Interference Cancellation (IC) receivers can be used in CDMA cellular systems to improve the capacity. The IC receivers can be divided into two main categories, Single-User Detectors (SUD) and Multi-User Detectors (MUD). They have different characteristics in terms of intra-cell and inter-cell interference cancellation ratios. In this paper we first introduce the Normalized Griffiths' algorithm, a SUD receiver, and compare its basic performance with the well-known Serial IC. Next we examine the multi-cell performance of SUD and MUD receivers by using multi-cell link-level simulations. The results show that even though MUD receiver has clearly better single-cell performance, the SUD receiver will gain in performance in the multi-cell cases. In the three-sector multi-cell case, their performance even becomes very similar. These results are obtained using ideal conditions to be able to study the receivers' basic properties related to intra-cell and inter-cell interference.

A shared-TDD scheme has been proposed for accommodation of asymmetric communications between uplink and downlink traffic. The application of shared-TDD scheme to CDMA cellular systems causes inter-link interference because CDMA cellular systems use the same frequency band for all cells. This paper proposes a transmission control scheme for uplink packets to relieve the effect of inter-link interference in CDMA/shared-TDD cellular packet systems. In the proposed scheme, mobile stations select transmission slots based on their location and the status of slot allocations in own and the adjacent cells. Computer simulations show that the proposed scheme relieves the effect of inter-link interference, and thus improves the downlink transmission efficiency.

Wireless networks are quickly becoming an integral part of the Internet. But, the TCP does not work well in wireless networks. Considerable research has tried to improve TCP performance in wireless networks, especially in the face of the wireless link loss problem. However, TCP performance is also deeply influenced by channel conditions, and the performance in variable channel conditions has not been studied widely. In this paper, we observe the behavior of the traditional standard TCP performance in the face of variable channel conditions. Then, we propose a new simple TCP flow control scheme. The traditional standard TCP performs poorly because it does not reflect current channel conditions. Our adaptive TCP receiver window control scheme, however, performs well on variable channel conditions. Our scheme efficiently improves TCP performance with minimum modification of TCP module on the wireless terminal. It adaptively adjusts the TCP receiver window size depending on the dynamic channel conditions. Thus, our scheme maintains network conditions properly and has good TCP performance over all wireless channel conditions. In addition, since our scheme is simple and the only the TCP receiver module on the wireless terminal needs to be changed, it is feasible. Through the simulation and analysis, we found that our scheme has good TCP throughput and short end-to-end delay over all variable channel conditions.

Power control error is well known for its negative effects on CDMA system capacity. In this Letter, an analytical model is developed to estimate the uplink capacity for a SIR-based power controlled CDMA cellular system. The voice capacity reduction due to power control error is numerically examined with this model.

A Virtual Cellular Network (VCN) is a wireless cellular network wherein a single Mobile Station (MS) can communicate simultaneously with more than one Base Station (BS). In this paper, we analyze handoff for two kinds of VCN: a 'Distributed Resource-control VCN' (DR-VCN) and a 'Centralized Resource-control VCN' (CR-VCN). A VCN can take advantage of the fact that the same data is received by multiple base stations. The DR-VCN is a system in which every BS controls its own channels, while the CR-VCN is a system wherein a central station controls all system channels. Results from analysis and simulation show that both the new call drop rate and handoff refusal rate of the CR-VCN are much lower than those of the DR-VCN.

The CDMA/NC-PRMA protocol has been proposed to deal with multimedia traffic flexibly in mobile communications systems. The Load-Balancing (LB) method has been investigated for information slot assignment in CDMA/NC-PRMA systems. However, the LB method may be not effective in multi-cell environments due to inter-cell interference although this method is effective for single cell environments. In this paper, we propose new information slot assignment methods for multi-cell environments; a total reception power based assignment method and a signal to interference ratio (SIR) based assignment method. The former one assigns information slots based on the total reception power from both inside and outside the cell for each slot in the previous frame. The latter one predicts the SIR of receiving packets and assigns information slots to MSs only when predicted SIR exceeds the target SIR. The results of computer simulation show that the proposed schemes have superior transmission performance to the conventional scheme.

This paper presents a two-tier coordinated checkpointing algorithm which can reduce the number of messages by being composed of two levels in mobile computing. Thus mobile devices have a high mobility and are lack of resources (e.g., storage, bandwidth, and battery power), traditional distributed algorithms like coordinated checkpointing algorithms could not be applied properly in mobile environment. In our proposed two-tier coordinated checkpointing algorithm, the messages to be transferred are requested by the mobile hosts and are handled by the appropriate MSS's (Mobile Support Stations). And the broadcast messages are handled by MSS instead of relaying the messages to all the mobile hosts directly as with the previous algorithms. This can reduce the communication cost and maintain the overall system consistency. In wireless cellular network, mobile computing based on a two-tier coordinated checkpointing algorithm reduces the number of synchronization messages. We perform performance comparisons by parametric analysis to show that a two-tier coordinated checkpointing algorithm can reduce communication cost compared to the previous algorithms in which the messages are directly sent to the mobile hosts.

Recent advances of Web information systems such as e-commerce and e-learning have created very large but hidden demands on conceptual multiresolution analysis for more generalized information analysis, cognition and modeling. To meet the demands in a general way, its modeling is formulated based on modern algebraic topology. To be specific, the modeling formulation is worked out in an incrementally modular abstraction hierarchy with emphasis on the two levels of the hierarchy appropriate for conceptual modeling: the adjunction space level and the cellular structured space level. Examples are shown to demonstrate the usefulness of the presented model as well as an implementation of a flower structure case.

In testing the possible biological effects of electromagnetic exposure from cellular telephones in small animals such as mice, it is essential to realize a highly localized head exposure as close as possible to that due to cellular telephones in humans. In this study, a 1.5GHz exposure setup was developed which has a highly localized specific absorption rate (SAR) of 2W/kg in the mouse brain and a low whole-body averaged SAR of 0.27W/kg. The low whole-body averaged SAR was realized by using a flexible magnetic sheet attachment on the mouse holder. Its validity has been carefully examined by both numerical simulation with an anatomically based mouse model and experimental simulation with a solid mouse phantom. Good agreement was obtained between the numerical and experimental results, which confirmed the effectiveness of the magnetic sheet attachment to the mouse holder.

This paper addresses the system throughput maximization problem for HAPS third generation cellular systems. We assume that the Stratospheric Platform is able to perform a perfect link gain estimation for all mobile terminals, such that a centralized resource allocation strategy is made possible. A classical 3G wireless scenario is considered, where traffics characterized by different bit rates coexist with Best Effort Traffic services without stringent bit rate constraints. In this scenario, we firstly envisage three Rate Assignment schemes for best effort terminals which aim at achieving the maximum system throughput subject to different bit rate constraints. For the second envisaged rate assignment scheme, which represents the best compromise between service fairness and throughput, we then propose a simplified approach that allows to noticeably decrease the implementation complexity with a slight performance degradation.

This paper reviews the antenna system for Japanese celullar systems and PHS (Personal Handphone System). The unique features of the Japanese cellualr system are multi-band operation, compact diversity antennas, electronic beam tilting, and indoor booster systems. The original antennas for the above purpose will be described. The PHS is also a unique mobile communication system in Japan, and is mainly used for high speed, low cost data transmission. Its original antennas are also presented in this paper.

Interference Cancellation (IC) receivers can be used in CDMA cellular systems to improve the capacity. The IC receivers can be divided into two main categories, Single-User Detectors (SUD) and Multi-User Detectors (MUD). They have different characteristics in terms of intra-cell and inter-cell interference cancellation ability. In this paper we propose two new IC receivers that combines the properties of SUD and MUD receivers. The first one is a Serial IC receiver followed by the Normalized Griffiths' algorithm (SING). The second one is an Integrated Serial IC and Normalized Griffiths' algorithm (iSING). We first compare their basic single-cell performance with the conventional RAKE receiver, the Serial IC and the Normalized Griffiths' Algorithm. Next, we examine their multi-cell performance by doing multi-cell link-level simulations. The results show that even though the Serial IC receiver has good single-cell performance, the proposed receivers have as much as 35-40% higher capacity than the Serial IC receiver in the multi-cell case under the ideal conditions assumed in this paper.

Studies of cellular automata (CA) based random number generators (RNGs) have focused mainly upon symmetrically connected networks with neighborhood sizes of three or five. Popular field programmable gate array configurations feature a four-input (i.e., 16-row) lookup table. Full utilization of the four-input lookup table leads to the potential for asymmetrically connected cellular automata networks with a neighborhood size of four. From each of various 1-d, 2-d, and 3-d networks with periodic boundary conditions, the 1000 highest entropy CA RNGs were selected from the set of 65,536 possible uniform (all CA truth tables the same) implementations. Each set of 1000 high-entropy CA was then submitted to Marsaglia's DIEHARD suite of random number tests. A number of 64-bit, neighbor-of-four CA-based RNGs have been discovered that pass all tests in DIEHARD without resorting to either site spacing or time spacing to improve the RNG quality.

Recent cellular systems have excellent performances, such as high quality, compactness, low power consumption and low cost, owing not only to digital technologies but also to various RF device technologies, especially amplifier technologies. This paper describes base station RF technologies that contributed for the improvement of base station equipment. Future mobile system will provide much higher bitrate services in the higher frequency band. Requirements and new technologies that are expected for RF equipment of the future base stations are also discussed.

The progress made in large-scale integration of the baseband circuits of digital cellular phones now makes it possible to implement a voice CODEC and its related functions in the baseband LSI rather than through a general-purpose digital signal processor. This paper describes an improved hardware solution that enables efficient application of the PSI-CELP CODEC-- the most complex CODEC for mobile systems--to the PDC half-rate system through its implementation as a DSP macro in a low-voltage, large-scale LSI. Specific circuit blocks are added as hardware engines to a general-purpose DSP-oriented core. These specific engines were implemented as peripheral circuits for a DSP macro that can be used as a single DSP with an added I/O circuit and is suitable for use in future highly integrated mobile baseband chips. With the assistance of these hardware engines and some additional ALU instructions to achieve efficient programming, the machine speed required for the CODEC can be relatively slow, thus allowing the same architecture to be repeatedly used without needing to set the transistor threshold voltage too low even when the use of deeper sub-micron technologies require a chip to run at a lower supply voltage. We evaluated this DSP-macro architecture using a 0.35 µm CMOS technology test chip. Then we developed a commercial base version using 0.25 µm technology and verified that it can operate at 1.2 V and that the PSI-CELP CODEC can be done at 40 MIPS with power consumption of 11 mW. We also verified that the circuit design can be applied up to 0.18 µm technology with a single threshold voltage of 0.3 V. Thus, the design of the DSP macro incorporating the hardware engines provides a great deal of flexibility that should allow its use in chips based on future technologies and the voice CODEC firmware can be effectively re-used. Although the DSP macro architecture was designed mainly through PSI-CELP application analysis, it can process other voice CODECs such as the AMR CODEC for third-generation mobile applications as well as some other mobile baseband functions such as channel CODECs. This approach can also be refined to permit its application to, for example, high-quality audio CODECs.

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.

We propose a new adaptive FEC scheme combined with ELN (Explicit Loss Notification) that was proposed for improving TCP performance in wireless cellular networks. In our method, transmission errors on the wireless link are measured at the packet level and the error status is notified the TCP sender with ELN. According to this information, an appropriate FEC code is determined in order to maximize the TCP performance. We first compare the TCP performance using Snoop Protocol, ELN and the fixed FEC, through which we find the appropriate FEC code against given BER (bit error ratio). We then show how the adaptive FEC can be realized using our solution, and also examine the appropriate observation period of measuring BER enough for the fading speed on the noisy wireless link. We finally demonstrate that our method can achieve better performance than the conventional fixed FEC by using the Gilbert model as a wireless error model.

Cellular Neural Networks (CNNs) have been developed as a high-speed parallel signal-processing platform. In this paper, a generalized two-layer cellular neural network model is proposed for image processing, in which two templates are introduced between the two layers. We found from the simulations that the two-layer CNNs efficiently behave compared to the single-layer CNNs for the many applications of image processing. For examples, simulation problems such as linearly non-separable task--logic XOR, center point detection and object separation, etc. can be efficiently solved with the two-layer CNNs. The stability problems of the two-layer CNNs with symmetric and/or special coupling templates are also discussed based on the Lyapunov function technique. Its equilibrium points are found from the trajectories in a phase plane, whose results agree with those from simulations.

The cooperative and competitive network suitable for circuit realization is presented, based on the network proposed by Amari and Arbib. To ensure WTA process, the output function of the original network is replaced with the piecewise linear function and supplying the inputs as pulse waveforms is obtained. In the SPICE simulations, it is confirmed that the network constructed by operational amplifiers attains WTA process, even if the scale of the network becomes large.

The Belousov-Zhabotinsky (BZ) reaction provides us important clues in controlling 2D phase-lagged stable synchronous patterns in an excitable medium. Because of the difficulty in computing reaction-diffusion systems in large systems using conventional digital processors, we here propose a cellular-automaton (CA) circuit that emulates the BZ reaction. In the circuit, a two-dimensional array of parallel processing cells is responsible for fast emulation, and its operation rate is independent of the system size. The operations of the proposed CA circuit were demonstrated by using a simulation program with integrated circuit emphasis (SPICE).