Abstract:
The present invention relates to a method of communicating in a network, comprising a secondary station transmitting to a primary station a data packet comprising a report, the secondary station monitoring before transmission of the packet whether said packet includes an indication of the order of transmission in a sequence of transmitted packets, and adding an indication of the order of transmission in a sequence of transmitted packets.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method for communicating in a network comprising a primary station and at least one secondary station, and to such a secondary station. More specifically, this invention relates to a method for communicating in a mobile telecommunication network, like a GSM (Global System for Mobile communications) or a UMTS (Universal Mobile Telecommunications System) network. 
     This invention is, for example, relevant for UMTS and UMTS Long Term Evolution, but as well to hubs which route calls from multiple terminals to base stations. 
     BACKGROUND OF THE INVENTION 
     In a mobile telecommunication network like a UMTS system, a primary station, for instance a Node B (or Base Station or eNB) communicates with at least one secondary station, for instance a User Equipment (or Mobile Station), by means of a plurality of channels. In order to transmit data to the primary station, a secondary station needs to request a resource to the primary station, which is then allocated. This request of allocation can be made in several ways depending on the considered channel. 
     In an example, in order to request a resource, it is required to indicate the amount of data to be transmitted, i.e. the data in the buffer of the secondary station. To this end, the secondary station transmits to the primary station a buffer status report indicative of the amount of data in the secondary station buffer. Thus, the primary station allocates a resource corresponding to both the capability of the network and the amount of data to be transmitted. This permits the allocation of resource to be adjusted. 
     In order to transmit this Report, the secondary station uses for instance an ARQ protocol, or an HARQ protocol. It means that the secondary station may retransmit the message until it receives a positive acknowledgement of reception from the primary station. In such a case, it is possible that a first report is finally correctly received long after having been transmitted, and in some cases even after a second report updating the first report. In such a case, the primary station may discard the second report believing that the first report is representative of the current status. This can lead to a waste of resources (if the second report indicated that no data was in the buffer), or in delays (if the first report indicated that no data was in the buffer). 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to propose a method enabling this problem to be alleviated. 
     It is still another object of the invention to propose a method enabling the reports in the transmission sequence to be reordered. 
     It is still another object of the invention to propose a method permitting the risk of confusion at the primary station to be reduced. 
     To this end, a method of communicating in a network is proposed, comprising a secondary station transmitting to a primary station a data packet comprising a report, the secondary station monitoring before transmission of the packet whether said packet includes an indication of the order of transmission in a sequence of transmitted packets, and adding an indication of the order of transmission in a sequence of transmitted packets. 
     In accordance with a second aspect of the invention, a secondary station is proposed comprising a transmitter for transmitting to a primary station a data packet comprising a buffer status report representative of the amount of data in a buffer of the secondary station, the secondary station further comprising a controller for monitoring before transmission of the packet whether said packet includes an indication of the order of transmission in a sequence of transmitted packets, and said controller being arranged for adding an indication of the order of transmission in a sequence of transmitted packets. 
     In accordance with a third aspect of the invention, a system of communication is proposed comprising a primary station communicating with a secondary station, said secondary station comprising a transmitter for transmitting to the primary station a data packet comprising a buffer status report representative of the amount of data in a buffer of the secondary station, the secondary station further comprising a controller for monitoring before transmission of the packet whether said packet includes an indication of the order of transmission in a sequence of transmitted packets, and said controller being arranged for adding an indication of the order of transmission in a sequence of transmitted packets. 
     As a consequence, the primary station is able to reorder the reports to reduce the risk of confusion of the primary station. It means that the primary station is able to know whether a report is representative of a current state of the secondary station and should take it into account or a report is representative of past state of the secondary station which may for example have been superseded by a later indication and should be discarded. 
     These and other aspects of the invention will be apparent from and will be elucidated with reference to the embodiments described hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will now be described in more detail, by way of example, with reference to the accompanying drawings, wherein: 
         FIG. 1  is a block diagram of a system in which is implemented the invention. 
         FIG. 2  is a time chart illustrating the exchange of messages in accordance with a conventional technique. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention relates to a system of communication  300  as depicted on  FIG. 1 , comprising a primary station  100 , like a base station, and at least one secondary station  200  like a mobile station. 
     The radio system  300  may comprise a plurality of the primary stations  100  and/or a plurality of secondary stations  200 . The primary station  100  comprises a transmitter means  110  and a receiving means  120 . An output of the transmitter means  110  and an input of the receiving means  120  are coupled to an antenna  130  by a coupling means  140 , which may be for example a circulator or a changeover switch. Coupled to the transmitter means  110  and receiving means  120  is a control means  150 , which may be for example a processor. The secondary station  200  comprises a transmitter means  210  and a receiving means  220 . An output of the transmitter means  210  and an input of the receiving means  220  are coupled to an antenna  230  by a coupling means  240 , which may be for example a circulator or a changeover switch. Coupled to the transmitter means  210  and receiving means  220  is a control means  250 , which may be for example a processor. Transmission from the primary radio station  100  to the secondary station  200  takes place on a downlink channel  160  and transmission from the secondary radio station  200  to the first radio station  100  takes place on an uplink channel  260 . 
     From time to time, the secondary station  200  transmits on the uplink channel  260  an indication of the status of its buffer containing data to be transmitted. This Buffer Status Report can be of different types. A short Buffer Status Report (BSR) comprises the identity of a single group of logical channels, together with a 6-bit indicator of the amount of data corresponding to that group of logical channels currently residing in the secondary station&#39;s buffer awaiting transmission. A long BSR comprises 4 concatenated short BSRs, each corresponding to a different group of logical channels. 
     Many communication systems operate using a centralised scheduler which is responsible for allocating transmission resources to different nodes. A typical example is the uplink of the UMTS LTE, where the uplink transmissions from different UEs are scheduled in time and frequency by the eNB; the eNB transmits a “scheduling grant” message to a UE, indicating a particular time-frequency resource for the UE&#39;s transmission typically around 3 ms after the transmission of the grant message. The grant message also typically specifies the data rate and/or power to be used for the UE&#39;s transmission. 
     In order for the eNB to issue appropriate grants, it needs to have sufficient information about the amount, type of data and the urgency of it awaiting transmission in the buffer of each UE. This information can be used to inform the scheduler in the eNB of either the satisfaction level of individual UEs or UEs whose service might be close to being dropped. 
     In LTE, a number of different types of buffer status report (BSR) messages are therefore defined, which may be transmitted from a UE to the eNB when certain triggers occur. The state of the art in this respect is defined by the current version of 3 GPP TS36.321 (as of June 2008), §5.4.5 incorporated for reference. 
     A short BSR comprises the identity of a single group of logical channels, together with a 6-bit indicator of the amount of data corresponding to that group of logical channels currently residing in the UE&#39;s buffer awaiting transmission. A long BSR comprises 4 concatenated short BSRs, each corresponding to a different group of logical channels. 
     This is currently defined in 36.321 (as of June 2008) §6.1.3.1 incorporated by reference. 
     As detailed in this paragraph, there are two main types of Buffer Status Reports (BSR) with different characteristics:
         Regular BSR which is triggered only if UL data arrives in the UE transmission buffer and the data belongs to a logical channel with higher priority than those for which data already existed in the UE transmission buffer.   Periodic BSR, which is triggered when the PERIODIC BSR TIMER expires.       

     If the UE has no UL resources allocated for new transmission for this TTI and if a Regular BSR has been triggered since the last transmission of a BSR a Scheduling Request (SR) shall be triggered. 
     The BSR mechanism has been designed so that only regular BSRs can trigger the sending of an SR if there is no UL resources available for the sending of the a regular BSR. When a periodic BSR is triggered and there is no UL resource allocated then the UE cannot send SR, as it is assumed that the network knows that the UE has data available and is deliberately not allocating any UL resources for the UE to use. 
     If the periodic BSR were allowed to send SR in the case of no UL resource available for the sending of the BSR then the system may become overloaded with UEs sending SR. Particularly if the UE has no PUCCH resources available, when an SR would require the sending of a RACH access. 
     Also, it is stated in 36.321 that an SR is considered pending and is repeated until UL-SCH resources are granted. 
     A problem with the BSR procedure defined above is that there is a possibility that the information that the network knows about the state of the buffers in the UE can be different from the actual state of the UE buffers. This can occur when BSRs are received in the eNB out of order. 
     If a network receives BSRs from a UE at different times there is no way for the eNB to determine which was the last BSR sent by the UE as an earlier BSR may just be being received late, for example due to HARQ retransmissions. This can lead to the problem that a BSR with zero may be received by the UE and then the network removes UL resource from the UE, even though the UE now has data to be sent in its buffer. The UE cannot send SR as the trigger for a regular BSR (new data with higher priority) is not met even if a periodic BSR is configured 
     An example of this is shown on  FIG. 2 . On this time chart, it can be seen that the buffer status report  1000 , which is sent before the buffer status report  1001 , is received only after, because of the number of retransmissions. This report may be a periodic report, which can indicate that no data is in the buffer status report. If the primary station receives the reports in the indicated order, it will wrongly believe that the current status is that no data is in the buffer of the secondary station. Because of that, it will remove the UL resource from UE, that should have been granted. 
     The main problem here is that an SR cannot be generated from a periodic BSR, because if an SR were generated from a periodic BSR then the UE would be constantly asking for UL resources when there may be none available. 
     In the case described above the UE UL data buffer is out of synchronisation with the network view of the buffer. The present invention provides a method for distinguishing the order in which the BSRs from the UE should be acted on, by means of information transmitted together with the BSR. 
     In the case where the BSR is included with data then there is already a sequence number present in the MAC packet arising from the RLC sequence number of the data segments in the MAC packet, and hence the said information comprises the RLC sequence number. This sequence number could be used to identify the timing of the included BSR, so that it is not acted on out of sequence. 
     If there is no data sent along with the BSR (as would occur for example when a zero BSR report is sent), then one possibility would be to generate an RLC packet with only the sequence number to accompany the BSR. One means for generating such a packet could be to generate a zero-payload RLC PDU, consisting of just (all or part of) the RLC header including the RLC sequence number. Alternatively an additional small-payload RLC PDU could be generated, containing data which would not otherwise have been transmitted, such as an extra report of a measurement of a system parameter which may be useful for the network. 
     Alternatively, the said information could comprise a sequence number generated by the MAC layer itself (i.e. the same protocol layer as processes the BSR, thus reducing cross-layer processing), for example derived from the last RLC sequence number sent. In some embodiments such a MAC-level sequence number could be generated regardless of whether there was other data to be sent along with the BSR, or alternatively only in cases when there was no data to be sent along with the BSR. 
     Some other possibilities would include the information being comprised of dedicated BSR sequence numbers or timestamps (absolute or relative) rather than sequence numbers. In cases where the information does not comprise the RLC sequence number, an association between the information and an RLC sequence number of a system frame number or a subframe number could be defined or signalled. 
     In a second embodiment, this invention could also be applied to other reports that a UE might generate, for example channel state information such as CQI (Channel Quality Information), PMI (Precoding Matrix Indication) or RI (Rank Indication). In general, these can be sent together with data, or separately. In the current LTE specification, channel state information is sent using physical layer signalling, but in principle it could be sent as MAC control elements. An applicable embodiment would be in a system like LTE-Advanced employing a relay between UE and eNodeB. Channel state information sent on the physical layer from the UE to the relay could be sent from the relay to the eNodeB using MAC control elements, along with BSR. This information would be used for scheduling by the eNodeB. 
     This invention may be implemented in mobile communication systems where communication devices utilize centralized scheduling, such as UMTS and LTE. 
     Moreover, this invention could as well be implemented for hubs which route connections from multiple terminals to base stations. Such devices would appear like a secondary station from the point of view of the network. 
     In the present specification and claims the word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. Further, the word “comprising” does not exclude the presence of other elements or steps than those listed. 
     The inclusion of reference signs in parentheses in the claims is intended to aid understanding and is not intended to be limiting. 
     From reading the present disclosure, other modifications will be apparent to persons skilled in the art. Such modifications may involve other features which are already known in the art of radio communication and the art of transmitter power control and which may be used instead of or in addition to features already described herein.