VTC fall presentation in Nanjing 2016. investigate the LTE signalling in C-RAN envirnoment

1. A C-RAN Architecture for LTE Control
Signalling
Imad Samman , Angela Doufexi &Mark Beach
Imad.Al-samman@bistol.ac.uk

2.  Introduction .
 C-RAN Size Constraints.
 Proposed C-RAN Network architectures.
 Control Signalling in C-RAN D-MME
 Control Signalling in C-RAN C-MME
 Results Analysis.
 Conclusion.

3.  The emerge of Software Define Network(SDN) as a networking archetype in wired
networks through its OpenFlow(OF) protocol and attractive features in separating the data
and control planes has inspired researchers in both academia and industry to develop and
deploy this architecture for wireless networks.
 There have been many recent studies on the advantages of applying SDN in LTE that have
only considered the Distributed Radio Access Network (D-RAN) architecture.
 This paper will investigate the potential performance gain of applying SDN LTE in cloud
RAN (C-RAN) deployment and compare it against D-RAN related studies.
 In this paper we present new architectures based on what is stated above and perform the
overall signalling load analysis. The objective is to determine a better architecture in terms
of lower signalling load.

4. Virtual BS Pool
Optical Network
C-RAN is composed of:
 Remote Radio Units
(RRUs) plus antennas,
located at the remote site.
 Optical transport network
connecting the RRUs and
BBU pool, of high bandwidth
and low-latency.
 Baseband Unit Pool (BBU
Pool), composed of high performance
programmable
processors and real-time
virtualisation technology.
(Source: CMRA,2013)

5. SGW-D
SGW-C
Control Plane
Data Plane
Policy Control
And Charging
Rules Function
(PCRF)
Home
Subscriber
Server (HSS)
MME
OF -Controller
SGW-D
Gateway
(P-GW)
Packet Data
OpenFlow
protocol
S5 (GTP-U)
API
eNB
UE
eNB
S5 (GTP-C)
S1 (GTP-U)
Internet/PDN
GW-U
GW-U
GW-U
eNB
eNB
UE
OF -Controller
MME SGW-C PGW-C
HSS PCRF
Control Plane
User Plane
Several architectural designs are introduced to integrate SDN into LTE network, SoftCell
[1] is high level SDN approach, it is based on replacing all legacy entities with commodity
middles boxes and OF switches.
Moreover the authors in [2] have adopted a partial SDN approach based on decoupling the
control and data planes at the SGW that turns into an advanced OF switch with a capability
of encapsulating and de-capsulating GTP packets.
While authors in [3] have proposed complementary vision which is fully realised in
Openflow where the PGW-C has been decoupled and virtualised as an application running
on top of the OF controller. ) In the same way the PGW-U will be left only as advanced
OF switch. This methodology is based on complete separation between the control and
data planes as fig 2.3 demonstrates

6. Antenna
Rx Tx
Antenna
Rx Tx
1.DATA
3. ACK/
NACK
Round trip
latency for
HARQ = 3ms+ TA
2.2 BBU
Processing
2.eNB
Processing ≤ 3ms
2.1 Rx antenna
to Modem (CO)
2.3 Modem(CO) to
Rx antenna (cell
site)
RRH
BBU
Antenna
TxRx
BBU
(L1,L2,L3)
Fronthaul(Fib
er Active
equipments
Tprop
Subframe
1(ms)
DATA
ACK/
NACK
 The UE in LTE should receive
ACK/NACK from eNB in
three sub-frames after UL data
to comply with HARQ
protocol.
 BBU design need to accelerate
DL process to be in the range
of 2.7 ms .
 Considering all related units
processes, the max fibre
distance between the BBU and
the RRH is 24.6 km .

7. PGW-C
SGW-C
OF
Controller
BBU
MME
CONTROL
PLANE
RRH
DATA
PLANE
BBU
RRH
PGW-C
OF
Controller
MME
SGW-C
Wi-Fi
hotsp
ot
(802.
11
RAN
PDN/
INTERNET
Wi-Fi
hotsp
ot
(802.
11
RAN
PDN/
INTERNET
 Two architectures are proposed:
A. C-RAN distributed MME for the study area .
B. C-RAN centralised MME for each single CRAN macro
cell .
(1) D-MME-CRAN (Sc.1): This architecture is based on
integration of the MME functionality within BBU in
the same data centre, in this aspect each C-RAN is
seen as single cell with its own BBU and MME.
(2) C-MME-CRAN (Sc.2): is intuited on central MME
rather than distributed, the functions of the central
MME are virtualised as an application like SGW-C,
PGW-C in former analysis where all of them run on
top of OF controller and communicate with its API.
 Five main signalling procedures are investigated:
1. Initial attachment.
2. UE-generated Services.
3. Network-Generated Services.
4. HandOver (HO).
5. Tracking Area Update (TAU).
A. D-MME-CRAN (Sc.1) B. C-MME-CRAN (Sc.2)

8. UE
HSS
Initial UE
msg
Attach Req
OF
(Create Session
Request)
OF(Modify Bearer
Req)
OF(Modify Bearer
Res)
OF
(Create Session
Response)
HSS Authentication
Update Location
RRC Connection
Reconfiguration
RRC Connection
Reconfiguration Complete
RRH BBU+MME
OF Controller
+SGW+PGW
OF
switch
User Data
UE
Attach Request
Identify Request
Modify Bearer
Response
User Data
Attach
Request
Identify Response
Identity Req /Res
Ciphered Options Req
Ciphered Options Res
Delete Session Req
Delete Session Res
Create
Session Req
Create
Session Req
Create
Session Res
Create
Session Res
Init Context
Setup Req/
Attach
Accept
RRC Connectino
Reconfiguration
RRC Connectino
Reconfiguration CompleteInit Context
Setup Resp
Direct Transfer Attach
Complete Modify
Bearer Req Modify
Bearer Req
Modify
Bearer
Response
HSS Authentication
Update Location
eNB MME Serving
GW
PDN
GW HSS

9. UE
Measurement
Control
Measurement Reports
UL allocation
HandOver
Decision
Handover
Request
Handover
Request Ack
Admission
Control
Dl allocation
RRC Conn. Reconfig inc
mobility confirmaion
Detach from old cell
and sync to new cell
SN Status
Transfer
Syncronisation
UL Allocation + TA for the UE
RRC Conn Reconf Complete
Path Switch
Request
Modify
Bearer
Request
Modify Bearer
ResponsePath Switch
Request AckUE Context
Release
Release
Resources
Switch DL
Path
Source
eNB
Target
eNB
MME
Serving
Gateway
L3
Signalling
L1/L2
Signalling
User Data
DL allocation L1/L2 signalling
UE
OF Controller
+SGW+PGW
RRC Reconfiguration including
mobility confirmation
Syncronisation
UL Allocation + TA for the UE
RRC reconfiguration complete
OF Packet_out
(Modify Bearer
Response)
OF
Packet_out
Switch DL
Path
HandOver
Decision
RRH BBU+MME
OF
switch
OF Packet_in
(Modify Bearer
Request)
Detach from
the old Cell
HO ReqHO Ack
SN Status
Transfer
Path
Switch
Request
Path
Switch
Request
Ack UE
Context
Release
LTE Legacy Arch LTE C-RAN Dist- MME

10. RRH
Deliver buffered and in
transit packets to target
RRH
BBU 1
OF Controller
+SGW+PGW+M
ME
BBU 2 OF Switch
Measurement
Reports
OF (HO
Required)
HO Command OF (HO
Required)
OF (HO
Request)
OF (HO
Request Ack)
OF (eNB
status transfer)
OF (MME
Status
Transfer)
HO Confirm
HO Notify
HO Packet-
Out
HO Packet-
Out
UE
Detach from the old cell
and sync to the new cell
Buffer packets from Source
RRH
RRH

11. 1000 1500 2000 2500 3000
1
2
3
4
5
6
7
x 10
7
Legacy support of X2 uni
Sc.1 support of X2 CRAN1
Sc.1 support of X2 CRAN2
Sc.1 support of X2 CRAN3
Sc.1 support of X2 CRAN4
Sc.2 support of X2 CRAN1
Literature OF DRAN
TotalSignallingLoad(messages/hour)
The considered Area ( km² )
 First analyzing case is based on increasing
the area of the study region, the area range
to analyze spans between [800...3000] km²
land excluding water.
 Four topologies forms are assumed. Where
the total number of RRHs is 108 regardless
what form type is used.
 Each form has different number of C-
RANs and RRHs within each.
 The evaluation is calculated based on X2
interface for inner HO and S1 outer HO
 Total signaling load is the sum of the five
aforementioned procedures.
 Scheme.1 of CRAN1 topology
experiences the least amount of the load
followed by the second form CRAN2,
nevertheless Scheme.2 CRAN1 shows
better performance than the rest of
topologies.
 CRAN1 has the highest number of RRHs
in single CRAN which means least
amount of related TAU and outer HO
signalling load.
CRAN
FORM
No. CRAN No. RRH in one CRAN
CRAN 1 3 C-RANs 36 RRHs
CRAN 2 4 C-RANs 27 RRHs
CRAN 3 6 C-RANs 18 RRHs
CRAN 4 9 C-RANs 12 RRHs

12. 10 20 30 40 50 60 70 80 90
0.5
1
1.5
2
2.5
3
x 10
6
Legacy LTE Network Support X2
Scheme.1 Support X2
Scheme.2 Support X2
Literature OF DRAN
Tracking Area Size
TotalSignallingLoad(messages/hour)
 Another metric to investigate is the TA size,
increasing the TA size will have an impact
on scenario 2 and OF-DRAN thanks to the
decrease of TAU rate as Fig 2.2 emphasizes.
 Scheme.1 doesn’t demonstrate any
amendment as it only relies on the number
of RRHs in single C-RAN as a TA size.
 Fig 2 further indicates that
scheme.1performs the optimum load than
scheme.2, literature OF DRAN and
definitely the legacy by saving up to 17%,
36% and 62.8% respectively of signalling
load for TA size of 6.
 The lesser the load for our legacy arch
which converges at very high TA size with
scheme.1 and shows no difference at all.

13.  In this paper we presented new C-RAN architectures by utilizing both a
SDN LTE architecture and C-RAN topology.
 Two new schemes have been proposed : C-RAN.D-MME and C-RAN.C-
MME architectures in order to reduce overall control signalling load.
 The paper considered multiple network parameters such as cell area and
tracking area update size. The proposed architectures are shown to offer
improvement in the overall signalling load as compared to the existing
literature and previous suggested topologies.
 The impact of tracking area size on system performance has been
investigated. We observed from our analysis that for small TA sizes, the
C-RAN.D-MME gives the best performance while C-RAN.C-MME is
better for higher TA sizes.

14. [1] X Jin, L E Li, L Vanbever, J Rexford, Softcell: scalable and flexible cellular core network architecture.in
Proceedings of 9th ACM International Conference on emerging Networking Experiments and Technologies (CoNEXT), (ACM,
California, USA, 2013), pp. 163–174.
[2] MR Sama, SBH Said, K Guillouard, L Suciu, Enabling network programmability in LTE/EPC architecture using
openflow. in Proceedings of 12th IEEE International Symposium on Modeling and Optimization in Mobile, Ad Hoc, and
Wireless Networks (WiOpt), (IEEE, Tunisia, 2014), pp. 395–402.
[3] VG Nguyen, Y Kim Proposal and evaluation of SDN-based, Mobile packet core networks. J Wireless Com
Network, 2015.

15. Questions &
Discussion
Imad Al-Samman
Imad.Al-samman@bistol.ac.uk