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Keysight Technologies
OFDMA Introduction and Overview for
Aerospace and Defense Applications
Application Note
Introduction
This application note is for Aerospace and Defense (A/D) engineers considering or developing systems
using OFDM or OFDMA. Understanding the complexities of OFDM and OFDMA can be challenging,
particularly if one has not previously worked with commercial wireless standards. The intent of this
application note is to provide a brief introduction to OFDM and OFDMA, with an eye toward the special
considerations and environments for A/D applications. The concepts presented in this application
note will serve as an initial basis to further understand commercial standards-based OFDM and OFDMA
such as LTE using additional reference provided at the end of this application note.
Orthogonal frequency division multiplexing (OFDM) has become attractive for a wide range of commercial
wireless systems because it delivers high data throughput in real-world environments, along with
spectral efficiency, and link flexibility. OFDM first came into wide use more than a dozen years ago in
wireless local area network (LAN) applications and has recently spread rapidly to support wireless
mobile voice and data in the form of the 3GPP long-term evolution (LTE) standard and the Worldwide
Interoperability for Microwave Access (WiMAX) standard.
The baseband processing power that OFDM demands for both signal generation and demodulation
is no longer a barrier to implementation, and in recent years systems have rapidly increased their
throughput and efficiency. Commercial systems have implemented progressively wider bandwidths
and sophisticated coding and multiplexing schemes to efficiently serve large numbers of users with
ever-greater data demands.
OFDM's low symbol rate and multicarrier structure, combined with coding and forward error correction,
allow it to operate effectively in channel conditions degraded by interference, jamming, and frequency
selective fading.
Because of its multicarrier structure, OFDM is readily extendable to simultaneous multiple-access
capability by mapping subcarriers to users in a scheme called orthogonal frequency division multiple
access or OFDMA. This multiple access approach is especially attractive because multiple users can
be supported in a flexible fashion with only minor changes in the air interface.
In addition, Multiple-Input Multiple-Output (MIMO) techniques can be used with OFDM and OFDMA
systems to further improve data throughput in the presence of multipath environments.
This combination of benefits makes OFDM attractive for flexible deployment in Aerospace and Defense
(A/D) applications, both terrestrial and marine. One attractive application example is video streaming
for improved situational awareness. A/D users could potentially take advantage of sophisticated existing
hardware and software solutions that offer proven commercial performance in different physical
environments from wide open terrain to complex obstructed urban environments. 0ff-the-shelf
solutions can be configured to meet many different commercial requirements in terms of number of
users, required average and peak data rates, cell sizes and configurations, and overall coverage areas.
They include not only network infrastructure but a range of handsets and terminals that implement
sophisticated roaming features that can include automatic switching to nearby LAN resources when
available. This is a powerful benefit when optimizing use of valuable metropolitan area network (MAN)
resources.
While these technologies were not designed with A/D applications in mind, particularly in the areas of
security and resistance to jamming, they are designed to handle environments with interference and
competing spectral users. They could potentially serve as a base layer, to which additional layers for
security and robustness or redundancy may be added.
03 | Keysight | OFDMA Introduction and Overview for Aerospace and Defense Applications - Application Note
OFDM and OFDMA benefits and flexibility for A/D
applications
OFDM is a digital multiplexing scheme that uses considerable digital signal processing
(DSP) to implement a large-scale multicarrier transmission technique providing important
benefits over real-world transmission channels. OFDM can achieve: