WO2013110212A1

WO2013110212A1 - Communication mechanism using group based demodulation reference signal

Info

Publication number: WO2013110212A1
Application number: PCT/CN2012/070719
Authority: WO
Inventors: Xiaoyi Wang; Chun Ye Wang; Klaus Hugl
Original assignee: Nokia Siemens Networks Oy; Nokia Corporation
Priority date: 2012-01-26
Filing date: 2012-01-26
Publication date: 2013-08-01

Abstract

There is provided a mechanism for conducting communications by using group based demodulation reference signals. A communication network control element such as an eNB multiplexes plural communications to plural UEs grouped in one UE group in at least one resource block of communication resources. A first group demodulation reference signal providing demodulation information for communications at the destinations is transmitted to each UE of the UE group in predetermined resource elements of the at least one resource block, wherein the transmission is caused via the same preconfigured transmitter port or ports and with the same preconfigured signaling sequence for all of the plural UEs in the UE group.

Description

COMMUNICATION MECHANISM USING GROUP BASED DEMODULATION

REFERENCE SIGNAL

DESCRIPTION

BACKGROUND OF THE INVENTION

Field of the invention

The present invention relates to a mechanism for conducting communications by using group based demodulation reference signals. Specifically, the present invention is related to an apparatus, a method and a computer program product which provide a communication mechanism in which a group based demodulation reference signal is provided for improving performance of a communication system, in particular with regard to a beamforming gain.

The following meanings for the abbreviations used in this specification apply:

BS : base station

CDM : code division multiplexing

CSI : channel state information

DL: downlink

DM RS : demodulation reference signal

eNB: enhanced node B

ePDCCH : enhanced physical downlink control channel

FDM : frequency division multiplexing

LTE : Long Term Evolution

LTE-A: LTE Advanced

MIMO : multiple input multiple output

MU : multiple user

PDCCH : physical downlink control channel

PDSCH : physical downlink shared channel PUCCH : physical uplink control channel

PUSCH : physical uplink shared channel

PRB: physical resource block

QPSK: quadrature phase shift keying

RE : resource element

SINR: signal interference plus noise ratio

SU : single user

TDM : time division multiplexing

UE : user equipment

UL: uplink

ZF: zero forcing

In the last years, an increasing extension of communication networks, e.g. of wire based communication networks, such as the Integrated Services Digital Network (ISDN), DSL, or wireless communication networks, such as the cdma2000 (code division multiple access) system, cellular 3rd generation (3G) and fourth generation (4G) communication networks like the Universal Mobile Telecommunications System (UMTS), enhanced communication networks based e.g. on LTE or LTE-A, cellular 2nd generation (2G) communication networks like the Global System for Mobile communications (GSM), the General Packet Radio System (GPRS), the Enhanced Data Rates for Global Evolution (EDGE), or other wireless communication system, such as the Wireless Local Area Network (WLAN), Bluetooth or Worldwide Interoperability for Microwave Access (WiMAX), took place all over the world. Various organizations, such as the 3rd Generation

Partnership Project (3GPP), Telecoms & Internet converged Services & Protocols for Advanced Networks (TISPAN), the International Telecommunication Union (ITU), 3rd Generation Partnership Project 2 (3GPP2), Internet Engineering Task Force (IETF), the IEEE (Institute of Electrical and Electronics Engineers), the WiMAX Forum and the like are working on standards for telecommunication network and access environments.

Generally, for properly establishing and handling a communication connection between communication elements such as a user equipment

(UE) and another communication element or user equipment, a database, a server, etc., one or more intermediate network elements such as communication network control elements, support nodes or service nodes are involved which may belong to different communication network. Current communication networks are adapted to be capable of MIMO communications, wherein both SU-MIMO and MU-MIMO scenarios are to be covered. MIMO is seen as a key technique in modern cellular communication systems such as LTE or LTE-A based networks and refers to the use of multiple antennas at both the transmitter and receiver sides. That is, both base stations like eNBs and terminal devices like UEs are equipped with multiple antenna elements intended to be used in transmission and reception to provide MIMO capabilities in both UL and DL.

In typical case of multi-user operation, communication channels of multiple users, such as the users' PDSCH, are multiplexed using different multiplexing methods. For example, a method based on a principle of an orthogonal precoder generated from zero forcing (ZF) beamforming is used.

Each user's PDSCH is associated with one or more reference signals which are precoded in the same way as data to be transmitted so as to enable a terminal to estimate communication conditions, such as the overall beamformed channel. A corresponding reference signal is, for example, a UE specific DM RS which is transmitted by using the same precoder. DM RS is introduced, for example, in 3GPP LTE based communication networks to enable a UE specific demodulation. With the presence of DM RS, UE specific beamforming gain can be achieved with fine granular of precoding weights from the transmitter side, wherein as one important gain multi-user operation is supported. It is possible to apply quasi-orthogonal or orthogonal DM RS between users.

Then, on the basis of the UE specific DM RS, the UE performs a channel estimation processing so as to decode the corresponding PDSCH .

In other words, as a general principle of multi-user operation, users can be separated by different transmission beam direction (spatial domain), wherein ZF is used to make the transmission beam null to another paired user. ZF (or null steering) precoding is a spatial signal processing by means of which a transmitter with plural antennas can null multiuser interference signals in wireless communications. Spatial domain multiplexing is a way to utilize the available spectrum but it is sensitive to the accuracy of measurements of channel properties, for example of CSI. In order to overcome problems related to inaccuracy of CSI, preferably orthogonal UE specific DM RS are used. However, when orthogonal DM RS is used, the number of effective DMRS RE which can be used by each UE is also reduced.

It is to be noted that besides spatial domain multiplexing there are other ways for multiplexing, e.g. FDM, TDM or CDM . However, in case spatial domain user multiplexing is not done, UE specific DM RS should be orthogonal to each other by some way as well. For example, in case a communication system using a control channel such as ePDCCH (ePDCCH may be multiplexed with other channels such as PDSCH or other ePDCCH for the same or a different UE) and the ePDCCH is multiplexed by multiple UEs within one or more PRBs, e.g. by using a CDM method, the UE specific DM RS should be orthogonal between users so as to guarantee an accurate channel estimation for demodulation.

The number of REs used for DM RS transmission is however limited. According to current settings, e.g. in LTE communication systems, altogether 24 RE per PRB can be used for DM RS. Thus, in a case where for example eight UEs are paired (multiplexed), each UE only has the power of three effective REs available for channel estimation. This may be however not sufficient for conducting reliable channel estimation, in particular at the edge of a cell.

The transmission scheme of DM RS according to current communication network specifications is shown as an example in Fig. 8. Fig. 8 shows a diagram illustrating a reference signal structure (normal cyclic prefix) in REs of a PRB transmitted by different antenna ports (here antenna ports 7 to 10 are depicted). Specifically, for each antenna port 7 to 10, special subframe configurations are indicated, wherein REs indicated by an entry "Ri" (i represents the antenna port number 7 to 10) represent the REs used for DM RS transmission. As can be seen from Fig. 8, in case only DMRS (antenna) port 7 is used, the number of effective REs for port 7 is twelve. In case antenna port 8 is added on top of antenna port 7 due to multiplexing operation using for example CDM, then the number of effective RE becomes

6 (since overlapping is to be prohibited). This happens also when ports 9 and 10 are considered. In case DMRS ports 11, 12 are required, they are further added overlapped with ports 7, 8 by using e.g. CDM type multiplexing. That is, the effective number of REs for each DM RS port is continuously reduced when multiplexing is employed reduced.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved mechanism for providing demodulation information for channel estimation in case of multiplexed communications. In particular, it is an object of the present invention to provide an apparatus, a method and a computer program product which allows to increase the number of effective DMRS REs for a terminal device such as a UE usable for conducting channel estimation.

These objects are achieved by the measures defined in the attached claims.

According to an example of an embodiment of the proposed solution, there is provided, for example, an apparatus comprising at least one processor, at least one interface to at least one other network element, and a memory for storing instructions to be executed by the processor, wherein the at least one processor comprises a multiplexing processing portion configured to multiplex plural communications between the at least one interface and plural destinations in at least one resource block of communication resources, and an allocator configured to allocate a first group demodulation reference signal providing demodulation information for communications at the destinations to each of the plural communications.

Furthermore, according to an example of an embodiment of the proposed solution, there is provided, for example, a method comprising multiplexing plural communications between the at least one interface and plural destinations in at least one resource block of communication resources, and allocating a first group demodulation reference signal providing demodulation information for communications at the destinations to each of the plural communications.

According to further refinements, these examples may comprise one or more of the following features:

- transmitting of the first group demodulation reference signal may be caused in predetermined resource elements of the at least one resource block, wherein the transmission may be caused via the same preconfigured transmitter port or ports of at least one interface and with the same preconfigured signaling sequence for all of the plural destinations;

- the multiplexing of the plural communications may be based on a grouping of terminal devices representing the plural destinations into at least one device group;

- a modulation scheme to which the demodulation information in the first group demodulation reference signal is related may be based on quadrature phase shift keying;

- a precoding may be conducted by applying a same precoder weight setting to all of the plural communications, wherein the precoder weight setting may be determined on the basis of channel state information received from a group of destinations of the plural communications;

- a second group demodulation reference signal being orthogonal to the first group demodulation reference signal may be allocated to at least one of the plural communications, and, from the plural communications, at least one of a first set of communications to which the first group demodulation reference signal is to be allocated, a second set of communications to which the second group demodulation reference signal is to be allocated, and a third set of communications to which the first group demodulation reference signal and the second group demodulation reference signal are to be allocated may be selected;

- transmitting of the second group demodulation reference signal may be caused in predetermined resource elements of the at least one resource block, wherein the transmission is caused via the same preconfigured transmitter port or ports of at least one interface and with the same preconfigured signaling sequence for all of the plural destinations, wherein at least one of the preconfigured transmitter port or ports of the at least one interface and the preconfigured signaling sequence used for the second group demodulation reference signal is different to a preconfigured transmitter port or ports of the at least one interface and a preconfigured signaling sequence used for the first group demodulation reference signal;

- the apparatus or method may be implemented in a communication network control element, in particular an enhanced Node B of a Long Term Evolution or Long Term Evolution Advanced communication network.

According to an example of an embodiment of the proposed solution, there is provided, for example, an apparatus comprising at least one processor, at least one interface to at least one other network element, and a memory for storing instructions to be executed by the processor, wherein the at least one interface is configured to receive multiplexed communications in at least one resource block of communication resources, and wherein the processor further comprises a demodulation reference signal determining portion configured to determine a first group demodulation reference signal allocated to the multiplexed communications and providing demodulation information for demodulating the communication, a channel estimation processing portion configured to conduct a channel estimation on the basis of the first group demodulation reference signal, and a decoding processing portion configured to conduct decoding of at least a part of the multiplexed communications.

According to an example of an embodiment of the proposed solution, there is provided, for example, a method comprising receiving multiplexed communications in at least one resource block of communication resources, determining a first group demodulation reference signal allocated to the multiplexed communications and providing demodulation information for demodulating the communication, conducting a channel estimation on the basis of the first group demodulation reference signal, and conducting decoding of at least a part of the multiplexed communications.

According to further refinements, these examples may comprise one or more of the following features: - the first group demodulation reference signal may be received in predetermined resource elements of the at least one resource block, wherein the first group demodulation reference signal may be received by a transmission from the same preconfigured transmitter port or ports and with the same preconfigured signaling sequence for all destinations of the multiplexed communications;

- the multiplexing of the communications may be based on a grouping of terminal devices representing destinations of the communications into at least one device group;

- a second group demodulation reference signal allocated to the multiplexed communications and providing demodulation information for demodulating the communication may be determined, wherein a channel estimation may be conducted on the basis of the second group demodulation reference signal, wherein is may be determined which of the first group demodulation reference signal and the second group demodulation reference signal is or are to be used.

- the second group demodulation reference signal may be received in predetermined resource elements of the at least one resource block, wherein the second group demodulation reference signal may be received by a transmission from the same preconfigured transmitter port or ports and with the same preconfigured signaling sequence for all destinations of the multiplexed communications, wherein at least one of the preconfigured transmitter port or ports and the preconfigured signaling sequence used for the second group demodulation reference signal may be different to a preconfigured transmitter port or ports and a preconfigured signaling sequence used for the first group demodulation reference signal;

- the apparatus or method may be implemented in a communication network element, in particular a terminal device or user equipment usable in a Long Term Evolution or Long Term Evolution Advanced communication network.

In addition, according to examples of the proposed solution, there is provided, for example, a computer program product for a computer, comprising software code portions for performing the steps of the above defined methods, when said product is run on the computer. The computer program product may comprise a computer-readable medium on which said software code portions are stored. Furthermore, the computer program product may be directly loadable into the internal memory of the computer and/or transmittable via a network by means of at least one of upload, download and push procedures.

By virtue of the proposed solutions, it is possible to provide a mechanism by means of which the number of the number of effective DMRS REs for a terminal device such as a UE, which are usable for conducting channel estimation, is increased. Specifically, by providing group based DMRS, for each paired UE, the number of effective DMRS RE is higher in case of a conventional orthogonal DMRS approach in case of multiplexing so that the DM RS power and the related decoding performance can be increased.

Thus, it is possible to achieve an enhanced channel estimation quality which is especially beneficial at cell edge located UEs. Furthermore, it is possible to combine group based DMRS with orthogonal DMRS scheme. When the communication network control element groups UEs having e.g. a similar location together by using the same group DM RS, beamforming gain can be achieved for the group of UEs. If furthermore orthogonal DM RS are assigned between UE groups, spatial reuse is possible, similar to basic DM RS based MU-MIMO. Hence, the group size of DMRS can be flexibly adjusted and a good balanced gain between UE specific beamforming gain and effective RE number can be achieved.

The above and still further objects, features and advantages of the invention will become more apparent upon referring to the description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a diagram illustrating a communication network configuration where examples of embodiments of the invention are implemented. Fig. 2 shows a diagram illustrating a communication network configuration where examples of embodiments of the invention are implemented.

Fig. 3 shows a diagram illustrating a communication network configuration where examples of embodiments of the invention are implemented.

Fig. 4 shows a flowchart illustrating a processing executed in a communication network control element according to examples of embodiments of the invention.

Fig. 5 shows a flowchart illustrating a processing executed in a communication network element according to examples of embodiments of the invention.

Fig. 6 shows a block circuit diagram of a communication network control element including processing portions conducting functions according to examples of embodiments of the invention.

Fig. 7 shows a block circuit diagram of a communication network element including processing portions conducting functions according to examples of embodiments of the invention.

Fig. 8 shows a diagram illustrating a reference signal structure (normal cyclic prefix) in a resource block.

DESCRIPTION OF PREFERRED EMBODIMENTS

In the following, examples and embodiments of the present invention are described with reference to the drawings. For illustrating the present invention, the examples and embodiments will be described in connection with a cellular communication network based on a 3GPP LTE or LTE-A system . However, it is to be noted that the present invention is not limited to an application using such types of communication system, but is also applicable in other types of communication systems and the like. A basic system architecture of a communication network where examples of embodiments of the invention are applicable may comprise a commonly known architecture of one or more communication systems comprising a wired or wireless access network subsystem and a core network. Such an architecture may comprise one or more access network control elements, radio access network elements, access service network gateways or base transceiver stations, such as a base station (BS) or eNB, which control a coverage area also referred to as a cell and with which one or more communication elements or terminal devices such as a UE or another device having a similar function, such as a modem chipset, a chip, a module etc., which can also be part of a UE or attached as a separate element to a UE, or the like, are capable to communicate via one or more channels for transmitting several types of data. Furthermore, core network elements such as gateway network elements, policy and charging control network elements, mobility management entities and the like may be comprised.

The general functions and interconnections of the described elements, which also depend on the actual network type, are known to those skilled in the art and described in corresponding specifications, so that a detailed description thereof is omitted herein. However, it is to be noted that several additional network elements and signaling links may be employed for a communication to or from a communication element like a UE or a communication network control element like an eNB, besides those described in detail herein below.

Furthermore, the described network elements, such as communication elements like UEs or communication network control elements like BSs or eNBs and the like, as well as corresponding functions as described herein may be implemented by software, e.g. by a computer program product for a computer, and/or by hardware. In any case, for executing their respective functions, correspondingly used devices, nodes or network elements may comprise several means and components (not shown) which are required for control, processing and communication/signaling functionality. Such means may comprise, for example, one or more processor units including one or more processing portions for executing instructions, programs and for processing data, memory means for storing instructions, programs and data, for serving as a work area of the processor or processing portion and the like (e.g. ROM, RAM, EEPROM, and the like), input means for inputting data and instructions by software (e.g. floppy disc, CD-ROM, EEPROM, and the like), user interface means for providing monitor and manipulation possibilities to a user (e.g. a screen, a keyboard and the like), interface means for establishing links and/or connections under the control of the processor unit or portion (e.g. wired and wireless interface means, an antenna, etc.) and the like. It is to be noted that in the present specification processing portions should not be only considered to represent physical portions of one or more processors, but may also be considered as a logical division of the referred processing tasks performed by one or more processors.

With regard to Fig. 1, a diagram illustrating a general configuration of a communication network where examples of embodiments of the invention are implemented. It is to be noted that the configuration shown in Fig. 1 shows only those devices network elements and parts which are useful for understanding principles underlying the examples of embodiments of the invention. As also known by those skilled in the art there may be several other network elements or devices involved in a connection between the communication elements (UEs) and the network which are omitted here for the sake of simplicity.

In Fig. 1, a communication network configuration is illustrated in which examples of embodiments of the invention are implementable. The network according to Fig. 1 is for example based on 3GPP LTE or LTE-A specifications. It is to be noted that the general functions of the elements described in connection with Fig. 1 as well as of reference points/interfaces therebetween are known to those skilled in the art so that a detailed description thereof is omitted here for the sake of simplicity. As shown in Fig. 1, in the exemplary communication network, one or more cells representing coverage areas of a communication network control element like an eNB 10 are provided, for example a cell 15. The eNB 10 is able to conduct MIMO operation, wherein users (UEs) are separated or grouped into UE groups, for example in accordance with different transmission beam directions (spatial domain multiplexing). For example, the eNB 10 forms plural beams (in Fig. 1 two beams 41 and 42 are shown but more than these are possible) in different directions, wherein UEs (such as UE 20) being located in the direction of e.g. beam 41 are grouped in a UE group 1 30.

It is to be noted that besides spatial domain multiplexing there are other ways of multiplexing, e.g. FDM, TDM or CDM, or hybrid methods based on FDM, TDM, CDM, which can be employed in examples of embodiments of the invention.

According to examples of embodiments of the invention, for providing demodulation information, a group based DM RS (or group DM RS) is used. That is, when communications to a group of UEs, such as UE group 1 30, are multiplexed in the same PRB(s), the UEs of this group of UE share the same group DM RS.

The group DM RS is transmitted in specific REs of a PRB with a preconfigured port and sequence (see e.g. Fig. 8). For example, in case of e.g. an ePDCCH, eight UEs may be multiplexed in PRB(s) by using, for example, CDM or other multiplexing method. Consequently, ePDCCH has 8 layers. According to examples of embodiments of the invention, all 8 layers share one group DM RS i.e. the same DM RS port and sequence. On the UE side, such as for example in UE 20 belonging to UE group 1 30 to which the group DM RS is allocated, each UE performs channel estimation processing based the group DM RS. Then, the channels such as ePDCCH are decoded by using a corresponding preset multiplexing code, such as an own CDM code (in case code division multiple access (CDMA) is used). It is to be noted that from each UE point of view, DM RS REs and data REs may have different transmit power. That is, it is possible that the effective transmission power of DM RS is several times (e.g. 8 times) higher than that of data REs. In order to overcome this, according to examples of embodiments of the invention, QPSK modulation is used in order to avoid that a UE has wrong power assumption from DM RS based channel estimation.

When using group DM RS, according to examples of embodiments of the invention, the same precoder weight matrix may be used for all communications to the respective destinations, i.e. to all UEs of the UE group 1 30, for example. According to examples of embodiments, the eNB 10 calculates the precoder by considering channel measurements from the UEs belonging to a group, e.g. by considering CSI from the UEs of UE group 1 30, rather than of a single UE. For example, according to one example of embodiments, a precoder is generated by the eNB 10 in such a manner that an averaging reception SINR from all UEs is maximized.

It is to be noted that due to the usage of the same precoder for all UEs, it is possible that the beamforming gain will be degraded to some extent since no UE specific precoder is applied. Therefore, according to examples of embodiments of the invention, the eNB performs a suitable scheduling of transmissions so as to minimize the degradation by grouping UEs with similar beam directions together. Such a suitable scheduling is set such that each UE in the UE group (e.g. UE group 1 30) can get a similar received signal strength gain comparable to that in a UE specific DMRS based beamforming scenario. Furthermore, for example, when considering a case of communications in ePDCCH, as a UE will do blind decoding of multiple PRBs, the eNB 10 is enabled to conduct flexible scheduling so as to achieve a proper beamforming gain. Besides, in some application cases, such as a scenario with 2Tx configuration, the potential beamforming gain is anyway rather small.

By means of using the group DM RS, it is possible to increase the effective number of REs for DM RS which each of the UEs in the UE group can use for channel estimation. That is, the group based DM RS allows that for each paired UE the number of effective DMRS RE is higher than e.g. in an orthogonal DMRS approach. For example, when there are eight UEs paired in one ePDCCH PRB(s), each of the UEs still have twelve effective REs per PRB (following current DMRS design). This allows to achieve a good channel estimation quality, in particular for UEs located near the cell edge.

In other words, according to examples of embodiments of the invention, in contrast to an approach where the PRBs are multiplexed/shared between different UEs (by means of MU-MIMO) and each UE is allocated its own DM RS, the same, single DM RS signal transmitted via one preconfigured antenna port (e.g. port 7 as shown in Fig. 8) is used as a phase reference for demodulation for the several UEs sharing the same resources, such as ePDCCH resources. With regard to Fig. 2, a diagram illustrating a general configuration of a communication network where examples of embodiments of the invention are implemented. It is to be noted that the configuration shown in Fig. 2 is similar to that shown in Fig. 1. Thus, for the sake of simplicity, only those parts of the configuration according to Fig. 2 are described which are related to the differences of the present example of embodiments of the invention.

As shown in Fig. 2, in addition to the one group of UEs (i.e. UE group 1 30 associated to beam 41) indicated in Fig. 1, there is provided a second group of UEs (UE group 2 35, comprising for example a UE 25), associated to beam 42.

That is, according to the present example of embodiments of the invention, there are two group DM RS provided which are preferably orthogonal. For example, when communications according to e.g. ePDCCHs for eight UEs are transmitted in a resource unit, such as one PRB pair (which may be a basic ePDCCH resource unit), two orthogonal DM RS are used. For example, when considering a configuration as depicted in Fig. 8, DMRS (antenna) ports 7 and 8 are used. Then, for example, a first group of UEs comprising e.g. 4 UEs shares DMRS port 7 (indicated in Fig. 2 by UE group 1 30 associated to beam 41) and hence a first group DM RS, and a second group of UEs comprising e.g. 4 UEs shares DMRS port 8 (indicated in Fig. 2 by UE group 2 35 associated to beam 42) and hence a second group DM RS.

By means of a configuration as described in connection with Fig. 2, a communication network control element such as eNB 10 is able to group the

UEs having e.g. a similar location together and to use the same group DM RS, so that beamforming gain can be achieved for a group of UEs, while at the same time orthogonal DM RS are assigned between the two groups 1 and 2 as shown in Fig. 2 so as to allow spatial reuse (similar to basic DMRS based MU-MIMO). Hence, a group size to which one group DMRS is allocated can be flexibly adjusted so as to achieve a balance in gain between UE specific beamforming gain and effective RE number.

With regard to Fig. 3, a diagram illustrating a general configuration of a communication network where examples of embodiments of the invention are implemented. It is to be noted that the configuration shown in Fig. 3 is similar to that shown in Fig. 1. Thus, for the sake of simplicity, only those parts of the configuration according to Fig. 3 are described which are related to the differences of the present example of embodiments of the invention.

As shown in Fig. 3, at least one UE (here UE 28) of one UE group (here UE group 1 30) is selected to use more than one antenna port (e.g. port 7 and port 9) for demodulation of at least one data stream . In other words, several ports may be used for generating a group DM-RS signaling usable for detection by the UE 28. For selecting the at least one UE, a corresponding request may be used which is sent from the communication network control element (e.g. eNB 10) and received and processed by UE 28. By means of the approach as described with Fig. 3, the number of REs of DM-RS can be further increased for the at least one UE, so that the DM¬

RS power (and the related decoding performance) can be increased. Moreover, when e.g. two (or more) DM-RS ports are used for a group DMRS to support a single layer, the UE combines estimates from the plural ports used for the group DM-RS so as to detect a single data stream . According to examples of embodiments of the invention, the communication network control element, such as the eNB 10, calculates a suitable precoding weight vector for a group of UEs (wherein more than one group may be present) and applies the weight vector to both data and DM RS signaling to the (respective) group of UEs.

Fig. 4 shows a flowchart illustrating a processing executed in a communication network control element like eNB 10 of Figs. 1 to 3 according to examples of embodiments of the invention in a mechanism for conducting communications by using group based DM RS.

In step S10, plural communications between the eNB 10 and plural destinations (i.e. UEs grouped in a UE group like UE group 1) are multiplexed in one or more same PRBs.

In step S20, a first group DM RS is allocated to the group of UEs for providing demodulation information for the communications at all of the destinations to each of the plural multiplexed communications. It is to be noted that in case it is decided that a further (second) DM RS being orthogonal to the first DM RS is to be used, in step S20, a corresponding allocation of the second group DM RS and a selection of which UE(s) is/are to be allocated to the first and/or second DM RS is conducted.

In step S30, transmission of the (first and/or second) group DM RS signal is caused in predetermined REs of the PRB(s), wherein the transmission is conducted via the same preconfigured logical transmitter port (e.g. port 7) of the antennas of the eNB 10 and with the same preconfigured signaling sequence for all UEs to which the group DM RS is allocated (wherein in case the second group DM RS is to be used as well, a different port/sequence is used).

Fig. 5 shows a flowchart illustrating a processing executed in a communication network element like UE 20, 25, 28 of Figs. 1 to 3 according to examples of embodiments of the invention in a mechanism for conducting communications by using group based DM RS. In step S110, the communication device or UE receives multiplexed communications from the eNB side, wherein communications directed to this specific UE are multiplexed with other communications related to UEs belonging to the same group of UEs.

In step S120, a (first and/or second) group DM RS allocated to the multiplexed communications, which provides demodulation information for demodulating the communication, is determined. The group DM RS is received in predetermined REs of a PRB in which the communications are multiplexed via a transmission from the same preconfigured antenna port and executed with the same preconfigured signaling sequence for all destinations of the multiplexed communications, i.e. for all UEs of the group of UEs concerned.

In step S130, a channel estimation processing is conducted on the basis of the determined (first and/or second) group DM RS.

In step S140, decoding of that part of the multiplexed communications being related to the UE is executed.

In Fig. 6, a block circuit diagram illustrating a configuration of a communication network control element, such as of eNB 10, is shown, which is configured to implement the processing for providing the group DM RS as described in connection with the examples of embodiments of the invention. It is to be noted that the communication network control element or eNB 10 shown in Fig. 6 may comprise several further elements or functions besides those described herein below, which are omitted herein for the sake of simplicity as they are not essential for understanding the invention. Furthermore, even though reference is made to an eNB, the communication network element may be also another device having a similar function, such as a modem chipset, a chip, a module etc., which can also be part of a control element or BS or attached as a separate element to a BS, or the like. The communication network control element or eNB 10 may comprise a processing function or processor 11, such as a CPU or the like, which executes instructions given by programs or the like related to the communication mechanism using group based DM RS. The processor 11 may comprise one or more processing portions dedicated to specific processing as described below, or the processing may be run in a single processor. Portions for executing such specific processing may be also provided as discrete elements or within one or more further processors or processing portions, such as in one physical processor like a CPU or in several physical entities, for example. Reference sign 12 denote transceiver or input/output (I/O) units (interfaces) connected to the processor 11. The I/O units 12 may be used for communicating with a communication element like a UE. The I/O unit 12 may be a combined unit comprising communication equipment towards several network elements, or may comprise a distributed structure with a plurality of different interfaces for different network elements. For example, the I/O units 12 are connected to respective antenna ports as indicated in Fig. 8. Reference sign 13 denotes a memory usable, for example, for storing data and programs to be executed by the processor 11 and/or as a working storage of the processor 11.

The processor 11 is configured to execute processing related to the above described communication mechanism using group based DM RS. In particular, the processor 11 comprises a sub-portion 111 as a processing portion which is usable for conducting multiplexing operation. The portion 111 may be configured to perform processing according to step S10 of Fig.

4, for example. Furthermore, the processor 11 comprises a sub-portion 112 usable as a portion for allocating communications/UEs to the (first and/or second) group DM RS. The portion 112 may be configured to perform processing according to step S20 of Fig. 4, for example. In addition, the processor 11 comprises a sub-portion 113 as a processing portion which is usable for conducting precoding. Furthermore, the processor 11 comprises a sub-portion 114 usable as a portion for selecting communications/UEs for allocation of a first group DM RS and/or a second group DM RS (if provided) to each of the communications/UEs of a specific group. In Fig. 7, a block circuit diagram illustrating a configuration of a communication element, such as of UE 20 shown in Fig. 1, is shown, which is configured to implement the processing for providing/using the group DM RS as described in connection with the examples of embodiments of the invention. It is to be noted that the communication element or UE 20 shown in Fig. 7 may comprise several further elements or functions besides those described herein below, which are omitted herein for the sake of simplicity as they are not essential for understanding the invention. Furthermore, even though reference is made to a UE, the communication element may be also another device having a similar function, such as a modem chipset, a chip, a module etc., which can also be part of a UE or attached as a separate element to a UE, or the like.

The communication element or UE 20 may comprise a processing function or processor 21, such as a CPU or the like, which executes instructions given by programs or the like related to the above described communication mechanism using group based DM RS. The processor 21 may comprise one or more processing portions dedicated to specific processing as described below, or the processing may be run in a single processor. Portions for executing such specific processing may be also provided as discrete elements or within one or more further processors or processing portions, such as in one physical processor like a CPU or in several physical entities, for example. Reference sign 22 denotes transceiver or input/output (I/O) units or interfaces connected to the processor 21. The I/O units 22 may be used for communicating with elements of the access network, such as a communication network control element like an eNB. The I/O units 22 may be a combined unit comprising communication equipment towards several of the network element in question, or may comprise a distributed structure with a plurality of different interfaces for each network element in question. Reference sign 23 denotes a memory usable, for example, for storing data and programs to be executed by the processor 21 and/or as a working storage of the processor 21. The processor 21 is configured to execute processing related to the above described communication mechanism using group based DM RS, for example. In particular, the processor 21 comprises a sub-portion 211 as a processing portion which is usable for receiving and processing multiplexed communications. The portion 211 may be configured to perform processing according to step S110 according to Fig. 5, for example. Furthermore, the processor 21 comprises a sub-portion 212 as a processing portion which is usable as a portion for determining the group based DM RS. The portion 212 may be configured to perform a processing according to step S120 according to Fig. 5, for example. Moreover, the processor 21 comprises a sub-portion 213 as a processing portion which is usable as a portion for conducting a channel estimation process based on the group based DM RS. The portion 213 may be configured to perform processing according to step S1300 according to Fig. 5, for example. In addition, the processor 21 may comprise a sub-portion 214 as a processing portion which is usable as a portion for conducting decoding of communications. The portion 214 may be configured to perform a processing according to step S140 according to Fig. 5, for example. According to further examples of embodiments of the invention, there is provided an apparatus comprising multiplexing processing means for multiplexing plural communications between the at least one interface and plural destinations in at least one resource block of communication resources, and allocating means for allocating a first group demodulation reference signal providing demodulation information for communications at the destinations to each of the plural communications.

Moreover, according to further examples of embodiments of the invention, there is provided an apparatus comprising receiving means for receiving multiplexed communications in at least one resource block of communication resources, demodulation reference signal determining means for determining a first group demodulation reference signal allocated to the multiplexed communications and providing demodulation information for demodulating the communication, channel estimation processing means for conducting a channel estimation on the basis of the first group demodulation reference signal, and decoding processing means for decoding at least a part of the multiplexed communications.

For the purpose of the present invention as described herein above, it should be noted that

- an access technology via which signaling is transferred to and from a network element may be any technology by means of which a network element or sensor node can access another network element or node (e.g. via a base station or generally an access node). Any present or future technology, such as WLAN (Wireless Local Access Network), WiMAX

(Worldwide Interoperability for Microwave Access), LTE, LTE-A, Bluetooth, Infrared, and the like may be used; although the above technologies are mostly wireless access technologies, e.g. in different radio spectra, access technology in the sense of the present invention implies also wired technologies, e.g. IP based access technologies like cable networks or fixed lines but also circuit switched access technologies; access technologies may be distinguishable in at least two categories or access domains such as packet switched and circuit switched, but the existence of more than two access domains does not impede the invention being applied thereto, - usable communication networks, stations and transmission nodes may be or comprise any device, apparatus, unit or means by which a station, entity or other user equipment may connect to and/or utilize services offered by the access network; such services include, among others, data and/or (audio-) visual communication, data download etc. ;

- a user equipment or communication network element (station) may be any device, apparatus, unit or means by which a system user or subscriber may experience services from an access network, such as a mobile phone or smart phone, a personal digital assistant PDA, or computer, or a device having a corresponding functionality, such as a modem chipset, a chip, a module etc., which can also be part of a UE or attached as a separate element to a UE, or the like;

- method steps likely to be implemented as software code portions and being run using a processor at a network element or terminal (as examples of devices, apparatuses and/or modules thereof, or as examples of entities including apparatuses and/or modules for it), are software code independent and can be specified using any known or future developed programming language as long as the functionality defined by the method steps is preserved;

- generally, any method step is suitable to be implemented as software or by hardware without changing the idea of the invention in terms of the functionality implemented;

- method steps and/or devices, apparatuses, units or means likely to be implemented as hardware components at a terminal or network element, or any module(s) thereof, are hardware independent and can be implemented using any known or future developed hardware technology or any hybrids of these, such as a microprocessor or CPU (Central Processing Unit), MOS

(Metal Oxide Semiconductor), CMOS (Complementary MOS), BiMOS (Bipolar MOS), BiCMOS (Bipolar CMOS), ECL (Emitter Coupled Logic), TTL (Transistor-Transistor Logic), etc., using for example ASIC (Application Specific IC (Integrated Circuit)) components, FPGA (Field-programmable Gate Arrays) components, CPLD (Complex Programmable Logic Device) components or DSP (Digital Signal Processor) components; in addition, any method steps and/or devices, units or means likely to be implemented as software components may for example be based on any security architecture capable e.g. of authentication, authorization, keying and/or traffic protection;

- devices, apparatuses, units or means can be implemented as individual devices, apparatuses, units or means, but this does not exclude that they are implemented in a distributed fashion throughout the system, as long as the functionality of the device, apparatus, unit or means is preserved; for example, for executing operations and functions according to examples of embodiments of the invention, one or more processors may be used or shared in the processing, or one or more processing sections or processing portions may be used and shared in the processing, wherein one physical processor or more than one physical processor may be used for implementing one or more processing portions dedicated to specific processing as described,

- an apparatus may be represented by a semiconductor chip, a chipset, or a (hardware) module comprising such chip or chipset; this, however, does not exclude the possibility that a functionality of an apparatus or module, instead of being hardware implemented, be implemented as software in a

(software) module such as a computer program or a computer program product comprising executable software code portions for execution/being run on a processor;

- a device may be regarded as an apparatus or as an assembly of more than one apparatus, whether functionally in cooperation with each other or functionally independently of each other but in a same device housing, for example.

As described above, there is provided mechanism for conducting communications by using group based demodulation reference signals. A communication network control element such as an eNB multiplexes plural communications to plural UEs grouped in one UE group in at least one resource block of communication resources. A first group demodulation reference signal providing demodulation information for communications at the destinations is transmitted to each UE of the UE group in predetermined resource elements of the at least one resource block, wherein the transmission is caused via the same preconfigured transmitter port or ports and with the same preconfigured signaling sequence for all of the plural UEs in the UE group.

Although the present invention has been described herein before with reference to particular embodiments thereof, the present invention is not limited thereto and various modifications can be made thereto.

Claims

1. An apparatus comprising

at least one processor,

at least one interface to at least one other network element, and a memory for storing instructions to be executed by the processor, wherein

the at least one processor comprises

a multiplexing processing portion configured to multiplex plural communications between the at least one interface and plural destinations in at least one resource block of communication resources, and

an allocator configured to allocate a first group demodulation reference signal providing demodulation information for communications at the destinations to each of the plural communications.

2. The apparatus according to claim 1, further comprising

a demodulation reference signal transmitting portion configured to cause transmitting of the first group demodulation reference signal in predetermined resource elements of the at least one resource block, wherein the transmission is caused via the same preconfigured transmitter port or ports of the at least one interface and with the same preconfigured signaling sequence for all of the plural destinations.

3. The apparatus according to claim 1 or 2, wherein

the multiplexing processing portion is configured to base the multiplexing of the plural communications on a grouping of terminal devices representing the plural destinations into at least one device group.

4. The apparatus according to any of claims 1 to 3, wherein a modulation scheme to which the demodulation information in the first group demodulation reference signal is related is based on quadrature phase shift keying.

5. The apparatus according to any of claims 1 to 4, further comprising

a precoding processing portion configured to apply a same precoder weight setting to all of the plural communications, wherein the precoding processing portion is configured to determine the precoder weight setting on the basis of channel state information received from a group of destinations of the plural communications.

6. The apparatus according to any of claim 1 to 5, wherein

the allocator is further configured to allocate a second group demodulation reference signal being orthogonal to the first group demodulation reference signal to at least one of the plural communications, wherein the at least one processor further comprises

a selection processing portion configured to select from the plural communications at least one of a first set of communications to which the first group demodulation reference signal is to be allocated, a second set of communications to which the second group demodulation reference signal is to be allocated, and a third set of communications to which the first group demodulation reference signal and the second group demodulation reference signal are to be allocated.

7. The apparatus according to claim 6, further comprising a demodulation reference signal transmitting portion configured to cause transmitting of the second group demodulation reference signal in predetermined resource elements of the at least one resource block, wherein the transmission is caused via the same preconfigured transmitter port or ports of the at least one interface and with the same preconfigured signaling sequence for all of the plural destinations, wherein at least one of the preconfigured transmitter port or ports of the at least one interface and the preconfigured signaling sequence used for the second group demodulation reference signal is different to a preconfigured transmitter port or ports of the at least one interface and a preconfigured signaling sequence used for the first group demodulation reference signal.

8. The apparatus according to any of claims 1 to 7, wherein the apparatus is comprised in a communication network control element, in particular an enhanced Node B of a Long Term Evolution or Long Term Evolution Advanced communication network.

9. A method comprising multiplexing plural communications between the at least one interface and plural destinations in at least one resource block of communication resources, and

allocating a first group demodulation reference signal providing demodulation information for communications at the destinations to each of the plural communications.

10. The method according to claim 9, further comprising

causing transmitting of the first group demodulation reference signal in predetermined resource elements of the at least one resource block, wherein the transmission is caused via the same preconfigured transmitter port or ports of at least one interface and with the same preconfigured signaling sequence for all of the plural destinations.

11. The method according to claim 9 or 10, wherein

the multiplexing of the plural communications is based on a grouping of terminal devices representing the plural destinations into at least one device group.

12. The method according to any of claims 9 to 11, wherein a modulation scheme to which the demodulation information in the first group demodulation reference signal is related is based on quadrature phase shift keying.

13. The method according to any of claims 9 to 12, further comprising

conducting a precoding by applying a same precoder weight setting to all of the plural communications, wherein the precoder weight setting is determined on the basis of channel state information received from a group of destinations of the plural communications.

14. The method according to any of claim 9 to 13, further comprising

allocating a second group demodulation reference signal being orthogonal to the first group demodulation reference signal to at least one of the plural communications, and

selecting from the plural communications at least one of a first set of communications to which the first group demodulation reference signal is to be allocated, a second set of communications to which the second group demodulation reference signal is to be allocated, and a third set of communications to which the first group demodulation reference signal and the second group demodulation reference signal are to be allocated.

15. The method according to claim 14, further comprising

causing transmitting of the second group demodulation reference signal in predetermined resource elements of the at least one resource block, wherein the transmission is caused via the same preconfigured transmitter port or ports of at least one interface and with the same preconfigured signaling sequence for all of the plural destinations, wherein at least one of the preconfigured transmitter port or ports of the at least one interface and the preconfigured signaling sequence used for the second group demodulation reference signal is different to a preconfigured transmitter port or ports of the at least one interface and a preconfigured signaling sequence used for the first group demodulation reference signal.

16. The method according to any of claims 9 to 15, wherein the method is implemented in a communication network control element, in particular an enhanced Node B of a Long Term Evolution or Long Term Evolution

Advanced communication network.

17. An apparatus comprising

at least one processor,

at least one interface to at least one other network element, and a memory for storing instructions to be executed by the processor, wherein the at least one interface is configured to receive multiplexed communications in at least one resource block of communication resources, and wherein the processor further comprises

a demodulation reference signal determining portion configured to determine a first group demodulation reference signal allocated to the multiplexed communications and providing demodulation information for demodulating the communication,

a channel estimation processing portion configured to conduct a channel estimation on the basis of the first group demodulation reference signal, and a decoding processing portion configured to conduct decoding of at least a part of the multiplexed communications.

18. The apparatus according to claim 17, wherein

the interface is configured to receive the first group demodulation reference signal in predetermined resource elements of the at least one resource block, wherein the first group demodulation reference signal is received by a transmission from the same preconfigured transmitter port or ports and with the same preconfigured signaling sequence for all destinations of the multiplexed communications.

19. The apparatus according to claim 17 or 18, wherein

the multiplexing of the communications is based on a grouping of terminal devices representing destinations of the communications into at least one device group.

20. The apparatus according to any of claims 17 to 19, wherein a modulation scheme to which the demodulation information in the first group demodulation reference signal is related is based on quadrature phase shift keying.

21. The apparatus according to any of claim 17 to 20, wherein

the demodulation reference signal determining portion is further configured to determine a second group demodulation reference signal allocated to the multiplexed communications and providing demodulation information for demodulating the communication, and

the channel estimation processing portion is further configured to conduct a channel estimation on the basis of the second group demodulation reference signal, wherein the processor further comprises a reference signal determination portion configured to determine which of the first group demodulation reference signal and the second group demodulation reference signal is or are to be used.

22. The apparatus according to claim 21, wherein

the interface is configured to receive the second group demodulation reference signal in predetermined resource elements of the at least one resource block, wherein the second group demodulation reference signal is received by a transmission from the same preconfigured transmitter port or ports and with the same preconfigured signaling sequence for all destinations of the multiplexed communications, wherein at least one of the preconfigured transmitter port or ports and the preconfigured signaling sequence used for the second group demodulation reference signal is different to a preconfigured transmitter port or ports and a preconfigured signaling sequence used for the first group demodulation reference signal.

23. The apparatus according to any of claims 17 to 22, wherein the apparatus is comprised in a communication network element, in particular a terminal device or user equipment usable in a Long Term Evolution or Long Term Evolution Advanced communication network.

24. A method comprising

receiving multiplexed communications in at least one resource block of communication resources,

determining a first group demodulation reference signal allocated to the multiplexed communications and providing demodulation information for demodulating the communication,

conducting a channel estimation on the basis of the first group demodulation reference signal, and

conducting decoding of at least a part of the multiplexed communications.

25. The method according to claim 24, wherein

the first group demodulation reference signal is received in predetermined resource elements of the at least one resource block, wherein the first group demodulation reference signal is received by a transmission from the same preconfigured transmitter port or ports and with the same preconfigured signaling sequence for all destinations of the multiplexed communications.

26. The method according to claim 24 or 25, wherein the multiplexing of the communications is based on a grouping of terminal devices representing destinations of the communications into at least one device group.

27. The method according to any of claims 24 to 26, wherein a modulation scheme to which the demodulation information in the first group demodulation reference signal is related is based on quadrature phase shift keying.

28. The method according to any of claim 24 to 27, further comprising

determining a second group demodulation reference signal allocated to the multiplexed communications and providing demodulation information for demodulating the communication, and

conducting a channel estimation on the basis of the second group demodulation reference signal, wherein the method further comprises

determining which of the first group demodulation reference signal and the second group demodulation reference signal is or are to be used.

29. The method according to claim 28, wherein

the second group demodulation reference signal is received in predetermined resource elements of the at least one resource block, wherein the second group demodulation reference signal is received by a transmission from the same preconfigured transmitter port or ports and with the same preconfigured signaling sequence for all destinations of the multiplexed communications, wherein at least one of the preconfigured transmitter port or ports and the preconfigured signaling sequence used for the second group demodulation reference signal is different to a preconfigured transmitter port or ports and a preconfigured signaling sequence used for the first group demodulation reference signal.

30. The method according to any of claims 24 to 29, wherein the method is implemented in a communication network element, in particular a terminal device or user equipment usable in a Long Term Evolution or Long Term Evolution Advanced communication network.

31. A computer program product for a computer, comprising software code portions for performing the steps of any of claims 9 to 16 or 24 to 30 when said product is run on the computer.

32. The computer program product according to claim 31, wherein

the computer program product comprises a computer-readable medium on which said software code portions are stored, and/or

the computer program product is directly loadable into the internal memory of the computer and/or transmittable via a network by means of at least one of upload, download and push procedures.