24 research outputs found
Event-Driven Optimal Feedback Control for Multi-Antenna Beamforming
Transmit beamforming is a simple multi-antenna technique for increasing
throughput and the transmission range of a wireless communication system. The
required feedback of channel state information (CSI) can potentially result in
excessive overhead especially for high mobility or many antennas. This work
concerns efficient feedback for transmit beamforming and establishes a new
approach of controlling feedback for maximizing net throughput, defined as
throughput minus average feedback cost. The feedback controller using a
stationary policy turns CSI feedback on/off according to the system state that
comprises the channel state and transmit beamformer. Assuming channel isotropy
and Markovity, the controller's state reduces to two scalars. This allows the
optimal control policy to be efficiently computed using dynamic programming.
Consider the perfect feedback channel free of error, where each feedback
instant pays a fixed price. The corresponding optimal feedback control policy
is proved to be of the threshold type. This result holds regardless of whether
the controller's state space is discretized or continuous. Under the
threshold-type policy, feedback is performed whenever a state variable
indicating the accuracy of transmit CSI is below a threshold, which varies with
channel power. The practical finite-rate feedback channel is also considered.
The optimal policy for quantized feedback is proved to be also of the threshold
type. The effect of CSI quantization is shown to be equivalent to an increment
on the feedback price. Moreover, the increment is upper bounded by the expected
logarithm of one minus the quantization error. Finally, simulation shows that
feedback control increases net throughput of the conventional periodic feedback
by up to 0.5 bit/s/Hz without requiring additional bandwidth or antennas.Comment: 29 pages; submitted for publicatio
Hyaluronan- and RNA-binding deubiquitinating enzymes of USP17 family members associated with cell viability
BACKGROUND: Protein degradation by the ubiquitin system plays a crucial role in numerous cellular signaling pathways. Deubiquitination, a reversal of ubiquitination, has been recognized as an important regulatory step in the ubiquitin-dependent degradation pathway. RESULTS: While identifying putative ubiquitin specific protease (USP) enzymes that contain a conserved Asp (I) domain in humans, 4 USP17 subfamily members, highly homologous to DUB-3, have been found (USP17K, USP17L, USP17M, and USP17N), from human chorionic villi. Expression analysis showed that USP17 transcripts are highly expressed in the heart, liver, and pancreas and are expressed moderately in various human cancerous cell lines. Amino acid sequence analysis revealed that they contain the highly conserved Cys, His, and Asp domains which are responsible for the deubiquitinating activity. Biochemical enzyme assays indicated that they have deubiquitinating activity. Interestingly, the sequence analysis showed that these proteins, with exception of USP17N, contain the putative hyaluronan/RNA binding motifs, and cetylpyridinium chloride (CPC)-precipitation analysis confirmed the association between these proteins and intracellular hyaluronan and RNA. CONCLUSION: Here, we report that the overexpression of these proteins, with exception of USP17N, leads to apoptosis, suggesting that the hyaluronan and RNA binding motifs in these enzymes play an important role in regulating signal transduction involved in cell death
Feedback-Topology Designs for Interference Alignment in MIMO Interference Channels
Interference alignment (IA) is a joint-transmission technique that achieves
the capacity of the interference channel for high signal-to-noise ratios
(SNRs). Most prior work on IA is based on the impractical assumption that
perfect and global channel-state information(CSI) is available at all
transmitters. To implement IA, each receiver has to feed back CSI to all
interferers, resulting in overwhelming feedback overhead. In particular, the
sum feedback rate of each receiver scales quadratically with the number of
users even if the quantized CSI is fed back. To substantially suppress feedback
overhead, this paper focuses on designing efficient arrangements of feedback
links, called feedback topologies, under the IA constraint. For the
multiple-input-multiple-output (MIMO) K-user interference channel, we propose
the feedback topology that supports sequential CSI exchange (feedback and
feedforward) between transmitters and receivers so as to achieve IA
progressively. This feedback topology is shown to reduce the network feedback
overhead from a cubic function of K to a linear one. To reduce the delay in the
sequential CSI exchange, an alternative feedback topology is designed for
supporting two-hop feedback via a control station, which also achieves the
linear feedback scaling with K. Next, given the proposed feedback topologies,
the feedback-bit allocation algorithm is designed for allocating feedback bits
by each receiver to different feedback links so as to regulate the residual
interference caused by the finite-rate feedback. Simulation results demonstrate
that the proposed bit allocation leads to significant throughput gains
especially in strong interference environments.Comment: 28 pages; 11 figures ; submitted to IEEE Trans. on Signal Processin
Pre-coder design over two-symbol extension for K-user cyclic interference channels
The authors consider K-user cyclic single-input–single-output (SISO) interference channel (IC) where each receiver is interfered with from only one neighbouring transmitter. In the K-user cyclic SISO IC, K/2 sum degrees of freedom can be achieved when two-symbol extension is applied even without channel state information at the transmitter. They derive an approximation of the ergodic sum rate as a function of pre-coders and propose designs of pre-coders to maximise the ergodic sum rate
Endoscopic Treatment of Intussusception due to Intestinal Tuberculosis
Traditionally, adult intussusception has required a bowel resection because of the malignancy risk. A patient with anorexia, weight loss, and abdominal pain visited our clinic. A physical exam and imaging study revealed no acute peritoneal signs. A colonoscopy for biopsy and bowel reduction was attempted. The tissue sample was consistent with intestinal tuberculosis. We report intestinal tuberculosis complicating intussusception which was treated without surgical intervention
Capacity Analysis of the Clustered Network MIMO with Overlap
In this paper, we analysis the capacity of the clustered network multiple-input multiple-output (MIMO) systems with overlap. We firstly propose a strategy for clustering base stations (BSs) for the analysis tractability. With an assumption of a large number of transmit and receive antennas, an analytical expression of the ergodic capacity using random matrix theorems is derived. In particular, we develop an asymptotic capacity in low signal to noise ratio (SNR) regime. Based on that, we suggest that the number of overlapping degree of freedom (ODOF) is larger than left [B/6] for the sake of the capacity increment, where B refers to the total number of BSs in the multicell network. We show through numerical examples that the analytical results match the simulation results even when the number of antennas is small
Hyaluronan- and RNA-binding deubiquitinating enzymes of USP17 family members associated with cell viability
Abstract Background Protein degradation by the ubiquitin system plays a crucial role in numerous cellular signaling pathways. Deubiquitination, a reversal of ubiquitination, has been recognized as an important regulatory step in the ubiquitin-dependent degradation pathway. Results While identifying putative ubiquitin specific protease (USP) enzymes that contain a conserved Asp (I) domain in humans, 4 USP17 subfamily members, highly homologous to DUB-3, have been found (USP17K, USP17L, USP17M, and USP17N), from human chorionic villi. Expression analysis showed that USP17 transcripts are highly expressed in the heart, liver, and pancreas and are expressed moderately in various human cancerous cell lines. Amino acid sequence analysis revealed that they contain the highly conserved Cys, His, and Asp domains which are responsible for the deubiquitinating activity. Biochemical enzyme assays indicated that they have deubiquitinating activity. Interestingly, the sequence analysis showed that these proteins, with exception of USP17N, contain the putative hyaluronan/RNA binding motifs, and cetylpyridinium chloride (CPC)-precipitation analysis confirmed the association between these proteins and intracellular hyaluronan and RNA. Conclusion Here, we report that the overexpression of these proteins, with exception of USP17N, leads to apoptosis, suggesting that the hyaluronan and RNA binding motifs in these enzymes play an important role in regulating signal transduction involved in cell death.</p
Efficient Feedback Design for Interference Alignment in MIMO Interference Channel
Interference alignment (IA) is a joint-transmission technique that achieves the capacity of the interference channel for high signal-to-noise ratios (SNRs). However, most prior works on IA are based on the impractical assumption that perfect and global channel-state information(CSI) is available at all transmitters, resulting in overwhelming feedback overhead. To substantially suppress the feedback overhead, this paper proposes an efficient design of the feedback framework for IA in the K-user multiple-input multiple-output (MIMO) interference channel. The proposed feedback topology supports sequential CSI exchange (feedback and feedforward) between transmitters and receivers and reduces the feedback overhead from a cubic function of K to a linear one, compared to conventional feedback approaches. Given the proposed feedback topology, we consider the limited feedback channel from the receivers to corresponding interferers and analyze the effect of quantization error which generates the residual interference. Also, an efficient feedback-bit allocation algorithm that minimizes the upper-bound of sum residual interference is proposed