WO2013114632A1

WO2013114632A1 - Method of framework for dci multiplexing and search space design

Info

Publication number: WO2013114632A1
Application number: PCT/JP2012/052570
Authority: WO
Inventors: Satha Sathananthan; Phong Nguyen
Original assignee: NEC Corp
Current assignee: NEC Corp
Priority date: 2012-01-30
Filing date: 2012-01-30
Publication date: 2013-08-08
Anticipated expiration: 2014-07-30
Also published as: WO2013115394A1

Description

DESCRIPTION

METHOD OF FRAMEWORK FOR DCI MULTIPLEXING AND SEARCH SPACE DESIGN

TECHNICAL FIELD

The present invention relates to DCI (downlink control information) multiplexing and search space design for E-PDCCH for LTE Rel-11 and beyond. BACKGROUND ART

There had been several discussions on the motivations for introducing Enhanced Physical Downlink Control Channel (E-PDCCH) in Rel-11 specifications. Recently, 3 GPP agreed to specify E-PDCCH in Rel-11 specifications (see, RP-113602, "Enhanced downlink control channel(s) for LTE- Advanced"), and the following requirements are to be satisfied by E-PDCCH design.

1. able to support increased control channel capacity

2. able to support frequency-domain ICIC,

3. able to achieve improved spatial reuse of control channel resource

4. able to support beamforming and/or diversity

5. able to operate on the new carrier type and in MB SFN subframes

6. able to coexist on the same carrier as legacy UEs

7. desirable characteristics include ability to be scheduled frequency-selectively, and ability to mitigate inter-cell interference.

These top level requirements shall lead to UE specific RS based E-PDCCH design, and pure FDM based multiplexing scheme for transmission of E-PDCCH with PDSCH. 3 GPP agreed to use Rel-10 DM-RS ports (port#7-10) for E-PDCCH

demodulation, but other details of E-PDCCH design are still open for discussion (see, RANI Chairman's Notes, RAN1#67). SUMMARY OF INVENTION

This invention shall intend to provide search space design and DCI multiplexing aspects for E-PDCCH design, which needs to satisfy the above requirements. This invention is considered as additional feature and functionality required for E-PDCCH operation and added to the previous patent by the inventors (see, Australian application No. 2011905034, "A METHOD OF PROVIDING CONTROL INFORMATION FOR USER EQUIPMENT IN AN LTE COMMUNICATION SYSTEM", NEC Corporation).

An exemplary aspect of this invention proposes new search space design for E-PDCCH. That includes the following.

1. DCI multiplexing for E-PDCCH.

2. Enhanced control channel element (E-CCE) definition for efficient resources utilization, and the concept of configurable E-CCE size.

3. Configurable E-PDCCH RE mapping.

A method of framework according to an exemplary aspect of the present invention includes: multiplexing DCI (downlink control information); and searching space design.

In the above-mentioned method, the DCIs of same UE may be multiplexed in single E-PDCCH codeword including single spatial stream, and DCIs of same UE may be not multiplexed in a spatial domain.

In the above-mentioned method, the DCIs of different UEs may be multiplexed in single E-PDCCH codeword including single spatial stream. In the above-mentioned method, the DCIs of different UEs may be multiplexed in a spatial domain including two codewords.

In the above-mentioned method, the E-CCE sizes may be configurable and the parameter for E-CCH size may be signalled to UE by higher layer signalling.

In the above-mentioned method, the PRB-pair region allocated for E-PDCCH may be partitioned into 3 E-CCE region.

In the above-mentioned method, the E-PDCCH symbol to RE mapping may be configurable by higher layer signalling to UE.

In the above-mentioned method, the E-PDCCH symbol may be mapped across either PRB-pair basis or E-CCE region basis, and E-PDCCH symbol may be first mapped in frequency and then time, and REs used for reference and control signals may be skipped.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows an E-PDCCH coding chain.

FIG. 2 shows Multiplexing DCI messages - Single codeword.

FIG. 3 shows Multiplexing DCI messages - Dual codewords.

FIG. 4 shows an Enhanced Control Channel Element (E-CCE).

FIG. 5 shows E-PDCCH mapping to RE on PRB-pair basis.

FIG. 6 shows E-PDCCH mapping to RE on E-CCE basis.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Exemplary novelty of an exemplary embodiment of this invention is the design of DCI multiplexing and search space for flexible and efficient E-PDCCH operation with reduced complexity. The proposed design aspects include: 1. Configurable E-CCE sizes for efficient resources utilizations, and signalling mechanism for UE (user equipment) notification.

2. Partitioning of PRB region into E-CCE region for efficient resources utilizations.

3. Configurable E-PDCCH RE mapping.

In FIGS. 4-6, a square with reference symbol A indicates "CRS port#0, 1". A square with reference symbol B indicates "CRS port#2, 3". A square with reference symbol C indicates "DM-RS port#7, 8". A square with reference symbol D indicates "DM-RS port#9, 10". A square with reference symbol E indicates "Legacy PDCCH Region". A square with no reference symbol indicates "Available RE for E-PDCCH".

(DCI multiplexing)

In contrast to legacy PDCCH, E-PDCCH is designed to support MIMO spatial multiplexing scheme. Therefore, DCI multiplexing for E-PDCCH spatial domain multiplexing shall be considered. As the result of spatial domain multiplexing, the following three levels of DCI multiplexing could be considered:

1. Multiplexing DCI messages of same UE on a single codeword

• This could be same as in legacy PDCCH. After rate matching operation of each DCI message, CCE aggregation is performed and they are multiplexed.

2. Multiplexing DCI messages of same UE on dual codeword

• Separate and independent coding chain for each codeword (i.e., similar to PDSCH approach) could be used for each layer.

3. Multiplexing DCI messages of different UEs

• This multiplexing could be same as in legacy PDCCH. Further, they could be multiplexed in spatial domain.

The above three multiplexing levels in E-PDCCH coding structure is illustrated in FIG. 1. From UE point of view, multiplexing DCI messages of same UE on spatial domain increases UE implementation complexity due to additional decoder. It is more beneficial to use higher order modulation schemes such as 16QAM and/or 64QAM with E-PDCCH instead of UE decoding dual E-PDCCH streams. Therefore, multiplexing DCI messages of same UE on dual codeword shall not be required. However, DCI messages of different UEs shall be multiplexed in spatial domain enabling MU-MIMO for

E-PDCCH. Therefore, multiplexing DCI messages of same UE on a single codeword is the key design aspect considering E-PDCCH mapping and search space design.

A number of PRB-pairs shall be either dynamically assigned or semi-statically signaled to UE or group of UEs. This determines available number of control channel elements for E-PDCCH (E-CCE), and the search space. E-PDCCH PRB-pairs shall be mapped either localized or distributed. However, E-PDCCH PRB-pairs are shared by UEs. DCIs are defined in terms of aggregation levels of E-CCE. Similar to legacy PDCCH, aggregation levels of 1, 2, 4 and 8 shall be considered for E-PDCCH. Thus, DCI multiplexing is based on aggregating allowed E-CCEs.

FIG. 2 and FIG. 3 illustrate how DCIs are multiplexed across the allocated

PRB-pairs for E-PDCCH for localized transmission for single codeword (i.e.,

SU-MIMO) and dual codewords (i.e., MU-MIMO) operation respectively. Same principle applies to distributed transmission as well. UE shall blindly decode DCIs by searching across its search space. This DCI multiplexing and search space is defined per codeword (i.e., per spatial stream). UE shall be notified PRB-pair allocations, number of layers and DM-RS antenna ports. It shall be noted that SU and MU-MIMO for

E-PDCCH can be configured on PRB basis and CCE basis to maximize the E-PDCCH performance for a UE or group of UE (i.e., individual UE or group of UE beam forming and multiplexing).

(Search space design) We define an enhanced control channel element (E-CCE) as the minimum unit for assigning the DCI for E-PDCCH, and it consists REs from a physical resource block (PRB) pair. Depending on the number of REs available in a PRB pair, 2 or 3 E-CCE could be defined within a PRB pair. However, number of REs available in a PRB pair mainly depends on number of OFDM symbols allocated for legacy PDCCH (or could be starting OFDM symbol number for PDSCH) and number of RS ports.

Table 1

Table 1 presents available REs in a PRB pair with different CRS and CFI configurations. We excluded CSI-RS, PRS and PSS/SSS/PBCH in the calculation. Considering the presence of various RS and PSS/SSS/PBCH, it will be more beneficial using configurable E-CCE size depending on CRS and CFI configuration. Fixed E-CCE size is not efficient from resources utilization point of view, considering unused REs. Further, not enough REs for E-CCE will degrade performance. Therefore, configurable E-CCE size shall be used with E-PDCCH design. E-CCE size could be cell specific and could be configured by higher layer signaling.

The number of configurable E-CCE sizes shall be either 2 or 3, defined per PRB-pair depending on the system configurations (i.e., depending on the number of OFDM symbols for PDCCH and the number of CRS ports). One of the E-CCE sizes shall be equal to that of legacy CCE, which is 36 REs. Other E-CCE sizes could be 30 and 42. The E-CCE size shall be signaled to UE by higher layer signaling, using 2 bits.

E-CCE region within a PRB-pair shall be based on pure FDM approach as shown in FIG. 2. In this case, PRB-pair contains 3 E-CCE region, and each E-CCE region contains same number of DM-RS, which would likely to be result in same level of performance from DM-RS channel estimation point of view. Irrespective of E-CCE size, there shall be 3 E-CCG regions per PRB-pair. It should be also noted that defining physical E-CCE or group of E-CCEs region within a PRB-pair is useful since it shall enable PDSCH transmission in the unused E-CCE region.

(E-PDCCH RE mapping)

As shown in FIG. 1, the interleaved E-PDCCH symbols from two code words shall be passed through layer mapping and pre-coding before mapped to RE. The symbol level interleaving shall be used to exploit frequency and/or time diversity and

randomizing the inter-cell interference. It also serves the purpose of ensuring that each E-CCE corresponding to a DCI spans virtually all the allocated PRB-pairs for E-PDCCH. The interleaving function defined in 36.211 shall be used.

Simple mapping of E-PDCCH symbols to RE shall be defined since there is already enough randomizations of E-PDCCH symbols achieved through scrambling and interleaving. E-PDCCH symbols shall be mapped to RE in a similar way as in PDSCH mapping with the following two options. That is first mapped in frequency then mapped in time, and the REs used by reference and common control signals were skipped.

• Option- 1 : E-PDCCH symbols shall be mapped across PRB-pair as shown in FIG. 5.

^■ This is beneficial in case of PDSCH transmitted in the unused E-CCE region.

• Option-2: E-PDCCH symbols shall be mapped across E-CCE region as shown in FIG.

6.

Higher layer signaling shall be used to configure UE with either Option- 1 or

Option-2 mapping. This requires 1 bit for signaling.

An exemplary embodiment of this invention has the following advantages.

1. Proposed DCI multiplexing scheme simplify implementation complexity for UE and network, while providing flexible SU-MIMO and MU-MIMO operation for E-PDCCH.

2. Proposed configurable E-CCE size enables efficient resources utilization,

considering deployment scenarios.

3. Proposed PRB partitioning into E-CCE region enables fair performance across E-CCE region due to availability of same number of DM-RS in each E-CCE region.

4. Proposed PRB partitioning enable PDSCH transmission in the unused E-CCE region resulting in efficient resources utilizations.

5. Proposed configurable E-PDCCH RE mapping simplifies implementation, and optimise performance.

INDUSTRIAL APPLICABILITY

The present invention may be applied to DCI multiplexing and search space design for E-PDCCH for LTE Rel-11 and beyond.

Claims

1. A method of framework comprising:

multiplexing DCI (downlink control information); and

searching space design.

2. The method according to claim 1, wherein the DCIs of same UE (user equipment) are multiplexed in single E-PDCCH codeword including single spatial stream, and DCIs of same UE are not multiplexed in a spatial domain.

3. The method according to claim 1, wherein the DCIs of different UEs are multiplexed in single E-PDCCH codeword including single spatial stream.

4. The method according to claim 1, wherein the DCIs of different UEs are multiplexed in a spatial domain including two codewords.

5. The method according to claim 1 , wherein the E-CCE sizes are configurable and the parameter for E-CCH size is signalled to UE by higher layer signalling.

6. The method according to claim 1, wherein the PRB-pair region allocated for E-PDCCH is partitioned into 3 E-CCE region.

7. The method of claim 1, wherein the E-PDCCH symbol to RE mapping is configurable by higher layer signalling to UE.

8. The method according to claim 7, wherein the E-PDCCH symbol is mapped across either PRB-pair basis or E-CCE region basis, and E-PDCCH symbol is first mapped in frequency and then time, and REs used for reference and control signals are skipped.