10,818 research outputs found
Space-Time Trellis and Space-Time Block Coding Versus Adaptive Modulation and Coding Aided OFDM for Wideband Channels
Abstract—The achievable performance of channel coded spacetime trellis (STT) codes and space-time block (STB) codes transmitted over wideband channels is studied in the context of schemes having an effective throughput of 2 bits/symbol (BPS) and 3 BPS. At high implementational complexities, the best performance was typically provided by Alamouti’s unity-rate G2 code in both the 2-BPS and 3-BPS scenarios. However, if a low complexity implementation is sought, the 3-BPS 8PSK space-time trellis code outperfoms the G2 code. The G2 space-time block code is also combined with symbol-by-symbol adaptive orthogonal frequency division multiplex (AOFDM) modems and turbo convolutional channel codecs for enhancing the system’s performance. It was concluded that upon exploiting the diversity effect of the G2 space-time block code, the channel-induced fading effects are mitigated, and therefore, the benefits of adaptive modulation erode. In other words, once the time- and frequency-domain fades of the wideband channel have been counteracted by the diversity-aided G2 code, the benefits of adaptive modulation erode, and hence, it is sufficient to employ fixed-mode modems. Therefore, the low-complexity approach of mitigating the effects of fading can be viewed as employing a single-transmitter, single-receiver-based AOFDM modem. By contrast, it is sufficient to employ fixed-mode OFDM modems when the added complexity of a two-transmitter G2 scheme is affordable
Droplet: A New Denial-of-Service Attack on Low Power Wireless Sensor Networks
In this paper we present a new kind of Denial-of-Service attack against the PHY layer of low power wireless sensor networks. Overcoming the very limited range of jamming-based attacks, this attack can penetrate deep into a target network with high power efficiency. We term this the Droplet attack, as it attains enormous disruption by dropping small, payload-less frame headers to its victim's radio receiver, depriving the latter of bandwidth and sleep time. We demonstrate the Droplet attack's high damage rate to full duty-cycle receivers, and further show that a high frequency version of Droplet can even force nodes running on very low duty-cycle MAC protocols to drop most of their packets
A Comparison of CP-OFDM, PCC-OFDM and UFMC for 5G Uplink Communications
Polynomial-cancellation-coded orthogonal frequency division multiplexing
(PCC-OFDM) is a form of OFDM that has waveforms which are very well localized
in both the time and frequency domains and so it is ideally suited for use in
the 5G network. This paper analyzes the performance of PCC-OFDM in the uplink
of a multiuser system using orthogonal frequency division multiple access
(OFDMA) and compares it with conventional cyclic prefix OFDM (CP-OFDM), and
universal filtered multicarrier (UFMC). PCC-OFDM is shown to be much less
sensitive than either CP-OFDM or UFMC to time and frequency offsets. For a
given constellation size, PCC-OFDM in additive white Gaussian noise (AWGN)
requires 3dB lower signal-to-noise ratio (SNR) for a given bit-error-rate, and
the SNR advantage of PCC-OFDM increases rapidly when there are timing and/or
frequency offsets. For PCC-OFDM no frequency guard band is required between
different OFDMA users. PCC-OFDM is completely compatible with CP-OFDM and adds
negligible complexity and latency, as it uses a simple mapping of data onto
pairs of subcarriers at the transmitter, and a simple weighting-and-adding of
pairs of subcarriers at the receiver. The weighting and adding step, which has
been omitted in some of the literature, is shown to contribute substantially to
the SNR advantage of PCC-OFDM. A disadvantage of PCC-OFDM (without overlapping)
is the potential reduction in spectral efficiency because subcarriers are
modulated in pairs, but this reduction is more than regained because no guard
band or cyclic prefix is required and because, for a given channel, larger
constellations can be used
Physical Layer Service Integration in 5G: Potentials and Challenges
High transmission rate and secure communication have been identified as the
key targets that need to be effectively addressed by fifth generation (5G)
wireless systems. In this context, the concept of physical-layer security
becomes attractive, as it can establish perfect security using only the
characteristics of wireless medium. Nonetheless, to further increase the
spectral efficiency, an emerging concept, termed physical-layer service
integration (PHY-SI), has been recognized as an effective means. Its basic idea
is to combine multiple coexisting services, i.e., multicast/broadcast service
and confidential service, into one integral service for one-time transmission
at the transmitter side. This article first provides a tutorial on typical
PHY-SI models. Furthermore, we propose some state-of-the-art solutions to
improve the overall performance of PHY-SI in certain important communication
scenarios. In particular, we highlight the extension of several concepts
borrowed from conventional single-service communications, such as artificial
noise (AN), eigenmode transmission etc., to the scenario of PHY-SI. These
techniques are shown to be effective in the design of reliable and robust
PHY-SI schemes. Finally, several potential research directions are identified
for future work.Comment: 12 pages, 7 figure
Near-Instantaneously Adaptive HSDPA-Style OFDM Versus MC-CDMA Transceivers for WIFI, WIMAX, and Next-Generation Cellular Systems
Burts-by-burst (BbB) adaptive high-speed downlink packet access (HSDPA) style multicarrier systems are reviewed, identifying their most critical design aspects. These systems exhibit numerous attractive features, rendering them eminently eligible for employment in next-generation wireless systems. It is argued that BbB-adaptive or symbol-by-symbol adaptive orthogonal frequency division multiplex (OFDM) modems counteract the near instantaneous channel quality variations and hence attain an increased throughput or robustness in comparison to their fixed-mode counterparts. Although they act quite differently, various diversity techniques, such as Rake receivers and space-time block coding (STBC) are also capable of mitigating the channel quality variations in their effort to reduce the bit error ratio (BER), provided that the individual antenna elements experience independent fading. By contrast, in the presence of correlated fading imposed by shadowing or time-variant multiuser interference, the benefits of space-time coding erode and it is unrealistic to expect that a fixed-mode space-time coded system remains capable of maintaining a near-constant BER
Deep Learning Framework for Wireless Systems: Applications to Optical Wireless Communications
Optical wireless communication (OWC) is a promising technology for future
wireless communications owing to its potentials for cost-effective network
deployment and high data rate. There are several implementation issues in the
OWC which have not been encountered in radio frequency wireless communications.
First, practical OWC transmitters need an illumination control on color,
intensity, and luminance, etc., which poses complicated modulation design
challenges. Furthermore, signal-dependent properties of optical channels raise
non-trivial challenges both in modulation and demodulation of the optical
signals. To tackle such difficulties, deep learning (DL) technologies can be
applied for optical wireless transceiver design. This article addresses recent
efforts on DL-based OWC system designs. A DL framework for emerging image
sensor communication is proposed and its feasibility is verified by simulation.
Finally, technical challenges and implementation issues for the DL-based
optical wireless technology are discussed.Comment: To appear in IEEE Communications Magazine, Special Issue on
Applications of Artificial Intelligence in Wireless Communication
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