Presentation on theme: "Chapter 4 of Hiroshi Harada Book (OFDM Transmission)"— Presentation transcript:
1 Chapter 4 of Hiroshi Harada Book (OFDM Transmission) EE578 Assignment #4Chapter 4 of Hiroshi Harada Book (OFDM Transmission)Abdul-Aziz .M Al-YamiNov 1st 2010
2 OUTLINE OVERVIEW ABOUT OFDM DEFINITION AND PRINCIPLES OFDM ADVANTAGES & DRAWBACKSAPPLICATIONSCONCLUSIONS AND PERSPECTIVESRESULTS
3 OVERVIEW ABOUT OFDM OFDM was invented more than 40 years ago. OFDM has been adopted for several technologies:Asymmetric Digital Subscriber Line (ADSL) services.IEEE a/g, IEEE a.Digital Audio Broadcast (DAB).Digital Terrestrial Television Broadcast: DVD inEurope, ISDB in Japan4G, IEEE n, IEEE , and IEEE
4 WHY OFDM ?High bit rate needs are clumped by the nature of communication channels.Multi-path Propagation effects forbid increasing of transmission rates.
5 OFDM DEFINITION OFDM = Orthogonal FDM Carrier centers are put on orthogonal frequenciesORTHOGONALITY - The peak of each signal coincides with trough of other signalsSubcarriers are spaced by 1/Ts
7 PRINCIPLESBASIC IDEA : Channel bandwidth is divided into multiple subchannels to reduce ISI and frequency-selective fading.Multicarrier transmission : Subcarriers are orthogonal each other in frequency domain.
8 PRINCIPLES Time-domain spreading: Spreading is achieved in the time-domain by repeating the same information in an OFDM symbol on two different sub-bands => Frequency Diversity.Frequency-domain spreading:Spreading is achieved by choosing conjugate symmetric inputs for the input to the IFFT (real output)Exploits frequency diversity and helps reduce the transmitter complexity/power consumption.
9 FDM OFDM Frequency Division Multiplexing OFDM frequency dividing EARN IN SPECTRAL EFFICIENCY
10 OFDM THEORY The baseband OFDM signals can be written as Where is the central frequency of the mth sub-channel and is the corresponding transmitted symbol.The signals are orthogonal over [0, T ] as illustrated below:
11 Generic OFDM Transmitter OFDM symbolbitsSerial toParallelPulse shaperFECIFFTLinear PA&DACadd cyclic extensionfcview this as a time tofrequency mapperComplexity (cost) is transferred back from the digital to the analog domain!
12 (of all tones sent in one OFDM symbol) Generic OFDM ReceiverSlot &TimingAGCSync.P/S andDetectionErrorSamplerFFTRecoveryfcgross offsetVCOFreq. Offsetfine offsetEstimation(of all tones sent in one OFDM symbol)
13 OFDM ADVANTAGES OFDM is spectrally efficient IFFT/FFT operation ensures that sub-carriers do not interfere with each other.OFDM has an inherent robustness against narrowband interference.Narrowband interference will affect at most a coupleof subchannels.Information from the affected subchannels can beerased and recovered via the forward errorcorrection (FEC) codes.Equalization is very simple compared to Single-Carrier systems
14 OFDM ADVANTAGESOFDM has excellent robustness in multi-path environments.Cyclic prefix preserves orthogonality between sub-carriers.Cyclic prefix allows the receiver to capture multi-path energy more efficiently.Ability to comply with world-wide regulations:Bands and tones can be dynamically turned on/offto comply with changing regulations.Coexistence with current and future systems:for enhanced coexistence with the other devices.
15 OFDM DRAWBACKS High sensitivity inter-channel interference, ICI OFDM is sensitive to frequency, clock and phase offsetThe OFDM time-domain signal has a relatively large peak-to-average ratiotends to reduce the power efficiency of the RF amplifiernon-linear amplification destroys the orthogonality of the OFDM signal and introduced out-of-band radiation
16 Standards Digital Audio Broadcasting (DAB) Digital Video Broadcasting (DVB)Asymmetric Digital Subscriber Line (ADSL)Wireless LAN IEEE aWireless networking, device connectivityProposed for standardConnection between subscriber's transceiver station and a base transceiver station
18 DRM For HF Frequencies 4.5 – 5 kHz for half channel Data Rates of 4 – 14.5 kbit/s9 – 10 kHz for full channelData Rates of 8 – 35kbit/s18-20 kHz for double channelData Rates of 31 – 72kbit/s
19 (V-OFDM) of Cisco, Iospan,etc. Proprietary OFDM FlavoursWideband-OFDM(W-OFDM) of Wi-LANFlash OFDMfrom FlarionVector OFDM(V-OFDM) of Cisco, Iospan,etc.-- Freq. Hopping forCCI reduction, reuseto 5.0MHz BW-- mobility supportGHz bandMbps in 40MHz-- large tone-width(for mobility, overlay)-- MIMO Technology-- non-LoS coverage,mainly for fixed access-- upto 20 Mbps in MMDSWi-LAN leads the OFDM Forum -- many proposals submitted toIEEE Wireless MANCisco leads the Broadand Wireless Internet Forum (BWIF)