MXPA00011125A - Data transmission over a communications link with variable transmission rates - Google Patents

Abstract

An optimal data block size is determined for use in transmitting data at variable rates over a communications link in predetermined time intervals, where each predetermined time interval has the same time duration. Rather than varying data block size according to changes in transmission rates, which adds unnecessary complexity, the data blocks all have the same fixed size, i.e., the same number of data bits in each block. That fixed data block size is determined so that for all of the available data transmission rates, each predetermined time interval is fully occupied with useful information. The fixed data block size is determined based on a maximum frequency at which the transmission rate may change on the communications link and a lowest available transmission rate. Preferably, the fixed size of each date block is limited by predetermined maximum and minimum data block sizes in order to reduce the number of bit errors per data block, maintain a certain data throughput, and limit the amount of overhead bits relative to the number of payload bits for each data block.

Description

TRANSMISSION OF DATA IN A COMMUNICATIONS LINK WITH VARIABLE TRANSMISSION SPEEDS TECHNICAL FIELD OF THE INVENTION "The present invention relates to data communications, and more particularly to the transmission of data blocks in a communication link where the transmission speed varies. BACKGROUND AND COMPENDIUM OF THE INVENTION In the area in constant evolution of communications • 10 wireless, the number of services that can be offered between a mobile station (MS) and a base station (BS) has increased significantly and these services include services in real time, for example voice and video, as well as services that are not offered in real time, for example file transfers and email messages. Each service typically has a different transmission format requirement. A format requirement • transmission is the transmission speed in the radio channel between the mobile station and the base station. A channel radio may correspond to a radio frequency in a frequency division multiple access (FDMA) system, a time segment in a time division multiple access (TDMA) system, and a dispersion code in the case of a code division multiple access system (CDMA). Due to the variation of the services that must be offered, the transmission speed in the radio channel can change with a relatively high frequency. In fact, in some systems, the speed with which the channel • Radio can change can be of the order of every 10 5 ilseconds. In the case of higher transmission rates, the number of data bits that are transmitted in each time frame can be quite large. On the other hand, in the case of relatively low transmission rates, a much smaller number of data bits are transmitted during the • 10 same time frame. This variation in transmission speeds poses a problem that is particularly complicated in the radio environment where the data is frequently corrupted as a result of fading, shading, interference, etc. To take into account the bit errors that result from such corruption, an Automatic Repeat reQuest (ARQ) protocol (Repetition Request) can be used.

• Automatic) which uses positive / negative acknowledgments with retransmission techniques to ensure reliable data communications. If a data message with errors is received, the recipient sends a retransmission request to the originator, and the originator automatically retransmits the data message. The message to be retransmitted is typically divided into numerous blocks of smaller data. Each block of data contains a sequence number for identification purposes that is used when the retransmitted blocks are received and sequenced in the receiver. • It is important to carefully select the size, that is, 5 the number of bits, in each of these small blocks. The larger the size of a data block, the greater the probability that the retransmitted block will be received with an excessively large number of errors. In order to keep low the number of errors in a block situation • 10 large of this type, it requires a radio channel of very high quality which either can not be obtained under current conditions or is "expensive" in the sense that it consumes a limited capacity. On the other hand, as the size of the data blocks decreases, the speed Effective data or performance also decreases since the number of general load bits used in each of the data blocks, for example, sequence number, • bits of detection and correction of errors, etc., increases in relation to the number of data bits of real "payload" that constitute the substantive data message. The fact that the transmission speed in a radio channel or any type of communication channel can vary frequently complicates the determination of the appropriate size of data block. Let's consider the example illustrated in Figure 1 in which the block size is 640 bits. The data transmission speed can change to one of two speeds: 64 kbit / s and 32 kbit / s. The frequency with which the transmission speed can change corresponds to the time interval of 10 milliseconds. In other words, the transmission rate can only change at the end of each 10 millisecond time interval and not during that time interval. At the highest 64 kbit / s transmission rate during the first frame interval, the entire 640 bit data block is allocated to a single 10 millisecond time frame interval. After this time interval, the transmission rate changes to 32 kbit / s and during the subsequent time frame interval of 10 milliseconds, only one half of the 640 bits in the next data block is transmitted during the second time frame interval . Following the second frame interval of 10 milliseconds, another speed change occurs by increasing the transmission rate back to 64 kbit / s. At this higher transmission rate, the transmission of the remaining 320 bits of the second half of the data block requires only half of the third frame interval of 10 milliseconds. This leaves "empty" the second half of the third frame interval that is then filled with "fictitious" bits the inability to transmit useful information during portions of frame intervals wastes precious resources (especially in the radio context) and slows down of effective data • on the radio channel. 5 One way to handle this variable transmission rate problem is to adapt the data block size (the number of bits in each block) to the current transmission speed. However, this approach causes difficulties when data blocks must be retransmitted as • 10 result of corruption in the communications link. For example, let's consider a situation in which a large block of data is initially transmitted at a high data rate in a frame interval of 10 milliseconds. This great block is corrupted, and for Consequently, it must be retransmitted. Subsequently, when the large data block is to be retransmitted, the transmission speed at this time may have changed, for example, at a lower transmission rate. Due to the lower speed, the large data block can not be transmitted in a single time interval of 10 ^ a milliseconds, and one or more additional frame intervals should be used to transmit the remaining data. Most likely, one of the frame intervals is transmitted with less than a full payload. It is an object of the present invention to provide a method for determining an optimal data block size for use in communication systems where variable transmission speeds may be employed. • It is a further object of the present invention to determine an optimal data block size in such a way that communication resources are not wasted. It is another object of the present invention to determine a fixed block size in order to eliminate the complexities associated with variable block sizes. • The present invention solves these problems and achieves the stated objectives by providing a method for determining an optimal data block size. The data block size can be used profitably to transmit data at variable speeds in a data link. communications at predetermined time intervals, where each predetermined time interval has the same duration of time. Instead of varying the block size of • data according to changes in transmission speeds which adds unnecessary complexity, data blocks according to the present invention all have the same fixed size, that is, they have the same number of data bits in each block. This fixed size of data block is determined in such a way that for all available variable speeds in which it can be In order to transmit data, each predetermined time interval is fully occupied with useful information, that is, there is no unused or "filled" portion of one of the time slots. Although data may initially be transmitted at a first transmission speed in the fixed data block sizes, when a change from the first transmission rate to a second transmission rate is detected, bits are assigned and transmitted in the second transmission speed. transmission speed in the same fixed size of taos blocks. • 10 The fixed size of data blocks is determined based on a maximum frequency at which the transmission rate can change in the communications link and a lower available transmission speed. Preferably, the fixed size of each data block is limited by maximum sizes and predetermined minimums of data block in order to reduce the number of errors in the bits per data block, to maintain a certain data production, and to • limit the amount of general load bits compared to the payload bits. In addition to initial data transmissions between two communication devices in a communication link, the present invention is also beneficial in the context of an Automatic Repeat reQuest (ARQ) procedure. If a message from data is considered as unreliable, for example, excessive bit errors, a request is sent to the transmission communication device for retransmission of this data message. Even though the data message was initially transmitted using a first transmission format that specifies a first transmission rate, the transmission format may have changed to a second format that specifies a different second transmission rate when the message is to be retransmitted. In an exemplary embodiment, the data message to be retransmitted is segmented or divided into a data link protocol layer in fixed-size protocol data units (PDUs) where each fixed-size PDU has the same number of bits regardless of the transmission speed or other format. The fixed-size PDUs are then transmitted in a first physical protocol layer using the second transmission format by specifying a second transmission rate different from the first transmission rate at which the data message was originally transmitted. The fixed size of PDU is selected in such a way that the time intervals are fully utilized despite frequent changes in transmission formats and speeds in the communications link. In other words, time slots are fully occupied with useful information without having to add bits of padding data to complete this time frame interval. Although the present invention can be profitably applied to any communication device in any data communication system, a preferred profitable application is data communication between a mobile station and a base station, and particularly its application to communication systems multiple division code access (CDMA) mobile phones. A first layer of communication protocol employs scatter codes in the • 10 transmission of PDUs on a radio link. A second communication protocol layer on the first layer corresponds to a radio link control protocol / medium access control (RLC / MAC) layer. The RRLC layer carries out the segmentation of data in the fixed PDUs for transmission on the radio interface. BRIEF DESCRIPTION OF THE DRAWINGS The previous objects as well as other objects, • characteristics and advantages of the invention will be apparent from the following description of exemplary embodiments Preferred as illustrated in the accompanying drawings in which the same reference numbers refer to the same parts in the various views. The drawings are not necessarily to scale, the illustration of the principles of the invention being emphasized on the contrary. Figure 1 is a diagram illustrating one of the problems resulting from variable communication speeds that the present invention solves; Figure 2 is a block diagram of functions that • illustrates exemplary communications devices and a communication link 5 therebetween where the present invention can be usefully employed in accordance with a first exemplary embodiment of the present invention; Figure 3 is a flowchart illustrating exemplary procedures in accordance with a routine 10 of • 10 fixed block size transmission in accordance with the first example mode; Fig. 4 is a flow diagram illustrating example procedures for determining a data block size in accordance with the first example embodiment; Figure 5 is a diagram illustrating an example of how the present invention can be employed in a communication link in which the transmission rate changes • on the communications link; Figure 6 is a diagram illustrating another application of example of the present invention; Figure 7 is a block diagram of functions of a mobile radio system in which the present invention can be usefully employed in another example embodiment of the present invention; Figure 8 is a diagram illustrating several layers of communication protocol that they employ in the communication between mobile station, base station, radio network controller and core network service nodes in a communication system. • mobile communication in figure 7; Figure 9 is a simplified diagram of a DPU format; And Figure 10 is a flowchart illustrating a data block retransmission routine 200 in accordance with an exemplary application of the present invention. DETAILED DESCRIPTION OF THE INVENTION In the following description, for purposes of explanation and not limitation, specific details are presented such as, for example, particular modes, data structures, equipment configurations, data rates, techniques, etc., in order to offer a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other cases, descriptions Detailed descriptions of well-known methods, devices and circuits are omitted so as not to obscure the description of the present invention with unnecessary detail. Figure 2 illustrates a general communication system in the The present invention can be employed in a first example embodiment. A sending communication device 1 communicates on a communication link 5 with a receiving communication device 6. the communication link 5 can Correspond to any type of communication means 5 including a wire, an optical fiber, a microwave link, a radio link, etc., and can employ any of a number of different communication formats suitable for transmission in any of the media of communications. The transmission speed in the link • Communication 5 can vary quite frequently at predetermined intervals. In the example illustrated in Figure 1 described above, the predetermined range corresponds to a frame interval of 10 ¼-second. The communication device 1 includes a transmitter 2, a data processing circuit 3 including one or more buffers, and a receiver 4. Similarly, communication device 6 includes a transmitter ", a • data processing circuit 8 including one or more buffers and a receiver 9. The circuit of data processing 3 in the sending communication device 1 transmits through the transmitter 2 information in the communication link 5 using data blocks of fixed size. The size is independent of the current transmission rate in the communication link 5. In regard to this aspect, reference is now made to the transmission routine 10 of fixed size blocks which is illustrated in the flowchart format of Figure 3. A first number of bits is assigned to each data block of • fixed size according to a first transmission speed. These 5 data blocks are sent via transmitter 2 in a communication link 5 to the receiver communication device 6 (block 12). A decision is made in block 14 as to whether the transmission speed for data transmission in communication link 5 has • 10 changed. If the speed has changed, a second number of bits is assigned to the same data blocks of fixed size in accordance with a second transmission rate. The transmitter 2 transmits these fixed blocks at this second transmission rate on the communications link 5 (block 16). An important aspect of the present invention is the determination of an optimum block size to be fixed for • all available data transmission speeds that can be used in communication link 5. by Accordingly, reference is now made to the block size routine 20 illustrated in the flowchart format of Figure 4. A frequency (F) in which the transmission rate in the communication link 5 can change is determined ( block 22) that is, the number of changes in transmission speed / unit of time. In addition, a minimum or lower available transmission rate (Tx (min)) is determined in the communication link (block 24). A fixed block size is then determined (block • 26) in accordance with the following equation: 5 Fixed block size = Tx (min) (1) F We will now consider the example transmission scenario in communications link 5 illustrated in Figure 5 where the present invention.

Considering a frame interval of ten milliseconds as the highest frequency at which the transmission speed in communication link 5 can change, and considering two available transmission speeds of 64 kbit / s and 32 kbit / s, the size of Fixed blockade of according to equation (1) above is ten milliseconds * 32 kbit / s. Accordingly, each fixed data block contains 320 bits. Considering that the initial transmission speed is the highest of 64 kbit / s, each frame interval of ten milliseconds transmitted contains two blocks of data of 320 bits which gives a total of 640 bits. When the transmission speed changes at the end of the frame interval from ten milliseconds to 32 kbit / s, only a single block of 320 bit data is transmitted for each frame interval.

Despite the fact that the transmission rate changes after only ten milliseconds, the optimally calculated fixed block size ensures that the ten millisecond intervals are fully occupied. Those skilled in the art will note that fully occupied means that the positions of bits in a frame interval are not wasted. In other words, there is no substantial portion of a frame interval that does not contain useful information including either general load bits or payload bits. For example, the present invention in accordance with that illustrated in Figure 5 contrasts with the similar scenario illustrated in Figure 1 wherein one half of a ten millisecond frame interval is transmitted without any useful information. The transmission of fictitious bits during this useless portion of the frame interval is wasteful and inefficient. It may be desirable to put some limits on the size of the fixed data block according to parameters of the variable speed communication link. For example, if the block size is too small, a greater percentage of the data bits transmitted in the communications link are general load bits, which reduces the overall performance and efficiency. On the other hand, larger blocks have a tendency to errors and therefore in this case one or several retransmissions may be required to reliably transmit so many bits. Accordingly, maximum and / or minimum limits of fixed data blocking size can be set according to the application. • We are going to consider an example in which the communications device 1 can transmit on the communications link 5 using any of the following available transmission speeds: 8 kbit / s, 32 kbit / s, 64 kbit / s. Using equation (1), the fixed block size is ten milliseconds * 8 kbit / s what is • 10 equals 80 kbit. It may be that a block size of 80 kbit is too small, for example, less than a threshold (T) as shown in decision block 28 in FIG. 4. In this case, the block size is set to 320 bits what is consistent with the highest speed below 32 kbit / s, but the highest frequency at which the transmission rate in the communication link 5 can change is reduced by a factor inversely • proportional to the difference between the lowest and the next lowest transmission speed. In this example, this factor is four. Therefore, the highest frequency at which the transmission speed can change in this example is 40 milliseconds when the transmission is 8 kbit / s. Figure 6 shows that the 320-bit fixed-size data block is transmitted using four frame intervals of 80 bits each.

During these four frame intervals, the transmission speed may not change. Accordingly, the invention limits the frequency with which the • transmission speeds when low transmission speeds are used (block 30). Again, the present invention ensures that even when the transmission rate can change dramatically, for example, from 68 kbit / s to 8 kbit / s, the size of the data block is determined in such a way that all frame time intervals HE • 10 use to transmit either general cargo information or payload information. The present invention can be profitably applied to any communication system that includes mobile communication network systems that are systems based on FDMA, TDMA, and CDMA. Figure 7 shows an example of mobile communication system 100. An external core network, oriented towards representative connection, illustrated as a cloud 120, * can be for example the Public Switched Telephone Network (PSTN) and / or the Integrated Services Digital Network (ISDN). A external core network, oriented without representative connection, illustrated as a cloud 140, may be for example Internet. Both networks are connected to corresponding service nodes 160. The network oriented towards connection PSTN / ISDN 120 is found connected to a service node oriented towards connection known as a mobile switching center (MSC) node 180 that provides circuit switched services. In a mobile communication system such as the well-known GSM system used in Europe and elsewhere, the mobile switching center 180 5 is connected through an interface A to a base station system (BSS) 220 which it is connected to a radio base station 230 on an interface A. "The network 140 oriented without an Internet connection is connected to a service node 20 • 10 General Packet Radio (GPRS) designed to provide packet-switched services. Each of the core network service nodes 180 and 200 is connected to a radio access network (RAN) 240 at a radio access network interface. Each network driver of radio access 260 is connected to several base stations 280 communicating in the radio interface with several mobile stations 3QQ. Even when you can • use any radio access,. radio access is preferably based on broadband CDMA (W-CDMA) with individual radio channels assigned using W-CDMA scatter codes. W-CDMA offers broadband for multimedia services and other high-speed requirements as well as robust features such as diversity transfer and RAKE receivers to ensure a high quality.

Fig. 8 illustrates a schematic view of a possible stack of lower communication protocol layer communication protocols for use in the mobile communication system 100 illustrated in Fig. 7. A layer of radio access control protocol / control Media access (RLC / MAC) is placed on top of a physical layer of protocol Ll. Considering a broadband CDMA physical layer, the physical protocol layer Ll as well as RLC / MAC terminate in the radio network controller (RNC) for diversity transfer purposes. The third protocol layer corresponds to a logical link control (LLC) that terminates in core networks (CNs). The RLC / MAC and LLC protocol layers can be viewed as lower and higher data link layer type protocol levels, respectively, in the context of the standard OSI model. While each of these three protocol layers offers numerous functions, for the purposes of describing this particular embodiment of the present invention, only a few tasks are described. In the physical layer, data streams that come from different communication services are multiplexed in a radio channel. These services may have different quality of service requirements, for example, different bit error requirements, different types of coding (convolutional coding, Reed-Solomon coding, etc.), and different transmission speeds. To change the transmission rate, for example, in the uplink path from the mobile station to the base station, the dispersion factor of the spreading code assigned to this mobile station is changed. The mobile station, therefore, can transmit data for different services at the same time while also using the limited radio resources efficiently by its I adaptation to the transmission speed required for a specific service. Reliable transmission is achieved in the radio interface, for example, using an Automatic Repeat reQuest scheme (ARQ) (automatic repeat request; in the RLC protocol layer.) Higher layer data packets provided by the LLC protocol layer are segmented into smaller blocks, known as appropriate RLC protocol data units (PDUs). for transmission in the radio interface An RLC PDU is the smallest relay unit An example R1C PDU is shown in Figure 9 and includes a header 32 which has, among other things, a sequence number , a payload data field 34 containing a portion of the LLC message to be retransmitted, and an error detection and / or correction field such as a cyclic code redundancy check (CRC) 36. Thus, if a packet it has not been received reliably, in a receiving device, it is retransmitted by the RLC layer In a manner similar to that described above, the RLC PDU size is fixed and determined based on the highest frequency at which the Transmission speed can change and the transmission speed minimum or lower. Typically, the transmission rate is specified in a transmission format together with other parameters such as coding information, interleaving information, and repetition / perforation schemes for velocity mapping.

Next, a data message retransmission routine 200 is described in combination with the flow chart illustrated in figure 10. An indication is made to retransmit a data message that was initially transmitted using a first transmission format (block 202). The RLC layer segments the data message into Fixed-size PDUs (block 204). The fixed size of the PDUs is determined in accordance with the routine of Block 20 illustrated in Figure 4. Fixed-size PDUs are retransmitted in the radio interface by fully occupying one or several radio frames using a second different transmission format (block 206). Even though the two different formats include two different transmission speeds, the fixed PDU size, which has been optimally selected, ensures that radio resources are used efficiently. While the present invention has been described in relation to particular embodiments, those skilled in the art • recognize that the present invention is not limited to these 5 specific exemplary embodiments. Different formats, modalities and adaptations in addition to those illustrated and described as well as many variations, modifications and equivalent arrangements can also be employed to implement the invention. Therefore, while the The present invention has been described with respect to its preferred embodiments, it will be understood that this disclosure is illustrative and exemplary only of the present invention and is solely for the purpose of illustrating the present invention. Accordingly, the invention is limited only by the spirit and scope of the appended claims. • twenty

Claims (1)

1. CLAIMS 1. A method for transmitting data at variable speeds in a communication link in time intervals • predetermined, where each of the intervals of The predetermined time has the same duration, which comprises: the reception of data for transmission in the communication link; the detection of a first transmission speed 10 for transmission in the communication link; the provision of data bits at the first transmission rate in data blocks of fixed size, each data block of fixed size has the same number of bits; 15 the transmission in the communication link at the first transmission rate during one or more of the predetermined time intervals of a first number • of data blocks of fixed size corresponding to the first transmission speed; 20 the detection of a change in the transmission speed in the communication link. of the first transmission speed at a second transmission speed; the supply of data bits at the second speed 25 transmission in the fixed-size data blocks; and transmitting a second number of fixed size blocks corresponding to the second transmission rate during one or more time intervals • default. The method accng to claim 1, wherein the fixed size of each data block is determined in such a way that the fixed-size data blocks occupy totally each of the predetermined time interval or the time intervals • 10 default for both the first transmission speed and the second transmission speed with useful information. 3. The method accng to claim 1, wherein the fixed size of each data block is determined with 15 base on a frequency with which you can change the transmission speed and a minimum data transmission speed. 4. The method accng to claim 3, wherein the frequency corresponds to a maximum frequency at 20 which can change the transmission speed and the minimum data transmission speed corresponds to the lowest available speed at which data can be transmitted. 5. The method accng to claim 3, wherein the fixed size of each of the data blocks of fixed size must exceed a predefined minimum size. The method accng to claim 3, wherein the maximum frequency at which the transmission rate can change is reduced. when the data transmission speed is below a predefined speed. The method accng to claim 1, wherein the transmission rate can not change during the predetermined time interval. The method accng to claim 1, further comprising: retransmitting at the second transmission rate one or more of a first number of data blocks during one of the predetermined time intervals, where the data block retransmitted or the data blocks are retransmitted. several blocks of retransmitted data of the first number of data blocks together with one or, several blocks of data of the second number of data blocks completely occupies one or more predetermined time intervals. The method accng to claim 1, wherein the communication link employs a wire or an optical cable for data transmission. The method accng to claim 1, wherein the communication link employs a wireless radio frequency resource to transmit data. A method for retransmitting data at variable rates in a first communication protocol layer at predetermined time intervals, wherein each of the predetermined time slots has the same duration, comprising: receiving a request for retransmission of a data message previously transmitted using a first transmission format that specifies a first transmission rate; segmenting in a second communication protocol layer above the first communication protocol layer the data message to be retransmitted in fixed-size protocol data units (PDUs), each fixed-size PDU has the same number of bits regardless of yes the PDU has the first transmission format or a second transmission format; and transmitting the fixed-size PDUs through the first communication protocol layer using a second transmission format that specifies a second transmission rate different from the first transmission rate at which the data message was originally transmitted during one or several of the predetermined time intervals. The method according to claim 11, wherein different transmission formats include different coding schemes, different interleaving lengths or different repetition schemes. • The method according to claim 11, wherein each PDU includes a header having a sequence number, at least a portion of the data message, and an error detection field. The method according to claim 11, wherein the fixed size of each PDU is selected in such a manner • 10 that the PDUs comprehensively occupy the predetermined time interval despite differences in transmission formats. The method according to claim 14, wherein the PDUs occupy the predetermined time interval 15 without having to add padding data bits to complete the predetermined time interval. 16. The method according to claim 11, wherein the fixed PDU size is determined on er basis. a frequency at which you can change the speed of 20 transmission and a minimum data transmission speed. 17. The method according to claim 16, wherein the frequency corresponds to a maximum frequency at which the transmission rate and the transmission speed may change. The minimum data transmission speed corresponds to the lowest available speed at which data can be transmitted. The method according to claim 17, wherein the maximum frequency at which the transmission rate may change is reduced when the data transmission rate is below a predefined speed. The method according to claim 11, wherein the transmission rate can not be captured during the predetermined time interval. A communication device comprising: a buffer that stores data for transmission on a communication link; a data processing circuit that detects a first transmission speed associated with data to be transmitted on the communication link, and which provides data bits at the first transmission rate in fixed size data blocks, each block of data size fixed has the same number of bits; and a transmitter transmitting on the communication link at the first transmission rate during one or more of the predetermined time intervals, each time interval having the same duration, a first number of the data blocks of fixed size by intervals of time corresponding to the first transmission speed; where the data processing circuit detects a • transmission rate change in the communication link from the first transmission rate to a second transmission rate, provides data bits at the second transmission rate in the fixed size data blocks, and transmits a second number of data. the fixed-size data blocks • 10 per time interval corresponding to the second transmission rate during one or more of the predetermined time intervals. 21. The communication device according to claim 20, wherein the fixed size of each block The data is determined in such a way that the fixed-size data blocks completely occupy one or more predetermined time intervals with useful information both in the case of the first transmission speed and in the case of the second transmission speed. 20 transmission. - * 22. The communication device according to claim 20, wherein 'the fixed size of each data block is determined based on a frequency at which the transmission rate can change and a 25 minimum data transmission speed. 23, The communication device according to claim 22, wherein the frequency corresponds to a maximum frequency at which the speed can change • transmission and the minimum data transmission speed corresponds to the minimum available speed at which data can be transmitted. 24, The communication device according to claim 22, wherein the fixed size of each of the data blocks of fixed size must exceed one • 10 predefined minimum size. 25. The communication device according to claim 24, wherein the maximum frequency at which the transmission rate may change is reduced when the transmission rate is 15 below a predefined speed. 26. The communication device according to claim 20, wherein the transmission rate can not change during the predetermined time interval. 20 27, The communication device according to claim 20, wherein the transmitter retransmits at the second transmission rate one or several of the first number of data blocks during one of the predetermined time intervals, and 25 where the data block or the various data blocks of the first number of data blocks retransmitted together with one or several of the second number of data blocks occupy (n) the entire time interval • default or the various predetermined time intervals. 28. The communication device according to claim 20, wherein the communication link employs a wire or an optical cable to transmit data. 29. The communication device according to claim 20, wherein the communication link employs a wireless radio frequency resource for transmitting data. 30, The communication device in accordance with the 15 claim 20, wherein the communication device is a mobile radiotelephone. 31 The communication device in accordance with the • claim 20, wherein the communication device is a radio base station. 32. A communication protocol for communication of data in a communication link between a mobile station and a base station, comprising: a first layer of communication protocol for transmitting data in the communication link to several .25 speeds at predetermined time intervals, where each of the predetermined time slots has the same duration, and a second communication protocol layer: • (a) that receives a request to retransmit a previously transmitted data message using a first transmission format specifying a first transmission rate, and (b) segmenting the data message into fixed-length protocol data units (PDUs), each PDU of The fixed size has the same number of bits, where the fixed-size PDUs are transmitted at a second transmission rate different from the first transmission rate at which the data message was originally transmitted during one or several of the transmission speeds. 15 the predetermined time intervals through the first communication protocol layer. 33. The communication protocol in accordance with the • claim 32, applied to a code division multiple access mobile communication system (CDMA) Wherein the first communication protocol layer employs a spreading code to transmit the PDUs on a radio communication link and the second communication protocol layer corresponds to a control link access control protocol layer. 25 radio (RLC).