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Computer Network
Yu-Jie Chen
2008/07/16
Outline
WiMAX Overview
Relay Topology (802.16j)
MIMO-OFDM System
IEEE 802.16
Features (1/2)
Broad bandwidth
Up to 134.4 Mbit/s in 28 MHz channel (in 2-66 GHz)
32Mb/s - 134.4Mb/s (>=20MHz per channel)
1.25/2.5/5/10/14/20/25/28MHz per channel
Supports multiple services simultaneously with full
QoS
Efficiently transport IPv4, IPv6, ATM, Ethernet, etc.
Wireless transportation system.
Bandwidth on demand (frame by frame)
Centralized control
MAC designed for efficient used of spectrum
Features (2/2)
Supports multiple frequency allocations from 2-66 GHz in
802.16 (10-66GHz) , 802.16a (2-11GHz) and 802.16e (<6GHz)
Single carrier (SC) for line-of-sight situations
OFDM and OFDMA for non-line-of-sight situations
OFDM : orthogonal frequency division multiplexing
OFDMA : orthogonal frequency division multiple access
Access schemes:
TDD (time division duplex) and FDD (frequency division duplex)
Link adaptation: Adaptive modulation and coding
Point-to-multipoint (star) topology and mesh network extension
Extensions to mobility.
Point-to-Multipoint configuration
Two components
Subscriber Stations (SSs)
Base Station (BS)
connected to public networks
BS serves Subscriber Stations
Compared to a Wireless LAN
Multimedia QoS
not only contention-based
connection-oriented
Many more users
Much higher data rates
Much longer distances
Mesh Topology
Dynamic topology
Self-organizing network
More complicated
Adaptive modulation and coding
Fixed + Mobile Standard
，
Features
MAC Layer
IEEE 802.16 reference model
CS SAP
Service-specific
convergence sublayer (CS)
MAC SAP
MAC common part
sublayer (MAC CPS)
Security sublayer
PHY SAP
Physical layer (PHY)
Scheduling services
Each connection is associated with a single data service
Each data service is associated with a set of QoS
parameters
Four services are supported in 802.16-2004
Unsolicited Grant Service (UGS)
Real-time Polling Service (rtPS)
Non-real-time Polling Service (nrtPS)
Best Effort (BE)
Five services are supported in 802.16e
UGS (Unsolicited Grant Service)
RT-VR (Real-Time - Variable Rate Service)
NRT-VR (Non-Real Time - Variable Rate service)
BE (Best Efforts)
ERT-VR (Extended Real -Time Variable Rate)
Unsolicited Grant Service (UGS)
Support real-time data streams consisting of fixed-size
data packets issued at periodic intervals
Such as T1/E1 and Voice over IP without silence suppression
Mandatory QoS service flow parameters
Maximum Sustained Traffic Rate
Maximum Latency
Tolerated Jitter
Request/Transmission Policy
In 802.16e
UGS is able to support variable length PDUs.
Maximum Sustained Traffic Rate is removed
Add Unsolicited Grant Interval and SDU size (if fixed)
Real-time Polling Service (rtPS)
Support real-time data streams consisting of variablesized data packets that are issued at periodic intervals
Such as moving pictures experts group (MPEG) video
Mandatory QoS service flow parameters
Minimum Reserved Traffic Rate
Maximum Sustained Traffic Rate
Maximum Latency
Request/Transmission Policy
In 802.16e
Add Traffic priority and Unsolicited Polling Interval
Non-real-time Polling Service (nrtPS)
Support delay-tolerant data streams consisting of
variable-sized data packets for which a minimum data
rate is required
such as FTP
Mandatory QoS service flow parameters
Minimum Reserved Traffic Rate
Maximum Sustained Traffic Rate
Traffic Priority
Request/Transmission Policy
Best Effort (BE)
Support data streams for which no minimum service level
is required and therefore may be handled on a spaceavailable basis
Mandatory QoS service flow parameters
Maximum Sustained Traffic Rate
Traffic Priority
Request/Transmission Policy
Extended Real-Time Variable Rate (ERT-VR)
Support real-time applications with variable data-rates,
which require guaranteed data and delay, for example
VoIP with silence suppression
QoS parameters (combines UGS and RT-VR)
Maximum Latency
Tolerated Jitter
Minimum Reserved Traffic Rate
Maximum Sustained Traffic Rate
Traffic Priority
Request/Transmission Policy
Unsolicited Grant Interval
WiMAX Applications and QoS
PHY Layer
PHY Layer of WiMAX
Modulation
Single carrier (SC) for line-of-sight situations
針對10~66 GHz頻段的無線接入系統
OFDM and OFDMA for non-line-of-sight situations
針對2~11GHz頻段的無線接入系統
Transport method
TDD (time division duplex)
FDD (frequency division duplex)
OFDMA Symbol Description
Based on OFDM modulation
Designed for NLOS operation
Frequency domain description
Subcarrier
Type：Data, Pilot, null (guard and DC)
Number：128, 512, 1024, 2048
Subchannel
A set of subcarriers forms a subchannel
The subcarriers may be adjacent or not
Feature
特點
好處
256點FFT OFDM波形
內含解決室外LOS和NLOS環境中multipath問題的能力
不同的距離使用不同的
信號調變技術
802.16可以支援由近到遠64QAM、16QAM、QPSK及
BPSK等信號調變。
支持TDD和FDD雙工模
式
適應世界各地不同的管制辦法，有的允許一種，有的允
許兩種
靈活的channel寬度（例
如3.5MHz、5MHz和
10MHz等）
提供必要的靈活性，以適應在世界各地不同Frequence
band與不同channel access要求情況下工作
支持智慧型天線系統
802.16的PHY可以設計成支援智慧型天線，這是一種主動
式天線，與MIMO等其他技術配合時，可以強化信號
品質並提高傳輸效率。
Outline
WiMAX Overview
Relay Topology (802.16j)
MIMO-OFDM System
IEEE 802.16j Mobile Multi-hop Relay
(MMR)
802.16j Mobile Multi-hop Relay (MMR)
IEEE 802.16 PMP based wireless multi-hop
technology named IEEE 802.16j MMR in order to
enhance coverage.
Relay Station (RS) relays traffic between BS and
SS.
Realities of Current Cellular Deployments
Current deployment suffer from
Limited spectrum and insufficient wire-line capacity
Low SNR at cell edge
Coverage holes due to shadowing
Out-of-range clusters of users
Non-uniformly distributed traffic load (e.g. hot spots)
Benefit (1/2)
Two benefits from Relay Station (RS)
Coverage extension
Expansion for coverage area of existing PMP mode
Throughput enhancement
Higher throughput over multi-hop paths
Benefit (2/2)
Non-Line-Of-Sight Transmission
=> Worse signal quality, lower rate.
Line-Of-Sight Transmission
=> Better signal quality, higher rate.
Network Architecture
Relay Station Type
Fixed relay station (FRS)
A relay station that is permanently installed at a fixed
location
Nomadic relay station (NRS)
A relay station that is intended to function from a
location that is fixed for periods of time comparable to
a user session
Mobile relay station (MRS)
A relay station that is intended to function while in
motion
Relay Concept
Two relay method
A&F (Amplify and Forward)
Relaying without FEC decoding and reencodings
Minimum delay
D&F (Decode and Forward)
More robust, higher modulation schemes
Takes time to decode and reencode
RS takes a few frames to relay
Relay Method (1/2)
Transparent RS
A transparent RS does not transmit preamble, FCH
and DL-/UL-MAP to MS
MS never recognizes the transparent RS
Centralized control
Capacity enhancement
Relay Method (2/2)
Non-transparent RS
A non-transparent RS transmits preamble, FCH and
DL-/UL-MAP to MS as an ordinary BS.
MS recognizes the non-transparent RS as a BS
Distributed control
Range extension
The Concept of Cooperative Relaying
Cooperative Relay
Original signal is received by several RSs, and forwarded
to the destination through different paths
Allowing a set of multiple signal sources to transmit
correlated data
Achieve cooperative diversity gain to improve the performance of
the relay network
Cooperative Relay Type (1/3)
Cooperative Relay using same source
Multiple signal source simultaneously transmit the
same signal using the same time frequency resource
Cooperative Relay Type (2/3)
Cooperative Relay using different source
Uses space-time block codes across different physical
signal source
This method is based on the use of transmit diversity
using STBC
Cooperative Relay Type (3/3)
Cooperative Relay using hybrid method
The two cooperative relaying schemes can be
combined
If the number of signal sources are greater than the
number M in a M×1 STBC scheme, multiple signal
source transmit the same STBC encoded signal
Benefit
Better BER performance
Link robustness
Technical Challenges (1/3)
System Configuration/management
Network topology
RS detection
Relay Path management
Path Selection
Multipath redundancy
Congestion control
QoS
Network load balance
Congestion control / flow control
Technical Challenges (2/3)
Routing
Centralized vs. distributed control
Radio resource Management
Bandwidth request
Resource allocation
Scheduling
Centralized Scheduling
Distributed Scheduling
Technical Challenges (3/3)
Data Delivery
Unicast/multicast/broadcast data
Cooperative relay
Security for mobile RS
Mobility Management
SS or RS handover
Handover decision
Reference
Christian Hoymann, Karsten Klagges, Marc
Schinnenburg, “MULTIHOP COMMUNICATION IN
RELAY ENHANCED IEEE 802.16 NETWORKS “, IEEE
PIMRC 2006
P802.16j PAR
http://grouper.ieee.org/groups/802/16/relay/
IEEE 802.16’s Mobile Multihop Relay Study Group
http://www.ieee802.org/16/sg/mmr/
Marks, R.B. : IEEE 802 Tutorial: 802.16 Mobile Multihop
Relay, March 2006
Outline
WiMAX Overview
Relay Topology (802.16j)
MIMO-OFDM System
An overview of MIMO-OFDM Systems in
Wireless Communications
Introduction
Future trend for wireless communications
Future wireless applications create insatiability
demand for “high data rate” and “high link quality”
wireless access
Spectrum has become a scarce and expensive resource
bandwidth is very limited
Regulation, device and system capacity concerns
transmit power is limited
Time and frequency domain processing are at limits, but
space is not
MIMO
MIMO Wireless system (1/3)
Wireless transmission is impaired by signal fading and
interference
The use of multiple antennas at both ends of a wireless
link promises significant improvements in terms of
spectral efficiency and link reliability
The technology is known as multiple-input multipleoutput (MIMO) wireless
MIMO systems offer diversity gain and multiplexing
gain
MIMO Wireless system (2/3)
What is MIMO
A MIMO system consists of several antenna elements, plus
adaptive signal processing, at both transmitter and receiver
TX
RX
MIMO Wireless system (3/3)
Four basic models
Benefits
Application of multiple antennas (at Transmitter and /or
Receiver ) to improve the link performance
Coverage (range)
Capacity (throughput)
Quality
Interference Reduction
Spectral Efficiency
MIMO can be sub-divided into two main categories
Spatial diversity and Spatial multiplexing
Spatial Diversity
Spatial Diversity
Receive and Transmit diversity mitigates fading and
significantly improves link quality
No additional bandwidth required
Increase of average SNR is possible
These benefits are NOT possible with time or frequency
Spatial Diversity Architecture
Spatial Multiplexing
Transmit independent data signals from different
antennas to increase the throughput
Provides some coding gain and diversity gain
Provides bandwidth efficiency
Increase data transmit rate
Require multipath to work
Spatial Multiplexing Architecture
Performance Improvement Using MIMO System
Array gain
Diversity gain
Multiplexing gain
efficiency
Increase coverage and QoS
Increase coverage and QoS
Increase throughput and spectral
Co-channel interference reduction
capacity
Increase cellular
MIMO-OFDM
Next generation Wireless Communication System
MIMO (Multi Input Multi Output)
－Using multiple antenna
－Increasing QoS
－Increasing Capacity by exploiting spatial diversity
OFDM (Orthogonal Frequency Division Multiplexing)
－Wide band transmission by multi-path environment
－High Spectrum efficiency
MIMO-OFDM
MIMO-OFDM Transmitter
MIMO-OFDM
MIMO-OFDM Receiver
Reference
A. J. Paulraj, D. Gore, R. U. Nabar, and H. B®olcskei “An Overview of
MIMO Communications- A Key to Gigabit Wireless”
A. van Zelst and T. C. W. Schenk, “Implementation of a MIMO OFDM
based wireless LAN system “, IEEE Transactions on Signal
Processing, vol. 52, No. 2, Feb. 2004
H. B¨olcskei and A. J. Paulraj, “ Space-frequency coded broadband
OFDM systems “, in Proc. IEEE WCNC, vol. 1, Chicago, IL, Sept. 2000
H. B¨olcskei, M. Borgmann, and A. J. Paulraj, “ Space-frequency coded
MIMO-OFDM with variable multiplexing-diversity tradeoff “, in Proc.
IEEE ICC, vol. 4, May 2003
Homework
請比較WiMAX與WiFi之間的差異，以及兩者分別在
PHY Layer與MAC Layer有何不同？
說明802.16j加入了Relay Station機制後，增強原來
WiMAX System哪些效能？
Thank you！