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WiMAX and Mobile WiMAX
802.16-2004 (d), 802.16-2005(e)
Presentation Overview• Standard Overview • WiMAX Family
– WiMAX, Mobile WiMAX Specification Overview• Algorithm descriptions
– PHY, MAC• Mobile WiMAX performance
– Link, System, Comparative• WiMAX Availability/Deployments• Further amendments
– 802.16h, 802.16j, 802.16m
Specification Overview
802.16 Family (WiMAX)• 802.16 LOS 10-66 GHz• 802.16a 2-11 GHz (superceded by 802.16-2004)• 802.16c 2-11 GHz (superceded by 802.16-2004)• 802.16d Combined 802.16, 802.16a, 802.16c into 802.16-2004• 802.16e Approved Dec 7 2005
– Published Feb 2006• 802.16f Network Management Information Base (MIB)
– Published Dec 1, 2005• 802.16g Network management plane
– Draft Feb 2006• 802.16h Coexistence with license-exempt 802.16 protocols
– Draft• 802.16i Mobile Management Information Base (explicitly to
handle updates from 802.16e) – Just accepted contributions• 802.16j Mobile Multihop Relay (More later in presentation)• 802.16k Network Management/Bridging• 802.16m 4G WiMAX
– Just startedhttp://grouper.ieee.org/groups/802/16/milestones_active.html
IEEE 802.16 Standards
Source: www.wimaxforum.org/news/events/wimax_day_agenda/Gordon_Member_IEEE_802.16.pdf
WiMAX Schedules
WiMAX Forum (2006): Mobile WiMAX – Part I: A Technical Overview and Performance Evaluation. Available at www.wimaxforum.org
Relationship Between Players
www.wimaxforum.org
Source: www.wimaxforum.org/news/events/wimax_day_agenda/Gordon_Member_IEEE_802.16.pdf
802.16 Standard and Usage Model Mapping
802.16-2004• Actually a suite of PHY protocols
High Speed Unlicensed MAN
Source: www.wimaxforum.org/news/events/wimax_day_agenda/Gordon_Member_IEEE_802.16.pdf
WirelessMAN-SC• Single Carrier• Licensed operation• LOS only, >10 GHz• FEC = Reed-Solomon, optional Block Turbo Codes, Convolutional
Turbo Codes• Power Control• Directional antennas at subscriber units• Channel quality measurements
– RSSI– CINR
Source: www.wimaxforum.org/news/events/wimax_day_agenda/Gordon_Member_IEEE_802.16.pdf
WirelessMAN-SCa• Licensed operation• < 11 GHz• TDD and FDD duplex• TDMA uplink• Single Carrier• Variable bandwidths• Reed-Solomon and trellis
coded modulation• Optional block and
convolutional Turbo codes
• Framing for equalization, channel performance
• Robust modes for low SINR
• Space time coding transmit diversity option
• Block adaptive modulation
WirelessMAN OFDM• Licensed operation• NLOS, < 11 GHz, TDD, FDD• TDMA• OFDM modulation, 256 point
FFT– BPSK, QPSK, 16-QAM, 64-
QAM• Reed Solomon, Optional BTC,
CTC
• Uplink power control• Optional space time coding
– 2 Tx (BS), 1 RX (SS)• RSSI, CINR measurements
– Adaptive modulation• Includes Mesh Frame (optional)
Subcarriers: 192 Data, 8 Pilot, 28 Low Guard Band, 27 High Guard Band
From IEEE Std 802.16-2004
• Licensed operation• NLOS, < 11 GHz, TDD, FDD• Channel Bandwidths > 1.0 MHz, 2-
nxregulatory bandwidth• OFDM modulation, 256 point FFT
– BPSK, QPSK, 16-QAM, 64-QAM• Subchannelization
– OFDM FDMA = OFDMA– Gives flexibiltiy in channel
assignment in time and frequency• Convolutional code, Optional BTC,
CTC• Uplink power control• Optional space time coding
– 2 Tx (BS), 1 RX (SS)• RSSI, CINR measurements
– Adaptive modulation
WirelessMAN OFDMAFrom IEEE Std 802.16-2004
Wireless HUMAN
• Unlicensed operation• NLOS, < 11 GHz, TDD• Supports all PHY but 802.11SC• Adds DFS to the MAC• Defines center frequencies at 5 GHz
– 5000 + 5 nch (MHz)
From IEEE Std 802.16-2004
802.16e (Mobile WiMAX, 802.16- 2005)
• Ideally, 802.16 + mobility– Really intended for nomadic or low mobility– Not backwards compatible with 802.16-2004
• http://www.unstrung.com/document.asp?doc_ id=76862
• Approved Dec 7 2005– Published Feb 2006– http://www.ieee802.org/16/tge/schedule.html
• Direct competitor to 3G, 4G, 802.20 though WiMAX Forum says otherwise
• Receiving significant attention• Not intended for compatibility with 802.16-
2004
Scalable OFDMA
• PHY for 802.16e• Modifies OFDMA so
FFT size varies with channel bandwidth– Keeps carrier spacing
constant
• Channel update rate of 1 KHz– Channel estimation,
equalization
H. Yaghoobi, “Scalable OFDMA Physical Layer in IEEE 802.16 WirelessMAN,” Intel Technology Journal, Volume 8, Issue 3, 2004.Available online: ftp://download.intel.com/technology/itj/2004/volume08issue03/art03_scalableofdma/vol8_art03.pdf
WiMAX Forum (2006): Mobile WiMAX – Part I: A Technical Overview and Performance Evaluation. Available at www.wimaxforum.org
Mobile WiMAX Peak Rates• Block Turbo Code
and Low Density Parity Check Code (LDPC) are optional
• Convolutional Codes (CC) and Convolutional Turbo Codes must be supported
WiMAX Forum (2006): Mobile WiMAX – Part I: A Technical Overview and Performance Evaluation. Available at www.wimaxforum.org
Optional Antenna Array Support• MIMO-STC (defined
in Matrix A)• MIMO-Spatial
Multiplexing (defined by Matrix C)
• Beamforming• Operation defined by
three classes matrices for antenna different number of antennas (2x2 STC is Alamouti)
• Support for switching between approaches
• Not being deployed initially, but more later
Peak Data Rates
WiMAX Forum (2006): Mobile WiMAX – Part I: A Technical Overview and Performance Evaluation. Available at www.wimaxforum.org
MAC/Mobility Features• Frame-by-frame resource allocation• Hybrid Automatic Repeat Request (HARQ)• UL and DL Scheduling• Variable QoS• Three handoff methods
– A traditional Hard Handoff (HHO)– Fast Base Station Switching (FBSS)
• A list of reachable base stations is maintained by mobile and base stations, but base stations discard packets if not the active BS
– Macro Diversity (MDHO)• Same list is maintained, but all base stations in the list
can participate in the reception and transmission of packets.
WiBro• Korean version of 802.16e
– Phase 1 standardized by TTA of Korea (2004)– Phase 2 standardized in 2005
• Korean spectrum allocated 2002– 2.3 GHz (100 MHz)
• Harmonization 802.16e/WiBro agreed Nov 2004 – Samsung joined WiMAX Forum Dec 2004– May indicate Samsung’s guess on 4G direction
• Plans for Nationwide Korean deployment– KT & SK Telecom launched June 30, 2006 in Seoul
http://kt.co.kr/kthome/kt_info/pr/news_center/news_view.jsp?pa ge=1&no=397&gubun=1
– KT and Hanaro Telecom to jointly deploy outside of Seoul and 6 other cities http://times.hankooki.com/lpage/tech/200501/kt2005011117243 611810.htm
How does WiBRO relate to 802.16e?
• WiMAX Forum: (http://www.wimaxforum.org/news/press_releases/WiBro_and_Mobile_WiMAX_Bac kgrounder.pdf)
– “WiBro is the service name for Mobile WiMAX in Korea. WiBro uses the Mobile WiMAX System Profile. The system profile contains a comprehensive list of features that the equipment is required or allowed to support, and, as a result, WiBro offers the same capabilities and features of Mobile WiMAX.”
– It’s Mobile WiMAX, just with a different profile (frequency, bandwidth…)• Vendors: WiBRO is compatible with 802.16e, but there’s more to Mobile WiMAX
than just 802.16e compatibility and many choices in WiBRO are different from what is mandatory in 802.16e
– From (http://www.nortel.com/solutions/wimax/collateral/wimax_wibro_white_paper.pdf)• Some more important differences from white paper
– Mandatory Handoff • 802.16e = HHO• WiBRO = FBSS
– HARQ• 80.16e = Chase combine HARQ• WiBRO = Incremental redundancy HARQ
– Likely (though unclear) network layer differences
Reality on compatibility• All of these different profiles would be quite
difficult for a hardware radio to support (as the white paper points out), but…
• 802.16 is likely the first SDR standard• Leading implementation approaches appear
to be using specialized processors• Further, there exists a certification body for
interoperability (WiMAX Forum) with the first certified Mobile WiMAX products expected for the end of 2006 or the first quarter of 2007
• And a Global Roaming Alliance
Algorithm Descriptions
PHY, MAC, Security
Mandatory Convolutional Encoder in 802.16e
• Constraint length 7• Rate ½• Initialization
– OFDM mode:• Zeros encoder• Blocks padded with byte
0x00 at end– OFDMA
• Tailbiting• 6 bits appended to front,
output from last six bits of previous block discarded
– Tailbiting is slightly more bandwidth efficient (and mandatory), but much more computationally intensive
Encoder
Supported Data Rates
J. Andrews, A. Ghosh, R. Muhamed, Fundamentals of WiMAX, Prentice Hall, 2007
Optional Codes
• Optional codes:– block turbo codes, – convolutional turbo
codes,– low density parity
check (LDPC) codes
• Significant performance gains over mandatory convolutional codes without a lot of added complexity
802.16-e Turbo Encoder
Code performance
J. Andrews, A. Ghosh, R. Muhamed, Fundamentals of WiMAX, Prentice Hall, 2007
Subcarrier Permutations• Subcarrier permutation – how subcarriers
are allocated across subchannels• Burst profile – predefined combinations of
modulation, code rate and FEC type• Full Usage of Subcarriers (FUSC)
– Pilots independent, data subcarriers evenly spread out
• Downlink Partial Usage of Subcarriers– Subcarriers “randomized”– Supports segmentation and frequency
reuse factors of 1• Uplink Partial Usage of Subcarriers
– Subcarriers divided into tiles (4 subcarriers over 3 symbols)
– 8 data, 4 pilot– Good for high Doppler spread
• Tile Usage of Subcarriers (TUSC)– Downlink version of uplink PUSC
• Band Adaptive Modulation and Coding (AMC)
– All subcarriers are adjacent• Hurts frequency diversity, but simplifies
multiuser divserity• “Bins” defined as 8 data symbols plus 1 pilot
(in center of data)•J. Andrews, A. Ghosh, R. Muhamed, Fundamentals of WiMAX, Prentice Hall, 2007
Specified PHY Information• Channel Quality
Measurements– Used to adapt transmission
parameters• Modulation, coding, burst
profiles, power– Received signal strength
indicator• Mean, standard deviation
– SINR• Mean, standard deviation• Requires demodulation
• Power Control– Only directly supported on
uplink– 30 dB/s fluctuations– Should account for PAPR– MS maintains same
transmit power density (power/subcarrier)
– Maximum MS power for various modulations (backoff can vary to control PAPR)
Open Loop MIMO• Transmit diversity/space time coding
– Numerous optional schemes for 2,3,4 antennas– Most common:
• Spatial Multiplexing• Alamouti
• Frequency Hopped Diversity Code– Optional mode– First antenna transmits without modification– Second encodes over two consecutive subchannels
J. Andrews, A. Ghosh, R. Muhamed, Fundamentals of WiMAX, Prentice Hall, 2007
Closed Loop MIMO• Feedback mechanisms
–Antenna selection. The MS indicates to the BS which transmit antenna(s) should be used • Useful at highspeeds
–Antenna grouping. The MS indicates to the BS the optimum permutation of the order of the various antennas to be used with the current space/time encoding matrix
–Codebook based feedback. The MS indicates to the BS the optimum precoding matrix to be used, based on the entries of a predefined codebook.
• Sum capacity and MMSE most popular–Quantized channel feedback. The MS quantizes the MIMO channel and sends this information to
the BS, using the MIMO_FEEDBACK message.• High bandwidth, but usable in low speed environments
–Channel sounding. The BS obtains exact information about the CSI of the MS by using a dedicated and predetermined signal intended for channel sounding.
• Maximum (theoretical) capacity, maximum required bandwidth
J. Andrews, A. Ghosh, R. Muhamed, Fundamentals of WiMAX, Prentice Hall, 2007
Hybrid ARQ• HARQ – ARQ, but receiver can
use previous failed transmissions to improve estimates
• Type I HARQ– Chase combining– Retransmits until receiver gets
the packet right of failure propagates up to the network layer
• Type II HARQ– Incremental redundancy– Retransmits with successively
lower rate codes until receiver gets the packet right of failure propagates up to the network layer
Type II HARQ
J. Andrews, A. Ghosh, R. Muhamed, Fundamentals of WiMAX, Prentice Hall, 2007
MAC Convergence Sublayers• Supported Networking protocols
– ATM CS– Packet CS IPv4– Packet CS IPv6– Packet CS 802.3 (Ethernet)– Packet CS 802.1/Q VLAN– Packet CS IPv4 over 802.3– Packet CS IPv6 over 802.3– Packet CS IPv4 over 802.1/Q VLAN– Packet CS IPv6 over 802.1/Q VLAN– Packet CS 802.3 with optional VLAN tags and ROHC header
compression– Packet CS 802.3 with optional VLAN tags and ERTCP header
compression– Packet IPv4 with ROHC header compression– Packet IPv6 with ROHC header compression
Scheduling/QoS• Actual algorithms vendor specific, but 802.16e
assumes MS requests performance based off of a number of messages which the BS may or may not be able (or willing) to accommodate. – Max data flow per stream– Requested minimum data rate– Request for MBS– Maximum latency– Retransmission policy– Traffic priority (8 classes)– Tolerated Jitter
Mobile WiMAX MAC QoS Classes
WiMAX Forum (2006): Mobile WiMAX – Part I: A Technical Overview and Performance Evaluation. Available at www.wimaxforum.org
Network Entry Process
Network Entry Steps Negotiated Parameters
J. Andrews, A. Ghosh, R. Muhamed, Fundamentals of WiMAX, Prentice Hall, 2007
Other Services• Network discovery
– WiMAX supports either manual or automatic selection of networks based on user preference
– Defines protocols to support this• IP address management
– Note: packet transmission in WiMAX is based on connection identifiers instead of MAC addresses, so multicasting in IPv6 needs work
• Radio Resource Management – Mostly information management in standard, vendors can do different
things with information– Activities
• Controlling measurements by BSs and MSs• Delivering measurements to required databases • maintaining RRM databases• exchanging information between these databases within or across ASNs,• making radio resource information available to other functional entities, such
as HO control and QoS management.
802.16-2004 Security Vulnerabilities
• Replay Attack– Resend detected valid messages– Intention is to induce BS to send SS a reset
message
• AP Spoof– Subscribers are authenticated, but not
access point
• MAC Address Spoof• RNG-RSP Denial of Service
– Weaknesses in ranging (not encrypted, automatic acceptance of adaptations by SS)
• Auth Invalid Attack– “Auth Invalid” (possibly spoofed) puts
subscriber in a vulnerable state– Followed with a “Permanent Auth Reject”
message prevents all future communications until MAC reset
Nonetheless, Boom writes:“In the author’s opinion, the standard is an excellent starting point for the basis of a military tactical network. Given that the above recommendations have been applied, there would remain changes required to create a military wireless network. Because of the unique military environment and requirement for very high availability, DoD should adopt an appropriately robust spread spectrum physical layer to improve conventional jamming resistance. Second, DoD should continue to use higher layer encryption to protect end-to-end transmissions.”
Based on D. Boom, “Denial of Service Vulnerabilities in IEEE 802.16 Wireless Networks,” Thesis, Naval Post Graduate School, Sep 2004. Available online: http://www.ieee802.org/16/tge/contrib/C80216e-04_406.pdf
802.16e Security• Multiple layers
of security• Many aspects
added to address WiMAX problems
D. Pang, L. Tian, J. Hu, J. Zhou, J. Shi, “Overview and Analysis of IEEE 802.16e Security,” Available online: http://hdl.handle.net/2100/172
Security Improvements in 802.16e
• Authentication– BS identity now verified in
PKMv2• Authorization
– RSA-based authorization and EAP
– PKMv1 (2004) AAA in application layer, but in PKMv2 (802.16e) in different hierarchy
• Data confidentiality– Many more crypto
algorithms
• Data authenticity– AES CCM-Mode
• Replay attack– Some added protection,
but still vulnerable• Handoff support
– Possibly problematic– 802.16e suggests, but
does not define, pre- authorization
– Leads to key sharing between BS
D. Pang, L. Tian, J. Hu, J. Zhou, J. Shi, “Overview and Analysis of IEEE 802.16e Security,” Available online: http://hdl.handle.net/2100/172
Mobile WiMAX Performance
Effect of varying parameters on link and system performance
Link Simulation Parameters• From Chapt 11 of J.
Andrews, A. Ghosh, R. Muhamed, Fundamentals of WiMAX, Prentice Hall, 2007
• Scenarios:– AMC vs PUSC– Effect of HARQ– MIMO + Fading +
AMC– Open loop vs closed
loop– Common nonlinear
receiver structures
SISO AMC vs PUSC, PedestrianB
ER
SNR10-4
10-3
10-2
10-1
10-0
0 5 10 15 20 25 30
AMC vs PUSC: QPSK, Ped BR1/2 PUSCR1/2 AMCR3/4 PUSC R3/4 AMC
BE
R
SNR10-4
10-3
10-2
10-1
10-0
0 5 10 15 20 25 30
R1/2 PUSCR1/2 AMCR3/4 PUSC R3/4 AMC
AMC vs PUSC: 16QAM, Ped B
BE
R
SNR10-4
10-3
10-2
10-1
10-0
0 5 10 15 20 25 30
R1/2 PUSCR1/2 AMCR3/4 PUSC R3/4 AMC
BE
R
SNR10-4
10-3
10-2
10-1
10-0
0 5 10 15 20 25 30
R1/2 PUSCR1/2 AMCR3/4 PUSC R3/4 AMC
AMC vs PUSC: 16QAM, Ped AAMC vs PUSC: QPSK, Ped A
SISO AMC vs PUSC, Vehicular
BE
RSNR
10-4
10-3
10-2
10-1
10-0
0 5 10 15 20 25 30
R1/2 PUSCR1/2 AMCR3/4 PUSC R3/4 AMC
BE
R
SNR10-4
10-3
10-2
10-1
10-0
0 5 10 15 20 25 30
R1/2 PUSCR1/2 AMCR3/4 PUSC R3/4 AMC
AMC vs PUSC: QPSK, VehA30 AMC vs PUSC: QPSK, VehA120
SISO AMC vs PUSC, Summary
• AMC (modulation adaptation) outperforms PUSC (carrier adaptation) at slow speeds
• PUSC outperforms AMC at high speeds• Why?
– At Pedestrian (3 kph) coherence time is 150 ms
– At 120 kph channel coherence time reduced to 3 ms
– Feedback duration (5 ms)– At high speeds channel feedback needed
for AMC is poor predictor
• Moving from Pedestrian to Vehicular 120 causes drop in link performance
–QPSK ~1-1.5 dB–16-QAM ~ 2-2.5 QAM
• Why?–OFDM sensitive to frequency offsets
(Doppler)–Higher order modulations more sensitive to
channel estimations• Insights:
–Channel state information very important to performance
–Value to adjusting adaptation schemes based on Doppler
Effect of Channel Estimation (PUSC)
• Channel estimation via frequency domain linear minimum mean square error + partial information about channel covariance (from RMS delay spread)
• At low SNR, noise dominates• At high SNR, estimation imperfections dominate• Higher order modulation more sensitive to estimation imperfections
BE
R
SNR10-4
10-3
10-2
10-1
10-0
0 5 10 15 20 25 30
QPSK Real vs Perfect
BE
R
SNR10-4
10-3
10-2
10-1
10-0
0 5 10 15 20 25 30
16-QAM Real vs PerfectR1/2 Veh A30R1/2 Veh A120R3/4 Veh A30 R3/4 Veh A120R1/2 PerfectR3/4 Perfect
R1/2 Veh A30R1/2 Veh A120R3/4 Veh A30 R3/4 Veh A120R1/2 PerfectR3/4 Perfect
Effect of Hybrid-ARQ
• Type I HARQ = Chase Combining– All retransmissions identical to first transmission
• Type II HARQ = Incremental Redundancy– Puncture patterns vary by retransmission
Tran
smis
sion
s
SNR0
1
2
3
4
6 9 12 15 18 24 2721 30
Tran
smis
sion
s
0
1
2
3
4
SNR0 3 6 9 15 1812 21
R1/2 No HARQR1/2 HARQ IR1/2 HARQ II R3/4 No HARQR3/4 HARQ IR3/4 HARQ II
R1/2 No HARQR1/2 HARQ IR1/2 HARQ II R3/4 No HARQR3/4 HARQ IR3/4 HARQ II
HARQ, QPSK HARQ, 16-QAM
Hybrid ARQ Summary
• Benefit of HARQ is at low SINR• No Benefit at high SINR• Type II HARQ gives highest gain due to
reducing code rates
SIMO Performance and CorrelationR1/2 Ped B Varying Correlation R3/4 Ped B Varying Correlation
• QPSK, MMSE receiver, AMC
SIMO Correlation Summary
• Performance gain– 1x2 yields 3 dB gain (low SINR)– 1x4 yields 6 dB gain (low SINR)– Even more at high SINR
Effect of Correlation
AMC, R 1/2, Ped B AMC, R 3/4, Ped B
Complex correlation, ρ=0.5
PUSC, R1/2 Ped B PUSC, R3/4 Ped B
Correlated/Uncorrelated Fading Summary
• At low SNR, correlation has little effect• At higher SNR, however, the multiantenna gain is reduced by 1dB to 0.5dB, owing to the correlation in the fading
waveform. • Lower code rates are more sensitive to this correlation than are higher code rates.
• Figure 11.20 and Figure 11.21 provide link-level results for various possible open-loop and closed-loop transmit diversity schemes in WiMAX. The open-loop diversity considered here is the 2 x 2 Alamouti pace/time block cde (STBC).
• For AMC subcarrier permutation, STBC’s benefit is marginal, especially with correlated fading because STBC hardens the channel variation that band AMC is designed to exploit. On the other hand
• PUSC subcarrier permutation, as shown in Figure 11.22 and Figure 11.23 benefits significantly from 2 x 2 STBC
Gain versus SISO with AMC
Open Loop MIMO with Multiple Streams
AMC QPSK R1/2 in Ped B AMC QPSK R3/4 in Ped B
Dual Stream, Matrix B
Open Loop Diversity Summary
• Greater benefit for higher rates• Why?
– More sensitive to fades and added diversity reduces fades
Open Loop Gains over 2x2, AMC, Ped B, Dual Streams
Closed Loop Scenarios
• Antenna selection feedback (1/frame)– 3-bits specify antenna pair for each subchannel
• Codebook feedback (1/frame)– 6-bits that specify code for linear precoding for each subchannel– Code minimizes postdetection mean square error of both streams
• Quantized channel feedback– MS quantizes channels; BS chooses code as above
• Per subcarrier SVD– Optimal precoding
AMC, QPSK, R1/2 Ped B AMC, QPSK, R3/4 Ped B
Open versus Closed Summary
• Closed loop reasonably close (~1-2 dB) to each other
• However, closed loop techniques can add 5 dB in link gain over open loop techniques
Effect of Receiver Structures
• Ordered Successive Interference Cancellation (O-SIC)– SIC from highest SINR to lowest
• Maximum Likelihood Detection (MLD)– Search for most likely combination of transmitted symbols– Simplified by using MMSE followed by sphere-decoding– Optimum noniterative algorithm for MIMO receivers
PUSC, QPSK, R1/2 Ped B PUSC, QPSK, R3/4 Ped B
Receiver Structure Summary
• An iterative MAP will outperform MLD• QRM-MLD is suboptimal (and “low-complexity”) but
performs within a dB of MLD– K. Kim, J. Yue, “Joint channel estimation and detection
algorithms for MIMO OFDM,” Proceedings of Asilomar Conference of Signals, Systems, and Computers, Nov 02.
Gain over MMSE receiver at 10-4 BER 2x2 PUSC, Ped B
Link Performance Summary• Adaptive modulation lets WiMAX approach at low SINR
– High SINR limited by discrete modulation set• Turbo codes yield significant performance gain over
mandatory convolutional codes• AMC is better at low speeds, PUSC at high speeds• HARQ most effective at low SINR,
– HARQ II better than HARQ I in terms of BER• Closed-loop gives > 5 dB gain over open-loop at low
speeds (not practical at high speeds) • Advanced MIMO structures can give another 5 dB gain
System Level Performance
• From Chapt 12 of J. Andrews, A. Ghosh, R. Muhamed, Fundamentals of WiMAX, Prentice Hall, 2007
Simulation Parameters
System Configurations
• Basic assumes the BS is able to separate the two MSs using the two receive antennas.
• Enhanced configuration 1 increases the number of receive antennas in the DL from two to four thus providing higher order receive diversity in the DL, but is otherwise the same
• Enhanced configuration 2 increases the number of transmit antennas in the UL and DL
• Enhanced configuration 3 uses 4 x 2 closed-loop MIMO in the DL with antenna selection and quantized channel-feedback-based closed loop MIMO . Feedback once every 10 ms over two bands.
Basic ConfigurationPed B Ped A
Average Throughput, Ped B Average Throughput, Ped A
• Handheld assumes omni- directional antennas
• Desktop device has low-gain (3dBi-6dBi) directional antennas
• Desktop implements selection diversity from 6-8 antenna
Basic Configuration Summary
• Directionality does better, but limited benefit when already sectored• (1,1,3) is more spectrally efficient, but has poor cell-edge
performance• General tradeoff between reliability and spectral efficiency
Effect of Scheduling and Sub- carrier permutations (Handheld)
• (1,1,3) configuration• Without precoding, AMC offers limited benefit
(though still non-negligible ~14-18%)• Proportional fairness scheduler has slightly more
flexibility in exploiting multi-user diversity so sees better performance in capacity (~25%)
PUSC vs AMC PF vs Round Robin
Effect of MIMO ConfigurationsUplinkDownlink
Note: Same uplink used for basic and enhanced 1 configurations
Enhanced Profile SummaryTotal Throughput per Cell, Ped B, (1,1,3), 30 MHz
• Both receive diversity and transmit diversity improve the average throughput of a WiMAX network.
• By increasing the number of transmit antennas from two to four, the per sector throughput improves by 50 percent.
• Similarly, by increasing the number of receive antennas from two to four, the per sector throughput is increased by 80 percent
• UL throughput results do not account for the fact that a part of the UL bandwidth is used by the closed-loop MIMO feedback
Enhanced ProfilesDownlink, Ped B Downlink, Ped A
Enhance Profile Summary
• Fifth and tenth percentile DL data rates are not improved by increasing either transmit or receive diversity order.
• Implies that transmit diversity with antennas in DL is not sufficient to improve the cell-edge data rate in the case of (1,1,3) reuse
• Closed loop (4x2) however, provides significant • (1,1,3) frequency reuse will not be able to provide carrier-grade
reliability and guaranteed data rate unless closed-loop MIMO features are used.
5% & 10% Data Rate, Band AMC, Ped B (1,1,3)
System Performance Comments• Frequency planning
– (1,1,3) gives highest per-sector• But unequal distribution – cell edge performs poorly
– (1,3,3) gives good cell edge performance• But requires additional spectrum
– (1,1,3) with segmentation is a compromise solution• Scheduling algorithms w/ multi-user diversity can significantly
improve cell throughput – up to 25%• Diversity (receiver more so than transmitter) gives significant gain in
average throughput – 50-80%– Cell-edge behavior still bad enough that (1,1,3) is hard to justify– Needs closed-loop MIMO
• Closed loop MIMO gives big gains• Overall spectral efficiency (throughput/sector/total deployment
bandwidth)– Open loop MIMO 1.7 Mbps/Hz– Closed loop pedestrian 3.9 Mbps/Hz
Interference Patterns with Reuse = 1
http://www.wimaxforum.org/technol ogy/downloads/mobile_wimax_depl oyment_alternatives.pdf
Relative Capacity as function of • 19 BS, 3 sectors,
spaced 2.8 km, mix of users
• Proportional Fair scheduling
WiMAX Performance Comparisons
Technology Comparison
WiMAX Forum (2006): Mobile WiMAX – Part II: Competitive Analysis. Available at www.wimaxforum.org
Performance Comparisons with Existing 3G, 3G+
WiMAX Forum (2006): Mobile WiMAX – Part II: Competitive Analysis. Available at www.wimaxforum.org
Performance Comparisons
Mobile WiMAX: The Best Personal Broadband Experience! June 2006, Available at www.wimaxforum.org
Cost Comparison• Fewer base stations to provide same level of service with Mobile WiMAX
than HSPA or EVDO RevB• Less cost tied up in IP royalties (~2-3% vs 10-15%)• New spectrum costs• http://www.wimaxforum.org/technology/faq/
– The second generation of Subscriber Equipment is expected to be priced from $200 - $300 in 2008.
– The third-generation CPEs will be integrated into laptops and other portable devices and are expected to initially cost approximately $100 and be available in 2nd half 2008.
Mobile WiMAX: The Best Personal Broadband Experience! June 2006, Available at www.wimaxforum.org
Summary of comparisons
• Mobile WiMAX is most directly comparable not to existing 3G or 3G+ standards, but to ones coming out in a few years– LTE– EVDO, Rev C (UMB)
• Similar performance comes from similar technologies– OFDMA, MIMO, MBS, HARQ, Turbo codes, Adaptive
modulations, bandwidths, IP core, VOIP• So some convergence in technologies (at last!)
– Yet these “converged” standards have a huge number of options available, so will be difficult for a single ASIC solution
– Likely need for SDR
Mobile WiMAX Deployments and Availability
Certification, Chipsets, Products, Spectrum, Deployments
WiMAX Certification Schedule• The WiMAX Forum plans to have
five certification test labs located in the U.S., Europe, China, Korea and Taiwan by end of 2007.
– http://www.wimax.com/commentar y/news/wimax_industry_news/wim ax-forumae-designates-first-north- american-based-certification-lab
• Certification Waves– (.16-2004) Wave 1 enables a
simple air link – (.16-2004) Wave 2 adds QoS,
security, and advanced radio features for outdoor CPEs
– (.16-2004) Wave 3, adds indoor CPEs and PCMCIA cards for fixed and nomadic networks
– (.16e) Wave 4, adds hand-offs and simple mobile for 802.16e or mobile WiMax
– (.16e) Wave 5 adds full mobility
Source: http://www.wimaxforum.org/technology/downloads/ WiMAX_and_IMT_2000.pdf
WiMAX Certification Labs• AT4 Wireless
Parque Tecnologico de Andalucia Calle Severo Ochoa 2 29590 Campanillas, Málaga Spain
• Telecommunications Technology Association 267-2 Seohyun-dong Bundang-gu Seongnam-City Gyeonggi-do 463-824 Korea
• China Academy of Telecommunication Research 52 Hua Yuan Bei Lu Haidian District Beijing 100083 China
• 31 certified products• http://www.wimaxforum.org/kshow
case/view/catalog_search
Chipsets (1/4)• Beceem Communications (BCS2000)
– Wave 2, SIMO, MIMO, – baseband IC + RFIC (all PHY, MAC, RF)– 2.x and 3.x GHz bands– http://www.beceem.com/products/ms120.shtml
• Fujitsu MB86K21 SoC is Wave 2 – Wave 2 SOC– 2-11 GHz, 802.16e compliant– Either base or subscriber– http://www.fujitsu.com/downloads/MICRO/fma/pdf/wimax_mobilefs.pdf
• Sequans Communications (3 mobile products)– SQN2110
• 3 FPGA chipset for base stations• Wave 2,
– SQN1130 SOC• Baseband PHY, MAC• Wave 2
– SQN 1110• Like 1130, but for Wave 1• http://www.sequans.com/site/products.html
Chipsets (2/4)• Wavesat Umobile SOC
– Wave 2– Programmable PHY, MAC– 2x2 MIMO– Support for 802.11a/g– www.wavesat.com
• Runcom Technologies Ltd– RNA 200
• 802.16e-2005• Full PHY/MAC (no RF)• http://www.runcom.com/upload/infocenter/info_images/28012007194733RNA200%20ASIC.pdf
– Others:• RNF2000 is FPGA version• RNA2000 ASIC version
• TeleCIS Wireless– TCW 1620 Portable 802.16-2004 implementation– Lowest power SoC– PHY/MAC– MAC supports Wave 2 and Wave 3– 2x2 MIMO– Built in PCI interface
Chipsets (3/4)• Comsys Mobile
– CM1100• Mobile WiMA baseband• Wave 2 compliant• High speed support• http://www.comsysmobile.com/commaxcm1100.html
– CM1125• GSM/EDGE + Mobile WiMAX• Baseband PHY/MAC• Class-12 E/GPRS mobile• http://www.comsysmobile.com/commaxcm1125.html.
• Altair Semiconductor– ALT2150
• Mobile WiMAX SOC• Wave 2 Handset • http://www.ccpu.com/
• ApaceWave Technologies– APW-2000 SoC– Wave 2 MIMO A,B– http://www.apacewave.com/
Chipsets (4/4)
• picoChip– WiMAX Reference Designs– http://www.picochip.com/solutions/wimax– PC8520 802.16-2004 base station– PC8530 Mobile WiMAX base station– PC6530 Femtocell base station– PC8532 Wave2 Basestation PHY– All software upgradable
Intel• Chipsets still in the works, but…• Service providers already have expressed a
preference for Intel– http://www.digitimes.com/systems/a20070831PD215.
html– Nokia already ordered
• http://www.wimaxday.net/site/2007/09/27/nokia-orders-intel- chips-intel/
– Microsoft working on WiMAX drivers• http://www.wimaxday.net/site/2006/11/07/runcom-signs-deal-
with-microsoft/– Apple rumored to want Intel chips
• http://www.macnn.com/articles/05/06/01/apple.and.wimax/
More Intel• Already secured deals for use of WiMAX chips in laptops
– Hoping to repeat Centrino success– 2008 "Montevina" both Wi-Fi networking and WiMAX– Deals: Lenovo, Acer, Asus, Panasonic and Toshiba– No Deals: Dell, HP– Part of a planned “WiMAX Inside” Marketing campaign
• http://www.wimaxday.net/site/2007/08/03/intel-plans-%e2%80%9cwimax- inside%e2%80%9d-marketing
• Investing in WiMAX service providers– Bulgaria with Nexcom Bulgaria
• http://www.wimax.com/commentary/news/wimax_industry_news/intel- capital-and-mci-have-invested-in-bulgarian-wimax-operator-nexcom
– Japan with KDDI• http://www.wimax.com/commentary/news/wimax_industry_news/intel-
capital-and-mci-have-invested-in-bulgarian-wimax-operator-nexcom
More 802.16e equipment• ArrayComm
– OFDM + smart antennas– Uses IntelliCell beamforming
technology– Applied to other standards
• Navini– Adds smart antennas to
nomadic OFDM– Wireless broadband Georgia –
BellSouth August 05– Multicarrier Synchronous
Beam Forming– Adaptive modulation QPSK –
64 QAM
• Adaptix– SDR OFDMA/TDD
platform – Salvaged technology
from Broadstorm• Alvarion
– Devices support 802.16-2004 and e
Other Product Vendors
• From http://www.wimaxforum.org/kshowcase/view– Redline, Selex, Nokia-Siemens, ET Industries,
Axxcelera, Aperto Netwrosk, Alvarion, Airspan, Siemens, SR Telecom, Telsima
WiMax Frequency Allocation
http://www.wimaxforum.org/news/downloads/supercomm_2005/WF_Day_in_a_Life_with_WiMAX_Final.pdf
3.5 GHz is the international band for WiMAX
Other WiMAX Spectrum Opportunities
• 700 MHz band– http://www.xchangemag.com/articles/501/79h139171
83935.html?cntwelcome=1– Needs to support public safety in the nationwide band– No plan for WiMAX certification profile unless band
becomes global• 3G Spectrum
– Push to be included as a 3G standard• http://www.livemint.com/2007/09/06000634/India-backs-
Wimax-techon-3G-n.html
WiMAX Spectrum Alliances• Regulatory Database
– AT4 Wireless– Launched November 2006– http://www.wimaxforum.org/join/spectrum_demo/
• WiMAX Global Roaming Alliance– Brought together unlicensed providers to promote global roaming– Now defunct – Will probably come back in some form– http://www.theregister.co.uk/2006/09/29/oz_wimax_roaming_alliance/
• WiMAX Spectrum Owners' Alliance– http://www.wisoa.com/– Promotes roaming agreements– Participants:– Unwired Australia, Network Plus Mauritius, UK Broadband, Irish Broadband,
Austar Australia/Liberty Group, Telecom New Zealand, WiMAX Telecom Group, Enertel and Woosh Telecom
WiMAX TrialsM. Giles, “Wireless Broadband,” EDUCAUSE 2006, October 9, 2006
150 Fixed WiMAX trials are underway around the world.
Technology Deployment Timeline
• 2006 – Mobile WiMAX Trials– Fixed WiMAX Ramp– >150 WiMAX Trials/Networks Planned
• 2007 – Mobile WiMAX (MIMO) Trials– Mobile WiMAX (SISO) Ramp
• 2008 – Dual-Mode & Multi-Mode Handhelds– Mobile WiMAX (MIMO) Ramp
• Source: M. Giles, “Wireless Broadband,” EDUCAUSE 2006, October 9, 2006.
Clearwire Coverage
• Provides Fixed WiMAX based wireline replacement service to home + portability within coverage area
• 2 Mbps data + voice
http://www.clearwire.com/
• Founded in October 2003 by Craig O. McCaw
Fixed WiMAX for AT&T
• Fixed WiMAX services as DSL/cable competitor (like ClearWire)– Launch in 2Q 2008 for the US South in old
BellSouth spectrum– 2.3 GHz band– Already trialing system in Alaska– http://www.unstrung.com/document.asp?doc_
id=133853&f_src=unstrung_gnews
Fixed WiMAX Deployments• WiMAX I – IEEE 802.16 – 2004
– IEEE Standard issued– WiMAX Forum specification– Fixed point-to-point/point-to-multipoint– First WiMAX certified products end of year– Certified in 3.5 GHz band
• Equipment– (Intel) Alvarion Ltd., Aperto Networks Inc., Proxim Corp., Redline
Communications Inc., Siemens AG, and China's Huawei Technologies Co. and ZTE Corp
– Other: Picochip, WaveSat• Current Deployments
– $1.4 billion in revenue in 2004 (Marvedis)– Altitude (France) voice over pre-WiMAX
• Trial Deployments– Seattle - Sprint
http://www.wimaxxed.com/wimaxxed_news/sprint_motorol.html– London (2006)
http://www.wimaxxed.com/wimaxxed_news/london_councils.html– Xbox360? http://wimax.com/commentary/spotlight/wimax-xbox
Sprint XOhm• Mobile WiMAX focus of next generation
Sprint cellular network XOhm– http://www.xohm.com/latestnews.html
• Expects $2-2.5 billion in revenue by 2010, of which 80% comes from new revenue and 20% is from cannibalization. Assuming an ARPU of $30 per month ($360/year), that means 6.2 million subscribers by 2010
– http://www.wimax.com/commentary/spotligh t/zoom-on-xohm-2013-an-update-from-the- sprint-technology-summit
• Sprint device expectations– Sprint partners (Motorola, Intel,
Samsung) have said embed 50 million units by 2010 in the US. These will be mainly laptops and PDAs. Sprint alluded that it expects chipset cost to go down to $5-$15
– WiMAX incorporated in cameras and televisions, household appliances, and security systems, as well as over 50 million hand-held devices
• Fast extensive rollout planned– http://www.wimaxday.net/site/200
7/09/28/sprint-dominates-and- tantilises-wimax-world-usa-with- xohm/
– Precommercial launch in two markets by end of 2007
– Multi-market launch in early 2008
– 10,000 sites in preparation– 1750 base stations delivered
in 2007, 20,000 antennas– 2010 coverage
• 48 million homes, 4.5 million offices, 130 million consumer electronic devices
• Open network– “As long as the device is WiMAX
certified, it will work on Sprint’s network after provisioning. Sprint wants to sell services, not devices.”
More Sprint• Partnering with ClearWire to accelerate WiMAX
deployment– Roam between networks and exchange spectrum– http://www.xohm.com/news_071907.html
• Going to provide federal government connectivity via WiMAX– http://www.wimaxday.net/site/2007/06/05/sprint-plans-wimax-for-
gov%e2%80%99t-services/• Partnering with Google to provide services
– Aiming for the “digital lifestyle”– Gmail, social networking tools, location-based services and
multi-media services.– http://www.wimaxday.net/site/2007/07/27/sprint-and-google-will-
partner-for-mobile-wimax-services/
Motorola
• Focusing on being an infrastructure vendor• Lots of test trials• 2.5 GHz band in Chicago for Sprint
– http://www.wimaxday.net/site/2007/09/26/it-works- motorola-takes-wimax-out-of-the-lab-and-into-the-city/
• 25 other trials around the world– http://www.wimaxday.net/site/2007/03/28/motorola-in-
25-wimax-trials/
First WiBRO Deployment
• Nov 15, 2005 – Launch of KT’s personal broadband service
• “To prove its mobility, KT delivered two-way video, Internet and messaging broadband services, a range of devices that were located in a traveling shuttle bus that allowed conference attendees to experience mobile broadband.”
• Given Mobile WiMAX certification in late 2006.– http://www.wimaxforum.org/news/press_releases/AP
EC_release_111505_FINAL_FINAL1.pdf
Additional Deployments of Mobile WiMAX
• Arialink with Samsung products (rural Michigan)– http://www.3g.co.uk/PR/April2006/2948.htm
• Islanet (Puerto Rico)– http://www.techweb.com/wire/networking/193402237
• Wateen in Pakistan (Motorola)– http://news.com.com/2100-1039_3-6075684.html
• AT&T (Soma) in Nevada– http://telephonyonline.com/wimax/marketing/att_mobile_wimax_111606/
• Taiwan (Far Eastone)– http://www.wimaxday.net/site/2007/09/28/far-eastone-plans-wimax-roll-
out/• Telecom (Bahrain)
– http://www.gulf-daily- news.com/Story.asp?Article=194068&Sn=BUSI&IssueID=30181
Projected Market Breakdown
http://www.wisoa.net/members_logos/ecosystem-2-big.jpg
Further amendments
802.16h, 802.16j, 802.16m
802.16h• Improved Coexistence
Mechanisms for License-Exempt Operation
• Basically, a cognitive radio standard
• Incorporates many of the hot topics in cognitive radio
– Token based negotiation
– Interference avoidance
– Network collaboration– RRM databases
• Coexistence with non 802.16h systems
– Regular quiet times for other systems to transmit
From: M. Goldhamer, “Main concepts of IEEE P802.16h / D1,” Document Number: IEEE C802.16h-06/121r1, November 13-16, 2006.
General Cognitive Radio Policies in 802.16h
• Must detect and avoid radar and other higher priority systems
• All BS synchronized to a GPS clock• All BS maintain a radio environment map (not
their name) • BS form an interference community to resolve
interference differences• All BS attempt to find unoccupied channels first
before negotiating for free spectrum– Separation in frequency, then separation in time
DFS in 802.16h• Adds a generic
algorithm for performing Dynamic Frequency Selection in license exempt bands
• Moves systems onto unoccupied channels based on observations
Generic DFS Operation Figure h1(fuzziness in original)
Adaptive Channel Selection
• Used when BS turns on• First – attempt to find a
vacant channel– Passive scan– Candidate Channel
Determination– Messaging with Neighbors
• Second – attempt to coordinate for an exclusive channel
• If unable to find an empty channel, then BS attempts to join the interference community on the channel it detected the least interference
Figure h37: IEEE 802.16h-06/010 Draft IEEE Standard for Local and metropolitan area networks Part 16: Air Interface for Fixed Broadband Wireless Access Systems Amendment for Improved Coexistence Mechanisms for License-Exempt Operation, 2006-03-29
Collaboration• BS can request interfering
systems to back off transmit power
• Master BS can assign transmit timings– Intended to support up to 3
systems (Goldhammer)• Slave BS in an interference
community can “bid” for interference free times via tokens.
• Master BS can advertise spectrum for “rent” to other Master BS– Bid by tokens
• Collaboration supported via Base Station Identification Servers, messages, and RRM databases
• Interferer identification by finding power, angle of arrival, and spectral density of OFDM/OFDMA preambles
• Every BS maintains a database or RRM information which can be queried by other BS– This can also be hosted
remotely
802.16h Status
• Currently in letter ballot– Draft 2c (password protected):
http://www.ieee802.org/16/private/drafts/le/P8 0216h_D2c.zip
• Expand coverage, capacity by adding relay stations
• Intended for licensed operation• Not intended as a mesh network
– Actually a tree• Support mobile units
802.16j Mobile Multi-hop Relay• Relays controlled from base
stations• Fixed Relay
– Permanent installation– Useful for coverage holes
• Nomadic Relay– Temporary fixed installation– Extra capacity for special
events (military SDR conferences)
• Mobile Relay– Placed on mobile platform to
support users on the platform– Useful for public transport
(buses, trains)
Modified from Fig 1 in IEEE 802.16mmr-05/032
802.16j Requirements• Backwards compatible frame structure supporting both
relay frames and legacy frames• Definition of RF requirements including the relay link
frequency, duplexing and channel B/W• Relay shall support network entry for the mobile station
QoS and HARQ shall be supported by relay as defined in legacy 16e systems
• Relay supports mobile station handover• The specification shall support relay mobility• The use of multiple antennas to enhance the spectral
efficiency of the relay link• The support of more than one relay hop between MMR-
BS and MS– http://www.ieee802.org/16/relay/docs/80216j-06_016r1.pdf
802.16j Status
• Failed letter ballot 9-25-07– 67% (needed 75%)
http://ieee802.org/16/ballots/ballot28/report28. html
• Last open draft– http://www.ieee802.org/16/relay/docs/80216j-
06_026r4.zip
Mesh in 802.16-2004• Mesh protocols not fully specified in 802.16-2004
– Network Entry supported, some neighbor services– Routing? Congestion?
• 802.16-2004.3 (WirelessMAN OFDM) PHY includes frames for Mesh operation between subscribers
• SkyPilot is developing a layer for Mesh operation that sits atop 802.16-2004.3– Targeted for Public safety applications in 4.9 GHz band– http://www.wi-fiplanet.com/news/article.php/3549846
• 802.16f should aid creation of fixed mesh networks• 802.16i may help for mobile devices• If market demand exists, would likely be an
amendment that specifies mechanisms for mesh as 802.11s did for 802.11’s ad-hoc mode
802.16m• Intended to be 4G (satisfy requirements of IMT-Advanced)• http://www.ieee802.org/16/tgm/• Requirements still being defined
– http://www.ieee802.org/16/tgm/docs/80216m-07_002r1.pdf – Backwards compatible with 802.16j– Support MMR (802.16j), though not specifically part of the standard– Will define new profile WirelessMAN-OFDMA/2008 – Support interoperability with other systems– Bands under 6 GHz– Bandwidths of 5-20 MHz (others may be used based on ITU and
operator requirements)– TDD and FDD– Support MIMO and beamforming– Mobile expected to have 1 transmit and 2 receive antennas– Support E-911 services
IEEE C802.16m-07/002r1
More Draft 802.16m requirements• Minimum Peak Rate
– Downlink 6.5 bps/Hz– Uplink 2.8 bps/Hz
• Latency less than 802.16e• Radio Resource Management
– Reporting, interference management– Multicast broadcast service– “High-resolution” location determination
• Internetworking with:– 802.11 3GPP, 3GPP2
• Coverage optimized for 5 km, functional to 30-100 km• Optimized for low mobility (<15kph), maintain connection up to 350 kph• Optimized for contiguous spectrum but support discontiguous• Reuse/share bandwidth with legacy systems• Direct migration from 802.16e
IEEE C802.16m-07/002r1
802.16m Usage models
• High data rates and improved performance in legacy cell sizes
• Very high data rates in smaller cells• High mobility support• Deployment with MMR• Co-deployment with other networks• Collocation/coexistence with
PAN/LAN/WAN
WiMAX Summary
Points to Remember• Very flexible standard
– Modulation, subcarriers, coding, antenna arrays• Big performance gain from Turbo codes and closed-loop
MIMO• Different scheduling/subcarrier allocation algorithms
work better in different environments• WiMAX receiving massive commercial interest at the
moment– Sprint is way out in front with XOhm in the US– WiBRO has been doing well in Korea for a while
• Intel is a little late, but will likely dominate– “WiMAX Inside” push on laptops– Backing service providers, so they’ve doubled their bet
Points to Remember
• People are already looking towards 802.16m
• WiMAX is emerging primarily as a cellular competitor– Previously viewed as more of a backhaul
• Lots of software radio based implementations coming out– picoChip,
Useful WiMAX Resources• WiMAX Standards
– http://ieee802.org/16/pubs/80216-2004.html– http://www.ieee802.org/16/pubs/80216e.html
• Mobile System Profile Rev 1.4 (May 2007)– http://www.wimaxforum.org/technology/documents/wi
max_forum_mobile_system_profile_v1_40.pdf• WiMAX News
– http://www.ieee802.org/16/relay/docs/80216j- 06_026r4.zip
• WiMAX Forum:– http://www.wimaxforum.org/home