7 Why OFDM Resiliency to RF interference The ISM Band Industrial Scientific and

7 why ofdm resiliency to rf interference the ism band

This preview shows page 7 - 15 out of 66 pages.

7 Why OFDM? Resiliency to RF interference. The ISM Band (Industrial Scientific and Medical) is a set of frequency ranges that are unregulated. Most popular consumer bands 915MHz Band (BW 26MHz) 2.45GHz Band (BW 100MHz) 5.8GHz Band (BW 100MHz) Typical RF transmitters in the ISM band include… Analog Cordless Phones (900MHz) Microwave Ovens (2.45 GHz) Bluetooth Devices (2.45GHz) Digital Cordless Phones (2.45GHz or 5.8GHz) Wireless LAN (2.45GHz or 5.8GHz).
Image of page 7

Subscribe to view the full document.

A G R E A T E R M E A S U R E O F C O N F I D E N C E © Copyright 2007-2008 Keithley Instruments, Inc. 8 The Multi-Path Problem Example: Bluetooth Transmitter & Receiver TX1 RX1 Ceiling Floor Maximum time for signal To travel D (Distance) D multipath > D direct TX to RX < 1us Symbol Rate = 1MSymbols/s Symbol Duration = 1/1E6 = 1us D direct Maximum Symbol Delay < 1us
Image of page 8
A G R E A T E R M E A S U R E O F C O N F I D E N C E © Copyright 2007-2008 Keithley Instruments, Inc. 9 Single Carrier – Single Symbol Bluetooth, GSM, CDMA and other communications standards use a single carrier to transmit a single symbol at a time. Data throughput is achieved by using a very fast symbol rate. W-CDMA - 3.14 Msymbols/sec Bluetooth – 1 Msymbols/sec A primary disadvantage is that fast symbol rates are more susceptible to Multi-path distortion.
Image of page 9

Subscribe to view the full document.

A G R E A T E R M E A S U R E O F C O N F I D E N C E © Copyright 2007-2008 Keithley Instruments, Inc. 10 Slow the symbol rate Reduce the previous examples symbol rate by a third TX1 RX1 Ceiling Floor Maximum time for signal To travel D (Distance) D multipath > D direct TX to RX < 3.3us Symbol Rate = 300kSymbols/s Symbol Duration = 1/300 = 3.3us D direct But the data throughput is reduced! Maximum Symbol Delay < 3.3us
Image of page 10
A G R E A T E R M E A S U R E O F C O N F I D E N C E © Copyright 2007-2008 Keithley Instruments, Inc. 11 Improve the throughput - use more than one carrier! 802.11a-g WLAN example Q I Q I Q 312.5kHz I 312.5kHz I Q 312.5kHz I Q 312.5kHz Low symbol rate per carrier * multiple carriers = high data rate 250 kbps symbol rate * 48 sub-carriers * 6 coded bits /sub-carrier * ¾ coding rate = 54 Mbps ( for 64QAM )
Image of page 11

Subscribe to view the full document.

A G R E A T E R M E A S U R E O F C O N F I D E N C E © Copyright 2007-2008 Keithley Instruments, Inc. 12 Sub Carrier Spacing • The sub-carriers are spaced at regular intervals called the sub-carrier frequency spacing ( F). • The sub-carrier frequency relative to the center frequency is k F where k is the sub- carrier number.
Image of page 12
A G R E A T E R M E A S U R E O F C O N F I D E N C E © Copyright 2007-2008 Keithley Instruments, Inc. 13 Symbol to Waveform Traditional – Serial Symbol Transmissions I Q
Image of page 13

Subscribe to view the full document.

A G R E A T E R M E A S U R E O F C O N F I D E N C E © Copyright 2007-2008 Keithley Instruments, Inc. 14 Symbol to Waveform OFDM – Parallel Symbol Transmissions f 1 f 2 f 3 f 4 …f n OFDM Symbol Period Multiple carriers will transmit multiple symbols in parallel.
Image of page 14
Image of page 15
  • Spring '16
  • WiMAX, Keithley Instruments

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern

Ask Expert Tutors You can ask 0 bonus questions You can ask 0 questions (0 expire soon) You can ask 0 questions (will expire )
Answers in as fast as 15 minutes