Patent Publication Number: US-2022231731-A1

Title: Apparatus, Methods and Machine-Readable Media Relating to Phase Tracking in a Wireless Network

Description:
TECHNICAL FIELD 
     Embodiments of the disclosure provide apparatus, methods and machine-readable media relating to phase tracking in a wireless network, and particularly relate to phase tracking of signals receives more a plurality of coordinated radio access network nodes. 
     BACKGROUND 
     The IEEE 802.11-16 standard (Wireless LAN Medium (MAC and Physical Layer (PHY) Specifications) specifies a set of orthogonal matrices, often called P matrices, which are employed as orthogonal cover codes for channel estimation when utilizing more than one space time stream, i.e., multiple-input-multiple-output (MIMO) system operation. These P matrices are applied to the Long Training Field (LTF), which comprises one or more sequences of values known by the receiver and used for channel estimation. 
     In 802.11n the orthogonal cover code is applied to all subcarriers. In contrast, in 802.11ac/ax, it is not applied to the pilot subcarriers. The purpose of the pilot subcarriers is to aid in phase tracking, which is used to mitigate performance degradation due to phase noise and Carrier Frequency Offset (CFO). CFO is due to the relative drift of the TX and RX clocks in the transmitter and the receiver. 
     In 802.11ac/ax the pilot subcarriers are transmitted in single-input-single-output (SISO) mode even when MIMO is employed, i.e., the same frequency domain symbol is transmitted in all space time streams when the subcarrier is a pilot subcarrier. This allows receivers supporting 802.11ac/ax to perform phase tracking over the LTF, even before the channel has been estimated. This is beneficial since residual CFO can lead to degraded channel estimates. 
     Recently, Extremely High Throughput (EHT) has been proposed as an enhancement of the IEEE 802.11 standard. In particular, it has been proposed to allow distributed downlink MIMO (D-DL-MIMO), where two or more coordinated access points (APs) transmit several space time streams simultaneously to the same receiving station (STA). 
     This type of transmission is typically transparent to the receiver STA. In other words, the STA is typically not aware that the transmission that it is receiving originates from multiple APs. From the point of view of the STA, the signal is subject to multi-path propagation. 
     A problem that did not occur in 802.11n/ac/ax but may do in EHT is that when D-DL-MIMO is used, the clocks of the transmitting APs will not be synchronized, i.e., the clocks of the transmitting APs and the receiving STA will all drift independently during transmission of a data frame. This drift happens independently of whether the clocks were previously synchronized (e.g. with the help of a trigger frame). The phase tracking methodology used in 802.11ac/ax implicitly assumes that there is only one clock on the TX side and one clock on the RX side and that any CFO is due to the relative clock drift between the two clocks. However, in EHT this may no longer be the case as there are three or more unsynchronized clocks. 
     A solution to this problem is therefore required. 
     SUMMARY 
     According to a first aspect of the disclosure, there is provided a method performed by a network node of a communication network. The communication network comprises a plurality of coordinated radio access network nodes for transmitting multiple streams of data to a wireless device in a given time resource. The method comprises: causing transmission, to the wireless device, of an indication that the wireless device should perform multiple separate phase-tracking processes on the signals received from the plurality of coordinated radio access network nodes in the given time resource. 
     Apparatus and machine-readable media are also provided for performing the method set out above. For example, in one embodiment, a network node is provided for a communication network. The communication network comprises a plurality of coordinated radio access network nodes for transmitting multiple streams of data to a wireless device in a given time resource. The network node comprises processing circuitry and a non-transitory machine-readable medium storing instructions which, when executed by the processing circuitry, cause the network node to: cause transmission, to the wireless device, of an indication that the wireless device should perform multiple separate phase-tracking processes on the signals received from the plurality of coordinated radio access network nodes in the given time resource. 
     In a second aspect of the disclosure, there is provided a method performed by a wireless device for receiving data from a plurality of coordinated radio access network nodes. The plurality of coordinated radio access network nodes transmit multiple streams of data to the wireless device in a given time resource. The method comprises: receiving, from a network node, an indication that the wireless device should perform multiple separate phase-tracking processes on the signals received from the plurality of coordinated radio access network nodes in the given time resource. 
     Apparatus and machine-readable media are also provided for performing the method set out above. For example, in one embodiment, a wireless device is provided for receiving data from a plurality of coordinated radio access network nodes. The plurality of coordinated radio access network nodes transmit multiple streams of data to the wireless device in a given time resource. The wireless device comprises processing circuitry and a non-transitory machine-readable medium storing instructions which, when executed by the processing circuitry, cause the wireless device to: receive, from a network node, an indication that the wireless device should perform multiple separate phase-tracking processes on the signals received from the plurality of coordinated radio access network nodes in the given time resource. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of examples of the present disclosure, and to show more clearly how the examples may be carried into effect, reference will now be made, by way of example only, to the following drawings in which: 
         FIG. 1  shows a system according to embodiments of the disclosure; 
         FIG. 2  is a signalling diagram of co-ordinated downlink transmissions according to embodiments of the disclosure; 
         FIG. 3  is a flowchart of a method performed by a network node according to embodiments of the disclosure; 
         FIG. 4  is a flowchart of a method performed by a wireless device according to embodiments of the disclosure; 
         FIGS. 5 and 6  are schematic diagrams of network nodes according to embodiments of the disclosure; 
         FIGS. 7 and 8  are schematic diagrams of wireless devices according to embodiments of the disclosure; 
         FIG. 9  shows a telecommunication network connected via an intermediate network to a host computer, according to embodiments of the disclosure; 
         FIG. 10  shows a host computer communicating via a base station with a user equipment over a partially wireless connection, according to embodiments of the disclosure; and 
         FIGS. 11 and 12  are flowcharts depicting methods in a communications system including a host computer, a base station and a user equipment, according to embodiments of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a wireless communication network or system  100  according to embodiments of the disclosure. The network  100  comprises a plurality of wireless access points  102   a ,  102   b ,  102   c  (collectively,  102 ) in communication with a mobile station  104 . In one embodiment, the network  100  implements the IEEE 802.11 standard (known as “Wi-Fi”) and may implement one or more of its amendments, and comprises a wireless local area network (WLAN). For convenience, the terminology used herein may correspond to that used in the 802.11 standard (e.g., “access point” or AP, “station” or STA). However, the concepts described herein may also find use in other radio-access technologies. For example, the network  100  may implement cellular radio-access technologies, such as those developed by the 3 rd  Generation Partnership Project (3GPP), e.g., Wideband Code-Division Multiple-Access (WCDMA), Long Term Evolution (LTE), New Radio (NR), etc. In such cases, the wireless access points  102  may be called base stations, NodeBs, eNodeBs, gNodeBs, transmission-reception points (TRP), etc. The mobile station  104  may be called a user equipment (UE), a wireless device, a wireless terminal device, etc. The term “node” is used herein to mean any wireless device and any suitable network node. 
     Each wireless access point  102  comprises one or, in some embodiments, multiple antennas (or antenna elements). Similarly, the wireless device  104  may also comprise multiple antennas. In this way, the wireless device  104  is able to use processing techniques to receive and decode multiple space time streams from the multiple access points simultaneously. 
     The plurality of wireless access points  102  are connected to each other via a backhaul network  108 , which may be wired or wireless. For example, the backhaul network  108  may be implemented using the Internet, and/or a dedicated network which may be wired or wireless. 
     In the illustrated embodiment, the system  100  further comprises a processing node  106  which is coupled to each of the wireless access points  102  via the backhaul network  108 . For example, the processing node  106  may be provided within a remote processing environment, such as a cloud server. In this embodiment, the specified functions of the wireless access points  102  are distributed between the wireless access points  102  and the processing node  106 . Thus, one or more of the functions of the wireless access points  102  may be performed in a remote processing environment, e.g., by the processing node  106 . Further detail regarding this aspect will be provided below. 
     As noted above, it has been proposed to provide distributed downlink MIMO (D-DL-MIMO), where two or more coordinated access points APs transmit multiple space time streams simultaneously to the same receiving station STA, i.e., using the same time resources. 
     According to one approach to such distributed downlink MIMO, one of the multiple access points (e.g., wireless access point  102   a ) is designated as a master access point and one or more others (e.g., access point  102   b ) are designated as slave access points.  FIG. 2  is a signalling diagram of co-ordinated downlink transmissions according to such embodiments, in which the transmissions of only a single master access point (AP1) and a single slave access point (AP2), as well as the wireless device, are shown. 
     The signalling begins with the master access point  102   a  transmitting an initial trigger message  200 . The trigger message  200  is received by the slave access point  102   b , and used to control the timing of subsequent transmissions of data frames  202   a  and  202   b  by the master access point  102   a  and the slave access point  102   b , respectively. 
     Specifically, the data frames  202   a ,  202   b  are transmitted simultaneously a certain timing offset after transmission of the trigger message  200 . In the illustrated embodiment, this timing offset is defined as the short inter-frame space (SIFS). However, alternative timing offsets may be used. The data frames  202   a ,  202   b  may be substantial duplicates of each other (e.g., comprising the same data), or may comprise different data. 
     After a further SIFS, the wireless device  104  acknowledges receipt of the data frames  202   a ,  202   b  through the transmission of an ACK message  204 . 
     Those skilled in the art will appreciate that the signalling shown in  FIG. 2  is just one possible embodiment for the co-ordination of simultaneous transmissions by distributed wireless access point. Alternative embodiments are possible, of course, without departing from the scope of the claims appended hereto. For example, the access points  102  may be synchronized with each other over a long period, and then controlled to transmit data frames to the wireless device  104  through a long-term scheduling co-ordinated via the backhaul network  108 . The present disclosure is not limited in that respect. 
     Returning to the system  100  shown in  FIG. 1 , we first illustrate an embodiment of the disclosure by means of a simple yet relevant example. Consider the case where there are two access points each having a rank one channel to the STA (e.g., the wireless access points  102   a  and  102   b ). This means that the channel between the wireless access point  102   a  and the wireless device  104  supports only one space time stream, and similarly the channel between the wireless access point  102   b  and the wireless device  104  supports only one space time stream. Such a situation may arise when the channels are essentially line of sight. However, the combined channel may support two space time streams. That is, the STA may successfully decode a first space time stream transmitted from the wireless access point  102   a  and a second space time stream transmitted from the wireless access point  102   b . We also assume that the wireless device  104  has two RX antennas k=1, 2, although in practice it may have many more. 
     Each wireless access point  102   a ,  102   b  transmits respective pilot symbols s and t to the wireless device  104  using a pilot subcarrier. The signal r k  received at the k-th antenna, in a pilot subcarrier, can be modelled as 
         r   k   =h   k1   e   jθ   s+h   k2   e   jφ   t+w, k= 1,2. 
     where h k1  and h k2  are the channels between the kth antenna and the wireless access points  102   a ,  102   b  respectively, θ and φ model the CFOs due to clock mismatch between the wireless device  104  and the wireless access points  102   a ,  102   b  respectively, and w represents the noise. 
     The wireless device  104  is able to estimate the channels {h km } from access points m=1,2 to receive antennas k=1,2 using any well-known technique. For example, if a physical layer (PHY) similar to the 802.11ax PHY is used, these estimates can be obtained by interpolating in the frequency domain any channel estimates that were obtained via earlier transmissions between the wireless device  104  and the wireless access points  102  with the help of the long training field. The pilot symbols s and t are also known, or can be determined by, the wireless device  104  using algorithms set out in the 802.11 (or equivalent) specifications. 
     Thus the terms r k , h km , s, and t are known (or previously estimated) at the wireless device  104 . Since there are two equations (one for each receive antenna k=1,2), it is possible to use well known statistical techniques to estimate the desired CFO terms θ, φ. 
     In this way, it is possible for the wireless device  104  to perform phase tracking (e.g., to determine the carrier frequency offset) for multiple simultaneously received data streams. 
     According to embodiments of the disclosure, the network informs the wireless device  104  that it should use perform multiple phase-tracking processes on signals received from a plurality of co-ordinated wireless access points. For example, in one embodiment, a network node causes the transmission, to the wireless device, of an indication that the wireless device should perform multiple separate phase-tracking processes on the signals received from the plurality of coordinated radio access network nodes in a given time resource. In this way, the wireless device is enabled to perform separate phase tracking processes for each of the multiple wireless access points, and/or for each of the multiple space time streams transmitted by the multiple wireless access points. The channel estimate for each wireless access point and/or each space time stream can then be determined using the LTF, and respective estimates of the CFO for that particular wireless access point or space time stream. 
       FIG. 3  is a flowchart of a method according to embodiments of the disclosure, performed by a network node. The network node may be a wireless access point, such as the master access point  102   a . Alternatively, the network node may be a remote network node, such as the processing node  106 . 
     The network node operates in the scenario of the network  100  described above with respect to  FIG. 1 . Thus a plurality of radio access nodes or wireless access points are co-ordinated to transmit to a wireless device simultaneously, using the same time resource (e.g., the same data frame). As noted above with respect to  FIG. 2 , the plurality of radio access nodes may transmit the same data to the wireless device (effectively increasing the received signal strength at the wireless device) or different data to the wireless device (increasing the potential data rate to the wireless device). 
     The method begins in step  300 , in which the network node determines whether a plurality of access points or radio access nodes are to transmit to the wireless device simultaneously. For example, step  300  may comprise determining whether distributed downlink MIMO is to be used for transmissions to the wireless device. Such a determination may be made for each potential transmission opportunity to the wireless device, or may be made in a persistent or semi-persistent way for multiple potential transmission opportunities. 
     Multiple access points or distributed downlink MIMO may be used for transmissions to the wireless device based on a quality of service required by the wireless device. For example, the wireless device may utilize one or more services requiring particular high data rates, or particularly high reliability of communications. In such cases, the network provider may determine that distributed downlink MIMO can be used for transmissions to the wireless device for those services. The capabilities of the wireless device may also be used to determine whether distributed downlink MIMO can be used. Certain wireless devices may not have the functionality to perform multiple phase tracking processes (e.g., through a lack of hardware such as multiple antennas or processing power, or through a lack of adequate software). 
     If a plurality of access points are to transmit to the wireless device simultaneously, the method proceeds to step  302 , in which the network node causes transmission to the wireless device of an indication that the wireless device should perform multiple separate phase-tracking processes on the signals received from the plurality of coordinated radio access network nodes. For example, where the network node is one of the plurality of access points (such as the master access point  102   a ), step  302  may comprise the network node itself transmitting the indication to the wireless device. Where the network node is a remote network node (such as the processing node  106 ), step  302  may comprise the network node instructing one or more (or all) of the wireless access points to transmit the indication to the wireless device. 
     Thus the wireless device receives multiple data streams simultaneously from the plurality of co-ordinated access points. The indication may be contained within a data packet transmitted to the wireless device in one or more of those data streams. For example, in one embodiment, the indication may be contained within a header of the data packet (such as the PHY header). 
     In one embodiment, the indication comprises an indication that the wireless device should perform a respective phase-tracking process on the one or more streams of data received from each access point of the plurality of coordinated access points. Here it will be noted that each access point may transmit one or multiple data streams to the wireless device. Phase tracking processes in this embodiment may be performed per access point, with the same carrier frequency offset used for each data stream received from that access point. As each data stream transmitted by a particular access point will utilize the same oscillator or clock, the carrier frequency offset will be similar for each data stream. 
     In an alternative embodiment, however, the indication comprises an indication that the wireless device should perform respective phase-tracking processes on each data stream received from the plurality of coordinated access points. This embodiment may be particularly relevant where each access point transmits each of the multiple data streams to the wireless device, i.e., each access point transmits the same, multiple data streams to the wireless. At any given time, one of the access points will contribute the most power for a particular data stream, and hence the CFO for that data stream will depend most on the mismatch between the clocks of the wireless device and that particular access point. In a different data stream, a different access point may contribute the most power and hence the CFO for that data stream will depend most on the mismatch between the clocks of the wireless device and that different access point. Phase tracking processes in this embodiment may be performed per data stream. 
     The indication may comprise a signalling field, which is set to a first value to indicate that multiple phase tracking processes should be performed by the wireless device, or to a second value to indicate that a single phase tracking process should be performed by the wireless device. 
     The indication may be implicit or explicit. In the former case, the indication may comprise an indication of a different property or configuration, which is interpreted by the wireless device as an instruction that it should perform multiple phase-tracking processes. For example, the indication may comprise an indication that distributed downlink MIMO is to be used for transmissions to the wireless device. The wireless device may be configured to interpret that indication so as to perform multiple phase-tracking processes as described above. 
     If a plurality of access points are not to transmit to the wireless device simultaneously, the method proceeds to step  304 , in which the network node causes transmission to the wireless device of an indication that the wireless device should perform a single phase-tracking process on signals received in the given time resource. For example, where a single access point is to transmit to the wireless device (using MIMO transmissions or not), the network node may cause transmission to the wireless device of an indication that the wireless device should perform a single phase-tracking process. The detail set out above in step  302  with respect to the indication applies equally to step  304 . 
     It will be noted that the embodiments above describe the network nodes as indicating that the wireless device should perform single or multiple phase tracking processes. Thus in one embodiment this indication is advisory, and the wireless device may choose to disregard the indication. Alternatively, the indication may be mandatory. For example, a telecommunications standard (such as the 802.11 specifications) may mandate that the wireless device follows the recommendation of the network node with regard to single or multiple phase tracking processes. 
       FIG. 4  is a flowchart of a method performed by a wireless device according to embodiments of the disclosure. The wireless device may correspond to the wireless device  104  described above with respect to  FIG. 1 , for example. 
     The wireless device operates in the scenario of the network  100  described above with respect to  FIG. 1 . Thus a plurality of radio access nodes or wireless access points are co-ordinated to transmit to the wireless device simultaneously, using the same time resource (e.g., the same data frame). As noted above with respect to  FIG. 2 , the plurality of radio access nodes may transmit the same data to the wireless device (effectively increasing the received signal strength at the wireless device) or different data to the wireless device (increasing the potential data rate to the wireless device). 
     The method begins in step  400 , in which the wireless device receives multiple data streams simultaneously, e.g., using the same time resources (such as the same data frame). At this stage, the wireless device may not have knowledge of which access point or access points transmitted the multiple streams of data. 
     In step  402 , the wireless device receives an indication from an access point as to whether the wireless device is to perform one or multiple phase tracking processes on the data streams received in step  400 . 
     The indication may be contained within a data packet transmitted to the wireless device in one or more of the data streams received in step  400 . For example, in one embodiment, the indication may be contained within a header of the data packet (such as the PHY header). The indication may be received in data packets transmitted from all of the data streams received in step  400 . 
     In one embodiment, the indication comprises an indication that the wireless device should perform a respective phase-tracking process on the one or more streams of data received from each access point of the plurality of coordinated access points. Here it will be noted that each access point may transmit one or multiple data streams to the wireless device. Phase tracking processes in this embodiment may be performed per access point, with the same carrier frequency offset used for each data stream received from that access point. As each data stream transmitted by a particular access point will utilize the same oscillator or clock, the carrier frequency offset will be similar for each data stream. 
     In an alternative embodiment, however, the indication comprises an indication that the wireless device should perform respective phase-tracking processes on each data stream received from the plurality of coordinated access points. This embodiment may be particularly relevant where each access point transmits each of the multiple data streams to the wireless device, i.e., each access point transmits the same, multiple data streams to the wireless. At any given time, one of the access points will contribute the most power for a particular data stream, and hence the CFO for that data stream will depend most on the mismatch between the clocks of the wireless device and that particular access point. In a different data stream, a different access point may contribute the most power and hence the CFO for that data stream will depend most on the mismatch between the clocks of the wireless device and that different access point. Phase tracking processes in this embodiment may be performed per data stream. 
     The indication may comprise a signalling field, which is set to a first value to indicate that multiple phase tracking processes should be performed by the wireless device, or to a second value to indicate that a single phase tracking process should be performed by the wireless device. 
     The indication may be implicit or explicit. In the former case, the indication may comprise an indication of a different property or configuration, which is interpreted by the wireless device as an instruction that it should perform multiple phase-tracking processes. For example, the indication may comprise an indication that distributed downlink MIMO is to be used for transmissions to the wireless device. The wireless device may be configured to interpret that indication so as to perform multiple phase-tracking processes as described above. 
     If the indication comprises an indication that the wireless device is to perform multiple phase-tracking processes on the data streams, the method proceeds to step  404 , in which the wireless device performs multiple phase tracking processes on the data streams. 
     It will be recalled that the signal r k  received at the k-th antenna of the wireless device, in a pilot subcarrier, can be modelled as 
         r   k   =h   k1   e   jθ   s+h   k2   e   jφ   t+w, k= 1,2. 
     where h k1  and h k2  are the channels between the kth antenna and the wireless access points  102   a ,  102   b  respectively, θ and φ model the CFOs due to clock mismatch between the wireless device  104  and the wireless access points  102   a ,  102   b  respectively, and w represents the noise. 
     The wireless device is able to estimate the channels {h km } from access points m=1,2 to receive antennas k=1,2 using any well-known technique. For example, if a physical layer (PHY) similar to the 802.11ax PHY is used, these estimates can be obtained by interpolating in the frequency domain any channel estimates that were obtained via earlier transmissions between the wireless device and the wireless access points with the help of the long training field. The pilot symbols s and t are also known, or can be determined by, the wireless device using algorithms set out in the 802.11 (or equivalent) specifications. 
     Thus the terms r k , h km , s, and t are known (or previously estimated) at the wireless device, and the carrier frequency offsets can be calculated using well known statistical techniques. 
     If the indication comprises an indication that the wireless device is to perform a single phase-tracking process on the data streams (e.g., because a single access point transmitted the multiple streams of data received in step  400 ), the method proceeds to step  406 , in which the wireless device performs a single phase tracking process on the data stream. Here the wireless device assumes that each of the data streams has the same value of carrier frequency offset. 
       FIG. 5  is a schematic diagram of a network node  500  according to embodiments of the disclosure. The network node  500  may be configured to carry out the method described above with respect to  FIG. 3 , for example. The network node  500  may comprise a radio access node (such as a wireless access point) or a network node coupled to such a radio access node. 
     The network node  500  may be configurable to form part of a communication network, which comprises a plurality of coordinated radio access network nodes for transmitting multiple streams of data to a wireless device in a given time resource. The network node  500  comprises processing circuitry  502  and a device-readable medium (such as memory)  504 . The device-readable medium  504  stores instructions which, when executed by the processing circuitry  502 , cause the network node  500  to: cause transmission, to the wireless device, of an indication that the wireless device should perform multiple separate phase-tracking processes on the signals received from the plurality of coordinated radio access network nodes in the given time resource. 
     In the illustrated embodiment, the network node  500  also comprises one or more interfaces  506 , for receiving signals from wireless devices or network nodes and/or transmitting signals to wireless devices or network nodes. The interfaces  506  may use any appropriate communication technology, such as electronic signalling, optical signalling or wireless (radio) signalling. 
     Although  FIG. 5  shows the processing circuitry  502 , the memory  504  and the interface(s)  506  coupled together in series, those skilled in the art will appreciate that the components of the network node  500  may be coupled together in any suitable manner (e.g. via a bus or other internal connection). 
       FIG. 6  is a schematic illustration of a network node  600  according to further embodiments of the disclosure. The network node  600  may be configured to perform the method of  FIG. 3 , for example. 
     The network node  600  may be configurable to form part of a communication network, which comprises a plurality of coordinated radio access network nodes for transmitting multiple streams of data to a wireless device in a given time resource. The network node  600  comprises a causing unit  602 , which is configured to cause transmission, to the wireless device, of an indication that the wireless device should perform multiple separate phase-tracking processes on the signals received from the plurality of coordinated radio access network nodes in the given time resource. 
     The network node  600  may also comprise one or more interface modules (not illustrated), for receiving signals from wireless devices or network nodes of the network and/or transmitting signals to wireless devices or network nodes of the network. The interfaces may use any appropriate communication technology, such as electronic signalling, optical signalling or wireless (radio) signalling. 
       FIG. 7  is a schematic diagram of a wireless device  700  according to embodiments of the disclosure. The wireless device  700  may be configured to carry out the method described above with respect to  FIG. 4 , for example. 
     The wireless device  700  may be configured to receive data from a plurality of coordinated radio access network nodes, the plurality of coordinated radio access network nodes transmitting multiple streams of data to the wireless device in a given time resource. The wireless device  700  comprises processing circuitry  702  and a device-readable medium (such as memory)  704 . The device-readable medium  704  stores instructions which, when executed by the processing circuitry  702 , cause the wireless device  700  to: receive, from a network node, an indication that the wireless device should perform multiple separate phase-tracking processes on the signals received from the plurality of coordinated radio access network nodes in the given time resource. 
     In the illustrated embodiment, the wireless device  700  also comprises one or more interfaces  706 , for receiving signals from network nodes and/or transmitting signals to network nodes. The interfaces  706  may use any appropriate communication technology, such as electronic signalling, optical signalling or wireless (radio) signalling. 
     Although  FIG. 7  shows the processing circuitry  702 , the memory  704  and the interface(s)  706  coupled together in series, those skilled in the art will appreciate that the components of the wireless device  700  may be coupled together in any suitable manner (e.g. via a bus or other internal connection). 
       FIG. 8  is a schematic illustration of a wireless device  800  according to further embodiments of the disclosure. The wireless device  800  may be configured to perform the method of  FIG. 4 , for example. 
     The wireless device  800  may be configured to receive data from a plurality of coordinated radio access network nodes, the plurality of coordinated radio access network nodes transmitting multiple streams of data to the wireless device in a given time resource. The wireless device  800  comprises a receiving unit  802 . The receiving unit  802  is configured to: receive, from a network node, an indication that the wireless device should perform multiple separate phase-tracking processes on the signals received from the plurality of coordinated radio access network nodes in the given time resource. 
     The wireless device  800  may also comprise one or more interface modules (not illustrated), for receiving signals from network nodes of the network and/or transmitting signals to network nodes of the network. The interfaces may use any appropriate communication technology, such as electronic signalling, optical signalling or wireless (radio) signalling. 
     The modules described above with respect to  FIGS. 6 and 8  may comprise any combination of hardware and/or software. For example, in an embodiment, the modules are implemented entirely in hardware. As noted above, hardware implementation may include or encompass, without limitation, digital signal processor (DSP) hardware, a reduced instruction set processor, hardware (e.g., digital or analog) circuitry including but not limited to application specific integrated circuit(s) (ASIC) and/or field programmable gate array(s) (FPGA(s)), and (where appropriate) state machines capable of performing such functions. In another embodiment, the modules may be implemented entirely in software. In yet further embodiments, the modules may be implemented in combinations of hardware and software. 
     The present disclosure therefore provides methods, apparatus and device-readable mediums for controlling phase tracking processes in a wireless device. Specifically, an indication is transmitted to the wireless device to indicate whether the wireless device should perform one or multiple phase-tracking processes on multiple data streams received simultaneously. Where the data streams are transmitted from different access points (e.g., distributed downlink MIMO is utilized), the wireless device may be advised to utilize multiple separate phase tracking processes for the data streams. Where the data streams are transmitted from a single access point (e.g., point-to-point MIMO is utilized), the wireless device may be advised to utilize a single phase tracking process for the data streams. 
     With reference to  FIG. 9 , in accordance with an embodiment, a communication system includes telecommunication network  910 , such as a 802.11 network or a 3GPP-type cellular network, which comprises access network  911 , such as a radio access network, and may also comprise core network  914 . Access network  911  comprises a plurality of base stations or access points  912   a ,  912   b ,  912   c , such as NBs, eNBs, gNBs or other types of wireless access points, each defining a corresponding coverage area  913   a ,  913   b ,  913   c . Each base station  912   a ,  912   b ,  912   c  may be connectable to core network  914  over a wired or wireless connection  915 . A first UE or wireless device (or STA, etc)  991  located in coverage area  913   c  is configured to wirelessly connect to, or be paged by, the corresponding base station  912   c . A second UE  992  in coverage area  913   a  is wirelessly connectable to the corresponding base station  912   a . While a plurality of UEs  991 ,  992  are illustrated in this example, the disclosed embodiments are equally applicable to a situation where a sole UE is in the coverage area or where a sole UE is connecting to the corresponding base station  912 . 
     Telecommunication network  910  is itself connected to host computer  930 , which may be embodied in the hardware and/or software of a standalone server, a cloud-implemented server, a distributed server or as processing resources in a server farm. Host computer  930  may be under the ownership or control of a service provider, or may be operated by the service provider or on behalf of the service provider. Connections  921  and  922  between telecommunication network  910  and host computer  930  may extend directly from core network  914  to host computer  930  or may go via an optional intermediate network  920 . Intermediate network  920  may be one of, or a combination of more than one of, a public, private or hosted network; intermediate network  920 , if any, may be a backbone network or the Internet; in particular, intermediate network  920  may comprise two or more sub-networks (not shown). 
     The communication system of  FIG. 9  as a whole enables connectivity between the connected UEs  991 ,  992  and host computer  930 . The connectivity may be described as an over-the-top (OTT) connection  950 . Host computer  930  and the connected UEs  991 ,  992  are configured to communicate data and/or signaling via OTT connection  950 , using access network  911 , core network  914 , any intermediate network  920  and possible further infrastructure (not shown) as intermediaries. OTT connection  950  may be transparent in the sense that the participating communication devices through which OTT connection  950  passes are unaware of routing of uplink and downlink communications. For example, base station  912  may not or need not be informed about the past routing of an incoming downlink communication with data originating from host computer  930  to be forwarded (e.g., handed over) to a connected UE  991 . Similarly, base station  912  need not be aware of the future routing of an outgoing uplink communication originating from the UE  991  towards the host computer  930 . 
     Example implementations, in accordance with an embodiment, of the UE, base station and host computer discussed in the preceding paragraphs will now be described with reference to  FIG. 10 . In communication system  1000 , host computer  1010  comprises hardware  1015  including communication interface  1016  configured to set up and maintain a wired or wireless connection with an interface of a different communication device of communication system  1000 . Host computer  1010  further comprises processing circuitry  1018 , which may have storage and/or processing capabilities. In particular, processing circuitry  1018  may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. Host computer  1010  further comprises software  1011 , which is stored in or accessible by host computer  1010  and executable by processing circuitry  1018 . Software  1011  includes host application  1012 . Host application  1012  may be operable to provide a service to a remote user, such as UE  1030  connecting via OTT connection  1050  terminating at UE  1030  and host computer  1010 . In providing the service to the remote user, host application  1012  may provide user data which is transmitted using OTT connection  1050 . 
     Communication system  1000  further includes base station  1020  provided in a telecommunication system and comprising hardware  1025  enabling it to communicate with host computer  1010  and with UE  1030 . Hardware  1025  may include communication interface  1026  for setting up and maintaining a wired or wireless connection with an interface of a different communication device of communication system  1000 , as well as radio interface  1027  for setting up and maintaining at least wireless connection  1070  with UE  1030  located in a coverage area (not shown in  FIG. 10 ) served by base station  1020 . Communication interface  1026  may be configured to facilitate connection  1060  to host computer  1010 . Connection  1060  may be direct or it may pass through a core network (not shown in  FIG. 10 ) of the telecommunication system and/or through one or more intermediate networks outside the telecommunication system. In the embodiment shown, hardware  1025  of base station  1020  further includes processing circuitry  1028 , which may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. Base station  1020  further has software  1021  stored internally or accessible via an external connection. 
     Communication system  1000  further includes UE  1030  already referred to. Its hardware  1035  may include radio interface  1037  configured to set up and maintain wireless connection  1070  with a base station serving a coverage area in which UE  1030  is currently located. Hardware  1035  of UE  1030  further includes processing circuitry  1038 , which may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. UE  1030  further comprises software  1031 , which is stored in or accessible by UE  1030  and executable by processing circuitry  1038 . Software  1031  includes client application  1032 . Client application  1032  may be operable to provide a service to a human or non-human user via UE  1030 , with the support of host computer  1010 . In host computer  1010 , an executing host application  1012  may communicate with the executing client application  1032  via OTT connection  1050  terminating at UE  1030  and host computer  1010 . In providing the service to the user, client application  1032  may receive request data from host application  1012  and provide user data in response to the request data. OTT connection  1050  may transfer both the request data and the user data. Client application  1032  may interact with the user to generate the user data that it provides. 
     It is noted that host computer  1010 , base station  1020  and UE  1030  illustrated in  FIG. 10  may be similar or identical to host computer  930 , one of base stations  912   a ,  912   b ,  912   c  and one of UEs  991 ,  992  of  FIG. 9 , respectively. This is to say, the inner workings of these entities may be as shown in  FIG. 10  and independently, the surrounding network topology may be that of  FIG. 9 . 
     In  FIG. 10 , OTT connection  1050  has been drawn abstractly to illustrate the communication between host computer  1010  and UE  1030  via base station  1020 , without explicit reference to any intermediary devices and the precise routing of messages via these devices. Network infrastructure may determine the routing, which it may be configured to hide from UE  1030  or from the service provider operating host computer  1010 , or both. While OTT connection  1050  is active, the network infrastructure may further take decisions by which it dynamically changes the routing (e.g., on the basis of load balancing consideration or reconfiguration of the network). 
     Wireless connection  1070  between UE  1030  and base station  1020  is in accordance with the teachings of the embodiments described throughout this disclosure. One or more of the various embodiments improve the performance of OTT services provided to UE  1030  using OTT connection  1050 , in which wireless connection  1070  forms the last segment. More precisely, the teachings of these embodiments may improve the security and thereby provide benefits such as greater security of user data and control data without unnecessarily increasing latency for services which do not require integrity protection. 
     A measurement procedure may be provided for the purpose of monitoring data rate, latency and other factors on which the one or more embodiments improve. There may further be an optional network functionality for reconfiguring OTT connection  1050  between host computer  1010  and UE  1030 , in response to variations in the measurement results. The measurement procedure and/or the network functionality for reconfiguring OTT connection  1050  may be implemented in software  1011  and hardware  1015  of host computer  1010  or in software  1031  and hardware  1035  of UE  1030 , or both. In embodiments, sensors (not shown) may be deployed in or in association with communication devices through which OTT connection  1050  passes; the sensors may participate in the measurement procedure by supplying values of the monitored quantities exemplified above, or supplying values of other physical quantities from which software  1011 ,  1031  may compute or estimate the monitored quantities. The reconfiguring of OTT connection  1050  may include message format, retransmission settings, preferred routing etc.; the reconfiguring need not affect base station  1020 , and it may be unknown or imperceptible to base station  1020 . Such procedures and functionalities may be known and practiced in the art. In certain embodiments, measurements may involve proprietary UE signaling facilitating host computer  1010 &#39;s measurements of throughput, propagation times, latency and the like. The measurements may be implemented in that software  1011  and  1031  causes messages to be transmitted, in particular empty or ‘dummy’ messages, using OTT connection  1050  while it monitors propagation times, errors etc. 
       FIG. 11  is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station and a UE which may be those described with reference to  FIGS. 9 and 10 . For simplicity of the present disclosure, only drawing references to  FIG. 11  will be included in this section. In step  1110 , the host computer provides user data. In substep  1111  (which may be optional) of step  1110 , the host computer provides the user data by executing a host application. In step  1120 , the host computer initiates a transmission carrying the user data to the UE. In step  1130  (which may be optional), the base station transmits to the UE the user data which was carried in the transmission that the host computer initiated, in accordance with the teachings of the embodiments described throughout this disclosure. In step  1140  (which may also be optional), the UE executes a client application associated with the host application executed by the host computer. 
       FIG. 12  is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station and a UE which may be those described with reference to  FIGS. 9 and 10 . For simplicity of the present disclosure, only drawing references to  FIG. 12  will be included in this section. In step  1210  of the method, the host computer provides user data. In an optional substep (not shown) the host computer provides the user data by executing a host application. In step  1220 , the host computer initiates a transmission carrying the user data to the UE. The transmission may pass via the base station, in accordance with the teachings of the embodiments described throughout this disclosure. In step  1230  (which may be optional), the UE receives the user data carried in the transmission. 
     It should be noted that the above-mentioned embodiments illustrate rather than limit the concepts disclosed herein, embodiments without and that those skilled in the art will be able to design many alternative departing from the scope of the appended following claims. The word “comprising” does not exclude the presence of elements or steps other than those listed in a statement, “a” or “an” does not exclude a plurality, and a single processor or other unit may fulfil the functions of several units recited in the statements. Any reference signs in the claims shall not be construed so as to limit their scope. 
     The following numbered paragraphs set out embodiments of the disclosure: 
     1. A communication system including a host computer comprising:
         processing circuitry configured to provide user data; and   a communication interface configured to forward the user data to a wireless network for transmission to a wireless device,   wherein the wireless network comprises a network node having a radio interface and processing circuitry, the base station&#39;s processing circuitry configured to perform the method of any of claims  1  to  10  appended hereto.       

     2. The communication system of embodiment 1, further including the network node. 
     3. The communication system of embodiment 2, further including the wireless device, wherein the UE is configured to communicate with the network node. 
     4. The communication system of embodiment 3, wherein:
         the processing circuitry of the host computer is configured to execute a host application, thereby providing the user data; and   the wireless device comprises processing circuitry configured to execute a client application associated with the host application.       

     5. A method implemented in a communication system including a host computer, a network node and a wireless device, the method comprising:
         at the host computer, providing user data; and   at the host computer, initiating a transmission carrying the user data to the wireless device via a wireless network comprising the network node, wherein the network node performs the method according to any one of claims  1  to  10  appended hereto.       

     6. The method of embodiment 5, further comprising:
         at the network node, transmitting the user data.       

     7. The method of embodiment 6, wherein the user data is provided at the host computer by executing a host application, the method further comprising:
         at the wireless device, executing a client application associated with the host application.       

     8. A communication system including a host computer comprising:
         processing circuitry configured to provide user data; and   a communication interface configured to forward user data to a wireless network for transmission to a wireless device,   wherein the wireless device comprises a radio interface and processing circuitry, the wireless device&#39;s processing circuitry configured to perform the method according to any one of claims  11  to  19  appended hereto.       

     9. The communication system of embodiment 8, further including the wireless device. 
     10. The communication system of embodiment 9, wherein the wireless network further includes a network node configured to communicate with the wireless device. 
     11. The communication system of embodiment 9 or 10, wherein:
         the processing circuitry of the host computer is configured to execute a host application, thereby providing the user data; and   the wireless device&#39;s processing circuitry is configured to execute a client application associated with the host application.       

     12. A method implemented in a communication system including a host computer, a network node and a wireless device, the method comprising:
         at the host computer, providing user data; and   at the host computer, initiating a transmission carrying the user data to the wireless device via a wireless network comprising the network node, wherein the wireless device performs the method according to any one of claims  11  to  19  appended hereto.       

     13. The method of embodiment 12, further comprising:
         at the wireless device, receiving the user data from the network node.