3G & 4G Mobile Communication Systems - Department of ...

3G/4G Mobile Communications Systems
Dr. Stefan Brück
Qualcomm Corporate R&D Center Germany

Chapter VII:
Fundamental Radio
Resource Management
2
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
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)
3
Slide 3

RRM – High-Level Requirements
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
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
4
Slide 4

Context of Radio Resource Management
System evaluation and standardisation activities on three levels:
(E)-UTRAN
Interfaces
Architecture
• Access Network (Architecture)
• Mobility Management
Cellular Network
Protocols
• Cellular Network Aspects (Layer 2&3)
• Radio Resource Management
• Radio Link (Physical Layer)
5
Slide 5

Radio Resource Management Components
Non-Access Stratum
Radio Resource Management
Handover
Control
Load
Control
Packet Data
Control
Power
Control
Medium
Access
Control
Physical layer
6
Slide 6

Example of Coverage and Best Server Map
coverage map
best server map
Application: RF engineering (cell layout)
Legend: red indicates high signal level, yellow
indicates low level
Application: HO decision
Legend: color indicates cell with best
CPICH in area
7
Slide 7

Interference in CDMA Networks
Interference
Multiple Access Interference
Intra-Cell Interference
Inter-Cell Interference
Problem
Different users interfere dependent on
the access scheme (T/F/CDMA)
Interference caused by users belonging
to the same cell
Interference caused by users belonging
to other cells
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
8
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
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
11
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
Yellow area: Connection may drop or be blocked
12
Slide 12

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:
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
13
Slide 13

Coverage vs. Capacity
3.5
13kbps circuit switched service capacity versus maximum cell radius
3
Maximum cell radius (km)
2.5
2
1.5
1
←Downlink
0.5
Uplink→
0
0 20 40 60 80 100 120 140 160 180 200
Erlangs (2% GOS)
Downlink limits capacity while uplink limits coverage
Downlink depends more on the load (user share total transmit BS power)
14
Slide 14

CDMA Power Control: Basics
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
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)
15
Slide 15

Near-Far Problem in CDMA
UE 1
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
NodeB
Problem can be resolved through dynamic
power control to equalize all received power levels
AND/OR: By means of joint multi-user detection (MUD)
UE 2
16
Slide 16

Impact of Power Control
Source: H. Holma, A. Toskala (Ed.), “WCDMA for UMTS”,
17
Slide 17

Power Control Results
7.5
7
Required UL SIR [dB]
6.5
6
5.5
5
PedA
VehA
0 20 40 60 80 100 120
Velocity [km/h]
SIR requirement strongly depends on the environment (due to different fast
fading conditions – Jakes models)
⇒ Outer loop power control needed to adapt SIR
18
Slide 18

Closed Loop Power Control in UMTS
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
User data
PA
Receiver
Decoder
User data
TPC
commands
Inner loop
Outer
loop
SIR-estimate
TPC
commands
BLER-estimate
Adjust SIR target
DeMUX
MUX
19
Mobile Station
Base Station/RNC
Slide 19

Inner/Outer Loop Power Control
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 SIR est > SIR target , then generate TPC “DOWN”
If SIR est ≤ SIR target , then generate TPC “UP”
Realisation in base station (Node B)
Similar mechanisms for up- and downlink
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 SIR target = SIR target – ∆ down
If CRC fails, then increase SIR target = SIR target + ∆ up
∆ down = ∆ up × BLER target / (1–BLER target )
Realisation in radio network controller (RNC)
20
Slide 20

Load Control: Basics
General limitations in 3 rd 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:
Coverage in CDMA systems depends on the cell loading: Cell breathing
CDMA systems may become unstable in highly loaded situations
due to fast inner-loop power control
21
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
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
22
Slide 22

Basic Resource Equations (CDMA)
R bi : data rate of user i
h i : channel coefficient of user i
P pilot : Pilot power
F i : Orthogonality factor of user i (multipath)
I th : thermal noise
Downlink
Quality (RAKE):
E
N
bi
t
=
F ⋅ h ⋅
i
i
W Rbi
⋅ hi
P + P
(∑ )
j
j
pilot
⋅ Pi
+ I
inter
+ I
th
Resource of user i:
α
i
=
Pi
P
o
P o
: Total Transmitted Power
Uplink
Quality (RAKE):
E
N
bi
t
W
=
∑ ≠
Pˆ
j
i
j
R
bi
+ I
⋅ Pˆ
i
inter
+ I
th
Resource of user i:
α
i
=
Pˆ
i
I
o
=
W
Eb
N
R + E
b
t
b
N
t
I
o
: Total Interference
Resource Consumption strongly depends on: data rate, quality (E b /N t ), receiver
structure (RAKE etc., channel estimation, path tracking, …)
Non-linear relation between resource, data rate and required E b /N t
23
Slide 23

Resource Consumption
E b/N t [dB ]
10
9
8
7
6
5
4
3
2
1
0
Voice (12.2 kbps)
BLER = 1%
10 100 1000
α
Data Rate Rb [kbps]
Data (144 kbps)
BLER = 10%
0,5% 1% 2% 5%
10% 20% 35% 50%
Service/BLER-dependent
resource consumption
Uplink example:
Service I: Voice
R b = 12.2kbps, E b /N t = 5dB
α I = 0.99%
Service II: Data
R b = 144kbps, E b /N t = 3.1dB
α II = 7.11%
II
with
α =
W
( Eb
Nt
)
R + ( E N
b
b
W is the channel bandwidth and
R b is the data rate
t
)
24
Slide 24

UL/DL Load Measures
Noise Rise/ Power Rise [dB]
20
18
16
14
12
10
8
6
4
2
0
thr_CAC = 75%
thr_ConC = 90%
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100
%
System Load
UL Measurement
I = ∑
ˆ
∈
+
0
P
i cell i
+ Iinter
Ith
Load Estimate
I − Ith
ηcurrent
=
I
NR =
I
0
1
0
0
I
th
= 1−
DL Measurement
P
0
= ∑ ∈
+
P
i cell i
P
Load Estimate
η
current
=
PR =
P
P
p
NR
0
− P
1
0
P
0
P
= 1−
PR
25
Slide 25

Call Admission Control
Noise Rise/ Power Rise [dB]
20
18
16
14
12
10
8
6
4
2
0
thr_CAC
η_current + α_new
η_current
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100
%
Admitting new call always
increases the cell loading
CAC avoids overload by limiting
this increase
CAC load check:
η
current
+ α
new
≤ thr
CAC
Threshold setting thr CAC
trade-off between
Maximize capacity: prevent
excessive blocking
Avoid overload: thr CAC < thr ConC
System Load
26
Slide 26

Call Admission Control (CAC)
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 ≤ thr CAC
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
27
Slide 27

Congestion Control
Noise Rise/ Power Rise [dB]
20
18
16
14
12
10
8
6
4
2
0
NR/PR_max
η_reduced
η_current
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100
%
System Load
thr_ConC
Even with efficient CAC overload
situations still occur due to
Mobility (esp. downlink)
Activity
During overload quality of all
users is deteriorated !
Triggered by measurement
η ≥
current
thr ConC
Action: reduce offered traffic by
downgrading one user
Threshold setting thr ConC to
preserve the coverage:
NR max : limitation of MS single
transmit power P imax
PR max : limitation of BTS total
transmit power P 0max
Slide 28
28

Congestion Control (ConC)
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 ≥ thr ConC
In order to overcome the overload situation the load must be lowered until
load < thr ConC
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
29
Slide 29

Call Admission Control: Simulation Results I
Tradeoff between blocking and dropping
Example: 64k per user, urban
50%
45%
40%
thr_CAC = 50%
thr_CAC = 75%
thr_CAC = 90%
20%
18%
16%
thr_CAC = 50%
thr_CAC = 75%
thr_CAC = 90%
Blocking Probability
35%
30%
25%
20%
15%
10%
5%
Dropping Probability
14%
12%
10%
8%
6%
4%
2%
0%
5 15 25 35 45 55
0%
5 15 25 35 45 55
Offered Traffic [Erlang per s ite ]
Offered Traffic [Erlang per s ite ]
30
Slide 30

Call Admission Control: Simulation Results II
Cell load depending on CAC threshold
Example: 64k per user, urban
90%
80%
Cell Loading
70%
60%
50%
40%
30%
20%
10%
0%
5 15 25 35 45 55
Offered Traffic [Erlang per site]
thr_CAC = 50%
thr_CAC = 75%
thr_CAC = 90%
31
Slide 31

Packet Data Control: Channel Switching
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
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)
32
Slide 32

Channel Switching – Example
CELL_DCH CELL_FACH CELL_DCH
DCH Active Time
Page Download Time
Reading 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
33
Slide 33

Packet Data Control
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 thr CAC
Time horizon: 100msec … 10sec
Rate Adaptation
Choose data rate according to transmit power
UE nearby NodeB
UE at cell edges
⇒ high data rate
⇒ low data rate
Decrease data rate in case of overload, cf. congestion control
34
Slide 34

Power Control vs. Rate Adaptation
NodeB
high data rate
area
UE 1
low data rate
area
UE 2
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
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
35
Slide 35

Rate Adaptation Performance
UM TS_urban, 50 k Byte
UM TS_urban, 50 k Byte
40%
35%
384k
64k
adaptive
8
7
30%
6
384k
Outage Probability
25%
20%
15%
10%
Mean Delay [sec]
5
4
3
2
64k
adaptive
5%
1
0%
200 300 400 500 600
Ce ll Throughput [kBit/s e c]
0
200 300 400 500 600
Ce ll Throughput [k Bit/s e c]
Rate adaptation significantly improves the RRM performance.
36
Slide 36

Spreading Code Management in HSDPA
a) OVSF Code Tree
Border adjusted by CRNC
SF=2
SF=4
SF=8
SF=16
C 16,15
Codes reserved for HS-PDSCH/ HS-SCCH
b) Transmit Power
Border adjusted by CRNC
Codes available for DCH/
common channels
C 16,0
Tx power available for HS-PDSCH/ HS-SCCH
Tx power available for DCH/
common channels
Note: CRNC assigns resources to Node B on a cell basis
37
Slide 37

Cell and User Throughput versus Load
Throughput [kbit/sec]
2500
2000
1500
1000
500
0
Mean User Throughput
Aggregated Cell Throughput
Load Impact
4 6 8 10 12 14 16 18
Number of Users/ Cell
36 cells network
UMTS composite channel model
FTP traffic model (2 Mbyte
download, 30 sec thinking time)
The user throughput is
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
38
Slide 38

HSDPA performance per UE Category
2500
2000
Mean User Throughput
Peak User Throughput
Aggregated Cell Throughput
Cat 6 - Cat 8 Comparison
36 cells network
UMTS composite channel model
FTP traffic model (2 Mbyte
download, 30 sec thinking time)
throughput (kbps)
1500
1000
500
Higher category offers higher
max. throughput limit
Cat.6: 3.6 MBit/sec
Cat.8: 7.2 MBit/sec
0
Cat 6/ 10 users Cat 8/ 10 users Cat 6/ 20 users Cat 8/ 20 users
Max. user perceived
performance increased at low
loading
Cell performance slightly better
39
Slide 39

HSDPA Coverage Prediction
Example Scenario
15 users/cell
Pedestrian A channel
model
Plot generated with field
prediction tool
HSDPA Throughput
depends on location
40
Slide 40

User vs. Aggregate Cell Throughput for HSUPA
10ms TTI, unlimited CE dec. rate
2ms TTI, next release
36 cells network
User Throughput [kbps]
1200
1000
800
600
400
200
0
1
2
3
#UEs/cell
200 400 600 800 1000 1200 1400 1600
Aggregated Cell Throughput [kbps]
4
5
10
6
7
8
9
UMTS composite channel
model
FTP traffic model (2 Mbyte
upload, 30 seconds thinking
time)
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
41
Slide 41

Single User Performance in HSUPA
3500
2ms, 1Tx
10ms, 1Tx
Average user throughput
(RLC layer) for different
channel profiles
1 UE in the network
3000
1 target HARQ transmission
Average User Throughput [kbps]
2500
2000
1500
1000
500
For AWGN channel
conditions:
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)
0
AW GN PedA3 PedA30 VehA30 VehA120
Scenario
E.g. due to restrictions
from RLC layer (window
size, PDU size)
42
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 (dBm) = α•PL (dB) + P0 nominal (dBm)
Target SINR on PUSCH is now a function
of the UE’s path loss:
PL dB : pathloss, estimated from DL reference signal
P0 nominal (dBm) = Γ nominal (dB) + I tot (dBm)
Sum of SINR target Γ nominal and total interference
I tot 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
SINR (dBm) = Γ nominal (dB) + (1–α)•PL (dB)
Slide 43
43

Interference Coordination - Flexible Frequency Reuse
Cell edge
Reuse > 1
Cell centre
Reuse = 1
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
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
44
Slide 44

Heterogeneous Networks
Core
Network
Backhaul
Relay
Backhaul
Need for Flexible and Low-
Cost Network Deployment
Using Mix of Macro, Pico,
Relay, RRH and Home eNBs
Internet
HeNB
Pico
Macro
Relay
Pico
Pico
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
45
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 pico
for 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
Pico
Macro
Pico
46
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
CSG
Macro
CSG
47
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
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
48
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
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
49
Slide 49

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
Invoke Indication M ENUMERATED
(ABS
Information, …)
Semantics description
–
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
IE/Group Name Presence Range IE type and reference Semantics description
DL ABS status M INTEGER (0..100) Percentage of ABS
resource allocated for
UEs protected by ABS
from strong inter-cell
interference.
50
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
Slide 50