WO2018028604A1

WO2018028604A1 - Methods and apparatus for ul data transmission

Info

Publication number: WO2018028604A1
Application number: PCT/CN2017/096639
Authority: WO
Inventors: Feifei SUN
Original assignee: MediaTek Singapore Pte Ltd
Current assignee: MediaTek Singapore Pte Ltd
Priority date: 2016-08-12
Filing date: 2017-08-09
Publication date: 2018-02-15
Anticipated expiration: 2019-02-12
Also published as: TW201806422A; CN108605364A; WO2018027917A1

Abstract

Methods and apparatus are provided for contention-based UL resource reservation and power control for UL non-orthogonal multiple access. In one novel aspect, the UE selects a resource block from a resource pool, sends an uplink message based on the selected resource block requesting a resource reservation with or without a reservation resource request (RRR), and receives a response signal indicating the success of resource reservation. In one embodiment, the resource pool is related to one or more identifications comprising a cell ID, a UE ID, a subframe number, and a frame number, and wherein the UE derives the resource pool based on the one or more identifications. In another novel aspect, the UE selects a power offset from a configured power offset pool and calculates a transmit power based on the path loss, a target power and the selected power offset.

Description

METHODS AND APPARATUS FOR UL DATA TRANSMISSION

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §111 (a) and is based on and hereby claims priority under 35 U.S.C. §120 and §365 (c) from PCT application PCT/CN2016/094911, entitled “UL DATA TRANSMISSION” filed on Aug. 12, 2016； the subject matter of which is incorporated herein by reference.

FIELD OF INVENTION

The disclosed embodiments relate generally to wireless communication, and, more particularly, to indication and implementation of uplink data transmission.

BACKGROUND OF THE INVENTION

Machine-Type Communication (MTC) is an important revenue stream for operators and has a huge potential from the operator perspective. Lowering the cost of MTC user equipment (UE) or devices is an important enabler for the implementation of the concept of "internet of things" (IOT) . Many MTC devices are targeting low-end (low average revenue per user, low data rate) applications that can be handled adequately by GSM/GPRS. Owing to the low-cost of these devices and good coverage of GSM/GPRS, there is very little motivation for MTC UE suppliers to use modules supporting the LTE radio interface. In order to ensure that there is a clear business benefit to MTC UE vendors and operators for migrating low-end MTC devices from GSM/GPRS to LTE networks, a new type of terminal, i.e. low cost (LC) MTC UE, is introduced in Rel-11. The design of the LC-MTC UEs is tailored for the low-end of the MTC market to be competitive with that of GSM/GPRS terminals. The low cost MTC device /UE is characterized by: 1) One Rx antenna； 2) Downlink and uplink maximum TBS size of 1000 bits； 3) Bandwidth reduction (BR) –resources for each channel transmission are limited to contiguous 6 PRBs (1.4MHz) for cost reduction, and 4) Coverage enhancement –some applications of LC-MTC UEs will require 15-20dB coverage extension and repeated transmission is a common technique to compensate penetration losses.

In LTE Rel. 12, it is shown that the implementation of half-duplex FDD (HD-FDD) MTC with single received antenna is cost-competitive. The bandwidth reduction technique can offer further cost reduction. The UE with bandwidth reduction (BR-UE) can be implemented with lower cost by reducing the buffer size, clock rate for signal processing, and so on. In IoT/MTC traffic, there is a lot of infrequent small UL traffic data, e.g., up to 100～200 bytes uplink traffic periodically reported 1/hour to 1/year.

The current cellular uplink (UL) data transmission requires random access channel (RACH) procedure to establish a radio resource control (RRC) connection. The signaling overhead is quite large with hundreds of bytes information exchanges before the RRC setup. It is not efficient especially for small UL traffic data. Improvements for uplink data transmission are needed.

SUMMARY OF THE INVENTION

Methods and apparatus are provided for contention-based UL resource reservation and power control for UL non-orthogonal multiple access (NOMA) .

In one novel aspect, the UE selects a resource block from a resource pool and sends a contention-based uplink message based on the selected resource block to a base station, wherein the uplink message indicates reserving corresponding uplink resources associated with selected resource block. The UE receives a response signal from the base station in response to the uplink message, wherein a positive response signal indicates a success reservation of the corresponding uplink resources. The UE transmits uplink data on the corresponding uplink resources upon receiving the positive response signal. In one embodiment, uplink message at least includes a reservation resource request (RRR) , and the positive response signal is an authorization signal. In another embodiment, the RRR is selected from a RRR types comprising a content-based RRR (CR) and a resource-based RRR (RR) , and wherein the response signal can be one of the response types: authorization signal (AR) or resource authorization signal (SR) . In another embodiment, the uplink message is transmitted on the selected resource block and includes one or more transport blocks, and wherein the response signal is an ACK or a NACK in response to the uplink message, and wherein the ACK response signal indicates a success reservation of resource blocks for subsequent uplink data and the NACK response signal triggers a UE retransmission or a new UE transmission. In one embodiment, the uplink message further includeds a UE identification (ID) . In another embodiment, the resource pool is preconfigured based on one or more elements received from the wireless network comprising information elements broadcasted in a system information and information elements in a radio resource control (RRC) message. In one embodiment, the resource pool is related to one or more identifications comprising at least one of the following: a cell ID, a UE ID, a subframe number, and a frame number, and wherein the UE derives the resource pool based on the one or more identifications. In another embodiment, the resource pool further comprising multiple sub-pools associates with multiple corresponding levels comprising at least one of the following: a coverage level, a channel status level, and a reference signal received power (RSRP) . In yet another embodiment, the response signal is transmitted by the base station on a resource block that is mapped from a resource block that the uplink message is transmitted based on a predefined mapping rule.

In another novel aspect, the UE measures downlink signals and obtaining a path loss, selects a power offset from a configured power offset pool, calculates a transmit power based on the path loss, a target power and the selected power offset, wherein the target power is configured by a network entity of the wireless network, and transmits an uplink message with the calculated transmit power. In one embodiment, the power offset is randomly selected from a set of preconfigured offset value. The set of preconfigured offset value is configured per uplink resource or is cell-specific. In another embodiment, the power set is generated with a distribution. In yet another embodiment, the power offset is generated based on a predefined rule using one or more identifications comprising a UE ID, a radio network temporary identifier (RNTI) , a UE-specific identification, a cell-specific identification, and a group-specific identification.

Other embodiments and advantages are described in the detailed description below. This summary does not purport to define the invention. The invention is defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, where like numerals indicate like components, illustrate embodiments of the invention.

Figure 1 illustrates an exemplary mobile communication network with UEs supporting contention-based UL resource reservation and improved uplink power control in accordance with embodiments of the current invention.

Figure 2A illustrates an exemplary message flow diagram for a contention-based UL resource reservation in accordance to embodiments of the current invention.

Figure 2B illustrates exemplary diagrams for different combinations of the contention-based UL resource reservation in accordance with embodiments of the current invention.

Figure 3 illustrates an exemplary flow diagram for contention-based resource reservation with UE identification information included in accordance with embodiments of the current invention.

Figure 4 illustrates an exemplary flow diagram for contention-based resource reservation with UE sending UL message on selected resources directly in accordance with embodiments of the current invention.

Figure 5 illustrates exemplary diagrams for resource pool and resource sub-pool for the contention-based UL resource reservation in accordance with embodiments of the current invention.

Figure 6 illustrates exemplary diagrams for resource allocation for RRR, response signal, and UL data transmission in accordance with embodiments of the current invention.

Figure 7 illustrates exemplary diagrams for resource allocation for RRR, response signal, and UL data transmission in contention based mapping and resource reservation in accordance with embodiments of the current invention.

Figure 8 illustrates exemplary diagram for resource mapping using DCI configuration in accordance with embodiments of the current invention.

Figure 9 illustrates exemplary diagram for resource mapping using DCI and UE identification configuration in accordance with embodiments of the current invention.

Figure 10 illustrates exemplary diagram for resource mapping using DL resource assignment in accordance with embodiments of the current invention.

Figure 11 illustrates exemplary diagrams for power control for UL non-orthogonal multiple access (NOMA) in accordance with embodiments of the current invention.

Figure 12 illustrates an exemplary flow chart for the contention-based UL resource reservation in accordance with embodiment of the current invention.

Figure 13 illustrates an exemplary flow chart for power control for UL non-orthogonal multiple access in accordance with embodiment of the current invention.

Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the embodiments and are not necessarily drawn to scale.

DETAILED DESCRIPTION

Reference will now be made in detail to some embodiments of the invention, examples of which are illustrated in the accompanying drawings.

Certain terms are used throughout the description and following claims to refer to particular components. As one skilled in the art will appreciate, manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following description and in the claims, the terms "include" and "comprise" are used in an open-ended fashion, and thus should be interpreted to mean "include, but not limited to ..." . Also, the term "couple" is intended to mean either an indirect or direct electrical connection. Accordingly, if one device is coupled to another device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. The making and using of the embodiments of the disclosure are discussed in detail below. It should be appreciated, however, that the embodiments can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative, and do not limit the scope of the disclosure. Some variations of the embodiments are described. Throughout the various views and illustrative embodiments, like reference numbers are used to designate like elements.

Figure 1 illustrates an exemplary mobile communication network 100 with UEs supporting contention-based UL resource reservation and improved uplink power control in accordance with embodiments of the current invention. Wireless communication system 100 includes one or more fixed base infrastructure units forming a network distributed over a geographical region. The base unit may also be referred to as an access point, an access terminal, a base station, a Node-B, an eNode-B (eNB) , or by other terminology used in the art. In Figure 1, the one or

more base stations

101 and 102 serve a number of remote units /user equipment (UEs) 103 and 104 within a serving area, for example, a cell, or within a cell sector. In some systems, one or more base stations are communicably coupled to a controller forming an access network that is communicably coupled to one or more core networks. The disclosure, however, is not intended to be limited to any particular wireless communication system.

Generally, the

eNB

101 and 102 respectively transmit downlink communication signals 112, 113 to UE 103, and 104 in the time and/or frequency and/or code domain. UE 103 and 104 communicate with one or more eNB 101 and 102 via uplink communication signals 111, and 114 respectively. The one or more eNB 101 and 102 may comprise one or more transmitters and one or more receivers that serve the UEs 103 and 104. UE 103 and 104 may be fixed or mobile user terminals. The UE may also be referred to as subscriber units, mobile stations, users, terminals, subscriber stations, user terminals, or by other terminology used in the art. UE 103 and 104 may also comprise one or more transmitters and one or more receivers. UEs 103 and 104 may have half-duplex (HD) or full-duplex (FD) transceivers. Half-duplex transceivers do not transmit and receive simultaneously whereas full-duplex terminals transmit and receive simultaneously. In one embodiment, one eNB 101 can serve different kind of UEs. UE 103 and 104 may belong to different categories, such as having different RF bandwidth or different subcarrier spacing. UE belonging to different categories may be designed for different use cases or scenarios. For example, some use case such as MTC may require very low throughput, delay torrent, the traffic packet size may be very small (e.g., 1000 bit per message) , extension coverage. Some other use cases, e.g. intelligent transportation system, may be very strict with latency, e.g. orders of 1ms of end-to-end latency. Different UE categories may be introduced for these diverse requirements. Different frame structures or system parameters may also be used in order to achieve some special requirement. For example, different UEs may have different RF bandwidths, subcarrier spacing, omitting some system functionalities (e.g., random access, CSI feedback) , or use physical channels/signals for the same functionality (e.g., different reference signals) .

Figure 1 also shows an exemplary diagram of

protocol stacks

121 and 122 for control-plane for MTC UE 103 and eNB 101. UE 103 has a protocol stack 121, which includes the physical (PHY) layer, the medium access control (MAC) layer, the radio link control (RLC) layer, the pack data convergence protocol (PDCP) layer, and the radio resource control (RRC) layer. Similarly, eNB 101 has a protocol stack 122. Protocol stack 122 connects with protocol stack 121. The UE-eNB protocol stack 122 includes the PHY layer, the MAC layer, the RLC layer the PDCP layer and the RRC layer, each of which connects with their corresponding protocol stack of UE protocol stack 121.

Figure 1 further illustrates simplified block diagrams 130 and 150 of UE 103 and eNB 101, respectively. UE 103 has an antenna 135, which transmits and receives radio signals. A RF transceiver module 133, coupled with the antenna, receives RF signals from antenna 135, converts them to baseband signals and sends them to processor 132. RF transceiver 133 also converts received baseband signals from processor 132, converts them to RF signals, and sends out to antenna 135. Processor 132 processes the received baseband signals and invokes different functional modules to perform features in UE 103. Memory 131 stores program instructions and data 134 to control the operations of UE 103.

As shown, UE 103 is configured with processor 132 that performs instruction stored in memory 131. the processor 132 is configured to carry out different functional tasks as shown. UE 103 also includes multiple function modules that carry out different tasks in accordance with embodiments of the current invention. A selector 141 selects a resource block from a resource pool in the wireless network. An uplink resource manager 142 sends an uplink message based on the selected resource block to a base station, wherein the uplink message indicates an uplink reservation for corresponding uplink resources associated with selected resource block. A reservation manager 143 receives a response signal from the base station in response to the uplink message, wherein a positive response signal indicates a success reservation of the corresponding uplink resources. A contention-based transmitter 144 transmits uplink data on the corresponding uplink resources upon receiving the positive response signal. A power-offset manager 145 handles new UL power control procedures for the UE by applying a power-offset value. In another embodiment, multiple circuits are configured to carry out one or more of the tasks. A resource managing circuit, which selects a resource block from a resource pool in the wireless network. An uplink message based on the selected resource block to a base station, wherein the uplink message indicates an uplink reservation for corresponding uplink resources associated with selected resource block. The resource managing circuit receives a response signal from the base station in response to the uplink message, wherein a positive response signal indicates a success reservation of the corresponding uplink resources. A power-offset managing circuit handles new UL power control procedures for the UE by applying a power-offset value.

Also shown in Figure 1 is exemplary block diagram 150 for eNB 101. eNB 101 has an antenna 155, which transmits and receives radio signals. A RF transceiver module 153, coupled with the antenna, receives RF signals from antenna 155, converts them to baseband signals, and sends them to processor 152. RF transceiver 153 also converts received baseband signals from processor 152, converts them to RF signals, and sends out to antenna 155. Processor 152 processes the received baseband signals and invokes different functional modules to perform features in eNB 101. Memory 151 stores program instructions and data 154 to control the operations of eNB 101. eNB 101 also includes function modules that carry out different tasks in accordance with embodiments of the current invention. A uplink resource manager 156 handles the contention-based UL resource reservations. A power control manager 157 handles the new UL power control procedures by applying a power offset value.

UPLINK DATA TRANSMISSION WITH CONTETNION-BASED RESOURCE RESERVATION

In IoT/MTC traffic, there are many infrequent small-sized UL data traffics. Such IoT/MTC traffic may be 100～200 bytes uplink traffic periodically reported from once an hour to once a year. The current cellular uplink data transmission, which requires RACH, establishing a RRC connection is not efficient. The signaling overhead is quite large with hundreds of bytes information exchanges before the RRC setup. In addition, in order to achieve UL coverage, narrow band (NB) system/signal carrier system provides a very promising coverage without increasing UL transmission (TX) power. Multiple tones/resources are available for UE to perform accessing. Furthermore, with longer CP and GP, timing advance (TA) is not needed before data transmission.

Contention based uplink transmission can significantly reduce signaling overhead. However, there are issues to be solved. For example, for UEs with poor coverage, the UE may need to transmit for a long time to compensate path-loss. It is too costly on power consumption if a long transmission collides with another UE. On the other hand, it is hard to support HARQ combination when the transmission is contention based instead of scheduling based. Methods and apparatus are provided for contention based UL transmission with contention based UL resource reservation.

Uplink control information (UCI) is transmitted in Physical Uplink Control Channel (PUCCH) or transmitted with or without a transport block in PUSCH. UCI includes HARQ, scheduling request (SR) , channel status information (CSI) . PUCCH is allocated the border PRBs in uplink system bandwidth. Frequency diversity gain for PUCCH is obtained by frequency hopping between two slots in one subframe. Code Division Multiplexing (CDM) is used for PUCCH multiplexing between different UEs on the same radio resource.

Figure 2A illustrates an exemplary message flow diagram for a contention-based UL resource reservation in accordance to embodiments of the current invention. A UE 201 is in the connected mode or IDLE mode in a wireless network with an eNB 202. At step 211, UE 201 sends a contention-based UL message with a Resource Reservation Request (RRR) to eNB 202. In one case, the RRR is a contention-based signal based on UE ID, or the RRR is a contention-based signal on a resource selected by the UE. At step 212, eNB 202 sends a response signal. In one embodiment, the response signal is an authorization on a reservation resource related to the RRR from UE, or an authorization signal about the RRR from UE. At step 213, UE 201 sends UL data transmission on the reserved resource for data transmission to eNB 202, or on the corresponding resources of the RRR. If UE successfully decodes an authorization signal, UE 201 transmits UL data the reserved resource for data transmission, or on the corresponding resources of the response in step 212. In one embodiment, a time window is set for UE 201 to decode the authorization signal. In another embodiment, if UE 201 does not decode an authorization signal correctly, such as no indication in resource mapping (RS_MAP) field, UE 201 assumes the reservation failed. UE 201 will select a new reservation resource from the resource pool and sends RRR again. In yet another embodiment if UE 201 does not receive ACK or NACK signal, UE 201 may wait for a random time, or wait for a configured period based on the configuration in SIB from eNB before transmitting the next request.

In one embodiment, UE 201 could perform retransmission after the first UL data transmission. Optional, at step 214, eNB 202 sends feedback with an ACK/NACK signal after UE transmits/retransmits UL data. Subsequently, if UE 201 received NACK, at step 215, UE 201 performs retransmission until an ACK is received from eNB 202. If UE 201 does not received ACK under some conditions, such as retransmission timer expires, or the maximum retransmission number reached, UE 201 turns into IDLE mode if UE 201 is in connected mode originally, otherwise UE 201 stays in IDLE mode if UE is in IDLE mode originally.

In one embodiment, the RRR include a sequence. eNB 202 can detect the RRR with low complexity. UE 201 can send RRR within a short time to avoid sending a large message. In one embodiment, the RRR message is content-based called contention-based-RRR (CR) . The CR may include contents such as UE ID, RNTI, and Random number. In another embodiment, the RRR message is resource based RRR called resource-based-RRR (RR) . The RR may include one or more resource information such as time /frequency resource, spreading code, scrambling code, and codebook. Similarly, the response signals to the RRR can be in different forms. In one embodiment, the response signal is an authorization signal called authorization-response (AR) . The AR indicates an authorization for the use of resource blocks or a success resource reservation of resource blocks. The AR is transmitted on the preconfigured or known resources to the UE and the eNB. The UE blind detected in a resource set, such as the pre-defined resource, or can be determined based the resource, such as the frequency hopping (FH) pattern used in RRR. Some one-to-one mapping can be defined to avoid blind detection in UE to save power consumption. In one embodiment, in some resource mapping (RS_MAP) field of MAC header the one-to-one mapping is defined. In another embodiment, the response signal is a resource of response signal called resource response (SR) . In one embodiment, there is a one-to-one mapping between the resource for RRR and the resource transmitting the SR. In another embodiment, the authorization signal SR may include UE identity (UE ID or RNTI) , which is similar as current message 4 (MSG4) for contention resolution. The following diagrams illustrate different scenarios for the RRR and the response signal. To sum up, the request signal could be a contention based signal, e.g. CR, or a resource, e.g. RR, and the response could be a signal, e.g. AR, or a resource for response signal, e.g. SR.

Figure 2B illustrates exemplary diagrams for different combinations of the contention-based UL resource reservation in accordance with embodiments of the current invention. Since there are two kinds of request signal, and two kinds of response, so, there are four combination of the above request signal and response, i.e., CR+AR, CR+SR (resource based) , RR (resource based) +AR, and RR (resource based) +SR (resource based) . In all diagrams of figure 2B, a UE 201 is in the connected mode or IDLE mode in a wireless network with an eNB 202.

Diagram 220 illustrates the scenario of UE receiving an AR in response to a CR. At step 221, UE 201 sends a UL message with RRR in the form of CR. At step 222, UE 201 receives a response signal in the form of AR. In one embodiment, UE 201 transmits sequence n for RRR. eNB 202 generates a response signal based on sequence n. In another embodiment, UE 201 transmits RRR with one message such as, UE ID, RNTI, and Random number, eNB 202 generates a response signal based on the message.

Diagram 230 illustrates the scenario of UE receiving an AR in response to a RR. At step 231, UE 201 sends a UL message with RRR in the form of RR. At step 232, UE 201 receives a response signal in the form of AR. In one embodiment, the authorization signal is generated by eNB 202 based on the resource of RRR. The resource of RRR (RR) is one or combination of more: time/frequency resource (one subcarrier is a special case) , spreading code, scrambling code, codebook. In one embodiment, UE 201 selects the resource n for RRR. On the resource n, UE 201 transmits RR in step 231. eNB 202 generates a response signal based on the resource n, for example, based on the index, indicator or location of the resource. The resource n could be one or combination of more: time/frequency resource (one subcarrier is a special case) , spreading code, scrambling code, or codebook. In step 232, eNB202 transmits the AR to UE 201.

In diagram 220 and 230, for the above two cases, the response signal AR is transmitted in a pre-known resource (or UE blind detected in a resource set) , e.g., pre-defined resource, or can be determined based the resource (e.g., FH pattern) used in step 231 (one on one mapping to the resource used by UE) . Some one-to-one mapping can be defined to avoid blind detection in UE to save power consumption. For example, the one-on-one mapping is defined in some RS_MAP field in the MAC header.

Diagram 240 illustrates the scenario of UE receiving an SR in response to a CR. At step 241, UE 201 sends a UL message with RRR in the form of CR. At step 242, UE 201 receives a response signal in the form of SR, e.g. resource m. in this case, the response signal is based on RR+SR, UE selects the resource n for RRR transmission, where the resource n is one or multiple of time/frequency resource, spreading code, code book, scrambling code, sequence, subcarrier index, etc. ； eNB transmit a response signal on resource m, where resource m is selected by eNB based on resource n. In another word, UE transmits RRR message on selected resource n； UE detects for response signal on resource m corresponding to resource n for RRR message transmission.

Diagram 250 illustrates the scenario of UE receiving an SR in response to a CR. At step 251, UE 201 sends a UL message with RRR in the form of RR, e.g. resource n. At step 252, UE 201 receives a response signal in the form of SR, e.g. resource m. UE 201 selects the resource n for RRR transmission. The resource n is one or multiple of time/frequency resource, spreading code, codebook, scrambling code, sequence, subcarrier index, etc. eNB 202 transmits a response signal on resource m. Resource m is selected by eNB 202 based on resource n. UE 201 transmits RRR message on selected resource n and detects for response signal on resource m corresponding to resource n for its RRR message transmission.

In diagram 250, the response signal is based on CR+SR, in this case, UE transmits RRR in a contention-based way (e.g., UE ID, RNTI, Random number) ； eNB transmit a response signal on resource m based on the contention in RRR. For example, UE transmits RRR message with C-RNTI and eNB successfully decodes the RRR message, obtains the content C-RNTI, and transmits a response signal on resource m, where resource m is based on the content C-RNTI. In this example, UE detects for the response signal on resource m based on its C-RNTI.

In one novel aspect, more than one UE may send the same or different RRR on the same resource. The eNB may or may not be able to detect it. If eNB detects that different UEs are using the same resource, the eNB would send NACK to the UE. Alternatively, the eNB would send nothing so that UE will re-transmit RRR later. If the eNB does not detect that multiple UEs are using the same resource, the collision may happen during data transmission. Subsequently, contention resolution is needed. In one advantageous aspect, only one-bit grant message is needed for the UL resource reservation, while following the current protocol using message 2 (MSG2) , large information bits, such as UL grant, TA, RNTI, are required.

Figure 3 illustrates an exemplary flow diagram for contention-based resource reservation with UE identification information included in accordance with embodiments of the current invention. A UE 301 is in the connected mode or IDLE mode in a wireless network with an eNB 302. At step 311, UE 301 sends a contention-based UL message with a resource reservation request (RRR) to eNB 302. In one embodiment, the RRR includes at least a UE identification, such as a UE ID. The UE identification can be the UE ID, the RNTI, a random number, the BSR, the CSI, or data volume (DV) . At step 312, eNB 302 sends a response signal. In one embodiment, the response signal includes the UL grant with a UE identification for contention resolution on the resource used for the response signal. At step 313, UE 301 performs UL data transmission on the reservation resource associated with the UL grant. If eNB 302 receives and decodes the UL data, eNB 302 transmits ACK to UE in step 314. eNB 302 transmits NACK to UE in step 314 if eNB does not successfully decode the information from UE 301. UE 301 could perform retransmission until an ACK is received. UE 301 turns in to IDLE mode or PSM mode for power saving. In one embodiment, after receiving NACK, SPS(semi-persistent scheduling) -liked scheme can be used by UE so that multiple TBs can be transmitted.

Similar to the procedure for PRACH, the RRR, or called the scheduling request can be on part of the reserved resource for PRACH. The eNB detects it is different from the normal PRACH and gives a larger UL grant than the ordinary UL grant for PRACH in the response signal. For eNB, it will consider the BSR or DV report in scheduling request for transport block size in UL grant. The eNB further considers the CSI in the scheduling request for MCS in UL grant. Especially in NB-IoT system, the reserved bit in MSG2 can be used for UL grant of MSG3, for UE to choose the reserved part of resource of PRACH to read the reserved resource.

In this embodiment, the “resource reservation request” includes an identity (e.g., UE ID (40bits) , or RNTI (16bits) , or a random ID selected by UE) , where the UE identity is used for eNB 202 to know which UE is sending message. Please refer to table. 1. For example in the second example, in NB-IoT system, Msg 3 is 88 bits, including: resume ID, Est Cause, short MAC-I, DCI (mac) , MAC spare, PHR, MAC overhead, RRC overhead, RRC spare. DVI is the data volume in MSG3 indicates the amount of user data (including SMS) and NAS signalling data volume sent over user plane or control plane. The DVI field is in MAC. And the 88bits of message 3 is the only TB size that is assumed, when specifying support for UL CCCH. In this example, the multi-tone capability bit should be interpreted as an IOT bit (inter operability test) .

Figure 4 illustrates an exemplary flow diagram for contention-based resource reservation with UE sending UL message on selected resources directly in accordance with embodiments of the current invention. A UE 401 is in the connected mode or IDLE mode in a wireless network with an eNB 402. At step 411, UE 401 transmits an UL message to eNB 402. In one embodiment, UE 401 transmits the UL message with the resource reservation without any request. In another embodiment, UE 401 may transmit more than one transport blocks on the reserved resource once or several times in step 411. In one embodiment, UE 401 may send a resource release message in the UL message at step 411. At step 412, eNB 402 sends an ACK /NACK to UE 401. From the eNB side, the reserved resources can be for one or multiple UEs. The UL message at step acts as a reservation request message without embedding the actual request in the UL transmission. Upon receiving this UL message, the eNB, reserves resource for the UE for further transmission. After decoding the UL message on the reserved resource, eNB 402 expects one or more UL transmission on a corresponding UL data transmission resource. No explicit UL grant is required. The UL transmission can be contention free. Furthermore, at step 412, eNB 402 may transmit an ACK or NACK signal to UE to trigger a retransmission or new transmission. At step 413, UE 401 sends UL data to eNB 402 on the reserved resource.

In one embodiment, the UL message can include a sequence. The sequence can further be used by eNB for channel estimation, to detect any requests from UEs. Moreover, the eNB upon detecting the sequence can determine if there are more than one UE requests for this resource. In embodiment, the eNB sends ACK/NACK signal based on the detection. In another embodiment, the eNB may be able to detect the sequence on a UL resource, but fails to decode an UL message. The eNB sends an NACK signal to trigger an retransmission of the UL message. In yet another embodiment, the UL message further includes one or more of the following information: BSR, FH pattern (frequency resource allocation in each subframe) , the start subframe, the end subframe, number of repetition, scrambling sequence, codebook index, and spreading code. The UL message includes UE request to eNB for all the information for following uplink data transmission without waiting for explicit grant from the eNB. In one embodiment, the UL message at step 411 includes all data for the transmission. A success transmission of step 411 UL message ends the process without step 413. The end subframe may be learned by eNB by receiving an “end transmission indicator. ” The end subframe is not necessary if a field indicating how many packets need to be transmitted is signaled by UE in step 411. In one embodiment, the reservation resources could be localized or distributed with FH. The distributed resource is called separated resource. There is no need for contention expected during the UL data transmission from other UE. The relationship between the reservation resource and the resource for response signal are mapped by predefined rules. In one embodiment, there is a binding relationship between the reservation resource and the resource for response signal, such as, a one-to-one mapping.

In one novel aspect, the UE can use a combination of UL message with or without RRR in different steps, such as for transmission and/or retransmission.

Figure 5 illustrates exemplary diagrams for resource pool and resource sub-pool for the contention-based UL resource reservation in accordance with embodiments of the current invention. Figure 5 illustrates a resource block diagram 500, a resource pool 510, and a resource sub-pool 520. Resource block diagram 500 illustrates different frequency hopping patterns are used to form resource blocks. Resource block 511 includes different resources in the frequency-time domain. Similarly, resource blocks 512, 513, 514, and 515 all have resources in the frequency-time domain. In one embodiment, resource blocks 511, 512, 513, 514, and 515 forms resource pool 510. UE can select a resource block from resource pool 510 for its UL message to perform the contention based resource reservation procedure. Resource sub-pool 520 includes a resource sub-pool 521, a resource sub-pool 522, and a resource sub-pool 523. Resource sub-pool 521 includes resource blocks 511 and 513. Resource sub-pool 522 includes resource blocks 512 and 515. Resource sub-pool 523 includes resource blocks 514.

For the reservation resources used in the UL message, the UE selects a resource from a resource pool. In one embodiment, the resource pool is pre-known to the UE. In one embodiment, the configuration of the resource pool is broadcasted in the system information, indicating by SIB information or other RRC message. In one embodiment, the resource pool may be related to a cell ID, a UE ID, a subframe number, or a frame number. The resource pool can be indicated to the UE explicitly or implicitly. The resource can be separated or shared. If separated, the resource can have 1-on-1 mapping.

Resource pool 520 further includes

several sub-pools

521, 522, and 523. The division of resource sub-pools can be based on different coverage class/level, different channel status class/level, or the RSRP. The resource pool may comprise one or more resources including time/frequency resource (one subcarrier is a special case) , spreading code, scrambling code, codebook. In another embodiment, the resource pool may be based on frequency hopping, and different sub-pools are divided based on different FH patterns or different frequency allocation. Based on the different requirements, different UEs could choose different reservation resources from the resource pool. In yet another embodiment, the eNB can configure one or more RSRP threshold for UE to select resource from different sub-pools. Since different UEs select in the same resource pool, the UL message is contention based. In one embodiment, the response signal could be transmitted in the RS_MAP field of MAC header.

In one advantageous aspect, since the relationship between the reservation resource and the resource used for response signal is associated, the overhead for decoding of UE or transmitting for eNB is low. In a first aspect, it is an easy way for eNB to detect this RRR since it may be only a sequence as PRACH. Further, if no RRR is received by eNB, the corresponding resource used for the response signal associated with the RRR can be scheduled by the eNB to other UEs for scheduling based UL transmission. The utilization of UL resource is improved since the resource reserved for RRR is much smaller than the one for contention based UL message with large payload. Furthermore, from the UE perspective, it minimizes the chance of UE wasting for a lot of power sending a message with large payload but failed to be decoded by eNB.

In other embodiments of this invention, different FH patterns are used for different UEs. In order to obtain a trade-off between supported users and the collision probability, the FH patterns are based on Orthogonality /Auto-correlation/Cross-correlation of UEs. In embodiment, the FH pattern could be hard coded. The available hopping pattern indices are broadcasted in the MAC layer (header, MAC CE) or RRC. The UE obtains the FH pattern from broadcasting information and randomly chooses one from the FH pattern pool. In one embodiment, the UE acquires or reacquires the system information before UL data transmission. In another embodiment, the eNB semi-statically configures FH patterns and informs UEs. The eNB determines the FH pattern based on UE’s channel quality. Similar to the generation of LTE preambles, FH pattern is generated according to a sequence. The UE randomly inputs parameters to generate the FH pattern. In yet another embodiment, FH pattern (FH pattern index) is assigned to each UE after the UE is RRC connected with network, so that the eNB can identify a UE through the used hopping pattern.

Figure 6 illustrates exemplary diagrams for resource allocation for RRR, response signal, and UL data transmission in accordance with embodiments of the current invention. At step 621, the UE sends a RRR in the resource 601. At step 622, the UE receives a response signal from the eNB/base station in resource 602. Subsequently, at step 623, the UE transmits the UL messages in

resource block

603, 604…610. And the mapping relationship between resources 601 for RRR, 602 for the response signal and 603, 604 to 610 the UL message are binding together based on one more predefined rules.

Figure 7 illustrates exemplary diagrams for resource allocation for RRR, response signal, and UL data transmission in contention based mapping and resource reservation in accordance with embodiments of the current invention. The UE sends a RRR on

resource

710 or 720. If a response signal is received that is authorization, UE transmit UL message later in latter subframe (s) on corresponding

resource

711 or 721 respectively.

Resources

711 and 721 maps to

resources

710 or 720 correspondingly. In one embodiment, the corresponding resources are the same in different subframes as 711. In another embodiment, the corresponding resources are different (with frequency hopping) in different subframes such as resource block 721.

Figure 8 illustrates exemplary diagram for resource mapping using DCI configuration in accordance with embodiments of the current invention. A resource 800 includes multiple resource blocks configured for the UE for UL transmission, including resource blocks 801, 802, and 803. The reservation resource for UL message is one-to-one mapping to the resource for ACK/NACK. The ACK/NACK for multiple reservation resources are transmitted together. In one embodiment, a special DCI format 810 is used for ACK/NACK of contention based UL message. The bits in DCI are 1-on-1 mapping to the resources of UL message. In one embodiment, the 3 bits are mapped to

resources

801, 802, and 803 respectively. The RNTI for the special DCI is cell-specific. The allocation of reservation resources could further be coverage level/channel condition specific, for example, if the reservation resources used for UL message for different coverage level or channel condition are different. Each reservation resource may have one RNTI. The DL control channel configuration is related to different coverage level. For example, in NB-IoT, the maximum repetition number of NPDCCH (Rmax) is PRACH level specific. The same RNTI can be used but the detection of downlink control channel could be under different configurations.

Figure 9 illustrates exemplary diagram for resource mapping using DCI and UE identification configuration in accordance with embodiments of the current invention. A resource 900 include multiple resource blocks configured for the UE for UL transmission, including resource blocks 901, 902, and 903. A DL message can contain at least one ACK/NACK response to at least one UL message. Within the DL message, several feedbacks can be transmitted. The one-to-one mapping between the reservation resources for UL message and resource for response signal is also suitable in this case. A DCI 910 and UE ID 920 are included in the response. Since more than one bit can be transmitted within the case, the different values could represent different meaning. For example, “0” may represent NACK, or there is UE colliding. In this embodiment, a new MAC CE could be introduced to indicate the meaning of “0. ” eNB can tell the collided UEs to use separate resources if the UL message contains UE ID 920. For ACK or NACK but no collision UE, one bit is enough for UEs to know the decoding status at eNB side. Another field on DL message may contains UE IDs if eNB successfully decoded more than one UE UL message at the same resource. In one embodiment, eNB is able to detect one or more UE transmitted UL message by detecting reference signal (e.g., sounding reference signal, UL demodulation reference, preamble) , which has 1-on-1 mapping to the resource for RRR or UL message. Therefore, eNB is able to send a NACK signal based on the detected signals to the UE (s) who transmitted UL message or RRR on the corresponding UL resource.

Figure 10 illustrates exemplary diagram for resource mapping using DL resource assignment in accordance with embodiments of the current invention. A resource 1000 include multiple resource blocks configured for the UE for UL transmission, including

resource blocks

1001, 1002, and 1003. A DL resource 1010 include multiple resource blocks configured for the UE for UL transmission, including

resource blocks

1011, 1012, and 1013. Multiple ACK/NACK signals are transmitted separated. A link downlink physical channel physical hybrid-arq indicator channel (PHICH) can be introduced as resource for response signal. The PHICH resource is 1-on-1 mapping to reservation resources used for UL message. The UE may transmit multiple TBs, e.g., each TB in on one subframe, and expect ACK/NACK from eNB for each TB. If UE receives ACK, UE may transmit a new data and flush the buffer； if UE receives NACK, UE may retransmit the data in the buffer again without flushing. In this case, no DTX is expected since the resource is reserved by the UE. On the other word, eNB will expect UE to transmit a signal on the reserved resource. UE may report how many TBs, or how large a TB is to transmit to eNB so that eNB and UE share the same understanding on how long the transmission is lasting. For MTC/NB-IoT/mMTC device, UE may only transmitted one TB since one subframe may only carry one bit. UE may report the TB size to eNB in the UL message for the TB size and/or modulation order and code rate. HARQ can also be supported. Although Figures 8, 9, and 10 are described as each bit used for one UE, but the format for ACK/NACK could be different, and used for different purpose.

POWER CONTROL WITH POWER OFFSET

There are different preambles in different reservation resources, if eNB does not find the associated preamble in the associated reservation resource, eNB determines there is no transmission request in the reservation resource, so eNB ignore the information in the reservation resource, or responds NACK. If eNB finds the associated preamble in the associated reservation resource, but it cannot decode the information correctly, it could determine error, so responds NACK to UE, to inform UE that, I Know you have transmitted information in the reservation resource, but I have not decoded information correctly, so please retransmit the UL data, and in meanwhile, eNB stores the information in a buffer, jointly decodes the information in the buffer and the next retransmission the next time. In this case, the NACK signal could be zero, or other value when the NACK signal has multiple bits. Since multiple UEs could choose the same reservation resource, so the transmission is contention based, and if the multiple UEs are non-orthogonal, or time division, or code division, or with different time offset, the eNB could successfully receive and decode the UL data from different UEs in the same reservation resources under some conditions. For the UE receiving NACK which means eNB does not successfully decoding the UL data, UE could retransmit the same UL date after a fixed time, which could be called a synchronous retransmission way, and the UE could hold the UL data, and retransmit the same UL data after the UE receiving indication for retransmission from eNB, which could be called a non-synchronous retransmission way.

Figure 11 illustrates exemplary diagrams for power control for UL non-orthogonal multiple access (NOMA) in accordance with embodiments of the current invention. A wireless network has multiple UEs, include UE 1101 and UE 1102. Resource block 1103 belongs to resource 1100. UE 1101 and UE 1102 both select resource block 1103 for uplink transmission. UE 1101 obtains RSRP and path-loss value and calculates a target power value 1111. Similarly, UE 1102 obtains RSRP and path-loss value and calculates a target power value 1121. The power difference 1131 between 1111 and 1112 is small. In one novel aspect, a power-offset value is generated by the UE and applied to the target power value. UE 1101 generates a power-offset value 1112 and applies it to get its transmitting power value. Similarly, UE 1102 generates a power-offset value 1122 and applies it to get its transmitting power value. The power difference 1132 after applying the power-offset is increased.

UL NOMA is proposed to improve spectral efficiency in the embodiments of this invention, for example, Multi-user shared access (MUSA) , Resource spread multiple access (RSMA) , Sparse code multiple access (SCMA) , Pattern defined multiple access (PDMA) , Non-orthogonal coded multiple access (NOMA) , Low code rate spreading, Frequency domain spreading, Non-orthogonal multiple access (NOMA) . Some of the techniques need interference cancelation, e.g., SIC (Successive Interference Cancellation) , which may be benefit from power difference. For example, the receiver of power domain multiple access (special case of NOMA) decodes UE with higher power first and then cancel the UE with higher power to decode UE with low power. For scheduled based, it is easy for eNB to pair UEs on the same resource. However, for contention-based uplink, open loop power control is expected for the first uplink transmission. In one case, it is proposed to divide into several resources and different resources corresponding to different path loss levels. However, this will increase collision possibility. in the embodiments of this invention, methods are provided to add a random power offset on top of open loop power control, comprising: UE measures DL signals and obtain path loss (e.g., RSRP) ； UE calculate transmit power based on path loss, target power (the target power in configured by eNB, e.g., in SIB) and a power offset (the random power offset is configured by eNB, e.g., in SIB) . The UE transmits UL message (preamble, UL traffic) on selected UL resource with the transmit power.

In one embodiment, the power offset for UE 1101 and UE 1102 is random chosen from a discrete value set, such as, [-3dB, 3dB] , or [-2dB, -1dB, 0dB, 1dB, 2dB] . The value can be configured by eNB. In one embodiment, the values sets are per UL resource configured. In another example, the value sets are cell-specific. In another example, the random power offset is generated with a distribution, such as the uniform distribution within [-2dB, 2dB] . The random power offset can be turn off by eNB. For the path loss needs max Tx power, it could also adopt to a random power offset, but only has minus values or zero with in the offset, such as, [-2dB, -1dB, 0dB] . The random power offset could be only added for the case with power ramping (that is, not max Tx power case) . For the UEs with max Tx power, the received signal power density has very little chance to be the same. The receiver can use the power different caused by path loss. In another embodiment, the power offset is calculated based on a pre-defined rule such as a UE ID, RNTI, or other UE-specific /group-specific configuration. The above method can also be adopted to other non-orthogonal multiple access which could benefit from power different.

Figure 12 illustrates an exemplary flow chart for the contention-based UL resource reservation in accordance with embodiment of the current invention. At step 1201, the UE selects a resource block from a resource pool in a wireless communication network. At step 1202, the UE sends an uplink message based on the selected resource block by the UE to a base station, wherein the uplink message indicates an uplink reservation for corresponding uplink resources associated with selected resource block. At step 1203, the UE receives a response signal from the base station in response to the uplink message, wherein a positive response signal indicates a success reservation of the corresponding uplink resources. At step 1204, the UE transmits uplink data on the corresponding uplink resources upon receiving the positive response signal.

Figure 13 illustrates an exemplary flow chart for power control for UL non-orthogonal multiple access in accordance with embodiment of the current invention. In this embodiment, at least two UE are using the resource based RRR (RR) request to access the system. When at least two UEs choose the RR request, at step 1301, the first UE measures downlink signals and obtaining a path loss in a wireless network. At step 1302, the first UE selects a power offset from a configured power offset pool. At step 1303, the first UE calculates a transmit power based on the path loss, a target power and the selected power offset, wherein the target power is configured by a network entity of the wireless network. At step 1304, the first UE transmits an uplink message with the calculated transmit power. And the second UE uses different power offset to transmit another uplink message with the calculated transmit power, so eNB could decode the two UE on the same resource successfully.

As shown in the above embodiments, there are n resources for contention based UL, where the resource could be time/frequency/code book index/scrambling sequence/interleaver/spreading code. The chance for two UEs choose the same resource is

If m power offset if introduced, the collision possibility is further reduced to

Compared with dividing one resource pool into several subsets. This method creates power domain to distinguish UEs.

The techniques described herein may be used for various wireless communication systems such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA and other systems. The terms "system" and "network" are often used interchangeably. A CDMA system may implement a radio technology such as Universal Terrestrial Radio Access (UTRA) , cdma2000, etc. UTRA includes Time Division Synchronous Code Division Multiple Access (TD-SCDMA) , Wideband-CDMA (W-CDMA) and other variants of CDMA. A TDMA system may implement a radio technology such as Global System for Mobile Communications (GSM) . An OFDMA system may implement a radio technology such as Evolved UTRA (E-UTRA) , Ultra Mobile Broadband (UMB) , IEEE 802.11 (Wi-Fi) , IEEE 802.16 (WiMAX) , IEEE 802.20, etc. UTRA and E-UTRA are part of Universal Mobile Telecommunication System (UMTS) . 3GPP Long Term Evolution (LTE) is a release of UMTS that uses E-UTRA, which employs OFDMA on the downlink and SC-FDMA on the uplink. UTRA, E-UTRA, UMTS, TD-SCDMA, LTE and GSM are described in documents from an organization named "3rd Generation Partnership Project" (3GPP) . Further, such wireless communication systems may additionally include peer-to-peer (e.g., mobile-to-mobile) ad hoc network systems often using unpaired unlicensed spectrums, 802. xx wireless LAN, BLUETOOTH and any other short-or long-range, wireless communication techniques. To the person skilled in the art, the above embodiments could be used in 5G system, especially NR (new radio) system, and the system uses beamforming or narrowband, and the evoled release. And the evolved release of narrow band system comprises evolved release of NB-IoT system.

Although the present invention has been described in connection with certain specific embodiments for instructional purposes, the present invention is not limited thereto. Accordingly, various modifications, adaptations, and combinations of various features of the described embodiments can be practiced without departing from the scope of the invention as set forth in the claims.

Claims

A method comprising:

selecting a resource block from a resource pool by a user equipment (UE) in a wireless communication network；

sending a contention-based uplink message based on the selected resource block by the UE to a base station, wherein the uplink message indicates to reserve the corresponding uplink resources associated with selected resource block；

receiving a response signal from the base station in response to the uplink message, wherein a positive response signal indicates a success reservation of the corresponding uplink resources； and

transmitting uplink data on the corresponding uplink resources upon receiving the positive response signal.
The method of Claim 1, wherein the uplink message at least includes a reservation resource request (RRR) .
The method of Claim 2, wherein the RRR is selected from RRR types comprising a contention based RRR (CR) and a resource based RRR (RR) , and wherein the response signal is selected from response types comprising an authorization signal (AR) and a resource authorization signal (SR) .
The method of Claim 3, wherein the response signal is the AR, and wherein the response signal is transmitted on a predefined or preconfigured resource.
The method of Claim 3, wherein the response signal is the SR, and wherein the response signal is transmitted on a resource that is selected by the base station based on the RRR.
The method of Claim 3, wherein the RRR message includes a number n, and wherein the number n is a sequence number in CR and a resource number in RR, and wherein the response signal is based on the number n.
The method of Claim 6, wherein the uplink message is transmitted on the selected resource block and includes one or more transport blocks, and wherein the response signal is an ACK or a NACK in response to the uplink message, and wherein the ACK response signal indicates a success reservation of resource blocks for subsequent uplink data and the NACK response signal triggers a UE retransmission or a new UE transmission.
The method of Claim 1, wherein the uplink message further comprises a UE identification (ID) .
The method of Claim 1, wherein the resource pool is preconfigured based on one or more elements received from the wireless network comprising information elements broadcasted in a system information and information elements in a radio resource control (RRC) message.
The method of Claim 1, wherein the resource pool is related to one or more identifications (IDs) comprising at least one of a cell ID, a UE ID, a subframe number, and a frame number, and wherein the UE derives the resource pool based on the one or more identifications.
The method of Claim 1, wherein the resource pool further comprising multiple sub-pools associates with multiple corresponding levels comprising at least one of a coverage level, a channel status level, and a reference signal received power (RSRP) .
The method of Claim 1, wherein the response signal is transmitted by the base station on a resource block that is mapped from a resource block that the uplink message is transmitted based on a predefined mapping rule.
A user equipment (UE) comprising:

a transceiver module that transmits and receives radio signals in a wireless network；

a selector that selects a resource block from a resource pool in the wireless network；

an uplink resource manager that sends an uplink message based on the selected resource block to a base station, wherein the uplink message indicates an uplink reservation for corresponding uplink resources associated with selected resource block；

a reservation manager that receives a response signal from the base station in response to the uplink message, wherein a positive response signal indicates a success reservation of the corresponding uplink resources； and

the transceiver module that transmits uplink data on the corresponding uplink resources upon receiving the positive response signal.
The UE of Claim 13, wherein the uplink message at least includes a reservation resource request (RRR) , and the positive response signal is a response signal.
The UE of Claim 13, wherein the uplink message is transmitted on the selected resource block and includes one or more transport blocks, and wherein the response signal is an ACK or a NACK in response to the uplink message, and wherein the ACK response signal indicates a success reservation of resource blocks for subsequent uplink data and the NACK response signal triggers a UE retransmission or a new UE transmission.
The UE of Claim 13, wherein the uplink message further comprises a UE identification (ID) .
The UE of Claim 13, wherein the resource pool is preconfigured based on one or more elements received from the wireless network comprising information elements broadcasted in a system information and information elements in a radio resource control (RRC) message.
The UE of Claim 13, wherein the resource pool is related to one or more identifications (IDs) comprising at least one of a cell ID, a UE ID, a subframe number, and a frame number, and wherein the UE derives the resource pool based on the one or more identifications.
The UE of Claim 13, wherein the resource pool further comprising multiple sub-pools associates with multiple corresponding levels comprising at least one of a coverage level, a channel status level, and a reference signal received power (RSRP) .
The UE of Claim 13, wherein the response signal is transmitted by the base station on a resource block that is mapped from a resource block that the uplink message is transmitted based on a predefined mapping rule.