WO2014085997A1

WO2014085997A1 - Apparatuses, methods and computer program products related to improvements in dmrs transmission

Info

Publication number: WO2014085997A1
Application number: PCT/CN2012/085910
Authority: WO
Inventors: Pengfei Sun; Chunyan Gao; Na WEI; Erlin Zeng; Wei Bai; Haiming Wang
Original assignee: Broadcom Corp
Current assignee: Broadcom Corp
Priority date: 2012-12-05
Filing date: 2012-12-05
Publication date: 2014-06-12
Anticipated expiration: 2015-06-05

Abstract

According to at least an aspect of the present invention, there is provided, under an network transceiver device aspect of e.g. an eNB, an apparatus, comprising a controller configured to cause a first set of reference signals to be transmitted at specific locations within a time and frequency resource grid, receive information indicative of a usability of a second set of reference signals within the resource grid, the second set comprising less reference signals as compared to the first set, analyse the received information, and responsive thereto generate control information, and cause to apply the second set of reference signals at specific locations within the time and frequency resource grid to be transmitted, and cause to transmit the generated control information in downlink so as to inform terminals being in communication with said apparatus of said second set of reference signals being applied. A corresponding apparatus in terms of a terminal device of e.g. a UE is also provided as well as respective corresponding methods and computer program products.

Description

APPARATUSES, METHODS AND COMPUTER PROGRAM PRODUCTS RELATED TO IMPROVEMENTS IN DMRS TRANSMISSION

Field of the invention

The present invention relates to apparatuses, methods and computer program products configured to achieve improvements in relation to transmission of demodulation reference signal, DMRS. Background

Mobile communication is constantly making progress. A typical scenario or environment in relation to a scenario to which some aspects of the present invention are applicable, is for example a scenario as applied in conjunction with e.g. the LTE™ (Long Term Evolution) or LTE-A™ (LTE- advanced) telecommunication standard. Some aspects at least can also be applicable to other wireless communication scenarios. According to such standard(s), a network transceiver device such as an evolved NodeB, eNB, communicates via control and payload channels with a terminal such as an user equipment UE.

According to one aspect of such progress, a goal is to achieve error free data transmission. To this end, data transmission from a network transceiver device such as an evolved NodeB, eNB, towards a terminal such as an user equipment, UE, is crucial. In order to allow for proper and error free data transmission and reception, an eNB transmits so-called reference signals and/or symbols to the UE. The UE being in receipt of and thus aware of the reference signals/symbols, uses these reference symbols to estimate the channel, and is subsequently enabled to properly decode payload transmissions received via that channel.

i Such reference symbols are assigned to (specific) physical resource elements RE within physical resource blocks PRB. A resource element RE is represented by a certain time interval and a frequency (bandwidth) assigned to it within the frequency-time domain. A plurality (defined number) of resource elements in frequency / bandwidth domain form a physical resource block PRB (in frequency domain), and a plurality of PRBs are present within a channel. A Resource Element RE is the smallest unit of transmission resource in LTE, in both uplink and downlink. An RE consists of 1 subcarrier in the frequency/bandwidth domain for a duration of 1, Orthogonal Frequency Division Multiplexing (OFDM) or Single Carrier- Frequency Division Multiplexing (SC-FDM), symbol in the time domain. A PRB in turn is thus a unit of transmission resources consisting of 12 sub- carriers (REs) in the frequency domain and 1 timeslot (0.5 ms) in the time domain. A radio frame comprises twenty such time-slots, while each time- slot normally consists of 7 OFDM symbols. Plural PRBs are grouped to a resource block group, RBG.

PDSCH (Physical Downlink Shared Channel) and PDCCH (Physical Downlink Control Channel), for example, carry control information in downlink from an eNB to a terminal such as a UE. A feedback in uplink from the UE to the eNB consists of e.g. a rank indicator (RI), a pre-coding matrix index (PMI) and a channel quality indicator (CQI) and hybrid automatic repeat requests HARQ. Such feedback is e.g. carried in a physical uplink control channel, PUCCH. Hence, the UE estimates the channel based on the received DMRS, selects rank and PMI and calculates the post-processing (after receiver) SINR (signal to interference noise ratio) and derives the CQI based on that.

Due to the recent booming of the wireless internet, it is easily expected that the requirement for wireless data service will keep on fast soaring in the near future. Among those advanced technologies proposed to meet the challenging request, reducing the cell size is one of the most prominent one. In the past years or even decades, the wireless network capacity has been increased by more than 2700 times from smaller cells. Therefore, the local area (LA) network will inevitably become the next research hotspot in LTE evolution. Consequently, the 3GPP RAN plenary has recently agreed on a study item definition, SID, on the local area networks (3GPP: 3^rd Generation Partnership Project; RAN : Radio Access Network).

One of the unique features of a local area network compared with the macro area network is the characteristics of the channel response. Due to the small coverage of local area networks, the channel delay spread is found much smaller than that of a macro channel. This is leading to a much flatter frequency domain response of local area networks' channels. In addition, as the local area network targets UEs with low mobility speed, a small Doppler shift can be expected for the channel used by such slowly moving terminals.

In such circumstance, one rising critical issue resides in the reference signal(s) used in the physical layer transmission. All the reference signals, either cell specific or UE specific, are designed for the macro channel, which may suffer large delay spread and high Doppler shift. According to the Nyquist sampling rate, the reference signals must be dense enough in time and frequency domain to achieve accurate channel estimation. However, these dense reference signals are not so necessary in local area network given the flat and slow varying channels of the local area network. The reference signal overhead may be reduced without compromising the performance. Therefore, it is proposed to study a possible reduction of the reference signal and related control overhead. It is likely that the RS density could be reduced in the time domain. For example, if a UE's speed is lOkm/h, the frequency of Doppler shift is f_d=19Hz, and thus the sampling interval could be up to 25ms based on the Nyquist sampling theorem, i.e. the sampling frequency could be (as low as) 40Hz which is still greater than twice the Doppler shift.

That is, DMRS, which is used for demodulation in local area network (CRS (Common Reference Signal) free new carrier type), may be periodically avoided in certain subframes to reduce the overhead. Within these DMRS subframes, the demodulation could be based on those channel estimates that were previously obtained. However, issues may be introduced if such DMRS blank subframes are supported:

- If DMRS are sent only in a scheduled bandwidth, BW, then it is not accurate enough for channel estimation of other resources; It means if there is DMRS in PRB i in subframe j, then it may suffer errors for decoding of data in PRB i+N and subframe j+M;

- If DMRS is sent only in certain subframes, how could UE know in which subframe the DRMS is present. Misinterpreting the existence of DMRS causes severe decoding errors. Hence, there is still a need to further improve such systems.

Summary

Various aspects of examples of the invention are set out in the claims.

According to an aspect of the present invention (e.g. related to a network transceiver device such as an evolved Node_B, eNB), there is provided an apparatus as defined in claim 1, and

an apparatus as defined in claim 24, and

a method as defined in claim 47. According to an aspect of the present invention (e.g. related to a terminal such as a user equipment, UE), there is provided

an apparatus as defined in claim 14, and

an apparatus as defined in claim 37, and

a method as defined in claim 60.

Advantageous further developments are set out in respective dependent claims. According to a further aspect of the present invention, as set out in claims 70 and 71, respectively, there are provided computer program products comprising respective computer-executable components which, when the program is run on a computer, are configured to perform the above method aspects, respectively.

That is, such computer program products also encompass computer readable storage media comprising a set of computer-executable instructions which, when the program is run on a device (or on a processor or processing unit thereof which may be part of a controller or control unit or control module, or any other suitable (hardware or software implemented) means for controlling), such as a terminal UE and its processor, or a network transceiver device eNB and its processor, cause the device to perform the respective method aspects. In particular, the above mentioned computer program product/products may be embodied as a computer-readable storage medium.

Accordingly, under at least some aspects of this invention, improvements are achieved in that, for example,

- reduction of the reference signal and control overhead is enabled, - such reduction is in particular enabled for local area network environments or any other environments exhibiting a "flat" (rather invariable) channel characteristic in at least one of frequency and time domain,

- a simple signalling to support a configurable DMRS is introduced,

- such signalling, according to at least individual aspects of the invention, includes new DCI bits, new DCI formats, and/or a new RRC signalling,

- and further, the elNB and U E easily use and adopt such signalling in relation to configured DMRS to be transmitted and/or received, respectively,

- some aspects of the invention enable a more flexible and more efficient DMRS usage,

- an increase of the resource utilization efficiency is enabled,

- a reduction in terms of the RS interference is enabled,

- the presence of (reduced) DMRS is scheduled by the eNB, and is achieved by implementation with little extra complexity,

- a control overhead may be only 1 or 2 bits for one subframe, according to at least an example of an aspect of the invention, compared to a reduction of DMRS, i.e. a RS saving, of at least 12 RE per PRB; hence, given that the PDSCH normally takes many PRBs, the saving will outweigh the overhead, and/or

- a flexible indication method with lower error case probability is enabled.

Some embodiments of the present invention can be applied to/embodied in relation to wireless communication systems and scenarios (e.g. in relation to LTE radio access or LTE-A radio access or other future 3GPP releases), in particular in

modems and/or wireless devices and/or modules and/or chipsets thereof, in particular those related to/inserted in or insertabie to devices such as terminals such as user equipments or "smartphones" or the like, as well as those related to/inserted in or insertabie to network transceiver devices such as a Node_B or evolved Node_B eNB. Brief description of drawings

For a more complete understanding of example embodiments of the present invention, reference is now made to the following descriptions taken in connection with the accompanying drawings in which:

Fig. 1 illustrates one example of a network transceiver device eNB and a terminal UE and some signalling exchanged between, as well as an outline of their internal construction, and

Fig. 2 illustrates one example of a normal DMRS pattern in Fig. 2A, and one example of a reduced DMRS pattern in Fig. 2B, resulting from at least some aspect of the invention being applied;

Fig. 3 illustrates one example of the basic flowchart for a processing as carried out on a side of a network transceiver device such as a eNB, and

Fig. 4 illustrates one example of the basic flowchart for a processing as carried out on a side of a terminal device such as a UE.

Description of example embodiments

Some exemplary aspects and/or embodiments of the invention will be described herein below.

Generally, the invention is implemented in a framework of e.g. a telecommunication system operating for example according to the LTE and/or LTE-A standard, or subsequent versions thereof, and more particularly, the invention affects a terminal (user equipment UE) as well as a network transceiver device (evolved NodeJ3) eNB operated within such a framework. It is to be noted that as a mere example only, the description refers to such modules or devices or apparatuses related to user equipments, UEs, which conform to the LTE / LTE-A standard and are arranged / configured for communication with correspondingly configured network transceiver devices such as evolved NodeB's, eNBs, as the wireless communication modules or devices or apparatuses. However, this does not preclude the use of other wireless communication modules achieving similar functionalities, or the use of other communication standards such as LTE- A and beyond, as long as a reduction of DMRS signals and correspondingly related signalling is applied/applicable. Also, the bandwidth of wireless communication is not crucial for the present invention.

General technical details of such scenarios, e.g. under LTE and adopted communication protocols are publicly available. A repeated detailed description of each such property/functionality of the known LTE system is considered dispensable as those skilled in the pertinent art of technology will readily understand the description as given herein. Examples of the present invention exploit those basic properties and at least in aspects modify the functionality so as to obtain the advantages of at least some embodiments of the present invention.

Fig . 1 illustrates one example of a network transceiver device eNB and a terminal UE and some signalling exchanged between, as well as an outline of their internal construction .

Fig. 1 illustrates one example of a typical scenario to which aspects of the invention are applicable and applied. As shown in Fig. 1, a network transceiver device such as a eNB, denoted by A, applies reduction of DMRS transmission for downlink transmission of (control) data to a terminal, e.g. a user equipment UE denoted by B. The (control) data carried in downlink comprise at least DL control channels such as the PDSCH and the PDCCH. At least the PDCCH as one of the DL control channels carries also control information, e.g. known as downlink control information, DCI. Downlink Control Information is used to describe control signalling messages transmitted on the Physical Downlink Control Channel (PDCCH), including for example downlink resource assignments (for the Physical Downlink Shared Channel (PDSCH)) and uplink transmission grants (for the Physical Uplink Shared Channel (PUSCH)).

The terminal B feeds back feedback control signals in uplink, UL, to the eNB A. The uplink feedback comprises at least an uplink control channel such as the PUCCH. Data and/or signals carried on the PUCCH comprise, for example, at least CSI/CQI information and HARQ related information (ACKs/NAC s). The uplink feedback of the terminal UE B is at least partly derived based on evaluation of DMRS signals transmitted by the network transceiver device eNB A in downlink.

The eNB A comprises an apparatus 1, which in turn comprises at least a controller (or control module) 11 which is configured to control, among other parts of the eNB (not shown/discussed herein) a receiver/ transmitter (or transceiver module) 12 of the eNB, at least in terms of DMRS transmission. The receiver/transmitter Rx/Tx 12, under control of the controller 11, is caused to transmit in the PDSCH and/or PDCCH in DL to the terminal UE B. The receiver/transmitter Rx/Tx 12, under control of the controller 11, is caused to receive the PUCCH in UL from the terminal UE B. As shown, the receiver/transmitter 12 is bi-directionally connected to the controller 11, which in turn is bi-directionally connected to a memory MEM 13. The memory stores various data, such as control code or the like used by the controller, data contained in feedback signals received in UL, data to be included in downlink control channels transmitted in DL, etc. As further shown in Fig. 1, a terminal device such as a UE, denoted by B, is enabled to cope with a reduction of DMRS transmission in downlink transmission of (control) data to a terminal, e.g. from a eNB denoted by A. The (control) data received in downlink comprise at least DL control channels such as the PDSCH and the PDCCH. At least one of the DL control channels carries also control information, e.g. known as downlink control information, DCL The terminal B causes to feed back feedback control signals in uplink, UL, to the eNB A. The uplink feedback comprises at least an uplink control channel such as the PUCCH. Data and/or signals carried on the PUCCH comprise, for example, at least CSI/CQI information and HARQ related information (ACKs/NACKs). The uplink feedback of the terminal UE B is at least partly derived based on evaluation of DMRS signals transmitted by the network transceiver device eNB A in downlink. The UE B comprises an apparatus 2, which in turn comprises at least a controller (or control module) 21 which is configured to control, among other parts of the UE (not shown/discussed herein) a receiver/ transmitter (or transceiver module) 22 of the UE, at least in terms of DMRS reception. The receiver/transmitter Rx/Tx 22, under control of the controller 21, is caused to receive the PDSCH and/or PDCCH in DL from the eNB. The receiver/transmitter Rx/Tx 22, under control of the controller 21, is caused to transmit the PUCCH in UL to the eNB. As shown further, the receiver/transmitter 12 is bi-directionally connected to the controller 21, which in turn is bi-directionally connected to a memory MEM 23. The memory stores various data, such as control code or the like used by the controller, data caused to be included in feedback signals transmitted in UL, data included in downlink control channels received in DL, and/or other data, e.g. configuration data, measurement data obtained by a measurement module ((not shown), which could be associated to e.g. the control module 21 or the Rx/Tx module 22, (or be regarded as a separate module of the UE B)). While herein before a focus was laid on aspects of the structural composition of entities to which some aspects of the present invention are applicable, herein below functional aspects will be explained. As derivable form the following, common to various aspects of the invention, which will be described herein beiow, is that there is proposed a (set of) scheme(s) enabling DMRS reduction, while keeping the impact of the error case at low level. Each such scheme allows an eNB flexibility in configuring a low DMRS density for a UE (or group of UEs), while such terminal UE utilizes a slow varying feature of the local area channel. This is, in brief and at least according to some aspects of the invention, accomplished by using a novel way to indicate the presence of (reduced) DMRS to one or a group of UEs, e.g. by means of new DCI bits or new DCI format(s) and/or by applying a predefined rule in a terminal's (UE's) assumption of (reduced or non-reduced) DMRS presence, until a certain feedback signal, e.g. a first HARQ-ACK, is fed back to the eNB, or until the reception of extra L1/L2 signalling. It is noted that the implementation examples assume that a UE decodes the control channel based on regular or reduced DMRS, and there is no error case in terms of the presence of DMRS in the PRB set corresponding to the search space of the control channel.

In brief, according to a first exemplary aspect involving one or more individual embodiments, one or a few bits in the DCI format are added/reused, or a new RNTI is applied, by the eNB to indicate to one or more terminals UE whether a current subframe contains DMRS for a UE's channel estimation. If "yes", UE will find the DMRS in the pre-defined or indicated resources within current subframe to perform channel estimation, whereas if "No", the UE will assume that no DMRS is available in the current subframe. In such case, instead, the UE re-uses previously obtained channel estimates. In more detail, according to a possible implementation of such embodiment's scenario, an example of introducing a DMRS indicator in an existing DCI format is as follows. The definition of DCI format for DL grant, for example DCI format 1, is amended as shown below. The part marked bold is the new content added.

DCI format 1 is used for the scheduling of one PDSCH codeword in one cell.

The following information is transmitted by means of the DCI

format 1 :

- DMRS indicator - 1 bit. This field is present according

higher layer configuration.

- Carrier indicator - 0 or 3 bits. This field is present according to

the definitions in [3].

-Resource allocation header (resource allocation type 0 / type 1)

- 1 bit as defined in section 7.1.6 of 3GPP TS 36.213: "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer

procedures

If downlink bandwidth is less than or equal to 10 PRBs, there is

no resource allocation header and resource allocation type 0 is assumed.

Based on above amendment, the UE knows if the DMRS indicator field is present based on higher layer configuration. Then, if UE receives the DNRS indicator bit with value "1", the UE knows that DMRS is transmitted within this subframe and updates the channel estimates based on the said DMRS. If UE receives the DMRS bit with value ^w0", the UE is aware that this subframe does not include DMRS and hence uses the previously obtained channel estimates for PDSCH demodulation.

It is also possible that when the new indicator bit is set to 1, DMRS is transmitted in a reduced frequency density in the current subframe to improve spectrum efficiency. In this case, UE knows the exact DMRS pattern by specification or by higher layer signalling. One more alternative is to derive the 1 bit DMRS indication implicitly based on the resource allocation field in the DCI. If the allocated resource is outside a certain BW threshold to the previous DMRS transmission resource, then assume the bit is set as "1", which means there is DMRS transmission; otherwise, it is assumed that no DMRS exists. Moreover, the derivation of the bit can also be determined by a combination of BW threshold and a time threshold. One more alternative is to use the new indicator to adjust the DMRS pattern on a per subframe basis. For example, the bit fields can be used to represent different DMRS density in the frequency domain, e.g., if the bit is set to 1 then UE should assume DMRS is present in one out of each N PRB (where N is a positive integer and is greater than 1), while if bit is set to 0 then UE assume DMRS is present in every PRB.

One more alternative is to use the new indicator to adjust the DMRS pattern in both time and frequency domain. In brief, according to a second exemplary aspect involving one or more individual embodiments, a new DCI format for DMRS fast configuration is introduced. The DMRS configuration of a group of UEs is included in this DCI, with each UE having e.g. one or two bits for its own DMRS configuration. The new DCI format may be transmitted by the eNB only when the DMRS setup is changed. Otherwise, the UE (or group of UEs) assumes that the DMRS pattern is the same as the one in the previous subframe. Different groups can be identified via RNTI, or by means of a group-ID embedded as one field in the new DCI format. (Note that RNTIs are used to identify terminals UE within E-UTRAN (Evolved Universal Terrestrial Radio Access Network), in particular in signalling messages between the UE and E-UTRAN. Several types of RNTI exist, including Cell- RNTI (C-RNTI), Paging-RNTI (P-RNTI), Random Access-RNTI (RA-RNTI) and System Information-RNTI (SI-RNTI).)

Note further that DCI formats 0 to 3 are hitherto defined, cf. 3GPP TS 36.212, version 8.8.0, Release 8, and at least some of those encompass "subformats" ranging from A through D. Thus, new DCI formats carrying information as suggested under at least some aspects of the present invention could be labelled as DCI formats 4 or 5, for example. In more detail, according to a possible implementation of such embodiment's scenario, some examples of implementation to realize indicating the DMRS configuration for a group of UEs is given below.

Alternative 1 : Dynamic DMRS presence indication :

A new DCI format is, for example, defined as follows as e.g. format 5 :

DCI format 5 is used for the transmission of indication of the

presence of DMRS for PDSCH with 1-bit indicator

- DMRS indicator 1, DMRS indicator 2,..., DMRS indicator N

The parameter dmrs-Index provided by higher layers determines the index to the DMRS indicator for a given UE.

Table 1 : Interpretation of DMRS indicator field in DCI format 5

Based on above definition, each UE monitors the DCI format 5 after configuration by higher layers, from which UE also knows its own corresponding DMRS index in the DCI format 5. If UE receives "1", UE knows DMRS is transmitted within this subframe and performs an update of the channel estimates based on the said DMRS. If UE receives "0", UE uses the previously obtained channel estimates for PDSCH demodulation.

Thus, by virtue of N DMRS indicators being provided, N groups of terminals UE can be controlled in terms of DMRS reception/channel updates. Each UE knows its DMRS index, pointing to one out of the N DMRS indicators.

Alternative 2: Differential DMRS presence indication:

We could define a new DCI format, for example format 5 as:

DCI format 5 is used for the transmission of indication of the presence of DMRS for PDSCH with 1-bit indicator

- DMRS indicator 1, DMRS indicator 2,..., DMRS indicator N

Table 2: Interpretation of differencial DMRS indicator field in DCI format 5

Based on above definition, each UE monitors the DCI format 5 after configuration by higher layers, from which UE also knows its own corresponding DMRS index in the DCI format 5. If a UE receives the respective UE knows that the DMRS status within this subframe is changed from the previous subframe. That is, if the previous subframe has no DMRS, then DMRS is transmitted in this subframe and vice versa. If a UE receives "0", the respective UE assumes that the DMRS status is unchanged. In brief, according to a third exemplary aspect involving one or more individual embodiments, a semi-static D RS cycle is configured by an eNB for each UE instead of indicating the presence of DMRS every subframe. After configuration, the respective UE finds the first PDSCH transmission with DMRS as the reference. Then, the respective UEs shall assume (or learn based on a validity information included in the control information received from eNB) that no DMRS is transmitted in the following N (within a configured cycle) subframes unless there is additional L1/L2 signalling received to indicate a new configuration or an independent DMRS during the DMRS cycle. In order to avoid missing the first DMRS in case UE misses the first PDCCH, certain restrictions are needed. One approach could be that UE and eNB shall always assume the presence of DMRS until the first A/N is transmitted back to the eNB. Another alternative is that different offset can be explicitly configured or implicitly defined for different UE or UE groups. In such case, the eNB may always schedule certain UE on its first subframe with certain offset to contain DMRS.

In more detail, according to a possible implementation of such aspect's /embodiment's scenario, for this aspect, the higher layer configures a cycle for DMRS transmission, that is, defines how long in the time domain a DMRS is transmitted.

For example, UE monitors the PDCCH and finds the first DL grant for PDSCH transmission, and then, the UE considers this PDSCH as the first occasion that DMRS is transmitted . Then UE calculates the next occasion when the DMRS can be transmitted. During the period in between, UE assumes no DMRS transmission and channel estimates obtained in the first DMRS occasion is stored and used . However, if the first DMRS is missed due to erroneous PDCCH detection, then UE has no channel estimates for following subframes before the second DMRS is transmitted. In such case serious errors are caused. Therefore, the DMRS scheduling restriction could be introduced to prevent errors. For example, eNB could transmit PDSCH with DM RS before the first A/N is sent back to eNB, then eNB knows at least one DMRS is received by the UE, then the semi-static DMRS cycle could be applied. On the UE side, it could always assume the presence of DMRS before the first A/N is sent back to eNB. After sending back A/N bits, UE will follow the semi-static DMRS cycle. Hence, insofar, there is further assigned a validity information to the control information, the validity information indicating the validity of presence or absence of reference signals for a specified duration in time domain. E.g. the validity can be indicated in units of seconds or ms, or in units of subframes, or the like.

In brief, according to a fourth exemplary aspect involving one or more individual embodiments, certain rules are defined to allow PDSCH resources shifted from the DMRS resource. If PDSCH resource is shifted from the DMRS resource within a certain range, UE could use the channel estimates based on the DMRS to demodulate PDSCH . The range of shift could be configured by higher layer signalling in units of PRBs. The eNB ensures that the PDSCH and DMRS resource shift is kept within the configured range, and the UE performs PDSCH demodulation based on the channel estimates obtained from the closest DMRS resources in the bandwidth/time space.

In more detail, according to a possible implementation of such embodiment's scenario, instead of transmitting DMRS signals, in the resources previously assigned for DMRS, PDSCH "content" is transmitted. Demodulation of such "newly allocated" PDSCH content is accomplished based on channel estimates derived from "neighbouring" DM RS resources, i.e. those closely located to the PDSCH resources in at least time and/or bandwidth within the grid of REs of PRBs or RGBs.

Hence, in such regard, the controller (on eNB side) is configured to generate control information by assigning an indication that data of a downlink shared channel being transmitted in those resources not used for reference signal transmission within both the first and the second set but the distance to the resources used for reference signal transmission in time and/or frequency domain is kept within an indicated range. Corresponding configuration/adaptation is made at UE side.

Various aspects and embodiments of the present invention have been described herein above, on a general as well as on a specific implementation oriented level.

Note that features of individual embodiments may be combined with those of other embodiments.

For example aspect 4 can be combined with all other aspects in that in non-DMRS assigned resources of PRBs, data of the PDSCH can be allocated.

For example, aspect 3 can be combined with all other aspects in that it is pre-configured, how long the principles of those aspects shall be valid/applicable.

Other combinations may also not be excluded. Fig. 2 illustrates one example of a normal DMRS pattern in Fig. 2A, and one example of a reduced DMRS pattern in Fig. 2B, resulting from at least some aspect of the invention being applied.

As shown in Fig. 2, a plural of resource elements RE are arranged in a grid in bandwidth (vertically illustrated) and time (horizontally illustrated). Those REs form one or more PRBs or even RGBs. Selected or predetermined ones of the REs are assigned to carry DMRS (illustrated in different representation compared to non-DMRS REs).

In Fig. 2A, a "normal" DMRS pattern is illustrated as an example. In that example, 36 REs carry DMRS within a time range covering time slots i until wherein in time slots i, i+2, i+4, ... until i+10 DMRS REs are present within subcarriers number 2, 7, and 12, respectively.

In Fig. 2B, a "reduced" DMRS pattern obtained by one or more aspects of the invention as described above is illustrated as an example. In that example, 12 REs only carry DMRS within a time range covering time slots i until i+11, wherein only in time slots i and i+10 DMRS REs are present within subcarriers number 2, 7, and 12, respectively. According to Fig. 2B, DMRS is thus reduced in time domain only.

However, in a further example (not shown), DMRS could be reduced in bandwidth domain only. In such case, based on the pattern of Fig. 2A, such pattern could be modified in that DMRS is removed from subcarriers 7 only over the time range of timeslots i to i+11, or from subcarriers 1 and 7, or the like.

Further, it is to be understood that DMRS reduction can be accomplished in time and frequency/bandwidth domain. In such case, based on the pattern of Fig, 2B, such pattern could be modified in that DMRS is further removed from subcarriers 7 over the time range of timeslots i to i+11 (resulting in only 8 REs carrying DMRS in such case), or the like.

Thus, it is understood that one or more of the above embodiments encompass an apparatus adapted or configured to implement corresponding methods as follows.

Namely, Fig. 3 illustrates a basic flowchart for a processing as carried out on a side of a network transceiver device such as a eNB according to one embodiment of the invention. As shown in Fig.3, the processing is carried out in an apparatus (e.g. of a eNB operating e.g. according to LTE or LTE- A) comprising at least a controller having an appropriate configuration as set out above in regard to some aspects. The process starts in a stage S30. In a stage S31, the controller causes a first set of reference signals to be transmitted at specific locations within a time and frequency resource grid. In a stage S32, the controller receives information indicative of a usability of a second set of reference signals within the resource grid, the second set comprising less reference signals as compared to the first set. In a stage S33, the controller analyses the received information, and responsive thereto, in a stage S34, generates control information. In a stage S35, the controller causes to apply the second set of reference signals at specific locations within the time and frequency resource grid to be transmitted, and further (stage S36) causes to transmit the generated control information in downlink so as to inform terminals being in communication with said apparatus of said second set of reference signals being applied. The process then "ends" in a stage S37, which may imply that it is waited for information indicative of the 2^nd set being not useable any longer, or any other signalling e.g. on L1/L2 indicative of terminating the usage of the 2^nd set, or a validity of the control information expires, or the like.

It is noted that the second set of reference signals comprises less reference signals as compared to the first set in at least one of time domain and frequency domain. The second set of reference signals differs from the first set in time domain in terms of the timeslots in which the reference signals are present or not, and/or differs in frequency domain in terms of the subcarriers in which the reference signals are present or not.

Further, the controller is configured to receive the information indicative of the usability of the second set of reference signals from a network management entity as configuration information for said apparatus. The configuration information received causes said apparatus to be configured for use as a network transceiver device of a local area network environment. Also, the controller is configured to receive the information indicative of the usability of the second set of reference signals from a terminal device. The information indicative of the usability of the second set of reference signals received from the terminal device is based on a channel delay spread for the terminal being below a threshold.

With reference to stage S34, the controller is configured to generate control information by assigning an indication of presence or absence of reference signals for at least one terminal, to at least one specific data field in a downlink control information message for said terminal.

For example with regard to the above mentioned first exemplary aspect the at least one specific data field comprises at least one existing re-used or at least one added bit of a downlink control information message, or a specific type of terminal identifier.

For example with regard to the above mentioned second exemplary aspect (1^st alternative) the at least one specific data field comprises a downlink control information message format, comprising an index for a respective terminal to assign the respective terminal to one of at least one of indicators of presence or absence of reference signals, and a value for each of said at least one of indicators indicating presence or absence of reference signals for each of the terminals indexed to that indicator. For example with regard to the above mentioned second exemplary aspect (2^nd alternative) the at least one specific data field comprises a downlink control information message format, comprising an index for a respective terminal to assign the respective terminal to one of at least one of indicators of presence or absence of reference signals, and a value for each of said at least one of indicators indicating a change in terms of presence or absence of reference signals for each of the terminals indexed to that indicator. For example with regard to the above mentioned third exemplary aspect the controller is configured to generate control information by further assigning a validity information to said control information, the validity information indicating the validity of presence or absence of reference signals for a specified duration in time domain.

For example with regard to the above mentioned fourth exemplary aspect the controller is configured to generate control information by assigning an indication that data of a downlink shared channel being transmitted in those resources not used for reference signal transmission within both the first and the second set but the distance to the resources used for reference signal transmission in time and/or frequency domain is kept within an indicated range.

Further, Fig. 4 illustrates a basic flowchart for a processing as carried out on a side of a terminal device (such as a UE) according to one embodiment of the invention. As shown in Fig. 4, the processing is carried out in an apparatus (e.g. of a terminal UE operating e.g. according to LTE or LTE-A) comprising at least a controller having an appropriate configuration as set out above in regard to some aspects.

The process starts in a stage S40. In a stage S41, the controller causes a receiver to receive a first set of reference signals at specific locations within a time and frequency resource grid. In a stage S42, the controller causes to transmit information indicative of a usability of a second set of reference signals within the resource grid, the second set comprising less reference signals as compared to the first set. In a stage S43, the apparatus and/or its controller receives control information. In stage S44, the controller analyses the received control information, and responsive thereto, in a stage S45, causes to apply, at the receiver, the second set of reference signals at specific locations within the time and frequency resource grid for reception. The process then "ends" in a stage S46, which may imply that it is waited for information indicative of the 2^nd set being not used any longer, or any other signalling e.g. on L1/L2 indicative of terminating the usage of the 2^nd set, or a validity of the control information expires, or the like.

It is noted that the second set of reference signals comprises less reference signals as compared to the first set in at least one of time domain and frequency domain . The second set of reference signals differs from the first set in time domain in terms of the timeslots in which the reference signals are present or not, and/or differs in frequency domain in terms of the subcarriers in which the reference signals are present or not.

Further, the transmitted information indicative of the usability of the second set of reference signals is based on a channel delay spread for the terminal being below a threshold.

Further, in terms of stage S44, the controller is configured to receive and analyse control information based on an assigned indication of presence or absence of reference signals for at least one terminal, to at least one specific data field in a downlink control information message for said terminal.

For example with regard to the above mentioned second exemplary aspect (1^st alternative) the at least one specific data field comprises a downlink control information message format, comprising an index for a respective terminal to assign the respective terminal to one of at least one of indicators of presence or absence of reference signals, and a value for each of said at least one of indicators indicating presence or absence of reference signals for each of the terminals indexed to that indicator. For example with regard to the above mentioned second exemplary aspect (2^nd alternative) the at least one specific data field comprises a downlink control information message format, comprising an index for a respective terminal to assign the respective terminal to one of at least one of indicators of presence or absence of reference signals, and a value for each of said at least one of indicators indicating a change in terms of presence or absence of reference signals for each of the terminals indexed to that indicator.

For example with regard to the above mentioned third second exemplary the controller is configured to receive and analyse control information based on a further assigned validity information to said control information, the validity information indicating the validity of presence or absence of reference signals for a specified duration in time domain. For example with regard to the above mentioned fourth second exemplary aspect the controller is configured to receive and analyse control information based on an assigned indication that data of a downlink shared channel being transmitted in those resources not used for reference signal transmission within both the first and the second set but the distance to the resources used for reference signal transmission in time and/or frequency domain is kept within an indicated range.

It is still to be noted that some embodiments of the invention may be implemented in software, hardware, application logic or a combination thereof, i.e. a combination of software, hardware and application logic. The software, application logic and/or hardware generally reside on control modules or modems, in general circuitry. In an example embodiment, the application logic, software or an instruction set is maintained on any one of various conventional computer-readable media. In the context of this document, a computer-readable medium" may be any media or means that can contain, store, communicate, propagate or transport the instructions for use by or in connection with an instruction execution system, apparatus, or device, such as a computer or smart phone, or user equipment.

As used in this application, the term 'circuitry' refers to all of the following: (a) hardware-only circuit implementations (such as implementations in only analog and/or digital circuitry) and

(b) to combinations of circuits and software (and/or firmware), such as (as applicable):

(i) to a combination of processor(s) or

(ii) to portions of processor(s)/software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or user equipment or any other terminal, or network entity such as a server, to perform various functions) and

(c) to circuits, such as a microprocessor(s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present.

This definition of 'circuitry' applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term "circuitry" would also cover an implementation of merely a processor (or multiple processors) or portion of a processor and its (or their) accompanying software and/or firmware. The term "circuitry" would also cover, for example and if applicable to the particular claim element, a baseband integrated circuit or applications processor integrated circuit for a mobile phone (terminal) or a similar integrated circuit in server, a cellular network device, or other network device. That is, it can be implemented as/in chipsets to such devices, and/or modems thereof.

If desired, the different functions discussed herein may be performed in a different order and/or concurrently with each other. Furthermore, if desired, one or more of the above-described functions may be optional or may be combined.

Although various aspects of the invention are set out in the independent claims, other aspects of the invention comprise other combinations of features from the described embodiments and/or the dependent claims with the features of the independent claims, and not solely the combinations explicitly set out in the claims. It is also noted herein that while the above describes example embodiments of the invention, these descriptions should not be viewed in a limiting sense. Rather, there are several variations and modifications which may be made without departing from the scope of the present invention as defined in the appended claims.

List of some acronyms used:

DMRS Demodulation Reference Signal

LTE Long Term Evolution

LTE-A LTE advanced

eNB evolved NodeB / enhanced NodeB

UE User Equipment

RE Resource Elements

PRB Physical Resource Block

PDSCH Physical Downlink Shared Channel

PDCCH Physical Downlink Control Channel

RI Rank Indicator

PMI Pre-coding Matrix Indicator CSI Channel State Information

CQI Channel Quality Indicator

HARQ Hybrid Automatic Repeat Requests

PUCCH Physical Uplink Control Channel

SINR Signal to Interference Noise Ratio

LA Local Area

LAN Local Area Network

3GPP 3^rd Generation Partnership Project

RAN Radio Access Network

SID Study Item Definition

CRS Common Reference Signal

BW Bandwidth

DCI Downlink Control Information

RRC Radio Resource Control

DL Downlink

UL Uplink

CE Control Element

A/N Acknowledgement / Non-acknowledgement

ACK Acknowledgement

RNTI Radio Network Temporary Identifier

OFDM Orthogonal Frequency Division Multiplexing

SC-FDM Single Carrier- Frequency Division Multiplexing

RBG Resource Block Group

E-UTRAN Evolved Universal Terrestrial Radio Access Network

Claims

WHAT IS CLAIMED IS:

1. An apparatus, comprising:

a controller configured to

cause a first set of reference signals to be transmitted at specific locations within a time and frequency resource grid,

receive information indicative of a usability of a second set of reference signals within the resource grid, the second set comprising less reference signals as compared to the first set,

analyse the received information, and responsive thereto generate control information, and

cause to apply the second set of reference signals at specific locations within the time and frequency resource grid to be transmitted, and

cause to transmit the generated control information in downlink so as to inform terminals being in communication with said apparatus of said second set of reference signals being applied.

2. An apparatus according to claim 1, wherein

the second set of reference signals comprises less reference signals as compared to the first set in at least one of time domain and frequency domain.

3. An apparatus according to claim 2, wherein

the second set of reference signals differs from the first set in time domain in terms of the timeslots in which the reference signals are present or not, and/or differs in frequency domain in terms of the subcarriers in which the reference signals are present or not.

4. An apparatus according to claim 1, wherein the controller is configured to receive the information indicative of the usability of the second set of reference signals from a network management entity as configuration information for said apparatus.

5. An apparatus according to claim 4, wherein

the configuration information received causes said apparatus to be configured for use as a network transceiver device of a local area network environment.

6. An apparatus according to claim 1, wherein

the controller is configured to receive the information indicative of the usability of the second set of reference signals from a terminal device.

7. An apparatus according to claim 6, wherein

the information indicative of the usability of the second set of reference signals received from the terminal device is based on a channel delay spread for the terminal being below a threshold.

8. An apparatus according to claim 1, wherein

the controller is configured to generate control information by

assigning an indication of presence or absence of reference signals for at least one terminal, to at least one specific data field in a downlink control information message for said terminal.

9. An apparatus according to claim 8, wherein

the at least one specific data field comprises at least one existing reused or at least one added bit of a downlink control information message, or a specific type of terminal identifier.

10. An apparatus according to claim 8, wherein

the at least one specific data field comprises a downlink control information message format, comprising an index for a respective terminal to assign the respective terminal to one of at least one of indicators of presence or absence of reference signals, and

a value for each of said at least one of indicators indicating presence or absence of reference signals for each of the terminals indexed to that indicator.

11. An apparatus according to claim 8, wherein

the at least one specific data field comprises a downlink control information message format, comprising

an index for a respective terminal to assign the respective terminal to one of at least one of indicators of presence or absence of reference signals, and

a value for each of said at least one of indicators indicating a change in terms of presence or absence of reference signals for each of the terminals indexed to that indicator.

12. An apparatus according to claim 8, wherein

the controller is configured to generate control information by

further assigning a validity information to said control information, the validity information indicating the validity of presence or absence of reference signals for a specified duration in time domain .

13. An apparatus according to claim 1, wherein

the controller is configured to generate control information by assigning an indication that data of a downlink shared channel being transmitted in those resources not used for reference signal transmission within both the first and the second set but the distance to the resources used for reference signal transmission in time and/or frequency domain is kept within an indicated range.

14. An apparatus, comprising:

a controller configured to

cause a receiver to receive a first set of reference signals at specific locations within a time and frequency resource grid,

cause to transmit information indicative of a usability of a second set of reference signals within the resource grid, the second set comprising less reference signals as compared to the first set,

receive control information,

analyse the received control information, and

responsive thereto

cause to

apply, at the receiver, the second set of reference signals at specific locations within the time and frequency resource grid for reception.

15. An apparatus according to claim 14, wherein

16. An apparatus according to claim 15, wherein

17. An apparatus according to claim 14, wherein

the transmitted information indicative of the usability of the second set of reference signals is based on a channel delay spread for the terminal being below a threshold.

18. An apparatus according to claim 14, wherein the controller is configured to receive and analyse control information based on

an assigned indication of presence or absence of reference signals for at least one terminal, to at least one specific data field in a downlink control information message for said terminal.

19. An apparatus according to claim 18, wherein

20. An apparatus according to claim 18, wherein

21. An apparatus according to claim 18, wherein

22. An apparatus according to claim 18, wherein the controller is configured to receive and analyse control information based on

a further assigned validity information to said control information, the validity information indicating the validity of presence or absence of reference signals for a specified duration in time domain.

23. An apparatus according to claim 14, wherein

the controller is configured to receive and analyse control information based on

an assigned indication that data of a downlink shared channel being transmitted in those resources not used for reference signal transmission within both the first and the second set but the distance to the resources used for reference signal transmission in time and/or frequency domain is kept within an indicated range.

24. An apparatus, comprising:

a means for controlling configured to

25. An apparatus according to claim 24, wherein

26. An apparatus according to claim 25, wherein

27. An apparatus according to claim 24, wherein

the means for controlling is configured to receive the information indicative of the usability of the second set of reference signals from a network management entity as configuration information for said apparatus.

28. An apparatus according to claim 27, wherein

29. An apparatus according to claim 24, wherein

the means for controlling is configured to receive the information indicative of the usability of the second set of reference signals from a terminal device.

30. An apparatus according to claim 29, wherein

31. An apparatus according to claim 24, wherein

the means for controlling is configured to generate control information by

32. An apparatus according to claim 31, wherein

33. An apparatus according to claim 31, wherein

34. An apparatus according to claim 31, wherein

35. An apparatus according to claim 31, wherein

the means for controlling is configured to generate control information by

further assigning a validity information to said control information, the validity information indicating the validity of presence or absence of reference signals for a specified duration in time domain.

36. An apparatus according to claim 24, wherein

the means for controlling is configured to generate control information by

assigning an indication that data of a downlink shared channel being transmitted in those resources not used for reference signal transmission within both the first and the second set but the distance to the resources used for reference signal transmission in time and/or frequency domain is kept within an indicated range.

37. An apparatus, comprising :

a means for controlling configured to

cause a means for receiving to receive a first set of reference signals at specific locations within a time and frequency resource grid,

receive control information,

analyse the received control information, and

responsive thereto

cause to apply, at the means for receiving, the second set of reference signals at specific locations within the time and frequency resource grid for reception.

38. An apparatus according to claim 37, wherein

39. An apparatus according to claim 38, wherein

40. An apparatus according to claim 37, wherein

41. An apparatus according to claim 37, wherein

the means for controlling is configured to receive and analyse control information based on

42. An apparatus according to claim 41, wherein

the at least one specific data field comprises at least one existing re- used or at least one added bit of a downlink control information message, or a specific type of terminal identifier.

43. An apparatus according to claim 41, wherein

44. An apparatus according to claim 41, wherein

45. An apparatus according to claim 41, wherein

46. An apparatus according to claim 37, wherein

the means for controlling is configured to receive and analyse control information based on an assigned indication that data of a downlink shared channel being transmitted in those resources not used for reference signal transmission within both the first and the second set but the distance to the resources used for reference signal transmission in time and/or frequency domain is kept within an indicated range.

47. A method, comprising :

causing a first set of reference signals to be transmitted at specific locations within a time and frequency resource grid,

receiving information indicative of a usability of a second set of reference signals within the resource grid, the second set comprising less reference signals as compared to the first set,

analyzing the received information, and responsive thereto generating control information, and

causing to apply the second set of reference signals at specific locations within the time and frequency resource grid to be transmitted, and

causing to transmit the generated control information in downlink so as to inform terminals being in communication of said second set of reference signals being applied.

48. A method according to claim 47, wherein

49. A method according to claim 48, wherein

50. A method according to claim 47, further comprising receiving the information indicative of the usability of the second set of reference signals from a network management entity as configuration information for said apparatus.

51. A method according to claim 50, wherein

the configuration information received configures an apparatus for use as a network transceiver device of a local area network environment.

52. A method according to claim 47, further comprising

receiving the information indicative of the usability of the second set of reference signals from a terminal device.

53. A method according to claim 52, wherein

54. A method according to claim 47, further comprising

generating control information by

55. A method according to claim 54, wherein

56. A method according to claim 54, wherein

57. A method according to claim 54, wherein

58. A method according to claim 54, further comprising

generating control information by

59. A method according to claim 47, further comprising

generating control information by

60. A method, comprising :

causing a receiver to receive a first set of reference signals at specific locations within a time and frequency resource grid,

causing to transmit information indicative of a usability of a second set of reference signals within the resource grid, the second set comprising less reference signals as compared to the first set,

receiving control information,

analyzing the received control information, and

responsive thereto

causing to

61. A method according to claim 60, wherein

62. A method according to claim 61, wherein

63. A method according to claim 60, wherein

the transmitted information indicative of the usability of the second set of reference signals is based on a channel delay spread for a terminal being below a threshold.

64. A method according to claim 60, further comprising

receiving and analyzing control information based on an assigned indication of presence or absence of reference signals for at least one terminal, to at least one specific data field in a downlink control information message for a terminal.

65. A method according to claim 64, wherein

66. A method according to claim 64, wherein

67. A method according to claim 64, wherein

68. A method according to claim 64, further comprising

receiving and analyzing control information based on a further assigned validity information to said control information, the validity information indicating the validity of presence or absence of reference signals for a specified duration in time domain.

69. A method according to claim 60, further comprising

receiving and analyzing control information based on

70. A computer program products comprising respective computer- executable components which, when the program is run on a computer, are configured to perform the above method according to any of claims 47 to 59.

71. A computer program products comprising respective computer- executable components which, when the program is run on a computer, are configured to perform the above method according to any of claims 60 to 69.

72. An apparatus according to any of claims 1 to 13, and 24 to 36, wherein the apparatus comprises a network transceiver device.

73. An apparatus according to any of claims 14 to 23, and 37 to 46, wherein the apparatus comprises a terminal device.

74. An apparatus according to claim 72 or 73, wherein the apparatus is deployed in a LTE or LTE-A system.