WO2019028720A1

WO2019028720A1 - Identification and localization of secondary anchor carrier

Info

Publication number: WO2019028720A1
Application number: PCT/CN2017/096745
Authority: WO
Inventors: Li Yang; Haijing LIU; He Wang; Srinivasan Selvaganapathy; Rapeepat Ratasuk; Muneender Chiranji; Nitin MANGALVEDHE
Original assignee: Nokia Shanghai Bell Co., Ltd.; Nokia Technologies Oy
Priority date: 2017-08-10
Filing date: 2017-08-10
Publication date: 2019-02-14
Also published as: CN111096016B; CN111096016A

Abstract

Implementations of the present disclosure relate to methods and devices for anchor carrier identification and localization. In example implementations, a method implemented by a terminal device in a communication system is provided. The method includes, in response to receiving primary synchronization information from a network device at a first time point, identifying a primary anchor carrier on which the primary synchronization information is detected. The method also includes detecting indication information from the network device on the identified primary anchor carrier at a second time point, the second time point being different from the first time point. The method further includes determining, based on the detection of the indication information, presence of a secondary anchor carrier for reception of system information.

Description

IDENTIFICATION AND LOCALIZATION OF SECONDARY ANCHOR CARRIER

TECHNICAL FIELD

Implementations of the present disclosure generally relate to the field of telecommunication， and in particular， to methods and devices for identifying and localizing a secondary anchor carrier in a narrowband-Internet of Things (NB-IoT) system.

BACKGROUND

A new generation of radio communication techniques is developing to deliver low latency connectivity and massive networking for the Internet of Things (IoT) . Among the new generation of techniques， narrowband-IoT (NB-IoT) techniques are envisioned to work on a narrowband channel such as a 180 kHz channel. The NB-IoT techniques may be deployed in some existing communication networks such as Long Term Evolution (LTE) networks. NB-IoT may have three different modes， including a standalone mode， an in-band mode with NB-IoT deployed on the same frequency band as a LTE carrier， and a guard band mode with NB-IoT deployed in the guard interval of a LTE carrier. In current communication specifications (for example， in Rel-13) ， it has been agreed that NB-IoT can support half-duplex Frequency Division Duplex (FDD) . To meet the increasing demand for NB-IoT， there is proposed to add support of Time Division Duplex (TDD) into NB-IoT.

In NB-IoT systems， a carrier carrying synchronization information and/or system information is called as an anchor carrier and a carrier carrying other information is called as a non-anchor carrier. The synchronization information includes a Narrowband Primary Synchronization Signal (NPSS) and a Narrowband Secondary Synchronization Signal (NSSS) while the system information includes Narrowband System Information Block -type 1 (NB-SIB1) and/or Narrowband Master Information Block (MIB) which occupies a Narrowband physical broadcast channel (NPBCH) . At the initial stage when a terminal device wants to access a network， it may try to receive synchronization information and system information from a base station within the network in the downlink (DL) direction.

According to the solution in FDD NB-IoT systems， a terminal device may perform blind detection to detect a PSS and identify a frequency band on which the PSS is detected as an anchor carrier. The terminal device may then detect other control information on the identified anchor carrier. However， due to the time limit for DL transmission in the TDD NB-IoT systems， the same solution in the FDD NB-IoT systems cannot be directly applied. In some scenarios of TDD NB-IoT systems， more than one anchor carrier (for example， a primary anchor carrier and a secondary anchor carrier) will be introduced. Therefore， there is a need for a solution of anchor carrier identification and localization in TDD narrowband systems (for example， NB-IoT systems) .

SUMMARY

In general， example implementations of the present disclosure provide methods and devices for identifying and localizing a secondary anchor carrier in a communication system.

In a first aspect， there is provided a method implemented by a terminal device in a communication system. The method includes， in response to receiving primary synchronization information from a network device at a first time point， identifying a primary anchor carrier on which the primary synchronization information is detected. The method also includes detecting indication information from the network device on the identified primary anchor carrier at a second time point， the second time point being different from the first time point. The method further includes determining， based on the detection of the indication information， presence of a secondary anchor carrier for reception of system information.

In a second aspect， there is provided a method implemented by a network device in a communication system. The method includes transmitting， to a terminal device， primary synchronization information on a primary anchor carrier at a first time point. The method also includes determining presence of a secondary anchor carrier based on an operating mode of the communication system. The secondary anchor carrier is to be used for transmission of system information to the terminal device. The method further includes transmitting， based on the presence of the secondary anchor carrier， indication information to the terminal device on the primary anchor carrier at a second time point， the second time point being different from the first time point.

In a third aspect， there is provided a terminal device. The terminal device includes a processor； and a memory coupled to the processing unit and storing instructions thereon， the instructions， when executed by the processing unit， causing the terminal device to perform the method according to the first aspect.

In a fourth aspect， there is provided a network device. The network device includes a processor； and a memory coupled to the processing unit and storing instructions thereon， the instructions， when executed by the processing unit， causing the network device to perform the method according to the second aspect.

In a fifth aspect， there is provided a computer readable medium having instructions stored thereon. The instructions， when executed on at least one processor， cause the at least one processor to carry out the method according to the first aspect.

In a sixth aspect， there is provided a computer readable medium having instructions stored thereon. The instructions， when executed on at least one processor， cause the at least one processor to carry out the method according to the second aspect.

In a seventh aspect， there is provided a computer program product that is tangibly stored on a computer readable storage medium. The computer program product includes instructions which， when executed on at least one processor， cause the at least one processor to carry out the method according to the first aspect or the second aspect.

Other features of the present disclosure will become easily comprehensible through the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

Through the more detailed description of some implementations of the present disclosure in the accompanying drawings， the above and other objects， features and advantages of the present disclosure will become more apparent， wherein：

Fig. 1 is a block diagram of a communication environment in which implementations of the present disclosure can be implemented；

Fig. 2 is a flowchart illustrating a process of anchor carrier identification according to some other implementations of the present disclosure；

Fig. 3 is a schematic diagram illustrating possible frequency locations of a secondary anchor carrier in accordance with some implementations of the present disclosure；

Figs. 4A and 4B are schematic diagrams illustrating different transmission patterns of secondary synchronization signals with different cyclic shift values in accordance with some implementations of the present disclosure；

Figs. 5A-5C are schematic diagrams illustrating different transmission patterns of synchronization information and system information on two anchor carriers in accordance with some implementations of the present disclosure；

Fig. 6 shows a flowchart of an example method in accordance with some implementations of the present disclosure；

Fig. 7 shows a flowchart of an example method in accordance with some other implementations of the present disclosure； and

Fig. 8 is a simplified block diagram of a device that is suitable for implementing implementations of the present disclosure.

Throughout the drawings， the same or similar reference numerals represent the same or similar element.

DETAILED DESCRIPTION

Principle of the present disclosure will now be described with reference to some example implementations. It is to be understood that these implementations are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure， without suggesting any limitations as to the scope of the disclosure. The disclosure described herein can be implemented in various manners other than the ones described below.

In the following description and claims， unless defined otherwise， all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure belongs.

As used herein， the term “network device” or “base station” (BS) refers to a device which is capable of providing or hosting a cell or coverage where terminal devices can communicate. Examples of a network device include， but not limited to， a Node B (NodeB or NB) ， an Evolved NodeB (eNodeB or eNB) ， a Remote Radio Unit (RRU) ， a radio head (RH) ， a remote radio head (RRH) ， a low power node such as a femto node， a pico node， and the like. For the purpose of discussion， in the following， some implementations will be described with reference to eNB as examples of the network device.

As used herein， the term “terminal device” refers to any device having wireless or wired communication capabilities. Examples of the terminal device include， but not limited to， user equipment (UE) ， personal computers， desktops， mobile phones， cellular phones， smart phones， personal digital assistants (PDAs) ， portable computers， image capture devices such as digital cameras， gaming devices， music storage and playback appliances， or Internet appliances enabling wireless or wired Internet access and browsing and the like. For the purpose of discussion， in the following， some implementations will be described with reference to UEs as examples of terminal devices and the terms “terminal device” and “user equipment” (UE) may be used interchangeably in the context of the present disclosure.

As used herein， the singular forms “a” ， “an” and “the” are intended to include the plural forms as well， unless the context clearly indicates otherwise. The term “includes” and its variants are to be read as open terms that mean “includes， but is not limited to. ” The term “based on” is to be read as “based at least in part on. ” The term “one implementation” and “an implementation” are to be read as “at least one implementation. ” The term “another implementation” is to be read as “at least one other implementation. ” The terms “first， ” “second， ” and the like may refer to different or same objects. Other definitions， explicit and implicit， may be included below.

In some examples， values， procedures， or apparatus are referred to as “best， ” “lowest， ” “highest， ” “minimum， ” “maximum， ” or the like. It will be appreciated that such descriptions are intended to indicate that a selection among many used functional alternatives can be made， and such selections need not be better， smaller， higher， or otherwise preferable to other selections.

1. Overview

Implementations of the present disclosure relate to communications in narrowband networks， such as narrowband-Internet of Things (NB-IoT) communication systems. The narrowband systems such as NB-IoT work on a narrowband with a small bandwidth such as 180 kHz， which is equal to the bandwidth of only one physical resource block (PRB) in existing LTE systems. NB-IoT can be deployed in some existing communication networks such as LTE networks and may follow some basic communication specifications of the existing networks. In the following， implementations of the present disclosure will be described with reference to NB-IoT in LTE systems. However， it would be appreciated that the implementations may also be adapted to other narrowband systems.

It has been discussed and agreed that NB-IoT can support half-duplex Frequency Division Duplex (FDD) . Although NB-IoT is mostly uplink (UL) oriented， some downlink (DL) signals/channels should be guaranteed， especially synchronization information in a Narrowband Primary Synchronization Signal (NPSS) and a Narrowband Secondary Synchronization Signal (NSSS) as well as system information in a Narrowband physical broadcast channel (NPBCH) (such as Narrowband Master Information Block (MIB) ) and a Narrowband System Information Block-type 1 (NB-SIB 1) .

For transmissions of synchronization information and system information in FDD NB-IoT， it has been specified in the communication specification (Rel-13) that a NPSS and a NPBCH are transmitted on subframe 5 and subframe 0 with the period of 10 ms， respectively， a NSSS is transmitted in subframe 9 in even numbered frames with the period of 20 ms， and a NB-SIB1 is transmitted in subframe 4 in even numbered frames or odd numbered frames depending on the parity of a physical cell identity (PCID) with a specific repetition. In addition to the time domain locations， the NPSS， NSSS， NB-SIB1， and NPBCH may be transmitted on the same frequency location of an anchor carrier. When a terminal device wants to access a network， it may perform blind detection to detect the NPSS without any prior knowledge of time and frequency localization of the network. After detecting the NPSS， the terminal device may identify the carrier on which the NPSS is transmitted as an anchor carrier and thus can continue to search NSSS， NPBCH， and/or NB-SIB1 on that anchor carrier.

To meet the increasing demand， it is proposed to add support of Time Division Duplex (TDD) in NB-IoT. Due to the time limit in TDD systems， there may not be sufficient time duration for DL transmission of the synchronization information and system information. In some possible implementations， the TDD NB-IoT systems may use the same UL/DL configurations as the TDD LTE systems. This is because the reuse of the UL/DL configurations may help reduce the interference between the TDD NB-IoT systems and the TDD LTE systems in the in-band or guard band mode. Although terminal devices working in the standalone mode in NB-IoT systems may not have the concern of interference degradation， for a unified solution for the three modes in TDD NB-IoT systems， the same UL/DL configurations as the TDD LTE systems would be employed.

There are seven different UL/DL configurations as specified in LTE communication specifications， which are shown in Table 1. In Table 1， “D” is referred to as a DL subframe， “S” is referred to as a special subframe， and “U” is referred to as a UL subframe. The ratios of UL to DL subframes are different for these UL/DL configurations.

Table 1

As can be seen from Table 1， some UL/DL configurations provide fewer DL subframes for transmission. For example， in UL/DL configuration 0 or 6， there are only two or three DL subframes in a radio frame， while four subframes are needed for transmission of all the synchronization and system information， including NPSS， NSSS， NPBCH， and NB-SIB1. The solution for transmission of the synchronization and system information as specified in the FDD NB-IoT systems cannot be directly applied into the TDD NB-IoT systems. For example， for UL/DL configurations 1 to 6，

subframes

0， 5， and 9 are DL subframes which are available for transmissions of NPBCH， NPSS， and NSSS. However， subframe 9 in UL/DL configuration 0 is a UL subframe which cannot be used for transmission of NSSS. In addition， subframe 4 in UL/

DL configurations

0， 3 and 6 cannot be for transmission of NB-SIB1.

One possible solution is to use some of the UL/DL configurations only that can support the DL transmissions of NPBCH， NPSS， NSSS， and NB-SIB1 as in FDD NB-IoT， which will constrained the flexibility of the LTE systems if the interference degradation has to be guaranteed. Another possible solution is to make use of special subframes in transmissions of the synchronization and system information. However， the numbers of symbols carried in downlink piloting time slots (DwPTS) of the special subframes varied from three to twelve， which also fails to ensure the transmission ofNPBCH， NPSS， NSSS， or NB-SIB1 that occupy 11 symbols in one subframe. Considering all the other possible solutions， DL subframes are suggested for the transmissions of NPBCH， NPSS， NSSS， and NB-SIB1.

In order to ensure detection of NPBCH， NPSS， NSSS， and NB-SIB1 in UL/DL configurations with scarce DL subframes (for example， fewer than four DL subframes) ， it is proposed to allocate two or more anchor carriers for those UL/DL configurations. For UL/DL configurations with more DL subframes， the use of only one anchor carrier may be sufficient. In such allocation of anchor carrier (s) ， there is a need for the terminal device to identify whether there is more than one anchor carrier and to localize the frequency location (s) of the anchor carrier (s) .

According to implementations of the present disclosure， there is proposed a solution for anchor carrier identification and localization in a narrowband communication system. In this solution， a terminal device identifies an anchor carrier (referred to as a “primary anchor carrier” ) by detecting primary synchronization information (for example， a NPSS) . The terminal device detects indication information on the identified primary anchor carrier and determines whether there is another anchor carrier (referred to as a “secondary anchor carrier” ) based on the detection of the indication information. Upon a determination of presence of the secondary anchor carrier， the terminal device may localize the secondary anchor carrier in the frequency domain for reception of system information and/or other synchronization information. Through this solution， a new solution for anchor carrier identification and/or localization is introduced， which may be employed in TDD NB-IoT systems for transmission of synchronization and system information.

2. Example Environment

Fig. 1 shows an example communication network 100 in which implementations of the present disclosure can be implemented. The network 100 includes a network device 110 and a terminal device 120 served by the network device 110. The serving area of the network device 110 is called as a cell 102. It is to be understood that the number of network devices and terminal devices is only for the purpose of illustration without suggesting any limitations. The network 100 may include any suitable number of network devices and terminal devices adapted for implementing implementations of the present disclosure. Although not shown， it would be appreciated that one or more terminal devices may be located in the cell 102 and served by the network device 110.

In the communication network 100， the network device 110 can communicate data and control information to the terminal device 120 and the terminal device 120 can also communication data and control information to the network device 110. A link from the network device 110 to the terminal device 120 is referred to as a downlink (DL) ， while a link from the terminal device 120 to the network device 110 is referred to as an uplink (UL) .

The communications in the network 100 may conform to any suitable standards including， but not limited to， Global System for Mobile Communications (GSM) ， Extended Coverage Global System for Mobile Internet of Things (EC-GSM-IoT) ， Long Term Evolution (LTE) ， LTE-Evolution， LTE-Advanced (LTE-A) ， Wideband Code Division Multiple Access (WCDMA) ， Code Division Multiple Access (CDMA) ， GSM EDGE Radio Access Network (GERAN) ， and the like. Furthermore， the communications may be performed according to any generation communication protocols either currently known or to be developed in the future. Examples of the communication protocols include， but not limited to， the first generation (1G) ， the second generation (2G) ， 2.5G， 2.75G， the third generation (3G) ， the fourth generation (4G) ， 4.5G， the fifth generation (5G) communication protocols.

3. Example Implementations

3.1. High-Level Interaction Process

Principle and implementations of the present disclosure will be described in detail below with reference to Fig. 2， which shows a process 200 for anchor carrier identification according to an implementation of the present disclosure. For the purpose of discussion， the process 200 will be described with reference to Fig. 1. The process 200 may involve the network device 110 and the terminal device 120 in Fig. 1. The process 200 relates to a procedure when the terminal device 120 wants to access the network device 110 and has no knowledge of the time and frequency synchronization information or system information about the network device 110. The process 200 may be implemented in narrowband communication systems， such as NB-IoT communication systems.

At 205， the network device 110 transmits primary synchronization information. The network device 110 may broadcast the primary synchronization information on a specific carrier in the frequency domain and in a specified time point (referred to as a first time point) or subframe. The carrier on which the primary synchronization information is transmitted is referred to as a primary anchor carrier. The frequency location of the primary anchor carrier in the frequency domain is allocated by the network device 110.

In some implementations of narrowband systems such as NB-IoT systems， the primary synchronization information may be indicated in a primary synchronization signal called as a Narrowband Primary Synchronization Signal (NPSS) . The primary synchronization information is used to attain time and frequency synchronization between the terminal device 120 and the network device 110 and may be repeated with a period of 10 ms， for example. In some implementations， the primary synchronization information may be transmitted by the network device 110 in every subframe 0 of a radio frame， where the duration of the frame is 10 ms. In other implementations， the primary synchronization information may also be allocated in other subframes.

The terminal device 120， which tries to access the network device 110， detects the primary synchronization information. Without any prior knowledge of the time and frequency localization in this network， the terminal device 120 may perform blind detection to search for the primary synchronization information in time and frequency domains. The terminal device 120 may be configured with some possible sequences of the primary synchronization information， and use each of the possible sequences to match any downlink signals received from the network device 110. If one of the sequences matches with a downlink signal received from the network device 110， the terminal device 120 may determine that the primary synchronization information is detected.

If the primary synchronization information is detected， at 210， the terminal device 120 identifies the primary anchor carrier on which the primary synchronization information is detected. The terminal device 120 can localize a frequency location of the primary anchor carrier in the frequency domain. In the implementations of NB-IoT， the primary anchor carrier may have a bandwidth of a physical resource block (PRB) of the LTE systems， which is 180 kHz. Other bandwidths for the primary anchor carrier are also possible. In some implementations， the frequency locations of the primary anchor carrier may be identified by a PRB index among all the PRB indexes of the system bandwidth.

The network device 110 determines， at 215， presence of a secondary anchor carrier. The secondary anchor carrier is used to transmit at least system information to the terminal device 120 because there are no DL transmission opportunities on the primary anchor carrier for the system information. In some implementations， other information such as secondary synchronization information may also be transmitted on the secondary anchor carrier as will be discussed below. The network device 110 may determine whether a secondary anchor carrier is needed based on an operating mode of the network 100. Additionally， the network device 110 may further determine the presence of the secondary anchor carrier based on a configuration of DL subframes that is currently employed in the network 100， for example， the UL/DL configuration as specified in LTE systems.

Ifthe operating mode is the TDD operating mode and the number ofDL subframes in the employed UL/DL configuration is not sufficient to transmit both the synchronization and system information， the network device 110 determines that the secondary anchor carrier is to be allocated. Otherwise， if the operating mode is the FDD operating mode or if the number of DL subframes in the UL/DL configuration is sufficient for the transmission in the TDD operating mode， the network device 110 determines that the secondary anchor carrier is absent. In some examples， the secondary anchor carrier may always present in the TDD operating mode regardless of the UL/DL configurations.

Depending on the presence of the secondary anchor carrier， the network device 110 transmits， at 220， indication information on the primary anchor carrier at a time point (referred to as a second time point) or subframe that is different from the first time point at which the primary synchronization information is transmitted. The indication information may indicate whether the secondary anchor carrier is present or absent.

Since the frequency location of the primary anchor carrier is identified， the terminal device 120 detects the indication information on the identified anchor carrier at the second time point without the blind detection. In some implementations， the second time point or subframe may be specified in the tenninal device 120. Although the time synchronization with the network device 110 may not be accomplished yet， the terminal device 120 can determine when to receive the indication information by determining a relative temporary distance from the first time point to the specified second time point. The detailed description of the time localization of the indication information will be discussed below with reference to some specific implementations. The terminal device 120 determines， at 225， presence of a secondary anchor carrier based on the detection of the indication information.

In implementations of the present disclosure， there are two types of indication information that can be used to indicate the presence of the secondary anchor carrier. In some implementations， the indication information may be included in one or more signals including secondary synchronization information. Such a signal may include a secondary synchronization signal such as a Narrowband Secondary Synchronization Signal (NSSS) that is typically transmitted by the network device 110 to the secondary synchronization information. In some other implementations， a new carrier indication is introduced between the network device 110 and the terminal device 120 to explicitly indicate the presence and/or localization of the secondary anchor carrier. The determination of the presence of the secondary anchor carrier based on the two types of indication information will be described in details below.

If the terminal device 120 determines that the secondary anchor carrier is present， it may receive， at 230， system information from the network device 110 on the secondary anchor carrier. The system information may be included in the NPBCH and/or NB-SIB1 signals. In some implementations， other information may also be received on the secondary anchor carrier as will be discussed below. In other cases， if the terminal device 120 determines that the secondary anchor carrier is absent， it means that only the primary anchor carrier is used for transmission. In this case， the terminal device 120 may receive， at 230， the system information from the network device 110 on the primary anchor carrier.

The process 200 may be suitable for NB-IoT systems where the bandwidth of a carrier is limited and the DL transmission opportunities (DL subframes) are not always sufficient in a TDD operating mode for transmission of all the synchronization and system information on a same anchor carrier in a radio frame. Through the process 200， when two anchor carriers are probably allocated by the network device 110 for transmission of the synchronization and system information， it is possible for the terminal device 120 to identify whether a secondary anchor carrier is present after detecting a primary anchor carrier and if present， to localize the secondary anchor carrier in the frequency domain.

3.2. Identification and Localization based on Secondary Synchronization Information

Typically， in addition to the primary synchronization information， the network device 110 transmits secondary synchronization information to the terminal device 120 for the purpose of time and frequency synchronization. Both the primary and secondary synchronization information may include information for time and frequency synchronization. The secondary synchronization information may additionally include a physical layer cell identity (PCID) of the network device 110. The secondary synchronization information may be included in a signal referred to as a NSSS in narrowband systems. The network device 110 may generate and transmit a plurality of NSSSs with a specific period. In an example， the network device 110 may transmit four NSSSs in a period of 80 ms with each NSSS transmitted at every time point of 20 ms. As a specific example， each of the NSSS may be transmitted in a specific subframe (for example， subframe 5) in even numbered radio frames. In some examples， the plurality of NSSSs may also be repeated by the network device 110 in several periods of 80 ms. Of course， other transmission patterns of the NSSSs are applicable.

The transmission pattern of NSSSs may be specified in the terminal device 120. Accordingly， upon reception of the primary synchronization information in the NPSS， the terminal device 120 may determine the time point for reception of each of the plurality of NSSSs. For example， if a NPSS is detected and received on subframe 0 in every radio frame， the terminal device 120 may determine to wait for 5 ms to detect whether the NSSS is received on the primary anchor carrier. In this way， the detection time may be reduced compared to blind detection in the time domain.

Typically， the plurality of NSSSs may be generated from a scrambling sequence based on corresponding cyclic shift values. For example， according to some communication specifications， a NSSS may be generated as follows：

where NSSS (n) represents a NSSS， b_q {m) represents a scrambling sequence， θ_frepresents a cyclic shift values， and n_f represents a value corresponding to a radio frame where the NSSS is to be transmitted. The parameters n， n’， m， u， and q are defined， respectively， as n＝0， 1， ...， 131， n′＝nmodl31， m＝nmod128，

and

where

represents a Narrowband physical layer cell identity. The scrambling sequence b_q (m) is selected from a set of predefined sequences based on the parameters q and m.

In existing communication systems， the cyclic shift values for the plurality of NSSS are limited to one specific combination. For example， in a FDD NB-IoT system， n_f is valued from {0， 2， 4， 6} in a period of 80 ms. Thus， the cyclic shift values θ_f for the four NSSSs transmitted in the period of 80 ms include {0，

}.

In some implementations of the present disclosure， instead of using a specific set of cyclic shift values to generate the plurality of NSSSs， the cyclic shift values for the NSSSs may be varied to indicate whether the secondary anchor carrier is present or not. For example， a first set of cyclic shift values may be predetermined to indicate that the secondary anchor carrier is present， and a second set of cyclic shift values that is different from the first set may be predetermined to indicate that the secondary anchor carrier is absent.

Depending on whether the secondary anchor carrier is present or not， the network device 110 may select one of the first and second sets of predetermined cyclic shift values to generate the plurality of NSSSs， for example， based on Equations (1) and (2) . The generated NSSSs may be transmitted to the terminal device 120 on the primary anchor carrier at corresponding time point/subframe. Upon reception of the plurality of NSSSs， the terminal device 120 may determine that cyclic shift values for generation of the received NSSSs， for example， based on Equations (1) and (2) .

The terminal device 120 may determine whether the secondary anchor carrier is present or not based on the determined cyclic shift values. Specifically， the terminal device 120 may compare the cyclic shift values with the first and second set of predetermined cyclic shift values. In response to a determination that the cyclic shift values match the first set of predetermined cyclic shift values， the terminal device 120 determines that the secondary anchor carrier is present. If the cyclic shift values match with the second set of predetermined cyclic shift values， the terminal device 120 determines that the secondary anchor carrier is absent.

In the cases where the secondary anchor carrier is present， the network device 110 may allocate the secondary anchor carrier at one of various frequency locations within the system bandwidth range depending on the frequency scheduling. The cyclic shift values of the NSSSs may also be varied to convey the actual frequency location of the secondary anchor carrier. In these implementations， in addition to indicating the presence of the secondary anchor carrier， one or more sets of cyclic shift values may be predetermined to be associated with one or more possible frequency locations of the secondary anchor carrier. That is， for each set of cyclic shift values indicating that the secondary anchor carrier is present， it may also indicate the frequency location of the secondary anchor carrier.

In the implementations of indicating the frequency location of the secondary anchor carrier， in generation of the NSSSs， if the network device 110 may determine that the secondary anchor carrier is present， it may determine the cyclic shift values for the NSSSs further based on the allocated frequency location of the secondary anchor carrier. At the side of the terminal device 120， if the cyclic shift values determined from the received NSSSs are determined to match a set of predetermined cyclic shift values indicating that the secondary anchor carrier is present， the terminal device 120 may further determine a frequency location of the secondary anchor carrier that is associated with the matched set of values.

In implementations of the present disclosure， the cyclic shift values for the plurality of NS SSs may be predetermined in various manners to indicate the presence of the secondary anchor carrier and if present， the frequency location of the secondary anchor carrier. The indication of different combinations of cyclic shift values may be specified in the network device 110 for generation of the NSSSs and in the terminal device 120 for identification and localization of the secondary anchor carrier. Some implementations will be described below in detail.

3.2.1. First Implementation based on Cyclic Shift Values

In this implementation， the terminal device 120 compares the cyclic shift values for generation of the received NSSSs with a plurality of sets of predetermined cyclic shift values. Depending on the comparison result， the terminal device 120 determines whether the presence of the secondary anchor carrier and if present， the frequency location of the secondary anchor carrier. The plurality of sets of predetermined cyclic shift values may be configured as different combinations of cyclic shift values. One of the sets of predetermined values may be configured to indicate that the secondary anchor carrier is absent. One or more other sets of predetermined values may be configured as being associated with an indication that the secondary anchor carrier is present. If the terminal device 120 determines that the cyclic shift values match any of the sets of predetermined values， it can be determined that the secondary anchor carrier is present or absent.

In some implementations， the same combination of cyclic shift values as that in the FDD NB-IoT may be used to indicate that the secondary anchor carrier is absent and only the primary anchor carrier is present. For example， such a combination of cyclic shift values may be

In some implementations， a different offset may be added in the traditional calculation of cyclic shift values for the NSSSs so as to obtain different cyclic shift values. An offset of zero indicates that the secondary anchor cartier is absent， and other offsets indicate that the secondary anchor carrier is present. Therefore， the above Equation (2) may be modified as follows：

where： (3)

In addition to indicating the presence of the secondary anchor carrier， different combinations of cyclic shift values may also be used to indicate different frequency locations of the secondary anchor carrier in the case that the secondary anchor carrier is present. The combinations of cyclic shift values that indicate the presence of the secondary anchor carrier may be associated with respective frequency locations of the secondary anchor carrier. For example， in Equation (3) ， different offsets that are not equal to zero may indicate different frequency locations of the secondary anchor carrier.

There may be various possible locations for allocation of the secondary anchor carriers. The frequency location of the secondary anchor carrier may be scheduled by the network device 110 and may be different from the primary anchor carrier. As shown in Fig. 3，

carrier locations

302， 303， and 304 are offset from the frequency anchor carrier 301 of the primary anchor carrier by different bandwidths， and they can be considered as the possible frequency locations of the secondary anchor carrier.

In these cases， depending on the allocation of the secondary anchor carrier， the network device 110 selects cyclic shift values that are associated with the frequency location of the allocated secondary anchor carrier to generate the NSSSs. At the side of the terminal device 120， if the terminal device 120 determines that the cyclic shift values match a specific set of predetermined values indicating that the secondary anchor carrier is present， it may also determine the frequency location associated with the matched set of predetermined values as the frequency location of the secondary anchor carrier. For example， in Fig. 3， cyclic shift values

with the of fset of 8 may be associated with the carrier location 302 of the secondary anchor cartier， while cyclic shift values

with the offset of 16 may be associated with the carrier location 304 of the secondary anchor carrier.

In the first implementation， the order of the cyclic shift values used for generation the NSSSs may be ignored in the comparison of the cyclic shift values and a set of predetermined values. That is， all the cyclic shift values in one set may all be different from the cyclic shift values in the other set. Therefore， every time the terminal device 120 receives a predetermined number of NSSSs (for example， four) ， it may determine and compare the cyclic shift values with each of the plurality of sets of predetermined values. As such， it may cost less time consumption for identification and localization of the secondary anchor carrier.

In this implementation， the number of possible frequency locations of the secondary anchor carrier identified by the cyclic shift values may only depend on the number of possible cyclic shift values. For example， in the cases of NSSS generation based on the Equations (1) and (2) ， if four different NSSSs are transmitted， the possible 132 cyclic shift values may be divided into 33 groups (132/4＝33) . Each of the groups is used to indicate a possible frequency location of the secondary anchor carrier except for the group that indicating the absence of the secondary anchor cartier. Thus， the number of possible frequency locations to be indicated by the cyclic shift values is limited to 32.

However， the limited number of possible frequency locations cannot provide sufficient flexibility to have the secondary anchor carrier in any location for a larger system bandwidth. For example， in the cases where a system bandwidth is 20 MHz and the carrier bandwidth is 180 kHz， the maximum number of possible frequency locations is at least 200 even considering guard intervals between carriers. Although the cyclic shift values in different groups may have appropriate intervals for decoding reliability and thus not all the 200 groups are used， the number of 32 is limited. Therefore， the first implementations may be more suitable for cases where the NB-IoT system has a small system bandwidth or have a restricted range for carriers， and/or where short identification and localization time is needed.

3.2.2. Second Implementation based on Cyclic Shift Values

In a second implementation， in order to increase the number of possible frequency locations of the secondary anchor carrier to be indicated by the cyclic shift values， the plurality of sets of predetermined values may include values sorted in a predetermined order (such as a descending order or an ascending order) . The cyclic shift values determined from the received NSSSs may also be sorted in the predetermined order for comparison with the sets of predetermined values. By considering the order of the values in the comparison， sometimes not all the possible cyclic shift values but only some of them are used to define the set of predetermined values for comparison. In addition， by considering the order， at least one of the cyclic shift values in a set may be configured to be different from the cyclic shift values in another set.

As an example， for a NB-IoT system with 20 MHz system bandwidth， at maximum 200 frequency locations o are possible for a carrier of 180 kHz. Thus， 10 cyclic shift values may be selected from all the 132 cyclic shift values (0 to 131/132) . If four cyclic shift values are selected from the 10 cyclic shift values and sorted to define set of predetermined values， there may be 210 different sets of predetermined values. Among those sets， one set of predetermined value is used to indicate the absence of the secondary anchor carrier， and the remaining ones are used to indicate different frequency locations of the secondary anchor carrier in the case that the secondary anchor carrier is present.

In some implementations， the cyclic shift values used for defining the sets of predetermined values may be evenly selected from the possible values for the purpose of decoding reliability. For example， ten cyclic shifts {0， 14/132， 28/132， 42/132， 56/132， 70/132， 84/132， 98/132， 112/132， 126/132} are selected from all possible 132 cyclic shift values. One example mapping between each predeterrnined set with sorted cyclic shift values and the frequency location of the secondary anchor carrier is provided in Table 2， where the frequency location of the secondary anchor carrier is identified as a PRB index offset from an index of PRB where the primary anchor carrier is localized.

Table 2

It would be appreciated that Table 2 is merely provided for purpose of illustration and any other predetermined values may be included in the sets for comparison with the cyclic shift values determined from the received NSSSs.

According to the second implementation， since all the predetermined number of cyclic shift values are needed to be determined from the received NSSSs before the comparison， the latency of the identification and localization may be longer compared to the first implementation. On the other hand， since a fewer number of cyclic shift values (10 instead of 132) will be used to generate the NSSSs， the detection times for all the four NSSSs may be reduced. In the example where 10 cyclic shift values are selected， the number of detection times at the terminal device 120 is 10+9+8+7＝34 times.

3.2.3. Third Implementation based on Cyclic Shift Values

In a third implementation， instead of configuring all the cyclic shift values for the NSSSs from various groups or combinations of values， different subsets of the cyclic shift values for generation of NSSSs may be valued from different subsets of predetermined cyclic shift values. As such， the different subsets of the cyclic shift values may be used to indicate different aspects of the presence and location of the secondary anchor cartier. As an implementation， some of the cyclic shift values may be configured to a subset of predetermined values to indicate the presence and the absolute frequency offset of the secondary anchor cartier， while the other cyclic shift values used for generation of the other NSSSs may be configured to another subset of different predetermined values to indicate the offset direction of the absolute frequency offset. In this way， not only the number of possible different sets of cyclic shift values can be obtained to indicate the presence and location of the secondary anchor carrier， but the detection times of the NSSSs may be also be reduced.

To illustrate the third implementation， a specific example will be provided below. In this example， it is supposed that there are four different NSSSs with four cyclic shift values to be transmitted in a period of 80 ms with each NSSS transmitted in every 20 ms. For the NSSS to be transmitted in the first 20 ms of the period of 80 ms， its cyclic shift value (denoted by “C1” ) is specified to be only selected from a first subset of predetermined values (denoted by “S1” ) ， for example， Sl＝ {value0， valuel} . For the NSSSs to be transmitted in the second and third 20 ms of the period of 80 ms， the cyclic shift values (denoted by “C2” and “C3， ” respectively) are specified to be only selected from a second subset of predetermined values (denoted by “S2” ) ， such as S2＝ {value2， value3， value 4， value 5， value 6} . For the NSSS to be transmitted in the fourth 20 ms of the period of 80 ms， its cyclic shift value (denoted by “C4” ) is specified to be only selected from a third subset of predetermined values (denoted by “S3” ) ， for example， S3＝ {value2， value3， value4， value5} . The third subset S3 may be the same or different from the second subset， or may be overlapped with the second subset S2. The first subset S1 may be different from the second and third subsets S2 and S3.

The transmission pattern 400 of NSSS with different cyclic shift values is illustrated in Fig. 4A. As shown， in a period of 80 ms， there are four NSSSs. One of the four NSSSs 402 is generated based on a cyclic shift value from S1， two of the four NSSSs 404 are generated based on cyclic shift values from S2， and the last one NSSSs 406 is generated based on a cyclic shift value from S3. In this example， only seven different cyclic shift values are selected for use.

Depending on the differentiation of the cyclic shift values for NSSSs transmitted in different time points， one or more of the cyclic shift values may be configured to indicate the presence of the secondary anchor carrier and the frequency location of the secondary anchor carrier if present. In addition， the remaining cyclic shift value (s) may be used to help indicate the frequency location only.

Generally， the actual frequency location of the secondary anchor carrier (denoted by “f” ) may be determined by offsetting the frequency location of the primary anchor carrier (denoted by “f₀” ) as below：

f ＝ f₀ +s·k·180kHz (4)

where 180 kHz is the bandwidth of the PRB in the frequency domain， s and k represents the PRB index offset. s indicates the offset direction (positive or negative) ， while k indicates the absolute frequency offset (represented by absolute PRB index offset) .

Based on the transmission pattern as discussed above， a cyclic shift value (C1) for a NSSS may be used to indicate the offset direction s， while other cyclic shift values (C2， C3， and C4) may be used to indicate the absolute frequency offset k. Therefore， depending on the allocated location of the secondary anchor carrier， the network device 110 may select the cyclic shift value C1 value from S1 (value0 or valuel) to indicate the offset indication s and generate the NSSS based on the value Cl. In one example， the offset indication s may be configured as below：

A smaller number of different combinations of cyclic shift values may be needed to indicate the absolute frequency offset compared to the indication of the actual frequency offset. For example， considering a system bandwidth of 20 MHz and a carrier of 180 kHz， as shown in Table 2 in the second implementation， 198 PRB index offsets have to be indicated for all the possible relative frequency location of the secondary anchor carrier to the frequency location of the primary anchor carrier. With the use of the absolute frequency offset k， 99 different absolute frequency offsets may be indicated. In this case， the combinations of cyclic shift values C2， C3， and C4 may be sufficient to cover all the 99 different absolute frequency offsets. Therefore， the different combinations of cyclic shift values C2， C3， and C4 may be used to indicate the absolute frequency offset of the secondary anchor carrier because the total number of different combinations of values in S2 to S3 is 5*5*4＝100. In addition， a special combination of C2， C3， and C4 may be used to indicate that the secondary anchor carrier is absent and thus the absolute frequency offset k is zero.

One example mapping between each combination of C2 to C3 and the frequency location of the secondary anchor carrier associated therewith is provided in the following Table 3， where the frequency location of the secondary anchor carrier is identified as an absolute PRB index offset from an index of PRB where the primary anchor carrier is localized.

Table 3

It would be appreciated that Table 3 is merely provided for purpose of illustration and any other predetermined values may be included in the sets for comparison with the cyclic shift values determined from the received NSSSs. The cyclic shift values C1 to C4 may be selected from any other possible cyclic shift values (for example， any value from 0 to 131/132) . In some other examples， more than seven values may be selected for C1 to C4. Since two values for C1 is enough for indicating the offset direction， C2 and C3 may be configured to be selected from a S2 with more than 5 cyclic shift values， while C4 may be configured to selected from a S3 with more than 4 cyclic shift values.

The specification of the cyclic shift values， including the subsets of predetermined values for different NSSSs transmitted in different time points may be configured in the network device 110 and the terminal device 120. In operation， as mentioned above， the network device 110 determines the cyclic shift values C1 to C4 for generation of the four NSSSs based on the absolute frequency offset and the offset direction of the secondary anchor carrier. Upon reception of the four NSSSs， the terminal device 120 compare each of the four cyclic shift values determined from the NSSSs with the two predetermined values in the subset S1. If one of the cyclic shift values match with a predetermined value in the subset S1， the terminal device 120 determines that the offset direction. The terminal device 120 may also compare each of the four cyclic shift values with the predetermined values in the subsets S2 and S3. If the cyclic shift values match with the predetermined values， the terminal device 120 may determine whether the secondary anchor carrier is present， and if present， where the secondary anchor carrier is located. According to the transmission pattern as shown in Fig. 4A， the number of detection times for finding the matching cyclic shift values is maximum 26.

It would be appreciated that an example of using different subsets of the cyclic shift values to indicate different aspects of the presence and location of the secondary anchor carrier. A subset of the cyclic shift values may be used to indicate the presence of the secondary anchor carrier only by selecting values from a first subset， a different subset of the cyclic shift values may be used to indicate the frequency location only by selecting different values from a second subset.

3.2.4. Fourth Implementation based on Cyclic Shift Values

A fourth implementation is provided for indicating the presence and location of the secondary anchor carrier by different sets of the cyclic shift values. The fourth implementation is similar as the third implementation in the term of dividing the cyclic shift values into different subsets to configure different values. The fourth implementation is similar as the first and second implementations in the term of all the cyclic shift values are combined to indicate the presence and the frequency location.

To illustrate the third implementation， a specific example will be provided below. In this example， it is supposed that there are four different NSSSs with four cyclic shift values to be transmitted in a period of 80 ms with each NSSS transmitted in every 20 ms. For the NSSSs to be transmitted in the first and second 20 ms of the period of 80 ms， their cyclic shift values C1 and C2 may be specified to be only selected from a fourth subset of predetermined values (denoted by “S4” ) ， for example， S4＝ {value0， valuel， value2， value3} . The cyclic shift values C1 and C2 may be set as the same or different values. For the NSSSs to be transmitted in the third and fourth 20 ms， their cyclic shift values C3 and C4 may be specified to be only selected from a fifth subset of predetermined values (denoted by “S5” ) ， for example， S5＝ {value4， value5， value6， value7} . The cyclic shift values C3 and C4 may be set as the same or different values. The fifth subset S5 includes values that are all different from those included in the fourth subset S4.

The transmission pattern 410 of the cyclic shift values is illustrated in Fig. 4B. As shown， in a period of 80 ms， there are four NSSSs. The first two NSSSs 401 are generated based on cyclic shift values from S4， while the other two NSSSs 402 are generated based on cyclic shift values from S5. In this example， only seven different cyclic shift values are selected for use.

In this implementation， the presence and frequency location of the secondary anchor carrier may be indicated by the combination of C1 to C4， which is similar as in the first and second implementations. However， by configuring different subsets of the cyclic shift values C1 to C4 with predetermined values from different subsets S4 and S5， the detection times for the terminal device 120 may be reduced while ensuring the indication of all possible frequency locations of the secondary anchor carrier. In the above example， with the use of seven predetermined cyclic shift values in two subsets S4 and S5， the number of detection times for finding the matching cyclic shift values is maximum 24.

Various implementations for identification and localization of the secondary anchor carrier based on the cyclic shift values of the secondary synchronization signals are described above. It would be appreciated that it is possible to design other transmission patterns of the NSSSs with the cyclic shift values so as to indicate the presence and frequency location of the secondary anchor carrier. In these implementations， both the primary and secondary synchronization signals (NPSS and NSSS) are transmitted on the primary anchor carrier. The system information (NPBCH and NB-SIB1) is transmitted on the secondary anchor carrier if the secondary anchor carrier is present or on the primary anchor carrier if the secondary anchor carrier is not present.

The time points of the transmission of the system information may be specified. For example， NPBCH may be transmitted in subframe 0 of every radio frame (the period is 10 ms) ， and NB-SIB1 may be transmitted in subframe 5 of even numbered frames or odd numbered frames depending on the parity of the PCID. If the terminal device 120 can achieve time and frequency synchronization with the network device 110 based on the NPSS and NSSS received on the primary anchor carrier， the terminal device 120 may know the exact time to receive the system information at the frequency location of the secondary anchor carrier.

To better illustrate the implementations based on the cyclic shift values of the secondary synchronization signals， Fig. 5A shows an example transmission pattern of the NPSS， NSSS， NPBCH， and NB-SIB1 on the primary and secondary anchor carriers. As shown， NPSS and

NSSS

501 and 503 are transmitted on the primary anchor carrier 502. The NPSS 501 is transmitted in subframe 0 of every radio frame， while the NSSS 503 is transmitted in subframe 5 of even numbered frames. NPBCH 505 and NB-SIB1 507 are transmitted on the secondary anchor carrier 504. The NPBCH 505 is transmitted in subframe 0 of every radio frame， while the NB-SIB1 507 is transmitted in subframe 5 of even numbered frames in this example. It would be appreciated that Fig. 5A is illustrated merely by way of example， and the synchronization and system information may be transmitted on the primary and secondary anchor carrier in other patterns.

In some implementations， the secondary synchronization signals (for example， NSSSs) may be transmitted in a different subframe (for example， subframe 5) in the TDD operating mode than the subframe used in the FDD mode (for example， subframe 9) . The NPSS may be transmitted in the same subframe in both the TDD and FDD operating modes (for example， in subframe 0) . As such， upon reception of a NSSS， the terminal device 120 may determine a time length between the time point when the NPSS is received and the time point when the NSSS is received， and then determine the subframe number of the time point when the NSSS is received based on the time length and the subframe number of the NPSS (subframe 0) . Depending on the determined subframe number， the terminal device 120 may determine whether the network 100 of the network device 110 is operating in a TDD mode or a FDD mode.

3.3. Identification and Localization based on Explicit Indication

In some implementations， instead of identifying the secondary anchor carrier in an implicit way by the cyclic shift values of the NSSS， an explicit indication may be introduced to indicate the presence of the secondary anchor carrier. In these implementations， the terminal device 120 may monitor on the primary anchor carrier at the corresponding second time point an indication that the secondary anchor carrier is present. The indication may be hereinafter referred to as carrier information for the secondary anchor carrier (represented as “NSCI” ) . If such an indication is successfully received by the terminal device 120 from the network device 110， the terminal device 120 may determine that the secondary anchor carrier is present. If the terminal device 120 fails to receive such an indication at the second time point， it means that the secondary anchor carrier is not present.

Additionally， the indication NSCI may further indicate a frequency location of the secondary anchor carrier. Ifthe terminal device 120 determines that the secondary anchor carrier is present upon a successful reception of the NSCI， it may determine the frequency location of the secondary anchor carrier based on the received indication. Some example implementations for indicating the frequency location of the secondary anchor carrier will be described below. It would be appreciated that the indication may be configured in any other manners to convey the information of the frequency location of the secondary anchor carrier.

In some implementations， the indication NSCI may be generated in a similar way as the secondary synchronization information (NSSS) . For example， the NSCI may be generated in a manner as shown in the above Equation (1) . For example， the NSCI may be generated as follows：

where d′ (n) represents a NSCI. The parameters in Equation (6) have the same definitions as in Equation (1) . Therefore， the parameter u may be valued from {3， 4， ...， 128} ， and the parameter q may be valued from {0， 1， 2， 3} .

In some implementations， the parameters u and q may be used to indicate the frequency location of the secondary anchor carrier. Specifically， some values of the parameters u and q may be used to identify the frequency locations by way of indexing the groups of the frequency locations in the case that the secondary anchor carrier is present. In one example， in order to localize the frequency location of the secondary anchor carrier， all the possible frequency locations of the secondary anchor carrier are divided into a plurality of groups， each groups consisting of different frequency locations (represented by the PRB index offsets) . In the example of 20 MHz system bandwidth， 200 possible frequency locations may be divided into 4 groups， each including 50 frequency locations. The parameter q may be used to indicate which group includes the frequency location the secondary anchor carrier is to be allocated， while the parameter u is used to indicate the specific frequency location in the group indicated by q.

In some implementations， the scrambling sequence b_q (m) used for generating the NSCI is the same as that used for generating NSSS. In some other implementations， the scrambling sequence used for generating the NSCI is different from that used for generating NSSS. In these implementations， the scrambling sequence that can be used is limited. In the above example， q is valued from {0， 1， 2， 3} ， which means that four different scrambling sequence may be used. To differentiate the scrambling sequences for the NSCI and NSSS， some of the scrambling sequences are assigned for generation of the NSCI， while the remaining are assigned for generation of the NSSS.

If two different scrambling sequences can be used for the generation of NSCI， which means that q can be set as two different values. In this case， all the possible frequency locations for the secondary anchor carrier may be divided into only two groups so as to be indexed by the parameter q. In this case， the parameter u may still be able to indicate different frequency locations divided in each of the groups since u is valued from {3， 4， ...， 128} with more than 100 values.

In the implementations where the NSCI is introduced to be transmitted on the primary anchor carrier to indicate the presence and frequency location of the secondary anchor carrier， the secondary synchronization information may still be transmitted on the primary anchor carrier at a different time point than the NSCI as well as the NPSS. For example， the NSCI may be introduced into the transmission pattern of NSS as shown in Fig. 5A. The new transmission pattern 510 including the NSCI is illustrated in Fig. 5B， where the NSCI 509 is transmitted on the primary anchor carrier 502 in subframe 5 of odd numbered frames. The transmitting time points of the NPSS 501， NSSS 503， NPBCH 505， and NB-SIB1507 are the same as in Fig. 5A.

In some implementations， if both the NSSS and NSCI are transmitted on the primary anchor carrier， the scrambling sequences used for generation of NSSS and NSCI may be different. For example， one scrambling sequence b_q (m) with q valued from {0， 1 } may be used to generate a NSCI， while another scrambling sequence b_q (m) with q valued from {2， 3} may be used to generate a NSSS. In this way， the terminal device 120 may be able to differentiate the NSCI and NSSS from the received signals.

In some implementations where the NSCI is introduced， the secondary synchronization information may be transmitted on the secondary anchor carrier instead of on the primary anchor carrier. As illustrated in Fig. 5C， the NSCI 509 is transmitted on the primary anchor carrier 502 in subframe 5 of even numbered frames， and the NSSS 503 is transmitted on the secondary anchor carrier 504 in subframe 5 of even numbered frames. The transmitting time points of the NPSS 501 and NPBCH 505 are the same as in Figs. 5A and 5B. In this example， NB-SIB1 carrying system information is not transmitted. In another example， NB-SIB1 may be transmitted to convey the system information while NPBCH is not transmitted. In yet another example， if there are available DL subframes， all of the NSSS， NPBCH， and NB-SIB 1 are transmitted on the secondary anchor carrier.

In the implementations where the NSSS and NSCI are transmitted on different anchor carriers， the same scrambling sequence may be used to generate the NSSS and NSCI. In some implementations， if the NPSS transmitted on the primary anchor carrier can help align better timing accuracy， the NSSS may not have to be transmitted on the secondary anchor carrier. In this case， the physical layer cell identity that was conveyed by the NSSS may be instead transmitted by another signal， such as a narrow physical downlink shared channel (NPDSCH) . The PDSCH may be transmitted in a DL subframe in the primary or secondary anchor carrier.

4.Example Processes

Fig. 6 shows a flowchart of an example process 600 in accordance with some implementations of the present disclosure. The process 600 can be implemented at the terminal device 120 as shown in Fig. 1. For the purpose of discussion， the process 600 will be described from the perspective of the terminal device 120 with reference to Fig. 1.

At block 610， the terminal device 120 identifies， in response to receiving primary synchronization information from a network device at a first time point， a primary anchor carrier on which the primary synchronization information is detected. At block 620， the terminal device 120 detects indication information from the network device on the identified primary anchor carrier at a second time point. The second time point is different from the first time point. At block 630， the terminal device 120 determines， based on the detection of the indication information， presence of a secondary anchor carrier for reception of system information.

In some implementations， the terminal device 120 may detect the indication information by receiving a plurality of signals including secondary synchronization information on the primary anchor carrier.

In some implementations， the terminal device 120 may determine presence of a secondary anchor carrier by determining cyclic shift values for generation of the plurality of signals and determining the presence of the secondary anchor carrier based on the cyclic shift values.

In some implementations， the terminal device 120 may determine the presence of the secondary anchor carrier based on the cyclic shift values by， in response to a determination that the cyclic shift values match a set of predetermined values， determining that the secondary anchor carrier is present.

In some implementations， the terminal device 130 may， in response to determining that the secondary anchor carrier is present， determine a frequency location of the secondary anchor carrier based on the set of predetermined values， wherein the frequency location is to be used to receive the system information.

In some implementations， the set of predetermined values may be sorted in a predetermined order. In these implementations， the terminal device 130 may further sort the cyclic shift values in the predetermined order for comparison with the set of predetermined values.

In some implementations， the terminal device 120 may determine the presence of the secondary anchor carrier by， in response to a determination that a first cyclic shift value among the cyclic shift values matches a first predetermined value， determining that the secondary anchor carrier is present.

In some implementations， the terminal device 130 may， in response to determining that the secondary anchor carrier is present， obtain a frequency offset associated with the first predetermined value. In response to a determination that a second cyclic shift value among the cyclic shift values matches a second predetermined value， the terminal device 130 may obtain an offset direction associated with the second predetermined value. The terminal device 130 may further determine a frequency location of the secondary anchor carrier by offsetting a frequency location of the primary anchor carrier by the frequency offset in the identified offset direction， wherein the frequency location is to be used to receive the system information.

In some implementations， the terminal device 120 may detect the indication information by monitoring， on the primary anchor carrier at the second time point， an indication that the secondary anchor carrier is present.

In some implementations， the terminal device 120 may determine presence of a secondary anchor carrier by， in response to a successful reception of the indication at the second time point， determining that the secondary anchor carrier is present.

In some implementations， the indication may further indicate a frequency location of the secondary anchor carrier. In these implementations， the terminal device 120 may， in response to determining that the secondary anchor carrier is present， determine， based on the indication， the frequency location of the secondary anchor carrier for the reception of the system information.

In some implementations， the terminal device 120 may receive secondary synchronization information on the secondary anchor carrier. The secondary synchronization information and the indication may be generated from a same scrambling sequence.

In some implementations， the terminal device 120 may receive secondary synchronization information on the primary anchor carrier at a third time point that is different from the first and second time points. The secondary synchronization information and the indication may be generated from different scrambling sequences.

In some implementations， the communication system may include a Narrowband-Intemet of Things (NB-IoT) communication system.

In some implementations， the first time point may be corresponding to a first subframe number in a radio frame. In these implementations， the terminal device 120 may determine a second subframe number in the radio frame for the second time point based on the first subframe number and a time length between the first and second time points. The terminal device 120 may further determine， based on the determined second subframe number， an operating mode for the communication system.

It is to be understood that all operations and features related to the terminal device 120 described above with reference to Figs. 2 to 5C are likewise applicable to the method 400 and have similar effects. For the purpose of simplification， the details will be omitted.

Fig. 7 shows a flowchart of an example process 700 in accordance with some implementations of the present disclosure. The process 700 can be implemented at the network device 110 as shown in Fig. 1. For the purpose of discussion， the process 700 will be described from the perspective of the network device 110 with reference to Fig. 1.

At block 710， the network device 110 transmits， to a terminal device， primary synchronization information on a primary anchor carrier at a first time point. At block 720， the network device 110 determines presence of a secondary anchor carrier based on an operating mode of the communication system. The secondary anchor carrier is to be used for transmission of system information to the terminal device. At block 730， the network device 110 transmits， based on the presence of the secondary anchor carrier， indication information to the terminal device on the primary anchor carrier at a second time point， the second time point being different from the first time point.

In some implementations， the network device 110 may transmit the indication information by determining cyclic shift values based on the presence of the secondary anchor carrier； generating a plurality of signals including secondary synchronization information based on the determined cyclic shift values； and transmitting the plurality of generated signals on the primary anchor carrier at the second time point.

In some implementations， the network device 110 may determine the cyclic shift values by， in response to determining that the secondary anchor carrier is to be present， determining the cyclic shift values further based on a frequency location of the secondary anchor carrier.

In some implementations， the network device 110 may determine the cyclic shift values by determining a first cyclic shift value among the cyclic shift values based on a frequency offset between the frequency location of the secondary anchor carrier and a frequency location of the primary anchor carrier； and determining a second cyclic shift value among the cyclic shift values based on an offset direction from the frequency location of the primary anchor cartier to the frequency location of the secondary anchor carrier.

In some implementations， the network device 110 may transmit the indication information by， in response to determining that the secondary anchor carrier is present， transmitting， on the primary anchor carrier at the second time point， an indication that the secondary anchor carrier is present.

In some implementations， the network device 110 may further transmit secondary synchronization information on the secondary anchor carrier. The secondary synchronization information and the indication are generated from a same scrambling sequence.

In some implementations， the network device 110 may further transmit transmitting secondary synchronization information on the primary anchor carrier at a third time point that is different from the first and second time points. The secondary synchronization information and the indication are generated from different scrambling sequences.

In some implementations， the network device 110 may determine the presence of the secondary anchor carrier by determining the presence of the secondary anchor carrier further based on a configuration of downlink subframes.

In some implementations， the communication system may include a Narrowband-Internet of Things (NB-IoT) communication system.

It is to be understood that all operations and features related to the network device 110 described above with reference to Figs. 2 to 5C are likewise applicable to the method 500 and have similar effects. For the purpose of simplification， the details will be omitted.

5. Example Device

Fig. 8 is a simplified block diagram of a device 800 that is suitable for implementing implementations of the present disclosure. The device 800 can be considered as a further example implementation of the terminal device 120 or the network device 110 as shown in Figs. 1 and 2. Accordingly， the device 800 can be implemented at or as at least a part of the terminal device 120 or the network device 110.

As shown， the device 800 includes a processor 810， a memory 820 coupled to the processor 810， a suitable transmitter (TX) and receiver (RX) 840 coupled to the processor 810， and a communication interface coupled to the TX/RX 840. The memory 820 stores at least a part of a program 830. The TX/RX 840 is for bidirectional communications. The TX/RX 840 has at least one antenna to facilitate communication， though in practice an Access Node mentioned in this application may have several ones. The communication interface may represent any interface that is necessary for communication with other network elements， such as X2 interface for bidirectional communications between eNBs， S1 interface for communication between a Mobility Management Entity (MME) /Serving Gateway (S-GW) and the eNB， Un interface for communication between the eNB and a relay node (RN) ， or Uu interface for communication between the eNB and a terminal device.

The program 830 is assumed to include program instructions that， when executed by the associated processor 810， enable the device 800 to operate in accordance with the implementations of the present disclosure， as discussed herein with reference to Figs. 2 to 7. The implementations herein may be implemented by computer software executable by the processor 810 of the device 800， or by hardware， or by a combination of software and hardware. The processor 810 may be configured to implement various implementations of the present disclosure. Furthermore， a combination of the processor 810 and memory 820 may form processing means 850 adapted to implement various implementations of the present disclosure.

The memory 820 may be of any type suitable to the local technical network and may be implemented using any suitable data storage technology， such as a non-transitory computer readable storage medium， semiconductor based memory devices， magnetic memory devices and systems， optical memory devices and systems， fixed memory and removable memory， as non-limiting examples. While only one memory 820 is shown in the device 800， there may be several physically distinct memory modules in the device 800. The processor 810 may be of any type suitable to the local technical network， and may include one or more of general purpose computers， special purpose computers， microprocessors， digital signal processors (DSPs) and processors based on multicore processor architecture， as non-limiting examples. The device 800 may have multiple processors， such as an application specific integrated circuit chip that is slaved in time to a clock which synchronizes the main processor.

The components included in the apparatuses and/or devices of the present disclosure may be implemented in various manners， including software， hardware， firmware， or any combination thereof. In one implementation， one or more units may be implemented using software and/or firmware， for example， machine-executable instructions stored on the storage medium. In addition to or instead of machine-executable instructions， parts or all of the units in the apparatuses and/or devices may be implemented， at least in part， by one or more hardware logic components. For example， and without limitation， illustrative types of hardware logic components that can be used include Field-programmable Gate Arrays (FPGAs) ， Application-specific Integrated Circuits (ASICs) ， Application-specific Standard Products (ASSPs) ， System-on-a-chip systems (SOCs) ， Complex Programmable Logic Devices (CPLDs) ， and the like.

Generally， various implementations of the present disclosure may be implemented in hardware or special purpose circuits， software， logic or any combination thereof. Some aspects may be implemented in hardware， while other aspects may be implemented in firmware or software which may be executed by a controller， microprocessor or other computing device. While various aspects of implementations of the present disclosure are illustrated and described as block diagrams， flowcharts， or using some other pictorial representation， it will be appreciated that the blocks， apparatus， systems， techniques or methods described herein may be implemented in， as non-limiting examples， hardware， software， firmware， special purpose circuits or logic， general purpose hardware or controller or other computing devices， or some combination thereof.

The present disclosure also provides at least one computer program product tangibly stored on a non-transitory computer readable storage medium. The computer program product includes computer-executable instructions， such as those included in program modules， being executed in a device on a target real or virtual processor， to carry out the process or method as described above with reference to any of Figs. 2， 6， and 7. Generally， program modules include routines， programs， libraries， objects， classes， components， data structures， or the like that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various implementations. Machine-executable instructions for program modules may be executed within a local or distributed device. In a distributed device， program modules may be located in both local and remote storage media.

Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. These program codes may be provided to a processor or controller of a general purpose computer， special purpose computer， or other programmable data processing apparatus， such that the program codes， when executed by the processor or controller， cause the functions/operations specified in the flowcharts and/or block diagrams to be implemented. The program code may execute entirely on a machine， partly on the machine， as a stand-alone software package， partly on the machine and partly on a remote machine or entirely on the remote machine or server.

The above program code may be embodied on a machine readable medium， which may be any tangible medium that may contain， or store a program for use by or in connection with an instruction execution system， apparatus， or device. The machine readable medium may be a machine readable signal medium or a machine readable storage medium. A machine readable medium may include but not limited to an electronic， magnetic， optical， electromagnetic， infrared， or semiconductor system， apparatus， or device， or any suitable combination of the foregoing. More specific examples of the machine readable storage medium would include an electrical connection having one or more wires， a portable computer diskette， a hard disk， a random access memory (RAM) ， a read-only memory (ROM) ， an erasable programmable read-only memory (EPROM or Flash memory) ， an optical fiber， a portable compact disc read-only memory (CD-ROM) ， an optical storage device， a magnetic storage device， or any suitable combination of the foregoing.

Further， while operations are depicted in a particular order， this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order， or that all illustrated operations be performed， to achieve desirable results. In certain circumstances， multitasking and parallel processing may be advantageous. Likewise， while several specific implementation details are contained in the above discussions， these should not be construed as limitations on the scope of the present disclosure， but rather as descriptions of features that may be specific to particular implementations. Certain features that are described in the context of separate implementations may also be implemented in combination in a single implementation. Conversely， various features that are described in the context of a single implementation may also be implemented in multiple implementations separately or in any suitable sub-combination.

Although the present disclosure has been described in language specific to structural features and/or methodological acts， it is to be understood that the present disclosure defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather， the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

A method implemented by a terminal device in a communication system， comprising：

in response to receiving primary synchronization information from a network device at a first time point， identifying a primary anchor carrier on which the primary synchronization information is detected；

detecting indication information from the network device on the identified primary anchor carrier at a second time point， the second time point being different from the first time point； and

determining， based on the detection of the indication information， presence of a secondary anchor carrier for reception of system information.
The method of claim 1， wherein detecting the indication information comprises：

receiving a plurality of signals including secondary synchronization information on the primary anchor carrier.
The method of claim 2， wherein determining presence of a secondary anchor carrier comprises：

determining cyclic shift values for generation of the plurality of signals； and

determining the presence of the secondary anchor carrier based on the cyclic shift values.
The method of claim 3， wherein determining the presence of the secondary anchor carrier based on the cyclic shift values comprises：

in response to a determination that the cyclic shift values match a set of predetermined values， determining that the secondary anchor carrier is present.
The method of claim 4， further comprising：

in response to determining that the secondary anchor carrier is present， determining a frequency location of the secondary anchor carrier based on the set of predetermined values， wherein the frequency location is to be used to receive the system information.
The method of claim 4， wherein the set of predetermined values are sorted in a predetermined order， the method further comprising：

sorting the cyclic shift values in the predetermined order for comparison with the set of predetermined values.
The method of claim 3， wherein determining the presence of the secondary anchor carrier based on the cyclic shift values comprises：

in response to a determination that a first cyclic shift value among the cyclic shift values matches a first predetermined value， determining that the secondary anchor carrier is present.
The method of claim 7， further comprising：

in response to determining that the secondary anchor carrier is present， obtaining a frequency offset associated with the first predetermined value；

in response to a determination that a second cyclic shift value among the cyclic shift values matches a second predetermined value， obtaining an offset direction associated with the second predetermined value； and

determining a frequency location of the secondary anchor carrier by offsetting a frequency location of the primary anchor carrier by the frequency offset in the identified offset direction， wherein the frequency location is to be used to receive the system information.
The method of claim 1， wherein detecting the indication information comprises：

monitoring， on the primary anchor carrier at the second time point， an indication that the secondary anchor carrier is present.
The method of claim 9， wherein determining presence of a secondary anchor carrier comprises：

in response to a successful reception of the indication at the second time point， determining that the secondary anchor carrier is present.
The method of claim 10， wherein the indication further indicates a frequency location of the secondary anchor carrier， the method further comprising：

in response to determining that the secondary anchor carrier is present， determining， based on the indication， the frequency location of the secondary anchor carrier for the reception of the system information.
The method of claim 9， further comprising：

receiving secondary synchronization information on the secondary anchor carrier， wherein the secondary synchronization information and the indication are generated from a same scrambling sequence.
The method of claim 9， further comprising：

receiving secondary synchronization information on the primary anchor carrier at a third time point that is different from the first and second time points， wherein the secondary synchronization information and the indication are generated from different scrambling sequences.
The method of claim 1， wherein the communication system includes a Narrowband-Internet of Things (NB-IoT) communication system.
The method of claim 1， wherein the first time point is corresponding to a first subframe number in a radio frame， the method further comprising：

determining a second subframe number in the radio frame for the second time point based on the first subframe number and a time length between the first and second time points； and

determining， based on the determined second subframe number， an operating mode for the communication system.
A method implemented by a network device in a communication system， comprising：

transmitting， to a terminal device， primary synchronization information on a primary anchor carrier at a first time point；

determining presence of a secondary anchor carrier based on an operating mode of the communication system， wherein the secondary anchor carrier is to be used for transmission of system information to the terminal device； and

transmitting， based on the presence of the secondary anchor carrier， indication information to the terminal device on the primary anchor carrier at a second time point， the second time point being different from the first time point.
The method of claim 16， wherein transmitting the indication information comprises：

determining cyclic shift values based on the presence of the secondary anchor carrier；

generating a plurality of signals including secondary synchronization information based on the determined cyclic shift values； and

transmitting the plurality of generated signals on the primary anchor carrier at the second time point.
The method of claim 17， wherein determining the cyclic shift values further comprises：

in response to determining that the secondary anchor carrier is to be present， determining the cyclic shift values further based on a frequency location of the secondary anchor carrier.
The method of claim 18， wherein determining the cyclic shift values further based on a frequency location of the secondary anchor carrier comprises：

determining a first cyclic shift value among the cyclic shift values based on a frequency offset between the frequency location of the secondary anchor carrier and a frequency location of the primary anchor carrier； and

determining a second cyclic shift value among the cyclic shift values based on an offset direction from the frequency location of the primary anchor carrier to the frequency location of the secondary anchor carrier.
The method of claim 16， wherein transmitting the indication information comprises：

in response to determining that the secondary anchor carrier is present， transmitting， on the primary anchor carrier at the second time point， an indication that the secondary anchor carrier is present.
The method of claim 20， further comprising：

transmitting secondary synchronization information on the secondary anchor carrier， wherein the secondary synchronization information and the indication are generated from a same scrambling sequence.
The method of claim 20， further comprising：

transmitting secondary synchronization information on the primary anchor carrier at a third time point that is different from the first and second time points， wherein the secondary synchronization information and the indication are generated from different scrambling sequences.
The method of claim 16， wherein determining the presence of the secondary anchor carrier further comprises：

determining the presence of the secondary anchor carrier further based on a configuration of downlink subframes.
The method of claim 16， wherein the communication system includes a Narrowband-Internet of Things (NB-IoT) communication system.
A terminal device， comprising：

a processor； and

a memory coupled to the processor and storing instructions thereon， the instructions， when executed by the processor， causing the terminal device to：

in response to receiving primary synchronization information from a network device at a first time point， identify a primary anchor carrier on which the primary synchronization information is detected；

detect indication information from the network device on the identified primary anchor carrier at a second time point， the second time point being different from the first time point； and

determine， based on the detection of the indication information， presence of a secondary anchor carrier for reception of system information.
The terminal device of claim 25， wherein the instructions， when executed by the processor， cause the terminal device to：

receive a plurality of signals including secondary synchronization information on the primary anchor carrier.
The terminal device of claim 26， wherein the instructions， when executed by the processor， cause the terminal device to：

determine cyclic shift values for generation of the plurality of signals； and

determine the presence of the secondary anchor carrier based on the cyclic shift values.
The terminal device of claim 27， wherein the instructions， when executed by the processor， cause the terminal device to：

in response to a determination that the cyclic shift values match a set of predetermined values， determine that the secondary anchor carrier is present.
The terminal device of claim 28， wherein the instructions， when executed by the processor， further cause the terminal device to：

in response to determining that the secondary anchor carrier is present， determine a frequency location of the secondary anchor carrier based on the set of predetermined values， wherein the frequency location is to be used to receive the system information.
The terminal device of claim 28， wherein the set of predetermined values are sorted in a predetermined order， and wherein the instructions， when executed by the processor， further cause the terminal device to：

sort the cyclic shift values in the predetermined order for comparison with the set of predetermined values.
The terminal device of claim 27， wherein the instructions， when executed by the processor， cause the terminal device to：

in response to a determination that a first cyclic shift value among the cyclic shift values matches a first predetermined value， determine that the secondary anchor carrier is present.
The terminal device of claim 31， wherein the instructions， when executed by the processor， further cause the terminal device to：

in response to determining that the secondary anchor carrier is present， obtain a frequency offset associated with the first predetermined value；

in response to a determination that a second cyclic shift value among the cyclic shift values matches a second predetermined value， obtain an offset direction associated with the second predetermined value； and

determine a frequency location of the secondary anchor carrier by offsetting a frequency location of the primary anchor carrier by the frequency offset in the identified offset direction， wherein the frequency location is to be used to receive the system information.
The terminal device of claim 25， wherein the instructions， when executed by the processor， cause the terminal device to：

monitor， on the primary anchor carrier at the second time point， an indication that the secondary anchor carrier is present.
The terminal device of claim 33， wherein the instructions， when executed by the processor， cause the terminal device to：

in response to a successful reception of the indication at the second time point， determine that the secondary anchor carrier is present.
The terminal device of claim 34， wherein the indication further indicates a frequency location of the secondary anchor carrier， and wherein the instructions， when executed by the processor， further cause the terminal device to：

in response to determining that the secondary anchor carrier is present， determine， based on the indication， the frequency location of the secondary anchor carrier for the reception of the system information.
The terminal device of claim 33， wherein the instructions， when executed by the processor， further cause the terminal device to：

receive secondary synchronization information on the secondary anchor carrier， wherein the secondary synchronization information and the indication are generated from a same scrambling sequence.
The terminal device of claim 33， wherein the instructions， when executed by the processor， further cause the terminal device to：

receive secondary synchronization information on the primary anchor carrier at a third time point that is different from the first and second time points， wherein the secondary synchronization information and the indication are generated from different scrambling sequences.
The terminal device of claim 25， wherein the communication system includes a Narrowband-Internet of Things (NB-IoT) communication system.
The terminal device of claim 25， wherein the first time point is corresponding to a first subframe number in a radio frame， and wherein the instructions， when executed by the processor， further cause the terminal device to：

determine a second subframe number in the radio frame for the second time point based on the first subframe number and a time length between the first and second time points； and

determine， based on the determined second subframe number， an operating mode for the communication system.
A network device， comprising：

a processor； and

a memory coupled to the processor and storing instructions thereon， the instructions， when executed by the processor， causing the network device to：

transmit， to a terminal device， primary synchronization information on a primary anchor carrier at a first time point；

determining presence of a secondary anchor carrier based on an operating mode of the communication system， wherein the secondary anchor carrier is to be used for transmission of system information to the terminal device； and

transmit， based on the presence of the secondary anchor carrier， indication information to the terminal device on the primary anchor carrier at a second time point， the second time point being different from the first time point.
The network device of claim 40， wherein the instructions， when executed by the processor， cause the network device to：

determine cyclic shift values based on the presence of the secondary anchor carrier；

generate a plurality of signals including secondary synchronization information based on the determined cyclic shift values； and

transmit the plurality of generated signals on the primary anchor carrier at the second time point.
The network device of claim 41， wherein the instructions， when executed by the processor， cause the network device to：

in response to determining that the secondary anchor carrier is to be present， determine the cyclic shift values further based on a frequency location of the secondary anchor carrier.
The network device of claim 42， wherein the instructions， when executed by the processor， cause the network device to：

determine a first cyclic shift value among the cyclic shift values based on a frequency offset between the frequency location of the secondary anchor carrier and a frequency location of the primary anchor carrier； and

determine a second cyclic shift value among the cyclic shift values based on an offset direction from the frequency location of the primary anchor carrier to the frequency location of the secondary anchor carrier.
The network device of claim 40， wherein the instructions， when executed by the processor， cause the network device to：

in response to determining that the secondary anchor carrier is present， transmit， on the primary anchor carrier at the second time point， an indication that the secondary anchor carrier is present.
The network device of claim 44， wherein the instructions， when executed by the processor， further cause the network device to：

transmit secondary synchronization information on the secondary anchor carrier， wherein the secondary synchronization information and the indication are generated from a same scrambling sequence.
The network device of claim 44， wherein the instructions， when executed by the processor， further cause the network device to：

transmit secondary synchronization information on the primary anchor carrier at a third time point that is different from the first and second time points， wherein the secondary synchronization information and the indication are generated from different scrambling sequences.
The network device of claim 40， wherein the instructions， when executed by the processor， cause the network device to：

determine the presence of the secondary anchor carrier further based on a configuration of downlink subframes.
The network device of claim 40， wherein the communication system includes a Narrowband-Internet of Things (NB-IoT) communication system.
A computer readable medium having instructions stored thereon， the instructions， when executed on at least one processor， causing the at least one processor to carry out the method according to any of claims 1 to 15.
A computer readable medium having instructions stored thereon， the instructions， when executed on at least one processor， causing the at least one processor to carry out the method according to any of claims 16 to 24.