This paper describes a method to design a predistorter (PD) for a GaN-FET power amplifier (PA) by using nonlinear parameters extracted from measured IMD which has asymmetrical peaks peculiar to a memory effect with a second-order lag. While, computationally efficient equations have been reported by C. Rey et al. for the memory effect with a first-order lag. Their equations are extended to be applicable to the memory effect with the second-order lag. The extension provides a recursive algorithm for cancellation signals of the PD each of which updating is made by using signals in only two sampling points. The algorithm is equivalent to a memory depth of two in computational efficiency. The required times for multiplications and additions are counted for the updating of all the cancellation signals and it is confirmed that the algorithm reduces computational intensity lower than half of a memory polynomial in recent papers. A computer simulation has clarified that the PD improves the adjacent channel leakage power ratio (ACLR) of OFDM signals with several hundred subcarriers corresponding to 4G mobile radio communications. It has been confirmed that a fifth-order PD is effective up to a higher power level close to 1 dB compression. The improvement of error vector magnitude (EVM) by the PD is also simulated for OFDM signals of which the subcarrier channels are modulated by 16 QAM.

In this paper a recursive form of Welch-Berlekamp (W-B) algorithm is provided which is a novel and fast decoding algorithm.

A novel cumulant based MUSIC like DOA estimation algorithm for multicarrier modulation has been proposed in this paper. While the conventional MUSIC algorithm is not applicable to a correlation matrix calculated from received signals transmitted over the different carriers, the proposed algorithm can estimate the DOA of the signals with multicarrier modulation. The proposed algorithm does not require the sensor array responses for the frequency range of the interest and the initial phases of the carriers. With the proposed algorithm the number of signals whose DOA are estimated can be increased and the accuracy of the DOA estimation can be improved by employing larger number of carriers.

In this paper, we attempt the comparison of the image/signal restoration between Projection Filter, which is regarded as one of the linear optimal filters, and the non-linear filter based on MEM. From the simulation, we show the advantage of MEM restoration filter in restoring noisy degraded images.

In multiple-input multiple-output (MIMO) systems, the multiuser MIMO (MU-MIMO) systems have the potential to provide higher channel capacity owing to multiuser and spatial diversity. Block diagonalization (BD) is one of the techniques to realize MU-MIMO systems, where multiuser interference can be completely cancelled and therefore several users can be supported simultaneously. When the number of multiantenna users is larger than the number of simultaneously receiving users, it is necessary to select the users that maximize the system capacity. However, computation complexity becomes prohibitive, especially when the number of multiantenna users is large. Thus simplified user scheduling algorithms are necessary for reducing the complexity of computation. This paper proposes a simplified capacity-based user scheduling algorithm, based on analysis of the capacity-based user selection criterion. We find a new criterion that is simplified by using the properties of Gram-Schmidt orthogonalization (GSO). In simulation results, the proposed algorithm provides higher sum rate capacity than the conventional simplified norm-based algorithm; and when signal-to-noise power ratio (SNR) is high, it provides performance similar to that of the conventional simplified capacity-based algorithm, which still requires high complexity. Fairness of the users is also taken into account. With the proportionally fair (PF) criterion, the proposed algorithm provides better performance (sum rate capacity or fairness of the users) than the conventional algorithms. Simulation results also shows that the proposed algorithm has lower complexity of computation than the conventional algorithms.

We present a highly integrated quasi-millimeter-wave receiver MMIC that integrates 22 circuits in a 3 2.3 mm area using three-dimensional MMIC (3D-MMIC) technology. The MMIC achieves low noise (3 dB) and high gain (41 dB) at 26 GHz by using an on-chip image reject filter. It integrates a multiply-by-eight (X8) local oscillator (LO) chain with the IF frequency of the 2.4 GHz band and can use low-cost voltage-controlled oscillators (VCOs) and demodulators in a 2–3 GHz frequency band. Multilayer inductors contribute to the miniaturization especially in a 2–12 GHz frequency band. Furthermore, it achieves a high dynamic range by using two step attenuators with a new built-in inverter using an N-channel depression field-effect transistor (FET). The power consumption of the MMIC is only 450 mW.

This paper attempts a complete analysis of circulator in reference to "circuit-invariance" in order to arrive at an invariant of and a canonical representation for circulator. Furthermore, a suitable figure of merit of circulator can be initially derive by means of this invariant, and a compensating circuit for circulator is discussed in as thorough a manner as possible.

Many experimentally and theoretically based models have been proposed to predict, quantitatively evaluate, and combat the fading phenomenon in mobile communication systems. However, to the best of the authors' knowledge, up to now there is no objective method to determine which is the most suitable distribution to model the fading phenomenon based on experimental data. In this work, the Minimum Description Length (MDL) criterion for model selection is proposed for that purpose. Furthermore, the MDL analysis is performed for some of the most widely used fading models based on measurements taken in a sub-urban environment.

In multiuser multiple-input multiple-output (MU-MIMO) wireless downlink systems, block diagonalization (BD) is a technique, where the transmit precoding matrix of each user is designed such that its subspace lies in the null space of all the other remaining users, so that multiuser interference (MUI) is completely canceled. In low signal to noise power ratio (SNR) or low signal to interference plus noise power ratio (SINR) environments, regularized BD, that lets some MUI remain and maximizes the sum rate capacity of the BD MIMO channel, was also proposed. One of the problems of both the approaches is high complexity of computation due to a lot of singular value decomposition (SVD) processes. In this paper we propose new BD techniques utilizing QR decomposition (QRD) which can be practically achieved by Gram-Schmidt orthogonalization (GSO) with lower complexity compared to the conventional method employing SVD. We can show that the performance of the proposed approaches is close to the conventional approaches, while the proposed approaches have much lower complexity.

In recent years, wireless communication technology has been studied intensively. In particular, MIMO which employs several transmit and receive antennas is a key technology for enhancing spectral efficiency. However, conventional MIMO architectures require some transceiver circuits for the sake of transmitting and receiving separate signals, which incurs the cost of one RF front-end per antenna. In addition to that, MIMO systems are assumed to be used in low spatial correlation environment between antennas. Since a short distance between each antenna causes high spatial correlation and coupling effect, it is difficult to miniaturize wireless terminals for mobile use. This paper shows a novel architecture which enables mobile terminals to be miniaturized and to work with a single RF front-end by means of adaptive analog beam-forming with parasitic antenna elements and antenna switching for spatial multiplexing. Furthermore, statistical analysis of the proposed architecture is also discussed in this paper.

The effect of antenna correlation on the Multiple-Input Multiple-Output (MIMO) channel capacity in the real propagation environment is a topic of interest. In this paper, we present the results of a measurement campaign conducted in an indoor Line-Of-Sight (LOS) office environment. Channel responses were taken with varying distance in a static indoor environment. Results showed measurements with high received Signal-to-Noise Ratio (SNR) and a high level of correlation among the antenna elements. Further analysis of the results showed that MIMO systems can achieve sufficient channel capacity compared to the Single-Input Single-Output (SISO) system, despite high antenna correlation. Theoretical analysis reveals that when the SNR is sufficiently high, the loss in channel capacity due to high antenna correlation is relatively low. Therefore it is shown that in the indoor LOS environment, MIMO systems can be sufficiently efficient because the MIMO channel is more robust to antenna correlation when the SNR is high.

To design secure blockciphers, estimating immunity against differential attack and linear attack is essential. Recently, Diffusion Switching Mechanism (DSM) is proposed as a design framework to enhance the immunity of Feistel structure against differential attack and linear attack. In this paper, we give novel results on the effect of DSM on three generalized Feistel structures, i.e. Type-I, Type-II and Nyberg's structures. We first show a method for roughly estimating lower bounds of a number of active S-boxes in Type-I and Type-II structures using DSM. Then we propose an improved search algorithm to find lower bounds for generalized structures efficiently. Experimental results obtained by the improved algorithm show that DSM raises lower bounds for all of the structures, and also show that Nyberg's structure has the slowest diffusion effect among them when SP-type F-functions are used.

In this paper, an ultra-thin wave absorber using a resistive patch array closely-placed in front of a back-metal is designed. The positively large susceptance is required for the patch array to cancel out the negatively large input susceptance of the short-circuited ultra-thin spacer behind the array. It is found that the array needs the gap of 1mm, sheet resistance of less than 20Ω/sq. and patch width of more than 15mm to obtain the zero input susceptance of the absorber with the 1/30 wavelength spacer. Moreover, these parameters were designed considering the electromagnetic coupling between the array and back-metal, and the square patch array absorbers with the thickness from 1/30 to 1/150 wavelength were designed.

While efficient use of network resources is an important control objective of call admission control (CAC), the issue of fairness among services should also be taken into account. Game theory provides a suitable framework for formulating such fair and efficient CAC problem. Thus, in this paper, a game theoretic framework for selecting fair-efficient threshold parameters of CAC for the asymmetrical traffic case in CDMA mobile multimedia systems is proposed. For the cooperative game, the arbitration schemes for the interpersonal comparisons of utility and the bargaining problem, including the Nash, Raiffa, and modified Thomson solutions, are investigated. Furthermore, since CAC should be simple and flexible to provide a fast response to diverse QoS call requests during a connection setup, this paper also applies the concept of load factor to the previous Jeon and Jeong's CAC scheme and proposes an approximation approach to reduce the computational complexity (proposed throughput-based CAC scheme). From the numerical results, the proposed throughput-based CAC scheme shows a comparable performance to the previous Jeon and Jeong's CAC scheme while achieving lower computational complexity. All the solutions attain the fairness by satisfying their different fairness senses and efficiency by the Pareto optimality.

This letter proposes the Pulse-position Multi-pulse Modulation (PMM) with multiple access DTR-UWB systems for the ECC's proposed radiation mask on September 2005 and Japan's radiation mask on March 2006. For the ECC's proposed radiation mask and Japan's radiation mask, the UWB system has to consider the effect from Remote Access Service (RAS) and Radar system between 4.8-5 GHz and 5-6 GHz, respectively. That will limit the bandwidth of the system to just 3.4-4.8 GHz. The simulation results show that the performance of the proposed system is superior to that of the conventional TR-UWB communication system. Moreover, compared to the FCC's system, the proposed PMM DTR-UWB and conventional system have better error performance and higher total throughput at low Eb/N0. So for power limiting system like UWB, ECC's and Japan's systems may become the strong candidates in the UWB communication system.

In this letter, the delay time error between transmitter and receiver that may be the main factor degrading TR-UWB system performance, is studied. Simulations show that although the MPM and PMM systems with using SCR have achieved high throughput performance, this advantage has been degraded by the delay time error effect. Therefore, in the real application, the delay time error effect is one of the main factors for selecting the suitable TR-UWB system.

This paper develops the first prototype hardware for a TDD two-way multi-hop relay network with MIMO network coding. Since conventional wireless multi-hop relay networks have the drawback of low data rate, TDD two-way multi-hop relay networks have been studied as a solution to realize high data rate recently. In these networks, forward and backward streams are spatially multiplexed by using interference cancellation techniques such as MIMO beamforming or MIMO network coding. In this paper, a demonstration system for the TDD two-way multi-hop relay network with MIMO network coding (called 2-way relay network hereafter) is developed using the prototype hardware. In the demonstration system, each transmitter and receiver performs network coded broadcast and MIMO multiple access, respectively. By using the demonstration system, network throughput is measured in an indoor environment to prove the realization and effectiveness of the 2-way relay network. From the results of network throughput, it is found that the 2-way relay network can achieve high network throughput approaching theoretical upper bound even in low average end-to-end SNR area where network throughput of the direct link degrades severely. From these results, the realization and effectiveness of the 2-way relay network can be proved in the real indoor environment.

For usage in fading environments, the idea of utilizing radio signal processing with software programmable devices promises greater flexibility and functionality. However, to realize these benefits very high performance DPSs and AD converters are required, especially for adaptive antennas with CDMA. One potential method of reducing the implementation complexity is to employ multicarrier (MC) modulation as it allows parallel signal processing in addition to its benefits in combating fading and ISI effects. This paper proposes a system utilizing MC DS/CDMA and a recursive adaptive array antenna processing algorithm for estimating the array response vector (array manifold) and hence the optimal weights. In order to evaluate this system performance results obtained through computer simulations are presented. The proposed MC system improves the accuracy of the direction-of-arrival (DOA) estimation of the signal by 2 degrees as compared with a single carrier system. It is also shown that the proposed adaptive array antenna algorithm for MC DS/CDMA reduces the number of iterations of the power method significantly and allows parallel processing of the adaptive algorithm.

In this paper it is pointed out that although an elegant differential-like approach is developed, Coppersmith' attacking method on NIKS-TAS cannot succeed to forge a shared key of legitimate entities especially when p-1 contains highly composite divisors, as well as decomposibility-hard divisors. This is mainly due to a severe reduction of modulo size. Computer simulation results confirm this assertion. The ambiguity in the solutions to the collusion equations in the first phase can be analyzed by the elementary divisor theory. Moreover, two basis vectors, qi,ri in the second phase, are found to be inadequate to represent the space spanned by xi-yi and ui-vi(i=1,...,N), because qi,ri exist frequently over the space with small modulo size. Then, the erroneous values of αi,βi,...,εi(i=1,...,N) are derived from the inadequate basis vectors, qi,ri. Also, when the degeneracy in modulo size happens, the solutions to αi,βi,...,εi(i=1,...,N) cannot be solved even by means of the exhaustive search over the small prime divisors of p-1.

This letter describes two low complexity receiver structures over a multi-broadcast channel of an orthogonal frequency division multiple access (OFDMA) multi-user system. The first is a one-group occupied receiver structure, whose complexity is much lower than that of a conventional OFDMA receiver structure. The other one, a multi-group occupied receiver structure, exploits multiple groups for one user, by which users' down-link data rate can be adaptively controlled by a base station (BS). Unlike unchangeable complexity of an OFDMA receiver structure that performs full-size of a fast Fourier transform (FFT) operation although only a few subcarriers are taken, its complexity linearly increases with the number of occupied subcarrier groups. The proposed receiver structures can meet the possible high-rate demand in the down-link and will become one of the strong candidates in next generation mobile communication systems.