Wimax Technology

1. WiMax Technology
Sangar N Qadir

2. What is WiMax?
 WiMax (Worldwide Interoperability for
Microwave Access) is a standards-based
technology enabling the delivery of last
mile wireless broadband access as an
alternative to cable and DSL.
 The technology is specified by the Institute
of Electrical and Electronics Engineers Inc.,
as the IEEE 802.16 standard.

3. WiMax Technology
 WiMAX is expected to provide fixed , nomadic, portable
and, eventually, mobile wireless broadband
connectivity without the need for direct line-of-sight
(LOS) with a base station.
 In a typical cell radius deployment of three to ten
kilometers, WiMAX Forum Certified™ systems can be
expected to deliver capacity of up to 40 Mbps per
channel, for fixed and portable access applications.
 Mobile network deployments are expected to provide
up to 15 Mbps of capacity within a typical cell radius
deployment of up to three kilometers.

4. Wi-Fi: The Predecessor of WiMax
 Wi-Fi (Wireless Fidelity) is a set of technologies
that are based on the IEEE 802.11a,b, and g
standards.
 Wi-Fi is considered to be one of the first widely
deployed fixed broadband wireless networks.
 The Wi-Fi architecture consists of a base station
that wireless hosts connect to in order to access
network resources.
 As long as the users remain within 100 meter of the
fixed wireless access point, they can maintain
broadband wireless connectivity.

5. Wi-Fi Standards
Standard Throughput Range Frequency
802.11a Up to 54 Mbps Up to 300 ft Between 5
and 6 Ghz
802.11b Up to 11 Mbps Up to 300 ft 2.4 Ghz
802.11g Up to 54 Mbps Up to 300 ft 2.4 Ghz

6. Strengths of Wi-Fi
 Simplicity and ease of deployment given that it uses
unlicensed radio spectrum which does not require
regulatory approval.
 Cost of rolling out this wireless solution is low.
 Users are able to be mobile for up to 300 feet from the
access point.
 There are many Wi-Fi compatible products that are
available at a low cost and can interoperate with other
network technologies. Wi-Fi clients can work seamlessly
in other countries with minimal configuration.

7. Weaknesses of Wi-Fi
 Limited level of mobility.
 Susceptible to interference.
 Designed technically for short-range
operations and basically an indoors
technology.
 Security is a concern.

8. Relation of Wi-Fi and WiMax
 WiMax eliminates the constraints of Wi-Fi.
 Unlike Wi-Fi, WiMax is intended to work
outdoors over long distances.
 WiMax is a more complex technology and has to
handle issues of importance such as QoS
guarantees, carrier-class reliability, NLOS.
 WiMax is not intended to replace Wi-Fi. Instead,
the two technologies complement each other.

9. WiMax Standards
802.16 802.16a 802.16-
2004
802.16e-
2005
Date
Completed
December
2001
January
2003
June
2004
December
2005
Spectrum 10-66 GHz < 11 GHz < 11 GHz < 6 GHz
Operation LOS Non-LOS Non-LOS Non-LOS and
Mobile
Bit Rate 32-134 Mbps Up to 75
Mbps
Up to 75
Mbps
Up to 15
Mbps
Cell
Radius
1-3 miles 3-5 miles 3-5 miles 1-3 miles

10. Channel Characteristics
 10-66 GHz
 Very weak multipath components (LOS is
required)
 Rain attenuation is a major issue
 Single-carrier PHY
 2-11 GHz
 Multipath
 NLOS
 Single and multi-carrier PHYs

11. WiMax is well suited to offer
both fixed and mobile access

12. How WiMax Works
 WiMax can provide 2 forms of wireless service:
- Non-LOS, Wi-Fi sort of service, where a small antenna on
a computer connects to the tower. Uses lower frequency
range (2 to 11 GHz).
- LOS, where a fixed antenna points straight at the WiMax
tower from a rooftop or pole. The LOS connection is
stronger and more stable, so it is able to send a lot of data
with fewer errors. Uses higher frequencies, with ranges
reaching a possible 66 GHz.
 Through stronger LOS antennas, WiMax transmitting
stations would send data to WiMax enabled computers or
routers set up within 30 (3,600 square miles of coverage)
mile radius.

13. WiMax Spectrum
 Broad Operating Range
 WiMax Forum is focusing on 3 spectrum bands for global
deployment:
 Unlicensed 5 GHz: Includes bands between 5.25 and 5.85
GHz. In the upper 5 GHz band (5.725 – 5.850 GHz) many
countries allow higher power output (4 Watts) that makes it
attractive for WiMax applications.
 Licensed 3.5 GHz: Bands between 3.4 and 3.6 GHz have
been allocated for BWA in majority of countries.
 Licensed 2.5 GHz: The bands between 2.5 and 2.6 GHz
have been allocated in the US, Mexico, Brazil and in some
SEA countries. In US this spectrum is licensed for MDS
and ITFS.

14. Benefits of Licensed and
License-Exempt Solutions
Licensed Solution License-Exempt Solution
Better QoS Fast Rollout
Better NLOS reception
at lower frequencies
Lower Costs
Higher barriers for
entrance
More worldwide options

15. Technical Similarities and Differences Between
Licensed and License-Exempt Bands
 Both solutions are based on IEEE 802.16-2004
standard, which uses OFDM in the physical
(PHY) layer.
 OFDM provides benefits such as increased SNR
of subscriber stations and improved resiliency to
multi-path interference.
 For creating bi-directional channels for uplink
and downlink, licensed solutions use FDD while
license exempt solutions use TDD.

16. Physical Layer Summary
Designation Applicability MAC Duplexing
WirelessMAN-SC 10-66 GHz Licensed Basic TDD, FDD, HFDD
WirelessMAN-SC 2-11 GHz Licensed Basic, (ARQ),
(STC), (AAS)
TDD, FDD
WirelessMAN-OFDM
2-11 GHz Licensed Basic, (ARQ),
(STC), (AAS)
TDD, FDD
2-11 GHz License-
exempt
Basic, (ARQ),
(STC), (DFS),
(MSH), (AAS)
TDD
WirelessMAN-OFDMA
2-11 GHz Licensed Basic, (ARQ),
(STC), (AAS)
TDD, FDD
2-11 GHz License-
exempt
Basic, (ARQ),
(STC), (DFS),
(MSH), (AAS)
TDD

17. Physical layer desicription
 OFDM Basics
 Orthogonal Frequency Division Multiplexing (OFDM) is a
multiplexing technique that subdivides the bandwidth into
multiple frequency sub-carriers as shown in the figure. In an
OFDM system, the input data stream is divided into several
parallel sub-streams of reduced data rate (thus increased
symbol duration) and each sub-stream is modulated and
transmitted on a separate orthogonal sub-carrier. The increased
symbol duration improves the robustness of OFDM to delay
spread. Furthermore, the introduction of the cyclic prefix (CP)
can completely eliminate Inter-Symbol Interference (ISI) as long
as the CP duration is longer than the channel delay spread.

19. OFDM Basics
Orthogonal SubcarriersOrthogonal Subcarriers

20. Cyclic Prefix
 The CP is typically a repetition of the last samples of data
portion of the block that is appended to the beginning of the
data payload as shown in Figure bellow. The CP prevents inter-
block interference and makes the channel appear circular and
permits low-complexity frequency domain equalization. A
perceived drawback of CP is that it introduces overhead, which
effectively reduces bandwidth efficiency. While the CP does
reduce bandwidth efficiency somewhat, the impact of the CP is
similar to the “roll-off factor” in raised-cosine filtered single-
carrier systems. Since OFDM has a very sharp, almost “brick-
wall” spectrum, a large fraction of the allocated channel
bandwidth can be utilized for data transmission, which helps to
moderate the loss in efficiency due to the cyclic prefix.

22.  All profiles currently defined by the WiMax Forum specify the
256-carrier OFDM air interface.
 Allows digital signal to be transmitted simultaneously on multiple
RF carrier waves. Adaptable to NLOS schemes.
 Resistant to multi-path effects.
 Spectrally efficient technique to transmit wireless digital data.
 Able to deliver higher bandwidth efficiency.
 There are some obstacles in using OFDM in transmission
system in contrast to its advantages. A major obstacle is that
the OFDM signal exhibits a very high Peak to Average
Power Ratio (PAPR).

23. Equalizers are avoided in
OFDM
timetime
Cyclic Prefix Useful SymbolCyclic Prefix Useful Symbol
TimeTime
timetime
Note: All signals & multipath overNote: All signals & multipath over
a useful symbol time are from thea useful symbol time are from the
same symbol & add constructivelysame symbol & add constructively
(no ISI)(no ISI)
Note: dashed linesNote: dashed lines
representrepresent
multipathmultipath
Narrow bandwidthNarrow bandwidth  long symbol timeslong symbol times  all significant multipaths arrive within a symbolall significant multipaths arrive within a symbol
time minimizing ISItime minimizing ISI  no equalizationno equalization  low complexitylow complexity
Tx SignalTx Signal
Rx SignalRx Signal
Source: LucentSource: Lucent

24. Tradeoffs of FFT size
 The FFT size determines the number of sub-
carriers in the specified bandwidth
 Larger FFT sizes lead to narrower subcarriers and
smaller inter-subcarrier spacing
 More susceptibility to ICI, particularly in high Doppler
(Note: Doppler shift for 125 km/hr for operation at 3.5
GHz is v/λ = 35 m/sec/0.086 m = 408 Hz)
 Narrower subcarriers lead to longer symbol times 
less susceptibility to delay spread
 Smaller FFT sizes the opposite is true
Source: LucentSource: Lucent

25. OFDMA Symbol Structure

26. OFDMA Scalability
(SOFDMA)
• Supports s wide range of frame sizes (2-20 ms)Supports s wide range of frame sizes (2-20 ms)
Source: Intel “Scalable OFDMA Physical Layer in IEEE 802.16 WirelessMAN”Source: Intel “Scalable OFDMA Physical Layer in IEEE 802.16 WirelessMAN”

27. Advantages of WiMax
 A single WiMAX main station can serve hundreds of
users.
 • Endpoints install within days instead of the weeks
required for wired connections.
 • Data rates as high as 280Mbps and distances of 30
miles are possible.
 • Users can operate mobile within 3-5 miles of a base
station at data rates up to 75Mbps.
 • No FCC radio licensing is required.

28. Disadvantages
 Line-of-sight (LOS) is required for long
distance (5-30 mile) connections
 Heavy rains can disrupt the service.
 Other wireless electronics in the vicinity
can interfere with the WiMAX
connection and cause a reduction in
data throughput or even a total
disconnect.

29. End of Presentation
Thank You.