Patent Description:
Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE)/LTE-Advanced systems and orthogonal frequency division multiple access (OFDMA) systems.

Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. This communication link may be established via a single-input single-output, multiple-input single-output or a multiple-input multiple-output (MIMO) system.

A wireless communication network may include a number of base stations that can support communication for a number of wireless devices. Wireless devices may include user equipments (UEs). Some UEs may be considered machine-type communication (MTC) UEs, which may communicate with a base station, another remote device, or some other entity. MTC UEs may include UEs that are capable of MTC communications with MTC servers and/or other MTC devices through Public Land Mobile Networks (PLMN), for example.

Wireless devices may communicate using relative narrowband regions of system bandwidth, such as narrowband internet of things (NB-IoT) devices. Certain NB-IoT devices may be considered MTC devices. To reduce the complexity of UEs, NB-IoT may allow for deployments utilizing a reduced bandwidth, as compared to for example, a wideband LTE channel. A new frame structure may be used for such devices allowing for increased compatibility along with greater capacity.

<CIT> describes a method for machine-type-communication in a single frequency network. The method comprises broadcasting at least one synchronization signal which provides timing for a subframe boundary and determining a subframe at a fixed time after detecting the synchronization signal. By this several UE can sequentially send information on the same single frequency network without interfering each other.

The dependent claims provide advantageous embodiments.

The techniques described herein may be used for various wireless communication networks such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA and other networks. A CDMA network may implement a radio technology such as universal terrestrial radio access (UTRA), cdma2000, etc. UTRA includes wideband CDMA (WCDMA), time division synchronous CDMA (TD-SCDMA), and other variants of CDMA. A TDMA network may implement a radio technology such as global system for mobile communications (GSM). An OFDMA network may implement a radio technology such as evolved UTRA (E-UTRA), ultra mobile broadband (UMB), IEEE <NUM> (Wi-Fi), IEEE <NUM> (WiMAX), IEEE <NUM>, Flash-OFDM®, etc. UTRA and E-UTRA are part of universal mobile telecommunication system (UMTS). 3GPP Long Term Evolution (LTE) and LTE-Advanced (LTE-A), in both frequency division duplex (FDD) and time division duplex (TDD), are new releases of UMTS that use E-UTRA, which employs OFDMA on the downlink and SC-FDMA on the uplink. For clarity, certain aspects of the techniques are described below for LTE/LTE-Advanced, and LTE/LTE-Advanced terminology is used in much of the description below. LTE and LTE-A are referred to generally as LTE.

<FIG> illustrates an example wireless communication network <NUM>, in which aspects of the present disclosure may be practiced. For example, techniques presented herein may be used to help UEs and BSs shown in <FIG> communicate on a machine type physical downlink control channel (mPDCCH) using a narrowband (e.g., one-PRB, six-PRB) based search space.

The network <NUM> may be an LTE network or some other wireless network. Wireless network <NUM> may include a number of evolved Node Bs (eNBs) <NUM> and other network entities. An eNB is an entity that communicates with user equipments (UEs) and may also be referred to as a base station, a Node B, an access point, etc. Each eNB may provide communication coverage for a particular geographic area. In 3GPP, the term "cell" can refer to a coverage area of an eNB and/or an eNB subsystem serving this coverage area, depending on the context in which the term is used. Some examples of UEs may include cellular phones, smart phones, personal digital assistants (PDAs), wireless modems, handheld devices, tablets, laptop computers, netbooks, smartbooks, ultrabooks, wearable devices (e.g., smart glasses, smart bracelets, smart wrist bands, smart rings, smart watches, smart clothing), drones, robotic devices, entertainment devices, gaming devices, vehicular devices, medical/healthcare devices, etc. Some UEs may be considered machine-type communication (MTC) UEs, which may include remote devices, such as sensors, meters, monitors, location tags, drones, robotic devices, etc., that may communicate with a base station, another remote device, or some other entity. Machine type communications (MTC) may refer to communication involving at least one remote device on at least one end of the communication and may include forms of data communication which involve one or more entities that do not necessarily need human interaction. MTC UEs and other types of UEs may be implemented as NB-IoT devices.

An eNB may provide communication coverage for a macro cell, a pico cell, a femto cell, and/or other types of cell. An eNB for a pico cell may be referred to as a pico eNB. An eNB for a femto cell may be referred to as a femto eNB or a home eNB (HeNB). In the example shown in <FIG>, an eNB 110a may be a macro eNB for a macro cell 102a, an eNB 110b may be a pico eNB for a pico cell 102b, and an eNB 110c may be a femto eNB for a femto cell 102c. An eNB may support one or multiple (e.g., three) cells. The terms "eNB", "base station" and "cell" may be used interchangeably herein.

A relay station is an entity that can receive a transmission of data from an upstream station (e.g., an eNB or a UE) and send a transmission of the data to a downstream station (e.g., a UE or an eNB). In the example shown in <FIG>, a relay station 110d may communicate with macro eNB 110a and a UE 120d in order to facilitate communication between eNB 110a and UE 120d. A relay station may also be referred to as a relay eNB, a relay base station, a relay, etc..

Wireless network <NUM> may be a heterogeneous network that includes eNBs of different types, e.g., macro eNBs, pico eNBs, femto eNBs, relay eNBs, etc. These different types of eNBs may have different transmit power levels, different coverage areas, and different impact on interference in wireless network <NUM>. For example, macro eNBs may have a high transmit power level (e.g., <NUM> to <NUM> Watts) whereas pico eNBs, femto eNBs, and relay eNBs may have lower transmit power levels (e.g., <NUM> to <NUM> Watts).

A network controller <NUM> may couple to a set of eNBs and may provide coordination and control for these eNBs. Network controller <NUM> may communicate with the eNBs via a backhaul. The eNBs may also communicate with one another, e.g., directly or indirectly via a wireless or wireline backhaul.

A UE may also be referred to as an access terminal, a terminal, a mobile station, a subscriber unit, a station, etc. A UE may be a cellular phone, a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a laptop computer, a cordless phone, a wireless local loop (WLL) station, a tablet, a smart phone, a netbook, a smartbook, an ultrabook, etc. In <FIG>, a solid line with double arrows indicates desired transmissions between a UE and a serving eNB, which is an eNB designated to serve the UE on the downlink and/or uplink. A dashed line with double arrows indicates potentially interfering transmissions between a UE and an eNB.

One or more UEs <NUM> in the wireless communication network <NUM> (e.g., an LTE network) may also be a narrowband bandwidth UE. These UEs may co-exist with legacy and/or advanced UEs (e.g., capable of operating on a wider bandwidth) in the LTE network and may have one or more capabilities that are limited when compared to the other UEs in the wireless network. For example, in LTE Rel-<NUM>, when compared to legacy and/or advanced UEs in the LTE network, the narrowband UEs may operate with one or more of the following: a reduction in maximum bandwidth (relative to legacy UEs), a single receive radio frequency (RF) chain, reduction of peak rate (e.g., a maximum of <NUM> bits for a transport block size (TBS) may be supported), reduction of transmit power, rank <NUM> transmission, half duplex operation, etc. In some cases, if half duplex operation is supported, the narrowband UEs may have a relaxed switching timing from transmit to receive (or from receive to transmit) operations. For example, in one case, compared to a switching timing of <NUM> microseconds (us) for legacy and/or advanced UEs, the narrowband UEs may have a relaxed switching timing of <NUM> millisecond (ms).

In some cases, the narrowband UEs (e.g., in LTE Rel-<NUM>) may also be able to monitor downlink (DL) control channels in the same away as legacy and/or advanced UEs in the LTE network monitor DL control channels. Release <NUM> narrowband UEs may still monitor downlink (DL) control channels in the same way as regular UEs, for example, by monitoring for wideband control channels in the first few symbols (e.g., physical downlink control channel (PDCCH)) as well as narrowband control channels occupying a relatively narrowband, but spanning a length of a subframe (e.g., enhanced or evolved PDCCH (ePDCCH)).

According to certain aspects, narrowband UEs may be limited to a particular narrowband assignment of <NUM> or six resource blocks (RBs) partitioned out of the available system bandwidth) while co-existing within a wider system bandwidth (e.g., at <NUM>/<NUM>/<NUM>/<NUM>/<NUM>/<NUM>). Additionally, narrowband UEs may also be able to support one or more coverage modes of operation. For example, the narrowband UE may be able to support coverage enhancements up to <NUM> dB.

As used herein, devices with limited communication resources, e.g. smaller bandwidth, may be referred to generally as narrowband UEs. Similarly, legacy devices, such as legacy and/or advanced UEs (e.g., in LTE) may be referred to generally as wideband UEs. Generally, wideband UEs are capable of operating on a larger amount of bandwidth than narrowband UEs.

In some cases, a UE (e.g., a narrowband UE or a wideband UE) may perform a cell search and acquisition procedure before communicating in the network. In one case, with reference to the LTE network illustrated in <FIG> as an example, the cell search and acquisition procedure may be performed when the UE is not connected to a LTE cell and wants to access the LTE network. In these cases, the UE may have just powered on, restored a connection after temporarily losing connection to the LTE cell, etc..

In other cases, the cell search and acquisition procedure may be performed when the UE is already connected to a LTE cell. For example, the UE may have detected a new LTE cell and may prepare a handover to the new cell. As another example, the UE may be operating in one or more low power states (e.g., may support discontinuous reception (DRX)) and, upon exiting the one or more low power states, may have to perform the cell search and acquisition procedure (even though the UE is still in connected mode).

<FIG> shows a block diagram of a design of base station/eNB <NUM> and UE <NUM>, which may be one of the base stations/eNBs and one of the UEs in <FIG>.

At base station <NUM>, a transmit processor <NUM> may receive data from a data source <NUM> for one or more UEs, select one or more modulation and coding schemes (MCS) for each UE based on CQIs received from the UE, process (e.g., encode and modulate) the data for each UE based on the MCS(s) selected for the UE, and provide data symbols for all UEs. Transmit processor <NUM> may also process system information (e.g., for SRPI, etc.) and control information (e.g., CQI requests, grants, upper layer signaling, etc.) and provide overhead symbols and control symbols. Processor <NUM> may also generate reference symbols for reference signals (e.g., the CRS) and synchronization signals (e.g., the PSS and SSS).

Each demodulator <NUM> may condition (e.g., filter, amplify, downconvert, and digitize) its received signal to obtain input samples. A channel processor may determine RSRP, RSSI, RSRQ, CQI, etc..

On the uplink, at UE <NUM>, a transmit processor <NUM> may receive and process data from a data source <NUM> and control information (e.g., for reports comprising RSRP, RSSI, RSRQ, CQI, etc.) from controller/processor <NUM>. Processor <NUM> may also generate reference symbols for one or more reference signals. The symbols from transmit processor <NUM> may be precoded by a TX MIMO processor <NUM> if applicable, further processed by modulators 254a through 254r (e.g., for SC-FDM, OFDM, etc.), and transmitted to base station <NUM>. Processor <NUM> may provide the decoded data to a data sink <NUM> and the decoded control information to controller/processor <NUM>.

Controllers/processors <NUM> and <NUM> may direct the operation at base station <NUM> and UE <NUM>, respectively. For example, processor <NUM> and/or other processors and modules at UE <NUM> may perform or direct operations <NUM> shown in <FIG>, and processor <NUM> and/or other processors and modules at base station <NUM> may perform or direct operations at base station <NUM>. Memories <NUM> and <NUM> may store data and program codes for base station <NUM> and UE <NUM>, respectively.

<FIG> shows an exemplary frame structure <NUM> for FDD (frequency division duplex) in LTE. Each radio frame may have a predetermined duration (e.g., <NUM> milliseconds (ms)) and may be partitioned into <NUM> subframes with indices of <NUM> through <NUM>. Each subframe may include two slots. Each radio frame may thus include <NUM> slots with indices of <NUM> through <NUM>. Each slot may include L symbol periods, e.g., seven symbol periods for a normal cyclic prefix (as shown in <FIG>) or six symbol periods for an extended cyclic prefix. The <NUM> symbol periods in each subframe may be assigned indices of <NUM> through <NUM>-<NUM>.

In LTE, an eNB may transmit a primary synchronization signal (PSS) and a secondary synchronization signal (SSS) on the downlink in the center of the system bandwidth for each cell supported by the eNB. The PSS and SSS may be transmitted in symbol periods <NUM> and <NUM>, respectively, in subframes <NUM> and <NUM> of each radio frame with the normal cyclic prefix, as shown in <FIG>. The PSS and SSS may be used by UEs for cell search and acquisition and may contain, among other information, the cell ID along with an indication of the duplexing mode. The indication of the duplexing mode may indicate whether the cell utilizes a time division duplexing (TDD) or frequency division duplexing (FDD) frame structure. The eNB may transmit a cell-specific reference signal (CRS) across the system bandwidth for each cell supported by the eNB. The CRS may be transmitted in certain symbol periods of each subframe and may be used by the UEs to perform channel estimation, channel quality measurement, and/or other functions. The eNB may also transmit a physical broadcast channel (PBCH) in symbol periods <NUM> to <NUM> in slot <NUM> of certain radio frames. The PBCH may carry some system information. The eNB may transmit other system information such as system information blocks (SIBs) on a physical downlink shared channel (PDSCH) in certain subframes. The eNB may transmit control information/data on a physical downlink control channel (PDCCH) in the first B symbol periods of a subframe, where B may be configurable for each subframe. The eNB may transmit traffic data and/or other data on the PDSCH in the remaining symbol periods of each subframe.

Channel quality measurements may be performed by a UE according to a defined schedule, such one based on the DRX cycle of the UE. For example, a UE may attempt to perform measurements for a serving cell at every DRX cycle. The UE may also attempt to perform measurements for non-serving neighboring cells. Measurements for non-serving neighbor cells may be made based on a different schedule than for serving cells and the UE may need to tune away from the serving cell to measure non-serving cells when the UE is in connected mode.

To facilitate channel quality measurements, an eNB may transmit a cell specific reference signal (CRS) on specific subframes. For example, an eNB may transmit CRS over subframes <NUM> and <NUM> for a given frame. A narrowband UE may receive this signal and measure the average power of the received signal, or RSRP. The narrowband UE may also calculate a Receive Signal Strength Indicator (RSSI) based on the total received signal power from all sources. A RSRQ may be also be calculated based on the RSRP and RSSI.

To facilitate measurements, an eNB may provide a measurement configuration to UEs in its coverage area. The measurement configuration may define event triggers for measurement reporting and each event trigger may have associated parameters. When the UE detects a configured measurement event, it may respond by sending a measurement report to the eNB with information about the associated measurement objects. A configured measurement event may be, for example, a measured reference signal received power (RSRP) or a measured reference signal received quality (RSRQ) satisfying a threshold. A time-to-trigger (TTT) parameter can be used to define how long a measurement event must persist before the UE sends its measurement report. In this way, the UE can signal changes in its radio conditions to the network.

<FIG> shows two exemplary subframe formats <NUM> and <NUM> with the normal cyclic prefix. Each resource block may cover <NUM> subcarriers in one slot and may include a number of resource elements. Each resource element may cover one subcarrier in one symbol period and may be used to send one modulation symbol, which may be a real or complex value.

Subframe format <NUM> may be used for two antennas. A CRS may be transmitted from antennas <NUM> and <NUM> in symbol periods <NUM>, <NUM>, <NUM> and <NUM>. A reference signal is a signal that is known a priori by a transmitter and a receiver and may also be referred to as pilot. A CRS is a reference signal that is specific for a cell, e.g., generated based on a cell identity (ID). In <FIG>, for a given resource element with label Ra, a modulation symbol may be transmitted on that resource element from antenna a, and no modulation symbols may be transmitted on that resource element from other antennas. Subframe format <NUM> may be used with four antennas. A CRS may be transmitted from antennas <NUM> and <NUM> in symbol periods <NUM>, <NUM>, <NUM> and <NUM> and from antennas <NUM> and <NUM> in symbol periods <NUM> and <NUM>. For both subframe formats <NUM> and <NUM>, a CRS may be transmitted on evenly spaced subcarriers, which may be determined based on cell ID. CRSs may be transmitted on the same or different subcarriers, depending on their cell IDs. For both subframe formats <NUM> and <NUM>, resource elements not used for the CRS may be used to transmit data (e.g., traffic data, control data, and/or other data).

The PSS, SSS, CRS and PBCH in LTE are described in <NPL>," which is publicly available.

An interlace structure may be used for each of the downlink and uplink for FDD in LTE. For example, Q interlaces with indices of <NUM> through Q - <NUM> may be defined, where Q may be equal to <NUM>, <NUM>, <NUM>, <NUM>, or some other value. Each interlace may include subframes that are spaced apart by Q frames. In particular, interlace q may include subframes q, q + Q, q + 2Q, etc., where q ∈ {<NUM>,. , Q - <NUM>}.

The wireless network may support hybrid automatic retransmission request (HARQ) for data transmission on the downlink and uplink. For HARQ, a transmitter (e.g., an eNB) may send one or more transmissions of a packet until the packet is decoded correctly by a receiver (e.g., a UE) or some other termination condition is encountered. For synchronous HARQ, all transmissions of the packet may be sent in subframes of a single interlace. For asynchronous HARQ, each transmission of the packet may be sent in any subframe.

A UE may be located within the coverage of multiple eNBs. One of these eNBs may be selected to serve the UE. The serving eNB may be selected based on various criteria such as received signal strength, received signal quality, pathloss, etc. Received signal quality may be quantified by a signal-to-noise-and-interference ratio (SINR), or a reference signal received quality (RSRQ), or some other metric. The UE may operate in a dominant interference scenario in which the UE may observe high interference from one or more interfering eNBs.

A UE may be configured to transmit a sounding reference signal (SRS) to one or more eNBs. This STS may be used by an eNB to estimate uplink channel quality over a bandwidth and used for uplink frequency selective scheduling. The SRS transmission may stretch over a relatively large frequency range in order to provide broad feedback over an entire bandwidth. To avoid collisions between an SRS transmitted by a first UE and an UL transmission of another UE, other UEs may avoid transmitting in the OFDM symbols in which SRS transmissions may occur. To achieve this, all UE within a cell may be aware of the set of subframes within which SRS may be transmitted by other UEs within the cell. The other UEs may then avoid UL transmissions during those subframes.

The focus of traditional LTE design is on the improvement of spectral efficiency, ubiquitous coverage, and enhanced quality of service (QoS) support. Current LTE system downlink (DL) and uplink (UL) link budgets are designed for coverage of high end devices, such as state-of-the-art smartphones, tablets, or other wideband device, which may support a relatively large DL and UL link budget.

As described above, one or more UEs in the wireless communication network (e.g., wireless communication network <NUM>) may be devices that have limited communication resources, such as narrowband UEs, as compared to other (wideband) devices in the wireless communication network. Narrowband devices may be relatively simple, low powered devices, and various requirements may be relaxed as only a limited amount of information may need to be exchanged. For example, maximum bandwidth may be reduced (relative to wideband UEs), a single receive radio frequency (RF) chain may be used, peak rate may be reduced (e.g., a maximum of <NUM> bits for a transport block size), transmit power may be reduced, Rank <NUM> transmission may be used, and half duplex operations may be performed.

In some cases, if half-duplex operations are performed, narrowband UEs may have a relaxed switching time to transition from transmitting to receiving (or receiving to transmitting). For example, the switching time may be relaxed from <NUM> for regular UEs to <NUM> for narrowband UEs. Release <NUM> narrowband UEs may still monitor downlink (DL) control channels in the same way as regular UEs, for example, monitoring for wideband control channels in the first few symbols (e.g., PDCCH) as well as narrowband control channels occupying a relatively narrowband, but spanning a length of a subframe (e.g., ePDCCH).

In some systems, for example, in LTE Rel-<NUM>, the narrowband may be limited to a particular narrowband assignment (e.g., of no more than six resource blocks (RBs)) within the available system bandwidth. However, the narrowband may be able to re-tune (e.g., operate and/or camp) to different narrowband regions within the available system bandwidth of the LTE system, for example, in order to co-exist within the LTE system.

As another example of coexistence within the LTE system, narrowband UEs may be able to receive (with repetition) legacy physical broadcast channel (PBCH) (e.g., the LTE physical channel that, in general, carries parameters that may be used for initial access to the cell, such as the MIB) and support one or more legacy physical random access channel (PRACH) formats. For example, the narrowband UEs may be able to receive the legacy PBCH with one or more additional repetitions of the PBCH across multiple subframes. As another example, the narrowband UEs may be able to transmit one or more repetitions of PRACH (e.g., with one or more PRACH formats supported) to an eNB in the LTE system. The PRACH may be used to identify the narrowband UE. Also, the number of repeated PRACH attempts may be configured by the eNB.

The narrowband UE may also be a link budget limited device and may operate in different modes of operation (e.g. entailing different amounts of repeated messages transmitted to the narrowband UE) based on its link budget limitation. For example, in some cases, the narrowband UE may operate in a normal coverage mode in which there is little to no repetition. In such cases, the amount of repetition needed for the UE to successfully receive a message may be low or repetition may not even be needed. Alternatively, in some cases, the narrowband UE may operate in a coverage enhancement (CE) mode in which there may be high amounts of repetition. For example, for a <NUM> bit payload, a narrowband UE in CE mode may need <NUM> or more repetitions of the payload in order to successfully receive the payload.

In some cases, for example, for LTE Rel-<NUM>, the narrowband UE may have limited capabilities with respect to its reception of broadcast and unicast transmissions. For example, the maximum transport block (TB) size for a broadcast transmission received by the narrowband UE may be limited to <NUM> bits. Additionally, in some cases, the narrowband UE may not be able to receive more than one unicast TB in a subframe. In some cases (e.g., for both the CE mode and normal mode described above), the narrowband UE may not be able to receive more than one broadcast TB in a subframe. Further, in some cases, the narrowband UE may not be able to receive both a unicast TB and a broadcast TB in a subframe.

Narrowband UEs that co-exist in the LTE system may also support new messages for certain procedures, such as paging, random access procedure, etc. (e.g., as opposed to conventional messages used in LTE for these procedures). In other words, these new messages for paging, random access procedure, etc. may be separate from the messages used for similar procedures associated with non-narrowband UEs. For example, as compared to conventional paging messages used in LTE, narrowband UEs may able to monitor and/or receive paging messages that non-narrowband UEs may not able to monitor and/or receive. Similarly, as compared to conventional random access response (RAR) messages used in a conventional random access procedure, narrowband UEs may be able to receive RAR messages that also may not be able to be received by non-narrowband UEs. The new paging and RAR messages associated with narrowband UEs may also be repeated one or more times (e.g., "bundled"). In addition, different numbers of repetitions (e.g., different bundling sizes) for the new messages may be supported. These various bundling sized may be used to determine a CE level. For example, CE levels may be determined in part from the bundle size used for various channels where larger bundling sizes are associated with larger CE levels.

According to certain aspects, multiple narrowband regions, each narrowband region spanning a bandwidth that is no greater than a total of <NUM> RBs, may be supported by narrowband UE and/or narrowband operation. In some cases, each narrowband UE in narrowband operation may operate within one narrowband region (e.g., at <NUM> or <NUM> RBs) at a time. However, narrowband UEs in narrowband operation, at any given time, may re-tune to other narrowband regions in the wider system bandwidth. In some examples, multiple narrowband UEs may be served by the same narrowband region. In other examples, multiple narrowband UEs may be served by different narrowband regions (e.g., with each narrowband region spanning <NUM> RBs). In yet other examples, different combinations of narrowband UEs may be served by one or more same narrowband regions and/or one or more different narrowband regions.

Some systems, for example, in LTE Rel-<NUM>, introduce coverage enhancements and support for narrowband UEs, as well as other UEs. As used herein, the term coverage enhancement generally refers to any type of mechanism that extends the coverage range of a device (such as a narrowband device) within a network. One approach for coverage enhancement (CE) is bundling which refers to transmitting the same data multiple times (e.g., across multiple subframes or, as will be described in greater detail below, across multiple symbols within a same subframe).

Certain systems may provide narrowband UEs with coverage enhancements of up to <NUM> dB, which maps to <NUM> dB maximum coupling loss between the UE and an eNB. Accordingly, narrowband UEs and eNB may perform measurements at low SNRs (e.g., -<NUM> dB to -<NUM> dB). In some systems, coverage enhancements may include channel bundling, wherein messages associated with narrowband UEs may be repeated (e.g., bundled) one or more times.

Certain devices may be able to communicate both with legacy type communications and non-legacy type communications. For example, some devices may be able to communicating in both narrowband regions (of overall system bandwidth) as well as wider band regions. While the examples above refer to low cost or MTC devices that communicate via narrowband regions, other (non-low-cost/non-MTC) types of devices may also communicate via narrowband regions, for example, taking advantage of frequency selectivity and directional transmissions.

Devices, such as narrowband internet of things (NB-IoT) devices may communicate using relative narrowband regions of system bandwidth, as compared to wideband LTE. Additionally, wideband LTE may utilize subcarriers which are spaced <NUM> apart from each other. NB-IoT devices, may also support a <NUM> subcarrier spacing, for example, on a single tone or multi-tone uplink (UL) data channel. NB-IoT devices may also support a single tone UL data channel with a tone spacing (e.g., UL subcarrier spacing) of <NUM> in addition to a <NUM> tone spacing.

A <NUM> tone spacing design offers more bandwidth capacity as compared to a <NUM> tone spacing. This is because <NUM> allows for a time domain to be expanded by a factor of four, as the spacing between subcarriers is reduced. This expansion allows for <NUM> subframes where the slots may be <NUM> in length, rather than. This increase in bandwidth capacity allows, for example, four UEs to be supported instead of one for a particular frequency domain. However, not all TDD modes may be supported as at least two consecutive uplink subframes are needed for certain TDD modes. Additionally, legacy LTE SRS transmissions may be inefficient when transmitted with <NUM> tone spacing.

A <NUM> tone spacing design offers compatibility with in-band LTE configurations, but has less capacity as compared to the <NUM> designs due to the larger tone spacing. This relative lack of capacity may be addressed, at least in part, through code division multiplexing (CDM), though handling SRS for multiple UEs operating together using CDM may be an issue.

A frame structure capable of handling both <NUM> and <NUM> tone spacing may be designed to increase compatibility and capacity, as well as support all TDD modes by fitting into <NUM> slots.

<FIG> illustrates an example uplink process <NUM> that may be performed by a first user equipment (UE), in accordance with aspects of the present disclosure. At <NUM>, determine a number of pilot symbols to transmit for one or more slots of a first subframe based, at least in part, on a coverage enhancement (CE) level. At <NUM>, transmit at least one uplink data channel having the determined number of pilot symbols in the one or more slots of the first subframe.

According to certain aspects of the present disclosure, the frame structure for the number of data and pilot symbols within each slot may be based on a coverage class (e.g., enhancement level). For example, the frame structure for UL control channels for UEs with a <NUM> tone spacing may be similar to a frame structure used for LTE UL data channels (e.g., physical uplink shared channel (PUSCH)), with a single pilot per slot, similar slot and sub-frame durations, cyclic prefix (CP), and data lengths, and number of demodulation reference signal (DMRS) and data symbols within each slot. Where a UE is operating in extended coverage, two DMRS pilots within each slot may be used. Where a UE is operating in extremely extended coverage, three DMRS pilots within each slot may be used.

According to certain aspects of the present disclosure, the number of pilots for each slot may be determined implicitly based on, for example, the coverage enhancement level or other information such as the PUSCH repetition level or MCS. The number of pilots may also be determined based on an explicitly signaled RRC configuration, or UL grant.

<FIG> illustrates an example frame structure <NUM> utilizing <NUM> tone spacing, according to aspects of the present disclosure. As the spacing between subcarriers are reduced, units of the radio frame may be expanded by a factor of four, resulting in a larger CP duration, along with larger data and DMRS durations. For example, using a <NUM> sampling rate, a data duration with a <NUM> tone spacing may be <NUM>, while a data duration with <NUM> tone spacing may be 4x128.

According to certain aspects of the present disclosure, the frame structure for UL control channels for UEs with a <NUM> tone spacing may also be based on coverage class. For example, a UE operating with <NUM> tone spacing may utilize six data symbols and one DMRS within each slot. A UE operating in extended coverage may utilize five data symbols two DMRS within each slot. A UE operating in extremely extended coverage may utilize four data symbols and three DMRS within each slot.

<FIG> illustrates an example multiplexed frame structure <NUM>, according to aspects of the present disclosure. A first UE may transmit a <NUM> tone spacing UL signal <NUM> and a second UE may transmit a <NUM> tone spacing UL signal <NUM>. As shown, each <NUM> OFDM symbol may be adjusted to be equivalent to four <NUM> OFDM symbols. CP durations within the <NUM> OFDM symbol is adjusted to match within each <NUM> FFT block such that within each <NUM> FFT block, orthogonality is maintained. With the adjusted CP in <FIG>, any tone l on the <NUM> grid, for which l/<NUM> is a whole number (l/<NUM> ∈ Z), is allowed to remain orthogonal relative to the <NUM> tone, and allows the symbols between the <NUM> and <NUM> tones to be aligned within a <NUM> signal length.

<FIG> illustrates example multiplexed frame structure having an extended CP 800A, according to aspects of the present disclosure. Where an extended CP may be utilized, orthogonality between <NUM> and <NUM> may be maintained by extending the CP lengths for the <NUM> tones relative to the <NUM> tones. For example, an extended CP in a subframe using <NUM> tone spacing 802A may have a length of <NUM> and the corresponding extended CP in a subframe using <NUM> tone spacing 804A may be <NUM>×<NUM> or <NUM>. Extending the CP for <NUM> may result in <NUM> OFDM symbols, instead of <NUM> ODFM symbols within a <NUM> slot.

According to other aspects of the present disclosure, multiplexing may be supported for subframes with extended CPs utilizing <NUM> tone spacing. For example, as shown in <FIG>, where extended CPs are utilized with <NUM> tone spacing along with normal CP formats utilized for <NUM> tone spacing, orthogonality would be lost for five out of <NUM><NUM> OFDM symbols. For these OFMD symbols, any tone on a <NUM> grid would interfere with tones on the <NUM> grid.

<FIG> illustrates example multiplexed frame structures with a SRS transmission, according to aspects of the present disclosure. Transmissions from multiple UEs may be received as a multiplexed signal(s) <NUM> and 900A by, for example, an eNB. The multiplexed signal may include a first UE transmitting using a <NUM> tone spacing UL signal <NUM> and a second UE transmitting using a <NUM> tone spacing UL signal <NUM>. Where a SRS transmission <NUM> is transmitted using <NUM> tone spacing, the corresponding OFDM symbol <NUM> of the first UE using <NUM> tone spacing needs to be silenced. This silencing corresponds to, e.g., a <NUM>% loss in bandwidth for <NUM>.

According to aspects of the present disclosure, to reduce the loss of bandwidth from silencing during a <NUM> SRS transmission, a UE transmitting utilizing a <NUM> tone spacing UL signal 902A may, for the specific OFDM symbol scheduled for SRS, switch to a <NUM> grid. This would convert a <NUM> symbol into four <NUM> symbols and allow the UE to only silence a single <NUM> OFDM symbol 910A corresponding to the SRS transmission <NUM> and allow three <NUM> symbols 912A to transmit.

Switching from <NUM> to <NUM> may introduce issues as the <NUM> tone spacing allows four UEs to transmit instead of a single UE for a particular frequency domain. For example, switching to a <NUM> grid from a <NUM> grid may require three out of four UEs to be silenced. According to aspects of the present disclosure, CDM (e.g., discrete Fourier transform (DFT) spreading) over time may be applied to allow recovery of three out of four UEs.

<FIG> illustrates an example multiplexed frame structure <NUM> with SRS and CDM, according to aspects of the present disclosure. For example, while all UEs may be silenced during the entirety of the <NUM> symbol <NUM> corresponding to the SRS transmission, UEs only need to be silenced for one symbol <NUM> of four <NUM> symbols corresponding to the SRS transmission. For the remaining three <NUM> symbols, three (out of the four) UEs <NUM> may transmit using CDM over time, through, for example, a DFT spreading code, to multiplex the three UEs. The fourth UE <NUM> may be silenced.

<FIG> illustrates example multiplexed frame structures <NUM> with SRS, according to aspects of the present disclosure. Multiplexing UEs while switching to a <NUM> grid from a <NUM> grid may also be performed without CDM. In this example, as before, four UEs may be silenced during the entirety of a <NUM> symbol <NUM>. UEs only need to be silenced for one symbol <NUM> of four <NUM> symbols corresponding to the SRS transmission. During one symbol <NUM> of the four <NUM> symbols, a first UE <NUM> may transmit, while the other three UEs are silenced. Two UEs <NUM> of the four UEs may then transmit in remaining OFDM symbol time <NUM>, in a manner similar to a frame structure with a <NUM> tone spacing with a 2x expansion in duration, while the other two UEs are silenced. The CP and data durations are twice that of <NUM>.

According to aspects of the present disclosure, NB-IoT transmissions may be configured in RBs at the edge of a wider system bandwidth and SRS configured to avoid the RBs used by NB-IoT. According to another aspect, a SRS may also be scheduled in subframes that are not NB-IoT subframes, such that the subframes assigned to NB-IoT would not be subject to SRS. According to another aspect, a SRS may be transmitted in conjunction with NB-IoT transmissions utilizing a <NUM> tone spacing. In such cases, interference between the SRS transmission and the NB-IoT transmissions would occur and an eNB receiver may be allowed to handle the interference via existing techniques, for example interference cancellation, at the receiver.

According to aspects of the present disclosure, a comb pattern may also be used for multiplexing NB-IoT transmissions with SRS. Generally for a SRS transmission, half of the tones are actually used at a time for SRS transmission in a comb pattern. Those tones actually in use may be vacated. The other half not currently in use by the SRS transmission may be used for NB-IoT transmissions without interference with the SRS transmission. The pattern for the tones to be used for SRS may be signaled, for example, to a UE within an UL or DL grant, or configured semi-statically. Where a tone scheduled for SRS transmission is needed for the data transmission, a UE may need to perform rate matching around the SRS OFDM symbol. This comb pattern technique may be combined with the techniques discussed, for example, in conjunction with <FIG> and <FIG>.

According to aspects of the present disclosure, all TDD configurations may be covered using a <NUM> tone spacing. With <NUM> tone spacing, the CP and data durations are extended in the time domain by a factor of two with a <NUM> slot and <NUM> subframe duration. To fit within the <NUM> slot duration, per-slot transmission is needed such that if only <NUM> UL subframe is available, an eNB may grant a <NUM> NB slot so that the UE is aligned with a legacy UE.

According to aspects of the present disclosure, all TDD configurations may also be covered using a <NUM> tone spacing. With <NUM> tone spacing, the CP and data durations are extended in the time domain by a factor of five. However, with a <NUM> tone spacing, the FFT size no longer is log2, and some CPs may be extended to fit within a <NUM> slot duration.

According to aspects of the present disclosure, all TDD configurations may be supported by only using a <NUM> tone spacing for in-band configurations. As indicated above, CDM in the time domain may be used to increase capacity as <NUM> has less capacity as compared to lower frequency tone spacing configurations. For example, a CDM of length four may be allowed such that Walsh or DFT spreading is applied over four slots with a coherence requirement of <NUM>. As another example, CDM may be performed across four different OFDM symbols such that the DMRS symbols are repeated four times. However, this may result in weak channel estimation for OFDM data symbols that are more distant from DMRS repetitions.

According to aspects of the present disclosure, all TDD configurations may be supported in conjunction with <NUM> tone spacing. <FIG> illustrates an example multiplexed frame structure <NUM>, according to aspects of the present disclosure. After three <NUM> OFDM symbols, two UEs <NUM> out of the four multiplexed UEs may be silenced. The other two UEs may transmit on the remaining OFDM symbol <NUM> such that the tonal spacing between the transmitting UEs is <NUM>.

According to aspects of the present disclosure, multi-tone assignments may be made based on a comb pattern. For example, within a RB, certain tones, such as tones #<NUM>, <NUM>, <NUM>, and <NUM>, may be assigned to a first UE, tones #<NUM>, <NUM>, and <NUM>, assigned to a second UE, and so forth. This allows for tones to span a wider bandwidth as compared to continuous tone assignments and better time tracking due to improved resolution.

According to aspects of the present disclosure, a computer generated sequence (CGS) design may be used for multi-tone allocations. LTE CGS may be used as a baseline with a corresponding QPSK (quadrature phase shift keying) sequence and updating tables based on the sequence length and extensive cross-correlation interference analysis. The cross-correlation interference analysis may consider all interfering UEs with all the possible number of tones that may be received from a neighboring cell.

<FIG> of <FIG> shows constellation diagrams 1300A-D of BPSK and QPSK modulations, according to aspects of the present disclosure. According to aspects of the present disclosure, pi/<NUM>-BPSK (binary phase shift keying) 1300B or pi/<NUM>-QPSK (quadrature phase shift keying) 1300D modulations may be used for data transmission over an uplink channel. Phase shift keying (PSK) is a modulation scheme for a reference signal (e.g., carrier wave) which encodes data by modulating the phase of the reference signal. BPSK 1300A is a form of PSK using two phases (e.g., offset) separated by <NUM> degrees and QPSK 1300C uses four phases separated by <NUM> degrees. As a PSK signal transitions from one constellation point to another constellation point, the signal may transition through a zero-point (<NUM> for BPSK and <NUM> for QPSK) of the respective axis and increasing peak-to-average power ratio (PAPR). A phase shift in different time instants may be used to avoid zero-crossings in the transmitted waveform (e.g., waveform trajectories that go through the origin) and reduce the PAPR. For example, in the case of pi/<NUM>-BPSK (1300B) a phase shift of pi/<NUM> (<NUM>) may be applied in odd transmission instances, and a phase shift of <NUM> (<NUM>) may be applied in even transmission instances. In some cases, the phase shift can be determined based on cell ID, UE ID, timing difference with respect to slot/subframe boundary, and/or timing difference with respect to hopping instants to reduce inter-cell and inter-UE interference. For example, in the case of pi/<NUM>-BPSK (1300B) a phase shift of pi/<NUM> (<NUM>) may be applied in odd transmission instances if the cell ID is odd, and a phase shift of <NUM> (<NUM>) may be applied in even transmission instances if the cell ID is even.

A counter may be utilized to track phase shifts in different time instants. This counter may be restarted when certain boundaries are reached. For example, the counter may be restarted at the subframe boundary. In such cases, the effective result is that the counter is never restarted as the number of symbols in a subframe is even. According to other aspects, the counter may be restarted after every slot or after frequency hopping is performed.

According to aspects of the present disclosure, inter-cell randomization may be further increased by adjusting starting constellation rotations <NUM> to be different for UEs in different cells as illustrated in <FIG>. For example, a first user <NUM> in a first cell using pi/<NUM> QPSK modulation may utilize a starting constellation rotation of pi/<NUM>, while a second user <NUM> in a second cell also using pi/<NUM> QPSK may utilize a starting constellation rotation of <NUM>. This starting rotation may be explicitly signaled in a grant, for example with the DMRS cyclic shift). In other cases, this starting rotation may be implicitly signaled, for example based on a cell ID or RNTI value. Where modulations are mixed with BPSK and pi/<NUM> QPSK, offsets may be different between BPSK and pi/<NUM> QPSK users.

A longer duration DMRS sequence may be defined. According to certain aspects, a <NUM> DMRS sequence may be defined with sequence lengths of <NUM> sequences. The UE may, after reception of a DMRS sequence, transmit the corresponding DMRS sequence based on the absolute timing. For example, where a UE transmits from SF0 to SF9 using the first ten symbols, a UE transmitting in SF <NUM> to SF19 uses the next ten symbols.

Using pi/<NUM>-BPSK or pi/<NUM>-QPSK may require changing the manner in which uplink pilots are inserted in an uplink channel and using BPSK as the pilot sequence may reduce inter-cell interference mitigation and offer less degrees of freedom than QPSK based pilot sequences. According to aspects of the present disclosure, QPSK or pi/<NUM>-QPSK may be used as uplink pilots so that different users can use sequences with good cross-correlation properties regardless of data being transmitted using, for example, pi/<NUM>-BPSK or pi/<NUM>-QPSK. Using a common modulation for the pilot sequence, such as QPSK or pi/<NUM>-QPSK, may increase the PAPR of some users (e.g., users using pi/<NUM>-BPSK with pi/<NUM>-BPSK pilots). As another example, BPSK, pi/<NUM>-BPSK or pi/<NUM>-BPSK may be used as uplink pilots regardless of the modulation used for data. In yet another example, the pilot modulation may be determined based on the modulation used for data. For example, the same modulation may be used for both data and pilots. The latter approach helps address inter-cell interference for the higher modulation cases, such as QPSK cases, while reducing the peak-to-average ratio of BPSK users.

Where pilots use different modulations for QPSK and BPSK, the resulting sequences should have good cross-correlation sequences. For example, a CGS may be defined for QPSK and BPSK, for example with two separate tables, and the UE may determine which table to use based on the modulation scheme and an index in the table based on the cell ID, slot index, or other characteristics. In case the modulation to be used for pilots is the same as the modulation used for data, the exact sequence to be used may be determined based on a plurality of factors. For example, a set of pilot sequences may be defined in the specification, and the UE would select the pilot sequence based on the modulation used for data. The set of pilot sequences may be different for different cells, such that inter-cell interference can be reduced. Further, a pilot sequence may be defined for a long transmission interval, and the UE will select the corresponding sub-sequence based on absolute timing. For example, if a sequence is defined with a length of <NUM>, a first UE transmitting in <NUM>-<NUM> will use the first half of the sequence, and a second UE transmitting in <NUM>-<NUM> will use the second half of the sequence.

In some cases, the modulation used for pilots may be the same as the modulation used for data, but different modulations may use the same set of sequences to construct the pilots. The construction of the pilot sequence (e.g., DMRS) may include selecting a subset of the modulation points (e.g., keep only two modulation points) between applying a sequence from the set of sequences. For example, DMRS may be generated from a binary sequence that has good cross-correlation properties, such as a Walsh code. The same set of binary sequences (e.g., a sequence of "<NUM>" and "<NUM>" or "<NUM>" and "-<NUM>") may be used to generate the pilots regardless of the modulation used, e.g., for either pi/<NUM>-QPSK and pi/<NUM>-BPSK. For example, each sequence may be used to select between two modulation symbols for the case of pi/<NUM>-BPSK.

<FIG> illustrate example constructions 1500A-1500D of a pilot sequence based on pilot modulation, according to aspects of the present disclosure. For example, where the modulation is pi/<NUM>-QPSK, then further steps may be taken. Calculation of the pilot sequences may be calculated by first applying a rotation (1500B) to pi/<NUM> QPSK (1500A) following the same pattern as for the data symbol. A down selection may be performed (1500C) where only two out of the four QPSK points are selected to construct a pi/<NUM> BPSK. This down-selection may be performed in such a way that the remaining two QPSK constellation points are antipodal (e.g., they are of the form [-x,x], with "x" a complex number). In some cases, the down-selection may be performed in such a way that the remaining constellation points are aligned with the constellation points of another modulation (e.g., with Pi/<NUM> BPSK) (1500D). The down selection may be performed based on cell ID, UE ID, subframe/symbol/slot number, higher layer parameters (e.g., signaled in SIB or RRC), cyclic shift, repetition level, definition in a specification and/or other parameters. This alignment between different modulation types provides better properties in terms of cross-correlation. In some cases, the rotation of pi/<NUM>-BPSK and pi/<NUM>-QPSK may be defined in a continuous manner, e.g., the rotations are performed as exp(j * pi/<NUM> * n) or exp(j * pi/<NUM> * n), resulting in a complete rotation of the QPSK/BPSK symbols (for example, for n=<NUM> the QPSK constellation is rotated <NUM> degrees, which is another QPSK but with a different bit mapping). If this continuous rotation is defined, then the mapping of the binary sequence to constellation points may need to take into account this rotation to preserve good correlation properties.

<FIG> illustrate aligned constellation points 1600A-C, according to aspects of the present disclosure. In some cases, the modulation used for pilots may be selected to be aligned between different modulations. For example, for pi/<NUM>-BPSK transmission, in some symbols the constellation points may be aligned with a subset of pi/<NUM>-QPSK transmissions (1600A and 1600B for normal CP (NCP) lengths and 1600C for extended CP (ECP) lengths). In such a case, the modulation used for pilot transmission is pi/<NUM>-BPSK or a subset of pi/<NUM>-QPSK (e.g., they are equivalent), for example. For some rotation values and in some symbols, the pi/<NUM>-QPSK may not be aligned with pi/<NUM>-BPSK. In such a case, the pi/<NUM>-BPSK user may use pi/<NUM>-QPSK as a pilot sequence, and may include a down selection process.

For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or combinations thereof.

Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the disclosure herein may be implemented as hardware, software, or combinations thereof.

The steps of a method or algorithm described in connection with the disclosure herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination thereof. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, phase change memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. Generally, where there are operations illustrated in Figures, those operations may be performed by any suitable corresponding counterpart means-plus-function components.

For example, means for determining, means for selecting, means for performing, means for monitoring, and/or means for attempting may include one or more processors (or a processing system), such as controller/processor <NUM>, scheduler <NUM>, transmitter processor <NUM>, receive processor <NUM>, MIMO detector <NUM>, TX MIMO processor <NUM>, and/or modulator(s)/demodulator(s) 232a-232t of the base station <NUM> illustrates in <FIG>, and/or controller/processor <NUM>, receive processor <NUM>, transmit processor <NUM>, MIMO detector <NUM>, TX MIMO processor <NUM>, and/or modulator(s)/demodulator(s) 254a-254r of the user equipment <NUM> illustrated in <FIG>. Means for transmitting, may include a transmitter, such as transmit processor <NUM>, TX MIMO processor <NUM>, modulator(s) 232a-232t, and/or antenna(s) 234a-234t of the base station <NUM> illustrated in <FIG>, and/or transmit processor <NUM>, TX MIMO processor <NUM>, modulator(s) 254a-254r, and/or antenna(s) 252a-252r of the user equipment <NUM> illustrated in <FIG>. Means for receiving and/or means for obtaining may include a receiver, such as receive processor <NUM>, MIMO detector <NUM>, demodulator(s) 232a-232t, and/or antenna(s) 234a-234t of the base station <NUM> illustrated in <FIG> and/or MIMO detector <NUM>, receive processor <NUM>, demodulator(s) 254a-254r, and/or antenna(s) 252a-252r of the user equipment <NUM> illustrated in <FIG>.

In one or more exemplary designs, the functions described may be implemented in hardware, software, or combinations thereof. A storage media may be any available media that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, flash memory, phase change memory, CD/DVD or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code means in the form of instructions or data structures and that can be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers.

As used herein, reference to an element in the singular is not intended to mean "one and only one" unless specifically so stated, but rather "one or more. " For example, the articles "a" and "an" as used in this application and the appended claims should generally be construed to mean "one or more" unless specified otherwise or clear from the context to be directed to a singular form. Unless specifically stated otherwise, the term "some" refers to one or more. Also, as used herein, including in the claims, "or" as used in a list of items (for example, a list of items prefaced by a phrase such as "at least one of" or "one or more of') indicates a disjunctive list such that, for example, a list of "at least one of A, B, or C" means A or B or C or AB or AC or BC or ABC ("ABC" indicating A and B and C), as well as any combination with multiples of the same element (e.g., AA, AAA, ABB, AAC, ABBCC or any other ordering of A, B, C).

Claim 1:
A method for wireless communications by a first apparatus, comprising:
determining (<NUM>) a number of pilot symbols to transmit for one or more slots of a first subframe based, at least in part, on a coverage enhancement, CE, level; and
transmitting (<NUM>) at least one uplink data channel having the determined number of pilot symbols in the one or more slots of the first subframe, characterized in that:
the first subframe has a longer duration relative to a second subframe used by a second apparatus; and
the first subframe has a lower frequency tone spacing scheme than the second subframe based on the first subframe duration.