scalable ofdma wp_mobile_wi_max_ic_stelecom
TRANSCRIPT
White Paper January 2007 Mobile WiMax From OFDM-256 to S-OFDMA Scalability
OFDMA
Software solutions in radiocommunications
QoS
Handoff
Abstract
Fixed WiMAX, based on 802.16d-2004, is a stationary technology with customer premises equipment (CPE) and antennas installed in a fixed location, even though some vendors have included portability and limited mobility into their equipment. Only with 802.16e-2005 and Mobile WiMAX comes the capability of mobile units to hand off between base stations. True mobility is therefore enabled in addition to what 802.16d-2004 already features. The management of different duplexing modes, AAS, and service flow provisioning (among others...) are already included in the d-2004 standard, and new items such as OFDMA sub-channelization techniques, hand off sessions and management of the multicast/broadcast service have to be supported to be compliant with the e-2005 version. WiMax evolves from OFDM-256 FFT to S-OFDMA, so must radio network design methodologies. This white paper highlights the different functionalities of ICS telecom dedicated to network design in OFDMA environment.
References
• WiMAX Forum: Mobile WiMAX -- Part I: A Technical Overview and Performance Evaluation • ATDI: A quickguide to 802.16 radio-planning with ICS telecom • ATDI: Signal propagation modeling in urban environment • Intel© Corporation / Hassan Yaghoobi: Scalable OFDMA Physical Layer in IEEE 802.16 WirelessMAN • Intel© Corporation / Sassan Ahmadi: Introduction to mobile WiMAX radio access technology : PHY and
MAC architecture • Motorola©: WiMAX: E vs. D – The advantages of 802.16e over 802.16d
• brief overview
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Table of Content
1 Acronyms ___________________________________________________________________ 5
2 Mobile WiMax basics__________________________________________________________ 7
2.1 What is mobile WiMax ? __________________________________________________ 7
2.2 Main features of mobile WiMax ____________________________________________ 7 2.2.1 OFDMA ____________________________________________________________ 7 2.2.2 High data rates _______________________________________________________ 7 2.2.3 Quality of Service _____________________________________________________ 7 2.2.4 Scalability ___________________________________________________________ 8 2.2.5 Security _____________________________________________________________ 8 2.2.6 Mobility_____________________________________________________________ 8
2.3 Mobile WiMAX certification profiles ________________________________________ 8
3 Review of mobile WiMax PHY Layer _____________________________________________ 9
3.1 Duplex mode ____________________________________________________________ 9 3.1.1 Concept _____________________________________________________________ 9 3.1.2 Impact on mobile WiMAX radio-planning with ICS telecom __________________ 10
3.2 OFDMA basics _________________________________________________________ 12 3.2.1 Concept ____________________________________________________________ 12
3.2.1.1 Frequency Division Multiplexing (FDM)________________________________ 12 3.2.1.2 Orthogonal Frequency Division Multiplexing (OFDM)_____________________ 13 3.2.1.3 Orthogonal Frequency Division Multiple Access (OFDMA) ________________ 14 3.2.1.4 Scalable Orthogonal Frequency Division Multiple Access (S-OFDMA) _______ 15
3.2.2 OFDMA symbol structure _____________________________________________ 16 3.2.3 Subchannelization schemes ____________________________________________ 18
3.2.3.1 Manual input ______________________________________________________ 18 3.2.3.2 Predifined tables ___________________________________________________ 19
3.3 Impact on mobile WiMAX radio-planning with ICS telecom ___________________ 20 3.3.1 Calculation of the system gain and the sensitivity ___________________________ 21
3.3.1.1 Downlink_________________________________________________________ 21 3.3.1.2 Uplink ___________________________________________________________ 23
3.3.2 Calculation of the throughput ___________________________________________ 24
3.4 SISO, MISO, SIMO, MIMO schemes_______________________________________ 26
3.5 Frequency reuse schemes _________________________________________________ 30 3.5.1 Concept ____________________________________________________________ 30 3.5.2 Impact on mobile WiMAX radio-planning with ICS telecom __________________ 32
4 Review of mobile WiMAX MAC layer____________________________________________ 34
4.1 QoS – Data service Types_________________________________________________ 34 4.1.1 Concept ____________________________________________________________ 34
3
4.1.2 Impact on mobile WiMax radio-planning with ICS telecom ___________________ 35
4.2 Handoff _______________________________________________________________ 37 4.2.1 FBSS / MDHO ______________________________________________________ 37
4.2.1.1 List of neighbors ___________________________________________________ 37 4.2.1.2 Active set allocation ________________________________________________ 38 4.2.1.3 FSBB/MDHO handover map within the same active set ____________________ 39
4.2.2 Hard handover_______________________________________________________ 40 4.2.3 Hand-over along a mobile path__________________________________________ 41
4.3 Multicast and broadcast service ___________________________________________ 42 4.3.1 Concept ____________________________________________________________ 42 4.3.2 Impact on mobile WiMAX radio-planning with ICS telecom __________________ 42
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NETWORK DESIGN WITH ICS TELECOM MOBILE WIMAX
Note : all provided values are FOR IN FORMATION ONLY
1 Acronyms
AAS Adaptive Antenna System also Advanced Antenna System
AMC Adaptive Modulation and Coding
MIMO Adaptive Multiple Input Multiple Output
BE Best Effort
BS Base Station
CCI Co-Channel Interference
CINR Carrier to Interference + Noise Ratio
CP Cyclic Prefix
DL Downlink
EIRP Effective Isotropic Radiated Power
ErtPS Extended Non-Real-Time Packet Service
FBSS Fast Base Station Switch
FDD Frequency Division Duplex
FFT Fast Fourier Transform
FRS Frequency reuse scheme
FFRS Fractionnal frequency reuse scheme
FTP File Transfer Protocol
FUSC Fully Used Sub-Channel
HHO Hard Hand-Off
HiperMAN High Performance Metropolitan Area Network
HO Hand-Off
IEEE Institute of Electrical and Electronics Engineers
ISI Inter-Symbol Interference
LOS Line of Sight
MAC Media Access Control
MAN Metropolitan Area Network
MBS Multicast and Broadcast Service
MDHO Macro Diversity Hand Over
MU Mobile Unit
nLOS Near Line-of-Sight
NLOS Non Line-of-Sight
nrtPS Non-Real-Time Packet Service
OFDM Orthogonal Frequency Division Multiplex
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OFDMA Orthogonal Frequency Division Multiple Access
PUSC Partially Used Sub-Channel
QAM Quadrature Amplitude Modulation
QPSK Quadrature Phase Shift Keying
RTG Receive/transmit Transition Gap
rtPS Real-Time Packet Service
SF Service Flow
SFN Single Frequency Network
SISO Single Input Single Output (Antenna)
SNIR Signal to Noise + Interference Ratio
SNR Signal to Noise Ratio
S-OFDMA Scalable Orthogonal Frequency Division Multiple Access
STC Space Time Coding
TDD Time Division Duplex
TTG Transmit/receive Transition Gap
UGS Unsolicited Grant Service
UL Uplink
VoIP Voice over Internet Protocol
WiMAX Worldwide Interoperability for Microwave Access
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2 Mobile WiMax basics
2.1 What is mobile WiMax ? Mobile WiMAX is a rapidly growing broadband wireless access technology based on IEEE 802.16-2004 and
IEEE 802.16e-2005 air-interface standards. The WiMax forum is developing mobile WiMAX system profiles that
define the mandatory and optional features of the IEEE standard that are necessary to build a mobile WiMAX
compliant air interface which can be certified by the WiMAX Forum. Mobile WiMAX is not the same as IEEE
802.16e-2005, rather a subset of the IEEE STD 802.16 standard features and functionalities.
The WiMAX Forum Network Working Group (NWG) is developing the higher-level networking specifications for
Mobile WiMAX systems beyond what is defined in the IEEE 802.16 standard that simply addresses the air
interface specifications.
The combined effort of IEEE 802.16 and the WiMAX Forum help define the end-to-end system solution for a
Mobile WiMAX network.
2.2 Main features of mobile WiMax
2.2.1 OFDMA The mobile WiMAX air interface uses Orthogonal Frequency Division Multiple Access (OFDMA) as the radio
access method for improved multipath performance in non-line-of-sight (NLOS) environments. See §3.2 for
further details.
2.2.2 High data rates The use of multiple-input multiple-output (MIMO) antenna techniques (see §3.4) along with flexible sub-
channelization schemes, adaptive modulation and coding enable the mobile WiMAX technology to support both
peak downlink and uplink high data rates. Concerning the adaptive modulation, kindly refer to the previous
white paper "WiMax radio-planning quickguide with ICS telecom", that can be downloaded from the ATDI web
sites.
2.2.3 Quality of Service The fundamental premise of the IEEE 802.16 medium access control (MAC) architecture is QoS. It defines
service flows which can be mapped to fine granular IP sessions or coarse differentiated-services code points to
enable end-to-end IP based QoS. See §4.1 for further details.
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2.2.4 Scalability The mobile WiMAX technology utilizes scalable OFDMA (S-OFDMA) and has the capability to operate in
scalable bandwidths from 1.25 to 20 MHz to comply with various spectrum allocations worldwide. See §3.2.1.4
for further details
2.2.5 Security The mobile WiMAX incorporates the most advanced security features that are currently used in wireless access
systems. These include Extensible Authentication Protocol (EAP) based authentication, Advanced Encryption
Standard (AES) based authenticated encryption, and Cipher-based Message Authentication Code (CMAC) and
Hashed Message Authentication Code (HMAC) based control message protection schemes.
This particular topic will not be addressed in this white paper, as it is not relevant in scope of radio-planning.
2.2.6 Mobility The mobile WiMAX supports optimized handover schemes with latencies less than 50 ms to ensure real-time
applications such as Voice over Internet Protocol (VoIP).
2.3 Mobile WiMAX certification profiles
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3 Review of mobile WiMax PHY Layer
3.1 Duplex mode
3.1.1 Concept The IEEE 802.16e-2005 air-interface supports both Time Division Duplexing (TDD) and Frequency Division
Duplexing (FDD) modes. However, the initial release of mobile WiMAX profiles only includes the TDD mode of
operation.
The TDD mode is preferred for the following reasons:
• It enables a dynamic allocation of DL and UL resources to support efficiently asymmetric DL/UL traffic
(adaptation of DL:UL ratio to DL/UL traffic).
• It ensures channel reciprocity for better support of link adaptation, advanced antenna techniques such
as transmit beam-forming or MIMO.
• Unlike FDD, which requires a pair of channels, TDD only requires a single channel for both downlink
and uplink providing greater flexibility for adaptation to varied global spectrum allocations.
• Transceiver designs for TDD implementations are less complex and therefore less expensive.
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3.1.2 Impact on mobile WiMAX radio-planning with ICS telecom
The choice of the duplex mode used by the WiMax base stations can be done in their technical parameters:
Definition of the WiMAX profile at the Base Station level
Note that the percentage specified in the UL/DL duration boxes in ICS telecom represents the percentage of
the UL duration wrt to the DL duration within the same frame.
Using the new OFDMA calculator of ICS telecom, the user can define:
• The number of symbols in the OFDMA frame (48 by default)
• The number of overhead symbols in the Downlink
• The number of overhead symbols in the Uplink
• The UL/DL duration ratio (1:1, 12:25, 9:28…)
• The number of symbols included in the Time Transition Gap (TTG)
Based upon these inputs, the software calculates the number of data symbols used in DL and UL. If crossed
with the modulation and the number of OFDMA data sub-carriers used per frame, ICS telecom can
automatically calculate the corresponding throughput in DL and UL (see §3.3.2).
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1:1 DL/UL duration (1.00 in ICS telecom)
2:1 DL/UL duration (0.5 in ICS telecom)
3:1 DL/UL duration (0.33 in ICS telecom)
OFDMA calculator in ICS telecom : calculation of the available data symbols per OFDMA frame according to the UL/DL duration
ratio
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3.2 OFDMA basics
3.2.1 Concept Different physical layer (PHY) have been used in order to define the WiMAX air interface. Each of them having
an impact on the network design.
3.2.1.1 Frequency Division Multiplexing (FDM) WiMAX air interface is based on OFDM/OFDMA PHY. To understand how OFDM and OFDMA work, it is useful
to start with the source namely FDM (Frequency Division Multiplexing).
Frequency Division Multiplexing Spacing is put between two adjacent sub-carriers
In FDM system, signals from multiple transmitters are transmitted simultaneously (at the same time slot) over
multiple frequencies. Each frequency range (sub-carrier) is modulated separately by different data stream and
a spacing (guard band) is placed between sub-carriers to avoid signal overlap.
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3.2.1.2 Orthogonal Frequency Division Multiplexing (OFDM) Like FDM, OFDM also uses multiple sub-carriers but the sub-carriers are closely spaced to each other without
causing interference, removing guard bands between adjacent sub-carriers. This is possible because the
frequencies (sub-carriers) are orthogonal, meaning the peak of one sub-carrier coincides with the null of an
adjacent sub-carrier.
Orthogonal Frequency Division Multiplexing (OFDM)
In an OFDM system, a very high rate data stream is divided into multiple parallel low rate data streams. Each
smaller data stream is then mapped to individual data sub-carrier and modulated using some Phase Shift
Keying Quadrature Amplitude Modulation (QPSK, 16-QAM, 64-QAM…).
OFDM needs less bandwidth than FDM to carry the same amount of information which translates to higher
spectral efficiency. Besides a high spectral efficiency, an OFDM system such as WiMAX is more resilient in
NLOS environment. It can efficiently overcome interference and frequency-selective fading caused by
multipath because equalizing is done on a subset of sub-carriers instead of a single broader carrier. The effect
of ISI (Inter Symbol Interference) is suppressed by virtue of a longer symbol period of the parallel OFDM sub-
carriers than a single carrier system and the use of a cyclic prefix (CP).
ICS telecom’s OFDM parameters box for simulating multipath reflection can highlight the cases where the
signal is damaged due to the reflected signal being greater (by a user-defined margin in dB) than the direct
path threshold and with a ToA outside of the OFDM receiver Guard interval:
Constructive and Destructive OFDM signals in ICS telecom
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3.2.1.3 Orthogonal Frequency Division Multiple Access (OFDMA) Like OFDM, OFDMA employs multiple closely spaced sub-carriers, but the sub-carriers are divided into groups
of sub-carriers. Each group is named a sub-channel. The sub-carriers that form a sub-channel do not need to
be adjacent.
Orthogonal Frequency Division Multiple Access (Sub-carriers with the same color represent a sub-channel)
Sub-channelization defines sub-channels that can be allocated to the mobile units depending on their channel
conditions and data requirements. Using sub-channelization, a Mobile WiMAX BS can allocate within the same
time slot more transmit power for lower SNR cases and less power for higher SNR cases.
In OFDM, only one MU transmits in one time slot.
In OFDMA, several MUs can transmit at the same time slot over several sub-channels.
Sub-channelization in the uplink can save a user device transmit power because it can concentrate power only
on certain sub-channel(s) allocated to it. This power-saving feature is particularly useful for battery-powered
user devices, the likely case in Mobile WiMAX.
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3.2.1.4 Scalable Orthogonal Frequency Division Multiple Access (S-OFDMA)
Additionally benefit over OFDMA is brought by scalable OFDMA (S-OFDMA). The FFT scales its size to the
channel bandwidth in order to keep constant carrier spacing. This brings higher spectral efficiency in wide
channels and a cost reduction in narrow channels.
OFDMA scalability parameters in the OFDMA calculator of ICS telecom
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3.2.2 OFDMA symbol structure There are three types of OFDMA sub-carriers:
• Data sub-carriers for data transmission.
• Pilot sub-carriers for various estimation and synchronization purposes.
• Null sub-carriers for no transmission at all, used for guard bands (left and right) and DC carriers
(used at the transmission frequency).
Active sub-carriers are divided into subsets of sub-carriers called sub-channels.
OFDMA sub-carrier structure
The sub-carriers forming one sub-channel may be, but not need to be, contiguous. Different ways of grouping
sub-carriers into channels in 802.16 are called permutations
Three main permutations:
• FUSC – Full Usage of Sub-channels (DL only): Achieves best frequency diversity by spreading the sub-
carriers over the entire band
• PUSC – Partial Usage of Sub-channels (UL and DL)
o Groups the sub-carriers into tiles to enable fractional frequency reuse scheme (FFRS).
o Still has distribution of sub-carriers across band for each sub-channel
• AMC (or Band AMC)–Adaptive Modulation and Coding (UL and DL)
o a.k.a. Adjacent Sub-carrier Permutation
o Uses adjacent sub-carriers for each sub-channel for use with beam forming
Note that alternative permutations, such as TUSC (supporting both beam forming and OFDMA permutation)
might be used as an option in the DL sub-frame.
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There are two main types of sub-carrier permutations: distributed (diversity) and localized (contiguous). In
general, distributed sub-carrier permutations perform very well in mobile applications while adjacent sub-
carrier permutations can be properly used for fixed, portable, or low mobility environments. These
options enable the system designers to trade mobility for throughput.
Diversity
(mobility users)
Contiguous
(fixed and nomadic users)
FUSC
PUSC DL
TUSC
AMC
UL PUSC AMC
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3.2.3 Subchannelization schemes In ICS telecom, the user can select a given OFDMA permutation and the number of data sub-carriers used
either manually or by pointing to predefined tables.
3.2.3.1 Manual input The user can to define its own configuration of the OFDMA permutation by:
• Selecting if he wants to work in DL or in UL
• Defining the total number of sub-channels in the OFDMA frame
Number of sub-channels
OFDMA
permutation
1.25 MHz BW 5 MHz BW 10 MHz BW 20 MHz BW
DL FUSC 2 8 16 32
DL PUSC 3 15 30 60
DL O-FUSC 2 8 16 32
DL O-AMC 2 8 16 32
UL PUSC 4 17 35 92
UL O-PUSC 6 24 48 96
UL O-AMC 2 8 16 32
• Defning the number of pilot, data and null sub-carrier per sub-channel (default respectively to 8, 16
and 1)
The number of occupied sub-carriers and occupied data sub-carriers impacts the cell edge radius, as well as
the throughput.
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3.2.3.2 Predifined tables The user can also select the OFDMA permutation to check by selecting it once he has defined the channel BW
and whether he wants to work in UL or in DL.
In that case, ICS telecom will automatically fill the number of sub-carriers used (cell edge calculation) and the
number of data sub-carriers used (throughput calculation).
OFDMA permutation 1.25 MHz BW 5 MHz BW 10 MHz BW 20 MHz BW
Nb of sub-carrier 105 426 851 1702 DL FUSC Nb of data sub-carrier 96 384 768 1536
Nb of sub-carrier 85 421 841 1681 DL PUSC
Nb of data sub-carrier 72 360 720 1440 Nb of sub-carrier 108 432 864 1728
DL O-FUSC Nb of data sub-carrier 96 384 768 1536
Nb of sub-carrier 108 432 864 1728 DL O-AMC
Nb of data sub-carrier 96 384 768 1536
Nb of sub-carrier 97 408 840 1681 UL PUSC
Nb of data sub-carrier 272 840
Nb of sub-carrier UL O-PUSC
Nb of data sub-carrier 109 433 865 1729 Nb of sub-carrier 108 432 864 1728
UL O-AMC Nb of data sub-carrier 96 384 768 1536
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3.3 Impact on mobile WiMAX radio-planning with ICS telecom With mobile WiMax, users operate on sub-channels, which only occupy a small fraction of the channel
bandwidth (FFRS), in order to avoid cell edge-interference. However, the fractional use of the channel
bandwidth is trade-off between:
• The link budget : the more sub-channel are used, the smaller the cell range
• The data rate : the more sub-channel are used, the bigger the throughput
• The interference : the more users, the more sub-division of the channel bandwidth will occur in order
to avoid co-channel interference.
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3.3.1 Calculation of the system gain and the sensitivity
3.3.1.1 Downlink The user specifies the following input parameters:
• Base Station
o The output power per antenna elements
o The number of transmitting antenna
elements
o The nominal antenna gain
o The number of antenna arrays (if AAS is
enabled)
o The pilot power boosting loss
• Mobile Unit
o The nominal receiving antenna gain
o The diversity receiving antenna gain
o The noise figure
• Advanced parameters
o SNR required
o Thermal noise
o The number OFDMA sub-carriers used per
OFDMA frame
ICS telecom will then calculate the system gain in downlink, as well as the receiving sensitivity of the mobile
unit for this given OFDMA permutation.
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Scalability for mobile WiMax : impact of the variation of the FTT size on the coverage
(Downlink – FUSC OFDMA permutation – Mobile handheld receiver – 16QAM1/2)
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3.3.1.2 Uplink The user specifies the following input parameters:
• Mobile unit
o The type of equipment
o The output power per antenna elements
o The number of transmitting antenna
elements
o The nominal antenna gain
o The number of antenna arrays (if AAS is
enabled)
o The pilot power boosting loss
• The base Station
o The nominal receiving antenna gain
o The diversity receiving antenna gain
o The noise figure
• Advanced parameters
o SNR required
o Thermal noise
o The number OFDMA sub-carriers used per
OFDMA frame
ICS telecom will then calculate the system gain in uplink, as well as the receiving sensitivity of the base station
for this given OFDMA permutation.
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Mobile WiMax coverage according to the type of receiver
1024 FFT size - PUSC Uplink permutation – 16QAM1/2
3.3.2 Calculation of the throughput In addition to the calculation of the receiving sensitivity in both uplink and downlink, ICS telecom calculates
the throughput according to:
• The specified modulation (if not in AMC permutation)
• The UL/DL duration ratio
• The number of data sub-carriers used per OFDMA frame
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In case the O-AMC is selected, ICS telecom can calculate the maximum achievable bit rate for every single
modulation.
Mobile WiMax coverage according in the O-AMC permutation
1024 FFT size O-AMC permutation
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3.4 SISO, MISO, SIMO, MIMO schemes Various technologies are used for smart antenna systems: Switched Beams, Adaptive Array Systems(AAS),
SIMO, MIMO, STC... The strategies used rely on optimising the gain or the directionality of the radiation
patterns, spatial multiplexing, combining multipath signals. These adaptive systems take advantage of their
ability to effectively locate and track various types of signals to dynamically minimize interferences and
maximize intended signal reception.
SISO case
SIMO case
MISO case
MIMO case
:
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The key parameters for field strength predictions are the antenna gain in the transmitting and receiving ways
and the sensitivity of the receiver.
• the radio planner can use ICS telecom to define manually its own parameters to set the antenna gain
and receiving threshold; • For adaptive antenna arrays, the user defines the composite pattern corresponding to all radiating
elements and the number of available elements. The "burst" gain" is calculated and the nominal gain
updated, based on the assumption that an antenna array containing M elements can provide a power
gain of M over white noise level.
• For switched beams, ICS telecom nG automatically detects the best predefined beam to offer/receive
the best signal in a given direction and then applies interference rejection from pattern discrimination
and location of the interferers.
Adaptive antenna systems in ICS telecom : the user specifies the number of arrays available in DL and UL
DL UL Calculation of the EIRP according to the number of antenna elements and antenna arrays in the OFDMA calculator of ICS telecom
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In addition to the features available to model adaptive antenna arrays, ICS telecom also includes not only
specific functions related to dynamic beam forming according to angle or arrival (off-axis angle) of the signals,
but also the capability to modify the coverage according to the directivity of a receiver and the location of its
most-probable server.
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Best server plot from BS1 and BS2
Coverage of BS 1 (left) and BS 2 (right) with an omni-directionnal Rx antenna
Coverage of BS 1 (left) and BS 2 (right) with 4 arrays Rx antenna pointing to its most-probable server and therefore reducing the
interfrering power of the other base stations
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3.5 Frequency reuse schemes
3.5.1 Concept OFDM works well in the channels with relatively high SINR. In multi-cell deployments, in order to avoid inter-
cell interference, basic OFDM requires directional antennas or relatively high frequency-reuse schemes and
careful radio-frequency (RF) planning.
OFDMA with its various subcarrier allocation schemes (FUSC and PUSC) improves performance in multi-cell
deployments by averaging the interference across multiple cells. The interference becomes a function of cell
loading and can be significantly reduced by efficient scheduling. OFDMA systems, on the other hand, are very
flexible in terms of RF planning and support a variety of frequency reuse schemes (FRS). These FRS may be
described by denotation NcxNsxNf, where
• Nc is number of independent frequency channels in the WiMAX network
• Ns is the number of sectors per cell
• Nf is the number of segments in exploited frequency channel.
Two of these FRS are for instance 1x3x1 and 1x3x3. Both schemes use three-sector base-stations and require
only one RF channel for all sectors and BS, hence opening the door for operators who have limited amount of
spectrum.
FRS 1x3x1 eliminates the need for any frequency planning. That is a significant advantage especially for heavy
urban areas where RF planning is very difficult. FRS 1x3x3 uses different (orthogonal) sets of tones (called
“segments”) for each sector of a base-station thereby reducing inter-cell interference and minimizing outage
area. This scheme also simplifies RF planning–one need only assign segments to sectors while using the same
RF channel among all base-stations.
FRS 1x3x1
FRS 1x3x3
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Since the OFDMA PHY layer has many choices of sub-carrier allocation methods, multiple zones can use
different sub-carrier allocation methods to divide each subframe. One benefit of using zone switching is that
different frequency schemes can be dynamically deployed in a cell, forming a fractional frequency reuse
scheme (FFRS). The image here below shows an example of deploying different FFRS in one frame. For the
first half of each frame, the entire frequency band is divided by three and allocated in each sector. For the
second half of each frame, the whole same frequency band is used in each sector. The benefits of deploying
FFRS in one frame are:
• edge users, who are receiving co-channel interference from other sectors in other cells, also have
suppressed co-channel interference (CCI)
• users around the cell center have the full frequency band because they are relatively less subject to
co-channel interference.
FFRS with 802.16 OFDMA wimax
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3.5.2 Impact on mobile WiMAX radio-planning with ICS telecom ICS telecom features the functionality of calculating SINR maps, in order to highlight the positive impact of
using segmented frequency channels with regards to the interference.
Mobile WiMax SINR map : FRS 1x3x1 Mobile WiMax SINR map : FRS 1x3x3
FFT 1024 – DL PUSC permutation – SIMO configuration with 4 antenna arrays at the Mobile Unit
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Map of the subchannel distribution in case of a non-fractionnal frequency reuse scheme (FRS 1x3x3)
Mobile WiMax sub-channel distribution with a FFRS 1x3x3
FFT 1024 – SIMO configuration with 4 antenna arrays at the Mobile Unit – PUSC 1/3
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4 Review of mobile WiMAX MAC layer
4.1 QoS – Data service Types
4.1.1 Concept
In the Mobile WiMAX MAC layer, Quality of Service (QoS) is provided via service flow (SF). Before providing
a certain type of data service, the base station and user-terminal first establish a unidirectional logical link
between the peer MACs called a connection. The outbound MAC then associates packets traversing the MAC
interface into a service flow to be delivered over the connection. The QoS parameters associated with the
service flow define the transmission ordering and scheduling on the air interface.
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4.1.2 Impact on mobile WiMax radio-planning with ICS telecom Depending on the customer profile, the user can specify per mobile unit its Service Flow repartition, and the
priorities to respect (the contention free SF have piority over the SF working in contention mode).
Traffic request and Service Flows provisioning at the Mobile Unit level in ICS telecom
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The overall QoS of each sector can be calculated according to:
• A service flow provisioning defined on a per mobile unit basis
• The throughput available at each sector, calculated according to the OFDMA permutation and the
number of data sub-carriers used, the UL/DL duration ratio, the modulation…
• A variation of the contention ratio according to the hour of the day
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4.2 Handoff There are three handoff methods supported within the 802.16e standard – Hard Handoff (HHO), Fast Base
Station Switching (FBSS) and Macro Diversity Handover (MDHO). Of these, the HHO is mandatory while
FBSS and MDHO are two optional modes.
4.2.1 FBSS / MDHO When the FSBB or MDHO are supported, the MS and BS maintain a list of BSs that are involved in
FBSS/MFDHO with the MU. This set is called an Active Set.
The MDHO hand off allow a mobile unit to transmit and receive from multiple BS at the same time.
In FBSS, the MS continuously monitors the base stations in the Active Set,. Among the BSs in the Active Set,
an Anchor BS is defined. When operating in FBSS, the MU only communicates with the Anchor BS for uplink
and downlink messages including management and traffic connections. Transition from one Anchor BS to
another (i.e. BS switching) is performed without invocation of explicit HO signaling messages.
4.2.1.1 List of neighbors
If it is not already known by the mobile operator, the use can locate BS per BS with what other BS it could be
a neighbor.
Highlighting the neighbours of the Base Station in order to define the Active Sets
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4.2.1.2 Active set allocation The radio-planner can specify for each BS the active set(s) it is belonging to :
Definition of the active sets each BS belongs to in ICS telecom
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4.2.1.3 FSBB/MDHO handover map within the same active set The user can specify the active set to be analyzed. By specifying the soft handover mode, ICS telecom will
highlight the areas where an FSBB/MDHO handover can occur. These areas are highlighted in yellow in the
pictures below, otherwise ICS telecom can give the color of the active set (or the color of the best server, if
needed).
FSBB handover map for a mobile unit anchored to active set 1
FSBB handover map for a mobile unit anchored to active set 2
FSBB handover map for a mobile unit anchored to active set 3
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4.2.2 Hard handover When the Mobile WiMAX unit switches from one active set area to another, it performs what is called a hard
handover (HHO). ICS telecom can display where the mobile anchored to a specific active set will have to hard
hand off to another one.
HHO map of a mobile anchored to Active set 1 with any other active set
HHO map of a mobile anchored to Active set 2 with any other active set
HHO map of a mobile anchored to Active set 3 with any other active set
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4.2.3 Hand-over along a mobile path If the radio planner is more particularly interested into a mobile path, a dedicated hand over analysis can be
performed, in UL or in DL.
Display of the FSBB hand-over of a mobile unit anchored to active set 3
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4.3 Multicast and broadcast service
4.3.1 Concept The Multicast and Boroadcast service (MBS) can be supported in two ways :
• Embedded MBS: a separate MBS zone is defined in the DL frame along with the unicast service
• Whole MBS: the whole frame can be dedicated to MBS (DL only) for standalone broadcast service.
The MBS zone supports multiple Base Stations working in MBS mode using Single Frequency Network (SFN)
operation It may be noted that multiple MBS zones are also feasible.
4.3.2 Impact on mobile WiMAX radio-planning with ICS telecom When working in MBS mode, all the BS participating the same MBS transmit the same data, use the same
permutation, subchanellization… The equivalent channel reception is the sum of the individual channels from
all the BS in the MBS. The delay in the signal that comes from a distant BS translates to a delayed impulse
response, which increase the delay spread of the equivalent/consolidated channel, generating therefore ISI in
the SFN area.
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WiMax coverage in Unicast situation (left) or in Multicast situation right)
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