14 research outputs found
Differential Modulation for Short Packet Transmission in URLLC
One key feature of ultra-reliable low-latency communications (URLLC) in 5G is
to support short packet transmission (SPT). However, the pilot overhead in SPT
for channel estimation is relatively high, especially in high Doppler
environments. In this paper, we advocate the adoption of differential
modulation to support ultra-low latency services, which can ease the channel
estimation burden and reduce the power and bandwidth overhead incurred in
traditional coherent modulation schemes. Specifically, we consider a
multi-connectivity (MC) scheme employing differential modulation to enable
URLLC services. The popular selection combining and maximal ratio combining
schemes are respectively applied to explore the diversity gain in the MC
scheme. A first-order autoregressive model is further utilized to characterize
the time-varying nature of the channel. Theoretically, the maximum achievable
rate and minimum achievable block error rate under ergodic fading channels with
PSK inputs and perfect CSI are first derived by using the non-asymptotic
information-theoretic bounds. The performance of SPT with differential
modulation and MC schemes is then analysed by characterizing the effect of
differential modulation and time-varying channels as a reduction in the
effective SNR. Simulation results show that differential modulation does offer
a significant advantage over the pilot-assisted coherent scheme for SPT,
especially in high Doppler environments.Comment: 15 pages, 9 figure
Evaluation of mixed permutation codes in PLC channels, using hamming distance profile
Abstract: We report a new concept involving an adaptive mixture of different sets of permutation codes (PC) in a single DPSK-OFDM modulation scheme. Since this scheme is robust and the algorithms involved are simple, it is a good candidate for implementation for OFDM-based power line communication (PLC) systems. By using a special and easy concept called Hamming distance profile, as a comparison tool, we are able to showcase the strength of the new PC scheme over other schemes reported in literature, in handling the incessant noise types associated with PLC channels. This prediction tool is also useful for selecting an efficient PC codebook out of a number of ! similar ones
On the MISO Channel with Feedback: Can Infinitely Massive Antennas Achieve Infinite Capacity?
We consider communication over a multiple-input single-output (MISO) block
fading channel in the presence of an independent noiseless feedback link. We
assume that the transmitter and receiver have no prior knowledge of the channel
state realizations, but the transmitter and receiver can acquire the channel
state information (CSIT/CSIR) via downlink training and feedback. For this
channel, we show that increasing the number of transmit antennas to infinity
will not achieve an infinite capacity, for a finite channel coherence length
and a finite input constraint on the second or fourth moment. This insight
follows from our new capacity bounds that hold for any linear and nonlinear
coding strategies, and any channel training schemes. In addition to the channel
capacity bounds, we also provide a characterization on the beamforming gain
that is also known as array gain or power gain, at the regime with a large
number of antennas.Comment: This work has been submitted to the IEEE Transactions on Information
Theory. It was presented in part at ISIT201
Dynamic Spectrum Sharing in Cognitive Radio and Device-to-Device Systems
abstract: Cognitive radio (CR) and device-to-device (D2D) systems are two promising dynamic spectrum access schemes in wireless communication systems to provide improved quality-of-service, and efficient spectrum utilization. This dissertation shows that both CR and D2D systems benefit from properly designed cooperation scheme.
In underlay CR systems, where secondary users (SUs) transmit simultaneously with primary users (PUs), reliable communication is by all means guaranteed for PUs, which likely deteriorates SUsâ performance. To overcome this issue, cooperation exclusively among SUs is achieved through multi-user diversity (MUD), where each SU is subject to an instantaneous interference constraint at the primary receiver. Therefore, the active number of SUs satisfying this constraint is random. Under different user distributions with the same mean number of SUs, the stochastic ordering of SU performance metrics including bit error rate (BER), outage probability, and ergodic capacity are made possible even without observing closed form expressions. Furthermore, a cooperation is assumed between primary and secondary networks, where those SUs exceeding the interference constraint facilitate PUâs transmission by relaying its signal. A fundamental performance trade-off between primary and secondary networks is observed, and it is illustrated that the proposed scheme outperforms non-cooperative underlay CR systems in the sense of system overall BER and sum achievable rate.
Similar to conventional cellular networks, CR systems suffer from an overloaded receiver having to manage signals from a large number of users. To address this issue, D2D communications has been proposed, where direct transmission links are established between users in close proximity to offload the system traffic. Several new cooperative spectrum access policies are proposed allowing coexistence of multiple D2D pairs in order to improve the spectral efficiency. Despite the additional interference, it is shown that both the cellular userâs (CU) and the individual D2D user's achievable rates can be improved simultaneously when the number of D2D pairs is below a certain threshold, resulting in a significant multiplexing gain in the sense of D2D sum rate. This threshold is quantified for different policies using second order approximations for the average achievable rates for both the CU and the individual D2D user.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201
Power allocation and signal labelling on physical layer security
PhD ThesisSecure communications between legitimate users have received considerable
attention recently. Transmission cryptography, which introduces
secrecy on the network layer, is heavily relied on conventionally to secure
communications. However, it is theoretically possible to break the
encryption if unlimited computational resource is provided. As a result,
physical layer security becomes a hot topic as it provides perfect secrecy
from an information theory perspective. The study of physical layer
security on real communication system model is challenging and important,
as the previous researches are mainly focusing on the Gaussian
input model which is not practically implementable.
In this thesis, the physical layer security of wireless networks employing
finite-alphabet input schemes are studied. In particular, firstly, the secrecy
capacity of the single-input single-output (SISO) wiretap channel
model with coded modulation (CM) and bit-interleaved coded modulation
(BICM) is derived in closed-form, while a fast, sub-optimal power
control policy (PCP) is presented to maximize the secrecy capacity performance.
Since finite-alphabet input schemes achieve maximum secrecy
capacity at medium SNR range, the maximum amount of energy that
the destination can harvest from the transmission while satisfying the
secrecy rate constraint is computed. Secondly, the effects of mapping
techniques on secrecy capacity of BICM scheme are investigated, the secrecy
capacity performances of various known mappings are compared on
8PSK, 16QAM and (1,5,10) constellations, showing that Gray mapping
obtains lowest secrecy capacity value at high SNRs. We propose a new
mapping algorithm, called maximum error event (MEE), to optimize the
secrecy capacity over a wide range of SNRs. At low SNR, MEE mapping
achieves a lower secrecy rate than other well-known mappings, but
at medium-to-high SNRs MEE mapping achieves a significantly higher
secrecy rate over a wide range of SNRs. Finally, the secrecy capacity and
power allocation algorithm (PA) of finite-alphabet input wiretap channels
with decode-and-forward (DF) relays are proposed, the simulation
results are compared with the equal power allocation algorithm
Spatial diversity in MIMO communication systems with distributed or co-located antennas
The use of multiple antennas in wireless communication systems has gained much attention during the last decade. It was shown that such multiple-input multiple-output (MIMO) systems offer huge advantages over single-antenna systems. Typically, quite restrictive assumptions are made concerning the spacing of the individual antenna elements. On the one hand, it is typically assumed that the antenna elements at transmitter and receiver are co-located, i.e., they belong to some sort of antenna array. On the other hand, it is often assumed that the antenna spacings are sufficiently large, so as to justify the assumption of independent fading. In this thesis, the above assumptions are relaxed. In the first part, it is shown that MIMO systems with distributed antennas and MIMO systems with co-located antennas can be treated in a single, unifying framework. In the second part this fact is utilized, in order to develop appropriate transmit power allocation strategies for co-located and distributed MIMO systems. Finally, the third part focuses on specific synchronization problems that are of interest for distributed MIMO systems
Semester Courses and Course Equivalents: Graduate Courses Summary
A list comprised of summaries of all graduate courses and course equivalents at Wright State University