Water-filling Method Research Articles

Power Allocation Method for OFDM System with both Total and Per-Antenna Power Constraints

In this paper, we propose an optimal power allocation method for OFDM system with both total transmit power constraint (TTPC) and per-antenna power constraint (PAPC). In contrast to traditional water-filling method, the new one takes into account of the signal distortion caused by PAPC in deducing system capacity, therefore can achieve a more accurate allocation between multiple sub-channels. Simulation results confirm that the new method can better reduce signal distortion and maximize system capacity, especially when the signal power approaches the limit of PAPC.

Theory and Practice of Rate Division in Distributed Video Coding

Wyner and Ziv characterized the rate distortion function for lossy source coding with side information at the decoder. It is well known that for the quadratic Gaussian case, the Wyner-Ziv rate-distortion function coincides with the conditional rate-distortion function. In this paper, we extend the problem to the coding of multivariate Gaussian source with multiple Gaussian side information at the decoder. The achievable region is obtained, and it is easily extended to the case that the difference between the source and the side information is multivariate Gaussian, no matter what distributions the source and the side information are. We apply this theoretical model to Distributed Video Coding (DVC) by considering the difference of the Distributed frame (D frame) and the Side-information frame (S frame) to be multivariate Gaussian distributed. This introduces rate allocation problem into DVC, which can be solved by a reverse water-filling method. Simulation results show that around 1.5-2 dB coding gain benefits from the multivariate Gaussian Wyner-Ziv coding model.

Limits on Data Communication Along the Drillstring Using Acoustic Waves

Summary The first commercial acoustic-telemetry system was introduced successfully in 2000 as part of a drillstem-testing system. However, duplicating the success of the acoustic telemetry to environmentally challenging logging-while-drilling (LWD) applications at high data throughput remains a formidable task. The primary limitation arises from normal drilling operations that produce inband acoustic noise at multiple sources at intensities comparable to the transmitter output. This noise, together with the signal attenuation along the drillstring, adversely affects the data throughput. To determine the communication capacity of the drillstring channel using acoustic waves, we examined the impact of channel characteristics, signal attenuation, and noise in detail. On the basis of a communication model that incorporates the effects of both drillstring acoustic channel and noise, we extensively studied the capacity of the system using the waterfilling method. For this analysis, realistic downhole transmitter power output, experimentally measured noise at the surface, and measured attenuation of acoustic waves in the drillstring channel were used as input parameters. The results show that a typical drillstring channel has a potential capacity of up to several hundred bits per second under noisy drilling conditions. Implications of the channel capacity on acoustic-telemetry-system designs are discussed. A communication technique that comes close to realizing a high-rate telemetry system is introduced. Methods to optimize various aspects of the system such that maximum drillstring-channel utilization can be realized under drilling conditions are also discussed. Potential enhancement to data rates through application of error control-coding is covered briefly.

Comparison of four methods for the estimation of intracranial volume: A gold standard study

Investigators can infer how much reduction in volume has occurred since brain volume was at its peak, by combining measures of brain volume with measures of intracranial volume (ICV). Several methodologies have been proposed to asses the ICV. However, we have not seen a gold-standard study evaluating the results of the methodologies for the assessment of ICV. In the present study, the actual intracranial volume of 20 dry skulls was measured using the water-filling method, using this as a gold standard. Anthropometry, cephalometry, point-counting, and planimetry techniques were applied to the same skulls to estimate the ICV. Anthropometric and cephalometric measurements were carried out directly on skulls and roentgenograms, respectively. Consecutive computed tomography sections at a thickness of 10 mm were used to estimate the ICV of the skulls by means of the point-counting and planimetry methods. The mean (+/-SD) of the actual ICV measured by the water-filling method was 1,262.0 +/- 160.4 cm(3) (1,389.5 +/- 96.5 cm(3) for males and 1,134.5 +/- 94.3 cm(3) for females, respectively). Our results showed that the estimated values obtained by all four methods differed from the actual volumes of the skulls (P < 0.05). The data obtained by anthropometry resulted in overestimation. However, cephalometry, point-counting, and planimetry methods produced underestimation. After calibration, there were no significant differences between the actual volumes and the results of the four methods (P > 0.05). While the anthropometric method is easy and quick to apply, its result may deviate from the actual values. The optimized stereological techniques of point-counting and planimetry methods may provide unbiased ICV results since they take the third dimension of the structures into account.

On the Downlink Transmission Strategies for MIMO-OFDM Systems

This paper addresses the downlink transmission strategies with dynamic resource allocation for multiuser MIMO-OFDM systems. The ultimate objective is to maximize the sum rate capacity subject to average power constraints. Considering that the performance of conventional Orthogonal Frequency Division Multiple Access (OFDMA) is limited by users' exclusive use to subcamer, while Dirty Paper Coding (DPC) is capable of supporting multiple users, we propose joint subcarrier and power allocation and precoding schemes based on OFDMA combined with DPC, which is called DPC-OFDMA. The analysis is considered in two stages with channel state information (CSI) at transmitter. The first stage applies water-filling method to address subcarriers allocation, in which users are allowable to share subcarriers. The second stage employs DPC combined with preceding to deal with simultaneous transmissions of the users sharing the same subcarriers. An efficient algorithm to choose the best possible ordering of users for DPC and the optimal preceding design of each user are also involved. To reduce the complexity for practice, two simplified strategies are proposed. One is called suboptimal DPC-OFDMA, where the number of users using the same subcamer is restricted. Another employs beamfonning (BF) at every subcamer referred as BF-DPC-OFDMA. Simulation results show that the proposed simplified strategies can approach the optimal performance for most cases, and have higher spectral efficiency than conventional time-sharing OFDMA.

Diagnosis of Gastric Cancer with MDCT Using the Water-Filling Method and Multiplanar Reconstruction: CT–Histologic Correlation

The purpose of this study was to assess the utility of MDCT with a thin-sliced multiplanar reconstruction (MPR) technique and water-filling method for the diagnosis of gastric cancers. Sixty-five patients with gastric cancers were preoperatively examined with MDCT using the water-filling method. The abdomen was dynamically scanned at 30 and 80 sec after the start of contrast medium administration. MPR images were reconstructed with a slice width of 1.25 mm and a slice interval of 1 mm. The detection rate and accuracy of T staging for gastric cancer were evaluated on MPR images and compared with 5-mm-slice axial images. In addition, MDCT images were correlated with pathologic findings. The detection rate of all gastric cancers using the MPR technique was 65%. The detection rate of advanced gastric cancers was 96.2% (25 of 26), whereas that of early gastric cancers was 41.2% (14 of 34). There was a statistically significant difference (p < 0.05) in the detection rate of early gastric cancers between MPR and 5-mm-slice axial images. The MDCT appearances of gastric cancers were well correlated with pathologic findings such as mucinous component or differences in infiltration of cancer cells. The overall accuracy of CT staging was 85%. MPR images were superior to axial images for the evaluation of the z-axis extent of tumor. MDCT with the water-filling method has advantages in acceptable evaluation of depth invasion of gastric carcinomas and in visualization of histologic changes in the tumors. MPR images may be a useful guide for the evaluation of the z-axis extent of tumor.

Preoperative diagnosis of gastric cancer using 2‐D magnetic resonance imaging with 3‐D reconstruction techniques

To investigate the clinical value of 2-D magnetic resonance imaging (MRI) with 3-D reconstruction techniques for the preoperative diagnosis and TNM-staging of gastric cancer. Using a Philips Gyroscan NT 1.0T superconductive unit, MRI using the water-filling method was performed in 15 patients with suspected gastric cancers. The 2-D MRI sequences included TSE-T1WI, TSE-T2WI and fat suppression (SPIR). The source images of magnetic resonance hydrography (heavily TSE-T2WI sequence) were reconstructed using the Philips EasyVision viewing workstation. Four 3-D postprocessing algorithms, including maximum intensity projection, surface shaded viewing, volume rendering and virtual endoscopy, were performed and compared with the results of a barium study and endoscopy. All 15 patients with 16 gastric cancers had their diagnosis confirmed by postoperative pathological findings. 2-D MRI and 3-D reconstruction images were successfully obtained for all 15 patients. The maximum intensity projection, surface shaded viewing, and volume rendering images corresponded to the upper gastrointestinal series findings, and the virtual endoscopy images corresponded to the gastroscopic views. In 16 gastric lesions, MRI correctly diagnosed 14 (87.5%) advanced gastric cancers, and the tumor location, size and classification were also accurately identified. The accuracy of MRI for determining the preoperative TNM stage was 64.3% (9/14), and there was significant correlation between these results and those from the histopathological studies (P < 0.01). Based on T, N and M factors, the staging accuracy of MRI was 71.4% (10/14), 57.1% (8/14) and 85.7% (12/14), respectively. 2-D MRI with 3-D reconstruction is an effective method for the preoperative diagnosis and TNM staging of gastric cancer. However, the detection of early cancers or benign lesions and N-staging should be further studied.

Two-phase dynamic contrast-enhanced computed tomography with water-filling method for staging of gastric carcinoma

The objective of the study was to evaluate the usefulness of two-phase incremental contrast-enhanced computed tomography (CT) with water-filling method in the preoperative assessment of stomach carcinoma. Dynamic CT was done in 20 patients with biopsy-proven gastric cancers and the findings were compared with surgery. A 150-ml ionic contrast medium was administered intravenously at a flow rate of 3.5 ml/s. CT scanning was done at 45 s (early phase) and 3 min (equilibrium phase) after the start of intravenous injection. Primary tumors were detected in all the cases. The overall accuracies of dynamic CT in determining depth of tumor invasion, pancreatic invasion, adjacent liver infiltration, and lymph node metastasis were 85% (17/20), 90% (18/20), 85% (17/20), and 69% (13/19), respectively. The early phase of dynamic CT is highly accurate in determining the depth of tumor invasion of advanced gastric cancers but has low sensitivity in the detection of nodal metastasis. The delayed phase scans do not add any additional information and hence, should not be routinely used for staging.