Method and apparatus for transmitting LTE waveforms in a shared spectrum by carrier wave sensing.

Abstract

To provide a method of operating a long term evolution (LTE) communication system on a shared frequency spectrum.SOLUTION: In a method, a user equipment (UE) is initialized on an LTE frequency band. A base station (eNB) monitors a shared frequency spectrum to determine if it is BUSY. The eNB transmits to the UE on the shared frequency spectrum if it is not BUSY. The eNB waits for a first time if it is BUSY and directs the UE to vacate the shared frequency spectrum after the first time.SELECTED DRAWING: Figure 4A

Description

[Technical Field]

[0001] In most countries, access to the radio frequency spectrum is strictly regulated by government agencies, such as the U.S. Federal Communications Commission (FCC) and the European Commission of the European Union. Like any other natural resource, radio spectrum frequencies must be shared among their users. Therefore, portions of the radio spectrum (e.g., bands) are either licensed to individual users (e.g., cell phone operators) or shared among multiple users, such as WiFi or Bluetooth (which operate on unlicensed bands). In some hybrid models, licensed spectrum is granted to a primary user with the highest priority (e.g., naval radar applications). Secondary users may also use the licensed band during periods of inactivity when the primary user is not transmitting waveforms in that band. These secondary users may have different priorities. For example, a given frequency band licensed to a primary user may be used by a public security organization for mission-critical communications. In this case, commercial users may be permitted to use such bands, but only if neither the primary nor a high-priority secondary user (e.g., a public security user) is occupying that band. Spectrum use based on such policies is sometimes referred to as Authorized Shared Access (ASA). From this perspective, there is no need to distinguish between unlicensed shared access and authorized shared access. This is because these same technologies can always be used to ensure fairness and policy compliance when a certain bandwidth is used by a large number of users.

[0002] In the above example of authorized shared access, spectrum sharing can be facilitated by a dynamic method, sometimes referred to as the LBT (listen-before-talk) method, and by a quasi-static method, such as geolocation databases (GLDBs). For example, such databases may map frequency usage of a certain band to geographical areas or time periods of the day. These databases cannot change dynamically, as time is required to update them and communicate them to all relevant users. The LBT method, as its name suggests, is more dynamic and does not rely on quasi-statically configured databases. Instead, the secondary user must ensure that the primary user or other users of equal priority are not interfered with by the secondary user's transmissions. Two well-known examples are carrier-sensing multiple access (CSMA / CA) with radar avoidance and collision avoidance in IEEE 802.11 wireless local area networks (WLANs). The former applies when the secondary user must grant priority to the primary user. Secondary users must cease transmission when they detect radar waveforms for military, meteorological, or automotive applications; this is sometimes referred to as Dynamic Frequency Selection (DFS). Therefore, when a secondary user detects a primary user, it frees up a given bandwidth or channel (a channel is a further subdivision of the bandwidth) and attempts to transmit on a different bandwidth or channel. This is why it's called Dynamic Frequency Selection. Similarly, in CSMA / CA, if a transmitter detects an ongoing transmission of the same priority, it chooses not to transmit in order to attempt transmission again at a later time. This is why it's called Carrier Sensing Multiple Access with Collision Avoidance. Thus, the main differences between DFS and CSMA / CA are the timescale at which sensing occurs and the actions taken by the transmitter when an ongoing transmission is detected. For example, a DFS transmitter must always switch channels / bandwidths to free up the current channel or bandwidth to the primary user, while a CSMA / CA transmitter may or may not switch channels.This is because in CSMA / CA, radio resources are shared among users with the same priority, which is regarded as a multiple access method. However, when using DFS, the primary user has a higher priority. As a result, to ensure the collision latency of the CSMA / CA method, carrier sensing (CS) and collision avoidance (CA) occur on the order of tens of microseconds (μs), while DFS can take several seconds.

[0003] The operation of the CS / CA multiple access method is in marked contrast to other common multiple access technologies such as time division multiple access (TDMA), frequency division multiple access (FDMA), code division multiple access (CDMA), or orthogonal frequency division multiple access (OFDMA). This is due to the nature of opportunistic random access for sharing the medium. TDMA and FDMA in GSM, CDMA in UMTS, and orthogonal frequency division multiple access (OFDMA) in the Long Term Evolution (LTE) of the 3rd Generation Partnership Project (3GPP) attempt to orthogonalize the available resources for sharing among multiple users. However, the orthogonalization operation requires precise coordination by predefined rules or a dynamic scheduler. The dynamic scheduler allocates resources in a given period in a given portion of the radio frequency spectrum to a specific user, so collisions are essentially avoided. This orthogonalization operation makes it particularly difficult to operate these resources in the radio resources shared by the CA / CA multiple access method. This is because when competing for the available radio resources, users following these types of protocols and procedures yield to users following predefined schedules or radio resource allocations according to these protocols and procedures.

[0004] In LTE, base stations are known as Evolved NodeBs (eNodeBs / eNBs) and have the power to freely control the Radio Resource Management (RRM) of cells under LTE control. E-UTRAN (Evolved Universal Terrestrial Radio Access Network) generally includes many eNodeBs, each with its own RRM functionality. A subset of these eNodeBs can coordinate their RRM via the X2 Application Protocol (X2AP), defined on the X2 interface connecting two eNodeBs. Similarly, each eNodeB connects to one or more Mobility Management Entities (MMEs) in the core network (CN) via the S1 interface, where the S1 Application Protocol (S1AP) is defined. The S1AP can also be used for RRM coordination. The RRM interface is an essential part of cellular communication because it enables important functions such as interference adjustment, mobility, and even SON (Self-Organizing Network).

[0005] Figure 1 shows an example of a conventional wireless long-range communication network. The illustrated long-range communication network includes a primary eNodeB 110 operating within a primary cell (PCell) 100, and eNodeBs 112, 114, 116, and 118 operating within secondary cells (SCell1-SCell4) 102, 104, 106, and 108. A handset or other user equipment (UE) 120 is shown communicating with the eNodeB 110 of PCell 100. The UE 120 may also communicate with one or more eNodeBs of the secondary cells. In this example, SCell is a logical concept, and therefore eNodeB 110 can operate multiple SCells 102-108.

[0006] Furthermore, the eNodeB 110 controls the radio resources within its cell 100 via the Radio Resource Control (RRC) protocol and also controls multiple access for users connected to that cell via the Media Access Control (MAC) protocol. For example, the RRC protocol configures the carriers on which user equipment (UEs) can send and receive data, and up to five so-called component carriers (CCs) can be configured per UE in LTE Advanced (LTE-A). Similarly, the MAC protocol, together with the RRC protocol, controls when and how the UE can use the radio resources available to send and receive data on the configured carriers. LTE Release 10 introduces a feature called carrier aggregation. In carrier aggregation, a UE can be configured with one primary cell (PCell) and up to four secondary cells (SCells). The PCell can only be changed by handover, while the SCells are configured by RRC signaling. In particular, it is not expected that a UE will receive system information by decoding the physical broadcast channel (PBCH) on the secondary component carrier (SCC), or by monitoring the SCell common search space and receiving the physical downlink control channel (PDCCH) whose CRC is scrambled by SI-RNTI to receive system information (SI) on the downlink shared channel (DL-SCH). Furthermore, a UE may assume that all system frame numbers (SFNs) on the SCC are consistent with the SFNs on the primary component carrier (PCC).

[0007] CA does not define Radio Link Monitoring (RLM) for SCells. Therefore, there is no identified means for the UE's physical layer (PHY) to indicate Radio Link Failure (RLF) to the upper layers of the UE via the MAC layer. This is because E-UTRA (Evolved Universal Terrestrial Radio Access) may always rely on the connectivity provided by the SCell, thereby providing robustness through RLM and other fallback procedures. Alternatively, the SCell may operate as a supplemental service-providing cell that can be activated when additional capacity is required for data communication with the UE. For this purpose, the MAC layer may activate a configured SCell via a MAC control element (CE). Activating an SCell may require 8 to 30 milliseconds, depending on the synchronization status of the UE and its SCell Control Cell (SCC). RRC reconfiguration of the SCell may require considerably longer, especially if the UE needs to perform intermediate frequency measurements. Therefore, the eNodeB can be configured to periodically measure the reference signal received power (RSRP) of a cell on a given carrier and report the measurement periodically or triggered by configurable offsets and thresholds. In 3GPP Long Term Evolution, the above is achieved through RRC signaling of the measured and configuration. When the measurement is readily available in the eNodeB, the latency of RRC reconfiguration of a SCell or PCell is dramatically reduced from a few seconds to tens or hundreds of milliseconds. The eNodeB only activates cells that are already configured as SCells, but the eNodeB can be configured to measure the RSRP of any cell. In comparison, the eNodeB can use the measurement report of any cell to activate a cell, as in the case of activating a SCell, or to RRC reconfigure the UE to add / remove SCells, or even to change a PCell.

[0008] After PCell or SCellS is activated, the eNodeB MAC scheduler assigns downlink (DL) and uplink (UL) assignments to the UE for downlink and uplink transmissions on the physical downlink shared channel (PDSCH) and physical uplink shared channel (PUSCH), respectively. In the downlink direction, the assignment received in the downlink control information (DCI) within subframe n schedules the corresponding PDSCH transmission within the same subframe. In comparison, for uplinks, this assignment schedules a PUSCH transmission within subframe n+k, where k>0 is determined by a predetermined rule.

[0009] E-UTRAN (especially eNodeB) has complete control over all radio resources, at least for UEs in RRC_CONNECTED mode. Except for the physical random access channel (PRACH), E-UTRAN controls all transmissions in both uplink and downlink directions, including resource allocation by time, frequency, or any other means such as CDMA, as well as transmission timing and power control.

[0010] While the eNodeB has RRM functionality, which controls all radio resources via RRC, it relies on the UE to discover cells and report relevant measurements. For this purpose, in LTE releases 8-11, the eNodeB transmits a primary synchronization signal (PSS), a secondary cell synchronization signal (SSS), and a cell-specific reference signal (CRS) in each radio frame. The PSS and SSS each occupy one OFDM symbol per half-frame, but the CRS is transmitted in each subframe of the radio frame, allowing the UE to discover and measure cells within a 6ms measurement window even if the timing of a given cell is not deductively known. Furthermore, to support inter-frequency measurements in time-division duplex (TDD) systems when the cell's UL / DL configuration may be unknown to the UE, or to support the measurement constraints introduced in LTE release 10 for the purpose of eICIC (enhanced Inter-cell Interface Coordination), the UE needs to be able to discover cells in just one subframe, and possibly in the DwPTS region of a special subframe. To promote energy conservation and interference reduction, LTE Release 12 introduces "discovery bursts" (including PSS, SSS, and CRS transmissions) and, where configured, Channel State Information Reference Signals (CSI-RS) for transmitting point (TP) identification in the context of shared cell IDs. For example, multiple TPs may share the same physical cell ID and can only be distinguished by their respective CSI-RS resource element (RE) configurations. PSS, SSS, CRS, and CSI-RS (if configured) form a Discovery Reference Signal (DRS) and are transmitted during DRS occasions. DRS occasions are similar to the Positioning Reference Signal (PRS) occasions in LTE Release 9, as they have a configured or specific length (e.g., number of subframes) and periodicity. Ideally, the length of a DRS occasion should not be longer than the 6ms UE measurement window and may be as short as one subframe.A reasonable periodicity for DRS occasions is several hundred milliseconds, and DRS bursts can function as beacons in other wireless communication systems (such as CSMA / CA). [Overview of the project]

[0011] In a first embodiment, a method for operating a Long-Term Evolution (LTE) communication system on a shared frequency spectrum is disclosed. A base station (eNB) initializes user equipment (UE) in the LTE frequency band. The base station (eNB) monitors the shared frequency spectrum to determine whether it is busy. If the shared frequency spectrum is not busy, the eNB transmits to the UE on the shared frequency spectrum. If the shared frequency spectrum is busy, the eNB waits for a first time. After the first time, the eNB instructs the UE to release the shared frequency spectrum.

[0012] In the second embodiment, the UE monitors the shared frequency spectrum to determine whether the shared frequency spectrum is busy. If the shared frequency spectrum is not busy, the UE transmits the shared frequency spectrum to the eNB. If the shared frequency spectrum is busy, the UE waits for a first time. After the first time, the UE reports the busy status to the eNB. [Brief explanation of the drawing]

[0013] [Figure 1] This is a diagram of a conventional Long-Term Evolution (LTE) communication system.

[0014] [Figure 2] This flowchart illustrates the operation of a Long-Term Evolution (LTE) communication system in the Authorized Shared Access (ASA) frequency spectrum.

[0015] [Figure 3] This diagram shows communication between a user device (UE) and a base station (eNB) according to an exemplary embodiment.

[0016] [Figure 4A] This flowchart shows the downlink operation of a Long-Term Evolution (LTE) communication system in the carrier-sensing multiple access (CSMA / CA) frequency spectrum with collision avoidance according to an exemplary embodiment.

[0017] [Figure 4B] This flowchart shows the uplink operation of a Long-Term Evolution (LTE) communication system in the carrier-sensing multiple access (CSMA / CA) frequency spectrum with collision avoidance according to an exemplary embodiment. [Modes for carrying out the invention]

[0018] The exemplary embodiments relate to apparatus and methods for operating an orthogonal frequency division multiple access (OFDMA) cellular communication system, such as 3GP Long-Term Evolution (LTE), on radio frequencies shared with a primary transceiver. The primary transceiver may be a naval, automotive radio, or other high-priority transceiver. Specific terminology is used herein, but these terms are used only in a general and descriptive sense and not to limit them. The following abbreviations are used throughout this specification. ASA: Authorized Shared Access eNB: Evolved Node B or Base Station UE: User Equipment CQI: Channel Quality Indicator CRS: Cell-Specific Reference Signal CSI: Channel Status Information CSI-RS: Channel Status Information Reference Signal CSMA / CA: Carrier Sense Multiple Access with Collision Avoidance DCI: Downlink Control Information DFS: Dynamic Frequency Selection DRS: Discovery Reference Signal DL: Downlink DwPTS: Downlink Pilot Time Slot E-UTRAN: Evolved Universal Terrestrial Radio Access Network LBT: Listen Before Talk LTE: Long Term Evolution MAC: Media Access Control Protocol MIMO: Multiple-Input Multiple-Output OFDMA: Orthogonal Frequency Division Multiple Access OOR: Out Of Range PBCH: Physical Broadcast Channel PCell: Primary Cell PCFICH: Physical Control Format Indicator Channel [[ID=X]]PDCCH: Physical Downlink Control Channel PDSCH: Physical Downlink Shared Channel PHICH: Physical Hybrid ARQ Indicator Channel PMCH: Physical Multicast Channel PSS: Primary Synchronization Signal PUCCH: Physical Uplink Control Channel PUSCH: Physical Uplink Shared Channel RI: Rank Indicator RRC: Radio Resource Control<X RRM: Radio Resource Management RSRP: Reference Signal Received Power SCell: Secondary Cell Note: There seems to be an error in the original text where the "X" is added in the "PDCCH" and "RRC" translations. I have removed them in the translation for consistency. If this is not correct, please adjust according to the actual requirements.SRS: Sounding Reference Signal SSS: Secondary Sync Signal TDD: Time division duplex TRS: Tracking Reference Signal UL: Uplink

[0019] Dynamic Frequency Selection (DFS) Using the 3GPP Long-Term Evolution (LTE) communication standard in a shared access spectrum is not straightforward. This is because the radio resource management function resides within the eNodeBs in the network, and radio resources are controlled solely by these eNodeBs. In dynamic frequency selection (DFS) schemes, there is typically sufficient time (e.g., several seconds) to change the frequency band or carrier after the primary user is detected. Therefore, handover-based RRC signaling and activation or deactivation of SCells under MAC control are sufficient to free up bandwidth for the primary user. The 3GPP LTE communication standard currently lacks protocols, procedures, and measurements to compel a UE to take any action when a primary user is detected on the carrier to which the UE is configured to transmit data. Furthermore, mobility control in LTE is entirely controlled by the eNodeB, whereas other wireless cellular communication standards require the UE to initiate a handover. Here, mobility balances the load, and in this case, the eNodeB can add or remove SCells or change PCells for stationary UEs. In both ASA-based systems with a primary user and CSMA / CA-based systems without a primary user, so-called "hidden stations" can exist. A hidden station is a transmitter, such as a primary user, and its transmissions can only be detected at the receiving end of a communication link sharing the wireless medium. For example, in LTE, only the UE can detect waveforms transmitted from a "hidden station," but the eNodeB is completely unaware of its presence.

[0020] Figure 2 is a flowchart illustrating the operation of the first embodiment. In step 200, the UE is initialized to operate in the LTE band with the PCell. The ASA band is configured and operated as a regular LTE band by the eNodeB, and the UE operates in the ASA band (202). The UE is prohibited from remaining in a cell operating in the ASA band by existing means, such as prohibition by broadcasting system information. As a result, all UEs connected in the ASA band are in RRC_CONNECTED mode, thereby being under the complete control of the eNodeB. The eNodeB configures all UEs connected in the ASA band to perform RRM measurements according to existing LTE specifications (e.g., releases 8-12) (204). DFS is supported by each UE through a non-standard (proprietary) implementation. When the UE detects a hidden terminal (from the UE's perspective, all primary users are hidden terminals) (206), the UE's physical layer (PHY) indicates the detected hidden terminal to the upper layers of its protocol stack and triggers an RRM measurement report according to existing LTE release 8 / 9 / 10 / 11 / 12 procedures. By specification (e.g., "DFS events"), RRM measurement reports triggered by non-standard (proprietary) DFS functionality in the UE may be associated with specific values ​​in the RRC Information Element (IE) RSRP range. For example, a DFS event may be indicated by the minimum value within the RRC IE RSRP range and may act as an out-of-range (OOR) indicator. The UE may report a DFS event (e.g., an RSRP measurement report with an OOR indicator indicating a DFS event) to the eNodeB using existing RRM measurement reporting procedures (208). The eNodeB's RRM functionality can reinterpret RSRP measurement reports as DFS / OOR events according to standardized linkages, and subsequently reconfigure the UE via existing RRC signaling to free up ASA bandwidth to the primary user (210) (212). Such RRC signaling includes handover in the case of PCell or SCell reconfiguration in the case of SCell.Alternatively, if the RRM function in the eNodeB determines that it is sufficient for the ASA bandwidth to be temporarily released to the primary user, the RRM function may simply expire the sCell_Deactivation_Timer in the UE, or deactivate the SCells comprising the ASA bandwidth by sending a deactivation command in the MAC control element. The 3GPP LTE specification may introduce performance requirements useful for testing whether the UE reports DFS / OOR events for each ASA bandwidth in accordance with the requirements of regulatory bodies worldwide, but no new measurements are defined in the specification to support 3GPP LTE.

[0021] In another embodiment, instead of reinterpreting existing measurement reports as DFS / OOR events, new measurement reports and associated procedures are defined, in particular, to indicate (to E-UTRAN) the presence of a hidden terminal or primary user. Any UE connected to a cell in ASA bandwidth can be configured to perform and report this new DFS measurement. The eNodeB RRC layer can be configured to report DFS measurements periodically or in response to a trigger, or periodically in response to a trigger. The eNodeB can configure measurement events and associated thresholds and offsets to control DFS measurement reporting for UEs connected in ASA bandwidth. Thus, the appropriate measurement procedure can be determined by identification. However, the actions taken by the network may be similar to those in the embodiments described above, including UE handover, SCell reconfiguration, and SCell deactivation. By reporting measurements (instead of binary information), the eNodeB RRM function can be trained from historical data and apply its own thresholds to improve primary user protection. Since eNodeB can analyze and combine DFS measurements from various UEs connected to it, the decision to select a different carrier for a given UE ultimately rests with eNodeB. However, if this decision were made at each UE, the network would have to comply with whatever the UE indicates to ensure the protection of potential primary users.

[0022] <Carrier-Sensing Multiple Access (CSMA / CA) with Collision Avoidance> Figure 3 shows communication between UE300 and eNodeB320 according to an exemplary embodiment. UE300 may be a mobile phone, computer, or other wireless network device. UE300 includes a memory 304 and a processor 306 coupled to a transceiver 310. Processor 306 may include several processors adapted to various operational tasks of the UE, including signal processing and channel measurement and calculation. The memory stores application software 302 that the processor can execute as instructed by the user, and also stores operational instructions for the UE. Processor 306 is also coupled to input / output (I / O) circuit elements 308, which may include a microphone, speaker, display, and associated software. Transceiver 310 includes a receiver 312 and a transmitter 314 suitable for wireless communication with eNodeB320. Transceiver 310 typically communicates with eNB320 over various communication channels. For example, transceiver 310 sends uplink information to eNodeB320 via the physical uplink control channel PUCCH and the physical uplink shared channel PUSCH. In response, transceiver 310 receives downlink information from eNodeB320 via the physical downlink control channel PDCCH and the physical downlink shared channel PDSCH.

[0023] The base station 320 includes a memory 324, a symbolic processing circuit 328, and a processor 326 coupled to the transceiver 330 via a bus 336. The processor 326 and the symbolic processing circuit 328 may include several processors adapted to various operational tasks, including signal processing and channel measurement and arithmetic. The memory stores application software 322 that the processor can execute for a particular user, and also stores operational instructions for the eNodeB 320. The transceiver 330 includes a receiver 332 and a transmitter 334 suitable for wireless communication with the UE 300. The transceiver 330 typically communicates with the UE 300 via various communication channels. For example, the transceiver 330 sends downlink information to the UE 300 via the physical downlink control channel PDCCH and the physical downlink shared channel PDSCH. Furthermore, the transceiver 330 sends special downlink information to the UE300 via the physical broadcast channel PBCH, the physical hybrid ARQ indicator channel PHICH, the physical control format indicator channel PCFICH, and the physical multicast channel PMCH. In response, the transceiver 330 receives uplink information from the UE300 via the physical uplink control channel PUCCH and the physical uplink shared channel PUSCH.

[0024] According to the exemplary embodiment, E-UTRAN cells such as eNodeB320 are used in the unlicensed or ASA band, in which LTE user equipment shares radio resources with other users of equal priority but who strictly adhere to the Carrier Sensitive Multiple Access (CSMA / CA) procedure / protocol with collision avoidance. A fundamental problem exists because 3GPP Long-Term Evolution is specifically designed to operate in the licensed spectrum.

[0025] Referring to Figure 4A, the situation in the downlink direction is similar to DFS described with reference to Figure 2. Here, CSMA / CA is implemented as a non-standard proprietary function according to the exemplary embodiment. The UE is initialized in the LTE band (400). The eNodeB monitors the CSMA / CA band (402). The eNodeB does not transmit on any downlink channel even if it detects an ongoing transmission (404). The eNodeB monitors the timeout criterion (408) and continues to monitor the CSMA / CA band (402). If the ongoing transmission ends before the timeout criterion 408, the eNodeB transmits to the UE in the CSMA / CA band (406). Otherwise, once the timeout criterion has passed, RRC signaling causes the UE to release the CSMA / CA band (410) and initiate a handover (412).

[0026] However, the eNodeB may need to transmit some signal regardless of whether an ongoing transmission is detected. The eNodeB transmits a Discovery Reference Signal (DRS) burst with a period of several hundred milliseconds. The DRS burst may consist of only one subframe and include at least PSS, SSS, and CRS, thereby enabling the UE to discover the cell and perform measurements. In the case of shared cell IDs, CSI-RS may also be transmitted during the DRS occasion. Additionally, periodic PSS / SSS transmissions allow the UE to obtain coarse time and frequency synchronization with this cell. On the network side, the RRM measurement report based on the DRS allows the eNodeB to determine whether a cell constitutes a given UE in a certain unlicensed or ASA bandwidth. In addition to the DRS, the eNodeB may need to periodically transmit some kind of tracking reference signal (TRS) with a periodicity much shorter than that of the DRS, such as 5ms or 10ms. The waveform of the TRS allows the UE to perform automatic gain control (AGC), as well as fine time and frequency synchronization (tracking). Such TRS waveforms can be based on existing CRS waveforms. This can provide the additional benefit of being useful for acquiring channel state information in CRS-based transmission modes. Furthermore, the eNodeB can periodically transmit a channel state reference signal (CSI-RS) that enables channel state information acquisition at the UE in CSI-RS-based transmission modes. The UE can be configured for CSI measurement and for reporting according to CSI transmission at the eNodeB.

[0027] Referring again to Figure 3, it is sometimes preferable not to use any downlink channel with CSMA / CA. For example, the Physical Broadcast Channel (PBCH) is not transmitted within a cell in the unlicensed or ASA bandwidth. Therefore, a UE cannot remain in such a cell. Similarly, system information is not transmitted either. For this reason, such a cell can only be configured as a SCell, and a PCell is always configured in the licensed spectrum. It may also be beneficial not to transmit the Physical Hybrid ARQ Indicator Channel (PHICH) in the unlicensed or ASA spectrum. Alternatively, a UL grant transmitted in DCI can act as an implicit ACK / NACK instruction by scheduling a retransmission of a previous UL grant. The Physical Control Format Indicator Channel (PCFICH) may or may not be transmitted in the unlicensed or ASA spectrum. If an extended PHICH duration is configured, the Control Format Indicator (CFI) is known through the specification. Similarly, the PCFICH is not required for PDSCH transmission in transmission mode 10 (TM10) scheduled by the Enhanced Physical Downlink Control Channel (EPDCCH). In cross-carrier scheduled PDSCH transmissions, the CFI is known throughout the configuration. By comparison, since PCFICH is transmitted as PDCCH within the same subframe, PCFICH can always be transmitted when PDCCH is transmitted. Finally, since physical multicast channels (PMCHs) are quasi-statically scheduled by MBMS Coordinating Entity (MCE) for reserved resources, it may be beneficial not to transmit PMCHs in unlicensed or ASA spectrum. Otherwise, in unicast downlink transmissions, if the CSMA / CA function in the eNodeB indicates that a given subframe may be used for (E)PDCCH or PDSCH transmission, the eNodeB transmits according to LTE Release 12. In one embodiment, the CSMA / CA function in the eNodeB returns a binary instruction.If the CSMA / CA function for a given cell indicates BUSY on a given carrier, the eNodeB will not transmit (E)PDCCH or PDSCH to any UE. The eNodeB may continue to transmit other signals or channels in accordance with the above recommendation. Alternatively, if the CSMA / CA function for a given cell indicates IDLE on a given carrier, the eNodeB may transmit (E)PDCCH and / or PDSCH transmissions, and the eNodeB will transmit them in accordance with LTE Release 12.

[0028] Referring to Figure 4B, uplink operation in the CSMA / CA band is similar to downlink operation. The UE is initialized in the LTE band (400). The UE monitors the CSMA / CA band (420). If the UE detects an ongoing transmission (422), it refrains from transmitting on any uplink channel. The UE monitors the timeout criterion (426) and continues monitoring the CSMA / CA band (420). If the ongoing transmission ends before the timeout criterion 426, the UE transmits to the eNodeB in the CSMA / CA band (424). Otherwise, once the timeout criterion has passed, the UE sends a BUSY report to the eNodeB (428). RRC signaling prompts the UE to release the CSMA / CA band (430), and the handover begins (432).

[0029] If the CSMA / CA function in the UE indicates that a given subframe cannot be used for uplink transmission, it may be beneficial to discard any configured sounding reference signal (SRS) transmissions to avoid interfering with ongoing transmissions. It may also be beneficial not to transmit physical uplink control channels (PUCCH) in unlicensed or ASA spectra. In this case, PUCCH is transmitted to PCell only in licensed spectra. PUCCH transmission is permitted in unlicensed or ASA spectra. In this case, several UE behaviors are expected.

[0030] In some cases, the UE follows its existing UE procedure for PUCCH transmissions, regardless of the CSMA / CA function instructions at the UE for the subframe in which the PUCCH transmission is scheduled. Generally, collisions with ongoing transmissions are unavoidable, and the PUCCH may not be properly received at the eNodeB.

[0031] Alternatively, the UE may base its PUCCH transmission on any PUCCH transmission for a subframe in which a PUCCH transmission is scheduled, based on the indication of the CSMA / CA function in the UE. If the CSMA / CA function in the UE indicates BUSY, the UE will not transmit a PUCCH in the subframe in question. Instead, if the CSMA / CA function in the UE indicates IDLE, the UE will transmit a PUCCH as scheduled.

[0032] The same principle can be applied to physical uplink shared channels (PUSCH). In one embodiment, the UE follows existing UE procedures for PUSCH transmissions for subframes in which PUSCH transmissions are scheduled, regardless of instructions from the UE's CSMA / CA function. Generally, collisions with ongoing transmissions are unavoidable, and PUSCH transmissions may not be properly received at the eNodeB.

[0033] Alternatively, the UE may base any PUSCH transmission on the indication of the CSMA / CA function in the UE for a subframe in which a PUSCH transmission is scheduled. If the CSMA / CA function in the UE indicates BUSY, the UE will not transmit a PUSCH in the subframe in question. Instead, if the CSMA / CA function in the UE indicates IDLE, the UE will transmit a PUSCH as scheduled.

[0034] As with DFS, hidden terminals must be considered. The above solutions for PUSCH and PUCCH transmissions concern the behavior of the UE when the CSMA / CA function at the UE indicates BUSY for subframes in which PUSCH / PUCCH transmissions are scheduled. In the case of a hidden terminal with a waveform detectable at the UE rather than the eNodeB, the eNodeB can continue scheduling for that UE. If the UE follows the standard LTE Release 12 behavior, this can result in poor performance for links from the eNodeB to the UE, as well as for links to and from hidden terminals. This is because collisions between transmissions may persist, potentially leading to excessive interference, so that (a) reliable communication is no longer possible, or (b) at least an acceptable quality of service (QoS) can no longer be provided. The opposite case, where the UE does not transmit PUSCH or PUCCH in subframes when the CSMA / CA function at the UE indicates BUSY, can also result in similar performance degradation. This is because packages and HARQ ACK / NACK transmissions in BUSY subframes are discarded. Theoretically, by reusing the DFS method described above, the UE can inform the eNodeB of the cell or carrier's busy state so that the eNodeB's MAC (or RRC) layer can schedule the UE in a different CC to avoid further collisions. Thus, instead of a “DFS event” triggered by the DFS function, the CSMA / CA function can indicate busy, but if not, these procedures can be reused. However, the time scale for DFS is generally much longer than the time scale for LBT, as is the case with CSMA / CA. Therefore, in the exemplary embodiment, an alternative procedure is provided for handling hidden terminals in the case of CSMA / CA.

[0035] One objective of the exemplary embodiments is to inform the upper layer of the UE of the eNodeB about the indication of the UE's CSMA / CA function in a subframe in which the UE is scheduled for uplink transmission. When the UE's CSMA / CA function indicates IDLE, this state is not communicated to the upper layer of the eNodeB, as the UE may always follow the existing LTE Release 12 specifications. Therefore, in some embodiments, actions that the upper layer of the eNodeB (e.g., the eNodeB MAC scheduler) can take in a subframe in which a PUSCH or PUCCH transmission is scheduled and the UE's CSMA / CA function indicates BUSY are provided.

[0036] Since overall system performance and especially the UE throughput perceived by the user are maximized, it is preferable to use a PHY or MAC layer mechanism so that the eNodeB can take earlier action by avoiding scheduling UEs on carriers occupied by hidden terminals. Here, the former has shorter latency than the latter. First, in order to reduce latency, we assume that the UE is already configured on the corresponding component carrier with up to five service-providing cells (Figure 1). According to the exemplary embodiment, the service-providing cells are ordered in ascending order based on the ServCellIndex configured by RRC signaling, but this does not exclude other ordering or addressing mechanisms. Next, the symbols {00, 01, 10, 11} are assigned to the four service-providing cells excluding the PCell, such that 00 corresponds to the service-providing cell (SCell) with the smallest ServCellIndex, 01 corresponds to the service-providing cell (SCell) with the second smallest ServCellIndex, and so on. If fewer than four SCells are configured, unused symbols (e.g., if one SCell is configured, {01, 10, 11}) are reserved. No other mappings are excluded. To ensure the shortest latency, L1(PHY) signaling is introduced to inform the upper layers of the eNodeB of BUSY instructions from the UE's CSMA / CA function in subframes where PUSCH or PUCCH transmissions are scheduled.

[0037] Therefore, a new PUCCH format is introduced to be always transmitted to the PCell. This new PUCCH format is exactly the same as the existing PUCCH format 1b, except that instead of representing ACK / ACK, ACK / NACK, NACK / ACK, and NACK / NACK / DTX, QPSK symbols encode the exponents {00, 01, 10, 11} of the four service-providing cells. For convenience, this new PUCCH format is referred to as format 1c. The eNodeB receiver can distinguish between PUCCH formats 1b and 1c by code division multiplexing, so that these two PUCCH formats can share the same time and frequency resources. Alternatively, this new PUCCH format may have its own time and frequency resources for the PUCCH region. When PUCCH capacity is not an issue, as in the case of small cells, CDM is preferred for improved spectral efficiency. In a subframe where a PUSCH or PUCCH transmission is scheduled, if the CSMA / CA function in the UE indicates BUSY, the UE will not transmit the PUSCH or PUCCH as scheduled, but instead will indicate BUSY (to the eNodeB) via a PUCCH format 1c transmission to the PCell. Several UE behaviors are possible, but all assume that the eNodeB schedules only one SCell at a time to prevent ambiguity in the eNodeB when a PUCCH format 1c is received.

[0038] In one embodiment, PUCCH format 1c indicates which service-providing cell has received a BUSY instruction. For example, eNodeB may schedule an uplink transmission in subframe n+k (where k>0) via a UL assignment in the DCI received in subframe n. Immediately before the uplink transmission is scheduled to occur, the CSMA / CA function in the UE begins sensing the medium and indicates to the upper layer of the UE whether the medium is IDLE or BUSY. If IDLE is indicated, the UE proceeds with processing the scheduled transmission according to the received DCI. If BUSY is indicated, the UE ignores the DCI that would schedule the uplink transmission in question and instead sends PUCCH format 1c to the PCell encoding (in QPSK notation) the service-providing cell where the collision occurred.

[0039] Since the eNodeB anticipated a PUSCH or PUCCH transmission to a specific service provider cell, the PUCCH format 1c transmission does not actually transmit any additional information to the upper layers of the eNodeB. Therefore, in a different embodiment, the CSMA / CA function in the UE senses all configured service provider cells before scheduled uplink transmissions. If IDLE is indicated for a service provider cell to which a transmission is scheduled, the UE proceeds with processing the scheduled transmission according to the received DCI. If BUSY is indicated, the UE ignores the DCI that schedules the uplink transmission in question and instead sends a PUCCH format 1c to a PCell that encodes (in QPSK notation) the service provider cell that indicated IDLE. This does not guarantee that the corresponding service provider cell will be IDLE in subsequent subframes n+k2 (k2>k), but at least the eNodeB will not continue scheduling uplink transmissions to the same service provider cell.

[0040] Introducing the new PUCCH format 1c requires the eNodeB receiver to monitor this new PUCCH format. Therefore, the MAC layer procedure may be preferred over the aforementioned PHY procedure. However, sending the MAC control element requires the UE to make available uplink resources available, in addition to the uplink resources that would otherwise remain unused by not sending a PUCCH or PUSCH because the medium is busy. Also, the time required to prepare a PUSCH transmission carrying the MAC CE may be longer, so carrier sensing must occur much earlier than in the case of the new PUCCH format, thereby increasing the probability that the CSMA / CA function at the UE will show IDLE, while the medium is busy for n+k subframes. Latency can be even longer if the UE has to send a scheduling request (SR) to send an AMC CE. Nevertheless, the MAC layer procedure may still have merits. For example, it may eliminate the need to impose the constraint that only one SCell can be scheduled at a time. Instead, all four SCells can be encoded simultaneously using one octet (8 bits) in the MAC CE. Up to four service providers (SCells) are represented by {00, 01, 10, 11} based on the ServCellIndex and reordered in ascending order. Thus, the service provider cell (SCell) with the smallest ServCellIndex corresponds to 00, the service provider cell (SCell) with the second smallest ServCellIndex corresponds to 01, and so on. Additionally, the eight bits within one octet of MAC CE correspond to the four SCells through the following mapping: the first two bits correspond to the service provider cell represented by {00}, the third and fourth bits correspond to the service provider cell represented by {01}, the fifth and sixth bits correspond to the service provider cell represented by {10}, and the last two bits correspond to the service provider cell represented by {11}, but other mappings and orderings are not excluded.If a bit at a certain position corresponds to that position itself, this indicates that the corresponding service-providing cell was indicated as IDLE. Otherwise, this indication is BUSY, and these two bits indicate the service-providing cell that the eNodeB should switch to. Thus, the bit positions within an octet encode the service-providing cell to which the bit at that position belongs, and these bits themselves encode the same information transmitted in the PUCCH format 1c above for a single cell. For example, the octet {00010011} means that the first, second, and fourth service-providing cells were IDLE, and that a transmission to the third service-providing cell should be transmitted to the first service-providing cell.

[0041] The embodiments described can be modified within the scope of the claims, and other embodiments are possible.

Claims

1. A method, The user equipment (UE) connects to a primary service provider cell (PCell) operating on the licensed frequency spectrum, The aforementioned UE connects to a secondary service provider cell (SCell) operating in an unlicensed frequency spectrum, The UE monitors the SCell in order to determine the IDLE state of the SCell, Based on the IDLE state of the SCell, the SCell transmits data, Based on the Carrier Sensitive Multiple Access (CSMA / CA) function with collision avoidance, the configured Sounding Reference Signal (SRS) transmission is discarded, Methods that include...

2. The method according to Claim 1, A method further comprising accessing the unlicensed frequency spectrum with a carrier-sensing multiplex access (CSMA / CA) equipped with collision avoidance.

3. The method according to Claim 1, A method further comprising reporting BUSY in an uplink control packet on the physical uplink control channel (PUCCH) of the PCell when the SCell is not IDLE.

4. The method according to Claim 1, A method by which a BUSY state is transmitted over a physical uplink control channel (PUCCH) resource that is semi-statically configured by radio resource control (RRC) signaling from a base station.

5. The method according to Claim 1, A method by which a BUSY state is transmitted over a physical uplink control channel (PUCCH) resource that is dynamically signaled by downlink control information (DCI) packets from a base station.

6. The method according to Claim 1, The determination that the state of SCell is BUSY, This involves determining the IDEL status of at least another secondary service provider cell (SCell), The identity of the aforementioned SCell is transmitted to the base station on the physical uplink control channel (PUCCH) of the PCell, Methods that further include the above.

7. User equipment (UE), A processor configured to determine the IDLE state of a secondary service-providing cell (SCell) operating in an unlicensed frequency spectrum, It is a transceiver, Connect to a primary service-providing cell (PCell) operating on the licensed frequency spectrum. Connect to the aforementioned SCell, The aforementioned SCell monitoring, Based on the IDLE state of the aforementioned SCell, data is transmitted using the aforementioned SCell. Based on the Carrier Sensitive Multiple Access (CSMA / CA) function with collision avoidance, the configured Sounding Reference Signal (SRS) transmission is discarded. The transceiver is configured as follows: UE, including.

8. The method according to claim 7, A method wherein the UE is further configured to access the unlicensed frequency spectrum with a carrier-sensing multiple access (CSMA / CA) with collision avoidance.

9. The method according to claim 7, A method further comprising: if the SCell is not IDLE, the transceiver is configured to report a BUSY state in an uplink control information (UCI) packet on the physical uplink control channel (PUCCH) of the PCell.

10. The method according to claim 7, A method further comprising configuring the transceiver to transmit a BUSY state on a physical uplink control channel (PUCCH) resource that is semi-statically configured by radio resource control (RRC) signaling from a base station.

11. The method according to claim 7, A method further comprising configuring the transceiver to transmit a BUSY state on a physical uplink control channel (PUCCH) resource that is dynamically signaled by downlink control information (DCI) packets from a base station.

12. The method according to claim 7, The processor is further configured to determine that the state of the SCell is BUSY and to determine the IDLE state of at least another secondary service providing cell (SCell), A method wherein the transceiver is further configured to transmit the identity of at least another SCell to a base station on the physical uplink control channel (PUCCH) of the PCell.

Images