Patent Application
20080052589
As shown in
The base station 1 is a wireless base station apparatus operated by a telecommunications business. The base station 1 is a wireless station that performs processing for controlling the connection of a mobile telephone terminal 2 belonging to a user who subscribes to the mobile telephone communications service provided by the telecommunications business, and processing for relaying communications between the mobile telephone terminal and the business's upper apparatus. There are also cases in which the base station 1 is called a “base transceiver station” (BTS).
The mobile telephone terminal 2 is a terminal apparatus used by a user who partakes in the provided mobile telephone communications service. There are also cases in which the mobile telephone terminal is called a “mobile terminal” or a “mobile station” (MS).
The upper apparatus is an already-present transmission apparatus, a wireless base station control apparatus, a mobile switching apparatus (switching center), or the like. The mobile telephone terminal 2 can perform communications with another mobile telephone terminal 2, a PHS terminal, a land-line telephone terminal, or the like via the base station 1 and the upper apparatus. Furthermore, it is also possible for the mobile telephone terminal 2 to perform communications with an Internet web server, an e-mail server, or the like.
The hardware and software configurations of the base station 1 and the mobile telephone terminal 2 are basically the same as in the conventional art. However, the base station 1 and the mobile telephone terminal 2 perform communications that apply the various methods described in order hereafter. Accordingly, software and hardware for applying these various methods, which shall be described below, are added to the base station 1 and the mobile telephone terminal 2.
Hardware or software for implementing a transmission frame generator 101, a retransmission request acceptor 102, a retransmission frame generator 103, and a frame transmission controller 104 is added to the base station 1, as shown in
On the other hand, hardware or software for implementing a frame examiner 201, a retransmission requestor 202, and a data reproducer 203 is added to the mobile telephone terminal 2, as shown in
In
In
The transmission frame generator 101 further converts the U-PDU frame 6 into data (frames) in a format compliant with the predetermined protocol of the lower layer. Specifically, the U-PDU frame 6 is divided into data of a length not greater than a predetermined data length. Then, protocol control information of that layer is attached to each piece of the divided data as a header.
Hereafter, data in this format shall be referred to as “Lower-Protocol Data Unit (L-PDU) frame 7”. In addition, an L-PDU frame 7 header shall be referred to as an “L-ARQ header”. There are cases where code for error detection and correction, such as, for example, Cyclic Redundancy Check (CRC) code or Turbo code, are included in the L-ARQ header. Furthermore, there are cases where other various information, which shall be described later, is included as well.
The L-PDU frame 7 generated in this manner is data (frames) of a format for transmission to the mobile telephone terminal 2.
The generated L-PDU frame 7 is transmitted to the target mobile telephone terminal 2 by the frame transmission controller 104.
In
In the case where the result of the examination performed by the frame examiner 201 shows that there is an error in the L-PDU frame 7 received from the base station 1 and it has been determined that the error cannot be corrected, or in other words, the case in which reception cannot be successfully completed, the retransmission requestor 202 performs processing requesting the base station 1 to once again transmit, or retransmit, the L-PDU frame 7. Essentially, a “NACK” signal is returned to the base station 1 as per the conventional art.
It should be noted that in the case where the frame examiner 201 has confirmed that there are no errors in the L-PDU frame 7 received from the base station 1, an “ACK” signal is transmitted to the base station 1 as per the conventional art.
In
As shown in
The frame transmission controller 104 performs control for transmitting, to the target mobile telephone terminal 2, the L-PDU frame 7 generated by the transmission frame generator 101 and the retransmission frame 8 generated by the retransmission request acceptor 102. In the present embodiment, control is performed through a multiplex channel Stop and Wait scheme, as described earlier in the “Description of the Related Art” section. However, in the present invention, to simplify explanations, it is assumed that control is performed through a multiplex channel Stop and Wait scheme having three processes.
In
Hereafter, various embodiments of communications performed between the base station 1 and the mobile telephone terminal 2 according to the present invention shall be explained in order.
When the retransmission request acceptor 102 accepts, from the mobile telephone terminal 2, a request indicating that the L-PDU frame 7 should be retransmitted, the retransmission frame generator 103 divides that L-PDU frame 7 into a plurality of retransmission frames 8, as shown in
Whereas the L-PDU frame 7 would conventionally be retransmitted, in the present embodiment, the frame transmission controller 104 sequentially transmits the retransmission frames 8. For example, as shown in
Note that in
In the example “first timing for transmission of the retransmission frame 8” provided above, the retransmission frame generator 103 divides an L-PDU frame 7 directly upon accepting a request indicating that the L-PDU frame 7 should be retransmitted. However, in the present example, the retransmission frame generator 103 does not perform processing only having accepted the first request. Instead, the frame transmission controller 104 retransmits the L-PDU frame 7 to the mobile telephone terminal 2 as per the conventional art.
Then, when the number of requests indicated by a threshold Pa have been received for the same L-PDU frame 7, the retransmission frame generator 103 performs processing for generating the retransmission frames 8, and the frame transmission controller 104 performs processing for sequentially transmitting these retransmission frames 8. Note that the threshold Pa is set as a natural number of “2” or more.
For example, in the case where the threshold Pa is set at “2”, it is assumed that the base station 1 has transmitted the L-PDU frame 7 with a TSN of “#4” through the “Pr#A” process. When the retransmission request acceptor 102 accepts a request for retransmission of that L-PDU frame 7, the retransmission request acceptor 102 checks what number retransmission request for that L-PDU frame 7 the current retransmission request is.
In the case where the request for retransmission is the first request, the frame transmission controller 104 performs processing in which the L-PDU frame 7 is retransmitted as-is via the same process, without being divided into retransmission frames 8.
In the case where the request for retransmission is the second request, or in other words, the same number as the threshold Pa, the retransmission frame generator 103 divides the L-PDU frame 7, thereby generating a plurality of retransmission frames 8. Then, the frame transmission controller 104 performs processing that sequentially sends these retransmission frames 8 through the same process.
There are instances where the quality state of the transmission channel changes while the base station 1 and the mobile telephone terminal 2 are communicating. The error rate drops when the quality is high; however, the error rate increases when the quality is poor. Therefore, the retransmission frame generator 103 divides the L-PDU frame 7 into retransmission frames 8 according to the following method.
The retransmission frame generator 103 acquires information regarding the quality of the transmission channel, or in other words, Channel Quality Information (CQI). Acquisition of the CQI may be performed periodically, or may be performed when division of the L-PDU frame 7 becomes necessary.
When the L-PDU frame 7 is divided, the retransmission frame generator 103 determines a bit size (data length) for the divisions based on the latest CQI and a rule prepared in advance. It is possible for this rule to be set in the form of a function, a table or the like, and so on; using the value of the quality indicated by the CQI as a parameter, a greater bit size is derived the higher the quality indicated by this value, and a lesser bit size is derived the lower the quality indicated by this value.
Then, the retransmission frame generator 103 divides the L-PDU frame 7 into parts according to the determined bit size. As a result, retransmission frames 8 of a large bit size (data length), as shown in
As explained earlier in the “Description of the Related Art” section, the number of retransmissions is limited in H-ARQ. In other words, a threshold Cmax is set, and the base station 1 only performs retransmissions up to the number indicated by the threshold Cmax, even if “NACK” is repeatedly returned for the same L-PDU frame 7.
However, in the case where the L-PDU frame 7 is divided into retransmission frames 8 and retransmitted, the overall retransmission process (number of steps) grows as the number of divisions increases (or in other words, the more finely the L-PDU frame 7 is divided). In such a case, there is the danger of an overall drop in performance.
Therefore, the number of divisions may be limited in the following manner. For example, the number of divisions of the L-PDU frame 7 may be limited to the division limit number Dm that fulfills the following formula (1).
α≧Rmax·Dm (1)
In formula (1), “α” is a constant. The threshold Cmax, for example, may be used for the constant α. Alternatively, a smaller value than the threshold Cmax may be used, taking into consideration the number of retransmissions prior to division of the L-PDU frame 7 (refer to
Alternatively, the number of retransmissions may be limited. It is assumed that, for example, the number of parts the L-PDU frame 7 for which retransmission has been requested is to be divided into has been determined according to the method described earlier under “adjustment of division size in accordance with CQI”. Such being the case, the frame transmission controller 104 substitutes the determined number with the division limit number Dm from formula (1) and calculates the retransmission limit number Rmax that fulfills formula (1). Then, the frame transmission controller 104 performs control so that the number of retransmissions of the retransmission frames 8, into which the L-PDU frame 7 has been divided, does not exceed the retransmission limit number Rmax.
In this manner, it is possible to prevent a decrease in overall performance by performing limitation so that the number of retransmissions decreases as the number of divisions increases, or so that the number of divisions decreases as the number of retransmissions increases.
Even when the base station 1 divides the L-PDU frame 7 into a plurality of retransmission frames 8 and performs retransmission, there are cases where a limit is placed on the number of retransmissions with some of the retransmission frames 8 not yet successfully received by the mobile telephone terminal 2. As a result, there are cases where the data reproducer 203 of the mobile telephone terminal 2 cannot reproduce the original data even if the remaining retransmission frames 8 are acquired.
Accordingly, the frame transmission controller 104 of the base station 1 may control transmission of the retransmission frames 8 through the method indicated in
As shown in
Here, it is assumed that the transmission frame generator 101 has attempted retransmission of the L-PDU frame 7 by transmitting the retransmission frame 8 indicated by “#4−1”, and a “NACK” signal has been returned even after a predetermined number of attempts.
Such being the case, the transmission frame generator 101 abandons transmission of that retransmission frame 8 as well as the remaining retransmission frames 8. In other words, retransmission of the L-PDU frame 7 indicated by “#4” is abandoned.
Incidentally, in the case where the prescribed maximum bit size (bit length) of the L-PDU frame 7 is greater than the size of the U-PDU frame 6, there are instances where the transmission frame generator 101 of the base station 1 generates the L-PDU frame 7 through a method different from the method indicated in
In other words, the transmission frame generator 101 of the base station 1 generates a single L-PDU frame 7 by compiling a plurality of U-PDU frames 6, as shown in
In the case where the mobile telephone terminal 2 could not successfully receive any one L-PDU frame 7, it is necessary for the mobile telephone terminal 2 to request the base station 1 to retransmit all U-PDU frames 6 corresponding to that L-PDU frame 7. For example, as shown in
However, when this occurs, it is necessary for the base station 1 to retransmit the entire U-PDU frame 6 regardless of the fact that some of the U-PDU frames 6, such as the U-PDU frame 6 with “#3”, have already been successfully received by the mobile telephone terminal 2.
In addition, according to the examples described thus far, in the case where a request for retransmission has been made for an L-PDU frame 7 that could not be successfully received by the mobile telephone terminal 2, the retransmission frame generator 103 of the base station 1 divides an L-PDU frame 7 into a predetermined data length; therefore, there are cases where retransmission frames 8 are generated based on a plurality of U-PDU frames 6, as indicated in
Accordingly, in the case where there is a request for retransmission of the L-PDU frame 7, the retransmission frame generator 103 divides the L-PDU frame 7, thereby generating retransmission frames 8, through the method indicated in
When the retransmission request acceptor 102 of the base station 1 accepts a request to retransmit the L-PDU frame 7, the retransmission frame generator 103 divides the L-PDU frame 7 by splitting it per U-PDU frame 6 (or part of the U-PDU frame 6), which forms the basis of that L-PDU frame 7. For example, in the case where there has been a request for retransmission of the L-PDU frame 7 with the TSN of “#1”, the L-PDU frame 7 is divided as shown in
As shown in
In the example shown in
In such a case, for example, three retransmission frames 8 are generated, as shown in
In the case where retransmission frames 8 are generated by the retransmission frame generator 103 in such a manner, the frame transmission controller 104 judges, through a method such as that shown in
It is assumed that the frame transmission controller 104 has attempted retransmission of a retransmission frame 8 having a TSN of #4−1” a predetermined number of times but a “NACK” signal has been returned each time. In such a case, the frame transmission controller 104 gives up on retransmission of that retransmission frame 8, and judges whether or not the data to be transmitted next in the same process, or in other words, the “#4−2” retransmission frame 8, should be transmitted.
This judgment is made by comparing, in the following manner, the U-PDU frames 6 that form the basis of each of the retransmission frames 8.
In the case where any of the U-PDU frames 6 that form the basis of data to be sent next, or in other words, the “#4−2” retransmission frame 8, are not the same as any of the U-PDU frames 6 that form the basis of the data for which retransmission was abandoned, or in other words, the “#4−1” retransmission frame 8, the frame transmission controller 104 sequentially attempts transmission of the “#4−2” retransmission frame 8 and the retransmission frames 8 that follow.
On the other hand, in the case where all of the U-PDU frames 6 that form the basis of the data to be transmitted next are the same as any of the U-PDU frames 6 that form the basis of the data for which retransmission was abandoned, transmission of the data that is to be transmitted next is suspended. Then, in the same manner, judgment of the data to be transferred thereafter, or in other words, the “#4−3” retransmission frame 8, is performed by comparing that retransmission frame 8 with the “#4−1” retransmission frame 8. Through such a judgment method, in the case where retransmission of the “#4−1” retransmission frame 8 shown in
It should be noted that in the case where the retransmission frames 8 have been generated through the method shown in
As has been described thus far, the base station 1 retransmits the L-PDU frame 7 that the mobile telephone terminal 2 could not properly receive by dividing the L-PDU frame 7 into retransmission frames 8 and transmitting the retransmission frames 8. At this time, it is necessary to reliably notify the mobile telephone terminal 2 of which L-PDU frame 7 these retransmission frames 8 belong to.
Accordingly, it is preferable to transmit information regarding the retransmission frames 8 to the mobile telephone terminal 2 through the following method.
In each example described thus far, the TSN of a retransmission frame 8 utilizes a number in which a separate serial number such as “−1” or “−2” is added to the TSN of the original L-PDU frame 7, resulting in TSNs of, for example, “#4−1” or “#4−2”.
However, rather than using such a TSN, a new TSN may be issued or acquired for the retransmission frame 8, in the same manner as the L-PDU frame 7. Moreover, division information may be written into the L-ARQ header of the retransmission frame 8, as shown in
If the base station 1 generates and transmits the retransmission frames 8 through such a method, when the mobile telephone terminal 2 receives some kind of data (frame), it can judge whether that data is a retransmission frame 8 or an L-PDU frame 7 by analyzing the L-ARQ header of the data and checking the presence/absence of the division information.
In the case where the mobile telephone terminal 2 has judged that the data is a retransmission frame 8, it temporarily stores that data (the retransmission frame 8) in a buffer. Other retransmission frames 8 are stored in the buffer in the same manner. Then, when all the retransmission frames 8 that belong to a single L-PDU frame 7 have been stored in the buffer, the data reproducer 203 reproduces the L-PDU frame 7 based on the division information of the retransmission frames 8.
Alternatively, the base station 1 may use a pre-retransmission L-ARQ header, instead of issuing or acquiring a new TSN. However, the abovementioned division information is added to the retransmission frames 8 in this case as well. Then, the mobile telephone terminal 2 may store the received retransmission frames 8 in the buffer and reproduce the L-PDU frame 7 based on the division information of the retransmission frames 8.
When adding division information in this manner, an area for that division information does not need to be provided in the L-ARQ header. This is because doing so would create a wasteful area in the L-ARQ header of the L-PDU frame 7, which does not need division information, and would put an unnecessary burden in the L-ARQ header. Accordingly, as shown in
It cannot be said with certainty that the mobile telephone terminal 2 can receive the retransmission frames 8 that belong to a single L-PDU frame 1. However, there are cases where some U-PDU frames 6 can be reproduced if some of the retransmission frames 8 are present.
Accordingly, the mobile telephone terminal 2 may handle the retransmission frames 8 received from the base station 1 through the following method.
As described earlier, when a sequence of retransmission frames 8 are sequentially sent from the base station 1 through a certain process, the mobile telephone terminal 2 stores these retransmission frames 8 in a buffer, one by one.
In the present embodiment, Stop and Wait is utilized, and thus when data that is not divided data (retransmission frames 8), or in other words, a different L-PDU frame 7 is transmitted through that process, it follows that the transmitting/receiving of the sequence of retransmission frames 8 has ended.
Therefore, when a different L-PDU frame 7 has been transmitted through that process, the data reproducer 203 attempts reproduction of a U-PDU frame 6 using the retransmission frames 8 that are stored in the buffer. That is, the retransmission frames 8 are passed from a lower layer to a higher layer, and reproduction of a U-PDU frame 6 is attempted.
Through such a method, even in the case where some of the retransmission frames 8 could not be received, the mobile telephone terminal 2 can still effectively utilize those retransmission frames 8 for the reproduction of the U-PDU frame 6. In addition, if a U-PDU frame 6 that could not be reproduced but which is necessary is present, a request may be made to the base station 1 for retransmission of that U-PDU frame 6 only. Furthermore, it is possible to quickly proceed to the next processing (for example, reordering buffer storage or the like), and therefore the overall performance can be improved.
Note that the retransmission frames 8 that could not be received can be identified easily by referring to the division information of the retransmission frames 8 that have been received.
Next, the flow of the processing performed by the base station 1 in the case where a request for retransmission of an L-PDU frame 7 has been made shall be explained with reference to the flowchart shown in
In
The base station 1 sequentially sends the retransmission frames 8 to the mobile telephone terminal 2, starting with the first retransmission frame 8 (S3 to S8). However, in the case where a “NACK” signal is returned for the xth (1≦x≦n) retransmission frame 8 (No in S5), retransmission of that retransmission frame 8 is attempted within a predetermined number of times (Yes in S6; S4). As described earlier, there are various ways of determining the predetermined number of times.
Note that in the case where the mobile telephone terminal 2 could not properly receive the retransmission frame 8 even after it has been retransmitted within the predetermined number of times, there are cases where transmission of subsequent retransmission frames 8 is stopped regardless of the condition of Step S7, as well as cases where transmission is continued, as was explained earlier. There are also case where, according to the configuration, the determination to stop or continue transmission is made per retransmission frame 8.
According to the present embodiment, in the case where the mobile telephone terminal 2 cannot successfully receive an L-PDU frame 7, the base station 1 divides that L-PDU frame 7 into a plurality of retransmission frames 8 and retransmits the retransmission frames 8, rather than simply retransmitting the L-PDU frame 7 as-is as per the conventional art. Thus, it is possible to reduce the amount of data sent each time, increase the reliability of error correction, and raise the reliability of retransmission of the L-PDU frame 7 beyond that of the conventional art. Furthermore, it is possible to suppress data puncture caused by rate matching beyond what is possible with the conventional art.
It should be noted that many modifications to part or all of the configuration of the communications system 100, the base station 1, and the mobile telephone terminal 2, the processing content, the processing order, the frame structure, and so on can be made without deviating from the scope of the present invention.
While example embodiments of the present invention have been shown and described, it will be understood that the present invention is not limited thereto, and that various changes and modifications may be made by those skilled in the art without departing from the scope of the invention as set forth in the appended claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| JP2006-225839 | Aug 2006 | JP | national |
