Method and apparatus for transmitting LTE waveforms in shared spectrum through carrier sensing

Abstract

The present invention relates to a method and an apparatus for transmitting LTE waveforms in a shared spectrum through carrier sensing. In described examples, a method of operating a Long Term Evolution (LTE) communication system on a shared spectrum is disclosed. A user equipment (UE) is initialized on an LTE band (400). A base station (eNB) monitors a shared spectrum (402) to determine whether it is BUSY (404). If the shared spectrum is not BUSY, the eNB transmits to the UE on the shared spectrum (406). If the shared spectrum is BUSY, the eNB waits for a first time (408) and, after the first time, instructs the UE to vacate the shared spectrum (410).

Description

[0001] This application is a divisional application of Chinese Patent Application No. 202010985330.6, which is a divisional application of Chinese Patent Application No. 201580029753.8, titled "Method and Apparatus for Transmitting LTE Waveforms in Shared Spectrum by Carrier Sensing", with an application date of June 5, 2015. Background Art

[0002] In most countries, access to the radio spectrum is strictly regulated by government agencies such as the Federal Communications Commission (FCC) in the United States or the European Commission in the European Union. Like any other natural resource, the frequencies of the radio spectrum need to be shared among its users. Thus, portions of the radio spectrum (e.g., frequency bands) are licensed to individual users (e.g., mobile operators) or shared among many users such as WiFi or Bluetooth (which operate in unlicensed bands). Also, in this hybrid model, licensed spectrum is granted to primary users with the highest priority (e.g., for naval radar applications). Additionally, secondary users are allowed to use the licensed band during inactive periods when the primary user is not transmitting waveforms in the considered frequency band. These secondary users can have different priorities. For example, a given frequency band licensed to a primary user may be used by a public safety group for mission-critical communications. In this case, commercial users may be allowed to use such a frequency band, and only if neither the higher-priority primary user nor the secondary user (e.g., public safety user) is occupying the band. This policy-based spectrum usage is sometimes referred to as authorized shared access (ASA). From this perspective, there is no need to distinguish between unlicensed and authorized shared access, because whenever a frequency band is used by many users, the same techniques can be used to ensure fairness and policy compliance.

[0003] In the above example of licensed shared access, spectrum sharing can be facilitated through a dynamic scheme (sometimes referred to as a listen-before-talk (LBT) scheme) and through a semi-static scheme such as through a geographical location database (GLDB). For example, such a database can map the frequency usage of such a frequency band to a geographical area or time of day. Due to the time required to update these databases and propagate them to all participating users, they cannot change dynamically. As the name implies, the LBT scheme is more dynamic and does not rely on a semi-statically configured database. Instead, the secondary user must ensure that the primary user or other users with the same priority are not interfered with by the secondary user's transmission. Two well-known examples are radar avoidance in IEEE 802.11 wireless local area networks (WLANs) and carrier sense multiple access with collision avoidance (CSMA / CA). The former is applicable when the secondary user must grant priority to the primary user. Since the secondary user must stop transmitting when it detects a military, meteorological, or automotive radar waveform, it is commonly referred to as dynamic frequency selection (DFS). Thus, the secondary user vacates a given frequency band or channel (a channel is a further subdivision of a frequency band) when it detects the primary user, and the secondary user attempts to transmit on a different frequency band or channel resulting in what is called dynamic frequency selection. Similarly, in the case of CSMA / CA, when the transmitter detects a transmission of the same priority in progress, it chooses not to transmit in order to attempt again at a later point in time. Thus, this is what is called carrier sense multiple access with collision avoidance. Thus, the two main differences between DFS and CSMA / CA are the time scale at which listening occurs and the action taken by the transmitter when a transmission in progress is detected. For example, a DFS transmitter will always have to switch channels / frequency bands to vacate the current frequency for the primary user, but a CSMA / CA transmitter may or may not switch channels. This is because in CSMA / CA, radio resources are shared among users with equal priority and it is considered a multiple access scheme. However, with DFS, the primary user has a higher priority. Therefore, to ensure the contention latency of the CSMA / CA scheme, carrier sense (CS) and collision avoidance (CA) occur on the order of tens of microseconds (us), but DFS can take several seconds.

[0004] The CS / CA multiple access scheme contrasts sharply with 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) because of the opportunistic random access nature of the shared medium. TDMA and FDMA in the Global System for Mobile Communications (GSM), CDMA in the Universal Mobile Telecommunications System (UMTS), and Orthogonal Frequency Division Multiple Access (OFDMA) in the 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) attempt to orthogonalize the available resources to share them among multiple users. However, orthogonal operation requires precise coordination through predefined rules or a dynamic scheduler that allocates resources to specific users for a given time interval in a given portion of the radio spectrum, thus essentially preventing collisions. This makes it particularly challenging to operate them in radio resources shared via the CS / CA multiple access scheme because users following these kinds of protocols and procedures will lose out to users following predefined scheduling or radio resource allocation when competing for available radio resources.

[0005] In LTE, the base station is called an evolved Node B (eNodeB / eNB), and has full control over the Radio Resource Management (RRM) of the cell under its control. The Evolved Universal Terrestrial Radio Access Network (E-UTRAN) typically consists of many eNodeBs, each with its own RRM function. A subset of these eNodeBs can coordinate their RRM via the X2 Application Protocol (X2AP), which is defined over the X2 interface connecting two eNodeBs. Similarly, each eNodeB is connected via the S1 interface to one or more Mobility Management Entities (MMEs) in the Core Network (CN), over which the S1 Application Protocol (S1AP) is defined. Additionally, S1AP can be used for RRM coordination. RRM interfaces are an essential part of cellular communication because they enable important functions such as interference coordination, mobility, and even Self-Organizing Networks (SON).

[0006] Figure 1 is an example radio telecommunications network of the prior art. The illustrative telecommunications network includes a primary eNodeB 110 operating in a primary cell (PCell) 100 and secondary cells (SCell 1 to SCell 4)eNodeBs 112, 114, 116, and 118 operating in 102, 104, 106, and 108. A handheld 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 a secondary cell. In this example, the SCell is a logical concept, so the eNodeB 110 may operate multiple SCell (102 to 108).

[0007] In addition, the eNodeB 110 controls the radio resources in its cell 100 by way of the radio resource control (RRC) protocol and by way of the medium access control (MAC) protocol for the multiple access of the users in its cell. For example, the RRC protocol configures the carriers on which the user equipment (UE) can send and receive data, and in advanced LTE (LTE-A), up to five so-called component carriers (CCs) can be configured per UE. Similarly, the MAC protocol, in combination with the RRC protocol, controls how and when the UE can use the available radio resources to send or receive data on the configured carriers. LTE Release 10 introduced a feature called carrier aggregation, in which a UE can be configured with one primary cell (PCell) and up to four secondary cells (SCell). The PCell can only be changed by handover, while the SCell is configured by RRC signaling. Specifically, the UE does not expect to receive system information by decoding the physical broadcast channel (PBCH) on the secondary component carrier (SCC), or to monitor the common search space of the SCell to receive the physical downlink control channel (PDCCH) whose CRC is scrambled by SI-RNTI to receive the system information (SI) on the downlink shared channel (DL-SCH). In addition, the UE can assume that the system frame number (SFN) on all SCCs is aligned with the SFN of the primary component carrier (PCC).

[0008] CA does not limit the radio link monitoring (RLM) of the SCell. Therefore, there is no specific device for the UE physical layer (PHY) to indicate radio link failure (RLF) to the UE higher layers through the MAC layer. This is because in Evolved Universal Terrestrial Radio Access (E-UTRA), the connectivity provided by the PCell can always be relied on, which provides robustness through RLM and other fallback procedures. Alternatively, the SCell operates as a supplementary serving cell, which can be activated when additional capacity is required for data communication with the UE. For this purpose, the MAC layer can activate the configured SCell through a MAC control element (CE). The activation of the SCell can take between 8 and 30 ms, depending on the synchronization state of the UE with respect to that SCC. The RRC reconfiguration of the SCell will obviously take more time, especially when the UE needs to perform inter-frequency measurements. Therefore, the eNodeB can configure the UE to periodically measure the reference signal received power (RSRP) of a certain cell on a certain carrier, and report the measurement results either periodically or through the triggering of configurable offsets and thresholds. In 3GPP Long Term Evolution, this is achieved through measurement objects and configured RRC signaling. If the measurement is easily available at the eNodeB, the RRC reconfiguration of the SCell or PCell can be significantly reduced with a delay ranging from a few seconds to dozens of seconds or hundreds of milliseconds. Although the eNodeB can only activate a cell that has been configured as an SCell, it can configure the UE to measure the RSRP on any cell. By comparison, the eNodeB can use the measurement reports of any cell to activate a cell, such as in the case of SCell activation, or RRC reconfigure the UE to add / remove an SCell or even change the PCell.

[0009] After the PCell or SCell is activated, the eNodeB MAC scheduler allocates 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) in subframe n schedules the corresponding PDSCH transmission in the same subframe. In contrast, in the uplink, it schedules the PUSCH transmission in subframe n + k, where k > 0 is determined by a predefined rule.

[0010] The E-UTRAN (specifically the eNodeB) has complete control over all radio resources, at least for UEs in the RRC-CONNECTED mode. Except for the Physical Random Access Channel (PRACH), the E-UTRAN controls all transmissions in both the uplink and downlink directions, including resource allocation in time, frequency, or any other means such as CDMA, as well as timing or power control of transmissions.

[0011] Although the RRM functions reside in the eNodeB, which in turn controls all radio resources via the RRC, it relies on the UE to discover the cell and report the associated measurements. To this end, in LTE Release 8 to 11, the eNodeB transmits the Primary Synchronization Signal (PSS), Secondary Synchronization Signal (SSS), and Cell-Specific Reference Signal (CRS) in each radio frame. In addition to transmitting the CRS in each subframe of the radio frame, each of the PSS and SSS occupies one OFDM symbol per half-frame, which allows the UE to discover and measure the cell within a 6 ms measurement window without prior knowledge of the timing of a given cell. Furthermore, to support inter-frequency measurements in Time Division Duplex (TDD) systems when the UL / DL configuration of the cell may not be known to the UE or for the purpose of enhanced inter-cell interference coordination (eICIC), and to support the measurement restrictions introduced in LTE Rel 10, the UE must be able to discover the cell and potentially discover the DwPTS region of a specific subframe in only one subframe. To promote energy conservation and reduce interference, LTE Release 12 introduced "Discovery Bursts" (including PSS, SSS, and CRS transmissions), and if configured, the Channel State Information Reference Signal (CSI-RS) for transmission point (TP) identification in the case of shared cell IDs. For example, multiple TPs can share the same Physical Cell ID and can only be identified by their respective CSI-RS resource element (RE) configurations. The PSS, SSS, CRS, and CSI-RS (if configured) form the Discovery Reference Signal (DRS) and are transmitted during the DRS occasion. The DRS occasion is similar to the LTE Release 9 Positioning Reference Signal (PRS) occasion in that they have a configured or specific length (e.g., number of subframes) and periodicity. Ideally, the length of the DRS occasion does not exceed the 6 ms UE measurement window and can be as short as one subframe. A reasonable periodicity for the DRS occasion is in the order of hundreds of milliseconds, and the DRS burst can operate as a beacon in other wireless communication systems such as CSMA / CA. Summary of the Invention

[0012] In a first embodiment, a method for operating a Long Term Evolution (LTE) communication system in a shared spectrum is disclosed. A base station (eNB) initializes a User Equipment (UE) on an LTE band. The eNB monitors the shared spectrum to determine if it is BUSY. If the shared spectrum is not BUSY, the eNB transmits to the UE on the shared spectrum. If the shared spectrum is BUSY, the eNB waits for a first time. The eNB instructs the UE to vacate the shared spectrum after the first time.

[0013] In a second embodiment, the UE monitors the shared spectrum to determine if it is BUSY. If the shared spectrum is not BUSY, the UE transmits to the eNB on the shared spectrum. If the shared spectrum is BUSY, the UE waits for a first time. The UE reports the BUSY state to the eNB after the first time. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 is a schematic diagram of a prior art Long Term Evolution (LTE) communication system.

[0015] Figure 2 is a flowchart showing the operation of a Long Term Evolution (LTE) communication system on an Authorized Shared Access (ASA) spectrum.

[0016] Figure 3 is a schematic diagram showing communication between a User Equipment (UE) and a base station (eNB) according to an example embodiment.

[0017] Figure 4A is a schematic diagram showing the downlink operation of a Long Term Evolution (LTE) communication system on a Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA) spectrum according to an example embodiment.

[0018] Figure 4B is a schematic diagram showing the uplink operation of a Long Term Evolution (LTE) communication system on a Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA) spectrum according to an example embodiment. DETAILED DESCRIPTION

[0019] Example embodiments are directed to apparatus and methods for operating an Orthogonal Frequency Division Multiple Access (OFDMA) cellular communication system, such as 3GPP Long Term Evolution (LTE), in a radio frequency shared with a primary transceiver. The primary transceiver can be a naval, automotive radio, or other transceiver with a higher priority. Although specific terms are employed herein, they are used only in a general and descriptive sense and not for purposes of limitation. The following abbreviations are used throughout this specification.

[0020] ASA: Authorized Shared Access

[0021] eNB: evolved Node B or base station

[0022] UE: User Equipment

[0023] CQI: Channel Quality Indicator

[0024] CRS: Cell-specific Reference Signal

[0025] CSI: Channel State Information

[0026] CSI-RS: Channel State Information Reference Signal

[0027] CSMA / CA: Carrier Sense Multiple Access with Collision Avoidance

[0028] DCI: Downlink Control Information

[0029] DFS: Dynamic Frequency Selection

[0030] DRS: Discovery Reference Signal

[0031] DL: Downlink

[0032] DwPTS: Downlink Pilot Time Slot

[0033] E-UTRAN: Evolved Universal Terrestrial Radio Access Network

[0034] LBT: Listen Before Talk

[0035] LTE: Long Term Evolution

[0036] MAC: Medium Access Control Protocol

[0037] MIMO: Multiple Input Multiple Output

[0038] OFDMA: Orthogonal Frequency Division Multiple Access

[0039] OOR: Out-of-Range

[0040] PBCH: Physical Broadcast Channel

[0041] PCell: Primary Cell

[0042] PCFICH: Physical Control Format Indicator Channel

[0043] PDCCH: Physical Downlink Control Channel

[0044] PDSCH: Physical Downlink Shared Channel

[0045] PHICH: Physical Hybrid ARQ Indicator Channel

[0046] PMCH: Physical Multicast Channel

[0047] PSS: Primary Synchronization Signal

[0048] PUCCH: Physical Uplink Control Channel

[0049] PUSCH: Physical Uplink Shared Channel

[0050] RI: Rank Indicator

[0051] RRC: Radio Resource Control

[0052] RRM: Radio Resource Management

[0053] RSRP: Reference Signal Received Power

[0054] SCell: Secondary Cell

[0055] SRS: Sounding Reference Signal

[0056] SSS: Secondary Synchronization Signal

[0057] TDD: Time Division Duplex

[0058] TRS: Tracking Reference Signal

[0059] UL: Uplink

[0060] Dynamic Frequency Selection (DFS)

[0061] The 3GPP Long Term Evolution (LTE) communication standard cannot be easily deployed in shared access spectrum. This is because the radio resource management function resides in the eNodeB in the network and the radio resources are only controlled by that eNodeB. The Dynamic Frequency Selection (DFS) scheme typically allows sufficient time (e.g., several seconds) to change the frequency band or carrier when detecting the primary user. Therefore, handover-based RRC signaling and SCell activation or deactivation under MAC control are sufficient to vacate the frequency band for the primary user. The 3GPP LTE communication standard currently lacks protocols, procedures, and measurements for the UE to take any action when a primary user is detected on the carrier on which the UE is configured to transmit data. In addition, although other wireless cellular communication standards do allow the UE to initiate handovers, mobility control in LTE is fully controlled by the eNodeB. Here, mobility includes the case of load balancing, where the eNodeB can add or remove SCell or change the PCell for a stationary UE. For both the ASA-based scheme with a primary user and the CSMA / CA-based scheme without a primary user, there can be a so-called "hidden station". A hidden station is a transmitter, such as a primary user, whose transmission can only be detected at the receiving end of the communication link of the shared wireless medium. For example, in LTE, in addition to the eNodeB completely ignoring the existence of hidden stations, only the UE can detect the waveform transmitted from a "hidden station".

[0062] Figure 2 A flowchart showing the operation of the first embodiment. The UE is initialized at step 200 to operate on the LTE band in combination with the PCell. The ASA band is configured by the eNodeB as a regular LTE band and operates as a regular LTE band, and the UE operates on the ASA band at 202. By existing means such as prohibiting the broadcast through system information, the UE is prohibited from camping on the cell operating on the ASA band. Thus, all UEs connected to the ASA band are in the RRC connected mode and are thus under the full control of the eNodeB. The eNodeB configures all UEs connected to the ASA band according to the existing LTE specifications (e.g., Release 8 to 12) to perform RRM measurements at 204. DFS is supported by each UE through a non-standardized (proprietary) implementation. If the UE detects a hidden station (from the UE's perspective, all primary users are hidden stations) at 206, the UE physical layer (PHY) indicates to the higher layer of its protocol stack to trigger an RRM measurement report according to the existing LTE Rel 8 / 9 / 10 / 11 / 12 procedures. Throughout the specification (e.g., "DFS event"), the RRM measurement report triggered by the non-standardized (proprietary) DFS function at the UE is bound to a specific value of the RRC information element (IE) RSRP range. For example, the DFS event may be indicated by the lowest value in the RRC IE RSRP range and may operate as an out-of-range (OOR) indication. The UE will use the existing RRM measurement report procedure to report the DFS event to the eNodeB (e.g., an RSRP measurement report with an OOR indicator indicating the DFS event) at 208. The eNodeB RRM function will reinterpret the RSRP measurement report as a DFS / OOR event according to the standardization link, and then vacate the ASA band for the primary user at 210, and will reconfigure the UE via the existing RRC signaling at 212. This RRC signaling covers handover in the case of the PCell or SCell reconfiguration in the case of the SCell. Alternatively, if the RRM function at the eNodeB believes that the ASA band needs to be vacated for the primary user only temporarily, the RRM function may simply let the sCellDeactivationTimer at the UE expire, or the RRM function can send a deactivation command in the MAC control element to deactivate the SCell configured on the ASA band. If the 3GPP LTE specification reports DFS / OOR events according to the requirements of global regulators for each ASA band, the 3GPP LTE specification will introduce performance requirements useful for test UEs, but will not define new measurements in the specification supporting DFS in 3GPP LTE.

[0063] In another embodiment, instead of reinterpreting existing measurement reports as DFS / OOR events, new measurement reports and associated procedures are specifically defined for the purpose of indicating (to the E-UTRAN) the presence of a hidden station or primary user. All UEs connected to a cell on the ASA band will be configured to measure and report this new DFS measurement. The eNodeB RRC layer can configure the UE to report the DFS measurement either periodically or triggered or periodically triggered. The eNodeB will configure the measurement events and associated thresholds and offsets to control the DFS measurement reports of the UEs connected on the ASA band. Thus, the exact measurement procedures will be determined by the specification. However, the actions taken by the network can be similar to those in the above embodiments to include UE handover, SCell reconfiguration, and SCell deactivation. Reporting measurements (instead of binary information) will enable the eNodeB RRM function to learn from historical data and enable the eNodeB RRM function to apply its own thresholds for improved protection of primary users. Since the eNodeB can analyze and combine the DFS measurements from the various UEs connected to it, the decision to select different carriers for a given UE ultimately resides with that eNodeB. However, if the decision is made at each UE, the network will have to follow whatever the UE indicates to ensure the protection of potential primary users.

[0064] Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA)

[0065] Figure 3 FIG. is a schematic diagram showing communication between a UE 300 and an eNodeB 320 according to an example embodiment. The UE 300 can be a mobile phone, a computer, or other wireless network device. The UE 300 includes a processor 306 coupled to a memory 304 and a transceiver 310. The processor 306 can include several processors suitable for various operational tasks of the UE including signal processing as well as channel measurement and calculation. The memory stores application software 302 that the processor can execute upon user instruction, and the memory stores operation instructions for the UE. The processor 306 is also coupled to an input / output (I / O) circuit 308, which can include a microphone, a speaker, a display, and associated software. The transceiver 310 includes a receiver 312 and a transmitter 314 suitable for wireless communication with the eNodeB 320. The transceiver 310 typically communicates with the eNodeB 320 over various communication channels. For example, the transceiver 310 sends uplink information to the eNodeB 320 over the Physical Uplink Control Channel PUCCH and the Physical Uplink Shared Channel PUSCH. Correspondingly, the transceiver 310 receives downlink information from the eNodeB 320 over the Physical Downlink Control Channel PDCCH and the Physical Downlink Shared Channel PDSCH.

[0066] The base station 320 includes a processor 326 coupled to a memory 324, a symbol processing circuit 328, and a transceiver 330 via a bus 336. The processor 326 and the symbol processing circuit 328 may include a number of processors adapted to perform various operational tasks including signal processing as well as channel measurement and calculation. The memory stores application software 322 that the processor may execute for a specific user, and stores operation instructions for the eNodeB 320. The transceiver 330 includes a receiver 332 and a transmitter 334 adapted to perform wireless communication with the UE 300. The transceiver 330 generally communicates with the UE 300 over various communication channels. For example, the transceiver 330 transmits downlink information to the UE 300 on the physical downlink control channel PDCCH and the physical downlink shared channel PDSCH. The transceiver 330 also transmits specific downlink information to the UE 300 on 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 on the physical uplink control channel PUCCH and the physical uplink shared channel PUSCH.

[0067] According to an example embodiment, an E-UTRAN cell such as the eNodeB 320 may be deployed in an unlicensed or ASA frequency band, where LTE user equipment shares radio resources with other users having equal priority, but follows a strict 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 issues.

[0068] Reference Figure 4A , in the downlink direction, the situation is similar to the DFS explained in reference Figure 2 . Here, according to an example embodiment, CSMA / CA is implemented as a non-standardized proprietary function. The UE is initialized on the LTE band 400. The eNodeB monitors the CSMA / CA band 402. If the eNodeB detects an ongoing transmission 404, the eNodeB does not transmit any downlink channels. The eNodeB monitors the timeout reference 408 and continues to monitor the CSMA / CA band 402. If the ongoing transmission ends before the timeout reference 408, the eNodeB transmits to the UE on the CSMA / CA band 406. Otherwise, if the timeout reference times out, the RRC signaling instructs the UE to vacate the CSMA / CA band 410 and initiate a handover 412.

[0069] However, the eNodeB may have to send some signals regardless of whether an ongoing transmission is detected. The eNodeB sends discovery reference signal (DRS) bursts periodically with a magnitude of several hundred milliseconds. A DRS burst can be just one subframe and includes at least the PSS, SSS, and CRS to allow the UE to discover the cell and perform measurements. For the case of sharing a cell ID, CSI-RS may also be sent during the DRS occasion. The periodic PSS / SSS transmission also enables the UE to obtain rough time and frequency synchronization with that cell. On the network side, the RRM measurement report based on the DRS enables the eNodeB to decide whether to configure a cell on a determined unlicensed or ASA band for a given UE. In addition to the DRS, the eNodeB needs to periodically send a tracking reference signal (TRS) with a much smaller periodicity than that of the DRS, such as 5 ms or 10 ms. The TRS waveform enables the UE to perform automatic gain control (AGC) as well as fine time and frequency synchronization ("tracking"). This TRS waveform can be based on the existing CRS waveform. This will have the additional benefit of being useful for channel state information acquisition in the case of a CRS-based transmission mode. Additionally, the eNodeB may periodically send a channel state information reference signal (CSI-RS) to allow the acquisition of channel state information at the UE for a CSI-RS-based transmission mode. The UE will be configured for CSI measurement and reporting according to the CSI transmission at the eNodeB.

[0070] Refer again to Figure 3, it may be preferable not to use some downlink channels with CSMA / CA. For example, the Physical Broadcast Channel (PBCH) will not be transmitted in cells on unlicensed or ASA frequency bands. Therefore, the UE will not be able to camp on such cells. Similarly, system information will also not be sent. Therefore, such cells can only be configured as SCell, and the PCell will always be configured on licensed spectrum. It may also be beneficial to transmit the Physical Hybrid ARQ Indicator Channel (PHICH) in unlicensed or ASA spectrum. Alternatively, the UL grant sent in the DCI may be used as an implicit ACK / NACK indicator by scheduling a retransmission of a previous UL grant. The Physical Control Format Indicator Channel (PCFICH) may or may not be transmitted in unlicensed or ASA spectrum. If the 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). And for PDSCH transmission with cross-carrier scheduling, the CFI is known through configuration. By comparison, since the PCFICH is transmitted in the same subframe as the PDCCH, it may be transmitted every time the PDCCH is transmitted. Finally, since the Physical Multicast Channel (PMCH) is semi-statically scheduled by the MBMS Coordination Entity (MCE) on reserved resources, it may be beneficial not to transmit the PMCH in unlicensed or ASA spectrum. Otherwise, for unicast downlink transmission, when 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 indicator. If the CSMA / CA function indication for a given cell on a given carrier is BUSY, the eNodeB does not send (E)PDCCH or PDSCH to any UE. The eNodeB may still send other signals or channels according to the above suggestions. Alternatively, if the CSMA / CA function indication for a given cell on a given carrier is IDLE, the eNodeB may send (E)PDCCH and / or PDSCH transmission, and the eNodeB transmits according to LTE Release 12.

[0071] Reference Figure 4B, The uplink operation on the CSMA / CA frequency band is similar to the downlink operation. Initialize the UE on LTE band 400. The UE monitors CSMA / CA frequency band 420. If the UE detects an ongoing transmission 422, the UE does not send any uplink channels. The UE monitors the timeout reference 426 and continues to monitor CSMA / CA frequency band 420. If the ongoing transmission ends before the timeout reference 426, the UE sends 424 to the eNodeB on the CSMA / CA frequency band. Otherwise, if the timeout reference expires, the UE sends a BUSY report 428 to the eNodeB. RRC signaling instructs the UE to vacate the CSMA / CA frequency band 430 and initiate a handover 432.

[0072] When the CSMA / CA function at 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) transmission so as not to interfere with ongoing transmissions. Transmitting the physical uplink control channel (PUCCH) in unlicensed or ASA spectrum may also be beneficial. In this case, the PUCCH is only transmitted on the PCell in licensed spectrum. If PUCCH transmission is allowed in unlicensed or ASA spectrum, several UE behaviors can be envisioned.

[0073] In one case, the UE follows the present UE procedure for PUCCH transmission, which is independent of the indication of the CSMA / CA function at the UE for the subframe for scheduling PUCCH transmission. Collisions with ongoing transmissions generally cannot be avoided, and the PUCCH may not be properly received at the eNodeB.

[0074] Alternatively, the UE may perform any PUCCH transmission based on the indication of the CSMA / CA function at the UE for the subframe for scheduling PUCCH transmission. If the CSMA / CA function at the UE indicates BUSY, the UE does not transmit on the PUCCH in the considered subframe. Otherwise, if the CSMA / CA function at the UE indicates IDLE, the UE transmits the PUCCH according to the schedule.

[0075] The same principle can apply to the physical uplink shared channel (PUSCH). In one embodiment, the UE follows the present UE procedure for PUSCH transmission, which is independent of the indication of the CSMA / CA function at the UE for the subframe for scheduling PUSCH transmission. Collisions with ongoing transmissions generally cannot be avoided, and the PUSCH may not be properly received at the eNodeB.

[0076] Alternatively, the UE may be based on any PUCCH transmission at the UE for the subframe used for scheduling PUCCH transmissions where there is an indication of the CSMA / CA function. If the CSMA / CA function at the UE indicates BUSY, the UE does not transmit on the PUSCH in the considered subframe. Otherwise, if the CSMA / CA function at the UE indicates IDLE, the UE transmits the PUSCH according to the schedule.

[0077] Similar to the DFS case, hidden stations must be considered. The above solutions for PUSCH and PUCCH transmissions are concerned with the UE behavior in cases where there is an indication of the CSMA / CA function at the UE for the subframe used for scheduling PUSCH / PUCCH transmissions. In the case of a hidden station whose waveform is detectable at the UE but not detected at the eNodeB, the eNodeB may continue to schedule that UE. If the UE follows conventional LTE Rel 12 operation, this will lead to performance degradation of the eNodeB-to-UE link and the link to / from the hidden station because the corresponding transmissions will continue to collide, potentially creating excessive interference such that: (a) reliable communication is no longer feasible; or (b) at least an acceptable quality of service (QoS) can no longer be provided. Wherein if the CSMA / CA function at the UE indicates BUSY, the opposite case where the UE does not transmit on the PUSCH or PUCCH in the subframe will also degrade performance because packets and HARQ ACK / NACK transmissions are discarded in the BUSY subframe. Theoretically, the above DFS scheme may be used again to allow the UE to notify the eNodeB about the BUSY state of the cell or carrier so that the eNodeB MAC (or RRC) layer may take action to schedule the UE on a different CC to prevent additional collisions. Thus, instead of the "DFS event" triggered by the DFS function, the CSMA / CA function will indicate BUSY and otherwise the procedure may be used again. However, the time scale for DFS is typically much larger than the time scale for LBT in the case of CSMA / CA. Therefore, the example embodiments provide a separate procedure for addressing hidden stations in the case of CSMA / CA.

[0078] The purpose of the example embodiments is to enable the UE higher layers to notify the eNodeB higher layers about the indication of the UE CSMA / CA function in the subframe in which the UE is scheduled for uplink transmission. Since the UE can always follow the existing LTE Rel 12 specification when the UE CSMA / CA function indicates IDLE, this state is not signaled to the eNodeB higher layers. Therefore, several embodiments provide actions that the eNodeB higher layers (e.g., the eNodeB MAC scheduler) may take in the subframe for scheduling PUSCH or PUCCH transmissions and where the UE CSMA / CA function indicates BUSY.

[0079] Because the overall system performance, and in particular the user throughput perceived at the UE, is maximized, the eNodeB can take faster actions by avoiding scheduling the UE on carriers occupied by hidden stations. It is preferred to use PHY or MAC layer mechanisms, with the former having lower latency compared to the latter. First, to reduce latency, assume that the UE has been configured with up to five serving cells on corresponding component carriers (Figure 1). According to an example embodiment, the serving cells are sorted in ascending order based on the ServCellIndex configured via RRC signaling. However, other sorting and addressing mechanisms are not excluded. Then, four serving cells other than the PCell are assigned symbols {00, 01, 10, 11}, such that the serving cell (SCell) with the lowest ServCellIndex corresponds to 00, the serving cell (SCell) with the second lowest ServCellIndex corresponds to 01, and so on. If less than four SCell are configured, the unused symbols are reserved (e.g., {01, 10, 11} in the case of a single SCell configuration). Other mappings are not excluded. To ensure the lowest latency, L1 (PHY) signaling is introduced to notify the higher layers of the eNodeB about the BUSY indication from the UE CSMA / CA function in the subframe for scheduling PUSCH or PUCCH transmissions.

[0080] Therefore, a new PUCCH format that is always transmitted on the PCell is introduced. The new PUCCH format is the same as the existing PUCCH format 1b. However, instead of representing ACK / ACK, ACK / NACK, NACK / ACK, and NACK / NACK / DTX, the QPSK symbols encode the four serving cell indices {00, 01, 10, 11}. For illustrative purposes, this new PUCCH format is referred to as format 1c. The eNodeB receiver can distinguish between PUCCH format 1b and PUCCH format 1c by code division multiplexing, such that the two PUCCH formats can share the same time and frequency resources. Alternatively, the new PUCCH format can have its own time and frequency resources for the PUCCH region. If the PUCCH capacity is not an issue, as in the case of small cells, CDM is preferred for improved spectral efficiency. In the case where the CSMA / CA function at the UE indicates BUSY in the subframe for scheduling PUSCH or PUCCH transmissions, the UE does not transmit the scheduled PUSCH or PUCCH, but instead transmits (to the eNodeB) the BUSY instruction via the PUCCH format 1c on the PCell. Several UE behaviors are envisioned, all of which assume that the eNodeB schedules only one SCell at a time to prevent any ambiguity at the eNodeB when receiving the PUCCH format 1c.

[0081] In one embodiment, PUCCH format 1c indicates in which serving cell the BUSY instruction occurs. For example, the eNodeB may schedule an uplink transmission in subframe n + k (k > 0) via a UL grant in the DCI received in subframe n. Shortly before the scheduled uplink transmission occurs, the CSMA / CA function at the UE starts listening to the medium and indicates to the higher layers of the UE whether it is IDLE or BUSY. If IDLE is indicated, the UE performs the scheduled transmission according to the received DCI. If BUSY is indicated, the UE ignores the DCI scheduling the uplink transmission under consideration and instead sends PUCCH format 1c on the PCell coding (in QPSK symbols) of the serving cell where the conflict occurs.

[0082] Since the eNodeB expects PUSCH or PUCCH transmission on a specific serving cell, the PUCCH format 1c transmission does not actually convey additional information to the higher layers of the eNodeB. Thus, in different embodiments, the CSMA / CA function at the UE listens to all configured serving cells shortly before the scheduled uplink transmission. If IDLE is indicated for the serving cell on the scheduled transmission, the UE performs the scheduled transmission according to the received DCI. If BUSY is indicated, the UE ignores the DCI scheduling the uplink transmission under consideration and instead sends PUCCH format 1c on the PCell of the serving cell that is coded (in QPSK symbols) and for which the CSMA / CA function at the UE indicates IDLE. This does not guarantee that the corresponding serving cell at subframe n + k 2 (k 2 (k > k) is IDLE, but at least the eNodeB does not continue to schedule uplink transmission on the same serving cell.

[0083] Introducing a new PUCCH format 1c requires the eNodeB receiver to monitor the new PUCCH format. Thus, MAC layer procedures can be superior to the above PHY procedures. However, in addition to the uplink resources that must remain unused by not sending PUCCH or PUSCH due to the medium being BUSY, transmitting a MAC control element requires the UE to have available uplink resources. Also, the time to prepare for PUSCH transmission carrying the MAC CE can take longer, such that carrier sensing must occur much earlier than in the case of the new PUCCH format, thereby increasing the likelihood of the CSMA / CA function indicating IDLE at the UE in addition to the medium being BUSY during subframe n + k. If the UE has to send a scheduling request (SR) to send the MAC CE, the delay will be further increased. However, MAC layer procedures can still have their advantages. For example, the necessity of imposing the limit of scheduling only a single SCell at a time will be removed. Instead, one octet (8 bits) in the MAC CE can be used to encode all four SCells simultaneously. Again, based on the ServCellIndex sorted in ascending order and represented by {00, 01, 10, 11} for up to four serving (SCells), so the serving cell (SCell) with the lowest ServCellIndex corresponds to 00, the serving cell (SCell) with the second lowest ServCellIndex corresponds to 01, and so on. Also, 8 bits in the octet of the MAC CE correspond to the four SCells through the following mapping. While other mappings and orderings are not excluded, the first two bits correspond to the serving cell represented by {00}, the third and fourth bits correspond to the serving cell represented by {01}, the fifth and sixth bits correspond to the serving cell represented by {10}, and the last two bits correspond to the serving cell represented by {11}. If the bit at a position corresponds to the position itself, the serving cell corresponding to this indication is indicated as IDLE. Otherwise, it is indicated as BUSY, and these two bits indicate to which serving cell the eNodeB should switch. Thus, the bit position in the octet encodes which serving cell the bit at that position belongs to, and the bit itself encodes the same information sent on PUCCH format 1c for the single cell above. For example, the octet {00010011} means that the first, second, and fourth serving cells are IDLE, while the transmission on the third serving cell should be sent on the first serving cell.

[0084] Within the scope of the claims, modifications of the described embodiments are possible, and other embodiments are possible.

Claims

1. A method for operating a wireless communication system on a shared spectrum, the method comprises: Initializing a user equipment, i.e., UE, on a primary serving cell, i.e., PCell, on a licensed spectrum; Configuring the UE to communicate with a secondary serving cell, i.e., SCell, operating on a carrier in the shared spectrum; Monitoring, by a base station, i.e., eNB, the shared spectrum to determine whether it is busy, i.e., BUSY; If the shared spectrum is not BUSY, transmitting to the UE on the shared spectrum; If the shared spectrum is BUSY, waiting for a first time period; and If the shared spectrum is BUSY after the first time period, instructing the UE to vacate the carrier in the shared spectrum.

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

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

4. The method according to claim 1, comprising, after the first time period, instructing the UE to vacate the shared spectrum via radio resource control signaling, i.e., RRC signaling.

5. The method according to claim 1, comprising, after the first time period, instructing the UE to deactivate the SCell via medium access control signaling, i.e., MAC signaling.

6. The method according to claim 1, the method comprises: If the shared spectrum is not BUSY, transmitting to the UE on a first plurality of channels; and Excluding a second plurality of channels from the shared spectrum.

7. The method according to claim 1, the method comprising excluding the physical broadcast channel, i.e., PBCH, from transmission on the shared spectrum.

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

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

10. A method for operating a communication system on a shared spectrum, the method comprises: Initializing a user equipment, i.e., UE, on a primary serving cell, i.e., PCell, operating on a licensed spectrum; Transmitting data from the UE to at least one secondary serving cell, i.e., SCell, operating on the shared spectrum; Monitoring, by the UE, the at least one SCell to determine a busy state, i.e., BUSY state; If the at least one SCell is not BUSY, transmitting to the base station on the at least one SCell; and If the at least one SCell is BUSY, reporting the BUSY state of the at least one SCell to the base station.

Images