IEEE Wireless Communications - April 2017 - page 9

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IEEE Wireless Communications • April 2017
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Spatiotemporal-MIMO Channel Estimator
and Beamformer for 5G
Vidhya Sridhar, Thibaud Gabillard, and Athanassios Manikas,
IEEE Trans. Wireless Communications, Vol. 15, No. 12, pp.
8025–8038, December 2016.
With requirements of spiraling data
rates and limited spectrum availability,
there is an increased interest in mm-wave
beamformer-based communications for
5G. For upcoming cellular networks, the
critical point is to exploit the increased
number of employable antennas at both Tx
and Rx to: 1) combat increased path loss;
2) tackle higher interference due to high-
er user density; and 3) handle multipath
effects in frequency selective channels.
Toward this, a multi-beam spatiotemporal
superresolution beamforming framework is
proposed in this paper as a promising can-
didate to design beampatterns that miti-
gate/suppress co-channel interference and
deliver massive gain in the desired direc-
tions. Initially, channel and signal models
suitable for the mm-wave MIMO system
are presented using the manifold vectors
of both Tx and Rx antenna arrays. Based
on these models, a novel subspace-based
channel estimator is employed, which esti-
mates delays, directions, velocities, and
fading coefficients of the desired signal
paths. This information is then exploited
by the proposed spatiotemporal beam-
former to provide a massive array gain that
combats path loss without increasing the
number of antenna array elements and to
be tolerant to the near-far problem in a
high interference environment. The perfor-
mance of the proposed channel estimator
and beamformer is examined using com-
puter simulation studies.
Performance Evaluation of Non-
Orthogonal Multiple Access in Visible Light
Communication
Liang Yin, Wasiu O. Popoola, Xiping Wu, and Harald Haas,
IEEE Trans. Communications, Vol. 64, No. 12,
pp. 5162–5175, December 2016.
In this paper, the performance of
non-orthogonal multiple access (NOMA)
is characterized in a downlink visible light
communication system for two separate
cases. In the case of guaranteed quality
of service (QoS) provisioning, the authors
derive an analytical expression of the sys-
tem coverage probability and show the
existence of optimal power allocation
coefficients on two-user paired NOMA.
In the case of opportunistic best-effort ser-
vice provisioning, they formulate a closed-
form expression of the ergodic sum rate,
which is applicable for arbitrary power
allocation strategies. The probability that
NOMA achieves higher individual rates
than orthogonal multiple access (OMA)
is derived. Also, the authors give an upper
bound of the sum rate gain of NOMA
over OMA in the high signal-to-noise ratio
regime. Both the theoretical and simula-
tion results prove that the performance
gain of NOMA over OMA can be further
enlarged by pairing users with distinctive
channel conditions. They also find that the
choice of light emitting diodes (LEDs) has
a significant impact on the system perfor-
mance. In the case of guaranteed QoS
provisioning, the LEDs with larger semi-an-
gles have better performance; while in the
case of opportunistic best-effort service
provisioning, the LEDs with 35° semi-an-
gle give nearly optimal performance.
Quantized Feedback-Based Differential
Signaling for Free-Space Optical
Communication System
Manav R. Bhatnagar, Zabih Ghassemlooy, Stanislav
Zvanovec, Mohammad-Ali Khalighi, and Mojtaba Mansour
Abadi,, IEEE Trans. Communications, Vol. 64, No. 12, pp.
5176–5188, October 2016.
The authors propose a quantized feed-
back-based differential signaling scheme
for 2 x 1 free space optical (FSO) multi-
ple-input single-output communication sys-
tems. The analytical bit error rate (BER) for
the proposed differential signaling scheme
is derived and compared with the existing
differential signaling scheme for FSO sys-
tems. The asymptotic BER of the proposed
scheme is also determined. It is shown by
using the asymptotic BER expression that
the proposed scheme achieves full spatial
diversity of two. Moreover, the effect of
the feedback error on the performance
of the proposed scheme is studied and it
is demonstrated by simulation-based and
analytical results that the proposed scheme
significantly outperforms a previously
proposed differential signaling scheme in
terms of turbulence fades reduction for tol-
erable feedback errors.
Codebook Design for Millimeter-Wave
Channel Estimation with Hybrid Precoding
Structure
Zhenyu Xiao, Pengfei Xia, and Xiang-Gen Xia, IEEE Trans.
Wireless Communications, Vol. 16, No. 1, pp. 141–153,
January 2017
This paper introduces the hierarchical
codebook design for channel estimation
in millimeter-wave (mmWave) communi-
cations with a hybrid precoding structure.
Due to the limited saturation power of the
mmWave power amplifier, the authors
consider the per-antenna power constraint
(PAPC). They first propose a metric, termed
generalized detection probability (GDP),
to evaluate the quality of an arbitrary
codeword. This metric not only enables
an optimization approach for mmWave
codebook design, but also can be used to
compare the performance of two different
codewords/codebooks. Considering that
GDP is the first such metric, particularly for
mmWave codebook design, the paper then
proposes a heuristic approach to design
a hierarchical codebook exploiting beam
widening with the multi-RF-chain sub-array
(BMW-MS) technique. To obtain crucial
parameters of BMW-MS, two solutions are
provided, namely, a low-complexity search
(LCS) solution to optimize the GDP metric
and a closed-form (CF) solution to pursue
a flat beam pattern. Performance compar-
isons show that BMW-MS/LCS and BMW-
MS/CF achieve very close performances,
and they outperform the existing alterna-
tives under the PAPC.
Cross-Layer Routing and Scheduling for
Onboard Processing Satellites with Phased
Array Antenna
Jihwan P. Choi, Seok-Ho Chang, Vincent W. S. Chan,
IEEE Trans. Wireless Communications, Vol. 16, No. 1, pp.
180–192, January 2017.
The advanced multibeam satellite
equipped with phased array antenna and
solid state power amplifiers can generate
flexible beams, by managing interbeam
interference to serve a very large number
of users effectively over its coverage area.
Onboard processing (OBP) functionality
can enhance the flexibility of a large-scale
antenna by speeding up computational pro-
cesses and saving precious radio link spec-
trum. This paper derives a cross-layer OBP
design of switching/routing, beamforming,
and user scheduling as taking advantage of
fine spatial resolution capability of phased
array antenna satellites. The authors evalu-
ate tradeoff between OBP computational
complexity and throughput performance,
showing that the additional complexity of
an increased number of switch ports and
phased array antenna gain patterning
is compensated by high throughput gain
achieved by mitigating interference. The
analysis shows that throughput gain for the
next generation satellite system can be as
high as 40, compared with the conventional
multiple beam antenna with travelling wave
tube amplifiers, and that beamforming is
critical for achieving high spectral efficien-
cy in the crowded service area. Finally,
the paper then investigates the impacts of
onboard switching and phased array anten-
na beamforming to practical routing pro-
tocols, such as open short path first and
routing information protocol.
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