Technical Presentation at
Columbia University
WiBro– A Mobile WiMAX System,
and Radio Resource Management
Sept 20, 2006
Byeong Gi Lee
Seoul National University
ICT Snapshot - Services
Penetration of high-speed Internet
(4Q 2005)
152M
30%
52M
USA
Denmark
Belgium
Japan
Netherland
Canada
Taiwan
Korea
39%
19M
43%
25M
73%
0
20
40
60
80
Seoul National University, BG Lee, Sept. 2006
2
ICT Snapshot - Devices
Mobile phone market share
25%
(4Q, 2005)
31%
7%
6%
13%
18%
Seoul National University, BG Lee, Sept. 2006
Nokia
Motorola
Samsung
Sony Ericsson
LG
Others
3
Wireless Internet in Korea
 Wireless Internet Subscribers
1
(Source KT)
Wireless Internet Subscribers
45
40
96%
97%
27M
94%
25
20
39M
33M
35
30
38M
78%
2001
2003
15
2005
2008
10
5
0
Mobile Phone
Subscribers2005
2001
2003
2006.7
Wireless Internet Subscribers
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Wireless Internet in Korea
2
 Wireless Internet Sales (wrt Total Sales)
6.7 billion USD
3.7 billion
35.7%
2 billion
19.8%
0.5 billion
11.6%
4.6%
2001
2003
2005
Seoul National University, BG Lee, Sept. 2006
2008
5
Part 1.
WiBro:
A Mobile WiMAX System
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What is WiBro?
WiBro (Wireless + Broadband)
Harmonization with Mobile WiMAX Based on IEEE 802.16e Standard
- An OFDMA based Profile of IEEE 802.16e Standard
Mobility
IP
 Vehicle speed (60
km/h, 120 km/h)
 Compatible with
Good performance
while on the move
 Diverse terminal types
(PC/PMP/PDA/Phones etc)
Internet world
Broadband
 1Mbps per user
 Broadband
uploading capability
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WiBro on the Evolution Paths to 4G
1995
2000
2005
2010+
4G
Fast
3G
2G
1G
(IMT2000)
(Digital)
(Analog)
WiBro
Slow
802.11b
2.4 GHz
WLAN
PAN
5 GHz
WLAN
5 GHz
WLAN
802.11a/g
~ 14.4 kbps
144 kbps
384 kbps
802.11n
50 Mbps
200 Mbps
Seoul National University, BG Lee, Sept. 2006
1Gbps
8
WiBro on the Evolution Paths to 4G
2000~2002
2003~2004
2Mbps/2Mbps
WCDMA
Cellular
Based
(3GPP,
3GPP2)
153kbps/
307kbps
EV-DO
153kbps/2.4Mbps
2005~2006
2Mbps/14.4Mbps
30Mbps
WCDMA(R5)
HSDPA
WCDMA(R6)
HSUPA
1.8Mbps/3.1Mbps
EV-DO
Rev. A
cdma2000 1x
2008~2010
1.8Mbps/4.9Mbps*
3G LTE
HSOPA
EV-DO
Rev. B
EV-DO
Rev. C
4G
Internet
Based
(IEEE)
11Mbps
54Mbps
802.11b
802.11a/g
6Mbps/18.4Mbps
100Mbps
WiBro
WiBro-2
75Mbps(Fixed)
802.16a/b/d
Harmonization
802.16e
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IEEE 802.16 Standardization
 IEEE 802.16 (~2001)
 PHY and MAC standard for fixed wireless users with LOS
(10~66GHz)
 IEEE 802.16a (~Apr. 2003)
 For fixed wireless users with NLOS (2~11GHz)
 Three PHY structures: SC, OFDM, OFDMA
 IEEE 802.16c (~Jan. 2003)
 System profile for interoperability (10~66GHz)
 IEEE 802.16d (Rev approval, June 2004)
 Consolidated standard of .16, .16a, and .16c
 IEEE 802.16e (WG ballot, June 2004)
 802.16d-based amendment for mobility
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Standards – 802.16 vs. WiBro
 IEEE 802.16 and WiBro
WiBro
Mobility
(Handoff & Sleep mode)
802.16 e
MAC
802.16 d
SC
OFDM
OFDMA
Scalable OFDMA, MIMO,
LDPC,
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WiBro Requirements
Major System
Parameters
Radio Access Requirement
Duplexing
TDD
Frequency Reuse
Factor
1
Multiple
Access
OFDMA
Mobility
≤ 60 [Km/h]
Channel
BW
10 [MHz]
Service Coverage
≤ 1 [Km]
Spectral
Efficiency
[bps/Hz/cell(sect.)]
Max. DL / UL = 6 / 2
Aver. DL / UL = 2 / 1
Handoff
≤ 150 [ms]
Throughput
(per user)
Max. DL / UL = 3 / 1 [Mbps]
Min.DL/UL = 512/128 [Kbps]
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Cellular vs. WiBro vs. WLAN
WiBro
Cellular
Cellular
WLAN
Metro
Zone
(2G, 3G)
WiBro
WLAN
AP
Hot
Spot
AP
AP
AP
Indoor
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WiBro Network Architecture
NMS : Network Management System
CMS : Contents Management System
PMS : Product Management System
VCC : Voice Call Continuity
MSC : Mobile Switching Center
IMS : IP Multimedia Subsystem
RAS : Radio Access Station
ACR : Access Control Router
AAA : Authentication, Authorization
and Accounting
PSTN
BTS
BSC
Toll
MSC
CDMA
WiBro
Trunk
Gatew
VCC ay
PMS CMS
IMS
Server Farm
RAS
ACR Edge Core
Router Router
(Portal, VOD,
etc)
AAA
Back End
Platform
A
Server
Mediation Billing
WiFi
Internet
AP
Edge
Router
Gateway
Core
Router
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WiBro System
by Samsung Electronics
 Access Control Router
 Radio Access Station
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WiBro System Functions
RAS
MIP FA
Function
Scheduling
MAC PDU Processing
MAC
ARQ
Control
Packet Header Suppression
Air Link
ACR
Handoff
Packet Classification
Handoff Control
(relay)
Packet Forwarding
Security
Management
Session Control
Core Network Traffic
Interface
Connection Control
Signaling Plane
Mobility
Management
User Traffic Plane
Physical Layer
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Deployment of WiBro Services
 Trials (’05~’06)
 Commercial services (’06)
 KT, SKT in Korea
 Service trial and commercial service TVA in Brasil
 Cooperation in progress with various operators
and vendors in Mobile WiMax Forum
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Commercial WiBro Service
BunDang
Area
Located 20km South of Seoul
Population: 450,000
Area: 70 Km2
by KT
22 Radio Access Stations
 RAS
 Repeater
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WiBro PHY - Features
 High spectral efficiency support
 TDD
 Minimize guard band
 10MHz BW/OFDMA
 Minimize multi-path interference
 High modulation order (QPSK, 16QAM, 64QAM) &
enhanced channel coding (convolutional turbo code)
 Full coverage support
 Cellular operation with frequency reuse factor 1
 High spectral efficiency & easy cell planning
 Minimize interference using diversity subchannel
 Compensate low SINR at cell edge using low rate coding
 Fast handover with mobile IP
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WiBro PHY – Features (cont’d)
 Performance enhancement considering mobility
 H-ARQ
 FEC and ARQ
 Band selection AMC & diversity subchannel
 For slowly moving users: allocate band selection AMC
subchannels which have high channel quality
 For fast moving users: allocate diversity subchannels
 Support mobility
 Short OFDM symbol
 Pilot structure supporting channel estimation while moving
 Support fast access during handover
 Short frame length
 Non-contention based control channel access
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WiBro PHY – Features (cont’d)
 Flexible resource allocation
 TDD: asymmetric DL / UL allocation
 Subchannel-level multiuser scheduling
 Power saving mechanisms
 Sleep mode
 Idle mode
 Advanced optional features
 Smart antenna support
 Space-time code/Spatial multiplexing support
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WiBro PHY – OFDMA
 Basic Concept of OFDM
 Orthogonal Frequency Division Multiplexing : Advanced
FDM
 Divide into N orthogonal subcarriers
 Transmit N symbols in N subcarriers respectively
 Reconstruct N symbols using orthogonality
 FDM: Use separated subcarriers (A, C, E)
 OFDM : Use overlapped orthogonal subcarriers (A,B,C,D,E)
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WiBro PHY – OFDMA (cont’d)
 One Big Stream
Huge bunch of small streams
 Long Symbol Period
 Robust to multipath fading
( Small guard time overhead)
 Huge bunch + Orthogonality
 Robust to narrowband
interference
 Efficient use of radio
spectrum
 Appropriate for
Broadband System
1Mbps Stream
(Ts : 1us)
10 X 100 Kbps
(Ts : 10 us)
1us delayed
path signal
Narrowband
interference
Strong Candidate for the Next-Generation
Wireless Access
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WiBro PHY – System Parameters
Parameter
Value
Duplex
TDD
Multiple Access
OFDMA
System Bandwidth
10 MHz
Sampling frequency
10 MHz
Number of used tones
864 out of 1,024
Number of data tones
768
Number of pilot tones
96
Tone spacing
9.765625 kHz
Signal bandwidth
8.447 MHz
Ratio of cyclic prefix time to basic OFDM symbol time
Basic OFDMA symbol time
1/8
102.4 ms
12.8 ms
Cyclic prefix time
115.2 ms
OFDMA symbol time
TDD frame length
5 ms
Number of symbols in a frame
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24
WiBro PHY – Subchannel
 DL-Diversity subchannel (FUSC, full usage)
 IDcell-based permutation
 Distributed data subcarriers in a symbol
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WiBro MAC – Features
 Flexible BW allocation
 On frame basis
 Flexible QoS provisioning
 UGS, rtPS, nrtPS, BE
 Efficient MAC PDU construction
 Variable size MAC PDU
 Fragmentation, packing, concatenation
 Support header suppression
 Energy-saving
 Sleep & idle mode
 Handover
 Hard & soft handover
 Multicast and Broadcast Services
 Security support
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WiBro MAC – Frame Structure
 Frame structure




Management messages (GMH & CRC)
DL-MAP, UL-MAP
Burst profile
Uplink control channel (CQI, ACK, ranging)
DOWNLINK
GMH
UPLINK
GMH
DL-MAP IE
UL-MAP IE
DL-MAP IE
UL-MAP IE
DL-MAP IE
UL-MAP IE
DL-MAP IE
UL-MAP IE
Burst #3
CRC
UL-MAP
UL Burst #1
Burst #1
UL Burst #2
ACK
CH
Burst #2
CRC
DL-MAP
CQICH
CDMA
Ranging
Seoul National University, BG Lee, Sept. 2006
UL Burst #3
27
WiBro Evolution Issues
 Scalability
 10/20/40MHz TDD, 10/20 MHz FDD
 Throughput enhancement
 MU-MIMO, LDPC
 Mobility improvement
 Up to ~300Km/h
 Spectral efficiency increase
 Up to ~10b/s/Hz/cell
 Control overhead minimization
 Multi-hop relay
 Backward compatibility
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Comparison of WiBro, HSPA, and EVDO
EVDO
Rev B
(3-carrier)
HSDPA
HSPA
Parameter
1xEVDO
Rev A
WiBro
(2x2)
Duplex
FDD
FDD
FDD
FDD
TDD
Occupied spectrum
2.5 MHZ
10 MHz
10 MHz
10 MHz
10 MHz
DL
1.25 MHZ
5 MHz
5 MHz
5 MHz
UL
1.25 MHZ
5 MHz
5 MHz
5 MHz
DL
3.1 Mbps
14.7 MHz
14 Mbps
14 Mbps
46 Mbps
UL
1.8 Mbps
5.4 MHz
2.0 Mbps
5.8 Mbps
14 Mbps
DL
0.85
bps/HZ
0.93
bps/Hz
0.78
bps/Hz
0.78 bps/Hz
1.93
bps/Hz
UL
0.36
bps/Hz
0.28
bps/Hz
0.14
bps/Hz
0.30 bps/Hz
0.88
bps/Hz
Channel BW
Peak data rate
Spectral efficiency
Net information
throughput per
channel/sector
10 MHz
DL
1.06 Mbps 4.65 Mbps
3.91 Mbps
3.91 Mbps
14.1 Mbps
UL
0.45 Mbps 1.38 Mbps
0.70 Mbps
1.50 Mbps
2.19 Mbps
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WiBro Services
Personal
• Integrated Messaging Service
- SMS/MMS, Group Messaging
- Instant Messaging/Chatting
• Mobile Blog
IP Telephony
• VoIP, Video Telephony
• PTA
- PTT (Push to talk- 1:N telephony)
- PTD (Push to Data - Send data during PTT)
- Web Blog + Mobile
• Telematics
- PTV (Push to Video - 1:N Video telephony)
- Traffic Information, Location Search, etc.
Internet
Entertainments
• AOD/MOD, VOD
• Web Service
- E-mail, Internet Browsing
• Information On Demand
- Personalized Information Service
• Streaming Broadcasting
• 3D/Interactive Game
• M-Commerce
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Part 2.
Radio Resource Management
for Next-Generation Broadband
Wireless Communications
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Radio Resource
 Radio Resource
 Something to allocate to each service traffic in order to
provide the requested service
 Categories of Resources




Bandwidth (time, frequency)
Transmission power
Transmit/receive antenna
Buffer space, MAC address, …
Three Fundamental
Radio Resources
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Radio Resource
(cont’d)
 Limitations in Using Radio Resources
 Bandwidth:
 Absolutely limited,
 License fee
 Transmission power:
 Available operation range of amplifier,
 Mitigation of interference,
 Lifetime of battery-powered devices
 Antenna:
 Difficulty in deployment,
 Operation complexity
Should utilize radio resources efficiently.
Need efficient radio resource management techniques.
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Radio Resource Management
(cont’d)
 Why Important?
Limited
Radio Resources
Service
Requirements
QoS
Provisioning
Radio
Resource
Management
Communication
Environments
High
System Efficiency
Plays a key role for efficiency enhancement for
next-generation wireless communications
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Radio Resource Management
 Radio Resource Management
 Determines the amount of each resource to allocate to
each service traffic
 In general RRM problem is formulated as a constrained
optimization.
Problem Objective:
Maximization of the system efficiency
Under constraints on:
Amount of available resources
User performances
(strongly related to QoS requirements)
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Radio Resource Management
(cont’d)
 Composition of RRM





Admission control
Scheduling
Channel adaptation; power and rate control
MAC state management
etc.
 Selected Issues in RRM




1.
2.
3.
4.
Opportunistic scheduling
RRM for OFDM
Antenna management
Inter-cell resource management
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Opportunistic Scheduling
1
 Time-Varying Nature of Wireless Channels
 Fading due to constructive and destructive interference
among multiple signal paths
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Opportunistic Scheduling
2
 Fading is viewed as a Source of Unreliability
 For delay-sensitive traffics (e.g. voice)
 Should be compensated by using more resources
 Power control, antenna diversity, …
 Fading may be viewed as a Source of Opportunity





Change of the viewpoint
For delay-tolerable traffics (e.g. best effort data)
Transmit only when the channel quality is near its peak
Can help to save resources
Can increase the system capacity
Opportunistic Scheduling
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Opportunistic Scheduling
3
 Communications in Shared Channels
 If the constituent users have independent channel
statistics,
 Schedule the user whose channel quality is near its peak
 Can increase of the capacity by multiuser diversity gain
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Opportunistic Scheduling
4
 User Performance in Multiuser Scheduling
 Most researches focused on the “fairness” among the
users with different average channel quality
 In terms of the served time or the throughput ratio
 Fairness criterion is not directly related to the service
requirement; it only provides relative differences among
the users (e.g. [Liu01, Borst01, Vis02])
 QoS Provisioning with Multiuser Diversity
 Prediction of the required amount of resources
 Determination of the fairness criterion according to the
predicted results
 Admission control for infeasible requirements
CDF-based scheduling [Park05]
→ A predictable opportunistic scheduler
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Opportunistic Scheduling
5
 CDF-based Scheduling Algorithm [Park05]
 Uses the CDF of each user’s channel quality as the
scheduling metric
 Exact calculation of user performance becomes possible
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RRM for OFDM
1
 OFDM in view of RRM
 High degree of flexibility in resource allocations
 Two-dimensional degree of freedom
 Subcarrier (bandwidth)
 Transmission power
 Exploits the multiuser diversity in frequency domain
 Becomes an opportunistic scheduling problem equipped
with power allocation for multiple parallel channels
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RRM for OFDM
2
 Subcarrier Allocation
 Straightforward extension of single-channel case possible
 Main source of performance gain
 Transmission Power Allocation
 Intra-user allocation
 Power distribution among subcarriers allocated to a specific
user
 Inter-user allocation
 Power distribution among different users
 Users with weak channel prefer the transmission power;
users with strong channel prefer the subcarrier
 About 10~20% additional gain is observed in several
papers [Song05, Shen05, Seo06]
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RRM for OFDM
3
 Performance Comparison
 Non-opportunistic
subcarrier allocation
 Opportunistic
subcarrier allocation
 Opportunistic
subcarrier allocation
with asymptotically
optimal power
allocation
- Single cell OFDMA
- Proportional fair throughput
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RRM for OFDM
4
 Issues in RRM for OFDM
 Feedback overhead in OFDM
 Channel state information of all the subcarriers are needed.
 How to reduce this feedback overhead?
 Service convergence
 Each service type has its own optimal allocation strategy
(e.g. scheduling metric).
 How can integrate different strategies in a single OFDM
system?
 Computational complexity
 Interactive relation between the subcarrier and transmission
power allocation
 Iterative determination  High complexity
 Equal power allocation  Performance loss
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Antenna Management
1
 MIMO Technique
 Multiple Input Multiple Output
 Use of multiple transmit/receive antenna
 Diversity, beamforming, spatial multiplexing, space
division multiple access (SDMA)
 One of the key technologies for high spectral efficiency
Tx
Data
MIMO
Encoder
Tx
Rx
Tx
Rx
Tx
Rx
MIMO
Decoder
Seoul National University, BG Lee, Sept. 2006
Rx
Data
46
Antenna Management
2
 Diversity




Makes individual point-to-point links reliable
All the antennas transmit the same information
Fading of each antenna is averaged
The number of independent copies  diversity order
 Multiplexing
 Splits the information stream into several parallel
substream
 Each antenna transmits different substream
 Proper signal processing such as BLAST is needed
 Increases the transmission rate of the link
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Antenna Management
3
 Beamforming
 Steers the transmission beam to a specific direction
 Improves the SNR of users in the direction while reducing
interference to others
 How to Apply These Techniques?
 Tradeoff relation among different antenna techniques
 What is the optimal combination of the above three
schemes?
 Different answers for different services and environments
(e.g. dependent on delay requirement, rank of channel
matrix, channel coding scheme and HARQ, …)
 A guideline is needed for switching the techniques.
 A hybridization can improve the performance.
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Antenna Management
4
 Switching between diversity and multiplexing
 [Heath05]
 2*2 MIMO
 Fixed tx rate;
4 bits/symbol
 Diversity,
multiplexing,
optimal selection
of them
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Antenna Management
5
 Hybridization of beamforming and diversity [Kwon]
 6 tx, 1 rx antenna
 N: number of
antenna groups
 Beamforming in
each group
 Diversity among
different groups
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Inter-cell Resource Management
1
Intra-Cell RM
-
Scheduling
Power and rate control
Admission control
MAC state control considering power saving, …
Inter-Cell RM
- Inter-cell interference management
- Frequency reuse factor adjustment
- Inter-cell load balancing
Decentralized Coordination
- Minimized inter-cell coordination
- Signaling protocol via the
backbone network
Autonomous RM
- No coordination
- Implicit signaling via
interference measurement
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Inter-cell Resource Management
2
 Illustration of cell and pseudo-cell
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Inter-cell Resource Management
3
 Necessity of Inter-cell RM
 Severe inter-cell interference to users at the cell
boundary in OFDM systems
 Cell planning?  Not a suitable solution when considering
the “plug-and-access” concept of all-IP networks
 Practical difficulties in cell planning because of different
size and shape of each cell
 Requirement on Inter-cell RM
 Distributed operation: No hierarchical structure in all-IP
networks
 Load balancing: Adjust the amount of the used resources
 Reduce the ICI of a heavily loaded cell
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Inter-cell Resource Management
4
 Decentralized Coordination [Kwon04]
 Pseudo cell structure; group of dominant interfering
sectors
 Inter-cell RM with coordination only within each pseudo
cell → limited signaling
 Autonomous RM [Kwon05]
 Inter-cell RM without any explicit signaling
 Implicit signaling via interference measurement
 Interpret the increment of ICI as a request of more
resources
 Multi-cell iterative water-filling with price adaptation
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Inter-cell Resource Management
5
 Signaling structure
Coordinated RM
Autonomous RM
Coordinating Function
Power update
Power allocation
information
BS
Channel & load
informaion
BS
BS
No signaling
BS
BS
MS
MS
Parameter
broadcast
BS
Channel
informaion
Channel
informaion
MS
MS
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Inter-cell Resource Management
6
 Performance comparison
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Summary – Advanced RRM
 Radio Resource Management
 Plays the key role in the next-generation wireless
communications
 System efficiency and QoS provisioning
 Current Issues in RRM




Opportunistic scheduling
RRM for OFDM
Antenna management
Inter-cell resource management
 Many interesting and important RRM
problems yet to be solved for the efficiencyenhancement of next-generation wireless
communications.
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Selected References
[Liu01] X. Liu et. al., "Opportunistic transmission scheduling with
resource-sharing constraints in wireless networks," IEEE J-SAC, Oct.
2001.
[Borst01] S. Borst et. al., "Dynamic rate control algorithms for HDR
throughput optimization," IEEE INFOCOM 2001.
[Vis02] P. Viswanath et. al., "Opportunistic beamforming using dumb
antennas," IEEE T-COM, June 2002.
[Park05] D. Park, et. al., "Wireless packet scheduling based on the
cumulative distribution function of user transmission rates," IEEE TCOM, Nov. 2005.
[And01] M. Andrews et. al., "Providing quality of service over a shared
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