METHOD AND APPARATUS FOR PERFORMING PACKET DUPLICATION IN A

MULTI-CONNECTIVITY SCENARIO

5 BACKGROUND:

Field:

Certain embodiments of the present invention relate to performing packet duplication in a multi-connectivity scenario during retransmissions. o Description of the Related Art:

5G and Long-term Evolution (LTE) are standards for wireless communication that seek to provide improved speed and capacity for wireless communications by using new modulation/signal processing techniques. These standards were proposed by the 3 ^rd Generation Partnership Project (3GPP), and are based upon previous network technologies. Since their inception, 5G and LTE have 5 seen extensive deployment in a wide variety of contexts involving the communication of data.

SUMMARY:

According to a first embodiment, a method can include attempting to receive, by a user equipment, a transmission via a first cell. Reception of the transmission is negatively acknowledged by the user o equipment. The method can also include receiving a retransmission of the transmission via the first cell. The method can also include receiving a retransmission of the transmission via at least one second cell.

In the method of the first embodiment, the first cell and the at least one second cell are served by 5 different base stations.

In the method of the first embodiment, the different base stations are connected by non-ideal backhaul. 0 In the method of the first embodiment, receiving the retransmissions includes receiving the retransmissions using automatic repeat request.

In the method of the first embodiment, receiving the retransmissions using automatic repeat request includes receiving the retransmissions using hybrid automatic repeat request with fast retransmissions5 on a medium access control layer.

In the method of the first embodiment, the receiving the retransmission via the first cell and the receiving the retransmission via the at least one second cell includes receiving a same redundancy version. In the method of the first embodiment, the receiving the retransmission via the first cell and the receiving the retransmission via the at least one second cell includes receiving different redundancy versions.

5 In the method of the first embodiment, the method may also further include receiving retransmission information from the first cell. The retransmission information indicates when to expect retransmissions from the at least one second cell and/or identifies the at least one second cell.

In the method of the first embodiment, the retransmission information is provided within scheduling o information of the retransmission via the first cell, and the retransmission information is provided in the physical downlink control channel.

In the method of the first embodiment, the method can also include configuring the user equipment with a timer. The user equipment is configured to transmit ACK/NAK information when the timer 5 expires. The ACK/NAK information is based on versions of the transmission that have been received by the user equipment.

According to a second embodiment, an apparatus can include attempting means to attempt to receive a transmission via a first cell. Reception of the transmission is negatively acknowledged by the o apparatus. The apparatus can also include first receiving means to receive a retransmission of the transmission via the first cell. The apparatus can also include second receiving means to receive a retransmission of the transmission via at least one second cell.

In the apparatus of the second embodiment, the first cell and the at least one second cell are served 5 by different base stations.

In the apparatus of the second embodiment, the different base stations are connected by non-ideal backhaul. 0 In the apparatus of the second embodiment, receiving the retransmissions comprises receiving the retransmissions using automatic repeat request.

In the apparatus of the second embodiment, receiving the retransmissions using automatic repeat request may include receiving the retransmissions using hybrid automatic repeat request with fast 5 retransmissions on a medium access control layer.

In the apparatus of the second embodiment, the receiving the retransmission via the first cell and the receiving the retransmission via the at least one second cell may include receiving a same redundancy version.

0

In the apparatus of the second embodiment, the receiving the retransmission via the first cell and the receiving the retransmission via the at least one second cell may include receiving different redundancy versions. In the apparatus of the second embodiment, the apparatus may also include comprising third receiving means to receive retransmission information from the first cell. The retransmission information indicates when to expect retransmissions from the at least one second cell and/or identifies the at least one second cell.

In the apparatus of the second embodiment, the retransmission information is provided within scheduling information of the retransmission via the first cell, and the retransmission information is provided in the physical downlink control channel.

In the apparatus of the second embodiment, the apparatus can also include configuring means to configure the user equipment with a timer. The user equipment is configured to transmit ACK/NAK information when the timer expires. The ACK/NAK information is based on versions of the transmission that have been received by the apparatus.

According to a third embodiment, a computer program product can be embodied on a non-transitory computer readable medium. The computer program product can be configured to control a processor to perform a method according to the first embodiment. According to a fourth embodiment, a method can include transmitting, by a user equipment, a transmission via a first cell to a first base station. Reception of the transmission is negatively acknowledged by the first base station. The method can also include transmitting a retransmission of the transmission via the first cell to the first base station. The method can also include transmitting a retransmission of the transmission via at least one second cell to at least one second base station.

In the method of the fourth embodiment, the first cell and the at least one second cell are served by different base stations.

In the method of the fourth embodiment, the different base stations are connected by non-ideal backhaul.

In the method of the fourth embodiment, transmitting the retransmissions can include transmitting the retransmissions using automatic repeat request. In the method of the fourth embodiment, transmitting the retransmissions using automatic repeat request includes transmitting the retransmissions using hybrid automatic repeat request with fast retransmissions on a medium access control layer.

In the method of the fourth embodiment, the transmitting the retransmission via the first cell and the transmitting the retransmission via the at least one second cell may include transmitting a same redundancy version. In the method of the fourth embodiment, the transmitting the retransmission via the first cell and the transmitting the retransmission via the at least one second cell can include transmitting different redundancy versions.

5 According to a fifth embodiment, an apparatus can include first transmitting means to transmit a transmission via a first cell to a first base station. Reception of the transmission is negatively acknowledged by the first base station. The apparatus can also include second transmitting means to transmit a retransmission of the transmission via the first cell to the first base station. The apparatus can also include third transmitting means to transmit a retransmission of the transmission via at least o one second cell to at least one second base station.

In the apparatus of the fifth embodiment, the first cell and the at least one second cell are served by different base stations. 5 In the apparatus of the fifth embodiment, the different base stations are connected by non-ideal backhaul.

In the apparatus of the fifth embodiment, transmitting the retransmissions can include transmitting the retransmissions using automatic repeat request.

0

In the apparatus of the fifth embodiment, transmitting the retransmissions using automatic repeat request may include transmitting the retransmissions using hybrid automatic repeat request with fast retransmissions on a medium access control layer. 5 In the apparatus of the fifth embodiment, the transmitting the retransmission via the first cell and the transmitting the retransmission via the at least one second cell may include transmitting a same redundancy version.

In the apparatus of the fifth embodiment, the transmitting the retransmission via the first cell and the 0 transmitting the retransmission via the at least one second cell may include transmitting different redundancy versions.

According to a sixth embodiment, a computer program product can be embodied on a non-transitory computer readable medium. The computer program product can be configured to control a 5 processor to perform a method according to the fourth embodiment.

According to a seventh embodiment, a method can include transmitting, by a first network node, a transmission via a first cell to a user equipment. Reception of the transmission is negatively acknowledged by the user equipment. The method can also include transmitting a retransmission of o the transmission via the first cell. The method can also include transmitting, to at least one second network node, data for performing a retransmission of the transmission. The at least one second network node is configured to transmit the retransmission to the user equipment via at least one second cell. In the method of the seventh embodiment, the first network node may include a first base station, and the at least one second network node may include at least one second base station.

5 In the method of the seventh embodiment, the first base station and the at least one second base station are connected by non-ideal backhaul.

In the method of the seventh embodiment, the transmitting data for performing the retransmission may include transmitting using an X2 interface.

0

In the method of the seventh embodiment, transmitting the retransmissions may include transmitting the retransmissions using automatic repeat request.

In the method of the seventh embodiment, the transmitting the retransmission via the first cell and the 5 transmitting the retransmission via the at least one second cell may include transmitting using a same redundancy version.

In the method of the seventh embodiment, the transmitting the retransmission via the first cell and the transmitting the retransmission via the at least one second cell may include transmitting different o redundancy versions.

In the method of the seventh embodiment, the method can also include transmitting control information via the first cell to the at least one second cell using an X2 interface. 5 In the method of the seventh embodiment, the control information may include at least one of a modulation and coding scheme and a redundancy version.

According to an eighth embodiment, an apparatus can include first transmitting means to transmit a transmission via a first cell to a user equipment. Reception of the transmission is negatively 0 acknowledged by the user equipment. The apparatus can also include second transmitting means to transmit a retransmission of the transmission via the first cell. The apparatus can also include third transmitting means to transmit, to at least a network node, data for performing a retransmission of the transmission. The at least one network node is configured to transmit the retransmission to the user equipment via at least one second cell.

5

In the apparatus of the eighth embodiment, the apparatus may include a first base station, and the at least one network node may include at least one second base station.

In the apparatus of the eighth embodiment, the first base station and the at least one second base o station are connected by non-ideal backhaul.

In the apparatus of the eighth embodiment, the transmitting data for performing the retransmission may include transmitting using an X2 interface. 5 In the apparatus of the eighth embodiment, transmitting the retransmissions may include transmitting the retransmissions using automatic repeat request. In the apparatus of the eighth embodiment, the transmitting the retransmission via the first cell and the transmitting the retransmission via the at least one second cell may include transmitting using a same redundancy version.

5

In the apparatus of the eighth embodiment, the transmitting the retransmission via the first cell and the transmitting the retransmission via the at least one second cell may include transmitting different redundancy versions. 0 In the apparatus of the eighth embodiment, the apparatus may also include fourth transmitting means to transmit control information via the first cell to the at least one second cell using an X2 interface.

In the apparatus of the eighth embodiment, the control information may include at least one of a modulation and coding scheme and a redundancy version.

5

According to a ninth embodiment, a computer program product can be embodied on a non-transitory computer readable medium. The computer program product configured to control a processor to perform a method according to the seventh embodiment. o According to a tenth embodiment, a method can include attempting to receive, by a first network node, a transmission via a first cell from a user equipment, wherein reception of the transmission is negatively acknowledged by the first network node. The method can also include receiving a retransmission of the transmission via the first cell. The method can also include transmitting, to at least one second network node, data for receiving a retransmission by the at least one second network 5 node. The at least one second network node is configured to receive the retransmission from the user equipment via at least one second cell.

In the method of the tenth embodiment, the first network node may include a first base station, and the at least one second network node may include at least one second base station.

0

In the method of the tenth embodiment, the first base station and the at least one second base station are connected by non-ideal backhaul.

In the method of the tenth embodiment, the transmitting data for receiving the retransmission may 5 include transmitting a help indication and/or a scheduling information.

In the method of the tenth embodiment, receiving the retransmissions may include receiving the retransmissions using automatic repeat request.

In the method of the tenth embodiment, the receiving the retransmission via the first cell and the o receiving the retransmission via the at least one second cell may include receiving a same redundancy version.

In the method of the tenth embodiment, the receiving the retransmission via the first cell and the receiving the retransmission via the at least one second cell may include receiving different 5 redundancy versions. In the method of the tenth embodiment, the at least one second cell is configured to provide received data to the first cell for uplink coordinated multipoint / joint reception via an X2 interface.

In the method of the tenth embodiment, the method can also include transmitting control information 5 for detecting the retransmission to the at least one second cell, wherein the control information is transmitted via an X2 interface.

According to an eleventh embodiment, an apparatus can include attempting means to attempt to receive a transmission via a first cell from a user equipment. Reception of the transmission is 0 negatively acknowledged by the apparatus. The apparatus can also include receiving means to receive a retransmission of the transmission via the first cell. The apparatus can also include first transmitting means to transmit, to at least one network node, data for receiving a retransmission by the at least one network node, wherein the at least one network node is configured to receive the retransmission from the user equipment via at least one second cell.

5

In the apparatus of the eleventh embodiment, the apparatus may include a first base station, and the at least one network node may include at least one second base station.

In the apparatus of the eleventh embodiment, the first base station and the at least one second base o station are connected by non-ideal backhaul.

In the apparatus of the eleventh embodiment, the transmitting data for receiving the retransmission may include transmitting a help indication and/or a scheduling information. 5 In the apparatus of the eleventh embodiment, receiving the retransmissions may include receiving the retransmissions using automatic repeat request.

In the apparatus of the eleventh embodiment, the receiving the retransmission via the first cell and the receiving the retransmission via the at least one second cell may include receiving a same redundancy o version.

In the apparatus of the eleventh embodiment, the receiving the retransmission via the first cell and the receiving the retransmission via the at least second cell may include receiving different redundancy versions.

5

In the apparatus of the eleventh embodiment, the at least one second cell is configured to provide received data to the first cell for uplink coordinated multipoint / joint reception via an X2 interface.

In the apparatus of the eleventh embodiment, the apparatus can also include second transmitting o means to transmit control information for detecting the retransmission to the at least one second cell.

The control information is transmitted via an X2 interface.

According to a twelfth embodiment, a computer program product can be embodied on a non-transitory computer readable medium. The computer program product configured to control a 5 processor to perform a method according to the tenth embodiment. According to a thirteenth embodiment, an apparatus can include at least one processor. The apparatus can also include at least one memory including computer program code. The at least one memory and the computer program code can be configured, with the at least one processor, to cause the apparatus at least to attempt to receive a transmission via a first cell. Reception of the 5 transmission is negatively acknowledged by the apparatus. The apparatus can also be caused to receive a retransmission of the transmission via the first cell. The apparatus can also be caused to receive a retransmission of the transmission via at least one second cell.

According to a fourteenth embodiment, an apparatus can include at least one processor. The 0 apparatus can also include at least one memory including computer program code. The at least one memory and the computer program code can be configured, with the at least one processor, to cause the apparatus at least to transmit a transmission via a first cell to a first base station. Reception of the transmission is negatively acknowledged by the first base station. The apparatus is also caused to transmit a retransmission of the transmission via the first cell to the first base station. The apparatus5 is also caused to transmit a retransmission of the transmission via at least one second cell to at least one second base station.

According to a fifteenth embodiment, an apparatus can include at least one processor. The apparatus can also include at least one memory including computer program code. The at least one memory and o the computer program code can be configured, with the at least one processor, to cause the apparatus at least to transmit a transmission via a first cell to a user equipment, wherein reception of the transmission is negatively acknowledged by the user equipment. The apparatus can also be caused to transmit a retransmission of the transmission via the first cell. The apparatus can also be caused to transmit, to at least one network node, data for performing a retransmission of the transmission, 5 wherein the at least one network node is configured to transmit the retransmission to the user equipment via at least one second cell.

According to a sixteenth embodiment, an apparatus can include at least one processor. The apparatus can also include at least one memory including computer program code. The at least one memory and 0 the computer program code can be configured, with the at least one processor, to cause the apparatus at least to attempt to receive a transmission via a first cell from a user equipment, wherein reception of the transmission is negatively acknowledged by the apparatus. The apparatus can also be caused to receive a retransmission of the transmission via the first cell. The apparatus can also be caused to transmit, to at least one network node, data for receiving a retransmission by the at least one network 5 node, wherein the at least one network node is configured to receive the retransmission from the user equipment via at least one second cell.

BRIEF DESCRIPTION OF THE DRAWINGS:

For proper understanding of the invention, reference should be made to the accompanying drawings, o wherein:

Fig. 1 illustrates the use of a helper cell, in accordance with certain embodiments of the present invention. Fig. 2 illustrates using incremental redundancy for performing Hybrid Automatic Repeat Request (HARQ), in accordance with certain embodiments of the present invention.

Fig. 3 illustrates using links for transmission and retransmission, in accordance with certain embodiments of the present invention.

Fig. 4 illustrates performing uplink reception, in accordance with certain embodiments of the present invention.

Fig. 5 illustrates performing uplink and downlink carrier aggregation, in accordance with certain embodiments of the present invention.

Fig. 6 illustrates a flowchart of a method in accordance with certain embodiments of the invention. Fig. 7 illustrates a flowchart of another method in accordance with certain embodiments of the invention.

Fig. 8 illustrates a flowchart of a method in accordance with certain embodiments of the invention. Fig. 9 illustrates a flowchart of a method in accordance with certain embodiments of the invention. Fig. 10 illustrates an apparatus in accordance with certain embodiments of the invention.

Fig. 11 illustrates another apparatus in accordance with certain embodiments of the invention. Fig. 12 illustrates another apparatus in accordance with certain embodiments of the invention. Fig. 13 illustrates another apparatus in accordance with certain embodiments of the invention. Fig. 14 illustrates another apparatus in accordance with certain embodiments of the invention DETAILED DESCRIPTION:

Certain embodiments of the present invention relate to performing packet duplication in a multi-connectivity scenario during retransmissions. Certain embodiments of the present invention address reliability in a mobile communication system such as an LTE or 5G system, where multiple links are available for transmitting information between a network and a terminal (i.e., a ' 'multi-connectivity' ' scenario) .

In particular, certain embodiments of the present invention are directed to using data duplication. By using data duplication, certain embodiments may achieve ultra-reliability by transmitting identical data across multiple links, where the links may have different properties from each other, in order to provide improved robustness against packet losses.

Certain embodiments of the present invention can also reduce a backhaul overhead and air interface overhead that is generally associated with performing data duplication. Although certain embodiments of the invention can be applicable to 5G technologies, other embodiments can also be applied to LTE technologies.

Within the context of 5G requirements, the need to perform ultra-reliable communication is becoming increasingly important/relevant. An increasing number of use cases will require a small rate of packet loss, while, at the same time, requiring conformance to a tight delay budget. This tight delay budget may not allow for the performing of many retransmissions.

One example use case is communication that is necessary for ensuring vehicular safety, with a particular emphasis on communication that is necessary for implementing autonomous-driving technologies, and on communication that is necessary for implementing certain industrial technologies (i.e., "Industry 4.0" communication).

Another trend in mobile communication is multi-connectivity, where a terminal is not merely 5 connected to only a single cell on a single frequency layer. Rather, with multi-connectivity, the terminal is simultaneously connected to multiple cells via different frequency layers or even via different, not necessarily co-sited, radio interfaces.

LTE already supports dual connectivity (as well as carrier aggregation), where a terminal can be o connected to multiple cells of 2 different base stations. 5G is anticipated to provide even more options for performing multi-connectivity. For example, in addition to enabling terminals to connect to different base stations (BSs) on different carrier frequencies, the terminals may also be able to connect to BSs on different radio interfaces (e.g., LTE+cmW, cmW+mmW, etc.). 5 The availability of multiple (independent) carrier frequency layers, for facilitating communication between terminals and base stations, offers potential benefits in improving reliability for the communication. The conventional use cases for using multiple frequency layers (as currently addressed in 3GPP) are typically based on splitting (i.e., de-multiplexing) data flows to different links. 0

Dual connectivity - where a data flow is split to different links - is one solution for improving robustness, because a connection with dual connectivity can survive a problem that occurs on one of the links. For example, the connection can survive a problem on one of the links by using end-to-end reliability schemes implemented by Transmission Control Protocol (TCP). However, 5 dual-connectivity is generally not adequate for implementing the aforementioned use cases for performing ultra-reliable communication with low-latency. Further, with dual-connectivity, packet losses will involve retransmissions (e.g., packet forwarding), which will likely exceed the tight delay budget allowed by the aforementioned use cases. 0 An improvement in the reliability of communication can be achieved by duplicating packets on available links. Specifically, an improvement in reliability can be achieved by transmitting multiple copies of the packets via each of the available links. Although transmitting these multiple copies will generally reduce spectral efficiency (because many of the packets will be transmitted twice), transmitting multiple copies may be preferred over other options for improving reliability because5 other options would likely introduce unacceptable delay as a result of retransmissions or link-switching.

Performing duplication generally increases the load on the backhaul as well as the load on the air interface, because the packets are transmitted multiple times. One problem with performing o duplication is that efficient duplication generally has to be pro-actively initiated. For example, the performing of the duplication may need to be initiated sufficiently early, before any duplication is necessary. Performing duplication in a pro-active manner may be necessary because performing reactive duplication may not be reliable enough. Specifically, when performing reactive duplication, it may be impossible to define reliable triggers to start duplication. Therefore, when performing reactive duplication, there is always a high risk that duplication is started too late.

In view of the above, although performing pro-active duplication may result in unnecessary packet 5 transmissions, certain embodiments of the present invention are directed at reducing an overhead (that is caused by performing duplication) on the backhaul and on the air interface, without sacrificing the benefits that are gained when performing data duplication.

With certain embodiments of the present invention, in order to reduce the above-described overhead, 0 data duplication may be used when performing retransmissions, while not using data duplication when performing a first, initial, transmission. Certain embodiments of the present invention may adapt pro-active duplication methods.

With certain embodiments, the overhead is generated only if there are retransmissions to be 5 performed. The price for this overhead reduction may be one retransmission delay, which is incurred because the first transmission is retransmitted.

As described above, the method of certain embodiments may perform data duplication when performing retransmissions, while not performing data duplication with the first, initial, transmission. o This method may be applicable when performing uplink communication, downlink communication, intra-frequency communication, inter-frequency communication, Hybrid A Q communication, and/or outer ARQ communication, for example.

Fig. 1 illustrates the use of a helper cell, in accordance with certain embodiments of the present 5 invention. The example of Fig. 1 illustrates performing packet duplication when performing HARQ communication in the downlink. The example system of Fig. 1 may perform intra-frequency communication. The user equipment (UE) is ready to receive data from multiple cells, from a master cell (as shown on the left) and at least from a helper cell (as shown on the right). In the example of Fig. 1, a first transmission is transmitted via the master cell (1). The first transmission may be a 0 transmission of a Media Access Control Protocol Data Unit (MAC PDU), for example. After the first transmission, in the event that the master cell receives a NAK from the UE (2), the master cell will initiate retransmission (4), as usual.

With certain embodiments, the master cell can forward the MAC PDU to the helper cells via, for 5 example, an X2 interface (3). While the master cell performs retransmission (4), the helper cells can perform retransmissions to the UE as well (5).

The retransmissions from the helper cells (5) will, most likely, not be received by the UE at the same time as the retransmissions from the master cell (4). The retransmissions generally will not be o received at the same time because the X2 interface will generally have some latency, and because the helper cells will generally have an independent scheduler that schedules the retransmissions from the helper cells to occur at different times compared to the master cell.

With certain embodiments, the UE can store all versions of the MAC PDU for decoding. In general, 5 when the UE receives a MAC PDU, the simplest option corresponds to the option where the UE attempts to decode each version of the MAC/PDU separately/independently. With this option, the UE does not store previously received versions of the MAC/PDU. The UE attempts to decode a version of the MAC/PDU and discards the version if the UE is unsuccessful in its attempt to decode. However, in general, it may be beneficial to store previous versions of the MAC PDU, because these 5 previous versions can contain valuable information, even if the previous versions cannot be correctly decoded. As described in more detail below, new versions of the MAC/PDU can be combined with previously received versions, and performing a joint decoding of the combined versions may havce a greater chance of successful decoding (but this combining requires storing of the previous approaches. For performing synchronous HARQ, storing all versions of the MAC PDU would lead0 to problems. However, with asynchronous HARQ, storing all versions of the MAC PDU is not a major issue.

With a first option, the UE can attempt to decode the different versions of the MAC PDU, received from multiple cells, independently.

5

With a second option, the UE can use chase combining (i.e. soft combining) of the different versions of the same MAC PDU. Afterwards, the UE may use either chase combining or incremental redundancy to combine a version of the MAC PDU with previously received transmissions. In general, chase combining can be similar to soft combining or maximum ratio combining. With chase o combining, soft values can be added. With incremental redundancy, the received MAC PDU versions are not identical to each other. Rather, the different versions may be different redundancy versions.

With a third option, the master cell could also create different redundancy versions (RV) of the MAC PDU for the helper cells, and the helper cells may then send these different RV to the UE. Therefore, 5 the helper cells would send a different redundancy version of the MAC PDU to the UE, as compared to the redundancy version that is used by the master cell. In this case, the UE would then use all versions of MAC PDU which have been received already, and then code-combine them.

Certain embodiments of the present invention may encode transmitted information with a mother 0 code and puncture the result into a different redundancy version (RV), where each RV may or may not be self-decodable.

Fig. 2 illustrates using incremental redundancy for performing HARQ, in accordance with certain embodiments of the present invention, for the case of two helper cells. In the case illustrated on the5 left, the helper cells can send the same redundancy versions as the versions sent by the master cell, RV2 and RV3. In order to combine the redundancy versions, either selection combining or chase combining can be used.

In the case illustrated on the right, the helper cells can send different RV (RV3 and RV4), as o compared to the RV transmitted by the master cell, which can result in additional coding gain. In both cases, the helper cells do not transmit anything at first transmission.

The UE may send an ACK/NAK to the master cell, whenever a new retransmission has been received from all helper cells (in the event that the first transmission lead to a NA ).

5 Referring to Fig. 2, the UE can send an ACK/NAK to the master cell when all packets in a row have been received, where each row corresponds to a transmission/retransmission.

Alternatively, the UE can also send an ACK/NAK whenever the UE receives any new version of the MAC PDU. In Fig. 2, ACK/NAK may also be sent whenever the UE receives any new MAC PDU version, regardless of which transmission the version belongs to.

In particular, if the UE sends an ACK/NAK whenever the UE receives any new version of the MAC PDU, the UE likely receives further versions of the MAC PDU after the UE has already successfully detected the MAC PDU (and has already acknowledged the MAC PDU). As such, the UE may need to be able to ignore / discard duplicate receptions.

If the UE sends an ACK/NAK to the master cell when all packets in a row have been received, when ACK/NAKs are generated per row in Fig. 2, the UE may need to be aware of how many versions are to be expected. If the UE sends an ACK/NAK at the end of a row, the UE has to know when the row is over. The UE has to know how long the row is. This depends on how many helper cells are used, and this, in turn, is decided by the base station. So, the decision is to be brought to the UE.

Providing the UE with an indication of how many versions are to be expected can be accomplished by the following methods.

When sending a retransmission via multiple helper cells, the information regarding how many versions (which can be expected by the UE) can be provided to the UE, for example, in the scheduling information, such as information transmitted via the Physical Downlink Control Channel (PDCCH). This information can be provided by a base station.

The information may be a single bit that indicates that duplication is performed via pre-configured helper cells, or that indicates that the information may contain identifiers for the cells (inside the pre-configured active set) that are to be used for retransmission. In addition (or alternatively), the UE can be configured with a timer. The UE can collect all MAC PDU versions that are received during a duration indicated by the timer, and the UE can send a corresponding ACK/NAK when the timer expires (based on all received versions).

Certain embodiments of the present invention may provide the advantage of reducing an overhead of unnecessary duplication by 80%, assuming operation at a target block error rate of 20% at first transmission.

Certainly, in a worst-case scenario (where duplication is definitely needed), there can be an additional delay of 1 F1ARQ cycle, as compared to pro-active duplication. The helper cells (which are relevant in this case) participate in the transmission only with the second transmission (i.e., after 1 F1ARQ cycle).

Certain embodiments of the present invention use a centralized outer Automatic Repeat Request network node, for performing intrafrequency and interfrequency communication, in accordance with certain embodiments of the present invention. With certain embodiments, a similar method could be applied at a higher layer, when there is a centralized ARQ node/mechanism for multiple links. The centralized ARQ node/mechanism can be, for example, a single Radio Link Control Layer / Radio Convergence Sublayer (RLC/RCS) outer Automatic Repeat Request (ARQ). For the first transmission (1), a single link can be chosen. However, for a retransmission, all links can be used for the retransmission (3). Fig. 3 illustrates using links for transmission and retransmission, in accordance with certain embodiments of the present invention.

In the event that the higher layer ARQ cycle is still within the latency budget, this embodiment may contribute to improved reliability, while significantly saving backhaul and air interface capacity.

Fig. 4 illustrates performing uplink reception, in accordance with certain embodiments of the present invention. For example, the uplink reception may be uplink coordinated multipoint joint reception. With regard to uplink coordinated multipoint (CoMP), uplink CoMP Joint Reception does not duplicate the packets on the air interface. However, uplink CoMP joint reception would generally cause a significant impact to the backhaul because signals have to be exchanged between the cells. In the best case, In-phase and Quadrature (I/Q) data can be exchanged. Soft information can be exchanged as well.

Referring to Fig. 4, with certain embodiments of the present invention, the helper cells would provide the I/Q data (or soft bits) to the master cell only for retransmissions (4), and not for the first transmission (1). Furthermore, the helper cells do not even need to listen to the UE during the first transmission, so as to reduce a complexity of the method.

Similar to the DL HARQ case described above, with certain embodiments, the master cell can send a "help" indication (2) to the helper cell(s), when a detection of a MAC PDU has failed. This indication may contain information that is relevant for detecting the signal that is transmitted from the UE (the information may include scheduling information (SI) such as information relating to, for example, modulation and coding scheme (MCS), multiple input and multiple output (MIMO) scheme, and/or scheduled physical resource blocks (PRBs)). As such, certain embodiments of the present invention can improve the reliability of uplink communication, while also saving a significant amount of backhaul capacity.

Fig. 5 illustrates performing uplink and downlink carrier aggregation, in accordance with certain embodiments of the present invention. With regard to uplink and downlink carrier aggregation, the current specification of carrier aggregation in LTE defines HARQ entities per carrier. If there is a single HARQ entity, retransmissions can be sent on different carriers compared to the carrier of a first transmission.

Certain embodiments of the present invention send the retransmission via all carriers. Fig. 5 illustrates a scenario where a macro and a small cell are remote radio heads (RRH) of a same baseband entity, and they use different carriers. In contrast to LTE, a centralized HARQ entity may be used for all carriers. The first transmission would use the macro cell (in this example), and the second transmission uses the macro cell and a small cell. Certain embodiments of the present invention may be directed to the case where the first transmission uses a small cell, and where the second transmission uses the small and a macro cell. Certain embodiments can benefit from offloading traffic to the small cell, while still attaining sufficient reliability by using the macro layer. As such, certain embodiments can meet tight latency requirements.

Fig. 6 illustrates a flowchart of a method in accordance with certain embodiments of the invention. The method illustrated in Fig. 6 includes, at 610, attempting to receive, by a user equipment, a transmission via a first cell. Reception of the transmission is negatively acknowledged by the user equipment. The method also includes, at 620, receiving a retransmission of the transmission via the first cell. The method also includes, at 630, receiving a retransmission of the transmission via at least one second cell.

Fig. 7 illustrates a flowchart of a method in accordance with certain embodiments of the invention. The method illustrated in Fig. 7 includes, at 710, transmitting, by a user equipment, a transmission via a first cell to a first base station. Reception of the transmission is negatively acknowledged by the first base station. The method also includes, at 720, transmitting a retransmission of the transmission via the first cell to the first base station. The method also includes, at 730, transmitting a retransmission of the transmission via at least one second cell to at least one second base station.

Fig. 8 illustrates a flowchart of a method in accordance with certain embodiments of the invention. The method illustrated in Fig. 8 includes, at 810, transmitting, by a first network node, a transmission via a first cell to a user equipment. Reception of the transmission is negatively acknowledged by the user equipment. The method also includes, at 820, transmitting a retransmission of the transmission via the first cell. The method also includes, at 830, transmitting, to at least one second network node, data for performing a retransmission of the transmission. The at least one second network node is configured to transmit the retransmission to the user equipment via at least one second cell.

Fig. 9 illustrates a flowchart of a method in accordance with certain embodiments of the invention. The method illustrated in Fig. 9 includes, at 910, attempting to receive, by a first network node, a transmission via a first cell from a user equipment. Reception of the transmission is negatively acknowledged by the first network node. The method also includes, at 920, receiving a retransmission of the transmission via the first cell. The method also includes, at 930, transmitting, to at least one second network node, data for receiving a retransmission by the at least one second network node. The at least one second network node is configured to receive the retransmission from the user equipment via at least one second cell.

Fig. 10 illustrates an apparatus in accordance with certain embodiments of the invention. In one embodiment, the apparatus can be a network node such as an evolved Node B and/or base station, for example. In another embodiment, the apparatus may correspond to a user equipment, for example.

Apparatus 10 can include a processor 22 for processing information and executing instructions or operations. Processor 22 can be any type of general or specific purpose processor. While a single processor 22 is shown in Fig. 10, multiple processors can be utilized according to other embodiments.

Processor 22 can also include one or more of general-purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), and processors based on a multi-core processor architecture, as examples.

5 Apparatus 10 can further include a memory 14, coupled to processor 22, for storing information and instructions that can be executed by processor 22. Memory 14 can be one or more memories and of any type suitable to the local application environment, and can be implemented using any suitable volatile or nonvolatile data storage technology such as a semiconductor-based memory device, a magnetic memory device and system, an optical memory device and system, fixed memory, and o removable memory. For example, memory 14 include any combination of random access memory

(RAM), read only memory (ROM), static storage such as a magnetic or optical disk, or any other type of non-transitory machine or computer readable media. The instructions stored in memory 14 can include program instructions or computer program code that, when executed by processor 22, enable the apparatus 10 to perform tasks as described herein.

5

Apparatus 10 can also include one or more antennas (not shown) for transmitting and receiving signals and/or data to and from apparatus 10. Apparatus 10 can further include a transceiver 28 that modulates information on to a carrier waveform for transmission by the antenna(s) and demodulates information received via the antenna(s) for further processing by other elements of apparatus 10. In 0 other embodiments, transceiver 28 can be capable of transmitting and receiving signals or data directly.

Processor 22 can perform functions associated with the operation of apparatus 10 including, without limitation, precoding of antenna gain/phase parameters, encoding and decoding of individual bits 5 forming a communication message, formatting of information, and overall control of the apparatus

10, including processes related to management of communication resources.

In an embodiment, memory 14 can store software modules that provide functionality when executed by processor 22. The modules can include an operating system 15 that provides operating system 0 functionality for apparatus 10. The memory can also store one or more functional modules 18, such as an application or program, to provide additional functionality for apparatus 10. The components of apparatus 10 can be implemented in hardware, or as any suitable combination of hardware and software. 5 With certain embodiments, apparatus 10 can attempt to receive a transmission via a first cell.

Reception of the transmission is negatively acknowledged by apparatus 10. Apparatus 10 can also be configured to receive a retransmission of the transmission via the first cell. Apparatus 10 can also be configured to receive a retransmission of the transmission via at least one second cell. o With certain embodiments, apparatus 10 can be configured to transmit a transmission via a first cell to a first base station. Reception of the transmission is negatively acknowledged by the first base station. Apparatus 10 can also be configured to transmit a retransmission of the transmission via the first cell to the first base station. Apparatus 10 can also be configured to transmit a retransmission of the transmission via at least one second cell to at least one second base station. With certain embodiments, apparatus 10 can be configured to transmit a transmission via a first cell to a user equipment. Reception of the transmission is negatively acknowledged by the user equipment. Apparatus 10 can be configured to transmit a retransmission of the transmission via the first cell. Apparatus 10 can also be configured to transmit, to at least one network node, data for performing a retransmission of the transmission. The at least one network node is configured to transmit the retransmission to the user equipment via at least one second cell.

With certain embodiments, apparatus 10 can be configured to attempt to receive a transmission via a first cell from a user equipment. Reception of the transmission is negatively acknowledged by apparatus 10. Apparatus 10 can also be configured to receive a retransmission of the transmission via the first cell. Apparatus 10 can also be configured to transmit, to at least one network node, data for receiving a retransmission by the at least one network node. The at least one network node is configured to receive the retransmission from the user equipment via at least one second cell.

Fig. 11 illustrates an apparatus in accordance with certain embodiments of the invention. Apparatus 1100 can be a user equipment, for example. Apparatus 1100 can include an attempting unit 1110 that attempts to receive a transmission via a first cell. Reception of the transmission is negatively acknowledged by the user equipment. Apparatus 1100 can also include a first receiving unit 1120 that receives a retransmission of the transmission via the first cell. Apparatus 1100 can also include a second receiving unit 1130 that receives a retransmission of the transmission via at least one second cell.

Fig. 12 illustrates an apparatus in accordance with certain embodiments of the invention. Apparatus 1200 can be a user equipment, for example. Apparatus 1200 can include a first transmitting unit 1210 that transmits a transmission via a first cell to a first base station. Reception of the transmission is negatively acknowledged by the first base station. Apparatus 1200 can also include a second transmitting unit 1220 that transmits a retransmission of the transmission via the first cell to the first base station. Apparatus 1200 can also include a third transmitting unit 1230 that transmits a retransmission of the transmission via at least one second cell to at least one second base station.

Fig. 13 illustrates an apparatus in accordance with certain embodiments of the invention. Apparatus 1300 can be a first network node, for example. Apparatus 1300 can include a first transmitting unit 1310 that transmits a transmission via a first cell to a user equipment. Reception of the transmission is negatively acknowledged by the user equipment. Apparatus 1300 can also include a second transmitting unit 1320 that transmits a retransmission of the transmission via the first cell. Apparatus 1300 can also include a third transmitting unit 1330 that transmits, to at least one second network node, data for performing a retransmission of the transmission. The at least one second network node is configured to transmit the retransmission to the user equipment via at least one second cell.

Fig. 14 illustrates an apparatus in accordance with certain embodiments of the invention. Apparatus 1400 can be a first network node, for example. Apparatus 1400 can include an attempting unit 1410 that attempts to receive a transmission via a first cell from a user equipment. Reception of the transmission is negatively acknowledged by the first network node. Apparatus 1400 can also include a receiving unit 1420 that receives a retransmission of the transmission via the first cell. Apparatus 1400 can also include a transmitting unit 1430 that transmits, to at least one second network node, data for receiving a retransmission by the at least one second network node. The at least one second network node is configured to receive the retransmission from the user equipment via at least one 5 second cell.

The described features, advantages, and characteristics of the invention can be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize that the invention can be practiced without one or more of the specific features or advantages of a particular l o embodiment. In other instances, additional features and advantages can be recognized in certain embodiments that may not be present in all embodiments of the invention. One having ordinary skill in the art will readily understand that the invention as discussed above may be practiced with steps in a different order, and/or with hardware elements in configurations which are different than those which are disclosed. Therefore, although the invention has been described based upon these preferred

15 embodiments, it would be apparent to those of skill in the art that certain modifications, variations, and alternative constructions would be apparent, while remaining within the spirit and scope of the invention.