Abstract:
A transmitting unit for use in sending data in packets in timeslots within time frames, each packet being sent in a timeslot, the unit comprising means to reserve for uplink transmission in the next uplink time frame a number of timeslots (X), the number of timeslots (X) being determined dependent upon a value which is the number of timeslots (Y) used for uplink transmission in the previous uplink time frame plus the number of packets (Z) remaining for uplink transmission during the last time frame minus the number of time slots (Q) to be used in the present uplink time frame.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims priority of European Application No. 01310536.6 filed on Dec. 17, 2001. 
   FIELD OF THE INVENTION 
   The present invention relates to a transmitting unit for use in sending data in packets in timeslots within time frames and a method of data transmission involving bandwidth reservation, in particular reservation of timeslots. 
   BACKGROUND OF THE INVENTION 
   In known time division protocols, a number of time slots per time frame are allocated to a modem to be used for voice or video. The disadvantage is that there must be means to calculate the number of timeslots, and it might allocate too many, causing bandwidth to be wasted, or too few, causing delay in transmission of the packets. In those known systems on the uplink, a packet waits two time intervals for transmission, one interval being for a timeslot to be requested, the second being for allocation of uplink timeslots by the access point of the core network; the access point can be considered as a master modem controlling communications with slave modems. 
   SUMMARY OF THE INVENTION 
   The present invention provides a transmitting unit for use in sending data in packets in timeslots within time frames, each packet being sent in a timeslot, the unit comprising means to reserve for uplink transmission in the next uplink time frame a number of timeslots, the number of timeslots being determined as the number of timeslots used for uplink transmission in the previous uplink time frame plus the number of packets remaining for uplink transmission during the last time frame minus the number of time slots to be used in the present uplink time frame. 
   The present invention in its advantageously addresses the problem of delay in known time division wireless systems on the uplink. The present invention seeks when possible to effectively eliminate the above-mentioned first interval in which to request a timeslot, and is particularly suitable for voice and/or video data. 
   The present invention has advantages of simple implementation, and low processing power (CPU) and memory requirements. In many cases the delay in packet transmissions on the uplink is cut in half. 
   The present invention may be advantageously a modem. Advantageously the modem, within three or four time frames, tends to reserve only the same number of time slots as used in the last uplink time frame. The process is adaptive in that the modem “learns” the current bandwidth (number of time slots) and the result of this adaption is reduced packet delay. 
   Advantageously, the number of time slots (X) reserved is said value. 
   Advantageously, the number of time slots (X) reserved is the largest of the values determined in a plurality of uplink time frames up to the present uplink time frame and stored in a memory. 
   The present invention also provides a network comprising the transmitting unit, and a receiving unit operative to transmit to the transmitting unit information of time slots allocated in the next uplink frame and to receive the packets sent by the transmitting unit. 
   The present invention also provides a method of sending data in packets in timeslots within time frames, each packet being sent in a timeslot, the method comprising reserving for uplink transmission in the next uplink time frame a number of timeslots (X), the number of timeslots (X) being determined dependent upon a value which is the number of timeslots (Y) used for uplink transmission in the previous uplink time frame plus the number of packets (Z) remaining for uplink transmission during the last time frame minus the number of time slots (Q) to be used in the present uplink time frame. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     The present invention will be better understood from reading the following description of non-limiting embodiments, with reference to the attached drawings, wherein below: 
       FIG. 1  depicts an embodiment of the present invention. 
   

   It should be emphasized that the drawings of the instant application are not to scale but are merely schematic representations, and thus are not intended to portray the specific dimensions of the invention, which may be determined by skilled artisans through examination of the disclosure herein. 
   DETAILED DESCRIPTION 
   For voice traffic over external wireless data (XWD) systems, delay should be minimized. The inventors realized that, and that a voice call requires approximately constant bandwidth on both uplink and downlink, so it was found possible to use information of the number of timeslots used in the previous uplink timeframe when allocating slots for the next uplink timeframe. 
   System Structure 
   As shown in  FIG. 1 , the system consists of an access point  2  and a modem  4  for time division wireless communication to the access point  2 . The access point is a master modem through which transmissions from the modem  4  are routed, hence it is the access point to the rest of the telecommunications world (also known as the core network). The modem  4  includes a transmitter  6  and receiver  8 . The transmitter includes a memory  10  in which unsent packets are queued to be transmitted. The modem  2  includes a controller  12 , which controls which timeslots to be used for uplink transmission in each uplink time frame. The controller  12  is informed by the access point  2  which timeslots of each time frame are allocated to the modem  4  for uplink communication. The modem  4  can thus be considered as a slave to the access point  2  in this regard. 
   Let us assume that voice packets are sent in 10 millisecond timeslots in both directions, uplink and downlink, and consider one Wireless Modem (WM) data stream. It will be seen that there is a time frame for downlink followed by a time frame for uplink and so on, i.e. the uplink and downlink time frames alternate. The packets arrive from an Ethernet cable (not shown) and are transmitted by the modem  4  to the access point  2 . Two new packets arrive during each time frame. 
   Comparative Example 
   In each uplink timeframe, the modem  4  is allocated by the access point  2  the full bandwidth, i.e. all the time slots which it requested (reserved) for this timeframe in the previous uplink transmission. In situations where more timeslots are reserved than the number of packets to be transmitted, the extra timeslots are unused (i.e. the bandwidth is wasted) although in some embodiments the wireless modem can use it for other tasks if it has any. 
   The number of time slots M reserved in each (uplink) time frame is the number of packets N remaining for transmission from the previous time frame (before the packets of the current time frame arrive for transmission) minus the number P of packets that are being transmitted in the current time frame. 
   
     
       
             
             
             
             
             
             
             
             
           
         
             
               a) TABLE 1 
             
             
                 
             
             
                 
               No. of 
               No. of 
                 
                 
                 
               No. of 
               Time frames 
             
             
                 
               timeslots 
               packets 
                 
                 
                 
               Remaining 
               in which 
             
             
               Time 
               RESERVED 
               TRANSMITTED 
               Total 
               Total 
               No. of 
               packets of 
               transmitted 
             
             
               Frame 
               in this time 
               in this time 
               transmitted 
               arrived 
               Remaining 
               Previous 
               packets 
             
             
               Number 
               frame M 
               frame P 
               packets 
               packets 
               packets 
               time frame N 
               arrived 
             
             
                 
             
           
           
             
               1 
               0 
               0 
               0 
                2 
               2 
                 
                 
             
             
               2 
               Downlnk 
               downlnk 
               0 
                4 
               4 
               2 
             
             
               3 
               4 
               0 
               0 
                6 
               6 
               4 
             
             
               4 
               Downlnk 
               downlnk 
               0 
                8 
               8 
               6 
             
             
               5 
               4 
               4 
               4 
               10 
               6 
               8 
               1,2 
             
             
               6 
               Downlnk 
               downlnk 
               4 
               12 
               8 
               6 
             
             
               7 
               4 
               4 
               8 
               14 
               6 
               8 
               3,4 
             
             
               8 
               Downlnk 
               downlnk 
               8 
               16 
               8 
               6 
             
             
               9 
               4 
               4 
               12  
               18 
               6 
               8 
               5,6 
             
             
               10  
               Downlnk 
               downlnk 
               12  
               20 
               8 
               6 
             
             
               11  
               4 
               4 
               16  
               22 
               6 
               8 
               7,8 
             
             
                 
             
             
               Notes to Table 1: 
             
             
               (a) The packets of a time frame arrive after reservation is made so they are not counted in the number of timeslots (packets) reserved in that time frame. 
             
             
               (b) The number of packets reserved in a time frame is the Wireless Modem reservation from the access point 2. This is included in the downlink signalling included in each downlink packet (and known as the piggy). 
             
             
               (c) The remaining packets are the number of packets which are left in the to be transmitted queues at the end of the time frame. 
             
           
        
       
     
   
   It will be seen in Table 1 that there is a constant delay of 3 to 4 time frames. 
   The Advantageous Scheme 
   An advantageous scheme is to reserve for the next uplink time frame a number X of time slots which is the number Y used to transmit in the previous uplink time frame, plus the number of remaining packets Z of the previous downlink time frame, minus the number of timeslots used (packets sent) Q in the present uplink time frame. An example is shown in Table 2 below. 
   It will be seen in Table 2 that from the 7 th  time frame onwards there is a delay of only one or two time frames between a packet arriving and being transmitted. 
   In the advantageous scheme the pattern of delay between arrival and transmission is not initially constant but becomes constant over a period, which includes four to five uplink time frames. This could take about 30 milliseconds. Therefore in a further embodiment of the invention a history is kept of the number of time slots required per time frame longer than just than number used in the last uplink time frame. 
   In the modem according to said further embodiment, each voice packet arriving, which is acceptable to be transmitted in the next uplink time frame, is counted in a counter. When the modem gets bandwidth i.e. timeslots for uplink transmission in the current time frame, a record of the number of timeslots allocated per time frame is stored in an array holding the latest 8 values, and the counter rezeroed. In each time frame, a check is made whether a poll signal has been received from the access point  2  and if not received, in every even numbered (i.e. downlink) time frame the count is taken to be zero. This mechanism yields a history of the time slot allocations for time frames numbered n to 2n, where n is greater than or equal to 0 and is less than or equal to 8. The maximum number of time slots from the history is included in the reservation request sent to the access point  2 . 
   
     
       
             
             
             
             
             
             
             
             
             
           
             
             
             
             
             
             
             
             
             
           
         
             
               TABLE 2 
             
             
                 
             
             
                 
               No. of 
               No. of 
               No. of 
                 
                 
                 
               No. of 
               Time frames 
             
             
                 
               timeslots 
               packets 
               packets 
                 
                 
                 
               Remaining 
               in which 
             
             
               Time 
               RESERVED 
               TRANSMITTED 
               TRANSMITTED 
               Total 
               Total 
               No. of 
               packets in 
               transmit. 
             
             
               Frame 
               in this time 
               in this time 
               in PREVIOUS 
               transmitted 
               arrived 
               Remaining 
               previous 
               packets 
             
             
               No. 
               frame X 
               frame Q 
               time frame Y 
               packets 
               packets 
               packets 
               time frame Z 
               arrived 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               1 
               0 
               0 
               0 
               0 
               2 
               2 
               0 
                 
             
             
               2 
               Downlnk 
               Downlnk 
               downlnk 
               0 
               4 
               4 
               2 
             
             
               3 
               4 
               0 
               0 
               0 
               6 
               6 
               4 
             
             
               4 
               Downlnk 
               Downlnk 
               downlnk 
               0 
               8 
               8 
               6 
             
             
               5 
               4 
               4 
               0 
               4 
               10 
               6 
               8 
               1,2 
             
             
               6 
               Downlnk 
               Downlnk 
               downlnk 
               4 
               12 
               8 
               6 
             
             
               7 
               8 
               4 
               4 
               8 
               14 
               6 
               8 
               3,4 
             
             
               8 
               Downlnk 
               Downlnk 
               downlnk 
               8 
               16 
               8 
               6 
             
             
               9 
               4 
               8 
               4 
               16 
               18 
               2 
               8 
               5,6,7,8 
             
             
               10 
               Downlnk 
               Downlnk 
               downlnk 
               16 
               20 
               4 
               2 
             
             
               11 
               8 
               4 
               8 
               20 
               22 
               6 
               4 
                9,10 
             
             
               12 
               Downlnk 
               Downlnk 
               downknk 
               20 
               24 
               4 
               6 
             
             
               13 
               4 
               4 
               4 
               24 
               26 
               2 
               4 
               11,12 
             
             
               14 
               Downlnk 
               Downlnk 
               downlnk 
               24 
               28 
               4 
               2 
             
             
               15 
               4 
               4 
               4 
               28 
               30 
               2 
               4 
               13,14 
             
             
                 
             
           
        
       
     
   
   While the particular invention has been described with reference to illustrative embodiments, this description is not meant to be construed in a limiting sense. It is understood that although the present invention has been described, various modifications of the illustrative embodiments, as well as additional embodiments of the invention, will be apparent to one of ordinary skill in the art upon reference to this description without departing from the spirit of the invention, as recited in the claims appended hereto. Consequently, the method, system and portions thereof and of the described method and system may be implemented in different locations, such as network elements, the wireless unit, the base station, a base station controller, a mobile switching center and/or a radar system. Moreover, processing circuitry required to implement and use the described system may be implemented in application specific integrated circuits, software-driven processing circuitry, firmware, programmable logic devices, hardware, discrete components or arrangements of the above components as would be understood by one of ordinary skill in the art with the benefit of this disclosure. Those skilled in the art will readily recognize that these and various other modifications, arrangements and methods can be made to the present invention without strictly following the exemplary applications illustrated and described herein and without departing from the spirit and scope of the present invention It is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention.