CN111601394A

CN111601394A - Random access mechanism for link budget limited devices

Info

Publication number: CN111601394A
Application number: CN202010428495.3A
Authority: CN
Inventors: 宿利; S·M·阿马尔福; V·R·曼尼帕丽
Original assignee: Apple Inc
Current assignee: Apple Inc
Priority date: 2015-07-17
Filing date: 2016-07-15
Publication date: 2020-08-28
Anticipated expiration: 2036-07-15
Also published as: DE102016212714A1; CN111601394B

Abstract

A random access mechanism for a link budget limited device is disclosed, comprising: broadcasting a Physical Random Access Channel (PRACH) configuration index (PCI) reserved for Link Budget Limited (LBL) devices; configuring the LBL device to use the PCI offset from the normal PCI of the current cell; configuring LBL equipment to send PRACH messages by using a substitute subframe set different from a conventionally defined subframe set; when the conventional PRACH configuration specifies an even frame, LBL equipment is configured to send a PRACH message on the odd frame; configuring the LBL device to generate and use additional PRACH preambles that are not used by non-LBL devices; configuring the LBL equipment to use the B group lead code, and configuring the non-LBL equipment to use the A group lead code; and boosting power of the random access response message after the Nth random access failure by using the preamble conforming to the LBL reservation mode of the preamble.

Description

Random access mechanism for link budget limited devices

This application is a divisional application of the inventive patent application having a filing date of 2016, 7, 15, and having a filing number of 201610556764.8 entitled "random access mechanism for a device with limited link budget".

Technical Field

The present application relates generally to wireless communications, and more particularly to mechanisms that enable enhanced random access procedures for user equipment devices that are link budget limited.

Background

Wireless User Equipment (UE) devices, such as smart phones and tablet computers, communicate with wireless networks to perform any of a wide variety of functions, such as phone calls, internet browsing, email, text messaging, social media updates, navigation using the Global Positioning System (GPS), and so forth.

In LTE, a random access procedure (referred to herein as "RACH") is a procedure for synchronizing a User Equipment (UE) device with a Network (NW). The RACH may be used to: initial access to the NW by the UE device; handover of a UE device from one cell to another cell; RRC reestablishment; uplink and/or downlink data arrival; positioning in RRC connection. RACH is a procedure that allows a UE to access the NW, synchronize with uplink signals from different UE devices, and obtain orthogonal resources. Therefore, it is important to ensure that the message of the RACH is successfully transmitted.

However, some wireless devices may be Link Budget Limited (LBL) and, therefore, experience difficulty in receiving messages transmitted by base stations of the network. The base station may also experience difficulties in receiving messages transmitted by devices with limited link budget. A device may be link budget limited for any of a variety of reasons, for example, if:

the antenna system of the device performs poorly; or

The antenna system of the device is designed to be accommodated within a housing that is too small for optimal transmission and/or reception performance in the frequency band of interest;

the device is located remotely from the base station; or

An obstacle intervenes between the base station and the device (e.g., if the device is located within a building); or

The battery power of the device is limited.

A UE device with limited link budget may have limited RF range in the downlink (receive) direction and/or in the uplink (transmit) direction. Therefore, there is a need for mechanisms that can enhance the ability of link budget limited devices and base stations to efficiently exchange messages. In particular, there is a need for mechanisms that can improve the performance of random access procedures for link budget limited UE devices. It would be desirable if such mechanisms could be compatible with (and/or easily extended from) existing LTE networks, e.g., with minimal or no impact on LTE network capacity, and/or with minimal or no impact on the LTE physical layer, to facilitate ease of implementation.

Disclosure of Invention

In one set of embodiments, a base station may be configured to broadcast an alternative PRACH configuration index for use by a link budget limited device, where the alternative PRACH configuration index is different from a conventional PRACH configuration index for a cell. A link budget limited device may be configured to transmit PRACH messages with a PRACH configuration identified by an alternative index, while a non-LBL device (and/or legacy device) uses a PRACH configuration identified by a conventional index. (the alternative PRACH configuration index may be selected such that the corresponding PRACH configuration has an allowable set of time opportunities for PRACH transmission that is disjoint from the allowable set of conventional PRACH configurations.) the base station receives PRACH messages from LBL devices based on the alternative PRACH configuration and receives PRACH messages from non-LBL devices (and/or legacy devices) based on the conventional PRACH configuration. Thus, when the base station receives a given PRACH message, the base station may easily determine whether the PRACH message was transmitted by the LBL device. The alternative index may be signaled by the base station in a new system information block, e.g., a new system information block created for signaling RACH parameter(s) to the LBL device.

In a set of embodiments, the LBL device may apply an offset to the conventional PRACH configuration index of the cell to obtain an LBL-specific index. The LBL device may send the PRACH message using the PRACH configuration identified by the LBL-specific index, while the non-LBL device (and/or legacy device) uses the PRACH configuration identified by the conventional index. (the offset may be determined such that the PRACH configuration corresponding to the LBL-specific index has an allowable set of time opportunities for PRACH transmission that is disjoint from the allowable set of conventional PRACH configurations).

In a set of embodiments, an LBL device may send a PRACH message with a modified PRACH configuration having (a) the same allowable set of PRACH formats and frames (SFN) as a conventional PRACH configuration of a cell, and (b) an allowable set of subframes that is disjoint from the allowable set of subframes of the conventional PRACH configuration. (in the context of LTE, the conventional PRACH configuration of a cell is identified by the PRACH configuration index signaled in the system information block of type 2.) non-LBL devices (and/or legacy devices) may use the conventional PRACH configuration to send their PRACH messages.

In one set of embodiments, the LBL device may transmit PRACH messages in odd frames when the conventional PRACH configuration of the cell specifies the use of even frames. When sending PRACH messages, non-LBL devices (and/or legacy devices) may adhere to the conventional PRACH configuration, including their restrictions on even frames. The base station may thus easily determine whether a given PRACH message corresponds to an LBL device based on whether the PRACH message occurs in odd-numbered or even-numbered frames.

In one set of embodiments, the LBL device may be configured to generate an extended set of preambles, including additional preambles beyond the regular set of preambles for the cell. The LBL device may select (e.g., randomly select) a preamble from the additional preambles instead of from the regular set. The selected preamble may then be used to transmit the PRACH message. The base station may thus easily determine whether a given PRACH message corresponds to an LBL device based on whether the included preamble is one of the additional preambles or a regular preamble.

In one set of embodiments, a conventional set of PRACH preambles (e.g., a conventional set defined by existing wireless communication standards such as LTE) may be divided into two groups, an a-group and a B-group. The base station may configure the use of group a and group B such that non-LBL devices (and/or legacy devices) will select preambles from group a and LBL devices will select preambles from group B. Accordingly, when the base station receives a given PRACH message, the base station may easily determine whether the PRACH message is transmitted by the LBL device by determining group membership (a or B) of a preamble included in the PRACH message.

The base station may employ any of the above mechanisms to determine whether a given PRACH message was sent by the LBL device. In response to determining that the PRACH message is sent by the LBL device, the base station may employ any of a variety of mechanisms to enhance the likelihood of successful completion of the random access procedure. For example, the base station may boost the transmit power of a random access response (msg2) sent to the LBL device in response to the received PRACH message, i.e., a power boost relative to the power to be used for non-LBL devices. (in the context of LTE, the random access response may be sent with an RA-RNTI that is consistent with the RA-RNTI of the received PRACH message.) as another example, the base station may employ more complex decoding algorithms and/or receive beamforming to increase the likelihood of successfully decoding the msg3 of the random access procedure. As yet another example, the base station may boost the power of downlink transmissions to the UE device after the random access procedure is completed. As yet another example, the base station may direct the UE device to employ a lower coding rate (more redundancy) and/or a lower modulation order for uplink transmissions.

In one set of embodiments, the base station may count the number of failed random access attempts whose preambles are consistent with an LBL-specific pattern of preamble indices or preamble index offsets. When the count exceeds a given threshold, the base station may begin boosting the power of msg2 (i.e., random access response message) for any subsequent random access attempts whose preambles conform to the LBL-specific pattern.

The state of the device as being link budget limited may be a permanent condition or a variable condition. For example, some devices may be link budget limited when located far from a serving base station, but become non-link budget limited (non-LBL) when located close to a base station. Some devices may be link budget limited due to design, e.g. due to having a small sized antenna system or having limited power consumption due to a smaller battery capacity, etc.

If the UE device is Link Budget Limited (LBL) by design, the UE device may perform any of the presently disclosed methods without an explicit step of determining whether the UE device is link budget limited (or has been classified as link budget limited). For example, whenever one of the presently disclosed methods calls the UE device to perform an action (or set of actions) in response to determining that the UE device is link budget limited, the UE device that is LBL by design may perform the action (or set of actions) without the step of determining LBL status. Knowledge of LBL status may be built into the software and/or hardware controlling the UE device.

It should be noted that the techniques described herein may be implemented in and/or used with a variety of different types of devices, including but not limited to base stations, access points, cell phones, portable media players, tablet computers, wearable devices, and any of a variety of other computing devices.

This summary is intended to provide a brief overview of some of the subject matter described in this document. Thus, it will be appreciated that the above-described features are merely examples and should not be considered in any way to narrow the scope or spirit of the subject matter described herein. Other features, aspects, and advantages of the subject matter described herein will become apparent from the following detailed description, the accompanying drawings, and the claims.

Drawings

A better understanding of the present subject matter may be obtained when the following detailed description of the embodiments is considered in conjunction with the following drawings.

Fig. 1A illustrates an example of a wireless communication system in accordance with some embodiments.

FIG. 1B illustrates a communication with three wireless devices 106, in accordance with some embodiments₁、106₂And 106₃Examples of a communicating base station 102.

Fig. 2 illustrates a base station 102 in wireless communication with wireless devices 106A and 106B, in accordance with some embodiments.

Fig. 3 illustrates an example of a wireless communication system in accordance with some embodiments.

Fig. 4 illustrates an example of a base station in accordance with some embodiments.

Fig. 5A shows a PRACH preamble transmitted as part of an uplink frame. (PRACH is an abbreviation for physical random Access channel.)

Fig. 5B shows the structure of a conventional PRACH according to one possible format.

Figure 6 shows the Cyclic Prefix (CP) and sequence portions of the PRACH.

Fig. 7 illustrates messages that may be exchanged between a User Equipment (UE) device and a base station (e.g., eNodeB) as part of a random access procedure.

Figure 8 is a copy of the PRACH configuration listed in table 5.7.1-2 of 3GPP TS 36.211.

Figure 9 illustrates a method, according to some embodiments, to enable a link budget limited UE device to transmit a PRACH message using an alternative PRACH configuration index different from a conventionally signaled PRACH configuration index.

Figure 10 illustrates a method, according to some embodiments, to enable a link budget limited UE device to transmit a PRACH message using a PRACH configuration index offset from a conventionally signaled PRACH configuration index.

Figures 11 and 12 illustrate methods, according to some embodiments, to enable a link budget limited UE device to transmit a PRACH message using a different allowable set of subframes than those identified by a conventionally signalled PRACH configuration index.

Fig. 13 illustrates a method, according to some embodiments, to enable a link budget limited UE device to transmit PRACH messages using odd frames when a conventional PRACH configuration specifies even frames as an allowable set of PRACH transmission frames.

Fig. 14 illustrates a method, according to some embodiments, to enable a link budget limited UE device to generate additional preambles beyond a conventionally defined set of preambles and transmit a PRACH message with a selected one of the additional preambles.

Fig. 15 illustrates a method, according to some embodiments, to enable a link budget limited UE device to perform PRACH transmission with preambles selected from one subset of a conventionally defined set of preambles when a non-LBL device uses another subset of the conventionally defined set of preambles.

Fig. 16A illustrates a method, according to some embodiments, that enables a UE device to signal (to a base station) a device whose status is link budget limited by using a predetermined sequence of PRACH preamble index offsets for consecutive PRACH transmissions until the current PRACH transmission results in the success of a random access procedure.

Fig. 16B illustrates a method, according to some embodiments, to enable a UE device to signal (to a base station) a device whose status is link budget limited by using a sequence of PRACH preamble index offsets.

Fig. 17 illustrates a method, according to some embodiments, to enable a base station to facilitate successful completion of a random access procedure for link budget limited devices without knowledge of which PRACH transmitting devices are link budget limited and which are not.

While the features described herein are susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to be limited to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the subject matter defined by the appended claims.

Detailed Description

Abbreviations

Various abbreviations are used throughout this disclosure. The following provides definitions of the most commonly used abbreviations that may appear throughout this disclosure:

BS: base station

DL: downlink link

LBL: with limited link budget

LTE: long term evolution

MIB: master information block

NW: network

PDCCH: physical downlink control channel

PDSCH: physical downlink shared channel

PRACH: physical random access channel

PUCCH: physical uplink control channel

PUSCH: physical uplink shared channel

RACH: random access procedure or random access channel

An RAR: random access response

RA-RNTI: random access-radio network temporary identifier

RRC: radio resource control

RRC IE: RRC information elements

RX: receiving

SFN: system frame number

SIB: system information block

And (3) SIBn: system information block of type n

TTI: transmission time interval

TX: sending

UE: user equipment

UL: uplink link

UMTS: universal mobile communication system

ZC sequence: Zadoff-Chu sequences

3 GPP: third generation partnership project

Term(s) for

The following is a glossary of terms used in this disclosure:

storage medium-any of various types of non-transitory memory devices or storage devices. The term "storage medium" is intended to include: mounting media such as CD-ROM, floppy disk, or tape devices; computer system memory or random access memory such as DRAM, DDR RAM, SRAM, EDO RAM, Lanbas (Rambus) RAM, etc.; non-volatile memory such as flash memory, magnetic media (e.g., hard disk or optical storage); registers or other similar types of memory elements, etc. The storage medium may also include other types of non-transitory memory or combinations thereof. In addition, the storage medium may be located in a first computer system in which the program is executed, or may be located in a different second computer system connected to the first computer system through a network (such as the internet). In the latter example, the second computer system may provide program instructions to the first computer for execution. The term "storage medium" may include two or more storage media that may reside in different locations, such as in different computer systems that are connected by a network. The storage medium may store program instructions (e.g., embodied as a computer program) that are executable by one or more processors.

Carrier medium-storage medium as described above and physical transmission medium such as a bus, network and/or other physical transmission medium conveying signals such as electrical, electromagnetic or digital signals.

Programmable hardware elements — including various hardware devices, including a plurality of programmable functional blocks connected via programmable interconnects. Examples include FPGAs (field programmable gate arrays), PLDs (programmable logic devices), FPOAs (field programmable object arrays), and CPLDs (complex PLDs). Programmable functional blocks can range from fine grained (combinational logic or look-up tables) to coarse grained (arithmetic logic units or processor cores). The programmable hardware elements may also be referred to as "reconfigurable logic".

Computer system-any of various types of computing or processing systems, including Personal Computer Systems (PCs), mainframe computer systems, workstations, network appliances (network appliances), Internet appliances (Internet appliances), Personal Digital Assistants (PDAs), television systems, grid computing systems, or other devices or combinations of devices. In general, the term "computer system" may be broadly defined to include any device (or combination of devices) having at least one processor that executes instructions from a storage medium.

User Equipment (UE) (or "UE device") -any of a variety of types of computer system apparatuses that are mobile or portable and perform wireless communications. Examples of UE devices include mobile phones or smart phones (e.g., iPhone-based)^TM、Android^TMCell phone, etc.), portable gaming devices (e.g., Nintendo DS)^TM、PlayStation Portable^TM、Gameboy Advance^TM、iPhone^TM) A laptop computer, a PDA, a portable internet appliance, a music player, a data storage device, other handheld devices, wearable devices (e.g., a smart watch), and the like. In general, the term "UE" or "UE device" may be broadly defined to include any electronic, computing, and/or telecommunications device (or combination of devices) that is readily transportable by a user and capable of wireless communication.

Base station-the term "base station" has its full scope in its ordinary meaning and includes at least a wireless communication base station installed at a fixed location and used to communicate as part of a wireless telephone system or radio system.

Processing element — refers to various elements or combinations of elements. Processing elements include, for example, circuitry such as an ASIC (application specific integrated circuit), portions or circuits of an individual processor core, an entire processor core, an individual processor, a programmable hardware device such as a Field Programmable Gate Array (FPGA), and/or a larger portion of a system that includes multiple processors.

Channel-a medium used to transmit information from a sender (sender) to a receiver. It should be noted that the term "channel" as used herein may be considered to be used in a manner consistent with the standard for the type of device to which the term is applied, since the characteristics of the term "channel" may differ from one wireless protocol to another. In some standards, the channel width may be variable (e.g., depending on device capabilities, band conditions, etc.). For example, LTE may support scalable channel bandwidths from 1.4MHz to 20 MHz. In contrast, a WLAN channel may be 22MHz wide, while a Bluetooth channel may be 1MHz wide. Other protocols and standards may include different definitions of channels. Further, some standards may define and use multiple types of channels, e.g., different channels for uplink or downlink and/or different channels for different purposes such as data, control information, and so on.

Frequency band-the term "frequency band" has its full scope in its ordinary meaning and includes at least a portion of the spectrum (e.g., the radio frequency spectrum) in which a channel is used or reserved for the same purpose.

Link budget is limited-including its full scope in its ordinary meaning and includes at least the characteristics of a wireless device (UE) that exhibits limited communication capabilities or limited power relative to devices that are not link budget limited or for which Radio Access Technology (RAT) standards have been developed. A UE with a limited link budget may experience relatively limited reception and/or transmission capabilities, which may be due to one or more factors such as device design, device size, battery size, antenna size or design, transmit power, receive power, current transmission medium conditions, and/or other factors. Such devices may be referred to herein as "link budget limited" (or "link budget constrained") devices. A device may be inherently link budget limited due to its size, battery power, and/or transmit/receive power. For example, a smart watch communicating with a base station via LTE or LTE-a may be inherently link budget limited due to its reduced transmit/receive power and/or reduced antenna size. Alternatively, the device may not be inherently link budget limited, e.g., may have sufficient size, battery level, and/or transmit/receive power for normal communications via LTE or LTE-a, but may be temporarily link budget limited due to current communication conditions (e.g., the smartphone is at the edge of a cell), etc. It should be noted that the term "link budget limited" includes or encompasses power limitations, and thus a power limited device may be considered a link budget limited device.

Automatic-refers to an action or operation being performed by a computer system (e.g., software executed by a computer system) or device (e.g., circuitry, programmable hardware elements, ASIC, etc.) without user input directly specifying or performing the action or operation. The term "automatically" is thus to be contrasted with an operation that is manually performed or specified by a user (where the user provides input to directly perform the operation). An automated process may be initiated by input provided by a user, but then actions performed "automatically" are not specified by the user, i.e., are not performed "manually," where the user specifies each operation to be performed. For example, a user filling out an electronic form by selecting each field and providing input specifying the information (e.g., by typing in the information, selecting a check box, a single check, etc.) is manually filling out the electronic form, even though the computer system must update the form in response to the user action. The form may be automatically filled in by a computer system, wherein the computer system (e.g., software executing on the computer system) analyzes the fields of the form and fills in the form without any user input specifying answers to the fields. As indicated above, the user may invoke automatic filling of the form, but not participate in the actual filling of the form (e.g., the user does not manually specify answers for the fields, but rather the answers for the fields are automatically completed). This specification provides various examples of operations that are automatically performed in response to actions that a user has taken.

FIG. 1-Wireless communication System

Fig. 1A illustrates one embodiment of a wireless communication system. It should be noted that FIG. 1A represents one possibility out of many, and the features of the present disclosure may be implemented in any of a variety of systems, as desired.

As shown, the exemplary wireless communication system includes a base station 102A that communicates with one or more wireless devices 106A, 106B, etc. to 106N via a transmission medium. The wireless device may be a user equipment, which may be referred to herein as a "user equipment" (UE) or UE device. Some wireless devices may be Link Budget Limited (LBL), while other devices may be non-LBL.

The base station 102A may be a Base Transceiver Station (BTS) or cell site and may include hardware that enables wireless communication with the UE devices 106A-106N. The base station 102A may also be equipped to communicate with a network 100 (e.g., a cellular service provider's core network, a telecommunications network such as the Public Switched Telephone Network (PSTN), and/or the internet, among various possibilities). Thus, the base station 102A may facilitate communication between UE devices 106 and/or between the UE devices 106 and the network 100.

The communication area (or coverage area) of a base station 102 may be referred to as a "cell". Base station 102A and UE 106 may be configured to communicate via a transmission medium using any of a variety of Radio Access Technologies (RATs) or wireless communication technologies, such as GSM, UMTS (WCDMA, TDS-CDMA), LTE-advanced (LTE-a), HSPA, 3GPP2 CDMA2000 (e.g., 1xRTT, 1xEV-DO, HRPD, eHRPD), Wi-Fi, WiMAX, or the like.

Thus, the base station 102A and other similar base stations (not shown) operating in accordance with one or more cellular communication techniques may be provided as a network of cells that may provide continuous or nearly continuous overlapping service to the UE devices 106A-N and similar devices over a wide geographic area via the one or more cellular communication techniques.

Thus, while the base station 102 may currently represent a "serving cell" for the UE devices 106A-N as shown in fig. 1A, each UE device 106 may also be capable of receiving signals from one or more other cells (e.g., cells provided by other base stations), which may be referred to as "neighbor cells. Such cells may also be capable of facilitating communication between user equipment and/or between user equipment and network 100.

FIG. 1B illustrates a communication with three wireless devices 106, in accordance with some embodiments₁、106₂And 106₃Examples of a communicating base station 102. Wireless device 106₁、106₂And 106₃May be implemented by any combination of the wireless devices described above and/or below.

It should be noted that, at least in some cases, the UE device 106 may be capable of communicating using multiple wireless communication technologies. For example, the UE 106 may be configured to communicate using two or more of GSM, UMTS, CDMA2000, WiMAX, LTE-A, WLAN, Bluetooth, one or more Global navigation satellite systems (GNSS, such as GPS or GLONASS), one or more mobile television broadcast standards (such as ATSC-M/H or DVB-H), and so forth. Other combinations of wireless communication standards, including more than two wireless communication technologies, are also possible. Also, in some cases, the UE device 106 may be configured to communicate using only a single wireless communication technology.

Fig. 2 shows a UE device 106 (e.g., one of devices 106A-106N) in communication with a base station 102. The UE device 106 may have cellular communication capabilities and, as described above, may be a device such as a mobile phone, a handheld device, a media player, a computer, a laptop or tablet device, a wearable device (such as a smart watch), or virtually any type of wireless device.

The UE device 106 may include a processor configured to execute program instructions stored in a memory. The UE device 106 may perform any of the method embodiments described herein by executing such stored instructions. Alternatively, or in addition, the UE device 106 may include programmable hardware elements, such as an FPGA (field programmable gate array) configured to perform, or any portion of, any of the method embodiments described herein.

In some embodiments, the UE device 106 may be configured to communicate using any of a variety of radio access technologies and/or wireless communication protocols. For example, the UE device 106 may be configured to communicate using one or more of GSM, UMTS, CDMA2000, LTE-A, WLAN, Wi-Fi, WiMAX, or GNSS. Other combinations of wireless communication technologies are also possible.

The UE device 106 may include one or more antennas for communicating using one or more wireless communication protocols or technologies. In some embodiments, the UE device 106 may be configured to communicate with a single shared radio. The shared radio may be coupled to a single antenna or may be coupled to multiple antennas (e.g., for MIMO) for performing wireless communications. Alternatively, the UE device 106 may include two or more radios. For example, the UE 106 may include a shared radio for communicating with LTE or 1xRTT (or LTE or GSM) and a separate radio for communicating with each of Wi-Fi and bluetooth. Other configurations are also possible.

FIG. 3-example block diagram of a UE

Fig. 3 shows one possible block diagram of the UE 106. As shown, the UE 106 may include a System On Chip (SOC)300, which system on chip 300 may include portions for various purposes. For example, as shown, SOC 300 may include processor(s) 302 that may execute program instructions for UE 106 and display circuitry 304 that may perform graphics processing and provide display signals to display 340. Processor(s) 302 may also be coupled to a Memory Management Unit (MMU)305 that may be configured to receive addresses from processor(s) 302 and translate those addresses to locations in memory (e.g., memory 306, Read Only Memory (ROM)350, NAND flash memory 310). MMU 305 may be configured to perform memory protections as well as page table translations or builds. In some embodiments, MMU 305 may be included as part of processor(s) 302.

The UE 106 may also include other circuitry or devices, such as display circuitry 304, radio 330, connector interface 320, and/or display 340.

In the illustrated embodiment, ROM 350 may include a boot program that is executable by processor(s) 302 during startup or initialization. As also shown, the SOC 300 may be coupled to various other circuits of the UE 106. For example, the UE 106 may include various types of memory (e.g., including NAND flash memory 310), a connector interface 320 (e.g., for coupling to a computer system), a display 340, and wireless communication circuitry (e.g., for communicating with LTE, CDMA2000, bluetooth, WiFi, GPS, etc.).

The UE device 106 may include at least one antenna, and in some embodiments multiple antennas, for performing wireless communications with base stations and/or other devices. For example, the UE device 106 may perform wireless communication using the antenna 335. As noted above, the UE may be configured in some embodiments to communicate wirelessly using multiple wireless communication standards.

As described herein, the UE 106 may include hardware and software components for implementing any of the UE-related method embodiments described herein.

The processor 302 of the UE device 106 may be configured to implement some or all of the methods described herein, e.g., by executing program instructions stored on a storage medium (e.g., a non-transitory computer-readable storage medium). In other embodiments, the processor 302 may be configured as a programmable hardware element, such as an FPGA (field programmable gate array), or as an ASIC (application specific integrated circuit).

FIG. 4-base station

Fig. 4 shows an embodiment of the base station 102. It should be noted that the base station of fig. 4 is only one example of possible base stations. As shown, base station 102 may include processor(s) 404 that may execute program instructions for base station 102. Processor(s) 404 may also be coupled to a Memory Management Unit (MMU)440, or to other circuits or devices, which may be configured to receive addresses from processor(s) 404 and translate those addresses to locations in memory (e.g., memory 460 and Read Only Memory (ROM) 450).

The base station 102 may include at least one network port 470. The network port 470 may be configured to couple to a telephone network and provide access to the telephone network as described above for a plurality of devices, such as the UE device 106.

The network port 470 (or additional network ports) may also or alternatively be configured to couple to a cellular network, e.g., a core network of a cellular service provider. The core network may provide mobility-related services and/or other services to multiple devices, such as UE device 106. In some cases, the network port 470 may be coupled to a telephone network via a core network, and/or the core network may provide the telephone network (e.g., between other UE devices served by a cellular service provider).

Base station 102 may include a radio 430, a communication chain 432, and at least one antenna 434. The base station may be configured to operate as a wireless transceiver and may also be configured to communicate with the UE device 106 via the radio 430, the communication chain 432, and at least one antenna 434. Communication chain 432 may be a receive chain, a transmit chain, or both. Radio 430 may be configured to communicate via various RATs including, but not limited to, GSM, UMTS, LTE, WCDMA, CDMA2000, WiMAX, etc.

The processor(s) 404 of the base station 102 may be configured to implement some or all of the methods described herein, e.g., by executing program instructions stored on a storage medium (e.g., a non-transitory computer-readable storage medium). Alternatively, the processor 404 may be configured as a programmable hardware element, such as an FPGA (field programmable gate array), or as an ASIC (application specific integrated circuit), or a combination thereof.

PRACH Specification in 3GPP

Fig. 5A illustrates a preamble 500 in a Physical Random Access Channel (PRACH) according to existing LTE specifications. The UE device sends a PRACH preamble in an uplink frame 510 in order to initiate a random access procedure. (the uplink frame includes multiple subframes.) the time offset and frequency offset of the PRACH preamble within the uplink frame may be determined by higher layer signaling.

Fig. 5B illustrates one particular implementation of a PRACH preamble according to the existing LTE specifications. Per frequency, the PRACH preamble (including guard subcarriers at the beginning and end) spans 6 RBs-1.08 MHz. Per time, including Cyclic Prefix (CP) and Guard Time (GT), the PRACH preamble spans one uplink subframe.

Formats 0-3 for the PRACH preamble each use Zadoff-Chu sequences of length 839, while format 4 uses Zadoff-Chu sequences of length 139.

The PRACH preamble occupies 6 Resource Blocks (RBs) in the uplink bandwidth (UL BW).

One PRACH subcarrier occupies 1.25kHz while the normal UL subcarrier occupies 15 kHz. The symbols of the Zadoff-Chu sequence are transmitted on the corresponding PRACH subcarriers.

For PRACH preamble, fig. 6 shows duration T_CPCyclic Prefix (CP) and duration T_SEQThe sequence portion of (a). (the sequence part contains Zadoff-Chu sequences.) table 1 below shows T in different formats of PRACH preamble_CPAnd T_SEQThe value of (c).

Table 1: random access preamble parameters

Overview of RACH procedures

The RACH procedure may involve a series of messages sent between the UE and the base station as shown in fig. 7.

In a first message (MSG1), the UE sends a PRACH preamble to the base station (i.e. the eNodeB in LTE parlance). The PRACH preamble may be configured according to one of the formats discussed above or any other desired format.

In response to decoding the first message, the eNodeB sends a second message (MSG 2). The second message may be referred to as a Random Access Response (RAR). The PDSCH of the RAR message may include an uplink grant. The uplink grant may identify uplink resources in the PUSCH for the UE to transmit uplink data.

In response to decoding the second message, the UE may send a third message (MSG 3). In the PUSCH of MSG3, the UE may transmit uplink data. The content of the third message may all be different in different contexts, e.g. may depend on the purpose for which the RACH procedure has been invoked. For example, the third message may include an RRC request, a Scheduling Request (SR), and the like.

In response to receiving the third message, the eNodeB may send a fourth message (MSG4), e.g., a contention resolution message.

Channel in LTE

LTE uses various channels so that data can be transmitted across the LTE radio interface. These channels are used to separate different types of data and allow them to be transmitted in an orderly fashion across the radio access network. The different channels effectively provide an interface to higher layers within the LTE protocol structure and enable an ordered and intended separation of data.

There are three categories or types of LTE data channels as follows.

Physical channel: these are transport channels that carry user data and control messages.

Transmission channel: the transport channel provides information transfer to the Medium Access Control (MAC) and higher layers.

Logical channel: services are provided for the Medium Access Control (MAC) layer within the LTE protocol structure.

LTE defines a number of physical downlink channels to carry information received from the MAC layer and higher layers. The LTE downlink includes a Physical Downlink Shared Channel (PDSCH) and a Physical Downlink Control Channel (PDCCH). The PDSCH is the primary data-carrying channel allocated to users on a dynamic and opportunistic basis. The PDCCH carries control information that indicates to the user equipment how resources in the PDSCH are allowed.

LTE random access configuration

In the random access procedure of LTE, there are many possible PRACH configurations. For each cell, the corresponding eNodeB will signal one of the PRACH configurations (by broadcasting the index of the PRACH configuration in SIB2) to be used by devices attempting random access in that cell. This PRACH configuration will identify a preamble format and allowable time resources for devices in the cell to use when transmitting PRACH. The allowable time resources may include an allowable System Frame Number (SFN) and an allowable subframe number (SFN). Fig. 8 shows the PRACH configuration defined in table 5.7.1-2 of 3GPP TS 36.211. Each PRACH configuration has a corresponding index identifying its position within the list of PRACH configurations.

LTE random access preamble

In LTE, a UE in a given cell may initiate random access by transmitting a preamble selected from a set of preambles. (each UE may randomly select a preamble from a set of preambles). The UE generates this set of preambles with a root sequence number provided by the eNodeB in SIB 2. For a given cell, the preamble set may include up to 64 preambles, and the 64 preambles are divided into two groups: group A and group B.

The eNodeB also broadcasts (in SIB2) the following parameters to configure the use of preamble groups:

numberOfRA-Preambles is the number of non-dedicated random access Preambles available in the cell;

messagesizeGroupA is the threshold (in bits) for preamble selection;

sizeOfRA-preamblsgroupa is the size (i.e., number) of random access preambles in group a.

These parameters are included in the RACH-ConfigCommon. The number of Preambles in the B group is equal to the difference 'numberOfRA-Preambles' - 'sizeoffra-preamblsgroupa'.

According to the LTE specifications, if the size of a potential UL message to be sent by a UE is larger than "messageSizeGroupA" and the path loss is smaller than the path loss threshold, the UE selects a preamble from group B.

The UE may measure the path loss based on the RSCP. (RSCP is an abbreviation for reference signal code power.) the network can broadcast the cell reference signal power transmitted at the eNodeB in a System Information Block (SIB). The UE measures the received cell reference signal power. The difference between the cell reference signal power and the received value is the path loss.

The path loss threshold may be determined based on the following expression:

PathLossThreshold＝P_CMAX–

preambleInitialReceivedTargetPower

-deltaPreamblemsg3-messagePowerOffsetGroupB wherein

P_CMAXIs the UE maximum transmit power;

preambinationalReceivedTargetPower is the network expected received power for the 1 st random access attempt (RACH preamble);

deltaPreamblemsg3 is the power offset between the power of the preamble and Msg3, and

messagePowerOffsetGroupB is the power offset for the preambles in the B-group.

The following is the definition of the RACH-ConfigCommon information element according to LTE:

random access-UE identification at MSG1(PRACH message)

In one set of embodiments, a link budget limited device may be configured to transmit PRACH messages with a different PRACH configuration than a non-LBL device. (non-LBL devices may use conventionally signaled PRACH configurations.) thus, the base station can determine whether the received PRACH message corresponds to an LBL device based on whether the PRACH message conforms to a different PRACH configuration or a conventionally signaled PRACH configuration. For devices determined to be LBLs, the base station may invoke one or more mechanisms to increase the likelihood that the random access procedure for the LBL device is successfully completed. For example, the base station may boost the transmit power for the LBL device msg2 (i.e., random access response message).

In one embodiment, the eNodeB may broadcast an alternative PRACH configuration index that is different from the conventional PRACH configuration index of the current cell for use by devices with limited link budget. (the alternative PRACH configuration index may also be different from the regular PRACH configuration index of the neighboring cell.) when the LBL devices send PRACH messages, they may use the PRACH configuration identified by the alternative PRACH configuration index. (the conventional PRACH configuration index is signaled in SIB 2. however, the alternative PRACH configuration indexes may be included in special SIBs for LBL UE devices, i.e. new SIBs created to facilitate broadcasting of RACH configuration information for LBL devices.) in contrast, when non-LBL devices transmit PRACH messages, they use PRACH configurations corresponding to the conventional PRACH configuration index.

In another embodiment, the LBL device may be configured to employ an alternative PRACH configuration index that is shifted from the conventional PRACH configuration index of the current cell by a predetermined offset. LBL devices in the cell may send PRACH messages according to the PRACH configuration identified by the alternate PRACH index, while non-LBL devices in the cell send PRACH messages according to the PRACH configuration identified by the conventional PRACH configuration index. Each LBL device may receive a conventional PRACH configuration index from the base station (e.g., from SIB2) and compute a substitute index by adding a predetermined offset. The base station may determine whether a given PRACH message corresponds to an LBL device by determining whether the PRACH format, SFN, and subframe number of the PRACH message are consistent with an alternative PRACH configuration or a legacy PRACH configuration.

In yet another embodiment, the LBL device may use a preamble format and SFN defined by the conventionally signaled PRACH configuration, but use a different set of allowable subframes than the allowable set of subframes defined by the conventionally signaled PRACH configuration. Thus, LBL devices transmit PRACH messages in the same frame but in different subframes than non-LBL devices. For example, according to PRACH configuration 6,

only subframes

1 and 6 are conventionally allowed for PRACH transmission. (see table in fig. 8). In this case, the eNodeB may allow the LBL device to use subframes 0, 2-5, 7-9 (or any subset of those subframes) for the transmission of PRACH messages. One or more subframes available to LBL devices may be broadcast in special SIBs.

In yet another embodiment, if the conventionally signaled PRACH configuration of a given cell specifies the use of even SFNs (e.g., configurations corresponding to indices 0-2 and 15-18) for PRACH messaging, the LBL device may instead use odd SFNs, but obey the preamble format and allowed subframes defined by the conventionally signaled PRACH configuration. As an example, when the conventionally signaled PRACH configuration index is 2, LBL devices send their PRACH message in odd frames-in subframe 7, and use preamble format 0.

In one set of embodiments, the set of available preambles in a cell may be extended to include additional preambles beyond the regular preamble set. The additional preambles may be used by LBL devices to send PRACH messages, while the regular set of preambles are used by non-LBL devices. For example, in one embodiment, the LBL device may generate an extended set of 128 preambles with a root sequence number provided by the eNodeB. The extended set of 128 preambles may include 64 preambles of the regular set and 64 additional preambles. The LBL device may select (e.g., randomly select) a preamble from the 64 additional preambles. Because LBL devices and non-LBL devices transmit their PRACH messages using disjoint sets of preambles, the base station may easily determine whether a given PRACH message corresponds to an LBL device by determining the set membership (regular set or LBL-specific set) of the preambles contained in the PRACH message. Although the above discussion gives an example in which the number of additional preambles is 64, it should be appreciated that this number may take any of a wide variety of values, e.g. depending on the expected or average number of LBL devices in a cell. In some embodiments, the number of additional preambles is dynamically configurable, e.g., based on system information broadcast by the base station.

In one set of embodiments, at least a subset of the preambles of group B may be reserved for PRACH transmissions (or connection establishment related PRACH transmissions) by devices with limited link budget. (see the above discussion of group a and group B.) the eNodeB may configure the cell such that the desired number of preambles is assigned to group B and the path loss threshold may be relaxed. (the path loss threshold may be relaxed by setting the path loss threshold to a sufficiently larger value to ensure that the LBL UE device will pass the path loss test using the B-group or increase the likelihood. Alternatively or additionally, the eNodeB may set "messageSizeGroupA" so that non-LBL devices will not use the B-group preamble (or will not use the B-group preamble very often).

In some embodiments, the eNodeB may determine whether the received preamble (i.e., the preamble of the received PRACH message) belongs to group a or group B. If the preamble belongs to group B, the eNodeB may identify the UE device that transmitted the preamble as an LBL device and transmit a random access response message to the UE device, thereby granting (grant) sufficient uplink resources to the UE device for connection establishment, but the granted uplink resources may have a total size less than "messageSizeGroupA". Also, after detecting that the preamble belongs to group B, the eNodeB may boost the power of the messages (MSG2 and following messages) to the LBL device.

In one set of embodiments, a method 900 for operating a User Equipment (UE) device may be performed as shown in fig. 9. (the method 900 may also include any subset of the features, elements, and embodiments described above in connection with fig. 1-8 and described below in connection with fig. 10-17.) the method 900 may be performed by a link budget limited UE device to facilitate a random access procedure. The method may be implemented by a processing agent of a UE device. The processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements such as FPGAs, by one or more special purpose hardware devices such as ASICs, or by any combination of the foregoing.

Although the method 900 is described below with respect to multiple steps, it should be understood that in various embodiments: one or more of the steps may be omitted; two or more of the steps may be performed at least partially in parallel; one or more steps may be added as desired; and the steps may be performed in a different order than described.

At 910, the processing agent may receive an index I that has been broadcast by the base station_LBL. Index I_LBLA first configuration is identified for Physical Random Access Channel (PRACH) transmission by a link budget limited UE device in a cell corresponding to the base station. Index I_LBLWith an index I also broadcast by the base station_NLBLIn contrast, i.e. index I_LBLNot equal to index I in terms of digital value_NLBL. Index I_NLBLIdentification of the cellA second configuration of PRACH transmissions is performed by non-link budget limited UE devices (and/or legacy devices) in the region, wherein the second configuration is different from the first configuration.

At 915, in response to determining that the UE device has been classified as link budget limited, the processing agent may transmit a PRACH to the base station, wherein the PRACH is transmitted according to the first configuration. (in contrast, in response to determining, e.g., at a later time, that the UE device has been classified as non-link budget limited, the UE device may perform PRACH transmission according to the second configuration).

In some embodiments, the base station may be configured to broadcast a first system information block and a second system information block, wherein the first information block comprises an index I_LBLAnd the second system information block includes an index I_NLBL. The link budget limited UE device may read the first SIB to determine the index I_LBL. More generally, each link budget limited UE device may recover index I from the first SIB_LBL. (in contrast, each UE device that is not link budget limited may recover index I from the second SIB_NLBL)。

In some embodiments, the second system information block is a type 2 system information block, e.g., as defined by the LTE standard.

In some embodiments, the first configuration specifies a first set of allowable time opportunities (e.g., allowable subframes) for PRACH transmissions by a link budget limited UE device, and the second configuration specifies a second set of allowable time opportunities for PRACH transmissions by a non-link budget limited UE device, wherein the first and second sets are disjoint sets.

In some embodiments, index I_LBLIdentifying a first configuration from a list of PRACH configurations defined by an existing wireless communication standard, and indexing I_NLBLThe second configuration is identified from the same list. (e.g., the list of configurations may be a list of PRACH configurations specified in 3GPP TS 36.211). The UE device may store a copy of the list and based on index I_LBLThe first configuration is accessed from the list. When the UE device is not link budget limited, e.g. at a later timeTime, UE device may be based on index I_NLBLA second configuration is accessed from the list and PRACH transmission is performed with the second configuration but not with the first configuration.

As indicated above, index I_LBLAnd index I_NLBLDifferent. In some embodiments, index I_LBLFurther distinct from one or more additional PRACH configuration indices broadcast by one or more neighboring base stations, respectively, wherein the one or more additional PRACH configuration indices are broadcast for use by non-link budget limited UE devices in one or more additional cells corresponding to the one or more additional base stations, respectively. In some embodiments, each of the plurality of neighboring base stations may be configured to perform method 900. The base stations may be configured such that each base station selects its index I_LBLSo as to be indexed with I_NLBLDifferent and different from the index I transmitted by other base stations_LBLAnd index I_NLBLDifferent.

In one set of embodiments, a method for operating a base station may be performed as follows. (the method may also include any subset of the features, elements, and embodiments described above in connection with fig. 1-9 and described below in connection with fig. 10-17.) the method may be performed by a base station to facilitate a random access procedure for a link budget limited UE device. The method may be implemented by a processing agent of a base station. The processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements such as FPGAs, by one or more special purpose hardware devices such as ASICs, or by any combination of the foregoing. The processing agent may be configured to transmit wireless signals via a transmitter of the base station and receive wireless signals via a receiver of the base station, e.g., as variously described above.

While the method is described below with respect to a number of steps, it should be understood that in various embodiments: one or more of the steps may be omitted; two or more of the steps may be performed at least partially in parallel; one or more steps may be added as desired; and the steps may be performed in an order different than that described.

The processing agent may broadcast an index I_LBL. Index I_LBLA first configuration is identified for Physical Random Access Channel (PRACH) transmission by a link budget limited UE device in a cell corresponding to a base station. Index I_LBLWith an index I also broadcast by the base station_NLBLIn contrast, i.e. index I_LBLNot equal to index I in terms of digital value_NLBL. Index I_NLBLA second configuration for PRACH transmission by non-link budget limited UE devices (and/or legacy devices) in the cell is identified, wherein the second configuration is different from the first configuration.

The processing agent may receive the PRACH, i.e., the PRACH that has been transmitted by the UE device. The processing agent may determine whether the PRACH has been transmitted according to the first configuration or according to the second configuration. The first and second configurations may have different preamble formats, and/or different allowed system frame numbers, and/or different allowed subframe numbers. Any or all of these differences may be used as a basis for determining whether the PRACH has been transmitted according to the first configuration or according to the second configuration.

In response to determining that the PRACH has been transmitted according to the first configuration, the processing agent may invoke one or more communication enhancement mechanisms for transmission to and/or reception from a UE device that transmitted the PRACH. (e.g., the processing agent may power up the random access response message, and/or power up downlink traffic transmission to the UE device.) in contrast, if the processing agent determines that the PRACH has been transmitted according to the second configuration, the processing agent may not invoke the one or more communication enhancement mechanisms.

In one set of embodiments, a method 1000 for operating a User Equipment (UE) device may be performed as shown in fig. 10. (the method 1000 may also include any subset of the features, elements, and embodiments described above in connection with fig. 1-9 and described below in connection with fig. 11-17.) the method 1000 may be performed by a link budget limited UE device to facilitate a random access procedure. The method may be implemented by a processing agent of a UE device. The processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements, by one or more special purpose hardware devices, such as ASICs, or by any combination of the preceding.

Although the method 1000 is described below with respect to multiple steps, it should be understood that in various embodiments: one or more of the steps may be omitted; two or more of the steps may be performed at least partially in parallel; one or more steps may be added as desired; and the steps may be performed in an order different than that described.

At 1010, the processing agent may receive a first index that has been broadcast by a base station, where the first index identifies a first configuration for Physical Random Access Channel (PRACH) transmissions by a non-link budget limited UE device in a cell of the base station. The first index may be a PRACH configuration index conventionally signaled by an eNodeB of LTE. In other words, the first index may be a PRACH configuration index compliant with the LTE wireless communication standard, e.g., as defined in 3GPP TS 36.211.

At 1015, the processing agent may add an offset (i.e., a non-zero offset) to the first index to obtain a second index, wherein the second index identifies a second configuration for PRACH transmission by a link budget limited UE device in the cell. The second configuration is different from the first configuration.

At 1020, in response to determining that the UE device has been classified as link budget limited, the processing agent may transmit a PRACH to the base station, wherein the PRACH is transmitted according to the second configuration. (in contrast, in response to determining, e.g., at a later time, that the UE device has been classified as not link budget limited, the UE device may perform PRACH transmission according to a first configuration, i.e., a configuration identified by a first index.) in some embodiments, the first configuration specifies a first set of allowable time opportunities (e.g., allowable subframes) for PRACH transmission, and the second configuration specifies a second set of allowable time opportunities for PRACH transmission, where the first and second sets are disjoint sets.

In some embodiments, the base station is configured to broadcast the first index as part of a SIB2 (i.e., a type 2 system information block), as defined by the specification in 3GPP TS 36.331.

In some embodiments, the first index identifies the first configuration from a list of PRACH configurations defined by existing wireless communication standards, and the second index identifies the second configuration from the same list of PRACH configurations. (e.g., the list of PRACH configurations may be a list defined by 3GPP TS 36.211.) in some embodiments, the addition of the above-described offset is additive modulo N_LISTIn which N is_LISTIs the number of PRACH configurations in the list.

In some embodiments, the method 1000 further comprises: (a) receiving a third index that has been broadcast by the second base station, wherein the third index identifies a third configuration for PRACH transmission by a non-link budget limited UE device in a second cell corresponding to the second base station; (b) adding the same offset (i.e., the offset of step 1015) to the third index to obtain a fourth index, wherein the fourth index identifies a fourth configuration for PRACH transmission by the link budget limited UE device in the second cell; and (c) transmitting the PRACH to the second base station, wherein the PRACH is transmitted according to a fourth configuration.

In some embodiments, the offset may be used by a plurality of base stations including the base station.

In some embodiments, each of the plurality of neighboring base stations may perform method 1000. Different base stations may transmit different values of the first index, respectively, but use the same offset to determine their respective values of the second index.

In one set of embodiments, a method for operating a base station may be performed as described below. (the method may also include any subset of the features, elements, and embodiments described above in connection with fig. 1-10 and described below in connection with fig. 11-17.) the method may be performed by a base station to facilitate a random access procedure for a link budget limited UE device. The method may be implemented by a processing agent of a base station. The processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements such as FPGAs, by one or more special purpose hardware devices such as ASICs, or by any combination of the foregoing. The processing agent may be configured to transmit wireless signals via a transmitter of the base station and receive wireless signals via a receiver of the base station, e.g., as variously described above.

The processing agent may broadcast an index I_CONVWherein index I_CONVA first configuration for Physical Random Access Channel (PRACH) transmission by a non-link budget limited UE device (and/or a legacy device) in a cell of a base station is identified. Index I_CONVMay be a PRACH configuration index conventionally signaled by an LTE base station. Non-link budget constrained UE devices and/or legacy UE devices in a cell may receive an index I_CONVAnd performing PRACH transmission with the first configuration. In contrast, a link budget limited UE device in a cell may perform PRACH transmission with a second configuration that is offset from the first configuration by a known distance in the allowable configuration list, i.e., a distance known to the base station and the link budget limited UE device. See, for example, fig. 8.

After broadcasting the index I_CONVThereafter, the processing agent may receive the PRACH, i.e., the PRACH that has been transmitted by the UE device.

The processing agent may analyze the PRACH to determine whether it has been transmitted according to the first configuration or according to the second configuration. The first and second configurations may have different preamble formats, and/or different allowed system frame numbers, and/or different allowed subframe numbers. Any or all of these differences may be used as a basis for determining whether the PRACH has been transmitted according to the first configuration or according to the second configuration.

In response to determining that the PRACH has been transmitted according to the second configuration, the processing agent may invoke one or more communication enhancement mechanisms for transmission to and/or reception from a UE device that transmitted the PRACH. (e.g., the processing agent may power up the random access response message, and/or power up downlink traffic transmission to the UE device.) in contrast, if the processing agent determines that the PRACH has been transmitted according to the first configuration, the processing agent may not invoke the one or more communication enhancement mechanisms.

In one set of embodiments, a method 1100 for operating a User Equipment (UE) device may be performed as shown in fig. 11. (the method 1100 may also include any subset of the features, elements, and embodiments described above in connection with fig. 1-10 and described below in connection with fig. 12-17.) the method 1100 may be performed by a link budget limited UE device to facilitate a random access procedure. The method may be implemented by a processing agent of a UE device. The processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements, by one or more special purpose hardware devices, such as ASICs, or by any combination of the preceding.

While the method 1100 is described below with respect to a number of steps, it should be understood that in various embodiments: one or more of the steps may be omitted; two or more of the steps may be performed at least partially in parallel; one or more steps may be added as desired; and the steps may be performed in an order different than that described.

At 1110, the processing agent may receive an index that has been broadcast by a base station, where the index identifies a configuration for transmission of a Physical Random Access Channel (PRACH) with a conventionally defined set of allowable subframes for PRACH transmission. The conventionally defined set may be used for PRACH transmissions by non-link budget limited UE devices and/or legacy devices in a cell corresponding to the base station. The conventionally defined set may be a set of allowable subframes defined by a wireless communication standard such as LTE. For example, the conventionally defined set may be a set of allowable subframes corresponding to a selected one of the PRACH configurations defined in 3GPP TS 36.211. (see Table 5.7.1-2 of the specification). The above index may be an index to table 5.7.1-2 of 3GPP TS 36.211.

At 1115, in response to determining that the UE device has been classified as link budget limited, the processing agent may transmit a PRACH to the base station. The PRACH may be transmitted in subframes from an alternate subset of the allowable subframes, where the alternate set is disjoint from the conventionally defined set of allowable subframes. In some embodiments, the UE device may randomly select a subframe from the alternative set. An alternate set of allowable subframes may be reserved for use by a link budget limited UE device. A link budget limited UE device may be designed to use an alternate set (rather than the conventionally defined set) in selecting subframes for PRACH transmission.

In some embodiments, the base station is configured to broadcast system information identifying an alternate set of allowable subframes.

The base station may be configured to monitor an alternate set of allowable subframes for PRACH transmissions from link budget limited UE devices and to monitor a conventionally defined set of allowable subframes for PRACH transmissions from non-link budget limited UE devices and/or legacy UE devices. Having link budget limited UE devices perform PRACH transmissions using allowable subframes that are disjoint from allowable subframes used by non-link budget limited UE devices and/or legacy UE devices allows a base station to receive PRACH transmissions from link budget limited UE device(s) with lower interference and thus decode these PRACH transmissions with lower error probability.

In some embodiments, the base station is configured to broadcast the index as part of a type 2 system information block, as defined by the LTE standard.

In some embodiments, the method 1100 may further include: in response to determining that the UE device has been classified as not link budget limited, transmitting another PRACH to the base station, wherein the another PRACH is transmitted in a subframe from the conventionally defined set of allowable subframes.

In some embodiments, the configuration for PRACH transmission also specifies a format for PRACH transmission, e.g., one of the PRACH formats defined in 3GPP TS 36.211. The PRACH described above (i.e., the PRACH of step 1115) may be transmitted according to a specified format.

In some embodiments, the configuration for PRACH transmission also specifies constraints on allowable frames, e.g., as shown in fig. 8. The PRACH described above may be transmitted in frames that comply with allowable frame constraints.

In one set of embodiments, a method for operating a base station may be performed as follows. (the method may also include any subset of the features, elements, and embodiments described above in connection with fig. 1-11 and described below in connection with fig. 12-17). The method may be performed by a base station to facilitate a random access procedure for a link budget limited UE device. The method may be implemented by a processing agent of a base station. The processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements such as FPGAs, by one or more special purpose hardware devices such as ASICs, or by any combination of the foregoing. The processing agent may be configured to transmit wireless signals via a transmitter of the base station and receive wireless signals via a receiver of the base station, e.g., as variously described above.

The processing agent may broadcast an index, where the index identifies a configuration for transmission of a Physical Random Access Channel (PRACH). The configuration may have (be associated with) a conventional defined set of allowable subframes for PRACH transmission. The conventionally defined set may be used for PRACH transmissions by non-link budget limited UE devices (and/or legacy devices) in a cell corresponding to the base station. (the conventionally defined set may be a set of allowable subframes defined by a wireless communication standard such as LTE.) in contrast, a link budget limited UE device may be configured to perform PRACH transmission with an alternate set of allowable subframes that is disjoint from the conventionally defined set.

In addition to having a conventionally defined set of allowable subframes, a PRACH configuration may identify a preamble format and specify constraints on allowable frames for PRACH transmission. (see, e.g., FIG. 8). When performing PRACH transmission, a link budget limited UE device may use the identified preamble format and use frames that comply with allowable frame constraints.

After broadcasting the index, the processing agent may receive the PRACH, i.e., the PRACH that has been transmitted by the UE device. The processing agent may determine whether the PRACH has been transmitted in one of the subframes of the alternative set or one of the subframes of the conventionally defined set.

In response to determining that the PRACH has been transmitted in one of the subframes of the alternative set, the processing agent may invoke one or more communication enhancement mechanisms for transmission to and/or reception from a UE device that transmitted the PRACH. (e.g., the processing agent may power up the random access response message, and/or power up downlink traffic transmissions to the UE device.) in contrast, if the processing agent determines that the PRACH has been transmitted in one of the subframes of the conventionally defined set, the processing agent may not invoke the one or more communication enhancement mechanisms.

In one set of embodiments, a method 1200 for operating a User Equipment (UE) device may be performed as shown in fig. 12. (the method 1200 may also include any subset of the features, elements, and embodiments described above in connection with fig. 1-11 and described below in connection with fig. 13-17.) the method 1200 may be performed by a link budget limited UE device to facilitate a random access procedure. The method may be implemented by a processing agent of a UE device. The processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements, by one or more special purpose hardware devices, such as ASICs, or by any combination of the preceding.

While the method 1200 is described below with respect to multiple steps, it should be understood that in various embodiments: one or more of the steps may be omitted; two or more of the steps may be performed at least partially in parallel; one or more steps may be added as desired; and the steps may be performed in an order different than that described.

At 1210, the processing agent may receive an index that has been broadcast by a base station. The index identifies a first configuration from a list of configurations for Physical Random Access Channel (PRACH) transmissions. Each configuration in the list may have:

a corresponding conventionally defined set of allowable subframes for PRACH transmissions by non-link budget limited UE devices (and/or legacy devices) in a cell corresponding to the base station; and

a corresponding alternate set of allowable subframes for PRACH transmission by a link budget limited UE device in the cell, wherein the corresponding alternate set is disjoint from a corresponding conventionally defined set.

The configuration list may be stored in a memory of the UE device.

At 1215, in response to determining that the UE device has been classified as link budget limited, the processing agent may transmit a PRACH to the base station. The PRACH may be transmitted in one of the subframes from the alternate set of allowable subframes corresponding to the index. If the state of the UE device becomes non-link budget limited, the UE device may transmit the PRACH in one of the subframes of the conventionally defined set.

In one set of embodiments, a method 1300 for operating a User Equipment (UE) device may be performed as shown in fig. 13. (the method 1300 may also include any subset of the features, elements, and embodiments described above in connection with fig. 1-12 and described below in connection with fig. 14-17.) the method 1300 may be performed by a link budget limited UE device to facilitate a random access procedure. The method may be implemented by a processing agent of a UE device. The processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements, by one or more special purpose hardware devices, such as ASICs, or by any combination of the preceding.

While the method 1300 is described below with respect to multiple steps, it should be understood that in various embodiments: one or more of the steps may be omitted; two or more of the steps may be performed at least partially in parallel; one or more steps may be added as desired; and the steps may be performed in an order different than that described.

At 1310, the processing agent may receive an index that has been broadcast by the base station. The index may identify a configuration for Physical Random Access Channel (PRACH) transmission. The configuration may specify that PRACH transmissions by non-link budget limited UE devices (and/or legacy devices) are limited to even frames and to a conventionally defined set of allowable subframes. (uplink frames are consecutively numbered, e.g., with system frame number).

At 1315, in response to determining that the UE device has been classified as link budget limited, the processing agent may transmit a PRACH to the base station, wherein the PRACH is transmitted in an odd frame and in one of the subframes from the conventionally defined set. By using odd frames, link budget limited UE devices avoid even frames, which are used for PRACH transmission by non-link budget limited UE devices. This strategy allows the base station to receive PRACH transmissions from link budget limited UE devices without interference from PRACH transmissions of non-LBLUE devices (and/or legacy devices) and, therefore, to decode PRACH transmissions from link budget limited UE devices with a lower probability of error. The base station may be configured to monitor even frames for PRACH transmissions from non-LBL UE devices (and/or legacy devices) and to monitor odd frames for PRACH transmissions from link budget limited UE devices.

In some embodiments, the configuration also specifies a format for PRACH transmission, e.g., one of those defined in the LTE standard and mentioned in the "preamble format" column of table 5.7.1-2 of 3GPP TS 36.211. (a copy of that table is given in fig. 8.) the transmission of PRACH to the base station, i.e. the transmission step 1315, may be performed according to the format. The index may be interpreted as the PRACH configuration index of the table. Each value of the PRACH configuration index may identify a corresponding PRACH configuration, including one or more of: a corresponding preamble format value, a corresponding constraint on the system frame number (e.g., selection of "even" or "any"), and a corresponding conventionally defined set of allowable subframes.

In some embodiments, method 1300 may further include: in response to determining that the UE device has been classified as not link budget limited, transmitting another PRACH to the base station, wherein the another PRACH is transmitted in an even frame and in one of the subframes from the conventionally defined set.

In some embodiments, the base station is configured to broadcast the index as part of the SIB2 (i.e., a type 2 system information block), as defined by the LTE standard.

In one set of embodiments, a method for operating a base station may be performed as follows. (the method may also include any subset of the features, elements, and embodiments described above in connection with fig. 1-12 and described below in connection with fig. 13-17.) the method may be performed by a base station to facilitate a random access procedure for a link budget limited UE device. The method may be implemented by a processing agent of a base station. The processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements such as FPGAs, by one or more special purpose hardware devices such as ASICs, or by any combination of the foregoing. The processing agent may be configured to transmit wireless signals via a transmitter of the base station and receive wireless signals via a receiver of the base station, e.g., as variously described above.

The processing agent may broadcast the index. The index may identify a configuration for transmission of a Physical Random Access Channel (PRACH). The configuration may specify (or indicate) that PRACH transmissions by non-link budget limited UE devices (and/or legacy devices) are limited to even-numbered frames and to a conventionally defined set of allowable subframes.

After broadcasting the index, the processing agent may receive the PRACH, i.e., the PRACH that has been transmitted by the UE device. The processing agent may determine whether the PRACH has been transmitted in even-numbered frames or odd-numbered frames. (the processing agent may maintain system frame numbers that are incremented from one uplink frame to the next).

In response to determining that the PRACH has been transmitted in odd-numbered frames, the processing agent may invoke one or more communication enhancement mechanisms for transmission to and/or reception from a UE device that transmitted the PRACH. (e.g., the processing agent may power up the random access response message, and/or power up downlink traffic transmissions to the UE device.) in contrast, if the processing agent determines that the PRACH has been transmitted in an even-numbered frame, the processing agent may not invoke the one or more communication enhancement mechanisms.

Background on conventional PRACH sequence set

In 3GPP TS36.211, a list of logical root sequence numbers and corresponding physical root sequence numbers is specified for the Physical Random Access Channel (PRACH). See tables 5.7.2-4 for TS 36.211. The eNodeB signals the logical root sequence number in SIB 2. The UE generates a set of 64 Zadoff-Chu sequences starting from the signaled logical root sequence number based on: parameter Ncs (also signaled in SIB 2); and physical root sequence numbers respectively corresponding to the consecutive logical root sequence numbers. In particular, the eNodeB generates a first subset of Zadoff-Chu sequences based on a cyclic shift of a first root sequence (corresponding to a first physical root sequence number) until the first root sequence is exhausted, then generates a second subset of Zadoff-Chu sequences based on a cyclic shift of a second root sequence (corresponding to a second physical root sequence number) until the second root sequence is exhausted, and so on until 64 sequences have been generated. According to TS36.211, the root sequence corresponding to the physical root sequence number u is given by:

wherein the root sequence x_uLength N of_ZCGiven by table 5.7.2.1 of TS 36.211.

For signallingSpecial preamble signaling LBL status of UE device

In one set of embodiments, a method 1400 for operating a User Equipment (UE) device may be performed as shown in fig. 14. (the method 1400 may also include any subset of the features, elements, and embodiments described above in connection with fig. 1-13 and described below in connection with fig. 15-17.) the method 1400 may be performed by a link budget limited UE device to facilitate a random access procedure. The method may be implemented by a processing agent. The processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements, by one or more special purpose hardware devices, such as ASICs, or by any combination of the preceding.

While the method 1400 is described below with respect to various steps, it should be understood that in various embodiments: one or more of the steps may be omitted; two or more of the steps may be performed at least partially in parallel; one or more steps may be added as desired; and the steps may be performed in an order different than that described.

At 1410, the processing agent may receive the logical root sequence number that has been broadcast by the base station.

At 1415, the processing agent may generate a set of preambles based on the data including the logical root sequence number. (this data may also include the parameter Ncs described below.) the act of generating the set of preambles may include determining the first physical root sequence number from a conventional mapping of logical root sequence numbers to physical root sequence numbers. (in the context of LTE, the conventional mapping may be a mapping defined by table 5.7.2.1 of 3GPP TS 36.211.) the set of preambles may include:

a first subset of preambles for Physical Random Access Channel (PRACH) transmission by a non-link budget limited UE device; and

a second subset of preambles for PRACH transmission by the link budget limited UE device, wherein the first subset and the second subset are disjoint subsets.

In some embodiments, the set of preambles may be generated by applying the sequence generation procedure of 3GPP TS36.211 section 5.7.2, but extending the procedure such that more than 64 preambles are generated. For example, the first 64 synchronization codes may form a first subset and the remaining preambles may form a second subset.

At 1420, in response to determining that the UE device has been classified as link budget limited, the processing agent may transmit the PRACH to the base station with one of the preambles from the second subset.

In some embodiments, the processing agent may generate only the second subset of preambles. For example, if the UE device is link budget limited, it may omit the act of generating the first subset of preambles.

The base station may be configured such that: whenever it receives a PRACH, the base station may determine whether the preambles included in the received PRACH belong to the first subset or the second subset, e.g., by correlating the received PRACH against the preambles in the first subset and against the preambles in the second subset. The subset membership of the largest related preamble indicates whether the UE device transmitting the PRACH is link budget limited. Thus, the UE device of method 1400 may signal its link budget limited status to the base station by transmitting the PRACH with a preamble selected from the second subset instead of the preamble from the first subset. Upon determining that the UE device is link budget limited, the base station may invoke one or more enhanced mechanisms for improving reliability of uplink and/or downlink communications with the UE device, such as, for example, mechanisms such as: employing a more complex decoding algorithm for decoding uplink transmissions from the UE device; transmitting a downlink transmission to the UE device with the increased power; and so on. (a non-LBL UE device may transmit prach with a preamble selected from the first subset-thus, the base station may recognize that the device is non-link budget limited.)

In some embodiments, the base station may also be configured to broadcast the logical root sequence number and parameter Ncs as part of the system information broadcast.

In some embodiments, the first subset of preambles is a set of preambles defined by existing LTE specifications.

In some embodiments, the method 1400 may further include: in response to determining that the UE device has been classified as not link budget limited, transmitting a PRACH to the base station with one of the preambles from the first subset. (the LBL status of a UE device may change as the UE device moves within a cell, as the UE device's battery power is depleted over time or replenished while charging, as other objects in the physical environment of the UE device change over time, etc.)

In some embodiments, the UE device may randomly select a preamble from the second subset of preambles.

In some embodiments, the set of preambles may be generated by: (1) generating a sequence of physical root sequence numbers based on the received logical root sequence numbers; and (2) applying a cyclic shift to a root sequence corresponding to a physical root sequence number of the sequence. The sequence of physical root sequence numbers may be generated by mapping consecutive logical root sequence numbers to corresponding physical root sequence numbers using a conventional mapping, starting with the signaled logical root sequence number.

In one set of embodiments, a method for operating a base station may be performed as follows. (the method may also include any subset of the features, elements, and embodiments described above in connection with fig. 1-14 and described below in connection with fig. 15-17.) the method may be performed by a base station to facilitate a random access procedure for a UE device with limited link budget. The method may be implemented by a processing agent of a base station. The processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements such as FPGAs, by one or more special purpose hardware devices such as ASICs, or by any combination of the foregoing. The processing agent may be configured to transmit wireless signals via a transmitter of the base station and receive wireless signals via a receiver of the base station, e.g., as variously described above.

The processing agent may broadcast the logical root sequence number. The non-link budget limited UE device (and/or legacy device) may use the logical root sequence number to generate a first subset of preambles for PRACH transmission, e.g., according to a conventionally defined algorithm. In contrast, a link budget limited UE device may generate a second subset of preambles for PRACH transmission, wherein the second subset is disjoint from the first subset.

After broadcasting the logical root sequence number, the processing agent may receive the PRACH, i.e., the PRACH that has been transmitted by the UE device. The processing agent may determine whether the PRACH has been transmitted using one of the preambles of the first subset or one of the preambles of the second subset.

In response to determining that the PRACH has been transmitted with one of the preambles of the second subset, the processing agent may invoke one or more communication enhancement mechanisms for transmission to and/or reception from a UE device that transmitted the PRACH. (e.g., the processing agent may boost the power of the random access response message, and/or the power of downlink traffic transmissions to the UE device.) if, on the other hand, the processing agent determines that the PRACH has been transmitted with one of the preambles of the first subset, the processing agent may not invoke the one or more communication enhancement mechanisms.

In one set of embodiments, a method 1500 for operating a User Equipment (UE) device may be performed as shown in fig. 15. (the method 1500 may also include any subset of the features, elements, and embodiments described above in connection with fig. 1-14 and described below in connection with fig. 16-17.) the method 1500 may be performed by a link budget limited UE device to facilitate a random access procedure. The method may be implemented by a processing agent. The processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements, by one or more special purpose hardware devices, such as ASICs, or by any combination of the preceding.

While the method 1500 is described below with respect to a number of steps, it should be understood that in various embodiments: one or more of the steps may be omitted; two or more of the steps may be performed at least partially in parallel; one or more steps may be added as desired; and the steps may be performed in an order different than that described.

At 1510, the processing agent may receive system information that has been broadcast by the base station. The system information may include one or more of the following elements:

a logical root sequence number;

a total number n of preambles included in the preamble set_TOTALWherein the set of preambles includes a first set of preambles and a second set of one or more preambles, wherein the first and second sets are disjoint (as a subset of the set of preambles); and

number n of preambles in the first group₁。

Number n₁Is a positive number but a specific number n_TOTALSmall:

0<n₁<n_TOTAL。

at 1515, the processing agent may generate a set of preambles based on the data including the logical root sequence number. The act of generating the set of preambles may comprise generating a set of preambles having a size equal to the number n₁And generating a first group of preambles having a size equal to the number n_TOTALAnd a number n₁A second set of one or more preambles of the difference. The first set of preambles may be reserved for Physical Random Access Channel (PRACH) transmissions by non-link budget limited UE devices (and/or legacy devices). The second set of one or more preambles may be used for PRACH transmission by a link budget limited UE device.

At 1520, in response to determining that the UE device has been classified as link budget limited, the processing agent may transmit a PRACH to the base station with one of the one or more preambles from the second group.

When the base station receives the PRACH, the base station may determine whether the preambles included in the received PRACH belong to the first group or the second group, e.g., by correlating the received PRACH against the preambles in the first group and against one or more preambles in the second group. The group membership (first or second group) indicates whether the UE device that transmitted the PRACH is link budget limited. In response to determining that a given UE device is link budget limited (based on group membership), the base station may invoke one or more communication enhancement mechanisms to improve reliability of uplink and/or downlink communications with the UE device.

In some embodiments, the system information may include a RACH-ConfigCommon information element compliant with the LTE standard. The RACH-ConfigCommon message may include a number n_TOTALN, number n₁And message size. The base station may be configured to set the message size equal to a sufficiently large value such that the number of non-link budget limited UE devices using preambles from the second group is reduced, (or such that the probability that a non-link budget limited UE device will use preambles from the second group is reduced).

In some embodiments, the system information may include a RACH-ConfigCommon message compliant with the LTE standard. The RACH-ConfigCommon message may include a number n_TOTALN, number n₁And a power offset. The base station may be configured to set the power offset to a value large enough so as to increase the number of link budget limited UE devices that use preambles from the second group, (or, to increase the probability that link budget limited UE devices will use preambles from the second group instead of preambles from the first group).

In some embodiments, the system information may also include a parameter N_CSWherein the data of step 1515 includes a parameter Ncs.

In some embodiments, the system information may include a RACH-ConfigCommon message compliant with the LTE standard. The RACH-ConfigCommon message may include a number n_TOTALN, number n₁An indication of a power offset, and an indication of a message size threshold. In these embodiments, the method 1500 may also include the following. In response to determining that the UE device has been classified as not link budget limited, the processing agent may perform operations comprising:

determining whether (a) a pathloss measured by the UE device is less than a pathloss threshold determined in part by a power offset, and (b) a size of an uplink message to be sent by the UE device is greater than a message size threshold;

in response to determining (a) and (b) are true, selecting a preamble from the first group; and transmitting the PRACH that includes the selected preamble.

In one set of embodiments, a method for operating a base station may be performed as follows. (the method may also include any subset of the features, elements, and embodiments described above in connection with fig. 1-15 and described below in connection with fig. 16-17.) the method may be performed by a base station to facilitate a random access procedure for a UE device with limited link budget. The method may be implemented by a processing agent of a base station. The processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements such as FPGAs, by one or more special purpose hardware devices such as ASICs, or by any combination of the foregoing. The processing agent may be configured to transmit wireless signals via a transmitter of the base station and receive wireless signals via a receiver of the base station, e.g., as variously described above.

The processing agent may broadcast system information. The system information may include one or more of the following elements:

a logical root sequence number;

a total number n of preambles included in the preamble set_TOTALWherein the set of preambles includes a first set of preambles and a second set of one or more preambles, wherein the first and second sets are disjoint; and

number n of preambles in the first group₁。

The UE device may be based on data including a logical root sequence numberA set of preambles is generated. The act of generating the set of preambles may comprise generating a set of preambles having a size equal to the number n₁And generating a first group of preambles having a size equal to the number n_TOTALAnd a number n₁A second set of one or more preambles of the difference. The first set of preambles may be reserved for Physical Random Access Channel (PRACH) transmissions by non-link budget limited UE devices (and/or legacy devices). In contrast, a link budget limited UE device may be configured to perform PRACH transmission with a second set of one or more preambles.

After broadcasting the system information, the processing agent may receive the PRACH, i.e., the PRACH that has been transmitted by the UE device. The processing agent may determine whether the PRACH includes a preamble from the first group or a preamble from the second group.

In response to determining that the PRACH includes a preamble from the second group, the processing agent may invoke one or more communication enhancement mechanisms for transmission to and/or reception from a UE device that transmitted the PRACH. (e.g., the processing agent may boost the power of the random access response message, and/or boost the power of downlink traffic transmissions to the UE device.) if, on the other hand, the processing agent determines that the PRACH includes a preamble from the first group, the processing agent may not invoke the one or more communication enhancement mechanisms.

Improving reception of random access MSG2 by link budget limited devices

According to existing LTE specifications, for each random access attempt, the UE may randomly select a preamble from a set of preambles and transmit the selected preamble in msg1 (i.e., a PRACH message). The PRACH message may be sent to the Network (NW) via the base station. The UE then waits for msg2, a so-called random access response message from the base station. Msg2 may be received in the PDCCH and PDSCH of a downlink subframe within a specific time window related to the time Msg1 is sent. If msg2 is not received in the time window, the UE backs off for a certain amount of time and randomly selects another preamble from the group and makes another random access attempt by sending another PRACH message (including the newly selected preamble).

A link budget limited UE device has an increased likelihood of missing (e.g., failing to decode) msg2 as compared to a non-link budget limited UE device. If the eNodeB knows that the UE device is link budget limited, the eNodeB may boost the power of msg2 to enable an increased likelihood of successful decoding of msg2 by the UE device. However, in some cases, the base station may not be able to determine from msg1 whether the UE is link budget limited.

In some embodiments, a Link Budget Limited (LBL) device may operate as follows.

1) The LBL device may randomly select a preamble from the group of preambles as defined by the 3GPP specifications and send the preamble in msg1 of the random access procedure. Such transmission may be referred to as a first preamble transmission. The LBL device may transmit msg3 for the random access procedure if msg2 is received within an expected time window after transmitting msg 1.

2) If the LBL device fails to receive msg2 within the expected time window after transmitting msg1, another random access attempt may be initiated. In particular, the LBL device may: returning for a certain amount of time; and another transmission of msg1 is performed (using the same preamble as the first preamble transmission, or alternatively, using the next preamble in the preamble sequence). Back-off refers to waiting a certain amount of time before sending. The back-off may be defined, for example, with respect to an RA (random access) window after MSG1 transmission, and may be fixed or random. For example, the back-off may be a fixed value for all preamble transmissions after the first transmission and/or for all LBL devices in the cell.

Thus, LBL devices may repeatedly transmit msg1 until msg2 is successfully received. The repeated transmission of msg1 may use the same preamble. Alternatively, the repeated transmission of msg1 may use a sequence of preambles whose pattern is known to the eNodeB. Successive transmissions of msg1 may use successive preambles from the sequence. (although the first preamble of a sequence may be randomly selected, the relationship between successive preambles of a sequence may be known by the eNodeB).

In some embodiments, the eNodeB may perform the following operations.

1) The eNodeB may count: the number of times the msg1 has been received with the same preamble, and the number of times the corresponding msg2 procedure failed. In other words, for a given preamble, the eNodeB may count the number of times the eNodeB performs the following operations:

msg1 was received and msg1 contained the given preamble; and

msg2 is sent, but msg3 is not received from the UE.

2) If the number of times reaches (or alternatively exceeds) a threshold N (e.g., N ═ 2, 3, 4, 5, or 6), the eNodeB may boost the power at which msg2 is transmitted in response to one or more subsequent instances of msg1 containing the given preamble until msg3 is received from the UE device. For example, the PDCCH and/or PDSCH of msg2 may be power boosted.

The "same preamble" mentioned above assumes that the LBL type UE uses the same preamble (as the first preamble transmission) for msg1 retransmissions. Alternatively, if an LBL type UE uses a preamble sequence for msg1 transmission, the eNodeB may follow the same preamble sequence. Thus, the eNodeB may count the number of times in which the eNodeB performs the following operations:

msg1 is received and msg1 contains a preamble that is consistent with the preamble sequence; and

msg2 is sent, but msg3 is not received from the UE.

In some embodiments, the LBL device may be configured to add a special MAC Control Element (CE) as an additional MAC PDU header in msg3 to indicate to the NW that it is link budget limited. When the base station receives msg3, the base station may determine whether the UE transmitting msg3 is link budget limited by determining whether a special MAC CE is present in msg 3.

In one set of embodiments, the LBL device may transmit the first PRACH message with a first preamble randomly selected from an available set of preambles. The LBL device may send an additional PRACH message if a random access attempt corresponding to a previous PRACH message (e.g., the first PRACH message) is not successfully completed. Thus, the LBL device may send successive PRACH messages until the random access is successfully completed. The consecutive PRACH messages may have preambles that conform to a sequence of preamble index offsets. Each PRACH message following the first PRACH message may include a respective preamble determined by:

(a) a respective index offset from the selected sequence of index offsets; and

(b) index I of the first preamble₀。

For example, the kth PRACH message after the first PRACH message may include the index I₀+ offset (k) identifies the preamble, where offset (k) is the kth offset in the selected index offset sequence.

In some embodiments, the random selection from the predetermined set may be based on the cell ID of the eNodeB, such that LBL devices in different cells will select different index offset sequences from the predetermined set.

The LBL device may use an index offset sequence selected from a predetermined set of offset sequences. In contrast, when a non-LBL device (and/or legacy device) experiences a failure with respect to any given random access attempt (e.g., due to missing msg2), it may randomly select another preamble from the available set of preambles and transmit another PRACH message based on the randomly selected preamble. Thus, successive PRACH transmissions from non-LBL devices will generally not coincide with any predetermined set of sequences. (the probability that a non-LBL device will randomly select a preamble sequence that is consistent with any predetermined set of sequences is very low.)

The eNodeB may count the number of failed RACH attempts whose preambles coincide with a given index offset sequence. As the count grows, the likelihood of RACH attempts to associate with LBL devices increases. When the eNodeB receives the current PRACH message consistent with a given sequence of index offsets, the eNodeB may determine whether the count has reached (c:)Or alternatively, greater) than the threshold N. If so, the eNodeB may transmit a random access response message (i.e., random access msg2) with increased power relative to the power (or powers) used for the previous N transmissions of msg 2. In some embodiments, the first N transmissions may utilize a given power P₀Is transmitted and any transmission of msg2 after the first N transmissions may utilize more than P₀Is transmitted. In one embodiment, successive transmissions of msg2 after the Nth transmission are transmitted with increasing power.

In one set of embodiments, a method 1600 for operating a User Equipment (UE) device may be performed as shown in fig. 16A. (the method 1600 may also include any subset of the features, elements, and embodiments described above in connection with fig. 1-15 and described below in connection with fig. 17.) the method 1600 may be performed by a link budget limited UE device to facilitate a random access procedure. The method may be implemented by a processing agent. The processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements, by one or more special purpose hardware devices, such as ASICs, or by any combination of the preceding.

While method 1600 is described below with respect to various steps, it should be understood that in various embodiments: one or more of the steps may be omitted; two or more of the steps may be performed at least partially in parallel; one or more steps may be added as desired; and the steps may be performed in an order different than that described.

At 1610, the processing agent may perform one or more iterations of the set of operations until a termination condition is implemented. The set of operations may include operations 1615 through 1620 described below.

At 1615, the processing agent may generate a preamble for the PRACH message.

In 1620, the processing agent may transmit a PRACH message to the base station, where the PRACH message includes a preamble. The termination condition may be a condition that the UE device successfully receives a Random Access Response (RAR) message in response to the PRACH message.

The one or more preambles in the one or more respective transmissions of the PRACH message may be generated based on:

a sequence of preamble index offsets, wherein the sequence has been configured (or reserved) for use by a link budget limited UE device; and

a first index of a first preamble generated for a first time among one or more transmissions of a PRACH message.

In some embodiments, method 1600 may further include selecting a sequence of preamble index offsets from a predetermined set of preamble index offset sequences, wherein the predetermined set is configured (or reserved) for use by a link budget limited UE device.

In some embodiments, the act of selecting from the predetermined set is based on a random selection of a cell ID of the base station.

In some embodiments, the UE device is link budget limited. A UE device with limited link budget may require more than one iteration of the set of operations to reach the termination condition.

In some embodiments, for each iteration after the first iteration, the set of operations further comprises backoff for a fixed amount of time before a next transmission of a PRACH message.

In one set of embodiments, a method for operating a base station may be performed as follows. (the method may also include any subset of the features, elements, and embodiments described above in connection with fig. 1-15 and described below in connection with fig. 16B-17.) the method may be performed by a base station to facilitate a random access procedure for a link budget limited UE device. The method may be implemented by a processing agent of a base station. The processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements such as FPGAs, by one or more special purpose hardware devices such as ASICs, or by any combination of the foregoing. The processing agent may be configured to transmit wireless signals via a transmitter of the base station and receive wireless signals via a receiver of the base station, e.g., as variously described above.

The processing agent may receive a current PRACH message, e.g., from a UE device in a cell. A UE device of the link budget limited type may be configured to repeatedly transmit PRACH messages with a preamble conforming to a known pattern until the random access procedure is successfully completed. In contrast, a non-LBL type UE device (and/or legacy device) may be configured to randomly select a preamble for each transmission of a PRACH message.

The processing agent may increment a failure count in response to determining that the current PRACH message results in a random access failure and that a preamble in the current PRACH message and one or more previous PRACH message preambles are consistent with a pattern of preambles reserved for LBL type UE devices.

In response to determining that the failure count exceeds (or alternatively reaches) the threshold, the processing agent may invoke one or more communication enhancement mechanisms for transmission to and/or reception from the UE device that transmitted the PRACH. (e.g., the processing agent may power up the random access response message, and/or power up downlink traffic transmissions to the UE device.) if, on the other hand, the processing agent determines that the failure count is less than or equal to (or alternatively, less than) the threshold, the processing agent may not invoke the one or more communication enhancement mechanisms.

In one set of embodiments, a method 1650 for operating a User Equipment (UE) device may be performed as shown in fig. 16B. (the method 1650 may also include any subset of the features, elements, and embodiments described above in connection with FIGS. 1-16A and below in connection with FIG. 17. the method 1650 may be performed by a UE device that is link budget limited to facilitate a random access procedure.

While the method 1650 is described below with respect to multiple steps, it should be understood that in various embodiments: one or more of the steps may be omitted; two or more of the steps may be performed at least partially in parallel; one or more steps may be added as desired; and the steps may be performed in an order different than that described.

At 1660, in response to determining that a Random Access Response (RAR) message has not been received after sending the previous PRACH message, the processing agent may perform a set of

operations including operations

1665 and 1670 described below. (the processing agent may monitor an expected time window for the RAR message, i.e. an expected time window after a previous PRACH transmission).

At 1665, the processing agent may generate a preamble based at least in part on a current offset in the sequence of preamble index offsets, e.g., as variously described above. The sequence of preamble index offsets may have been configured (or may be dedicated) for use by a link budget limited UE device.

At 1670, the processing agent may send the current PRACH message including the generated preamble.

In some embodiments, the preamble may be generated based on the current offset and the initial index, e.g., as described differently above. The initial index may be an index of an initial preamble used in initial transmission of the PRACH message.

In some embodiments, method 1650 may further include selecting a sequence of preamble index offsets from a predetermined set of preamble index offset sequences, wherein the predetermined set has been configured (or reserved) for use by a link budget limited UE device.

In some embodiments, the action selected from the predetermined set is based on a random selection of a cell ID of the base station.

In some embodiments, the sequence of preamble index offsets may be an alternating sequence, i.e. alternating between two different offset values.

In some embodiments, the sequence of preamble index offsets may be a cyclic sequence, i.e., cycling through n_CYCAn offset value, where n_CYCGreater than or equal to 2.

In some embodiments, the sequence of preamble index offsets may be a sequence of non-zero values, or a sequence of positive values, or a sequence including two or more non-zero values and one or more zero values.

In some embodiments, the sequence of preamble index offsets may be a sequence of zero values.

In some embodiments, the UE device is link budget limited.

In some embodiments, the set of operations further comprises falling back a fixed amount of time before said sending of the current PRACH message.

In one set of embodiments, a method 1700 for operating a base station device may be performed as shown in fig. 17. (the method 1700 may also include any subset of the features, elements, and embodiments described above in connection with fig. 1-16B.) the method 1700 may be performed to facilitate random access by a link budget limited UE device. The method may be implemented by a processing agent of a base station. The processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements, by one or more special purpose hardware devices, such as ASICs, or by any combination of the preceding.

Although method 1700 is described below with respect to a number of steps, it should be understood that in various embodiments: one or more of the steps may be omitted; two or more of the steps may be performed at least partially in parallel; one or more steps may be added as desired; and the steps may be performed in an order different than that described.

At 1710, the processing agent may receive the current PRACH message after a plurality of previous PRACH messages have been received. Previous PRACH message:

(a) corresponding preamble having a sequence consistent with a preamble index offset, wherein

The sequence of preamble index offsets is configured (or, alternatively, dedicated) for use by a link budget limited User Equipment (UE) device, an

(b) Has resulted in random access failure.

The memory of the base station may store a count of previous PRACH messages.

At 1715, the processing agent may send a Random Access Response (RAR) message in response to receiving the current PRACH message. The power of the transmission of the RAR message may be less than or equal to the first power level if the current value of the count is less than or equal to a threshold N, where N is an integer greater than one. Alternatively, the power of said sending of the RAR message may be greater than the first power level if the current value of the count is greater than the threshold N.

In some embodiments, method 1700 may further include incrementing the count in response to determining:

(1) the preamble of the current PRACH message coincides with an expected preamble, wherein the expected preamble is based on a next preamble index offset of the sequence of preamble index and preamble index offsets of the first message among the previous PRACH messages; and

(2) in response to the RAR message, the third random access message is not received by the base station.

In some embodiments, the predetermined sequence of preamble index offsets is a sequence of zero values.

In some embodiments, a first one of the link budget limited UE devices is configured to randomly select a sequence of preamble index offsets from a predetermined set of preamble index offset sequences, and to generate a preamble for a subsequent random access attempt with the selected sequence of preamble index offsets.

Embodiments of the present disclosure may be implemented in any of various forms. For example, some embodiments may be implemented as a computer-implemented method, a computer-readable storage medium, or a computer system. Other embodiments may be implemented using one or more custom designed hardware devices, such as ASICs. Still other embodiments may be implemented using one or more programmable hardware elements, such as FPGAs.

In some embodiments, a non-transitory computer-readable storage medium may be configured such that it stores program instructions and/or data, wherein the program instructions, if executed by a computer system, cause the computer system to perform a method, e.g., any of the method embodiments described herein, or any combination of the method embodiments described herein, or any subset of any of the method embodiments described herein, or any combination of the subsets.

In some embodiments, a device (e.g., UE 106) may be configured to include a processor (or a set of processors) and a storage medium, wherein the storage medium stores program instructions, wherein the processor is configured to read and execute the program instructions from the storage medium, wherein the program instructions are executable to implement a method, such as any of the various method embodiments described herein (or any combination of the method embodiments described herein, or any subset of any of the method embodiments described herein, or any combination of these subsets). The device may be implemented in any of various forms.

Although embodiments have been described above in considerable detail, various modifications and adaptations will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.

Claims

1. A method for operating a base station, the method comprising:

at the base station:

transmitting a first system information block, SIB, comprising a first index, wherein the first index identifies a first configuration in a list of PRACH configurations, wherein the first configuration specifies a first set of allowable time opportunities for transmitting a randomly selected PRACH preamble by a link budget limited user equipment device, UE;

transmitting a second SIB comprising a second index, wherein the second index identifies a second configuration in the list of PRACH configurations, wherein the second configuration specifies a second set of allowable time opportunities for transmitting the randomly selected PRACH preamble by the non-link budget limited UE, wherein the first and second sets of allowable time opportunities for transmitting the randomly selected PRACH preamble by the link budget limited UE and the non-link budget limited UE are disjoint;

receiving, at a first time, a first preamble from a UE, wherein the first PRACH preamble is received according to a first configuration indicating that the UE is link budget limited; and

at a second time, a second preamble is received from the UE, wherein the second PRACH preamble is received according to a second configuration indicating that the UE is non-link budget limited.

2. The method of claim 1, wherein the first SIB is SIB type 2, SIB 2.

3. The method of claim 2, wherein the second SIB is not SIB 2.

4. The method of claim 2, wherein the second SIB is a special SIB.

5. The method of claim 1, wherein the first preamble and the second preamble are selected from different preamble sets.

6. The method of claim 1, wherein the first set of allowable time opportunities comprises odd frames.

7. The method of claim 1, wherein the second set of allowable time opportunities comprises even frames.

8. An apparatus for operating a user equipment device, UE, the apparatus comprising:

a processor configured to cause a UE to:

receiving from a base station:

a first system information block, SIB, comprising a first index corresponding to a first configuration, wherein the first configuration specifies a first set of allowable time opportunities for transmission of a randomly selected physical random access channel, PRACH, preamble by a link budget limited UE, wherein the first index identifies a first configuration of a list of PRACH configurations;

a second SIB comprising a second index corresponding to a second configuration, wherein the second configuration specifies a second set of allowable time opportunities for transmission of a randomly selected PRACH preamble by a non-link budget limited UE, wherein the second index identifies a second configuration in the list of PRACH configurations;

at a first time, in response to determining that the UE has been classified as link budget limited, transmitting a first randomly selected PRACH preamble according to a first configuration; and

at a second time, in response to determining that the UE is not classified as link budget limited, transmitting a second randomly selected PRACH preamble according to a second configuration;

determining whether the UE is classified as link budget limited; and

transmitting a particular randomly selected PRACH preamble to the base station, wherein the particular randomly selected PRACH preamble is selected in accordance with a determination of whether the UE is classified as link budget limited.

9. The apparatus of claim 8, in which the first SIB is SIB type 2, SIB 2.

10. The apparatus of claim 9, wherein the second SIB is not SIB 2.

11. The apparatus of claim 9, wherein second SIBs are special SIBs.

12. The apparatus of claim 8, wherein the particular randomly selected PRACH preamble is transmitted during a first set of allowable time opportunities in response to determining that the UE is link budget limited.

13. The apparatus of claim 8, wherein the particular randomly selected PRACH preamble is transmitted during a second set of allowable time opportunities in response to determining that the UE is non-link budget limited.

14. The apparatus of claim 8, wherein the first set of allowable time opportunities comprises odd frames.

15. A user equipment device, UE, comprising:

a radio device; and

a processor operably connected to the radio and configured to cause a UE to:

at a first time, in response to determining that the UE has been classified as link budget limited:

randomly selecting a first physical random access channel, PRACH, preamble according to a first configuration, wherein the first configuration is identified according to a first index received in a first system information block, SIB, from the base station, wherein the first configuration specifies a first set of allowable subframes for transmitting the randomly selected PRACH preamble by a link budget limited UE, wherein the first index identifies a first configuration of a list of PRACH configurations; and

transmitting a first PRACH preamble to a base station during subframes of a first set of allowable subframes; and

at a second time, in response to determining that the UE has been classified as non-link budget limited:

randomly selecting a second PRACH preamble according to a second configuration, wherein the second configuration is identified according to a second index received in a second SIB from the base station, wherein the second configuration specifies a second set of allowable subframes for transmitting the randomly selected PRACH preamble by the non-link budget limited UE, wherein the second index identifies a second configuration in the list of PRACH configurations; and

transmitting a second PRACH preamble to the base station during subframes of the second set of allowable subframes, wherein respective sets of allowable subframes for transmitting randomly selected PRACH preambles by link budget limited and non-link budget limited UEs are disjoint.

16. The UE of claim 15, wherein the first SIB is SIB type 2, SIB 2.

17. The UE of claim 16, wherein the second SIB is not SIB 2.

18. The UE of claim 15, wherein the UE operates according to LTE.

19. The UE of claim 15, wherein the first set of allowable subframes specifies odd frames.

20. The UE of claim 19, wherein the second set of allowable subframes specifies even frames.