Method and apparatus for transmitting LTE waveforms in shared spectrum by carrier 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 Federal Communications Commission (FCC) in the United States and the European Commission of the European Union. Similar to any other natural resource, the frequencies of the radio spectrum need to be shared among its users. Therefore, a portion of the radio spectrum (e.g., a band) is licensed to individual users (e.g., mobile phone operators), or shared among a large number of users such as WiFi or Bluetooth (which operate in unlicensed bands). Also, in a certain hybrid model, the licensed spectrum is assigned to the primary users with the highest priority (e.g., for naval radar applications). Additionally, secondary users can use the licensed band during the inactive periods when the primary users are not transmitting waveforms in the targeted band. These secondary users can have different priorities. For example, a given frequency band licensed to a primary user can be used by a public security organization for mission-critical communications. In this case, commercial users may be permitted to use such a band, but only if neither the primary nor the high-priority secondary users (e.g., public security users) are occupying this band. The use of the spectrum based on such a policy 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 the same technologies can always be used to ensure fairness and policy compliance when a given band 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 approach, sometimes referred to as the listen-before-talk (LBT) approach, and by a quasi-static approach such as geolocation databases (GLDBs). For example, such databases can map the frequency usage of a given band to a geographical area or time of day. Since these databases need to be updated and communicated to all relevant users, they cannot change dynamically. The LBT approach is more dynamic, as its name suggests, and does not rely on a quasi-statically configured database. Instead, the secondary user needs to ensure that the primary user or other users of equal priority are not interfered with by the secondary user's transmission. Two well-known examples are carrier sense multiple access with collision avoidance (CSMA / CA) with radar avoidance in IEEE 802.11 wireless local area networks (WLANs). The former applies when the secondary user must give priority to the primary user. The secondary user may sometimes refer to this as dynamic frequency selection (DFS) because it must stop transmitting when it detects radar waveforms used for military, meteorological, or automotive purposes. Thus, when the secondary user detects the primary user, it vacates the given band or channel (a channel is a further division of a band) and attempts to transmit on a different band or channel. Hence the name dynamic frequency selection. Similarly, in the case of CSMA / CA, when the transmitter detects an ongoing transmission of the same priority, the transmitter chooses not to transmit in order to attempt retransmission at a later time. Hence the name carrier sense multiple access with collision avoidance. Therefore, the main differences between DFS and CSMA / CA are the time scale at which sensing occurs and the action taken by the transmitter when an ongoing transmission is detected. For example, a DFS transmitter always has to switch channels / bands to vacate the current channel or band for 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 dozens 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 opportunistic random access nature of 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 a given period of resources 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, the base station is known as the evolved NodeB (eNodeB / eNB) and freely controls the radio resource management (RRM) of the cells under LTE control. The Evolved Universal Terrestrial Radio Access Network (E-UTRAN) generally includes many eNodeBs, and each eNodeB has its own RRM function. A subset of these eNodeBs can coordinate their RRM via the X2 Application Protocol (X2AP) defined on the X2 interface that connects two eNodeBs. Similarly, each eNodeB is connected to one or more of the Mobility Management Entities (MMEs) in the core network (CN) via the S1 interface on which the S1 Application Protocol (S1AP) is defined. S1AP can also be used for RRM coordination. The RRM interface is an essential part of cellular communication. This is because the RRM interface enables important functions such as interference coordination, mobility, and even Self-Organizing Network (SON).

[0005] Figure 1 is an example of a prior art wireless long-distance communication network. The illustrated long-distance 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 to SCell4) 102, 104, 106, and 108. A handset or other user equipment (UE) 120 is shown communicating with the eNodeB 110 of the PCell 100. The UE 120 can also communicate with one or more eNodeBs of the secondary cells. In this example, the SCell is a logical concept, and thus, the eNodeB 110 can operate multiple SCell 102 to 108.

[0006] In addition, the eNodeB 110 controls the radio resources within its cell 100 via the Radio Resource Control (RRC) protocol, and also controls the multiple access of the users connected to the cell via the Medium Access Control (MAC) protocol. For example, the RRC protocol configures carriers through which user equipment (UE) can transmit and receive data, and up to five so-called component carriers (CCs) can be configured for each UE in Long Term Evolution - Advanced (LTE-A). Similarly, the MAC protocol, together with the RRC protocol, controls how and when the UE can use the radio resources available for transmitting and receiving data on the configured carriers. In LTE Release 10, a feature called carrier aggregation is introduced. In carrier aggregation, a UE can be configured using one primary cell (PCell) and up to four secondary cells (SCells). The PCell can only be changed by handover, while the SCell is configured by RRC signaling. In particular, it is not expected that the UE receives system information by decoding the Physical Broadcast Channel (PBCH) on a secondary component carrier (SCC), or receives the Physical Downlink Control Channel (PDCCH) scrambled by the SI-RNTI by monitoring the common search space of the SCell to receive the system information (SI) on the Downlink Shared Channel (DL-SCH). Also, the UE may assume that the system frame number (SFN) on all SCCs is consistent with the SFN of the primary component carrier (PCC).

[0007] For the SCell, radio link monitoring (RLM) is not defined. Therefore, there is no means specified 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 in E-UTRA (Evolved Universal Terrestrial Radio Access), connectivity provided by the PCell can always be relied upon, thereby providing robustness through RLM and other fallback procedures. Alternatively, the SCell can operate as a supplementary service providing cell that can be activated when additional capacity for data communication with the UE is required. For this purpose, the MAC layer can activate the configured SCell via a MAC control element (CE). Activating the SCell may require 8 to 30 milliseconds depending on the synchronization state between the UE and its SCC. The RRC reconfiguration of the SCell may require a longer time, especially when the UE needs to perform intermediate frequency measurements. Therefore, the eNodeB can periodically measure the reference signal received power (RSRP) of a cell on a certain carrier and configure the UE to report the measurement values periodically or triggered by configurable offsets and thresholds. In 3GPP Long Term Evolution, the above is achieved via RRC signaling for measurement objects and configurations. When the measurement values are readily available at the eNodeB, the latency of the RRC reconfiguration of the SCell or PCell is dramatically reduced from several seconds to tens or hundreds of milliseconds. The eNodeB only activates cells that are already configured as SCell, but the eNodeB can configure the UE to measure the RSRP in any cell. In comparison, the eNodeB can use the measurement reports of any cell to activate a cell, or to RRC reconfigure the UE to add / remove an SCell, or even to change the PCell, as in the case of activating an SCell.

[0008] After a PCell or SCellS is activated, the eNodeB MAC scheduler assigns downlink (DL) and uplink (UL) grants 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 grant received in the downlink control information (DCI) within subframe n schedules the corresponding PDSCH transmission within the same subframe. In contrast, in the uplink, this grant schedules the PUSCH transmission within subframe n + k, where k > 0 is determined by a predefined rule.

[0009] E-UTRAN (especially the eNodeB) freely controls all radio resources for at least RRC_CONNECTED mode UEs. Except for the physical random access channel (PRACH), E-UTRAN controls all transmissions in both the 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] The eNodeB has an RRM function, which controls all radio resources via RRC, but depends on the UE for discovering cells and reporting related measurement values. For this purpose, in LTE Releases 8 to 11, the eNodeB transmits the Primary Synchronization Signal (PSS), Secondary Cell Synchronization Signal (SSS), and Cell-Specific Reference Signal (CRS) in each radio frame. The PSS and SSS each occupy one OFDM symbol per half-frame, while the CRS is transmitted in each subframe of the radio frame. Therefore, the UE can discover and measure cells within a 6 ms measurement window even if it does not know the timing of a given cell deductively. Also, to support inter-frequency measurements in a Time Division Duplex (TDD) system when the UL / DL configuration of the cell may be unknown to the UE, or to support the measurement constraints introduced in LTE Release 10 for the purpose of enhanced Inter-cell Interface Coordination (eICIC), the UE needs to be able to discover cells in just one subframe, and in some cases, in the DwPTS region of a special subframe. To promote energy saving and interference reduction, in LTE Release 12, a "discovery burst" (including PSS, SSS, and CRS transmissions) is introduced, and when configured, a Channel State Information Reference Signal (CSI-RS) for transmission point (TP) identification is introduced in the context of a shared cell ID. 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. The PSS, SSS, CRS, and CSI-RS (when configured) form a Discovery Reference Signal (DRS), which is transmitted during DRS occasions. DRS occasions are similar to the positioning reference signal (PRS) occasions of LTE Release 9 in that they have a configured or specific length (e.g., number of subframes) and periodicity. Ideally, the length of a DRS occasion is not longer than the 6 ms UE measurement window and can be as short as one subframe.The appropriate periodicity of the DRS occasion is several hundred milliseconds, and the DRS burst can operate as a beacon in other wireless communication systems (such as CSMA / CA).

Summary of the Invention

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

[0012] In a 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 to the eNB in the shared frequency spectrum. If the shared frequency spectrum is BUSY, the UE waits for a first period of time. After the first period of time, the UE reports the BUSY state to the eNB.

Brief Description of the Drawings

[0013]

Figure 1

[0014]

Figure 2

[0015]

Figure 3

[0016]

Figure 4A

[0017]

Figure 4B

[0018] Exemplary embodiments are directed to apparatuses and methods for operating an Orthogonal Frequency Division Multiple Access (OFDMA) cellular communication system, such as 3GPP Long Term Evolution (LTE), at a radio frequency shared with a primary transceiver. The primary transceiver can be a naval, automotive radio, or other high-priority transceiver. Specific terms are used herein, but these terms are used only in a general and illustrative sense and are not intended to be limiting. 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 State Information CSI-RS: Channel State 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 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 RRM: Radio Resource Management RSRP: Reference Signal Received Power SCell: Secondary Cell SRS: Sounding Reference Signal SSS: Secondary Synchronization Signal TDD: Time Division Duplex TRS: Tracking Reference Signal UL: Uplink

[0019] <Dynamic Frequency Selection (DFS)> It is not easy to use the 3GPP Long Term Evolution (LTE) communication standard in a shared access spectrum. This is because the radio resource management function exists within the eNodeBs in the network and the radio resources are controlled only by these eNodeBs. In the Dynamic Frequency Selection (DFS) method, typically, sufficient time (e.g., several seconds) is obtained to change the frequency band or carrier after the primary user is detected. Therefore, in order to release the band to the primary user, handover-based RRC signaling and activation or deactivation of SCell under MAC control are sufficient. The 3GPP LTE communication standard currently lacks protocols, procedures, and measurements to make this UE take some action when a primary user is detected on the carrier configured for the UE to transmit data. Also, although mobility control in LTE is completely controlled by the eNodeB, in other wireless cellular communication standards, the UE is made to initiate a handover. Here, the mobility balances the load, and in this case, the eNodeB can add or remove an SCell or change the PCell for a stationary UE. In either the ASA-based method with a primary user or the CSMA / CA-based method without a primary user, a so-called "hidden station" may exist. A hidden station is a transmitter such as a primary user, and transmissions by these can be detected only at the receiving end of the communication link sharing the wireless medium. For example, in LTE, only the UE can detect the waveform transmitted from the "hidden station", and the eNodeB is completely unaware of the existence of the hidden station.

[0020] Figure 2 is a flowchart showing the operation of the first embodiment. At step 200, the UE is initialized to operate in the LTE band together 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 camping on cells operating in the ASA band by existing means such as broadcast of system information. As a result, all UEs connected in the ASA band are in the RRC_CONNECTED mode, and thereby are under the complete control of the eNodeB. The eNodeB is configured to perform RRM measurements on all UEs connected in the ASA band 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 physical layer (PHY) of the UE triggers an RRM measurement report to the upper layers of its protocol stack indicating the detected hidden terminal, according to existing LTE Release 8 / 9 / 10 / 11 / 12 procedures. A measurement report triggered by a non-standard (proprietary) DFS function in the UE can be associated with a specific value in the RRC information element (IE) RSRP range by a specification (e.g., a "DFS event"). For example, the DFS event can be indicated by the minimum value within the RRC IE RSRP range and can operate as an out-of-range (OOR) indication. The UE can report a DFS event (e.g., an RSRP measurement report with an OOR indicator indicating the DFS event) to the eNodeB using existing RRM measurement reporting procedures (208). The RRM function of the eNodeB can reinterpret the RSRP measurement report as a DFS / OOR event according to a standardized linkage, and subsequently can reconfigure the UE via existing RRC signaling (212) to release the ASA band to the primary user (210). Such RRC signaling includes handover in the case of the PCell or SCell reconfiguration in the case of the SCell.Alternatively, if the RRM function in the eNodeB determines that the ASA band may be temporarily released to the primary user, the RRM function may simply expire the sCell_Deactivation_Timer in the UE or send a deactivation command in the MAC control element to deactivate the SCell configured with the ASA band. In the 3GPP LTE specification, performance requirements useful for testing the UE on whether the UE reports DFS / OOR events for each ASA band according to the requirements of regulatory authorities worldwide may be introduced, but no new measurements are defined in the specification for supporting 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 the presence of hidden terminals or primary users (to the E-UTRAN). Any UE connected to the cell in the ASA band can be configured to perform and report this new DFS measurement. The eNodeB RRC layer can configure the UE 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 the DFS measurement reporting of the UE connected in the ASA band. Therefore, accurate measurement procedures can be determined by a particular. However, the actions taken by the network can be similar to the actions in the previously described embodiments, including UE handover, SCell reconfiguration, and SCell deactivation. By reporting measurement values (instead of binary information), the eNodeB RRM function can be made to learn from historical data and apply its own thresholds to the eNodeB RRM function to improve the protection of primary users. Since the eNodeB can analyze and combine DFS measurement values from various UEs connected to the eNodeB, the decision to select different carriers for a given UE ultimately lies with the eNodeB. However, if this decision is made at each UE, the network will have to comply with whatever the UE indicates to ensure the protection of potential primary users.

[0022] <Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA)> FIG. 3 is a diagram showing communication between UE 300 and eNodeB 320 according to an exemplary embodiment. UE 300 may be a mobile phone, a computer, or other wireless network device. UE 300 includes a processor 306 coupled to a memory 304 and a transceiver 310. The 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 can be executed by the processor as directed by the user, and also stores operational instructions for the UE. The processor 306 is also coupled to input / output (I / O) circuit elements 308 that may include a microphone, a speaker, a display, and related software. The transceiver 310 includes a receiver 312 and a transmitter 314 suitable for wireless communication with eNodeB 320. The transceiver 310 typically communicates with the eNB 320 via various communication channels. For example, the transceiver 310 sends uplink information to the eNodeB 320 via the physical uplink control channel PUCCH and the physical uplink shared channel PUSCH. Correspondingly, the transceiver 310 receives downlink information from the eNodeB 320 via the physical downlink control channel PDCCH and the physical downlink shared channel PDSCH.

[0023] The base station 320 includes a processor 326 coupled via a bus 336 to a memory 324, a symbol processing circuit 328, and a transceiver 330. The processor 326 and the symbol processing circuit 328 may include several processors adapted to various operation tasks including signal processing and channel measurement and calculation. The memory stores application software 322 that the processor can execute for a specific user, and also stores operation 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 transmits downlink information to the UE 300 via the physical downlink control channel PDCCH and the physical downlink shared channel PDSCH. Also, the transceiver 330 transmits special downlink information to the UE 300 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. Correspondingly, the transceiver 330 receives uplink information from the UE 300 via the physical uplink control channel PUCCH and the physical uplink shared channel PUSCH.

[0024] According to an exemplary embodiment, an E-UTRAN cell such as the eNodeB 320 is used in an unlicensed or ASA band, in which an LTE user equipment shares radio resources with other users of equal priority but who strictly follow a carrier sense multiple access with collision avoidance (CSMA / CA) procedure / protocol. Since 3GPP Long Term Evolution is specifically designed to operate in licensed spectrum, there are fundamental problems.

[0025] Referring to FIG. 4A, the downlink direction situation is similar to the DFS described with reference to FIG. 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 any downlink channels even if it senses 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, when the timeout criterion elapses, RRC signaling causes the UE to release the CSMA / CA band (410) and start a handover (412).

[0026] However, the eNodeB may have to transmit some signal regardless of whether an ongoing transmission is detected. The eNodeB transmits discovery reference signal (DRS) bursts at a period on the order of hundreds of milliseconds. A DRS burst can consist of only one subframe and includes at least the PSS, SSS, and CRS, whereby the UE can discover the cell and perform measurements. In the case of a shared cell ID, CSI-RS may also be transmitted during DRS occasions. Also, through periodic PSS / SSS transmission, the UE obtains coarse time and frequency synchronization with this cell. On the network side, the RRM measurement report based on DRS enables the eNodeB to determine whether to configure a cell in a given unlicensed or ASA band for a given UE. In addition to DRS, the eNodeB needs to periodically transmit some kind of tracking reference signal (TRS) having a periodicity much shorter than that of DRS, such as 5 ms or 10 ms. From the waveform of the TRS, the UE performs automatic gain control (AGC) and fine time and frequency synchronization (tracking). Such a TRS waveform can be based on the existing CRS waveform. Thereby, an additional benefit of being useful for channel state information acquisition in the case of a CRS-based transmission mode can be obtained. Furthermore, the eNodeB may periodically transmit a channel state information reference signal (CSI-RS) that enables channel state information acquisition in the UE in a CSI-RS-based transmission mode. The UE can be configured for CSI measurement and for reporting according to CSI transmission at the eNodeB.

[0027] Referring again to FIG. 3, it may be preferable not to use any downlink channel together with CSMA / CA. For example, the Physical Broadcast Channel (PBCH) is not transmitted within a cell in an unlicensed or ASA band. Therefore, the UE cannot camp on such a cell. Similarly, system information is not transmitted. Thus, such a cell can only be configured as a Secondary Cell (SCell), and the Primary Cell (PCell) is always configured with licensed spectrum. It may also be beneficial not to transmit the Physical Hybrid ARQ Indicator Channel (PHICH) in an unlicensed or ASA spectrum. Alternatively, the UL grant transmitted in the Downlink Control Information (DCI) can act as an implicit ACK / NACK indication by scheduling a retransmission of the previous UL grant. The Physical Control Format Indicator Channel (PCFICH) may or may not be transmitted in an unlicensed or ASA spectrum. When an extended PHICH duration is configured, the Control Format Indicator (CFI) is known through the specification. Similarly, the PCFICH is not required for Physical Downlink Shared Channel (PDSCH) transmission in Transmission Mode 10 (TM10) scheduled by the Enhanced Physical Downlink Control Channel (EPDCCH). In cross-carrier scheduled PDSCH transmission, the CFI is known through the configuration. In contrast, since the PCFICH is transmitted in the same subframe as the Physical Downlink Control Channel (PDCCH), the PCFICH can always be transmitted when the PDCCH is transmitted. Finally, since the Physical Multicast Channel (PMCH) is quasi-statically scheduled by the Multimedia Broadcast Multicast Service (MBMS) Coordination Entity (MCE) for reserved resources, it may be beneficial not to transmit the PMCH in an unlicensed or ASA spectrum. Otherwise, in unicast downlink transmission, if the CSMA / CA function at the eNodeB indicates that a given subframe can be used for (E)PDCCH or PDSCH transmission, the eNodeB transmits according to LTE Release 12. In one embodiment, the CSMA / CA function at the eNodeB returns a binary indication.If the CSMA / CA function for a given cell indicates BUSY on a given carrier, the eNodeB does not transmit (E)PDCCH or PDSCH to any UE. The eNodeB may continue to transmit other signals or channels in accordance with the above recommendations. 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 transmits in accordance with LTE Release 12.

[0028] Referring to Figure 4B, the uplink operation in the CSMA / CA band is similar to the downlink operation. The UE is initialized in the LTE band (400). The UE monitors the CSMA / CA band (420). When the UE senses an ongoing transmission (422), it does not transmit any uplink channels. The UE monitors a timeout criterion (426) and continues to monitor 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, when the timeout criterion elapses, the UE sends a BUSY report to the eNodeB (428). RRC signaling causes the UE to release the CSMA / CA band (430) and 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 so as not to interfere with ongoing transmissions. It may also be beneficial not to transmit the physical uplink control channel (PUCCH) in unlicensed or ASA spectrum. In this case, the PUCCH is transmitted only to the PCell in licensed spectrum. If PUCCH transmission is permitted in unlicensed or ASA spectrum several UE behaviors are assumed.

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

[0031] Alternatively, the UE may be based on any PUCCH transmission with respect to the indication of the CSMA / CA function in the UE for the subframe in which PUCCH transmission is scheduled. When the CSMA / CA function in the UE indicates BUSY, the UE does not transmit on the PUCCH in the target subframe. Otherwise, when the CSMA / CA function in the UE indicates IDLE, the UE transmits the PUCCH as scheduled.

[0032] The same principle may be applied to the physical uplink shared channel (PUSCH). In one embodiment, regardless of the indication of the CSMA / CA function in the UE for the subframe in which PUSCH transmission is scheduled, the UE follows the existing UE procedures for PUSCH transmission. Generally, collisions with ongoing transmissions cannot be avoided, and the PUSCH may not be properly received at the eNodeB.

[0033] Alternatively, the UE may be based on any PUSCH transmission with respect to the indication of the CSMA / CA function in the UE for the subframe in which PUSCH transmission is scheduled. When the CSMA / CA function in the UE indicates BUSY, the UE does not transmit on the PUSCH in the target subframe. Otherwise, when the CSMA / CA function in the UE indicates IDLE, the UE transmits the PUSCH as scheduled.

[0034] Similar to the case of DFS, hidden terminals must be considered. The above solutions for PUSCH and PUCCH transmissions relate to the behavior of the UE when the CSMA / CA function in the UE indicates BUSY for the subframe in which the PUSCH / PUCCH transmission is scheduled. In the case of a hidden terminal having a detectable waveform at the UE rather than the eNodeB, the eNodeB may continue to schedule that UE. If the UE follows the normal LTE Release 12 operation, as a result, the performance of the link from the eNodeB to the UE, as well as the performance of the link to and from the hidden terminal, may degrade. This is because collisions of each transmission may continue, thereby potentially causing excessive interference, so that (a) reliable communication is no longer achievable, or (b) at least, an acceptable quality of service (QoS) can no longer be provided. In the opposite case where the UE does not transmit on PUSCH or PUCCH in a subframe when the CSMA / CA function in the UE indicates BUSY, the performance may similarly degrade. This is because packets and HARQ ACK / NACK transmissions in the BUSY subframe are discarded. Theoretically, by reusing the DFS method described above, the MAC (or RRC) layer of the eNodeB can be informed by the UE of the BUSY state of the cell or carrier so that the UE is scheduled in different CCs to avoid further collisions. Thus, instead of the "DFS event" triggered by the DFS function, the CSMA / CA function may indicate BUSY, but otherwise, these procedures can be reused. However, the time scale for DFS is generally much longer than the time scale for LBT, similar to the case of CSMA / CA. Therefore, in the exemplary embodiment, another procedure for dealing with hidden terminals in the case of CSMA / CA is provided.

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

[0036] By avoiding scheduling the UE on carriers occupied by hidden terminals, the eNodeB can take earlier actions, so it is preferable to use PHY or MAC layer mechanisms so that the overall system performance and in particular the user-perceived UE throughput are maximized. Here, the former has a shorter latency than the latter. First, to reduce latency, assume that the UE is already configured on the corresponding component carriers together with up to five serving cells (Figure 1). According to the exemplary embodiments, the serving cells are ordered in ascending order based on the ServCellIndex configured by RRC signaling. However, other ordering and addressing mechanisms are not excluded. Next, the symbols {00, 01, 10, 11} are assigned to the four serving cells excluding the PCell such that the serving cell (SCell) with the smallest ServCellIndex corresponds to 00, the serving cell (SCell) with the second smallest ServCellIndex corresponds to 01, and so on. If less than four SCells are configured, the unused symbols (e.g., if one SCell is configured, {01, 10, 11}) are reserved. Other mappings are not excluded. To ensure the shortest latency, L1 (PHY) signaling is introduced to inform the upper layer of the eNodeB about the BUSY indication from the UE's CSMA / CA function in the subframe in which PUSCH or PUCCH transmission is scheduled.

[0037] Accordingly, a new PUCCH format that is always transmitted to the PCell is introduced. This new PUCCH format is exactly the same as the existing PUCCH format 1b. However, instead of representing ACK / ACK, ACK / NACK, NACK / ACK, and NACK / NACK / DTX, QPSK symbols encode the indices {00, 01, 10, 11} of the four serving 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, and thus these two PUCCH formats can share the same time and frequency resources. Alternatively, this new PUCCH format can have its own time and frequency resources in the PUCCH region. CDM is preferred for improving spectral efficiency when PUCCH capacity is not a problem, as in the case of small cells. In a subframe in which a PUSCH or PUCCH transmission is scheduled, if the CSMA / CA function in the UE indicates BUSY, the UE does not transmit the PUSCH or PUCCH as scheduled. Instead, it indicates the BUSY indication (to the eNodeB) via a PUCCH format 1c transmission to the PCell. Although the behavior of several UEs is assumed, it is assumed that the eNodeB schedules only one SCell at a time to prevent ambiguity at the eNodeB when PUCCH format 1c is received.

[0038] In one embodiment, PUCCH format 1c indicates which service providing cell has a BUSY indication. For example, the eNodeB may schedule uplink transmission in subframe n + k (where k > 0) via UL grant in the DCI received in subframe n. Immediately before being scheduled for uplink transmission to occur, the CSMA / CA function in the UE starts 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 the scheduled transmission according to the received DCI. If BUSY is indicated, the UE ignores the DCI scheduling the target uplink transmission and instead transmits PUCCH format 1c to the PCell that encodes (in QPSK symbols) the service providing cell where the collision occurred.

[0039] Since the eNodeB was expecting PUSCH or PUCCH transmission for a particular service providing cell, the PUCCH format 1c transmission actually does not convey additional information to the upper layer of the eNodeB. Therefore, in different embodiments, the CSMA / CA function in the UE senses all the configured service providing cells before the scheduled uplink transmission. If IDLE is indicated for the service providing cell where the transmission is scheduled, the UE proceeds with the scheduled transmission according to the received DCI. If BUSY is indicated, the UE ignores the DCI scheduling the target uplink transmission and instead transmits PUCCH format 1c to the PCell that encodes (in QPSK symbols) the service providing cell where the CSMA / CA function in the UE indicated IDLE. This does not guarantee that the corresponding service providing cell will be IDLE in a later subframe n + k2 (k2 > k), but at least the eNodeB does not continue scheduling uplink transmission to the same service providing cell.

[0040] Introducing a new PUCCH format 1c requires the eNodeB receiver to monitor this new PUCCH format. Therefore, MAC layer procedures may be preferred over the foregoing PHY procedures. However, transmitting a MAC control element requires the UE to obtain available uplink resources in addition to the uplink resources that remain unused by not transmitting PUCCH or PUSCH because the medium is BUSY. Also, the time required to prepare for 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 in the UE indicates IDLE, but the medium is BUSY during subframe n + k. If the UE has to send a scheduling request (SR) to transmit the AMC CE, the latency can be even longer. Nevertheless, there can still be advantages to MAC layer procedures. For example, this may eliminate the need to impose the constraint that only one SCell is scheduled at a time. Instead, all four SCells can be simultaneously encoded using 1 octet (8 bits) in the MAC CE. Up to four service providers (SCells) are represented by {00, 01, 10, 11} based on ServCellIndex and reordered in ascending order again, so 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. Also, the 8 bits within 1 octet of the MAC CE correspond to the four SCells according to 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 the bit at a certain position corresponds to that position itself, this indicates that the corresponding serving cell has been indicated as IDLE. Otherwise, this indication becomes BUSY, and these two bits indicate the serving cell that the eNodeB should switch to. Therefore, the bit position within the octet encodes the serving cell to which the bit at that position belongs, and these bits themselves encode the same information transmitted in the above PUCCH format 1c for one cell. For example, the octet {00010011} means that the first, second, and fourth serving cells were IDLE, and that the transmission for the third serving cell should be transmitted for the first serving cell.

[0041] Within the scope of the claims, modifications are possible in the described embodiments, and other embodiments are possible.

Claims

1. A method for operating a wireless communication system using a shared frequency spectrum, comprising: Initializing a user equipment (UE) in a primary service providing cell (PCell) with a licensed frequency spectrum; Configuring the UE to communicate with a secondary service providing cell (SCell) operating on a carrier of the shared frequency spectrum; Monitoring, by a base station (eNB), the shared frequency spectrum to determine whether the shared frequency spectrum is BUSY; Transmitting to the UE on the shared frequency spectrum when the shared frequency spectrum is not BUSY; Waiting for a first period of time when the shared frequency spectrum is BUSY; and Instructing the UE to release the carrier in the shared frequency spectrum after the first period of time when the shared frequency spectrum is BUSY. A method comprising the above.

2. The method according to claim 1, wherein the shared frequency spectrum is an unlicensed frequency spectrum.

3. The method according to claim 1, comprising accessing the shared frequency spectrum using carrier sense multiple access with collision avoidance (CSMA / CA).

4. The method according to claim 1, comprising instructing the UE to release the shared frequency spectrum by radio resource control (RRC) signaling after the first period of time.

5. The method according to claim 1, comprising instructing the UE to deactivate the SCell by medium access control (MAC) signaling after the first period of time.

6. The method according to claim 1, wherein when the shared frequency spectrum is not BUSY, transmitting to the UE on a first plurality of channels; and excluding a second plurality of channels from the shared frequency spectrum. A method comprising the above.

7. The method according to claim 1, comprising excluding a physical broadcast channel (PBCH) from transmission on the shared frequency spectrum.

8. The method according to claim 1, comprising transmitting a discovery reference signal on the shared frequency spectrum by the eNB when the shared frequency spectrum is BUSY.

9. The method according to claim 1, comprising transmitting a tracking reference signal in the shared frequency spectrum by the eNB.

10. A method for operating a communication system in a shared frequency spectrum, the method comprising: Initializing a user equipment (UE) in a primary service providing cell (PCell) in a licensed frequency spectrum; Transmitting data from the UE to at least one secondary service Providing cell (SCell) operating in the shared frequency spectrum; Monitoring, by the UE, the at least one SCell to determine a BUSY state; Transmitting to a base station on the at least one SCell when the at least one SCell is not BUSY; and Reporting the BUSY state of the at least one SCell to the base station when the at least one SCell is BUSY. A method comprising:

11. The method according to claim 10, Wherein the shared frequency spectrum is an unlicensed frequency spectrum.

12. The method according to claim 10, Including accessing the shared frequency spectrum using carrier sense multiple access with collision avoidance (CSMA / CA).

13. The method according to claim 10, Including reporting the BUSY state in an uplink control information packet on a physical uplink control channel of the PCell.

14. The method according to claim 10, Wherein the BUSY state is transmitted on a physical uplink control channel resource configured quasi-statically by radio resource control signaling from the base station.

15. The method according to claim 10, Wherein the BUSY state is transmitted on a physical uplink control channel resource signaled dynamically by a downlink control information packet from the base station.

16. The method according to claim 10, the method comprising: Determining that the state of the at least one SCell is BUSY; Determining the IDLE state of at least one other secondary service providing cell; and Transmitting, on a physical uplink control channel of the PCell, an identity of the at least one other secondary service providing cell to the base station , a method comprising. [

17. ] A method of operating a wireless communication system in a shared frequency spectrum, the method comprising Initializing a user equipment (UE) in a primary service providing cell in a licensed frequency spectrum Configuring the UE to communicate with a secondary service providing cell (SCell) in the shared frequency spectrum, and Receiving, from the UE, a radio resource management (RRM) report of the SCell when a primary user is detected in the shared frequency spectrum , a method comprising. [

18. ] The method according to claim 17, wherein The shared frequency spectrum is an authorized shared access (ASA) frequency spectrum, and the primary user has a higher access priority than the SCell [

19. ] The method according to claim 17, wherein The RRM report is periodic [

20. ] The method according to claim 17, wherein The RRM report is a dynamic frequency selection (DFS) event

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