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LTEHaul: SDN-based mobile backhaul
ew technologies are emerging as
the LTE and LTE-A standards go
commercial, including coordinated
multiple point (CoMP) and evolved
multimedia broadcast multicast service (eMBMS),
both defined in 3GPP R11. CoMP is used to
mitigate inter-cell interference, improve cell
capacity, and enhance network performance
through coordination of both transmission and
reception among multiple eNodeBs; eMBMS
provides point-to-multipoint interfaces, through
which operators can use their existing spectrum
and mobile networks more efficiently so that high-
2012 was a watershed year for LTE commercialization. Its end saw 145 commercial LTE networks in operation,
covering some 43.7 million subscriptions, according to the Global mobile Suppliers Association (GSA). These growing
networks bear revolutionary services for a diverse field of scenarios, posing high requirements on backhaul.
N
By Sun Xinwu
quality/ bandwidth-hungry services are intact.
With legacy GSM/UMTS backhaul, all base
station data converges at the BSC/RNC nodes for
further processing, and this makes for a physical
division between the backhaul and core networks.
In addition, the capacity for these base stations
has a general limit of 42Mbps, which lags behind
user demand for data services. LTE/LTE-A,
with its greater bandwidth and more integrated
architecture, is solving these problems.
Huawei’s LTEHaul solution ensures smooth
interoperations among the fronthaul, backhaul, and
core network layers, while separating the bearer & SoftMobile
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control functions via SDN and centrally managing
and automatically configuring the cell site gateway
(CSG) and small cell site gateway (SCSG) on
the aggregation site gateway (ASG). This helps
operators simplify network O&M, reduce OPEX
by up to 60%, and enhance service TTM.
New features of LTEHaul
To meet the booming demand for throughput
(150Mbps per eNodeB in a certain case), LTE must
operate at higher frequency bands (2.6/3.5GHz)
in dense urban areas and offer a peak rate ten times
that for 3G. However, to achieve the same coverage,
an operator needs ten times as many eNodeBs as
base stations/NodeBs, while a high-frequency radio
system must encompass hotspots and blind spots,
creating additional fronthaul requirements.
LTEHaul architecture has two major differences
from GSM/UMTS backhaul (Figure 1). First, LTE
fronthaul is located at the downstream network
layer after backhaul, and second, the BSC/RNC
nodes are no longer present, enabling a backhaulcore connection.
Indoor & outdoor hotspot
coverage
With GSM/UMTS, fronthaul is normally
located at a lower network layer, but with
LTEHaul, it is the last mile, covering indoor (Wi-Fi
& small cell) and outdoor hotspots.
Wi-Fi indoor fronthaul is typically required at
mobile oases (hotels, cafes, airports). Supplemented
b y G S M / U M TS , t h i s a c c e s s s c e n a r i o i s
characterized by low mobility, a large amount of
data, and no voice. As access media vary (P2P
fiber/copper/PON) and power supply for RRUs is
required, the fronthaul in this case must be mediaagnostic and enable Power over Ethernet (PoE)
functionality. Furthermore, bearer devices should
be small, easy-to-install, energy efficient, and
maintenance free, so that OPEX is held in check.
Small cell indoor fronthaul is primarily used
for shopping malls. It is characterized by high
mobility and a large amount of voice and data over
a broad area. To ensure quick service provisioning
and high-quality service experience, the fronthaul
network should allow remote RRU power supply,
hierarchical quality of service (HQoS), and access
by any medium, while bearer devices should be
easy-to-install, maintenance-free, and plug-andplay to reduce costs.
Small cell outdoor fronthaul applies to crowded
outdoor scenarios, such as bustling streets, city
plazas, and open-air cafes. It is characterized by heavy
voice and data traffic, and its challenges include site
acquisition and access diversity. The access media in
place must be leveraged, and bearer devices should
be ecofriendly, have a minimal footprint (walls
and poles work well), and feature surge protection
and resistance to the elements. If fixed access is
unavailable, full outdoor microwave can be used,
though it should be deployed (with parabolic
Figure 1 E2E LTEHaul architecture
Core
Fronthaul
Backhaul
LTE-A ready: Giga small cell access w/any media, 10GE macro cell access, 100GE to EPC, low latency (80μs/hop).
SDN-based mobile backhaul: Introduces SDN to mobile backhaul, transforms CSGs into dumb boxes.
Low deployment costs: Integrated installation with small cells.
Low OAM costs:Minimal site visits, automatic service configuration, real-time monitoring of E2E network performance.
HSS
RRU
BBU
EPC
Small cells
PS/CS core
Wi-Fi
Macro cells
SRC
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antennas for rapid focusing) and commissioned (USB
configuration) quickly, and be easy to maintain.
Converged CSG backhaul
For a GSM/UMTS network, a cell site gateway
(CSG) will serve only one base station, while an
LTE CSG aggregates traffic from various hotspots.
Taken on its own terms, this sounds great, but
it calls for measures that ensure greater system
reliability, including carrier-grade 1+1 10GE ring
protection, 1+1 backup for system control units,
and multi-node failure protection.
VoLTE’s commercial maturation is accelerating
GSM/UMTS spectrum refarming, and this poses
a challenge to network scalability. For a blade
RRU solution that supports multi-band & multimode refarming (seven bands, four modes), the
CSG nodes must have six service slots and a large
switching capacity (120Gbps), as well as smooth
LTE-A evolution capability (from 400 to 1000Mbps
per eNodeB). New VoLTE services also require CSG
node support for hierarchical QoS, so that multiservice scheduling and quality are guaranteed.
Since they will share the same cabinet as the
BBU, a CSG device should also share the power
and network management system (NMS), all
while being plug-and-play, so that base station
deployment stays timely.
ASG backhaul
As traffic balloons and base stations move to IP,
FMC-enabled nodes for IP backhaul are migrating
downstream to the legacy transmission equipment
rooms that housed OLT/SDH devices. Cabinets
in these rooms are typically 300mm deep and
accommodate equipment that converge fixed and
mobile traffic, so an aggregation site gateway (ASG)
must be co-sited with said OLT/SDH devices,
sharing the cabinet, power supply, and NMS so
that network deployment/cost is more efficient. To
enable FMC service backhaul, ASG nodes should
also feature a large capacity (over 480Gbps) and
integration of BRAS/SR/VPN PE functionality, all
while being ready to support new services (such as
eMBMS multicast/L3/IPv6).
The increasing scale and complexity of LTEHaul
poses a challenge to O&M, but ASG nodes can
aggregate traffic from macro & small sites while
supporting centralized & intelligent management
of remote modules and CSG SDN, through
which operators can simplify network architecture,
configuration, and O&M.
Core layer – E2E service
provisioning and O&M
As stated previously, BSCs/RNCs divide
the backhaul and core layers in a GSM/UMTS
network, and yet this boundary is fading with LTE,
as BSC/RNC functionality is distributed across
eNodeBs and evolved packet cores (EPCs). In
this context, E2E service provisioning, protection
switching, and fault diagnostics for eNodeBs and
EPCs need to be redefined. Traditional backto-back backhaul fails to deliver 50ms cross
autonomous system (AS) protection switching,
lacks E2E troubleshooting, and prolongs service
delivery, so a ‘PE Labeled MPLS + Hierarchical
VPN (HVPN)’ solution is needed.
Numerous mobile operators are exploring LTE/
LTE-A enterprise virtual private network (VPN)
services. PE labeled MPLS + HVPN for LTEHaul
would be an optimal choice as it supports sub-
50ms cross-AS protection switching and is easily
scalable between eNodeBs and EPCs. With E2E
service configuration and fault diagnostics, this
solution offers efficient service provisioning and
troubleshooting for enterprise VPN services.
Evolution to SDN
Evolution to LTEHaul SDN architecture may
span three phases. The first is the building of an AllIP architecture based on network processors (NPs),
while the second is the assurance of centralized &
intelligent management of remote modules, with
simplified network O&M and service configuration
for emerging LTE/LTE-A services. And finally, a
unified control platform is needed to smoothly work
with self-optimization network (SON) and single
radio controller (SRC) technology.
Large-scale commercial deployment of LTE/
LTE-A is spawning service opportunities while
posing challenges to mobile backhaul. Being wellsuited to the aforementioned coverage scenarios,
Huawei’s LTEHaul solution helps bridge the
backhaul divide, enabling smooth evolution to
LTE-A.
Editor: Michael huangzhuojian@huawei.com