Introduction to Audio Compression

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					Seminar Nachrichtentechnik SS 2009




          Mobile WiMAX Part I
                       Zhou  Shen 




                          1
Contents

• Introduction to WiMAX
      Broadband Wireless
      General Description of WiMAX

• The Physical Layer of WiMAX
      Introduction
      OFDMA
      Functional Stages of PHY Layer


                       2
Broadband Wireless
• Necessity of Broadband Wireless Transmission
 • Increasing Requirement of Data Networks
 • Growing Demand for Networks Coverage

• Evolution of Broadband Wireless
 • Different Types of Wireless Networks
     WPAN   ( Wireless Personal Area Network )
     WLAN   ( Wireless Local Area Network )
     WMAN   ( Wireless Metropolitan Area Network )
     WAN    ( Wide Area Network )


                            3
Broadband Wireless
               • Evolution of Broadband Wireless

                    • Problems In The Past
                         Standardization
                         Price
                         Line of Sight Requirement
                         Services




               How to resolve them?

                               WiMAX

                4
General Description of WiMAX
  • Overview   of WiMAX




                          5
 General Description of WiMAX
• Fixed WiMAX ( 802.16-2004)       • Mobile WiMAX (802.16e-2005)




                               6
General Description of WiMAX
• Spectrum Options for Broadband Wireless
  • Importance of The Availability of Frequency Spectrum
  • 2.3GHz, 2.5GHz, 3.5GHz, and 5.8GHz bands are most likely to
    see WiMAX Deployments

• Challenges for Broadband Wireless and WiMAX
    Improvement of The Traditional Broadband
    Differences in Global Spectrum Availability
    Competition with 3G
    Device Development



                              7                              1/31/2009
Introduction of PHY layer
• Arrangement of OSI layers for WiMAX




                      8
OFDMA
• Review of OFDM




                   9
Review of OFDM
• Time and Frequency Domain Considerations of OFDM




                        10
From OFDM to OFDMA
• Multiple-Access Strategies for OFDM
    Why Multiple-Access is needed?
    --- The Requirement of Utilization of Multiple User
    How to realize it in OFDM?
    --- Mix OFDM with TDMA and FDMA and CDMA (optional)




                          11
From OFDM to OFDMA




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OFDMA
• Advantages
   multipath suppression and frequency diversity
   flexible multiple-access technique for widely varying applications,
   data rate and QoS requirements
   reduce the transmit power
   relax the peak-to-average-power ratio (PAPR) problem




                               13
OFDMA
• Scalable OFDMA
   another difference between OFDM and OFDMA




• OFDMA Symbol




                          14
OFDMA
• WiMAX OFDMA Frame Structure




• Brief introduction to the key two principles that enable high performance in
  OFDMA: multiuser diversity and adaptive modulation.


                                   15
Functional Stages of PHY Layer




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Randomization
• Randomizer aims to provide encryption over the air to
  avoid sniffing.




                         17
Convolutional Coding




                18
Bit Interleaving and Repetition

• Bit Interleaving
     Interleaving is used to protect the transmission against long sequences
    of consecutive errors
         Distribute the coded bits over subcarriers
         Adjacent coded bits are mapped alternately onto less or more
         significant bits of the constellation.

•    Repetition
     Repetition coding is used to increase the robustness.




                                  19
 Symbol Mapping

• Convert the binary sequence to a sequence of complex
  valued symbols
   • QPSK
   • 16 QAM
   • 64 QAM ( optional )

• The constellation-mapped data are subsequently modulated
  onto the allocated subcarriers and each subcarrier multiplied
  by the factor
                                     1
                           sk = 2 ⋅ ( − wk )
                                     2

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Thanks a lot for your coming !
Any Questions?




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