Several subband array methods have been proposed as useful means to perform joint spatio-temporal equalization in digital mobile communications. These methods can be applied to mitigate problems caused by the inter-symbol interference (ISI) and co-channel interference (CCI). The subband array methods proposed so far can be classified into two major schemes: (1) a centralized feedback scheme and (2) a localized feedback scheme. In this paper, we propose subband arrays with partial feedback scheme, which generalize the above two feedback schemes. The main contribution of this paper is to derive the steady-state mean square error (MSE) performance of subband arrays implementing these three different feedback schemes. Unlike the centralized feedback scheme which can be designed to provide the optimum equalization performance, the subband arrays with localized and partial feedback schemes are in general suboptimal. The performance of these two suboptimal feedback schemes depends on the channel characteristics, the filter banks employed, and the number of subbands.

This paper proposes serially arranged two parasitic elements above a fed dipole to obtain broad bandwidth in resonant frequency of a parasitic element. The above antenna can be used in triple-bands with one feed point. Its design method using FDTD is also presented. Next, application of the triple-bands antenna is proposed for 3-sector base station antenna. Its characteristics of return loss and radiation patterns are indicated. Calculated values are in good agreement with measured ones.

The efficiency-fractional bandwidth product (EB), which is expressed as a ratio of the radiation resistance to the absolute value of the input reactance of an antenna, is used as a performance criterion for small dielectric loaded monopole antennas (DLMAs). The dependence of the EB on the permittivity of the dielectric loading (i.e., the electrical volume) is experimentally and numerically investigated for the first time in antenna research. As a result, it is found that the EBs of the some DLMAs are enhanced over a bare monopole antenna and an EB characteristic curve has a maximum point. This result suggests the presence of the optimum electrical volume for the dielectric loading in order to obtain the best EB performance. A general reason for the existence of the peak value is also explained using a mathematical deduction. Finally the system EB, which is an efficiency-fractional bandwidth product of the DLMA with a practical matching circuit, is defined and its dependence on the relative permittivity is illustrated. Consequently, the existence of the peak value is also confirmed for the system EBs. In addition, it is demonstrated that the enhancement of the system EB is mainly due to the enhancement in the efficiency of the antenna system.

Broadband fixed wireless access (FWA) systems offer significantly higher bit rates than current cellular systems to which adaptive arrays are partly applied. Digital beam forming is being eagerly explored on account of its flexibility, but it will be difficult to apply to the high-speed systems, because its digital signal processing requires huge resources and power consumption. Conventional phased arrays, on the other hand, utilize phase shifters through RF or IF signal lines, but the phase shifters are usually both bulky and expensive. The authors propose an adaptive array steered by IF local signal phase shifters in this paper. The phase shift and the frequency shift of the signal from each antenna element can be simultaneously accomplished at the down conversion stage by the phase-controlled local signal. A prototype receiver operated in the K-band with the proposed configuration and its beam pattern measurement results are also described.

This paper presents a novel image coding scheme based on separate coding of region and residue sources. In a subband image coding scheme, quantization errors in each subimage spread over the reconstructed image and result in a blurring or a boundary artifact. To obtain high compression ratio without considerable degradation, an input image, in our scheme, is separated into region and residue sources which are coded using different coding schemes. The region source is coded by adaptive arithmetic coder. The residue source is coded using multiresolution subimages generated by applying a subband filter. Each block in the subimages is predicted by an affine transformation of blocks in lower resolution subimages. Experimental results show that a high coding efficiency is achieved using the proposed scheme, especially in terms of the subjective visual quality and PSNR at low bit-rate compression.

Sector antennas provide many advantages such as when combined with a narrow beam antenna, they become particularly effective in achieving high-speed wireless communication systems and they aid in simplifying the structure. These antennas have a drawback in that as the number of sectors increases, the antenna size rapidly increases. Therefore, downsizing the sector antenna has become a major research topic. A promising candidate is utilizing a phased-array type antenna; however, this antenna requires a phase-shifter circuit for beam scanning and generally the feeding circuit for this type of antenna is very complicated. To address these issues, we propose a self-selecting feeding circuit that is controlled by the same control circuit and is operated similarly to the conventional single port n-th throw (SPNT) switch. We fabricated a small cylindrical 12-sector antenna at 19 GHz employing the proposed feeding circuit for verification purposes. Furthermore, this paper clarifies the design method of this feeding circuit where the antenna diameter is 71 mm, and the results clearly show that the gain is more than 12 dBi.

To generalize characteristics of a received signal level distribution from narrow- to wide-bands in a mobile radio channel, a new propagation parameter called equivalent received bandwidth (2ΔfΔLmax) has been proposed. The distributions are discussed mainly with computer simulation results. The simulation results shows the level distribution depends on 2ΔfΔLmax and power ratio a of direct to indirect waves, and the value of 2ΔfΔLmax classifies the radio channel as narrow- or wide-bands transmission. To confirm these simulated results, a field test was performed with a 3.35 GHz radio wave. This paper describes that the field test demonstrated the simulation results. It is concluded that the equation representing received signal level in the computer simulation is valid. And the fading depth depends directly on 2ΔfΔLmax, and the 2ΔfΔLmax is effective for generalizing the received signal level distribution. Furthermore, a method for calculating the power ratio was found to be better for a peak level model.

Interest in service offerings at Ka-band (20/30 GHz) and above has been increasing recently, driven mainly by the availability at higher frequencies of wider bandwidths, which are attractive for many multimedia applications, for example. A dominant concern in implementing systems to operate in such bands is the severe propagation environment that exists on many transmission paths, such as paths in rainy climates or at low path elevation angles. Adequate understanding of the propagation environment is imperative in the design of economically viable telecommunication systems at these frequencies. A propagation measurement campaign that addressed many of these concerns was conducted in North America with 20.2 and 27.5 GHz radio beacons on NASA's Advanced Communications Technology Satellite (ACTS). Data were collected at seven locations over a continuous 5-year period to supply statistics of propagation impairments for a variety of climate types and path geometry. The primary results of the ACTS campaign as reported to date are reviewed. Studies performed to address related issues, including fading dynamics, site diversity and mobile-satellite performance, are also described. Elements of this paper were presented at the 2000 International Symposium on Antennas and Propagation (ISAP 2000), Fukuoka, Japan, 21-25 August 2000.

In this paper we study the scalability issue in the design of a centralized bandwidth broker model for dynamic control and management of QoS provisioning. We propose and develop a path-oriented, quota-based dynamic bandwidth allocation mechanism for efficient admission control operations under the centralized bandwidth broker model. We demonstrate that this dynamic bandwidth allocation mechanism can significantly reduce the overall number of QoS state accesses/updates, thereby increasing the overall call processing capability of the bandwidth broker. Based on the proposed dynamic bandwidth allocation mechanism, we also extend the centralized architecture with a single bandwidth broker to a hierarchically distributed architecture with multiple bandwidth brokers to further improve its scalability. Our study demonstrates that the bandwidth broker architecture can be designed in such a manner that it scales with the increase in the network capacity.

Negative differential conductance based on lateral interband tunnel effect is demonstrated in a planar degenerate p+-n+ diode (Esaki tunnel diode). The device is fabricated with the current silicon ultralarge scale integration (Si ULSI) process, paying attention to the processing damage so as to reduce an excess tunnel current that flows over some intermediate states in the tunnel junction. I-V characteristics at a low temperature clearly show an intrinsic electron transport, indicating phonon-assisted tunneling in Si as in the case of the previous Esaki diodes fabricated by the alloying method. In addition, a simple circuit function of bistable operation is demonstrated by connecting the planar Esaki diode with conventional Si metal-oxide-semiconductor field effect transistors (MOSFETs). The planar Esaki diode will be a promising device element in the functional library for enhancing the total system performance for the coming system-on-a-chip (SoC) era.

A unified polyphase representation of analysis and synthesis filter banks is introduced in this paper, and then the efficient implementation on digital signal processors (DSP) is investigated. Especially, the number of memory accesses, power consumption, processing accuracy and the required instruction cycles are discussed. Firstly, a unified representation is given, and then two types of procedures, SIMO system-based and MISO system-based procedures, are shown, where SIMO and MISO are abbreviations for single-input/multiple-output and multiple-input/single-output, respectively. These procedures are compared to each other. It is shown that the number of data load in SIMO system-based procedure is a half of that in MISO system-based procedure for two-channel filter banks. The implementation of M-channel filter banks is also discussed.

Space division multiple access (SDMA) is an attractive technique to increase the channel capacity of wireless communication systems. In this paper, we first propose a new process to accomplish SDMA using an adaptive array at a base station receiver of broadband fixed wireless access (FWA) systems. Unlike other methods, the proposed process does not need highly accurate direction-of-arrival (DOA) estimation and is suitable to Directionally Constrained Minimization of Power (DCMP) algorithm in order to serve multiple fixed terminals. A newly modified DCMP with phase only control is proposed as well. The algorithm to control phase weights, uses only the array output power and does not require the complex baseband signals from individual array elements. The pattern measurement results in an anechoic chamber show that the proposed algorithm can direct a null to an interference while maintaining the gain to the desired signal.

Providing results of a series of link-level simulations for a class of spatial and temporal equalizer (S/T-equalizer) is the primary objective of this letter, which is supplemental to this letter's companion article. The S/T-equalizers discussed in this letter have a configuration that can be expressed as the cascaded connection of adaptive array antenna and maximum likelihood sequence estimator (MLSE): each of the adaptive array antenna elements has a fractionally spaced tapped delay line (FTDL), and the MLSE has taps covering a portion of the channel delay profile. Both the desired and interference signals suffer from severe inter-symbol interference (ISI). A major difference of this article from its companion letter is that account is taken of the presence of co-channel interference (CCI). Bit error rate (BER) performance of the S/T-equalizer is presented as a result of the link-level simulations that use field measurement data.

This paper proposes a beam and null simultaneous steering Space-Time Equalizer (S/T-Equalizer). The proposed S/T-Equalizer performs separated S/T-signal processing in order to reduce computational complexity to a practical level. For spatial signal processing, a new Adaptive Array Antenna algorithm is used that combines the beam and null steering concepts. For temporal signal processing, a conventional delayed decision feedback sequence estimation equalizer may be used. The proposed S/T-Equalizer was prototyped, and a series of field tests was conducted using a 5 GHz frequency band to evaluate transmission performances of the proposed system. Results show that the proposed S/T-Equalizer can reduce inter-symbol interference effects while maintaining reasonable signal strength, thereby improving BER performance.

This paper evaluates high-speed broadband packet wireless access in the forward link using coherent Time Division-Orthogonal Frequency and Code Division Multiplexing (TD-OFCDM) by applying time-multiplexed pilot symbol assisted channel estimation and integrating efficient multi-level modulation, hybrid automatic repeat request (ARQ), and code-multiplexing over a 50-100 MHz bandwidth. Computer simulation results first clarify that the common time-multiplexed pilot symbols with the transmit power of 6 dB higher than that of data symbols should be placed at both the beginning and end of a packet, and that the optimum averaging interval of channel estimates in the frequency domain is different according to the delay spread of a channel. Based on these optimized parameters for packet transmission, we show that the orthogonality among the code-multiplexed channels is destroyed due to severe frequency selective (multipath) fading and the accumulation of spread signals using equal gain combining (EGC) in the frequency domain. This degrades the achievable throughput performance especially when employing multi-level modulation and a high coding rate. Consequently, coherent TD-OFCDM with 8PSK data modulation and the convolutional coding of rate R = 2/3 employing sixteen-code multiplexing (spreading factor (SF) is 16) achieves the highest throughput of approximately 105 Mbps at the average received Eb/N0 (signal energy per bit-to-noise power spectrum density ratio) of approximately 24 dB in a 3-path Rayleigh fading channel (rms delay spread, σ= 0.1 µsec). Furthermore, in coherent TD-OFCDM with QPSK and R = 4/5 or 8PSK and R = 1/2, throughput performance greater than 80 Mbps is achieved at the average received Eb/N0 of approximately 20 dB even in a 24-path Rayleigh fading channel (σ= 0.2 µsec).

AAL2 technology, which will be used in 3rd generation mobile communications systems, can be used to efficiently transmit low-bit-rate traffic. Because user connections are multiplexed at virtual-channel connections in AAL2 networks, conventional ATM QoS management, which operates in units of VC connections, may be inadequate for managing the QoS of AAL2 connections. In this paper, we argue that for efficient utilization of network resources, it is advantageous to accommodate AAL2 connections with different QoS conditions in the same VC connection. We present a multiplexing configuration that enables QoS to be controlled at the AAL2-connection level. It works by matching the AAL2-packet-multiplexing timing to the cell-transmission timing. We also address the issue of AAL2-bandwidth management. To calculate the bandwidth, we evaluate the characteristics of multiplexing CPS packets into the ATM cell payload.

This paper proposes and investigates optimum modulation assignment and band allocation scheme according to subband channel status for BST-OFDM system. The proposed system can adaptively optimize modulation assignment and band allocation according to the conditional parameter under independently fading subband channels. Specifically, in this paper only two optimization problems are treated in terms of modulation assignment. At first, an optimization criterion is a total Bit Error Rate (BER) subject to the constraint conditions of a desired total information bit rate under a fixed effective bandwidth. Another optimization problem is the maximization of a total information bit rate to satisfy a desired BER under a fixed effective bandwidth. Knowledge of the subband channel status is assumed to be updated by the feedback information from a receiver. This paper shows that the proposed system can overperform the conventional system in which all subbands employ the same modulation schemes in terms of BER. In addition, it is shown that the proposed system improves the overall information bit rate, which is not accomplishable in the conventional system.

An unwrapping of signal coefficients in transform domain is proposed for applications in which a lossy operation is performed on the coefficients between analysis and synthesis. It is shown that the unwrapping-based modification of signal-to-additive-signal ratio can employ the fact that an implementation of a biorthogonal decomposition is characterized by a mutually orthogonal eigenvectors. An example to illustrate the benefits of the presented approach in lossy image compression applications is shown.

This letter shows the results of a series of link level simulations conducted to evaluate the performances of spatial and temporal equalizers (S/T-equalizers) using field measurement data. The configuration of the spatial and temporal equalizer discussed in this letter can be expressed as a cascade of an adaptive array antenna and maximum likelihood sequence estimator (MLSE): each of the adaptive array antenna elements has a fractionally spaced tapped delay line (FTDL), and the MLSE has taps covering a portion of channel delay profile. Bit error rate (BER) performances of the S/T-equalizers are presented, and performance sensitivity to symbol timing offset is investigated.

The differentiated services (diffserv) architecture has been proposed for implementing scalable service differentiation in the Internet. Expedited forwarding and assured forwarding have been standardized as Per-Hop Behaviors (PHB) in diffserv. Assured forwarding can be utilized to realize the service, which provides each user with a minimum guaranteed rate and a fair share of the residual bandwidth. We call it guaranteed rate (GR) service. With GR service, each packet for flow i is marked in or out based on comparison between the sending rate and the minimum guaranteed rate. When congestion occurs in networks, out packets are dropped more aggressively than in packets. Recently, several fair queuing schemes have been proposed for core stateless networks. They can achieve fairer bandwidth allocation than random early detection (RED). However, there have not been any studies that consider in/out bit usage to support GR service. This paper proposes how to extend the schemes that have been proposed for core stateless networks to allow the support of in/out bit usage. We present the performance of one of the extended schemes and compare the scheme to RED with in/out bit (RIO) in terms of fair bandwidth allocation.