This paper presents a fuzzy control-based intelligent medium access controller (FiMAC), which optimizes random access control between heterogeneous traffic aiming at more efficient voice/data integrated services in dynamic reservation TDMA-based broadband radio access networks. In order to achieve the design objective, viz. a differentiated quality-of-service (QoS) guarantee for individual service plus maximal system resource utilization, the FiMAC intelligently and independently controls the random access parameters such as the lengths of random access regions dedicated to respective service traffic and the corresponding permission probabilities, frame-by-frame basis. In addition, we have adopted a mobile-assisted random access mechanism where the voice terminal readjusts a global permission probability from the FiMAC, to handle the 'fair access' issue resulting from distributed queueing problems inherent in the access network. Our extensive simulation results indicate that the FiMAC is well coordinated with a mobile-assisted mechanism such that significant improvements are achieved in terms of voice capacity, delay, and fairness over most of the existing MAC schemes for the integrated services.

This paper presents laboratory and field experimental results of the coherent adaptive antenna array diversity (CAAAD) receiver employing receiver antenna-weight generation common to all Rake-combined paths (hereafter path-common weight generation method) in the W-CDMA reverse link, in order to elucidate the suitability of the path-common weight generation method in high-elevation antenna environments such as cellular systems with a macrocell configuration. Laboratory experiments using multipath fading simulators and RF phase shifters elucidate that even when the ratio of the target Eb/I0 of the desired to interfering users is Δ Eb/I0=-12 dB, the increase in the average transmit Eb/N0 employing the CAAAD receiver coupled with fast transmission power control (TPC) using outer-loop control from that for Δ Eb/I0=0 dB is within only 1.0 dB owing to the accurate beam and null steering associated with fast TPC. Furthermore, field experiments demonstrate that the required transmission power at the average block error rate (BLER) of 10-2 employing the CAAAD receiver with four antennas is reduced by more than 2 dB compared to that using a four-branch space diversity receiver using maximum ratio combining (MRC) with the fading correlation between antennas of 0 when Δ Eb/I0=-15 dB and that the loss in the required transmission power of the CAAAD receiver in the same situation as that in a single-user environment is approximately 1 dB. The field experimental results in an actual propagation environment suggest that the CAAAD receiver is effective in suppressing multiple access interference, thus decreasing the required transmission power when the gap in the direction of arrival between the desired user and interfering users is greater than approximately 20 degrees.

In this paper, two types of multi-stage partial parallel interference cancellation (PIC) receivers are considered for multi-rate DS-CDMA system: multi-stage PIC receiver with partial cancellation factors and multi-stage PIC receiver with decision thresholds. Bit error rate (BER) of the multi-stage partial PIC receivers is obtained by simulation in a Rayleigh fading channel. It is shown that the multi-stage partial PIC receivers achieve smaller BER than the matched filter (MF) receiver, multi-stage PIC receiver, group-wise successive interference cancellation (GSIC) receiver, and extended GSIC receiver (EGSIC) for the multi-rate DS-CDMA system in a Rayleigh fading channel.

This paper investigates transmission power control for packet transmissions by using code division multiplexing (CDM) in the downlink common (shared) channel of CDMA cellular packet systems and proposes a transmission power control scheme to improve throughput performance and geographical fairness of communication services. In the proposed scheme, downlink transmission power is controlled based on the signal-to-interference ratio predicted at mobile stations. Throughput performance and transmission delay are evaluated under perfect power control conditions. Simulation results show that by using site diversity technique the proposed scheme improves the downlink throughput for light load conditions and geographical fairness for all offered channel loads under both non-fading and fading environments.

This paper proposes a multipath interference canceller (MPIC) employing multipath interference (MPI) replica generation (MIG) utilizing previously transmitted packet combining (PTPC), which is well-suited to incremental redundancy, in order to achieve a peak throughput of nearly 8 Mbps in a multipath fading environment in high-speed downlink packet access (HSDPA). In our scheme, more accurate MPI replica generation is possible by generating MPI replicas utilizing the soft-decision symbol sequence of the previously transmitted packets in addition to that of the latest transmitted packet. Computer simulation results elucidate that the achievable throughput of the MPIC employing MIG-PTPC is increased by approximately 100 kbps and 200 kbps and the required average received signal energy per symbol-to-background noise power spectrum density ratio (Es/N0) per antenna at the throughput of 0.8 normalized by the maximum throughput is improved by about 0.3 and 0.7 dB compared to that of the MPIC using the soft-decision symbol sequence after Rake combining of the last transmitted packet both in 2- and 3-path Rayleigh fading channels for QPSK and 16QAM data modulations, respectively. Furthermore, we clarify that the maximum peak throughput using the proposed MPIC with MIG-PTPC coupled with incremental redundancy achieves approximately 7 Mbps and 8 Mbps with 16QAM and 64QAM data modulations in a 2-path Rayleigh fading channel, respectively, within a 5-MHz bandwidth.

We propose a new multiple access communication system based on finite field wavelet spread signature (FFWSS). In addition to the function of frequency diversity and multiple access, which are typically provided by traditional spreading codes, the FFWSS spreads data symbols in time, resulting in robustness against frequency selective slow fading. Using the FFWSS to spread a data symbol so that it is overlapped with neighboring symbols, a FFWSS-CDMA system is developed. It is observed that the ratio of the maximum nontrivial value of periodic correlation function to the code length of FFWSS is the same as that of a Sidelnikov sequence. Using RAKE-based receivers, simulation results show that the proposed FFWSS-CDMA system yields lower bit error rate (BER) than conventional DS-CDMA and MT-CDMA systems in multipath fading channels.

Approximately synchronized CDMA (AS-CDMA) can reduce the inter-channel interference in a cell to zero. This property of AS-CDMA is an advantage over the conventional DS-CDMA. However, the inter-cell interference of the AS-CDMA cellular system has not been sufficiently examined previously. Therefore, the synthetic performance of AS-CDMA cellular system also has not been sufficiently clarified previously. Some factors that affect the inter-cell interference of the AS-CDMA cellular system were theoretically examined, and evaluated by using computer simulation. As the result, we found that transmission power control is effective for reducing the inter-cell interference of the AS-CDMA cellular system. In addition, the synthetic performance of AS-CDMA cellular system was clarified for the first time. Consequently, it was also found that the synthetic performance of the AS-CDMA cellular system is higher than that of the conventional DS-CDMA cellular system.

This paper studies the optimization of signature waveforms and power allocation for synchronous code-division multiple access (CDMA) systems under the root-mean-square (RMS) bandwidth constraint. The optimization is considered for two types of receivers, namely the conventional matched filter (MF) receiver and the minimum mean-square error (MMSE) receiver. For both cases, the optimization criterion is to maximize the average signal to interference ratios (SIRs) at the receivers' outputs. For a given RMS bandwidth constraint and an arbitrary power allocation scheme, a procedure to obtain the optimal signature waveforms is provided. Based on this procedure, it is then shown that the optimal power allocation is achieved when all the received powers are equal. With the optimal power allocation, solutions for the optimal signature waveforms are presented and discussed in detail. It is also demonstrated that, compared to the previously obtained Welch-bound-equality (WBE) signature waveforms, the proposed signature waveforms can significantly improve the user performance.

We introduce efficient algorithms for the τ-adic sliding window method, which is a scalar multiplication algorithm on Koblitz curves over F2m. The τ-adic sliding window method is divided into two parts: the precomputation part and the main computation part. Until now, there has been no efficient way to deal with the precomputation part; the required points of the elliptic curves were calculated one by one. We propose two fast algorithms for the precomputation part. One of the proposed methods decreases the cost of the precomputation part by approximately 30%. Since more points are calculated, the total cost of scalar multiplication is decreased by approximately 7.5%.

This paper presents an effective approach for estimating of the load matching conditions for dielectric barrier discharge (DBD) load. By the simulation method proposed here, optimal working frequency and optimal applied voltage for driving of DBD load can be calculated. Estimation results for the DBD ultraviolet generation lamp as a load of series resonant inverter are presented here, together with their evaluations.

Traditional soft-handoff algorithms are based on the static threshold handoff algorithm recommended in the IS-95 standard. They are characterized by two parameters, an add threshold Tadd and a drop threshold Tdrop. These two parameters are assumed to have some constant values irrespective of the received signal strength of the pilot in the active set. To improve the performance of the soft-handoff, a dynamic threshold concept was proposed in previous work, where Tadd and Tdrop are dynamically determined according to the received signal strength of the pilot channel in the active set. In this study, previous work of the dynamic threshold algorithm is extended by including additional handoff criteria based on absolute signal strength and/or drop timer. Some functional forms with two new parameters, called boundary thresholds, and slope constant are proposed to dynamically determine Tadd and Tdrop. The dynamic threshold algorithms are compared with static ones in four different cases. Computer simulations show that the dynamic threshold algorithms outperform the static algorithms. We can see that the performance improvements differ from case to case. For example, when a pure dynamic threshold algorithm is compared with a pure static one (case 1), the decrease in the number of active set is about 13.7%. When the absolute threshold and the drop timer are also included in the handoff decision criteria (case 4), however, the decrease is only about 6.2%.

Multiple access interferecnce (MAI) is a major factor limiting the performance of direct-sequence code-division multiple access (DS-CDMA) systems. Since the amount of MAI is dependent on the correlation among user signals, one way to reduce it is to reduce such correlation. In mobile multiuser communication, each user experiences a different time-varying channel response. This user-dependent characteristic in channel variation can be exploited to assist the separation of different user signals, in addition to the capability provided by the spreading codes. As the correlation among different user channels are expected to decrease with increase in time span, enhanced decorrelation among different users' signals can be effected by spacing out the chips of one modulated symbol in time. Thus we consider chip-interleaving DS-CDMA (CI-DS-CDMA) in this study. We investigate its performance through theoretical analysis and computer simulation. Employing only a slightly modified rake receiver structure, CI-DS-CDMA is shown to attain significant performance gain over conventional DS-CDMA, in multiple access communication over single- and multi-path fading channels, without complicated multiuser detection. CI-DS-CDMA also has a lower demand for short-term power control than conventional DS-CDMA, especially in one-path Rayleigh fading. Results of the theoretical analysis and the computer simulation agree well with each other.

A digit-recurrence algorithm for computing reciprocal square-root which appears frequently in multimedia and graphics applications is proposed. The reciprocal square-root is computed by iteration of carry-propagation-free additions, shifts, and multiplications by one digit. Different specific versions of the algorithm are possible, depending on the radix, the redundancy factor of the digit set, and etc. Details of a radix-2 version and a radix-4 version and designs of a floating-point reciprocal square-root circuit based on them are shown.

In cryptography, we want a Boolean function which satisfies PC(l) of order k for many (l,k). Let PCn(l,k) be a set of Boolean functions with n input bits satisfying PC(l) of order k. From a view point of construction, it is desirable that there exists (l0,k0) such that PCn(l0, k0) PCn(li,ki) for many i 1. In this paper, we show a negative result for this problem. We prove that PCn(l1,k1) PCn(l2,k2) for a large class of l1, k1, l2 and k2.

This paper presents a performance comparison of the channel-interleaving method in the frequency domain, i.e., bit interleaving after channel encoding, symbol interleaving after data modulation, and chip interleaving after spreading, for Variable Spreading Factor-Orthogonal Frequency and Code Division Multiplexing (VSF-OFCDM) wireless access with frequency domain spreading, in order to reduce the required average received signal energy per symbol-to-background noise power spectrum density ratio (Es/N0) and achieve the maximum radio link capacity. Simulation results show that, for QPSK data modulation employing turbo coding with the channel coding rate R=3/4, the chip-interleaving method decreases the required average received Es/N0 the most for various radio parameters and propagation model conditions, where the number of code-multiplexing, Cmux, the spreading factor, SF, the r.m.s. delay spread, σ, the number of multipaths, L, and the maximum Doppler frequency, fD, are varied as parameters. For example, when Cmux=12 of SF=16, the improvement in the required average received Es/N0 from the case without interleaving at the average packet error rate (PER) of 10-2, is approximately 0.3, 0.3, and 1.4 dB for the bit, symbol, and chip interleaving, respectively, in a L=12-path exponential decayed Rayleigh fading channel with σ of 0.043 µsec and fD of 20 Hz. This is because the chip interleaving obtains a higher diversity gain by replacing the chip assignment over the entire bandwidth. Meanwhile, in 16QAM data modulation with R=1/2, the performance of the chip interleaving is deteriorated, when Cmux/SF>0.25, due to the inter-code interference caused by different fading variations over the spreading duration since the successive chips during the spreading duration are interleaved to the separated sub-carriers. Thus, bit interleaving exhibits the best performance although the difference between bit interleaving and symbol interleaving is slight. Consequently, we conclude that the bit-interleaving method is the best among the three interleaving methods for reducing the required received Es/N0 considering the tradeoff between the randomization effect of burst errors and the mitigation of inter-code interference assuming the application of adaptive modulation and channel coding scheme in OFCDM employing frequency domain spreading.

Serious BER performance degradation due to finite numeric precision in VLSI implementation of Log-MAP and MAX-Log-MAP decoders where forward state metric is calculated using reverse tracing method, is analyzed, and two methods are proposed to overcome this problem, the loser storing method for MAX-Log-MAP and the periodic storing method for Log-MAP and MAX-Log-MAP. Both methods can reduce memory storage size effectively by half, but with additional circuit overhead. Our VLSI implementation examples show that, compared with original method, both methods give about 15% improvement in area and power consumption with identical BER performance.

The encryption algorithm Camellia is a 128 bit block cipher proposed by NTT and Mitsubishi, Japan. Since the algebraic degree of the outputs after 3 rounds is greater than 128, designers estimate that it is impossible to attack Camellia by higher order differential. In this paper, we show a new higher order differential attack which controls the value of differential using proper fixed value of plaintext. As the result, we found that 6-round F-function can be attacked using 8th order differentials. The attack requires 217 chosen plaintexts and 222 F-function operations. Our computer simulation took about 2 seconds for the attack. If we take 2-R elimination algorithm, 7-round F-function will be attacked using 8th order differentials. This attack requires 219 chosen plaintexts and 264 F-function operations, which is less than exhaustive search for 128 bit key.

This paper describes truncated and impossible differentials of Feistel block ciphers with round functions of 2-layer SPN (Substitution and Permutation Network) transformation modules such as the 128-bit block cipher Camellia, which was proposed by NTT and Mitsubishi Electric Corporation. Our work improves on the best known truncated and impossible differentials, and has found a nontrivial 9-round truncated differential that may lead to a possible attack against a reduced-round version of Camellia without input/output whitening, FL or FL-1 (Camellia-NFL), in the chosen plain text scenario. Previously, only 6-round differentials were known that may suggest a possible attack of Camellia-NFL reduced to 8-rounds. We also show a nontrivial 7-round impossible differential, whereas only a 5-round impossible differential was previously known. We also consider the truncated differential of a reduced-round version of Camellia (Camellia-DS) whose round functions are composed of D-S (Diffusion and Substitution) transformation modules and without input/output whitening, FL or FL-1 (Camellia-DS-NFL), and show a nontrivial 9-round truncated differential, which may lead to a possible attack in the chosen plain text scenario. This truncated differential is effective for general Feistel structures with round functions composed of S-D (Substitution and Diffusion) or D-S transformation.

This paper shows an extensive software performance analysis of dedicated hash functions, particularly concentrating on Pentium III, which is a current dominant processor. The targeted hash functions are MD5, RIPEMD-128 -160, SHA-1 -256 -512 and Whirlpool, which fully cover currently used and future promised hashing algorithms. We try to optimize hashing speed not only by carefully arranging pipeline scheduling but also by processing two or even three message blocks in parallel using MMX registers for 32-bit oriented hash functions. Moreover we thoroughly utilize 64-bit MMX instructions for maximizing performance of 64-bit oriented hash functions, SHA-512 and Whirlpool. To our best knowledge, this paper gives the first detailed measured performance analysis of SHA-256, SHA-512 and Whirlpool.

To improve the CT image degraded by radiographic noise (such as quantum mottle), we propose a method based on the wavelet transform modulus sum (WTMS). The noise and regular parts of a signal can be observed by tracing the evolution of its WTMS across scales. Our results show that most of the quantum mottle in the projections of Shepp-Logan phantom has been removed by the proposed method with the supposed cranium well preserved. The denoised CT images show good signal to noise ratio in the region of interest. We also have investigated the relation between the number of X-ray photons and the quality of images reconstructed from denoised projections. From experimental results, this method shows the possibility to reduce a patient's dose about 1/10 with the same visual quality.