NSA Networking and Functions
Technical Poster
This technical poster provides only a general overview and does not constitute any offers or commitments. For detailed
information, see the product or feature documentation delivered with the software.
5G Networking Overview
There are two types of 5G networking schemes: non-standalone (NSA) networking and standalone
(SA) networking. In NSA networking, Huawei base stations support the Option 3 and Option 3x
architectures. In SA networking, Huawei base stations support the Option 2 architecture. This
technical poster focuses on NSA networking.
NSA Networking Options
NSA NR: The gNodeB requires the eNodeB working as the control plane anchor to connect to
the EPC or the eLTE base station working as the control plane anchor to connect to the 5GC.
Option 3 HW
Option 3x HW
EPC
eNodeB
Option 3a
EPC
gNodeB
eNodeB
EPC
gNodeB
eNodeB
gNodeB
Option 7
Option 7x
Option 7a
5GC
5GC
5GC
eLTE base station
gNodeB
eLTE base station
gNodeB
eLTE base station
gNodeB
NSA E-UTRA: The eLTE base station requires the gNodeB working as the control plane anchor
to connect to the 5GC.
Option 4
Option 4a
5GC
5GC
eLTE base station
gNodeB
eLTE base station
gNodeB
SA Networking Options
Option 2 HW
Option 5
5GC
5GC
gNodeB
eLTE base station
Control plane anchor
4G control-plane data
4G user-plane data
Data split anchor HW Supported by Huawei
5G control-plane data
5G user-plane data
NSA Networking
1
Benefits
● The NSA Networking based on EPC feature takes full advantage of the wide coverage of LTE
and sufficient spectrum resources of NR, allowing operators to quickly deploy NR networks on the
existing LTE networks.
● This feature allows fast deployment of commercial NR networks and protects operators' LTE
network investments.
● This feature improves service continuity and avoids frequent UE handovers and service interruptions
caused by UEs moving on NR networks.
Protection of investment
in legacy networks
Fast deployment
of NE networks
2
Improvement of
service continuity
Concepts
In EPC-based NSA networking, if a UE supports both LTE and NR NSA dual connectivity (DC), it can
connect to both an LTE eNodeB and an NR gNodeB, and use radio resources provided by these base
stations to transmit data on both base stations.
Supported Architecture Options
Option 3
Option 3x
EPC
EPC
S1
S1
S1
eNodeB
X2
gNodeB
eNodeB
X2
gNodeB
Uu Uu
Uu Uu
UE
UE
Control-plane data
Option 3 Architecture
User-plane data is split on the eNodeB, and
MCG split bearers are used.
That is, user-plane data is preferentially carried
on the eNodeB and dynamically distributed to
the gNodeB for transmission.
Option 3x Architecture
User-plane data is split on the gNodeB, and
SCG split bearers are used.
That is, user-plane data is preferentially carried
on the gNodeB and dynamically distributed to
the eNodeB for transmission.
User-plane data
Supported Bearer Types
SCG Split Bearer
MCG Split Bearer
S1-U
PDCP
S1-U
X2
X2
PDCP
RLC
RLC
RLC
RLC
MAC
MAC
MAC
MAC
MeNB (LTE)
SgNB (NR)
MeNB (LTE)
SgNB (NR)
Key Technologies
1
Carrier Management
Overview
Carrier management involves master cell group (MCG) carrier management and secondary cell
group (SCG) carrier management. The MCG of an NSA DC UE is an LTE cell group configured on the
LTE side. The SCG of an NSA DC UE is the NR cell group configured on the NR side.
CC1(LTE)
CC2(LTE)
eNodeB (MeNB)
CC5(LTE)
X2
CCa(NR)
UE
CCb(NR)
gNodeB (SgNB)
MCG carrier management: refers to LTE carrier management, and involves:
● PCC anchoring: is controlled by the NSA DC PCC anchoring policy switch.
● SCC management: is the same as the SCC selection policy in LTE carrier management. For details,
see Carrier Aggregation for LTE.
SCG carrier management: refers to NR carrier management, and involves:
● PSCell (primary cell of the SgNB) configuration: supports measurement-based PSCell configuration
and blind PSCell configuration.
● SCC management: is the same as the SCC selection policy in NR carrier management. For details,
see Carrier Aggregation for NR.
Key Technologies
NSA PCC Anchoring
NSA PCC anchoring can be performed separately for UEs in idle mode and connected mode.
● When an NSA UE enters idle mode after the first connection release, dedicated anchoring priorities can be notified to the UE through an IMMCI IE. (IMMCI stands for IdleModeMobilityControlInfo.)
NSA UE
eNodeB
The camping policy for NSA
UEs in idle mode is the same
as that for LTE-only UEs.
First connection procedure (Attach/TAU/...)
● Determines whether the UE supports
NSA based on UE capabilities.
● Delivers dedicated priority information
in the IMMCI IE if the UE supports NSA.
RRC connection release (with the IMMCI IE delivered)
Reselects to a cell with a higher
anchoring priority based on the priority
information in the IMMCI IE.
● When an NSA UE initiates a service request in idle mode and enters connected mode in an LTE
cell, if the NSA anchoring priority of the cell is not the highest, a handover is triggered to a cell
with the highest priority for NSA DC.
NSA UE
eNodeB
The camping policy for NSA
UEs in idle mode is the same
as that for LTE-only UEs.
Initiates a service request and enters connected mode.
● Determines whether the UE supports
NSA based on UE capabilities.
● Determines whether the current NSA
anchoring priority is the highest for the
NSA UE. If not, delivers measurement
configurations about the frequencies
with the highest priority.
Performs A4/A5 inter-frequency measurement.
Selects an LTE cell with the highest
priority to initiate a handover.
Delivers a handover command (RRC Connect Recfg).
Performs a handover to a cell
with the highest anchoring
priority (HO CMP).
NSA PCC Anchoring Enhancement
In NSA networking, the LTE side is mainly used to carry control-plane signaling and VoLTE
services. When the uplink coverage of the LTE anchor is limited, a frequency with a better uplink
coverage can be selected as an anchor to carry LTE services. When an NSA UE is handed over
from a low-priority cell to a high-priority cell, MLB may be triggered and multiple handovers may
be performed if multiple cells have high priorities but some of them are heavily loaded. The
following factors are considered for NSA PCC anchoring enhancement.
For the
basic function
For the
enhanced function
NSA PCC
anchoring priority
LTE load
Downlink coverage of
the strongest cell in the
measurement report
NSA DC combinations
supported by the UE
Uplink coverage
NSA PCC Anchoring Based on NR Coverage
Without NR coverage
When an NSA UE camps on an anchor cell and
there is no NR coverage, the UE can be handed
over to a non-anchor cell based on non-anchor
frequency priority.
Handover from
an anchor cell to
a non-anchor cell
NR
With NR coverage
When an NSA UE camps on a non-anchor cell
and there are anchor cells with NR coverage, the
UE can be handed over to an anchor cell based
on NSA anchor frequency priority and configured
with an SCG.
Handover from a
non-anchor cell to
an anchor cell
NR
NSA PCC anchoring based on NR coverage
NSA PCC anchor cell
2
Movement path
LTE PCC anchor cell
NSA Virtual Grids
LNR Virtual Grid Model Building
UEs with the same radio signal characteristics can be classified into a category based on
multi-dimensional measurements. The eNodeB considers the UEs with the same RSRP measurement
result on a frequency to be in the same virtual grid. The eNodeB uses machine learning technology
with virtual grids as features to construct a signal characteristics mapping from all virtual grids in a
cell to a frequency. This mapping is contained in an entity called virtual grid model.
No
Start
Scope
determining
Data
collection
Model
building
Model
available?
Yes
End
LNR virtual grid model building in NSA scenarios
LNR Virtual Grid Model Updating
No
Model
retesting
Accuracy
decreased?
Yes
Model
rebuilding
Start
KPI
monitoring
KPI
degraded?
Yes
No
LNR virtual grid model updating in NSA scenarios
End
Fast SCG Addition Based on LNR Virtual Grids
LTE-NR (LNR) virtual grid models include only RSRP prediction models. After determining a UE's virtual
grid in an LTE cell, the eNodeB can quickly predict the UE's RSRP on a neighboring NR frequency by
querying the RSRP prediction model oriented to this NR frequency.
In scenarios with continuous LTE coverage but discontinuous NR coverage, LNR virtual grids can be used to
predict the RSRP of NR cells based on the RSRP of the serving cell and neighboring cells obtained from LTE
intra-frequency A3 measurement results. This reduces the number of invalid gap-assisted measurements in
areas without NR coverage. When a UE moves from an area without NR coverage to an area with NR
coverage, the NR RSRP can be quickly predicted and an SCG can be added for the UE.
158°
215°
UE1@Cell
RSR
P1
58°
P2
RSR
RSRP3
Intra-frequency
characteristics
[RSRP1, RSRP2, RSRP3, ...]
F1
+
Intra-frequency
F2 characteristics
F3 [RSRP4, RSRP5, ...]
Output Virtual
grid
model
Machine learning
Input
[RSRP4, RSRP5, ...]@F3
3
Without NR Coverage
With NR Coverage
Without
virtual grids
Gap-assisted measurement is triggered
but no measurement result is produced,
reducing the throughput.
Gap-assisted measurement is triggered for
NR at intervals of 5s to 60s. Therefore, SCG
addition may not be performed in a timely
manner.
With
virtual grids
It is predicted that there is no NR
coverage, and gap-assisted
measurement is not triggered.
NR coverage status is predicted every 2s.
Therefore, SCG addition can be performed
in a timely manner.
Mobility Management in NSA DC
In an area with both LTE and NR coverage, cells must be configured as external neighboring cells of
the MeNB. In the following figure, the cells under SgNB1 and SgNB2 must be configured as external
neighboring cells of the cells under MeNB1 and MeNB2.
MeNB1
SgNB1
SgNB2
MeNB2
UE
MeNB
SgNB
SgNB
SgNB
Addition Modification Handover 1 Change
MeNB
Handover 2
SgNB
Release
Mobility Scenario
Procedure
SgNB Addition
SgNB addition initiated by MeNB1
SgNB Modification
SgNB modification initiated by SgNB1, and SgNB modification initiated
by MeNB1
MeNB Handover 1
Intra-MeNB change without an SgNB change initiated by MeNB1
SgNB Change
SgNB change initiated by SgNB1
MeNB Handover 2
Inter-MeNB change without an SgNB change initiated by MeNB1
SgNB Release
SgNB release initiated by the MeNB2 or SgNB2
4
Data Split in NSA DC
Data Split Configuration
Operators select bearer types based on UE service QCIs, and then set the uplink and downlink data
split policies.
UL/DL Data Split Policy
Selection
Bearer Type Selection
SCG SPLIT
BEARER
Selection of
QCI-specific
bearer types
LTE-NR dynamic
data split
Setting of
data split
policy
SCG transmission
MCG SPLIT
BEARER
MCG transmission
MCG BEARER
(LTE ONLY)
Fast Retransmission for Downlink Data Split
When an NSA UE is moving, the air interface
quality on the LTE or NR side may deteriorate suddenly due to factors such as interference and the transmission rate may drop. If
this occurs, there will be serious misalignment between PDCP SNs on the UE side or
serious stop and wait for PDCP reordering. As
a result, the upper-layer TCP traffic is unstable and data is overstocked on the LTE or NR
side, affecting the throughput on the other
side.
4 8
…
123 567
EPC
NR
LTE
UE
123 4 5678
…
The base station periodically checks the difference
between the duration for the RLC buffer to be
empty on the LTE side and that on the NR side to
quickly detect air interface changes on the two
sides. Then, it migrates the data buffered on the
side with a long delay to the other side for fast
retransmission, reducing the impact of data
accumulation on TCP window sliding and the
impact on the overall throughput. Source-side
data packets corresponding to the migrated data
are discarded to reduce the transmissions of
repeated data packets.
4 8
…
123 5678
EPC
NR
LTE
UE
…
12345678
…
…
Uplink Fallback to LTE
In NSA DC scenarios, the network side controls the UE to dynamically send uplink data to the
gNodeB or eNodeB based on the uplink SINR on the NR side, using the uplink coverage capability
of LTE to compensate for the insufficient uplink coverage of NR.
● When the uplink SINR on the NR side is high, the UE sends uplink data on the NR side.
● When the uplink SINR on the NR side is low, the UE sends uplink data on the LTE side.
NSA UE
LTE
NR
SRS SINR < Threshold – Configured offset
SgNB Modification Required
RRC Connection Reconfiguration (to instruct
the UE to change the uplink data path)
RRC Connection Reconfiguration Complete
SgNB Modification Confirm
SRS SINR > Threshold + Configured offset
SgNB Modification Procedure (to
change the uplink data path to
the originally configured path)
Uplink Data Transmission Path Selection
If NSA UEs do not support uplink data split in NSA DC scenarios, uplink services can be carried only
on the LTE or NR side. Uplink experience will vary with UE movement, as there are differences
between LTE and NR in factors such as bandwidth, subframe configuration, and load. Therefore, the
optimal uplink data transmission path needs to be selected to improve uplink user experience by
estimating the uplink LTE and NR data rates based on factors such as air interface status and load.
For NSA UEs with uplink data transmission only on the NR side, NR coverage is divided into
three areas based on uplink user experience. The optimal uplink data transmission path can be
selected for UEs in different areas.
● Uplink NR-preferred area: The uplink NR air interface quality is good in this area. The UE camps
on the NR side in the uplink to enjoy low latency.
● Uplink LTE-NR selection area: The uplink NR air interface quality is average in this area. If the UE
has large packets to send, the base station periodically compares the estimated uplink data rates on
the two sides and selects the optimal uplink carrier. If the UE does not have large packets to send,
the original mode is retained.
● Uplink NR-limited area: The uplink NR air interface quality is poor in this area. The UE camps on
the LTE side in the uplink to ensure uplink coverage.
NR
LTE
Uplin
k tra
nsm
Uplin
ission
on th
e LTE
side
mal
carri
miss
er se
ion o
lectio
n the
n
NR s
ide
k tra
ns
Opti
UE
Uplink
NR-preferred area
UE
UE
Uplink
Uplink
LTE-NR selection area NR-limited area
For NSA UEs supporting data split:
● When the uplink NR air interface quality is good, uplink data is transmitted in the original mode.
● When the uplink NR air interface quality is poor, uplink data is transmitted only on the LTE side.
Data Split Example: Uplink and Downlink Separation
In Option 3x, to overcome poor uplink coverage at the NR cell edge, uplink data and downlink data
can be configured to be transmitted through the MCG and SCG, respectively to implement uplink
and downlink separation.
EPC
S1
S1
UL
DL
eNodeB
eNodeB
gNodeB
gNodeB
Uu Uu
UE
UE
Area with poor uplink NR coverage
5
X2
Control-plane data
User-plane data
Uplink Power Control in NSA DC
Initial Power Control
For an NSA DC-capable UE initially accessing the network, the sum of the maximum uplink transmit
power on the LTE and NR sides cannot exceed 23 dBm.
Uplink power
on the LTE side
MAX
＋
Uplink power
on the NR side
MAX
≤ 23 dBm
Network-Coordinated Dynamic UE Power Sharing
If a UE supports dynamic power sharing, the power is preferentially allocated to the LTE side and
then to the NR side, according to 3GPP specifications. The total transmit power of a UE is 23 dBm. It
is likely that most or all of the UE power is allocated to the LTE side but only little or even no power
is allocated to the NR side. As a result, uplink data cannot be sent on the NR side and the SCG may
be released.
In subframes with both LTE and NR, power control and coordinated scheduling are performed
to limit the uplink power on the LTE side and ensure that there is available uplink power on
the NR side. The following uses LTE FDD and NR TDD with a slot configuration of dual-period
8:2 as an example. In time synchronization scenarios, the maximum uplink transmit power
assigned by the eNodeB to the LTE and NR sides of a UE is 23 dBm and 23 dBm respectively
when the UE is at the LTE cell edge, or 20 dBm and 23 dBm respectively when the UE is not
at the edge. In non-time-synchronization scenarios, the maximum uplink transmit power
assigned by the eNodeB to the LTE and NR sides of a UE is the maximum uplink transmit
power on the MCG side and 23 dBm, respectively.
LTE and NR are time-synchronized, and only the
maximum transmit power in dual-mode subframes is restricted.
0
U
LTE
1
U
2
U
3
U
4
U
5
U
6
U
7
U
8
U
9
U
The maximum power on the LTE side The maximum power in a
in a dual-mode subframe is 20 dBm. single-mode subframe is 23 dBm.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
D D D S U D D D S U D D D S U D D D S U
NR
LTE and NR are not time-synchronized,
and the restriction is applied through configuration.
LTE
0
U
1
U
2
U
3
U
4
U
5
U
6
U
7
U
8
U
9
U
The maximum uplink transmit power that can be used
in each subframe is equal to that on the MCG side.
The maximum uplink transmit power that
can be used in each subframe is 23 dBm.
NR
6
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
D D D S U D D D S U D D D S U D D D S U
Interference Avoidance in NSA DC
Intermodulation signals are generated when LTE and NR simultaneously transmit uplink data,
affecting LTE downlink reception. To avoid NR uplink subframes and ensure that LTE common
channels are not affected, secondary intermodulation interference avoidance is implemented, in
which time division scheduling is used on the LTE side. To ensure that NR common channels are
not affected, secondary harmonic interference avoidance is implemented, in which NR common
channels are avoided at the time-frequency position during LTE uplink scheduling.
The preceding two interference avoidance methods ensure UE mobility. The following uses
secondary intermodulation interference avoidance as an example: In an LTE FDD+NR TDD
combination scenario, assume that the uplink-downlink subframe configuration of NR TDD is
DDDSU, and the scheduling unit is 0.5 ms. When an LTE U subframe collides with an NR U
subframe, LTE signals are not transmitted in this subframe.
7
RAT
Scheduling Unit
LTE 1.8 GHz UL
NR 3.5 GHz UL
1 ms
0.5 ms
Subframe Number
0
1
2
3
4
5
6
7
8
9
U
U
U
U
U
U
D D D S U D D D S U D D D S U D D D S U
NSA Carrier Combination Selection Based on User Experience
In NSA networking, after an NSA UE enters the EN-DC state, the number of carriers used on the LTE
side may be less than that used for LTE CA when the UE works in LTE-only state. In this case, the
downlink experience of the UE in EN-DC may be worse than that in LTE CA. NSA carrier
combination selection based on user experience can be used to provide the best service experience
for NSA UEs. The eNodeB can select the most suitable combination from EN-DC or LTE CA
combinations supported by the UE based on the EN-DC capability and LTE CA capability reported by
the UE as well as the signal strength, load, available bandwidth, and other factors of LTE and NR
cells.
The eNodeB evaluates the available bandwidths
of all candidate LTE CA combinations and
selects the optimal combination.
The eNodeB
generates candidate
LTE CA band
combinations and
EN-DC band
combinations.
CC1(LTE)
CC6(LTE)
CC2(LTE)
CC7(LTE)
CC5(LTE)
CC9(LTE)
Candidate LTE CA
combination 1
Candidate LTE CA
combination N
CC6(LTE)
CC7(LTE)
The eNodeB evaluates the available bandwidths
of all candidate EN-DC combinations and
selects the optimal combination.
eNodeB
CC1(LTE)
CC6(LTE)
CC2(LTE)
CC7(LTE)
CC5(LTE)
Candidate EN-DC
combination 1
(LTE CA + single NR
carrier)
CC9(LTE)
eNodeB
CC2(NR)
CC1(NR)
8
The eNodeB selects the
final optimal combination.
CC3(NR)
Candidate EN-DC
combination N
(LTE CA + NR CA)
NSA Anchor Coverage Extension Based on User Experience
In NSA networking with an LTE medium frequency, an LTE low frequency, and an NR low frequency,
when the LTE medium frequency serves as the anchor for NSA UEs and the UEs do not support the
EN-DC combination that includes the LTE low frequency and NR low frequency, the 5G online
duration of the UEs may be short and NR low-frequency resources cannot be fully used.
NSA anchor coverage extension based on user experience extends the coverage edge of LTE medium
frequencies and increases the 5G online duration of UEs. This feature provides the following
functions:
• Threshold adaptation for inter-frequency handovers based on LTE coverage, which delays the
handovers of NSA UEs from LTE medium-frequency cells to LTE low-frequency cells
• Threshold adaptation for NSA PCC anchoring based on NR coverage, which increases the
probability of handing over UEs from LTE low-frequency cells to LTE medium-frequency cells and the
probability of adding NR low-frequency cells as SCG cells for the UEs accordingly
The eNodeB on LTE 1.8 GHz defines
the farthest cell coverage boundary.
2
LTE 1.8G
Basic coverage area
Area in which 5G online duration increases
LTE 800M
Extended coverage area
1
1
The handovers of NSA UEs from
LTE medium-frequency cells to LTE
low-frequency cells are delayed.
2
The probability of handovers from
low-frequency LTE cells to
medium-frequency LTE cells is increased.
NR 700M
The coverage of the LTE medium-frequency anchor
is extended to increase the 5G online duration.
9
Other Functions
Uplink Smart Preallocation
● In a single mode (LTE or NR), uplink preallocation is triggered by downlink packets. In NSA DC
scenarios, if uplink and downlink data split modes are inconsistent, smart preallocation on the
LTE or NR side cannot be triggered, increasing the end-to-end delay.
● In NSA DC scenarios, this function increases the number of times that the base station proactively schedules UEs to reduce the duration of uplink data packet buffering on UEs, speed up the
response to UE services, and improve user experience.
The following uses Option 3x as an example to describe the NSA uplink preallocation procedure.
The NSA uplink preallocation procedure is as follows:
NR PDCP
2
1
1
preallocation indications to the LTE and NR sides
based on the uplink and downlink packets transmitted on the LTE and NR sides.
2 The NR PDCP instructs the LTE and NR sides to
enable uplink preallocation.
3 The LTE MAC and NR MAC start uplink preallocation after receiving the uplink preallocation
instructions from the NR PDCP.
2
LTE RLC
NR RLC
3
1
1
1 The NR PDCP determines whether to send uplink
3
NR MAC
LTE MAC
NSA Networking Scenarios
The following networking scenarios and interconnection modes are supported in NSA DC:
● Co-site scenarios: LTE and NR base stations in NSA networking support CI interconnection,
intra-BBU backplane interconnection, and IP transmission interconnection.
● Inter-site scenarios: LTE- and NR-only base stations in NSA networking support only IP
transmission interconnection.
1
1
LTE and NR Co-Site Scenarios
Separate-MPT
LTE-NR co-BBU separate-MPT
BBU5900
UMPT(L)
UMPT(NR)
LTE-NR separate-BBU separate-MPT
LTE BBU39X0&BBU5900
NR BBU5900
UMPT(L)
UMPT(NR)
CI
CI
IP network
IP network
LTE and NR are interconnected
through the panel or backplane.
X2 control-plane data between LTE and NR is transmitted through IP
transmission interconnection, and X2 user-plane data is transmitted
through either CI interconnection or IP transmission interconnection.
Co-MPT
LTE-NR co-BBU co-MPT
BBU5900
UMPT(L*NR)
IP network
2
LTE and NR Inter-Site Scenarios
IP transmission interconnection between LTE- and NR-only base stations
LTE BBU39X0&BBU5900
UMPT(L)
NR BBU5900
UMPT(NR)
IP network
Engineering Deployment
Hardware
Networking
License
Software
Activation
Main control boards, baseband processing units, RF modules, and
core network equipment that meet requirements, as well as NSA
DC-capable UEs.
• The LTE and NR frequency band combinations support this feature.
• The LTE and NR cells meet the bandwidth requirements of this feature.
•
•
•
•
EN-DC Performance Enhancement
EN-DC Optimal Carrier Selection
NSA Carrier Combination Selection Based on User Experience
NSA Anchor Coverage Extension Based on User Experience
The LTE-NR X2 self-setup function is enabled and the X2 link can be set up
successfully.
• Turn on the NSA DC switches on the LTE and NR sides.
• Set the following parameters: neighboring NR frequencies, external NR cells,
neighboring NR cells, PCC and SCG frequencies, data split polices, and others.
For details about NSA networking deployment, see NSA Networking based on EPC Feature
Parameter Description.
Glossary
5GC 5G Core Network
E-UTRA Evolved Universal Terrestrial Radio Access
MeNB Master eNodeB
NSA Non-Standalone
PCell Primary Cell
SCC Secondary Component Carrier
SgNB Secondary gNodeB
Copyright © Huawei Technologies Co., Ltd. 2022. All rights reserved.
EPC Evolved Packet Core
MCG Master Cell Group
NR New Radio
PCC Primary Component Carrier
PSCell Primary SCG Cell
SCG Secondary Cell Group
TDM Time Division Multiplexing