WO2020029924A1

WO2020029924A1 - Transmission resource sharing

Info

Publication number: WO2020029924A1
Application number: PCT/CN2019/099294
Authority: WO
Inventors: Virgile Garcia; Umer Salim; Bruno Jechoux
Original assignee: JRD Communication (Shenzhen) Ltd.
Priority date: 2018-08-08
Filing date: 2019-08-05
Publication date: 2020-02-13
Also published as: GB2576195B; GB201812919D0; GB2576195A; CN112272956A; CN112272956B

Abstract

Methods for providing fair access to shared transmission resources between multiple devices. A set of devices belonging to a group select a common value for a contention window size to enable fair competition with other unrelated devices for transmission resources.

Description

Transmission Resource Sharing

Technical Field

The following disclosure relates to sharing transmission resources in a cellular wireless network, and in particular to the sharing of unlicensed transmission resources between cellular and other devices.

Background

Wireless communication systems, such as the third-generation (3G) of mobile telephone standards and technology are well known. Such 3G standards and technology have been developed by the Third Generation Partnership Project (3GPP) . The 3rd generation of wireless communications has generally been developed to support macro-cell mobile phone communications. Communication systems and networks have developed towards a broadband and mobile system.

In cellular wireless communication systems User Equipment (UE) is connected by a wireless link to a Radio Access Network (RAN) . The RAN comprises a set of base stations which provide wireless links to the UEs located in cells covered by the base station, and an interface to a Core Network (CN) which provides overall network control. As will be appreciated the RAN and CN each conduct respective functions in relation to the overall network. For convenience the term cellular network will be used to refer to the combined RAN &CN, and it will be understood that the term is used to refer to the respective system for performing the disclosed function.

The 3rd Generation Partnership Project has developed the so-called Long Term Evolution (LTE) system, namely, an Evolved Universal Mobile Telecommunication System Territorial Radio Access Network, (E-UTRAN) , for a mobile access network where one or more macro-cells are supported by a base station known as an eNodeB or eNB (evolved NodeB) . More recently, LTE is evolving further towards the so-called 5G or NR (new radio) systems where one or more cells are supported by a base station known as a gNB. NR is proposed to utilise an Orthogonal Frequency Division Multiplexed (OFDM) physical transmission format.

The NR protocols are intended to offer options for operating in unlicensed radio bands, to be known as NR-U. When operating in an unlicensed radio band the gNB and UE must compete with other devices for physical medium/resource access. For example, Wi-Fi, NR-U, and LAA may utilise the same physical resources.

In order to share resources a device (for example, a gNB or UE) monitors the available resources and only commences a transmission if there is no conflict with another device already utilising the resources. This is known as a Clear Channel Assessment (CCA) . This is typically performed using a Listen Before Talk (LBT) protocol in which a device “listens” for transmissions on the resources for a period to determine if other devices are transmitting on those resources. If no transmissions are detected above any applicable thresholds, the LBT process is successful and the resources are “won” . The device gNB or UE gains access to the resources for up to a Maximum Channel Occupancy Time (MCOT) provided there is no interruption of transmissions for more than a pre-defined interval (for example 16μs) .

If a CCA indicates resources are occupied, the device waits until the transmission stops and then resumes the LBT process until a “backoff” time has expired (typically monitored using a “backoff counter” ) . This ensures there will be a minimum time that the resources are clear for between transissions. The duration of the contention window is typically selected at random by each device within a defined range to mitigate conflicts between multiple devices trying to transmit at the same time.

In a system requiring a CCA prior to transmission, each device applies the LBT period during the contention window and can only start transmitting at the end of that contention window if the LBT process is successful.

Figure 1 shows an example in which a Wi-Fi device is transmitting when two devices/users (User 1 and User 2) initially seek access to the same resources. The first device picks the shorter back-off time, and hence starts transmitting first. The second device detects the first device’s transmission during its LBT period and hence cannot start transmitting. The first device thus prevents the second device from transmitting.

In systems with uncoordinated, equal, devices this process ensures equal prospects of access for all devices. However, access is distributed less fairly if a number of devices from one system or group are attempting to utilise the resources. For example, a number of UEs may be attempting to use the resources for connections to a cellular base station. If there are N devices, N LBT durations will be selected by the UEs, whereas a single pair of Wi-Fi devices they will only obtain a single LBT duration for access to the resources. The Wi-Fi devices therefore only have a 1 in (N+1) chance of obtaining access to the resources.

If N is large the Wi-Fi devices are unfairly prevented from access to the resources by the cellular system (which is effectively a single group of devices) . The probability of a Wi-Fi device obtaining access to resources, in competition with N cellular devices, can be calculated as: -

Where C _win is the maximum duration of the contention window (the same Wi-Fi and cellular devices) . In order to access the resources the Wi-Fi device must draw a time (t _wifi) shorter than the duration (t _u) picked by all N users. Values from this equation are plotted in Figure 2, with the probability of success by the Wi-Fi device on the y-axis, and the contention window size drawn by the Wi-Fi device on the x-axis.

The above examples are intended for example only, and precise fairness and utilisation may vary.

Furthermore, if one of the cellular devices wins access, other cellular devices of the same system will be prevented from accessing the resources even though they could potentially share those resources due to their wireless protocols.

There is therefore a requirement for a system which permits fair access to transmission resources between device types and groups.

An improved LBT process is thus required to provide fair sharing of resources.

Summary

This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

There is provided a method of resource sharing in a cellular communication system, the method performed by a set of devices and comprising the steps of at each device generating a seed for a pseudo-random number generator algorithm, wherein the same seed is generated at each device, utilising the seed with the pseudo-random number generator algorithm to generate the first number in the sequence of numbers that would be generated by the algorithm from the seed; generating a contention window size based on the first number generated by the algorithm; and performing a listen before talk procedure and commencing transmission at the end of the contention window size if the listen before talk procedure indicates transmission resources are accessible.

Each device of the set of devices may be a UE.

Each UE may be connected to a common base station.

Each device may be a base station.

The seed may be generated based on a time-varying parameter.

The seed may be generated based on a system time value.

The seed may also be generated based on at least one of an identity value known to each of the set of devices, a frequency reference for resources on which the devices wish to transmit, and common data values known to all devices.

The seed may be based at least partly on information received from the base station.

The algorithm may be configured by a transmission from the base station.

There is also provided a method of resource sharing in a cellular communication system, the method performed by a set of devices and comprising the steps of at each device generating a contention window size utilising a predefined table of contention window sizes, wherein the contention window size is selected from the predefined table utilising an index and wherein each device utilises the same index and selects the same contention window size; and performing a listen before talk procedure and commencing transmission at the end of the contention window size if the listen before talk procedure indicates transmission resources are accessible.

Each device of the set of devices may be a UE.

Each UE may be connected to a common base station.

Each device may be a base station.

The index may be based on a time-varying parameter.

The index may be based on a system time value.

The index may also be based on at least one of an identity value known to each of the set of devices, a frequency reference for resources on which the devices wish to transmit, and common data values known to all devices.

The index may be based at least partly on information received from the base station.

There is also provided a set of devices, or set of UEs, configured to perform the above methods.

The non-transitory computer readable medium may comprise at least one from a group consisting of: a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a Read Only Memory, a Programmable Read Only Memory, an Erasable Programmable Read Only Memory, EPROM, an Electrically Erasable Programmable Read Only Memory and a Flash memory.

Brief description of the drawings

Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. Like reference numerals have been included in the respective drawings to ease understanding.

Figure 1 shows an example of a contention window;

Figure 2 shows a chart of access probability;

Figure 3 shows a schematic diagram of parts of a cellular network; and

Figure 4 shows a flow-chart of a method of defining a contention window.

Detailed description of the preferred embodiments

Those skilled in the art will recognise and appreciate that the specifics of the examples described are merely illustrative of some embodiments and that the teachings set forth herein are applicable in a variety of alternative settings.

The following disclosure provides an improved mechanism to fairly share resources between devices.

Figure 3 shows a schematic diagram of three base stations (for example, eNB or gNBs depending on the particular cellular standard and terminology) forming a cellular network. Typically, each of the base stations will be deployed by one cellular network operator to provide geographic coverage for UEs in the area. The base stations form a Radio Area Network (RAN) . Each base station provides wireless coverage for UEs in its area or cell. The base stations are interconnected via the X2 interface and are connected to the core network via the S1 interface. As will be appreciated only basic details are shown for the purposes of exemplifying the key features of a cellular network.

The base stations each comprise hardware and software to implement the RAN’s functionality, including communications with the core network and other base stations, carriage of control and data signals between the core network and UEs, and maintaining wireless communications with UEs associated with each base station. The core network comprises hardware and software to implement the network functionality, such as overall network management and control, and routing of calls and data.

As set out below, a mechanism is provided to co-ordinate LBT or contention window durations to provider a fairer sharing of resources between devices. A set of UEs in a cellular network may be considered a single group of devices seeking access to transmission resources, and hence may coordinate their access requests to allow fair access between the group and different devices. In order to respect regulations for using unlicensed resources each UE must perform its own LBT process before trying to transmit. However, that LBT process can be co-ordinated between UEs such that all UEs have the same listening time/contention window and hence start their transmissions at the same time. That is, each UE may select the same contention window size for a transmission attempt.

UEs in a group may therefore be configured to select the same duration for an LBT period/contention window, and then to transmit at the end of that period. The group of UEs may be all UEs of a cell, beam, group of cells, group of beams, or subset thereof, or other grouping which may be configured at a system level. Although all UEs commence transmission at the same time, cellular systems are configured and designed to effectively share resources between the UEs and hence the system operates as would be expected. Since all UEs are part of the same group, any interference between those UEs is a matter for the system itself and is not impacted by regulations for the use of unlicensed resources which apply to sharing between unrelated devices.

Since all relevant devices select the same contention window size, rather than an unrelated device competing against N other contention window sizes for access, that unrelated device is only competing against 1 window size. That is, if the unrelated device selects a shorter duration than that used by the cellular devices, the unrelated device gains access and none of the cellular devices do. Whereas if the cellular device picks a shorter duration, all of them gain access, and the unrelated device does not. The unrelated device thus has a 1 in 2 chance of gaining access (if there are only two devices or groups competing) , even though there can be an arbitrary number of cellular devices. Equal chances of access are thus granted to all competing devices or groups.

The random nature of the contention window is important for fair access to the transmission resources and hence a static value cannot be pre-configured. Furthermore, transmission of a value to or between UEs each time a contention window is required will need a large signalling overhead which is unlikely to be practical, thus precluding central generation.

Random values for parameters such as the LBT duration are typically selected utilising a pseudo-random algorithm which generates a distribution of values which is close to truly randomised values, but which, for a given seed, always generates the same sequence of values. Utilising a common seed and synchronising the algorithms of a plurality of devices thus allows alignment of the values generated.

A seed for an algorithm to generate durations may be transmitted to each UE through higher-layer signalling (for example RRC) . This reduces overhead compared to transmitting individual values as only one value needs to be transmitted to each UE which can then be utilised to generate a number of durations. Other signalling types, such as DCI, may be utilised. DCI may enable more dynamic configuration as DCI messages are intended for dynamic configuration and may enable more flexibility in the definition of groups, both statically and dynamically over time.

Each UE must utilise the same algorithm, which may be predefined by the standards, or selected and signalled to each UE with or separate from the seed value. The actual value of a seed value is not important, provided the same value is used by all UEs in a group.

Since it is the sequence of values generated by an algorithm that is predictable, the values generated by independent devices will only be consistent if the same number of values have been generated by each device; that is the algorithms must be synchronised to be at the same point in their sequences. In the current context, if one device requires more contention window durations than another, even if they have been seeded with the same value, the algorithms will lose synchronisation and will generate different values. For example, a first device may succeed in an access effort and does not thus require a contention window, whereas a second device may not succeed and does require a contention window. The two devices are then at different positions in the sequence, and the algorithm cannot be used to reliably generate the same contention window at a future opportunity.

The above problem can be solved by synchronising the algorithms at intervals, but this may be difficult to coordinate, particularly for UEs where coordination may be harder. It would be necessary to resynchronise all devices as soon as at least device loses synchronisation. Regular synchronisation also requires additional network overhead.

The loss of synchronisation may be addressed by using a new, common, seed for each value to be generated. Provided each device utilises the same seed they will generate the same pseudo-random value (the first in the sequence) at each occasion. This effectively re-synchronises each algorithm at every generated value because only the first value of the sequence is utilised and so there is no opportunity for the algorithms to lose synchronisation.

Examples of common reference values to use as, or in the generation of, the seed may include a time reference, a frequency reference, an identification known to all relevant devices (for example, cell ID, RNTI, group ID) ) , or any data known to all devices, for example part of a common signalling message.

In order to ensure the value utilised is random the seed value must change over time such that it is different for each contention window generated (otherwise, if the same seed value is used the first value generated in each sequence will be the same) . Since the first value in the sequence is utilised if the same seed is used twice, the same value will be generated. It appears the most straightforward reference to utilise is the system time value, optionally combined with other values such as an ID value.

All devices in a network should have a common time value and so utilising a time reference as a seed should permit all devices to retain a common seed value. Utilising a resource identifier provides a common reference for the devices sharing that resource, for example in MU-MIMO or frequency multiplexed devices, frequency or other relevant resource identifier may be utilised.

Utilising identification numbers allows group-specific seeds to be utilised according to the UEs grouped until the particular identification number utilised. Such identifiers may enable devices (e.g. UEs) that are related to different cells to share the same resources where they do not belong to a common group. This may be particularly relevant for uplink transmissions where it may be desirable for frequency resources to be shared amongst UEs in different cells.

Combinations of various values and parameters, or parts therefore, may be utilised as the seed values. The actual value of seed is not relevant, and hence the most convenient source can be utilised.

Where devices in different cells are utilising resource sharing and common contention windows, it is assumed that the slot timing of the cells is coordinated between cells.

Figure 4 shows a flow chart of an example according to the above disclosure. At step 400 a device requires a contention window. At step 401 a seed is generated for use in the relevant algorithm. As set out above the seed may be based on one or more common reference values known to all relevant devices. For example, a time reference optionally combined with other values such as an ID value. At step 402 the contention window is generated utilising the seed.

In a modified system, the generation algorithm and seed can be replaced by an index to a predefined table of contention window sizes, thus simplifying the computation of random values. The reference may also be to a sequence of values which users can use in case of a need for more than one contention window before a new value is received. The lookup process would replace the calculation of a window size using an algorithm in the foregoing description. For example, the index to the table may be derived from a system time value such that all devices will select the same entry in the table. The system time value may be used directly or may be modified or combined with other parameters.

The operation of the above processes may be turned on or off for devices, or generally, using network configuration signalling. For example, if a network detects the presence of other devices the process may be activated to ensure fair sharing. Also, the configuration of seed generation can be varied and configured according to groups of devices. New devices may be added or removed from groups as they become active in relevant areas to allow alignment of all devices in the area that may wish to share resources.

The above description has been given with reference to uplink transmissions from UEs connected to a base station, however the same principles apply to other devices and configurations as well. For example, a set of base stations may utilise the process to share downlink resources, or a set of UEs may utilise the techniques for communications between UEs (rather than to a base station) .

Although not shown in detail any of the devices or apparatus that form part of the network may include at least a processor, a storage unit and a communications interface, wherein the processor unit, storage unit, and communications interface are configured to perform the method of any aspect of the present invention. Further options and choices are described below.

The signal processing functionality of the embodiments of the invention especially the gNB and the UE may be achieved using computing systems or architectures known to those who are skilled in the relevant art. Computing systems such as, a desktop, laptop or notebook computer, hand-held computing device (PDA, cell phone, palmtop, etc. ) , mainframe, server, client, or any other type of special or general purpose computing device as may be desirable or appropriate for a given application or environment can be used. The computing system can include one or more processors which can be implemented using a general or special-purpose processing engine such as, for example, a microprocessor, microcontroller or other control module.

The computing system can also include a main memory, such as random access memory (RAM) or other dynamic memory, for storing information and instructions to be executed by a processor. Such a main memory also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by the processor. The computing system may likewise include a read only memory (ROM) or other static storage device for storing static information and instructions for a processor.

The computing system may also include an information storage system which may include, for example, a media drive and a removable storage interface. The media drive may include a drive or other mechanism to support fixed or removable storage media, such as a hard disk drive, a floppy disk drive, a magnetic tape drive, an optical disk drive, a compact disc (CD) or digital video drive (DVD) read or write drive (R or RW) , or other removable or fixed media drive. Storage media may include, for example, a hard disk, floppy disk, magnetic tape, optical disk, CD or DVD, or other fixed or removable medium that is read by and written to by media drive. The storage media may include a computer-readable storage medium having particular computer software or data stored therein.

In alternative embodiments, an information storage system may include other similar components for allowing computer programs or other instructions or data to be loaded into the computing system. Such components may include, for example, a removable storage unit and an interface , such as a program cartridge and cartridge interface, a removable memory (for example, a flash memory or other removable memory module) and memory slot, and other removable storage units and interfaces that allow software and data to be transferred from the removable storage unit to computing system.

The computing system can also include a communications interface. Such a communications interface can be used to allow software and data to be transferred between a computing system and external devices. Examples of communications interfaces can include a modem, a network interface (such as an Ethernet or other NIC card) , a communications port (such as for example, a universal serial bus (USB) port) , a PCMCIA slot and card, etc. Software and data transferred via a communications interface are in the form of signals which can be electronic, electromagnetic, and optical or other signals capable of being received by a communications interface medium.

In this document, the terms ‘computer program product’ , ‘computer-readable medium’a nd the like may be used generally to refer to tangible media such as, for example, a memory, storage device, or storage unit. These and other forms of computer-readable media may store one or more instructions for use by the processor comprising the computer system to cause the processor to perform specified operations. Such instructions, generally 45 referred to as ‘computer program code’ (which may be grouped in the form of computer programs or other groupings) , when executed, enable the computing system to perform functions of embodiments of the present invention. Note that the code may directly cause a processor to perform specified operations, be compiled to do so, and/or be combined with other software, hardware, and/or firmware elements (e.g., libraries for performing standard functions) to do so.

The non-transitory computer readable medium may comprise at least one from a group consisting of: a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a Read Only Memory, a Programmable Read Only Memory, an Erasable Programmable Read Only Memory, EPROM, an Electrically Erasable Programmable Read Only Memory and a Flash memory. In an embodiment where the elements are implemented using software, the software may be stored in a computer-readable medium and loaded into computing system using, for example, removable storage drive. A control module (in this example, software instructions or executable computer program code) , when executed by the processor in the computer system, causes a processor to perform the functions of the invention as described herein.

Furthermore, the inventive concept can be applied to any circuit for performing signal processing functionality within a network element. It is further envisaged that, for example, a semiconductor manufacturer may employ the inventive concept in a design of a stand-alone device, such as a microcontroller of a digital signal processor (DSP) , or application-specific integrated circuit (ASIC) and/or any other sub-system element.

It will be appreciated that, for clarity purposes, the above description has described embodiments of the invention with reference to a single processing logic. However, the inventive concept may equally be implemented by way of a plurality of different functional units and processors to provide the signal processing functionality. Thus, references to specific functional units are only to be seen as references to suitable means for providing the described functionality, rather than indicative of a strict logical or physical structure or organisation.

Aspects of the invention may be implemented in any suitable form including hardware, software, firmware or any combination of these. The invention may optionally be implemented, at least partly, as computer software running on one or more data processors and/or digital signal processors or configurable module components such as FPGA devices.

Thus, the elements and components of an embodiment of the invention may be physically, functionally and logically implemented in any suitable way. Indeed, the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units. Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognise that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term ‘comprising’ does not exclude the presence of other elements or steps.

Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by, for example, a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. Also, the inclusion of a feature in one category of claims does not imply a limitation to this category, but rather indicates that the feature is equally applicable to other claim categories, as appropriate.

Furthermore, the order of features in the claims does not imply any specific order in which the features must be performed and in particular the order of individual steps in a method claim does not imply that the steps must be performed in this order. Rather, the steps may be performed in any suitable order. In addition, singular references do not exclude a plurality. Thus, references to ‘a’ , ‘an’ , ‘first’ , ‘second’ , etc. do not preclude a plurality.

Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognise that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term ‘comprising’ or “including” does not exclude the presence of other elements.

Claims

A method of resource sharing in a cellular communication system, the method performed by a set of devices and comprising the steps of

at each device generating a seed for a pseudo-random number generator algorithm, wherein the same seed is generated at each device,

utilising the seed with the pseudo-random number generator algorithm to generate the first number in the sequence of numbers that would be generated by the algorithm from the seed;

generating a contention window size based on the first number generated by the algorithm; and

performing a listen before talk procedure and commencing transmission at the end of the contention window size if the listen before talk procedure indicates transmission resources are accessible.
A method according to claim 1, wherein each device of the set of devices is a UE.
A method according to claim 2, wherein each UE is connected to a common base station.
A method according to claim 1, wherein each device is a base station.
A method according to any preceding claim, wherein the seed is generated based on a time-varying parameter.
A method according to any preceding claim, wherein the seed is generated based on a system time value.
A method according to claim 6, wherein the seed is also generated based on at least one of an identity value known to each of the set of devices, a frequency reference for resources on which the devices wish to transmit, and common data values known to all devices.
A method according to claim 3, wherein the seed is based at least partly on information received from the base station.
A method according to claim 3, wherein the algorithm is configured by a transmission from the base station.
A method of resource sharing in a cellular communication system, the method performed by a set of devices and comprising the steps of

at each device generating a contention window size utilising a predefined table of contention window sizes, wherein the contention window size is selected from the predefined table utilising an index and wherein each device utilises the same index and selects the same contention window size; and

performing a listen before talk procedure and commencing transmission at the end of the contention window size if the listen before talk procedure indicates transmission resources are accessible.
A method according to claim 10 wherein each device of the set of devices is a UE.
A method according to claim 11, wherein each UE is connected to a common base station.
A method according to claim 10, wherein each device is a base station.
A method according to any of claims 10 to 13, wherein the index is based on a time-varying parameter.
A method according to any of claims 10 to 14, wherein the index is based on a system time value.
A method according to claim 15, wherein the index is also based on at least one of an identity value known to each of the set of devices, a frequency reference for resources on which the devices wish to transmit, and common data values known to all devices.
A method according to claim 11 or claim 12, wherein the index is based at least partly on information received from the base station.
A set of devices configured to perform the method of any preceding claim.
A set of devices according to claim 18, wherein each device is a UE.