WO2018165941A1

WO2018165941A1 - Random access optimization for narrow-band system

Info

Publication number: WO2018165941A1
Application number: PCT/CN2017/076947
Authority: WO
Inventors: Sivashankar Sekar; Saket BATHWAL; Peng Wu; Haiqin LIU; Gang Xiao
Original assignee: Qualcomm Incorporated
Priority date: 2017-03-16
Filing date: 2017-03-16
Publication date: 2018-09-20

Abstract

Certain aspects of the present disclosure relate to methods and apparatus for optimizing performance of random access procedures by a user equipments (UE). According to aspects, the UE may be configured to obtain one or more settings for uplink transmissions to an eNodeB, the one or more settings having been determined from a previous connection with the eNodeB, and perform a random access procedure based on the obtained one or more settings.

Description

RANDOM ACCESS OPTIMIZATION FOR NARROW-BAND SYSTEM

Field

The present disclosure relates generally to wireless communication, and more particularly, to methods and apparatus for optimizing the performance of random access procedures for Narrow-Band Internet of Things (NB-IoT) user equipments (UE) .

BACKGROUND

Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasts. Typical wireless communication systems may employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power) . Examples of such multiple-access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency divisional multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems.

These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example of an emerging telecommunication standard is Long Term Evolution (LTE) . LTE/LTE-Advanced is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) mobile standard promulgated by Third Generation Partnership Project (3GPP) . It is designed to better support mobile broadband Internet access by improving spectral efficiency, lower costs, improve services, make use of new spectrum, and better integrate with other open standards using OFDMA on the downlink (DL) , SC-FDMA on the uplink (UL) , and multiple-input multiple-output (MIMO) antenna technology. However, as the demand for mobile broadband access continues to increase, there exists a need for further improvements in LTE technology. Preferably, these improvements should be applicable to other multi-access technologies and the telecommunication standards that employ these technologies.

SUMMARY

Certain aspects of the present disclosure provide a method for wireless communications by a user equipment (UE) . The method generally includes obtaining one or more settings for uplink transmissions to an eNodeB, the one or more settings having been determined from a previous connection with the eNodeB, and performing a random access procedure based on the obtained one or more settings.

Aspects generally include methods, apparatus, systems, computer program products, computer-readable medium, and processing systems, as substantially described herein with reference to and as illustrated by the accompanying drawings. “LTE” refers generally to LTE, LTE-Advanced (LTE-A) , LTE in an unlicensed spectrum (LTE-whitespace) , etc.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a network architecture.

FIG. 2 is a diagram illustrating an example of an access network.

FIG. 3 is a diagram illustrating an example of a DL frame structure in LTE.

FIG. 4 is a diagram illustrating an example of an UL frame structure in LTE.

FIG. 5 is a diagram illustrating an example of a radio protocol architecture for the user and control plane.

FIG. 6 is a diagram illustrating an example of an evolved Node B (eNodeB) and user equipment in an access network, in accordance with certain aspects of the disclosure.

FIG. 7 illustrates an example deployment of NB-IoT, according to certain aspects of the present disclosure.

FIG. 8 illustrates example operations performed by a UE for performing a random access procedure based on settings obtained in a previous connection with an eNodeB, in accordance with certain aspects of the present disclosure.

DETAILED DESCRIPTION

Narrow-Band Internet of Things (NB-IoT) is a technology being standardized by the 3GPP standards body. This technology is a narrowband radio technology specially designed for the IoT, hence its name. Special focuses of this standard are on indoor coverage, low cost, long battery life, and large number of devices. The NB-IoT technology may be deployed “in-band, ” utilizing resource blocks within a normal LTE or GSM spectrum. In addition, NB-IoT may be deployed in the unused resource blocks within a LTE carrier’s guard-band, or “standalone” for deployments in dedicated spectrum.

NB-IoT devices may be deployed as devices in fixed locations. In such cases, these devices may experience consistent radio conditions over time (e.g., consistent reference signal received power (RSRP) and/or reference signal received quality (RSRQ) measurements over time) . Because these devices may experience consistent radio conditions, random access procedures may be optimized, for example, to accelerate completion of random access procedures when an NB-IoT device initially connects to a network. Aspects of the present disclosure provide techniques for accelerating completion of random access procedures by initializing random access procedures using settings determined for previous connections with an eNodeB.

The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well-known structures and components are shown in block diagram form in order to avoid obscuring such concepts.

Several aspects of telecommunication systems will now be presented with reference to various apparatus and methods. These apparatus and methods will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, modules, components, circuits, steps, processes, algorithms, etc. (collectively referred to as “elements” ) . These elements may be implemented using hardware, software, or combinations thereof. Whether such elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system.

By way of example, an element, or any portion of an element, or any combination of elements may be implemented with a “processing system” that includes one or more processors. Examples of processors include microprocessors, microcontrollers, digital signal processors (DSPs) , field programmable gate arrays (FPGAs) , programmable logic devices (PLDs) , state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionality described throughout this disclosure. One or more processors in the processing system may execute software. Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software modules, applications, software applications, software packages, firmware, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise.

Accordingly, in one or more exemplary embodiments, the functions described may be implemented in hardware, software, or combinations thereof. If implemented in software, the functions may be stored on or encoded as one or more instructions or code on a computer-readable medium. Computer-readable media includes computer storage media. Storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, PCM (phase change memory) , flash memory, CD-ROM 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 in the form of instructions or data structures and that can be accessed by a computer. 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. Combinations of the above should also be included within the scope of computer-readable media. An exemplary storage medium is coupled to a processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

FIG. 1 is a diagram illustrating an LTE network architecture 100 in which aspects of the present disclosure may be practiced.

In certain aspects, a UE, which may be an NB-IoT UE operating in a narrowband region located in a wideband region of resources, (e.g., UE 102) determines subframes available for a random access procedure for each of a first, lower coverage enhancement (CE) level and a second, higher CE level. The UE determines an overlap in the subframes available for the random procedure for the first CE level and the subframes available for the random access procedure for the second CE level. The UE performs the random access procedure using the subframes available for the second CE level.

The LTE network architecture 100 may be referred to as an Evolved Packet System (EPS) 100. The EPS 100 may include one or more user equipment (UE) 102, an Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) 104, an Evolved Packet Core (EPC) 110, a Home Subscriber Server (HSS) 120, and an Operator’s IP Services 122. The EPS can interconnect with other access networks, but for simplicity those entities/interfaces are not shown. Exemplary other access networks may include an IP Multimedia Subsystem (IMS) PDN, Internet PDN, Administrative PDN (e.g., Provisioning PDN) , carrier-specific PDN, operator-specific PDN, and/or GPS PDN. As shown, the EPS provides packet-switched services, however, as those skilled in the art will readily appreciate, the various concepts presented throughout this disclosure may be extended to networks providing circuit-switched services.

The E-UTRAN includes the evolved Node B (eNB) 106 and other eNBs 108. The eNB 106 provides user and control plane protocol terminations toward the UE 102. The eNB 106 may be connected to the other eNBs 108 via an X2 interface (e.g., backhaul) . The eNB 106 may also be referred to as a base station, a base transceiver station, a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS) , an extended service set (ESS) , an access point, or some other suitable terminology. The eNB 106 may provide an access point to the EPC 110 for a UE 102. Examples of UEs 102 include a cellular phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a personal digital assistant (PDA) , a satellite radio, a global positioning system, a multimedia device, a video device, a digital audio player (e.g., MP3 player) , a camera, a game console, a tablet, a netbook, a smart book, an ultrabook, a drone, a robot, a sensor, a monitor, a meter, a camera/security camera, a gaming/entertainment device, a virtual reality/augmented reality device, a wearable device (e.g., smart watch, smart glasses, smart goggles, smart ring, smart bracelet, smart wrist band, smart jewelry, smart clothing, etc. ) , a vehicular device, a position location/navigation device (e.g., satellite-based, terrestrial-based, etc. ) , any other similar functioning device, etc. Some UEs may be considered machine-type communication (MTC) UEs, which may include remote devices, 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 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. Examples of MTC devices include sensors, meters, location tags, monitors, drones, robots/robotic devices, etc. MTC UEs, as well as other types of UEs, may be implemented as NB-IoT (narrowband internet of things) devices. The UE 102 may also be referred to by those skilled in the art as a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a user agent, a mobile client, a client, or some other suitable terminology.

The eNB 106 is connected by an S1 interface to the EPC 110. The EPC 110 includes a Mobility Management Entity (MME) 112, other MMEs 114, a Serving Gateway 116, and a Packet Data Network (PDN) Gateway 118. The MME 112 is the control node that processes the signaling between the UE 102 and the EPC 110. Generally, the MME 112 provides bearer and connection management. All user IP packets are transferred through the Serving Gateway 116, which itself is connected to the PDN Gateway 118. The PDN Gateway 118 provides UE IP address allocation as well as other functions. The PDN Gateway 118 is connected to the Operator’s IP Services 122. The Operator’s IP Services 122 may include, for example, the Internet, the Intranet, an IP Multimedia Subsystem (IMS) , and a PS (packet-switched) Streaming Service (PSS) . In this manner, the UE 102 may be coupled to the PDN through the LTE network.

FIG. 2 is a diagram illustrating an example of an access network 200 in an LTE network architecture in which aspects of the present disclosure may be practiced. For example, UEs 206 may be configured to implement techniques for optimizing CE level enhancement selection as described in aspects of the present disclosure.

In this example, the access network 200 is divided into a number of cellular regions (cells) 202. One or more lower power class eNBs 208 may have cellular regions 210 that overlap with one or more of the cells 202. A lower power class eNB 208 may be referred to as a remote radio head (RRH) . The lower power class eNB 208 may be a femto cell (e.g., home eNB (HeNB) ) , pico cell, or micro cell. The macro eNBs 204 are each assigned to a respective cell 202 and are configured to provide an access point to the EPC 110 for all the UEs 206 in the cells 202. There is no centralized controller in this example of an access network 200, but a centralized controller may be used in alternative configurations. The eNBs 204 are responsible for all radio related functions including radio bearer control, admission control, mobility control, scheduling, security, and connectivity to the serving gateway 116. The network 200 may also include one or more relays (not shown) . According to one application, a UE may serve as a relay.

The modulation and multiple access scheme employed by the access network 200 may vary depending on the particular telecommunications standard being deployed. In LTE applications, OFDM is used on the DL and SC-FDMA is used on the UL to support both frequency division duplexing (FDD) and time division duplexing (TDD) . As those skilled in the art will readily appreciate from the detailed description to follow, the various concepts presented herein are well suited for LTE applications. However, these concepts may be readily extended to other telecommunication standards employing other modulation and multiple access techniques. By way of example, these concepts may be extended to Evolution-Data Optimized (EV-DO) or Ultra Mobile Broadband (UMB) . EV-DO and UMB are air interface standards promulgated by the 3rd Generation Partnership Project 2 (3GPP2) as part of the CDMA2000 family of standards and employs CDMA to provide broadband Internet access to mobile stations. These concepts may also be extended to Universal Terrestrial Radio Access (UTRA) employing Wideband-CDMA (W-CDMA) and other variants of CDMA, such as TD-SCDMA； Global System for Mobile Communications (GSM) employing TDMA； and Evolved UTRA (E-UTRA) , Ultra Mobile Broadband (UMB) , IEEE 802.11 (Wi-Fi) , IEEE 802.16 (WiMAX) , IEEE 802.20, and Flash-OFDM employing OFDMA. UTRA, E-UTRA, UMTS, LTE and GSM are described in documents from the 3GPP organization. CDMA2000 and UMB are described in documents from the 3GPP2 organization. The actual wireless communication standard and the multiple access technology employed will depend on the specific application and the overall design constraints imposed on the system.

The eNBs 204 may have multiple antennas supporting MIMO technology. The use of MIMO technology enables the eNBs 204 to exploit the spatial domain to support spatial multiplexing, beamforming, and transmit diversity. Spatial multiplexing may be used to transmit different streams of data simultaneously on the same frequency. The data streams may be transmitted to a single UE 206 to increase the data rate or to multiple UEs 206 to increase the overall system capacity. This is achieved by spatially precoding each data stream (e.g., applying a scaling of an amplitude and a phase) and then transmitting each spatially precoded stream through multiple transmit antennas on the DL. The spatially precoded data streams arrive at the UE (s) 206 with different spatial signatures, which enables each of the UE (s) 206 to recover the one or more data streams destined for that UE 206. On the UL, each UE 206 transmits a spatially precoded data stream, which enables the eNB 204 to identify the source of each spatially precoded data stream.

Spatial multiplexing is generally used when channel conditions are good. When channel conditions are less favorable, beamforming may be used to focus the transmission energy in one or more directions. This may be achieved by spatially precoding the data for transmission through multiple antennas. To achieve good coverage at the edges of the cell, a single stream beamforming transmission may be used in combination with transmit diversity.

In the detailed description that follows, various aspects of an access network may be described with reference to a MIMO system supporting OFDM on the DL. OFDM is a spread-spectrum technique that modulates data over a number of subcarriers within an OFDM symbol. The subcarriers are spaced apart at precise frequencies. The spacing provides “orthogonality” that enables a receiver to recover the data from the subcarriers. In the time domain, a guard interval (e.g., cyclic prefix) may be added to each OFDM symbol to combat inter-OFDM-symbol interference. The UL may use SC-FDMA in the form of a DFT-spread OFDM signal to compensate for high peak-to-average power ratio (PAPR) .

FIG. 3 is a diagram 300 illustrating an example of a DL frame structure in LTE. A frame (10 ms) may be divided into 10 equally sized sub-frames with indices of 0 through 9. Each sub-frame may include two consecutive time slots. A resource grid may be used to represent two time slots, each time slot including a resource block. The resource grid is divided into multiple resource elements. In LTE, a resource block contains 12 consecutive subcarriers in the frequency domain and, for a normal cyclic prefix in each OFDM symbol, 7 consecutive OFDM symbols in the time domain, or 84 resource elements. For an extended cyclic prefix, a resource block contains 6 consecutive OFDM symbols in the time domain and has 72 resource elements. Some of the resource elements, as indicated as R 302, R 304, include DL reference signals (DL-RS) . The DL-RS include Cell-specific RS (CRS) (also sometimes called common RS) 302 and UE-specific RS (UE-RS) 304. UE-RS 304 are transmitted only on the resource blocks upon which the corresponding physical DL shared channel (PDSCH) is mapped. The number of bits carried by each resource element depends on the modulation scheme. Thus, the more resource blocks that a UE receives and the higher the modulation scheme, the higher the data rate for the UE.

In LTE, an eNB may send a primary synchronization signal (PSS) and a secondary synchronization signal (SSS) for each cell in the eNB. The primary and secondary synchronization signals may be sent in

symbol periods

6 and 5, respectively, in each of

subframes

0 and 5 of each radio frame with the normal cyclic prefix (CP) . The synchronization signals may be used by UEs for cell detection and acquisition. The eNB may send a Physical Broadcast Channel (PBCH) in symbol periods 0 to 3 in slot 1 of subframe 0. The PBCH may carry certain system information.

The eNB may send a Physical Control Format Indicator Channel (PCFICH) in the first symbol period of each subframe. The PCFICH may convey the number of symbol periods (M) used for control channels, where M may be equal to 1, 2 or 3 and may change from subframe to subframe. M may also be equal to 4 for a small system bandwidth, e.g., with less than 10 resource blocks. The eNB may send a Physical HARQ Indicator Channel (PHICH) and a Physical Downlink Control Channel (PDCCH) in the first M symbol periods of each subframe. The PHICH may carry information to support hybrid automatic repeat request (HARQ) . The PDCCH may carry information on resource allocation for UEs and control information for downlink channels. The eNB may send a Physical Downlink Shared Channel (PDSCH) in the remaining symbol periods of each subframe. The PDSCH may carry data for UEs scheduled for data transmission on the downlink.

The eNB may send the PSS, SSS, and PBCH in the center 1.08 MHz of the system bandwidth used by the eNB. The eNB may send the PCFICH and PHICH across the entire system bandwidth in each symbol period in which these channels are sent. The eNB may send the PDCCH to groups of UEs in certain portions of the system bandwidth. The eNB may send the PDSCH to specific UEs in specific portions of the system bandwidth. The eNB may send the PSS, SSS, PBCH, PCFICH, and PHICH in a broadcast manner to all UEs, may send the PDCCH in a unicast manner to specific UEs, and may also send the PDSCH in a unicast manner to specific UEs.

A number of resource elements may be available in each symbol period. Each resource element (RE) 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. Resource elements not used for a reference signal in each symbol period may be arranged into resource element groups (REGs) . Each REG may include four resource elements in one symbol period. The PCFICH may occupy four REGs, which may be spaced approximately equally across frequency, in symbol period 0. The PHICH may occupy three REGs, which may be spread across frequency, in one or more configurable symbol periods. For example, the three REGs for the PHICH may all belong in symbol period 0 or may be spread in

symbol periods

0, 1, and 2. The PDCCH may occupy 9, 18, 36, or 72 REGs, which may be selected from the available REGs, in the first M symbol periods, for example. Only certain combinations of REGs may be allowed for the PDCCH. In aspects of the present methods and apparatus, a subframe may include more than one PDCCH.

A UE may know the specific REGs used for the PHICH and the PCFICH. The UE may search different combinations of REGs for the PDCCH. The number of combinations to search is typically less than the number of allowed combinations for the PDCCH. An eNB may send the PDCCH to the UE in any of the combinations that the UE will search.

FIG. 4 is a diagram 400 illustrating an example of an UL frame structure in LTE. The available resource blocks for the UL may be partitioned into a data section and a control section. The control section may be formed at the two edges of the system bandwidth and may have a configurable size. The resource blocks in the control section may be assigned to UEs for transmission of control information. The data section may include all resource blocks not included in the control section. The UL frame structure results in the data section including contiguous subcarriers, which may allow a single UE to be assigned all of the contiguous subcarriers in the data section.

A UE may be assigned

resource blocks

410a, 410b in the control section to transmit control information to an eNB. The UE may also be assigned

resource blocks

420a, 420b in the data section to transmit data to the eNB. The UE may transmit control information in a physical UL control channel (PUCCH) on the assigned resource blocks in the control section. The UE may transmit only data or both data and control information in a physical UL shared channel (PUSCH) on the assigned resource blocks in the data section. An UL transmission may span both slots of a subframe and may hop across frequency.

A set of resource blocks may be used to perform initial system access and achieve UL synchronization in a physical random access channel (PRACH) 430. The PRACH 430 carries a random sequence and cannot carry any UL data/signaling. Each random access preamble occupies a bandwidth corresponding to six consecutive resource blocks. The starting frequency is specified by the network. That is, the transmission of the random access preamble is restricted to certain time and frequency resources. There is no frequency hopping for the PRACH. The PRACH attempt is carried in a single subframe (1 ms) or in a sequence of few contiguous subframes and a UE can make only a single PRACH attempt per frame (10 ms) .

FIG. 5 is a diagram 500 illustrating an example of a radio protocol architecture for the user and control planes in LTE. The radio protocol architecture for the UE and the eNB is shown with three layers: Layer 1, Layer 2, and Layer 3. Layer 1 (L1 layer) is the lowest layer and implements various physical layer signal processing functions. The L1 layer will be referred to herein as the physical layer 506. Layer 2 (L2 layer) 508 is above the physical layer 506 and is responsible for the link between the UE and eNB over the physical layer 506.

In the user plane, the L2 layer 508 includes a media access control (MAC) sublayer 510, a radio link control (RLC) sublayer 512, and a packet data convergence protocol (PDCP) 514 sublayer, which are terminated at the eNB on the network side. Although not shown, the UE may have several upper layers above the L2 layer 508 including a network layer (e.g., IP layer) that is terminated at the PDN gateway 118 on the network side, and an application layer that is terminated at the other end of the connection (e.g., far end UE, server, etc. ) .

The PDCP sublayer 514 provides multiplexing between different radio bearers and logical channels. The PDCP sublayer 514 also provides header compression for upper layer data packets to reduce radio transmission overhead, security by ciphering the data packets, and handover support for UEs between eNBs. The RLC sublayer 512 provides segmentation and reassembly of upper layer data packets, retransmission of lost data packets, and reordering of data packets to compensate for out-of-order reception due to hybrid automatic repeat request (HARQ) . The MAC sublayer 510 provides multiplexing between logical and transport channels. The MAC sublayer 510 is also responsible for allocating the various radio resources (e.g., resource blocks) in one cell among the UEs. The MAC sublayer 510 is also responsible for HARQ operations.

In the control plane, the radio protocol architecture for the UE and eNB is substantially the same for the physical layer 506 and the L2 layer 508 with the exception that there is no header compression function for the control plane. The control plane also includes a radio resource control (RRC) sublayer 516 in Layer 3 (L3 layer) . The RRC sublayer 516 is responsible for obtaining radio resources (i.e., radio bearers) and for configuring the lower layers using RRC signaling between the eNB and the UE.

FIG. 6 is a block diagram of an eNB 610 in communication with a UE 650 in an access network, in which aspects of the present disclosure may be practiced.

In certain aspects, a UE (e.g., UE 650) determines subframes available for a random access procedure for each of a first, lower coverage enhancement (CE) level and a second, higher CE level, determines an overlap in the subframes available for the random procedure for the first CE level and the subframes available for the random access procedure for the second CE level, and performs the random access procedure using the subframes available for the second CE level.

The UE noted above configured to optimize CE level selection in accordance with certain aspects of the present disclosure may be implemented by a combination of one or more of the controller 659, the RX processor 656, the channel estimator 658 and/or transceiver 654 at the UE 650, for example.

In the DL, upper layer packets from the core network are provided to a controller/processor 675. The controller/processor 675 implements the functionality of the L2 layer. In the DL, the controller/processor 675 provides header compression, ciphering, packet segmentation and reordering, multiplexing between logical and transport channels, and radio resource allocations to the UE 650 based on various priority metrics. The controller/processor 675 is also responsible for HARQ operations, retransmission of lost packets, and signaling to the UE 650.

The TX processor 616 implements various signal processing functions for the L1 layer (i.e., physical layer) . The signal processing functions includes coding and interleaving to facilitate forward error correction (FEC) at the UE 650 and mapping to signal constellations based on various modulation schemes (e.g., binary phase-shift keying (BPSK) , quadrature phase-shift keying (QPSK) , M-phase-shift keying (M-PSK) , M-quadrature amplitude modulation (M-QAM) ) . The coded and modulated symbols are then split into parallel streams. Each stream is then mapped to an OFDM subcarrier, multiplexed with a reference signal (e.g., pilot) in the time and/or frequency domain, and then combined together using an Inverse Fast Fourier Transform (IFFT) to produce a physical channel carrying a time domain OFDM symbol stream. The OFDM stream is spatially precoded to produce multiple spatial streams. Channel estimates from a channel estimator 674 may be used to determine the coding and modulation scheme, as well as for spatial processing. The channel estimate may be derived from a reference signal and/or channel condition feedback transmitted by the UE 650. Each spatial stream is then provided to a different antenna 620 via a separate transmitter 618TX. Each transmitter 618TX modulates an RF carrier with a respective spatial stream for transmission.

At the UE 650, each receiver 654RX receives a signal through its respective antenna 652. Each receiver 654RX recovers information modulated onto an RF carrier and provides the information to the receiver (RX) processor 656. The RX processor 656 implements various signal processing functions of the L1 layer. The RX processor 656 performs spatial processing on the information to recover any spatial streams destined for the UE 650. If multiple spatial streams are destined for the UE 650, they may be combined by the RX processor 656 into a single OFDM symbol stream. The RX processor 656 then converts the OFDM symbol stream from the time-domain to the frequency domain using a Fast Fourier Transform (FFT) . The frequency domain signal comprises a separate OFDM symbol stream for each subcarrier of the OFDM signal. The symbols on each subcarrier, and the reference signal, is recovered and demodulated by determining the most likely signal constellation points transmitted by the eNB 610. These soft decisions may be based on channel estimates computed by the channel estimator 658. The soft decisions are then decoded and deinterleaved to recover the data and control signals that were originally transmitted by the eNB 610 on the physical channel. The data and control signals are then provided to the controller/processor 659.

The controller/processor 659 implements the L2 layer. The controller/processor can be associated with a memory 660 that stores program codes and data. The memory 660 may be referred to as a computer-readable medium. In the UL, the controller/processor 659 provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover upper layer packets from the core network. The upper layer packets are then provided to a data sink 662, which represents all the protocol layers above the L2 layer. Various control signals may also be provided to the data sink 662 for L3 processing. The controller/processor 659 is also responsible for error detection using an acknowledgement (ACK) and/or negative acknowledgement (NACK) protocol to support HARQ operations.

In the UL, a data source 667 is used to provide upper layer packets to the controller/processor 659. The data source 667 represents all protocol layers above the L2 layer. Similar to the functionality described in connection with the DL transmission by the eNB 610, the controller/processor 659 implements the L2 layer for the user plane and the control plane by providing header compression, ciphering, packet segmentation and reordering, and multiplexing between logical and transport channels based on radio resource allocations by the eNB 610. The controller/processor 659 is also responsible for HARQ operations, retransmission of lost packets, and signaling to the eNB 610.

Channel estimates derived by a channel estimator 658 from a reference signal or feedback transmitted by the eNB 610 may be used by the TX processor 668 to select the appropriate coding and modulation schemes, and to facilitate spatial processing. The spatial streams generated by the TX processor 668 are provided to different antenna 652 via separate transmitters 654TX. Each transmitter 654TX modulates an RF carrier with a respective spatial stream for transmission.

The UL transmission is processed at the eNB 610 in a manner similar to that described in connection with the receiver function at the UE 650. Each receiver 618RX receives a signal through its respective antenna 620. Each receiver 618RX recovers information modulated onto an RF carrier and provides the information to a RX processor 670. The RX processor 670 may implement the L1 layer.

The controller/processor 675 implements the L2 layer. The controller/processor 675 can be associated with a memory 676 that stores program codes and data. The memory 676 may be referred to as a computer-readable medium. In the UL, the controller/processor 675 provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover upper layer packets from the UE 650. Upper layer packets from the controller/processor 675 may be provided to the core network. The controller/processor 675 is also responsible for error detection using an ACK and/or NACK protocol to support HARQ operations. The controllers/

processors

675, 659 may direct the operations at the eNB 610 and the UE 650, respectively.

The controller/processor 659 and/or other processors, components and/or modules at the UE 650 may perform or direct operations, for example, operations 800 in FIG 8, and/or other processes for optimizing CE level selection. In certain aspects, one or more of any of the components shown in FIG. 6 may be employed to perform

example operations

800 and 900, and/or other processes for the techniques described herein. The

memories

660 and 676 may store data and program codes for the UE 650 and eNB 610 respectively, accessible and executable by one or more other components of the UE 650 and the eNB 610.

NB-IoT

Devices may communicate using relative narrowband regions of system bandwidth, such as narrowband internet of things (NB-IoT) devices. To reduce the complexity of UEs, NB-IoT may allow for deployments utilizing one Physical Resource Block (PRB) (180kHZ + 20 kHZ guard band) . NB-IoT deployments may utilize higher layer components of LTE and hardware to allow for reduced fragmentation and cross compatibility with, for example, NB-LTE and eMTC (enhanced or evolved Machine Type Communications) .

FIG. 7 illustrates an example deployment 700 of NB-IoT, according to certain aspects of the present disclosure. According to certain aspects, NB-IoT may be deployed in three broad configurations. In certain deployments, NB-IoT may be deployed in-band and coexist with legacy GSM/WCDMA/LTE system (s) deployed in the same frequency band. Wideband LTE channel, for example, may be deployed in, e.g., various bandwidths between 1.4 MHz to 20 MHz, and there may be a dedicated RB 702 available for use by NB-IoT, or the RBs allocated for NB-IoT may be dynamically allocated 704. In an in-band deployment, one resource block (RB) , or 200 kHz, of a wideband LTE channel may be used for NB-IoT. LTE implementations may include unused portions of radio spectrum between carriers to guard against interference between adjacent carriers. In some deployments, NB-IoT may be deployed in a guard band 706 of the wideband LTE channel. In other deployments, NB-IoT may be deployed standalone (not shown) . In a standalone deployment, one 200 mHz carrier may be utilized to carry NB-IoT traffic and GSM spectrum may be reused.

Deployments of NB-IoT, may include synchronization signals such as PSS for frequency and timing synchronization and SSS to convey system information. According to certain aspects of the present disclosure, synchronization signals of NB- IoT operations occupy narrow channel bandwidths and can coexist with legacy GSM/WCDMA/LTE system (s) deployed in the same frequency band. NB-IoT operations may include PSS/SSS timing boundaries. In certain aspects, these timing boundaries may be extended as compared to the existing PSS/SSS frame boundaries in legacy LTE systems (e.g., 10 ms) to, for example, 40 ms. Based on the timing boundary, a UE is able to receive a PBCH transmission, which may be transmitted in subframe 0 of a radio frame.

EXAMPLE RANDOM ACCESS OPTIMIZATION FOR NARROW-BAND INTERNET OF THINGS (NB-IOT)

The Internet of Things (IoT) is a network of physical objects or “things” embedded with, e.g., electronics, software, sensors, and network connectivity, which enable these objects to collect and exchange data. IoT allows objects to be sensed and controlled remotely across existing network infrastructure, creating opportunities for more direct integration between the physical world and computer-based systems, and resulting in improved efficiency, accuracy and economic benefit. When IoT is augmented with sensors and actuators, the technology becomes an instance of the more general class of cyber-physical systems, which also encompasses technologies such as smart grids, smart homes, intelligent transportation and smart cities. Each “thing” is generally uniquely identifiable through its embedded computing system but is able to interoperate within the existing Internet infrastructure.

Narrow-Band IoT (NB-IoT) is a technology being standardized by the 3GPP standards body. This technology is a narrowband radio technology specially designed for the IoT, hence its name. Special focuses of this standard are on indoor coverage, low cost, long battery life and large number of devices.

The NB-IoT technology may be deployed “in-band” , utilizing resource blocks within, e.g., a normal LTE or GSM spectrum. In addition, NB-IoT may be deployed in the unused resource blocks within a LTE carrier’s guard-band, or “standalone” for deployments in dedicated spectrum.

While NB-IoT may be inspired by LTE, it focuses on low data rates and technology that transmit periodically transmit information, such as parking meters or other devices that may be installed in a fixed location (e.g., power meters, water meters, and the like) . NB-IoT devices may have a high battery life. Further, despite poor general conditions, the NB-IoT devices should reliably transmit information. For example, the NB-IoT devices may be underground or otherwise deployed in environments with high penetration loss.

In an effort to achieve a high tolerance towards adverse channel conditions, NB-IoT devices have different coverage enhancement (CE) levels. Narrowband Physical Random Access Channel (NPRACH) is a newly designed channel, since the legacy LTE PRACH uses a bandwidth of 1.08 MHz, which is more than NB-IoT uplink bandwidth. To serve UEs in different coverage classes (CE levels) that have different ranges of path loss, the network may configure up to three NPRACH resources configurations (e.g., 3 CE levels) in each cell. In each configuration, a repetition value is specified for repeating a basic random access preamble. A UE may measure its downlink received signal power in an effort to estimate its CE level. The network associates each CE level with a threshold reference signal receive power (RSRP) value. A UE may compare the its channel condition (such as a RSRP) measurement to the threshold values to determine its CE level. The UE may transmit a random access preamble in the NPRACH resources configured for its estimated CE level.

Thus, the UE may determine its CE level by measuring downlink received signal power. After reading system information regarding NPRACH resource configurations, the UE may determine the NPRACH resource configured and the number of repetitions needed for its estimated CE level as well as a random access preamble transmit power.

Per the LTE specification (36.321) , once the UE selects the CE level based on the RSRP and threshold values, the UE may perform a RACH procedure. The NPRACH is a shared channel for many UEs. According to one example, a first UE may be transmitting at CE level 1 and anther UE may be transmitting at CE level 2 based on each of the first and second UE’s measured channel conditions for the same network. CE levels may have overlapping resources in their allocation of NPRACH resources. When a collision occurs, the higher CE level takes priority. Per the specification, lower NPRACH CE levels resources (e.g., slots) which collide with higher CE level resources are invalid.

Because IoT UEs may be installed in fixed locations, radio conditions for connections between these devices and an eNodeB may remain relatively constant for an extended period of time. Thus, an IoT UE may use the same settings, such as transmission power, timing adjustment, CE level, and the like for performing a RACH procedure to connect with the eNodeB. However, these UEs may begin each RACH procedure by transmitting a RACH preamble using an initial set of settings. This initial set may include a default CE level (e.g., CE level 0) and timing advance and transmission power settings provided by an eNodeB (e.g., in a master information block or system information block broadcast by the eNodeB) . The UE may adjust these settings (e.g., changing to higher CE levels) based on failures to successfully perform a RACH procedure until a RACH procedure is successfully performed. Because channel conditions may not have changed between a previous connection and a new connection between the UE and the eNodeB, performing a RACH procedure based on an initial set of settings may entail wasting resources and delaying the establishment of a connection between the UE and the eNodeB.

According to aspects of the present disclosure, a UE can store settings for performing a RACH procedure with an eNodeB at the UE (e.g., in non-volatile memory) . Based on measured signal quality metrics and signal quality metrics associated with the stored settings, the UE can determine whether to perform a RACH procedure based on the stored settings or default settings which may, in some cases, be defined a priori (e.g., according to a specification) .

FIG. 8 illustrates example operations that may be performed by a UE to perform a RACH procedure based on settings determined from previous connections with the eNodeB, according to an aspect of the present disclosure. As illustrated, operations 800 begin at 802, where the UE obtains one or more settings for uplink transmissions to an eNodeB. The one or more settings may have been determined from a previous connection with the eNodeB. At 804, the UE performs a random access procedure based on the obtained one or more settings.

In some cases, by performing a random access procedure based on settings that were determined previously (e.g., from a previous establishment of a connection with the eNodeB) , the UE can begin the RACH procedure with settings that the UE used to successfully perform a previous RACH procedure. A UE may, for example, initiate a RACH procedure by transmitting a random access preamble using an uplink transmission power that is higher than an initial uplink transmission power (e.g., specified by an eNodeB) . The uplink transmission power level used to transmit the random access preamble may allow the UE to successfully transmit the random access preamble to the eNodeB (in contrast to the initial uplink transmission power, which may result in a failed preamble transmission from the UE to the eNodeB) .

In some cases, the UE may monitor channel conditions associated with a connection with an eNodeB to determine whether to perform a RACH procedure using stored settings (e.g., settings determined from a previous connection with the eNodeB) or to perform a RACH procedure using the initial set of settings. In some cases, the UE can use a threshold signal quality difference to determine which settings to use for performing a RACH procedure. The signal quality difference may be based on a reference signal received power (RSRP) measurement, a reference signal received quality (RSRQ) measurement, or other signal quality metric. A UE can measure the signal quality of a connection with the eNodeB and compare the measured signal quality with the signal quality associated with the stored settings to determine a signal quality difference (e.g., a ΔRSRP or ΔRSRQ measurement) . If the signal quality difference is less than the threshold difference amount, the UE can perform a RACH procedure using the stored settings. Otherwise, if the signal quality difference exceeds the threshold difference amount, the UE can perform a RACH procedure using an initial set of settings and can overwrite the stored settings with the settings that resulted in successfully performing a RACH procedure for the current channel conditions between the UE and the eNodeB.

FIG. 9 illustrates example operations 900 for wireless communication, in accordance with certain aspects of the present disclosure. In certain aspects, the operations 900 may be performed by a UE such as the UE 120.

The operations 900 may begin, at 902, by determining a capability of the UE with respect to multi-tone transmission. At 904, the UE selects a coverage enhancement (CE) level for transmitting one or more random access channel (RACH) messages based on the capability of the UE. At block 906, the UE transmits the one or more RACH messages to a base station based on the determined CE level.

In some cases, to perform a RACH procedure using an initial set of settings, the UE may select a CE level based, at least in part, on UE support for multi-tone transmission (e.g., multi-tone transmission on the physical uplink shared channel (PUSCH) ) . In some cases, a UE may experience a RACH failure in transmitting RACH MSG3, where the UE transmits a UE identification message to the eNodeB. Upon such a failure, the UE may move to another CE level after experiencing a threshold number of RACH failures. To select a CE level, a UE may, in some cases, consider UE capabilities for multi-tone transmissions and the availability of a single tone subcarrier. If, for example, a single-tone subcarrier is not available, the UE may move to the next CE level that supports single-tone transmissions from the UE.

It is understood that the specific order or hierarchy of steps in the processes disclosed is an illustration of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged. Further, some steps may be combined or omitted. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented. Generally, where there are operations illustrated in Figures, those operations may be performed by any suitable corresponding counterpart means-plus-function components.

Moreover, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or. ” That is, unless specified otherwise, or clear from the context, the phrase, for example, “X employs A or B” is intended to mean any of the natural inclusive permutations. That is, for example the phrase “X employs A or B” is satisfied by any of the following instances: X employs A； X employs B； or X employs both A and B. 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. A phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c, as well as any combination with multiples of the same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b, b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c) . As used herein, including in the claims, the term “and/or, ” when used in a list of two or more items, means that any one of the listed items can be employed by itself, or any combination of two or more of the listed items can be employed. For example, if a composition is described as containing components A, B, and/or C, the composition can contain A alone； B alone； C alone； A and B in combination； A and C in combination； B and C in combination； or A, B, and C in combination.

The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language of claims. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed as a means plus function unless the element is expressly recited using the phrase “means for. ”

Claims

A method for wireless communications by a user equipment (UE) , comprising:

obtaining one or more settings for uplink transmissions to an eNodeB, the one or more settings having been determined from a previous connection with the eNodeB； and

performing a random access procedure based on the obtained one or more settings.
The method of claim 1, wherein the one or more settings comprises a coverage enhancement (CE) level.
The method of claim 1, wherein the one or more settings comprises a time alignment (TA) value.
The method of claim 1, wherein the one or more settings comprises an initial transmission power level.
The method of claim 1, further comprising:

detecting that a signal quality metric associated with the obtained one or more settings differs from a current signal quality metric by at least a threshold amount； and

initiating a random access procedure using a default set of settings.
The method of claim 5, further comprising:

determining that the random access procedure succeeded； and

overwriting the obtained one or more settings with one or more settings used for the successful random access procedure.
The method of claim 5, wherein initiating the random access procedure using a default set of settings comprises:

selecting a coverage enhancement (CE) level based, at least in part, on a signal quality metric； and

upon determining that the selected CE level is associated with multi-tone transmission, selecting a second CE level associated with a single tone transmission.
The method of claim 7, wherein the signal quality metric comprises a reference signal received power (RSRP) measurement.
The method of claim 1, wherein the one or more settings are stored at the UE.
A method, apparatus, system, computer program product, and processing system as substantially described herein with reference to and as illustrated by the accompanying drawings.