Patent Document

TECHNOLOGICAL FIELD  
         [0001]    The invention concerns generally the task of controlling the transmission power of radio transmitters in a cellular radio system. Especially the invention concerns the task of making the power control mechanisms independent of the possibly discontinuous nature of payload transmissions.  
         BACKGROUND OF THE INVENTION  
         [0002]    Discontinuous transmission, also known by the acronym DTX, is a method where, in a radio communications device taking part in a circuit-switched communication connection, the radio transmitter is only switched on during those periods for which there is meaningful payload information to be transmitted. As an example, a radio telephone using DTX will only have its radio transmitter on during the periods when its user is actually speaking. The advantages gained through the application of DTX are mainly related to savings in transmitter power consumption and a decrease in the general level of radio interference experienced by other simultaneous communication connections.  
           [0003]    On the other hand, fast power control that is also known by the acronym FPC is an arrangement applied in cellular radio systems where the transmission power of either a base station or a mobile station or both is controlled in a fast feedback loop. In a typical FPC arrangement both the base station and the mobile station monitor the power level or other feature of the radio signals received over an active communication connection. The base station converts its monitoring results into power control commands that it sends with little additional delay to the mobile station so that the latter can quickly adapt its transmission power to counteract fluctuations noticed at the base station. In the other direction the mobile station sends its monitoring results back to the base station, so that it is left to the base station to decide, whether it should change the transmission power used for transmissions to that particular mobile station. An exemplary FPC method and arrangement is described in the technical specifications “Digital Cellular Telecommunications System (Phase 2+), Channel Coding (GSM 05.03 version 8.5.0 Release 1999” and “Digital Cellular Telecommunications System (Phase 2+), Radio Subsystem Link Control (GSM 05.08 version 8.5.0 Release 1999”, which are published by the European Telecommunications Standards Institute and incorporated herein by reference.  
           [0004]    The FPC method disclosed in said technical specifications depends on the continuous transmission of payload data bursts in both uplink and downlink directions, because FPC-related information is mapped on certain so-called stealing flag symbols of the payload data bursts. The mobile station inserts the so-called fast signal quality reports into the payload data bursts that it sends in the uplink direction, and the base station inserts the fast power control commands into the payload data bursts that it sends in the downlink direction. Obviously, discontinuous transmission would interfere with such a fast power control arrangement, because silencing the payload transmissions in the uplink direction would prevent the fast signal quality reports from reaching the base station and silencing the payload transmissions in the downlink direction would correspondingly prevent the fast power control commands from reaching the mobile station.  
           [0005]    Said technical specifications have specified the use of the fast power control arrangement described therein to the context of Enhanced Circuit Switched Data, also known as ESCD, where DTX is not used and consequently no problems are to be expected. However, essentially the same fast power control arrangement has been suggested for use on the 8PSK-modulated AMR speech traffic channels of GERAN (eight-level Phase Shift Keying; Adaptive Multi-Rate, General EDGE Radio Access Network, where EDGE comes from Enhanced Datarates for GSM Evolution). Discontinuous transmission will also be applied on these channels, which means that the fast power control arrangement in its known form would not work properly.  
         SUMMARY OF THE INVENTION  
         [0006]    It is an object of the present invention to provide a method and an arrangement for enabling fast power control also on circuit-switched traffic channels where discontinuous transmission is used.  
           [0007]    The objects of the invention are achieved by reverting, for the purposes of transmitting information related to fast power control, to certain regularly transmitted updating messages during the pauses in payload transmission that are caused by discontinuous transmission.  
           [0008]    The features that are characteristic to the method according to the invention are recited in the characterising portion of the independent method claim.  
           [0009]    The invention applies also to a mobile station and a base station. The characteristic features of the mobile station according to the invention are recited in the characterising portion of the independent patent claim directed to a mobile station. The characteristic features of the base station according to the invention are recited in the characterising portion of the independent patent claim directed to a base station.  
           [0010]    The AMR speech traffic channels specified for GERAN comprise the feature of scantly but regularly transmitting so-called updating messages during a pause caused by discontinuous transmission. The original purpose of these updating messages, which in the specific context of the AMR speech traffic channels specified for GERAN are also known as SID_UPDATE messages, is to update the generated comfort noise on the receiving side, to convey AMR in-band signalling and to improve the measurement of the link quality by the radio subsystem. According to the present invention, information related to fast power control could be added into the updating messages.  
           [0011]    According to the invention, when a discontinuity period starts on an AMR speech channel, the transmitting device redirects the FPC-related information that it has to transmit into a unit that composes and transmits the SID_UPDATE messages. Similarly the start of a discontinuity period causes the receiving device to immediately look into the SID_UPDATE messages it receives, in order to find the FPC-related information that it used to receive within speech bursts before the discontinuation.  
           [0012]    The known structure of SID_UPDATE messages as well as the known channel coding and burst formatting procedures used in their transmission are not optimally suited for the addition of FPC-related information. Therefore, according to a certain aspect of the invention, it is also proposed that the modulation level used in transmitting SID_UPDATE messages is increased e.g. by employing 8PSK-modulation instead of GMSK (Gaussian Minimum Shift Keying). The increasing vulnerability to interference brought up by the introduction of a higher-level modulation method is more or less compensated for by the fact that the transmission capacity in bits per unit time is simultaneously remarkably increased, allowing more effective channel coding methods to be used. The physical location within the SID_UPDATE messages that is suitable for accommodating the FPC-related information is for example the set of stealing flag symbols the appearance of which is known as such. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0013]    The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.  
         [0014]    [0014]FIG. 1 illustrates the principle of the invention,  
         [0015]    [0015]FIG. 2 illustrates a known way of generating SID_UPDATE bursts,  
         [0016]    [0016]FIG. 3 illustrates an exemplary way of adding FPC-related information into SID_UPDATE bursts,  
         [0017]    [0017]FIG. 4 illustrates another exemplary way of adding FPC-related information into SID_UPDATE bursts,  
         [0018]    [0018]FIG. 5 illustrates another exemplary way of adding FPC-related information into SID_UPDATE bursts,  
         [0019]    [0019]FIG. 6 illustrates an aspect of a method according to an embodiment of the invention,  
         [0020]    [0020]FIG. 7 illustrates another aspect of a method according to an embodiment of the invention and  
         [0021]    [0021]FIG. 8 illustrates another aspect of a method according to an embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]    [0022]FIG. 1 illustrates, in its part shown as FIG. 1 a  in the drawings, schematically certain functions of a radio access network  101  according to an embodiment of the invention. The radio access network  101  is called the RAN for short. It is equipped for receiving both speech frames and updating messages from mobile stations. To comply with the customary terminology in the field, the updating messages are in the following called the SID_UPDATE messages. The reception means for speech frames and SID_UPDATE messages are shown separately in FIG. 1 a  as blocks  102  and  103  respectively, although physically there is typically only one receiver that receives whatever there is to be received.  
         [0023]    There is, within the RAN  101 , a certain functional unit  104  the task of which is to know, whether actual payload transmission is on in the uplink direction or whether there is a pause caused by discontinuous transmission. These situations are known as the UL DTX OFF and UL DTX ON conditions respectively. In the functional diagram of FIG. 1 a  this unit  104  uses a switch  105  to couple the output of either the speech reception means  102  or the SID_UPDATE reception means  103  to uplink signal quality measurement  106  and reception of quality reports  107 . The latter means the reception of reports that describe signal quality observed by a mobile station in the downlink direction. From the uplink signal quality measurement function  106  there is a coupling to the generation of uplink fast power control commands at block  108  that are to be conveyed to the mobile station. From the reception of quality reports function  107  there is a coupling to the selection of downlink transmission power at block  109 .  
         [0024]    The compilation of downlink transmissions is schematically shown in FIG. 1 a  as block  110 . It receives, among others, as input information the uplink FPC commands originating from block  108 . Correspondingly to unit  104  there is, within the RAN  101 , a certain functional unit  111  the task of which is to know, whether actual payload transmission is on in the downlink direction or whether there is a pause caused by discontinuous transmission. In the functional diagram of FIG. 1 a  this unit  111  uses a switch  112  to couple the output of the downlink transmission compiler  110  either to the transmission of speech frames at functional block  113  or to the transmission of downlink SID_UPDATE messages at functional block  114 .  
         [0025]    [0025]FIG. 1 illustrates also, in its part shown as FIG. 1 b  in the drawings, schematically certain functions of a mobile station  121  according to an embodiment of the invention. The mobile station  121  is called the MS for short. It is equipped for receiving both speech frames and updating messages from radio access networks. The updating messages are again called the SID_UPDATE messages. The reception means for speech frames and SID_UPDATE messages are shown separately in FIG. 1 b  as blocks  122  and  123  respectively, although physically there is typically only one receiver that receives whatever there is to be received.  
         [0026]    There is, within the MS  121 , a certain functional unit  124  the task of which is to know, whether actual payload transmission is on in the downlink direction or whether there is a pause caused by discontinuous transmission. These situations are known as the DL DTX OFF and DL DTX ON conditions respectively. In the functional diagram of FIG. 1 b  this unit  124  uses a switch  125  to couple the output of either the speech reception means  122  or the SID_UPDATE reception means  123  to downlink signal quality measurement  126  and reception of FPC commands  127 . The latter means the reception of the commands that a RAN has generated on the basis of the uplink signal quality measurements that it has performed. From the downlink signal quality measurement function  126  there is a coupling to the generation of downlink signal quality reports at block  128 . From the reception of FPC commands function  127  there is a coupling to the selection of uplink transmission power at block  129 .  
         [0027]    The compilation of uplink transmissions is schematically shown in FIG. 1 b  as block  130 . It receives, among others, as input information the downlink signal quality reports originating from block  128 . Correspondingly to unit  124  there is, within the MS  121 , a certain functional unit  131  the task of which is to know, whether actual payload transmission is on in the uplink direction or whether there is a pause caused by discontinuous transmission. In the functional diagram of FIG. 1 b  this unit  131  uses a switch  132  to couple the output of the uplink transmission compiler  130  either to the transmission of speech frames at functional block  133  or to the transmission of downlink SID_UPDATE messages at functional block  134 .  
         [0028]    In order to give some additional background to the insertion of FPC-related information into SID_UPDATE messages, FIG. 2 is discussed briefly. According to prior art, comfort noise parameters  201 , an identification marker  202  and in-band data for the purpose of link adaptation  203  were combined (multiplexed)  210  in a certain order to produce a SID_UPDATE block  211 . This combined block was subjected to channel coding  220  at a coding ratio of approximately ½. The channel coded SID_UPDATE block  221  was split and interleaved in a burst formatting operation  230  to produce four SID_UPDATE bursts  231 ,  232 ,  233  and  234 . GMSK modulation  240  was used to modulate a carrier wave in the transmission of the bursts.  
         [0029]    According to the invention, FPC-related information is combined with the SID_UPDATE bursts. Several possibilities exist for accomplishing this task. FIG. 3 shows an alternative where in addition to a channel coded SID_UPDATE block  221 ′, also FPC-related information  322  is given as input information to the burst formatting step  230 ′. In the latter the FPC-related information  322  is mapped into the stealing symbol positions to produce the FPC-carrying bursts  331 ,  332 ,  333  and  334 . These are used in an 8PSK modulation step  340  to produce the actual RF transmission bursts. The three-fold bit capacity of 8PSK means that a different coding ratio must be used at the channel coding step  221 ′, making the coding ratio now to be approximately ⅙. This decrease in coding ratio, which means that heavier channel coding is used, compensates for the fact that when modulation order is increased, the C/I (carrier to interference) requirements at reception get more difficult.  
         [0030]    In the known structure of a GMSK-modulated SID_UPDATE burst there are two stealing symbols in each burst. In GMSK this means that each stealing symbol is the equivalent of one bit in transmission. Tripling the bit capacity means that also each stealing symbol may now convey the equivalent of three bits. There are four bursts related to each SID_UPDATE block, which means that the method of FIG. 3 allows 24 FPC-related bits to be transmitted per each SID_UPDATE block. Taken that the SID_UPDATE blocks are transmitted according to the known timetable where the first SID_UPDATE block occurs t=2*20 ms after the DTX ON condition has been reached and subsequent SID_UPDATE blocks occur at t=2*20 ms+n*8*20, where n=1, 2, 3 . . . , this embodiment of the invention enables the transmission of enough FPC-related bits per unit time for implementing effective fast power control.  
         [0031]    [0031]FIG. 4 illustrates another alternative where the additional bit capacity resulting from the use of 8PSK modulation  340  is partly used to convey the FPC-related information in the payload parts of the bursts  431 ,  432 ,  433  ja  434 . In this case the FPC-related information is another piece of input information already into the multiplexing step  410 . If the amount of FPC-related information per burst is limited, then also the method shown in FIG. 5 is applicable. Here the procedure is otherwise the same as in FIG. 3, but instead of using the values of the stealing symbols, the burst formatting block  230 ′ maps the FPC-related information into the training sequences of the bursts  531 ,  532 ,  533  and  544  by selecting into each burst an appropriate one from a limited number of allowable training sequences. If the number of allowable training sequences is K, the number of discrete FPC-related values that can be conveyed per SID_UPDATE block by using the method of FIG. 5 is K 4 . If this method is used for conveying the FPC-related information, any modulation method can be used for the SID_UPDATE bursts.  
         [0032]    When either a mobile station or a network element in a radio access network is executing a method according to the invention, its operation may be coarsely characterised by the states shown in FIG. 6. A kind of a basic state is state  601  where DTX is not on in either direction and all FPC-related information is transmitted in the speech frames. If uplink DTX goes on, a transition to state  602  occurs where FPC-related information to be transmitted in the uplink direction goes into the SID_UPDATE messages. Uplink DTX going off causes a return to state  601 . A transition from state  601  to state  603  is a result of downlink DTX going on; in state  603  FPC-related information to be transmitted in the downlink direction goes into the SID_UPDATE messages. Again DTX going off causes a return to state  601 . If, during state  602  or  603  also the DTX in the other direction goes on, there occurs a transition to state  604  where all FPC-related information goes into the SID_UPDATE messages. The occurrence of exactly simultaneous DTX on/off transitions (e.g. uplink DTX going off simultaneously with downlink DTX going on) is not shown in FIG. 6 because such occurrences are rare; however it is straightforward for the person skilled in the art to see also the state transitions they would cause in FIG. 6.  
         [0033]    [0033]FIGS. 7 and 8 are simple flow diagrams that illustrate the operation of either a mobile station or a network element in a radio access network in transmitting (FIG. 7) or receiving (FIG. 8) FPC-related information. In FIG. 7 whenever the device has FPC-related information to transmit according to step  701 , it examines at step  702  whether DTX is on in the direction concerning transmission. If no, it inserts the piece of FPC-related information into a speech frame at step  703  and transmits the speech frame at step  704 . If DTX was on, the device inserts the piece of FPC-related information into a SID_UPDATE message at step  705  and transmits the message at step  706 . In FIG. 8 when the device is about to receive FPC-related information it examines according to step  801 , whether DTX is on in the direction concerning reception. If no, it receives a speech frame at step  802  and extract the piece of FPC-related information from the speech frame at step  803 . If DTX was on, the device receives a SID_UPDATE message at step  804  and extract the piece of FPC-related information from the SID_UPDATE message at step  805 .  
         [0034]    The hardware components required to implement the method according to the invention in a mobile station or a network element in a radio access network are basically similar to known hardware elements, with the exception that a control block that controls the placing of pieces of FPC-related information and the possibly associated changes in modulation and channel coding arrangements must be programmes to execute the methods described above. Such programming is as such believed to be within the capabilities of a person skilled in the art.  
         [0035]    The exemplary embodiments of the invention presented in this patent application are not to be interpreted to pose limitations to the applicability of the appended claims. The verb “to comprise” is used in this patent application as an open limitation that does not exclude the existence of also unrecited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated.

Technology Category: 5