This paper proposes Variable Spreading Factor-Orthogonal Frequency and Code Division Multiplexing (VSF-OFCDM) as the most promising forward link wireless access method in broadband packet wireless transmission using an approximate 50 to 100 MHz bandwidth. The proposed OFCDM employing VSF can flexibly realize near optimum wireless access satisfying higher radio link capacity both in isolated cell environments such as hot-spot areas and indoor offices and in multi-cell environments such as cellular systems by adaptively changing the appropriate spreading factor, SF, in the frequency domain based on the cell structure, radio link conditions such as the delay spread, and major radio link parameters such as the data modulation scheme and channel coding rate. Furthermore, by establishing SF=1, i.e., no spreading mode, VSF-OFCDM can be used as orthogonal frequency division multiplexing (OFDM). Computer simulation results demonstrate that, while SF=1 (OFDM) achieves higher link capacity than SF>1 in an isolated-cell environment, OFCDM with the optimized SF value over 1 achieves approximately 1.4 times higher capacity compared with OFDM in a multi-cell environment associated with the advantageous one-cell frequency reuse. Consequently, VSF-OFCDM can provide seamless deployment of broadband packet wireless access with higher radio link capacity, that is, OFDM in an isolated-cell environment, and OFCDM with the adaptively optimized SF value over 1 in a multi-cell environment according to the major radio link conditions and radio link parameters, by only changing the spreading factor.

A new optical access system based on the synchronous transfer mode - passive double star system has been developed to provide high-speed LAN-like access. It uses a shared-band method that enables multiple users to efficiently share a single bandwidth of up to 10 Mb/s and a grouping function that divides the access network into several logical networks, each of which can provide a virtual LAN to users. This paper describes an information model and a framework for configuration management and fault management and discusses the requirements for element management, which involves data-link establishment, logical group management, and testing. Element management mainly requires appropriate remote handling on data cards installed in each optical network unit on user premises. A method is proposed that satisfies these requirements. With this method, the element operations system can provide the required operational functionality.

This paper proposes an adaptive radio parameter control scheme that utilizes an optimum radio parameter set comprising the maximum number of retransmissions in hybrid automatic repeat request (HARQ) in addition to the data modulation and channel coding scheme (MCS) according to the Quality of Service (QoS) requirements (i.e., the required packet error rate and delay) and propagation conditions such as the delay spread in the forward link of Orthogonal Frequency and Code Division Multiplexing (OFCDM) broadband wireless access. We elucidate by simulation evaluation that most of the optimum MCSs are common regardless of the delay requirement of traffic data, i.e., common between non-real time (NRT) and real-time (RT) class data. Concretely, the three MCSs of QPSK with the coding rate of R=1/2, 16QAM with R=1/2 and 3/4 are optimum ones, although the additional MCS of QPSK with R=1/3 is effective only for the RT class data in the lower received average received signal energy per symbol-to-background noise power density ratio (Es/N0) region. Furthermore, application of a much higher MCS set, 16QAM with R=5/6 and 64QAM with R=3/4, in addition to the three common MCSs improves the throughput under much higher Es/N0 conditions in a small delay spread environment. The simulation results show that the delay requirement, i.e., the maximum number of retransmissions, in HARQ does not affect the key radio parameter such as MCS, because of informative results such as a smaller number of retransmissions associated with a less-efficient MCS achieves a higher throughput than does using a more highly-efficient MCS allowing a larger number of retransmissions. Consequently, it is concluded that the proposed adaptive radio parameter control according to the QoS requirements substantially results in the selection of the optimum MCS irrespective of the delay requirement except for the extreme case where no retransmissions are allowed and for special propagation channel conditions.

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.

This paper proposes a three-step cell search algorithm that utilizes only the common pilot channel (CPICH) in the forward link and employs spreading by a combination of a cell-specific scrambling code (CSSC) and an orthogonal short code for Orthogonal Frequency and Code Division Multiplexing (OFCDM) broadband packet wireless access. In the proposed cell search algorithm, the OFCDM symbol timing, i.e., Fast Fourier Transform (FFT) window timing, is estimated by detecting the guard interval timing in the first step. Then, in the second step, the frame timing and CSSC group are simultaneously detected by taking the correlation of the CPICH based on the property yielded by shifting the CSSC phase in the frequency domain. Finally, the CSSC within the group is identified in the third step. The most prominent feature of the proposed cell search algorithm is that it does not employ the conventional synchronization channel (SCH), which is exclusively used for the cell search. Computer simulation results elucidate that when the transmission power ratio of the CPICH to one code channel of the traffic channel (TCH) is 12 dB, the proposed cell search method achieves faster cell search time performance compared to the conventional method using the SCH with the transmission power ratio of the SCH to one code channel of the TCH of 6 dB. Furthermore, the results show that it can accomplish the cell search within 1.7 msec at 95% of the locations in a 12-path Rayleigh fading channel with the maximum Doppler frequency of 80 Hz and the r.m.s. delay spread of 0.32 µs.

This paper investigates the impact of inter-carrier interference (ICI) due to Doppler spread on the packet error rate (PER) performance in Orthogonal Frequency and Code Division Multiplexing (OFCDM) packet wireless access employing turbo coding in a multipath fading channel, and describes the optimization of the sub-carrier spacing, Δ f, i.e., the number of sub-carriers, Nc, with an approximate 50-100 MHz bandwidth. Simulation results show that although the uncoded OFCDM in a 1-path flat Rayleigh fading channel is affected by the ICI caused by the Doppler spread when the maximum Doppler frequency, fD, becomes more than 5% of Δ f, OFCDM employing turbo coding in a 24-path Rayleigh fading channel is robust against Doppler spread and the degradation is not apparent until fD reaches more than 10% of Δ f. This is because the turbo coding gain and the frequency diversity effect compensate for the degradation due to ICI. Meanwhile, the PER performance with a larger Nc is degraded, since the effect of the error correction capability becomes smaller due to the larger variance of the despread OFCDM symbols associated with the narrower spreading bandwidth in the frequency domain. Consequently, along with the packet frame efficiency for accommodating the guard interval to compensate for the maximum multipath delay time of 1 µsec, we clarify that the optimum number of sub-carriers is approximately 512-1024 (the corresponding Δ f becomes 156.3-78.1 kHz) for broadband OFCDM packet wireless access assuming a 50-100 MHz bandwidth.

A wireless communications system with a transmission speed of 18 Mbit/s is presented using the 2.4 GHz ISM band. This system employs the Carrier Frequency Offset-Spread Spectrum (CFO-SS) scheme and the Dual-Polarization Staggered Transmission (DPST) scheme. The 18 Mbit/s CFO-SS system (named CFO-SS18) was developed and its performance evaluated in fields. In this paper, the detailed operating principle of CFO-SS and DPST schemes, together with the specifications and structures of CFO-SS18, are presented. Results of indoor and field tests obtained by using CFO-SS18 are also presented.

The optimization of path bandwidth allocation in large-scale telecommunication networks is studied. By introducing a decomposition-coordination scheme to global optimization of the path bandwidth allocation which aims at minimizing the worst case call blocking probabilities in the network, the spatial and time complexities are both reduced, while the accuracy is almost the same as that given by direct optimization.

This paper presents the theoretical analysis of subband adaptive array combining cyclic prefix transmission scheme (SBAA-CP) in multipath fading environment. The exact expressions for optimal weights, array outputs and the output signal to interference plus noise ratio (SINR) are derived. The analysis shows that use of the cyclic prefix data transmission scheme can significantly improve the performance of subband adaptive array (SBAA). An example of implementing SBAA-CP as a software antenna is also presented.

In this paper, a digital compensation scheme for coefficient errors of a complex filter bank parallel A/D converter in low-IF receivers is presented. The complex filter bank is employed to suppress DC offset and image signals in the low-IF receivers and relax the requirements on the conversion rate and resolution of A/D converters. The proposed compensation scheme regenerates interference due to coefficient errors and subtracts it from the digital signal converted by an A/D converter. The proposed scheme also improves the effective resolution of A/D converters.

This paper proposes a three-step cell search algorithm utilizing a synchronization channel (SCH) and common pilot channel (CPICH) in the forward link for OFCDM (Orthogonal Frequency and Code Division Multiplexing) broadband packet wireless access, and evaluates the cell search time performance by computer simulation. In the proposed three-step cell search algorithm, the OFCDM symbol timing, i.e., Fast Fourier Transform (FFT) window timing is estimated employing SCH or guard interval (GI) correlation in the first step. Then, the frame timing is detected by employing the SCH and the cell-specific scrambling code (CSSC) is identified by the CPICH in the second and third steps, respectively. Computer simulation results elucidate that the proposed three-step cell search algorithm achieves fast cell search time performance, i.e., cell detection probability of 90% within approximately 50 msec, assuming the number of CSSCs of 512 in a 19 hexagonal-cell model. We also clarify that there is no prominent difference in cell search time performance between the two employed SCH structures, time-multiplexed and frequency-multiplexed, assuming that the total transmit power of the SCH is the same. Based on the comparison of four substantial cell search algorithms, the GI-plus-SCH correlation method, in which FFT windowing timing detection, frame timing detection, and CSSC identification are performed by GI correlation, frequency-multiplexed SCH, and CPICH, respectively, exhibits the cell search time of approximately 44 msec at the detection probability of 90% with an optimized averaging parameter in each step.

Adaptive beamforming, using the Conjugate Gradient Normal Equation Residual problem, is applied to a base station array, in the UTRA-TDD up-link. A Wideband Directional Channel Model is used, characterising specific micro-cell, street-type scenarios. These differ in the number of mobile terminals, grouped and placed along the street axis, and on their distances to the base station. Time- and angle-of-arrival spreads, and on-the-air interference content are the main parameters inherently varied and analysed. The average beamforming gain and signal-to-noise ratio are evaluated, also varying the number of array elements. The high number of arriving correlated and closely correlated signals, together with the composed nature of the correlation matrix in the algorithm's cost function, result in that other than the MMSE solutions may lead to the best interference suppression, for the tested scenarios. Among the several weighted interfering power components, the most relevant is due to the delayed signals from all the other links. The combination of the number of arriving orthogonal codes, time-of-arrival and angle-of-arrival spreads condition beamforming performance: the number of array elements affect performance, depending on the mobile terminal distance to the base station, and on the number of active links; for short distances and large number of users, larger time-of-arrival spread degrades beamformer performance, over the opposing effect of angle-of-arrival spread; the number of active users affects beamforming gain especially in the case that delay spreads are larger, i.e., for shorter mobile terminal distances to the base station.

A 4-12 GHz 2 W GaAs HFET amplifier has been developed. It employs two novel circuit design techniques. One is a pre-matching circuit for dual gate-bias feed. It is comprised of two shunt LCR circuits, which makes dual gate-bias feed possible. The other one is a tapered power splitting/combining FET (tapered PS/PC FET), which makes amplitude and phase imbalance between FET cells small over a wide bandwidth. In this paper, the schematic diagram and impedance characteristic of the pre-matching circuit for dual gate-bias feed are described first, showing the conditions that the impedance of FETs becomes purely resistive. Then the amplitude and phase imbalance between FET cells are compared by electromagnetic simulation for both the conventional and tapered PS/PC FETs, demonstrating that the tapered PS/PC FET has smaller amplitude and phase imbalance. Furthermore, the MSG/MAG are compared by experiment for both FETs, confirming that the tapered PS/PC FET has higher MSG/MAG. Finally, the design, fabrication, and performance of the 4-12 GHz 2 W GaAs HFET amplifier using the pre-matching circuit for dual gate-bias feed and tapered PS/PC FETs are presented to make sure that two novel circuit design techniques introduced in this paper are useful for the design of wideband lossy match power amplifiers.

This paper presents a second-generation CMOS current conveyor (CCII) consisting of a rail-to-rail complementary n- and p-channel differential input stage for the voltage input, a class AB push-pull stage for the current input, and current mirrors for the current outputs. The CCII was implemented using a double-poly triple-metal 0.6 µm n-well CMOS process, to confirm its operation experimentally. A prototype chip achieves a rail-to-rail swing 2.3 V under 2.5 V power supplies and shows the exact voltage and current following performances up to 100 MHz. Because of its high performances, the CCII proposed herein is quite useful for a building block of current-mode circuits.

A basestation power amplifier requires high linearity and stable operation for common amplification of a multiplexed wideband signal. Nonlinearity compensation techniques with the feedforward or predistorter are useful for this purpose. This paper presents a predistortion amplifier with automatic control at RF band for application at a basestation. In this method, the predistorter distorts an RF input signal by referring to a look-up table (LUT) corresponding to the input power. Out-of-band radiation power are directly monitored at IF band to determine the LUT. A DSP with an iterative algorithm updates the content of the LUT to minimize the out-of-band radiation power. Computer simulation experiment is carried out. The use of this proposed method promises a highly linear wideband and high power-efficiency amplifier.

In this letter, our proposed approach exploits the use of original and simplest Cellular Neural Network (CNN) for 2D Doubly Complementary (DC) Infinite Impulse Response (IIR) filter banks design. The properties of feedback and feedforward templates are studied for this purpose. Through some examples it is shown how generalizations of these templates can be used for DC IIR filter banks design. We modify Lagrangian function which is used for optimizing a low-pass filter design considering the constraint for stability of CNN. The brief conclusions with design examples that illustrate the proposed method and an image enhancement and restoration applications of designed filter banks are presented.

A new graphic and display processor, which is suitable for high-performance car navigation systems or next-generation ITS mobile terminals, has been developed. The performance bottleneck of conventional consumer graphic systems exists not only in the rendering performance of the graphic processor itself, but also in CPU-capability and CPU-bus bandwidth. To release this latter bottleneck, the new processor has Controller/DSP Unit and FPU for graphic-macro-command parsing and geometric operations, respectively, which used to be the CPU tasks and occupy some amount of CPU-bus bandwidth to transfer their results. The architecture of the new processor is organized so as to carry out macro-pipelined operations of graphic and display processing smoothly. One of the features of this processor is having special hardware, Polygon-Engine and Short-Vector-Accelerator, for the rapid rendering of 2D maps, where complex polygons and short line-segments are the dominant objects to be rendered. Another feature is the hardware support of multi-layer/window display with alpha-blend overlapping. This function and additional video processing capability, such as MPEG4 decoding, would be useful in the next generation intelligent terminals. The processor LSI has been successfully fabricated by using 0.18 µm standard CMOS technology. More than five million transistors are implemented on this chip. The peak rendering speed of this processor has been measured as 200 Mpixel/s at 133 MHz processor internal clock frequency. Other results of the graphic system evaluation have demonstrated that this new processor has appropriately high performance and useful functions for the next generation mobile terminals.

We present an efficient scheme for progressive fractal coding in a wavelet multiresolution pyramid. In our proposed scheme, range blocks are selectively coded, based on energy localization in wavelet bands. In order to form domain pools with blocks yielding less distortion, domain blocks are also selectively searched in the wavelet bands of either the same or a different orientation from that of each range block at the next lower resolution. It is shown that the performance of the non-hybrid fractal coder presented is much better than that of predictive pyramid coding (PPC).

This paper presents an optimum antenna diversity combining method associated with despreading that employs Minimum Mean Square Error (MMSE) combining over the frequency domain in a frequency-selective fading channel for forward link Orthogonal Frequency and Code Division Multiplexing (OFCDM) wireless access, in order to achieve the maximum radio link capacity. Simulation results considering various propagation channel conditions elucidate that the antenna diversity combining method with Equal Gain Combining (EGC) subsequent to the despreading employing MMSE combining based on pilot symbol-assisted channel estimation and interference power estimation can decrease the required average received signal energy per bit-to-background noise power spectrum density ratio (Eb/N0) the most, taking into account the impact of the inter-code interference. Furthermore, we clarify that the required average received Eb/N0 for the average packet error rate of 10-2 employing the diversity combining scheme with EGC after despreading with MMSE combining is improved by approximately 0.3 dB compared to the diversity combining scheme with EGC before despreading with MMSE combining at the number of code-multiplexing of 24 for the spreading factor of 32 in a 24-path Rayleigh fading channel.

This paper presents a new operation and maintenance system for PON (Passive Optical Network) subscriber loops and an assessment of its feasibility through experiments. This system adopts a broadband continuous wave light source as a testing signal and a fiber grating filter as a reflective component. The fiber grating filter is inserted somewhere in each subscriber loop for reflection of the testing signal. Our results show that the proposed system operates well for the purposes of quick decision of loop state and easy testing for PON subscriber loops.