WO2013020268A1

WO2013020268A1 - Provisioning of resource element allocations within physical resources of a downlink channel

Info

Publication number: WO2013020268A1
Application number: PCT/CN2011/078120
Authority: WO
Inventors: Shuang TAN; Erlin Zeng; Tommi Koivisto; Timo Roman; Mihai Enescu
Original assignee: Renesas Mobile Corporation
Priority date: 2011-08-08
Filing date: 2011-08-08
Publication date: 2013-02-14
Also published as: CN103703846A; DE112011105506B4; DE112011105506T5; CN103703846B

Abstract

The present invention proposes methods, computer program products and devices for provisioning of resource element allocations within physical resources of a downlink channel, wherein the physical resources of the downlink channel are provided in time domain and frequency domain, wherein an individual resource element is defined by a respective interval in time domain and a respective subcarrier bandwidth in frequency domain, and wherein a plurality of resource elements defined by a first number of consecutive intervals in time domain and a second number of consecutive subcarriers in frequency domain define a respective block of resource elements, the invention involving dividing a respective block of resource elements into a plurality of sub-groups of resource elements, and allocating the plurality of sub-groups of resource elements to at least two terminals.

Description

PROVISIONING OF RESOURCE ELEMENT ALLOCATIONS WITHIN PHYSICAL RESOURCES OF A DOWNLINK CHANNEL

Field of the invention

The present invention relates to methods, devices and computer program products conceived for provisioning of resource element allocations within physical resources of a downlink channel. Background

Mobile data transmission and data services are constantly making progress. With the increasing penetration of such services, more and more users will apply for data transmission using limited transmission resources. It is thus important, that available resources are efficiently used.

Currently, a communication system and/or standard known as Long- Term Evolution LTE and already the advanced version thereof, LTE-A, is being developed. One aspect of those developments is a so-called multiple input multiple output, MIMO, transmission principle for enhancing reliability and throughput of transmission.

Generally, in mobile communication systems, a network is represented by a least a network transceiver station known as Node_B (in UMTS) or as evolved Node„B, eNB, in LTE/LTE-A. Such transceiver station transmits towards one or more user terminals known as UE. This transmission direction is referred to as downlink DL, while transmission from a UE towards an eNB is referred to as uplink UL. Transmission relies on physical as well as logical channels. Physical channels are determined mainly by time and/or frequency/bandwidth and transport logical channels. Generally, logical channels can be distinguished into dedicated channels (used for a specific device only) and shared channels (shared by plural devices), as well as control channels (used for carrying control information) as well as data channels (used for carrying payload/data).

In relation to the present invention to be described in greater detail herein after, a physical downlink control channel PDCCH and/or a physical downlink shared channel PDSCH are mainly considered.

Note that although the present invention will be explained with exemplary reference to LTE/LTE-A, this serves as an example only. Thus, even in case some terminology used herein is based on or similar to terminology as used in LTE/LTE-A, the present invention is applicable to other communication systems as long as they are based on the same principles. Also, even in case some terminology used herein is different from terminology as used in LTE/LTE-A, the present invention is nevertheless applicable to the LTE/LTE-A communication systems.

For Long Term Evolution (LTE) -Advanced, Rel-ll in 3GPP, a study item of downlink multiple input multiple output (MIMO) enhancement has been agreed, (see RP-110457, Study on Downlink MIMO Enhancement for LTE-Advanced, 3GPP TSG-RAN Meeting #51, Kansas City, United States, March 15-18, 2011). One topic thereof relates to enhanced physical downlink control channel (referred to as E-PDCCH), which is also considered in relation to the present invention. The need for enhancement of a PDCCH is also basically investigated in references such as Rl-104607, Discussion on PDCCH capacity considering MU-MIMO, Samsung, 3GPP TSG RAN WG1 Meeting #62, Madrid, Spain, August 23-27, 2010, and Rl-111636, DL Control Channel Enhancement for DL MIMO in Rel-11, NTT Docomo, 3GPP TSG RAN WG1 Meeting #65, Barcelona, Spain, May 9-13, 2011.

The motivations of such work include for example the desire of avoiding a PDCCH capacity limit for a system with multi-user (MU) - MIMO and coordinated multiple point (CoMP) transmission / reception. Apart there form, it is driven by the possibility of better inter-cell interference coordination by moving the control to legacy physical downlink shared channel (PDSCH) region. Another topic which is also being studied currently in 3GPP and likewise addressed by the invention here is machine type communication (MTC) or machine-to-machine (M2M) communication. On the physical layer, MTC may require simultaneous transmission from a large number of UEs. Under existing definitions of PDSCH/PDCCH, however, this will quickly lead to exhausted transmission capacities.

The E-PDCCH can be multiplexed with the PDSCH. Regarding such multiplexing of E-PDCCH with PDSCH, from some company contributions that were submitted to 3GPP RANI #65 meeting, it seems as if a frequency division multiplexing (FDM) structure of E- PDCCH and PDSCH would be the preference of the majority. The FDM here means that E-PDCCH and PDSCH will not be mapped to the same physical resource blocks (PRBs), i.e., no time division multiplexing (TDM) of E-PDCCH and PDSCH in the same PRB. Rather, E-PDCCH will be mapped to a PRB that is located in a different bandwidth/frequency region compared to the PDSCH. A physical resource block denotes a block of physical resources assigned for use by a channel. Generally, a physical resource block is constituted by a plurality of so-called resource elements (REs), with the physical resources of the e.g. downlink, channel being provided in time domain and frequency domain.

From the perspective of multiplexing, E-PDCCH will be similar to PDSCH, i.e. multiplexed to a number of PRBs. The PRBs allocated for use by the E-PDCCH would be signaled by higher layers (radio resource control, RRC) to the UE.

There have been also internal discussions on the remaining issues of E-PDCCH design .

Namely, among the plurality of resource elements constituting a physical resource block there are resource elements that carry common references signals (CRS) and/or demodulation reference signals (DMRS), or the like (at least no payload data) . A receiving device needs to know which resource elements carry such reference signals for proper reception and decoding. Such receiving device then monitors/listens to those resource elements to obtain knowledge of the reference signals needed for decoding. Hence, E-PDCCH design needs to take into account the way of indicating demodulation reference signals (DMRS) port index or scrambling identity (SCID) used for E-PDCCH to a given user equipment (UE).

One open issue still is how to define a control channel element (CCE) for E-PDCCH. Control channel element means essentially a set of resource elements from which the UE searches for the E-PDCCH. For example in current LTE PDCCH, one CCE is defined as 36 Es mapped in distributed manner over the whole system bandwidth (i.e. in more than one PRB), and the UE searches for the DL/UL grants from 1, 2, 4 or 8 concatenated CCEs, called aggregation level. The different numbers of CCEs essentially enable link adaptation for PDCCH as the eNB will be able to control the coding rate by selecting the number of CCEs for a given UE and downlink control information, DCI, format (PDCCH payload) appropriately based on e.g. channel quality indication, CQI, reports received from the UE.

With E-PDCCH, the problem is the dimensioning of the CCE.

According to the assessment of the present inventors, there seem to be two ways to do this:

Way #1 :

Defining a CCE as all the REs in a PRB, except for those occupied by reference signals (i.e. CRS, DM-RS, CSI-RS and potentially other/new reference symbols) or those muted (i.e. unused or reserved for other purposes). An example of this is shown in Figure 1(a).

Way #2;

Following the design for Rel-10 Relay PDCCH (R-PDCCH), Physical layer for relaying operation, (e.g. as described in 3GPP TS 36.216, Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer for relaying operation, V10.3.0, June 2011), i.e., to divide a PRB into two CCEs by the slot boundary, i.e. after 7 OFDM symbols in time domain. An example of this is shown in Figure 1(b). With reference to Fig. 1, some basically applicable definitions/relations are explained for better understanding. Fig. 1 (a) & (b) show resource elements within physical resources of a downlink channel, such as PDCCH / PDSCH. As shown, the physical resources of the downlink channel are provided in time domain and frequency domain (bandwidth illustrated with reference to subcarriers). An individual resource element is defined by a respective interval in time domain and a respective subcarrier bandwidth in frequency domain; it is graphically represented by a square box.

For a given subcarrier, a plurality of resource elements is defined by a first number of consecutive intervals in time domain. They are numbered with index 0 to 13. Thus, 14 resource elements in time domain (each representing an OFDM symbol) constitute 1 sub-frame, of 1 ms duration, which consists of 2 slots. Thus, a respective slot comprises 7 OFDM symbols and has duration of 0.5 ms. Also, for a given time interval, a plurality of resource elements are defined by a second number of consecutive subcarriers in frequency domain. They are numbered with index 0 to 11. Thus, 12 subcarriers are grouped with respective 14 OFDM symbols in time to form a respective block of resource elements, also referred to as physical resource block PRB. Further PRBs (not shown) are present in bandwidth areas above and below the extract of bandwidth shown in Fig. 1.

As shown in Fig. 1(a), three (consecutive) OFDM symbols 0, 1, and 2, for example, are reserved for all subcarriers and define a PDCCH control area. They constitute a respective block of resource elements referred to herein below as special resource elements which are excluded from carrying payioad. Other resource elements (for OFDM symbols 3 to 13 for all subcarriers) comprise resource elements available for carrying payioad. Among those plural resource elements, several ones are referred to as reserved resource elements which carry reference signals such as CRS, DMRS. This being said, a PRB comprises in total 12 times 14 (OFDM) resource elements RE, while among those in the illustrated example 3*12 are special resource elements and 28 RE's are reserved ones. Hence, within such a PRB, 104 REs are available for carrying payload data of E-PDCCH in a control channel element CCE. A CCE denotes a set of REs within one or more PRBs in which (control) information associated to a channel is conveyed and which is searched/monitored by a receiving device. Thus, a DL CCE sent by an eNB is searched for by a receiving UE.

Thus, resource inefficiency can be recognized in such scenario or scenarios shown in Figs. 1(a) and (b). Namely, the number of REs for CCE #k in Figure 1(a) is as many as 104, while CCE #m in Figure 1(b) still has 66 REs and CCE #k in Fig. 1(b) has 38 RE's.

In the table shown in Fig. 2, the number of REs and the probability of use for different CCE designs are compared. For the probability of using different aggregation levels the inventors of this invention refer to evaluations in [2]0 and [5]. It thus turns out that the CCE size as in Figure 1(a) would be too large in most cases, while the CCE size in Figure 1(b) is also inefficient since a CCE size of 36 REs will be sufficient with a probability of greater than 50%. (in the leftmost column, "1 CCE" denotes aggregation level 1, while "2 CCE" denotes aggregation level 2).

Note that for the case when there are less than three PDCCH OFDM symbols in the subframe (i.e. for a smaller PDCCH control area) and/or when there are less than four common reference signal (CRS) ports configured, the resource inefficiency will be even more severe than what is shown in these examples, because in those cases the number of RE's per CCE will even be greater than mentioned above.

Furthermore, E-PDCCH will support closed-loop precoding (beamforming gain) and even to some extent frequency domain scheduling, both implying improved link budget. Given this, the problem will be even more pronounced.

Simple splitting of the PRB at the slot boundary comes along with the problem that the reference signals (RS) have been designed to be used together with the whole PRB. In R-PDCCH (Figure 1 (b)) the problem is circumvented such that both the first and second slot are always used for the same relay node, in other words actually the whole PRB is allocated still to one UE even though part of it (e.g. CCE #m or #k in Fig. 1(b)) may be unused.

Such a restriction of having the whole PRB for the same UE cannot be used now e.g. in a MU-MIMO arrangement, since that would be wasting resources,

A similar problem may appear with PDSCH transmission in case one wants to transmit small packets to multiple UEs: One PRB may turn out to be in fact too much given that 64QAM and MI O with multiple parallel data streams are supported. Hence in such a case PDSCH is as well resource inefficient.

So, there is apparently a problem in terms of enabling small allocations within the PDSCH region, used for either CCEs of E-PDCCH, or for normal PDSCH transmission, as resources are wasted and/or difficulties in support for reference signals RS are encountered. Thus, there is sti!i a need to further improve such systems. Summary Various aspects of examples of the invention are set out in the claims.

According to a first aspect of the present invention in relation to a method implemented at an eNB, there is provided a method, comprising provisioning of resource element allocations within physical resources of a downlink channel, wherein the physical resources of the downlink channel are provided in time domain and frequency domain, wherein an individual resource element is defined by a respective interval in time domain and a respective subcarrier bandwidth in frequency domain, and wherein a plurality of resource elements defined by a first number of consecutive intervals in time domain and a second number of consecutive subcarriers in frequency domain define a respective block of resource elements, the method further comprising dividing a respective block of resource elements into a plurality of sub-groups of resource elements, and allocating the plurality of sub-groups of resource elements to at least two terminals.

Advantageous further developments are defined in the respective dependent claims. According to a second aspect of the present invention in relation to a method implemented at an terminal UE, there is provided a method, comprising receiving, at a terminal, a transmission comprising an indication of sub-groups of resource elements and reserved resource elements carrying reference signals for said respective sub-groups, and determining the at least one sub-group allocated to the terminal and determining the resource elements carrying reference signals for said at least one allocated sub-group.

Advantageous further developments are defined in the respective dependent claims.

According to a third aspect of the present invention, there is provided a computer program product comprising computer-executable components which, when the program is run on a computer, are configured to carry out the method aspects as defined herein above.

The above computer program product may further comprise computer-executable components which, when the program is run on a computer, perform the method aspects mentioned above in connection with the method aspects. The above computer program product/products may be embodied as a computer-readable storage medium.

According to a fourth aspect of the present invention in relation to a device or module implemented to a network transceiver device such as an ei\IB, there is provided a device, comprising a control module configured to provision resource element allocations within physical resources of a downlink channel, wherein the physical resources of the downlink channel are provided in time domain and frequency domain, wherein an individual resource element is defined by a respective interval in time domain and a respective subcarrier bandwidth in frequency domain, and wherein a plurality of resource elements defined by a first number of consecutive intervals in time domain and a second number of consecutive subcarriers in frequency domain define a respective block of resource elements, the control module being further configured to divide a respective block of resource elements into a plurality of sub-groups of resource elements, and to allocate the plurality of sub-groups of resource elements to at least two terminals. Advantageous further developments are defined in the respective dependent claims.

According to a fifth aspect of the present invention in relation to a device or module implemented to an terminal such as a user equipment UE, there is provided a device, comprising a receiver module, configured to receive a transmission comprising an indication of sub-groups of resource elements and reserved resource elements carrying reference signals for said respective sub-groups, and a control module configured to determine the at least one sub-group allocated to the terminal and to determine the resource elements carrying reference signals for said at least one allocated sub-group.

The methods, devices and computer program products described in this document use, at least in exemplary embodiments, propose several P B designs which respectively improve resource efficiency. Also, together with the PRB designs, the present invention proposes as well as a corresponding D RS support to enable also reliable MU- IMO transmissions. In this regard, the present invention enables transmissions via the E-PDCCH and/or PDSCH downlink channels requiring only very small portions of the overall usable radio resource space. Thus this invention addresses the design and operation of small allocations in the downlink of LTE at increased resource efficiency. Thus, performance improvement is based on methods, devices and computer program products according to exemplary aspects and/or embodiment of the present invention. 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:

FIGURE 1 illustrates a basic outline of a PRB in time/frequency domain for outlining resource inefficiency in existing scenarios; FIGURE 2 illustrates a table indicating a probability of use of a CCE comprising a certain number of resource elements as a function of aggregation level;

FIGURE 3 (a) through (d) illustrate scenarios according to embodiments of the present invention in relation to dividing a respective block of resource elements into a plurality of sub-groups of resource elements;

FIGURE 4 illustrates an exemplary scenario according to an embodiment of the present invention in relation to adding reference signals to resource elements of a sub-group;

FIGURE 5 illustrates a signaling diagram of in relation to an aspect of the present invention between a network transceiver device such as an eNB and a terminal such as a UE. Description of exemplary embodiments

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

Generally, the invention is implemented in a communication system configured e.g. in line with the LTE and/or LTE-A standard, though it may also be applied to other standards. Namely, the present invention, at least according to exemplary aspects thereof, and in relation to the above or other communication systems to which it is applicable, deals with provisioning of resource element allocations within physical resources of a downlink channel, wherein the physical resources of the downlink channel are provided in time domain and frequency domain. An individual resource element is defined by a respective interval in time domain and a respective subcarrier bandwidth in frequency domain. A plurality of resource elements defined by a first number of consecutive intervals in time domain and a second number of consecutive subcarriers in frequency domain define a respective block of resource elements

In principle, according to an aspect of the present invention in relation to a method implemented at/carried out by a eNB, for example, such a method involves dividing a respective block of resource elements into a plurality of sub-groups of resource elements, and allocating the plurality of sub-groups of resource elements to at least two terminals. Such sub-groups are also referred to as mini- PRB" hereinafter. Various aspects of the invention will be set out herein in greater detail with reference to the drawings. In this regard, an aspect referred to as

- "proposal #1" herein below addresses sub-aspects of such dividing, an aspect referred to as

- "proposal #2" herein below addresses sub-aspects of reference signals within divided sub-groups, and an aspect referred to as

- "proposal #3" herein below addresses sub-aspects of signaling between / processing at involved devices such as an eNB and a UE.

Proposal #1 Pdividinq"V.

Resources of a PRB in time/frequency domain as defined in existing standard is referred to as "legacy" resource herein below.

Based on such PRB resources, according to an aspect of the invention, those legacy (e.g. PDSCH) resources are divided within one PRB into multiple sub-groups or "mini-PRBs". This enables increase in efficiency for E-PDCCH or small PDSCH allocations, as each mini-PRB can be allocated to a respective terminal. Thus, a (legacy) PRB can be assigned to /used by more than one user terminal.

At least four possible definitions in terms of dividing a legacy PRB to obtain plural of such mini-PRBs are outlined below.

Definition #1 :

Divide one PRB in frequency domain into multiple mini-PRBs. Each mini-PRB covers all OFDM symbols in the legacy PDSCH area and several consecutive subcarriers as a subset of the PRBs bandwidth. An example of such dividing applied to a legacy PRB is shown in 3(a). Definition #2:

Divide one PRB in time-domain into more than two mini-PRBs, Each mini-PRB covers the entire bandwidth of the PRB and several consecutive OFDM symbols as a subset of the legacy PD5CH area. An example of such dividing applied to a legacy PRB is shown in 3(b).

Definition #3

Divide the PRB in both frequency domain and time domain.

An example of such dividing applied to a legacy PRB is shown in 3(c).

Definition #4:

Divide one PRB into multiple mini-PRBs in the unit of REs. These mini-PRBs are non-overlapped, and have nearly equal size of consecutive resources. (This could also be regarded as a special case of definition #3 above). An example of such dividing applied to a legacy PRB is shown in 3(d).

Note that dividing in line with definitions #1 to #3 above will lead to rectangular shaped mini-PRBs, while a dividing in line with definition #4 may lead to non-rectangular shaped mini-PRBs. E.g. when numbering the 104 available REs (those that are not located in the PDCCH control area comprising so-called special resource elements) from 1 to 104 in order. Then, for example, the first mini-PRB #k occupies REs #l-#34, the 2^nd mini-PRB #m occupies REs #35-#68, and the 3^rd mini-PRB #n occupies REs #69-#104. Hence, the REs in one OFDM symbol or one subcarrier may belong to different mini- PRBs.

It should be noted that a respective block of resource elements (legacy PRB) comprises special resource elements excluded from carrying payload (PDCCH ctrl. area), and resource elements available for carrying payioad. According to definition #4, the dividing is performed based on the number of resource elements available for carrying payioad and a number of sub-groups to be obtained. Likewise, according to definition #2, and #3, the dividing does not consider those e.g. 3 OFDM symbols occupied by the special resource elements.

According to definitions #1 to #3, the dividing is performed by defining a border between sub-groups of resource elements in time domain, or frequency domain, or in time and frequency domain, whereas according to definition #4 the dividing comprises defining a border between sub-groups of resource elements by a number count of resource elements. As becomes evident from Figures 3(a), 3(b), and 3(c), respectively, in case the border between sub-groups is defined in time domain, a respective sub-group comprises one or more consecutive resource elements in time domain and all resource elements in frequency domain, while in case the border between sub-groups is defined in frequency domain, a respective sub-group comprises one or more consecutive resource elements in frequency domain and all resource elements in time domain, while in case the border between subgroups is defined in time and frequency domain, a respective subgroup comprises one or more consecutive resource elements in frequency domain and one or more resource elements in time domain. In those cases, the one or more resource elements in time domain are less than the first number, and the one or more resource elements in frequency domain are less than the second number. In the examples shown in Figures 3(a), (b) and (d), respectively, illustrating examples of mini-PRBs obtained based on definitions #1, #2, and #4, a PRB is divided for example into three mini-PRBs, whereas as shown in Figure 3(c), based on definition #3 a PRB is divided for example into four mini-PRBs. - Definition #1

divides the PRB in the frequency domain so that each of the three mini-PRBs #k, #m, and #n will have four consecutive subcarriers, as shown In Figure 3(a). - Definition #2

divides the PRB in the time domain, in the unit of OFDM symbols, as shown for instance in Figure 3(b), in which mini-PRB #k comprises 4 OFDM symbols, mini-PRB #m comprises 3 OFDM symbols, and mini-PRB #n comprises 4 OFDM symbols.

- Definition #3

divides the PRB in time and frequency domain such that each mini-PRB #k, #m, #n, and #1 comprises 6 subcarriers, while mini- PRBs #k and #m comprise 6 OFDM symbols each and mini-PRBs #1 and #n comprise 5 OFDM symbols each.

- Definition #4

divides the PRB in the unit of REs. For example let us assume there are M (=104) available REs in the PRB, then in case of three mini-PRBs to be obtained within the PRB, the size of the respective mini-PRBs is determined in terms of a number count of Res as (the truncated integer value of)

h and (^{M _ 2 X} IYD RES (=36), respectively.

Hence, mini-PRBs #k and #m have 34 REs each, while mini-PRB #n has 36 REs. Proposal #2 : Introducing DMRS support for the mini-PRBs

As mentioned before, the plurality of resource elements within a legacy PRB comprises reserved resource elements carrying reference signals, which are used by a receiving device in relation to decoding payload transmitted. Demodulation references signals DMRS and common reference signals CRS are indicated throughout the figures using distinctive hatching . In MIMO arrangements, transmission occurs from e.g. various antennas, as an example of a respective port. Support for reference signals, in particular for DMRS support, according to aspects of the present invention can be obtained in line with at least two alternatives.

Principally, according to a first alternative,

the dividing of the respective block of resource elements into a plurality of sub-groups comprises reusing the reserved resource elements carrying reference signals in respective sub-groups, and may further comprise to add reference signals to resource elements of a sub-group which does not contain reused (or reusable) reserved resource elements.

Further, principally, according to a second alternative,

as the plurality of resource elements comprise reserved resource elements carrying reference signals, and as the reserved resource elements are transmitted via a plurality of ports, implementing DMRS support may comprise linking reserved resource elements transmitted via a respective port to at least one sub-group.

It is even possible, if needed, to combine the above two alternatives so as to form a third alternative.

The individual alternatives #1 and # 2 will be set out herein below in more detail. DMRS alternative #1 :

According to this alternative it is proposed to design specified DMRS for each mini-PRB. Any such new DMRS design for the mini-PRBs (obtained from dividing) in terms of sequence generation and orthogonal cover code (OCC) selection should reuse the current (i.e. legacy) DMRS of PDSCH as much as possible.

This will have the benefit of keeping DMRS orthogonality in the case of MU-MIMO transmission of both E-PDCCH and PDSCH, and of avoiding interference to legacy UEs' PDSCH transmission.

Within the same PRB, the same precoding shall be applied to a spatial layer over a given mini-PRB and the subset of DMRS REs corresponding to the same spatial layer over that mini-PRB.

For the perspective of improved performance, extra DMRS REs could be inserted using an independent sequence and mapping without changing legacy DMRS. According to DMRS alternative #1, the DMRS design for the respective mini-PRB definitions could be different for the above examples: For example, for Definition #1, the DMRS pattern remains the same as that of Rel-10 DMRS design in terms of sequence generation and mapping to physical resources. But the DMRS REs in one PRB are accordingly divided into three groups with four REs each, as seen in Figure 3(a). In other words, only the DMRS within the corresponding mini-PRB are utilized for channel estimation for that respective mini- PRB. For each of the three mini-PRBs, the same precoding will be applied to the E-PDCCH or PDSCH REs and the corresponding DMRS REs. Note that since the mini-PRBs in one PRB may be allocated to different UEs, the precoding vectors/matrices among different mini- PRBs could also be independent.

Following the example in Figure 3(a), the channel estimation for decoding an E-PDCCH or PDSCH will only be based on four (for a mini-PRB) out of twelve DMRS REs within one (legacy) PRB.

Definition #1 is more suitable to less frequency-selective and more time-variant channel scenarios. Likewise, the above is applicable in a similar manner to the example in Fig. 3(d), which shows a dividing into mini-PRBs based on definition #4. That is, only the DMRS within the corresponding mini- PRB are utilized for channel estimation for that respective mini-PRB. Following the example in Figure 3(d), the channel estimation for decoding an E-PDCCH or PDSCH will only be based on four (for a mini-PRB) out of twelve DMRS REs within one (legacy) PRB. Likewise, the above is applicable in a similar manner to the example in Fig. 3(c), which shows a dividing into mini-PRBs based on definition #3. That is, only the DMRS within the corresponding mini-PRB are utilized for channel estimation for that respective mini-PRB. Following the example in Figure 3(c), the channel estimation for decoding an E- PDCCH or PDSCH will only be based on four (for mini-PRBs #k and #1) and will only be based on two (for mini-PRBs #m and #n) out of twelve DMRS REs within one (legacy) PRB.

According to a modification, extra DMRS could be added also to those mini-PRBs #m and #n, respectively, (which have less DMRS REs than the other mini-PRBs) so as to have a uniform number of DMRS REs throughout the number of divided mini-PRBs.

For Definition #2, the current DMRS REs could be naturally divided into two groups by keeping the capability of time-domain orthogonal cover, and serve for two mini-PRBs respectively. However, one mini- PRB in the example, i.e. mini-PRB #m in Figure 3(b), has no corresponding DMRS resources at all. Therefore, new DMRS design is needed for this particular mini-PRB.

The exact DMRS design should obey the following principles:

- The newly added DMRS REs should not affect the current existed DMRS REs, including pattern, signal sequence, resource mapping, etc.

- The new added DMRS REs should locate within the resource area of the mini-PRB which has no corresponding DMRS (or less DMRS REs than the other mini-PRBs, as stated above in relation to the modification), in order to achieve good channel estimation performance. - The pattern, sequence and resource mapping of new!y added DMRS should use similar design as legacy DMRS as a baseline.

- Extra DMRS REs could be inserted using independent sequence and mapping without changing legacy DMRS for the perspective of performance.

Definition #2 is more suitable to more frequency-selective and less time-variant channel scenarios. An example of added DMRS REs is shown in Fig. 4 based on the scenario illustrated in Fig. 3(b). Of course, similar addition of DMRS REs could be applicable for mini-PRBs #m and #n in Figure 3(c), as mentioned as a modification herein above. DMRS alternative #2:

According to DMRS alternative #2, it is proposed to utilize existing DMRS by taking into use DMRS typically intended for higher-order MIMO only, e.g. DMRS ports 9 and 10. Furthermore an (implicit) linkage between the used DMRS port and the allocated mini-PRB is introduced.

In line with DMRS alternative #2, each mini-PRB is allocated one or several of the existing DMRS ports. In this case, the (receiving) UE estimates the channel for the whole PRB, but then decodes only the relevant part, i.e. the allocated mini-PRB(s).

There may be a predefined linkage between the allocated DMRS port and the allocated mini-PRB, for example such that (in case of above definitions of the mini-PRB yielding 3 mini-PRBs):

- DMRS port 7 is linked to mini-PRB #1, - DMRS port 8 is linked to mini-PRB #2,

- DMRS port 9 (with orthogonal cover code length 2) or DMRS port 11 (with orthogonal cover code length 4) is linked to mini-PRB #3. Furthermore when the PRB dividing is utilized for E-PDCCH or in case multiple mini-PRBs are allocated to the same UE, the DMRS port number may be linked to a plurality of mini-PRBs (a mini-PRB corresponds to a control channel element CCE in case of E-PDCCH) . In case of E-PDCCH the number of this plurality is determined by the aggregation level. For example, for aggregation level 2, DMRS port 7 might be linked to mini-PRBs (CCEs) # 1 and #2, i.e. the UE would use DMRS port 7 for both . In case of PDSCH, this port number is signaled on PDCCH within the resource allocation fieid. In relation to DMRS alternative #2, besides DMRS ports 7&8, ports 9&10 (or ports 11&13) are also needed in order to provide enough number of DMRS ports (4 ports totally) to link DMRS REs / ports to multiple mini-PRBs. An example of the linkage between DMRS ports and mini-PRBs is given . But for the 3^rd mini-PRB, the exact linkage has at least two possible ways, since the other two DMRS ports could be either 9&10 (OCC length 2 with 24 DMRS REs) or 11&13 (OCC length 4 with 12 DMRS REs). Namely, in Rel.10, there are totally 24 REs defined for up to 8 DMRS ports per PRB. Those 24 REs are divided into two groups occupying different subcarriers, and each group supports up to 4 ports. The DMRS ports in different groups naturally are orthogonal. The orthogonality of intra-group DMRS ports is achieved via time-domain orthogonal code cover. When the number of DMRS ports in one group is 2, the length of OCC needs to be 2. When the number of DMRS ports in one group is more than 2, OCC length 4 is needed. Proposal #3:

The network, e.g. an eNB, is able to configure each UE to switch between the respective mini-P B definitions and therefore the corresponding DMRS designs. This can be accomplished e.g. through radio resource control (RRC) signaling, according to the channel properties and system requirements. Above, the mini-PRB may then be used for transmitting one CCE of E-PDCCH, or a very small PDSCH allocation, hence solving the issue of resource inefficiency. MU-MIMO transmission is a key technology for PDCCH enhancements as well as PDSCH transmission. This spatial multiplexing could happen among multiple E-PDCCHs or between E-PDCCH and PDSCH from separate UEs. For E-PDCCH multiplexing, DMRS orthogonality and channel estimation performance can be guaranteed under proper scheduling. However, multiplexing between E-PDCCH and PDSCH is more challenging. Fortunately, quasi-orthogonal design as in Rel-ll MU- MIMO can be applied here to decrease inter-user interference.

Fig. 5 shows a signaling diagram of in relation to an aspect of the present invention between a network transceiver device such as an eNB and a terminal such as a UE.

From the eNB point of view,

the operation related to this invention is as follows:

- The eNB /and or a scheduler module thereof (denoted by numeral 1) determines a resource allocation in terms of mini-PRBs for the UE (as shown in a step Sll).

This may comprise either

- determining a mini-PRB (CCE) allocation for E-PDCCH within the PRBs allocated for E-PDCCH, in which case the eNB scheduler would choose the mini-PRB(s) for the CCE(s) based on UE E-PDCCH search space in the particular subframe, or

- determining a small PDSCH mini-PRB allocation, in which case the allocation would be within any PRBs not allocated for any other transmissions, e.g. E-PDCCH, based on usual scheduling decision logic.

- In both cases, the mini-PRBs may be allocated according to any of definitions #1 to definition #4. Together therewith, in a step S12, the eNB determines DMRS associated to the allocated mini-PRBs. This may comprise either

- using only a subset of REs of one of the existing DMRS ports, in particular those that are located within the allocated mini-PRB, i.e. DMRS alternative #1 with e.g. mini-PRB definition #1, #3 or #4, or - using newly defined REs that are located only within the allocated mini-PRB, i.e. DMRS alternative #1 with e.g. mini-PRB definition #2, or #3 (when adding DMRS only to mini-PRBs #m and #n in Fig. 3(c)), or

- choosing one of the existing DMRS ports linked to the allocated mini-PRB in which case the DMRS span the whole PRB, i.e. DMRS alternative #2.

- The eNB transmits in a step S13 the data (PDSCH) or control (E- PDCCH) in the allocated mini-PRBs, and the associated DMRS (in a step S14) to the UE (denoted by 2).

Furthermore in case of PDSCH, the eNB 1 transmits the associated control signaling which indicates to the UE 2 which mini-PRBs were allocated. From the UE point of view,

the operation related to this invention is as follows: - The UE 2 receives in a step S21 the transmissions from the eNB 1,

- The UE, in a step S22, first determines the mini-PRB allocation. This may comprise either one of:

- In case of PDSCH, receiving resource allocation signaling from the eNB indicating which mini-PRB(s) have been allocated to the UE.

- In case of E-PDCCH, determining the relevant mini-PRBs based on the UE E-PDCCH search space in the current subframe.

- UE then determines in a step S23 the associated DMRS REs. Again this may comprise either DMRS alternative #1 or #2 where in case of DMRS alternative #1 the chosen DMRS approach may depend on how the mini-PRB is arranged (definition #1, #2, #3 or #4).

- UE in step S24 estimates the channel only for the mini-PRB (DMRS alternative #1) or for the whole PRB (DMRS alternative #2) based on the associated DMRS.

- UE receives the resource elements according to the mini-PRB resource mapping and decodes in step S25 the data (PDSCH) or control (E-PDCCH).

Insofar, the eNB transmits an indication of sub-groups of resource elements and reserved resource elements carrying reference signals for said respective sub-groups towards the terminal UE, and furthermore sends the sub-groups of resource elements carrying payload and reference signals towards said terminal. Likewise, insofar as the terminal UE is concerned, the terminal receives a transmission comprising an indication of sub-groups of resource elements and reserved resource elements carrying reference signals for said respective sub-groups, and determines the at least one sub-group allocated to the terminal and determines the resource elements carrying reference signals for said at least one allocated sub-group. Then, the terminal estimates a channel based on the reference signals received in the resource elements, and decodes the payload data contained in the resource elements of the at least one sub-group based on the channel estimation . Although hereinbefore a focus of the description has been laid on method aspects involved, it is to be understood that those method aspects can be implemented by computer program products or in hardware. Namely, a device such as the eNB or UE typically comprises an interface for communication (e.g. a transceiver or transceiver module), an internal memory and a control module controlling the operation of the entire device based on data received and/or fetched from the internal memory. The control module can be an application specific integrated circuit ASIC which is configured to implement the method, or a digital signal processor DSP, or another processor configured to implement the method, or the like.

Thus, the present invention likewise encompasses a (eNB) device comprising a control module configured to provision resource element allocations within physical resources of a downlink channel, wherein the physical resources of the downlink channel are provided in time domain and frequency domain, wherein an individual resource element is defined by a respective interval in time domain and a respective subcarrier bandwidth in frequency domain, and wherein a plurality of resource elements defined by a first number of consecutive intervals in time domain and a second number of consecutive subcarriers in frequency domain define a respective block of resource elements, the control module being further configured to divide a respective block of resource elements into a plurality of subgroups of resource- elements, and allocate the plurality of sub-groups of resource elements to at least two terminals. In such device,

the control module is configured to define a border between subgroups of resource elements in time domain, or frequency domain, or in time and frequency domain;

5 - the control module is configured to define a border between subgroups of resource elements by a number count of resource elements; wherein in case the border between sub-groups is defined in time domain, a respective sub-group comprises one or more consecutive resource elements in time domain and all resource elements in

10 frequency domain, while in case the border between sub-groups is defined in frequency domain, a respective sub-group comprises one or more consecutive resource elements in frequency domain and all resource elements in time domain, while in case the border between sub-groups is defined in time and frequency domain, a respective i s sub-group comprises one or more consecutive resource elements in frequency domain and one or more resource elements in time domain ;

- wherein the one or more resource elements in time domain are less than the first number, and the one or more resource elements in frequency domain are less than the second number;

20 - wherein a respective block of resource elements comprises special resource elements excluded from carrying payload, and resource elements available for carrying payload, and wherein the control module is configured to divide based on the number of resource elements available for carrying payioad and a number of sub-groups

25 to be obtained;

- wherein the plurality of resource elements comprise reserved resource elements carrying reference signals, and wherein the control module is configured to divide the respective block of resource elements into a plurality of sub-groups by reusing the reserved

30 resource elements carrying reference signals in respective sub-groups; - the control module is further configured to add reference signals to resource elements of a sub-group which does not contain reused reserved resource elements.;

- wherein the plurality of resource elements comprise reserved resource elements carrying reference signals, wherein the reserved resource elements are transmitted via a plurality of ports, and the control module is further configured to link reserved resource elements transmitted via a respective port to at least one sub-group;

- the downlink channel is a physical downlink control channel, PDCCH, or a physical downlink shared channel, PDSCH;

- the above outlined device further comprises a transmitter module configured to transmit an indication of sub-groups of resource elements and reserved resource elements carrying reference signals for said respective sub-groups towards a terminal;

- wherein the transmitter module is further configured to send the sub-groups of resource elements carrying payioad and reference signals towards said terminal.

Also, the present invention likewise encompasses a (terminal UE) device, comprising a receiver module, configured to receive a transmission comprising an indication of sub-groups of resource elements and reserved resource elements carrying reference signals for said respective sub-groups, and a control module configured to determine the at least one sub-group allocated to the terminal and to determine the resource elements carrying reference signals for said at least one allocated sub-group.

In such device,

- the control module is further configured to estimate a channel based on the reference signals received in the resource elements, and to decode the payload data contained in the resource elements of the at least one sub-group based on the channel estimation.

Other systems can benefit also from the principles presented herein 5 as long as they have identical or similar properties in terms of resource elements in time/frequency domain.

Embodiments of the present invention may be implemented in software, hardware, application logic or a combination of software,

10 hardware and application logic. The software, application logic and/or hardware resides, from one perspective, on the networks side such as at an eNB or a module thereof as well as, from another perspective, on the terminal side such as at a user terminal/equipment, UE or a module thereof. Examples of a UE may comprise terminals such as i s mobile phones, personal digital assistants PDAs or so-called smart phones.

In an example embodiment, the application logic, software or an instruction set is maintained on any one of various conventional

20 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

25 equipment.

The present invention relates in particular but without limitation to mobile communications, for example to LTE and can advantageously be implemented (under transmitter aspects) in network transceiver 30 devices such as eNBs and (under receiver aspects) in user equipments such as smart phones, or personal computers connectable to such networks. 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 abbreviations/acronyms:

CCE Control Channel Element

CoMP Coordinated Multiple Point Transmission/Reception

CRS Common Reference Signal

CQI channel quality indication

DCI downlink control information

DMRS Demodulation Reference Symbols

E-PDCCH Enhanced Physical Downlink Control Channel

FDM Frequency Division Multiplexing

LTE Long Term Evolution

M2M Machine-to-Machine

MIMO Multiple Input Multiple Output

MTC Machine Type Communication

MU-MIMO Multi-user MIMO

OFDM Orthogonal Frequency Division Multiplexing

PDA Personal Digital Assistant

PDCCH Physical Downlink Control Channel

PDSCH Physical Downlink Shared Channel

PRB Physical Resource Block

RE Resource Element

RRC Radio Resource Control

RS Reference Signal

R-PDCCH Relay Physical Downlink Control Channel

SCID Scrambling Identity

TDM Time Division Multiplexing

UE User Equipment

Prior art: - RP-110457, Study on Downiink MIMO Enhancement for LTE- Advanced, 3GPP TSG-RAN Meeting #51, Kansas City, Unitied States, March 15-18, 2011

- Rl-104607, Discussion on PDCCH capacity considering MU-MIMO, Samsung, 3GPP TSG RAN WGl Meeting #62, Madrid, Spain, August

23-27, 2010

- Rl-111636, DL Control Channel Enhancement for DL MIMO in Rel- 11, NTT Docomo, 3GPP TSG RAN WGl Meeting #65, Barcelona, Spain, May 9-13, 2011

- 3GPP TS 36.216, Evolved Universal Terrestrial Radio Access (E- UTRA); Physical layer for relaying operation, V10.3.0, June 2011

- Rl-103084, PDCCH blind decoding in LTE-A, Huawei, 3GPP TSG RAN WGl Meeting #61, Montreal, Canada, May 10-14, 2010

Claims

What is claimed is:

1. A method, comprising

provisioning of resource element allocations within physical resources of a downlink channel,

wherein the physical resources of the downlink channel are provided in time domain and frequency domain,

wherein an individual resource element is defined by a

respective interval in time domain and a respective subcarrier bandwidth in frequency domain, and

wherein a plurality of resource elements defined by a first number of consecutive intervals in time domain and a second number of consecutive subcarriers in frequency domain define a respective block of resource elements,

the method further comprising:

dividing a respective block of resource elements into a plurality of sub-groups of resource elements, and

allocating the plurality of sub-groups of resource elements to at least two terminals.

2. The method according to claim 1, wherein the dividing comprises defining a border between sub-groups of resource elements in time domain, or frequency domain, or in time and frequency domain.

3. The method according to claim 1, wherein the dividing comprises defining a border between sub-groups of resource elements by a number count of resource elements.

4. The method according to claim 2, wherein

in case the border between sub-groups is defined in time domain, a respective sub-group comprises one or more consecutive resource elements in time domain and all resource elements in frequency domain, while

in case the border between sub-groups is defined in frequency domain,

a respective sub-group comprises one or more consecutive resource elements in frequency domain and all resource elements in time domain, while

in case the border between sub-groups is defined in time and frequency domain,

a respective sub-group comprises one or more consecutive resource elements in frequency domain and one or more resource elements in time domain.

5. The method according to claim 4, wherein

the one or more resource elements in time domain are less than the first number, and

the one or more resource elements in frequency domain are less than the second number.

6. The method according to claim 3, wherein

a respective block of resource elements comprises special resource elements excluded from carrying payload, and resource elements available for carrying payload,

and wherein the dividing is performed based on the number of resource elements available for carrying payload and a number of sub-groups to be obtained.

7. The method according to any of claims 1 to 6, wherein

the plurality of resource elements comprise reserved resource elements carrying reference signals, and wherein the dividing of the respective block of resource elements into a plurality of sub-groups comprises

reusing the reserved resource elements carrying reference signals in respective sub-groups.

8. The method according to claim 7, further comprising

adding reference signals to resource elements of a sub-group which does not contain reused reserved resource elements,

9. The method according to any of claims 1 to 6, wherein

the plurality of resource elements comprise reserved resource elements carrying reference signals, wherein the reserved resource elements are transmitted via a plurality of ports, and further comprising

linking reserved resource elements transmitted via a respective port to at least one sub-group.

10. The method according to claim 1, wherein the downlink channel is a physical downlink control channel, PDCCH, or a physical downlink shared channel, PDSCH.

11. The method according to any of the preceding claims 1 to 10, further comprising

transmitting an indication of sub-groups of resource elements and reserved resource elements carrying reference signals for said respective sub-groups towards a terminal.

12. The method according to claim 11, further comprising

sending the sub-groups of resource elements carrying payload and reference signals towards said terminal.

13. A method, comprising:

receiving, at a terminal, a transmission comprising an indication of sub-groups of resource elements and reserved resource elements carrying reference signals for said respective sub-groups, and

determining the at least one sub-group allocated to the terminal and

determining the resource elements carrying reference signals for said at least one allocated sub-group.

14. The method according to 13, further comprising

estimating a channel based on the reference signals received in the resource elements, and

decoding the payload data contained in the resource elements of the at least one sub-group based on the channel estimation.

15. A computer program product comprising computer-executable components which, when the program is run on a computer, are configured to execute the method according to any of claims 1 to 12, or according to any of the claims 13 to 14.

16. A device, comprising a control module configured to

provision resource element allocations within physical resources of a downlink channel,

wherein an individual resource element is defined by a

the control module being further configured to

divide a respective block of resource elements into a plurality of sub-groups of resource elements, and

allocate the plurality of sub-groups of resource elements to at least two terminals.

17. The device according to claim 16, wherein the control module is configured to

define a border between sub-groups of resource elements in time domain, or frequency domain, or in time and frequency domain.

18. The device according to claim 16, wherein the control module is configured to

define a border between sub-groups of resource elements by a number count of resource elements.

19. The device according to claim 17, wherein

in case the border between sub-groups is defined in frequency domain,

in case the border between sub-groups is defined in time and frequency domain, a respective sub-group comprises one or more consecutive resource elements in frequency domain and one or more resource elements in time domain.

20. The device according to claim 19, wherein

21. The device according to claim 18, wherein

a respective block of resource elements comprises special resource elements excluded from carrying pay!oad, and resource elements available for carrying payload,

and wherein the control module is configured to divide based on the number of resource elements available for carrying payload and a number of sub-groups to be obtained.

22. The device according to any of claims 16 to 21, wherein

the plurality of resource elements comprise reserved resource elements carrying reference signals, and wherein the control module is configured to

divide the respective block of resource elements into a plurality of sub-groups by

reusing the reserved resource elements carrying

reference signals in respective sub-groups.

23. The device according to claim 22, wherein the control module is further configured to

add reference signals to resource elements of a sub-group which does not contain reused reserved resource elements.

24. The device according to any of claims 16 to 21, wherein

the plurality of resource elements comprise reserved resource elements carrying reference signals, wherein the reserved resource elements are transmitted via a plurality of ports, and the control module is further configured to

link reserved resource elements transmitted via a respective port to at least one sub-group.

25. The device according to claim 16, wherein the downlink channel is a physical downlink control channel, PDCCH, or a physical downlink shared channel, PDSCH.

26. The device according to any of the preceding claims 16 to 25, further comprising a transmitter module configured to

transmit an indication of sub-groups of resource elements and reserved resource elements carrying reference signals for said respective sub-groups towards a terminal.

27. The device according to claim 26, wherein the transmitter is further configured to send the sub-groups of resource elements carrying payload and reference signals towards said terminal.

28. A device, comprising:

a receiver module, configured to receive a transmission comprising an indication of sub-groups of resource elements and reserved resource elements carrying reference signals for said respective sub-groups, and

a control module configured to

determine the at least one sub-group allocated to the terminal and to determine the resource elements carrying reference signals for said at least one allocated sub-group.

29. The device according to 28, wherein the control module is further configured to

estimate a channel based on the reference signals received in the resource elements, and to

decode the payload data contained in the resource elements of the at least one sub-group based on the channel estimation.