3g & 4g mobile communication systems - chapter vii
TRANSCRIPT
Dr. Stefan BrückQualcomm Corporate R&D Center Germany
3G/4G Mobile Communications Systems
Chapter VII: Fundamental Radio Resource Management
2
Resource Management
Slide 2
Fundamental Radio Resource Management
� Scope of Radio Resource Management
� Radio Resource Management in UMTS� Cell Breathing
� Capacity – Coverage Trade-off
� Power Control� Near Far Problem
� Inner and outer loop power control
� Load Control
3
� Load Control
� Spreading Code Management in HSDPA
� Examples of HSDPA and HSUPA Performance
� Radio Resource Management in LTE� LTE UL Power Control
� Inter Cell Interference Coordination in LTE� Flexible Frequency Reuse
� Heterogeneous Deployments
� Enhanced Inter Cell Interference Coordination in LTE� Almost Blank Subframes (ABS)
Slide 3
� Efficient use of limited radio resources (power, code space, spectrum, time)
� Minimizing interference
� Flexibility regarding services (Quality of Service, user behaviour)
� Simple algorithms requiring small signalling overhead only
� Stability and overload protection
� Self adaptive in varying environments
RRM – High-Level Requirements
4
� Allow interoperability in multi-vendor environments
Radio Resource Management algorithms control the efficient use of resources with respect to interdependent objectives:
� cell coverage� cell capacity� quality of service
Slide 4
System evaluation and standardisation activities on three levels:
• Access Network (Architecture)• Mobility Management
(E)-UTRANInterfaces Architecture
Context of Radio Resource Management
5
• Radio Link (Physical Layer)
• Cellular Network Aspects (Layer 2&3) • Radio Resource Management
Cellular Network Protocols
Slide 5
Radio Resource Management
Packet DataControl
LoadControl
HandoverControl
Non-Access Stratum
Radio Resource Management Components
6
MediumAccessControl
PowerControl
Physical layer
Slide 6
Example of Coverage and Best Server Mapco
vera
ge
map
bes
t se
rver
map
7
Application: RF engineering (cell layout)Legend: red indicates high signal level, yellow indicates low level
cove
rag
e m
ap
Application: HO decisionLegend: color indicates cell with best CPICH in area
bes
t se
rver
map
Slide 7
Interference in CDMA Networks
Interference Problem
Multiple Access Interference Different users interfere dependent on the access scheme (T/F/CDMA)
Intra-Cell Interference Interference caused by users belonging to the same cell
Inter-Cell Interference Interference caused by users belonging to other cells
8
� Frequency reuse factor = 1
� CDMA is subject to high Multiple Access Interference (MAI)
� MAI can be separated in intra-cell and inter-cell interference
� Soft capacity: CDMA capacity (max. number of users) determined by interference is soft� TDMA capacity is given by available number of time slots
� Handling of interference is the main challenge in designing CDMA networks
Slide 8
Interference in CDMA - Uplink
9 Slide 9
Interference in CDMA - Downlink
10 Slide 10
Cell Breathing in CDMA
� Specified service specific C/I needs to be maintained at receiver to guarantee QoS
� Growth of traffic leads to an increase in interference power� Both inter-cell and intra-cell power
� If transmitter power cannot be further increased (max. link power), maximum cell size decreases since specific C/I at far receiver is required
� Load dependent maximum cell is referred to as cell breathing
11
� Load dependent maximum cell is referred to as cell breathing
� As network load changes over day, also the maximum cell size changes over day� Especially during busy hours the interference rises ⇒ small cell size
� Breathing is determined by intra-cell interference
⇒⇒⇒⇒ Active Load Control is needed
Slide 11
Cell Breathing
� Coverage depending on load: Load causes interference which reduces the area where a SIR sufficient for communication can be provided
Coverage low load Coverage medium load Coverage high load
12 Slide 12
Yellow area: Connection may drop or be blocked
Coverage vs. Capacity
� Capacity depends on:� QoS of the users (data rate, error performance (bit-error-rate))
� User behaviour (activity)
� Interference (intra- & inter-/noise)
� Number of carriers/ sectors
� Coverage (service area) depends on:
13
� Coverage (service area) depends on:� Interference (intra- & inter-cell) + noise
� Pathloss (propagation conditions)
� QoS of the users (data rate, error performance (bit-error-rate))
� Thus, trade-off between capacity and coverage
Slide 13
Coverage vs. Capacity
1
1.5
2
2.5
3
3.5
←Downlink
Max
imum
cel
l rad
ius
(km
)
13kbps circuit switched service capacity versus maximum cell radius
14
� Downlink limits capacity while uplink limits coverage
� Downlink depends more on the load (user share total transmit BS power)
0 20 40 60 80 100 120 140 160 180 2000
0.5
1
Uplink→
Erlangs (2% GOS)
Max
imum
cel
l rad
ius
(km
)
Slide 14
� Controls the setting of the transmit power in order to:� Keep the QoS within the required limits, e.g. data rate, delay and BER� Minimise interference, i.e. the overall power consumption
� Power control handles:� Path Loss (Near-Far-Problem), Shadowing (Log-Normal-Fading) and Fast
Fading (Rayleigh-, Ricean-Fading) � Environment (delay spread, UE speed, …) which implies different performance
of the deinterleaver and decoder
CDMA Power Control: Basics
15
� Three types of power control:� Inner loop power control� Outer loop power control (SIR-target adjustment)� Open loop power control (Power allocation)
� Downlink power overload control to protect amplifier� Gain Clipping (GC)� Aggregated Overload Control (AOC)
Slide 15
� Near-Far Problem:� Spreading sequences are not orthogonal
(multi-user interference)� Near mobile dominates� Signal to interference ratio (SIR) is lower for far
mobiles and performance degrades
� Problem can be resolved through dynamic NodeBNodeB
UE 1UE 1
Near-Far Problem in CDMA
16
� Problem can be resolved through dynamic power control to equalize all received power levels
� AND/OR: By means of joint multi-user detection (MUD)
NodeBNodeB
UE 2UE 2
Slide 16
Impact of Power Control
17
Source: H. Holma, A. Toskala (Ed.), “WCDMA for UMTS”,
Slide 17
6
6.5
7
7.5
Req
uir
ed U
L S
IR [
dB
]
Power Control Results
18
5
5.5
0 20 40 60 80 100 120
Velocity [km/h]
Req
uir
ed U
L S
IR [
dB
]
PedA
VehA
SIR requirement strongly depends on the environment (due to different fast fading conditions – Jakes models) ⇒ Outer loop power control needed to adapt SIR
Slide 18
� Closed loop power control is used on channels which are established in both directions, such as DCH
� The receiver generates transmit power commands (TPC) based on the estimated received quality; the TPC are send back to the transmitter in the opposite direction
� The transmit power is adjusted according to the received TPC
ReceiverReceiver DecoderDecoderPAPAUser dataUser dataUser dataUser data
Closed Loop Power Control in UMTS
19
ReceiverReceiver DecoderDecoder
SIRSIR--estimateestimate
BLERBLER--estimateestimate
MUXMUXDeMUXDeMUX
PAPA
TPCTPCcommandscommands
TPCTPCcommandscommands
Adjust SIRAdjust SIRtargettarget
Inner loopInner loop
OuterOuterlooploop
Slide 19
Mobile Station Base Station/RNC
� Inner Loop Power Control (1500 Hz)� Objective: Adjust transmit power to keep the received SIR at a given SIR target
� Realisation using the SIR-estimate after RAKE combining:� If SIRest > SIRtarget, then generate TPC “DOWN”
� If SIRest ≤ SIRtarget, then generate TPC “UP”
� Realisation in base station (Node B)
� Similar mechanisms for up- and downlink
� Outer Loop Power Control (100 Hz max)
Inner/Outer Loop Power Control
20
� Outer Loop Power Control (100 Hz max)� Objective: Meet the required reception quality, e.g. average BLER
� Realisation using the CRC attachment� If CRC ok, then decrease SIRtarget = SIRtarget – ∆down
� If CRC fails, then increase SIRtarget = SIRtarget + ∆up
∆down = ∆up × BLERtarget / (1–BLERtarget)
� Realisation in radio network controller (RNC)
Slide 20
� General limitations in 3rd generation mobile systems:
� Limited resources: spectrum, power, (code space)
� Not all service requests can be granted
� Different types of services in the same cellular environment
� Service parameters (user behaviour and QoS) and environmental conditions (propagation) vary over time
� CDMA-specific impacts:
Load Control: Basics
21
� CDMA-specific impacts:� Coverage in CDMA systems depends on the cell loading: Cell breathing
� CDMA systems may become unstable in highly loaded situationsdue to fast inner-loop power control
Slide 21
Load Control
� Main objective:� Avoid overload situations by controlling system load
� Monitor and controls radio resources of users
� Call Admission Control (CAC)� Admit or deny new users, new radio access bearers or new radio links
� Avoid overload situations, e.g. by means of blocking a new call
� Decisions are based on interference and resource measurements
22
� Congestion Control (ConC)� Monitor, detect and handle overload situations with the already connected users
� Bring the system back to a stable state, e.g. by means of dropping an existing call
� CAC and ConC decisions are based on network measurements averaged over hundreds of ms� No fast fading impacts in these measurments
Slide 22
Basic Resource Equations (CDMA)Rbi: data rate of user i hi: channel coefficient of user i
Ppilot: Pilot power Fi: Orthogonality factor of user i (multipath)
Ith: thermal noise
Downlink
Quality (RAKE):
Resource of user i:
thinterpilotj jii
iibi
t
bi
IIPPhF
PhRW
N
E
+++⋅⋅⋅⋅=
∑ )(
Power dTransmitte Total:Poo
ii P
P=α
23
Uplink
Quality (RAKE):
Resource of user i:
� Resource Consumption strongly depends on: data rate, quality (Eb/Nt), receiver structure (RAKE etc., channel estimation, path tracking, …)
� Non-linear relation between resource, data rate and required Eb/Nt
thinterij j
ibi
t
bi
IIP
PRW
N
E
++⋅=
∑ ≠ˆ
ˆ
ceInterferen Total:Iˆ
otbb
tb
o
ii NERW
NE
I
P
+==α
Slide 23
� Service/BLER-dependent resource consumption
� Uplink example:� Service I: Voice
Rb = 12.2kbps, Eb/Nt = 5dBαI = 0.99%
� Service II: DataRb = 144kbps, Eb/Nt = 3.1dBαII = 7.11%3
4
5
6
7
8
9
10
Eb
/Nt [
dB
]
Voice (12.2 kbps)BLER = 1%
Resource Consumption
24
II
with
W is the channel bandwidth and Rb is the data rate
0
1
2
10 100 1000
Data Rate Rb [kbps]
0,5% 1% 2% 5%
10% 20% 35% 50%
BLER = 1%Data (144 kbps)
BLER = 10%
αααα
)(
)(
tbb
tb
NERW
NE
+=α
Slide 24
8
10
12
14
16
18
20
No
ise
Ris
e/ P
ow
er R
ise
[dB
]
thr_CAC = 75%
thr_ConC = 90%
� UL Measurement
� Load Estimate
�
thintercelli i IIPI ++=∑ ∈ˆ
0
th
thcurrent
IINR
NRI
II
0
0
0 11
=
−=−=η
UL/DL Load Measures
25
0
2
4
6
8
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
System Load
No
ise
Ris
e/ P
ow
er R
ise
[dB
]
� DL Measurement
� Load Estimate
Pcelli i PPP +=∑ ∈0
p
Pcurrent
PPPR
PRP
PP
0
0
0 11
=
−=−=η
Slide 25
Call Admission Control
� Admitting new call always increases the cell loading
� CAC avoids overload by limiting this increase
� CAC load check:
� Threshold setting thrCAC
trade-off between
?CACnewcurrent thr≤α+η
8
10
12
14
16
18
20
No
ise
Ris
e/ P
ow
er R
ise
[dB
]
η_current + α_new
thr_CAC
26
CAC
trade-off between� Maximize capacity: prevent
excessive blocking � Avoid overload: thrCAC < thrConC
0
2
4
6
8
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
System Load
No
ise
Ris
e/ P
ow
er R
ise
[dB
]
η_current
η_current + α_new
Slide 26
� Admitting a new call always increases the cell load
� In order to avoid overload situations, the admission control will limit this load increase
� The principle is to check the current system load plus the expected resource consumption of the new call against the call admission threshold:
load + consumption ≤ thrCAC ?
Call Admission Control (CAC)
27
� In case the admission check fails, the basic strategy is to protect ongoing calls by denying the new user access to the system since dropping is assumed to be more annoying than blocking
� Admission control is required for uplink and downlink
� Arrivals of high-data-rate users that require a large amount of resources (especially in the downlink) may demand global information
Slide 27
Congestion Control
8
10
12
14
16
18
20
No
ise
Ris
e/ P
ow
er R
ise
[dB
]
η_current
NR/PR_max
� Even with efficient CAC overload situations still occur due to� Mobility (esp. downlink)� Activity
� During overload quality of allusers is deteriorated !
� Triggered by measurement
� Action: reduce offered traffic by
ConCcurrent thr≥η
28
0
2
4
6
8
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
System Load
No
ise
Ris
e/ P
ow
er R
ise
[dB
]
η_reducedthr_ConC
� Action: reduce offered traffic by downgrading one user
� Threshold setting thrConC to preserve the coverage:� NRmax: limitation of MS single
transmit power Pimax� PRmax: limitation of BTS total
transmit power P0max
Slide 28
� Due to the mobility (especially of high data rate users) overload situations occur even if an efficient admission control algorithm is used!
� The congestion control is activated once the system load exceeds the congestion threshold:
load ≥ thrConC
� In order to overcome the overload situation the load must be lowered until
Congestion Control (ConC)
29
� In order to overcome the overload situation the load must be lowered until load < thrConC
� This is done by reducing the offered traffic� Lowering the data rate of one or several services that are insensitive to increased
delays – this might be the most preferred method
� Performing inter-frequency (inter-system) handover
� Removing one or several connections
� Global information may be required to minimize the number of altered connections
Slide 29
30%
35%
40%
45%
50%
Blo
ckin
g P
rob
abili
ty
thr_CAC = 50%thr_CAC = 75%thr_CAC = 90%
12%
14%
16%
18%
20%
Dro
pp
ing
Pro
bab
ility
thr_CAC = 50%thr_CAC = 75%thr_CAC = 90%
Tradeoff between blocking and droppingExample: 64k per user, urban
Call Admission Control: Simulation Results I
30
0%
5%
10%
15%
20%
25%
5 15 25 35 45 55
Offered Traffic [Erlang per s ite ]
Blo
ckin
g P
rob
abili
ty
0%
2%
4%
6%
8%
10%
5 15 25 35 45 55
Offered Traffic [Erlang per s ite ]
Dro
pp
ing
Pro
bab
ility
Slide 30
50%
60%
70%
80%
90%
Cel
l L
oad
ing
Cell load depending on CAC thresholdExample: 64k per user, urban
Call Admission Control: Simulation Results II
31
0%
10%
20%
30%
40%
5 15 25 35 45 55
Offered Traffic [Erlang per site]
Cel
l L
oad
ing
thr_CAC = 50%thr_CAC = 75%thr_CAC = 90%
Slide 31
� Flexibility� Asymmetrical data rates
� Very low to very high data rates
� Control information/user information
� Efficient transmission making good use of CDMA characteristics� Dedicated channel (DCH)
� Minimise transmission power by closed-loop power control
Packet Data Control: Channel Switching
32
� Minimise transmission power by closed-loop power control
� Independence between uplink and downlink capacity
� Common channel� Random access in the uplink (RACH)
� Dynamic scheduling in the downlink (FACH)
� Adaptive channel usage depending on traffic characteristics� Infrequent or short packets ⇒ Common channel (Cell_FACH)
� Frequent or large packets ⇒ Dedicated channel (Cell_DCH)
Slide 32
CELL_DCH CELL_FACH CELL_DCH
DCH Active Time
Channel Switching – Example
33
Page Download Time Reading Time
DCH Active Time“Chatty Applications”
� Example: Web service
� Chatty apps.: keep alive message, stock tickers, etc.(e.g. 100 bytes every 15 sec)
� Second stage: when no activity in CELL_FACH then switch to URA_PCH
Slide 33
� Burst Admission Control� Decision on starting packet data transmission
� Similar principle like call admission control, i.e. check the system load against a threshold that is usually different from thrCAC
� Time horizon: 100msec … 10sec
� Rate Adaptation� Choose data rate according to transmit power
Packet Data Control
34
� Choose data rate according to transmit power� UE nearby NodeB ⇒ high data rate
� UE at cell edges ⇒ low data rate
� Decrease data rate in case of overload, cf. congestion control
Slide 34
� Power Control:� Balances user received quality (BLER, SIR)� Users at cell center get less share of BTS
transmit power assigned than at cell edge� Occurrence of power overload
� Rate Adaptation:� Transmit power ~ data rate
UE 1UE 1
Power Control vs. Rate Adaptation
35
� Transmit power ~ data rate� Users at cell edge get lower data rate
assigned than at cell center� Reduces also power overload
� In UMTS combination of power control and rate adaptation on DCH
NodeBNodeB
UE 2UE 2low data ratelow data rateareaarea
high data ratehigh data rateareaarea
Slide 35
UMTS_urban, 50 kByte
20%
25%
30%
35%
40%
Ou
tag
e P
rob
abili
ty
384k64kadaptive
UMTS_urban, 50 kByte
4
5
6
7
8
Mea
n D
elay
[se
c]
384k
64k
adaptive
Rate Adaptation Performance
36
Rate adaptation significantly improves the RRM performance.
0%
5%
10%
15%
200 300 400 500 600
Cell Throughput [kBit/sec]
Ou
tag
e P
rob
abili
ty
0
1
2
3
200 300 400 500 600
Cell Throughput [kBit/sec]M
ean
Del
ay [
sec]
Slide 36
Spreading Code Management in HSDPA
a) OVSF Code Tree
SF=8
SF=4
SF=2
C16,0 C16,15
Border adjusted by CRNC
37
b) Transmit Power
SF=16
Codes reserved for HS-PDSCH/ HS-SCCH
C16,0 C16,15
Codes available for DCH/ common channels
Tx power available for HS-PDSCH/ HS-SCCH Tx power available for DCH/ common channels
Border adjusted by CRNC
� Note: CRNC assigns resources to Node B on a cell basis
Slide 37
� 36 cells network
� UMTS composite channel model
� FTP traffic model (2 Mbytedownload, 30 sec thinking time)
� The user throughput is decreased when increasing load
Load Impact
1000
1500
2000
2500
Throughput [kbit/sec]
Mean User Throughput
Aggregated Cell Throughput
Cell and User Throughput versus Load
38
decreased when increasing load due to the reduced service time
� The cell throughput increases with the load because overall more bytes are transferred in the same time
0
500
1000
4 6 8 10 12 14 16 18
Number of Users/ Cell
Throughput [kbit/sec]
Slide 38
� 36 cells network
� UMTS composite channel model
� FTP traffic model (2 Mbyte download, 30 sec thinking time)
� Higher category offers higher max. throughput limit
Cat 6 - Cat 8 Comparison
1500
2000
2500
thro
ug
hp
ut
(kb
ps)
Mean User ThroughputPeak User ThroughputAggregated Cell Throughput
HSDPA performance per UE Category
39
max. throughput limit� Cat.6: 3.6 MBit/sec
� Cat.8: 7.2 MBit/sec
� Max. user perceived performance increased at low loading
� Cell performance slightly better
0
500
1000
Cat 6/ 10 users Cat 8/ 10 users Cat 6/ 20 users Cat 8/ 20 users
thro
ug
hp
ut
(kb
ps)
Slide 39
� Example Scenario� 15 users/cell
� Pedestrian A channel model
� Plot generated with field
HSDPA Coverage Prediction
40
� Plot generated with field prediction tool
HSDPA Throughput depends on location
Slide 40
800
1000
1200
Use
r Th
roug
hput
[kbp
s]
10ms TTI, unlimited CE dec. rate 2ms TTI, next release
User vs. Aggregate Cell Throughput for HSUPA
� 36 cells network
� UMTS composite channel model
� FTP traffic model (2 Mbyte upload, 30 seconds thinking time)
#UEs/cell1
2
3
4
41
0
200
400
600
200 400 600 800 1000 1200 1400 1600
Aggregated Cell Throughput [kbps]
Use
r Th
roug
hput
[kbp
s]
� Maximum cell throughput reached for about 7…8 UEs per cell
� Cell throughput drops if #UEs increases further since the associated signaling channel consume UL resources too
5
6
7
8
910
Slide 41
Single User Performance in HSUPA
� Average user throughput (RLC layer) for different channel profiles
� 1 UE in the network
� 1 target HARQ transmission
� For AWGN channel conditions:
� 10ms TTI: up to 1.7 Mbps 2000
2500
3000
3500
Ave
rag
e U
ser
Th
rou
gh
pu
t [k
bp
s]
2ms, 1Tx 10ms, 1Tx
42
� 10ms TTI: up to 1.7 Mbps (near theoretical limit of 1.88 Mbps)
� 2ms TTI: up to 3 Mbps (below theoretical limit 5.44 Mbps)
� E.g. due to restrictions from RLC layer (window size, PDU size)
0
500
1000
1500
AWGN PedA3 PedA30 VehA30 VehA120
Scenario
Ave
rag
e U
ser
Th
rou
gh
pu
t [k
bp
s]
Slide 42
LTE Uplink Power Control
� Open-loop power control is the baseline uplink power control method in LTE (compensation for path loss and fading)� Open-loop PC is needed to constrain the dynamic
range between signals received from different UEs
� Unlike CDMA, there is no intra cell interference to combat; rather, fading is exploited by rate control
� Transmit power per PRB
TxPSD = α•PL + P0Target SINR on PUSCH is now a function of the UE’s path loss:
43
TxPSD(dBm) = α•PL(dB) + P0nominal (dBm)
� PLdB: pathloss, estimated from DL reference signal
� P0nominal (dBm) = Γnominal (dB) + Itot (dBm)
Sum of SINR target Γnominal and total interference Itot sent on BCH
� Fractional compensation factor α ≤ 1 (PUSCH) → only a fraction of the path loss is compensated
� Additionally, (slow) closed loop PC can be used
Target SINR
of the UE’s path loss:
SINR(dBm) = Γnominal (dB) + (1–α)•PL(dB)
Slide 43
Interference Coordination - Flexible Frequency ReuseCell edge
Reuse > 1
Cell centre
Reuse = 1
44
� Cell edge users with frequency reuse > 1,
� eNB transmits with higher power
� Improved SINR conditions
� Cell centre users can use whole frequency band
� eNB transmits with reduced power
� Less interference to other cells
� Flexible frequency reuse realized through intelligent scheduling and power allocation
� Scheduler can place restriction on which PRBs can be used in which sectors
� Achieves frequency reuse > 1
� Reduced inter-cell interference leads to improved SINR, especially at cell-edge
� Reduction in available transmission bandwidth leads to poor overall spectral efficiency
Slide 44
Need for Flexible and Low-Cost Network Deployment Using Mix of Macro, Pico, Relay, RRH and Home eNBs
Heterogeneous Networks
MacroHeNB
Core Network
Internet
Relay
Pico
Backhaul
Relay Backhaul
Pico Pico
45
� Network expansion due to varying traffic demand & RF environment� Cell-splitting of traditional macro deployments is complex and iterative� Indoor coverage and need for site acquisition add to the challenge
� Future network deployments based on Heterogeneous Networks (HeNBs)� Deployment of Macro eNBs for initial coverage only� Addition of Pico, HeNBs and Relays for capacity growth & better user experience
� Improved in-building coverage and flexible site acquisition with low power base stations� Relays provide coverage extension with no incremental backhaul expense
Slide 45
HetNet: Macro-Pico (open access hot-spot)
� Macro-pico deployments with UEs operating in range expansion
� Large bias to compensate the power difference between macro and picofor traffic offloading
� Nominally a UE associates with a base station with strong DL SINR
� With range expansion, a UE can associate with a low power node based on smaller path loss, thus offloading the macro station
� With range expansion the serving cell is not necessarily the strongest one
46
MacroPicoPico
� With range expansion the serving cell is not necessarily the strongest one
Slide 46
HetNet: Macro-Femto (CSG node, HeNB)
� Macro-femto deployments with UEs (or femto cells) operating under strong co-channel interference
� UEs in close proximity of a CSG femto cell they are not allowed to connect to (i.e. are still served by macro cell) may be:
� strongly interfered in DL by the CSG cell
� causing severe interference in UL to towards the femto cell
� Interference management helps the UE to survive
47
� Interference management helps the UE to survive
MacroCSG CSG
Slide 47
Extending X2 to HeNB – 3GPP Status Rel. 10
� During Rel. 10 work, several contributions have been discussed related to introduction of X2 interface for HeNB for mobility enhancement
� HeNB X2 scenarios� HeNB-HeNB when the target cell is an open access HeNB
� HeNB-HeNB for closed/hybrid access with same CSG ID
� The existing X2 functionality is available for eNB and HeNB
48
� The existing X2 functionality is available for eNB and HeNB� There is no separate X2 specification for HeNB and eNB
� The X2 functionality is optional
� X2 interface between eNB and HeNB has been also discussed but no agreement could be reached so far� Scenario is more complex, as there may be a need for X2-GW which requires
additional standardization work
� Postponed to Rel. 11
Slide 48
Enhanced ICIC in Rel. 10
� ICIC includes frequency and time domain components� Frequency domain ICIC was already available in Rel. 8 and Rel. 9
� See lecture chapter 4 for details
� For the time domain ICIC, Almost Blank Subframes (ABSs) are used to protect resources receiving strong inter-cell interference (R3-103775)� Extensions to X2AP are needed� Time domain updates in Rel. 10 are called enhanced ICIC
49
� Time domain updates in Rel. 10 are called enhanced ICIC
� Both scenarios are handled differently, since there is no eNB – HeNB X2� Semi-static eICIC in macro eNB – pico eNB
� Static eICIC in eNB – HeNB scenario� ABS are defined by OAM for time domain eICIC (R3-103775)
� References: � R3-103775, “X2 procedure and OAM requirements to support eICIC”, TSG-RAN WG3 Meeting #70,
November 2010
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Updates of the X2AP to support eICIC in Rel10
� Information of ABS pattern is added to the ‘Load Indication’ procedure� The ABS pattern (40ms period for FDD) is sent from the aggressor to the victim
� The ABS patterns are semi-statically updated
� The ‘Load indication’ also contains an invoke indication� This indicator is sent from the victim to the aggressor to ask for eICIC activation
IE/Group Name Presence Range IE type and reference
Semantics description
Invoke Indication M ENUMERATED (ABS
Information, …)
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� Information about the status of the ABS is added to the ‘Resource Status Reporting’ procedure� Its initialization is enabled in the ‘Resource Status Reporting Initiation’ procedure
� This information is sent from the victim to the aggressor
� References: � R3-103667, “Introduction of X2 signaling support for eICIC”, TSG-RAN WG3 Meeting #70, November 2010
� R3-103776, “Enabling reporting of ABS resource status for eICIC purposes”, TSG-RAN WG3 Meeting #70, November 2010
IE/Group Name Presence Range IE type and reference Semantics descriptionDL ABS status M INTEGER (0..100) Percentage of ABS
resource allocated for UEs protected by ABS from strong inter-cell interference.
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