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

Abstract

The present invention relates to a method and apparatus for transmitting an LTE waveform in a shared spectrum by carrier sensing. In the described example, 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 the 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 201580029753.8, whose application date is June 5, 2015 and whose name is “Method and apparatus for transmitting LTE waveform in shared spectrum through carrier sensing”. 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. Therefore, parts 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 frequency bands). Moreover, in this hybrid model, the licensed spectrum is granted to the primary user with the highest priority (e.g., for naval radar applications). In addition, secondary users are allowed to use the licensed frequency band during the inactive segment during which the primary user does not send a waveform in the frequency band under consideration. These secondary users can have different priorities. For example, a given frequency band authorized 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 this frequency band, and only under the condition that neither the primary user nor the secondary user (e.g., public safety user) with a higher priority occupies the frequency band. This policy-based spectrum use is sometimes referred to as authorized shared access (ASA). From this perspective, there is no need to distinguish between unlicensed and licensed shared access, because the same technology can be used to ensure fairness and policy compliance whenever the band is used by many users.

[0003] In the above example of authorized shared access, spectrum sharing can be facilitated by dynamic schemes, sometimes referred to as listen-before-talk (LBT) schemes, and by semi-static schemes, such as through a geographic location database (GLDB). For example, such a database can map the frequency usage of such a band to a geographic area or time of day. Due to the time used to update these databases and propagate them to all participating users, they cannot change dynamically. As the name implies, LBT schemes are more dynamic and do not rely on semi-statically configured databases. 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 transmissions. 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 applies to situations when a secondary user must grant priority to a primary user. Because the secondary user must stop transmitting when the secondary user detects a military, meteorological, or automotive radar waveform, it is often called dynamic frequency selection (DFS). Hence, the secondary user vacates a given frequency band or channel (a channel is a further subdivision of a frequency band) when it detects a primary user, and the secondary user attempts to transmit on a different frequency band or channel resulting in what is known as dynamic frequency selection. Similarly, in case of CSMA / CA, when the transmitter detects an ongoing transmission of the same priority, it chooses not to transmit in order to try again at a later point in time. Hence, this is what is known as carrier sense multiple access with collision avoidance. Hence, the two main differences between DFS and CSMA / CA are the time scale over which the sensing occurs and the action taken by the transmitter when an ongoing transmission 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, the radio resources are shared between users of equal priority and it is considered a multiple access scheme. However, with DFS, the primary user has a higher priority. Therefore, to guarantee the contention delay of the CSMA / CA scheme, carrier sensing (CS) and collision avoidance (CA) occur in the order of tens of microseconds (us), but DFS may require several seconds.

[0004] The CS / CA multiple access scheme is in sharp contrast to other common multiple access techniques 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 Global System for Mobile Communications (GSM), CDMA in Universal Mobile Telecommunications System (UMTS) and Orthogonal Frequency Division Multiple Access (OFDMA) in Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) attempt to orthogonalize 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 given time slots in a given portion of the radio spectrum, thereby essentially preventing conflicts. This makes it particularly challenging to operate them in radio resources shared by way of CS / CA multiple access schemes, as users following these kinds of protocols and procedures will lose out to users following the predefined scheduling or radio resource allocation according to their protocols and procedures when competing for the available radio resources.

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

[0006] FIG1 is an example wireless telecommunication network of the prior art. The exemplary telecommunication network includes a master eNodeB 110 operating in a primary cell (PCell) 100 and eNodeBs 112, 114, 116, and 118 operating in secondary cells (SCell1 to SCell4) 102, 104, 106, and 108, respectively. A handset or other user equipment (UE) 120 is shown communicating with the eNodeB 110 of the PCell 100. The UE 120 may also communicate with one or more eNodeBs of the secondary cells. In this example, SCell is a logical concept, so the eNodeB 110 may operate multiple SCells (102 to 108).

[0007] In addition, the eNodeB 110 controls the radio resources in its cell 100 by means of a Radio Resource Control (RRC) protocol and multiple access of users connected to its cell by means of a Medium Access Control (MAC) protocol. For example, the RRC protocol configures the carriers on which a 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 combines with the RRC protocol to control 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 known as carrier aggregation, in which a UE can be configured with one primary cell (PCell) and up to four secondary cells (SCells). The PCell can only be changed by switching, while the SCell is configured by RRC signaling. Specifically, the UE does not wish to receive system information by decoding the physical broadcast channel (PBCH) on the secondary component carrier (SCC), or does not wish to monitor the common search space of the SCell to receive the physical downlink control channel (PDCCH) whose CRC is scrambled by the SI-RNTI to receive system information (SI) on the downlink shared channel (DL-SCH). In addition, the UE may 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 means for the UE physical layer (PHY) to indicate the Radio Link Failure (RLF) to the UE higher layers through the MAC layer. This is because in Evolved Universal Terrestrial Radio Access (E-UTRA), one can always rely on the connectivity provided by the PCell, which provides robustness through RLM and other fallback procedures. Alternatively, the SCell operates as a supplementary serving cell, which can be activated if additional capacity is required for data communications with the UE. To this end, the MAC layer can activate the configured SCell through the MAC Control Element (CE). SCell activation can require The time between the RRC reconfiguration of the SCell and the PCell depends 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 triggered by a configurable offset and threshold. In 3GPP Long Term Evolution, this is achieved through measurement objects and configured RRC signaling. If the measurements are readily available at the eNodeB, the RRC reconfiguration of the SCell or PCell can be significantly reduced in latency from a few seconds to tens of seconds or hundreds of milliseconds. Although the eNodeB can only start a cell that has been configured as an SCell, it can configure the UE to measure RSRP on any cell. By comparison, the eNodeB can use the measurement report of any cell to start a cell, such as in the case of SCell startup, or RRC reconfigure the UE to add / remove SCells or even change PCells.

[0009] After a 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 PUSCH transmission in subframe n+k, where k>0 is determined by a predetermined rule.

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

[0011] Although the RRM functionality resides in the eNodeB, which in turn controls all radio resources through RRC, it relies on the UE to discover cells and report associated measurements. To this end, in LTE Release 8 to 11, the eNodeB sends a primary synchronization signal (PSS), a secondary synchronization signal (SSS), and a cell-specific reference signal (CRS) in each radio frame. In addition to sending the CRS in each subframe of the radio frame, the PSS and SSS each occupy one OFDM symbol per half frame, which allows the UE to discover and measure cells within a 6ms measurement window without a priori knowledge of the timing of a given cell. In addition, in order 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), the measurement restrictions introduced in LTE Rel 10 are supported, and the UE must be able to discover cells in only one subframe and potentially discover the DwPTS area of ​​a specific subframe. To promote energy saving and reduce interference, LTE Release 12 introduces "discovery bursts" (including PSS, SSS and CRS transmissions) and, if configured, introduces channel state information reference signals (CSI-RS) for transmission point (TP) identification in shared cell ID situations. For example, multiple TPs can share the same physical cell ID and can only be identified by their corresponding CSI-RS resource element (RE) configurations. PSS, SSS, CRS and CSI-RS (if configured) form discovery reference signals (DRS) and are sent during DRS situations. DRS situations are similar to LTE Release 9 positioning reference signal (PRS) situations in that they have a configured or specific length (e.g., the number of subframes) and periodicity. Ideally, the length of the DRS situation does not exceed the UE measurement window of 6ms and may be as short as one subframe. Reasonable periodicity for the DRS situation is hundreds of milliseconds, and DRS bursts can operate as beacons in other wireless communication systems (such as CSMA / CA). Summary of the invention

[0012] In a first embodiment, a method of 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 whether 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 Long Term Evolution (LTE) communication system according to the prior art.

[0015] Figure 2 The present invention is a flow chart showing a Long Term Evolution (LTE) communication system operating on an Authorized Shared Access (ASA) spectrum.

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

[0017] Figure 4A A schematic diagram illustrating 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 A schematic diagram illustrating 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 an Orthogonal Frequency Division Multiple Access (OFDMA) cellular communication system, such as 3GPP Long Term Evolution (LTE) apparatus and methods operating in a radio frequency shared with a primary transceiver. The primary transceiver may be a naval, automotive radio, or other transceiver with a higher priority. Although specific terms are employed herein, they have only a general and descriptive meaning 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 you talk

[0035] LTE: Long Term Evolution

[0036] MAC: Media Access Control Protocol

[0037] MIMO: Multiple Input Multiple Output

[0038] OFDMA: Orthogonal Frequency Division Multiple Access

[0039] OOR: Out of Scope

[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: Ranking 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: Subsynchronous 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 a shared access spectrum. This is because the radio resource management function resides in the eNodeB in the network and the radio resources are controlled only by the eNodeB. The dynamic frequency selection (DFS) scheme usually allows enough time (e.g., a few seconds) to change the frequency band or carrier when the primary user is detected. Therefore, the RRC signaling based on the handover and the SCell activation or deactivation under the MAC control are sufficient to free up the frequency band for the primary user. The 3GPP LTE communication standard currently lacks protocols, procedures and measurements that allow the UE to take any action when the primary user is detected on the carrier where the UE is configured to send data. In addition, although other wireless cellular communication standards do allow the UE to initialize handover, mobility control in LTE is completely controlled by the eNodeB. Here, mobility includes load balancing situations, in which the eNodeB can add or remove SCells or change PCells for stationary UEs. For both the ASA-based scheme with a primary user and the CSMA / CA-based scheme without a primary user, there can be so-called "hidden sites". Hidden sites are transmitters, such as primary users, whose transmissions can only be detected at the receiving end of a communication link sharing the wireless medium. For example, in LTE, only UEs can detect waveforms sent from "hidden sites", except that the eNodeB is completely oblivious to the existence of hidden sites.

[0062] Figure 2 Flowchart showing the operation of the first embodiment. The UE is initialized in step 200 to operate on the LTE band in conjunction with the PCell. The ASA band is configured by the eNodeB as a conventional LTE band and operates as a conventional LTE band, and the UE operates in the ASA band 202. The UE is prohibited from camping on a cell operating in the ASA band by existing means such as prohibiting broadcasting through system information. Therefore, all UEs connected to the ASA band are in RRC connection mode and are thus under the full control of the eNodeB. The eNodeB configures all UEs connected to the ASA band to perform RRM measurements 204 according to the existing LTE specifications (e.g., Release 8 to 12). DFS is supported by each UE through a non-standardized (proprietary) implementation. If the UE detects a hidden site (from the UE perspective, all primary users are hidden sites) 206, the UE physical layer (PHY) indicates to the higher layers of its protocol stack that an RRM measurement report is triggered according to the existing LTE Rel 8 / 9 / 10 / 11 / 12 procedure. Throughout the specification (e.g., "DFS Event"), RRM measurement reports triggered by a non-standardized (proprietary) DFS function at the UE are bound to specific values ​​of the RRC Information Element (IE) RSRP Range. For example, a 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 report the DFS event to the eNodeB using the existing RRM measurement reporting procedure (e.g., RSRP measurement report with an OOR indicator indicating a DFS event) 208. The eNodeB RRM function will reinterpret the RSRP measurement report as a DFS / OOR event according to the standardized link and subsequently vacate the ASA band for the primary user 210 and will reconfigure the UE via existing RRC signaling 212. Such RRC signaling covers handover in the case of a PCell or SCell reconfiguration in the case of an SCell. Alternatively, if the RRM function at the eNodeB believes that the ASA band needs to be vacated only temporarily for the primary user, 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 specifications report DFS / OOR events as required by regulators worldwide for each ASA band, the 3GPP LTE specifications will introduce performance requirements that are useful for testing UEs, but no new measurements will be defined in the specifications to support DFS in 3GPP LTE.

[0063] In another embodiment, instead of reinterpreting the existing measurement reports as DFS / OOR events, new measurement reports and associated procedures are specifically defined for the purpose of indicating (to E-UTRAN) the presence of hidden sites or primary users. All UEs connected to cells 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 DFS measurements periodically or triggered or periodically triggered. The eNodeB will configure measurement events and associated thresholds and offsets to control DFS measurement reports for UEs connected to the ASA band. Therefore, the precise measurement procedure will be determined by the specification. However, the actions taken by the network can be similar to those in the above-described embodiments to include UE switching, SCell reconfiguration, and SCell deactivation. Reporting measurements (rather than 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. Because the eNodeB is able to analyze and combine DFS measurements from various UEs connected to it, the decision to select different carriers for a given UE ultimately resides at the eNodeB. However, if the decision is made at each UE, the network will have to follow the UE instructions anyway to ensure protection of potential primary users.

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

[0065] Figure 3 Schematic diagram showing communication between UE 300 and eNodeB 320 according to an example 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. Processor 306 may include several processors suitable for various operational tasks of UE including signal processing and channel measurement and calculation. The memory stores application software 302 that the processor can execute by the user's instructions, and the memory stores operating instructions for UE. Processor 306 is also coupled to input / output (I / O) circuit 308, which may include a microphone, a speaker, a display and related software. Transceiver 310 includes a receiver 312 and a transmitter 314 suitable for wireless communication with eNodeB 320. Transceiver 310 typically communicates with eNodeB 320 on various communication channels. For example, transceiver 310 sends uplink information to eNodeB 320 via a physical uplink control channel PUCCH and a physical uplink shared channel PUSCH. Accordingly, the transceiver 310 receives downlink information from the eNodeB 320 on a physical downlink control channel, PDCCH, and a 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 several processors suitable for various operational 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 stores operating 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 generally communicates with the UE 300 on various communication channels. For example, the transceiver 330 sends downlink information to the UE 300 on the physical downlink control channel PDCCH and the physical downlink shared channel PDSCH. The transceiver 330 also sends 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. Accordingly, 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 eNodeB 320 may be deployed in an unlicensed or ASA band, where LTE user equipment shares radio resources with other users of equal priority, but follows a strict Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA) procedure / protocol. Because 3GPP Long Term Evolution was specifically designed to operate in licensed spectrum, a fundamental problem exists.

[0068] refer to Figure 4A , in the downlink direction, the situation is similar to that of reference Figure 2 The DFS explained. 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 hears 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 sends 406 to the UE on the CSMA / CA band. Otherwise, if the timeout reference times out, 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 a discovery reference signal (DRS) burst with a periodicity of hundreds of milliseconds. The DRS burst may be only one subframe and include at least PSS, SSS and CRS to allow the UE to discover the cell and perform measurements. For the case of shared cell IDs, CSI-RS can also be sent during the DRS situation. Periodic PSS / SSS transmission also enables the UE to obtain coarse time and frequency synchronization with that cell. On the network side, DRS-based RRM measurement reports enable the eNodeB to decide whether to configure a cell on a determined unlicensed or ASA band for a given UE. In addition to DRS, the eNodeB needs to periodically send a tracking reference signal (TRS) with a periodicity much smaller than that of DRS, such as 5ms or 10ms. The TRS waveform enables the UE to perform automatic gain control (AGC) and fine time and frequency synchronization ("tracking"). This TRS waveform can be based on an 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. In addition, the eNodeB may periodically transmit a channel state information reference signal (CSI-RS) to allow acquisition of channel state information at the UE for CSI-RS based transmission modes. The UE will be configured for CSI measurement and reporting based on the CSI transmission at the eNodeB.

[0070] Reference again 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 bands. Therefore, the UE will not be able to camp on such a cell. Similarly, system information will not be sent. Therefore, such a cell can only be configured as an SCell, and the PCell will always be configured on the licensed spectrum. It may also be beneficial to send the physical hybrid ARQ indicator channel (PHICH) in the unlicensed or ASA spectrum. Alternatively, the UL grant sent in the DCI may be used as an implicit ACK / NACK indication by scheduling the retransmission of the previous UL grant. The physical control format indicator channel (PCFICH) may or may not be transmitted in the unlicensed or ASA spectrum. If the extended PHICH duration is configured, the control format indicator (CFI) is known by 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 transmissions scheduled across carriers, the CFI is known by configuration. By comparison, because the PCFICH is sent in the same subframe as the PDCCH, it may be sent every time the PDCCH is sent. 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 send the PMCH in unlicensed or ASA spectrum. Otherwise, for unicast downlink transmissions, 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 LTERelease12. In one embodiment, the CSMA / CA function at the eNodeB returns a binary indication. If the CSMA / CA function of a given cell on a given carrier indicates 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 recommendations. Alternatively, if the CSMA / CA functionality of a given cell on a given carrier indicates IDLE, the eNodeB may send (E)PDCCH and / or PDSCH transmissions, which the eNodeB transmits in accordance with LTE Release-12.

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

[0072] When the CSMA / CA functionality 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) transmissions so as not to interfere with ongoing transmissions. It may also be beneficial to send the Physical Uplink Control Channel (PUCCH) in unlicensed or ASA spectrum. In this case, the PUCCH is sent only on the PCell in the licensed spectrum. If PUCCH transmissions are allowed in the unlicensed or ASA spectrum, several UE behaviors may be envisioned.

[0073] In one case, the UE follows existing UE procedures for PUCCH transmissions, which are independent of the indication of CSMA / CA functionality at the UE for the subframes scheduling PUCCH transmissions.Collisions with ongoing transmissions generally cannot be avoided and the PUCCH may not be properly received at the eNodeB.

[0074] Alternatively, the UE may transmit any PUCCH based on an indication of CSMA / CA functionality at the UE for the subframe for which PUCCH transmission is scheduled. If the CSMA / CA functionality at the UE indicates BUSY, the UE does not transmit on the PUCCH in the subframe under consideration. Otherwise, if the CSMA / CA functionality at the UE indicates IDLE, the UE transmits PUCCH as scheduled.

[0075] The same principle may apply to the Physical Uplink Shared Channel (PUSCH). In one embodiment, the UE follows existing UE procedures for PUSCH transmissions, which is independent of the indication of CSMA / CA functionality at the UE for the subframes that schedule PUSCH transmissions. Collisions with ongoing transmissions cannot generally be avoided, and the PUSCH may be inappropriately received at the eNodeB.

[0076] Alternatively, the UE may transmit any PUCCH based on an indication of CSMA / CA functionality at the UE for the subframe for which PUCCH transmission is scheduled. If the CSMA / CA functionality at the UE indicates BUSY, the UE does not transmit on the PUSCH in the subframe under consideration. Otherwise, if the CSMA / CA functionality at the UE indicates IDLE, the UE transmits PUSCH as scheduled.

[0077] Similar to the case of DFS, hidden sites must be considered. The above solution for PUSCH and PUCCH transmissions is concerned with the UE behavior in the case where the UE indicates CSMA / CA functionality at BUSY for a subframe used to schedule PUSCH / PUCCH transmissions. In the case of a hidden site 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 result in a degradation in the performance of the eNodeB-to-UE link and the link to / from the hidden site, as 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. Where the CSMA / CA functionality at the UE indicates BUSY, the opposite case where the UE does not transmit in a subframe on PUSCH or PUCCH will similarly degrade performance because packets and HARQ ACK / NACK transmissions are dropped in BUSY subframes. In theory, it is possible to use the above-described DFS scheme again to allow the UE to inform the eNodeB about the BUSY state of a cell or carrier so that the eNodeB MAC (or RRC) layer may take action to schedule the UE on a different CC to prevent further conflicts. Therefore, instead of a "DFS event" triggered by the DFS function, the CSMA / CA function will indicate BUSY, otherwise the procedure can be used again. However, the time scale for DFS is typically much larger than the time scale for LBT as in the case of CSMA / CA. Therefore, the example embodiments provide a separate procedure to address hidden sites in the case of CSMA / CA.

[0078] The purpose of the example embodiments is to have the UE higher layers inform the eNodeB higher layers about the indication of the UE CSMA / CA function in the subframes in which the UE is scheduled for uplink transmission. Because the UE can always follow the existing LTE Rel 12 specification in the case where 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) can take in the subframes for which PUSCH or PUCCH transmissions are scheduled and 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 is able to take faster action by avoiding scheduling the UE on a carrier occupied by a hidden site, using a PHY or MAC layer mechanism is preferred, where the former has lower latency compared to the latter. First, in order to reduce latency, it is assumed that the UE has been configured with up to five serving cells on the corresponding component carrier (Figure 1). According to an example embodiment, the serving cells are sorted in ascending order based on the ServCellIndex configured by RRC signaling. However, other sorting and addressing mechanisms are not excluded. Then, the four serving cells other than the PCell are assigned symbols {00, 01, 10, 11}, so 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 SCells are configured, unused symbols are reserved (e.g., {01, 10, 11} in the case of configuring a single SCell). Other mappings are not excluded. To guarantee the lowest delay, L1 (PHY) signaling is introduced to inform the eNodeB higher layers about the BUSY indication from the UE CSMA / CA function in the subframes for scheduled PUSCH or PUCCH transmissions.

[0080] Therefore, a new PUCCH format is introduced that is always transmitted on the PCell. 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 four serving cell indices {00, 01, 10, 11}. For illustration purposes, this new PUCCH format is called format 1c. The eNodeB receiver can distinguish between PUCCH format 1b and PUCCH format 1c by code division multiplexing, so 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 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 functionality at the UE indicates BUSY in a subframe for a scheduled PUSCH or PUCCH transmission, the UE does not transmit PUSCH or PUCCH as scheduled, but instead indicates a BUSY instruction (to the eNodeB) via a PUCCH format 1c transmission 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 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 begins listening to the medium and indicates to the UE higher layers whether it is IDLE or BUSY. If IDLE is indicated, the UE proceeds to the scheduled transmission based on the received DCI. If BUSY is indicated, the UE ignores the DCI for scheduling the uplink transmission being considered, and instead sends PUCCH format 1c on the PCell encoding (in QPSK symbols) of the serving cell where the conflict occurs.

[0082] Because the eNodeB expects a PUSCH or PUCCH transmission on a specific serving cell, the PUCCH format 1c transmission actually conveys no additional information to the eNodeB higher layers. Therefore, in different embodiments, the CSMA / CA function at the UE listens to all configured serving cells before the scheduled uplink transmission. If IDLE is indicated for the serving cell on the scheduled transmission, the UE proceeds to 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 encoded (in QPSK symbols) of the serving cell (the serving cell on which the CSMA / CA function at the UE indicates IDLE). This does not guarantee that the corresponding serving cell is IDLE at the future subframe n+k2 (k2>k), but at least the eNodeB does not continue to schedule uplink transmissions on the same serving cell.

[0083] The introduction of the new PUCCH format 1c requires the eNodeB receiver to monitor the new PUCCH format. Therefore, the MAC layer procedures can be superior to the above-mentioned PHY procedures. However, in addition to the fact that unused uplink resources must be reserved by not sending PUCCH or PUSCH because the medium is BUSY, sending MAC control elements requires the UE to have available uplink resources. In addition, the time to prepare the PUSCH transmission carrying the MAC CE can take longer, so that carrier sensing must occur much earlier than in the case of the new PUCCH format, thereby increasing the possibility that the CSMA / CA function at the UE indicates IDLE in addition to the medium being BUSY during subframe n+k. If the UE must send a scheduling request (SR) to send a MAC CE, the delay will be further increased. However, the MAC layer procedures can still have their advantages. For example, the necessity of the imposed restriction of scheduling only a single SCell at a time will be stopped. Instead, one octet (8 bits) in the MAC CE can be used to encode all four SCells at the same time. Up to four services (SCells) are again sorted in ascending order based on ServCellIndex and represented by {00, 01, 10, 11}, so the service cell (SCell) with the lowest ServCellIndex corresponds to 00, the service cell (SCell) with the second lowest ServCellIndex corresponds to 01, and so on. In addition, the 8 bits in the eight-bit byte of the MAC CE correspond to the four SCells through the following mapping. Although other mappings and orderings are not excluded, the first two bits correspond to the service cell represented by {00}, the third and fourth bits correspond to the service cell represented by {01}, the fifth and sixth bits correspond to the service cell represented by {10}, and the last two bits correspond to the service cell represented by {11}. If the bit at the position corresponds to the position itself, the service cell corresponding to this indication is indicated as IDLE. Otherwise, the indication is BUSY, and the two bits indicate which service cell the eNodeB should switch to. 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 a single cell above. For example, the octet {00010011} means that the first, second and fourth serving cells are IDLE, and transmissions on the third serving cell should be sent on the first serving cell.

[0084] Modifications of the described embodiments are possible, and other embodiments are possible, within the scope of the claims.

Claims

1. A method for operating a wireless communication system on a shared spectrum, comprising: Initialize a user equipment (UE) on a primary serving cell (PCell) on a licensed spectrum; configuring the UE to communicate with a secondary serving cell (SCell) operating on a carrier in the shared spectrum; After configuring the UE to communicate in the shared spectrum, a base station, i.e., an eNB, monitors the shared spectrum to determine whether it is busy, i.e., BUSY; If the shared spectrum is not BUSY, sending 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. The method according to claim 1 , wherein the shared spectrum is an unlicensed spectrum.

3. The method of claim 1, comprising accessing the shared spectrum using Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA). 4 . The method according to claim 1 , comprising instructing the UE to vacate the shared spectrum through radio resource control signaling (RRC signaling) after the first time period. 5 . The method according to claim 1 , comprising instructing the UE to deactivate the SCell through medium access control signaling (MAC signaling) after the first time period.

6. The method according to claim 1, comprising: If the shared spectrum is not BUSY, sending to the UE on a first plurality of channels; as well as A second plurality of channels is excluded from the shared spectrum.

7. The method of claim 1, comprising excluding a Physical Broadcast Channel (PBCH) from transmission on the shared spectrum. 8 . The method according to claim 1 , comprising sending, by the eNB, a discovery reference signal on the shared spectrum when the shared spectrum is BUSY.

9. The method of claim 1, comprising sending, by the eNB, a tracking reference signal on the shared spectrum.

10. A method of operating a communication system on a shared spectrum, comprising: Initializing a user equipment (UE) on a primary serving cell (PCell) operating on a licensed spectrum; Sending data from the UE to at least one secondary serving cell (i.e., at least one SCell) operating on the shared spectrum; After sending the data in the shared spectrum, the UE monitors the at least one SCell to determine a busy state, i.e., a BUSY state; If the at least one SCell is not BUSY, sending 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. The method of claim 10 , wherein the shared spectrum is an unlicensed spectrum.

12. The method of claim 10, comprising accessing the shared spectrum using Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA).

13. The method of claim 10, comprising reporting the BUSY status in an uplink control information packet on a physical uplink control channel of the PCell.

14. The method of claim 10, wherein the BUSY state is sent on a physical uplink control channel resource, the physical uplink control channel resource being semi-statically configured by radio resource control signaling from the base station.

15. The method of claim 10, wherein the BUSY state is sent on a physical uplink control channel resource, which is dynamically signaled by a downlink control information packet from the base station.

16. The method according to claim 10, comprising: Determine that the state of the at least one SCell is busy, that is, BUSY; Determine an idle state, i.e., an IDLE state, of at least another secondary serving cell; as well as The identity of the at least another secondary serving cell is sent to the base station on a physical uplink control channel of the PCell.

17. An apparatus comprising: Circuitry for initializing a user equipment (UE) on a primary serving cell (PCell) operating on a licensed spectrum; Circuitry for sending data from the UE to at least one secondary serving cell (SCell) operating on a shared spectrum; A circuit configured to monitor, by the UE, the at least one SCell to determine a busy state, i.e., a BUSY state, after sending the data in the shared spectrum; circuitry for transmitting to a base station on the at least one SCell if the at least one SCell is not BUSY; as well as A circuit is configured to report the BUSY state of the at least one SCell to the base station if the at least one SCell is BUSY. The apparatus of claim 17 , wherein the shared spectrum is an unlicensed spectrum.

19. The apparatus of claim 17, comprising accessing the shared spectrum using Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA).

20. The apparatus of claim 17, comprising reporting the BUSY status in an uplink control information packet on a physical uplink control channel of the PCell.

21. The apparatus of claim 17, wherein the BUSY state is transmitted on a physical uplink control channel resource, the physical uplink control channel resource being semi-statically configured by radio resource control signaling from the base station.

22. The apparatus of claim 17, wherein the BUSY state is sent on a physical uplink control channel resource, the physical uplink control channel resource being dynamically signaled by a downlink control information packet from the base station.

23. The apparatus of claim 17, comprising: Determine that the state of the at least one SCell is busy, that is, BUSY; Determine an idle state, i.e., an IDLE state, of at least another secondary serving cell; as well as The identity of the at least another secondary serving cell is sent to the base station on a physical uplink control channel of the PCell.

Images