Chapter 4 of Hiroshi Harada Book (OFDM Transmission) EE578 Assignment #4 Chapter 4 of Hiroshi Harada Book  (OFDM Transmission) Abdul-Aziz .M Al-Yami Nov 1st 2010

OUTLINE OVERVIEW ABOUT OFDM DEFINITION AND PRINCIPLES OFDM ADVANTAGES & DRAWBACKS APPLICATIONS CONCLUSIONS AND PERSPECTIVES RESULTS

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 802.11a/g, IEEE 802.16a. Digital Audio Broadcast (DAB). Digital Terrestrial Television Broadcast: DVD in Europe, ISDB in Japan 4G, IEEE 802.11n, IEEE 802.16, and IEEE 802.20.

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

OFDM DEFINITION OFDM = Orthogonal FDM Carrier centers are put on orthogonal frequencies ORTHOGONALITY - The peak of each signal coincides with trough of other signals Subcarriers are spaced by 1/Ts

Modulation

PRINCIPLES BASIC 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.

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.

FDM  OFDM Frequency Division Multiplexing OFDM frequency dividing EARN IN SPECTRAL EFFICIENCY

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:

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

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

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 couple of subchannels. Information from the affected subchannels can be erased and recovered via the forward error correction (FEC) codes. Equalization is very simple compared to Single-Carrier systems

OFDM ADVANTAGES OFDM 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/off to comply with changing regulations. Coexistence with current and future systems: for enhanced coexistence with the other devices.

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

Standards Digital Audio Broadcasting (DAB) Digital Video Broadcasting (DVB) Asymmetric Digital Subscriber Line (ADSL) Wireless LAN IEEE 802.11a Wireless networking, device connectivity Proposed for 802.16 standard Connection between subscriber's transceiver station and a base transceiver station

COFDM Transmitter   Digital Radio Coded OFDM Transmitter

DRM For HF Frequencies 4.5 – 5 kHz for half channel Data Rates of 4 – 14.5 kbit/s 9 – 10 kHz for full channel Data Rates of 8 – 35kbit/s 18-20 kHz for double channel Data Rates of 31 – 72kbit/s

(V-OFDM) of Cisco, Iospan,etc. Proprietary OFDM Flavours Wideband-OFDM (W-OFDM) of Wi-LAN www.wi-lan.com Flash OFDM from Flarion www.flarion.com Vector OFDM (V-OFDM) of Cisco, Iospan,etc. www.iospan.com -- Freq. Hopping for CCI reduction, reuse -- 1.25 to 5.0MHz BW -- mobility support -- 2.4 GHz band -- 30-45Mbps in 40MHz -- large tone-width (for mobility, overlay) -- 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 802.16 Wireless MAN Cisco leads the Broadand Wireless Internet Forum (BWIF)

MATLAB Results Program 4.2 (ofdm_fading)