WO2020154877A1

WO2020154877A1 - Adaptive high level operating system retry timeout mechanism

Info

Publication number: WO2020154877A1
Application number: PCT/CN2019/073585
Authority: WO
Inventors: Rajendran Kumarasamy; Hamza Ijaz Abbasi; Rohit TRIPATHI; Murali Bharadwaj; Liangchi Hsu; Ralph Akram Gholmieh; Elmira Mazloomian; Nagarjuna Reddy CHAGANTI; Xiantao LIU; Poonam Mishra
Original assignee: Qualcomm Incorporated
Priority date: 2019-01-29
Filing date: 2019-01-29
Publication date: 2020-08-06

Abstract

Aspects of adaptively calculating retransmission timer values are disclosed. In an example, a modem of a first device calculates a delay time of a packet that was transmitted to a second device and determines a coverage enhancement level (CE-level) indicating a communication condition between the first device and the second device. A high level operating system (HLOS) of the first device determines a retransmission timer value based on at least the delay time and the CE-level and sets a retransmission timer based on the retransmission timer value. The first device then retransmits the packet according to the retransmission timer.

Description

ADAPTIVE HIGH LEVEL OPERATING SYSTEM RETRY TIMEOUT MECHANISM

BACKGROUND

The present disclosure relates generally to communication systems, and more particularly, to adaptive high level operating system (HLOS) retry timeout mechanism.

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

These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example telecommunication standard is fifth generation (5G) New Radio (NR) . 5G NR is part of a continuous mobile broadband evolution promulgated by Third Generation Partnership Project (3GPP) to meet new requirements associated with latency, reliability, security, scalability (e.g., with Internet of Things (IoT) ) , and other requirements. 5G NR include services associated with enhanced mobile broadband (eMBB) , massive machine type communications (mMTC) , and ultra reliable low latency communications (URLLC) . Some aspects of 5G NR may be based on the 4G Long Term Evolution (LTE) standard.

Some 5G NR technologies, such as but not limited to narrowband internet of things (IoT) technologies, may have a throughput that is very low and therefore may require a significant amount of time when transmitting packets over-the-air (OTA) . Under poor radio frequency (RF) conditions, packet retransmission may result in redundant retransmitted packets and congestion. Accordingly, there exists a need for further improvements in 5G NR technologies.

SUMMARY

The following presents a simplified summary of one or more aspects in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated aspects, and is intended to neither identify key or critical elements of all aspects nor delineate the scope of any or all aspects. The sole purpose of this summary is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.

In an aspect, a method for adaptively calculating a retransmission timer value by a first device is disclosed. The method may include calculating a delay time of a packet that was transmitted to a second device, determining a coverage enhancement -level (CE-level) indicating a communication condition between the first device and the second device, determining a retransmission timer value based on at least the delay time and the CE-level, setting a retransmission timer based on the retransmission timer value, and retransmitting the packet according to the retransmission timer.

In another aspect, a first device for wireless communication is disclosed. The first device may include a memory and a processor coupled with the memory. The processor may be configured to calculate a delay time of a packet that was transmitted to a second device, determine a CE-level indicating a communication condition between the first device and the second device, determine a retransmission timer value based on at least the delay time and the CE-level, set a retransmission timer based on the retransmission timer value, and retransmit the packet according to the retransmission timer.

In another aspect, an apparatus for wireless communication is disclosed. The apparatus may include means for calculating a delay time of a packet that was transmitted to a device, means for determining a CE-level indicating a communication condition between the apparatus and the device, means for determining a retransmission timer value based on at least the delay time and the CE-level, means for setting a retransmission timer based on the retransmission timer value, and means for retransmitting the packet according to the retransmission timer.

In another aspect, a computer-readable medium storing computer code executable by a processor of a first device for wireless communications is disclosed. The computer-readable medium may include code to calculate a delay time of a packet that was transmitted to a second device, code to determine a CE-level indicating a communication condition between the first device and the second device, code to determine a retransmission timer value based on at least the delay time and the CE-level, code to set a retransmission timer based on the retransmission timer value, and code to retransmit the packet according to the retransmission timer.

To the accomplishment of the foregoing and related ends, the one or more aspects comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative features of the one or more aspects. These features are indicative, however, of but a few of the various ways in which the principles of various aspects may be employed, and this description is intended to include all such aspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed aspects will hereinafter be described in conjunction with the appended drawings, provided to illustrate and not to limit the disclosed aspects, wherein like designations denote like elements, and in which:

FIG. 1 is a schematic diagram of an example wireless communications system;

FIG. 2 is a flow diagram of an example call flow for adaptively calculating retransmission timer according to aspects of the present disclosure;

FIG. 3 is a conceptual diagram of an example of determining a delay time according to aspects of the present disclosure;

FIG. 4 is a flowchart of an example method of wireless communications;

FIG. 5 is a schematic diagram of example components of a user equipment (UE) of FIG. 1; and

FIG. 6 is a schematic diagram of example components of a network of FIG. 1.

DETAILED DESCRIPTION

This disclosure includes apparatuses, methods, and computer-readable mediums for adaptively calculating retransmission timer values by a high level operating system (HLOS) of a user equipment (UE) based on feedback from lower protocol levels of a modem of the UE to avoid redundant retransmitted packets and congestion in the UE and the network.

For fifth generation (5G) New Radio (NR) technologies including, for example, Node B to Internet of Things (IoT) (NB-IoT) systems, bandwidth may be very small. Due to the limited bandwidth, packet transmissions may take a long time for a modem (e.g., L1 and L2 layers and/or data services) of a UE (e.g., NB-IoT device) while sending the packet transmission over-the-air (OTA) . This may be especially true during poor radio frequency (RF) conditions. Typically, an upper protocol layer (e.g., an application layer, a datagram transport layer security (DTLS) protocol layer, and/or a domain name server (DNS) layer) running on a high level operating system (HLOS) of the UE, is not aware of the current RF conditions at one or more lower protocol layers (e.g., L1 (physical layer) , L2 (media access control (MAC) , radio link protocol (RLP) , and/or packet data convergence protocol (PDCP) /modem layer) , and/or data services layer) of the modem of the UE. Hence, under some conditions (e.g., poor RF conditions) , the upper protocol layer may retransmit packets based on a retransmission timer of the upper protocol layer even though initial packets have not been transmitted by the UE. In some examples, the upper protocol layer may retransmit packets until the retransmission timer ends or an acknowledgment (ACK) is received from the network. This may result in redundant retransmitted packets within queues/buffers of the modem. Further, this behavior may lead to congestion between the modem and the HLOS on the UE, and may consume unnecessary power of the UE.

The present disclosure provides mechanisms to mitigate the occurrence of redundant retransmitted packets and congestion between the modem and the HLOS of the UE. In an aspect, the HLOS of the UE may be notified of the current RF channel conditions in a network (e.g., 5G NR network) . The HLOS may also receive feedback from lower protocol layers in modem (e.g., L1, L2, or data service layers) to determine an optimal retransmission policy and to determine how long the lower protocol layers of the modem may take to transmit a single packet successfully via the network. In an aspect, the lower protocol layers may be responsible for notifying HLOS of a delay time and a coverage enhancement level (CE-level) . In an aspect, the delay time may be an indication of the time for the lower protocol layers to transmit a single packet successfully OTA and receive an ACK in response. In an aspect, the CE-level may be an indication of current RF conditions and/or network conditions. In some examples, the CE-level may include the values 0, 1, 2, where 0 may indicate the best RF/network conditions and 2 may indicate the worst RF/network conditions. The HLOS may adaptively calculate optimal retransmission timer values based on the delay time and the CE-level at lower protocol layers.

Implementation of aspects of the present disclosure may be used by protocols including, but not limited to, DTLS protocol, DNS protocol, constrained application protocol (CoAP) , or TCP retransmission timers. The following examples describe the implementation of the DTLS retransmission timer but implementation of other protocols may be performed using similar techniques. Typically the DTLS retransmission timer may only be used during a DTLS handshake, thereby leaving timer values up to implementation choice. For example, current protocols recommend the use of an initial timer value of 1 second be used and the value to be doubled for each retransmission, up to no less than the maximum of 60 seconds. According to this example, the default retransmission timer values may be, for example, 1, 2, 4, 8, 16, 32, and 60 seconds.

According to aspects of the present application, additional parameters may be applied when determining timer values for the DTLS retransmission timer. For example, the upper protocol layer of the HLOS may consider one or more of the following when calculating adaptive retransmission timer values: lower protocol layer (e.g., L1, L2, or data service layer) delay times (e.g., delay times between UE and the network) , CE-level, prior context (e.g., retransmission timer values used in recent successful DTLS handshakes) , a maximum timer value (e.g., a maximum possible time interval between any two retransmissions) , or the DTLS protocol specific default timer values (i.e. 1, 2, 4, 8, 16, 32, and 60 seconds) .

In some aspects, the retransmission timer value may be a function of the following parameters: a current delay time; a CE-level; a protocol value, which may include DTLS retransmission timer value as per current protocol (e.g., 1, 2, 4, 8, 16, 32, and 60 seconds) ; a context of the retransmission value, which may include a previous retransmission delay value at protocol level; and a maximum timer value. Accordingly, the retransmission timer value may equal the function (current delay time, CE-level, protocol value, context, maximum timer value) . The function definition may be left up to implementation as the function may be optimized differently for each scenario.

Accordingly, based on the aspects of the present disclosure, upper protocol layers (e.g., application layer of HLOS) of the UE may take into account feedback from lower protocol layers (e.g., L1, L2, or data service layers of modem) to determine an appropriate retransmission policy and optimal retransmission timers. Further, the CE-level (e.g., 0, 1, or 2) and corresponding repetitions from the lower protocol layers may be shared with the upper protocol layers of the UE. Also, a roundtrip delay time between a segment transmission (e.g., first segment of packet) and the reception of an ACK from the network may be determined and then shared with the upper protocol layers.

In some aspects, the upper protocol layers may maintain a context /history of retransmission timers, losses, etc., which may also be used when determining the retransmission timers for subsequent retransmissions. Further, the retransmission timers may also depend on the protocol (e.g. DTLS, DNS, CoAP, TCP) being used, and a maximum allowed timer value between any two subsequent retransmissions.

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

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

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

Accordingly, in one or more example aspects, the functions described may be implemented in hardware, software, or any combination thereof. If implemented in software, the functions may be stored on or encoded as one or more instructions or code on a computer-readable medium. Computer-readable medium includes computer storage media. Storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable medium may comprise a random-access memory (RAM) , a read-only memory (ROM) , an electrically erasable programmable ROM (EEPROM) , optical disk storage, magnetic disk storage, other magnetic storage devices, combinations of the aforementioned types of computer-readable media, or any other medium that can be used to store computer executable code in the form of instructions or data structures that can be accessed by a computer.

Referring to FIG. 1, an example of a wireless communications system 100 is illustrated. The wireless communications system 100 (also referred to as a wireless wide area network (WWAN) ) includes one or more base stations 102 and one or more UEs 104.

In an aspect, the UE 104 may include one or more components, such as a modem 140 having a retransmission timer component 142, that operate to determine a retransmission timer value for retransmitting a packet. In particular, the retransmission timer component 142 may be configured to calculate a delay time of a packet that was transmitted to a base station 102. The retransmission timer component 142 may also be configured to determine a CE-level indicating a communication condition between the UE 104 and the base station 102. The retransmission timer component 142 may further be configured to determine a retransmission timer value based on at least the delay time and the CE-level. The retransmission timer component 142 may also be configured to set a retransmission timer based on the retransmission timer value. The retransmission timer component 142 may further be configured to retransmitting the packet according to the retransmission timer.

The wireless communications system 100 also includes an Evolved Packet Core (EPC) 160, and a 5G Core (5GC) 190. The base stations 102 may include macro cells (high power cellular base station) and/or small cells (low power cellular base station) . The macro cells include base stations. The small cells include femtocells, picocells, and microcells.

The base stations 102 configured for 4G LTE (collectively referred to as Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN) ) may interface with the EPC 160 through backhaul links 132 (e.g., S1 interface) . The base stations 102 configured for 5G NR (collectively referred to as Next Generation RAN (NG-RAN) ) may interface with 5GC 190 through backhaul links 184. In addition to other functions, the base stations 102 may perform one or more of the following functions: transfer of user data, radio channel ciphering and deciphering, integrity protection, header compression, mobility control functions (e.g., handover, dual connectivity) , inter-cell interference coordination, connection setup and release, load balancing, distribution for non-access stratum (NAS) messages, NAS node selection, synchronization, radio access network (RAN) sharing, multimedia broadcast multicast service (MBMS) , subscriber and equipment trace, RAN information management (RIM) , paging, positioning, and delivery of warning messages. The base stations 102 may communicate directly or indirectly (e.g., through the EPC 160 or 5GC 190) with each other over backhaul links 134 (e.g., X2 interface) . The backhaul links 134 may be wired or wireless.

The base stations 102 may wirelessly communicate with the UEs 104. Each of the base stations 102 may provide communication coverage for a respective geographic coverage area 110. There may be overlapping geographic coverage areas 110. For example, the small cell 102'may have a coverage area 110'that overlaps the coverage area 110 of one or more macro base stations 102.

A network that includes both small cell and macro cells may be known as a heterogeneous network. A heterogeneous network may also include Home Evolved Node Bs (eNBs) (HeNBs) , which may provide service to a restricted group known as a closed subscriber group (CSG) . The communication links 120 between the base stations 102 and the UEs 104 may include uplink (UL) (also referred to as reverse link) transmissions from a UE 104 to a base station 102 and/or downlink (DL) (also referred to as forward link) transmissions from a base station 102 to a UE 104. The communication links 120 may use multiple-input and multiple-output (MIMO) antenna technology, including spatial multiplexing, beamforming, and/or transmit diversity. The communication links may be through one or more carriers. The base stations 102 /UEs 104 may use spectrum up to Y MHz (e.g., 5, 10, 15, 20, 100, 400, etc. MHz) bandwidth per carrier allocated in a carrier aggregation of up to a total of Yx MHz (x component carriers) used for transmission in each direction. The carriers may or may not be adjacent to each other. Allocation of carriers may be asymmetric with respect to DL and UL (e.g., more or less carriers may be allocated for DL than for UL) . The component carriers may include a primary component carrier and one or more secondary component carriers. A primary component carrier may be referred to as a primary cell (PCell) and a secondary component carrier may be referred to as a secondary cell (SCell) .

Certain UEs 104 may communicate with each other using device-to-device (D2D) communication link 158. The D2D communication link 158 may use the DL/UL WWAN spectrum. The D2D communication link 158 may use one or more sidelink channels, such as a physical sidelink broadcast channel (PSBCH) , a physical sidelink discovery channel (PSDCH) , a physical sidelink shared channel (PSSCH) , and a physical sidelink control channel (PSCCH) . D2D communication may be through a variety of wireless D2D communications systems, such as for example, FlashLinQ, WiMedia, Bluetooth, ZigBee, Wi-Fi based on the IEEE 802.11 standard, LTE, or NR.

The wireless communications system 100 may further include a Wi-Fi access point (AP) 150 in communication with Wi-Fi stations (STAs) 152 via communication links 154 in a 5 GHz unlicensed frequency spectrum. When communicating in an unlicensed frequency spectrum, the STAs 152 /AP 150 may perform a clear channel assessment (CCA) prior to communicating in order to determine whether the channel is available.

The small cell 102'may operate in a licensed and/or an unlicensed frequency spectrum. When operating in an unlicensed frequency spectrum, the small cell 102'may employ NR and use the same 5 GHz unlicensed frequency spectrum as used by the Wi-Fi AP 150. The small cell 102', employing NR in an unlicensed frequency spectrum, may boost coverage to and/or increase capacity of the wireless communications system 100.

A base station 102, whether a small cell 102'or a large cell (e.g., macro base station) , may include an evolved Node B (eNB) , next generation Node B (gNodeB or gNB) , or other type of base station. Some base stations, such as gNB 180 may operate in a traditional sub 6 GHz spectrum, in millimeter wave (mmW) frequencies, and/or near mmW frequencies in communication with the UE 104. When the gNB 180 operates in mmW or near mmW frequencies, the gNB 180 may be referred to as an mmW base station. Extremely high frequency (EHF) is part of the RF in the electromagnetic spectrum. EHF has a range of 30 GHz to 300 GHz and a wavelength between 1 millimeter and 10 millimeters. Radio waves in the band may be referred to as a millimeter wave (mmWave) . Near mmW may extend down to a frequency of 3 GHz with a wavelength of 100 millimeters. The super high frequency (SHF) band extends between 3 GHz and 30 GHz, also referred to as centimeter wave. Communications using the mmW /near mmW radio frequency band has extremely high path loss and a short range. The mmW base station 180 may utilize beamforming 182 with the UE 104 to compensate for the extremely high path loss and short range.

The EPC 160 may include a Mobility Management Entity (MME) 162, other MMEs 164, a Serving Gateway 166, a Multimedia Broadcast Multicast Service (MBMS) Gateway 168, a Broadcast Multicast Service Center (BM-SC) 170, and a Packet Data Network (PDN) Gateway 172. The MME 162 may be in communication with a Home Subscriber Server (HSS) 174. The MME 162 is the control node that processes the signaling between the UEs 104 and the EPC 160. Generally, the MME 162 provides bearer and connection management. All user Internet protocol (IP) packets are transferred through the Serving Gateway 166, which itself is connected to the PDN Gateway 172. The PDN Gateway 172 provides UE IP address allocation as well as other functions. The PDN Gateway 172 and the BM-SC 170 are connected to the IP Services 176. The IP Services 176 may include the Internet, an intranet, an IP Multimedia Subsystem (IMS) , a PS Streaming Service, and/or other IP services. The BM-SC 170 may provide functions for MBMS user service provisioning and delivery. The BM-SC 170 may serve as an entry point for content provider MBMS transmission, may be used to authorize and initiate MBMS Bearer Services within a public land mobile network (PLMN) , and may be used to schedule MBMS transmissions. The MBMS Gateway 168 may be used to distribute MBMS traffic to the base stations 102 belonging to a Multicast Broadcast Single Frequency Network (MBSFN) area broadcasting a particular service, and may be responsible for session management (start/stop) and for collecting MBMS related charging information.

The 5GC 190 may include a Access and Mobility Management Function (AMF) 192, other AMFs 193, a Session Management Function (SMF) 194, and a User Plane Function (UPF) 195. The AMF 192 may be in communication with a Unified Data Management (UDM) 196. The AMF 192 is the control node that processes the signaling between the UEs 104 and the 5GC 190. Generally, the AMF 192 provides QoS flow and session management. All user Internet protocol (IP) packets are transferred through the UPF 195. The UPF 195 provides UE IP address allocation as well as other functions. The UPF 195 is connected to the IP Services 197. The IP Services 197 may include the Internet, an intranet, an IP Multimedia Subsystem (IMS) , a PS Streaming Service, and/or other IP services.

The base station may also be referred to as a gNB, Node B, eNB, an access point, a base transceiver station, a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS) , an extended service set (ESS) , a transmit reception point (TRP) , or some other suitable terminology. The base station 102 provides an access point to the EPC 160 or 5GC 190 for a UE 104.

Examples of UEs 104 include a cellular phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a personal digital assistant (PDA) , a satellite radio, a global positioning system, a multimedia device, a video device, a digital audio player (e.g., MP3 player) , a camera, a game console, a tablet, a smart device, a wearable device, a vehicle, an electric meter, a gas pump, a large or small kitchen appliance, a healthcare device, an implant, a sensor/actuator, a display, or any other similar functioning device. Some of the UEs 104 may be referred to as IoT devices (e.g., parking meter, gas pump, toaster, vehicles, heart monitor, etc. ) . The UE 104 may also be referred to as a station, a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a user agent, a mobile client, a client, or some other suitable terminology.

Referring to FIG. 2, in an example 200 of wireless communication using 5G NR technologies, the UE 104 may perform an initial transmission attempt 210 with the base station 102 followed by a retransmission attempt 230. In this example, the initial transmission attempt 210 may correspond to any transmission attempt prior to a retransmission attempt. For example, the initial transmission attempt 210 may correspond to a second retransmission attempt and the retransmission attempt 230 may correspond to a third retransmission attempt.

During the initial transmission attempt 210, the HLOS 202 of the UE 104 may send a transmission request to the modem 140 of the UE 104, at 212. The transmission request may include, for example, data associated with an application and instructions for transmitting the data. At 214, in response to the transmission request, the modem 140 may transmit a packet corresponding to the data and the instructions to the base station 102. At 216, when the modem 140 transmits the packet, the modem 140 may initiate a timer to calculate a delay time.

At 218, the base station 102 may acknowledge the packet by transmitting an ACK to the UE 104, once the packet is received by the base station 102. In response to receiving the ACK, the modem 140 may stop the timer and determine the delay time of the communication between the UE 104 and the base station 102. In an example, the delay time may be the time required for the modem 140 to transmit a single packet successfully OTA and receive the ACK in response to the single packet. In some examples, the delay time may include the time for the modem 140 to transmit any one or more segments of a packet successfully and receive the ACK from the base station 102 in response to the one or more segments, as described in further detail below.

In some examples, at 220, the base station 102 may optionally transmit CE-level information to the UE 104. In an example, the CE-level information may be one of set value (e.g., 0, 1, or 2) indicating a condition of the RF and/or the network.

At 222, the modem 140 may determine the CE-level. In some examples, the modem 140 determines the CE-level based on the CE-level information received from the base station 102. For example, the modem 140 may read the set value indicated by the CE-level information and determine the condition of the RF/network based on the set value.

At 224, the modem 140 may send feedback to the HLOS 202. In an aspect, the feedback may include information associated to the delay time and the CE-level.

At 226, the HLOS 202 may determine a retransmission timer value for retransmitting the packet. In an aspect, the retransmission timer value is determined as a function of the delay time and the CE-level. In some examples, the retransmission timer value may be determined based on additional parameters. For example, the retransmission timer value may be determined based on one or more of prior context (e.g., history of a retransmission timer) , a maximum timer value based on a maximum time interval between any two retransmissions of the packet, or default timer values (i.e. 1, 2, 4, 8, 16, 32, and 60 seconds) corresponding to a protocol (e.g., DTLS, DNS, CoAP, or TCP) of the retransmission timer.

In some examples, the HLOS 202 may be tasked with maintaining the history of retransmission timers, losses, etc., in order to determine prior context. In an example, the HLOS 202 cause previous delay values successfully used in a handshake corresponding to the protocol of the retransmission timer to be stored in memory. The HLOS 202 may also be tasked with maintaining (i.e., storing in memory) the maximum time interval between any two retransmissions of the packet and the default timer values corresponding to the protocol.

During the retransmission attempt 230, the HLOS 202 may send a retransmission request to the modem 140 based on the determined retransmission timer value, at 232. The retransmission request may include, for example, the data associated with the application and instructions for transmitting the data. At 234, in response to the retransmission request, the modem 140 may retransmit the packet corresponding to the data and the instructions to the base station 102. At 238, the base station 102 may acknowledge the packet by transmitting an ACK to the UE 104.

During the retransmission attempt 230, the modem 140 may initiate a timer to determine a delay time of the retransmitted packet when the packet is retransmitted, and stop the timer when the ACK is received, as previously described. Further, the modem 140 may also determine a CE-level and transmit feedback to the HLOS 202, as previously described. The HLOS 202 may use the feedback to update retransmission timer values using the delay time and CE-level obtained during retransmission.

While prior examples focused on DTLS protocols, as previously discussed, techniques of the present disclosure may be used for other protocols including DNS, CoAP, or TCP. Below are some parameters that may be used in determining retransmission timer values for some of the protocols. These parameters may be used, for example, when determining default timer values.

For DTLS, retransmission may be necessary for handshakes but not dataflow. In an aspect, retransmission timer values may be left up to implementation of the retransmission timer. In some aspects, mishandling of a retransmission timer in DTLS may lead to serious congestion problems (e.g., if many instances of a DTLS time out early and/or retransmit too quickly on a congested link) . DTLS protocol typical use an initial timer value of 1 second and double the value at each retransmission, up to no less than a maximum of 60 seconds. For time sensitive applications, DTLS protocol may use a 1 second timer rather than the 3 second timer in order to improve latency. As DTLS may only uses retransmission for handshake and not during dataflow, the effect on congestion may be minimal. DTLS protocol may retain a current timer value until a transmission without loss occurs, at which time the timer value may be reset to an initial value. In an aspect, after a long period of idleness (e.g., no less than 10 times the current timer value) , implementations of DTLS may reset the timer to the initial value. For example, one situation where a long period of idleness may occur while using the DTLS protocol is when a re-handshake is used after substantial data transfer.

For CoAP, retransmission of confirmable (CON) messages may be required after timeouts. In an example, a UE retransmits the CON message at exponentially increasing intervals, until the UE receives an ACK (or reset message) or runs out of transmission attempts. In some examples, an initial timeout may be set to a random duration based on an ACK timeout (i.e., ACK_TIMEOUT) and a random ACK factor (i.e., ACK_RANDOM_FACTOR) , and the retransmission counter may be set to 0. For example, the initial timeout may be set to a random duration between ACK_TIMEOUT and (ACK_TIMEOUT *ACK_RANDOM_FACTOR) . In some aspects, the combination of the ACK_TIMEOUT, the ACK_RANDOM_FACTOR, and a MAX_RETRANSMIT may influence a timing of retransmissions, which, in turn, may influence how long certain information items should be kept by an implementation. Additionally, the following values for CoAP may be used in calculating retransmission timer values. Default values for CoAP protocol parameters may include, for example, ACK_TIMEOUT being 2 seconds, ACK_Random_Factor being 1.5, MAX_RETRANSMIT being 4, NSTART being 1, DEFAULT_LEISURE being 5 seconds, and PROBING_RATE being 1 byte/second. Default values for derived CoAP protocol parameters may include, for example, MAX-TRANSMIT_SPAN being 45 seconds, MAX_TRANSMIT_WAIT being 93 seconds, MAX_LATENCY being 100 seconds, PROCESSING_DELAY being 2 seconds, MAX_RTT being 202 seconds, EXCHANGE_LIFETIME being 247 seconds, and NON_LIFETIME being 145 seconds.

For DNS, typical standards do not recommend any particular retransmission policy. Based on these standards, the UE is recommended to back-off exponentially, probably to a maximum timeout value, and a retransmission policy is recommended to be based on round trip time estimates of name servers. In some aspects, user datagram protocol (UDP) is used as a transport protocol for DNS. In an aspect, a Berkeley full-service resolver may start with a time-out equal to the greater of 4 seconds and two times the round-trip time estimate of the server. The time-out may be backed off with each cycle, exponentially, to a ceiling value of 45 seconds.

For TCP, a retransmission timer may be determined dynamically using adaptive retransmission. In some examples, if the retransmission timer is set too low, excessive retransmissions may occur. In some examples, if the retransmission timer is set too high, performance may be reduced due to unnecessary delays in re-sending lost segments.

Referring to FIG. 3, in an example 300 of wireless communication between the UE 104 and the base station 102, a delay time 302 is calculated by the modem 140 based on the time from transmitting a packet 304 to receiving an ACK 320. In some examples, the modem 140 separates the packet 304 into segments based on certain restraints including the amount of data being transmitted and/or the bandwidth for transmitting the packet 304. For example, the modem 140 may separate the packet 304 into segment_1 310 through segment_N 312, where N may be any integer.

As shown by FIG. 3, the segments may be transmitted by the modem 140 at different times due to the restraints. In aspect, a segment that is the last segment of the packet 304 may include an indication for the base station 102 to determine that the segment is the last segment. In response to receiving the indication, the base station 102 transmits the ACK 320 to acknowledge that the packet 304 has been received by the base station 102. The modem 140 may calculate the delay time 302 based on the time from transmitting any one or more of the segments of the packet 304 to receiving the ACK 320 from the base station 102.

As shown by FIG. 3, the delay time 302 may calculated based on the time from transmitting the segment_1 310 to receiving the ACK 320. However, in some examples, the delay time 302 may be calculated based on the amount of time from transmitting any segment (e.g., segment_N 312) to receiving ACK 320.

Referring to FIG. 4, an example of a method 400 of wireless communications may be performed by the UE 104 or the base station 102 to determine a retransmission timer value. Aspects of the method 400 may be performed by the UE 104 or base station 102 of FIG. 1 and/or by one or more components of the UE 104 of FIG. 5 or the base station 102 of FIG. 6. For example, one or more components, including but not limited to processors 512, the modem 140, a transceiver 502, a memory 516, a radio frequency (RF) front end 588, and/or the retransmission timer component 142, of the UE 104 may perform the method 400. In some examples, the retransmission timer component 142 may include one or more subcomponents that are configured to perform specific functions, actions, or processes associated with the method 400. In another example, one or more components, including but not limited to processors 612, the modem 142, a transceiver 602, and/or a memory 616, an RF front end 688, of the base station 102 may perform the method 400.

At block 402, the method 400 may include calculating a delay time of a packet that was transmitted to a second device. For example, one or more components of the modem 140 of the UE 104 may calculate a delay time 302 of a packet 304 that was transmitted to the base station 102. In an example, the delay time 302 may be based on a time from a transmission of the packet 304 to a reception of an ACK 320, corresponding to the packet, received from the base station 102. In some examples, the delay time 302 is further based on a time from a transmission of one or more segments (e.g., segment_1 310, segment_N 312) of the packet 304.

At block 404, the method 400 may also include determining a CE-level indicating a communication condition between the first device and the second device. As an example, one or more components of the UE 104 may determine a CE-level indicating a communication condition between the UE 104 and the base station 102. In some examples, the modem 140 may determine the CE-level. The CE-level may be determined based on CE-level information received from the base station 102. For example, the modem 140 may read a set value (e.g., 0, 1, or 2) indicated by the CE-level information and determine the condition of the RF/network based on the set value.

At block 406, the method 400 may further include determining a retransmission timer value based on at least the delay time and the CE-level. For example, one or more components of the UE 104 may determine a retransmission timer value based on at least the delay time and the CE-level. For example, the HLOS 202 may determine the retransmission timer value as a function of the delay time and the CE-level received from the modem 140.

In some examples, the retransmission timer value may be determined based on one or more additional parameters. For example, the retransmission timer value may be determined based on one or more of prior context (e.g., history of a retransmission timer) , a maximum timer value based on a maximum time interval between any two retransmissions of the packet, or default timer values (i.e. 1, 2, 4, 8, 16, 32, and 60 seconds) corresponding to a protocol (e.g., DTLS, DNS, CoAP, or TCP) of the retransmission timer.

In some aspects, the prior context may be used when a CE-level or delay time value is not available. For example, if the CE-level or the delay time value is not available, the prior context may be determined prior to an initial retransmission and used during the initial retransmission. In some aspects, the maximum timer value may be defined based on a protocol, and when a retransmission timer value is greater than the maximum timer value, the HLOS may abort a connection instead of retransmitting. In an example, the maximum timer value is an upper boundary of an adaptive retransmission value. In some examples, the maximum timer value may be determined based on an implementation choice (e.g., 3 retransmissions, each 60 seconds apart, means a maximum timer value of 180 seconds) . In some aspects, the default timer values may be used based on requirements of a protocol of the HLOS.

At block 408, the method 400 may include setting a retransmission timer based on the retransmission timer value. For example, one or more components of the UE 104 may set a retransmission timer based on the retransmission timer value. In some examples, the HLOS 202 may set the retransmission timer.

At block 410, the method 400 may also include retransmitting the packet according to the retransmission timer. For example, one or more components of the UE 104 may retransmitting the packet according to the retransmission timer. In an example, the modem 140 may retransmit the packet.

In some aspects, the method 400 may also include maintaining a history of the retransmission timer including a history of successful packet transmissions and a history of packet losses, and determining the retransmission timer value further based on the history of the retransmission timer.

In some aspects, the method 400 may further include determining a maximum timer value based on a maximum time interval between any two retransmissions of the packet, and determining the retransmission timer value further based on the maximum timer value. For example, one or more components (e.g., one or more lower protocol layers of the modem 140) of the UE 104 may store retransmission timing information and, based on the retransmission timing information, determine a maximum timer value based on a maximum time interval between any two retransmissions of the packet.

In some aspects, the method 400 may also include determining default timer values corresponding to a protocol of the retransmission timer, and determining the retransmission timer value further based on the default timer values.

Referring to FIG. 5, example hardware components and subcomponents of a wireless communications device (e.g., UE 104) for implementing the techniques for adaptively calculating retransmission timer values is provided by this disclosure. For example, one implementation of the wireless communications device may include a variety of components, including components such as the processors 512, the memory 516, the transceiver 502, and the modem 140 in communication via one or more buses 544, which may operate in conjunction with the retransmission timer component 142 to enable one or more of the functions described herein as well as one or more methods (e.g., method 400) of the present disclosure. For example, the one or more processors 512, the memory 516, the transceiver 502, and/or the modem 140 may be communicatively coupled via the one or more buses 544. Further, the one or more processors 512, the modem 140, the memory 516, the transceiver 502, as well the RF front end 588, may be configured to support resource configuring operations.

In an aspect, the one or more processors 516 may include the modem 140 that may use one or more modem processors. The various functions related to the retransmission timer component 142 may be included in the modem 140 and/or the one or more processors 512 and, in an aspect, can be executed by a single processor, while in other aspects, different ones of the functions may be executed by a combination of two or more different processors. For example, in an aspect, the one or more processors 512 may include any one or any combination of a modem processor, or a baseband processor, or a digital signal processor, or a transmit processor, or a receiver processor, or a transceiver processor associated with the transceiver 502. In other aspects, some of the features of the one or more processors 512 and/or the modem 140 associated with the retransmission timer component 142 may be performed by the transceiver 502.

Also, the memory 516 may be configured to store data used herein and/or local versions of applications or the retransmission timer component 142 and/or one or more of its subcomponents being executed by at least one processor 512. The memory 516 can include any type of computer-readable medium usable by a computer or at least one processor 512, such as random access memory (RAM) , read only memory (ROM) , tapes, magnetic discs, optical discs, volatile memory, non-volatile memory, and any combination thereof. In an aspect, for example, the memory 516 may be a non-transitory computer-readable storage medium that stores one or more computer-executable codes defining the resource configuration component 155 and/or one or more of its subcomponents, and/or data associated therewith, when the wireless communications device is operating at least the processors 512 to execute the retransmission timer component 142 and/or one or more of its subcomponents. The transceiver 502 may include at least one receiver 506 and at least one transmitter 508. The receiver 506 may include hardware, firmware, and/or software code executable by a processor for receiving data, the code comprising instructions and being stored in a memory (e.g., computer-readable medium) . The receiver 506 may be, for example, an RF receiver. In an aspect, the receiver 506 may receive signals transmitted by at least one wireless communications device (e.g., base station 102) . Additionally, the receiver 506 may process such received signals, and also may obtain measurements of the signals, such as, but not limited to, Ec/Io, SNR, RSRP, RSSI, etc. The transmitter 508 may include hardware, firmware, and/or software code executable by a processor for transmitting data, the code comprising instructions and being stored in a memory (e.g., computer-readable medium) . A suitable example of the transmitter 508 may include, but is not limited to, an RF transmitter.

Moreover, in an aspect, the wireless communications device may include the RF front end 588 mentioned above, which may operate in communication with the one or more antennas 565 and the transceiver 502 for receiving and transmitting radio transmissions. The RF front end 588 may be connected to the one or more antennas 565 and can include one or more low-noise amplifiers (LNAs) 590, one or more switches 592, one or more power amplifiers (PAs) 598, and one or more filters 596 for transmitting and receiving RF signals.

In an aspect, the LNA 590 can amplify a received signal at a desired output level. In an aspect, each LNA 590 may have a specified minimum and maximum gain values. In an aspect, the RF front end 588 may use the one or more switches 592 to select a particular LNA 590 and its specified gain value based on a desired gain value for a particular application.

Further, for example, the one or more PA (s) 598 may be used by the RF front end 588 to amplify a signal for an RF output at a desired output power level. In an aspect, each PA 598 may have specified minimum and maximum gain values. In an aspect, the RF front end 588 may use the one or more switches 592 to select a particular PA 598 and its specified gain value based on a desired gain value for a particular application.

Also, for example, the one or more filters 596 may be used by the RF front end 588 to filter a received signal to obtain an input RF signal. Similarly, in an aspect, for example, a respective filter 596 can be used to filter an output from a respective PA 598 to produce an output signal for transmission. In an aspect, each filter 596 can be connected to a specific LNA 590 and/or PA 598. In an aspect, the RF front end 588 can use one or more switches 592 to select a transmit or receive path using a specified filter 596, LNA 590, and/or PA 598, based on a configuration as specified by the transceiver 502 and/or the one or more processors 512.

As such, the transceiver 502 may be configured to transmit and receive wireless signals through the one or more antennas 565 via the RF front end 588. In an aspect, the transceiver 502 may be tuned to operate at specified frequencies. In an aspect, for example, the modem 140 can configure the transceiver 502 to operate at a specified frequency and power level based on the configuration of the wireless communications device or UE 104 and the communication protocol used by the modem 140.

In an aspect, the modem 140 can be a multiband-multimode modem, which can process digital data and communicate with the transceiver 502 such that the digital data is sent and received using the transceiver 502. In an aspect, the modem 140 can be multiband and be configured to support multiple frequency bands for a specific communications protocol. In an aspect, the modem 140 can be multimode and be configured to support multiple operating networks and communications protocols. In an aspect, the modem 140 can control one or more components of the wireless communications device (e.g., the RF front end 588, the transceiver 502) to enable transmission and/or reception of signals based on a specified modem configuration. In an aspect, the modem configuration may be based on the mode of the modem and the frequency band in use. In another aspect, the modem configuration may be based on UE configuration information associated with the wireless communications device.

FIG. 6 describes hardware components and subcomponents of the base station 102 for implementing the techniques for adaptively calculating retransmission timer values is provided by this disclosure. The base station 102 may include the processors 612, the memory 616, the modem 144, and the transceiver 602, which may communicate between them using a bus 644. For example, the one or more processors 612, the memory 616, the transceiver 602, and/or the modem 144 may be communicatively coupled via the one or more buses 644. The transceiver 602 may include a receiver 606 and a transmitter 608. Moreover, the base station 102 may include the RF front end 688 and one or more antennas 665, where the RF front end 688 may include LNA (s) 690, switches 692, filters 696, and PA (s) 698. Each of these components or subcomponents of the base station 102 may operate in a similar manner as the corresponding components described above in connection with the UE 104 of FIG. 5.

The one or more processors 612, the memory 616, the transceiver 602, and the modem 144 may operate to enable one or more of the functions described herein in connection with techniques for adaptively calculating retransmission timer values.

The above detailed description set forth above in connection with the appended drawings describes examples and does not represent the only examples that may be implemented or that are within the scope of the claims. The term “example, ” when used in this description, means “serving as an example, instance, or illustration, ” and not “preferred” or “advantageous over other examples. ” The detailed description includes specific details for the purpose of providing an understanding of the described techniques. These techniques, however, may be practiced without these specific details. In some instances, well-known structures and apparatuses are shown in block diagram form in order to avoid obscuring the concepts of the described examples.

Information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, computer-executable code or instructions stored on a computer-readable medium, or any combination thereof.

The various illustrative blocks and components described in connection with the disclosure herein may be implemented or performed with a specially-programmed device, such as but not limited to a processor, a digital signal processor (DSP) , an ASIC, a FPGA or other programmable logic device, a discrete gate or transistor logic, a discrete hardware component, or any combination thereof designed to perform the functions described herein. A specially-programmed processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A specially-programmed processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The functions described herein may be implemented in hardware, software executed by a processor, firmware, or any combination thereof. If implemented in software executed by a processor, the functions may be stored on or transmitted over as one or more instructions or code on a non-transitory computer-readable medium. Other examples and implementations are within the scope and spirit of the disclosure and appended claims. For example, due to the nature of software, functions described above can be implemented using software executed by a specially programmed processor, hardware, firmware, hardwiring, or combinations of any of these. Features implementing functions may also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations. Also, as used herein, including in the claims, “or” as used in a list of items prefaced by “at least one of” indicates a disjunctive list such that, for example, a list of “at least one of A, B, or C” means A or B or C or AB or AC or BC or ABC (i.e., A and B and C) .

Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage medium may be any available medium that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code means in the form of instructions or data structures and that can be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL) , or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disc, as used herein, include compact disc (CD) , laser disc, optical disc, digital versatile disc (DVD) , floppy disk and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above are also included within the scope of computer-readable media.

The previous description of the disclosure is provided to enable a person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the common principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. Furthermore, although elements of the described aspects may be described or claimed in the singular, the plural is contemplated unless limitation to the singular is explicitly stated. Additionally, all or a portion of any aspect may be utilized with all or a portion of any other aspect, unless stated otherwise. Thus, the disclosure is not to be limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. §112 (f) , unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for. ”

Claims

A method of wireless communication by a first device, comprising:

calculating a delay time of a packet that was transmitted to a second device;

determining a coverage enhancement level (CE-level) indicating a communication condition between the first device and the second device;

determining a retransmission timer value based on at least the delay time and the CE-level;

setting a retransmission timer based on the retransmission timer value; and

retransmitting the packet according to the retransmission timer.
The method of claim 1, wherein the calculating of the delay time is based on a time from a transmission of the packet to a reception of an acknowledge (ACK) , corresponding to the packet, received from the second device.
The method of claim 2, wherein the calculating of the delay time is further based on a time from a transmission of one or more segments of the packet to the reception of the ACK.
The method of claim 1, further comprising:

maintaining a history of the retransmission timer including a history of successful packet transmissions and a history of packet losses; and

determining the retransmission timer value further based on the history of the retransmission timer.
The method of claim 1, further comprising:

determining a maximum timer value based on a maximum time interval between any two retransmissions of the packet; and

determining the retransmission timer value further based on the maximum timer value.
The method of claim 1, further comprising:

determining default timer values corresponding to a protocol of the retransmission timer; and

determining the retransmission timer value further based on the default timer values.
The method of claim 1, wherein the calculating of the delay time and the determining of the CE-level are performed by a first protocol layer of the first device and the determining of the retransmission timer value is performed by a second protocol layer of the first device, wherein the second protocol layer is higher in a protocol stack than the first protocol layer.
The method of claim 1, wherein a protocol of the retransmission timer includes one of a datagram transport layer security (DTLS) protocol, a domain name server (DNS) protocol, a constrained application protocol (CoAP) , or a transmission control protocol (TCP) .
The method of claim 1, wherein the CE-level is received from the second device.
The method of claim 1, wherein the first device is a user equipment (UE) and the second device is a network device or the first device is network device and the second device is the UE.
A device for wireless communication, comprising:

a memory; and

a processor coupled with the memory and configured to:

calculate a delay time of a packet that was transmitted to a second device;

determine a coverage enhancement level (CE-level) indicating a communication condition between the device and the second device;

determine a retransmission timer value based at least on the delay time and the CE-level;

set a retransmission timer based on the retransmission timer value; and

retransmit the packet according to the retransmission timer.
The device of claim 11, wherein the processor is further configured to:

calculate the delay time based on a time from a transmission of the packet to a reception of an acknowledge (ACK) , corresponding to the packet, received from the network.
The device of claim 12, wherein the delay time is further based on a time from a transmission of one or more segments of the packet to the reception of the ACK.
The device of claim 11, wherein the processor is further configured to:

maintain a history of the retransmission timer including a history of successful packet transmissions and a history of packet losses; and

determine the retransmission timer value further based on the history of the retransmission timer.
The device of claim 11, wherein the processor is further configured to:

determine a maximum timer value based on a maximum time interval between any two retransmissions of the packet; and

determine the retransmission timer value further based on the maximum timer value.
The device of claim 11, wherein the processor is further configured to:

determine default timer values corresponding to a protocol of the retransmission timer; and

determine the retransmission timer value further based on the default timer values.
The device of claim 11, wherein the processor includes a modem processor configured to calculate the delay time and determine the CE-level, and an application processor configured to determine the retransmission timer value.
The device of claim 11, wherein a protocol of the retransmission timer includes one of a datagram transport layer security (DTLS) protocol, a domain name server (DNS) protocol, a constrained application protocol (CoAP) , or a transmission control protocol (TCP) .
The device of claim 11, wherein the CE-level is received from the second device.
The device of claim 11, wherein the device is a user equipment (UE) and the second device is a network device, or the device is the network device and the second device is the UE.
An apparatus for wireless communication, comprising:

means for calculating a delay time of a packet that was transmitted to a device;

means for determining a coverage enhancement level (CE-level) indicating a communication condition between the apparatus and the device;

means for determining a retransmission timer value based on at least the delay time and the CE-level;

means for setting a retransmission timer based on the retransmission timer value; and

means for retransmitting the packet according to the retransmission timer.
The apparatus of claim 21, wherein the means for calculating the delay time calculates the delay time based on a time from a transmission of the packet to a reception of an acknowledge (ACK) , corresponding to the packet, received from the device.
The apparatus of claim 22, wherein the means for calculating the delay time calculates the delay time further based on a time from a transmission of one or more segments of the packet to the reception of the ACK.
The apparatus of claim 21, further comprising:

means for maintaining a history of the retransmission timer including a history of successful packet transmissions and a history of packet losses;

wherein the means for determining the retransmission timer value determines the retransmission timer value further based on the history of the retransmission timer.
The apparatus of claim 21, further comprising:

means for determining a maximum timer value based on a maximum time interval between any two retransmissions of the packet;

wherein the means for determining the retransmission timer value determines the retransmission timer value further based on the maximum timer value.
The apparatus of claim 21, further comprising:

means for determining default timer values corresponding to a protocol of the retransmission timer;

wherein the means for determining the retransmission timer value determines further based on the default timer values.
The apparatus of claim 21, wherein the apparatus is a user equipment (UE) and the device is a network device, or the apparatus is the network device and the device is the UE.
A computer-readable medium storing computer code executable by a processor of a first device for wireless communications, comprising:

code to calculate a delay time of a packet that was transmitted to a second device;

code to determine a coverage enhancement level (CE-level) indicating a communication condition between the first device and the second device;

code to determine a retransmission timer value based on at least the delay time and the CE-level;

code to set a retransmission timer based on the retransmission timer value; and

code to retransmit the packet according to the retransmission timer.
The computer-readable medium of claim 28, further comprising code to calculate the delay time based on a time from a transmission of the packet to a reception of an acknowledge (ACK) , corresponding to the packet, received from the second device.
The computer-readable medium of claim 29, further comprising code to calculate the delay time further based on a time from a transmission of one or more segments of the packet to the reception of the ACK.
The computer-readable medium of claim 28, further comprising:

code to maintain a history of the retransmission timer including a history of successful packet transmissions and a history of packet losses; and

code to determine the retransmission timer value further based on the history of the retransmission timer.
The computer-readable medium of claim 28, further comprising:

code to determine a maximum timer value based on a maximum time interval between any two retransmissions of the packet; and

code to determine the retransmission timer value further based on the maximum timer value.
The computer-readable medium of claim 28, further comprising:

code to determine default timer values corresponding to a protocol of the retransmission timer; and

code to determine the retransmission timer value further based on the default timer values.
The computer-readable medium of claim 28, wherein the first device is a user equipment (UE) and the second device is a network device, or the first device is the network device and the second device is the UE.