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Wired or wireless?
When it comes to backhauling high-speed cellular networks,
should operators choose fibre or microwave? DR. SERGEY
MAKOVEJS discusses the pros and cons of each technology.
T
he changes in the telecommunications
consumer market, mainly the proliferation
of smartphones and tablets with
associated requirements for higher speed, are
driving the adoption of new access technologies,
such as high-speed 3G (HSPA and CDMA2000)
and LTE. The introduction of the iPhone in 2007
radically and irreversibly changed the game while
tablets such as the iPad and Android OS have
further contributed to a dramatic reshuffling of the
mobile market toward more data-driven traffic1.
This has led to the decline of copper T1
(1.55Mbps) and E1 (2Mbps) lines in mobile
backhaul, since their speeds became inadequate
for backhauling faster 3G and LTE signals.
Stacking multiple T1/E1 lines to increase the
aggregate capacity is not an economically viable
solution, and so the replacement of copper in
mobile backhaul therefore appears to be imminent.
The steady displacement of copper over the next
few years is also confirmed in a report published
by Infonetics. It says that copper will constitute
“five per cent” of worldwide backhaul connections
by 2016 – the rest will be almost equally divided
between fibre and microwave2. Indeed, these are
unanimously considered to be the technologies of
the future to support an increasing number of
bandwidth-hungry services.
The co-existence of fibre and microwave is driven
by two main considerations. On the one hand, fibre
is generally regarded as a preferred medium due to
virtually unlimited capacity (hence complete futureproofing), long reach, and guaranteed service
availability. On the other hand, microwave is often
viewed to be cheaper and faster to deploy, especially
Dr. Sergey
Makovejs,
Market
development
manager,
Corning
Optical
Fiber
in areas where optical fibre cable deployment is an
expensive and lengthy process. So do these
perceived advantages and limitations of fibre and
microwave represent the reality?
Capacity
Fibre does indeed provide a very large capacity. As
an example, long-haul commercial optical transport
systems (like those used in the mobile network
backbone) can provide up to 8.8Tbps of bidirectional
capacity per fibre pair. In mobile backhaul, the
characteristics of fibre transceivers are typically
governed by Ethernet standards to obtain the desired
cost-effectiveness (USD40-300 for a 1Gbps Ethernet
transceiver, and USD500-2,700 for a 10Gbps
transceiver3). Higher speed 40Gbps and 100Gbps
Ethernet transceivers are also available from some
vendors at a higher price. Further increases in
capacity can be achieved by lighting multiple fibre
pairs in the cable, therefore making fibre a futureproof medium for mobile backhaul.
It must be noted that over the years, tremendous
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progress has been achieved in increasing the capacity
10km rated
40km rated
80km rated
120km rated
of point-to-point and point-to-multipoint microwave
systems. While traditional microwave platforms oper131
161
1Gbps
39
275
ated at approximately 155Mbps, the latest generation
10Gbps
445
1,255
2,695
of equipment can reach 1-4Gbps (depending on the
Figure 2: Cost in USD of fibre Ethernet transceivers for different data rates and different reach (from a
configuration and the technology used). Although
particular distributor, for example)3.
these capacities still lag behind those achievable by
fibre, 1-4Gbps is sufficient for backhauling 3G and
LTE signals from the cell tower. However, as we
the desired capacity is achievable at all times,
as direct cable burying (plouging), machine trenching
move closer to the backbone network, higher capacpotentially leading to disruption of some real-time
(in areas not suitable for ploughing), and aerial
ities may be needed to accommodate the aggregate
applications such as video transmission.
deployment could be used instead and at a cost of
traffic from multiple cell towers (see figure 1 below).
approximately USD7, USD14 and USD4 per metre,
The likely path towards increasing microwave
respectively. The exact cost will depend on other
Costs
system capacity is to adopt a higher-density moduvariables, such as soil condition, type of terrain, etc.
lation scheme (such as 4096-QAM), ‘4x4’ MIMO,
For both fibre and microwave backhaul, the
In general however, the cost of fibre versus microand to utilise larger frequency bands. But the full
overall costs consist of several components. For
wave backhaul must be considered on a country-byimpact of applying those techniques is unclear:
microwave, operators will need to invest in: radio
country and project-by-project basis. There are many
it is likely that denser modulation will reduce the
equipment; building a tower to mount the outdoor cases when microwave is cheaper to deploy than
link budget, causing reduction in reach, service
equipment (around USD50,000); building an
fibre and should therefore be used in the backhaul
availability or both; ‘4x4’ MIMO will contribute
aggregation hut in the case of a split-mount
when cost is the main concern. However, microwave
to the system cost due to the increased number of
equipment configuration (around USD100,000may not always be the cheaper option – particularly
antennae; and larger frequency bands may increase
150,000); and recurring spectrum costs.
in areas where strong rains necessitate the use of
opex due to higher recurring spectrum costs.
For fibre backhaul, the costs include: transceivers
multiple microwave hops to achieve the desired
(almost negligible); the fibre cable; cable deployment; distance, thus requiring the build-out of frequently
and building the aggregation hut which is the same
spaced backhaul towers at a higher overall cost.
Reach and service availability
as microwave. The cost of deployment is one of the
Another aspect that needs to be accounted for
Fibre backhaul can provide a guaranteed reach
largest contributors to the overall outlay, and consists when building a mobile backhaul network is power
of ~100km, which is sufficient for most mobile
of right of way costs as well as the physical
consumption. Two Ethernet transceivers (required
backhaul connections. Similarly to the data rate,
deployment. While the former is governed by the
for bidirectional transmission) consume around 2W,
the reach is determined by transceiver grade (see
regulations within a specific country (and is typically compared to a few tens of Watts for an equivalent
figure 2). Fibre also provides guaranteed service
outside the control of a mobile network operator),
outdoor microwave transmit-receive system. While
availability where the backhaul can be designed to
the latter could be controlled through the selection
this difference per backhaul link may appear to be
provide both main and protection routes in order
of a particular fibre cable deployment technique.
small, it quickly escalates for the whole network
to provision for a potential cable cut.
Microtrenching, horizontal directional drilling
with hundreds of backhaul connections. The
Contrary to fibre transmission, microwave
(HDD) and manual trenching are well suited for
difference becomes even more dramatic for an
transmission experiences frequency dependent
urban areas, and cost approximately USD50,
LTE network, where more cells (and hence more
impairments in the presence of rain, with E-band
USD37 and USD25 per metre respectively. The
backhaul connections) are needed to cover a given
spectrum (i.e. 70-80GHz) affected more than
term ‘microtrenching’ is used to emphasise the
territory compared to a 3G network due to the
traditional frequencies (6-38GHz). This means that small size of trench in the ground where the cable
lower coverage radius of LTE cells.
for the same capacity and service availability, the
is deployed, and is typically in the range of 1.5Finally, the presence of fibre in the vicinity may
microwave transmission will have a lower reach
5cm in width and 20-40cm ‘in depth’. HDD on
affect the operator’s decision to deploy even more
in areas with frequently occurring monsoons,
the other hand, is a completely trenchless cable
cable. For example, fibre could be a preferred
compared to less rainy regions.
deployment method. Here, an inner duct is placed
medium for small cell backhauling if it already
In practice, radio planning engineers prefer to
in a drilled path and the cable is subsequently
has a point of presence in a building. In this case,
set the required reach and service availability, and
pulled through. Both techniques are extremely
a small cell could be placed on the building wall,
let the system adaptively switch the modulation
effective in areas where significant disruption of
so that the fibre infrastructure could be shared
between high spectral-efficiency (high capacity) and
surface is undesirable. However, if cost is the main between fixed and mobile services.
low spectral efficiency (low capacity) as the rain
concern, manual trenching could be used instead.
Overall, the industry consensus is that microwave
intensity increases. Thus, there is no guarantee that
In rural areas, more cost-effective techniques, such and fibre will co-exist in mobile backhaul, at least
over the next several years. There is no single golden
rule that will determine when to use fibre and when
to use microwave. Instead, all considerations such as
cost, required capacity, distance, service availability,
future upgrades and regulatory environment need
Backbone
to be taken into account. However, the growing
demand for even higher bandwidth in the access
part of the network is likely be followed by
the adoption of next-generation LTE Advanced
technology, therefore pushing fibre even deeper into
access to satisfy the required backhaul capacities. !
Low capacity
Medium capacity
High capacity
References
Fibre – yes
Fibre – yes
Fibre – yes
1
Internet, mobile and the cloud – a dynamic convergence,
Microwave – yes
Microwave – maybe
Microwave – no
Coady Diemar 2012
2
Figure 1: Schematic diagram of a mobile backhaul network. Thick lines illustrate the fact that higher
Mobile backhaul equipment and services, Infonetics 2012
3
link capacity is required as more signals are aggregated closer to the backbone network.
http://datainterfaces.com/Fiber_Transceivers.aspx
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SOUTH ASIAN WIRELESS COMMUNICATIONS Q4 2012