Hyunsung Park

Optimal Beamforming and Power Allocation for Sensing-Based Spectrum Sharing in Cognitive Radio Networks

In this paper, the optimal beamforming and power allocation strategy for the secondary transmitter based on the sensing result on the state of the primary user in a multiantenna cognitive radio (CR) network is proposed. Unlike the existing sensing-based spectrum sharing, where the secondary transmitter employs a single antenna and adjusts only its transmit power, in the proposed scheme, the secondary transmitter employs multiple transmit antennas and adjusts the beamforming vector as well as the transmit power. An iterative algorithm that can efficiently obtain the optimal beamforming vector and power allocation is developed. Simulation results show that the proposed scheme achieves a significant rate gain over the existing sensing-based spectrum sharing schemes.

Energy-Efficient Power Control of Cognitive Femto Users for 5G Communications

We study the energy efficiency issue in 5G communications scenarios, where cognitive femtocells coexist with picocells operating at the same frequency bands. Optimal energy-efficient power allocation based on the sensing-based spectrum sharing (SBSS) is proposed for the uplink cognitive femto users operating in a multiuser MIMO mode. Both hard-decision and soft-decision schemes are considered for the SBSS. Different from the existing energy-efficient designs in multiuser scenarios, which consider system-wise energy efficiency, we consider user-wise energy efficiency and optimize them in a Pareto sense. To resolve the nonconvexity of the formulated optimization problem, we include an additional power constraint to convexify the problem without losing global optimality. Simulation results show that the proposed schemes significantly enhance the energy efficiency of the cognitive femto users compared with the existing spectral-efficient designs.

A Case of Malignant Granular Cell Tumor in the Sigmoid Colon

Granular cell tumor (GCT) is an uncommon, usually benign neoplasm; however, a malignant potential has been described. Malignant GCT is an extremely rare neoplasm showing rapid growth and invasion into adjacent muscles, lymph nodes, or vessels, or even distant metastasis. We recently experienced a case of a histologically benign or atypical but clinically malignant GCT, with invasion of the lymph nodes and vessels in the sigmoid colon, diagnosed by segmental colon resection with lymph node dissection. We also performed a review of relevant medical literature.

Energy Spreading Transform Approach to Achieve Full Diversity and Full Rate for MIMO Systems

Full-diversity full-rate (FDFR) space-time codes achieve both high data rate and good reliability at the cost of high decoding complexity. In this paper, we propose a low-complexity MIMO scheme that achieves both full diversity and full rate over flat fading channels for a sufficiently large number of transmit and receive antennas. The proposed scheme is constructed by applying energy spreading transforms (ESTs) to multiple data streams and spatially multiplexing the streams to multiple transmit antennas. Simulation results show that the proposed FDFR scheme outperforms the threaded algebraic space-time (TAST) code, which is a FDFR code based on maximum likelihood (ML) detection, when the number of transmit antennas (with the same number of receive antennas) are three and four. However, its detection complexity is only that of a decision-feedback detector.

Salvage therapy using self-expandable metal stents for recalcitrant anastomotic strictures after living-donor liver transplantation

Background: Recently, there has been an increase in clinical success rates using nonsurgical methods to resolve anastomotic biliary strictures (ABSs) that develop after liver transplantation (LT). However, some strictures are particularly refractory and cannot be completely resolved by an endoscopic or percutaneous procedure. Consequently, the aim of this study was to examine the feasibility and efficacy of using a newly designed fully covered self-expandable metal stent (FCSEMS) to resolve refractory ABS. Methods: A total of 35 patients with an ABS that developed after LT, but could not be resolved by an endoscopic or percutaneous procedure, were included in this study. FCSEMSs were positioned endoscopically and removed after 2–3 months. After stent removal, the patients were followed to assess complications, including re-stenosis. Results: The mean period from LT to stricture was 13.7 months, and the mean duration of the stricture was 31.8 months. The type and mean number of procedures previously attempted were endoscopic retrograde cholangiopancreatography (ERCP) (9.1 ± 5.1) in 19 patients and percutaneous transhepatic biliary drainage (9.2 ± 4.8) in 16 patients. All patients had successful FCSEMS insertions and removals; the mean stent indwelling time was 3.2 months. The mean follow-up period was 18.7 months (range: 6.4–37.8 months). Stricture recurrence was observed in 6 of 29 patients (recurrence rate: 20.7%). The anastomotic stricture resolved with the FCSEMS insertion in 29 of 35 patients (clinical success rate: 82.9%). Conclusions: The newly designed FCSEMS is a potentially feasible and effective treatment for anastomotic strictures that develop after LT but are not amenable to treatment by conventional procedures.

A new prognostic model using absolute lymphocyte count in patients with primary central nervous system lymphoma

PURPOSE Primary central nervous system lymphoma (PCNSL) is an aggressive and rare extranodal non-Hodgkin lymphoma (NHL). Absolute lymphocyte count (ALC) has been suggested to have a prognostic value in several subtypes of NHL. We evaluated the prognostic significance of clinical factors, including ALC, in patients with PCNSL to develop a new prognostic model. METHODS We analysed prognostic factors, including ALC, at diagnosis in 81 PCNSL patients receiving high-dose methotrexate-based therapy. RESULTS The median ALC at diagnosis was 1210 × 10(6)/L (range, 210-3610), with lymphopenia (≤ 875 × 10(6)/L) being detected in 27 (33.3%) patients. In the multivariate analysis, Eastern Cooperative Oncology Group performance status (ECOG PS) >1 (hazard ratio [HR] 3.18, P=0.003), age >50 years (HR 4.23, P=0.012), and lymphopenia at diagnosis (HR 2.83, P=0.008) remained independent prognostic factors for low overall survival (OS). Lymphopenia was also a significant prognostic factor for progression-free survival (HR 3.17, P=0.001). By means of a new three-factor prognostic model using ECOG PS >1, age >50 years, and presence of lymphopenia, with 1 point assigned to each factor, we successfully classified the patients into three risk groups: low (0 and 1), intermediate (2), and high (3). The 5-year OS rates of the patients in the low-, intermediate-, and high-risk groups were 74.3%, 21.7%, and 12.5%, respectively (P<0.001). CONCLUSIONS Low ALC is a useful indicator of poor prognosis in patients with PCNSL. The proposed three-factor model should be validated in large-scale studies.

The role of upfront autologous stem cell transplantation in high-risk younger patients with primary central nervous system lymphoma

Upfront autologous stem cell transplantation (ASCT) has shown favourable outcome in patients with primary central nervous system lymphoma (PCNSL), but the role of risk‐adapted upfront ASCT consolidation has not been evaluated in PCNSL. As PCNSL patients with the International Extranodal Lymphoma Study Group (IELSG) prognostic score ≥2 or those who did not achieve complete response after two courses of induction chemotherapy (non‐CR1) have shown inferior outcomes, we retrospectively analysed the role of upfront ASCT in 66 high‐risk (IELSG ≥2 and/or non‐CR1) younger (age <65 years) immunocompetent PCNSL patients who achieved at least partial response after initial high‐dose methotrexate‐based chemotherapy. Nineteen patients who received upfront ASCT exhibited significantly better overall survival (OS, P = 0·021) and progression‐free survival (PFS, P = 0·005) compared to 47 patients who did not. In univariate and multivariate analyses, upfront ASCT was associated with better OS (P = 0·037 and P = 0·025, respectively) and PFS (P = 0·009 and P = 0·007, respectively). In a propensity score‐matched cohort (n = 36), patients who received upfront ASCT also showed better outcome (P = 0·037 for OS, P = 0·001 for PFS). Our results suggest that upfront ASCT consolidation might be especially beneficial for high‐risk PCNSL patients.

Optimal Beamforming and Power Allocation for Cognitive Femto Base Stations Based on Soft Decision

In this paper, an optimal beamforming and power allocation for the sensing-based spectrum sharing (SBSS) that employs a soft decision on the state of the primary user is proposed. Different from the existing soft-decision-based SBSS that employs a single antenna and adjusts only transmit power, in the proposed scheme, the secondary transmitter employs multiple transmit antennas and controls the beamforming direction and the transmit power. We design the optimal beamforming and power allocation under the constraints of total transmit power and interference power, where both average and instantaneous power constraints are considered. Simulation results demonstrate that the proposed technique can significantly improve the average throughput of the secondary user compared with the existing methods. The proposed beamforming for the soft-decision-based SBSS is a promising scheme, particularly for cognitive femto base stations (BSs) to boost up the spectral efficiency while managing the interference to the macro BSs.

Energy-Efficient Adaptation of Pilot Power, Data Power, and Transmission Rate for Downlink Multiuser MIMO Systems

This paper addresses energy-efficient link adaptation for downlink multiuser multiple-input-multiple-output (MIMO) systems. Different from the previous works on energy efficient MIMO techniques, we take into account finite pilot power and the corresponding effect of imperfect channel state information (CSI) at the users. We analyze the average throughput and define the energy efficiency (EE) of downlink multiuser MIMO systems. We show that the EE of the system is not jointly quasi-concave with respect to pilot power, data power, and transmission rate. For this reason, we propose an efficient algorithm that alternately updates pilot power, data power, and transmission rate to improve the EE of the system. Simulation results show that the proposed scheme significantly enhances the EE, and the resulting EE is comparable to the maximal EE obtained by the exhaustive search.

Decitabine as a first-line treatment for older adults newly diagnosed with acute myeloid leukemia

Purpose Decitabine, a DNA hypomethylating agent, was recently approved for use in Korea for older adults with acute myeloid leukemia (AML) who are not candidates for standard chemotherapy. This study aimed to evaluate the role of decitabine as a first-line treatment for older adults with AML. Materials and Methods Twenty-four patients with AML who received at least one course of decitabine (20 mg/m2/d intravenously for 5 days every 4 weeks) as a first-line therapy at Severance Hospital were evaluated retrospectively. Results The median age of the patients was 73.5 years. The longest follow-up duration was 502 days. A total of 113 cycles of treatment were given to 24 patients, and the median number of cycles was four (range, 1–14). Thirteen patients dropped out because of death, no or loss of response, patient refusal, or transfer to another hospital. Twenty-one (87.5%) and 12 (50%) patients completed the second and fourth cycles, respectively, and responses to treatment were evaluated in 17. A complete response (CR) or CR with incomplete blood-count recovery was achieved in six (35.3%) patients, and the estimated median overall survival was 502 days. Ten patients developed grade >2 hematologic or non-hematologic toxicities. In univariate analysis, bone marrow blasts, lactate dehydrogenase, serum ferritin level, and bone marrow iron were significantly associated with response to decitabine. Conclusion Five-day decitabine treatment showed acceptable efficacy in older patients with AML who are unfit for conventional chemotherapy, with a CR rate 35.3% and about a median overall survival of 18 months.