1. Field of the Invention
The present invention relates to a method used in a wireless communication system and related communication device, and more particularly, to a method of performing retransmissions by using different resources and related communication device.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3GPP Rel-8 standard and/or the 3GPP Rel-9 standard are developed by the 3rd Generation Partnership Project (3GPP) as a successor of a universal mobile telecommunications system (UMTS), for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a new radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes multiple evolved Node-Bs (eNBs) for communicating with multiple UEs, and communicating with a core network including a mobility management entity (MME), a serving gateway, etc., for Non-Access Stratum (NAS) control.
A LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, and includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint transmission/reception (CoMP), UL multiple-input multiple-output (MIMO), etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-10 standard or later versions.
A hybrid automatic repeat request (HARQ) process is used in a communication system (e.g., the LTE system and the LTE-A system) to provide both efficient and reliable communications. Different from an automatic repeat request (ARQ) process, a forward error correcting code (FEC) and soft combining are used for the HARQ process. In detail, before a transmitter (e.g., eNB) transmits a packet (e.g., a data stream, a frame or a transport block) including multiple coded bits to a receiver (e.g., UE), the transmitter divides the packet into multiple blocks, i.e., multiple redundancy versions. The transmitter only transmits one of the redundancy versions in each transmission or retransmission. According to whether the same redundancy version is transmitted in the retransmission, the soft combining used for the HARQ can be classified into two categories: chase combining (CC) and incremental redundancy (IR). When the same redundancy version of the packet is transmitted in each retransmission, the HARQ is a CC-based HARQ. When a different redundancy version of the packet is transmitted in each retransmission, the HARQ is an IR-based HARQ.
For example, after the transmitter transmits a redundancy version of the packet to the receiver in the first transmission, the receiver feeds back an acknowledgment (ACK) if the receiver can recover the packet by decoding the redundancy version. Oppositely, the receiver feeds back a negative acknowledgment (NACK) to the transmitter, if the receiver cannot recover the packet by decoding the redundancy version. In this situation, the receiver stores the redundancy reversion of the packet in a soft buffer of the receiver, and waits for the transmitter to retransmit a redundancy version of the packet in the second transmission (i.e., the first retransmission). The redundancy versions in the first transmission and the second transmission are the same if the HARQ is the CC-based HARQ, and are different if the HARQ is the IR-based HARQ. After the receiver receives the redundancy version in the second transmission, the receiver decodes the redundancy versions (either the same or different) jointly, to recover the packet. Thus, the packet can be recovered with a high probability. The receiver continues the HARQ process (i.e., accumulates redundancy versions of the packet) until the packet is recovered or a maximum number of retransmissions is reached. Since the packet with few errors can be recovered by using the FEC without feeding back the NACK, i.e., requesting a retransmission, and the packet with more errors can be recovered by decoding the redundancy versions jointly, throughput of the communication system is increased due to fewer retransmissions.
The CA is introduced to the LTE-A system by which more than one component carriers (CCs) are aggregated to achieve a wide-band transmission. Accordingly, the LTE-A system can support a wide bandwidth up to 100 MHz by aggregating a maximum number of 5 CCs, where a maximum bandwidth of each CC is 20 MHz and is backward compatible with the 3GPP Rel-8 standard. The LTE-A system supports the CA for both contiguous and non-contiguous CCs. The CA increases bandwidth flexibility by aggregating the CCs. When a UE is configured with the CA, the UE has the ability to receive and/or transmit packets on one or multiple CCs to increase throughput. In the LTE-A system, it is possible that an eNB configures the UE different numbers of uplink (UL) CCs and downlink (DL) CCs. Moreover, the CCs configured to the UE necessarily consists of one DL primary CC (PCC) and one UL PCC. The most important feature of the DL PCC and the UL PCC is exchanging control information between the UE and the eNB. CCs other than the PCCs are named UL secondary CCs (SCCs) or DL SCCs. Numbers of the UL and DL SCCs are arbitrary, and are related to capability of the UE and available radio resources.
On the other hand, when the CoMP is configured to a UE and multiple transmission points (e.g., an eNB, a relay node or a remote antenna of an eNB), the UE may communicate with the transmission points simultaneously, i.e., access a service via all or part of the transmission points. For example, a transmission point can be an eNB, a relay node or a remote antenna of an eNB (e.g., remote radio head (RRH)). More specifically, an eNB may manage only one transmission point, or may manage multiple transmission points. That is, Cell IDs of different transmission points may be different (e.g., when being managed by different eNBs), or may be the same (e.g., when being managed by the same eNB). Thus, signals transmitted between the UE and the transmission points can be easily recovered due to better quality of the signals.
In detail, when the transmission points are involved in the CoMP, one of the transmission points is a serving point (i.e., serving cell). In general, link quality between the serving point and the UE is better than link qualities between other transmission points and the UE. Further, the CoMP can be classified into two main categories: Joint Processing (JP) and Coordinated Scheduling/Beamforming (CS/CB). A main difference between the JP and the CS/CB is that data of the UE is available at all the transmission points when the JP is configured (i.e. enabled), while the data of the UE is only available at the serving point when the CS/CB is configured. The JP can be further classified into two categories: joint transmission and dynamic point selection. When the joint transmission is configured, the data of the UE can be transmitted from multiple transmission points (e.g., coherently or noncoherently) to the UE to improve signal quality and/or cancel interferences. When the dynamic point selection is configured, the data of the UE is transmitted from only one of the transmission points (e.g., according to a choice or suggestion of the UE) to the UE to improve the signal quality and/or avoid the interferences. On the other hand, when the CS/CB is configured, the data of the UE is only transmitted from the serving point to the UE, while other transmission points may adjust scheduling (e.g., stop their transmissions), or adjust beamforming (e.g., move their beams) to mitigate the interferences.
However, according to the prior art, when the HARQ process is operated with the CoMP, a packet for a UE can only be transmitted from the same transmission point by using the same resource to the UE. That is, after a transmission point transmits the packet is to the UE by using a set of resource blocks, retransmissions of the packet can only be performed by the same transmission point by using the same set of resource blocks. If link quality between the UE and the transmission point is bad or a channel experienced by the set of resource blocks is bad, a large number of retransmissions are required for recovering the packet. Thus, diversity supported by the CoMP is not realized due to the rule of performing the retransmissions of the packet by the same transmission point by using the same resource. As a result, throughput of the UE can not be maximized when operating the CoMP. Therefore, how to maximize the throughput of the UE when the HARQ process is operated with the CoMP is a topic to be discussed.
The present invention therefore provides a method and related communication device for performing retransmissions by using different resources to solve the abovementioned problems.
A method of performing a retransmission of a packet from at least one transmission point of a wireless communication system to a mobile device in the wireless communication system is disclosed. The method comprises transmitting the packet from the at least one transmission point to the mobile device by using a first resource group in a first transmission; and transmitting the packet from the at least one transmission point to the mobile device by using a second resource group in a second transmission, after transmitting the packet in the first transmission, wherein the first resource group and the second resource group are different resource groups.
At least one transmission point of a wireless communication system for performing a retransmission of a packet to a mobile device in the wireless communication system is disclosed. The at least one transmission point comprises means for transmitting the packet from the at least one transmission point to the mobile device by using a first resource group in a first transmission; and means for transmitting the packet from the at least one transmission point to the mobile device by using a second resource group in a second transmission, after transmitting the packet in the first transmission, wherein the first resource group and the second resource group are different resource groups.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
Please refer to
Please note that, the UE and the transmission points TP1-TP7 are simply utilized for illustrating a structure of the wireless communication system 10. Practically, the transmission points TP1-TP7 can be referred as NodeBs (NBs) in a universal terrestrial radio access network (UTRAN) of the UMTS, or evolved NodeBs (eNBs), relay nodes and/or remote radio heads (RRHs) in an evolved UTRAN (E-UTRAN) of the LTE system or the LTE-A system, and are not limited herein. The UE can be mobile devices such as mobile phones, laptops, tablet computers, electronic books, and portable computer systems. Besides, a transmission point and the UE can be seen as a transmitter or a receiver according to transmission direction, e.g., for an uplink (UL), the UE is the transmitter and the transmission point is the receiver, and for a downlink (DL), the transmission point is the transmitter and the UE is the receiver.
Besides, the wireless communication system 10 can be seen as a multi-point cooperative network composed of multiple transmission points. That is, the UE may transmit a signal (e.g., a packet) to a first set of the transmission points TP1-TP7, and the UE may receive the signal transmitted by a second set of the transmission points TP1-TP7, wherein the first set and the second set may be the same or different. As a result, signal quality of the signal is improved. For example, when the wireless communication system 10 is referred to the LTE-A system, it means that the wireless communication system 10 supports coordinated multi-point transmission/reception (CoMP). The CoMP can be configured as Joint Processing (JP) (e.g. joint transmission or dynamic point selection) or Coordinated Scheduling/Beamforming (CS/CB), and is not limited. Further, without loss of generality, the transmission point TP1 can be seen as a serving point (i.e., serving cell) for the UE, wherein link quality between the transmission point TP1 and the UE is better than link qualities between other transmission points and the UE.
Please refer to
Please refer to
Step 300: Start.
Step 302: Transmit the packet from at least one of the transmission points TP1-TP7 to the UE by using a first resource group in a first transmission.
Step 304: Transmit the packet from the at least one of transmission points TP1-TP7 to the UE by using a second resource group in a second transmission, after transmitting the packet in the first transmission, wherein the first resource group and the second resource group are different resource groups.
Step 306: End.
According to the process 30, after at least one of the transmission points TP1-TP7 transmits the packet to the UE by using a first resource group in a first transmission, the UE is unable to recover (e.g., decode) the packet successfully and requests the retransmission of the packet. Then, in a second transmission (i.e., a first retransmission), the at least one of transmission points TP1-TP7 transmits the packet to the UE by using a second resource group, wherein the first resource group and the second resource group are different resource groups. Since channels experienced by the packet are usually uncorrelated (e.g., different), when the packet is transmitted by using the first resource group and the second resource group. It is unlikely that channel qualities of the channels are both poor at the same time and the UE is unable to recover the packet. Thus, after the UE receives and combines the packets transmitted by using the two resource groups, it is highly possible that the UE can recover the packet successfully. Even if the UE is still unable to recover the packet after the second transmission, the UE can continue the process 30, i.e., the packet is retransmitted from the at least one of transmission points TP1-TP7 to the UE by using a third resource group in a third transmission wherein the third resource group is different from the second resource group, until that the packet is recovered or a maximum number of retransmissions is reached. Therefore, diversity is provided by transmitting the packet by using different resource groups, and the packet can be recovered in fewer retransmissions. As a result, throughput of the UE can be improved.
Please note that, a spirit of the present invention is that a retransmission of a packet is performed by using different resource groups to realize (i.e., obtain) diversity provided by the different resource groups, such that throughput of the UE can be improved. Realization of the process 30 is not limited.
For example, please refer to
Transmission of the packet PKT1 is first described as follows. In the initial transmission, the packet PKT1 is transmitted from the transmission points TP1, TP3 and TP4 to the UE by using the resource group RG1. After the UE receives the packet PKT1 by using the resource group RG1, the UE is unable to recover the packet PKT1. The UE requests a first retransmission of the packet PKT1, e.g., by feeding back a negative acknowledgment (NACK) corresponding to the packet PKT1. Then, the transmission points TP1, TP3 and TP4 retransmit the packet PKT1 to the UE by using the resource group RG3 in the first retransmission. That is, the first retransmission is performed by using a resource group different from that used in the initial transmission. If the UE is still unable to recover the packet PKT1 after the first retransmission, the transmission points TP1, TP3 and TP4 can retransmit the packet PKT1 to the UE by using the resource group RG2 in a second retransmission. The above description is operated until the UE can recover the packet PKT1 (e.g., after the second retransmission) or a maximum number of retransmission is reached. Similarly, the packet PKT2 is transmitted from the transmission points TP1, TP3 and TP4 by using the resource groups RG2, RG1 and RG3 in the initial transmission, the first retransmission and the second retransmission, respectively. Besides, the packet PKT3 is transmitted from the transmission points TP1, TP3 and TP4 by using the resource groups RG3, RG2 and RG1 in the initial transmission, the first retransmission and the second retransmission, respectively.
Therefore, according to the above illustration, transmissions (e.g., retransmissions) of a packet are performed by using different resource groups. Diversity can be realized for the retransmissions such that the packet can be recovered in fewer retransmissions. As a result, throughput of the UE is improved. Besides, since multiple packets are transmitted to the UE in each of the transmissions, the throughput of the UE is further improved.
On the other hand, the present invention can also be realized by using multiple component carriers, to provide different resource groups. The resource groups are used by one of the transmission points TP1-TP7 (e.g., the transmission point TP1), for transmitting packets to the UE. For example, please refer to
In detail, the UE prepares to receive packets PKT1a-PKT3a from the transmission point TP1 by using resource groups 500-508 at the component carriers CC1-CC3. Since the incremental redundancy is used for the HARQ in
Similarly, the redundancy versions ReV0-ReV2 of the packet PKT2a are transmitted from the transmission point TP1 to the UE by using the resource group 503 at the component carrier CC2, the resource group 507 at the component carrier CC3 and the resource group 502 at the component carrier CC1 in the initial transmission, the first retransmission and the second retransmission, respectively, since the UE is unable to recover the packet PKT2a before the second retransmission. Besides, the redundancy versions ReV0-ReV1 of the packet PKT3a are transmitted from the transmission point TP1 to the UE by using the resource group 506 at the component carrier CC3 and the resource group 501 at the component carrier CC1 in the initial transmission and the first retransmission, respectively. Then, the redundancy version ReV1 of the packet PKT3a is transmitted again from the transmission point TP1 to the UE by using the resource group 505 at the component carrier CC2 in the second retransmission, since the UE is unable to recover the packet PKT3a before the second retransmission. In other words, the redundancy versions of the packets are not required to be the same in the same retransmission, and the redundancy version of the packet is not required to be different in successive transmissions.
Please note that, the packets are transmitted by the transmission point TP1 (i.e., only one transmission point) to the UE in the above example. However, the packets can also be transmitted by a set of the transmission points TP1-TP7 (e.g., the transmission points TP1 and TP3), and is not limited. Therefore, according to the above illustration, transmissions (e.g., retransmissions) of redundancy versions of a packet are performed by using different component carriers (i.e., resource groups). Diversity can be realized for the retransmissions such that the packet can be recovered in fewer retransmissions. As a result, throughput of the UE is improved. Besides, since multiple packets are transmitted to the UE in each of the transmissions, the throughput of the UE is further improved.
Please refer to
In detail, the UE prepares to receive packets PKT1b-PKT3b from one of the transmission points TP1-TP7 (e.g., the transmission point TP1) by using resource blocks 600-608 at 3 component carriers CC1a-CC3a, wherein the painted squares in the same row are represented by a corresponding resource block (i.e. one of the resource blocks 600-608). Reference axes such as time (i.e., transmissions and retransmissions), frequency (i.e., resource blocks) and carrier (i.e., component carriers) are also shown in
Transmission of the packet PKT1 is first described as follows. In the initial transmission, the packet PKT1b is transmitted from the transmission point TP1 to the UE by using the resource group RG1a. After the UE receives the packet PKT1b by using the resource group RG1a, the UE is unable to recover the packet PKT1b. The UE requests a first retransmission of the packet PKT1b, e.g., by feeding back a NACK corresponding to the packet PKT1b. Then, the transmission point TP1 retransmits the packet PKT1b to the UE by using the resource group RG3a in the first retransmission. That is, the first retransmission is performed by using a resource group different from that used in the initial transmission. If the UE is still unable to recover the packet PKT1b after the first retransmission, the transmission point TP1 can retransmit the packet PKT1b to the UE by using the resource group RG2a in a second retransmission. The above description is operated until the UE can recover the packet PKT1b (e.g., after the second retransmission) or a maximum number of retransmission is reached. Similarly, the packet PKT2b is transmitted from the transmission point TP1 to the UE by using the resource groups RG2a, RG1a and RG3a in the initial transmission, the first retransmission and the second retransmission, respectively. Besides, the packet PKT3b is transmitted from the transmission point TP1 to the UE by using the resource groups RG3a, RG2a and RG1a in the initial transmission, the first retransmission and the second retransmission, respectively.
Please note that, the packets are transmitted by the transmission point TP1 (i.e., only one transmission point) to the UE in the above example. However, the packets can also be transmitted by a set of the transmission points TP1-TP7 (e.g., the transmission points TP1 and TP3), and is not limited. Therefore, according to the above illustration, transmissions (e.g., retransmissions) of a packet are performed by using different resource groups. Diversity can be realized for the retransmissions such that the packet can be recovered in fewer retransmissions. As a result, throughput of the UE is improved. Besides, since multiple packets are transmitted to the UE in each of the transmissions, the throughput of the UE is further improved.
On the other hand, the present invention can also be realized by using both multiple transmission points and multiple component carriers, to provide different resource groups. Different from
In detail, the UE prepares to receive packets PKT1c-PKT6c from the transmission points TP1 and TP3 by using resource groups 700-717 at the component carriers CC1-CC3. In an initial transmission, the packets PKT1c-PKT3c are transmitted from the transmission points TP1 to the UE by using the resource groups 700-702, respectively, and the packets PKT4c-PKT6c are transmitted from the transmission points TP3 to the UE by using the resource groups 703-705, respectively. If a first retransmission is required for transmitting the packets PKT1c-PKT6c, a resource group different from that used in the first transmission is used for each of the packets PKT1c-PKT6c. As shown in
Similarly, if the UE is still unable to recover the packets PKT1c-PKT6c after the first retransmission, the UE requests a second retransmission. As shown in
It is worth noting that both the resource group and the transmission point can be changed at the same time when retransmitting a packet. For example, the resource group and the transmission point used for retransmitting the packets PKT3c and PKT6c are changed in the first retransmission, and the resource group and the transmission point used for retransmitting the packets PKT2c and PKT5c are changed in the second retransmission. Thus, more diversities (i.e., frequency and space) are obtained when both the resource group and the transmission point are changed at the same time in a single retransmission. Besides, a more general example can be obtained from
Therefore, according to the above illustration, transmissions (e.g., retransmissions) of a packet are performed by using different component carriers (i.e., resource groups) and different transmission points. Diversity can be realized for the retransmissions such that the packet can be recovered in fewer retransmissions. As a result, throughput of the UE is improved. Besides, since multiple packets are transmitted to the UE in each of the transmissions, the throughput of the UE is further improved.
On the other hand, the present invention can also be realized by using multiple layers of a transmission point (e.g., the transmission point TP1). That is, multiple layers of the transmission point TP1 are used for providing multiple resource groups. For example, please refer to
In detail, the UE prepares to receive packets PKT1d and PKT2d from the transmission point TP1 by using resource groups 800-803 provided by the layers LR1 and LR2. Transmission of the packet PKT1d is described as follows. After the transmission point TP1 transmits the packet PKT1d to the UE in an initial transmission by using the resource group 800 provided by the layer LR1, the UE is unable to recover the packet PKT1d. The UE requests a first retransmission of the packet PKT1d, e.g., by feeding back a NACK corresponding to the packet PKT1d. Then, the transmission point TP1 retransmits the packet PKT1d in the first retransmission by using the resource group 803 provided by the layer LR2. That is, the first retransmission is performed by using a layer (i.e., a resource group) different from that is used in the initial transmission. The above description can be operated until the UE can recover the packet PKT1d (e.g., after the second retransmission) or a maximum number of retransmission is reached. Similarly, the packet PKT2d is transmitted from the transmission point TP1 to the UE by using the resource group 802 (provided by the layer LR2) and the resource group 801 (provided by the layer LR1) in the initial transmission and the first retransmission, respectively, since the UE is unable to recover the packet PKT2d before the first retransmission.
Therefore, according to the above illustration, transmissions (e.g., retransmissions) of a packet are performed by using different resource groups provided by different layers. Diversity can be realized for the retransmissions such that the packet can be recovered in fewer retransmissions. As a result, throughput of the UE is improved. Besides, since multiple packets are transmitted to the UE in each of the transmissions, the throughput of the UE is further improved.
Please note that, as shown in
Besides, the transmission points TP1, TP3 and TP4 used in
Furthermore, a resource group used in the above figures can be seen as a concept of resource, and should not be limited to a specific amount of resource, a specific type of resource or a specific resource pattern. For example, the resource group can include only a single resource block or a set of resource blocks, wherein the set of resource blocks may be composed of consecutive and/or nonconsecutive resource blocks (e.g.,
On the other hand, packets transmitted from respective transmission points to the UE in a transmission can be the same, partly different or completely different. In other words, differences between the packets are not limited. For example, please refer back to
Those skilled in the art should readily make combinations, modifications and/or alterations on the abovementioned examples (e.g.,
To sum up, the present invention provides a method of performing retransmissions by using different resources (i.e., resource groups). According to the present invention, retransmissions of a packet are performed from at least one transmission point to the UE by using different resource groups. Diversity can be realized for the retransmissions such that the packet can be recovered in fewer retransmissions. As a result, throughput of the UE is improved. Besides, since more resource groups are provided by using (i.e., aggregating) more component carriers, more resource groups are provided in a single transmission (e.g., retransmission). The throughput of the UE can be further improved.
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.
This application claims both the benefit of U.S. Provisional Application No. 61/509,481, filed on Jul. 19, 2011, entitled “Method of Data Processing for Retransmission”, and the benefit of U.S. Provisional Application No. 61/509,472, filed on Jul. 19, 2011, entitled “Data Swapping Scheme among Different Transmission Resources”, the contents of which are incorporated herein in their entirety.
Number | Date | Country | |
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61509472 | Jul 2011 | US | |
61509481 | Jul 2011 | US |