, in which like reference numerals in the various figures refer to like features. It is to be understood that the following description of the example of the invention is not intended to limit the invention to the specific forms described herein, but rather the present invention is intended to cover all modifications, similarities and features within the spirit and scope of the present invention. . alternatives as defined in the appended claims. I 15 six.

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BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic representation of a prior art

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'20 arrangements;

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Fig. 2 is a schematic representation of an arrangement according to one embodiment of the invention; Figure 3 illustrates one possible modem according to the invention. switching; • · • · • «« · · «

Figure 4 schematically shows a signal stream to be observed and evaluated after dividing a prior art signal stream and a signal stream distributed according to the invention; and

Figure 5 shows a flowchart for one embodiment of the invention.

7 105758

DETAILED DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic representation of a prior art arrangement whereby the distribution is controlled by MTX software (ETC board; Exchange Terminal Circuit) of the analogue mobile system switching center. MTX._o_n arranged between base station BS and PSTN. As can be seen, the receivers behind the PSTN may be fixed line telephones and / or mobile phones of any suitable system. As explained above, the distribution of the signal stream from the BS is controlled by the ETC card before the voice signal together with silence, it is transferred to the GS (Group Switch) and thence to ·. ·, via PSTN to the recipient party. Signaling goes to · · • * 15 modem MDM (Modulator-Demodulator) and further to MTX control devices, which in turn control the ETC card

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activity. Such a circuit arrangement causes a delay,!. which in turn causes some of the signaling to go to the atr PSTN and arrive at the receiving end, which is not pleasant to hear, and furthermore, the speech is cut in an undesirable manner, causing an additional drop in the received aa ". * in sound quality. ~ "« at · »___________ • * ·· Figure 2 shows a schematic representation of one embodiment of the invention.

25 arrangements. From the mobile station MS, the base station BS

The signal stream through the receiver is received by an • · ____ ^ ____: MTX ETC card of the switchboard system. It is not • «· • · ......—: - shared with the ETC card, but instead transmitted to the GS switch group and then to the MDM modem on MTX. According to the principles of the invention, the MDM is arranged behind the GS, i.e., the incoming signal stream first passes through the GS before it arrives at the MDM.

8 105758 The MDM is configured to divide the signal and forward the signal stream portion (signaling frames} of the signal stream to the MTX control means and the speech stream portion of the speech stream back to the GS) Implementing the splitting operation in the 5 MDM alone minimizes delay in the signal stream in the arrangement of the invention, the delay may be as low as nearly 0 s. In prior art systems, some of the signaling was always transferred to GS due to the delay in the MTX control circuit. 10 In the inventive arrangement, the MDM distributes the signal stream without any additional control signals from the MTX No modifications are required to the functions of the modem known per se, but its connections are arranged in a new way so that the necessary connections can be made.

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We now refer to Figure 3, which shows three MDMs

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'arranged behind the center GS. A separate MDM for each of the six channels from the six base stations (and

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20 so their ETCs) there is no need but ... one MDM behind GS can be selectively connected

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;;; channels that have ongoing calls.

f · "* This is possible because there are always channels ·· • '·· that do not carry simultaneous calls, and thus · · m! ... · 25 in prior art solutions comprising one ETC for each modem There are always MDMs that are · · inactive By using MDMs that can be selectively linked to a desired channel, their use can be optimized.

As speech and signaling are transmitted on the same physical path, signaling frames 42 from the base station BS are closed. During signaling, i.e., signaling frames 42, the voice path is closed, which is perceived by users as having a short delay during signaling (silence portions 44 in streams 32 of prior art 5). Signaling frames 42 contain bits having a predetermined bit order in a manner known per se, as indicated by an example sequence. The bit transfer arrangement may be a frequency shifted signal according to the Fast Frequency Shift Keying (FFSK) method as described above.

The described system employs a binary signaling method with a single block or frame length of 166 bits. Sig- ·, ·. nalization uses an error correction code (called the "·" __ 15 Hagelbarger code) that protects frames from errors that • av. consist of a maximum of six bits in the case that • a a the distance between the errors is at least 9 bits. As mentioned, the modulation of user data is FSK, where 1200 Hz a «<corresponds to a logical one and 1800 Hz corresponds to a logical zero.

a a a 20 The bit rate can be, for example, 1200 bits / s or more. Each signaling frame 42 includes one command, an acknowledgment, a «a · ___!. *! call, control data, etc. Several successive signaling frames • generate signaling sequences which are capable of performing more complex and extensive control operations, such as call setup.

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Referring now also to the flowchart of Figure 5, in step 102, the signaling frames 42 are transmitted within the signal stream 30 from the MS to the MTX. The MTX is arranged to evaluate background-30 tan acoustic noise (step 104) during transmission so that it can generate pleasant noise in the signal stream at a later stage (step 112) after splitting in MDM, as will be described in more detail later.

The MDM continuously monitors the signal stream 30 as the signal stream arrives at the MDM, step 106. More specifically, the sequential frames of the sig-5 signal stream are monitored to detect certain sequences of frames 42 that indicate signaling. If the signaling is not detected at step 108, there is no need for splitting operations and the speech is forwarded to the final destination. If, in step 108 ha-10, a signaling frame is required and signaling needs to be split out of the signal stream, the MDM immediately initiates the splitting operation (step 110) with a minimal delay in response to monitoring. In step 112, signaling portion 42 is moved to MTX. jaimelle. Meaningful noise is generated in speech, exactly ·. ·, 15 further presented in the “blank” portions 44 that

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. include the silence of the prior art signal stream 32 on the basis of said evaluation performed in step 104.

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: \ In other words, MDM is designed to generate meaningful noise

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the speech stream for periods of the signal stream in which some of the speech has been cut off during splitting.

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The meaningful noise is preferably arranged to respond to a near (

acoustic noise (i.e., the speech of the MS side) tyspuolen. MTX

Evaluate noise characteristics by continuously monitoring puffs so that it is possible to generate meaningful noise using MDM based on the speech characteristics in the speech section 40 just before the signaling frame 40. Thus, the signal stream 34 exiting the MDM includes speech portions 40 and blocks 46 containing meaningful noise-30 corresponding to speech prior to the signaling frames, said blocks 46 replacing prior art "silent" blocks 44. This signal stream 34 is then transferred to the final destination in step 114. such as the headset of the receiving telephone 11 105758. Meaningful noise 46 is substantially equivalent to the actual (original) speech, and the listener will not detect any difference between the actual repeated speech and those parts that contain meaningful noise.

The MTX may comprise a voice activity detector for the aforementioned evaluation purposes. These are arranged to evaluate acoustic noise in speech so that they are capable of generating speech-specific parameters. Meaningful noise is then generated based on the evaluation mentioned in MTX with the help of a voice activity detector. An example of a voice activity detector is further specified in GSM Recommendation GSM 06.32, "Voice * · * Activity Detection", which is incorporated herein by reference, lv, 15 • a: · 'Since MDM both detects and distributes the signal stream, '; there is no legal delay that would otherwise be due to the connection to some • additional control devices or circuits. The speech signal and signaling bit sequences are separated as accurately as possible with minimum delay.

Thus, the invention provides a device and method for providing a significant improvement in the field of communication systems incorporating analog transmission. It should be noted that the above examples of embodiments of the invention do not · · - -: · V,! limit the scope of protection of the invention as claimed in the claims; meters. All further embodiments, modifications, and applications that will be apparent to those skilled in the art are thus within the spirit and scope of the invention as defined in the appended claims.

Claims (16)

A method for dividing signaling and tai into a signal stream in a telephone system comprising analog mobile telecommunication, wherein signaling and tai are transmitted on the same communication channel, the method comprising arranging the signaling in frames included in the signal stream, monitoring the signal stream for detecting the frames containing the signaling bit sequences, dividing the signal stream during the transmission of the signal stream into a signaling part and a number part on the basis of said monitoring, characterized in that it further comprises evaluating acoustic noise during transmission. sensible noise for areas removed from the signal stream at the base of said evaluation to fill in the areas of the speech portion removed from the signal stream during the • <: split. • * «20" ti Method according to claim 1, characterized in that the signal is transmitted from a mobile station to a mobile telephone exchange, and that the signal stream is monitored by means of a mobile telephone exchange modem. • · • · ·. ···. 25 · · · 3. A method according to claim 1 or 2, characterized in that the partitioning in the mobile telephone exchange mode is realized. • · • · · »i · • · t t:. '· Ί 30 4. A method according to claim 1, 2 or 3, characterized in that the division is performed only after the unified tai and signal stream has passed through the group selector of the switchboard. 17 105758 5. A method according to any of claims 1-4, characterized in that the stage at which the signal stream frames are monitored comprises the reception of the frames containing signaling which is transmitted as a frequency shifted signal according to the fast frequency shift modulation method (FFSK) and in the modem, the detected signal frames separate from the speech signal. 10 Method according to any one of claims 1-5, characterized in that the evaluation stage comprises detecting tai by means of a voice activity detector, evaluating acoustic noise present in the speech to create characteristic parameters for the speech, and thus generating sensible noise in the mobile telephone exchange corresponding to said acoustic noise. • f A method according to any preceding claim; characterized in that the "analog system comprises an NMT-I I I in '·': 20 mobile telephone system. An arrangement in a telephone system comprising analog mobile telecommunications, wherein signaling and tai are transmitted on the same communication channel, the arrangement comprising at least one base station arranged to communicate with at least one mobile station over an analog wireless. ... interface, a mobile telephone exchange arranged to communicate with said at least one base station, the arrangement being characterized by further comprising modem means arranged to monitor. the signal stream from a transmitting mobile station to detect signaling information containing signaling frames included in the signal stream and to divide speech and signaling in the analog mobile telecommunication system in response to said monitoring during means of transmitting the signal, means for evaluating audibly during transfer and the means for generating sensible noise for the areas removed from the signal stream on the basis of the evaluation of the acoustic noise to replace the areas of the speech signal that were possibly removed during the split. 10 Arrangement according to claim 8, characterized in that the frames of the signal stream are transmitted as a frequency-shifted signal according to the fast-frequency shift modulation method (FFSK). Arrangement according to claim 8 or 9, characterized in that the evaluation means comprise a voice activity detector for detecting tai, means for evaluating the acoustic noise to obtain: for the speech characteristic parameters, and the generating means realized for generating in the mobile telephone exchange. such sensible noise corresponding to said acoustic noise. Arrangement according to any of claims 8-10, characterized ***; Characterized in that the mobile on-call center comprises a plurality of / modems and a group selector arranged between a plurality of channels coming from a plurality of base stations, the arrangement being such that each modem of said plurality · Modems can be selectively coupled to which channel heisted by "the said plurality of channels. 19 105758 Arrangement according to any of claims 8-11, characterized in that the analog system comprises an NMT mobile telephone system. A mobile telephone exchange comprising means for communicating via a base station with a mobile station where the communication between the mobile station and the base station is realized via an analog wireless interface, characterized in that it further comprises modem means arranged to monitor the signal stream from a base station. transmitting mobile station for detecting signaling information containing signaling frames included in the signal stream and dividing the signal stream and signaling in response to said monitoring during the transmission of the signal stream, and means for generating sensible noise for the areas removed from the signal stream at a base the transmission performed evaluation of acoustic noise to replace the areas of the speech signal that may have been removed during the split. r [i: v: 20 Mobile telephone exchange according to claim 13, characterized by: T; in that it further comprises means for evaluating said acoustic noise. Mobile telephone exchange according to claim 13 or 14, characterized in that it comprises a plurality of modems and a group selector arranged between a plurality of channels coming from a channel. a plurality of bus stations, the arrangement being such that each modem of said plurality of modems can • · «« «'*'! 30 is selectively coupled to which channel is raised by said plurality of channels.