MXPA00012128A - System for elimination of audible effects of handover - Google Patents

Abstract

Audible effects of handover of a mobile subscriber station (M1, 22) in a digital cellular system are eliminated in either the uplink (UL) or the downlink (DL) by implementing discontinuous transmission (DTX) within the system on either or both of the links. A voice activity detector (VAD) monitors whether speech or non-transparent data is originating from a party and, if not, the transmission of that party is interrupted and only a single SID frame is sent during each SACCH period to update the background noise characteristics being generated at the other parties'receiver. Once it is determined by the system that a handover of a mobile needs to be performed (32), that handover is delayed until the party on the link on which DTX is implemented is neither talking nor sending non-transparent data (34) ensuring that the other party is having comfort noise being generated in its receiver and, thus, will not hear any audible effect of the handover.

Description

"SYSTEM FOR ELIMINATING AUDIBLE DELIVERY EFFECTS" BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to cellular radio telecommunications systems and, more particularly, to a method and system for eliminating the audible effects of delivery of a cellular radio subscriber terminal from one cell to another.

DESCRIPTION OF THE RELATED TECHNIQUE In a cellular radio telecommunications system, the area within which a plurality of mobile stations are served by the system is divided into cells. Each unoccupied and active mobile station within the cell remains in radio contact with a base station serving that cell. In a conventional operation, when the mobile station is coupled in active communication it moves from one cell to another cell, the cellular system performs a handover (delivery) in which the movable mobile station is instructed to return its radio to a new traffic channel that is being served by the base station of the cell in which it is entering. The main reason for performing the delivery is the deterioration of the quality of the signal experienced by the mobile station for its service cell and the existence of a signal from a base station of a neighboring cell that would provide the same with better signal quality . A cellular system must know the approximate location of each of the mobile stations coupled in active communication in order to provide efficient handover and traffic management functionality. The location information is generally provided by measuring the signal strength of the radio signals passing between the mobile station and its service base station as well as the radio signals from the neighboring base stations serving the the cells in the surrounding geographical area. The basic criteria defining a good radio air interface connection between a mobile terminal and a base station in a cellular system are an intensity of the carrier signal above a preselected threshold value, a relatively high speech quality in the connection as defined by the carrier-to-interference ratio (C / I), and a sufficient number of available channels in the service cell. As soon as any of these criteria - can no longer be satisfied by the base station with which the subscriber's terminal is in communication, the system will try to transfer the connection to a more appropriate cell within the system. Since the operators of the system try to increase the capacity of their networks to service the increased number of mobile subscribers, the geographical size of the cell within the system is continuously decreasing. This is to allow the system operator to reuse the limited number of frequency channels available more frequently to increase system capacity. This increase in frequency reuse also prescribes that there will be a higher number of deliveries per call as a result of the smaller size of the cells. The delivery of a mobile radio terminal from one cell to another is carried out by sending the necessary signals between the mobile terminal and the cellular network in the old traffic channel within the current service cell after which the radio connection The call is transferred directly to a new traffic channel that belongs to the largest cell. This necessarily produces a short conversation interruption during the actual transfer of the traffic channel from one cell to another, which is typically within the order of a few hundred milliseconds. These traffic channel interruptions are audible to both parties regarding the conversation and can be extremely annoying when many deliveries occur in a row during a single call. The system of the present invention provides a solution to the problem of audible delivery effects that will eliminate, in most cases interruptions of conversation perceived towards one or both parties regarding the conversation. A known solution to this problem is provided in Patent Number WO 98/09454 where it is disclosed that there must be an input and output voice activity from the communications system monitor to detect that a number of images have occurred. of entrance and exit which have no voice. When this is detected, a necessary handover is carried out.

BRIEF COMPENDIUM OF THE INVENTION One aspect of the present invention relates to reducing the audible effect of delivery on at least one link in the traffic channel of a radio air interface of a cellular radio system. Discontinuous transmission (DTX) is implemented within the link within which the audible delivery effects will be reduced by detecting whether each traffic image on the link consists of conversation, non-transparent data or background noise. A silence descriptor image (SID) is sent containing the information related to background noise within the link from the transmitter to the receiver in response to the detection that neither the conversion nor the non-transparent data are present in the link. The incoming traffic images in the receiver are monitored and when an SID image is detected in the receiver, the effective noise characteristics are updated and the effective noise within the receiver is generated. When it is determined that a delivery of a mobile station on the link must be carried out in response to the measurements of the signal within the system, the operation of that delivery is delayed until a preselected number of SID images have been received in sequence in the receptor. This indicates that the parts in the transmitter are not generating neither conversion nor non-transparent data and that the receiver is instead receiving the effective noise. In response to this condition, the delivery of the mobile station from one BTS to another is carried out which eliminates the audible effect of the delivery to the party at the receiver, since the effective noise will still be generated through the process of delivery.

In another aspect of the invention, the audible effect of delivery is reduced in a digital cellular radio system where discontinuous transmission (DTX) is implemented in at least one of the uplink or downlink radio channels of the system . DTX radio transmissions from a party on the link that is not currently sending a communication and instead sends regular periodic indications to another party indicating that the reference noise must be generated at the party's receiver. The transmission of the periodic indications sent by the party not currently sending a communication is monitored together with the need through the system to carry out a delivery from one cell to another of a mobile station which is a part with respect to that communication. The performance of the necessary delivery is delayed until a preselected number of regular periodic indications has been received from the party that is not currently sending a communication to ensure that the other party is at that moment receiving only the effective noise and, therefore, you will not hear the audible effects of the delivery that is taking place. Once that condition exists, the necessary delivery is carried out.

BRIEF DESCRIPTION OF THE DRAWINGS For an understanding of the present invention and for the objects and additional advantages thereof, reference may now be made to the following description, which is taken in conjunction with the accompanying drawings, in which: Figure 1 is a diagrammatic illustration of a cellular radio system including a plurality of cells and base stations with which an embodiment of the present invention may be used; Figure 2 is a functional diagram representative of a cellular communication system employing sectorized antennas within which one embodiment of the present invention may be incorporated; Figure 3 is an illustrative diagram of the manner in which measurements of signal strength are carried out and a mobile subscriber terminal is passed from one cell to another in a cellular radio system; Figure 4 is a flow chart illustrating certain aspects of an algorithm used in the system of the present invention; Figure 5 is a time diagram illustrating the removal of audible delivery effects in accordance with an aspect of the invention; Figure 6 is a time diagram illustrating the removal of audible delivery effects in accordance with another aspect of the invention; and Figure 7 is a time diagram illustrating the removal of audible delivery effects in accordance with still another aspect of the invention.

DETAILED DESCRIPTION OF THE PREFERRED MODALITY To provide a context within which the details of the present invention can be pointed out, the general construction and operation or operation of a cellular mobile radio system will be described first. Figure 1 is a diagrammatic representation of this system containing ten cells, C1-C10. Of course, a cellular radio system would contain many more cells of ten but for purposes of this illustration, the system shown in Figure 1 can be considered as being an isolated portion of a larger system, only ten cells from which it is shown. Within each of the cells C1-C10 there is a corresponding respective base station B1-B10 serving that cell. In the exemplary embodiment of Figure 1, the base stations B1-B10 are shown as having omni-directional antennas and being placed in proximity to the center of the cells, however, a person skilled in the art will recognize that the base can typically be placed in other cell areas, for example, at the intersection of three adjacent cells and have sectorized antennas so that a single base station can service three cells. Also shown in Figure 1 are a plurality of mobile stations, M1-M10 that are subject to movement within each cell and from one cell to another cell. Of course, a typical cellular system would have many more mobile stations that work within it, other than ten. A mobile switching center MSC1 is connected to each of the base stations B1-B10 by means of a cable or microwave and with a switched telecommunication network (PSTN). Each cellular radio telecommunication system is assigned a specific frequency band within which it must operate. This frequency band is subdivided into units called frequencies, the groupings of which are assigned to the cells placed in a specific area. Due to the limited radio frequency spectrum since the need for numbers of traffic channels within each cell increases due to increased traffic within the system, system operators tend to continually reconfigure their systems, generally reducing the geographical degree covered by each cell in order to increase the reuse of the frequency within the system. This decrease in cell size means that there will be an increased number of deliveries during each call where the mobile station is moving through a cell-to-cell system. Figure 2 illustrates another exemplary cellular radio telecommunications system employing base stations each having three sectorized antennas. The system, generally shown at 10, comprises a cellular network 12 that includes a plurality of fixed site base stations 16 placed in separate locations across a geographic area. In the illustration of Figure 2, each of the base stations 16 defines a cell 18 and groups of three base stations 16 are placed together and each of the co-located base stations serves a defining coverage area. three adjacent but separate cells 18--18. Each base station 16 typically includes a fixed-site transceiver that uses a sectorized antenna that covers approximately 120 ° and which is positioned on the periphery of the cell to which it is serving. Each of the base stations 16 allows wireless radio communication to be performed with remotely placed mobile subscriber terminals, such as the subscriber terminal 22, when the mobile station is placed within the communication scale of one of the base stations. The cells 18--18 defined by the coverage areas of the base stations are shown as being hexagonal only for purposes of illustration. In the real system, the communication scale, that is, the coverage area, of a base station must differ from that shown in the figure. That is, the cells 18--18 may be non-symmetric with respect to the base station and the cells defined by those different from the base stations 16--16 may differ in form from one another. Also, within the actual cellular radio communication system, the coverage areas (such as the adjacent base stations) would overlap each other to a certain degree. The groups of the base stations 16--16 are coupled with a base station controller (BSC) 24. The communication lines 26 couple the base station 16--16 to BSCs 24 which in turn are coupled with the mobile switching centers (MSCs), such as MSC 27, through the communication lines 28. As shown in Figure 2, when the terminal of the mobile subscriber 22 communicates with another mobile communication station connected to the network, those communications are made through the base station 16 within the network 12. When the mobile terminal 22 moves between the cells 18--18 of the network 12, the communications in progress are passed between the successive stations of the stations. base 16--16. If the mobile terminal is in the idle mode, the selection of the cell, such as that which occurs during the matching or registration procedures, is carried out when the mobile station moves from cell to cell. Referring to Figure 3, the manner in which a mobile station 22 that is in communication with a first service cell A of the base station, has its radio air interface connection subjected to periodic measurements for criteria of quality through both its service cell and its neighboring cells. Once it is decided that one or more of the quality criteria have decreased to less than the preselected minimum values, the network then causes the radio air interface to be transferred from Cell A to a base station that is serving mobile stations within cell B. During this transfer of the radio connection from Cell A to Cell B, there is a short interruption in the traffic channel that is normally audible to one or both of the parties with usually for resynchronization . It is said that this technique allows the disruption to be masked by the conversation decoder and to be restricted to less than 40 milliseconds. Still another attempt to solve this problem has been the use of quieting the level of effective noise in order to reduce the audible effects of the uplink instead of quieting down to silence. An improved algorithm is used to gradually quiet the effective noise level to be the least audible delivery for the listener. In addition, the SID update interpolation provides an increasingly uniform transition between consecutive SID update images and thus improves the quality of effective noise at the receiving end during silent periods. From the point of view of the quality of conversation one of the main problems with the delivery is the times of interruption of conversation and, in the networks of reuse of frequency, the importance of minimizing the times of interruption of conversation during the delivery It is significant. However, none of the above mentioned techniques completely eliminates the speech degradation perceived during the handover but rather only reduces the apparent talk interruption time and the apparent effect on them. The method and system of the present invention employ a technique that has been implemented by many cellular radio networks and is called discontinuous tansmission (DTX). TDMA cellular radio systems employing frequency hopping such as the global system for mobile communication (GSM) or American PC 1900 TDMA systems supplied by Ericsson Radio Systems particularly benefit from the addition of DTX. The DTX functionality is defined and described, for example, in the GSM specification, GSM 06.31 and is covered by the European Telecommunications Standard ETS300 580-5, both of which are expressly incorporated herein by reference thereto. In general, the DTX functionality is based on the proposition that during a conversation, each participant is traditionally silent on average for approximately 50 percent of the time. If nothing has been said in the microphone of a mobile radio terminal, there is no point in sending anything through the radio transmission to the air and, therefore, transmissions are made from the radio only when it is detected the conversation through the connection. The DTX procedure decreases the power consumption of the mobile subscriber terminal (MS) as well as the base station transceiver system (BTS) and also reduces the amount of radio power emitted into the air. Since the power level used when it is actually transmitted is not affected, the C / I ratio is raised for all connections when DTX is implemented. DTX is used to decrease both the power consumption MS and BTS as well as to reduce interference within the system and is only used in the transmission of traffic channel images (TCH). DTX can be implemented separately in either the uplink (UL) traffic channels (from the mobile station to the base station) or the downlink (UL) traffic channels (from the base station to the mobile station) or both. An integral part of the DTX functionality is the inclusion of a voice activity detector (VAD) in the BTS and / or MS transmitter. The general function and functioning of a VAD is defined and described, for example, in the global system for the specification of mobile communication (GSM), GSM 06 32 and is covered in ETSI Standard ETS 300 580-6, both of which are which are expressly incorporated herein by reference thereto. In general, the VAD in the transmitter of either a BTS or MS detects whether a traffic image consists of conversation, non-transparent data or background noise. If the image consists only of noise, the transmitter sends a silence descriptor image (SID), and then the transmission stops. After the initial SID image, a new SID image is sent during each SACCH period until either the conversation or non-transparent data is detected again within a traffic image. Measurement reports of signal quality are sent as usual in SACCH. Each of the SID images contains information about the background noise of the established connection that is being monitored by VAD. In the MS or BTS receivers where the DTX functionality is being carried out, the SID image detector checks all the input images. The SID image detector is capable of separating the SID images from the non-transparent data or conversation images and, after an SID image is detected, the effective noise characteristics within the receiver are updated and the effective noise is generated in accordance with those characteristics. The effective noise generation is interrupted when a conversation image is detected and the conversation is decoded for the listener. In this way, the SID images are sent between the transmitter and the receiver during periods of silence mainly due to two reasons: (1) to update the effective noise characteristics on the receiving side and (2) to allow them to be carried out and transmit the signal strength and signal quality measurements. The VAD must be running at all times in order to assess whether an input signal contains conversation or non-transparent data. The mobile station and / or BTS send the information in the measurement report every 480 milliseconds informing whether DTX has been used during that interval or not. In most contemporary networks, DTX is frequently used in the uplink (UL) to economize battery consumption of mobile stations. However, DTX in the downlink (DL) is rarely used since most operators perceive that the degradation of the conversation caused by the use of the DTX functionality is worse than the economy and benefits of the power in terms of the reduced interference. The method and system of the present invention operate somewhat differently from the prior art discussed above. From this, instead of reducing the interruption times in the traffic channels, the technique of the present invention "hides" or "masks" the effects of those interruptions of the audible perception by the end user. The system of the present invention incorporates the existing DTX functionality within the cellular radio systems described above and employs that functionality by carrying out the delivery during the silent periods of a conversation when it is only created for the listener of the effective noise . With the present technique the delivery is delayed until several SID images (a number selectable by the operator) have been received in a row indicating that the user at that moment is listening to the other person instead of simply breathing between two sentences in one conversation. When the DTX functionality is in use, only one SID image is sent during the entire SACCH period and in this way, when several SID images have been detected in sequence indicating that several SACCH periods have passed without any conversation from that part, the delivery is It performs quickly in less than 200 milliseconds. Using this technique to synchronize the delivery, the audible effects of the interruption of conversation for one of the two parties are eliminated until a communication that at that moment is receiving the effective noise in the receiver. In addition, the delivery between two cells, in most cases, will be made when the signal strength of the reference cell is more intense than that of the current service cell within a certain number of dBs. Usually, the delivery can be considerably delayed without any serious quality problems in terms of the specific radio air interface of that mobile station or the network as a whole. However, the implementation of the control of the proposed functionality, which incorporates the delay of the delivery for a certain time, also employs a synchronizer that is selectable by the operator up to a certain value. In that case, if either one or an insufficient number of SID images have not been detected in sequence before the expiration of the preselected time period after the system has determined that a delivery is necessary, the delivery is carried out from any way to avoid inadvertent connection loss. The current implementation algorithm to carry out the delivery in accordance with the present technique also preferably includes monitoring the quality of the radio interface of the connection air.- If the parameters of signal quality, such as the intensity of the signal or the bit error rate (BER) decrease to less than the pre-selected values or the rate of decrease of those parameters exceeds a pre-selected threshold regime, a delivery is carried out regardless of whether the data is supervised in terms of DTX parameters such as the SID periods. However, most deliveries are made during relatively good signal quality and signal strength and in these cases, a delay of 5 to 10 seconds in terms of the current delivery has no impact on that quality. Referring now to Figure 4, an exemplary implementation algorithm is illustrated in the form of a flow chart. At 31 the system starts and moves up to 32 where it determines whether the delivery criteria have been filled or not. If the answer is no, the current radio connection is maintained. However, if the 32 delivery criteria have been filled, the system moves up to 33 and determines whether the quality and / or resistance of the connection signal has been degraded or degraded to less than a predetermined threshold or its degradation to a regime that is greater than the selected threshold value. If the answer is no, the system moves to 34 and asks if a sufficient number of SID images have been detected on the link selected by the operator, ie UL or DL, to conclude that the radio connection is currently in a period of silence or silence and only effective noise is being generated. If the answer is yes, the system moves up to 35 and the delivery is carried out. If a determination is made at 33 that the quality of the signal and / or the signal strength has degraded to less than a pre-selected threshold of the regime or the degradation rate is faster than a threshold value, the system does not it further delays a delivery to stop if the radio air interface is in a quiet period or not but moves immediately up to 35 and carries out the delivery to avoid the risk of losing the connection. The technique of the present invention is applicable to an air interface and radio connection between two parts only of one link at a time. Which link is selected for application of the technique is based on the selection of the operator and is applied either to the uplink (UL) or to the downlink (DL). The solution of the present invention has been shown to be highly significant with respect to eliminating the audible effects of a delivery and essentially eliminates completely the reception of the audible delivery effects on the selected link of one of the links. Referring now to Figure 5, a timing or synchronization diagram is shown illustrating a situation where the DTX functionality is disabled for the uplink of a radio air interface connection but not for the downlink thereof. . In general, for those cellular system operators who currently implement DTX, the 90 percent implementation of the functionality in only the uplink is taken for granted in Figure 5. The reason for this is that the actual economic gain produced by interrupting the transmitter when the user is not speaking occurs at the mobile station, which economizes battery power, and not BTS. In addition, the slowness of the VAD operation in the DTX system slightly degrades the quality of the plosives (sounds such as "p", "t" and "") and the DTX function prevents signal quality measurements through the Mobile station and BTS are carried out as frequently as is normal. In the uplink of Figure 3, the "disconnected" DTX condition means that the conversation is being transmitted between the mobile station and the base station and the "connected" DTX condition means that there is a period of silence by the user of the mobile station and only the SID images are being sent through the uplink between the mobile station and the base station. To simplify the example, the diagram of Figure 5 represents a call between a mobile user and a person on a landline, however, the following reasoning would also be true for a MS to MS call. The dotted timeline marked "HOI" represents the time at which a delivery is carried out regardless of the silent periods and "H02" is the time to which a delivery time has been adjusted in accordance with the silent periods in the link ascending in accordance with the principles of the present invention. If all deliveries that had happened during the mobile user's talk periods are delayed instead of this to occur during the silent periods, as illustrated in H02, none of these deliveries would have been audibly detected by the "fixed" user. Deliveries in this case always happen when the "fixed" user is talking and receiving the effective noise in the receiver since the mobile user is not talking and DTX is connected. In this way, the effects of the delivery would be inaudible for the fixed part of the communication. However, the mobile user in this case would hear the delivery interruption since the DTX functionality is not being implemented in the downlink (DL). Other techniques of the previous branch, such as those previously discussed, could be used to minimize the talk interruption time on this link to minimize the audible effect. Referring now to Figure 6, another time diagram illustrating the opposite situation is shown, even though relatively unusual in current practice, that which is illustrated in Figure 5. In Figure 6, the DTX functionality is trained for the downlink but not for the uplink of a radio air interface interconnect between the two parties. With this example it is better to delay the delivery based on the downlink since the uplink is always transmitting. In this situation, each of the deliveries will happen during the periods of conversation of the user that is supposed to be fixed in the downlink are delayed from HOI (when there is no DTX either in the uplink or the downlink) until H02 when DTX is able to operate during the silent periods of the fixed user in the downlink. In this way, none of the deliveries will be audibly detected by the mobile user who is receiving only the effective noise. Instead, deliveries would always happen when the mobile user is talking (or at least the person at the other end of the connection is not talking) and the mobile user would never hear them. The "fixed" user in this case would always hear the delivery interrupts since the DTX functionality is not working in the uplink. Under these circumstances, it is possible that the operator of the cellular system to buy your network as being superior with respect to the aspects of quality, since they are not being detected - H & .-- 'conversation interrupts by mobile subscribers connected to their network. Referring finally to Figure 7, a still further aspect of the present invention is also illustrated in the form of a timing diagram. In this situation, it is assumed that both users in the uplink and the downlink are either silent or do not speak at the same time, in each delivery it will happen during a silent period for one of the two parties with respect to the communication. In the example of Figure 7, the delivery event that is observed by the timeline "H01" is carried out when the mobile user is silent and DTX is functional in the uplink, and therefore, not perceptible to the user. the "fixed" user. The delivery illustrated by dotted line "H02" occurs when the "fixed" user is silent and DTX is active in the downlink, this delivery is therefore not audibly audible to the mobile user. frequently occur randomly both the mobile user and the "fixed" user of these deliveries frequently happen randomly both the mobile user and the "fixed" user will hear on average approximately 50 percent of the delivery interruptions.

Silent periods of one of the links, perceived delivery interruptions are completely eliminated for either the mobile user or the "fixed" user but not both. Of course it would be a rare circumstance when both parties were silent for a prolonged period (and DTX was working both on the uplink and downlink simultaneously) and it was not necessary to carry out a delivery. The operator of the system selects a specific parameter within the present system to select the direction in which the system is brought to the optimum, that is, either the uplink or the downlink when DTX is able to operate in both directions. For example, if all deliveries were made during the silent periods of the "fixed" user, the quality of the network would appear from the perspective of the user of the station. mobile as being improved since the mobile user will never experience any audible interruptions. Unemployment. a call from MS to MS on the same network, a mobile user will hear other deliveries from the mobile station but not their own deliveries if the same strategy of carrying out deliveries during the silent periods of the downlink is used. It can be seen from the foregoing description of the invention, that the method and system of the present invention can be implemented in different ways. In any case, the audible effect of delivery to one or the other of two parties to a conversation through an air and radio interface in a cellular radio system can be completely masked from any audible perception. In this way, the system contains great advantages for the operators of the system, all of whom wish to improve their respective claims for the quality of the signal and its systems. Since increased amounts of frequency reuse occur within the cellular system, the method and system of the present invention become increasingly important to reduce the audible annoying effects of delivery.

Claims (18)

CLAIMS;

1. A method for reducing the audible effect of delivery in a cellular radio system (10) wherein discontinuous transmission (DTX) is implemented in at least one of the uplink or downlink radio channels of the system to interrupt the radio transmissions from a first party in the link that at that moment is not sending a conversation of non-transparent communication or data and instead send regular periodic indications to a second part indicating that the effective noise must be generated in the receiver of the second part, the method is characterized by the steps of: monitoring for the DTX transmission of the periodic indications sent by the first part; monitoring (32) for the need to carry out a delivery from one cell to another of a mobile station (22) that is one of the parties to these communications; delay (34) the operation of the necessary delivery until a preselected number of regular periodic indications have been received from the first party that is not currently sending a communication to ensure that the second party is receiving only the effective noise and will not hear the audible effects of the delivery that is taking place; and carrying out (35) the delivery when the pre-selected number is satisfied.

2. The method as set forth in claim 8, wherein the communication being held between a mobile station and one of the links and another part, is a voice call and wherein the step of monitoring the need to carry A delivery of the mobile station further comprises: monitoring the signal strength and the bit error rate (BER) both in the uplink and the downlink of the mobile station together with the rate at which they are deteriorating the quality of the the signal BER; compare (33) the supervised signal intensity and the deterioration regime of the signal intensity to perceive the preselected threshold values; carrying out (35) the delivery independently of the receipt of the preselected number of regular periodic indications in response to either the deterioration of the supervised signal strength to less than the preselected threshold value or the rate of deterioration of the signal strength supervised that becomes greater than the threshold value.

The method as set forth in claim 2, wherein the step of monitoring the need to carry out a delivery of the mobile station further comprises the steps of: comparing (33) the BER and the deterioration regime of BER to respective pre-selected threshold values; carry out (35) the delivery regardless of the receipt of the preselected number of regular periodic indications in response to either the deterioration of supervised BER to less than the preselected threshold value or the deterioration regime of the supervised BER that is becoming greater than the threshold value. .

The method as set forth in claim 1, wherein DTX is trained only on the uplinks of the system, the communication being between one mobile station and one of the uplinks and another part is a voice call, and wherein the delivery necessary is delayed until the mobile station in the uplink is not talking and the other party in the conversation with the mobile station is receiving only effective noise to eliminate the audible effect of the delivery to another party.

5. The method as set forth in claim 1, wherein DTX is disabled only in the downlinks of the system, the communication being between one mobile station and in one of the uplinks and another part is a voice call, and in where the necessary delivery is delayed until the mobile station in the uplink is talking, the other part of the conversation is not talking and the mobile station is only receiving the effective noise to eliminate the audible effect of the delivery to the mobile station.

6. The method as set forth in claim 1, wherein the regular periodic indications sent by the party not at the time a communication is sent are in the form of an SID image during each SACCH period and wherein the step of monitoring the transmission of the periodic indications includes monitoring and counting the number of successive SID images that are received from that part.

The method as set forth in claim 8, wherein the regular periodic indications sent by the party that is not currently sending a communication are in the form of an SID image during a £ aBMaaM¡¡ga | B¡a each SACCH period and wherein the delay step includes the step of: counting (34) the number of successive SID images received from the part; compare (34) the number with a preselected value; and carrying out (35) the handover when the number exceeds the preselected value.

The method as set forth in claim 1, wherein the radio transmissions from a party in the link that is not currently sending communications are interrupted by a voice activity detector (VAD) which instead causes the sending of regular periodic indications to the other party indicating that the effective noise should not be generated in the receiver of that part.

The method as set forth in claim 9, wherein the communication that is being carried out between the mobile station and one of the links and another part is a non-transparent data call.

10. A system for reducing the audible effect of delivery in a digital cellular radio system (10) wherein discontinuous transmission (DTX) is implemented in at least one of the uplink or downlink radio channels of the system to interrupt the radio transmissions from the first part in the link when it is not at that moment sending a conversation or communication of non-transparent data and instead sending regular periodic indications to a second part indicating that the effective noise should not be generated in the receiver of that part, the system being characterized by: means (16, 24, 27) to monitor the transmission of the periodic indications sent by the first part; means (16, 24, 27, 32) within the system for monitoring the need to carry out a delivery from one cell to another of a mobile station (22) which is one of the parties to said communications; means (16, 24, 27, 34) to delay the operation of the necessary delivery until a preselected number of regular periodic indications have been received from the party to the communication that is not currently sending a communication to ensure that the another party is receiving only the effective noise and will not hear the audible effects of the delivery that is taking place and then carrying out (35) the delivery.

The system as set forth in claim 10, wherein the communication that is being carried out between a mobile station and one of the links and another part is a voice call and where the means to monitor the need to carry a delivery of the mobile station further comprises: means for monitoring the signal strength and the bit error rate (BER) both in the uplink and the downlink of the mobile station together with the rate at which they are deteriorating the intensity of the BER signal; means (16, 24, 27, 33) for comparing the intensity of the monitored signal and the rate of deterioration of the signal strength to the respective pre-selected threshold values; means (16, 24, 27, 35) for carrying out the delivery independently of receipt of the preselected number of regular periodic indications in response either to the intensity of the supervised signal that deteriorates to less than the preselected threshold value or rate of deterioration in the intensity of the supervised signal that is becoming greater than the threshold value.

The system as set forth in claim 11, wherein the means for monitoring the need to carry out a delivery of the mobile station further comprises: means (16, 24, 27, 33) for comparing BER and the rate of deterioration of BER to the respective preselected threshold values; means (16, 24, 27, 35) to carry out the delivery independently of the receipt of the preselected number of regular periodic indications in response to either the supervised BER deteriorating to less than the preselected threshold value or the deterioration regime of the BER supervised that is becoming greater than the threshold value.

13. The method as set forth in claim 10, where DTX is trained only in the uplinks of the system, obtaining communication in the mobile station in one of the uplinks and another part is a voice call, and where the necessary delivery is delayed until the mobile station in the uplink is not talking and the other part of the conversation with the mobile station is receiving only the effective noise to eliminate the audible effect of the delivery to the other party.

The system as set forth in claim 10, wherein DTX is trained only on the downlinks of the system, the communication is obtained between a mobile station on one of the uplinks and another part is a voice call, and on where the necessary delivery is delayed until the mobile station in the uplink is talking, the other part of the conversation is not talking and the mobile station is receiving only the effective noise to eliminate the audible effect of the delivery to the mobile station.

The system as set forth in claim 10, wherein the regular periodic indications sent by the party that is not currently sending a communication are in the form of an SID image during each SACCH period and wherein the means for monitoring the transmission of the periodic indications includes means for monitoring and counting the number of successive SID images that are received from that part.

The system as set forth in claim 10, wherein the regular periodic indications sent by the party that is not currently sending a communication are in the form of a SID image during each SACCH period and wherein the delay step includes: means (16, 24, 27) to count the number of successive SID images received from that part; means for comparing (16, 24, 27, 34) the number with a preselected value; and means for carrying out (16, 24, 27, 35) the handover when the number exceeds the preselected value.

17. The system as set forth in claim 10, wherein the radio transmissions from a party in the link that is not currently sending communications, is interrupted by the voice activity detector (VAD) which instead causes the sending regular periodic indications to the other party indicating that the effective noise must be generated in the receiver of that part.

18. The system as set forth in claim 10, wherein the communication that is being made between a mobile station in one of the links and another party, is not a non-transparent data call.