Patent Abstract:
What is provided is a method for communicating with a cellular network. The method is performed by a mobile computing device that comprises a transmitter and a receiver. One or more communication channels are monitored for one or more data packets that are transmitted by a base station of the cellular network during a transmission period. The transmission period can include one or more time slots. The mobile computing device determines whether one or more data packets have been received during a first time slot of the transmission period. In response to determining that no data packet has been received during the first time slot, the mobile computing device switches to an idle state until the transmission period ends.

Full Description:
CLAIM FOR PRIORITY 
       [0001]    This application is a national stage application of PCT/EP2007/054352, filed May 4, 2007, which claims the benefit of priority to German Application No. 10 2006 021 100.6, filed May 5, 2006, the contents of which hereby incorporated by reference. 
     
    
     TECHNICAL FIELD OF THE INVENTION 
       [0002]    The invention relates to a method for transmitting data in a transmission interval using a plurality of time slots and a plurality of transmission channels to a receiver of a radio network comprising a transmitter and at least one additional receiver, and to a radio network and a receiver set up for carrying out the method. 
       BACKGROUND OF THE INVENTION 
       [0003]    Methods for transmitting data in a radio network comprising a transmitter and a multiplicity of receivers are well known. For example, digital mobile telephone radio networks use Frequency Division Multiplex Access (FDMA) methods, Time Division Multiplex Access (TDMA) methods and Code Division Multiplex Access (CDMA) methods for transmitting data to a multiplicity of receivers of a radio cell via a common air interface. 
         [0004]    Other transmission methods provide for multiplexing both in the time and in the frequency domains, for example data transmissions according to the Enhanced Data Rates for GSM Evolution (EDGE) standard or by means of the so-called Orthogonal Frequency Division Multiplexing (OFDM). In order to achieve a data transmission rate as high as possible with OFDM systems and an efficient volume with the available bandwidth, the transmission characteristics of individual channels orthogonal relative to each other between a base station and a multiplicity of mobile stations are taken into account and the data transmission is continuously adapted to these. In this way, only those channels on which good receiving properties exist are used for each receiver. This principle is also known under the term “Multi User Diversity” (MUD). 
         [0005]    The disadvantages of the known methods are that the scheduling of the use of the available transmission channels is relatively complex and receivers continuously have to monitor a multiplicity of transmission channels for data directed to them, which results in a high energy requirement on the part of the receiver. 
       SUMMARY OF THE INVENTION 
       [0006]    The invention provides a method for transmitting data in a radio network, which is flexible and allows an efficient use of the resources available. Further, a radio network and a receiver will be described which are suitable for carrying out such a method. 
         [0007]    According to one embodiment of the invention, there is a method including: 
         [0008]    transmitting at least one data packet having an embedded identifier on at least one transmission channel in a time slot of the transmission interval by the transmitter, 
         [0009]    monitoring the at least one transmission channel by means of the receiver for data packets transmitted in the time slot, the data packets having embedded identifiers that are assigned to the receiver, and 
         [0010]    switching the receiver to an idle state until the end of the transmission interval, if the receiver has received no data packet with an embedded identifier assigned to the receiver during the time slot. 
         [0011]    By monitoring at least one transmission channel in the time slot for any data packets directed to a receiver, the receivers which have not received any data in the time slot may be switched to an idle state for any further time slots of the transmission interval. Further, so-called in-band signalling is made possible by embedding an identifier assigned to the receiver, so that no dedicated control channel needs to be used. 
         [0012]    In an another embodiment of the invention, the method steps are repeated for each subsequent time slot of the transmission interval for as long as the receiver has received in a previous time slot a data packet having embedded therein identifiers assigned to the receiver. In this way, the receiver may be switched to an idle state, as soon as no further data transmissions are carried out to it. 
         [0013]    In a further embodiment of the invention, channel properties of the at least one transmission channel are determined in a measuring phase during an additional step. By determining channel properties, a data transmission to the receiver of the radio network may be scheduled with due consideration of the transmission characteristics or may be adapted to these. 
         [0014]    In a further embodiment of the invention, predetermined requirements with regard to data rates, real time conditions or connection qualities are taken into account during the determination of a transmission schedule for the transmission interval, so that connection-specific quality requirements may be met. 
     
    
     
       BRIEF DESCRIPTION OF THE INVENTION 
         [0015]    Further embodiments of the invention are given in the sub-claims. The invention will now be explained in more detail below by means of an embodiment example with reference to the drawings, wherein: 
           [0016]      FIG. 1  shows a radio network according to an embodiment of the invention. 
           [0017]      FIG. 2  shows a schematic illustration of a transmission schedule. 
           [0018]      FIG. 3  shows a flow chart of a method for transmitting data. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]      FIG. 1  shows a radio network  100  including a radio cell  101 , to which a core network  102  is connected. The radio cell  101  includes a base station  103  and five mobile stations  104 A to  104 E. Each of the mobile stations  104  has a unique identifier  105 A to  105 E. 
         [0020]    The base station  103  includes a connection unit  106 , a transmission scheduler  107  and a transmission and receiving antenna  110 . By means of the connection unit  106 , data connections between the core network  102  and the mobile stations  104  are established and any data packets associated with these connections, if any, are buffered. 
         [0021]    On the basis of the available connection data, such as a required data rate of an already established connection and the amount of data buffered in the connection unit  106  for each of the mobile stations  104 , the transmission scheduler  107  generates a transmission schedule for the transmission of data from the connection unit  106  to one or a group of mobile stations  104 . The transmission scheduler  107  may be a hardware component or a computer program implemented on a processor of the base station  103  or on a computer connected therewith. A combination of hardware and software components is also possible. 
         [0022]    When generating the transmission schedule, the transmission scheduler  107  will also take into account the respective channel quality for each of the available transmission channels in each scheduled time slot of the transmission interval. Any information with regard to this will be taken from statistical data, in particular from quality information, bit error rates or signal-to-noise ratios sent back from the mobile stations  104 . 
         [0023]    Each of the mobile stations  104  has a receiving part  108  and a transmission part  109 . Both of these are connected to a combined transmission and receiving antenna  110 . The receiving part  108  is set up to monitor a multiplicity of channels of the radio cell  101 , in order to detect and filter out any data packets with the unique identifier  105  of the respective mobile station  104 . In this connection, the unique identifier  105  or a key independent thereof may also be used for decoding any data transmitted via the radio network  100  in an encoded form, so that each mobile station  104  can decode only data packets directed to it. 
         [0024]    In the embodiment example, the radio network  100  is a so-called OFDM radio network. For example, the base station  103  and the mobile stations  104  are a base station of a mobile telephone radio cell and mobile phones within the cell. They may, of course, also be other transmitters and receivers of a radio network  100 , for example devices in a so-called wireless LAN (WLAN) data network. Characteristic of each of these radio networks  100  is that a multiplicity of transmission channels and time slots is available, so that the data transmission may be multiplexed both in the time domain and in the frequency domain, which means that both different transmission channels and different time slots may be assigned to individual mobile stations  104 . 
         [0025]      FIG. 2  shows an example of a transmission schedule  200  for a transmission interval  201 . The transmission interval  201  is subdivided into twenty time slots  202  also referred to as “frames”. Odd numbered time slots  202  are used for data transmissions from the base station  103  to the mobile stations  104  and are designated as  202 P and  202 A to  202 I. Even numbered time slots  202  are used for data transmissions from the mobile stations  104  back to the base station  103  and are shown shaded in  FIG. 2 . 
         [0026]    In the embodiment example, the transmission interval  201  is additionally subdivided into an optional measuring phase  205  and a data transmission phase  206 . The measuring phase  205  comprises a time slot  202 P in the downlink direction and a further time slot  202  in the uplink direction and is used for determining channel properties. The data transmission phase  206  comprises the remaining 18 time slots  202  and is used for transmitting payload data. 
         [0027]    In this connection, the following general conditions apply for the data transmission phase  206 :
       a receiver, for example a mobile station  104 , which has not received any data from a transmitter, for example the base station  103 , within the current time slot  202 , will not receive any data in any of the subsequent time slots  202  either and may therefore be switched to an idle state for the duration of these;   a receiver, in which the data reception is terminated during the current time slot  202 , will not be considered in any of the subsequent time slots  202  and can therefore also be switched to an idle state for the duration of the transmission interval  201 ;   in each subsequent time slot  202 , more or less transmission channels  203  may be assigned to each receiver.       
 
         [0031]    In the description following below, only the data transmission from the base station  103  to the mobile stations  104  will be described in more detail. Of course, the method according to the present invention may also be used for the return transmission from the mobile stations  104  to the base station  103 . 
         [0032]    Each time slot  202  is additionally subdivided into a multiplicity of transmission channels  203 . In the embodiment example, 20 transmission channels  203  are available for data transmission. The transmission channels  203  may, for example, be different frequency ranges of a transmission band. 
         [0033]    During the measuring phase  205 , information will be transmitted to all of the mobile stations  104 A to  104 E in the illustrated transmission schedule  200  corresponding to the first time slot  202 P. For example, a predetermined measuring signal may be transmitted from the base station  103  to the mobile stations  104 . Alternatively, also control information or other data may be transmitted to the mobile stations  104 A to  104 E. 
         [0034]    During this measuring phase, all of the mobile stations  104 A to  104 E which are included in a radio cell  101  and are thus assigned to the base station  103 , monitor the transmission channels  203  for information, in particular the measuring signal. For the determination of channel properties, for example a reception power of the received measuring signal, a signal-to-noise ratio or a specific bit error rate may be used. In the subsequent time slot  202 , these or any values derived there from, which allow the channel quality to be determined, will be transmitted from the mobile stations  104 A to  104 E back to the base station  103 . 
         [0035]    As an alternative to a separate measuring phase  205 , also other means may be used for determining channel properties. For example, any bit error rates determined in a previous transmission interval  201  or data transmission phase  205  may be used for evaluating the channel quality and thus for scheduling the data transmission in the current transmission interval  201 . In order to allow a particularly good evaluation to be made, the measuring phase  205  should be timed so that it is as close as possible to the data transmission phase  206 . 
         [0036]    The transmission scheduler  107  of the base station  103  generates the transmission schedule  200  for the data transmission phase  206  shown in  FIG. 2  on the basis of the determined channel properties. Accordingly, the three mobile stations  104 A to  104 C are served by the base station  103 . Any possible further receivers, for example, any further mobile stations  104 D to  104 E, are not considered during the data transmission phase  206  for which the transmission schedule  200  was generated. 
         [0037]    The reason for this may be, on the one hand, that not enough transmission capacity for serving all of the mobile stations  104  may be available, that no data for transmission to a mobile station  104 D is available in the connection unit  106  or that error-free communication is not possible due to interference between the base station  103  and a mobile station  104 E. 
         [0038]    In all of these cases, the mobile stations  104 D and  104 E or at least parts of their receiving parts  108 , particularly those used for decoding and further processing of received data packets  204 , may be switched off or switched to an idle state in order to reduce power consumption. In this way, increased run times of the mobile stations  104 D and  104 E with the same battery capacity may be made possible. As an alternative to saving energy, the idle state may also be used to accelerate other functions of the mobile stations  104 D or  104 E, for example by providing more processor time for other tasks. 
         [0039]    In spite of these limitations and simplifications on the part of the mobile stations  104 , the transmission schedule  200  for the data transmission phase  206  from the base station  103  and its transmission scheduler  107  may be implemented in a flexible manner, so that, for example, different data transmission rates may be made possible within the data transmission phase  206 , as is illustrated in  FIG. 2 . 
         [0040]    In the illustrated example, the first mobile station  104 A will initially receive data on eight transmission channels  203  at the same time. This data transmission over a relatively broad band, however, will be continued only for the duration of four time slots  202 A to  202 D. After that, no further data packets  204  will be transmitted to the mobile station  104 A. During the time slots  202 A to  202 D, data will respectively be transmitted to the mobile station  104 B or to the mobile station  104 C on five or seven transmission channels  203  at the same time. 
         [0041]    From time slot  202 E onwards, data will be transmitted exclusively to the mobile stations  104 B and  104 C, so that for the data transmission from this time slot  202 E onwards, eight or twelve transmission channels  203  will respectively be available. Since the mobile station  104 A does not receive any further data from the base station  103  during the transmission interval  202 E, it, too, may be switched to an idle state until the end of the transmission interval  201 . 
         [0042]    In this way, data transmission rates between the base station  103  and the various mobile stations  104 A,  104 B and  104 C may be adapted to current requirements and channel qualities. If, for example, a data transmission between the base station  103  and the mobile station  104 A is possible only in the first time slots  202 A to  202 D, because after that data transmission is disturbed by interference, data may be transmitted initially in a relatively broad band, so that during the subsequent radio transmission pause, the mobile station  104 A will still have available any buffered data for further processing. Conversely, data transmissions to the mobile stations  104 B and  104 C will initially be limited, in order to enable a broadband data transmission to the mobile station  104 A to be carried out to, and will thereafter be expanded, in order to transmit, if applicable, any data buffered in the connection unit  106  in the meantime to the mobile stations  104 B and  104 C during the time slots  202 E to  202 I. 
         [0043]      FIG. 3  shows a flow chart of a method  300  for transmitting data from a transmitter, for example the base station  103 , to a receiver, for example the mobile station  104 A, of a radio network  100 . 
         [0044]    To start with, the channel properties of the radio network  101  are determined in an optional step  301 . These may be determined, for example, during a measuring phase  205  by transmitting a measuring signal to all mobile stations  204  of the radio network and the subsequent return transmission of any reception powers measured by the mobile stations  104 . Alternatively, however, the channel properties may be evaluated on the basis of the error rates of previous transmission intervals  201 . 
         [0045]    In a further optional step  302 , the base station  103  generates a transmission schedule  200  for the current transmission interval  201  or its data transmission phase  206 . Therein, in particular specific requirements of the mobile stations  104  with regard to required data rates, real time conditions or connection qualities may be taken into account. 
         [0046]    However, as an alternative, scheduling for the complete transmission interval  201  may be dispensed with. For example, it is also possible to schedule in advance only for a single or a few time slots  202  of the transmission interval  201 , for example, depending on any data buffered in the connection unit  106 . 
         [0047]    In a further step  303 , any data packets  204  will be transmitted from the base station  103  to the mobile stations  104 . For example, any payload data made available by a connection unit  106  may be transmitted to the mobile stations  104 . To this end, an identifier, for example the unique identifier  105 , is embedded into each of the data packets  204 , so that a receiver  104  assigned to the identifier may detect any data packets  204  directed to it. In the embodiment example, according to the transmission schedule  200  illustrated in  FIG. 2 , data packets will be transmitted to the receivers  104 A to  104 C in the time slot  202 A. 
         [0048]    In a step  304 , all of the active mobile stations  104 A to  104 E of a radio cell  101  of the radio network  100  monitor at least one of the transmission channels  203  for any data packets  204  directed to them. This may be carried out, for example, by monitoring an identifier embedded in the data packets  204  and by comparing it with a unique identifier  105  of the mobile stations  104 . 
         [0049]    In a preferred embodiment, a mobile station  104  is set up to monitor all of the transmission channels  203  at the same time. However, due to technical limitations of the receiving part  108  and interferences on individual transmission channels  203  it is also possible to have only individual transmission channels  203  monitored by a mobile station  104 . 
         [0050]    In a further step  305 , each individual mobile station  104 A to  104 E checks whether any data packets  204  have been transmitted to it from the base station  103  during the previous time slot  202 . In the embodiment example, in time slot  202 A this applies to the mobile stations  104 A,  104 B and  104 C, not, however, to the stations  104 D and  104 E. 
         [0051]    If in step  305  it is determined that at least one data packet  204  was transmitted to the mobile stations  104 A, the data contained therein will be processed in an optional step  306 . For example, any payload data contained therein may be decoded or reproduced. 
         [0052]    In a further step  307 , it will then be checked whether the current time slot  202 A was the last time slot of the current transmission interval  201 . If this is not the case, the method will be continued in step  303  with the next time slot  202 B. Otherwise, the method will restart in step  301  with the determination of channel properties. 
         [0053]    As an alternative it is also possible to determine the channel properties anew after each time slot  202 . To this end, for example, the time slots  202  shown shaded in  FIG. 2  may be used, so that the transmission schedule  200  may be continuously adapted to changing transmission characteristics of the radio cell  101 . 
         [0054]    If, however, it is determined in step  305  that no data packets were transmitted to the mobile station  104 A, as this is the case, for example, in the fifth time slot  202 E, an idle state will be activated for the mobile station  104 A in a step  308 . For example, a reception part  108  of the mobile station  104  may be deactivated. 
         [0055]    In step  309 , a delay loop checks whether the end of the transmission interval  201  has been reached. During this time, the receiver  104 A is in an idle state, so that its energy consumption is reduced. Alternatively, the mobile station  104 A may also preferably carry out other tasks during that time, such as an internal data processing, without paying any further attention to any transmitted data packets  204 . 
         [0056]    At the end of the transmission interval  201 , the idle state will be deactivated again in a step  310 . Thus, for example, the reception part  108  of the mobile station  104  will again be available in the subsequent measuring phase  205  or data transmission phase  206  of a subsequent transmission interval  201 .

Technology Classification (CPC): 8