ETSI GS mWT 002 V1.1.1 (2015-08)

millimetre Wave Transmission (mWT); Applications and use cases of millimetre wave transmission

DGS/mWT-002

General Information

• Status: Published
• Publication Date: 24-Aug-2015
• Technical Committee: mWT - millimetre Wave Transmission
• Current Stage: 12 - Completion
• Due Date: 29-Aug-2015
• Completion Date: 25-Aug-2015

Standards Content (Sample)

GROUP SPECIFICATION
millimetre Wave Transmission (mWT);
Applications and use cases of millimetre wave transmission
Disclaimer
This document has been produced and approved by the millimetre Wave Transmission (mWT) ETSI Industry Specification
Group (ISG) and represents the views of those members who participated in this ISG.
It does not necessarily represent the views of the entire ETSI membership.

2 ETSI GS mWT 002 V1.1.1 (2015-08)

Reference
DGS/mWT-002
Keywords
application, millimetre wave, mWT, transmission,
use case
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3 ETSI GS mWT 002 V1.1.1 (2015-08)
Contents
Intellectual Property Rights . 4
Foreword . 4
Modal verbs terminology . 4
Executive summary . 4
Introduction . 5
1 Scope . 7
2 References . 7
2.1 Normative references . 7
2.2 Informative references . 7
3 Abbreviations . 8
4 Millimetre wave spectrum technology: Overview and benefits . 9
5 Applications and use cases: Overview . 11
6 Applications and use cases: Description . 12
6.1 Macro-cell mobile backhaul application . 12
6.1.1 Use Case 1: Mobile network upgrade (existing cells) . 12
6.1.2 Use Case 2: Mobile network expansion (new cells) . 13
6.2 Small-cell mobile backhaul application . 14
6.2.1 Use Case 1: Rooftop-to-street/Street-to-street connectivity . 14
6.2.2 Use Case 2: Multi-hop (in-clutter extensions) . 15
6.3 Fronthaul for small cells application . 16
6.3.1 Use Case 1: Rooftop-to-street/Street-to-street connectivity . 16
6.3.2 Use Case 2: Multi-hop (in-clutter extensions) . 17
6.4 Fronthaul for macro cells application . 18
6.4.1 Use Case 1: Mobile network upgrade (existing cells) . 18
6.4.2 Use Case 2: Mobile network expansion (new cells) . 19
6.5 Next-generation mobile transmission applications . 20
6.6 Fixed broadband application . 20
6.6.1 Use Case 1: Wireless to the home . 20
6.6.2 Use Case 2: Wireless to the cabinet . 21
6.7 Temporary infrastructure application . 22
6.7.1 Use Case 1: Special events . 22
6.7.2 Use Case 2: Public safety . 23
6.8 Business-to-business application . 23
6.9 Business-to-government application . 24
6.9.1 Use Case 1: Broadband connectivity to governmental buildings. 24
6.9.2 Use Case 2: Public Wi-Fi hotspot backhaul . 25
6.10 Redundant network application . 26
6.11 Video surveillance backhaul application . 27
6.12 TV signal relay application . 28
7 Millimetre wave spectrum technology enablers for transmission applications and use cases . 28
8 Conclusions . 30
Annex A (informative): Authors & contributors . 32
History . 33

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Intellectual Property Rights
IPRs essential or potentially essential to the present document may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
server (http://ipr.etsi.org).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Foreword
This Group Specification (GS) has been produced by ETSI Industry Specification Group (ISG) millimetre Wave
Transmission (mWT).
Modal verbs terminology
In the present document "shall", "shall not", "should", "should not", "may", "need not", "will", "will not", "can" and
"cannot" are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of
provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
Executive summary
Modern consumers, individuals and corporate entities, request for advanced personalized services to perform their daily
activities. Social interactions, entertainment, news, HD video streaming, distant learning, e-health, commercial
transactions, e-business, cloud services, M2M applications represent a sample of a countless list of digital services that
are requested from either stationary or moving end-users. Whilst different growth rates of broadband data are
envisioned per region due to the existence of local idiosyncrasies, such as broadband market maturity, operators' pricing
policy, consumers' psychographic characteristics and buying patterns, degree of access to the latest technological
advancements, overall macro-economic climate and so forth, the demand for packet-based broadband data will continue
to soar both in mobile and fixed access domains.
In order to address the increasingly diversified needs of digital natives and enterprises of the 2010s and onwards,
telecommunication networks will have to be modernized at different segments. Fixed transmission networks represent a
critical part of this effort and they play a pivotal role to achieve the target end-to-end KPIs per service and enhance end-
users' QoE.
A variety of wireline as well as wireless technologies are available to build transmission infrastructures and usually a
mixed environment of physical media is adopted. While optical fibre is perceived as the physical medium with the top
performance, there are techno-economic factors that make installation or even extension of optical fibre network not
always the most appropriate solution. Hence, wireless technologies represent today a significant or even a dominant
percentage of various operators' transmission networks to serve efficiently the increasing upward trend for providing
data-hungry applications.
While microwave solutions at traditional bands are more or less employed by all kinds of service providers (mobile,
fixed), it becomes clear that moving to millimetre wave frequency bands, where underutilized massive bandwidth is
available, will assist to deliver transmission services of equal to optical fibre performance avoiding the constraints that
the latter might impose at particular scenarios. In this sense, millimetre wave frequency bands can be used in an
immense number of current and future high-speed wireless transmission applications.
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Introduction
Information society's foreseeable demand for additional broadband data consumption is further augmented by the high
uptake of faster connections and the popularity of powerful data devices. In the mobile access domain, technology
advances as a result of the ceaseless evolution of 3GPP standardizations that has taken mobile broadband to the next
level. Similarly, at fixed access domain, increased broadband speeds become available as technologies, like fibre to the
home (FTTH) or business, VDSL variants and so on are adopted. Furthermore, use of devices like smart-phones,
802.11ac routers will contribute to increase of broadband applications' usage, like video streaming, web surfing, etc.
The above dynamic situation puts more pressure on transmission networks, in order for services to be delivered tailored
to consumers' expectations. While from client perspective services' data rate, response and uninterrupted availability
constitute key metrics, from operators' experience additional parameters have to be carefully thought and designed to
achieve the desired overall performance. In this sense, the challenges for the next generation transmission networks are
multiple and are related to factors, such as:
• Network architecture, topology and density.
• Throughput.
• Range and service availability (with reference to wireless transmission networks).
• Latency and jitter.
• Interference management (with reference to wireless transmission networks).
• Network automation.
• Networking and synchronization features for advanced packet-based/mobile networks.
• Improved match between spectrum resource consumption and consumers' traffic patterns requirements.
• Equipment physical form factor.
• Power consumption.
• Security for data transport.
In the light of the expected emerging broadband communication demands and the increased challenges for the next
generation transmission networks, ETSI Industry Specification Group (ISG) on millimetre Wave Transmission (mWT)
aims to be a worldwide initiative with global reach that will facilitate the use of [i.1]:
• the V-band (57 - 66 GHz);
• the E-band (71 - 76 & 81 - 86 GHz); and
• - in the future - higher frequency bands from 50 GHz up to 300 GHz.
ETSI ISG mWT envisions that established and emerging broadband transmission services would benefit from high-
speed wireless transmission that millimetre wave spectrum technology can accomplish.
It should be noted that although the addressed by ETSI ISG mWT spectrum ranges between 50 GHz and 300 GHz
bands, as Figure 1 [i.1] shows, presently the 57 - 66 GHz, 71 - 76 GHz and 81 - 86 GHz bands or parts of them are open
at various, but not all, countries across the world for broadband wireless fixed services. Moreover, as per
Recommendation ITU-R F.2107-2 Report [i.2], frequencies up to 134 GHz band were also approved.
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6 ETSI GS mWT 002 V1.1.1 (2015-08)

…300
Figure 1: Millimetre wave spectrum (50 GHz to 300 GHz)
The present document, as part of ISG mWT framework, intends to propose the wireless transmission applications and
use cases that can be addressed by millimetre wave spectrum, focusing on frequency bands from 50 GHz up to 300 GHz
(or wavelengths from 6 mm down to 1 mm).
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1 Scope
The purpose of the present document is to provide information on the following topics:
• Millimetre wave spectrum technology overview.
• Millimetre wave spectrum technology key performance benefits.
• Potential transmission applications and use cases for millimetre wave spectrum technology.
• Key requirements per transmission application/use case of millimetre wave spectrum technology.
• Enablers of millimetre wave spectrum technology per transmission application/use case.
2 References
2.1 Normative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
reference document (including any amendments) applies.
Referenced documents which are not found to be publicly available in the expected location might be found at
http://docbox.etsi.org/Reference.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are necessary for the application of the present document.
Not applicable.
2.2 Informative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
reference document (including any amendments) applies.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are not necessary for the application of the present document but they assist the
user with regard to a particular subject area.
[i.1] An Introduction to mWTISG.
NOTE: Available at
https://portal.etsi.org/Portals/0/TBpages/mWT/Docs/Introduction%20to%20mWT%20ISG%20v1-0.pdf.
[i.2] Report Recommendation ITU-R F.2107-2 (11/2011): "Characteristics and applications of fixed
wireless systems operating in frequency ranges between 57 GHz and 134 GHz".
[i.3] ECC Recommendation (09)01: "Use of the 57 - 64 GHz frequency band for point-to-point fixed
wireless systems".
[i.4] ECC Recommendation (05)07: "Radio frequency channel arrangements for fixed service systems
operating in the bands 71-76 GHz and 81-86 GHz".
[i.5] ECC Recommendation (14)01: "Radio frequency channel arrangements for fixed service systems
operating in the band 92-95 GHz".
[i.6] ECC Recommendation (05)02 (2009): "Use of the 64-66 GHz frequency band for fixed service".
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[i.7] Report Recommendation ITU-R F.2323: "Fixed service use and future trends".
[i.8] ERC Recommendation 12-11 (2015): "Radio frequency channel arrangements for Fixed Service
systems operating in the bands 48.5 to 50.2 GHz/50.9 to 52.6 GHz".
[i.9] ERC Recommendation 12-12 (2015): "Radio frequency channel, arrangement for Fixed Service
Systems operating in the band 55.78 to 57.0 GHz".
[i.10] Report Recommendation ITU-R M.2134: "Requirements related to technical performance for
IMT-Advanced radio interface(s)".
[i.11] MEF 22.1.1, Mobile Backhaul Phase 2, Amendment 1 - Small Cells, July 2014.
[i.12] CPRI Specification V6.0 (2013-08-30), Common Public Radio Interface (CPRI); Interface
Specification.
[i.13] OBSAI, Reference Point 3 Specification, Version 4.2.
[i.14] ETSI GS ORI 002-1 (V4.1.1) (2014-10): "Open Radio equipment Interface (ORI); ORI interface
Specification; Part 1: Low Layers (Release 4)".
[i.15] ETSI GS ORI 002-2 (V4.1.1) (2014-10): "Open Radio equipment Interface (ORI); ORI Interface
Specification; Part 2: Control and Management (Release 4)".
[i.16] "NGMN 5G WHITE PAPER", a Deliverable by NGMN Alliance, 17th of February 2015.
[i.17] "Understanding 5G: Perspectives on future technological advancements in mobile", GSMA
Intelligence, December 2014.
[i.18] Milestones: First Millimeter-wave Communication Experiments by J.C. Bose.
NOTE: Available at http://www.ieeeghn.org/wiki/index.php/Milestones:First_Millimeter-
wave_Communication_Experiments_by_J.C._Bose.
3 Abbreviations
For the purposes of the present document, the following abbreviations apply:
2G Second Generation of Mobile Networks
3GPP Third Generation Partnership Project
5G Fifth Generation of Mobile Networks
B2B Business-to-Business
B2G Business-to-Government
BBU Baseband Unit
BER Bit Error Rate
CNR Carrier-to-Noise Ratio
CoMP Coordinated Multipoint
CPRI Common Public Radio Interface
CSP Communication Service Provider
DL Downlink
FTTH Fibre To The Home
HD High Definition
HD-SDI High Definition Serial Digital Interface
HetNet Heterogeneous Network
IMT-Advanced International Mobile Telecommunications-Advanced
IPTV Internet Protocol Television
IQ In-phase and Quadrature components
ITU-R International Telecommunication Union - Radiocommunication Sector
KPI Key Performance Indicator
LOS Line Of Sight
LTE Long Term Evolution
LTE-A LTE-Advanced
M2M Machine-to-Machine
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MIMO Multiple Input Multiple Output
MNO Mobile Network Operator
nLOS near Line Of Sight
NLOS Non Line Of Sight
OBSAI Open Base Station Architecture Initiative
OpEx Operational Expenditures
ORI Open Radio equipment Interface
PoP Point of Presence
PtMP Point to Multipoint
PtP Point to Point
QoE Quality of Experience
QoS Quality of Service
RAN Radio Access Network
RF Radio Frequency
RRU Remote Radio Unit
SISO Single Input Single Output
SLA Service-Level Agreement
TCO Total Cost of Ownership
TV Television
UL Uplink
VDSL Very-high-bit-rate Digital Subscriber Line
WCDMA Wideband Code Division Multiple Access
4 Millimetre wave spectrum technology: Overview and
benefits
The high interest in millimetre wave bands has risen due to the enormous amount of bandwidth that lies in this part of
the electromagnetic spectrum. With respect to the present regulatory status, typically V-band offers 7 GHz bandwidth of
contiguous spectrum (57 - 64 GHz), extendable to 9 GHz whenever also the 64 - 66 GHz is open for fixed services and
E-band provides two times 5 GHz bandwidth, namely 10 GHz aggregate spectrum (71 - 76 GHz and 81 - 86 GHz).
Similarly, at frequency bands above 100 GHz, there are blocks of plentiful spectrum, which could be allowed for extra
bandwidth for future broadband wireless transmission services. Figure 2 [i.1] illustrates the channel spacing of the fixed
radio systems as function of the corresponding frequency band. The obvious advantage is that over 1 Gbps capacity
figures could be provided in SISO configurations and with average physical modulations (e.g. 500 MHz and 16QAM
combination), while over 2 Gbps capacity figures could be achieved by having more capable physical modulations
(e.g. 64QAM).
Another significant advantage of millimetre wave spectrum apart from being massive is that it is congested-free. The
requirement for non-crowded spectrum becomes more critical in urban and sub-urban environments, especially as the
number of installed links begins to grow as more high-capacity sites at smaller distances are to be served. Since
multiple network operators already use the long-established microwave bands in the same area, at some point in time
excessive bandwidth might become more difficult to be sourced at legacy bands to cover their needs adequately. In
order to avoid any potential "spectrum asphyxia", networks operators could turn to higher frequency bands. Millimetre
wave bands have not been extensively used, so this part of the electromagnetic spectrum offers an alternative path to
evolve wireless transmission networks effectively.
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Figure 2: Channel spacing of the fixed radio systems
Additionally, it is worthwhile stating that the extraordinary amount of millimetre bandwidth facilitates the fulfilment
not only of existing wireless transmission applications, but aids the development of wireless systems of future-proof
performance, as well. The engineering of wide-spectrum radio systems leads to very high throughput and low packet
delay figures that will be increasingly required in the next-generation transmission applications, for instance LTE-A and
5G mobile backhaul. Considering channel sizes, physical modulations and coding rates that are supported by recent
implementations, it could be extrapolated that only by employing wider channels, a capacity in the range of 10 Gbps
could be achieved. Also, increase of capacity, by keeping other things equal, results to further reduction of packet delay,
which is observed in millimetre wave spectrum technology. At present, the one-way latency of millimetre wave radios
can be lower than half a millisecond even down to 100 microseconds or less, depending on actual implementation. As
specifications of certain transmission applications become increasingly stricter and require fibre-like performance even
at the last-mile, millimetre wave spectrum technology could be the enabler to meet upcoming stricter demands and be
conceived as a future-proof over-the-air technology.
With reference to their radio propagation properties, millimetre wave bands are defined by short-to-medium ranges
(from a few hundred metres up to several kilometres), making technology at this spectrum suitable for applications in
urban and sub-urban areas. It has to be stressed though that transmission distances are subject to exact frequency
channel, bandwidth, target link availability at reference physical modulation and rain zone, besides system capabilities,
such as transmitting power, receiver's sensitivity and antenna performance.
Furthermore, millimetre wave spectrum technology provides very high-frequency re-use capabilities. Due to the high
operating frequency and resulting short wavelength even physically small antennas would provide relatively high
directivity and low side lobe level. That antenna directivity ensures good spatial isolation between links operating in
close proximity and reduces significantly the probability of generating interference or being subject to interference. The
high operating frequency and short wavelength are further effective to reduce specular reflections from many physical
surfaces (as they would appear rough at these wavelengths), in case such a surface is illuminated by the main lobe or a
side lobe of a millimetre wave antenna. The reduced reflection levels would further contribute to the reduction of the
chances of unintended interference. The frequent re-use gain of a single frequency channel becomes even more obvious
at cases where atmospheric absorption is a significant degradation factor at some frequency bands, as shown in Figure 3
of [i.2].
Network design and implementation benefit from millimetre wave spectrum technology. Sizeable number of available
frequency channels and very high frequency re-use ease frequency planning. Also, seeing that millimetre wave
spectrum technology is capable of employing wider channels, for example in the order of 200 MHz or more, by
transmitting fewer bits per symbol, target data rates could be attained for certain cases. Thus, respective CNR thresholds
-6
(at a BER of 10 or better) could be low and robustness of millimetre wave rises. Moreover, lower probability of
undesired interference and availability of antennas of high directivity allow the installation of more millimetre wave
links per area unit by supporting any type of interconnectivity options, e.g. chain, star, tree, ring, mesh. Consequently,
millimetre wave spectrum technology facilitates increased deployment density, before exhausting the expandability cap
in a given area. Another benefit of millimetre wave related to network implementation appears in cases where demand
for high-capacity data-centric connectivity is in locations that are fully or partially isolated by surrounding obstacles
(trees, buildings, hills, rivers, etc.). In such cases, when the path length permits, use of millimetre wave offers the
advantage, as compared to use of lower frequencies, that its short wavelength results in narrow Fresnel zone radius, so
enabling reliable transmission over the obstacle without requiring tall masts or towers.
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Figure 3: Specific attenuation due to rain attenuation and atmospheric gases
In addition, millimetre wave spectrum technology facilitates the manufacturing of compact products. Antenna size
depends on wavelength of electromagnetic signal, so in principle millimetre wave antennas of very small dimensions
can be designed. In fact, millimetre technology allows entire digital and analogue circuitry, such as network interfaces
and processor, modem, radio transceiver and antenna to be accommodated at full-outdoor and small-form factor
architecture, thus contributing to discreet and fast installations.
Last, but not least, another important trait of millimetre wave spectrum is that it can significantly contribute to an
optimized TCO and an accelerated roll-out of a wireless transmission network. Based on the individual radio
propagation characteristics of each millimetre wave frequency band, license-exempt or light licensing regimes are
feasible (see [i.3], [i.4], [i.5], [i.6], [i.7], [i.8] and [i.9]). Whilst licensed regime could be of course wanted for ensuring
more certainty in the expected QoS performance, the capability of adopting unlicensed and light licensing schemes can
really benefit transmission network applications as a consequence of:
• Reduced OpEx due to zero or low annual spectrum fees.
• Rapid deployment, because of none or simplified (no time-consuming) registration processes.
5 Applications and use cases: Overview
The attributes of the millimetre wave spectrum technology facilitate its usage in a sizeable number of wireless
transmission applications. The applications and use cases (latter are shown within brackets) that are discussed in this
paper are:
• Macro-cell mobile backhaul application (mobile network upgrade, expansion)
• Small-cell mobile backhaul application (rooftop-to-street/street-to-street connectivity, multi-hop)
• Fronthaul for small cells application (rooftop-to-street/street-to-street connectivity, multi-hop)
• Fronthaul for macro cells application (mobile network upgrade, expansion)
• Next-generation mobile transmission application
• Fixed broadband application (wireless to the home, wireless to the cabinet)
• Temporary infrastructure application (special events, public safety)
• Business-to-business application
• Business-to-government application (broadband connectivity, public Wi-Fi hotspot backhaul)
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• Redundant network application
• Video surveillance backhaul application
• TV signal relay application
The aforementioned applications and their respective use cases are analysed in the following clauses including current
and new features that could favour them. It should be noted that certain features are not conventional with current
millimetre wave spectrum technology. The key technologies listed hereafter can be considered the critical ones to fully
address the applications and use cases mentioned in the present document and will be considered in future works of the
ISG mWT:
• above 10 Gbps data rates
• PtMP/mesh topologies
• nLOS/NLOS radio propagation
• automation (self-configuration, self-optimization, self-healing)
• smart antennas (antenna beam-steering/beam-forming capabilities)
In this regard, the present ISG mWT paper sets also the future targets for the millimetre wave transmission technology.
6 Applications and use cases: Description
6.1 Macro-cell mobile backhaul application
6.1.1 Use Case 1: Mobile network upgrade (existing cells)
The growing demand of mobile broadband data and the high popularity of mobile devices, like smartphones and tablets
drive mobile network operators to lay access technologies that are more spectrally efficient. The roll-out of LTE and
LTE-A access networks has already launched, featuring Carrier Aggregation (3GPP Rel. 10) and CoMP (3GPP Rel. 11)
that put higher throughput and lower packet delay requirements per cell site compared to the ones needed for 2G and
WCDMA networks.
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Figure 4: Macro-cell backhaul application
Mobile network operators could upgrade current macro-cell sites to host LTE/LTE-A technologies by preserving their
2G/WCDMA access layers to satisfy also their existing subscribers' base. In this use case, PtP LOS links are installed at
the telecom infrastructure and connect each mobile site back to a pre-aggregation point. The pre-aggregation site could
be connected to an aggregation site either via fibre or by a consecutive PtP LOS radio link. Regulation schemes that
ensure interference-managed operation are preferred.
Inside urban and sub-urban environments, MNOs typically utilize microwave links at frequency bands equal to and
greater than 18 GHz, reaching last-mile distances of up to 5 km and target availability (at reference physical
modulation) ranging from 99,99 % - 99,999 %. The target DL peak rates per site could range from 400 Mbps at present
and reach up to 2 Gbps over the next 5 years with respect to gradual increase of mobile access bandwidth and spectral
efficiency (15 bps/Hz at minimum as per [i.10] and up to 30 bps/Hz under current specifications). At achieved
transmission distances, target DL peak rates should be provided and target availability figures should be guaranteed.
Subject to the evolution of RAN technology and expected performance, backhaul packet delay should be reduced to
sub-1 ms (even down to 200 us or less), to meet the stringent requirements of certain CoMP features via the LTE-A X2
interface. Auto-alignment of radio units might be handy, in case it expedites drastically the installation time over
relatively long transmission distances.
6.1.2 Use Case 2: Mobile network expansion (new cells)
Apart from improving the spectral efficiency of their current macro-cell network, MNOs could add macro-cell sites into
their network in order to enlarge their cellular coverage and/or augment their cellular capacity.
At both cases, new backhaul links will have to be established to serve the new LTE/LTE-A sites. Besides the
requirements described in clause 6.1.1 above, another design and deployment difficulty for backhaul network arises
from the densification of macro-cell layer that reduces the inter-site distances among cell sites in a given area. As
pre-aggregation site will have to accommodate more backhaul links, unless more fibre is deployed, which is often
prohibitively expensive, the need for suitable spectrum and of a solution with very high frequency re-use capabilities
becomes more probable.
Table 1 summarizes the key requirements of macro-cell backhaul application.
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Table 1: Macro-cell backhaul application key requirements
Requirement Indicative Value Comment
RF Path Clearance LOS
Connectivity PtP
Capacity 0,4 - 2 Gbps (DL) (a) w.r.t to annual cell site spectrum
efficiency increase
(b) subject to number/type/channel
size/antennas' number of served
macro cells
Range < 5 km
Availability (at reference 99,99 % - 99,999 %
physical modulation)
Latency (one-way) Sub -1 ms (even ≤ 0,2 ms) w.r.t target RAN
implementation/efficiency
Form Factor typical radio unit
Automation Yes (optional) w.r.t. alignment (if it improves
alignment time over relatively long
distances), configuration,
optimization, healing, etc.
Spectrum Regulation interference-managed
operation (link/block-allocated)

6.2 Small-cell mobile backhaul application
6.2.1 Use Case 1: Rooftop-to-street/Street-to-street connectivity
Network densification in urban environment represents a strategic option to manage the mobile data crunch and
HetNets plays a vital role to enhance subscribers' QoE by providing additional capacity under congested macro cells,
additional coverage (and in turn more capacity) where macro coverage is weak and better service delivery by leveraging
higher QoE.
Figure 5: Small-cell backhaul application
MNOs could start building their small-cell layer by leveraging their current telecom assets, where backbone connection
and power supply infrastructure are available. Single-hop connections could begin from a macro-cell site (rooftop-to-
street connectivity) and/or from a fibre-enabled PoP site, such as a micro-cell site and/or multi-function street cabinet
(street-to-street connectivity) and serve reachable small cells. Outdoor operator-managed small cells are placed at
lampposts, outside buildings' walls, payphones, notice boards and similar public spots. This introduces a few new
requirements for the backhaul solution.
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At street-level radio propagation conditions express a more dynamic behaviour compared to macro-cell layer due to the
increased phenomenon of multipath resulting from the environment's geometry. Moving vehicles (e.g. cars, buses)
might cause fast fading at the receiver by impacting severely its reception levels. In addition, clear LOS conditions are
not always found because of obstacles (e.g. signposts) or could be variable (e.g. seasonal trees' foliage). Moreover, roll-
out has to be easy and fast, due to the "non-telecom" working environment and because in certain cases only the cities'
personnel is allowed to have access to cities' street furniture. Therefore, automation mechanisms, such as self-alignment
(beam-forming/beam-steering), self-configuration, self-optimization, self-healing and so on, look to be quite significant
for efficient small-cell backhaul. Additionally, small-cell backhaul equipment's aesthetics need to blend into urban
environment, thus small form factor and built-in antenna are preferred, while its power consumption should be low.
Furthermore, this type of application could greatly benefit not only from LOS connectivity, but also from nLOS/NLOS
capabilities of a small-cell backhaul solutions. Given also the nature of site locations and their limited space, a small-
cell backhaul solution that apart from PtP topology could additionally support PtMP/mesh topologies would allow a
more flexible network deployment.
Typically, target transmission distances for mature small cell deployments are below 500 m. (few small cell backhaul
links during early deployments could reach 1 km distance) with target availability (at reference physical modulation)
between 99,9 % - 99,99 % (as macro-cell coverage is assumed). Except for LTE/LTE-A small cells, it is subject to each
operator's policy to include WCDMA and Wi-Fi at small-cell spots to serve greater number of subscribers, but this also
increases the throughput requirements per small cell backhaul link. As a result, the target DL peak rates per site could
range from 300 Mbps in the short-term and reach up to 1 Gbps over the next 5 years. As always, backhaul packet delay
has to be as low as possible and depends on evolution of RAN technology and desired efficiency. In this sense, small-
cell backhaul packet delay should be less than 1 ms.
Increased backhaul network density, resulting from relatively low inter-site distances among small cells, as well as a
need of very low recurring costs, makes this application benefit from technologies that facilitate high frequency re-use
and could be regulated at free, coordinated (light licensed) or block-allocated spectrum.
6.2.2 Use Case 2: Multi-hop (in-clutter extensions)
Further hops can be founded inside urban street canyon as small-cell layer expands. The requirements are the same as
use case described in clause 6.2.1, but extra emphasis has to be put on:
First hop is transformed into a "fat pipe" that carries the entire capacity of in-clutter small-cell backhaul connections.
Delay budget of in-clutter network increases as small-cell backhaul network scales; however it should remain within
acceptable limits, keeping also in mind that the gain of LTE-A CoMP feature-set (tight coordination between macro-cell
and small-cells) becomes optimum as packet delay decreases, see [i.11]. Thus, each additional small-cell backhaul link
of the in-clutter chain should respect the total planned delay budget.
The key requirements discussed above for small-cell backhaul application are shown in Table 2.
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Table 2: Small-cell backhaul application key requirements
Requirement Indicative Value Comment
RF Path Clearance LOS/nLOS/NLOS
Connectivity PtP/PtMP/mesh
Capacity 0,3 - 1 Gbps (DL) (a) w.r.t to annual cell site spectrum
efficiency increase
(b) subject to number/type/channel
size/antennas' number of served
small cells
Range ≤ 500 m
Availability (at reference 99,9 % - 99,99 % macro-cell coverage is assumed
physical modulation)
Latency (one-way) Sub - 1 ms (a) w.r.t target RAN
implementation/efficiency
(b) about use case 2, each additional
link's delay should respect total
≤ 1 ms)
planned delay budget (i.e.
Form Factor "Non-telecom"-shaped unit
with built-in antenna
Automation Yes w.r.t. alignment, configuration,
optimization, healing, etc.
Spectrum Regulation unlicensed/light licensed
(link)/block-allocated
6.3 Fronthaul for small cells application
6.3.1 Use Case 1: Rooftop-to-street/Street-to-street connectivity
Mobile network operators could adopt fronthaul architecture to deploy RRUs at different spots of urban small-cell layer
and aggregate the entire traffic (here, digital samples) at designated BBU hotels. Such an approach allows centralized
management of shared baseband resources amongst several RRUs and facilitates the implementation of certain latency-
sensitive LTE-A features, like CoMP DL Coordinated beamforming and UL Joint processing, see [i.11].

Figure 6: Fronthaul for small cells application
Mobile network operators could deploy single-hop connections either from rooftop down to street level and/or from in-
clutter PoP sites to the reachable RRUs. The core differences from the small-cell backhaul application lie on the
throughput and latency requirements, which are now much more stringent. Data rates become higher per link if
additional to LTE access technologies are deployed per site (e.g. WCDMA).
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Table 3: CPRI [i.12] fronthaul data rate requirements for LTE/LTE-A small cell configurations
Total Bandwidth MIMO Fronthaul Line Rate(s) per Channel Total Fronthaul
Data Rate
20 MHz 2x2 2 457,6 Mbps 2 457,6 Mbps
[20 + 20] MHz 2x2 [2 457,6 + 2 457,6] Mbps 4 915,2 Mbps
[20 + 20 + 20] MHz 2x2 [2 457,6 + 2 457,6 + 2 457,6] Mbps 7 372,8 Mbps
[20 + 20 + 20 + 20] MHz 2x2 [2 457,6 + 2 457,6 + 2 457,6 + 2 457,6] Mbps 9 830,4 Mbps

Table 4: OBSAI [i.13] fronthaul data rate requirements for LTE/LTE-A small cell configurations
Total Bandwidth MIMO Fronthaul Line Rate(s) per Channel Total Fronthaul
Data Rate
20 MHz 2x2 3 072,0 Mbps 3 072,0 Mbps
[20 + 20] MHz 2x2 3 072,0 + 3 072,0 Mbps 6 144,0 Mbps
[20 + 20 + 20] MHz 2x2 [3 072,0 + 3 072,0 + 3 072,0] Mbps 9 216,0 Mbps
[20 + 20 + 20 + 20] MHz 2x2 [3 072,0 + 3 072,0 + 3 072,0 + 3 072,0] Mbps 12 288,0 Mbps

CPRI and OBSAI transmit the I and Q samples of the signals and this increases significantly the
...