The present disclosure relates generally to coverage in wireless communications and, more specifically, to providing small cells having overlapping areas with other cells to improve coverage in a wireless communications system.
Coverage within a geographic area for a wireless communications network that is generally provided by a base station may be augmented using small cells, to increase the capacity of the wireless communications network in that area. For example, the service areas along roadways that are heavily traveled, or the interiors of shopping malls or sports arenas where large numbers of users may congregate, may benefit from additional capacity. In adding small cells to augment a “macro” cell, however, issues such as resource allocation to particular user equipment (UE) within the overlapping coverage areas, hand-off and inter-cell interference must be addressed.
There is, therefore, a need in the art for improved utilization of small cells in wireless communications systems.
Orthogonal multi-user, multiple input, multiple output (MU-MIMO) multiplexing capacity for demodulation reference signals (DMRSs) is increased without increasing the overhead in resource elements per physical resource block by using length-4 orthogonal cover codes (OCC-4). A base station switches between legacy DMRS antenna port mappings and OCC-4 mapping based upon either a transmission mode or a channel station information process configuration field value.
Before undertaking the DETAILED DESCRIPTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, where such a device, system or part may be implemented in hardware that is programmable by firmware or software. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases.
For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts:
The following documents and standards descriptions are hereby incorporated into the present disclosure as if fully set forth herein:
[REF1]—3GPP TS 36.211 v10.1.0, “E-UTRA, Physical channels and modulation”;
[REF2]—3GPP TS 36.212 v10.1.0, “E-UTRA, Multiplexing and Channel coding”;
[REF6]—R1-130691, Initial evaluation of DM-RS reduction for small cell, LG Electronics.
Small Cell Enhancement
3GPP TR 36.932 [REF4] describes target scenarios of a small-cell study, indicating that small cell enhancement should target deployment both with and without macro coverage, both outdoor and indoor small cell deployments, and both ideal and non-ideal backhaul. In addition, both sparse and dense small cell deployments should be considered.
One or more user device(s) (not shown in
Coverage area regions 102a-102c in
Base station 101 and each small cell 103a-103n includes one or more processor(s) 110 coupled to a network connection 111 over which signals may be received and selectively transmitted—that is, a connection to a backhaul network and/or to the Internet. The base station 101 and each small cell 103a-103n also includes memory 112 containing an instruction sequence for processing communications in the manner described below, and data used in the processing of communications. The base station 101 and each small cell 103a-103n each further include a transceiver 113 and associated antenna(a) 114 for wireless communications with user equipment.
User device(s) 105, not depicted in
With and without Macro Coverage
Referring back to
Sparse and Dense
Small cell enhancement should consider sparse and dense small cell deployments. In some scenarios (e.g., hotspot indoor/outdoor places, etc.), only a single or a few small cell node(s) are sparsely deployed, for example to cover the traffic hotspot(s). Meanwhile, in some scenarios (e.g., dense urban residential areas, a large shopping mall, etc.), a lot of small cell nodes are densely deployed to support huge traffic over a relatively wide area covered by the small cell nodes. Furthermore, smooth future extension/scalability (e.g.,: from sparse to dense, from small-area dense to large-area dense, or from normal-dense to super-dense) should be considered. For throughput performance, dense deployments should be prioritized compared to sparse deployments. For mobility/connectivity performance, both sparse and dense deployments should be considered with equal priority.
Synchronization
Both synchronized and un-synchronized scenarios should be considered between small cells as well as between small cell and macro layers. For specific operations such interference coordination, carrier aggregation and inter-eNB coordinate multi-point (COMP) communications, small cell enhancement can benefit from synchronized deployments with respect to small cell search/measurements and interference/resource management. Therefore time synchronized deployments of small cell clusters are preferably prioritized and new means to achieve such synchronization should be considered.
Spectrum
Small cell enhancement should address the deployment scenario in which different frequency bands are separately assigned to macro layer and small cell layer, respectively, where F1 and F2 correspond to different carriers in different frequency bands as described above.
Small cell enhancement should be applicable to all existing and as well as future cellular bands, with special focus on higher frequency bands, e.g., the 3.5 giga-Hertz (GHz) band, to enjoy the more available spectrum and wider bandwidth.
Small cell enhancement should also take into account the possibility for frequency bands that, at least locally, are only used for small cell deployments.
Co-channel deployment scenarios between macro layer and small cell layer should be considered as well. The duplication of activities with existing and coming standards items should be avoided.
Some example spectrum configurations are:
1. Carrier aggregation on the macro layer with bands X and Y, and only band X on the small cell layer;
2. Small cells supporting carrier aggregation bands that are co-channel with the macro layer; and
3. Small cells supporting carrier aggregation bands that are not co-channel with the macro layer.
One potential co-channel deployment scenario is dense outdoor co-channel small cells deployment, considering low mobility UEs and non-ideal backhaul, where all small cells are under the macro coverage.
Small cell enhancement should be supported irrespective of duplex schemes—frequency division duplex (FDD) or time division duplex (“TDD”)—for the frequency bands for macro layer and small cell layer. Air interface and solutions for small cell enhancement should be band-independent, and aggregated bandwidth per small cell should be no more than 100 mega-Hertz (MHz), at least for Rel-12.
System Information Acquisition in Release 8/10
RP-121186 proposes introduction of dormant cells in the following manner:
Some of the main motivations for defining new carriers types (NCT) were reducing energy use and reducing generated interference due to common reference signal transmission by partially loaded or unloaded cells. Clearly the Rel-11 NCT design, which is also part of the NCT Work Item Description (WID) [REF4] is a step towards this goal; however, that design achieves only moderate gains. Another, and possibly more natural, alternative is simply to enable turning off signal transmission completely in unloaded cells. This could be used in conjunction with the Rel-11 NCT design or used in itself. This then gives the following schemes to consider:
Option 1: Reduced common reference signal (CRS) (Rel-11 NCT), (useful mainly in macro cells);
Option 2: Dormant mode of unloaded cells, (useful in both small cells and macro cells); and
Option 3: Dormant mode of unloaded cells+Reduced CRS.
1Four out of five subframes do not contain CRS.
2Assume cell detection signals equivalent to 20 CRS symbols transmitted once every 320 milli-seconds (ms).
3Makes assumption that Tx circuitry is switched On/Off on a per-subframe basis rather than on a per-symbol basis.
4Rel-8-11 UEs are not able to get service in NCT.
5Rel-8-11 UEs can get service when the cell is active, although some mobility problems can be expected.
The Multicast-Broadcast Single-Frequency Network (MBSFN) option of LTE and DeModulation Reference Signals (DM-RS) are referenced in the above analysis.
In R1-124931, two cases were identified for an NCT cell to neighbor a backward compatible cell (e.g., R11 compatible cell), as shown in
When the cell is configured to an advanced UE as an Scell, the advanced UE synchronizes to the Scell (and to the quasi-cell when the quasi-cell is close to the Scell) relying on PSS/SSS, and may receive other configurations with respect to the Scell from the Pcell. The advanced UE can be configured to receive PDSCH and other downlink (DL) physical signals from either the cell or the quasi-cell or both. In this case, the advanced UE can be configured with two virtual cell IDs (VCIDs), one (VCID1) for the cell and the other (VCID2) for the quasi-cell. When the advanced UE is configured (or scheduled) to receive a PDSCH from the cell, then VCID1 is used for PDSCH and/or UE-RS scrambling for the PDSCH. When the advanced UE is configured (or scheduled) to receive a PDSCH from the quasi-cell, then VCID2 is used for PDSCH and/or UE-RS scrambling for the PDSCH. The configuration of the DL physical signal origin can change either dynamically or semi-statically. When the configuration changes dynamically, a one-bit field can included in a DL scheduling assignment DCI format (e.g., DCI formats 1A, 2B, 2C, 2D and any extension of these DCI formats) to indicate the DL physical signal origin, i.e., whether the DL physical signal is from the cell (in which case VCID1) or the quasi-cell (in which case VCID2).
In some embodiments associated with
In some embodiments associated with
The deployment scenario shown in
In
In the first circumstance described above, an advanced UE can acquire synchronization to the quasi-cell relying on PSS/SSS (and TRS or CRS) transmitted by the quasi-cell. Once the UE acquires synchronization from PSS/SSS, the advanced UE obtains a physical cell ID (PCI) and cyclic prefix (CP) length (e.g., whether the CP length is normal-CP or extended-CP). In the legacy LTE system, PCI ranges from 0 to 503.
On the other hand, for the discovery and synchronization to the quasi-cells, the advanced UE relies on the discovery signal transmitted by the quasi-cell. Once the UE discovers a quasi-cell relying on the discovery signal, the UE obtains a discovery ID. In one example, a discovery ID is used to generate at least one of a set of time-frequency locations where a discovery channel is transmitted and the (scrambling) sequence for the discovery signal. In this case, when a UE detects strong energy across the set of time-frequency locations, the UE can identify the existence of a quasi-cell having the discovery ID (using the sequence).
The discovery ID detected from the discovery signals would be able to have wider range of values than otherwise available. In one example, the value range for the discovery ID is chosen as [0, MSCI], where MSCI is the maximum possible value for the discovery ID, which is greater than 503, e.g., 2006. In another example, to distinguish the discovery ID and PCI from the values, the value range for the discovery ID is chosen as [504, MSCI], where MSCI is the maximum possible value for the discovery ID. In one example, when 2000 discovery IDs are defined, MSCI=1000+504−1=2503. It is noted that the number of discovery IDs should be large enough to assign a number of small cells in a geographical area, and here 2000 discovery IDs are considered just as an example.
When an advanced UE is configured with a serving cell on the carrier according to the embodiments associated with
Convertible-Type Cell
When the subframe type is BCT, the subframe can be either an MBSFN subframe or a non-MBSFN subframe. In an MBSFN subframe, CRSS are transmitted only in the first two OFDM symbols of the subframe, while in a non-MBSFN subframe, full CRSs are transmitted according to the CRS pattern for Antenna Ports (APs) 0-NAP, where NAP is the number of configured CRS APs. In each BCT subframe, PDCCH, PCFICH and Physical Hybrid-Automatic Repeat request (ARQ) Indicator CHannel (PHICH) are transmitted in the first a few OFDM symbols of the subframe.
When the subframe type is NCT and when the subframe does not carry PSS/SSS, no CRSs are mapped in the subframe. In addition, in each NCT subframe, none of PDCCH, PCFICH and PHICH are transmitted, and hence PDSCH can be transmitted from the first OFDM symbol.
To illustrate a use case of the convertible quasi-cell signaling illustrated in
In some BCT subframes, legacy CRS(s) may be transmitted to support the legacy PDCCH transmission and legacy TMs relying on legacy CRS.
In some BCT subframes, in order to comply with the legacy specification, the legacy rate matching of the PDSCH (around the CRS REs) for the legacy UEs can be applied, even if the legacy CRS is not transmitted.
Advanced UE Behavior for the Convertible-Type Cell:
The network can configure an Scell for an advanced UE that is a convertible-type cell. The type of Scell can be either explicitly indicated by an information element conveyed by an RRC signal configuring the Scell or implicitly indicated by the OFDM symbol location of PSS/SSS (in case the OFDM symbol location of PSS/SSS in the convertible-type cell is different from the BCT cells). Here, the information element can be of the ENUMERATION type, and the possible information element values would be codes for {BCT, NCT, CT}, where CT implies convertible-type.
When the network configures a convertible-type cell to an advanced UE, some impact to any advanced UE that has been receiving/transmitting from/to the small cell is to be expected. In contrast to the legacy UEs, the advanced UEs are aware that the small cell is a convertible type cell. The system protocol may therefore be designed so that the advanced UEs take advantage of the knowledge of the cell type. When the advanced UE knows the cell (or subframe) type, the advanced UEs can:
Subframe-Type Indication:
Furthermore, the subframe type can be indicated to the advanced UE so that the advanced UE can apply the proper method. The indication of the subframe type can be done in a UE-specific RRC configuration containing a 40-bit bitmap field, the i-th bit of which indicates whether the i-th subframe of a super-frame of Nsuper (e.g., 40) subframes is BCT or NCT. For example, if the i-th bit is 1, the i-th subframe is NCT; if the i-th bit is 0, the i-th subframe is BCT.
Number of CRS Antenna Ports when the CT Cell Becomes BCT
The TRS in the NCT is transmitted on the resource elements (REs) where the legacy CRS for AP 0 is transmitted. To seamlessly support legacy operation, the number of CRS ports should not vary over subframes. Hence, the number of CRS APs in the BCT cell (or subframe) should be constant, which is 1. In one example scenario, the cell-type switching can happen only in an Scell on a first carrier, and a UE maintains a basic connection with the network in a Pcell on a second carrier. Then, if the eNB 100 configures an SCell that is a convertible type (between NCT and backward-compatible-type) for the advanced UE, the number of CRS APs in BCT subframes in the convertible-type cell is constant, i.e., one.
Method X:
When the cell type is either NCT or convertible-type, the advanced UEs should perform RSRP measurement only in those subframes where PSS/SSS/TRS are transmitted, and rely on TRS (or reduced CRS); on the other hand, when the cell type is BCT, the advanced UEs can rely on the legacy mechanism to perform RSRP measurement without any subframe restriction.
A few alternatives to inform the advanced UEs of the cell type are considered below.
According to the current agreement in 3GPP RAN1, the subframes where PSS/SSS/TRS are transmitted are subframes #0 and #5.In 36.331 v10.5.0, the following pseudo-code is captured for the E-UTRA measurement object, i.e., MeasObjectEUTRA information element (IE):
In one alternative (Alt 1), in order for the network to inform an advanced UE of the cell type of neighbor cells for which the UE performs RSRP measurement, CellsToAddMod may be modified to include the cell type of each neighbor cell.
In one example, the following change is made according to the current alternative:
Here, NCTIndicator is TRUE if the cell is NCT or convertible-type, FALSE if the cell is BCT.
In another example, the following change can be made according to the current alternative:
Here, cellType is NCT if the cell is NCT or convertible-type, backwardCompatible if the cell is BCT.
In another alternative (Alt 2), the type of the neighbor cell is implicitly indicated by the time location of PSS/SSS. When the UE detects PSS/SSS according to the legacy specification (or according to
Method Y:
When the cell (or subframe) type is NCT, the advanced UE should read PDSCH symbols from the first OFDM symbol (OFDM symbol 0 in the first time slot) within the assigned Physical Resource Blocks (PRBs); furthermore, in those subframes where TRS is not transmitted, the advanced UE does not apply rate matching around CRS. On the other hand, when the cell (or subframe) type is BCT, the advanced UE should read PDSCH symbols from the configured OFDM symbol number within the assigned PRBs with rate matching around the PDCCH region and CRS REs (according to the MBSFN subframe configuration).
Here, the configured OFDM symbol number is indicated to the advanced UE by at least one of the following alternatives:
Method Z:
Depending on the cell (or subframe) type, the advanced UE calculate CQI differently. In BCT subframes (or cells), when deriving the CQI index, some of the UE assumptions for the CSI resource are:
In NCT subframes (or cells), in order to facilitate more accurate CQI derivation for the NCT, the UE assumptions above for the CSI reference resource are modified for the NCT subframes (cells) as follows:
Note that this embodiment also extends to other TMs supported in the extension carrier.
In Rel-10 LTE, for TM8 and TM9, the transmission scheme of PDSCH uses DM RS ports (7-8 for TM8 and 7-14 for TM9) when the PDCCH uses downlink control information (DCI) format 2B and 2C, respectively. For DCI format 1A, the transmission scheme in Rel-10 may use CRS ports (see Table 7.1-5 in TS 36.213). If TM8 and/or TM9 are supported in the extension carrier, in order to support PDSCH transmission using DCI format 1A in the NCT cell (or subframe), for TM8 and/or 9, a transmission scheme that uses DM RS ports is always used for PDSCH transmission using DCI format 1A, hereafter referred to as the basic DM-RS transmission scheme (TS). Note that this proposal extends to any transmission modes that are supported in the NCT cell (or subframe).
Alternatives of the Basic DM-RS TS
Alternatives of the basic DM-RS TS are as follows:
The network may make decision to convert the network configuration from
On the other hand, the network may make a decision to convert the network configuration from
When a UE moves from a coverage area of small cell S1 to a coverage area of small cell S2 in
Beyond LTE-Adv Air Standards
3GPP TS 36.211 [REF1] Sec. 6.10.3.2 (“Mapping to resource elements”) describes the following for UE-specific RS in 3GPP Rel-11 specifications:
For antenna ports p=7, p=8 or p=7, 8 . . . υ+6, in a physical resource block (PRB) with a frequency-domain index assigned for the corresponding PDSCH transmission, a part of the reference signal sequence r(m) shall be mapped to complex-valued modulation symbols ak,l(p) in a subframe according to
The sequence
Resource elements (k,l) used for transmission of UE-specific reference signals to one UE on any of the antenna ports in the set S, where S={7, 8, 11, 13} or S={9, 10, 12, 14} shall
3GPP TS 36.212 [REF2] Section 5.3.3.1.5C (“Format 2C”) describes DCI format 2C as in the following:
The following information is transmitted by means of the DCI format 2C:
In addition, for transport block 1:
In addition, for transport block 2:
If both transport blocks are enabled; transport block 1 is mapped to codeword 0; and transport block 2 is mapped to codeword 1.
In case one of the transport blocks is disabled, the transport block to codeword mapping is specified according to Table 5.3.3.1.5 2. For the single enabled codeword, Value=4, 5, 6 in TABLE VI below are only supported for retransmission of the corresponding transport block if that transport block has previously been transmitted using two, three or four layers, respectively.
If the number of information bits in format 2C carried by PDCCH belongs to one of the sizes in Table 5.3.3.1.2-1, one zero bit shall be appended to format 2C.
5.3.3.1.5D Format 2D
The following information is transmitted by means of the DCI format 2D:
. . . (Same field descriptions as in Format 2C until redundancy version for transport block 2)
If both transport blocks are enabled; transport block 1 is mapped to codeword 0; and transport block 2 is mapped to codeword 1.
In case one of the transport blocks is disabled; the transport block to codeword mapping is specified according to Table 5.3.3.1.5 2. For the single enabled codeword, Value=4, 5, 6 in Table 2 are only supported for retransmission of the corresponding transport block if that transport block has previously been transmitted using two, three or four layers, respectively.
If the number of information bits in format 2D carried by PDCCH belongs to one of the sizes in Table 5.3.3.1.2-1, one zero bit shall be appended to format 2D.
[REF3] describes PQI field and quasi co-location as in the following:
7.1.9 PDSCH resource mapping parameters
A UE configured in transmission mode 10 for a given serving cell can be configured with up to 4 parameter sets by higher layer signaling to decode PDSCH according to a detected PDCCH/EPDCCH with DCI format 2D intended for the UE and the given serving cell. The UE shall use the parameter set according to the value of the ‘PDSCH RE Mapping and Quasi-Co-Location indicator’ field (mapping defined in TABLE VII below) in the detected PDCCH/EPDCCH with DCI format 2D for determining the PDSCH RE mapping (defined in Section 6.3.5 of [REF1]) and PDSCH antenna port quasi co-location (defined in Section 7.1.10). For PDSCH without a corresponding PDCCH, the UE shall use the parameter set indicated in the PDCCH/EPDCCH with DCI format 2D corresponding to the associated SPS activation for determining the PDSCH RE mapping (defined in Section 6.3.5 of [REF1]) and PDSCH antenna port quasi co-location (defined in Section 7.1.10).
The following parameters for determining PDSCH RE mapping and PDSCH antenna port quasi co-location are configured via higher layer signaling for each parameter set:
7.1.10 Antenna Ports Quasi Co-Location for PDSCH
A UE configured in transmission mode 1-10 may assume the antenna ports 0-3 of a serving cell are quasi co-located (as defined in [REF1]) with respect to delay spread, Doppler spread, Doppler shift, average gain, and average delay.
A UE configured in transmission mode 8-10 may assume the antenna ports 7-14 of a serving cell are quasi co-located (as defined in [REF1]) for a given subframe with respect to delay spread, Doppler spread, Doppler shift, average gain, and average delay.
A UE configured in transmission mode 1-9 may assume the antenna ports 0-3, 5, 7-22 of a serving cell are quasi co-located (as defined in [REF1]) with respect to Doppler shift, Doppler spread, average delay, and delay spread.
A UE configured in transmission mode 10 is configured with one of two quasi co-location types by higher layer signaling to decode PDSCH according to transmission scheme associated with antenna ports 7-14:
In [REF1], the following paragraph is captured to define the quasi co-location:
Two antenna ports are said to be quasi co-located if the large-scale properties of the channel over which a symbol on one antenna port is conveyed can be inferred from the channel over which a symbol on the other antenna port is conveyed. The large-scale properties include one or more of delay spread, Doppler spread, Doppler shift, average gain, and average delay.
In [REF1], the following is captured for ePDCCH DMRS:
6.10.3A Demodulation Reference Signals Associated with EPDCCH
The demodulation reference signal associated with EPDCCH
A demodulation reference signal associated with EPDCCH is not transmitted in resource elements (k,l) in which one of the physical channels or physical signals other than the demodulation reference signals defined in 6.1 are transmitted using resource elements with the same index pair (k,l) regardless of their antenna port p.
6.10.3A.1 Sequence Generation
For any of the antenna ports pε{107,108,109,110}, the reference-signal sequence r(m) is defined by
The pseudo-random sequence c(i) is defined in Section 7.2. The pseudo-random sequence generator shall be initialized with
c(i)=(└n
at the start of each subframe where nSCIDEPDCCH=2 and 2ID,iEPDCCH is configured by higher layers. The EPDCCH set to which the EPDCCH associated with the demodulation reference signal belong is denoted iε{0,1}.
6.10.3A.2 Mapping to Resource Elements
For the antenna port pε{107,108,109,110} in a physical resource block nPRB assigned for the associated EPDCCH, a part of the reference signal sequence r(m) shall be mapped to complex-valued modulation symbols ak,l(p) in a subframe according to Normal cyclic prefix:
The sequence
Resource elements (k,l) used for transmission of demodulation reference signals to one UE on any of the antenna ports in the set S, where S={107,108} or S={109,110} shall
Replacing antenna port numbers 7-10 by 107-110 in
In TS 36.213 [REF3], the following is captured for the resource mapping parameters for EPDCCH:
9.1.4.3 Resource Mapping Parameters for EPDCCH
For a given serving cell, if the UE is configured via higher layer signalling to receive PDSCH data transmissions according to transmission mode 10, and if the UE is configured to monitor EPDCCH, for each EPDCCH-PRB-set, the UE shall use the parameter set indicated by the higher layer parameter re-MappingQCLConfigListId-r11 for determining the EPDCCH RE mapping (defined in Section 6.8A.5 of [REF1]) and EPDCCH antenna port quasi co-location. The following parameters for determining EPDCCH RE mapping and EPDCCH antenna port quasi co-location are included in the parameter set:
In 36.213 [REF3], the following is captured for MCS index:
7.1.7.1 Modulation Order Determination
The UE shall use Qm=2 if the DCI cyclic redundancy check (CRC) is scrambled by Paging Radio Network Temporary Identifier (P-RNTI), Random Access Radio Network Temporary Identifier (RA-RNTI), or System Information Radio Network Temporary Identifier (SI-RNTI); otherwise, the UE shall use the modulation and coding scheme (MCS) index IMCS and Table 7.1.7.1-1 (TABLE IX below) to determine the modulation order (Qm) used in the physical downlink shared channel for a given transport block size index) (ITBS).
TABLE VI explains a field in DCI formats 2C and 2D, which indicates antenna port(s), scrambling identity (SCID) and number of layers. According to TABLE VI, the interpretation of the 3-bit field is different depending upon how many codewords (CWs) are enabled. When one CW is enabled, the 3-bit field can indicate one of 7 possibilities comprising one-layer, two-layer, three-layer and four-layer transmissions. Among the 7 states, four of those states indicate one-layer transmissions, on (AP 7, SCID 0), (AP 7, SCID 1), (AP 8, SCID 0) and (AP 8, SCID 1). The other three states indicate two-layer, three-layer and four-layer transmissions that are used only for retransmission of a single CW, out of two initially transmitted CWs in a previous subframe. When two CWs are enabled, the 3-bit field can indicate one of 8 possibilities comprising 2-8 layer transmissions. Among the 8 states, two of those states indicate two-layer transmissions, on (AP 7-8, SCID 0) and (AP 7-8, SCID 1). The other six states indicate 3-8 layer transmissions.
The 3GPP LTE Rel-10 supports multi-user multiple input, multiple output (MU-MIMO) transmissions. Up to four layers can be multiplexed in a MU-MIMO transmission, relying on APs 7-8 and SCIDs 0-1. To multiplex 4 rank-1 UEs in the same PRB, eNB may configure (AP 7, SCID 0), (AP 7, SCID 1), (AP 8, SCID 0) and (AP 8, SCID 1) to the 4 UEs, relying on the indication mechanism of TABLE VI. A UE configured with (AP 7, SCID 0) may see intra-cell interference on the DMRS REs, corresponding to (AP 7, SCID 1), (AP 8, SCID 0) and (AP 8, SCID 1). The interference caused by DMRS of (AP 8, SCID 0) is likely to be orthogonal to the DMRS of (AP 7, SCID 0) thanks to the OCCs used for APs 7 and 8. However, the interference caused by DMRS of (AP 7, SCID 1) and (AP 8, SCID 1) is not orthogonal because of the different scrambling sequence generated by SCID 1.
[REF5] introduces a field jointly indicating the number of layers (antenna ports), the pilot resource allocation (AP numbers), and SU/MU MIMO. However, [REF5] did not disclose which codepoints to use in a DCI to indicate the information.
In addition, SU-MIMO and MU-MIMO are non-transparently indicated here (for example, state 0 is identical to state 8 except for MU-MIMO and SU-MIMO difference), which reduces scheduling flexibility.
Considering that the non-orthogonal interference could degrade performance much worse than the orthogonal interference, although Rel-10 support MU-MIMO multiplexing of up to 4 layers it may not be practically feasible for a UE to deal with the non-orthogonal interference in case the UE is co-scheduled with other UEs configured with the a scrambling ID.
To better deal with multi-user interference in DMRS channel estimation, [REF5] proposed to apply length-4 Walsh cover to the 4 REs on the same subcarrier, and support MU-MIMO multiplexing of up to 4 layers with corresponding 4 orthogonal DMRS. As seen in
Similarly, for SU-MIMO of rank 3 and rank 4, when the SU-MIMO UE is moving in low speed, length-4 Walsh covers can be considered for keeping DMRS overhead low while at the same time achieving the orthogonal DMRS for the 3 or 4 layers.
It may be observed that the benefits of applying length-4 Walsh covers on the 4 DMRS REs on the same subcarrier out of the set of 12 DMRS REs for AP 7 are:
This disclosure describes methods for an eNB to indicate information to UEs involved in the SU-MIMO and MU-MIMO transmissions with the 4 orthogonal DMRS on the set of 12 REs for AP 7. According to the current LTE standards specifications (
As seen in TABLE VI, the current LTE specifications has a field in DCI formats 2C and 2D to indicate AP number, scrambling ID, and number of layers.
In Rel-11 LTE, a newly introduced parameter, nIDDMRS (or DMRS VCID), replaces NIDcell, or physical cell ID, in the scrambling initialization equation. The value of nIDDMRS can dynamically change, depending upon the value of nSCID, as in the following (Section 6.10.3.1 in [REF1]):
The pseudo-random sequence generator shall be initialised with
c
init=(└n
at the start of each subframe.
The quantities nID(i), i=0,1, are given by
However, in the case of allowing four orthogonal DMRS for MU-MIMO, it is not necessary to use nSCID for MU-MIMO.
Hence, in one design of a new signaling table for supporting four orthogonal DMRS for MU-MIMO, it is proposed to exclude nSCID, and replace those values associated with nSCID=1 with entries associated with AP 11 and AP 13 from TABLE VI. When relying on the legacy mechanism of indicating the VOID (i.e., the value of nIDDMRS is indicated as a function of the value of nSCID), one possible side effect of this is that dynamic switching of nIDDMRS cannot be supported.
Alt 1: No Dynamic Switching of VCIDs when Four Orthogonal DMRS is Configured for MU-MIMO
However, this may not necessarily a bad thing when UE distribution and their channels are relatively static, where dynamic point selection does not give much gain. Considering this scenario, a first alternative (Alt 1) is proposed: that for the UE configured with the four orthogonal DMRS for MU-MIMO, a single value of DMRS VOID, nIDDMRS, is configured, and the UE generates scrambling initialization as in the following:
c
init=(└n
where nID=NIDcell if no value for nIDDMRS is provided by higher layers or if DCI format 1A, 2B or 2C is used for the DCI associated with the PDSCH transmission, and nID=nIDDMRS otherwise.
Coupled with Alt 1, one example of the new signaling table design is shown in TABLE X below:
When this table is used, when 1 or 2 layer transmission is signaled to a UE, the UE should assume DMRS overhead of 12 REs for PDSCH rate matching, demodulation and CQI estimation; and the UE should assume traffic-to-pilot ratio of 0 dB.
Alt 2: Dynamic Switching of VCIDs
In a second alternative (Alt 2), we propose to introduce a new way to dynamically indicate nIDDMRS, by including or re-interpreting a one-bit field in a new DCI format for scheduling PDSCH coupled with the four orthogonal DMRS.
Two options are considered for this alternative
Alt 2-1: The NDI of disabled TB (a one-bit field) indicates nIDDMRS.
Alt 2-2: A new explicit one-bit field is included in the new DCI format for scheduling PDSCH, to indicate nIDDMRS.
Assuming that the signaled value of the one-bit field either in Alt 2-1 or in Alt 2-2 is X, the scrambling initialization would be done according to the following:
c
init=(└n
where nID(X)=NIDcell if no value for nID,XDMRS is provided by higher layers or if DCI format 1A, 2B or 2C is used for the DCI associated with the PDSCH transmission, and nID(X)=dID,XDMRS otherwise.
Coupled with Alt 2, number of layers and antenna port(s) can be indicated as in the new signaling table design in TABLE X.
The introduction of length-4 Walsh cover for SU-MIMO is for overhead reduction. For this purpose, it is proposed to replace 3 and 4 layer entries in TABLE VI with new entries associated with the set of DMRS REs for AP 7 and length-4 Walsh covers.
In one example design shown in TABLE XI, three layer entries indicate ports 7, 8 and 11, the DMRS for the three ports of which are multiplexed relying on 3 Walsh covers on the same set of REs (See TABLE V and
When TABLE XI is configured for a UE, and the UE is scheduled to receive on 1, 2, 3, 4 layers, the UE should assume DMRS overhead of 12 REs for PDSCH rate matching, demodulation and CQI estimation; and the UE should assume traffic-to-pilot ratio of 0 dB.
A new signaling table can be defined to support length-4 Walsh cover transmissions for MU-MIMO and SU-MIMO with rank 3 and 4, as in TABLE XII below:
Example of higher-layer configuration to indicate which table to use:
A New TM
AP_Layer_Config_R12: An explicit one-bit field to indicate which table to use.
PQI may include table index, to facilitate dynamic switching between two tables, i.e. the information on which table to use by the UE is jointly coded with the other existing PQI information.
Benefit 1: (Scheduling flexibility) Use legacy table for MU-MIMO multiplexing with legacy UEs; Use new table for MU-MIMO multiplexing between R12 UEs.
A new TM, say TM A, can be defined to support the use of a transmission scheme relying on length-4 Walsh covers for SU/MU-MIMO (e.g., transmission schemes associated with Embodiment 1, 2 and 3).
Which table out of two tables, i.e., the legacy table (TABLE VI) and a new table (one of TABLE X, TABLE XI and TABLE XII), should be used for determining number of layers, antenna port(s), and scrambling ID, may be indicated by a configured transmission mode. For example, when TM 9 or 10 is configured for a UE, the UE should use TABLE VI; on the other hand when TM A is configured, the UE should use the new table.
As for CSI estimation associated with a CSI process, the DMRS overhead assumption associated with 3 or 4 layers (rank 3 or rank 4) changes upon which of the two tables is used. Suppose that the last reported rank is 3 or 4. Then, when the legacy table is used, the DMRS overhead is 24 REs; on the other hand, when the new table is used, the DMRS overhead is 12 REs.
A first alternative to configure the DMRS overhead assumption would be to couple the assumption with the configured TM. When a UE is configured with TM A, the UE should assume the new table for the DMRS overhead assumption in the CSI (CQI) derivation for all the configured CSI processes; while when the UE is configured with TM 9 or 10, the UE should assume TABLE VI for the DMRS overhead assumption in the CSI (CQI) derivation for all the configured CSI processes.
A second alternative is that the CSI process information element includes a field to indicate which table to assume to account for the DMRS overhead for rank 3 and rank 4. In one example, the new CSI process is defined as in the following:
In another example, the Rel-11 CSI process can be extended as in the following. The new field can be conditioned on the configuration of TM A.
Here, the state of the field cqi-OverheadRank3Rank4 indicates whether to assume 12 RE overhead (re12) or 24 RE overhead for the configured CSI process when report CQI associated with rank 3 or rank 4 PMI.
In another example, the new CSI process is defined as in the following:
Alternatively, the Rel-11 CSI process can also be extended as follows. The new field can be conditioned on the configuration of TM A.
Here, the state of the field antennaPortTable indicates whether to use TABLE VI or the new table to take the DMRS overhead into account in deriving CQI associated with rank 3 or rank 4 PMI.
A third alternative is that cqi-OverheadRank3Rank4 or antennaPortTable is included as a field in PDSCH-RE-MappingQCL-Config, as shown below:
Alternatively,
Alternatively,
It is noted that PDSCH-RE-MappingQCL-Config corresponds to a parameter set in TABLE VII, and hence a UE can be configured with up to four separate PDSCH-RE-MappingQCL-Config information elements. Then, the selection of table can be dynamically indicated by PQI carried as a field in a DL grant (DCI format 2D). One benefit of configuring antennaPortTable field in PDSCH-RE-MappingQCL-Config is better scheduling flexibility. With this, eNB can dynamically change user pairing, either by using legacy table for MU-MIMO multiplexing with legacy UEs, or by using the new table for MU-MIMO multiplexing among R12 UEs.
Precoding for TM A
In TM A, the antenna port allocation is done according to one of TABLE X, TABLE XI and TABLE XII. In that case, the indicated numbers of antenna ports may not be consecutive, especially when 3 or 4 layers are scheduled. To allow for precoding with non-consecutive numbers of antenna ports for TM A, the following change of the current text is proposed. In the proposal, the precoding method is dependent upon the configured TM.
Precoding for Transmission on a Single Antenna Port
For transmission on a single antenna port, precoding is defined by
y
(p)(i)=x(0)(i)
where pε{0, 4, 5, 7, 8, 11, 13} is the number of the single antenna port used for transmission of the physical channel and i=0, 1, . . . , Msymbap−1, Msymbap=Msymblayer.
Precoding for spatial multiplexing using antenna ports with cell-specific reference signals
Precoding for spatial multiplexing using antenna ports with UE-specific reference signals is only used in combination with layer mapping for spatial multiplexing as described in Section 6.3.3.2 of [REF1].
When TMs 8, 9, 10 are configured, spatial multiplexing using antenna ports with UE-specific reference signals supports up to eight antenna ports and the set of antenna ports used is p=7, 8, . . . , υ+6.
For transmission on v antenna ports, the precoding operation is defined by
where i=0, 1, . . . , Msymbap−1, Msymbap=Msymblayer.
When TM A is configured, spatial multiplexing using antenna ports with UE-specific reference signals supports up to eight antenna ports and the set of antenna ports used is p=p1, . . . , pυ, as indicated in the new AP mapping table (examples of which are shown in TABLE X, TABLE XI and TABLE XII).
For transmission on v antenna ports, the precoding operation is defined by
where i=0, 1, . . . , Msymbap−1, Msymbap=Msymblayer.
ePDCCH DMRS
Similarly, the length-4 Walsh covers can be considered for multiplexing four ePDCCH DMRS in the set of DMRS REs for AP 107, for reducing ePDCCH DMRS overhead.
In order to increase system configuration flexibility, whether to use the length-4 Walsh covers or to use the legacy APs should be able to be UE-specifically configured for each ePDCCH set (or EPDCCH-PRB-set) according to a parameter signaled in the RRC layer.
When the length-4 Walsh covers are used for ePDCCH associated with localized transmissions, APs 107, 108, 111 and 113 are used. Here, replacing antenna port numbers 11 and 13 by 111 and 113 in
When the length-4 Walsh covers are used for ePDCCH associated with distributed transmissions, APs 107 and 108 are used.
For this operation, a field ap-mapping-ePDCCH can be configured in the RRC layer, which is ENUMERATED{ap-107-108-109-110 or ap-107-108-111-113}, where ap-107-108-109-110 implies that antenna ports 107-110 are used for EPDCCH, and ap-107-108-111-113 implies that antenna ports 107, 108, 111, 113 are used for EPDCCH. When ap-107-108-109-110 is configured, the UE should assume that the DMRS overhead is 24 REs, according to the DMRS RE mapping associated with APs 107-110. On the other hand, when ap-107-108-111-113 is configured, the UE should assume that the DMRS overhead is 12 REs, according to the DMRS RE mapping associated with APs 107,108,111 and 113.
In order to allow for a UE to be able to be configured with either of the two different antenna port configurations, it is proposed to include the field of ap-mapping-ePDCCH in the associated parameter set configured by an information element re-MappingQCLConfigListId-r11 conveyed in the RRC layer.
[REF6] shows that demodulation performance of PDSCH relying on a reduced-overhead UE-RS outperforms the performance relying on a legacy UE-RS generated according to Rel-10 3GPP LTE standards, especially for PDSCH with higher MCS and higher rank. Based upon this observation, it may be useful to introduce reduced-overhead UE-RS for small cells where higher SNR can be obtained.
This disclosure describes proposals for introducing reduced-overhead UE-RS for small cells in the 3GPP LTE standards.
Switching Between a Reduced-Overhead DMRS Pattern and the Legacy UE-RS Pattern
In one embodiment (embodiment 1), reduced-overhead UE-RS can be configured to an advanced UE capable of receiving/transmitting signals according to 3GPP LTE standards. For the same rank (or the same number of transmission layers), number of REs per PRB pair used for the reduced-overhead UE-RS is smaller than that of legacy UE-RS REs.
In an advanced system supporting the 3GPP LTE standards, a UE can be configured with a new one-bit message conveyed in the higher-layer (e.g., RRC layer), wherein if the new one-bit message is a first state (e.g., 0), the UE is configured to receive PDSCH with the legacy UE-RS and if the new one-bit message is a second state (e.g., 1), the UE is configured to receive PDSCH with the reduced-overhead UE-RS.
Alternatively, in an advanced system supporting the 3GPP LTE standards, a UE can be configured with a new transmission mode (TM), say TM X, which supports transmission schemes relying on a reduced-overhead UE-RS. Two alternatives are considered below, for the PDSCH reception of a UE configured with TM X:
Alt 1) When a UE is configured with TM X, the UE receives PDSCH with reduced-overhead UE-RS.
Alt 2) When a UE is configured with TM X, the UE receives PDSCH with reduced-overhead UE-RS if a first condition is met; with legacy UE-RS if a second condition is met. This alternative is explained in TABLE XIV below:
In one example, when the second condition is met, the UE-RS indication is done according to the legacy specification (i.e., according to TABLE VI); when the first condition is met, the UE-RS indication is done according to TABLE XV below:
When the reduced-overhead UE-RS is used for rank 1 and 2, the reduced UE-RS can be used for MU-MIMO as well as single user MIMO (SU-MIMO). However, the reduced-overhead UE-RS may significantly degrade channel estimation performance when UE-RS are multiplexed with different scrambling IDs, because the interference randomization relying on scrambling may not be effective with the small number of UE-RS REs. Hence, removal of scrambling ID indication may be considered when reduced-overhead UE-RS is used. In this case, nSCID=0 is always assumed for scrambling initialization, and the antenna port indication can be performed according to either TABLE XVI or XVII below instead of TABLE XV, when reduced-overhead UE-RS is configured.
It is noted that in TABLE XVII a new parameter nVCID is introduced for indicating a virtual cell ID (VCID) out of two higher-configured VCIDs. In this case, the pseudo-random sequence generator for the UE-RS sequence shall be initialised with
c(i)=(└n
at the start of each subframe.
It is also noted that Alt 2 is motivated by the fact that reduced-overhead UE-RS is advantageous when signal-to-interference-plus-noise ratio (SINR) is high, and/or MCS is high, and/or rank is high; at the same time the reduced-overhead UE-RS may hurt the performance otherwise. According to these motivations, it may make sense to switch UE-RS patterns according to Method 1 as in the following.
Method 1:
The switching conditions for the UE-RS patterns depend on at least one of MCS and rank. In other words, the first and the second conditions are defined as at least one of threshold numbers associated with MCS and rank.
A few examples according to the method above are presented below:
When a UE is configured with TM X, the UE receives PDSCH with reduced-overhead UE-RS if the MCS configured in the PDCCH scheduling the PDSCH is greater than or equal to M; with legacy UE-RS if the MCS is less than M. In this case, the UE is indicated to use antenna ports according to the legacy table (i.e., TABLE VI) if the MCS is less than M, and according to the new table (i.e., one of TABLE XII, TABLE XIII and TABLE XIV) if the MCS is greater than or equal to M.
When a UE is configured with TM X, the UE receives PDSCH with reduced-overhead UE-RS if the rank configured in the PDCCH scheduling the PDSCH is greater than or equal to R; with legacy UE-RS if the rank is less than R.
In one example, R=3. Up to rank 2, APs 7 and 8 are used; the 8 APs for reduced overhead UE-RS are denoted by a, b, c, d, e, f, g, h and are used only when the rank is greater than or equal to 3. Then, the legacy antenna port indication table of TABLE VI can be revised into a new table as shown in TABLE XVIII below:
When a UE is configured with TM X, the UE receives PDSCH with reduced-overhead UE-RS if the rank configured in the PDCCH scheduling the PDSCH is equal to R and the MCS is greater than or equal to M or if the rank is greater than R; with legacy UE-RS if the rank is less than R or if the rank is equal to R and the MCS is less than M. In this case, the UE is indicated to use antenna ports according to the legacy table (i.e., TABLE VI) if the rank is less than R or if the rank is equal to R and the MCS is less than M, and according to the new table (i.e., one of TABLE XV, TABLE XVI and TABLE XVIII) if the rank is equal to R and the MCS is greater than or equal to M or if the rank is greater than R.
The UE receives PDSCH with reduced-overhead UE-RS if both codewords are enabled and both MCS indices (IMCS) for the two CWs are greater than or equal to M, where M is an integer; with legacy UE-RS otherwise. In one example, M is chosen such that 64 quadrature amplitude modulation (64QAM) is transmitted. In one example, M=18, which is the minimum MCS index associated with 64QAM (modulation order Qm=6) as seen from TABLE IX. In another example, M=28, which is the maximum MCS index associated with 64QAM. This option is motivated from observation that reduced overhead DMRS achieves a better throughput than the legacy DMRS when the rank is high and 64QAM are chosen for both CWs.
Method 2:
The switching conditions for the UE-RS patterns depend on whether a UE is indicated to use antenna ports that support MU-MIMO or not.
When a UE is configured with TM X, the UE receives PDSCH with reduced-overhead UE-RS if the layer indication does not explicitly include nSCID; with legacy UE-RS if the layer indication explicitly includes nSCID, as shown in TABLE XIX below. It is noted that this table has an advantage over other tables because it allows MU-MIMO multiplexing between advanced UEs and legacy UEs. The MU-MIMO codepoints, i.e., Values 0-3 for one-CW enabled case, and Values 0-1 for two-CW enabled case, are kept the same as the legacy table, i.e., TABLE VI.
Method 3:
For ensuring the best flexibility of eNodeB operation, a new one-bit field can be introduced in the DCI format scheduling the PDSCH (i.e., DCI format 2B/2C/2D and any DCI formats derived from these formats) for indicating a UE-RS out of the two. In this case, the indication of UE-RS is performed according to the following table.
Method 4:
Alternatively, for ensuring some flexibility of eNodeB operation and at the same time to reduce the PHY-layer signaling overhead, the UE-RS pattern information (TABLE XI) can be carried along with quasi co-location (QCL) information, which is included in the PDSCH RE Mapping and Quasi-Co-Location indicator (PQI) field in the DCI format 2D. In this case, the relevant section in TS 36.213 can be revised into:
The following parameters for determining PDSCH RE mapping and PDSCH antenna port quasi co-location are configured via higher layer signaling for each parameter set:
In one example, the multiple configured UE-RS patterns are the legacy UE-RS and a reduced-overhead UE-RS.
In another example, the multiple configured UE-RS patterns are the legacy UE-RS and the NCT UE-RS.
In another example, the multiple configured UE-RS patterns are the legacy UE-RS, a reduced-overhead UE-RS and the NCT UE-RS.
In another example, the multiple configured UE-RS patterns are the legacy UE-RS, a first reduced-overhead UE-RS and a second reduced-overhead UE-RS.
In another example, the multiple configured UE-RS patterns are at least two of Patterns 1, 2, 3 and 4 in TABLE XXI or TABLE XXII below.
Method 5:
The channel estimation performance of reduced-overhead UE-RS can be improved when PRB bundling is applied. Hence, it is proposed that PRB bundling is always assumed when reduced-overhead UE-RS is configured. When PRB bundling is configured precoding granularity is multiple resource blocks in the frequency domain.
Switching Between a Reduced-Overhead DMRS Pattern and the Legacy UE-RS Pattern in the NCT
In one embodiment (embodiment 2), a serving cell of a first or a second type can be configured to an advanced UE capable of receiving/transmitting signals according to 3GPP LTE standards. The first type is the legacy carrier type (LCT) serving cell, and the second type is the NCT serving cell. Furthermore, the advanced UE can be configured with reduced-overhead UE-RS.
The advanced UE should support potentially four UE-RS patterns, i.e., Patterns 1, 2, 3 and 4 as shown in TABLE XVIII. Depending on the combination of the configurations, the UE support one out of the four patterns. For example, if the UE is configured with a serving cell of LCT, and the UE is configured with reduced overhead, the UE should assume Pattern 2 for PDSCH demodulation. It is noted that the UE-RS overhead configuration (or configuration of whether to use legacy or reduced-overhead UE-RS) can be performed according to some of the examples considered in embodiment 1.
Pattern 1 is the same as the Rel-10 UE-RS pattern, depicted in
An example of Pattern 2 is depicted in
UE-RS Power Boosting Aspects
In the legacy system, when rank=1 or 2, the same power is allocated to each UE-RS RE and each PDSCH RE for every antenna port. Suppose that the total available power in each OFDM symbol in a PRB pair is 12P. Then, each UE-RS RE and each PDSCH RE are assigned with the same power, i.e., P. This relation is illustrated in
In the legacy system, when rank=3 or above, twice large power is allocated for each UE-RS RE as the power for each PDSCH RE for every antenna port. When rank=3 or above, the number of PDSCH REs on an OFDM symbol where UE-RS is transmitted is 6, and the number of UE-RS REs in the OFDM symbol is 3. Suppose that the total available power in each OFDM symbol in a PRB pair is 12P. Then, each UE RS RE has power 2P, while each PDSCH RE has power P, and 3×2P+6×P=12P. This relation is illustrated in
This legacy power relation is captured in the legacy specification (TS 36.213 [REF3]) as in the following:
For transmission mode 8, if UE-specific RSs are present in the PRBs upon which the corresponding PDSCH is mapped, the UE may assume the ratio of PDSCH EPRE to UE-specific RS EPRE within each OFDM symbol containing UE-specific RSs is 0 dB.
For transmission mode 9 or 10, if UE-specific RSs are present in the PRBs upon which the corresponding PDSCH is mapped, the UE may assume the ratio of PDSCH EPRE to UE-specific RS EPRE within each OFDM symbol containing UE-specific RS is 0 dB for number of transmission layers less than or equal to two and −3 dB otherwise.
When the same power relation is applied to a reduced-overhead UE-RS as illustrated in
As an alternative to this baseline power allocation method, power boosting may be applied to the reduced-overhead UE-RS as illustrated in
Method 6:
An advanced UE can be configured with traffic-to-pilot power ratio (or PDSCH EPRE to UE-RS EPRE power ratio) in the higher-layer signaling (RRC signaling), which indicates x decibels (dB) to assume for the traffic-to-pilot power ratio. The advanced UE assumes the configured power ratio when a reduced-overhead UE-RS is used; the advanced UE assumes the legacy power ratio when the legacy UE-RS is used. The indication of reduced-overhead UE-RS can be performed according to the methods in embodiments 1 and 2.
The RRC signaling message can indicate one dB value out of two values, e.g., {3 dB, 6 dB}.
Method 7:
The advanced UE assumes x dB power traffic-to-pilot power ratio when a reduced-overhead UE-RS is used, where x is (Alt 1) a constant or (Alt 2) determined as a function of the rank; the advanced UE assumes the legacy power ratio when the legacy UE-RS is used. The indication of reduced-overhead UE-RS can be performed according to the methods in embodiments 1 and 2.
Consider rank=1 or 2 first. When the one UE-RS RE in
This example ensures that the UE-RS in the reduced-overhead UE-RS pattern has the same total power as the UE-RS in the legacy pattern. However, the large traffic-to-pilot ratio in case of rank=3 or higher may create inter-modulation/error vector magnitude (EVM) issues at the transmitter and the receiver.
To cope with these issues, other examples are considered below:
Regardless of rank (or for all rank=1, . . . , 8), the traffic to pilot power ratio is x=−5.6 dB.
Regardless of rank (or for all rank=1, . . . , 8), the traffic to pilot power ratio is x=−3 dB.
For rank=1 or 2, the traffic to pilot power ratio is x=−3 dB; for rank=3 or higher, the traffic to pilot power ratio is x=−6 dB.
Regardless of rank (or for all rank=1, . . . , 8), the traffic to pilot power ratio is x=−6 dB.
When power boosting is considered for reduced-overhead UE-RS, if all the UEs use the same reduced-overhead UE-RS pattern, then the boosted power collides in the same RE location all the time, which potentially nullify the gain of power boosting. To cope with the inter-cell or inter-user interference caused from the UE-RS power boosting, a UE-specific reduced-overhead UE-RS pattern may be allocated.
Method 8:
An advanced UE can be instructed to use a reduced-overhead UE-RS pattern out of a number of candidate reduced-overhead UE-RS patterns.
The UE can be instructed to use one out of three candidate reduced-overhead UE-RS patterns.
Which pattern out of the three patterns to be used for each PDSCH reception can be indicated to the UE by:
(PCI) of the serving cell satisfies (PCI mod 3)=i.
Although the present disclosure has been described with an exemplary embodiment, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.
This application hereby incorporates by reference U.S. Provisional Patent Application No. 61/724,619, filed Nov. 9, 2012, entitled “METHODS AND APPARATUS FOR IDENTIFICATION OF SMALL CELLS,” U.S. Provisional Patent Application No. 61/745,417, filed Dec. 21, 2012, entitled “DEMODULATION REFERENCE SIGNALS FOR ADVANCED WIRELESS COMMUNICATION SYSTEMS,” U.S. Provisional Patent Application No. 61/761,631, filed Feb. 6, 2013, entitled “DEMODULATION REFERENCE SIGNALS FOR ADVANCED WIRELESS COMMUNICATION SYSTEMS,” and U.S. Provisional Patent Application No. 61/809,087, filed Apr. 5, 2013, entitled “DEMODULATION REFERENCE SIGNALS FOR ADVANCED WIRELESS COMMUNICATION SYSTEMS.”
Number | Date | Country | |
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61724619 | Nov 2012 | US | |
61745417 | Dec 2012 | US | |
61761631 | Feb 2013 | US | |
61809087 | Apr 2013 | US |