The present invention discloses a method and a device for improved allocation of uplink resources.
Some modern cellular access technologies such as, for example, Mobile WiMAX, offer high data rates for single users. Data rates over 20 Mbits/s are possible in the downlink direction, i.e. to the user from the so called Base Station. A system such as for example the WiMAX system will comprise a number of such Base Stations, each of which is used to route the traffic to and from users in a specific area, a so called cell. The traffic from the Base Station to the users is referred to as Down Link, DL, and the traffic from the users to the Base Station is referred to as Up Link, UL. The terminal of a user is sometimes referred to as a Mobile Station, MS
Most packet applications which use high data rates, such as HTTP and FTP, TCP uses retransmissions in order to ensure reliable data delivery. WiMAX and similar cellular access technologies are mainly used for transporting packet data.
Data sent via TCP needs to be acknowledged by the receiving party, and a characteristic in TCP is that the amount of unacknowledged data is limited by the size of the receive buffer, or receive window. The TCP receive window size depends on the configuration of the TCP/IP stack, but is typically in the area of 64 kbytes.
Using, as an example, a TCP receive buffer size with the typical size of 64 kbytes, and a data rate of 10 Mbit/s, it will take 64*103*8/10*106=51*10−3 seconds, i.e. in the area of 50 ms, to fill the receive buffer.
The example of 50 ms required to fill a receive buffer can be used to show that the latency for TCP acknowledgement in the example must be less than 15 ms, otherwise the sender will start to decrease the data rate, and the high data rate offered by the WiMAX access technology cannot be utilized. This may cause a problem in WiMAX systems, particularly in Mobile WiMAX systems, as explained in the following:
In Mobile WiMAX, data is transmitted in so called frames, with the frame length being 5 ms. Uplink bandwidth, i.e. transmit bandwidth for the MSs, is typically requested by the MSs and granted by the BS via contention-based bandwidth requests from the MSs. The concept of contention based requests is well known to those skilled in the field, and will thus not be explained in more detail here. However, the uplink latency in WiMAX systems when contention-based bandwidth request is used will usually be about 12 frames or 60 ms.
The latency of 60 ms is partly due to the WiMAX standard, and partly due to the processing time in the Base Station. However, to increase the Base Station's power in order to reduce the latency time would mean designing the Base Station's processing power for a case which may only occur rarely, something which is not desirable.
Thus, the latency caused by the Base Station, and in part also by the air interface, will be far too high to allow a downlink TCP throughput of 20 Mbits/s if the size of the TCP receive window in the MS is about 64 kbytes, which is a normal size.
As explained above, there is thus a need for a mechanism by means of which the Up Link latency can be reduced in a wireless telecommunications system such as the WiMAX system.
This need is addressed by the present invention in that it provides a method for use in a wireless telecommunications system in which there can be a number of users with mobile terminals, MSs. In the system in which the invention may be applied, there is also a function, a Base Station, BS, through which traffic to and from the MSs in a specific area, a cell, is routed.
Traffic from the BS of a cell to the MSs in that cell is referred to as Down Link, DL, traffic, and traffic from the MSs to their Base Station is referred to as Up Link, UL, traffic.
In the system, at least part of the UL traffic is contention based, and DL data to an MS must be acknowledged by the MS. The method comprises letting the BS of a cell detect MSs in the cell whose DL traffic rate exceeds a certain limit, and the method also comprises a mechanism for allocating to those detected MSs an UL bandwidth which enables them to acknowledge DL traffic within a certain time period from the reception by the MS of the traffic.
Thus, by means of the invention, if an MS has a high DL traffic rate, it is assumed that such an MS will also have a need for a low UL latency, which is thus provided to the MS. In this way, many of the problems caused by low UL latency in for example a WiMAX system can be reduced or eliminated.
This and other advantages of the invention will become even more evident by means of the following detailed description.
The invention will be described in more detail in the following, with reference to the appended drawings, in which
In addition, the system 100 comprises a number of Base Stations, BSs, one for each of the cells, with the base stations of the cell 110 being shown as 140 in
Traffic from the BSs to the MSs is referred to as Down Link, DL, traffic, while traffic in the other direction, i.e. from the MSs to the BSs is referred to as Up Link, UL, traffic
The numbers below refer to the corresponding numbers next to the arrows in
As can be seen from
An alternative and more attractive improvement to the process of
The present invention discloses a number of alternative embodiments for accomplishing the goal stated above, i.e. to offer an increased UL bandwidth to MSs which have a high DL traffic rate. Those embodiments will be described below, and can be referred to as embodiments A, B, C and D.
The choice of mechanism could be based on, for example, the DL data rate of the MS. As an alternative, it is entirely possible to have more than one DL threshold, so that there, for example, could be one threshold for each of the mechanisms A, B, C and D.
Thus, when the BS detects an MS which passes the threshold shown in
Mechanism A:
When a contention based message such as the Bandwidth Request code of the WiMAX system is received, indicating that an MS in the cell wishes to transmit data, always allocate enough bandwidth to transmit a TCP acknowledgement for the MS which has exceeded the threshold. The BS does not know which MS that transmitted the Bandwidth Request code, but allocates sufficient bandwidth to the MS which exceeded the threshold “T” of
An event diagram corresponding to mechanism A is shown in
As can be seen in
Mechanism B:
Allocate a specific channel to an MS which exceeded the DL threshold, and allocate sufficient bandwidth to transmit a TCP acknowledgement when a bandwidth request is received from such an MS on said specific channel. An example of a channel which can be used for this is the CQICH, the Channel Quality Indicator Channel in WiMAX.
An event diagram corresponding to mechanism B is shown in
As can be seen in
Mechanism C:
Allocate enough bandwidth to transmit a Bandwidth Request header in each frame to an MS which exceeded the DL threshold. An event diagram corresponding to mechanism C is shown in
As can be seen in
Mechanism D:
Allocate enough bandwidth for the MS to transmit TCP acknowledgement in each frame. An event diagram corresponding to mechanism D is shown in
Thus, as has been shown above, with the use of the present invention, a high DL traffic rate can be obtained with a minimum of wasted UL resources.
As can be seen from
As shown in step 820, in the system in which the invention is applied, there can be Down Link, DL, traffic from the BS of a cell to the MSs in that cell, and Up Link, UL, traffic from those MSs to their BS.
Step 830 shows that at least part of the UL traffic in the system should be contention based. The notion of “contention based” traffic is well known to those skilled in the field, and will thus not be explained in detail here. Step 835 shows that in the system, DL data to an MS must be acknowledged 835 by the MS.
As shown in step 840, the method of the invention comprises letting the BS of a cell detect MSs in the cell whose DL traffic rate exceeds a certain limit, in this case the threshold T which has been shown in
As indicated in steps 860, 870 and 880, the mechanism for allocating UL bandwidth to the MSs may have different embodiments within the scope of the invention:
As shown in step 860, the mechanism may comprises letting a BS allocate sufficient UL bandwidth for data acknowledgement to one of said detected MS which transmits a contention based message to the BS indicating that it wishes to transmit data, the contention based message being, for example, the Bandwidth Request Code of the WiMAX system.
In an alternative embodiment, as indicated in step 870, the mechanism comprises allocating a certain channel to at least one of the detected MSs with a high DL traffic rate, and then allocating sufficient UL bandwidth for data acknowledgement to the at least one MS which transmits a message to the BS on said channel indicating a request to transmit data on that channel. The request can for example be the Bandwidth Request Header of the WiMAX system, and the channel which is allocated may, for example, be a channel for conveying a channel quality indicator to the BS, such as the CQICH channel.
As indicated in step 880, in the system in which the invention is applied, the UL transmissions may take place in time frames, and the mechanism for allocating UL bandwidth may then comprise allocating, in each of a certain number of said frames, i.e. in one of N frames, 1/N, sufficient UL bandwidth to at least one of said detected MSs to transmit a message indicating that it wishes to transmit data. The message in question may be the Bandwidth Request Header. Thus, in
As an alternative, the mechanism for allocating UL bandwidth may comprise allocating, in each of a certain number of said frames, sufficient UL bandwidth to at least one of said detected MSs for data acknowledgement, i.e. for TCP ACK.
The invention is also directed towards a Base Station with functions according to the invention. A schematic block diagram of such a base station 900 is shown in
As can be seen in
The Base Station 900 also comprises a receiver part, Rx, 920, a transmitter part Tx 930, a computer such as a microprocessor 940 and a memory 950.
The antenna 910 together with the receiver 920, the transmitter 930, the computer 940 and the memory 950 may be used for detecting MSs in an area such as a cell whose DL traffic rate exceeds a certain limit, such as the threshold T shown in
The antenna/interface 910 is used together with the receiver 920 to receive traffic from the external party, the traffic is then processed by the computer 940, and redirected to the MSs in the cell via the transmitter 930 and the antenna 910. The computer 940 may use either the received or the outgoing traffic for comparisons with a threshold which is suitably stored in the memory 950.
The computer 940 notes which MSs that should be allocated the UL bandwidth according to the invention, and may store a list of such MSs in the memory 950.
The invention is not limited to the examples of embodiments described above and shown in the drawings, but may be freely varied within the scope of the appended claims.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/SE2007/050543 | 8/13/2007 | WO | 00 | 2/11/2010 |
Publishing Document | Publishing Date | Country | Kind |
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WO2009/022949 | 2/19/2009 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
20020114295 | Takahiro et al. | Aug 2002 | A1 |
20020144269 | Connelly | Oct 2002 | A1 |
20030048765 | Jang | Mar 2003 | A1 |
20030058796 | Anderson, Sr. | Mar 2003 | A1 |
20030179720 | Cuny | Sep 2003 | A1 |
20040224697 | Hakkinen et al. | Nov 2004 | A1 |
20050192018 | Jang | Sep 2005 | A1 |
20060079221 | Grant et al. | Apr 2006 | A1 |
20070133458 | Chandra et al. | Jun 2007 | A1 |
20070140165 | Kim et al. | Jun 2007 | A1 |
20070183353 | Malladi | Aug 2007 | A1 |
20080089250 | Jung | Apr 2008 | A1 |
20080233964 | McCoy et al. | Sep 2008 | A1 |
20080316959 | Bachl et al. | Dec 2008 | A1 |
20090143071 | Bergstrom et al. | Jun 2009 | A1 |
Number | Date | Country | |
---|---|---|---|
20110200021 A1 | Aug 2011 | US |