CROSS REFERENCE TO RELATED APPLICATIONS

This application is a 35 U.S.C. § 371 national stage application of PCT International Application No. PCT/SE2016/050907 filed on Sep. 26, 2016, the disclosure and content of which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

Embodiments herein relate generally to a first communications device and to a method therein. In particular, embodiments herein relate to handling of active mode operation in a wireless communications network.

BACKGROUND

Communications devices such as terminals are also known as e.g. User Equipments (UEs), mobile terminals, stations (STAs), wireless devices, wireless communications devices, wireless terminals and/or mobile stations. Terminals are enabled to communicate wirelessly in a wireless communications network, such as a Wireless Local Area Network (WLAN) or a cellular communications network sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two terminals, between a terminal and a regular telephone and/or between a terminal and a server via an access network and possibly one or more core networks, comprised within the wireless communications network.

The above communications devices may further be referred to as mobile telephones, cellular telephones, laptops, tablets or sensors with wireless capability, just to mention some further examples. The communications devices in the present context may be, for example, portable, pocket-storable, hand-held, wall-mounted, computer-comprised, or vehicle-mounted mobile devices. The communications devices are enabled to communicate voice and/or data, via an access network, such as a Radio Access Network (RAN), with another entity, such as e.g. an Access Point (AP), another communications device or a server.

The communications network covers an area, e.g. a geographical area, which is divided into subareas, such as coverage areas, cells or clusters. In a cellular communications network each cell area is served by an access node such as a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. eNodeB (eNB), NodeB, B node, or Base Transceiver Station (BTS), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB, micro eNode B or pico base station, based on transmission power, functional capabilities and thereby also cell size. A cell is the area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the communications devices within range of the base stations. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the communications device. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the communications device to the base station.

A Universal Mobile Telecommunications System (UMTS) is a third generation (3G) telecommunication network, which evolved from the second generation (2G) Global System for Mobile Communications (GSM). The UMTS terrestrial radio access network (UTRAN) is essentially a RAN using wideband code division multiple access (WCDMA) and/or High Speed Packet Access (HSPA) for user equipment. In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks, and investigate enhanced data rate and radio capacity. In some RANs, e.g. as in UMTS, several radio network nodes may be connected, e.g., by landlines or microwave, to a controller node, such as a radio network controller (RNC) or a base station controller (BSC), which supervises and coordinates various activities of the plural radio network nodes connected thereto. This type of connection is sometimes referred to as a backhaul connection. The RNCs and BSCs are typically connected to one or more core networks.

Specifications for the Evolved Packet System (EPS), also called a Fourth Generation (4G) network, have been completed within the 3rd Generation Partnership Project (3GPP) and this work continues in the coming 3GPP releases, for example to specify a Fifth Generation (5G) network. The EPS comprises the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), also known as the Long Term Evolution (LTE) radio access network, and the Evolved Packet Core (EPC), also known as System Architecture Evolution (SAE) core network. E-UTRAN/LTE is a variant of a 3GPP radio access network wherein the radio network nodes are directly connected to the EPC core network rather than to RNCs. In general, in E-UTRAN/LTE the functions of an RNC are distributed between the radio network nodes, e.g. eNodeBs in LTE, and the core network. As such, the RAN of an EPS has an essentially “flat” architecture comprising radio network nodes connected directly to one or more core networks, i.e. they are not connected to RNCs. To compensate for that, the E-UTRAN specification defines a direct interface between the radio network nodes, this interface being denoted the X2 interface.

Multi-antenna techniques can significantly increase the data rates and reliability of a wireless communication system. The performance is in particular improved if both the transmitter and the receiver are equipped with multiple antennas, which results in a Multiple-Input Multiple-Output (MIMO) communication channel. Such systems and/or related techniques are commonly referred to as MIMO systems.

A Wireless Local Area Network (WLAN) is a wireless communications network that links two or more communications devices using a wireless distribution method, such as spread-spectrum or OFDM radio, within a limited area such as a home, school, computer laboratory, or office building. This gives users the ability to move around within a local coverage area and yet still be connected to the communications network. A WLAN can also provide a connection to the wider Internet.

Most modern WLANs are based on the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards and are marketed under the Wi-Fi brand name.

The IEEE 802.11 is a set of Media Access Control (MAC) and Physical layer (PHY) specifications for implementing WLAN communication in the 900 MHz and 2.4, 3.6, 5, and 60 GHz frequency bands. They are created and maintained by the IEEE LAN/MAN Standards Committee (IEEE 802).

In the future, many communications devices, e.g. Internet of Things (loT) devices, are expected to run on battery and thus require power conservation schemes from the wireless communications network they are operating in. Most power conservation schemes, such as the Discontinuous Reception (DRX) in the 3GPP wireless systems such as 3G and 4G, as well as the power save mode in Wi-Fi with Traffic Indication Map (TIM), may be used to define when the IoT device is reachable, or more generally, how to reach the IoT device. To configure these mechanisms in an optimal way, the traffic characteristics need to be understood.

Application characteristics, and higher layer protocols, e.g. the protocols above the Internet Protocol (IP), used, define how often the end device, e.g. the IoT device, needs to be reachable for successful communication. For example, with an application transmitting only seldom and a protocol stack based on the User Datagram Protocol (UDP) and the Constrained Application Protocol (CoAP), the IoT device does not need to be reachable often, unless actuation is performed.

However, when a Transmission Control Protocol (TCP) based stack is used in the same scenario, with an application layer protocol such as the Message Queue Telemetry Transport (MQTT), the IoT device needs to be more responsive for the TCP to work properly, as the TCP expects a bi-directional link to confirm delivery of data.

Delivery of a single packet over the TCP and the UDP is schematically illustrated inFIG. 1.FIG. 1shows how a connection set up is done for the TCP through a three way handshake. The TCP three-way handshake starts with the initiating party sending a synchronization “SYN” message, to which the receiving party answers with a synchronization acknowledgement “SYN-ACK” thus acknowledging the reception of the SYN and sending its own SYN in return. Finally, the initiating party answers with ACK and DATA, which may be sent together. Reception of data is then confirmed with an ACK in the reverse link, i.e. from the receiving party to the initiating party.

To optimize the procedure for high bitrates, the TCP also typically implements delayed ACKs, where the ACK response to data is not sent immediately, but a period of time, e.g. 200 milliseconds in many implementations, is used to wait for more data before replying with an ACK.

Communication in Downlink (DL)

When a TCP connection is initiated in the DL, i.e. from an access point to a communications device, the communications device, e.g. the IoT device, needs to be regularly available for the TCP connection to even start and after that be available for new data as long as it is expected. The current sleeping mechanisms such as DRX and TIM are mainly designed to solve the problem of initial availability.FIG. 2schematically illustrates communications in the downlink from a cloud comprising a clod node to a device such as an STA, using the TCP protocol. InFIG. 2, the upper part is referred to as cloud but it could also be referred to as a server, and the lower part referred to as a device/STA inFIG. 2could also be referred to as a Client. As depicted in theFIG. 2, in order to optimize the sleeping, the system should be aware of the TCP Round Trip Time (RTT). The RTT is the length of time it takes for a signal to be sent plus the length of time it takes for an acknowledgment of that signal to be received. In other words, in order to optimise the sleeping of the device, e.g. the STA that has entered sleep mode after transmission, such as after transmission of the SYN-ACK inFIG. 2, should know the TCP RTT in order to wake up in right time to be able to receive the ACK+Data transmitted in the DL.

Communication in the Uplink (UL)

When a TCP connection is initiated in the UL, the communications device, e.g. the IoT device, needs to regularly be available for TCP acknowledgements, e.g. ACKs, after each UL transmission. The 4G connected mode DRX has several parameters and timers available to tune the IoT device's behaviour for this case. Examples of already existing parameters are the inactivity timer which defines how long the receiver is kept open after an UL transmission, and the DRX short cycle which gives a shorter regular cycle for a period of time after UL activity.FIG. 3schematically illustrates communications in the uplink using the TCP protocol. As illustrated, also for UL communication the TCP RTT should be known to the device in order for the device to wake up to receive the SYN-ACK and the ACK transmitted in the DL after the device has entered sleep mode after the respective transmission of the Data and the ACK-Data in the UL.

A common drawback with existing solutions is that the TCP RTT is typically not known in the beginning of the connection. Therefore, optimization of the sleep period, e.g. optimization of the length of the sleep period, is not possible. For example, if the communications device inFIG. 2enters sleep mode after the transmission of the UL SYN-ACK or if the communications device inFIG. 3enters sleep mode after the transmission of the UL Data, the communications device will not have knowledge about the TCP RTT, and thus the device does not have knowledge of when to expect a response in the DL. Since the communications device will not have knowledge about when to expect the response in the DL, the communications device will not know when to wake up from a sleep mode that it entered after transmission of the UL SYN-ACK or the UL Data.

In 4G LTE, the solution is to introduce an inactivity timer and a DRX short cycle parameter that will be used after the communications device has been active in order to stay more responsive in case more data follows. However, recent agreements in 3GPP RAN2 denote that the DRX short cycle parameter is not used for narrow band communications devices, e.g. Narrow Band IoT (NB-IoT) devices. By the expression “narrow band communications device” when used in this disclosure is to be understood to refer to communications device configured to operate within a narrow frequency band, such as within 180 kHz. Another solution would be to configure the communications device with a long enough inactivity timer which basically means keeping the communications device awake over the expected RTT plus the possible delayed ACK timer value used at the cloud or server side.

In Wi-Fi, no mechanism exists to optimize sleep cycle for response in the DL. The wake-up schemes for DL responses rely mostly on the regular TIM.

Thus, in order to make the communications device available for data coming as a response to an earlier sent UL packet, the basic cycle needs to be configured short, which is consuming resources from a power resources perspective, e.g. a battery perspective, or the communications device needs to be configured to stay awake over the expected RTT, also consuming power resources.

Some possible solutions are described in the reference U.S. Pat. No. 9,237,523 to Hsu et al. U.S. Pat. No. 9,237,523 discloses a method of establishing a sleep mode operation between a mobile station and its serving base station in a wireless communications system. When sleep mode operation is active, the MS enters into a series of sleep cycle and each sleep cycle comprises a listening window followed by a sleep window. In one aspect, each sleep cycle is associated with a set of sleep cycle parameters including a Sleep Cycle Length and an adjustable Listening Window Length. Each set of sleep cycle parameters is determined based on a predefined traffic characteristic of a data communication flow between the MS and it serving BS. Different embodiments of sleep cycle parameters are provided for real-time traffic, non-real-time traffic, real-time and non-real-time mixed traffic, and multi-rate transmission traffic.

A drawback with the method disclosed in U.S. Pat. No. 9,237,523 is that the disclosed method requires determining a predefined traffic characteristic before applying optimized sleep cycle parameters.

SUMMARY

An object of embodiments herein is to address at least some of the above-mentioned drawbacks among others and to improve the performance in a wireless communications network.

According to one aspect of embodiments herein, the object is achieved by a method performed by a first communications device for handling of active mode operation after transmitting data to a second communications device. The first communications device and the second communications device are operating in a wireless communications network.

The first communications device transmits a first data transmission to the second communications device and enters a sleep mode.

At a number of points in time, the first communications device temporarily wakes up from the sleep mode to an active mode for a respective active mode period.

The first communications device indicates to the second communications device, a point of time of the respective active mode period.

According to another aspect of embodiments herein, the object is achieved by a first communications device for handling of active mode operation after transmitting data to a second communications device. The first communications device and the second communications device are configured to operate in a wireless communications network.

The first communications device is configured to transmit a first data transmission to the second communications device and to enter a sleep mode.

The first communications device is configured to, at a number of points in time, temporarily wake up from the sleep mode to an active mode for a respective active mode period.

Further, the first communications device is configured to indicate to the second communications device, a point of time of the respective active mode period.

According to another aspect of embodiments herein, the object is achieved by a computer program, comprising instructions which, when executed on at least one processor, causes the at least one processor to carry out the method performed by the first communications device.

According to another aspect of embodiments herein, the object is achieved by a carrier comprising the computer program, wherein the carrier is one of an electronic signal, an optical signal, a radio signal or a computer readable storage medium.

Since the first communications device indicates to the second communications device, a point of time of the respective active mode period, the handling of the first communications device's active mode operation is optimised or at least improved, and correspondingly also the handling of the sleep mode operation, and at the same time ensuring that the second communications device has knowledge about the point of time of the respective active mode period so it may transmit transmission to the first communications device during its active mode period. Thereby the utilization of power resources may be optimised or at least improved. This results in an improved performance in the wireless communications network.

An advantage with embodiments herein is that they provide handling of active mode operation without needing to know the round trip time for bi-directional communication, e.g. without needing to determine the traffic pattern, which a prior art communications device needs to know in order to stay awake to receive a response to a transmission it has made.

A further advantage with embodiments herein is that they enable a simple scheme for making a sleepy device, e.g. the first communications device entering the sleep mode, available for DL data after an UL oriented transmission to better account for bi-directional reliable communication protocols that may be used above the MAC layer of the radio communication.

A yet further advantage with embodiments herein is that even if the first communications device is configured with a long sleeping cycle or that is always asleep by default, it will still be responsive in case bi-directional communication is needed due to, e.g., the use of TCP on the transport layer. The reason for this is that the first communications device has indicated to the second communications device, the point of time of the respective active mode period. This enables optimized energy conservation while still maintaining reliable and fast data delivery. A first communications device that is always asleep may be a sensor designed to only transmit a transmission but occasionally may need to receive a transmission.

