1,345 research outputs found
Advanced digital modulation: Communication techniques and monolithic GaAs technology
Communications theory and practice are merged with state-of-the-art technology in IC fabrication, especially monolithic GaAs technology, to examine the general feasibility of a number of advanced technology digital transmission systems. Satellite-channel models with (1) superior throughput, perhaps 2 Gbps; (2) attractive weight and cost; and (3) high RF power and spectrum efficiency are discussed. Transmission techniques possessing reasonably simple architectures capable of monolithic fabrication at high speeds were surveyed. This included a review of amplitude/phase shift keying (APSK) techniques and the continuous-phase-modulation (CPM) methods, of which MSK represents the simplest case
Novel Time Asynchronous NOMA schemes for Downlink Transmissions
In this work, we investigate the effect of time asynchrony in non-orthogonal
multiple access (NOMA) schemes for downlink transmissions. First, we analyze
the benefit of adding intentional timing offsets to the conventional power
domain-NOMA (P-NOMA). This method which is called Asynchronous-Power
Domain-NOMA (AP-NOMA) introduces artificial symbol-offsets between packets
destined for different users. It reduces the mutual interference which results
in enlarging the achievable rate-region of the conventional P-NOMA. Then, we
propose a precoding scheme which fully exploits the degrees of freedom provided
by the time asynchrony. We call this multiple access scheme T-NOMA which
provides higher degrees of freedom for users compared to the conventional
P-NOMA or even the modified AP-NOMA. T-NOMA adopts a precoding at the base
station and a linear preprocessing scheme at the receiving user which
decomposes the broadcast channel into parallel channels circumventing the need
for Successive Interference Cancellation (SIC). The numerical results show that
T-NOMA outperforms AP-NOMA and both outperform the conventional P-NOMA. We also
compare the maximum sum-rate and fairness provided by these methods. Moreover,
the impact of pulse shape and symbol offset on the performance of AP-NOMA and
T-NOMA schemes are investigated
Rate-Splitting Multiple Access: The First Prototype and Experimental Validation of its Superiority over SDMA and NOMA
In multi-user multi-antenna communications, it is well-known in theory that
Rate-Splitting Multiple Access (RSMA) can achieve a higher spectral efficiency
than both Space Division Multiple Access (SDMA) and Non-Orthogonal Multiple
Access (NOMA). However, an experimental evaluation of RSMA's performance,
relative to SDMA and NOMA, is missing in the literature, which is essential to
address the ongoing debate between RSMA and NOMA over which is better suited to
handle most efficiently the available resources and interference in 6G. In this
paper, we address this critical knowledge gap by realizing the first-ever RSMA
prototype using software-defined radios. Through measurements using our
prototype, we empirically solve the modulation and coding scheme limited sum
throughput maximization problem for RSMA, SDMA and NOMA for the two-user
multiple-input single-output (MISO) scenario over (a) different pairs of
line-of-sight channels that vary in terms of their relative pathloss and
spatial correlation, and with (b) different channel state information quality.
We observe that RSMA achieves the highest sum throughput across all these
cases, whereas SDMA and NOMA are effective only in some cases. Furthermore,
RSMA also achieves better fairness at a higher sum throughput than both SDMA
and NOMA.Comment: major revisions of IEEE Transactions on Wireless Communication
Resolution-Enhanced All-Optical Analog-to-Digital Converter Employing Cascade Optical Quantization Operation
In this paper, a cascade optical quantization scheme is proposed to realize all-optical analog-to-digital converter with efficiently enhanced quantization resolution and achievable high analog bandwidth of larger than 20 GHz. Employing the cascade structure of an unbalanced Mach-zehnder modulator and a specially designed optical directional coupler, we predict the enhancement of number-of-bits can be up to 1.59-bit. Simulation results show that a 25 GHz RF signal is efficiently digitalized with the signal-tonoise ratio of 33.58 dB and effective-number-of-bits of 5.28-bit
Probing the electron EDM with cold molecules
We present progress towards a new measurement of the electron electric dipole
moment using a cold supersonic beam of YbF molecules. Data are currently being
taken with a sensitivity of . We
therefore expect to make an improvement over the Tl experiment of Commins'
group, which currently gives the most precise result. We discuss the systematic
and statistical errors and comment on the future prospect of making a
measurement at the level of .Comment: 8 pages, 6 figures, proceedings of ICAP 200
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