Abstract:
Method and system for selecting the most suitable logic channel for transmitting packet data in a third generation cellular communications system enables a radio network controller ( 102 ) to set bit rate, spread factor and frames required from information supplied by user equipment ( 104 ) and the node B&#39;s ( 110 ) comprising the system. Such information comprises queue size, reported by the user equipments, and noise rise measurements due to user equipment activity, reported by the node B&#39;s. The invention advantageously allows a logic channel to be chosen based on the prevailing system state conditions. Hence performance of the system is optimised.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to transmission procedures in cellular communications systems. More particularly, this invention relates to the selection of procedures for the transmission of data packets in third generation cellular communications systems.  
         BACKGROUND OF THE INVENTION  
         [0002]    Wireless communications systems typically comprise a number of radios, which may be linked in a variety of ways. These ‘radios’ may be mobile phones. They may alternatively be mobile or portable radios, usually referred to as ‘PMR’ radios. The term mobile station (MS) will be used henceforth for mobile telephones and portable- or mobile radios.  
           [0003]    The mobile stations may communicate through base stations of the system. Each base station typically serves a cell of the wireless communications system. The base stations offer interconnection either to the fixed line telephone system (‘POTS’), or to other mobile stations in the system. Mobiles that communicate through base stations may or may not be in the same cell of the network. Alternatively, mobile. stations may communicate directly with one another, in ‘direct mode’ communication.  
           [0004]    In third generation partnership project (3GPP) wideband code division multiple access (WCDMA) systems and other such third generation (3G) systems, there are various methods which may be utilised for the transmission of packet data for both uplink and downlink. The communication between a mobile subscriber or user equipment (UE) and a network is termed uplink and between the network and the UE is termed downlink. These may be found in the latest  3 GPP specification.  
           [0005]    Currently, three kinds of transport/logical channel are provided for uplink packet transmission. These channels enable the transmission of packets from the UE to the network. The first channel is the random access channel (RACH), the second is the common packet channel (CPCH) or enhanced access channel (for CDMA 2000) and the third is the dedicated channel (DCH).  
           [0006]    Similarly, there are currently two kinds of transport logic channel provided for downlink packet transmission. These are the forward access channel (FACH) and the downlink shared channel (DSCH). The latter of these two is associated with the dedicated channel (DCH) for downlink.  
           [0007]    At the present time, a network or system has no knowledge of which procedure should be invoked by the Radio Network Controller (RNC) for an uplink or downlink packet data transfer. As such, it is not possible for the system to utilise the most suitable channel or procedure without being instructed which channel is the most suitable. There is thus a problem in that the system is unable to optimise its performance. Additionally, there is no provision in the 3GPP specifications which provides for a procedure enabling selection of an appropriate packet data transfer procedure.  
           [0008]    The present invention addresses one or more of the above disadvantages.  
         SUMMARY OF THE INVENTION  
         [0009]    According to a first aspect of the invention, there is provided a method of selecting a transmission procedure for transmitting queued data packets in a cellular communications system, characterised by the steps of; a user equipment (UE) transmitting a measurement report message to a radio network controller (RNC);  
           [0010]    a node B computing noise rise and reporting it to the RNC;  
           [0011]    the RNC computing a bit rate, a corresponding spread factor (SF) and a number of frames required to transmit the queued packets; and  
           [0012]    the RNC determining ( 204 ) the most appropriate channel to transmit upon.  
           [0013]    According to a second aspect of the invention there is provided an apparatus for selecting a transmission procedure for transmitting queued data packets in a cellular communications system the apparatus including; a node B, a radio network controller and a user equipment for transmitting a measurement report to the radio network controller (RNC) and characterised in that the node B is adapted to compute a noise rise and report it to the RNC and the RNC is adapted to compute a bit rate, a corresponding spread factor and a number of frames required to transmit the queued data packets and to determine the most appropriate channel to transmit on.  
           [0014]    If a uni-directional transmission on uplink is required, each mobile subscriber or user equipment requiring uplink sends a measurement report message relating to packet queue size, associated quality of service requirements, pilot strength and number of fingers locked.  
           [0015]    If a unidirectional transmission on downlink is required, the BTS [Node B] from which the downlink transmission is to originate computes the size of a packet data queue and then measures an amount of unused linear power amplifier (LPA) capacity available to it.  
           [0016]    Similarly, if a bidirectional transmission is required, a dedicated channel (DCH) may be used on uplink and a dedicated shared channel (DSCH) in association with the dedicated downlink channel (DCH) may be used on downlink irrespective of the size of the queue of packet data awaiting transmission.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    Embodiments of the present invention will now be described, by way of example only, with reference to the drawings of which:  
         [0018]    [0018]FIG. 1 depicts the interaction between a 3G cellular communications network and its users;  
         [0019]    [0019]FIG. 2 shows a flow diagram illustrating the selection of transmission procedure for a uni-directional packet data transfer on uplink in accordance with the present invention;  
         [0020]    [0020]FIG. 3 shows a flow diagram illustrating the selection of transmission procedure for a uni-directional packet data transfer on downlink in accordance with the present invention;  
         [0021]    [0021]FIG. 4 illustrates the general scheme of a wireless communications system  10  operating in accordance with the present invention; and  
         [0022]    [0022]FIG. 5 illustrates a mobile station (MS) for use in the system of Figure 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    As may be seen in FIG. 1, in a third generation cellular communications system, a radio network controller (RNC)  102  communicates with a number (I to k) of BTS&#39;s [or Node B&#39;s] which in turn communicate with a number (1 to n) of users  104 , 106 , 108  known as user equipment (UE). The user equipment may be a mobile telephone, laptop computer, paging device, etc. Communication takes place through a source node B  110 . Each source node B is a component of the network and is in communication with the RNC. These elements equate to the base station controller-(BSC), mobile station or subscriber (MS) and base transceiver station (BTS) of a global mobile communications system (GSM) or general packet radio system (GPRS).  
         [0024]    The method of selecting an appropriate transmission procedure depends upon the type of transmission required. The available types of transmission may be expressed as i) uni-directional packet data transfer on uplink, ii) uni-directional packet data transfer on downlink, and iii) bi-directional packet data transfer on uplink and downlink. The RNC is aware of the type of transmission to be carried out because it is either initiating transmission, or is involved in the allocation of resource for a requested uplink. As such, the selection of transmission procedure is carried out in accordance with the type of transmission to be made. The selection for each type of transmission is described in detail below.  
         [0025]    The choice of logical channel to be utilised in packet data transfer, whilst dependent upon the type of transmission to be made (as detailed above), is primarily dependent upon a number of factors. These factors include the queue size at the UE or at the RNC for a particular UE, i.e. the number of data packets awaiting transmission, the quality of service (QoS) requirements associated with the queued data packets, the number of voice and data users currently using the system, the location of those users, the current level of interference being experienced and the LPA capacity, etc.  
         [0026]    The choice of logical channel for unidirectional packet data transfer on uplink is detailed with regard to FIG. 2. Function box  202  shows the step of a UE sending a measurement report message to an RNC via a source node B. The measurement report message comprises queue size information, QoS requirements of the packets accumulated at the UE the number of locked fingers and pilot strength measurement messages, etc. This step is carried out by each UE currently operating within the system which requires uplink. Function box  204  details the step of each node B, which is handling within its area of operation a UE requiring uplink, computing the noise rise (increase in noise) which it experiences due to UE activity and reporting this value to the RNC. As stated previously, the node B in a 3G system is equivalent to the BTS in a GSM or GPRS system. As such, each node B is responsible for the UEs within its&#39; specified area (the area of the cell within which it operates).  
         [0027]    When all the above information has been received, the RNC computes the information/channel bit rate, the SF and the number of data frames which will be required in order to transmit the queued data packets at the computed rate. These values are calculated based upon the queue size (function box  206 ) and other system information such as noise rise, etc. Data is transmitted using physical channels at an information bit rate computed at the RNC for a predetermined number of frames to the destination device. Each frame has a specific duration and comprises a number of time slots which may be utilised for transmission by the UE or node B in uplink and downlink.  
         [0028]    Function box  208  shows an example step of the RNC determining which of the three logical channels suitable for use in uplink should be utilised. Such determination is carried out in accordance with the following sequential conditions:  
         [0029]    Condition 1:  
                                                       IF   number of   &lt; T 1  AND   Channel   &lt; R 1  USE   Random Access           frames       bit rate       Channel           required to               (RACH)           transmit           packets                  
 
         [0030]    wherein T 1 . and R 1 . are thresholds, the values of which are implementation dependent and are set by the system operator in the RNC.  
         [0031]    Condition 2:  
                                                       IF T 1     &lt;   number of   &lt; T 2  AND R 1     &lt; channel   &lt; R 2                 frames       bit rate               required to                   transmit                   packets           AND   Noise   &lt; I 1  AND   Number of   &lt; V 1  USE   Common           rise at       voice users       Packet           target               Channel           node B               (CPCH) or                           Enhanced                           Access                           Channel                           (EACH)                  
 
         [0032]    again, T 1 , T 2 . R 1 , R 2 . I 1  and V 1  are thresholds, the values of which are implementation dependent and are system operator defined. Additionally, T 2 &gt;T 1  and R 2 &gt;R 1 .  
         [0033]    Condition 3:  
                                               IF   neither of conditions 1 or 2 are   USE   Dedicated Channel (DCH)           met                  
 
         [0034]    The above conditions show a typical way of determining which logical channel is to be used for transferring data packets on uplink. Thresholds therein are set to values which ensure that RACH is used for short messages or transmissions (1 or 2 frames for example), CPCH or EACH is used for medium length messages or transmissions (3 to 10 frames for example) and DCH is used for long messages or transmissions (&gt;10 frames for example).  
         [0035]    The choice of logical channel for uni-directional packet data transfer on downlink is illustrated in FIG. 3. As may be seen, for downlink, the packets to be transmitted queue up at the RNC for the particular user. The Node B computes the queue size and measures the amount of unused linear power amplifier (LPA) capacity, which it then forwards to the RNC. The LPA is a hardware component of the system which resides within node B.  
         [0036]    Function box  304  depicts the step of the RNC utilising the provided information (in the form of queue size) to compute the channel bit rate and the number of frames required in order to transmit the queuing data packets. This information is then used in the following condition to determine which of the two logic channels available for downlink should be used (function box  306 ):  
                                               IF   number of   &lt; T 3  AND   channel  &lt; R 3             frames       bit rate           required to               transmit               packets           USE   Forward   OTHERWISE USE   Dedicated Shared Channel           Access       (DSCH) in association with           Channel       Decicated Channel (DCH)           (FACH)                  
 
         [0037]    once again, T 3  and R 3  are implementation dependent thresholds, the values of which are set by the system operator.  
         [0038]    The above condition ensures that FACH is used for shorter duration transmissions (1 to 2 frames for example) and that DSCH (in association with downlink DCH) is used for longer duration transmissions (greater than 2 frames for example).  
         [0039]    The final type of transmission that may be utilised is bi-directional packet data transfer on uplink and downlink. When such a transmission is to be initiated, no determination of transmission procedure to be used needs to be carried out. In this instance, DCH should always be used on uplink, and DSCH associated with a DCH should always be used on downlink, utilising a rapid initialisation procedure for packet data transfer, regardless of queue size. Rapid initialisation procedure is a procedure which involves the termination of the dedicated channel when no data requires transmission, and its associated rapid restart when data next requires transmission. Similarly, this allows for transmission of packets in bursts.  
         [0040]    The above methodology has the advantage of ensuring that the most appropriate and suitable logic channel is utilised for the transmission of data packets whether on uplink or downlink, and whether the transmission is to be unidirectional or bidirectional. The logic channel is generally chosen in view of the prevailing system state and conditions, in order to refine the choice and optimise the system performance.  
         [0041]    In addition to the method described above, there is provided a system comprising the means to carry out that method, thereby achieving the advantages inherent therein.  
         [0042]    [0042]FIG. 4 illustrates the general scheme of one example of a wireless communications system  10  in accordance with the present invention. Mobile stations  2 ,  4  and  6  of FIG. 4 can communicate with a base station  8 . Mobile stations  2 ,  4  and  6  could be mobile telephones. Alternatively, they could be PMR radios, i.e. portable radios or mobile radios mounted in vehicles.  
         [0043]    Each of the mobile stations shown in FIG. 4 can communicate through base station  8  with one or more other mobile stations. If mobile stations  2 ,  4  and  6  are capable of direct mode operation, then they may communicate directly with one another or with other mobile stations, without the communication link passing through base station  8 .  
         [0044]    [0044]FIG. 5 illustrates a mobile station (MS) operating in accordance with the present invention. The mobile station (MS) of FIG. 5 is a radio communication device, and may be either a portable-or a mobile radio, or a mobile telephone.  
         [0045]    The mobile station  2  of FIG. 5 can transmit speech from a user of the mobile station. The mobile station comprises a microphone  34  which provides a signal for transmission by the mobile station. The signal from the microphone is transmitted by transmission circuit  22 . Transmission circuit  22  transmits via switch  24  and antenna  26 .  
         [0046]    Mobile station  2  also has a controller  20  and a read only memory (ROM)  32 . Controller  20  may be a microprocessor.  
         [0047]    ROM  32  is a permanent memory, and may be a non-volatile Electrically Erasable Programmable Read Only Memory (EEPROM). ROM  32  is connected to controller  20  via line  30 .  
         [0048]    The mobile station  2  of FIG. 5 also comprises a display  42  and keypad  44 , which serve as part of the user interface circuitry of the mobile station. At least the keypad  44  portion of the user interface circuitry is activatable by the user. Voice activation of the mobile station may also be employed. Similarly, other means of interaction with a user may be used, such as for example a touch sensitive screen.  
         [0049]    Signals received by the mobile station are routed by the switch to receiving circuitry  28 . From there, the received signals are routed to controller  20  and audio processing circuitry  38 . A loudspeaker  40  is connected to audio circuit  38 . Loudspeaker  40  forms a further part of the user interface.  
         [0050]    A data terminal  36  may be provided. Terminal  36  would provide a signal comprising data for transmission by transmitter circuit  22 , switch  24  and antenna  26 . Data received by receiving circuitry  28  may also be provided to terminal  36 . The connection to enable this has been omitted from FIG. 5 for clarity of illustration.  
         [0051]    It will be appreciated that although this method has been described with reference to wideband code division multiple access (WCDMA) systems, it applies equally to other third generation cellular communications systems, including universal mobile telecommunications systems (U MTS).  
         [0052]    It will of course be understood that the present invention has been described by way of example only, and that modifications of detail can be made within the scope of the appended claims.