|
| |
| [ Also see: WLAN
Glossary Wireless
Tutorials Bluetooth
IEEE 802.11 WLAN IEEE
802.16 WMAN UWB ]
|
Introductory information about Orthogonal Frequency Division Multiplexing (OFDM),
Coded OFDM (COFDM), Vector OFDM (VOFDM) and related technologies.
|
|
| 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. |
|
|
|
