A cell edge UE suffers most from the interference of neighbouring cells, and a cell has only so many orthogonal resources to share among its users. The three techniques on this page attack these two limits in different ways. Each of them either lets users share the same resource or lets the UE remove the interference it receives.
NOMA stands for Non Orthogonal Multiple Access. Enhanced MU-MIMO stands for Enhanced Multi User MIMO and NAIC stands for Network Assisted Interference Cancellation.
Followings are the topics to be covered in this page.
Concept of NOMA, MUST and NAIC
OFDMA separates users in frequency, so users in the same cell do not interfere with each other. That separation has a price: each user gets only part of the band. NOMA and MUST give up the separation on purpose and separate users by power instead, which only works if the receiver can remove the other user's signal.
Overall concept and motivations on why these concepts are being considered can be illustrated as below.
OFDMA on the left gives each user its own frequency region. NOMA on the right stacks users in the power domain on the same frequency region. The OFDMA side labels two different blocks as User 2; the purple block is probably meant to be User 3.
The diagram reads from the bottom up. The OFDMA side places each user in its own frequency region, so there is little interference between users but also a limit on throughput, especially at the cell edge. The NOMA side places two users in the same frequency region at different power levels. The pros and cons above each side follow from that single choice.
The top of the NOMA side names the cure for its main drawback: an advanced interference cancellation receiver and a matching power allocation. A typical pairing puts a near UE and a far UE on the same PRBs. The far UE gets most of the power and decodes its own signal directly. The near UE first decodes and subtracts the far UE's signal, which is successive interference cancellation (SIC), and then decodes its own. NAIC applies the same receiver idea to interference from a neighbouring cell rather than from a paired user.
OFDMA : users separated in frequency, little intra-cell interference.NOMA and MUST : users share frequency and are separated in power.SIC and NAIC receivers : remove the known interference before decoding the wanted signal.
Standardization Status
Which of these three ideas actually reached the LTE specifications? The note below records the state in March 2016, when only NAIC was in the specifications. MUST has been specified since then, so the note needs an update rather than a correction.
As of now (Mar 2016), Only NAIC is officially included in 3GPP TS 36.300 / 36.331. Enhanced MU-MIMO is at the stage of TR under the name of MUST (TR 36.859) and NOMA may be combined into the activities of TR 36.859.
NAIC was introduced in Release 12, and 3GPP calls it NAICS, network-assisted interference cancellation and suppression. 36.300 v19.2.0 clause 23.9 describes it: a NAICS UE mitigates the PDSCH and CRS interference of aggressor cells, and the network may configure the UE with NAICS information about those cells. The eNB may exchange that information with its neighbour eNBs over X2.
The MUST study of TR 36.859 led to Multiuser Superposition Transmission in Release 14. In 36.211 v19.3.0, the layer mapping and the modulation mapper handle the superposed signal. A 2-bit DCI field, MUSTIdx, gives the interference presence and power ratio. The RRC configuration is must-Config-r14 in PhysicalConfigDedicated, with k-max-r14 and p-a-must-r14. The table below lists where each technique ended up.
Technique | Release | Where it is specified | Key signalling |
NAICS | Rel-12 | 36.300 clause 23.9, 36.213 clauses 5.2 and 7.1.6 | naics-Info-r12, naics-Capability-List-r12 |
MUST | Rel-14 | 36.211 clauses 6.3.3 and 7.1, 36.212 DCI field | must-Config-r14, MUSTIdx, must-CapabilityPerBand-r14 |
NOMA | study only | TR 36.859 for the downlink | none in the 36-series specifications |
NOMA as a general scheme was not specified for LTE. Its downlink form lives on as MUST, which is a limited version of the power-domain idea shown in the diagram above.
NAICS : Release 12, assistance information for neighbour cell interference.MUST : Release 14, superposed users with a 2-bit DCI indication.NOMA : no LTE specification beyond MUST.
NAIC in RRC
A NAICS receiver needs to know how the aggressor cell transmits before it can remove that cell's signal. RRC delivers that knowledge per neighbour cell. The capture below shows the red-highlighted NAICS fields inside an RRC Connection Reconfiguration.
Following is the RRC components of NAIC included in Rel 12 ASN.
Decoded RRC message,
+-rrcConnectionReconfiguration-r8 ::= SEQUENCE [000100] +-measConfig ::= SEQUENCE OPTIONAL:Omit +-mobilityControlInfo ::= SEQUENCE OPTIONAL:Omit +-dedicatedInfoNASList ::= SEQUENCE OF OPTIONAL:Omit +-radioResourceConfigDedicated ::= SEQUENCE [000001] OPTIONAL:Exist | +-srb-ToAddModList ::= SEQUENCE OF OPTIONAL:Omit | +-drb-ToAddModList ::= SEQUENCE OF OPTIONAL:Omit | +-drb-ToReleaseList ::= SEQUENCE OF OPTIONAL:Omit | +-mac-MainConfig ::= CHOICE OPTIONAL:Omit | +-sps-Config ::= SEQUENCE OPTIONAL:Omit | +-physicalConfigDedicated ::= SEQUENCE [0000000000] OPTIONAL:Exist | | +-pdsch-ConfigDedicated ::= SEQUENCE OPTIONAL:Omit | | +-pucch-ConfigDedicated ::= SEQUENCE OPTIONAL:Omit | | +-pusch-ConfigDedicated ::= SEQUENCE OPTIONAL:Omit | | +-uplinkPowerControlDedicated ::= SEQUENCE OPTIONAL:Omit | | +-tpc-PDCCH-ConfigPUCCH ::= CHOICE OPTIONAL:Omit | | +-tpc-PDCCH-ConfigPUSCH ::= CHOICE OPTIONAL:Omit | | +-cqi-ReportConfig ::= SEQUENCE OPTIONAL:Omit | | +-soundingRS-UL-ConfigDedicated ::= CHOICE OPTIONAL:Omit | | +-antennaInfo ::= CHOICE OPTIONAL:Omit | | +-schedulingRequestConfig ::= CHOICE OPTIONAL:Omit | | +-EXTENSION ::= SEQUENCE [11111] | +-EXTENSION ::= SEQUENCE [1111] | +-VERSION-BRACKETS1 ::= SEQUENCE [0] OPTIONAL:Exist | | +-rlf-TimersAndConstants-r9 ::= CHOICE OPTIONAL:Omit | +-VERSION-BRACKETS2 ::= SEQUENCE [0] OPTIONAL:Exist | | +-measSubframePatternPCell-r10 ::= CHOICE OPTIONAL:Omit | +-VERSION-BRACKETS3 ::= SEQUENCE [0] OPTIONAL:Exist | | +-neighCellsCRS-Info-r11 ::= CHOICE OPTIONAL:Omit | +-VERSION-BRACKETS4 ::= SEQUENCE [1] OPTIONAL:Exist | +-naics-Info-r12 ::= CHOICE [setup] OPTIONAL:Exist | +-setup ::= SEQUENCE [111] | +-neighCellsToReleaseList-r12 ::= SEQUENCE OF SIZE(1..maxNeighCell-r12[8]) [1] | | +-PhysCellId ::= INTEGER (0..503) [0] | +-neighCellsToAddModList-r12 ::= SEQUENCE OF SIZE(1..maxNeighCell-r12[8]) [1] | | +-NeighCellsInfo-r12 ::= SEQUENCE [0] | | +-physCellId-r12 ::= INTEGER (0..503) [0] | | +-p-b-r12 ::= INTEGER (0..3) [0] | | +-crs-PortsCount-r12 ::= ENUMERATED [n1] | | +-mbsfn-SubframeConfig-r12 ::= SEQUENCE OF OPTIONAL:Omit | | +-p-aList-r12 ::= SEQUENCE OF SIZE(1..maxP-a-PerNeighCell-r12[3]) [1] | | | +-P-a ::= ENUMERATED [dB-6] | | +-transmissionModeList-r12 ::= BIT STRING SIZE(8) [00000000] | | +-resAllocGranularity-r12 ::= INTEGER (1..4) [1] | | +-EXTENSION ::= SEQUENCE | +-servCellp-a-r12 ::= ENUMERATED [dB-6] OPTIONAL:Exist
In the capture, naics-Info-r12 sits in an extension group of radioResourceConfigDedicated and is set to setup. It removes one neighbour cell, PCI 0, and adds one with PCI 0, p-b-r12 = 0, one CRS port, PA = -6 dB and a resource allocation granularity of 1 PRB. It also gives the serving cell's own PA of -6 dB in servCellp-a-r12. Every bit of transmissionModeList-r12 is 0, so this capture indicates none of the listed transmission modes for the neighbour cell.
The current definitions are unchanged since Release 12. The tile below shows the assistance information and the UE capability that allows it.
Following is based on
NAICS-AssistanceInfo-r12 ::= CHOICE {
release NULL,
setup SEQUENCE {
neighCellsToReleaseList-r12 NeighCellsToReleaseList-r12 OPTIONAL , -- Need ON
neighCellsToAddModList-r12 NeighCellsToAddModList-r12 OPTIONAL, -- Need ON
servCellp-a-r12 P-a OPTIONAL -- Need ON
}
}
NeighCellsToReleaseList-r12 ::= SEQUENCE (SIZE (1..maxNeighCell-r12)) OF PhysCellId
NeighCellsToAddModList-r12 ::= SEQUENCE (SIZE (1..maxNeighCell-r12)) OF NeighCellsInfo-r12
NeighCellsInfo-r12 ::= SEQUENCE {
physCellId-r12 PhysCellId,
p-b-r12 INTEGER (0..3),
crs-PortsCount-r12 ENUMERATED {n1, n2, n4, spare},
mbsfn-SubframeConfig-r12 MBSFN-SubframeConfigList OPTIONAL, -- Need ON
p-aList-r12 SEQUENCE (SIZE (1..maxP-a-PerNeighCell-r12)) OF P-a,
transmissionModeList-r12 BIT STRING (SIZE(8)),
resAllocGranularity-r12 INTEGER (1..4),
...
}
NAICS-Capability-List-r12 ::= SEQUENCE (SIZE (1..maxNAICS-Entries-r12)) OF NAICS-Capability-Entry-r12
NAICS-Capability-Entry-r12 ::= SEQUENCE {
numberOfNAICS-CapableCC-r12 INTEGER(1..5),
numberOfAggregatedPRB-r12 ENUMERATED {
n50, n75, n100, n125, n150, n175,
n200, n225, n250, n275, n300, n350,
n400, n450, n500, spare},
...
}
Each field tells the UE one thing it would otherwise have to guess from the interfering signal. The list holds up to maxNeighCell-r12 = 8 cells, and each cell can carry up to maxP-a-PerNeighCell-r12 = 3 power offsets. The leftmost bit of transmissionModeList-r12 stands for transmission mode 1, and the eight bits cover modes 1, 2, 3, 4, 6, 8, 9 and 10. The field resAllocGranularity-r12 gives the resource allocation and precoding granularity N in PRB pairs, as used in 36.213 v19.4.0 clause 7.1.6. The UE may then assume the same precoding in each group of N PRB pairs.
The UE may assume that a signalled neighbour cell is synchronized to the serving cell in subframe and SFN. It may also assume the same bandwidth, UL/DL configuration and cyclic prefix. A UE reports its support with naics-Capability-List-r12, where each entry gives the number of NAICS-capable component carriers and the number of aggregated PRBs (36.306 v19.3.0 clause 4.3.4.35).
naics-Info-r12 : per-neighbour transmission parameters for the NAICS receiver.Up to 8 neighbour cells : each with p-b, CRS ports, PA list, TM list and granularity.Capture shows PCI 0 : with an all-zero transmissionModeList-r12.
Reference
[1] RP-141405 :
Motivation for Enhanced MU-MIMO and Network Assisted Interference Cancellation
[2] RP-141165 :
Justification for NOMA in New Study on Enhanced MU-MIMO and Network Assisted Interference Cancellation
[3] Non-orthogonal Multiple Access and Massive MIMO for Improved Spectrum Efficiency
by Anritsu
[4] 3GPP TR 36.859 - Study on Downlink Multiuser Superposition Transmission (MUST) for LTE (Release 13)
[5] 3GPP 36.300 - 23.9 Network-assisted interference cancellation/suppression
[6] 3GPP TS 36.331 v19.3.0 - NAICS-AssistanceInfo-r12, NeighCellsInfo-r12, NAICS-Capability-List-r12 and must-Config-r14
[7] 3GPP TS 36.211 v19.3.0 - clause 6.3.3, Layer mapping, and clause 7.1, Modulation mapper, for MUST
[8] 3GPP TS 36.212 v19.3.0 - clause 5.3.3.1, DCI formats with the MUST interference fields
[9] 3GPP TS 36.213 v19.4.0 - clause 5.2, Downlink power allocation, and clause 7.1.6, Resource allocation
[10] 3GPP TS 36.306 v19.3.0 - clause 4.3.4.35, naics-Capability-List-r12, and clause 4.3.4.81, must-CapabilityPerBand-r14