OFDM

• BBC / Proceeding of 20th International Television Symposium 1997	Explaining some of the magic of COFDM Coded Orthogonal Frequency Division Multiplexing (COFDM) [1, 2] has been specified for digital broadcasting systems for both audio -- Digital Audio Broadcasting (DAB) [3] and (terrestrial) television -- Digital Video Broadcasting (DVB-T) [4, 5, 6]. COFDM is particularly well matched to these applications, since it is very tolerant of the effects of multipath (provided a suitable guard interval is used).
  Cisco Systems	Overcoming Multipath in Non-Line-of-Sight High-Speed Microwave Communication Links Since the beginning of development of microwave wireless transmission equipment, manufacturers and operators have tried to mitigate the effects of reflected signals associated with signal propagation. These reflections are called multipath. In real world situations, microwave systems involve careful design in order to overcome the effects of multipath. Most existing multipath mitigation approaches fall well short of the full reliable information rate potential of many wireless communications systems. This paper discusses how to create a digital microwave transmission system that can not only tolerate multipath signals, but can actually take advantage of them.
  CSD	Enabling Fast Wireless Networks with OFDM Spread-spectrum technology gives respectable data rates for many WLAN types, but for media-rich data, OFDM could provide a better solution. Spread spectrum modulation has been the basis for many proprietary and IEEE 802.11-based WLANs. Through the use of frequency hopping and direct sequence, these WLANs provide data rates from 1 to 11 Mbps. In addition, new activity within the IEEE 802.11 committee is considering a 22-Mbps version of direct sequence. Regardless of these relatively high data rates, the demand for wireless broadband LANs and MANs, is pushing the envelope on spread spectrum technologies. Because of relatively inefficient use of bandwidth, spread spectrum systems will probably not satisfy the even higher data rates that multimedia applications require. In addition, multimedia applications operating outdoors or within industrial environments require a wireless network capable of operating more effectively in "RF hostile" areas.
  Michael Speth	OFDM Receivers for Broadband-Transmission OFDM and the orthogonality principle, The general problem: Data transmission over multipath channels, Single carrier approach, Multi carrier approach, Orthogonal Frequency Division Multiplexing, An OFDM receiver for DVB-T, Tasks of the inner receiver and receiver structure, Channel estimation for OFDM, Performance of the complete receiver...
  Andrew McCormick University of Edinburgh	Interactive OFDM Tutorial An introduction to Orthogonal Frequency Division Multiplexing.
  WAVE Report	OFDM Tutorial Frequency division multiplexing (FDM) is a technology that transmits multiple signals simultaneously over a single transmission path, such as a cable or wireless system. Each signal travels within its own unique frequency range (carrier), which is modulated by the data. Orthogonal FDM's (OFDM) spread spectrum technique distributes the data over a large number of carriers that are spaced apart at precise frequencies. This spacing provides the "orthogonality" in this technique which prevents the demodulators from seeing frequencies other than their own. The benefits of OFDM are high spectral efficiency, resiliency to RF interference, and lower multi-path distortion.
  Wi-LAN	OFDM Technology Introduction, Messages, Carrier Waves, Modulation
  IEEE 802.16 Working Group on Broadband Wireless Access Standards (wirelessman.org)	Coded Orthogonal Frequency Division Multiple Access (PDF) Coded Orthogonal Frequency Division Multiple Access (COFDMA) technique. The tutorial contains explanation on the OFDM basics and coverage options, including Single Frequency Network (SFN) and its possible application for fixed and mobile applications. Coding and multiplexing implementations, including scenarios for multiple access and bandwidth on demand allocations. Multiple access allocation using Reed Solomon series, which allows a better Carrier Allocation.

  Other Resources in OFDM
  

  CSU	High-Throughput, High-Performance OFDM via Pseudo-Orthogonal Carrier Interferometry Coding (PDF) OFDM is susceptible to poor probability of error performance in fading channels. To enhance OFDM’s performance, many architectures utilize channel coding. The addition of coding, adds both redundancy and frequency diversity, but comes at a cost of reduced overall throughput (typically by a factor of 2). This paper introduces a novel carrier interferometry phase coding to enhance performance in OFDM systems without bandwidth expansion or decreased throughput. It is shown that at a bit error rate of 10 -3 , this method gains 14 dB over OFDM, equaling the performance of COFDM. A system is now available demonstrating the benefits of Coded OFDM, which maintains the throughput of OFDM. The cost is one of increased receiver complexity.
  IEEE	IEEE 802.16 Tutorial Frequency Domain Equalization for 2-11 GHz Broadband Wireless Systems. In this tutorial we survey recent advances in frequency domain equalization (FDE) for single carrier (SC) systems. SC modulation systems have lower peak-to average-ratios than OFDM, and when combined with FDE, their performance is at least as good as OFDM systems (in some cases better); furthermore, they have the same reduced signal processing complexity enjoyed by OFDM systems. IEEE 802.16 Tutorials 802.16 MAN documents.
  IEEE 802.16 Working Group on Broadband Wireless Access Standards (wirelessman.org)	Frequency Domain Equalization for 2-11 GHz Broadband Wireless Systems (1/2001, 304Kb, PDF) Broadband wireless systems deployed in outdoor non-line of sight environments may encounter delay spreads of over 5 to 10 us - which can cause potential intersymbol interference over 50 or more data symbol intervals. OFDM (orthogonal frequency division multiplexing) has been suggested to combat this ISI problem with reasonable complexity. However OFDM systems generate high transmitted peak-to-average ratios and are sensitive to phase noise; this can increase RF subsystem cost and complexity.
  mobilecomms-technology	T-Mobile FLASH-OFDM Mobile Broadband Network, Slovakia In October 2005 T-Mobile launched a new and faster mobile broadband internet access network in Slovakia. The network is Europe's first commercial mobile broadband service (also a world first) and uses Flarion Technologies' (now acquired by Qualcomm Inc. for $600 million) Fast, Low-latency Access with Seamless Handoff - Orthogonal Frequency Division Multiplexing (FLASH-OFDM) network technology.