In multicarrier code division multiple access (MC-CDMA) systems, the orthogonality among the spreading codes is destroyed because the channels exhibit frequency-selective fading and the despreading stage performs gain control; that is, inter-code interference (ICI) can significantly degrade system performance. This paper proposes an optimum spreading code assignment method that reflects our analysis of ICI for up and downlink MC-CDMA cellular systems over correlated frequency-selective Rayleigh fading channels. At first, we derive theoretical expressions for the desired-to-undesired signal power ratio (DUR) as a quantitative representation of ICI; computer simulation results demonstrate the validity of the analytical results. Next, based on the ICI imbalance among code pairs, we assign specific spreading codes to users to minimize ICI (in short, to maximize the multiplexing performance); our proposed method considers the quality of service (QoS) policy of users or operators. We show that the proposed method yields better performance, in terms of DUR, than the conventional methods. The proposed method can maximize the multiplexing performance of a MC-CDMA cellular system once the channel model, spreading sequence, and combining strategy have been set. Three combining strategies are examined at the despreading stage for the uplink, equal gain combining (EGC), orthogonality restoring combining (ORC), and maximum ratio combining (MRC), while two are considered for the downlink, EGC and MRC.

This paper proposes the dynamic resource assignment (DRA) scheme in the multi-carrier mesh-topology millimeter-wave (MMW) broadband entrance networks. In the DRA scheme, the radio path allocation and the frequency channel assignment techniques are deployed to maximize the network throughput. In the radio path allocation technique, the traffic load is distributed into the appropriate paths. On the other hand, the frequency channel assignment is performed based on the linear programming (LP) method. As the results, the proposed DRA scheme yields higher throughput performance than the conventional scheme using the random frequency channel assignment. In addition, the proposed scheme can guarantee the throughput performance when the number of frequency channels is 36 and the input load is no more than 9 Gbps. Moreover, the proposed scheme can yield the satisfaction sub-optimum throughput with the small computational complexity.

In this paper, the design of a mobile satellite Internet access (MSIA) system and a mobile broadband satellite access system, called Mobile Broadband Interactive Satellite Multimedia Access Technology System (MoBISAT) are presented. MSIA system provides Internet service, broadcasting, and digital A/V service in both fixed and mobile environments using Ku-band geostationary earth orbit (GEO) satellite. A Ku-band two-way active phased array antenna installed on top of the transportation vehicles can enable the transmission of signals to satellite as well as signal tracking and reception. The forward link and return link are a high speed Time Division Multiplex (TDM) and TDMA transmission media, respectively, both of which carry signaling and user traffic. The MoBISAT, which is a next generation mobile broadband satellite access system, provides both Ku-band satellite TV and Ka-band high-speed Internet to the passengers and crews for land, maritime, and air vehicles. This paper addresses the main technological solutions adopted for the implementation and test results for the MSIA system and the main design features of the MoBISAT system.

Recently, broadband access is widely spreading, and many broadband network E-commerce services are planned and developed. This article proposes a broadband online shop where a videoconferencing system is used to enable direct, face-to-face communication. It is important for a broadband online shop to understand what preference their customers want in order to provide them with more appropriate information. By using customer preferences, a salesclerk can have a serviceable conversation with few questions to his online customers. So, we are developing a visual Customer Relationship Management system (v-CRM system) that offers customer preferences to broadband network service such as broadband online shop. In this paper, we classify customer preferences, and describe three visualization methods that enable customer preferences to be intuitively understood quickly. We outline the v-CRM evaluation system and describe an experiment where we evaluated how accurately customer preferences can be recognized using these methods. The results show that v-CRM system is effective for understanding customer preferences.

In this paper, a meander-type microstrip patch antenna for application in 5 GHz-band is designed and fabricated. To obtain enough bandwidth in VSWR<2, the foam is inserted between substrate and ground plane, the coaxial probe source is used. The measured result of fabricated antenna is obtained 1 GHz (17.5%) of bandwidth in VSWR<2, the gain of 7.3-9.5 dBi and unidirectional pattern.

FEC (Forward Error Correction) can repair the damage to communication quality due to packet loss. The growing requirement of FEC for high-quality video transmission is inevitable on broadband networks. We have designed and implemented FEC, and integrated it to our developed video transmission system named "mpeg2ts." Our goal is to make it possible to deploy this system on the broadband Internet. However, the problem with constant redundancy of FEC is that weakness to fluctuation of network condition. To resolve this problem, in this paper, we propose and evaluate an efficient FEC method for high-quality video transmission. The proposed mechanisms can provide robustness as well as saving of processing load and optimization of bandwidth consumption. Moreover, we integrate it into a system to deploy it on the real broadband Internet. Transmission experiment demonstrates availability of developed system deployed on the network.

10-Gbit/s wireless data transmission using 120-GHz millimeter-wave (MMW) photonic technologies is presented. For such high-data-rate transmission, we have newly developed a planar broadband receiver that employs a > 200-GHz Schottky diode and a slot-ring antenna with a 10-dB bandwidth of 30 GHz. The receiver achieves a high video sensitivity of 190 mV/mW at 120 GHz due to its optimized data output circuit. The MMW wireless link using the receiver and photonic transmitter has data transmission bandwidth of 8.5 GHz, and succeeded in 10-Gbit/s data transmission, which is the fastest ever achieved through a MMW wireless link.

This paper first presents an active integrated antenna configuration designed for broadband mobile wireless access systems using the 25-GHz band. This active integrated antenna comprises a microstrip antenna array and RF front-end circuits adopting spatial power combining schemes for reduced power consumption of the power amplifiers. Furthermore, the antenna and RF circuits are integrated into each side of a thick copper backing plate and both are connected through microstrip line /slot transitions. The developed active integrated antenna achieves the output power of 14.6 dBm and a noise figure of less than 5 dB. The wireless system using the developed active integrated antenna achieves a 6-dB improvement in the packet error rate compared to that using a passive antenna with the same array design as the active integrated antenna. Furthermore, we obtained the first license of the active integrated antenna for commercial use in high-speed wireless communication systems in Japan.

In this paper, we first address the current state of broadband services in Korea. Here, we introduce relevant statistics, current access network architectures, and activities of some major carriers. We also briefly introduce Korean government's policies on research and development projects and plans for promoting the country toward an advanced information society. We then introduce a large-scale, collaborative project named "Photonic Access To the Home (PATH)" with five-year period of performance, started in year 2002. The project is under leadership of the government and ETRI in collaboration with universities and industry. We finally provide a rather detailed description of the FTTH (Fiber To The Home) technology based on the wavelength division multiplexing technology, which has been under research in our laboratory as a part of the PATH project. We show some of our achievement including new architectures and networking principles for the FTTH network, analysis of the dynamic allocation of user bandwidth, and the experiment for a low-cost WDM optical source.

The fiber-optic sectorized remote antenna system by using the radio frequency (RF) optical transmission technique was promising for increasing the number of subscribers in the millimeter-wave broadband wireless access (MMW BWA) networks. To realize the cost-effectiveness of the fiber-optic sectorized remote antenna system covering four areas, we reached the conclusion that the best multiplexing schemes were the sub-carrier division multiplexing (SCM) of the intermediate frequency (IF) signals of 2 GHz for the down link, the coarse wavelength division multiplexing (CWDM) with the IF signals optical transmission for the up link and 1.3/1.55 µm-WDM for multiplexing the down link and the up link. In addition, the target specifications of this SCM-CWDM system were described, and the designs of the carrier to noise ratio (CNR) and the third order intermodulation distortion (IM3) were examined.

The authors propose a circular polarization generator using a square waveguide with L-type probe located on a side wall of waveguide. The sides of the L-probe forming the right angle are placed perpendicular to the direction of propagation. The position of the right angle is kept at a distance of a quarter-wave length from the side wall. The device provides 27% bandwidth for 3 dB axial ratio at 8.4 GHz on azimuth interval of 160.

This paper compares the radio link capacity between multi-carrier/DS-CDMA (MC/DS-CDMA) and multi-carrier CDMA (MC-CDMA) for reverse-link broadband packet wireless access taking into consideration: the asynchronous signal reception at the receiver; the path timing or symbol timing detection of all major subject factors; and the channel estimation error. Simulation results show that although the influence of the asynchronous signal reception on the packet error rate (PER) performance in MC-CDMA is slight, the degradation caused by the channel estimation error in MC-CDMA is severe compared to that caused by the path timing detection error in MC/DS-CDMA. Consequently, the required average received signal energy per bit-to-background noise spectrum density ratio (Eb/N0) at the average PER of 10-2 in MC/DS-CDMA is reduced by approximately 4.5 dB compared to that in MC-CDMA assuming a 12-path exponential decayed Rayleigh fading channel. Furthermore, the number of accommodated users in MC/DS-CDMA is 2.5 fold greater than that in MC-CDMA employing two-branch antenna diversity reception. Therefore, we conclude that MC/DS-CDMA is more appropriate than MC-CDMA for the reverse link broadband packet wireless access, and that it has advantageous features such as an inherently much lower peak-to-average power ratio compared to MC-CDMA, which accompanies a high peak-to-average power ratio causing an increase in the back-off of the power amplifier.

This paper proposes an efficient random access channel (RACH) transmission method that utilizes soft-combined consecutively retransmitted message data packets according to the Quality of Service (QoS) requirements for broadband multi-carrier/DS-CDMA (MC/DS-CDMA) in the reverse link. In the proposed scheme, the relative transmission power of a message from that of a successfully detected preamble for non-real time (NRT) type traffic data is significantly reduced by soft-combining several retransmitted message data packets thanks to time diversity since the delay requirement is relaxed. Meanwhile, for real time (RT) type traffic data, the relative transmission power of the message from that of the detected preamble is increased in order to reduce the packet error rate with a limited number of retransmissions. Simulation results elucidate that the total required average received signal energy per bit-to-background noise power spectrum density ratio (Eb/N0) for error-free transmission with time diversity for NRT type traffic data is reduced by more than 2 dB compared to that for conventional RACH without the relative transmission power control for a wide rage of fading maximum Doppler frequencies.

High-speed streaming services are considered to be among the most promising services for the broadband Internet of the next generation. A contents delivery network (CDN) that allows effective and scalable content delivery will be required in this role. However, the actual requirements for the CDN, such as quality of service (QoS), the service deployment strategy and technical issues are not yet to be defined. In this paper, the bandwidth requirement of the CDN is derived through QoS evaluation. On the basis of this requirement, we propose two feasible CDN configurations: an IP technology based configuration and an optical video distribution technology based configuration. Finally, we make lists of technical issues for the configurations and discuss some of the possible solutions.

This letter investigates an effect of diversity techniques on the performance of OFDM-CDMA based broadband wireless access networks and evaluates the maximum achievable diversity gain for a two-path Rayleigh fading environment. Simulation results show that the OFDM-CDMA system applying a space-time-frequency diversity with a full-rate full diversity code can give the diversity of D=4 and D=8 for both multi-user cases of maximum user and half user capacities, respectively.

This paper reviews the historical development of adaptive antennas in Japan. First of all, we watch basic adaptive algorithms. In 1980s, particularly, the following issues were a matter of considerable concern to us; (a) behavior to the coherent interference like multipath waves or radar clutters, (b) signal degradation in case that the direction of arrival (DOA) of desired signal is different from the DOA specified beforehand in the adaptive antennas with the DOA of the desired signal as a prior knowledge, and (c) performance of adaptive antennas when the desired signal and interference are broadband. Although there are a lot of development and modification of adaptive algorithms in Japan, we refer in this paper only to the above-mentioned topics. Secondly, our attention is paid to implementation of adaptive antennas and advanced technologies. A large number of researches on the subjects have been carried out in Japan. Particularly, we focus on the initiative studies in Japan toward mobile communication application. They include researches of mobile radio propagation for adaptive antennas, calibration methods, and adaptive antenna for mobile terminals. As a matter of course, we also refer to adaptive antenna technologies for advanced communication schemes such as CDMA, SDMA, OFDM and so on. Finally, we take notice of some pilot products which were developed to verify the effect of the adaptive antenna in the practical environments. As the initiative ones, a couple of equipments are introduced in this paper.

This paper presents a miniaturized reverse-phase hybrid ring by the use of shunt capacitors, and successfully designs a very miniature hybrid ring of a 0.28-wavelength circumference with a wide bandwidth comparable to the regular reverse-phase hybrid ring based on the equivalent admittance approach. Moreover, a method of broadening the bandwidth with adding a matching network consisting of a very short transmission line and two shunt capacitors at each port is also described. The validity of the proposed design is demonstrated by electromagnetic simulator (Sonnet em) for a uniplanar hybrid ring.

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.

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 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.