Patent Application
20110317642
1. Field
Aspects of the present disclosure relate generally to wireless communication systems, and more particularly, to intra-Node B unsynchronized serving cell changes.
2. Background
Wireless communication networks are widely deployed to provide various communication services such as telephony, video, data, messaging, broadcasts, and so on. Such networks, which are usually multiple access networks, support communications for multiple users by sharing the available network resources. One example of such a network is the UMTS Terrestrial Radio Access Network (UTRAN). The UTRAN is the radio access network defined as a part of the Universal Mobile Telecommunications System (UMTS), a third generation (3G) mobile phone technology specified by the 3rd Generation Partnership Project (3GPP). UMTS, which is the successor to Global System for Mobile Communications (GSM) technologies, currently supports various air interface standards, such as Wideband-Code Division Multiple Access (W-CDMA), Time Division-Code Division Multiple Access (TD-CDMA), and Time Division-Synchronous Code Division Multiple Access (TD-SCDMA). UMTS also supports enhanced 3G data communications protocols, such as High Speed Packet Access (HSPA), which provides higher data transfer speeds and capacity to associated UMTS networks.
As the demand for mobile broadband access continues to increase, research and development continue to advance the UMTS technologies not only to meet the growing demand for mobile broadband access, but to advance and enhance the user experience with mobile communications. For example, as the number of base stations increases, and as the number of cells provided by each base station also increases, handover procedures from one cell to another dramatically increase in frequency. As the number of handovers continues to increase, the importance of improved handover procedures rises. That is, any loss of data caused by handover issues becomes more noticeable when handovers occur more often.
In particular, an intra-Node B synchronized serving cell change typically utilizes a reset procedure to reset the MAC entity, causing internal buffers at the Node B to be flushed and resulting in a loss of packets. Further, an intra-Node B unsynchronized serving cell change, while it may utilize the reset procedure and accordingly lose packets, frequently does not perform the reset and can, in certain circumstances, still result in a substantial loss of packets. Thus, there is a need in the art for an improved handover procedure, for example, for an intra-Node B unsynchronized serving cell change.
Various aspects of the disclosure address an issue in an intra-Node B unsynchronized serving cell change (USCC) in an HSPA system, where a transmission sequence number (TSN) wraps around in such a way as to cause numerous issues such as lost or corrupted packets. In various aspects of the present disclosure, the TSN may be stalled during the intra-Node B USCC procedure by extending the number of HARQ retransmissions beyond the configured maximum number of retransmissions until the SCC is complete, or halting scheduling and transmission of packets from the Node B until the SCC is complete.
Some aspects of the present disclosure may relate to wireless user equipment in a cellular telecommunication system. For example, in an exemplary aspect of the disclosure, a method of wireless communication may include utilizing a receiver to receive a first packet having a first sequence number on a first downlink channel from a source cell, reconfiguring the receiver during an unsynchronized intra-Node B serving cell change to receive a second downlink channel from a target cell, and receiving a second packet over the second downlink channel. Here, the second packet may have a second sequence number sequentially incremented from the first sequence number.
In another exemplary aspect of the disclosure, an apparatus for wireless communication may include means for receiving a first packet having a first sequence number on a first downlink channel from a source cell, means for reconfiguring the means for receiving, during an unsynchronized intra-Node B serving cell change, to receive a second downlink channel from a target cell, and means for receiving a second packet over the second downlink channel. Here, the second packet may have a second sequence number sequentially incremented from the first sequence number.
In yet another exemplary aspect of the disclosure, a computer program product may include a computer-readable medium having code for utilizing a receiver to receive a first packet having a first sequence number on a first downlink channel from a source cell, code for reconfiguring the receiver during an unsynchronized intra-Node B serving cell change to receive a second downlink channel from a target cell, and code for receiving a second packet over the second downlink channel. Here, the second packet may have a second sequence number sequentially incremented from the first sequence number.
In yet another exemplary aspect of the disclosure, an apparatus for wireless communication may include at least one processor and a memory coupled to the at least one processor. Here, the at least one processor may be configured to utilize a receiver to receive a first packet having a first sequence number on a first downlink channel from a source cell, to reconfigure the receiver during an unsynchronized intra-Node B serving cell change to receive a second downlink channel from a target cell, and to receive a second packet over the second downlink channel. Here, the second packet may have a second sequence number sequentially incremented from the first sequence number.
Some aspects of the present disclosure may relate to network nodes in a wireless telecommunication system, such as a base station, a radio network controller, a combination of the two, or any other suitable network node or combination of nodes. For example, in an exemplary aspect of the disclosure, a method of wireless communication may include allocating a first sequence number to a first packet to be sent to a UE, transmitting the first packet on a first downlink channel from a source cell to the UE, incrementing the sequence number to a sequential sequence number, allocating the sequential sequence number to a second packet to be sent to the UE, providing a reconfiguration message for a UE to change from the source cell to a target cell, and stalling a continued incrementing of the sequence number until an indication is received from the UE that the change from the source cell to the target cell is complete.
In another exemplary aspect of the disclosure, an apparatus for wireless communication may include means for allocating a first sequence number to a first packet to be sent to a UE, means for transmitting the first packet on a first downlink channel from a source cell to the UE, means for incrementing the sequence number to a sequential sequence number, means for allocating the sequential sequence number to a second packet to be sent to the UE, means for providing a reconfiguration message for a UE to change from the source cell to a target cell, and means for stalling a continued incrementing of the sequence number until an indication is received from the UE that the change from the source cell to the target cell is complete.
In another exemplary aspect of the disclosure, a computer program product may include a computer-readable medium having code for allocating a first sequence number to a first packet to be sent to a UE, code for transmitting the first packet on a first downlink channel from a source cell to the UE, code for incrementing the sequence number to a sequential sequence number, code for allocating the sequential sequence number to a second packet to be sent to the UE, code for providing a reconfiguration message for a UE to change from the source cell to a target cell, and code for stalling a continued incrementing of the sequence number until an indication is received from the UE that the change from the source cell to the target cell is complete.
In another exemplary aspect of the disclosure, an apparatus for wireless communication may include at least one processor and a memory coupled to the at least one processor. Here, the at least one processor may be configured to allocate a first sequence number to a first packet to be sent to a UE, to transmit the first packet on a first downlink channel from a source cell to the UE, to increment the sequence number to a sequential sequence number, to allocate the sequential sequence number to a second packet to be sent to the UE, to provide a reconfiguration message for a UE to change from the source cell to a target cell, and to stall a continued incrementing of the sequence number until an indication is received from the UE that the change from the source cell to the target cell is complete.
These and other aspects of the invention will become more fully understood upon a review of the detailed description, which follows.
The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well known structures and components are shown in block diagram form in order to avoid obscuring such concepts.
In accordance with various aspects of the disclosure, an element, or any portion of an element, or any combination of elements may be implemented with a “processing system” that includes one or more processors. Examples of processors include microprocessors, microcontrollers, digital signal processors (DSPs), field programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionality described throughout this disclosure.
One or more processors in the processing system may execute software. Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software modules, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise. The software may reside on a computer-readable medium. The computer-readable medium may be a non-transitory computer-readable medium. A non-transitory computer-readable medium includes, by way of example, a magnetic storage device (e.g., hard disk, floppy disk, magnetic strip), an optical disk (e.g., compact disk (CD), digital versatile disk (DVD)), a smart card, a flash memory device (e.g., card, stick, key drive), random access memory (RAM), read only memory (ROM), programmable ROM (PROM), erasable PROM (EPROM), electrically erasable PROM (EEPROM), a register, a removable disk, and any other suitable medium for storing software and/or instructions that may be accessed and read by a computer. The computer-readable medium may also include, by way of example, a carrier wave, a transmission line, and any other suitable medium for transmitting software and/or instructions that may be accessed and read by a computer. The computer-readable medium may be resident in the processing system, external to the processing system, or distributed across multiple entities including the processing system. The computer-readable medium may be embodied in a computer-program product. By way of example, a computer-program product may include a computer-readable medium in packaging materials. Those skilled in the art will recognize how best to implement the described functionality presented throughout this disclosure depending on the particular application and the overall design constraints imposed on the overall system.
The processor 104 is responsible for managing the bus 102 and general processing, including the execution of software stored on the computer-readable medium 106. The software, when executed by the processor 104, causes the processing system 114 to perform the various functions described infra for any particular apparatus. The computer-readable medium 106 may also be used for storing data that is manipulated by the processor 104 when executing software.
The various concepts presented throughout this disclosure may be implemented across a broad variety of telecommunication systems, network architectures, and communication standards. By way of example and without limitation, the aspects of the present disclosure illustrated in
Communication between a UE 210 and a Node B 208 may be considered as including a physical (PHY) layer and a medium access control (MAC) layer. Further, communication between a UE 210 and an RNC 206 by way of a respective Node B 208 may be considered as including a radio resource control (RRC) layer.
The geographic region covered by the RNS 207 may be divided into a number of cells, with a radio transceiver apparatus serving each cell. A radio transceiver apparatus is commonly referred to as a Node B in UMTS applications, but may also be referred to by those skilled in the art as a base station (BS), a base transceiver station (BTS), a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS), an extended service set (ESS), an access point (AP), or some other suitable terminology. For clarity, three Node Bs 208 are shown in each RNS 207; however, the RNSs 207 may include any number of wireless Node Bs. The Node Bs 208 provide wireless access points to a core network (CN) 204 for any number of mobile apparatuses. Examples of a mobile apparatus include a cellular phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a notebook, a netbook, a smartbook, a personal digital assistant (PDA), a satellite radio, a global positioning system (GPS) device, a multimedia device, a video device, a digital audio player (e.g., MP3 player), a camera, a game console, or any other similar functioning device. The mobile apparatus is commonly referred to as user equipment (UE) in UMTS applications, but may also be referred to by those skilled in the art as a mobile station (MS), a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal (AT), a mobile terminal, a wireless terminal, a remote terminal, a handset, a terminal, a user agent, a mobile client, a client, or some other suitable terminology. In a UMTS system, the UE 210 may further include a universal subscriber identity module (USIM) 211, which contains a user's subscription information to a network. For illustrative purposes, one UE 210 is shown in communication with a number of the Node Bs 208. The downlink (DL), also called the forward link, refers to the communication link from a Node B 208 to a UE 210, and the uplink (UL), also called the reverse link, refers to the communication link from a UE 210 to a Node B 208.
The core network 204 interfaces with one or more access networks, such as the UTRAN 202. As shown, the core network 204 is a GSM core network. However, as those skilled in the art will recognize, the various concepts presented throughout this disclosure may be implemented in a RAN, or other suitable access network, to provide UEs with access to types of core networks other than GSM networks.
The core network 204 includes a circuit-switched (CS) domain and a packet-switched (PS) domain. Some of the circuit-switched elements are a Mobile services Switching Centre (MSC), a Visitor Location Register (VLR), and a Gateway MSC (GMSC). Packet-switched elements include a Serving GPRS Support Node (SGSN) and a Gateway GPRS Support Node (GGSN). Some network elements, like EIR, HLR, VLR and AuC may be shared by both of the circuit-switched and packet-switched domains.
In the illustrated example, the core network 204 supports circuit-switched services with a MSC 212 and a GMSC 214. In some applications, the GMSC 214 may be referred to as a media gateway (MGW). One or more RNCs, such as the RNC 206, may be connected to the MSC 212. The MSC 212 is an apparatus that controls call setup, call routing, and UE mobility functions. The MSC 212 also includes a visitor location register (VLR) that contains subscriber-related information for the duration that a UE is in the coverage area of the MSC 212. The GMSC 214 provides a gateway through the MSC 212 for the UE to access a circuit-switched network 216. The GMSC 214 includes a home location register (HLR) 215 containing subscriber data, such as the data reflecting the details of the services to which a particular user has subscribed. The HLR is also associated with an authentication center (AuC) that contains subscriber-specific authentication data. When a call is received for a particular UE, the GMSC 214 queries the HLR 215 to determine the UE's location and forwards the call to the particular MSC serving that location.
The illustrated core network 204 also supports packet-data services with a serving GPRS support node (SGSN) 218 and a gateway GPRS support node (GGSN) 220. GPRS, which stands for General Packet Radio Service, is designed to provide packet-data services at speeds higher than those available with standard circuit-switched data services. The GGSN 220 provides a connection for the UTRAN 202 to a packet-based network 222. The packet-based network 222 may be the Internet, a private data network, or some other suitable packet-based network. The primary function of the GGSN 220 is to provide the UEs 210 with packet-based network connectivity. Data packets may be transferred between the GGSN 220 and the UEs 210 through the SGSN 218, which performs primarily the same functions in the packet-based domain as the MSC 212 performs in the circuit-switched domain.
The UMTS air interface may be a spread spectrum Direct-Sequence Code Division Multiple Access (DS-CDMA) system. The spread spectrum DS-CDMA spreads user data through multiplication by a sequence of pseudorandom bits called chips. The W-CDMA air interface for UMTS is based on such DS-CDMA technology and additionally calls for a frequency division duplexing (FDD). FDD uses a different carrier frequency for the uplink (UL) and downlink (DL) between a Node B 208 and a UE 210. Another air interface for UMTS that utilizes DS-CDMA, and uses time division duplexing (TDD), is the TD-SCDMA air interface. Those skilled in the art will recognize that although various examples described herein may refer to a W-CDMA air interface, the underlying principles are equally applicable to a TD-SCDMA air interface.
A high speed packet access (HSPA) air interface includes a series of enhancements to the 3G/W-CDMA air interface, facilitating greater throughput and reduced latency. Among other modifications over prior releases, HSPA utilizes hybrid automatic repeat request (HARQ), shared channel transmission, and adaptive modulation and coding. The standards that define HSPA include HSDPA (high speed downlink packet access) and HSUPA (high speed uplink packet access, also referred to as enhanced uplink, or EUL).
The radio protocol architecture between the UE and the UTRAN may take on various forms depending on the particular application. An example for an HSPA system will now be presented with reference to
Turning to
At Layer 3, the RRC layer 316 handles the control plane signaling between the UE and the Node B. RRC layer 316 includes a number of functional entities for routing higher layer messages, handling broadcast and paging functions, establishing and configuring radio bearers, etc.
In the UTRA air interface, the L2 layer 308 is split into sublayers. In the control plane, the L2 layer 308 includes two sublayers: a medium access control (MAC) sublayer 310 and a radio link control (RLC) sublayer 312. In the user plane, the L2 layer 308 additionally includes a packet data convergence protocol (PDCP) sublayer 314. Although not shown, the UE may have several upper layers above the L2 layer 308 including a network layer (e.g., IP layer) that is terminated at a PDN gateway on the network side, and an application layer that is terminated at the other end of the connection (e.g., far end UE, server, etc.).
The PDCP sublayer 314 provides multiplexing between different radio bearers and logical channels. The PDCP sublayer 314 also provides header compression for upper layer data packets to reduce radio transmission overhead, security by ciphering the data packets, and handover support for UEs between Node Bs.
The RLC sublayer 312 provides segmentation and reassembly of upper layer data packets, retransmission of lost data packets, and reordering of data packets to compensate for out-of-order reception due to a hybrid automatic repeat request (HARQ).
The MAC sublayer 310 provides multiplexing between logical and transport channels. The MAC sublayer 310 is also responsible for allocating the various radio resources (e.g., resource blocks) in one cell among the UEs. The MAC sublayer 310 is also responsible for HARQ operations.
The MAC sublayer 310 includes various MAC entities, including but not limited to a MAC-d entity and MAC-hs/ehs entity. The Radio Network Controller (RNC) houses protocol layers from MAC-d and above. For the high speed channels, the MAC-hs/ehs layer is housed in the Node B.
From the UE side, The MAC-d entity is configured to control access to all the dedicated transport channels, to a MAC-c/sh/m entity, and to the MAC-hs/ehs entity. Further, from the UE side, the MAC-hs/ehs entity is configured to handle the HSDPA specific functions and control access to the HS-DSCH transport channel. Upper layers configure which of the two entities, MAC-hs or MAC-ehs, is to be applied to handle HS-DSCH functionality.
In
The UE side MAC-hs entity 500 is illustrated in
The HARQ entity 502 is configured to handle MAC functions and tasks related to the HARQ protocol, such as generating ACKs or NACKs. That is, when the Node B transmits a MAC-hs PDU 400 having a particular QID 406 to the UE, the UE may respond as to whether it successfully received the PDU by sending an acknowledgment signal, i.e., a HARQ ACK or NACK. If the PDU was not successfully received, i.e., the Node B received a NACK, the Node B may retransmit part of the symbols that make up the original PDU to the UE, in an attempt to allow recovery of the PDU. The Node B generally keeps retransmitting these further packets until it receives an ACK or reaches a maximum number of allowed retransmissions. After the maximum number is reached, the Node B generally ceases the retransmissions, discards the PDU, and transmits the next PDU with the next sequential TSN to the UE.
Although the UE unsuccessfully decoded a PDU and sent a NACK, the received but unsuccessfully decoded PDU is generally not discarded by the UE. Rather, when retransmissions are received, the UE combines the first unsuccessfully recovered PDU with the retransmissions and performs error correction to recover the contents of the PDU. With each additional retransmission, the probability of recovering the original PDU may increase.
Returning to
The disassembly entity 508 is configured to disassemble MAC-hs PDUs. Here, when a MAC-hs PDU is disassembled, the MAC-hs header is removed, the MAC-d PDU is extracted, and any present padding bits are removed. Thus, the MAC-d PDUs can be delivered to a higher layer.
The MAC-ehs entity was standardized with Release 7 of the 3GPP family of standards. The MAC-ehs provides support for flexible RLC PDU sizes, and MAC segmentation and reassembly. The MAC-ehs also provides for the multiplexing of data from several priority queues within one TTI.
The MAC-ehs header 602 may include a plurality of logical channel identifiers (LCH-ID) 606, TSNs 608, and system information (SI) bits 610. Here, the QID parameter 406 from MAC-hs has been replaced with the LCH-ID 606. This way, the MAC-ehs entity enables packets from multiple logical channels to be combined into one MAC-ehs packet. Similar to its use in MAC-hs, the TSN 608 is still based on the priority queues. Also similar to the MAC-hs, in MAC-ehs the HARQ retransmissions are based on the TSN numbering.
The LCH-ID 606 and L fields are repeated per reordering SDU. The TSN 608 and SI 610 fields are repeated per reordering PDU 604. Thus, if multiple logical channels are mapped to the same priority queue and they both have packets, then they share the same TSN space. In this case, the TSN 608 and S1610 information for the second reordering PDU 604 will be empty, and the receiver uses the values from the previous reordering PDU 604 of the same MAC-ehs PDU 600. That is, in general, the presence of the TSNi and SIi fields is based on the value of the LCH-IDi; if the LCH-IDi is mapped to the same reordering queue as LCH-IDi-1 or if the value of LCH-IDi-1 is equal to the value of LCH-IDi, there is no TSNi or SIi field.
The UE side MAC-ehs entity 700 is illustrated in
There is generally one HARQ entity 702 per HS-DSCH transport channel. The HARQ entity 702 performs substantially the same function as described for the HARQ entity 502 within the MAC-hs entity 500. Further, as shown in
Referring now to
In a cell that is divided into sectors, the multiple sectors within a cell can be formed by groups of antennas with each antenna responsible for communication with UEs in a portion of the cell. For example, in cell 802, antenna groups 812, 814, and 816 may each correspond to a different sector. In cell 804, antenna groups 818, 820, and 822 each correspond to a different sector. In cell 806, antenna groups 824, 826, and 828 each correspond to a different sector.
The cells 802, 804 and 806 may include several UEs that may be in communication with one or more sectors of each cell 802, 804 or 806. For example, UEs 830 and 832 may be in communication with Node B 842, UEs 834 and 836 may be in communication with Node B 844, and UEs 838 and 840 may be in communication with Node B 846. Here, each Node B 842, 844, 846 is configured to provide an access point to a core network 204 (see
In Release 5 of the 3GPP family of standards, High Speed Downlink Packet Access (HSDPA) was introduced. One difference on the downlink between HSDPA and the previously standardized circuit-switched air-interface is the absence of soft-handover in HSDPA. This means that data is transmitted to the UE from a single cell called the HSDPA serving cell. As the user moves, or as one cell becomes preferable to another, the HSDPA serving cell may change.
In HSDPA, at any instance a UE has one serving cell. Here, a serving cell is that cell on which the UE is camped. According to mobility procedures defined in Release 5 of 3GPP TS 25.331, the Radio Resource Control (RRC) signaling messages for changing the HSPDA serving cell are transmitted from the current HSDPA serving cell (i.e., the source cell), and not the cell that the UE reports as being the stronger cell (i.e., the target cell).
Further, with HSDPA the UE generally monitors and performs measurements of certain parameters of the downlink channel to determine the quality of that channel. Based on these measurements the UE can provide feedback to the Node B on an uplink transmission. This feedback can include a channel quality indicator (CQI). Thus, the Node B may provide subsequent MAC-hs/MAC-ehs packets to the UE on downlink transmissions having a size, coding format, etc., based on the reported CQI from the UE.
For example, during a call with the source cell 804a, or at any other time, the UE 836 may monitor various parameters of the source cell 804a as well as various parameters of neighboring cells such as cells 804b, 806, and 802. Further, depending on the quality of these parameters, the UE 836 may maintain communication with one or more of the neighboring cells. During this time, the UE 836 may maintain an Active Set, that is, a list of cells that the UE 836 is simultaneously connected to (i.e., the UTRA cells that are currently assigning a downlink dedicated physical channel DPCH or fractional downlink dedicated physical channel F-DPCH to the UE 836 may constitute the Active Set).
In a Serving Cell Change (SCC) procedure, the UE requests that the serving cell be changed from the currently serving source cell to a target cell. This request is sent to the UTRAN through a so-called “event 1D” message. The UTRAN and the UE exchange several messages and when the procedure is complete the HS data is served from the target cell.
In accordance with various aspects of the present disclosure, the access network 800 may be a dual cell (DC-HSDPA) system, wherein a single UE is adapted to receive a downlink on each of two carrier frequencies. Further, the access network 800 may be a multi-cell (MC-HSDPA) system, wherein the single UE is adapted to receive a plurality of downlinks, e.g., four or eight downlinks, on different carriers. In accordance with a further aspect of the present disclosure, the access network 800 may be a multi-point HSDPA system (also sometimes called a single frequency dual cell SFDC-HSDPA system or a coordinated multi-point CoMP system), wherein a single UE is adapted to receive a plurality of downlinks from different cells, each provided on the same carrier frequency. In these systems, the plural cells may be provided by the same Node B, or by different Node Bs. In any of these systems, a SCC procedure may involve changing the primary serving cell, one or more secondary serving cells, or a plurality of the serving cells including but not limited to all of the serving cells.
An SCC may be an inter-Node B SCC or an intra-Node B SCC. In the case of an intra-Node B SCC, both the source and the target cells belong to the same Node B (e.g., cells 804a and 804b). In an inter-Node B SCC, the source cell belongs to a different Node B than the target cell.
Further, an SCC may be a synchronized SCC or an unsynchronized SCC. A synchronized SCC is where the RNC tells the UE to change to a new serving cell at a particular time. Here, the Node B and the UE are synchronized such that the Node B knows exactly when the UE will start listening to the new cell. In this case, there is less confusion between the UE and the Node B. In a synchronized SCC, it is generally required to provide adequate time for every type of UE and Node B. Thus, a very conservative assignment of the time for the synchronized SCC is used, perhaps as long as one second. Thus, even though a particular UE may be capable of a faster SCC, the slow, conservative delay is still utilized, potentially resulting in a dropped call where the signal drops quickly.
On the other hand, in an unsynchronized SCC an RRC message called the Physical Channel Reconfiguration message is sent from the RNC to the UE. As soon as the UE receives this message, it starts monitoring the target cell. Once the UE is capable of latching onto the target cell, it sends the Physical Channel Reconfiguration Complete message. Aspects of the present disclosure relate to an improved unsynchronized intra-Node B SCC.
Referring to
Based on the measurements made by the UE 902, a signal quality of cell 2904b may cross a certain threshold. In this case, in step 3, the UE 902 provides an RRC Measurement Report message including “event 1A” to the RNC 906, requesting that cell 2904b be added to the Active Set for the UE 902. In response, in step 4, the RNC 906 provides an Active Set Update command to the UE. With the Active Set Update Complete message sent by the UE 902 in step 5, the Active Set for the UE 902 includes two cells, that is, cell 1904a and cell 2904b.
At some point in time the signal quality of cell 2904b may exceed that of cell 1904a, at which time the UE 902 may wish to have cell 2904b become its serving cell. Thus, based on further measurements that indicate that cell 2904b is better than cell 1904a, in step 6 the UE 902 may provide a Measurement Report message including “event 1D” to the RNC 906, requesting a serving cell change to cell 2904b. In response, in step 7 the RNC 906 may provide a Physical Channel Reconfiguration message to the UE 902 indicating that the UE 902 may change its serving cell to cell 2904b.
At this point, based on information from the network in step 7, in step 8 the UE 902 begins to align its HS-DPCCH with the CPICH of cell 2904b, so that the UE 902 may monitor the target cell 904b. Thus, the UE 902 stops listening to cell 1904a, and any information transmitted from cell 1904a and directed to the UE 902 is not received.
In step 9, after successfully aligning with the target cell 904b, the UE 902 starts monitoring the HS-SCCH from cell 2904b. In step 10, the UE 902 provides a Physical Channel Reconfiguration Complete message to the RNC 906 indicating that the UE 902 is ready to receive packets from cell 2904b. In steps 11 and 12, the RNC 906 configures cell 2904b for Enhanced Uplink (EUL) communication with the UE 902. Finally, in step 13, the Node B 904 is configured to begin sending data from cell 2904b.
During the time between step 8, when the UE 902 ceases listening for data from cell 1904a, and step 10, when the UE 902 indicates that it is configured and ready to receive packets from cell 2904b, the RNC 906 may still believe that the UE 902 is listening for data from cell 1904a, and thus the Node B 904 may continue transmitting packets to the UE 902 from cell 1904a. When those packets are not acknowledged, after a certain time, the network transmits a number of retransmission packets directed to the UE 902 from cell 1904a. When a maximum number of these retransmissions is not acknowledged, since the UE 902 is not listening for them, the network stops trying to send that packet, increments the transmission sequence number (TSN), and attempts to transmit the next packet. Thus, depending on the length of time it takes for the UE 902 to become ready to receive from cell 2904b and to indicate in step 10 that it is ready, a number of packets may be lost, and the TSN may be incremented a corresponding number of times.
During a SCC procedure the UTRAN has the option of either continuing the previous MAC-hs TSN sequence or resetting it. This information is communicated to the UE in one of the Layer 3 messages. If the MAC-hs/MAC-ehs is reset, the TSN starts from 0 for all the priority queues when the target cell starts transmitting. If MAC-hs/MAC-ehs is not reset, the TSN numbering is continued for all the priority queues from the source cell. In an intra-Node B SCC, because the MAC-hs packets are sent from the same Node B, the TSNs are continued and the MAC-hs/MAC-ehs is generally not reset. As discussed below, this may result in a number of issues during the time when the UE is listening to the target cell, yet packets are still being provided from the source cell.
In one example, a MAC-hs/MAC-ehs packet is retransmitted for a maximum of 1 time and the reconfiguration time is 132 ms. In this example, with 132 ms and 4 ms per packet (first time+1 retransmission), this comes to missing 33 TSNs (132/4). In
At the UE, a state variable called RcvWindow_UpperEdge (corresponding to the last received MAC PDU, which has the highest TSN of all received MAC PDUs) would have been 10 when the UE received a packet from the target cell having TSN 44. Assuming there were no holes in the TSN space, a state variable for the UE called Next_expected_TSN (corresponding to the TSN following the TSN of the last in-sequence MAC PDU received) would be 11. The lower edge of the receive window would have been 43 (RcvWindow_UpperEdge−RECEIVE_WINDOW_SIZE+1, where RECEIVE_WINDOW_SIZE is a parameter at the UE, configured by higher layers). Thus, the receive window would have been (42, 10). Because TSN 44 falls within this receive window, the receive window will continue to be (42, 10), even after receiving TSN 44. Further, because 44 falls within the receive window and is less than the Next_expected_TSN, the UE would assume that the next packet is a repeat of the previously received packet having a TSN 44, and thus it will be dropped by the UE. Further, all the following packets from 44 to 10 (wherein the TSN wraps around after reaching its maximum of 63) will also be dropped for the same reason. Once a packet having the TSN 11 is received by the UE, it is combined with the previous packet having the TSN 10, and a wrong RLC PDU is formed. Furthermore, if there were holes in the TSN space from (41, 10), then a new packet fills that hole and another wrong RLC PDU is formed. Thus, it is seen that the conventional intra-Node B unsynchronized SCC can potentially be very problematic. The TSN wrap around issue described above generally arises when the 6-bit TSN changes by more than 32 numbers without the UE receiving any packets, such that the next received packet falls within the receive window.
Various issues can arise due to the TSN wrap around issue. For example, the packets that went through the maximum number of HARQ retransmissions until the Node B gave up transmitting those packets, are later required to go through RLC retransmissions. Further, a number of newly transmitted packets will be dropped and would also result in RLC level retransmission. Still further, the reassembly layer may assemble wrong packets resulting in further errors at the RLC and higher layers.
In order to address this TSN wrap around issue, various aspects of the present disclosure may stall the TSN space during the intra-Node B unsynchronized SCC, such that the Node B continues to send retransmissions of a packet beyond the maximum number of retransmissions, and does not advance to the next TSN until an ACK is received or the unsynchronized SCC is complete. In various other aspects of the disclosure, the network may stop scheduling packets to the UE during the intra-Node B unsynchronized SCC, such that packets are not transmitted to the UE until the unsynchronized SCC is complete.
In the illustrated example, steps numbered 1-7 are substantially the same as steps numbered 1-7 in
Some aspects of the disclosure may address the TSN wrap-around issue by stalling the TSN space from the time when the Physical Channel Reconfiguration (PCR) message (sent from the RNC 1106 in step 7) is sent to the UE 1102 until the Physical Channel Reconfiguration Complete (PCRC) message (sent from the UE 110211) is sent to the RNC 1106. That is, in step 8, the RNC 1106 may send information to the Node B 1104 to prepare the Node B 1104 to stall the TSN space.
Therefore, in one aspect of the disclosure, during this period after the Node B 1104 receives this message from the RNC 1106, the Node B 1104 may continue to retransmit HARQ packets beyond the maximum number of HARQ retransmissions that it communicated to the UE. That is, in step 9, the UE begins to align its HS-DPCCH with the CPICH of ce112, 1104b, so that in step 10, the UE 1102 may monitor the target cell 1104b. Thus, the UE stops listening to cell 1, 1104a, and any packet sent from cell 1 addressed to the UE 1102 may not be acknowledged with a HARQ ACK/NACK.
In a conventional system, the Node B transmits packets to the UE when it receives channel quality information (CQI) from the UE. This way, the Node B can adapt the transmissions to the UE in accordance with the channel as seen by the UE. However, the Node B is not generally required only to transmit packets to the UE when it receives the CQI. That is, in accordance with some aspects of the disclosure, the Node B may continue transmitting retransmissions of MAC PDUs to the UE despite failing to receive feedback from the UE in the form of HARQ ACK/NACK or CQI information. Thus, in some aspects of the present disclosure, the Node B may utilize a previously-received CQI value to configure transmissions to the UE. This re-use of previous CQI values may continue indefinitely (i.e., until the Node B receives feedback such as a HARQ ACK/NACK and/or a CQI from the UE), or may continue for a predetermined number of transmissions or retransmissions.
Returning to
In step 11, the UE 1102 provides a PHYSICAL CHANNEL RECONFIGURATION COMPLETE message to the RNC 1106, indicating that it is ready to receive the HS-SCCH from cell 2, 1104b. Thus, in steps 12 and 13, the RNC configures cell 2, 1104b, for Enhanced Uplink (EUL) communication with the UE 1102, and in step 14, the RNC 1106 directs the Node B 1104 to start sending data from cell 2, 1104b. At this point, the Node B 1104 may reschedule the packet undergoing retransmission at cell 1, 1104a, to be transmitted from cell 2, 1104b, or may cease retransmissions and begin transmission of the subsequent packet from cell 2, 1104b.
In a conventional network, the scheduler generally treats HARQ retransmissions as higher priority than new data. However, in a further aspect of the instant disclosure, once the maximum number of transmissions is reached, the retransmissions may be treated as having the same priority as new packets destined for some other UEs. Because these retransmitted packets have the same priority as initially transmitted packets to other UEs, these retransmitted packets will not hog the HS-PDSCH channel.
By stopping the Node B from incrementing the TSN, various aspects of the disclosure address a number of issues discussed above. For example, the number of unnecessarily dropped new MAC-hs packets may be reduced or eliminated. Further, unnecessary RLC retransmissions may be reduced or eliminated. Even further, the incorrectly assembled RLC PDU should not occur.
In another aspect of the disclosure, rather than continuing retransmissions between steps 7 and 11, the TSN stall may instead cause the Node B 1104 to cease transmissions to the UE 1102 until the handover to cell 2, 1104b, is completed. This may reduce overhead, and achieve the same result as continuing the retransmissions.
At the UE 1250, a receiver 1254 receives the downlink transmission through an antenna 1252 and processes the transmission to recover the information modulated onto the carrier. The information recovered by the receiver 1254 is provided to a receive frame processor 1260, which parses each frame, and provides information from the frames to a channel processor 1294 and the data, control, and reference signals to a receive processor 1270. The receive processor 1270 then performs the inverse of the processing performed by the transmit processor 1220 in the Node B 1210. More specifically, the receive processor 1270 descrambles and despreads the symbols, and then determines the most likely signal constellation points transmitted by the Node B 1210 based on the modulation scheme. These soft decisions may be based on channel estimates computed by the channel processor 1294. The soft decisions are then decoded and deinterleaved to recover the data, control, and reference signals. The CRC codes are then checked to determine whether the frames were successfully decoded. The data carried by the successfully decoded frames will then be provided to a data sink 1272, which represents applications running in the UE 1250 and/or various user interfaces (e.g., display). Control signals carried by successfully decoded frames will be provided to a controller/processor 1290. When frames are unsuccessfully decoded by the receiver processor 1270, the controller/processor 1290 may also use an acknowledgement (ACK) and/or negative acknowledgement (NACK) protocol to support retransmission requests for those frames.
In the uplink, data from a data source 1278 and control signals from the controller/processor 1290 are provided to a transmit processor 1280. The data source 1278 may represent applications running in the UE 1250 and various user interfaces (e.g., keyboard) Similar to the functionality described in connection with the downlink transmission by the Node B 1210, the transmit processor 1280 provides various signal processing functions including CRC codes, coding and interleaving to facilitate FEC, mapping to signal constellations, spreading with OVSFs, and scrambling to produce a series of symbols. Channel estimates, derived by the channel processor 1294 from a reference signal transmitted by the Node B 1210 or from feedback contained in the midamble transmitted by the Node B 1210, may be used to select the appropriate coding, modulation, spreading, and/or scrambling schemes. The symbols produced by the transmit processor 1280 will be provided to a transmit frame processor 1282 to create a frame structure. The transmit frame processor 1282 creates this frame structure by multiplexing the symbols with information from the controller/processor 1290, resulting in a series of frames. The frames are then provided to a transmitter 1256, which provides various signal conditioning functions including amplification, filtering, and modulating the frames onto a carrier for uplink transmission over the wireless medium through the antenna 1252.
The uplink transmission is processed at the Node B 1210 in a manner similar to that described in connection with the receiver function at the UE 1250. A receiver 1235 receives the uplink transmission through the antenna 1234 and processes the transmission to recover the information modulated onto the carrier. The information recovered by the receiver 1235 is provided to a receive frame processor 1236, which parses each frame, and provides information from the frames to the channel processor 1244 and the data, control, and reference signals to a receive processor 1238. The receive processor 1238 performs the inverse of the processing performed by the transmit processor 1280 in the UE 1250. The data and control signals carried by the successfully decoded frames may then be provided to a data sink 1239 and the controller/processor, respectively. If some of the frames were unsuccessfully decoded by the receive processor, the controller/processor 1240 may also use an acknowledgement (ACK) and/or negative acknowledgement (NACK) protocol to support retransmission requests for those frames.
The controller/processors 1240 and 1290 may be used to direct the operation at the Node B 1210 and the UE 1250, respectively. For example, the controller/processors 1240 and 1290 may provide various functions including timing, peripheral interfaces, voltage regulation, power management, and other control functions. The computer readable media of memories 1242 and 1292 may store data and software for the Node B 1210 and the UE 1250, respectively. A scheduler/processor 1246 at the Node B 1210 may be used to allocate resources to the UEs and schedule downlink and/or uplink transmissions for the UEs.
It is to be understood that the specific order or hierarchy of steps in the methods disclosed hereinbelow is an illustration of exemplary processes. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the methods may be rearranged. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented unless specifically recited therein.
Here, as described above, the UE may have a plurality of cells in its Active Set. Further, the UE may measure various characteristics of neighboring cells, and if one or more neighboring cells in the Active Set has a characteristic such as a pilot power greater than a certain threshold, then in block 1302 the process may provide a Measurement Report message including event 1D, requesting that the serving cell be changed from the source cell to a target cell, e.g., cell 2. In response, in block 1306 the network may provide a Physical Channel Reconfiguration message to the UE, indicating for the UE to reconfigure its receiver to listen to the target cell, i.e., cell 2. Thus, in block 1308 the process may reconfigure the receiver of the UE during the unsynchronized intra-Node B SCC to receive a downlink channel (e.g., the HS-DSCH) from the target cell, i.e., cell 2. When the receiver of the UE is configured to monitor the HS-SCCH from the target cell, i.e., cell 2, in block 1310 the process may provide an indication from the UE that the SCC from the source cell, cell 1, to the target cell, cell 2, is complete. For example, the UE may transmit a Physical Channel Reconfiguration Complete message to the RNC.
Upon reception of the indication that the SCC is complete, the network may reconfigure the Node B such that further transmissions on the downlink HS-DPCCH come from the target cell, i.e., cell 2. Here, in step 1312, a packet (e.g., a MAC PDU) transmitted from the target cell may have a sequence number that is sequentially incremented from the first sequence number. That is, if the first packet, received just prior to the reconfiguration of the receiver, had a TSN of n, then the second packet, received after the SCC is complete, may have a TSN of n+1. In this way, the TSN wrap-around issue described above may be avoided.
In some aspects of the disclosure, the second packet may have been unsuccessfully transmitted from the source cell, i.e., cell 1, after the time that the UE reconfigured to receive from the target cell, i.e., cell 2. Thus, the second packet may have undergone HARQ retransmissions. In accordance with an aspect of the present disclosure, the TSN space may have been halted, and therefore, the second packet may have undergone HARQ retransmissions beyond the preconfigured maximum number of HARQ retransmissions. In a further aspect of the disclosure, a counter for counting the number of HARQ retransmissions for the second packet may be reset after the UE provides a Physical Channel Reconfiguration Complete message to indicate that the receiver of the UE was reconfigured to receive the HS-DPCCH from the target cell, i.e., cell 2.
In other aspects of the disclosure, the second packet transmitted after the UE reconfigured its receiver to monitor the HS-DPCCH from the target cell, may have been delayed. That is, the transmission of the second packet may have been stalled until after the UE provided the Physical Channel Reconfiguration Complete message to indicate that the receiver of the UE was reconfigured to receive the HS-DPCCH from the target cell, i.e., cell 2. In this fashion the TSN wrap-around issue discussed above may be avoided.
In block 1402, the process may allocate a TSN having number n to a first packet, e.g., a MAC PDU, to be sent to a UE. The allocation may take place at the Node B, at the RNC, or at any other suitable node in the network. If the allocation is performed at a node other than the Node B, then the PDU is provided to the Node B for transmission to the UE. In block 1404, the first packet, having the TSN of n is transmitted to the UE from a first cell of a plurality of cells provided by the Node B. Following receipt of a HARQ acknowledgment of the packet, in block 1406 the process increments the TSN to n+1, and in block 1408 the process allocates the TSN of n+1 to a second packet to be transmitted to the UE.
Meanwhile, the UE may be moving and/or signal conditions may be changing. As such, the UE may decide that another cell provided by the Node B, say cell 2, is preferable, and may request a SCC to cell 2. Thus, in block 1410, the process may receive a Measurement Report message including event 1D, requesting that the serving cell be changed from cell 1 to cell 2. In response, the network may determine to hand over the UE from cell 1 to cell 2, utilizing an intra-Node B unsynchronized SCC. That is, in block 1412, the process may send a Physical Channel Reconfiguration message to the UE ordering the UE to change to cell 2, thereby causing the UE to stop listening to the HS-PDCCH provided from cell 1.
In some implementations in accordance with the disclosure, the process may be configured to stall the TSN space in accordance with the intra-Node B unsynchronized SCC. That is, in block 1414, the process may continue to attempt to transmit the PDU having the TSN n+1 to the UE utilizing cell 1, at the time prior to completion of the intra-Node B unsynchronized SCC. However, because the UE is no longer monitoring the cell 1, the Node B may not receive a HARQ ACK/NACK from the UE. Thus, the network may attempt HARQ retransmissions of the packet. Here, in block 1416, the process may stall the TSN space. That is, the process may stall incrementing the TSNs and may continue retransmissions of the packet having TSN of n+1 beyond the predetermined maximum number of retransmissions.
In other implementations in accordance with the disclosure, the process may be configured to halt the scheduling and transmission of packets to the UE until the intra-Node B unsynchronized SCC is complete. That is, in block 1424, after sending the Physical Channel Reconfiguration message to the UE ordering the UE to switch its serving cell to cell 2, the process may halt further transmissions to the UE from the Node B that provides cell 1 and cell 2, and concomitantly halt scheduling additional packets to the UE. This way, the process may avoid any TSN wrap-around issues. When the process receives in block 1418 the Physical Channel Reconfiguration Complete message from the UE indicating that the SCC to cell 2 is complete, then in block 1420, the process may transmit the packet having the TSN of n+1 from cell 2.
After the SCC is complete and the Node B has transmitted from cell 2 the packet having the TSN of n+1, in block 1422 the process may receive a HARQ ACK/NACK corresponding to the packet having the TSN of n+1. Thus, normal processing may continue, and the TSN wrap-around issue may be avoided.
Referring now once again to
In another configuration, the apparatus 1210 for wireless communication may include means for allocating TSNs to packets, e.g., MAC-hs and/or MAC-ehs PDUs, means for incrementing a TSN or changing a TSN in any suitable manner to be allocated to a packet, means for stalling the TSN space, and/or means for stopping the scheduling of packets to the UE during the intra-Node B unsynchronized SCC procedure. In one aspect, the aforementioned means may be the channel processor 1244, the controller/processor 1240, and/or the scheduler/processor 1246 configured to perform the functions recited by the aforementioned means. In another aspect, the aforementioned means may include the processing system 114 illustrated in
Several aspects of a telecommunications system have been presented with reference to a W-CDMA system. As those skilled in the art will readily appreciate, various aspects described throughout this disclosure may be extended to other telecommunication systems, network architectures and communication standards.
By way of example, various aspects may be extended to other UMTS systems such as TD-SCDMA and TD-CDMA. Various aspects may also be extended to systems employing Long Term Evolution (LTE) (in FDD, TDD, or both modes), LTE-Advanced (LTE-A) (in FDD, TDD, or both modes), CDMA2000, Evolution-Data Optimized (EV-DO), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Ultra-Wideband (UWB), Bluetooth, and/or other suitable systems. The actual telecommunication standard, network architecture, and/or communication standard employed will depend on the specific application and the overall design constraints imposed on the system.
The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language of the claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” Unless specifically stated otherwise, the term “some” refers to one or more. A phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a; b; c; a and b; a and c; b and c; and a, b and c. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. §112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.”
This application claims the benefit of U.S. Provisional Patent Application No. 61/358,821, titled “SYSTEM AND PROCESS FOR TRANSMISSION SEQUENCE NUMBER MANAGEMENT IN AN INTRA-NODE B UNSYNCHRONIZED SERVING CELL CHANGE” and filed on Jun. 25, 2010, the disclosure of which is expressly incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61358821 | Jun 2010 | US |
