Short latency fast retransmission triggering

Abstract

The invention relates to an improved transmission protocol for uplink data packet transmission in a communication system. A receiver of a user equipment receives a Fast Retransmission Indicator, referred to as FRI. The FRI indicates whether or not a base station requests a retransmission of a previously transmitted data packet. A transmitter of the user equipment retransmits the data packet using the same redundancy version as already used for the previous transmission of the data packet.

Claims

1. An integrated circuit which, in operation, controls a process of a user equipment operating a transmission protocol for uplink data packet transmission in a communication system, the process comprising: receiving a Fast Retransmission Indicator (FM), wherein the FRI indicates that a base station requests a retransmission of a previously-transmitted data packet using identical transmission parameters as the previously-transmitted data packet; and retransmitting the data packet using the identical transmission parameters as used for the previously-transmitted data packet.

2. The integrated circuit according to claim 1, wherein the FRI indicates that the retransmission is to be performed with an identical redundancy version as used for the previously-transmitted data packet, and wherein the integrated circuit is further operative to use the identical redundancy version as the previously-transmitted data packet for retransmitting the data packet.

3. The integrated circuit according to claim 2, wherein the identical transmission parameters include a scrambling code of the previously-transmitted data packet.

4. The integrated circuit according to claim 1, wherein the FRI indicates that a retransmission of a part of the previously-transmitted data packet is to be performed, and wherein the integrated circuit is further operative to cause the indicated part of the previously-transmitted data packet to be retransmitted.

5. The integrated circuit according to claim 4, wherein the retransmission further uses a transmit power for the retransmission of the part of the previously transmitted data packet such that a total transmit power for the retransmission equals a total transmit power of the previously transmitted data packet.

6. The integrated circuit according to claim 5, wherein using 50% of the data packet results in a transmission power increase of the part of the previously-transmitted data packet by a factor 2.

7. The integrated circuit according to claim 4, wherein the part of the previously-transmitted data packet is 50% or 25% of the previously-transmitted data packet.

8. The integrated circuit according to claim 1, wherein receiving the FRI includes receiving the FRI at a first timing after the transmission of the previously-transmitted data packet, wherein the first timing is fixed or semi-statically configurable by the base station.

9. The integrated circuit according to claim 1, wherein the data packet is retransmitted at a second timing after receiving the FM, and wherein the second timing is fixed, semi-static configurable by the base station, or variable based on a respective information included in the received FRI.

10. The integrated circuit according to claim 1, wherein the retransmission of the data packet is triggered by a Downlink Control Information (DCI) or a HARQ Indicator (HI), and wherein a first time period between the previous transmission of the data packet and the reception of the FM, or a second time period between the reception of the FRI and the retransmission of the data packet is smaller than a third time period between reception of the DCI or HI and its corresponding retransmission of the data packet, wherein at least one of the first and second time periods is smaller than 4 ms.

11. The integrated circuit according to claim 10, wherein in case that a request for performing the retransmission of the data packet by the FRI is received and a request for performing, at the same time, transmission of another data packet by the DCI or HI, the integrated circuit is further operative to follow the request by the FRI and to ignore the request by the DCI or HI.

12. The integrated circuit according to claim 1, wherein the FRI further comprises a HARQ process number indicator for indicating a HARQ process that was used by the integrated circuit for the previous transmission of the data packet.

13. The integrated circuit according to claim 1, wherein the previous transmission of the data packet is an initial transmission or a retransmission of the data packet.

14. The integrated circuit according to claim 1, wherein the FRI is received in radio resources used for receiving an HI the FRI is received as a DCI, the FRI is received in preconfigured radio resources of a common search space or the FRI is received in preconfigured radio resources of a user-equipment-specific search space.

15. The integrated circuit according to claim 1, wherein when the user equipment uses multiple transmitting antennas for transmission of data packets: receiving the FRI triggers a retransmission of the data packets, and the retransmission includes retransmitting the data packets to the base station using the multiple transmitting antennas; or receiving the FRI triggers a retransmission of one of the data packets, and the retransmission includes retransmitting the one of the data packets to the base station using the multiple transmitting antennas.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) In the following exemplary embodiments are described in more detail with reference to the attached figures and drawings.

(2) FIG. 1 shows an exemplary architecture of a 3GPP LTE system,

(3) FIG. 2 shows an exemplary downlink resource grid of a downlink slot of a subframe as defined for 3GPP LTE (Release 8/9),

(4) FIG. 3 exemplary illustrates the transmission protocol operation between the UE and the eNodeB for an uplink transmission and its retransmissions,

(5) FIG. 4 schematically illustrates a block diagram including coding chain functionalities within the physical layer for a single codeword/transport block,

(6) FIG. 5 schematically illustrates a block diagram including physical channel processing functionalities within the physical layer,

(7) FIG. 6 illustrates a timing diagram of the transmission requests and the corresponding transmissions, according to the embodiment, and

(8) FIG. 7 illustrates a timing diagram of the transmission requests and the corresponding transmissions in case of a conflict between simultaneously requested retransmissions, according to the embodiment.

DETAILED DESCRIPTION

(9) As can be seen from FIG. 3 and the description thereof in the background section, there is currently a delay of 4 ms between a PDCCH/PHICH and a corresponding PUSCH uplink transmission. This delay is mainly caused due to the processing that needs to be done at the UE side, including the detection of PDCCH/PHICH as well as the coding chain and physical channel processing steps outlined above. Even though this latency of 4 ms could be reduced by shortening the TTI as is being discussed within the scope of the above-described Short Latency study item, the main savings in time would be due to the smaller transport block sizes and a potentially improved hardware/software design that allows faster processing. Nevertheless, the savings are still bounded by the need for processing all the functional blocks in the transmission chain as outlined above, even for a retransmission, especially when a different RV is used for a retransmission compared to the previous transmission of the same transport block (data packet).

(10) Another delay that is currently 4 ms long is the gap between a PUSCH transmission and the next potential trigger by PDCCH/PHICH for the same HARQ process. This gap is caused by the need of the eNB to process the PUSCH and attempt the decoding of same, and in case of an unsuccessful decoding attempt, to determine again the proper scheduling and link adaptation procedures to determine an appropriate set of physical layer transmission parameters (including the MCS, number and position of RBs, RV, transmit power) for the retransmissions, which needs to take other users' needs for uplink transmission into account as well. Finally, once these parameters are determined, they need to be conveyed to the UE by a DCI on (E)PDCCH (for an adaptive retransmission) and/or by an HI on a PHICH (for a non-adaptive retransmission).

(11) Even though a PHICH could be seen as a compact method to trigger a non-adaptive retransmission, especially due to the different RV version and the subframe-dependent scrambling, the UE would still need to execute a substantial number of steps before being able to transmit.

(12) The object of the invention is to reduce the delay between the transmission on PUSCH from the UE and a corresponding retransmission indication by the eNodeB. A further object is to also to reduce the delay between an indication for a retransmission by the eNodeB and the corresponding retransmission on PUSCH from the UE.

(13) The following exemplary embodiment is conceived by the inventors to mitigate one or more of the problems explained above.

(14) Particular implementations of the several variants of the embodiment are to be implemented in the wide specification as given by the 3GPP standards and explained partly in the background section, with the particular key features being added as explained in the following pertaining to the described embodiment. It should be noted that the embodiment may be advantageously used for example in a mobile communication system, such as 3GPP LTE-A (Release 10/11/12/13) communication systems as described in the Technical Background section above, but the embodiment is not limited to its use in this particular exemplary communication networks.

(15) The explanations should not be understood as limiting the scope of the disclosure, but as a mere example of the embodiment to better understand the present disclosure. A skilled person should be aware that the general principles of the present disclosure as laid out in the claims can be applied to different scenarios and in ways that are not explicitly described herein. For illustration purposes, several assumptions are made which however shall not restrict the scope of the following embodiment.

(16) In the following, an embodiment for solving the above-mentioned problem(s) will be described in detail. Different implementations and variants of the embodiment will be explained as well.

(17) The embodiment provides a user equipment (UE) operating a transmission protocol for uplink data packet transmission in a communication system. According to the transmission protocol, a Fast Retransmission Indicator (FM) is used for triggering a faster retransmission at the UE with reduced timing in case of an unsuccessful PUSCH decoding attempt at the eNodeB. If employing this FM, it is possible to transmit a retransmission request earlier by the eNodeB than it is possible with the use of a DCI/HI.

(18) In order for the UE to retransmit a data packet quicker than it would be possible in response to a DCI, the UE may use, according to one variant of the embodiment, for its retransmission of the data packet not only the same radio resources as if a non-adaptive retransmission is triggered by HI, but also uses other identical parameters as they were applicable for the latest transmitted data packet, which was triggered by a DCI or HI.

(19) Likewise, the embodiment provides a base station operating a transmission protocol for uplink data packet transmission where the FRI is transmitted to the UEs so as to indicate whether or not a retransmission of a previously transmitted data packet is requested. In reaction to such request, the base station receives from the UE the retransmitted data packet with the same redundancy version as already used for the previous transmission of the data packet.

(20) As a general consideration, if the eNodeB intends to trigger a fast retransmission of a data packet, e.g., due to a time-critical Quality-of-Service requirement, it is more important to have a retransmission as fast as possible at the possible expense of a non-optimum use of the radio channel capacity. As a key aspect for achieving such a fast retransmission of the data packet, the eNodeB does not need to make a full link adaptation assessment since all parameters are already decided for the previous transmission of the data packet.

(21) In the background section it has already been explained that, even if using a HI for retransmission, the redundancy version will change for the retransmitted data block. In this case, the redundancy version is cycled through the predefined sequence of redundancy versions, which is 0, 2, 3, 1, for instance. The specific selected redundancy version for the retransmission is an input value for the “rate matching” block, as illustrated in FIG. 4. Hence, for each retransmitted data block that uses a different redundancy version (RV), at least the blocks “rate matching,” “Code block concatenation,” “Data and Control multiplexing,” and “Channel Interleaver” have to be processed again. Also, the output of the “Channel Interleaver” block then is input to the entire physical channel processing, which is illustrated in FIG. 5.

(22) In order to achieve a significant reduction of the time needed for transmitting a retransmission of the data packet, in one implementation of the embodiment the UE uses for its retransmission of the data packet the same redundancy version as already used for the previous transmission of the data packet. Due to the UE using for its retransmission of the data packet a subset of identical transmission parameters as for the previous DCI-triggered transmission, namely the same redundancy version as for the previously transmitted data packet, all processing steps involved with the change of the redundancy version of the data packet can be skipped.

(23) That is, even in case of only using the same RV as for the previous DCI (or HI) triggered transmission of a data packet, no new “rate matching” and subsequent blocks (as shown in FIG. 4) up to the beginning of the scrambling (as shown in FIG. 5) need to be processed. In other words, for a fast retransmission it is sufficient, if the UE buffers the codewords as they are transmitted in the most recent transmission, and does feed those buffered codewords into the physical channel processing procedure, as shown in FIG. 5.

(24) In FIG. 6, a timing diagram of the transmission requests and the corresponding transmissions is shown. As can be seen from this figure, the time period between the transmission of a DCI by the eNodeB as well as the corresponding transmission of the data packet by the UE is indicated as time period t0, wherein the time period t0 may be named as “third timing.” For an uplink HARQ protocol as employed since LTE Release 8, time period t0 corresponds to the time period of 4 ms as shown in FIG. 3, where the conventional case is illustrated that relates to triggering an uplink data transmission by a DCI. As can be obtained from FIG. 6, and in contrast to FIG. 3, the time period t1 (as also shown in FIG. 6) between the transmission of a data packet by the UE (PUSCH) and the transmission of the FRI by the eNodeB may be equal to or shorter than t0, whereas in a preferred variant of the embodiment, t1, however, is smaller than time period t0. While time period t0 may become smaller than 4 ms in the further development in the future, not limiting the scope of the invention the description of the embodiments assumes that time period t0 is 4 ms, unless otherwise stated.

(25) Thereby, as a further variant of the embodiment, the time period t1, which may be named as “first timing,” is a fixed time period or a time period that is semi-statically configurable by the base station, and wherein, preferably, time period t1 may be smaller than 4 ms.

(26) It is to be noted that an FRI generally can indicate at least two states. According to “State 1,” the FRI is a “positive FRI” and triggers a fast retransmission, whereas in this case, the FRI could be seen as a negative acknowledgment of a received data packet. According to “State 2,” the FRI is a “negative FRI” and does not trigger a faster retransmission, since in this case, the FRI could be seen as a positive acknowledgment of a received data packet. A functionally equivalent interpretation of states is therefore that a “positive FRI” is equivalent to an FRI carrying a “negative acknowledgement (NACK),” and a “negative FRI” is equivalent to an FRI carrying an “acknowledgement (ACK).” For simplicity and without restricting the scope of the embodiment, the description hereafter uses only the terminology “positive FRI” and “negative FRI.”

(27) As further derivable from FIG. 6, the time period t2, which is defined as the time between a positive FRI sent by the eNodeB and its corresponding PUSCH transmission sent by the UE, must be smaller than time period t0, which is the time period between a DCI (or HI) and its corresponding PUSCH transmission. The shorter time period t2 compared to the time period t0 is the result of saving calculation time at the UE due to using, for a retransmission of a data packet, a subset of identical transmission parameters as for the previous DCI-/HI-triggered transmission as described above. The use of the identical redundancy version is illustrated in FIG. 6. For example, for both, the PUSCH transmission that is initiated by the DCI as well as the PUSCH transmission that is initiated by the FRI are carried out by using redundancy version RV #0. In other words, RV #0 was determined according to the DCI initiated PUSCH transmission and reused by the FRI initiated PUSCH transmission.

(28) Thereby, as a further variant of the embodiment, the time period t2, which may be named as “second timing,” is a fixed time period or a time period that is semi-statically configurable by the base station or variable based on a respective information comprised in the transmitted/received FRI. Preferably, time period t2 may be smaller than 4 ms.

(29) According to a further implementation of the embodiment, the positive FRI indicates that the retransmission is to be performed with additional transmission parameters identical to same used for the previous transmission of the data packet, whereas these additional identical transmission parameters are then used for retransmitting the data packet by the UE and for receiving the retransmitted data packet at the base station.

(30) According to a further implementation of the embodiment, the additional identical transmission parameter to be used for retransmitting the data packet is at least the scrambling code of the previously transmitted data packet. As an advantage of having further identical transmission parameters such as the same scrambling code is that in addition to the above mentioned skipping of the blocks “rate matching” to “Channel Interleaver” as shown in FIG. 4, also the “scrambling” block as shown in FIG. 5 does not need to be processed for the retransmitted data packet.

(31) In further variants of the embodiment, additional identical transmission parameters may be re-used from a previous DCI initiated PUSCH transmission, up to the point where the precoded information is available, i.e., after the block “Precoding” in FIG. 5. For example, further additional identical transmission parameters may be re-using the modulation scheme and the layer mapping from a previous DCI initiated PUSCH transmission, so that the same transmission scheme is used for the retransmission as for the previous transmission, i.e., the same number of transmission layers and the same antenna ports are used. Using the same precoding vector(s) as in the previous transmission is most reasonable in case the FRI does not indicate a different precoder to be used.

(32) However, if re-using further identical transmission parameters from a previous DCI initiated PUSCH transmission beyond the block “Precoding” as shown in FIG. 5, then only a part of the resources are utilized for the retransmission. For example, the “Resource Element Mapper” block would only map data to a part of the resources that had been used for the previous transmission, e.g., a fraction of the resource blocks such as, for example, 50% of the resource blocks. Equivalently, for a fast retransmission, only a fraction of the output of the “Resource Element Mapper” block is used as input to the “SC-FDMA signal generation” block. Therefore, it would be sufficient if the UE buffers the output of the “Resource Element Mapper” block(s) of the previous transmission, and upon being triggered for a partial retransmission, reads only the corresponding parts from the buffer and applies these as the input to the SC-FDMA signal generation. Preferably, the fraction used for a fast retransmission consists of a non-negative integer multiple of a basic time or frequency resource unit, such as a “resource block” or a “resource block group” as defined in TS 36.213. This has the advantage that unused resources can be optimally assigned to other UEs, i.e., without wasting resources caused by a fractional resource block or resource block group. In addition, the fraction should result in a bandwidth of the PUSCH in terms of resource blocks M.sub.RB.sup.PUSCH, where M.sub.RB.sup.PUSCH=2.sup.α.sup.2.Math.3.sup.α.sup.3.Math.5.sup.α.sup.5 and where α.sub.2, α.sub.3, α.sub.5 is a set of non-negative integers. Therefore, if the indicated fraction would result in a non-integer number of resource blocks, or resource block groups, or if the resulting bandwidth M.sub.RB.sup.PUSCH would not fulfill the condition M.sub.RB.sup.PUSCH=2.sup.α.sup.2.Math.3.sup.α.sup.3.Math.5.sup.α.sup.5, the UE should preferably round up to the smallest integer number of resource blocks, or resource block groups than the indicated fraction, or to the smallest integer value M.sub.RB.sup.PUSCH greater than the indicated fraction that fulfils M.sub.RB.sup.PUSCH=2.sup.α.sup.2.Math.3.sup.α.sup.3.Math.5.sup.α.sup.5, respectively.

(33) In a further variant of the embodiment, as an additional identical transmission parameter, the same “cyclic shift parameter” may be used as for the generation of the reference signals for the retransmission of the data packet. In this regard, reference is made to section 5.5.2 of 3GPP technical standard 36.211. Using the identical “cyclic shift parameter” for the generated reference signals results in a further reduction of the overall processing time for the retransmission. In another variant, the FRI transmitted by the eNodeB may further comprise information with regards to the “cyclic shift parameter,” which is to be used by the UEs for the generation of the reference signals for the retransmission of the data packet.

(34) It may happen that the most recent transmission of a data block does not only consist of UL-SCH data, but includes uplink control information (UCI) such as ACK/NACK, CSI. As can be seen in FIG. 4, such information is added to the data in the block “Data and control multiplexing.” Generally, such information is preferably also added in a retransmission triggered by FRI in the same way as in the most recent transmission of the data block. However, transmitting the identical ACK/NACK or CSI information is not necessarily reasonable, as the content would be outdated due to the delay between the previous transmission and the triggered retransmission. Therefore, an alternative embodiment does not include the UCI in the retransmission, but reserves those resources as if the information was present. As a consequence, the order of data block bits can be unchanged, so that no further bit reordering procedure is necessary for a retransmission.

(35) Likewise, a part of the resources of an uplink subframe may contain sounding reference symbols (SRS), preferably at the end of a subframe. In such a case, a fast retransmission may then also contain the SRS as in the previous transmission, or the resources are reserved (e.g., muted). As a consequence, the mapping of the PUSCH to the resource elements can remain unchanged, so that no further RE reordering procedure is necessary for a retransmission.

(36) With reference to FIGS. 6 and 7, it is to be noted that the eNodeB may flexibly determine in case a data packet has not successfully been received, whether a retransmission for the data packet is requested from the UE by using the FRI, or by using a DCI, or by using a HI and thus to transmit either the FRI, the DCI, or the HI to the UE. Likewise, the UE may also flexibly react on the reception of either an FRI, a DCI, or an HI and perform a corresponding transmission/retransmission of the data packet based on the received FRI, DCI, or the HI, as described above.

(37) According to a further implementation of the embodiment, the FRI indicates that a retransmission of a part of the previously transmitted data packet is to be performed, optionally wherein a part is 50% or 25% of the previously transmitted data packet. In such a case, the UE retransmits the indicated part of the previously transmitted data packet. The UE may adapt the transmit power for the retransmission of the part of the previously transmitted data packet so that the total transmit power for the retransmission equals the total transmit power of the previously transmitted data packet, optionally wherein using 50% of the data packet results in a transmission power increase of the part of the previously transmitted data packet by a factor 2.

(38) If for a retransmission only a fraction of the frequency resources of the previous transmission are utilized, the total power that the UE would transmit for the partial retransmission would also be a fraction. However, in order to improve the quality of the partial retransmission data, its power can be boosted reciprocally to the fraction of the frequency resources. For example, if a partial retransmission utilizes only 50% of the frequency resources, then each RE of the partial retransmission can be boosted by a factor of 2, so that the total transmit power when regarding all transmitted REs for the partial retransmission and the full retransmission is equal. Such a partial retransmission is particularly attractive, if there is no need for a full retransmission to arrive at a successful decoding of the transport block, or if the eNodeB intends to use only parts of the frequency resources for the retransmission so that the remaining parts can be scheduled to another UE.

(39) The amount of frequency resources to be utilized for a partial retransmission can be determined according to:

(40) 1. A semi-static configuration: Whenever a positive FRI triggers a fast retransmission, the UE looks up the configured value and applies it accordingly.

(41) 2. An indication within the FRI: The FRI can carry an indicator to determine the amount of partial resources. For example, a first FRI value triggers a partial retransmission of 50%, a second FRI value triggers a partial retransmission of 25%, a third value triggers a full retransmission (i.e., 100%), while a fourth FRI value triggers no fast retransmission. Therefore, there would be three positive and one negative FRI values in this example.

(42) Combinations of these are possible, e.g., the eNodeB configures three different partial retransmission values (possibly including 100%), and then each of the positive FRI values points to the corresponding semi-static partial retransmission value, respectively (with one FRI value indicating no fast retransmission, i.e., one negative FRI value).

(43) In a further implementation of the embodiment, the user equipment may comprise multiple transmitting antennas for transmission of data packets. In this case, the received FRI triggers a retransmission of the data packets so that the UE retransmits the data packets to the eNode B using the multiple transmitting antennas. That is, in case that a transmission contains two transport blocks (codewords) as in SU-MIMO, a positive FRI would preferably indicate a retransmission of both transport blocks to re-use the transmission buffer as much as possible without excessive PHY re-processing, as can be appreciated in relation to FIG. 5. According to this case and referring to FIG. 5, re-using the transmission buffer in case of retransmitting both transport blocks involves that there is no need for processing the illustrated blocks of FIG. 5 at all. That is, the retransmission of the two transport blocks takes place right after the respective “SC-FDMA signal generation” block and can be directly transmitted to the eNodeB without further processing.

(44) At the eNodeB side, which may also use multiple antennas, upon transmitting the FRI that triggers the retransmission of the transport blocks, the retransmitted transport blocks are received at the eNodeB using the multiple receiving antennas.

(45) However, triggering a retransmission of both transport blocks by (one single) FRI comes at the expense of radio resource efficiency and signal-to-noise ratio. Therefore an alternative implementation of the embodiment would trigger a retransmission of one transport block per FRI so that the retransmission of the one transport block to the eNodeB as well as the reception of the one transport block at the eNodeB is carried out by using the multiple transmitting antennas. It is to be noted that in this case, more processing is required at the UE until the SC-FDMA signals are available for transmission. That is, with reference to FIG. 5, if the FRI triggers a retransmission of only one transport block, this involves the processing of the “Layer mapping” block up to the “SC-FDMA signal generation” blocks.

(46) The above description relates to the behavior for retransmission, according to which it is assumed that data for the same transport blocks is used in transmissions and retransmissions, i.e., implying that a retransmission applies to the same HARQ process. However, there may also be multiple HARQ processes that can be scheduled concurrently-following a synchronous or an asynchronous protocol.

(47) In both cases, a fast retransmission would occur in a TTI at time “#t_pusch,” as illustrated in FIG. 7. A PUSCH transmission at time “#t_pusch” could therefore be triggered by a positive FRI at time “#t_pusch-t2,” or by a DCI (or HI) at time “#t_pusch-t0,” and generally for different HARQ processes. Therefore, in FIG. 7, different HARQ processes P0 and P1 are illustrated. In the exemplary case as shown in FIG. 7, HARQ process P0 relates to the FRI initiated retransmission at time “#t_pusch,” whereas HARQ process P1 relates to the DCI initiated retransmission at the time “#t_pusch-t0.”

(48) As further shown in FIG. 7, the retransmissions for both HARQ processes P0 and P1 would result in a retransmission at time “#t_pusch.” However, in order to avoid a transmission collision, the UE needs to decide what it should do at time “#t_pusch.” The first option would be to carry on with a retransmission for HARQ process P0, i.e., follow the FRI trigger received at time “#t_pusch-t2.” The second option would be to carry on with a retransmission for HARQ process P1, i.e., follow the DCI (or HI) received at time “#t_pusch-t0.”

(49) In this regard, a preferred implementation of the embodiment relates to the specific behavior of the UE, such that it follows the request by the FRI (that is, the afore-mentioned first option) and ignores the request by the DCI or HI, in case of receiving a request for performing the retransmission of the data packet by the FRI as well as a request for performing, at the same time, transmission of another data packet by the DCI or HI.

(50) As shown in the background section, when there is a conflict between HI and DCI, the UE follows the DCI and ignores the HI. However, contrary thereto, in the case as provided by the alternative implementation of the embodiment, the fast retransmission should be followed and the DCI (or HI) should be ignored. This is because the positive FRI has been transmitted at a later point in time than the DCI corresponding to the same subframe. Consequently, it should be assumed that the eNodeB would only transmit a positive FRI in case it intends the UE to follow the positive FRI—and not the DCI. Otherwise it would not have triggered a retransmission by a positive FRI for that subframe.

(51) As already described in connection with FIG. 6, also for the case that the UE follows the request by the FRI so as to avoid a transmission collision, as illustrated in FIG. 7, the use of the identical redundancy version for both, the PUSCH transmission that is initiated by the DCI as well as the PUSCH transmission that is initiated by the FRI are carried out by using redundancy version RV #0. In other words, RV #0 was determined according to the DCI initiated PUSCH transmission and re-used by the FRI initiated PUSCH transmission.

(52) Moreover, in a further variant of the embodiment, the FRI further comprises an HARQ process number indicator so as to indicate the particular HARQ process that was used by the transmitter for the previous transmission of the data packet.

(53) In the table below, the UE behavior is shown for several cases with respect to the content of received FRI and DCI/HI.

(54) TABLE-US-00002 Content Content of the of the FRI DCI (or HI) received received by the by the UE UE UE behavior Negative Request for New transmission according to DCI FRI New (or HI) Transmission Negative Request for Retransmission according to DCI FRI Retransmission (adaptive retransmission) or according to HI (non-adaptive retransmission) Negative None No (re)transmission FRI Positive None Fast retransmission FRI Positive Request for Fast retransmission, wherein data for FRI New the HARQ process is kept Transmission corresponding to the DCI/HI in the or for buffer. A DCI is required to resume Retransmission retransmissions for that HARQ process.

(55) In the table below, an alternative UE behavior is shown for several cases with respect to the content of received FRI and DCI/HI.

(56) TABLE-US-00003 HARQ Content of feedback the FRI seen by received by the UE DCI seen by the UE (HI) the UE UE behavior Negative ACK or Request for New transmission FRI NACK New according to DCI Transmission Negative ACK or Request for Retransmission according to FRI NACK Retransmission DCI (adaptive retransmission) Negative ACK None No (re)transmission FRI Negative NACK None Non-adaptive FRI retransmission Positive ACK None Fast retransmission FRI Positive NACK None Fast retransmission, wherein FRI data is kept for the HARQ process corresponding to the HI in the buffer. A DCI is required to resume retransmissions for that HARQ process. Positive ACK or Request for Fast retransmission, wherein FRI NACK New data is kept for the HARQ Transmission or process corresponding to the Retransmission DCI/HI in the buffer. A DCI is required to resume retransmissions for that HARQ process.

(57) With reference to the description provided above, the FRI may, according to one variant of the embodiment, indicate at least one of the following elements: Whether or not a fast retransmission is triggered (positive FRI or negative FRI, or alternatively NACK or ACK); In case of a triggered fast retransmission: The HARQ process number indicator for the triggered retransmission; In case of a triggered fast retransmission: A fractional retransmission parameter indicating the requested part of the data block to be retransmitted; In case of a triggered fast retransmission: An indication about the time period t2 until the UE should transmit accordingly.

(58) According to another implementation of the embodiment, the UE receives the FRI in radio resources used for receiving the HI, or receives the FRI as a DCI (for example, in DCI format 7), or receives the FRI in preconfigured radio resources of a common search space, or receives the FRI in preconfigured radio resources of a user-equipment-specific search space.

(59) Generally, the FRI can be transmitted in one of the following ways: In the same RE(s) where a UE would expect to find a PHICH (but in a different subframe in case that time period t1 is smaller than the time between a PUSCH transmission and the subframe carrying the corresponding HI), i.e., in RE(s) belonging to REGs within the control channel region of a subframe/TTI, or In RE(s) belonging to a common search space for DCI, i.e., in REs where all UEs detect FRI, or In a DCI, where preferably FRI for multiple UEs and/or subframes are multiplexed. For example, the DCI could contain four FRI, where the first FRI is applicable to UE1, the second FRI is applicable to UE2, and so on. Especially for TDD systems, several FRI could be multiplexed or bundled for one UE into a DCI, so that e.g., the first four FRI are applicable to four PUSCH transmissions of UE1, the next three FRI are applicable to three PUSCH transmissions of UE2, and so on. In case that FRI for multiple UEs are multiplexed, preferably the DCI is transmitted in the common search space. In case that FRI for only one UE are transmitted, preferably the DCI is transmitted in the UE-specific search space.

(60) As a variant of the embodiment, instead of including one or more of the above contents into the FRI, one or more of the above could be used to determine the RE(s) where the FRI is transmitted. For example, the HARQ process could determine the RE(s) where the FRI is transmitted. A UE would then monitor multiple FRI resources and preferably evaluates only the FRI that is received with the strongest power.

(61) As described with respect to the several variants of the embodiment above, a positive FRI would not imply an implicit or explicit change of the RV for the retransmission, in contrast to retransmissions triggered by HI described in the background section. However, as a further variant of the embodiment, a retransmission triggered by an FRI should not affect a potential RV determination rule for non-adaptive retransmissions by PHICH. As indicated previously in the background section, a retransmission triggered by PHICH implicitly cyclically switches between RV {0, 2, 3, 1}. According to this variant, a positive FRI should be ignored for purposes of RV determination for later non-adaptive retransmissions, i.e., the RV switching/cycling should only take the RV of previous DCI/HI-triggered (re-)transmissions into account.

(62) As a further variant of the embodiment, in addition to using the FRI as described above, in case the PUSCH occupies not a full 1 ms TTI, but a short TTI (as being discussed in the Short Latency study item above), the transport blocks are smaller than in a 1 ms TTI, so that the decoding result (OK/failure) at the eNodeB would be available sooner. Hence, in this case, the FRI could be transmitted earlier than a DCI/HI in a conventional system.

(63) As another implementation of the embodiment, a previous transmission of the data packet may be an “initial transmission of the data packet” or a “retransmission of the data packet.”

(64) Hardware and Software Implementation of the Present Disclosure

(65) Other exemplary embodiments relate to the implementation of the above described various embodiments using hardware, software, or software in cooperation with hardware. In this connection a user equipment (mobile terminal) is provided. The user equipment is adapted to perform the methods described herein, including corresponding entities to participate appropriately in the methods, such as receiver, transmitter, processors.

(66) It is further recognized that the various embodiments may be implemented or performed using computing devices (processors). A computing device or processor may for example be general purpose processors, digital signal processors (DSP), application specific integrated circuits (ASIC), field programmable gate arrays (FPGA) or other programmable logic devices, etc. The various embodiments may also be performed or embodied by a combination of these devices. In particular, each functional block used in the description of each embodiment described above can be realized by an LSI as an integrated circuit. They may be individually formed as chips, or one chip may be formed so as to include a part or all of the functional blocks. They may include a data input and output coupled thereto. The LSI here may be referred to as an IC, a system LSI, a super LSI, or an ultra LSI depending on a difference in the degree of integration. However, the technique of implementing an integrated circuit is not limited to the LSI and may be realized by using a dedicated circuit or a general-purpose processor. In addition, a FPGA (Field Programmable Gate Array) that can be programmed after the manufacture of the LSI or a reconfigurable processor in which the connections and the settings of circuits cells disposed inside the LSI can be reconfigured may be used.

(67) Further, the various embodiments may also be implemented by means of software modules, which are executed by a processor or directly in hardware. Also a combination of software modules and a hardware implementation may be possible. The software modules may be stored on any kind of computer readable storage media, for example RAM, EPROM, EEPROM, flash memory, registers, hard disks, CD-ROM, DVD, etc. It should be further noted that the individual features of the different embodiments may individually or in arbitrary combination be subject matter to another embodiment.

(68) It would be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present disclosure as shown in the specific embodiments. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive.

(69) The various embodiments described above can be combined to provide further embodiments. All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet are incorporated herein by reference, in their entirety. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications and publications to provide yet further embodiments.

(70) These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.