Aerospace and Electronic Systems Magazine February 2018 - 5

noise-modulated multiuser superposition transmission framework
is introduced, where nonorthogonal multiple access (NOMA) is
deployed at the transmitter side to transmit aggregated signals
to multiple users1 simultaneously over the same frequency band.
Moreover, the transmitted signal is noise modulated with a locally
generated reference noise waveform to enhance the covertness of
data transmission. At the receiver side, users first extract the aggregated signals from the noise-like received signals. Then, successive interference cancellation (SIC) is applied to recover the
information.
A digital watermarking technique is applied as a stealthy method with high resiliency by embedding digital data inside the information, where the watermark carries unique information about the
owner of the message. The purpose of watermarking is to validate
the originality of data with low cost and high efficiency, especially
when dealing with streaming large-scale data [14], [15]. The primary idea is to deploy network sensors for generating identical
and synchronized watermarks that will be transmitted to the utility
through wireless channels in real time. However, this channel may
not be secure and could be prone to attack during data transmission.
A validation test is eventually conducted at the receiver to evaluate the data integrity on the basis of embedded watermarks. To be
specific, a pseudonoise (PN) code is initially selected to spread the
original signal over a wider bandwidth [16]. Each bit of transmitted
signal is spread by random watermarks controlled by the PN code,
then the spread signal is used to modulate the data characteristics
(e.g., avionics information and sensing data), and the signal is embedded with watermarks into the data flow from the transmitter.
At the receiver, the spread signal is extracted and demodulated by
correlation testing to retrieve the original signal. If the recovered
data flow contains the watermarks that means the original signal is
secured and not manipulated during the transmission.
A noise-modulated communication system is exploited in [17],
[18], [19] to conceal data sent over wireless channels, wherein a
band-limited noise signal is used to spread the transmitted signal's
power over a large bandwidth, thereby greatly increasing the pro1

Throughout the article, we use "user or users" and "receiver or
receivers" interchangeably.

FEBRUARY 2018

cessing gain and communication system reliability within noisy
and jamming environments. The noise-like signal is transmitted
along with the noise signal over orthogonal polarization channels.
Due to the random behavior and featureless characteristics of a
noise waveform, such a noise modulation technique can increase
the difficulty for a third party to detect the transmitted signal. The
drawback of a noise-modulated communication system is coexistence of the noise signal in the transmitted signal, which results in
the degradation of the system capacity.
To leverage the problem, the design of a multiple access approach is an important aspect in improving the system capacity in
a cost-effective manner. Generally, three types of multiple access
presently used with communications satellites are code-division,
frequency-division (e.g., FDMA, orthogonal frequency-division
multiple access [OFDMA], single-carrier frequency-division
multiple access [SC-FDMA]), and time-division multiple access
(TDMA). In particular, orthogonal multiple access (OMA) on the
basis of OFDMA or SC-FDMA is a reasonable choice for achieving good system level throughput in packet domain services by
using channel-aware time- and frequency-domain scheduling [20].
However, further enhancements are required to enhance the avionics system efficiency and quality of service (QoS), especially in
network resource-limited and harsh environments. To accommodate such demands, NOMA is introduced as a novel and promising
multiple access scheme for future system enhancement. The fundamental idea behind NOMA is to exploit user multiplexing in the
power domain, where multiple users are multiplexed in the power
domain on the transmitter side and demultiplexed on the receiver
side by using a successive interference canceler. Signals intended
for different users are assigned with different transmission power
levels and are transmitted over the same spectrum simultaneously
[21]. Because more information can be delivered to multiple users
by the same spectrum resource, NOMA can potentially achieve a
high spectrum efficiency and multiuser capacity region. Some preliminary studies of NOMA in commercial communication systems
have been conducted in [22], [23], [24] and have demonstrated the
performance enhanced by NOMA. The need for protection from
cyber intrusion and attacks complicates avionics systems beyond
the challenges encountered in commercial wireless and cellular

IEEE A&E SYSTEMS MAGAZINE

Table of Contents for the Digital Edition of Aerospace and Electronic Systems Magazine February 2018