[0001] METHOD AND APPARATUS FOR
INTER-NODE-B MACRO DIVERSITY IN A SINGLE CARRIER FREQUENCY DIVISION MULTIPLE ACCESS SYSTEM
[0002] FIELD OF INVENTION
[0003] The present invention is related to a wireless communication system. More particularly, the present invention is related to a method and apparatus for inter-Node-B macro diversity in a single carrier frequency division multiple access (SC-FDMA) system.
[0004] BACKGROUND
[0005] The third generation partnership project (3GPP) and 3GPP2 are currently considering a long term evolution (LTE) of the universal mobile telecommunication system (UMTS) terrestrial radio access (UTRA). Currently, SC-FDMA is adopted for the uplink air interface of the evolved UTRA. [0006] In an SC-FDMA system, a plurality of orthogonal subcarriers are transmitted simultaneously. The subcarriers are divided into a plurality of subcarrier blocks, (also known as resource blocks (RBs)). A block of subcarriers is a basic resource unit in an SC-FDMA system. The subcarrier block may be either a localized subcarrier block or a distributed subcarrier block. The localized subcarrier block is a set of consecutive subcarriers and the distributed subcarrier block is a set of equally spaced non-consecutive subcarriers. [0007] Figure IA illustrates two localized subcarrier blocks, each comprising four consecutive subcarriers. The localized subcarrier block is a basic scheduling unit for uplink transmissions in a localized-mode SC-FDMA system. Figure IB illustrates two distributed subcarrier blocks. In this example, the distributed subcarrier block 1 includes subcarriers 1, 5 and 9, and the distributed subcarrier block 2 includes subcarriers 3, 7 and 11. The distributed subcarrier block is a basic scheduling unit for uplink transmissions in a distributed-mode SC-FDMA system. Depending on a data rate or a buffer status, a Node-B assigns at least one subcarrier block for uplink transmissions for a wireless transmit/receive unit (WTRU).
[0008] Currently, frequency and time domain channel dependent scheduling is considered for SC-FDMA in 3GPP and 3GPP2 LTE. In the uplink of wideband code division multiple access (WCDMA), (up to Release 6), inter- Node-B macro diversity is easy to achieve for both dedicated channel (DCH) and enhanced dedicated channel (E-DCH) since channel resources for both DCH and E-DCH are fixed and a WTRU may use the same uplink channel resources in cells controlled by different Node-Bs during inter-Node-B soft handover. However, when the frequency and time domain channel dependent scheduling is applied for SC-FDMA, the WTRU will not have fixed channel resources as in WCDMA Release 6. This makes it very difficult to achieve inter-Node-B soft handover in the SC-FDMA system.
[0009] SUMMARY
[0010] The present invention is related to a method and apparatus for inter-Node-B macro diversity in an SC-FDMA system. In accordance with a first embodiment, a distributed subcarrier block including sufficient number of subcarriers to guarantee sufficient frequency diversity for a WTRU for uplink transmission. The location of the subcarriers is fixed. The information regarding the assigned distributed subcarrier block is sent to Node-Bs in an active set of the WTRU and the Node-Bs receive and decode uplink transmission of the WTRU based on the information.
[0011] In accordance with a second embodiment, a subcarrier block, (either a distributed subcarrier block or a localized subcarrier block), and a starting seed in a frequency and time hopping sequence is allocated to a WTRU for uplink transmission. The information regarding the assigned subcarrier block and the starting seed is sent to Node-Bs in an active set of the WTRU and the Node-Bs receive and decode uplink transmission based on the information. [0012] BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Figure IA shows a set of localized subcarrier blocks.
[0014] Figure IB shows a set of distributed subcarrier blocks.
[0015] Figure 2 shows an exemplary wireless communication system configured in accordance with the present invention.
[0016] Figures 3 and 4 show exemplary resource unit assignment in accordance with a first embodiment of the present invention.
[0017] Figures 5 and 6 illustrate an inter-Node-B handover of a low data rate WTRU and a high data rate WTRU, respectively, in accordance with the first embodiment of the present invention.
[0018] Figures 7 and 8 show exemplary resource unit assignment for localized mode and distributed mode, respectively, in accordance with a second embodiment of the present invention.
[0019] Figure 9 illustrates an inter-Node-B handover in accordance with the second embodiment of the present invention.
[0020] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0021] Hereafter, the terminology "WTRU" includes but is not limited to a user equipment (UE), a mobile station (STA), a fixed or mobile subscriber unit, a pager, or any other type of device capable of operating in a wireless environment. When referred to hereafter, the terminology "Node-B" includes but is not limited to a base station, a site controller, an access point (AP) or any other type of interfacing device in a wireless environment.
[0022] The features of the present invention may be incorporated into an integrated circuit (IC) or be configured in a circuit comprising a multitude of interconnecting components.
[0023] Figure 2 shows an exemplary wireless communication system 200 configured in accordance with the present invention. The system 200 includes at least one WTRU 202, a plurality of Node-Bs 204a-204c, a plurality of cells 208a- 208i, and optionally an access gateway (aGW) 206, (or a radio network controller). The Node-B 204a controls the cells 208a-208c, the Node-B 204b controls the cells 208d-208f, and the Node-B 204c controls the cells 208g-208i. The Node-Bs 204a-204c may be directly connected to each other via a link 212 or via the aGW 206, (or a radio network controller).
[0024] The WTRU 202 is currently associated with the cell 208a, (i.e., serving cell), and the Node-B 204a, (i.e., serving Node-B). For uplink transmissions, the WTRU 202 sends a request for resource unit allocation to the Node-B 204a. The Node-B 204a assigns at least one subcarrier block, (either a distributed subcarrier block or a localized subcarrier block) to the WTRU 202, based on data rate requirements and/or buffer occupancy of the WTRU 202. [0025] In accordance with a first embodiment of the present invention, in order to achieve both inter-Node-B macro diversity and frequency and/or time diversity within a cell, a distributed mode SC-FDMA is implemented without channel dependent scheduling. The Node-B assigns at least one distributed subcarrier block to the WTRU and the location of the assigned distributed subcarrier block(s) is fixed. One distributed subcarrier block includes a plurality of subcarriers and the number of subcarriers is large enough to provide sufficient frequency diversity. Since it is unlikely that all equally-spaced subcarriers in the assigned distributed subcarrier block go under deep fading simultaneously, good frequency diversity is achieved.
[0026] For a WTRU that has a high data rate requirement or large buffer occupancy, at least one distributed subcarrier block including sufficient number of subcarriers is assigned to the WTRU and the WTRU transmits data via the assigned subcarrier block.
[0027] For a WTRU that has a low data rate requirement or small buffer occupancy, at least one distributed subcarrier block having sufficient number of subcarriers is assigned to the WTRU, and uplink transmissions are multiplexed with other WTRUs. The uplink transmissions may be multiplexed over multiple transmission time intervals (TTIs) with other WTRUs in a persistent manner. The length of a TTI is one or several sub-frames. That is, the WTRU is allowed to transmit on the assigned subcarrier block every X out of Y TTIs. For example, assume that the WTRU requests only 8 subcarriers. However, the Node-B assigns 32 subcarriers in one distributed subcarrier block to the WTRU in order to guarantee frequency diversity allowing the WTRU to transmit only one TTI out of 4 TTIs in a persistent manner. Therefore, the average data rate is equivalent to the case providing 8 subcarriers allowing the WTRU to transmit every TTI.
[0028] Figure 3 shows exemplary resource unit assignment in accordance with this option. WTRU A and WTRU C require high data rates but WTRU B requires a low data rate. WTRU A and WTRU C are assigned with distributed subcarrier blocks 1 and 3, respectively and may transmit data on the assigned subcarrier blocks without any restriction in time domain. WTRU B is assigned with a distributed subcarrier block 2, which includes a sufficient number of subcarriers to guarantee frequency diversity, but is allowed to transmit only one TTI out of 4 TTIs.
[0029] Alternatively, the uplink transmissions may be multiplexed within one TTI among other WTRUs. The WTRU is allowed to transmit every X out of Y symbols within one TTI in a persistent manner. Figure 4 shows exemplary resource unit assignment in accordance with this alternative option. WTRU D requires high data rates, WTRU A and WTRU B require a medium data rate, and WTRU C, WTRU E, WTRU F, WTRU G and WTRU H require a low data rate. WTRU D is assigned with distributed subcarrier block 3 and may transmit data on the subcarrier block 3 without any restriction in the time domain. WTRU A and WTRU B are assigned with distributed subcarrier block 1, and transmissions from the WTRUs A and B are multiplexed on the subcarrier block 1 in time domain. WTRU C and WTRU E- WTRU H are assigned with distributed subcarrier block 2 and their transmissions are multiplexed in time domain. [0030] Figures 5 and 6 illustrate an inter-Node-B handover of a low data rate WTRU 502 and a high data rate WTRU 602, respectively, in accordance with the first embodiment of the present invention. During an inter-Node-B handover, transmissions from a WTRU 502, (602) are received and processed by at least two Node-Bs 504a, 504b, (604a, 604b). The Node-Bs 504a, 504b, (604a, 604b) received information about the resource unit assignment for the WTRU 502, (602) via a control plane aGW, an RNC or other entity (such as, a primary Node- B selected among the Node-Bs associated with the active set). [0031] The information includes the number of subcarrier blocks assigned to the WTRU 502, (602), and the location of assigned subcarrier blocks and time schedule, (e.g., X out of Y TTIs or X out of Y symbols within one TTI), that the WTRU 502, (602) may transmit on the assigned subcarrier block(s). Both Node- Bs 504a, 504b, (604a, 604b) process data blocks transmitted by the WTRU 502, (502) and forward correctly decoded data blocks to a centralized entity such as a user plane aGW 210 or an RNC, (as shown in Figure 2). If there are more than one successfully decoded data block is forwarded, redundant data blocks are ignored.
[0032] Since the Node-Bs 504a, 504b, (604a, 604b) know the subcarrier block(s) and time schedule that the WTRU 502, (502) is transmitting, the Node- Bs 504a, 504b, (604a, 604b) may receive and process the signals transmitted by the WTRU 502, (602). In this way, the macro diversity is achieved while keeping the frequency and time diversity within the cell.
[0033] In accordance with a second embodiment of the present invention, in order to achieve both inter-Node-B macro diversity and frequency and/or time diversity within a cell, a frequency and time hopping is implemented. When a WTRU requests a resource unit for uplink transmission, a Node-B assigns at least one subcarrier block, (either a distributed subcarrier block or a localized subcarrier block) to the WTRU, based on data rate requirement and/or buffer occupancy of the WTRU. The location of the assigned subcarriers is not fixed, but changed in accordance with a pseudo random frequency and time hopping sequence.
[0034] Each WTRU is assigned to a unique seed, (or starting point), of the pseudo random frequency and time hopping sequence. With the frequency and time hopping, a WTRU transmits on different subcarrier blocks and/or in different TTIs in accordance with the frequency and time hopping sequence. [0035] Figure 7 shows exemplary resource unit assignment for a localized mode in accordance with the second embodiment of the present invention. In the first TTI, WTRU A and WTRU B transmit on localized subcarrier blocks 1 and 2, respectively. In the next TTI, WTRU B and WTRU C transmit on localized subcarrier blocks 1 and 2, respectively. In the next TTI, WTRU C and WTRU A transmit on localized subcarrier blocks 1 and 2, respectively. [0036] Figure 8 shows exemplary resource unit assignment for a distributed mode in accordance with the second embodiment of the present invention. In the first TTI, WTRU A transmits on a distributed subcarrier block 1, WTRU B transmits on a distributed subcarrier block 4, and WTRU C transmits on a distributed subcarrier block 2. In the next TTI, WTRU A transmits on a distributed subcarrier block 4, and WTRU B transmits on a distributed subcarrier block 1. In the next TTI, WTRU A transmits on a distributed subcarrier block 2, WTRU B transmits on a distributed subcarrier block 3, and WTRU C transmits on a distributed subcarrier block 1. [0037] Figure 9 illustrates a'n inter-Node-B handover in accordance with the second embodiment of the present invention. During an inter-Node-B handover, transmissions from a WTRU 902 are received and processed by at least two Node-Bs 904a, 904b. The Node-Bs 904a, 904b received information about the resource unit assignment for the WTRU 902 via a control plane aGW 210 or an RNC, (as shown in Figure 2) or other entity (such as, a primary Node-B selected among the Node-Bs associated with the active set).
[0038] The information includes the number of subcarrier blocks assigned to the WTRU 902 and the seed of the pseudo random frequency and time hopping sequence assigned to the WTRU 902. The Node-Bs 904a, 904b process data blocks transmitted by the WTRU 902 and forward correctly decoded data blocks to the centralized entity such as a user plane aGW 210 or an RNC. If there are more than one successfully decoded data block is forwarded, redundant data blocks are ignored.
[0039] Although the channels, (combination of subcarrier blocks and TTIs), used by the WTRU 902 changes from time to time, since the Node-Bs 904a, 904b know the seed of the pseudo random frequency and time hopping sequence used by the WTRU 902, the Node-Bs 904a, 904b know the subcarrier blocks and time instances that the WTRU 902 is transmitting and may receive and process the signals transmitted by the WTRU 902. In this way, the macro diversity is achieved while keeping the frequency and time diversity within the cell.
[0040] Embodiments.
[0041] 1. A method for uplink inter-Node-B macro diversity in an SC-
FDMA system including at least one WTRU and a plurality of Node-Bs.
[0042] 2. The method of embodiment 1 comprising allocating a distributed subcarrier block and time schedule for uplink transmission to a
WTRU, the number of subcarriers in the distributed subcarrier block being large enough to provide frequency diversity and location of the subcarriers being fixed.
[0043] 3. The method of embodiment 2 comprising sending information regarding the assigned distributed subcarrier block(s) with fixed positions for the
WTRU to Node-Bs in an active set of the WTRU.
[0044] 4. The method of embodiment 3 comprising at least two Node-Bs in the active set receiving and decoding an uplink transmission of the WTRU based on the information.
[0045] 5. The method as in any embodiments 2-4, wherein the distributed subcarrier block is assigned to the WTRU based on at least one of data rate requirements and buffer occupancy of the WTRU.
[0046] 6. The method as in any embodiments 1-5, wherein uplink transmissions from WTRUs having low data rate requirements or low buffer occupancy are multiplexed in time domain.
[0047] 7. The method of embodiment 6, wherein the uplink transmissions from the WTRUs are multiplexed on a TTI basis.
[0048] 8. The method of embodiment 6, wherein the uplink transmissions from the WTRUs are multiplexed on an SC-FDMA symbol basis.
[0049] 9. The method as in any embodiments 3-8, wherein the information regarding allocation of the distributed subcarrier block for the
WTRU is sent to Node-Bs in the active set of the WTRU via a control plane access gateway. [0050] 10. The method as in any embodiments 3-8, wherein the information regarding allocation of the distributed subcarrier block for the WTRU is sent to Node-Bs in the active set of the WTRU via a radio network controller.
[0051] 11. The method as in any embodiments 3-8, wherein the information regarding allocation of the distributed subcarrier block for the WTRU is sent to Node-Bs in the active set of the WTRU via a primary Node-B that is designated among Node-Bs in the active set.
[0052] 12. A method for uplink inter-Node-B macro diversity in an SC-
FDMA system including at least one WTRU and a plurality of Node-Bs. [0053] 13. The method of embodiment 12 comprising assigning at least one subcarrier block including a plurality of subcarriers and a seed in a frequency and time hopping sequence to a WTRU for uplink transmission. [0054] 14. The method of embodiment 13 comprising sending information regarding the assigned subcarrier block(s) and the seed for the WTRU to Node-Bs in an active set of the WTRU.
[0055] 15. The method of embodiment 14 comprising at least two Node-
Bs in the active set receiving and decoding the data packets transmitted by the WTRU in at least one of frequency hopping and time hopping manner based on the information.
[0056] 16. The method as in any embodiments 13-15, wherein the subcarrier block is a localized subcarrier block.
[0057] 17. The method as in any embodiments 13-15, wherein the subcarrier block is a distributed subcarrier block.
[0058] 18. The method as in any embodiments 14-17, wherein the information regarding allocation of the subcarrier block and the seed is sent to the Node-Bs in the active set of the WTRU via an access gateway. [0059] 19. The method as in any embodiments 14-17, wherein the information regarding allocation of the subcarrier block and the starting seed is sent to the Node-Bs in the active set of the WTRU via a radio network controller. [0060] 20. The method as in any embodiments 14-17, wherein the information regarding allocation of the subcarrier block and the starting seed is sent to the Node-Bs in the active set of the WTRU via a primary Node-B that is designated among Node-Bs in the active set.
[0061] 21. The method as in any embodiments 13-20, wherein the subcarrier block is assigned based on at least one of data rate requirement and buffer occupancy of the WTRU.
[0062] 22. A Node-B for supporting uplink inter-Node-B macro diversity in an SC-FDMA system.
[0063] 23. The Node-B of embodiment 22 comprising a radio resource allocation unit configured to allocate at least one distributed subcarrier block and time schedule for uplink transmission to a WTRU, the number of subcarriers in the distributed subcarrier block being large enough to provide frequency diversity and location of the subcarriers being fixed
[0064] 24. The Node-B of embodiment 23, wherein the radio resource allocation unit is configured to send information regarding the allocated distributed subcarrier block(s) to Node-Bs in an active set of the WTRU.
[0065] 25. The Node-B as in any embodiments 23-24 comprising a receiver configured to receive and decode uplink transmission of the WTRU based on the information.
[0066] 26. The Node-B as in any embodiments 23-25, wherein the distributed subcarrier block is assigned to the WTRU based on at least one of data rate requirement and buffer occupancy of the WTRU.
[0067] 27. The Node-B as in any embodiments 23-26, wherein uplink transmissions from WTRUs having low data rate requirements or low buffer occupancy are multiplexed in time domain in a persistent manner.
[0068] 28. The Node-B of embodiment 27, wherein the uplink transmissions from the WTRUs are multiplexed in a TTI basis.
[0069] 29. The Node-B of embodiment 27, wherein the uplink transmissions from the WTRUs are multiplexed on an SC-FDMA symbol basis. [0070] 30. The Node-B as in any embodiments 24-29, wherein the information regarding allocation of the distributed subcarrier block for the
WTRU is sent to the Node-Bs in the active set of the WTRU via an access gateway.
[0071] 31. The Node-B as in any embodiments 24-29, wherein the information regarding allocation of the distributed subcarrier block for the
WTRU is sent to the Node-Bs in the active set of the WTRU via a radio network controller.
[0072] 32. The Node-B as in any embodiments 24-29, wherein the information regarding allocation of the distributed subcarrier block for the
WTRU is sent to the Node-Bs in the active set of the WTRU via a primary Node-
B that is designated among Node-Bs in the active set.
[0073] 33. The Node-B of embodiment 22 comprising a radio resource allocation unit configured to allocate at least one subcarrier block and a seed in a frequency and time hopping sequence to a WTRU.
[0074] 34. The Node-B of embodiment 33, wherein the radio resource allocation unit is configured to send information regarding the allocated subcarrier block(s) and the seed to Node-Bs in an active set of the WTRU.
[0075] 35. The Node-B as in any embodiments 33-34, comprising a receiver configured to receive and decode data packets transmitted by the WTRU in at least one of frequency hopping and time hopping manner based on the information.
[0076] 36. The Node-B as in any embodiments 33-35, wherein the subcarrier block is a localized subcarrier block.
[0077] 37. The Node-B as in any embodiments 33-35, wherein the subcarrier block is a distributed subcarrier block.
[0078] 38. The Node-B as in any embodiments 33-37, wherein the subcarrier block is assigned based on at least one of data rate requirement and buffer occupancy of the WTRU. [0079] 39. The Node-B as in any embodiments 34-38, wherein the information regarding allocation of the subcarrier block and the starting seed is sent to the Node-Bs in the active set of the WTRU via an access gateway. [0080] 40. The Node-B as in any embodiments 34-38, wherein the information regarding allocation of the subcarrier block and the starting seed is sent to the Node-Bs in the active set of the WTRU via a radio network controller. [0081] 41. The Node-B as in any embodiments 34-38, wherein the information regarding allocation of the subcarrier block and the starting seed is sent to the Node-Bs in the active set of the WTRU via a primary Node-B that is designated among Node-Bs in the active set.
[0082] Although the features and elements of the present invention are described in the preferred embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the preferred embodiments or in various combinations with or without other features and elements of the present invention.