OFDM, Quick Intro K7DEN

OUTLINE zOVERVIEW ABOUT OFDM zDEFINITION AND PRINCIPLES zOFDM ADVANTAGES & DRAWBACKS zAPPLICATIONS zCONCLUSIONS AND PERSPECTIVES

OVERVIEW ABOUT OFDM zOFDM was invented more than 40 years ago. zOFDM has been adopted for several technologies: y Asymmetric Digital Subscriber Line (ADSL) services. y IEEE a/g, IEEE a. y Digital Audio Broadcast (DAB). y Digital Terrestrial Television Broadcast: DVD in Europe, ISDB in Japan y 4G, IEEE n, IEEE , and IEEE

WHY OFDM ? zHigh bit rate needs are clumped by the nature of communication channels. zMulti-path Propagation effects forbid increasing of transmission rates.

OUTLINE zOVERVIEW ABOUT OFDM zDEFINITION AND PRINCIPLES zOFDM ADVANTAGES & DRAWBACKS

OFDM DEFINITION zOFDM = Orthogonal FDM zCarrier centers are put on orthogonal frequencies zORTHOGONALITY - The peak of each signal coincides with trough of other signals zSubcarriers are spaced by 1/Ts

Modulation

PRINCIPLES zBASIC IDEA : Channel bandwidth is divided into multiple subchannels to reduce ISI and frequency-selective fading. zMulticarrier transmission : Subcarriers are orthogonal each other in frequency domain.

PRINCIPLES zTime-domain spreading: ySpreading is achieved in the time-domain by repeating the same information in an OFDM symbol on two different sub-bands => Frequency Diversity. zFrequency-domain spreading: ySpreading is achieved by choosing conjugate symmetric inputs for the input to the IFFT (real output) yExploits frequency diversity and helps reduce the transmitter complexity/power consumption.

FDM  OFDM zFrequency Division Multiplexing zOFDM frequency dividing EARN IN SPECTRAL EFFICIENCY

z The baseband OFDM signals can be written as Where is the central frequency of the mth sub- channel and is the corresponding transmitted symbol. z The signals are orthogonal over [0, T ] as illustrated below: OFDM THEORY

FEC IFFT DAC Linear PA add cyclic extension bits fcfc OFDM symbol Pulse shaper & view this as a time to frequency mapper Generic OFDM Transmitter Complexity (cost) is transferred back from the digital to the analog domain! Serial to Parallel

AGC fcfc VCO Sampler FFT Error gross offset Slot & fine offset Freq. Offset Estimation Timing Sync. (of all tones sent in one OFDM symbol) Generic OFDM Receiver Recovery P/S and Detection

OUTLINE zOVERVIEW ABOUT OFDM zDEFINITION AND PRINCIPLES zOFDM ADVANTAGES & DRAWBACKS zAPPLICATIONS

OFDM ADVANTAGES zOFDM is spectrally efficient y IFFT/FFT operation ensures that sub-carriers do not interfere with each other. zOFDM has an inherent robustness against narrowband interference. y Narrowband interference will affect at most a couple of subchannels. y Information from the affected subchannels can be erased and recovered via the forward error correction (FEC) codes. zEqualization is very simple compared to Single-Carrier systems

OFDM ADVANTAGES zOFDM has excellent robustness in multi-path environments. y Cyclic prefix preserves orthogonality between sub- carriers. y Cyclic prefix allows the receiver to capture multi- path energy more efficiently. zAbility to comply with world-wide regulations: y Bands and tones can be dynamically turned on/off to comply with changing regulations. zCoexistence with current and future systems: y Bands and tones can be dynamically turned on/off for enhanced coexistence with the other devices.

OFDM DRAWBACKS zHigh sensitivity inter-channel interference, ICI zOFDM is sensitive to frequency, clock and phase offset zThe OFDM time-domain signal has a relatively large peak- to-average ratio y tends to reduce the power efficiency of the RF amplifier y non-linear amplification destroys the orthogonality of the OFDM signal and introduced out-of-band radiation

OUTLINE zOVERVIEW ABOUT OFDM zDEFINITION AND PRINCIPLES zOFDM ADVANTAGES & DRAWBACKS zAPPLICATIONS

Standards zDigital Audio Broadcasting (DAB) zDigital Video Broadcasting (DVB) zAsymmetric Digital Subscriber Line (ADSL) zWireless LAN IEEE a yWireless networking, device connectivity zProposed for standard yConnection between subscriber's transceiver station and a base transceiver station

Digital Radio zCoded OFDM Transmitter COFDM Transmitter

DRM zFor HF Frequencies y4.5 – 5 kHz for half channel xData Rates of 4 – 14.5 kbit/s y9 – 10 kHz for full channel xData Rates of 8 – 35kbit/s y18-20 kHz for double channel xData Rates of 31 – 72kbit/s

Products zAOR ARD9800 yhttp:// zIcom D-Star zWinDRM

Proprietary OFDM Flavours Wideband-OFDM (W-OFDM) of Wi-LAN Flash OFDM from Flarion Vector OFDM (V-OFDM) of Cisco, Iospan,etc GHz band Mbps in 40MHz -- large tone-width (for mobility, overlay) -- Freq. Hopping for CCI reduction, reuse to 5.0MHz BW -- mobility support -- MIMO Technology -- non-LoS coverage, mainly for fixed access -- upto 20 Mbps in MMDS Wi-LAN leads the OFDM Forum -- many proposals submitted to IEEE Wireless MAN Cisco leads the Broadand Wireless Internet Forum (BWIF)