PurposeTo evaluate clinical and radiological outcome of the full cementation technique in revision total knee arthroplasty (TKA) using a constrained condylar knee (CCK) prosthesis.Materials and MethodsBetween January 2008 and March 2012, 18 cases (16 patients) of fully cemented revision TKA were performed using a CCK prosthesis. Fifteen cases of aseptic loosening (13 patients) and 3 cases of infection were included. There were 2 males and 14 females with a mean age of 76.7 years at the time of surgery, and the average follow-up was 81 months. Clinically, the pain score, function score and Hospital for Special Surgery (HSS) score were evaluated. Radiologically, loosening, radiolucent lines and migration of implant were evaluated.ResultsPreoperatively, the pain score, function score and HSS score were 50.3, 24.4 and 61.8 points, respectively. At the latest follow-up, the scores were improved to 84.8, 63.6 and 85.6 points, respectively (p<0.05). Loosening or migration of implant was not observed in any cases. Radiolucent lines were observed in 5 cases underneath the tibial component without progression during the follow-up.ConclusionsThe full cementation technique in revision TKA using a CCK showed excellent clinical results. Although radiolucent lines were observed in 27.8% underneath the tibial component, there was no progression to loosening or instability.

Recently, as the demand for data rate of users has increased, wireless communication systems have aimed to offer high throughput. For this reason, various techniques which guarantee high performance have been invented, such as massive multiple-input multiple-output (MIMO). However, the implementation of huge base station (BS) antenna array and decrease of reliability as the number of users increases are chief obstacles. In order to mitigate these problems, this paper proposes an adaptive precoder which provides high throughput and bit error rate (BER) performances to achieve the desired data rate in multi user (MU) MIMO downlink systems which have a practical BS antenna array (up to 16). The proposed scheme is optimized with a modified minimum mean square error (MMSE) criterion in order to improve BER gain and reduce data streams in order to obtain diversity gain at low signal to noise ratio (SNR). It is shown that the BER and throughput performances of the proposed scheme are improved.

Recently, as the demand for tremendous spectral efficiency has increased, the massive multiple-input multiple-output (MIMO) system has attracted attention in the wireless communication system. In massive MIMO, the zero forcing (ZF) precoder provides optimal performance. However, the complexity for process of matrix inversion is burden in terms of practical implementation. Therefore, many researches for approximate inversion of channel matrix have been performed in order to reduce the complexity. The typical linear precoder based on approximate matrix inversion is the Gauss Seidel (GS) precoder. The GS precoder provides the similar precoded signals to ZF precoder with low complexity. However, the GS precoder does not adopt parallel implementation because of inner structure. Consequently, precoder for the GS iterative method spends a lot of times in order to estimate precoded signal. Therefore, this problem makes the GS precoder impractical. In this paper, the punctured GS (PGS) is proposed in order to mitigate the problem of parallel operation by modifying inner structure for the GS precoder. However, the performance for the PGS precoder is degraded due to modified inner structure. Therefore, the ordering PGS precoder which performance degradation due to modified inner structure is mitigated is additionally introduced. As a result, although the delay when precoded signal for the PGS precoder is obtained decreases than the GS precoder, the BER performance for the PGS precoder is degraded than the GS precoder. In contrast, the ordering PGS precoder provides improved BER performance with decrease of delay compared with the GS precoder.

This paper proposes an estimation scheme of the number iterations for optimal Gauss–Seidel (GS) pre-coding in the downlink massive multiple input multiple output (MIMO) systems for the first time. The number of iterations in GS pre-coding is one of the key parameters and should be estimated accurately prior to signal transmission in the downlink systems. For efficient estimation without presentations of the closed-form solution for the GS pre-coding symbols, the proposed estimation scheme uses the relative method which calculates the normalized Euclidean distance (NED) between consecutive GS solutions by using the property of the monotonic decrease function of the GS solutions. Additionally, an efficient initial solution for the GS pre-coding is proposed as a two term Neumann series (NS) based on the stair matrix for improving the accuracy of estimation and accelerating the convergence rate of the GS solution. The evaluated estimation performances verify high accuracy in the downlink massive MIMO systems even in low loading factors. In addition, an additional complexity for estimating the number of the optimal iterations is nearly negligible.

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