164 research outputs found
Rate Analysis of Two-Receiver MISO Broadcast Channel with Finite Rate Feedback: A Rate-Splitting Approach
To enhance the multiplexing gain of two-receiver Multiple-Input-Single-Output
Broadcast Channel with imperfect channel state information at the transmitter
(CSIT), a class of Rate-Splitting (RS) approaches has been proposed recently,
which divides one receiver's message into a common and a private part, and
superposes the common message on top of Zero-Forcing precoded private messages.
In this paper, with quantized CSIT, we study the ergodic sum rate of two
schemes, namely RS-S and RS-ST, where the common message(s) are transmitted via
a space and space-time design, respectively. Firstly, we upper-bound the sum
rate loss incurred by each scheme relative to Zero-Forcing Beamforming (ZFBF)
with perfect CSIT. Secondly, we show that, to maintain a constant sum rate
loss, RS-S scheme enables a feedback overhead reduction over ZFBF with
quantized CSIT. Such reduction scales logarithmically with the constant rate
loss at high Signal-to-Noise-Ratio (SNR). We also find that, compared to RS-S
scheme, RS-ST scheme offers a further feedback overhead reduction that scales
with the discrepancy between the feedback overhead employed by the two
receivers when there are alternating receiver-specific feedback qualities.
Finally, simulation results show that both schemes offer a significant SNR gain
over conventional single-user/multiuser mode switching when the feedback
overhead is fixed.Comment: accepted to IEEE Transactions on Communication
User-Centric Interference Nulling in Downlink Multi-Antenna Heterogeneous Networks
In heterogeneous networks (HetNets), strong interference due to spectrum
reuse affects each user's signal-to-interference ratio (SIR), and hence is one
limiting factor of network performance. In this paper, we propose a
user-centric interference nulling (IN) scheme in a downlink large-scale HetNet
to improve coverage/outage probability by improving each user's SIR. This IN
scheme utilizes at most maximum IN degree of freedom (DoF) at each macro-BS to
avoid interference to uniformly selected macro (pico) users with
signal-to-individual-interference ratio (SIIR) below a macro (pico) IN
threshold, where the maximum IN DoF and the two IN thresholds are three design
parameters. Using tools from stochastic geometry, we first obtain a tractable
expression of the coverage (equivalently outage) probability. Then, we analyze
the asymptotic coverage/outage probability in the low and high SIR threshold
regimes. The analytical results indicate that the maximum IN DoF can affect the
order gain of the outage probability in the low SIR threshold regime, but
cannot affect the order gain of the coverage probability in the high SIR
threshold regime. Moreover, we characterize the optimal maximum IN DoF which
optimizes the asymptotic coverage/outage probability. The optimization results
reveal that the IN scheme can linearly improve the outage probability in the
low SIR threshold regime, but cannot improve the coverage probability in the
high SIR threshold regime. Finally, numerical results show that the proposed
scheme can achieve good gains in coverage/outage probability over a maximum
ratio beamforming scheme and a user-centric almost blank subframes (ABS)
scheme.Comment: Transactions on Wireless Communications (under revision). arXiv admin
note: text overlap with arXiv:1504.0528
Analysis and Optimization of Inter-tier Interference Coordination in Downlink Multi-Antenna HetNets with Offloading
Heterogeneous networks (HetNets) with offloading is considered as an
effective way to meet the high data rate demand of future wireless service.
However, the offloaded users suffer from strong inter-tier interference, which
reduces the benefits of offloading and is one of the main limiting factors of
the system performance. In this paper, we investigate an interference nulling
(IN) scheme in improving the system performance by carefully managing the
inter-tier interference to the offloaded users in downlink two-tier HetNets
with multi-antenna base stations. Utilizing tools from stochastic geometry, we
first derive a tractable expression for the rate coverage probability of the IN
scheme. Then, by studying its order, we obtain the optimal design parameter,
i.e., the degrees of freedom that can be used for IN, to maximize the rate
coverage probability. Finally, we analyze the rate coverage probabilities of
the simple offloading scheme without interference management and the
multi-antenna version of the almost blank subframes (ABS) scheme in 3GPP LTE,
and compare the performance of the IN scheme with these two schemes. Both
analytical and numerical results show that the IN scheme can achieve good
performance gains over both of these two schemes, especially in the large
antenna regime
Influence of Healing Period Upon Bone Turn Over on Maxillary Sinus Floor Augmentation Grafted Solely with Deproteinized Bovine Bone Mineral: A Prospective Human Histological and Clinical Trial
PurposeTo investigate the influence of maturation timing upon histological, histomorphometric and clinical outcomes when deproteinized bovine bone mineral (DBBM) was used as a sole biomaterial for staged maxillary sinus floor augmentation (MSFA).Materials and methodsPatients with a posterior edentulous maxillary situation and a vertical bone height ≤ 4 mm were included in this study. A staged MSFA was carried out. After MSFA with DBBM as a sole grafting material, biopsy cores were harvested with simultaneous implant placement followed by a healing period of 5, 8, and 11 months, respectively. Micro‐CT, histologic and histomorphometric analyses were performed.ResultsForty‐one patients were enrolled and 38 bone core biopsies were harvested. Significantly greater BV/TV was observed between 5‐ and 8‐month healing from micro‐CT analysis. Histomorphometric analyses showed the ratio of mineralized newly formed bone increased slightly from 5 to 11 months; however, no statistically significant difference was reached (p = .409). Residual bone substitute decreased from 37.3 ± 5.04% to 20.6 ± 7.45%, achieving a statistical significant difference from of 5 up to 11 months (p < .01). Moreover, no implant failure, biological or technical complication occurred after 12‐month follow‐up of functional loading.ConclusionDBBM utilized as sole grafting material in staged MSFA demonstrated to be clinically effective regardless of the healing period. Histomorphometrical and micro‐CT assessments revealed that at later stages of healing (8 and 11 months) there is a higher proportion of newly‐bone formation compared to earlier stages (5 months). Moreover, the longer the maturation period, the substantially lesser remaining biomaterial could be expected. Even though, these facts did not seem to negatively impact on the implant prognosis 1‐year after loading.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136437/1/cid12463_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136437/2/cid12463.pd
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