ETSI TR 101 534 V1.1.1 (2012-03)

Technical Report
Broadband Radio Access Networks (BRAN);
Very high capacity density BWA networks;
System architecture, economic model and
derivation of technical requirements

2 ETSI TR 101 534 V1.1.1 (2012-03)

Reference
DTR/BRAN-0040008
Keywords
architecture, broadband
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ETSI
3 ETSI TR 101 534 V1.1.1 (2012-03)
Contents
Intellectual Property Rights . 5
Foreword . 5
1 Scope . 6
2 References . 6
2.1 Normative references . 6
2.2 Informative references . 6
3 Definitions and abbreviations . 7
3.1 Definitions . 7
3.2 Abbreviations . 7
4 Introduction . 9
5 Architecture for 1 Gbit/s/km network . 9
5.1 Access Stratum Architecture . 10
5.2 Simplified Network Architecture . 11
6 Access Stratum Functionality . 11
6.1 Topology . 12
6.2 Physical Deployment . 12
6.2.1 Basic Cross and Square Deployments for Access. 12
6.2.2 Combined Access and Backhauling . 13
6.2.2.1 Square Topology, HBS above Roof-Top . 15
6.3 Antennas . 16
6.4 Multi-beam Assisted MIMO . 16
6.4.1 Overview . 16
6.4.2 Uplink Operation in Licensed Bands . 17
6.4.3 Downlink Operation in Licensed Bands . 18
6.4.4 Interference Mitigation in Lower LE Bands (< 6 GHz) . 19
6.5 Collaborative MIMO, Network MIMO Support . 19
6.5.1 Introduction. 19
6.5.2 Collaborative MIMO . 19
6.5.3 Network MIMO . 21
6.6 Hybrid MIMO Schemes . 23
6.7 Radio Resource Management . 25
6.7.1 Dynamic Frequency Band Allocation . 25
6.7.1.1 Selection Principle . 25
6.7.2 Self-Organizing Frequency Allocation . 27
6.8 Cognitive Frequency Band Allocation . 27
6.8.1 Cognitive Radios . 27
6.8.2 Cognition . 27
6.8.3 Reconfiguration . 28
6.8.4 Cognitive Channel Assignment . 28
6.8.4.1 Frequency Awareness . 28
6.8.4.2 Channel Assignment . 29
6.8.5 Application of Algorithm . 30
6.9 Time Resource Allocation . 31
6.9.1 Spectrum Sharing between Access and Hub Wireless Networks . 31
6.9.1.1 Frame Structures for Spectrum Sharing in Time Domain . 31
6.9.1.1.1 Frame Structure Elements for SON Support . 33
6.10 RRM for joint access and self-backhaul networks . 33
6.10.1 Cognitive and Docitive RRM . 33
6.10.1.1 Problem Statement . 33
6.10.2 System-Wide Simulation Results . 35
6.11 Direct Communication . 37
6.11.1 Time-domain Frame Structures . 37
6.11.1.1 DCO in the ABS and HBS Radio Frame . 37
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4 ETSI TR 101 534 V1.1.1 (2012-03)
6.11.2 Assignment of Frequency and Time Resources . 38
6.12 Out-of-band self backhauling . 39
6.12.1 Capacity and Spectrum Calculation in 5 GHz . 39
6.12.2 Backhaul Capacity at 60 GHz . 39
6.12.2.1 Rollout Scenario . 40
6.12.2.2 Backhaul Data Rate Calculations . 42
6.12.2.3 Theoretical Scenario Analysis . 43
6.12.2.4 Practical Scenario Analysis . 43
6.12.2.5 Calculation Details . 44
6.12.2.5.1 One frequency theoretical system results . 45
6.12.2.5.2 Two frequencies theoretical system results . 45
6.12.2.5.3 One frequency practical system results . 45
6.12.2.6 Two frequencies practical system results . 45
6.12.2.7 Spectral efficiency and required channel BW . 45
7 Identification of Requirements . 46
7.1 General Requirements . 46
7.2 Access Wireless Network . 46
7.3 Self-Backhauling Wireless Network . 47
7.4 Joint Access & Self-Backhaul . 47
7.4.1 First approach . 47
7.4.2 Second approach . 48
7.5 Requirements related to the Lower Layers of DCO . 48
7.6 Conclusion . 48
8 Business aspects . 48
8.1 Frequency License Fees . 48
8.2 Site Related Cost . 49
8.3 Network Equipment Cost . 49
8.4 Self-Backhaul Cost . 49
8.5 Conclusions . 50
9 General Conclusions. 50
History . 51

ETSI
5 ETSI TR 101 534 V1.1.1 (2012-03)
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 Technical Report (TR) has been produced by ETSI Technical Committee Broadband Radio Access Networks
(BRAN).
ETSI
6 ETSI TR 101 534 V1.1.1 (2012-03)
1 Scope
The present document addresses the architecture, the economic model and the derivation of technical requirements for a
BWA system, providing 1 Gbit/s/km , using 40 MHz of licensed spectrum and including self-backhauling in both
licensed and un-licensed bands, network MIMO, cognitive-radio based self-organization, etc.
2 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.
2.1 Normative references
The following referenced documents are necessary for the application of the present document.
Not applicable.
2.2 Informative references
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] ETSI TR 125 942 (2009): "Universal Mobile Telecommunications System (UMTS); Radio
Frequency (RF) system scenarios (3GPP TR 25.942 version 9.0.0)".
[i.2] A. Papadogiannis and A. G. Burr: "Multi-beam Assisted MIMO - A Novel Approach to Fixed
Beamforming", Future Network and Mobile Summit (FNMS 2011), Warsaw, Poland, June 2011.
[i.3] UMTS Forum: "Mobile Broadband Evolution: the roadmap from HSPA to LTE", Feb., 2009.
[i.4] FCC: "Notice of Proposed Rule Making and Order," ET Docket No 03-222, 2003.
[i.5] F. Akyildiz, et al.: "Next generation/dynamic spectrum access/cognitive radio wireless networks:
A survey", Computer Networks, vol. 50, pp. 2127-2159, Sep, 2006.
[i.6] J. Mitola: "Cognitive Radio Architecture: The Engineering Foundations of Radio XML", 2006.
[i.7] J. Mitola and G. Maguire: "Cognitive radio: making software radios more personal", IEEE
Personal Communication, vol. 6, pp. 13-18, Aug, 1999.
[i.8] R. S. Sutton and A. G. Barto: "Reinforcement learning : An Introduction: The MIT Press", 1998.
[i.9] Farahmand, A.-M.: "Interaction of culture-based learning and cooperative co-evolution and its
application to automatic behavior-based system design", Evolutionary Computation, IEEE
Transactions on, vol. 14, pp. 23 -57, Feb. 2010.
[i.10] Ahmadabadi, M.N., et al: "Expertness measuring in cooperative learning", vol. 3, pp. 2261 -2267
vol.3, 2000.
[i.11] Mischa Dohler: "Docitive Radios - Centroid of Cognition and Cooperation", Keynote, WWRF23,
October 2009, Beijing, China.
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7 ETSI TR 101 534 V1.1.1 (2012-03)
[i.12] Mischa Dohler: "Docitive Networks - A Step Beyond Cognition", Keynote, ISABEL 2009,
November 2009, Bratislava, Slovakia.
[i.13] Mischa Dohler, L. Giupponi, A. Galindo-Serrano, P. Blasco: "Docitive Networks: A Novel
Framework Beyond Cognition", IEEE Communications Society, Multimdia Communications TC,
E-Letter, January 2010.
[i.14] ITU-R Recommendation P.530-12: "Propagation data and prediction methods required for the
design of terrestrial line-of-sight systems".
[i.15] P. Blasco, L. Giupponi, A. Galindo, M. Dohler: "Aggressive Joint Access & Backhaul Design For
Distributed-Cognition 1Gbps/km2 System Architecture", in Proceedings of 8th International
Conference on Wired/Wireless Internet Communications (WWIC 2010), 1-3 June, 2010, Lulea
(Sweden).
[i.16] BuNGee deliverable D3.1: "Baseline RRM & Joint Access/Self-Backhaul Protocols".
3 Definitions and abbreviations
3.1 Definitions
For the purposes of the present document, the following terms and definitions apply:
Adaptive Antenna System (AAS): system adaptively exploiting more than one antenna to improve the coverage and
the system capacity
self-backhauling: wireless links between HBS and ABS, which may share a frequency channel with the access
operation (in-band) and use in addition license-exempt spectrum, as 5 GHz or 60 GHz bands (out-of-band)
3.2 Abbreviations
For the purposes of the present document, the following abbreviations apply:
4G 4th Generation
AAA Authentication, Authorization, and Accounting
ABS Access BS
ACK Acknowledge
ADC Analogue To Digital Converter
AP Access Point
ART Above Roof Top
ASN Access Service Network
BCC BWA Control Channel
BER Bit Error Rate
BF Beam Forming
BM Buttler Matrix
BRT Below Roof Top
BS Base Station
BS-BS Base Station to Base Station
BW Bandwidth
BWA user Fixed, Nomadic or Mobile user
BWA Broadband Wireless Access
CAPEX Capital Expenditure
CAPEX Capital Expenditure
CINR Carrier to Interference and Noise Ratio
CQI Channel Quality Indicator
CR Cognitive Radio
CSI Channel State Information
CTC Clear Timer on Compare
DCO Direct Communication Operation
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8 ETSI TR 101 534 V1.1.1 (2012-03)
DCS Dynamic Channel Selection
DFS Dynamic Frequency Selection
DL Downlink
FBS Femto BS
FCC Forward Error Correction
FDD Frequency Division Duplex
FEC Forward Error Correction
FFR Fractional Frequency Reuse
GW Gateway
HBS Hub Base Station
HDC HBS DCO
HSS Subscriber Station connected to HBS
IF Intermediate Frequency
IMT International Mobile Telecommunication
ITU-R International Telecommunication Union - Radio
LAN Local Area Network
LE License Exempt
LE License Exempt
LOS Line Of Sight
LTE Long Term Evolution
LTE-A LTE - Advanced
MAC Medium Access Control
MBA-MIMO Multi-beam assisted MIMO
MCS Modulation and Coding Scheme
MDP Markov Decision Process
MIMO Multiple Input Multiple Output
MMSE Minimum Mean Square Error
MP Multi Point
MS Mobile Station
MS/SS Mobile Station / Subscriber Station
MSE Mean Square Error
MS-MS Mobile Station to Mobile Station
MU Multi-User
NF Noise Factor
NLOS Non LOS
NMS Network Management System
NRM Network Reference Model
OFDM Orthogonal Frequency Division Multiplexing
OFDMA Orthogonal Frequency Division Multiple Access
OPEX Operational Expenditure
OPEX Operational Expenditure
OR Opportunistic Radio
OSIC Ordered Successive Interference Cancellation
PC Power Control
PER Packet Error Rate
PHY Physical Layer
PIC Parallel Interference Cancelation
PL Path Loss
P-P, P2P Point-to-Point
PTX Transmit Power
QAM Quadrature Amplitude Modulation
QoS Quality Of Service
QPSK Quadrature Phase Shift Keying
RAN Radio Access Network
RF Radio Frequency
RL Reinforcement Learning
RMS Root Mean Square
RPE Radiation Pattern Envelope
RRM Radio Resource Management
RRM-E RRM-Entity
RS Relay Station
RSSI Received Signal Strength Indicator
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9 ETSI TR 101 534 V1.1.1 (2012-03)
Rx Receive
SDMA Space Division Multiple Access
SDR Software Defined Radio
SF Shadow Fading
SIC Successive Interference Cancelation
SINR Signal To Noise And Interference Ratio
SISO Single Input Single Output
SM Spatial Multiplexing
SON Self Organizing Network
STC Space Time Coding
SU Single User
TDD Time Division Duplex
TF Frame Time
THP Tomlinson-Harashima Precoding
TTG Transmit Transition Gap
TTI Transmission Time Interval
Tx Transmitter
UE User Equipment
UL Uplink
UL/DL Uplink/Downlink
UMi Urban Micro Cell
V-BLAST Vertical-Bell Laboratories Layered Space Time [Code]
VDSL Very High Bit Rate DSL
VR Visibility Regions
WiFi Wireless Fidelity
WiMAX Worldwide Interoperability for Microwave Access
XPIC Cross Polarization
ZF Zero Forcing
4 Introduction
The present document presents a new possible wireless BWA network, including heterogeneous elements (a two tier
approach), combined use of licensed and license-exempt spectrum, very low delay communications between network
elements, enabling the operation of the network MIMO technology.
The description of the networking features is in general done using the WiMAX terminology, however should be no
barrier in using the 3GPP network for implementing this network.
5 Architecture for 1 Gbit/s/km network
The architecture presented in the present document represents a number of promising features that contribute to the
overall increase in access network capacity and link throughput characteristics. The list includes the following features:
• Multiple access links aggregation;
• Self-Backhauling link aggregation;
• Network MIMO (for Downlink and Uplink);
• Radio Resource Management;
• Direct BS-BS or MS-MS communication.
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10 ETSI TR 101 534 V1.1.1 (2012-03)
5.1 Access Stratum Architecture
The present document addresses only the access stratum architecture. The architecture aims to offer a cost efficient
capacity density of 1 Gbit/s/km . Here, a HBS serves several below-rooftop ABSs, which in turn serve the associated
MSs. The HBS possesses several beams which are used to communicate with ABSs in its beam-space. ABSs can
communicate with each other via the serving HBS. A topic for further study is the direct ABS-ABS communication
while using the air interface.
The Femto-BS and their associated subscribers may also operate in the un-licensed spectrum.
To simplify the presentation, the HBS-ABS links, which are self-backhaul links inside this system, may be named in the
present document "backhaul links". This naming should not be understood as HBS backhauling, which is outside of the
scope of the present document.
The system presented in the present document has the following basic architecture:
ACCESS
SELF-
BACKHAUL
BACKHAUL
Figure 5.1: Basic architecture
The scheme in figure 5.1 provides an overview of most of the possible wireless links in the present document. At the
top level of the architecture, HBSs are directly connected to the wired backhaul. If in some cases a wired link could not
be done, this link should be replaced by LE high data rate connectivity.
An in-band backhaul link and a LE link between HBSs may not be systematically done but could offer additional
networking capacities and an alternative, in case of a router failure for example.
At the ABS location there are two elements, which are the HSS and the ABS. The HSS component is associated to an
HBS or to another HSS (for direct communication and collaborative MIMO). ABS provides connectivity for the BWA
users.
To increase the coverage or to provide a larger throughput in a given area exists the possibility to deploy additional
stations called pico-ABS. Those stations are basically similar to ABSs as they are providing connectivity to BWA users.
The lower level of the architecture shows mobile station connectivity possibilities. MS connects itself to ABS as in the
standard P-MP architecture, but can also directly connect one to each other, and associate with two ABSs for MIMO
support.
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11 ETSI TR 101 534 V1.1.1 (2012-03)
5.2 Simplified Network Architecture
The simplified network architecture of a BWA system is summarized in figure 5.2.
The following notations are used for the reference points:
A1 - GW to GW reference point.
B2 - GW to HBS reference point.
C3 - HBS to ABS reference point.
D4 - ABS to ABS reference point.
A1
GW GW
B2 B2
B2
HBS
HBS HBS
C3
C3
C3 C3
C3
C3
ABS ABS ABS ABS ABS ABS
D4 D4
D4 D4
D4
Figure 5.2: Network Architecture
The system-specific of interfaces in figure 5.2 are:
A1: Reference Point A1 consists of the set of Control and Bearer Plane protocols
originating/terminating in GWs that coordinate MS mobility between GWs.
B2: Reference Point B2 consists of the set of Control Plane message flows and Bearer Plane data flows
between the base stations and the GW.
C3, D4: Reference Points C3, D4 consists of the set of Control Plane message flows and optionally Bearer
Plane data flows between the base stations to ensure fast and seamless handover. The Bearer Plane
consists of protocols that allow the data transfer between Base Stations involved in handover of a
certain MS. In addition, C3 can carry RRM control messages for the joint usage of the spectrum
by HBS and ABS.
For the purpose of this discussion, it is important to note that according to the network architecture each BS may be
engaged in signalling transactions and traffic exchange with multiple GWs and vice versa.
6 Access Stratum Functionality
Those basic elements of the access operation which are characteristic for the studied system are presented in
continuation.
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12 ETSI TR 101 534 V1.1.1 (2012-03)
6.1 Topology
The system deployment will use the ABSs located below roof-tops and HBSs located either below or above rooftops.
The ABS deployment can have two flavours:
• ABSs located on streets;
• ABSs located in those areas with insufficient radio coverage.
Two deployment variants, named "cross" and "square", are proposed for deployment.
6.2 Physical Deployment
6.2.1 Basic Cross and Square Deployments for Access
The basic cross and square deployments, using four frequency channels of 10 MHz each for TDD or 2 × 5 MHz for
FDD, are illustrated in figures 6.1 and 6.2. These deployments assume a Manhattan-like grid, having a block raster of
90 m. The figures illustrate a frequency planning strategy, having as scope to minimize the inter-ABS interference
between adjacent HBS cells.
ABS
a a
a
a
a
ABS
a a
a a
a
ABS
a a
a a
a a a
a a a
a
a a a a
ABS ABS ABS ABS ABS ABS
a a a a a
a a a
a a a
a
a a a a a
ABS
a a
a a
a
ABS
a a
a a
a
ABS
a a
a a
Figure 6.1: Cross deployment
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13 ETSI TR 101 534 V1.1.1 (2012-03)

ABS ABS ABS ABS ABS
ABS
a
a a a
a
a a a
a
ABS ABS
a a a a
a a
a a
ABS ABS
a a
a a
a a
a a
ABS ABS
a a a a
a
a a a
ABS ABS
a a a a
a a a a
ABS ABS ABS ABS ABS
a a
a a
a a
a a
HBS-
street
Figure 6.2: Square deployment
6.2.2 Combined Access and Backhauling
The following figures show the combined access and backhauling. In figure 6.3 the HBS is located below roof-top
while in figure 6.4 the HBS is located above roof-top. In figure 6.3 there are still coverage holes which are covered by
an above-rooftop HBS operating in 5 GHz.
In the figures below, "a" means access, while "b" means backhaul. One color is used for each of the four available
frequency channels.
b
b
a
b
a
b
a a a
a a a
a a a
bbb a a
b b a a a
b
a a a
a
a a a a a
b
a
b
a
b
Figure 6.3: HBS under roof-top for cross topology
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14 ETSI TR 101 534 V1.1.1 (2012-03)
ABS ABS ABS ABS ABS ABS
a
a
a
a b
b a b b b b
a
a
a b a
ABS ABS
a a a a
a a a a
b
b
b b
ABS ABS
b a
a b a
a
a
a a a
HBS
b b
b b
ABS ABS
a
a a a
a
b
a b
a a
b
b
b
b
b
ABS ABS
a a a a
a a
a a
ABS ABS ABS ABS ABS
a
a a
a b b
b b b b
a a a
a
HBS-
street
Figure 6.4: HBS above roof-top for square topology
Figure 6.5 indicates a combined deployment of a self-backhauling cell at 2,6 GHz/3,5 GHz, with HBS above roof-top
and a 60 GHz self-backhaul, deployed in LOS at street level.
b
b
b
Figure 6.5: Combined in-band and 60GHz backhaul
NOTE: In all the above figures, the sophisticated frequency planning for allowing a high reuse of the four
available frequencies in the licensed spectrum.
In figure 6.6 is shown an example of the multi-cell deployment when the HBS is placed over the roof. Note the de-
lineated placement of HBS, to create a more pronounced special isolation between antenna beams. Un-regular
beam-widths may be needed, due to the ABS placement on the main cross directions; in other directions the capacity
requirement is lower such that larger antenna beam widths can be used.
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15 ETSI TR 101 534 V1.1.1 (2012-03)
b
b
b
b
b
b
b
b
b
b
b
b
Figure 6.6: Star topology, HBS above roof-top
6.2.2.1 Square Topology, HBS above Roof-Top
In figure 6.7 is shown the multi-cell deployment in the case of the square topology. This deployment has some
properties of reducing the interference between beams arriving from adjacent HBS cells, if spatial separation is used.
b
b
b
b
b
b
b
b
b
b
b
b b
b
b
b
b
b b
Figure 6.7: Square topology, HBS above roof-top
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16 ETSI TR 101 534 V1.1.1 (2012-03)
6.3 Antennas
The spatial multiplexing is an important technology for achieving very high data rates in the wireless networks. While
in other access network the antennas illuminate the full sector, in this system the HBS antenna is composed from
multiple cross-polarized adjacent narrow beams.
The provision of high capacity densities in the system self-backhaul can be achieved if the HBS is able to generate a
large number of fixed narrow beams. In the described system this technique is used to provide wireless backhaul to a
large number of ABSs, which then serve user terminals. The HBS can create multiple fixed narrow beams with the use
of an antenna array fed by a Butler matrix (BM). A BM is a passive external circuit operating at microwave frequencies
having N ports feeding/receiving signals to/from the antennas and n ports feeding/receiving signals to/from the RF
chains [i.2]. A BM consisting of phase shifters, quadrature hybrids and couplers, essentially implements a fixed RF
beamformer creating n narrow beams, where n ≤ N. This fixed beamformer allows the application of MIMO techniques
in the beam domain as opposed to the conventional antenna domain; in order to minimize inter-beam interference the
received signals at the n ports of the BM are jointly processed in the baseband and this concept is defined as multi-beam
assisted MIMO (MBA-MIMO) [i.2].
Such an antenna may use six dual-polarized beams in a 90 degrees sector. An example of the antenna characteristics
taken from is presented in figure5.3.
Meas Plane Azimuth 0000
Peak Gain  17.5 dBi
Co-Polar
X-Polar
)
i
B
d
(
n
i
a
G
e
t-5
u
l
o
s
-10
b
A
-15
-20
-25
-180 -150 -120 -90 -60 -30 0 30 60 90 120 150 180
Angle (degrees)
Figure 6.8: Azimuth characteristics of a multi-beam antenna
It should be noted that the maximum system performance is obtained when the MIMO technology is used in
conjunction with such multi-beam antenna.
6.4 Multi-beam Assisted MIMO
6.4.1 Overview
Multi-beam assisted MIMO (MBA-MIMO) is employed on the HBS - ABS links in conjunction with the multi-beam
antenna. Hence it applies at frequencies relevant to the multi-beam antenna, i.e. in the licensed bands and at the license-
exempt bands below 6 GHz. It does not apply to 60 GHz backhauling.
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17 ETSI TR 101 534 V1.1.1 (2012-03)
The principle is to apply multi-user MIMO techniques in the beam-space of the multi-beam antenna rather than on a
per-element basis. This requires signal processing modules to be implemented in the HBS which we refer to as joint
beam processing, and which is analogous to the signal processing techniques employed at the base-station end of a
multi-user MIMO cellular system. The ABS will also be equipped with multiple antennas, and MIMO processing
techniques will also be applied there, in particular for interference avoidance from other HBSs, but also to exploit
polarization multiplexing, given that the HBS antenna also allows dual polarized operation.
The advantage of the multi-beam antenna as compared with an array antenna at the HBS of equivalent size as applied to
the multi-user system formed by the ABSs served by the HBS is that it makes the multi-user channel much more sparse,
in the sense that signals related to one user impinge on only a small number of HBS beams. In contrast in a multi-user
MIMO system employing a conventional array signals from all users in a given quadrant impinge on all antenna
elements in the array. This reduces the complexity of the signal processing required and improves the numerical
stability of the algorithms. It also simplifies and improves the performance of channel estimation.
In the following two clauses we review the functions required at HBS and ABS ends of the link for operation in the
licensed band for uplink and for downlink operation. We then consider additional requirements for use in unlicensed
bands for mitigation where possible of other-user interference.
Note that at the ABS location will be three antenna types:
• oriented towards HBS, actually an HSS antenna, used for the backhauling network in lower frequencies;
• oriented towards MSs, serving the access network in the lower frequencies;
• For the P-P link at 60 GHz.
6.4.2 Uplink Operation in Licensed Bands
The ABS functions are listed below:
• Polarisation multiplexing: if the ABS is equipped with dual polarized antenna elements (±45° to match those
at the HBS antenna), the data to be transmitted on the uplink may be multiplexed between the two
polarizations, thereby doubling the available capacity.
• Precoding: if the ABS is equipped with multiple (possibly dual polarized) antenna elements to serve the link to
the HBS additionally precoding may be applied across these antennas. Since most ABSs are likely to be served
primarily by one HBS beam, it is likely that only one data stream ("layer" in 3GPP-LTE terminology) will be
available, so the precoding will consist in selection of an optimum beam-former. However the architecture
presented in the present document allows joint beam processing to be applied at the HBS for reception on the
uplink, and in some cases it may be possible and advantageous to allow transmission on multiple layers. Note
that this will require channel state information (CSI) which may be obtained from a downlink pilot
transmission or by means of feedback from the HBS via a control channel on the downlink. Note that in the
present document CSI is not used in a mode similar to existing 3GPP standards.
• Interference mitigation: if the ABS transmission may be liable to cause interference to HBSs serving
neighbouring cells, the precoder selection may take account of the interfering signals received from these
HBSs on the downlink, so as to minimise interference caused to them. This may require the ABS to be able to
decode pilot signals from such HBSs. It also assumes reciprocity of these links, which is likely to hold if
uplink to desired HBS and downlink from interfering HBS is at the same frequency. Even in the absence of
reciprocity, sufficient information may be available to allow interference mitigation.
• Modulation and coding: the ABS will provide appropriate modulation and coding according to CSI feedback
from the HBS.
• Channel estimation support: the ABS will need to transmit pilot signals to the HBS to allow estimation of the
ABS - HBS channel response. Note that it is likely that the backhaul links will be relatively slowly time-
varying, so the pilot overhead required for this purpose is likely to be small.
ETSI
18 ETSI TR 101 534 V1.1.1 (2012-03)
The HBS functions are listed below:
• Joint beam processing: signal processing for multi-user detection, to separate the signals originating from
different ABSs and received on multiple beams of the HBS. These may be linear - zero forcing (ZF) or
minimum mean square error (MMSE) or non-linear - successive interference cancellation (SIC), ordered
successive interference cancellation (OSIC) or parallel interference cancellation (PIC) - and may also involve
iterative processing with the FEC decoder. This may also involve separation of multiple data streams from one
ABS, if these are provided.
• Polarisation demultiplexing: it will also incorporate demultiplexing of the dual polarised signals, using the
dual polar beams of the HBS antenna.
• Demodulation and decoding: demodulation and FEC decoding will be performed: if iterative techniques are to
be applied, soft input, soft output (SISO) decoding will be required.
• Channel estimation: the HBS will estimate the channel response from all antennas of all ABSs to the beams of
the HBS which receive significant power, on both polarisations. The resulting CSI will be signalled back to the
ABS via a control channel on the downlink.
6.4.3 Downlink Operation in Licensed Bands
The HBS functions are listed below:
• Multi-user precoding: this is the dual of the joint beam processing for multi-user detection performed on the
uplink; data for the ABSs is precoded, exploiting CSI for all HBS - ABS links. Precoding may be linear or
non-linear, using Tomlinson-Harashima precoding (THP).
• Polarisation multiplexing: again, if the ABS is equipped with dual polarised antennas, data on the downlink
also may be multiplexed across the polarisations at the HBS.
• Interference mitigation: if the HBS may be liable to cause interference to ABSs served by neighbouring HBSs,
precoder selection may take account of interference received at the HBS from such ABSs, so as to minimise
interference caused to them. The same issues of reciprocity apply here as in bullet above.
• Modulation and coding: the HBS will provide appropriate modulation and coding according to CSI feedback
from the ABS.
• Channel estimation support: the HBS will need to transmit pilot signals to the ABS to allow estimation of the
HBS - ABS channel response.
The ABS functions are listed below:
• Maximum ratio combining: of signals on the multiple ABS antennas. Nonlinear processing will also be
required if non-linear precoding is employed at the HBS.
• Interference mitigation: this should also take account of interference from neighbouring HBSs: the combining
criterion should be max-SINR beamforming, again with nonlinear processing if appropriate.
• Polarisation demultiplexing: if the ABS is equipped with dual polar antennas, the two data streams should be
demultiplexed.
• Demodulation and decoding: demodulation and FEC decoding will be performed: for iterative
decoding/detection, soft input, soft output (SISO) decoding will be required.
• Channel estimation: the ABS will estimate the channel response to all antennas of the ABSs from the beams of
the HBS from which significant power is received, on both polarisations. The resulting CSI will be signalled
back to the HBS via a control channel on the uplink.
ETSI
19 ETSI TR 101 534 V1.1.1 (2012-03)
6.4.4 Interference Mitigation in Lower LE Bands (< 6 GHz)
Backhaul operation in the lower LE bands will require the same functions as for the licensed bands, as described in the
previous two clauses. However it may additionally require, or benefit from, interference mitigation for signals from
other unlicensed users sharing the same band. This will additionally require the following functions, on both up- and
downlink:
• Interference estimation: estimation at the receiver of the correlation matrix of the interference, to enable
minimisation of its effect. This will form part of the CSI to be fed back to the transmitter on the control
channel. Note that interference may vary relatively rapidly, and is not synchronised to the wanted signals, so
means should be provided for the receiver to estimate this interference at regular intervals.
• Optimum signal combining: taking account of this interference to maximise the SINR of the received signal at
the receiver. Note that since the format of the interfering signal is unknown, non-linear interference
cancellation techniques are probably not feasible.
• Optimum precoding: the precoder selection at the transmitter should take account of the CSI regarding this
interference fed back from the receiver.
6.5 Collaborative MIMO, Network MIMO Support
6.5.1 Introduction
In this clause, the functional blocks for each cooperation configuration to be exploited in this system are listed and
briefly described. This is particularized for
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