Turbo codes are of particular use in applications of wireless communication systems, where various types of communication are required and the data rate must be changed, depending on the situation. In such applications, adaptation of turbo coding specifications is required in terms of coding block size, data speed, parity bit arrangement or configuration of a convolutional coder, as well as the need for real time processing. We present new ideas to provide these capabilities for a low power decoder circuit by focusing on the configuration of a convolutional decoding algorithm, which occupies a significant proportion of the hardware circuit. We utilize the Soft Output Viterbi Algorithm (SOVA) for the base algorithm, produced by adding the concept of a soft output to the Viterbi Algorithm (VA). The Maximum A Posteriori (MAP) algorithm and its simplified version of MAX-LOG-MAP are also widely known. MAP is recognized as a means of achieving very good bit error rate (BER) characteristics. On the other hand SOVA has been regarded as a method which can be simply implemented with less computational resources, but at a cost of higher degradation. However, in many of recent systems we combine turbo coding with some other method such as Automatic Repeat Request (ARQ) to maintain a good error correction performance and we only have to pay attention to the performance in the range of low carrier-to-noise ratio (CNR), where SOVA has fairly satisfactory BER characteristics. This makes the SOVA approach attractive for a low power programmable IP macro solution, when the fundamental advantage of SOVA is fully utilized in the implementation of an LSI circuit. We discuss the processing algorithm and circuit configuration and show that about 40% reduction in power consumption can be achieved. It is also shown that the IP macro can handle 1.5 Mbps information decoding at 100 MHz clock rate.

In this paper, we provide an efficient algorithm for GMD (Generalized Minimum Distance) decoding of BCH codes over q-valued logic, when q is pl (p: prime number, l: positive integer). An algebraic errors-and-erasures decoding procedure is required to execute only one time, whereas in a conventional GMD decoding at mostd/2algebraic decodings are necessary, where d is the design distance of the code. In our algorithm, Welch-Berlekamp's iterative method is efficiently employed to reduce the number of algebraic decoding procedures. We also show a method for hardware implementation of this GMD decoding based on q-valued logic.

Setting relays can address the shadowing problem between a transmitter (Tx) and a receiver (Rx). Moreover, the Multiple-Input Multiple-Output (MIMO) technique has been introduced to improve wireless link capacity. The MIMO technique can be applied in relay network to enhance system performance. However, the efficiency of relaying schemes and relay placement have not been well investigated with experiment-based study. This paper provides a propagation measurement campaign of a MIMO two-hop relay network in 5 GHz band in an L-shaped corridor environment with various relay locations. Furthermore, this paper proposes a Relay Placement Estimation (RPE) scheme to identify the optimum relay location, i.e. the point at which the network performance is highest. Analysis results of channel capacity show that relaying technique is beneficial over direct transmission in strong shadowing environment while it is ineffective in non-shadowing environment. In addition, the optimum relay location estimated with the RPE scheme also agrees with the location where the network achieves the highest performance as identified by network capacity. Finally, the capacity analysis shows that two-way MIMO relay employing network coding has the best performance while cooperative relaying scheme is not effective due to shadowing effect weakening the signal strength of the direct link.

This paper proposes optimal beam patterns of analog beamforming for SU (Single User) massive MIMO (Multi-Input Multi-Output) transmission systems. For hybrid beamforming in SU massive MIMO systems, there are several design parameters such as beam patterns, the number of beams (streams), the shape of array antennas, and so on. In conventional hybrid beamforming, rectangular patch array antennas implemented on a planar surface with linear phase shift beam patterns have been used widely. However, it remains unclear whether existing configurations are optimal or not. Therefore, we propose a method using OBPB (Optimal Beam Projection Beamforming) for designing configuration parameters of the hybrid beamforming. By using the method, the optimal beam patterns are derived first, and are projected on the assumed surface to calculate the achievable number of streams and the resulting channel capacity. The results indicate OBPB with a spherical surface yields at least 3.5 times higher channel capacity than conventional configurations.

The Direct Sampling Mixer (DSM) with a complex coefficient transfer function is demonstrated. The operation theory and the detail design methodology are discussed for the high order complex DSM, which can achieve large image rejection ratio by introducing the attenuation pole at the image frequency band. The proposed architecture was fabricated in a 65 nm CMOS process. The measured results agree well with the theoretical calculation, which proves the validity of the proposed architecture and the design methodology. By using the proposed design method, it will be possible for circuit designers to design the DSM with large image rejection ratio without repeated lengthy simulations.

Vertical- and horizontal-polarization RCS of a dipole antenna was reduced using a switchable reflector. The switchable reflector can switch reflection level for the vertical-polarization and have absorption for the horizontal-polarization. The reflection level of the reflector for the vertical-polarization can be switched using pin diodes and the reflection for the horizontal-polarization can be reduced using resistor on the surface. The switchable reflector was designed to operate at 9 GHz and fabricated. The vertical-polarized reflection coefficient was switched -28 dB with OFF-state diodes and -0.7 dB with ON-state diodes, and horizontal-polarized one was less than -18 dB at 9 GHz. The reflector with ON-state diodes was applied to an antenna reflector of a dipole antenna and comparable radiation pattern to that with a metal reflector was obtained at 9 GHz. Moreover the reflector with OFF-state diodes was applied to the reflector of the dipole antenna and the RCS of the dipole antenna was reduced 18 dB for the vertical-polarization and 16 dB for the horizontal-polarization. Therefore the designed switchable reflector can contribute to antenna RCS reduction for dual-polarization at the operating frequency without degrading antenna performance.

A new type of edge-guided mode (E. G. Mode) isolator is proposed, which has the following desirable characteristics: (a) high isolation (more than 40 dB with 1dB insertion loss), (b) simple structure without additional lossy materials, and (c) considerably broad band (40% relative bandwidth). Moreover, a new type of E. G. mode circulator for which the scattering matrix is of the non-cyclic from is also proposed.

MIMO two-way multi-hop networks are considered in which the radio resource is fully reused in all multi-hop links to increase spectrum efficiency while the adjacent interference signals are cancelled by MIMO processing. In addition, the nodes in the multi-hop network optimize their transmit powers to mitigate the remaining overreach interference. Our main contribution in this paper is to investigate an efficient relay placement method with power allocation in such networks. We present two formulations, namely QoS-constrained optimization and SINR balancing, and solve them using a sequential geometric programming method. The proposed algorithm takes advantage of convex optimization to find an efficient configuration. Simulation results show that relay placement has an important impact on the effectiveness of power allocation to mitigate the interference. Particularly, we found that an uniform relay location is optimal only in power-limited scenarios. With optimal relay locations, significant end-to-end rate gain and power consumption reduction are achieved by SINR balancing and QoS-constrained optimization, respectively. Furthermore, the optimal number of hops is investigated in power or interference-limited scenarios.

The arithmetic operations over the finite field GF(pn) has many important applications. There is a need for a fast inverter circuit over the finite field GF(pn), because inversion' is must complicated and lengthy operation. In this paper, we will propose a design method of fast inverter circuit that is based on Euclid's algorithm. The inverter circuit is composed of a number of identical basic circuits. Therefore the designed circuit has a regular and expandable feature and has a modular structure.

An equivalent circuit of a circular patch array absorber has been proposed, however the method to identify a winding ratio of a transformer in its circuit have never been reported. In this paper, it is indicated that the ratio is proportionate to the area ratio between patch and unit cell of the absorber, and the design method of the winding ratio is proposed. The winding ratio derived by the proposed method is agreed well with that by using electromagnetic simulator within 3% error. Moreover, the operating frequency and 15 dB bandwidth of the fabricated absorber designed by proposed method are agreed with those derived by the circuit simulation within 0.4% and 0.1% errors. Thus the validity of the proposed method is verified.

In this paper, we show a collusion attack on the novel and sophisticated ID-based non-interactive key sharing scheme proposed by Tanaka [2], [3]. It is based on a linear algebraic approach [4]. We discuss its complexity and provide numerical simulation results of the success probability in forging the shared keys.

It is known that demand and supply power balancing is an essential method to operate power delivery system and prevent blackouts caused by power shortage. In this paper, we focus on the implementation of demand response strategy to save power during peak hours by using Smart Grid. It is obviously impractical with centralized power control network to realize the real-time control performance, where a single central controller measures the huge metering data and sends control command back to all customers. For that purpose, we propose a new architecture of hierarchical distributed power control network which is scalable regardless of the network size. The sub-controllers are introduced to partition the large system into smaller distributed clusters where low-latency local feedback power control loops are conducted to guarantee control stability. Furthermore, sub-controllers are stacked up in an hierarchical manner such that data are fed back layer-by-layer in the inbound while in the outbound control responses are decentralized in each local sub-controller for realizing the global objectives. Numerical simulations in a realistic scenario of up to 5000 consumers show the effectiveness of the proposed scheme to achieve a desired 10% peak power saving by using off-the-shelf wireless devices with IEEE802.15.4g standard. In addition, a small-scale power control system for green building test-bed is implemented to demonstrate the potential use of the proposed scheme for power saving in real life.

In this paper, three new ultra wideband (UWB) communication systems with quadrature-phase shift keying (QPSK) impulse modulation are proposed. First, direct-sequence (DS) multiple-access scheme is applied. The second proposed system is based on time-hopping (TH) multiple-access scheme. The last proposed system applies TH multiple-access scheme with QPSK impulse modulation and pulse position modulation (PPM). The conventional UWB communications as TH scheme with PPM modulation and DS scheme with binary-phase shift keying (BPSK) are used to compare. The simulation results show that all proposed UWB communication systems can provide obviously better performances compared with the conventional TH-PPM and DS-BPSK UWB communication systems. The comparisons in aspects of transmission bit rate and the number of users are also investigated.

To reduce laborious tasks of the phase determination, our previous paper has proposed a method to derive phase reference for two-tone intermodulation distortion (IMD) measurement of a power amplifier (PA) by using small-signal S-parameters. Since the method is applicable to low output power level, this paper proposes an iterative process to extend the applicable power level up to 1-dB compression. The iterative process is based on extraction of linear response: the principle of the extraction is described theoretically by using an accurate model of the PA with memory effect. Measurement of two-tone IMD is made for a GaN FET PA. Validity of the iteration is confirmed as convergence of the extracted linear response to that given by the product of S21 and input signal. Measured results also show validity of the physical model of the memory effect provided by Vuolevi et al. because beat frequency dependences of IMD's are accurately fitted by bias impedances at even order harmonics of envelope frequency. The PA is characterized by using measured results and the third and fifth order inverses of the PA are designed. Improvement of IMD is theoretically confirmed by using the inverses as predistorters.

This paper reports the prehistory of software defined radio (SDR) studies in Japan. In 1999, a boom in the field of SDR started in Japan, and this year an ARIB study group completed its final report on SDR. SDR is a recently proposed technology concept and has attracted the attention of many communication engineering researchers. SDR will become one of the most important technologies in advanced communication, broadcasting and intelligent transportation systems on the 21st century. Although SDR has several attractive features, there are also many design issues to be solved. In this work we have examined these issues and discussed a new design methodology for wireless receivers in the SDR era.

It is expected that software receivers will be widely available for radio communication, broadcasting and radio monitoring applications because they are able to be equipped with multimode, multirate and multiband functions in a single hardware platform. This paper describes the basic techniques required for software receivers for both hardware and software. The evaluation items and methods were studied and some evaluations done with an experimental software receiver model fabricated for radio monitoring applications. Future concepts in radio communication, broadcasting and radio monitoring applications where software receivers are thought to be suitable, were studied, and problems for realization identified.

An optimization of the smoothing preprocessing for the correlated signal parameter estimation was considered. Although the smoothing factor (the number of subarrays) is a free parameter in the smoothing preprocessing, a useful strategy to determine it has not yet been established. In this paper, we investigated thoroughly about the smoothing factor and also proposed a new scheme to optimize it. The proposed method, using the smoothed equivalent diversity profile (SED profile), is able to evaluate the effect of smoothing preprocessing without any a priori information. Therefore, this method is applicable in the real multipath parameter estimation.

This paper proposes a new methodology to design optimal antennas for MIMO (Multi-Input Multi-Output) communication systems by using spherical mode expansion. Given spatial channel properties of a MIMO channel, such as the angular profile at both sides, the optimal MIMO antennas should provide the largest channel capacity with a constraint of the limited implementation space (volume). In designing a conventional MIMO antenna, first the antenna structure (current distribution) is determined, second antenna directivity is calculated based on the current distribution, and thirdly MIMO channel capacity is calculated by using given angular profiles and obtained antenna directivity. This process is repeated by adjusting the antenna structure until the performance satisfies a predefined threshold. To the contrary, this paper solves the optimization problem analytically and finally gives near optimal antenna structure (current distribution) without any greedy search. In the proposed process, first the optimal directivity of MIMO antennas is derived by applying spherical mode expansion to the angular profiles, and second a far-near field conversion is applied on the derived optimal directivity to achieve near optimal current distributions on a limited surface. The effectiveness of the proposed design methodology is validated via numerical calculation of MIMO channel capacity as in the conventional design method while giving near optimal current distribution with constraint of an antenna structure derived from proposed methodology.