Patent Application
20180084464
Aspects of the present disclosure relate generally to wireless communications systems, and more particularly, to LTE handover with a same secondary link, for example, a handover in an LTE-WLAN aggregation (LWA), dual connectivity, and/or 5G scenario.
Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasts. Typical wireless communication systems may employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power). Examples of such multiple-access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency divisional multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems.
In some examples, a wireless multiple-access communication system may include a number of base stations, each simultaneously supporting communication for multiple communication devices, otherwise known as user equipment (UEs). In LTE or LTE-A network, a set of one or more base stations may define an eNodeB (eNB). In other examples (e.g., in a next generation or 5G network), a wireless multiple access communication system may include a number of distributed units (DUs) (e.g., edge units (EUs), edge nodes (ENs), radio heads (RHs), smart radio heads (SRHs), transmission reception points (TRPs), etc.) in communication with a number of central units (CUs) (e.g., central nodes (CNs), access node controllers (ANCs), etc.), where a set of one or more distributed units, in communication with a central unit, may define an access node (e.g., a new radio base station (NR BS), a new radio node-B (NR NB), a network node, 5G NB, gNB, gNodeB, etc.). A base station or DU may communicate with a set of UEs on downlink channels (e.g., for transmissions from a base station or to a UE) and uplink channels (e.g., for transmissions from a UE to a base station or distributed unit).
These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example of an emerging telecommunication standard is new radio (NR), for example, 5G radio access. NR is a set of enhancements to the LTE mobile standard promulgated by Third Generation Partnership Project (3GPP). It is designed to better support mobile broadband Internet access by improving spectral efficiency, lowering costs, improving services, making use of new spectrum, and better integrating with other open standards using OFDMA with a cyclic prefix (CP) on the downlink (DL) and on the uplink (UL) as well as support beamforming, multiple-input multiple-output (MIMO) antenna technology, and carrier aggregation.
However, as the demand for mobile broadband access continues to increase, there exists a need for further improvements in NR technology. Preferably, these improvements should be applicable to other multi-access technologies and the telecommunication standards that employ these technologies.
The systems, methods, and devices of the disclosure each have several aspects, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of this disclosure as expressed by the claims which follow, some features will now be discussed briefly. After considering this discussion, and particularly after reading the section entitled “Detailed Description” one will understand how the features of this disclosure provide advantages that include improved communications between access points and stations in a wireless network.
Techniques for LTE handover with a same secondary link are described herein. For example, the aspects may be applied in an LTE managing Wi-Fi connection (e.g., LTE+Wi-Fi aggregation, LWA) or a dual connectivity scenario wherein the UE maintains a same link with a secondary eNB (SeNB) when handing over from a first, master BS (e.g., Master eNB, MeNB) to a second master BS. Similarly, aspects may be applied to a handover in a 5G wireless communication system wherein a UE may maintain a same secondary link while handing over from a serving BS to a target BS. Aspects may advantageously minimize disruption on a secondary link during a handover on a primary link.
In an aspect, a method for wireless communication is provided. The method may be performed, for example, by a UE. The method generally includes receiving a handover (HO) indication from a source wireless wide area network (WWAN) base station (BS) to handover to a target WWAN BS, and in response to the HO indication, taking one or more actions to maintain an existing connection between the UE and a wireless local area network (WLAN) access point (AP).
In an aspect, a method for wireless communication is provided. The method may be performed, for example, by a source BS. The method generally includes transmitting a handover (HO) indication for handing over a user equipment (UE) from the source BS to a target WWAN BS, and in response to the HO indication, taking one or more actions to maintain an existing connection between the UE and a WLAN access point (AP).
In an aspect, a method for wireless communication is provided. The method may be performed, for example, by a target BS. The method generally includes receiving a handover (HO) indication from a source WWAN BS serving a user equipment (UE), and in response to the HO indication, taking one or more actions to maintain an existing connection between the UE and a WLAN access point (AP).
In an aspect, an apparatus for wireless communication by a UE is provided. The apparatus generally includes means for receiving a handover (HO) indication from a source wireless wide area network (WWAN) base station (BS) to handover to a target WWAN BS, and in response to the HO indication, means for taking one or more actions to maintain an existing connection between the UE and a wireless local area network (WLAN) access point (AP).
In an aspect, an apparatus for wireless communication by a source BS is provided. The apparatus generally includes means for transmitting a handover (HO) indication for handing over a user equipment (UE) from the source BS to a target WWAN BS, and in response to the HO indication, means for taking one or more actions to maintain an existing connection between the UE and a WLAN access point (AP).
In an aspect, an apparatus for wireless communication by a target BS is provided. The apparatus generally includes means for receiving a handover (HO) indication from a source WWAN BS serving a user equipment (UE), and in response to the HO indication, means for taking one or more actions to maintain an existing connection between the UE and a WLAN access point (AP).
In an aspect, an apparatus for wireless communication by a UE is provided. The apparatus includes at least one processor and a memory coupled to the at least one processor. The at least one processor is configured to receive a handover (HO) indication from a source wireless wide area network (WWAN) base station (BS) to handover to a target WWAN BS, and in response to the HO indication, take one or more actions to maintain an existing connection between the UE and a wireless local area network (WLAN) access point (AP).
In an aspect, an apparatus for wireless communication by a source BS is provided. The apparatus includes at least one processor and a memory coupled to the at least one processor. The at least one processor is configured to transmit a handover (HO) indication for handing over a user equipment (UE) from the source BS to a target WWAN BS, and in response to the HO indication, take one or more actions to maintain an existing connection between the UE and a WLAN access point (AP).
In an aspect, an apparatus for wireless communication by a target BS is provided. The apparatus includes at least one processor and a memory coupled to the at least one processor. The at least one processor is configured to receive a handover (HO) indication from a source WWAN BS serving a user equipment (UE), and in response to the HO indication, take one or more actions to maintain an existing connection between the UE and a WLAN access point (AP).
Certain aspects of the present disclosure provide a computer readable medium for wireless communication by a UE having computer-executable instructions stored thereon for receiving a handover (HO) indication from a source wireless wide area network (WWAN) base station (BS) to handover to a target WWAN BS, and in response to the HO indication, taking one or more actions to maintain an existing connection between the UE and a wireless local area network (WLAN) access point (AP).
Certain aspects of the present disclosure provide a computer readable medium for wireless communication by a source BS having computer-executable instructions stored thereon for transmitting a handover (HO) indication for handing over a user equipment (UE) from the source BS to a target WWAN BS, and in response to the HO indication, taking one or more actions to maintain an existing connection between the UE and a WLAN access point (AP).
Certain aspects of the present disclosure provide a computer readable medium for wireless communication by a target BS having computer-executable instructions stored thereon for receiving a handover (HO) indication from a source WWAN BS serving a user equipment (UE), and in response to the HO indication, taking one or more actions to maintain an existing connection between the UE and a WLAN access point (AP).
To the accomplishment of the foregoing and related ends, the one or more aspects comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative features of the one or more aspects. These features are indicative, however, of but a few of the various ways in which the principles of various aspects may be employed, and this description is intended to include all such aspects and their equivalents.
So that the manner in which the above-recited features of the present disclosure can be understood in detail, a more particular description, briefly summarized above, may be had by reference to aspects, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only certain typical aspects of this disclosure and are therefore not to be considered limiting of its scope, for the description may admit to other equally effective aspects.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one aspect may be beneficially utilized on other aspects without specific recitation.
Aspects of the present disclosure provide apparatus, methods, processing systems, and computer program products for new radio (NR) (new radio access technology) cell measurement. New radio (NR) may refer to radios configured to operate according to a new air interface (e.g., other than Orthogonal Frequency Divisional Multiple Access (OFDMA)-based air interfaces) or fixed transport layer (e.g., other than Internet Protocol (IP)). NR may include enhanced mobile broadband (eMBB) targeting wide bandwidth (e.g. 80 MHz beyond), millimeter wave (mmW) targeting high carrier frequency (e.g. 60 GHz), massive MTC (mMTC) targeting non-backward compatible MTC techniques, and mission critical targeting ultra reliable low latency communications (URLLC). For these general topics, different techniques are considered, such as coding, low-density parity check (LDPC), and polar. NR cell may refer to a cell operating according to the new air interface or fixed transport layer. A NR Node B (e.g., 5G Node B, gNB) may correspond to one or multiple transmission reception points (TRPs).
NR cells can be configured as access cell (ACells) or data only cells (DCells). For example, the RAN (e.g., a central unit or distributed unit) can configure the cells. DCells may be cells used for carrier aggregation or dual connectivity, but not used for initial access, cell selection/reselection, or handover. In some cases DCells may not transmit synchronization signals—in some case cases DCells may transmit SS. TRPs may transmit downlink signals to UEs indicating the cell type. Based on the cell type indication, the UE may communicate with the TRP. For example, the UE may determine TRPs to consider for cell selection, access, handover, and/or measurement based on the indicated cell type.
In some cases, the UE can receive measurement configuration from the RAN. The measurement configuration information may indicate ACells or DCells for the UE to measure. The UE may monitor/detect measurement reference signals from the cells based on measurement configuration information. In some cases, the UE may blindly detect MRS. In some cases the UE may detect MRS based on MRS-IDs indicated from the RAN. The UE may report the measurement results.
Various aspects of the disclosure are described more fully hereinafter with reference to the accompanying drawings. This disclosure may, however, be embodied in many different forms and should not be construed as limited to any specific structure or function presented throughout this disclosure. Rather, these aspects are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Based on the teachings herein one skilled in the art should appreciate that the scope of the disclosure is intended to cover any aspect of the disclosure disclosed herein, whether implemented independently of or combined with any other aspect of the disclosure. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, the scope of the disclosure is intended to cover such an apparatus or method which is practiced using other structure, functionality, or structure and functionality in addition to or other than the various aspects of the disclosure set forth herein. It should be understood that any aspect of the disclosure disclosed herein may be embodied by one or more elements of a claim.
The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects.
Although particular aspects are described herein, many variations and permutations of these aspects fall within the scope of the disclosure. Although some benefits and advantages of the preferred aspects are mentioned, the scope of the disclosure is not intended to be limited to particular benefits, uses, or objectives. Rather, aspects of the disclosure are intended to be broadly applicable to different wireless technologies, system configurations, networks, and transmission protocols, some of which are illustrated by way of example in the figures and in the following description of the preferred aspects. The detailed description and drawings are merely illustrative of the disclosure rather than limiting and the scope of the disclosure is being defined by the appended claims and equivalents thereof.
The techniques described herein may be used for various wireless communication networks such as LTE, CDMA, TDMA, FDMA, OFDMA, SC-FDMA and other networks. The terms “network” and “system” are often used interchangeably. A CDMA network may implement a radio technology such as Universal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includes Wideband CDMA (WCDMA) and other variants of CDMA. cdma2000 covers IS-2000, IS-95 and IS-856 standards. A TDMA network may implement a radio technology such as Global System for Mobile Communications (GSM). An OFDMA network may implement a radio technology such as NR (e.g. 5G RA), Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDMA, etc. UTRA and E-UTRA are part of Universal Mobile Telecommunication System (UMTS). NR is an emerging wireless communications technology under development in conjunction with the 5G Technology Forum (5GTF). 3GPP Long Term Evolution (LTE) and LTE-Advanced (LTE-A) are releases of UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described in documents from an organization named “3rd Generation Partnership Project” (3GPP). cdma2000 and UMB are described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2). The techniques described herein may be used for the wireless networks and radio technologies mentioned above as well as other wireless networks and radio technologies. For clarity, while aspects may be described herein using terminology commonly associated with 3G and/or 4G wireless technologies, aspects of the present disclosure can be applied in other generation-based communication systems, such as 5G and later, including NR technologies.
The system illustrated in
Each BS 110 may provide communication coverage for a particular geographic area. In 3GPP, the term “cell” can refer to a coverage area of a BS and/or a BS subsystem serving this coverage area, depending on the context in which the term is used.
A BS may provide communication coverage for a macro cell, a pico cell, a femto cell, and/or other types of cell. A macro cell may cover a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscription. A pico cell may cover a relatively small geographic area and may allow unrestricted access by UEs with service subscription. A femto cell may cover a relatively small geographic area (e.g., a home) and may allow restricted access by UEs having association with the femto cell (e.g., UEs in a Closed Subscriber Group (CSG), UEs for users in the home, etc.). A BS for a macro cell may be referred to as a macro BS. A BS for a pico cell may be referred to as a pico BS. A BS for a femto cell may be referred to as a femto BS or a home BS. In the example shown in
The wireless network 100 may also include relay stations. A relay station is a station that receives a transmission of data and/or other information from an upstream station (e.g., a BS or a UE) and sends a transmission of the data and/or other information to a downstream station (e.g., a UE or a BS). A relay station may also be a UE that relays transmissions for other UEs. In the example shown in
The wireless network 100 may be a heterogeneous network that includes BSs of different types, e.g., macro BSs, pico BSs, femto BSs, relays, transmission reception points (TRPs), etc. These different types of BSs may have different transmit power levels, different coverage areas, and different impact on interference in the wireless network 100. For example, macro BSs may have a high transmit power level (e.g., 20 Watts) whereas pico BSs, femto BSs and relays may have a lower transmit power level (e.g., 1 Watt).
The wireless network 100 may support synchronous or asynchronous operation. For synchronous operation, the BSs may have similar frame timing, and transmissions from different BSs may be approximately aligned in time. For asynchronous operation, the BSs may have different frame timing, and transmissions from different BSs may not be aligned in time. The techniques described herein may be used for both synchronous and asynchronous operation.
A network controller 130 may couple to a set of BSs and provide coordination and control for these BSs. The network controller 130 may communicate with the BSs 110 via a backhaul. The BSs 110 may also communicate with one another, e.g., directly or indirectly via wireless or wireline backhaul.
The UEs 120 (e.g., 120x, 120y, etc.) may be dispersed throughout the wireless network 100, and each UE may be stationary or mobile. A UE may also be referred to as a terminal, a mobile station, a subscriber unit, a station, etc. A UE may be a cellular phone, a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a laptop computer, a cordless phone, a wireless local loop (WLL) station, a tablet, a netbook, a smart book, etc. A UE may be able to communicate with macro BSs, pico BSs, femto BSs, relays, etc. In
LTE utilizes orthogonal frequency division multiplexing (OFDM) on the downlink and single-carrier frequency division multiplexing (SC-FDM) on the uplink. OFDM and SC-FDM partition the system bandwidth into multiple (K) orthogonal subcarriers, which are also commonly referred to as tones, bins, etc. Each subcarrier may be modulated with data. In general, modulation symbols are sent in the frequency domain with OFDM and in the time domain with SC-FDM. The spacing between adjacent subcarriers may be fixed, and the total number of subcarriers (K) may be dependent on the system bandwidth. For example, the spacing of the subcarriers may be 15 kHz and the minimum resource allocation (called a ‘resource block’) may be 12 subcarriers (or 180 kHz). Consequently, the nominal FFT size may be equal to 128, 256, 512, 1024 or 2048 for system bandwidth of 1.25, 2.5, 5, 10 or 20 megahertz (MHz), respectively. The system bandwidth may also be partitioned into subbands. For example, a subband may cover 1.08 MHz (i.e., 6 resource blocks), and there may be 1, 2, 4, 8 or 16 subbands for system bandwidth of 1.25, 2.5, 5, 10 or 20 MHz, respectively.
While aspects of the examples described herein may be associated with LTE technologies, aspects of the present disclosure may be applicable with other wireless communications systems, such as NR. NR may utilize OFDM with a CP on the uplink and downlink and include support for half-duplex operation using TDD. A single component carrier bandwidth of 100 MHZ may be supported. NR resource blocks may span 12 sub-carriers with a sub-carrier bandwidth of 75 kHz over a 0.1 ms duration. Each radio frame may consist of 50 subframes with a length of 10 ms. Consequently, each subframe may have a length of 0.2 ms. Each subframe may indicate a link direction (i.e., DL or UL) for data transmission and the link direction for each subframe may be dynamically switched. Each subframe may include DL/UL data as well as DL/UL control data. Beamforming may be supported and beam direction may be dynamically configured. MIMO transmissions with precoding may also be supported. MIMO configurations in the DL may support up to 8 transmit antennas with multi-layer DL transmissions up to 8 streams and up to 2 streams per UE. Multi-layer transmissions with up to 2 streams per UE may be supported. Aggregation of multiple cells may be supported with up to 8 serving cells. Alternatively, NR may support a different air interface, other than an OFDM-based. NR networks may include entities such central units or distributed units.
In LTE, a BS may send a primary synchronization signal (PSS) and a secondary synchronization signal (SSS) for each cell in the BS. The primary and secondary synchronization signals may be sent in symbol periods 6 and 5, respectively, in each of sub-frames 0 and 5 of each radio frame with the normal cyclic prefix, as shown in
The BS may send a Physical Control Format Indicator Channel (PCFICH) in only a portion of the first symbol period of each sub-frame, although depicted in the entire first symbol period in
The BS may send the PSS, SSS and PBCH in the center 1.08 MHz of the system bandwidth used by the BS. The BS may send the PCFICH and PHICH across the entire system bandwidth in each symbol period in which these channels are sent. The BS may send the PDCCH to groups of UEs in certain portions of the system bandwidth. The BS may send the PDSCH to specific UEs in specific portions of the system bandwidth. The BS may send the PSS, SSS, PBCH, PCFICH and PHICH in a broadcast manner to all UEs, may send the PDCCH in a unicast manner to specific UEs, and may also send the PDSCH in a unicast manner to specific UEs.
A number of resource elements may be available in each symbol period. Each resource element may cover one subcarrier in one symbol period and may be used to send one modulation symbol, which may be a real or complex value. Resource elements not used for a reference signal in each symbol period may be arranged into resource element groups (REGs). Each REG may include four resource elements in one symbol period. The PCFICH may occupy four REGs, which may be spaced approximately equally across frequency, in symbol period 0. The PHICH may occupy three REGs, which may be spread across frequency, in one or more configurable symbol periods. For example, the three REGs for the PHICH may all belong in symbol period 0 or may be spread in symbol periods 0, 1 and 2. The PDCCH may occupy 9, 18, 32 or 64 REGs, which may be selected from the available REGs, in the first M symbol periods. Only certain combinations of REGs may be allowed for the PDCCH.
A UE may know the specific REGs used for the PHICH and the PCFICH. The UE may search different combinations of REGs for the PDCCH. The number of combinations to search is typically less than the number of allowed combinations for the PDCCH. A BS may send the PDCCH to the UE in any of the combinations that the UE will search.
A UE may be within the coverage of multiple BSs. One of these BSs may be selected to serve the UE. The serving BS may be selected based on various criteria such as received power, path loss, signal-to-noise ratio (SNR), etc.
A UE may be assigned resource blocks 310a, 310b in the control section to transmit control information to a BS. The UE may also be assigned resource blocks 320a, 320b in the data section to transmit data to the BS. The UE may transmit control information in a physical UL control channel (PUCCH) on the assigned resource blocks in the control section. The UE may transmit only data or both data and control information in a physical UL shared channel (PUSCH) on the assigned resource blocks in the data section. A UL transmission may span both slots of a subframe and may hop across frequency.
A set of resource blocks may be used to perform initial system access and achieve UL synchronization in a physical random access channel (PRACH) 330. The PRACH 330 carries a random sequence and cannot carry any UL data/signaling. Each random access preamble occupies a bandwidth corresponding to six consecutive resource blocks. The starting frequency is specified by the network. That is, the transmission of the random access preamble is restricted to certain time and frequency resources. There is no frequency hopping for the PRACH. The PRACH attempt is carried in a single subframe (1 ms) or in a sequence of few contiguous subframes and a UE can make only a single PRACH attempt per frame (10 ms).
At the base station 110, a transmit processor 420 may receive data from a data source 412 and control information from a controller/processor 440. The control information may be for the PBCH, PCFICH, PHICH, PDCCH, etc. The data may be for the PDSCH, etc. The processor 420 may process (e.g., encode and symbol map) the data and control information to obtain data symbols and control symbols, respectively. The processor 420 may also generate reference symbols, e.g., for the PSS, SSS, and cell-specific reference signal. A transmit (TX) multiple-input multiple-output (MIMO) processor 430 may perform spatial processing (e.g., precoding) on the data symbols, the control symbols, and/or the reference symbols, if applicable, and may provide output symbol streams to the modulators (MODs) 432a through 432t. Each modulator 432 may process a respective output symbol stream (e.g., for OFDM, etc.) to obtain an output sample stream. Each modulator 432 may further process (e.g., convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a downlink signal. Downlink signals from modulators 432a through 432t may be transmitted via the antennas 434a through 434t, respectively.
At the UE 120, the antennas 452a through 452r may receive the downlink signals from the base station 110 and may provide received signals to the demodulators (DEMODs) 454a through 454r, respectively. Each demodulator 454 may condition (e.g., filter, amplify, downconvert, and digitize) a respective received signal to obtain input samples. Each demodulator 454 may further process the input samples (e.g., for OFDM, etc.) to obtain received symbols. A MIMO detector 456 may obtain received symbols from all the demodulators 454a through 454r, perform MIMO detection on the received symbols if applicable, and provide detected symbols. A receive processor 458 may process (e.g., demodulate, deinterleave, and decode) the detected symbols, provide decoded data for the UE 120 to a data sink 460, and provide decoded control information to a controller/processor 480.
On the uplink, at the UE 120, a transmit processor 464 may receive and process data (e.g., for the PUSCH) from a data source 462 and control information (e.g., for the PUCCH) from the controller/processor 480. The transmit processor 464 may also generate reference symbols for a reference signal. The symbols from the transmit processor 464 may be precoded by a TX MIMO processor 466 if applicable, further processed by the demodulators 454a through 454r (e.g., for SC-FDM, etc.), and transmitted to the base station 110. At the base station 110, the uplink signals from the UE 120 may be received by the antennas 434, processed by the modulators 432, detected by a MIMO detector 436 if applicable, and further processed by a receive processor 438 to obtain decoded data and control information sent by the UE 120. The receive processor 438 may provide the decoded data to a data sink 439 and the decoded control information to the controller/processor 440.
The controllers/processors 440 and 480 may direct the operation at the base station 110 and the UE 120, respectively. The processor 440 and/or other processors and modules at the base station 110 may perform or direct, e.g., the execution of various processes for the techniques described herein. The processor 480 and/or other processors and modules at the UE 120 may also perform or direct, e.g., the execution of the functional blocks and/or operations illustrated in
In the user plane, the L2 layer 508 includes a media access control (MAC) sublayer 510, a radio link control (RLC) sublayer 512, and a packet data convergence protocol (PDCP) 514 sublayer, which are terminated at the Node B on the network side. Although not shown, the UE may have several upper layers above the L2 layer 508 including a network layer (e.g., IP layer) that is terminated at the PDN gateway 118 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 514 provides multiplexing between different radio bearers and logical channels. The PDCP sublayer 514 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 BSs. The RLC sublayer 512 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 hybrid automatic repeat request (HARQ). The MAC sublayer 510 provides multiplexing between logical and transport channels. The MAC sublayer 510 is also responsible for allocating the various radio resources (e.g., resource blocks) in one cell among the UEs. The MAC sublayer 510 is also responsible for HARQ operations.
In the control plane, the radio protocol architecture for the UE and BS is substantially the same for the physical layer 506 and the L2 layer 508 with the exception that there is no header compression function for the control plane. The control plane also includes a radio resource control (RRC) sublayer 516 in Layer 3 (L3 layer). The RRC sublayer 516 is responsible for obtaining radio resources (i.e., radio bearers) and for configuring the lower layers using RRC signaling between the BS and the UE.
Subframe format 610 may be used for a BS equipped with two antennas. A CRS may be transmitted from antennas 0 and 1 in symbol periods 0, 4, 7 and 11. A reference signal is a signal that is known a priori by a transmitter and a receiver and may also be referred to as a pilot. A CRS is a reference signal that is specific for a cell, e.g., generated based on a cell identity (ID). In
The PSS, SSS, CRS and PBCH in LTE are described in 3GPP TS 36.211, entitled “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation,” which is publicly available.
An interlace structure may be used for each of the downlink and uplink for FDD in LTE. For example, Q interlaces with indices of 0 through Q−1 may be defined, where Q may be equal to 4, 6, 8, 10, or some other value. Each interlace may include subframes that are spaced apart by Q frames. In particular, interlace q may include subframes q, q+Q, q+2Q, etc., where q ∈ {0, . . . , Q−1}.
The wireless network may support hybrid automatic retransmission (HARQ) for data transmission on the downlink and uplink. For HARQ, a transmitter (e.g., a BS) may send one or more transmissions of a packet until the packet is decoded correctly by a receiver (e.g., a UE) or some other termination condition is encountered. For synchronous HARQ, all transmissions of the packet may be sent in subframes of a single interlace. For asynchronous HARQ, each transmission of the packet may be sent in any subframe.
A UE may be located within the coverage area of multiple BSs. One of these BSs may be selected to serve the UE. The serving BS may be selected based on various criteria such as received signal strength, received signal quality, pathloss, etc. Received signal quality may be quantified by a signal-to-noise-and-interference ratio (SINR), or a reference signal received quality (RSRQ), or some other metric. The UE may operate in a dominant interference scenario in which the UE may observe high interference from one or more interfering BS.
As shown in
As shown in
According to certain aspects, with RAN aggregation (e.g., LWA) a UE may be simultaneously connected to an LTE eNB and a Wi-Fi (i.e., Wi-Fi AP), which provides radio access links to transport a user's signaling and data traffic, as shown in
New radio (NR) may refer to radios configured to operate according a wireless standard, such as 5G (e.g. wireless network 100). NR may include enhanced mobile broadband (eMBB) targeting wide bandwidth (e.g. 80 MHz beyond), millimeter wave (mmW) targeting high carrier frequency (e.g. 60 GHz), massive MTC (mMTC) targeting non-backward compatible MTC techniques, and mission critical targeting ultra reliable low latency communications (URLLC).
NR cell may refer to a cell operating according in the NR network. A NR BS (e.g., Node B 110) may correspond to one or multiple transmission reception points (TRPs). As used herein, a cell may refer to a combination of downlink (and potentially also uplink) resources. The linking between the carrier frequency of the downlink resources and the carrier frequency of the uplink resources is indicated in the system information (SI) transmitted on the downlink resources. For example, system information can be transmitted in a physical broadcast channel (PBCH) carrying a master information block (MIB).
NR RAN architecture may include a central unit (CU) (e.g., central unit 140). The CU may be an Access node controller (ANC). The CU terminates backhaul interface to RAN-CN, terminates backhaul interface to neighbor RAN node. The RAN may include a Distributed unit that may be one or more TRPs that may be connected to one or more ANCs (not shown). TRPs may advertise System Information (e.g., Global TRP ID), may include PDCP/RLC/MAC functions, may comprise one or more antenna ports, may be configured to individually (dynamic selection) or jointly (joint transmission), and may serve traffic to the UE.
A UE may establish and maintain connections with one or more networks including a wireless wide area network (WWAN) (e.g., an LTE network) and a wireless local area network (WLAN) (e.g., a Wi-Fi network). A WWAN BS may support radio access network (RAN) aggregation (i.e., LTE+Wi-Fi aggregation or “LWA”). LWA may refer to LTE managing WLAN connectivity. LWA is an interworking between LTE and WLAN including data aggregation at the radio access network. In LWA, a WWAN BS may schedule packets to be served on LTE and Wi-Fi radio links. According to aspects, “aggregation” or “radio aggregation” may refer to LWA.
LWA, introduced in 3GPP Release 13, is being enhanced in Release-14 as “enhanced LWA” (eLWA). In Release 13, when an LTE handover (HO) occurs for a UE served by a BS managing WLAN connectivity, the data transmission on WLAN is interrupted. Data transmission on the WLAN may be interrupted because the UE has to re-associate with WLAN after the HO on LTE.
In Release-14, the UE may keep the same WLAN AP during LTE HO. However, interruption for data transmission on WLAN may still occur on the DL since the connection to the PDCP layer is re-established at the UE during LTE HO. A similar problem may exist on uplink through WLAN as well since data packets may need to be forwarded from the target BS (instead of the source BS) to the WLAN AP after the LTE HO.
In LTE, four access stratum (AS) keys include KeNB, KRRCint, KRRCenc, and KUPenc. The AS keys may change upon handover and connection re-establishment. For handover from a source BS to a target BS, the UE and the source BS may derive the KeNB used at the target BS. The KeNB is specific for one session of an UE at one BS and is used as the root key for the AS security, i.e. the security between the UE and the BS. The KeNB may be used to derive keys used for ciphering data to be transmitted or deciphering received data.
The other AS keys, KRRCint, KRRCenc, and KUPenc, may be derived from the KeNB used at the target BS. KRRCint is a key which may be used for the protection of RRC traffic with a particular integrity algorithm. KRRCint may be derived by the UE and the BS from the KeNB and an identifier for an integrity algorithm. KRRCenc is a key which may be used for the protection of RRC traffic with a particular encryption algorithm. KRRCenc may be derived by the UE and the BS from the KeNB as well as an identifier for the encryption algorithm. KUPenc is a key which may be used for the protection of UL traffic with a particular encryption algorithm. The key may be derived by the UE and the BS from the KeNB as well as an identifier for the encryption algorithm.
The KeNB may change upon handover and connection re-establishment. When the UE receives the new KeNB in the handover command, the UE may apply the new KeNB and may also reset the MAC layer connection and re-establish PDCP connection.
Aspects of the present disclosure provide methods to minimize interruption for UL and/or DL transmission via a secondary link during a handover on a primary link (e.g., an LTE HO). For example, a BS serving a UE may manage WLAN connections. As another example, the UE may be dual connected to a master and secondary BS. Aspects provide techniques to allow a UE to continue to receive and/or transmit via the secondary link during handover on the primary link.
For example, a WWAN BS serving the UE may be managing the UE's WLAN connectivity. Aspects of the present disclosure describe how a wireless device may cipher PDCP PDUs to be transmitted and decipher PDCP PDUs received over WLAN during LTE HO. Aspects also describe when and how a logical node called a WLAN Termination (WT) may change the forwarding of uplink PDUs to the WLAN from source BS to a target BS. In accordance with aspects described herein, a UE may advantageously experience minimized disruption on a second link during handover on a primary link.
In the aggregation architecture, a WLAN AP may be similar to the secondary BS (Secondary eNB, SeNB) in the user plane. A new interface between the BS and WLAN, called Xw, may be defined having a functionality similar to the Xn interface between the MeNB and SeNB in a dual connectivity scenario. The Xw interface may also include some functionality for WLAN interworking. According to Release-13, in an LWA architecture, an BS may be connected to a WT over an Xw interface. This interface may have both a control plane and user plane and may be similar to an X2 interface. The termination point of Xw at WLAN is a WT logical node. WT may be implemented at an access point, access controller, or another physical entity.
At 802, the UE may receive a handover (HO) indication from a source wireless wide area network (WWAN) base station (BS) to handover to a target WWAN BS. At 804, the UE may take one or more actions to maintain an existing connection between the UE and a wireless local area network (WLAN) access point (AP).
For illustrative purposes, aspects are described with reference to a UE having a connection to a WWAN and a WLAN; however, as described above, the UE may be a dual connected UE with connections to a master and secondary BS. According to aspects, the UE may also be connected to a 5G network on a primary or secondary link. The UE may handover on a primary link, while maintaining a connection on a secondary link, thereby minimizing disruption on the secondary link.
At 902, the source BS may transmit a handover (HO) indication for handing over a user equipment (UE) from the source BS to a target WWAN BS. At 904, the source BS may take one or more actions to maintain an existing connection between the UE and a WLAN access point (AP).
At 1002, the target be may receive a handover (HO) indication from a source WWAN BS serving a user equipment (UE). At 1004, the target BS may take one or more actions to maintain an existing connection between the UE and a WLAN access point (AP). The existing connection that is maintained as described in
At step 0, LWA may be activated for the UE using the WT and source BS. The source BS may perform measurements and decide to handover the UE to the target BS 1108. At step 1, the source BS may transmit a HO request to the target BS. At step 2, the target BS may request addition of the WT. At step 3, the WT may acknowledge the received addition request. Thereafter, at step 4, the target BS may transmit a HO request acknowledgement. After the link between the WT and target BS is set up, at step 5, the source BS may request releasing the connection to the WT.
At step 6, the source BS may transmit, to the UE, an RRC connection reconfiguration message. At step 7, the UE and the target BS may perform a random access procedure. At step 8, the UE may transmit, to the target BS, an RRC connection reconfiguration complete message.
At step 9, the source BS may transmit a sequence number (SN) status to the target BS. At step 10, the target BS may transmit a path switch request to the MME. At step 11, the MME may transmit a path switch request acknowledgement. At step 12, the target BS may transmit a UE context release to the source BS. At step 13, LWA may be activated for the UE using the WT and the target BS.
The steps illustrated in
According to aspects, at step 1, the source BS may transit a handover request to the target BS. In handover request may signal the last SN associated with a DL PDCP PDU which was transmitted (e.g., forwarded) to the WLAN AP. The last SN transmitted to the WLAN may be referred to as the last_SN_WLAN_eNB.
According to aspects, the source BS may also signal, to the UE, the last SN associated with a DL PDCP PDU transmitted (e.g., forwarded) to the WLAN. For example, the source BS may signal the last_SN_WLAN_eNB to the UE in step 6, as illustrated in
According to aspects the source BS may also signal, to the target BS, the highest received SN of the PDU on WLAN, called HRW. The source BS may signal the HRW at step 1, as illustrated in
The UE and the target BS may take one or more actions to maintain an existing connection between the UE and the WT based, at least in part, on a SN associated with a last PDCP PDU forwarded by the source BS to the WLAN or a highest received SN on WLAN (HRW). According to aspects, the source BS may transmit, to the UE, an indication of the highest received SN associated with the last PDCP PDU forwarded by the source BS to the WLAN or a highest received SN on WLAN (HRW).
The UE may use a ciphering key associated with the source BS for deciphering PDUs received having a SN less than a last PDU forwarded to the AP by the source BS. The UE may use a ciphering key associated with the target BS for ciphering packets for UL transmission after the handover to the target BS is complete.
The target BS may take one or more actions in an effort to maintain a UE's connection to the WT based on the SN of the last PDU forwarded to the AP by the source BS. According to aspects, the target BS may only forward PDUs on WLAN having a SN that is greater than the last PDU forwarded to the AP by the source BS.
The target BS may optionally transmit (via LTE) to the UE, PDUs with SN less than last_SN_WLAN_eNB. This may be enabled if WLAN does not continue transmission after the change of Xw from the source BS to the target BS. Such behavior may be signalled on Xw interface.
The source BS may forward unciphered PDCP PDUs, for which delivery has not been confirmed by WLAN, to target eNB. In other words, the source BS may determine one or more PDCP PDUs have not been forwarded to the WLAN AP. In response, the source BS may forward the unciphered PDCP PDUs to the target BS. According to aspects, the Xw change from source to target BS for the WT may occur before the HO request acknowledgment. For example, with reference to
For UL transmission, the UE may signal, to the target BS, the SN associated with a last transmitted UL PDU over WLAN, which may be referred to as the last_SN_WLAN_UE. As shown in
At times, the target BS may determine that it is missing one or more UL PDCP PDUs based on the last_SN_WLAN_UE. The target BS may determine that is missing PDUs when a PDU received from the WLAN has an SN that is less than last_SN_WLAN_UE. Three options may exist for the target BS to handle PDCP PDUs received from WLAN with SN less than last_SN_WLAN_UE.
According to a first option, the target BS may transmit a PDCP status report indicating missing PDUs. The target BS may transmit this report to the UE. In response, the UE may retransmit missing PDUs using a ciphering key associated with the target BS. The target BS may discard PDUs received from the WLAN with a SN less than the last transmitted PDU over WLAN.
According to a second option, the UE may retransmit, to the source BS or to the AP, PDUs having a SN less than the last transmitted PDU over WLAN and greater than the highest received SN of a PDU on WLAN (e.g., last_SN_WLAN_UE>SN>HRW). The target BS may discard PDUs received from WLAN with SN less than last_SN_WLAN_UE. The target BS may transmit, to the AP, PDUs with SNs greater than the SN associated with the last PDU forwarded to the AP by the source BS.
According to a third option, the target BS may decipher PDUs having a SN less than the last_SN_WLAN_UE with a key associated with the source BS. To facilitate the target BS's use of the source BS's key, the source BS may signal its KeNB or KUPenc to the target BS in HO Request, at step 1 (see
According to aspects, during HO on the primary link, both the UE and the target BS may use the ciphering key associated with the source BS for data transmitted over WLAN. The target BS may switch from using the key associated with the source BS to using a key associated with the target BS after the handover. As described above, the source BS may signal its KeNB or KUPenc to the target BS in HO Request, at step 1.
According to aspects, instead of using a ciphering key associated with the source BS until the HO is complete, the target BS and UE may use a permanent ciphering key associated with the WLAN AP for data transmitted over WLAN. The permanent key may be a separate key used only for data transmission over WLAN. For example, the permanent key may be used before, during, and after the HO on the primary link.
According to aspects, the UE may transmit a ciphering key in a WLAN PDU itself. For example, bits in the header of the WLAN PDU may indicate the ciphering key that is to be used by the target BS. Accordingly, the target BS may receive the WLAN PDU, determine the ciphering key, and use the determined the ciphering key to decipher the WLAN PDU. According to aspects, the target BS may similarly include an indication of a ciphering key in a WLAN PDU to be used by a UE to decipher the received WLAN PDUs.
According to aspects, a “dummy packet” may be used to indicate how to cipher and decipher packets on the secondary link. A UE may receive a dummy packet (dummy PDU) from the source BS, which may indicate the last SN of a PDU forwarded by the source BS to the AP. The UE may decipher subsequently received packets using a ciphering key associated with the target BS.
According to aspects, the UE may transmit a dummy packet to the target BS. The dummy packet may indicate the SN of the last PDU ciphered and transmitted using a ciphering key associated with the source BS. After transmitting the dummy packet, the UE may transmit WLAN PDUs using a ciphering key associated with the target BS.
Thus, the dummy packet transmitted by the source BS to the UE may indicate a DL switch in ciphering keys and the dummy packet transmitted by the UE to the target BS may indicate an UL switch in ciphering keys.
As described herein, aspects of the present disclosure provide techniques to minimize interruption for UL and/or DL transmission via a secondary link during a handover on a primary link.
The methods disclosed herein comprise one or more steps or actions for achieving the described method. The method steps and/or actions may be interchanged with one another without departing from the scope of the claims. In other words, unless a specific order of steps or actions is specified, the order and/or use of specific steps and/or actions may be modified without departing from the scope of the claims.
As used herein, 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-b, a-c, b-c, and a-b-c, as well as any combination with multiples of the same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b, b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c).
As used herein, the term “determining” encompasses a wide variety of actions. For example, “determining” may include calculating, computing, processing, deriving, investigating, looking up (e.g., looking up in a table, a database or another data structure), ascertaining and the like. Also, “determining” may include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory) and the like. Also, “determining” may include resolving, selecting, choosing, establishing and the like.
The various operations of methods described above may be performed by any suitable means capable of performing the corresponding functions. The means may include various hardware and/or software component(s) and/or module(s), including, but not limited to a circuit, an application specific integrated circuit (ASIC), or processor. Generally, where there are operations illustrated in figures, those operations may have corresponding counterpart means-plus-function components with similar numbering.
The various illustrative logical blocks, modules and circuits described in connection with the present disclosure may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device (PLD), discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any commercially available processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.
If implemented in hardware, an example hardware configuration may comprise a processing system in a wireless node. The processing system may be implemented with a bus architecture. The bus may include any number of interconnecting buses and bridges depending on the specific application of the processing system and the overall design constraints. The bus may link together various circuits including a processor, machine-readable media, and a bus interface. The bus interface may be used to connect a network adapter, among other things, to the processing system via the bus. The network adapter may be used to implement the signal processing functions of the PHY layer. In the case of a user terminal 120 (see
If implemented in software, the functions may be stored or transmitted over as one or more instructions or code on a computer-readable medium. Software shall be construed broadly to mean instructions, data, or any combination thereof, whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise. Computer-readable media include both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. The processor may be responsible for managing the bus and general processing, including the execution of software modules stored on the machine-readable storage media. A computer-readable storage medium may be coupled to a processor such that the processor can read information from, and write information to, the storage medium. Alternatively, or in addition, the machine-readable media, or any portion thereof, may be integrated into the processor, such as the case may be with cache and/or general register files. Examples of machine-readable storage media may include, by way of example, RAM (Random Access Memory), flash memory, ROM (Read Only Memory), PROM (Programmable Read-Only Memory), EPROM (Erasable Programmable Read-Only Memory), EEPROM (Electrically Erasable Programmable Read-Only Memory), registers, magnetic disks, optical disks, hard drives, or any other suitable storage medium, or any combination thereof. The machine-readable media may be embodied in a computer- program product.
Thus, certain aspects may comprise a computer program product for performing the operations presented herein. For example, such a computer program product may comprise a computer-readable medium having instructions stored (and/or encoded) thereon, the instructions being executable by one or more processors to perform the operations described herein. The operations may include, for example, instructions for receiving a handover (HO) indication from a source wireless wide area network (WWAN) base station (BS) to handover to a target WWAN BS, and in response to the HO indication, taking one or more actions to maintain an existing connection between the UE and a wireless local area network (WLAN) access point (AP). As another example, the operations may include transmitting a handover (HO) indication for handing over a user equipment (UE) from the source BS to a target WWAN BS, and in response to the HO indication, taking one or more actions to maintain an existing connection between the UE and a WLAN access point (AP). As another example, the operations may include receiving a handover (HO) indication from a source WWAN BS serving a user equipment (UE), and in response to the HO indication, taking one or more actions to maintain an existing connection between the UE and a WLAN access point (AP).
Further, it should be appreciated that modules and/or other appropriate means for performing the methods and techniques described herein can be downloaded and/or otherwise obtained by a user terminal and/or base station as applicable. For example, such a device can be coupled to a server to facilitate the transfer of means for performing the methods described herein. Alternatively, various methods described herein can be provided via storage means (e.g., RAM, ROM, a physical storage medium such as a compact disc (CD) or floppy disk, etc.), such that a user terminal and/or base station can obtain the various methods upon coupling or providing the storage means to the device. Moreover, any other suitable technique for providing the methods and techniques described herein to a device can be utilized.
It is to be understood that the claims are not limited to the precise configuration and components illustrated above. Various modifications, changes and variations may be made in the arrangement, operation and details of the methods and apparatus described above without departing from the scope of the claims.
This application claims priority to U.S. Provisional Application Ser. No. 62/398,423, entitled “LTE HANDOVER WITH THE SAME SECONDARY LINK,” filed on Sep. 22, 2016, which is expressly incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62398423 | Sep 2016 | US |
