WO2020030255A1

WO2020030255A1 - Reducing dmrs overhead

Info

Publication number: WO2020030255A1
Application number: PCT/EP2018/071401
Authority: WO
Inventors: Xiaohui Liu; Neng Wang
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2018-08-07
Filing date: 2018-08-07
Publication date: 2020-02-13

Abstract

In order to demodulate data received via a physical downlink control channel, PDCCH, or a physical downlink shared channel, PDSCH, a client device needs to receive a demodulation reference signal, DMRS. The client device may use the DMRS to compensate for physical phenomena that may affect the data during wireless transmission. On the other hand, radio resources used for DMRS transmission and reception may be unavailable to be used for data transfer. This may be referred to as DMRS overhead. It is an object to provide a procedure for reducing DMRS overhead in wireless radio communication. The client device may use the same DMRS to estimate the channels of PDCCH and PDSCH. A client device, a network access device, methods, and a computer program are described.

Description

REDUCING DMRS OVERHEAD

TECHNICAL FIELD

The disclosure relates to the field of wireless radio communications, and more particularly to a client device, a network access device, and a procedure for reducing DMRS overhead. Furthermore, the disclosure relates to corresponding methods and a computer program.

BACKGROUND

In New Radio, NR, enhanced Mobile Broad Band, eMBB, and Ultra Reliable and Low Latency Communication, URLLC, are intended for different types of scenarios with respect to target block error rate, BLER, and latency even though they can be unified into the same framework. eMBB may provide a greater data bandwidth complemented by moderate latency improvement compared to 4G LTE. The target BLER for eMBB may be 10 ¹ which is the same as in LTE. URLLC is designed for mission critical applications that can be especially latency- sensitive, and the target BLER for URLLC can be 10 ⁵, which may be more challenging to achieve than the 10 ¹ target in eMBB.

In order to demodulate data received via a physical downlink control channel, PDCCH, or a physical downlink shared channel, PDSCH, in eMBB or URLLC, a client device may need to receive a demodulation reference signal, DMRS. The client device may use the DMRS to compensate for physical phenomena, such as the Doppler shift, that may affect the data during wireless transmission. On the other hand, radio resources used for DMRS transmission and reception may be unavailable to be used for data transfer. This may be referred to as DMRS overhead.

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 to limit the scope of the claimed subject matter.

It is an object to provide a procedure for reducing DMRS overhead in wireless radio communication. The object is achieved by the features of the independent claims. Further implementation forms are provided in the dependent claims, the description and the figures. According to a first aspect, a network access device is configured to: configure a demodulation reference signal, DMRS, of a physical downlink control channel, PDCCH, for transmission to a client device, wherein the DMRS of the PDCCH is also configured to operate as a DMRS of a physical downlink shared channel, PDSCH; and schedule the PDSCH and the PDCCH based on the configured DMRS, wherein the DMRS is configured for each transmission of the PDCCH and PDSCH. With these configurations, the network access device can, for example, transmit a DMRS that can be used for both of the PDCCH and the PDSCH. This may reduce DMRS overhead, since less resource elements need to be used for transmitting the DMRSs.

In an implementation form of the first aspect, the network access device is further configured to: receive a category report from a client device; and in response to the category report indicating that the client device is capable of joint channel estimation for the PDCCH and the PDSCH, omit transmitting a front-loaded DMRS before a first PDSCH orthogonal frequency division multiplexing, OFDM, symbol. With these configurations, the network access device can, for example, efficiently utilise information about the capabilities of the client device so that the network access device does not need to transmit unnecessary front-loaded DMRSs.

In a further implementation form of the first aspect, the DMRS is a combined reference signal for both the PDCCH and the PDSCH. With these configurations, the network access device can, for example, transmit a DMRS and the client device can use this DMRS to estimate the channel of both the PDCCH and the PDSCH.

In a further implementation form of the first aspect, the network access device is further configured to: transmit a second DMRS in another OFDM symbol. With these configurations, the network access device can, for example, transmit a second DMRS if a second DMRS is needed or utilized for channel estimation.

In a further implementation form of the first aspect, the network access device is further configured to: transmit the DMRS at a first orthogonal frequency-division multiplexing, OFDM, symbol of a subframe. With these configurations, the network access device can, for example, transmit the DMRS without obstructing any OFDM symbols that may be used for PDSCH data.

In a further implementation form of the first aspect, the first DMRS and the second DMRS comprise the same frequency structure for each antenna port between the first and the second DMRS. With these configurations the network access device can, for example, enable the DMRS to be used to estimate the channels of the PDSCH and the PDCCH. In a further implementation form of the first aspect, the DMRS is a front-loaded DMRS at a first PDCCH OFDM symbol. With these configurations, the network access device can, for example, transmit the DMRS without obstructing any OFDM symbols that may be used for PDSCH data.

In a further implementation form of the first aspect, the network access device is further configured to: transmit PDCCH data by multiplexing the DMRS with PDCCH data in a frequency domain. With these configurations, the network access device can, for example, transmit the DMRS and the PDCCH data during the same OFDM symbol.

In a further implementation form of the first aspect, the network access device is further configured to: transmit a third DMRS at PDSCH OFDM symbols, wherein the time spacing in OFDM symbols between the third DMRS and the second DMRS is equal to the time spacing in OFDM symbols between the second DMRS and the first DMRS. With these configurations, the network access device can, for example, transmit a third DMRS during a subframe. This may be needed, for example, if the channel changes rapidly in time.

In a further implementation form of the first aspect, the network access device is further configured to: transmit a fourth DMRS at PDSCH OFDM symbols, wherein the time spacing between two adjacent OFDM symbols is equal. With these configurations, the network access device can, for example, transmit a fourth DMRS during a subframe. This may be needed, for example, if the channel changes rapidly in time.

In a further implementation form of the first aspect, an OFDM symbol index is [0, 6, 12]; or an OFDM symbol index is [0, 4, 8, 12] With these configurations, the network access device can, for example, divide the DMRS transmission equally in time, or appropriately to standardisation.

In a further implementation form of the first aspect, the network access device is further configured to: configure another DMRS of the PDSCH for another antenna port of the PDSCH. With these configurations, the network access device can configure another DMRS, for example, in situations where the PDSCH requires more antenna ports than the PDCCH.

In a further implementation form of the first aspect, the network access device is further configured to: transmit a radio resource control, RRC, signal and/or a downlink control information, DCI, signal to the client device for enabling or disabling the client device for the common DMRS. With these configurations, the network access device can, for example, efficiently configure the client device to use or not to use the common DMRS. Thus, radio resources may be used efficiently, since the network access device and the client device can agree on the DMRS pattern used. In a further implementation form of the first aspect, the network access device is further configured to: schedule the PDSCH and the PDCCH with associated antenna ports and aligned frequency resources based on the configured DMRS. With these configurations, the network access device can, for example, further reduce the DMRS overhead, since the DMRS may be utilised more efficiently for the PDSCH and the PDCCH.

According to a second aspect, a client device is configured to: receive a demodulation reference signal, DMRS, via a physical downlink control channel, PDCCH, from a network access device; receive physical downlink shared channel, PDSCH, data; and jointly estimate a channel of the PDCCH and the received PDSCH data using the received DMRS of the PDCCH. With these configurations, the client device can, for example, use the channel of both the PDCCH and the PDSCH using a single DMRS, which may reduce DMRS overhead.

According to a third aspect, a method comprises: configuring a demodulation reference signal, DMRS, of a physical downlink control channel, PDCCH, for transmission to a client device, wherein the DMRS of the PDCCH is also configured to operate as a DMRS of a physical downlink shared channel, PDSCH; and scheduling the PDSCH and the PDCCH based on the configured DMRS, wherein the DMRS is configured for each transmission of the PDCCH and PDSCH.

According to a fourth aspect, a method comprises: receiving a demodulation reference signal, DMRS, via a physical downlink control channel, PDCCH, from a network access device; receiving physical downlink shared channel, PDSCH, data; and jointly estimating a channel of the PDCCH and the received PDSCH data using the received DMRS of the PDCCH.

According to a fifth aspect, a computer program is provided, comprising program code configured to perform a method according to the third aspect or the fourth aspect when the computer program is executed on a computer.

Many of the attendant features will be more readily appreciated as they become better understood by reference to the following detailed description considered in connection with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

The present description will be better understood from the following detailed description read in light of the accompanying drawings, wherein:

FIG. 1 illustrates a schematic representation of a client device configured for reducing DMRS overhead according to an embodiment; FIG. 2 illustrates a schematic representation of a network access device configured for reducing DMRS overhead according to an embodiment;

FIG. 3 illustrates a schematic representation of a time- frequency diagram according to a comparative example;

FIG. 4 illustrates a schematic representation of a time- frequency diagram according to another comparative example;

FIG. 5 illustrates a schematic representation of a signalling diagram for reducing DMRS overhead according to an embodiment;

FIG. 6 illustrates a schematic representation of a time-frequency diagram according to a comparative example;

FIG. 7 illustrates a schematic representation of a time-frequency diagram with no front- loaded PDSCH DMRS according to an embodiment;

FIG. 8 illustrates a schematic representation of a time- frequency diagram with a combined reference signal for the PDCCH and the PDSCH according to an embodiment;

FIG. 9 illustrates a schematic representation of a time- frequency diagram with a combined reference signal for the PDCCH and the PDSCH and an additional DMRS according to an embodiment;

FIG. 10 illustrates a schematic representation of a time-frequency diagram with a combined reference signal for the PDCCH and the PDSCH and two additional DMRSs according to an embodiment;

FIG. 11 illustrates a schematic representation of a time-frequency diagram with a combined reference signal for the PDCCH and the PDSCH and three additional DMRSs according to an embodiment;

FIG. 12 illustrates a schematic representation of a time-frequency diagram with a combined reference signal for the PDCCH and the PDSCH and with frequency domain multiplexing according to an embodiment;

FIG. 13 illustrates a schematic representation of a time-frequency diagram with a combined reference signal for the PDCCH and the PDSCH and with frequency domain multiplexing according to another embodiment;

FIG. 14 illustrates a schematic representation of simulation results for an extended pedestrian A, EPA, 30 model, according to an embodiment;

FIG. 15 illustrates a schematic representation of simulation results for an EPA 70 model, according to an embodiment; FIG. 16 illustrates a schematic representation of simulation results for an EPA 120 model, according to an embodiment; and

FIG. 17 illustrates a schematic representation of simulation results for an EPA 300 model, according to an embodiment.

Like references are used to designate like parts in the accompanying drawings.

DETAILED DESCRIPTION

The detailed description provided below in connection with the appended drawings is intended as a description of the embodiments and is not intended to represent the only forms in which the embodiment may be constructed or utilized. However, the same or equivalent functions and structures may be accomplished by different embodiments.

FIG. 1 schematically illustrates a client device 100, such as a wireless device, in a wireless communication system according to an embodiment. The client device 100 comprises a processor 101, a transceiver 102, and memory 103. The client device 100 may be configured to perform the functionalities and operations relating to it as described in the embodiments. According to an embodiment, the wireless communication system also comprises a network access (node) device 200 schematically illustrated in FIG. 2, such as a transmission and reception point, TRP, or a 5G base station, gNB, which may also comprise a processor 201 and a transceiver 202. The network access device 200 may also be configured to perform the functionalities and operations relating to the network access device 200 as described in the embodiments.

According to an embodiment, the client device 100 is configured to receive a demodulation reference signal, DMRS, via a physical downlink control channel, PDCCH, from the network access device 200. The client device may be further configured to receive physical downlink shared channel, PDSCH, data and jointly estimate a channel of the PDCCH and the received PDSCH data using the received DMRS of the PDCCH.

According to an embodiment, the network access device 200 is configured to configure a demodulation reference signal, DMRS, of a physical downlink control channel, PDCCH, for transmission to a client device. The DMRS of the PDCCH can also be configured to operate as a DMRS of a physical downlink shared channel, PDSCH. The network access device 200 may be further configured to schedule the PDSCH and the PDCCH based on the configured DMRS, wherein the DMRS is configured for each transmission of the PDCCH and PDSCH.

Since the DMRS may be used as a reference signal for both of the PDCCH and the PDSCH, DMRS overhead may be reduced. According to an embodiment, the DMRS may be configured as a combined reference signal for both the PDCCH and the PDSCH. According to another embodiment, the network access device 200 is configured to schedule the PDSCH and the PDCCH with associated antenna ports and aligned frequency resources based on the configured DMRS.

The client device 100 and the network access device 200 may further comprise other components that are not illustrated in FIGs 1 and 2. The client device 100 may communicate with, for example, the network access device 200 using the transceiver 102. The network access device 200 may communicate with, for example, a single or a plurality of client devices 100 using the transceiver 202. The client device 100 may communicate with, for example, a single or a plurality of network access devices 200 using the transceiver 102. The client device 100 may also comprise a plurality of transceivers 102 and communicate with the plurality of network access devices 200 using the plurality of transceivers 102. For example, the client device 100, such as a mobile phone, can be served by one gNodeB or multiple gNodeBs. For example, in dual connectivity, the client device 100 can be served by two gNodeBs. In carrier aggregation, the client device 100 can be served by more than one carrier.

The client device 100 may be any of a User Equipment (UE) in Long Term Evolution (LTE) or 5G new radio (NR), mobile station (MS), wireless terminal, or mobile terminal which is enabled to communicate wirelessly in a wireless communication system, sometimes also referred to as a cellular radio system. The client device 100 may further be referred to as a mobile telephone, a cellular telephone, a computer tablet or a laptop with wireless capability. The client device 100 in the present context may be, for example, a portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile device, enabled to communicate voice or data, via a radio access network, with another entity, such as another receiver or a server. The client device 100 can be a Station (STA) which is any device that contains an IEEE 802.11 -conformant Media Access Control (MAC) and Physical Layer (PHY) interface to the Wireless Medium (WM).

The network access device 200 may be a transmission or reception point, TRP, or a NR 5G base station, gNB. The network access device 200 may be a base station, a (radio) network node or an access node or an access point or a base station, e.g., a Radio Base Station (RBS), which in some networks may be referred to as a transmitter,“eNB”,“eNodeB”,“gNB”, “gNodeB”,“NodeB”, or“B node”, depending on the technology and terminology used. The radio network nodes may be of different classes such as, e.g., macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. The radio network node can be a Station (STA) which is any device that contains an IEEE 802.11 -conformant Media Access Control (MAC) and Physical Layer (PHY) interface to the Wireless Medium (WM).

FIG. 3 illustrates a schematic representation of a time-frequency diagram for downlink, DL, transmission in eMBB according to a comparative example. In FIG. 3 and in similar figures herein, time runs along the horizontal direction, and frequency runs along the vertical direction. Each square in FIG. 3 may correspond to a single orthogonal frequency-division multiplexing, OFDM, subcarrier frequency in the frequency dimension and a single OFDM symbol in the time dimension. Each such square may be referred to as a resource element. FIG. 3 comprises 14 OFDM symbols. Such collection of OFDM symbols may be referred to as a subframe.

Herein, the pattern illustrated in each resource element may indicate a function the resource element is allocated for. For example, in FIG. 3 resource elements illustrated with white colour and without a pattern may be allocated for data transmission even though all such resource elements are not marked with a reference number for clarity purposes.

Each resource element may be assigned for a certain function. For example, in FIG. 3, first two OFDM symbols (0 and 1) are assigned for a physical downlink control channel, PDCCH, 301. OFDM symbol 2 is assigned for reference signals, RS, and the reference signals are divided into code division multiplexing, CDM, group 0 302 2 and CDM group 1 302 1. The reference signals may be, for example, dedicated demodulation reference signals, DMRSs. The reference signals belonging to CDM group 0 302 2 or to CDM group 1 302 1 may be referred to as reference signals. Some resource elements are also assigned for data 304. The data 304 may be, for example, physical downlink shared channel, PDSCH, data.

FIG. 4 illustrates a schematic representation of a time-frequency diagram for downlink, DF, transmission in URFFC according to another comparative example. The time- frequency diagram presented in FIG. 4 may be similar to that presented for eMBB in FIG. 3. However, the diagram in FIG. 4 comprises only 7 OFDM symbols. Such collection of OFDM symbols may be referred to as a resource block. Each subframe may comprise two resource blocks. URFFC may have only one DMRS symbol 302 1 for channel estimation due to overhead considerations. Other DMRSs may be configured, for example, on OFDM symbol 4. This may only be desirable for edge cases with extremely high Doppler shift due to the additional 20% DMRS overhead. Furthermore, less OFDM symbols may be assigned for PDSCH data 304 in URFFC compared to eMBB as can be seen by comparing FIG. 3 with FIG. 4.

In order to decode the PDSCH data 304, the client device 100 may need to first decode the PDCCH data 301 in order to obtain related control information of the DMRSs 302 1, 302 2 and the PDSCH 304. The control information may comprise, for example, a frequency domain resource assignment which may indicate where the DMRS 302 1, 302 2 and PDSCH 304 are allocated in frequency.

Herein, the term DMRS pattern or simply pattern may refer to the manner in which resource elements in frequency and/or in time are allocated for reference signals, such as demodulation reference signals. For example, the fact that OFDM symbols 2 and 11 are used for DMRSs in FIG. 3 may be referred to as a DMRS pattern.

The embodiments described herein may improve receiver performance and physical layer efficiency via reducing DMRS overhead. This can be achieved, for example, via exploring advanced receiver and joint optimization of the PDCCH and the PDSCH. The network access device 200 may schedule the PDCCH and the PDSCH over associated antenna ports and across an aligned bandwidth with a new DMRS pattern, and the client device 100 may perform joint processing on PDCCH and PDSCH via exploring reference signals, data or both from the PDCCH. DMRS overhead reduction may be especially desirable in URLLC, since overhead from the control channel and the DMRS can be relatively higher compared with eMBB due to less OFDM symbols available. The embodiments described in this disclosure are applicable in both eMBB and URLLC, both downlink and uplink, even though URLLC downlink is mainly described as an example. For example, DMRS patterns can be defined without front-loaded symbols.

FIG. 5 illustrates a schematic representation of a signalling diagram according to an embodiment. Based on, for example, radio resource control, RRC, signalling and/or DCI, the client device 100 may report capability of an advanced receiver to the network access device 200. The client device 100 may, for example, transmit a category report 501 to the network access device 200. The category report 501 may, for example, indicate the capability of the client device 100 to jointly estimate the channel of the PDCCH and the PDSCH. The network access device 200 may in turn indicate the client device 100 to enable or disable the advanced receiver using, for example, an enable/disable advanced receiver signal 502. The advanced receiver signal 502 may also reconfigure the reference signal and pattern of the PDCCH and the PDSCH. The network access device 200 may indicate a new reference signal and its mapping to physical resources via the signalling 502 to enable the advanced receiver or the extension of current parameters, such as DL-DMRS-config-type, DL-DMRS-add-pos, DL- DMRS-typeA-pos. The client device 100 may optionally confirm the enabling/disabling using a confirmation signal 503 transmitted to the network access device 200.

Hence, according to such an embodiment, the network access device 200 is configured to receive a category report from the client device 100. In response to the category report indicating that the client device 100 is capable of joint channel estimation for the PDCCH and the PDSCH, the network access device 200 may configure a joint or common DMRS for the PDCCH and PDSCH. For example, the network access device 200 may omit transmitting a front-loaded DMRS before a first PDSCH orthogonal frequency division multiplexing, OFDM, symbol.

Then, a new reference signal and mapping may be applied by the network access device 200 for each transmission of the PDCCH and PDSCH. In operation 504, the network access device 200 may schedule the PDCCH and the PDSCH to utilise the advanced receiver, and transmit PDCCH and PDSCH transmissions 505 to the client device 100. The client device 100 can jointly process the PDCCH and the PDSCH based on the new reference signal and mapping using the advanced receiver 506. As indicated above, according to an embodiment, the network access device 200 is configured to transmit a radio resource control, RRC, signal and/or a downlink control information, DCI, signal to the client device for enabling or disabling the client device for the common DMRS (see step 502).

FIG. 6 illustrates a schematic representation of a time- frequency diagram according to a comparative example. In this example, 2 OFDM symbols are used for the PDCCH and 5 OFDM symbols are used for the PDSCH. At OFDM symbols 0 and 1, PDCCH data 301 and PDCCH RSs are transmitted. PDSCH DMRS 302 is transmitted at both OFDM symbol 2, which may be called a frontloaded DMRS, and OFDM symbol 4, which may be called an additional DMRS. During OFDM symbols 2 - 6, also PDSCH data 304 is transmitted as illustrated by the empty or clean squares in FIG. 6.

FIG. 7 illustrates a schematic representation of a time-frequency diagram with no front- loaded PDSCH DMRS according to an embodiment. In this embodiment, it may be unnecessary to transmit a front-loaded PDSCH DMRS symbol. Instead, the client device 100 can use a PDCCH reference signal, RS, PDCCH decoded data, or both as virtual pilots for channel estimation together with the optional additional PDSCH DMRS, which may be located, for example, at OFDM symbol 4. In this embodiment, all resources in OFDM symbol 2 can be used to transmit, for example, PDSCH data 304, and only the additional PDSCH DMRS 302 in OFDM symbol 4 may be needed to estimate the channel of the PDSCH.

FIG. 8 illustrates a schematic representation of a time- frequency diagram with a combined reference signal for the PDCCH and the PDSCH according to an embodiment. According to an embodiment, the DMRS is a front-loaded DMRS at a first PDCCH OFDM symbol. For example, in the embodiment illustrated in FIG. 8, OFDM symbol 0 comprises a front-loaded DMRS 302. OFDM symbol 0 may also be referred to as the first PDCCH OFDM symbol. The DMRS 302 may be part of CDM group 0 302 2 and/or CDM group 1 302 1. OFDM symbol 1 may comprise PDCCH data 301, and OFDM symbols 2 - 6 may comprise PDSCH data 304. The DMRS 302 may comprise the same frequency structure of the PDSCH DMRS, and the DMRS 302 may be used as an RS for both of the PDCCH and PDSCH. According to an embodiment, the network access device 200 is configured to transmit the DMRS at a first orthogonal frequency-division multiplexing, OFDM, symbol of a subframe.

FIG. 9 illustrates a schematic representation of a time- frequency diagram with a combined reference signal for the PDCCH and the PDSCH and an additional DMRS according to an embodiment. According to an embodiment, the network access device 200 may transmit a second DMRS in another OFDM symbol. This DMRS may be present in addition to a front- loaded DMRS. In the embodiment presented in FIG. 9, in addition to the front-loaded DMRS 302 at OFDM symbol 0, also an additional DMRS 302’ is used at OFDM symbol 4. The additional DMRS 302’ may be, for example, at any of the OFDM symbols 2 - 13.

According to an embodiment, the first DMRS and the second DMRS comprise the same frequency structure for each antenna port between the first and the second DMRS. For example, in case of a single port, the frequency pattern can be the same between the first and the second DMRS. In case of multiple ports, the frequency pattern can be the same for each port between the first and the second DMRS. An antenna port may be implemented, for example, as a single physical transmit/receive antenna or as a combination of multiple antenna elements. Same frequency/time orthogonal cover code, OCC, can be applied to ports for both the first and the second DMRS. For example, in the embodiment presented in FIG. 9, the front-loaded DMRS 302 and the additional DMRS 302’ may comprise the same frequency structure for each antenna port.

FIG. 10 illustrates a schematic representation of a time-frequency diagram with a combined reference signal for the PDCCH and the PDSCH and two additional DMRSs according to an embodiment. In this embodiment, DMRSs are transmitted at OFDM symbols 0, 6, and 12. The DMRS 302 at OFDM symbol 0 may be referred to as a front-loaded DMRS. The DMRs at OFDM symbols 6 and 12 may be referred to as additional DMRSs 302’.

According to an embodiment, the network access device is configured to transmit a third DMRS at PDSCH OFDM symbols, wherein the time spacing in OFDM symbols between the third DMRS and the second DMRS is equal to the time spacing in OFDM symbols between the second DMRS and the first DMRS. For example, in the embodiment illustrated in FIG. 10, the time spacing between the additional DMRSs may be equal to the time spacing between the previous DMRSs. In this embodiment, the spacing between the first front-loaded DMRS 302 (OFDM symbol 0) and the first additional DMRS 302’ (OFDM symbol 6) is six OFDM symbols, which is equal to the spacing between the first additional DMRS 302’ (OFDM symbol 6) and the second additional DMRS 302’ (OFDM symbol 12).

FIG. 11 illustrates a schematic representation of a time-frequency diagram with a combined reference signal for the PDCCH and the PDSCH and three additional DMRSs according to an embodiment. According to an embodiment, the network access device 200 is configured to transmit a fourth DMRS at PDSCH OFDM symbols, wherein the time spacing between two adjacent OFDM symbols is equal. For example, in the embodiment illustrated in FIG. 11, DMRSs are transmitted at OFDM symbols 0, 4, 8, and 12. The DMRS 302 at OFDM symbol 0 may be referred to as a front-loaded DMRS. The DMRs at OFDM symbols 4, 8, and 12 may be referred to as additional DMRSs 302’. It should be appreciated that the time spacing between the additional DMRSs 302’ may be equal to the time spacing between the previous DMRSs. In this embodiment, the time spacing between the DMRSs is four OFDM symbols.

FIG. 12 illustrates a schematic representation of a time-frequency diagram with a combined reference signal for the PDCCH and the PDSCH with frequency domain multiplexing according to an embodiment. According to an embodiment, the network access device 200 is configured to transmit PDCCH data by multiplexing the DMRS with PDCCH data in the frequency domain. For example, in the embodiment illustrated in FIG. 12, PDCCH data 301 and/or PDSCH data 304 may be multiplexed in the frequency domain with the DMRSs 302 2. This may require time domain orthogonal cover code, OCC, to be configured. In this embodiment, only DMRSs comprised in CMD group 0 are illustrated. However, multiple CMD groups may be used simultaneously. In this embodiment, at OFDM symbols 0 and 1, DMRSs 302 2 are frequency multiplexed with PDCCH data 301, and at OFDM symbols 10 and 11, DMRSs 302 2 are frequency multiplexed with PDSCH data 304.

According to an embodiment, the network access device 200 is configured to configure another DMRS of the PDSCH for another antenna port of the PDSCH. Additional DMRSs may be defined in the PDSCH region for additional antenna ports or layers of the PDSCH. In some cases, the PDSCH may require more antenna ports than the PDCCH. For example, one DMRS may be required for each such antenna port.

FIG. 13 illustrates a schematic representation of a time-frequency diagram with a combined reference signal for the PDCCH and the PDSCH and with frequency domain multiplexing according to another embodiment. In this embodiment, both CDM group 0 and CMD group 1 are used for the DMRSs 302. Additional DMRSs 302 may be defined in the PDSCH region for additional antenna ports (layers) of the PDSCH. This may be useful, for example, if more additional ports are required by the PDSCH.

The patterns of the DMRSs 302 in frequency and time described in the embodiments above are only examples of possible patterns for the DMRSs. A DMRS pattern described in an embodiment can be combined with a pattern described in another embodiment. Furthermore, when a DMRS is transmitted at an OFDM symbol, all subcarriers at that OFDM symbol are not necessarily used for DMRS.

FIG. 14 illustrates a schematic representation of simulation results for an extended pedestrian A, EPA, 30 model, according to an embodiment. Curve 141 illustrates the effective signal-to -noise ratio, SNR, as a function of the SNR of the channel when the embodiment is used. Curve 142 illustrates the effective SNR as a function of the SNR of the channel when the embodiment is not used.

FIG. 15 illustrates a schematic representation of simulation results for an EPA 70 model, according to an embodiment. Curve 151 illustrates the effective SNR as a function of the SNR of the channel when the embodiment is used. Curve 152 illustrates the effective SNR as a function of the SNR of the channel when the embodiment is not used.

FIG. 16 illustrates a schematic representation of simulation results for an EPA 120 model, according to an embodiment. Curve 161 illustrates the effective SNR as a function of the SNR of the channel when the embodiment is used. Curve 162 illustrates the effective SNR as a function of the SNR of the channel when the embodiment is not used.

FIG. 17 illustrates a schematic representation of simulation results for an EPA 300 model, according to an embodiment. Curve 171 illustrates the effective SNR as a function of the SNR of the channel when the embodiment is used. Curve 172 illustrates the effective SNR as a function of the SNR of the channel when the embodiment is not used.

The functionality described herein can be performed, at least in part, by one or more computer program product components such as software components. According to an embodiment, the network access device 200 and/or the client device 100 comprise the processor 101, 201 configured by the program code when executed to execute the embodiments of the operations and functionality described. Alternatively, or in addition, the functionality described herein can be performed, at least in part, by one or more hardware logic components. For example, and without limitation, illustrative types of hardware logic components that can be used include Field-programmable Gate Arrays (FPGAs), Program-specific Integrated Circuits (ASICs), Program-specific Standard Products (ASSPs), System-on-a-chip systems (SOCs), Complex Programmable Logic Devices (CPLDs), Graphics Processing Units (GPUs). Any range or device value given herein may be extended or altered without losing the effect sought. Also any embodiment may be combined with another embodiment unless explicitly disallowed.

Although the subject matter has been described in language specific to structural features and/or acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as embodiments of implementing the claims and other equivalent features and acts are intended to be within the scope of the claims.

It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages. It will further be understood that reference to 'an' item may refer to one or more of those items. The term‘and/or’ may be used to indicate that one or more of the cases it connects may occur. Both, or more, connected cases may occur, or only either one of the connected cases may occur.

The operations of the methods described herein may be carried out in any suitable order, or simultaneously where appropriate. Additionally, individual blocks may be deleted from any of the methods without departing from the spirit and scope of the subject matter described herein. Aspects of any of the embodiments described above may be combined with aspects of any of the other embodiments described to form further embodiments without losing the effect sought.

The term 'comprising' is used herein to mean including the method, blocks or elements identified, but that such blocks or elements do not comprise an exclusive list and a method or apparatus may contain additional blocks or elements.

It will be understood that the above description is given by way of example only and that various modifications may be made by those skilled in the art. The above specification, embodiments and data provide a complete description of the structure and use of exemplary embodiments. Although various embodiments have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this specification.

Claims

1. A network access device (200), configured to:

configure a demodulation reference signal, DMRS, of a physical downlink control channel, PDCCH, for transmission to a client device, wherein the DMRS of the PDCCH is also configured to operate as a DMRS of a physical downlink shared channel, PDSCH; and

schedule the PDSCH and the PDCCH based on the configured DMRS, wherein the DMRS is configured for each transmission of the PDCCH and PDSCH.

2. The network access device of claim 1, further configured to:

receive a category report from a client device; and

in response to the category report indicating that the client device is capable of joint channel estimation for the PDCCH and the PDSCH, omit transmitting a front-loaded DMRS before a first PDSCH orthogonal frequency division multiplexing, OFDM, symbol.

3. The network access device of claim 1 or 2, wherein the DMRS is a combined reference signal for both the PDCCH and the PDSCH.

4. The network access device of any preceding claim, further configured to:

transmit a second DMRS in another OFDM symbol.

5. The network access device of claim 3 or 4, further configured to:

transmit the DMRS at a first orthogonal frequency-division multiplexing, OFDM, symbol of a subframe.

6. The network access device of claim 4, wherein the first DMRS and the second DMRS comprise the same frequency structure for each antenna port between the first and the second DMRS.

7. The network access device of claim 3, wherein the DMRS is a front-loaded DMRS at a first PDCCH OFDM symbol.

8. The network access device of any preceding claim, further configured to:

transmit PDCCH data by multiplexing the DMRS with PDCCH data in a frequency domain.

9. The network access device of claim 4, further configured to:

transmit a third DMRS at PDSCH OFDM symbols, wherein the time spacing in OFDM symbols between the third DMRS and the second DMRS is equal to the time spacing in OFDM symbols between the second DMRS and the first DMRS.

10. The network access device of claim 9, further configured to:

transmit a fourth DMRS at PDSCH OFDM symbols, wherein the time spacing between two adjacent OFDM symbols is equal.

11. The network access device of claim 9, wherein an OFDM symbol index is [0, 6, 12]; or the network access device of claim 10, wherein an OFDM symbol index is [0, 4, 8, 12]

12. The network access device of any preceding claim, further configured to: configure another DMRS of the PDSCH for another antenna port of the PDSCH.

13. The network access device of any preceding claim, further configured to:

transmit a radio resource control, RRC, signal and/or a downlink control information,

DCI, signal to the client device for enabling or disabling the client device for the common DMRS.

14. The network access device of any preceding claim, further configured to:

schedule the PDSCH and the PDCCH with associated antenna ports and aligned frequency resources based on the configured DMRS.

15. A client device (100), configured to:

receive a demodulation reference signal, DMRS, via a physical downlink control channel, PDCCH, from a network access device;

receive physical downlink shared channel, PDSCH, data; and

jointly estimate a channel of the PDCCH and the received PDSCH data using the received DMRS of the PDCCH.

16. A method, comprising:

configuring a demodulation reference signal, DMRS, of a physical downlink control channel, PDCCH, for transmission to a client device, wherein the DMRS of the PDCCH is also configured to operate as a DMRS of a physical downlink shared channel, PDSCH; and

scheduling the PDSCH and the PDCCH based on the configured DMRS, wherein the

DMRS is configured for each transmission of the PDCCH and PDSCH.

17. A method, comprising:

receiving a demodulation reference signal, DMRS, via a physical downlink control channel, PDCCH, from a network access device;

receiving physical downlink shared channel, PDSCH, data; and

jointly estimating a channel of the PDCCH and the received PDSCH data using the received DMRS of the PDCCH.

18. A computer program comprising program code configured to perform a method according to claim 16 or claim 17 when the computer program is executed on a computer.