Alamouti proposed a very attractive transmit diversity technique which ensures orthogonality across two transmit antennas. This technique alone, however, offers no coding gain. In this work, powerful binary turbo codes are combined with Alamouti's diversity technique to achieve a coding gain on top of the diversity gain. Performance analysis on the combined scheme is presented and optimum turbo codes with transmit diversity on fading channels are proposed. Simulation results are shown to illustrate the improvement this scheme can offer.

In this paper, we propose a new approach to the adaptive MLSE receiver, which is based on the delay estimation of the paths in the fading channel. The path delays are estimated by using the known training sequence, and based on this estimation the proposed MLSE tracks not the T-spaced equivalent channel but the variations of each path in the frequency-selective channel directly. It will be shown through computer simulations that the proposed MLSE can improve the performance of the conventional MLSE receivers, when the number of paths is small.

This paper deals with a cellular system based on Code Division Multiple Access (CDMA) and investigates the performance of Signal-to-Interference (SIR)-based Closed Loop-Power Control (CLPC) schemes taking into account errors on the feedback channel that conveys the power control command from the base station to the mobile terminals. We have evaluated both the distribution of the received power at the base station and the optimum control step size that minimizes the Control Error (CE) standard deviation, a useful measure of the CLPC performance. The impact of interference variations has been deeply investigated for different mobility scenarios and for different feedback channel error conditions.

A method for estimating propagation characteristics is described that uses the characteristics of pilot-data-inserted orthogonal frequency division multiplexing (OFDM) signal and is suitable for high-mobility OFDM transmission scheme. Several pilot data are inserted periodically along the frequency axis before the inverse fast Fourier transformation (IFFT) process in the transmitter. At the receiver, the received OFDM signal is correlated with a prepared distinctive OFDM signal in which several pilot data are inserted in the same positions as in the transmitted OFDM symbols and zeros are inserted in the other positions. The propagation characteristics can be estimated precisely and used to cancel any interference caused by delayed waves. Computer simulation shows that this method can estimate the propagation characteristics, which can then be used to cancel the interference caused by delayed waves before the FFT at the receiver under fast multipath fading conditions.

This paper considers combining receptions with multiple receive antennas for space time coded MPSK signals over correlated Rayleigh fading channels. For the system with dual-antenna at receiver, a new transform is proposed, which can convert the correlated fading signals into uncorrelated ones. With the results obtained by using the proposed transform, the equivalent selective combining (SC) reception and maximum likelihood (ML) reception are presented. Theoretical analysis shows that ML reception has better performance than SC reception in terms of bit error rate. For the system with triple antenna at receiver, the simulation results are presented by using Monte Carlo method. All the results show that compared to using a receive antenna, a considerable signal to noise ratio gain can be obtained by using multiple receive antennas when the correlation coefficients among the receive antennas is not too high.

We propose a subchannel power control scheme in the OFDM system, which transmits data with a variable power level for each subchannel based on the received SNR. The OFDM system, employing the D-QPSK modulation and the proposed subchannel power control with a grouping coefficient equal to 3, gives about 2.3 dB gain in E_b/N₀ comparing with the conventional OFDM system, under the two-ray multipath channel with the mean value of the second-ray's attenuation coefficient equal to 0.25, for the required BER equal to 10^-5.

This paper proposes a radio repeater, cell enhancer (CE), that targets 5-GHz broadband wireless access systems to improve the coverage probability without the need to establish a new access point (AP). The CE adopts a non-regenerative repeating scheme to transfer signals and implements two novel approaches, timing control and gain control, to apply to the target systems. By monitoring the control signals broadcast from the AP, the CE behaves as an AP using the same frame timing and transmitting power level, but using a second frequency channel. Thus, the CE can extend the coverage area of one AP. It appears that, however, in the orthogonal frequency division multiplexing (OFDM) system, over two hops with non-regenerative repeating, the additive effect of multipath fading from the two paths results in more violent subcarrier fluctuations and increased delay spread. Computer simulations in multipath fading environments derive the required CNR values for each path, which are required when the CE is installed in the field. In addition, we clarify that multiple CEs can use the same second frequency and provide better coverage with useful macro diversity gain in 5-GHz indoor environments.

This paper addresses a classic question about whether transmit power control (TPC) can increase the spectrum efficiency of a TDMA system and an FDMA cellular system as in the case of a DS-CDMA cellular system. Two types of TPC schemes are considered; one is slow TPC that regulates the distance dependent path loss and shadowing loss, while the other is fast TPC that regulates multipath fading as well as path loss and shadowing loss. In addition to TPC, antenna diversity reception is considered. The allowable interference rise factor χ, which is defined as the interference plus background noise-to-background noise power ratio, is introduced. The simple expressions for the signal-to-interference plus background noise power ratio (SINR) at the diversity combiner output using maximal-ratio combining (MRC) are derived to obtain the reuse distance by computer simulations. The impact of joint use of TPC and antenna diversity reception on the spectrum efficiency is discussed. It is found that the joint use of fast TPC and antenna diversity is advantageous and larger spectrum efficiency can be achieved than with no TPC. On the other hand, the use of slow TPC is found advantageous only for small values of standard deviation of shadowing loss; however, the improvement in the spectrum efficiency is quite small.

This paper presents the analysis of integrated voice and data cellular networks with channel borrowing. Our considered system gives higher priority to handoff calls over new calls from users' point of view and reflects each characteristics of voice and data traffic types. Data handoff calls can wait in a queue while they are in handoff areas if there are no channels available. Voice handoff calls can borrow at most l channels from data calls if there are no idle channels upon their arrivals. We mathematically model this system by applying queueing theory. Then, we analyze its performance to derive the forced termination probability of data handoff calls, the blocking probabilities of the new and handoff calls of voice and data, and the Laplace Stieltjes transform for the distribution of waiting time in a queue. In numerical results, the analytical results for the mean waiting time of data handoff calls are compared with the simulation results to validate our analytical approach. Our system is also compared with the system where channel borrowing cannot be allowed (nonborrowing system) with respect to the blocking probabilities of the new and handoff calls of voice and data, the forced termination probability of data handoff calls, the mean and the coefficient of variation of the waiting time of data handoff calls.

We investigated the use of the Wireless 1394 standard in an intra-vehicle environment. Wireless 1394 services are expected to be used both in homes and in vehicles, however the installation of twisted wire pairs in a car is difficult. In a vehicular environment, there is a problem of interference from nearby vehicles using the same frequency. In this paper, we examined the above problem of interference for vehicles using Wireless 1394 equipments, and measured the propagation characteristics between a transmitter in one vehicle and a receiver in another vehicle. We developed a mitigation method, based on the use of directional antennas as a solution to the problem of interference.

A closed-form solution of mobile location can be obtained by minimizing the norm of the error vector of a set of linear equations in spherical interpolation (SI) method. However, it assumes that the intermediate variables are independent though they are related by a quadratic equation. To give an improved position estimate, we use this relationship to help SI method and a new location method is proposed based on the approximate linearization of spherical intersecting constraint. Simulation results for line-of-sight and non-line-of-sight situations show that the proposed method performs significantly better than SI and Chan's method, especially for the cases where large bias and large standard deviation exist in range difference measurements.

We consider equalizer initialization problems when the transmitted symbol rate is higher than the available channel bandwidth. In this case, the coefficients of an adaptive equalizer in the receiver can be updated only once per a predefined symbol period, requiring unacceptably long training time. The training time can be reduced significantly if the equalizer begins the training process from a properly initialized condition. In this letter, a fast initialization method is analytically designed for a minimum mean squared error (MMSE) type equalizer. Finally, the initialization performance is verified by computer simulation.

This letter is concerned with a performance analysis of a VPG DS/CDMA acquisition system employing a reference filter based on the statistical evaluation of the decision threshold. The probabilities of detection and false alarm are derived, and the mean acquisition time is evaluated as a measure of the system performance. From the results, it is shown that in the performance analysis of the parallel acquisition system with reference filtering, the statistical evaluation of the decision threshold seems more appropriate than the approximation of the decision threshold adopted in other acquisition schemes.

Blind adaptive channel identification of communication channels is a problem of important current theoretical and practical concerns. Recently proposed solutions for this problem exploit the diversity induced by antenna array or time oversampling, leading to the so-called, second order statistics techniques. Adaptive blind channel identification techniques based on a off-line least-squares approach have been proposed but this method assumes noise-free case. The method resorts to an adaptive filter with a linear constraint. This paper proposes a new approach based on eigenvalue decomposition. Indeed, the eigenvector corresponding to the minimum eigenvalue of the covariance matrix of the received signals contains the channel impulse response. And we present a adaptive algorithm to solve this problem. The performance of the proposed technique is evaluated over real measured channel and is compared to existing algorithms.

The circular decoding algorithm for tail-biting convolutional codes is executed using a fixed number of computations and is suitable for DSP/ASIC implementations. This letter presents the performance and complexity trade-off in the circular decoding algorithm using an analytic bound on the error probability. An incremental performance improvement is shown as the complexity increases from O(L) to O(L+10K) where L is the length of the decoding trellis and K is the constraint length. The decoding complexity required to produce the maximum-likelihood performance is presented, which is applicable to many codes of practical interest.

It is known that MUSIC and ESPRIT algorithms can estimate simultaneously both the instantaneous Direction of Arrival (DOA) and the instantaneous Angular Spread (AS) in multiple scattering environments. These algorithms use the Extended Array Mode Vector (EAMV) with complex angle. The previous work evaluated the performance of those algorithms by comparing the estimated DOA and the estimated AS with the DOA and the AS given in the EAMV, which uses the first-order approximation. Thus, this evaluation method has not clearly reflected the estimation accuracy of MUSIC and ESPRIT. This paper presents the joint estimation performance of MUSIC and ESPRIT by introducing the criteria for evaluation. For this, the spatial signature (SS) is reconstructed from the estimates of the DOA and the AS, and compared to the true SS in the meaning of data fitting.

We propose two novel blind LMS algorithms, called exponential step size LMS algorithms (ES-LMS), for adaptive array antennas with fast convergence speeds. Both of the proposed algorithms are much better at tracking signal sources than the conventional LMS algorithms. In addition, they require neither spatial knowledge nor reference signals since they use the finite symbol property of digital signal. Computer simulations verify performances of the two proposed algorithms.

This letter investigates sidelobe levels of a two-bit digital phased array composed of a small number of elements. Among several phase shifter designs applicable to phased arrays, a two-bit design needs the least number of circuit elements so that the development and manufacturing need the lowest cost. Now the following questions arise. Is a two-bit phased array practical? How low can its sidelobe level be reduced? To answer the questions, three methods are tried to reduce the sidelobe level of a uniformly-excited linear array of isotropic elements. The methods are the quadratic-phase feed method, the partially randomizing method of periodic phase errors, and the genetic algorithm (GA) approach. Among the methods, the quadratic-phase feed method provides the lowest sidelobe level around -12.5 dB - -13.2 dB in the steering angles from 0 to 48 degrees for a 21-element, half-wavelength spacing array, and -11.2 dB - -13.0 dB in the steering angles from 0 to 30 degrees for an 11-element, 0.6-wavelength spacing array. Although it depends on the system requirement, these values would be acceptable in some applications, hence a two-bit phased array designed properly may be practical in an actual system.

In this paper, we propose a new consolidation algorithm called the Selective Backward Resource Management (BRM) cell Feedback (SBF) algorithm. It achieves a fast response and low consolidation noise by selectively forwarding BRM cell from the most congested branch to the source instead of waiting from all branches. Mathematical models are derived to quantitatively characterize the performance, i.e. the response time and ACR of the source, of SBF and previously proposed algorithms. The interoperation of consolidation algorithms in point-to-multipoint available bit rate (ABR) is investigated. We address response time, consolidation noise and the effect of asymmetrical round trip delay (RTD) from branch point to destinations aspects. All combinations of four different consolidation algorithms are interoperated in both local/metropolitan area network (LAN/MAN) and wide area network (WAN) configuration. By a simulation method, we found that the consolidation algorithm used at the uppermost stream branch point, especially in WAN configuration, plays an important role in determining the performance of the network. However, consolidation algorithm used at the lower stream branch point affects the network performance insignificantly. Hence, in order to achieve a good and effective performance of the consolidation algorithms interoperated network, a fast response with low consolidation noise algorithm should be used at the uppermost stream branch point and a simple and easy to implement algorithm should be used at the lower stream branch point.

Progress in the fields of broadband access networks and information appliances has led to the introduction of a new network domain called Home Network. In 1999, HomePNA 2.0 using phone lines was proposed, and we believe it is one of the most promising solutions, because of its cost-effectiveness. However, it is not able to guarantee the QoS due to the adaptation of the mature IEEE802.3 CSMA/CD technology which is used for Ethernet. In light of this, we propose and evaluate a new MAC protocol for the Home Network called the HomeMAC that provides guaranteed QoS for appliances and PCs. HomeMAC features a hybrid CSMA/CD-Timed Token protocol which combines the CSMA/CD with timed token protocol and transmits real-time traffic based on the QoS Level Table (QLT) for guaranteeing QoS. In the HomeMAC, there are two different transmission modes, namely, the CSMA/CD Mode when there is no real-time traffic, and the Timed Token Mode when there is real-time traffic taking place. By dynamically switching the transmission mode between CSMA/CD Mode and Timed Token Mode in accordance with the different kinds of traffic, the hybrid protocol provides low delay, low jitter, and low loss rate to multimedia appliances such as TVs, DVDs, and PCs. Moreover, by providing flexible bandwidth allocation based on QLT, the HomeMAC can serve high QoS whole covering entire offered load.

In order for a service discipline to be used for guaranteed service networks at very high speed, its overall implementation must be scalable while it provides as wide a network schedulability region as possible. From this point of view, GPS-based service disciplines provide a narrow network schedulability region while EDF-based disciplines suffer from the implementation complexities of rate-controllers and admission control. Alternatively, although service disciplines based on service-curves can provide a wider network schedulability region than GPS-based and EDF-based disciplines, they may have even worse implementation complexities than EDF-based disciplines. In this paper, we propose to employ a service discipline based on our specific service-curves. We show that our service discipline has comparable implementation complexity to GPS-based disciplines while providing the same wide network schedulability region that EDF-based disciplines can provide. In fact, this service discipline is an SCED service discipline proposed in [14]. However, our specific service-curves provide the SCED service discipline with the same network schedulability region that EDF-based disciplines can provide, O(1) complexity for deadline calculation, and O(N) complexity for admission control where N is the number of sessions.

The advances in services using the present Internet mean that there will be increasing demand for Video on Demand (VoD) on the Internet in the near future. However, because of the best-effort characteristics of the Internet, it is important to suppress the degradation of communication quality caused by packet dropping when Internet traffic is congested. This paper focuses on MPEG transmission over the Internet, and suitable control mechanisms are established for an acceptable Quality of Service (QoS) improvement through detailed evaluation. Packets are classified using a frame-based scheme. The server applies the proposed End-to-End control scheme and shuffles the order of packets to avoid burst dropping, and may omit selected packets belonging to certain frames prior to forwarding. At the intermediate routers, transferred packets are transmitted according to Round Robin (RR) or Weighted Round Robin (WRR) scheduling, and are dropped statistically using selective Random Early Detection (RED) corresponding to frame attributes when there is congestion. We evaluate the proposed performance of transmission method using both computer simulations and empirical measurements of picture quality. The results show that when the traffic volume cannot be estimated in the intermediate routers, the combined use of RR, shuffling and conditional RED is effective, and when the traffic volume can be estimated, the combination of WRR, rate control and RED is effective.

This paper presents a new decoupling circuit for suppressing radiated emissions due to power plane resonance in multilayer printed circuit boards (PCBs). This circuit is based on transmission line theory, and consists of two decoupling capacitors and one power trace. The two capacitors, one mounted on the power pin of an IC and the other mounted on the common power distribution bus in a board, are connected through the power trace. The characteristic impedance of the trace is much higher than the impedance of the capacitors. In addition, the length of the trace between the capacitors is less than 1/4 the effective wavelength for high frequency (e.g., 1 GHz). Tests we performed on simple PCBs confirm that our decoupling circuit suppresses radiated emissions due to power plane resonance.

Measuring traffic dynamics during intervals of a few seconds is important in the management of network performance. If the distribution of average traffic volume during a few seconds is measured, an administrator can manage the quality of the networks using the α percentile of the distribution. We propose a method of estimating the distribution of traffic volume during short intervals, such as a few seconds, by using only traffic information from the management information base (MIB) of routers or switches. This estimation method is based on traffic characteristics that are observed in traffic measurements in actual networks. It imposes little additional load on routers or switches and the computation time required to estimate the distribution is also short. Numerical examples using actual traffic data are also given.

In this paper the authors propose a method for designing the Virtual Private Network (VPN) that guarantees a strict Quality of Service (QoS) over IP networks. The assumed QoS metric is PLP (Packet Loss Probability), and it is guaranteed probabilistically by the provision of an appropriate equivalent bandwidth. We consider two network architectures for constructing VPN, the customer pipe scheme and the Hose scheme, and we present an analytic model to compute the amount of the required bandwidth for the two schemes. Finally, we investigate the validity of the proposition via numerical experiments.

This paper proposes three-phased traffic conditioner (3PTC) to be installed at edge routers in Differentiated Services (DiffServ) networks. 3PTC ensures that Assured Service (AS) flows are supplied with the throughput assurance, which stems from alleviating the impact of the size of TCP reserved rate, UDP/TCP interaction, Round Trip Time (RTT) and number of microflows. 3PTC is composed of token bucket phase, writing probability (WP) calculation phase and queue management phase. Computer simulation results show that 3PTC guarantees throughput assurance and provides end users with expected service levels.

Multicast is an efficient way to send messages to a group of members. It is becoming the basis for a number of applications, such as teleconferencing, news groups, and on-line games. Security is one of the main issues in realizing multicast communications. A working group within IETF dedicated to multicast security has been formed and RFCs and working drafts concerning multicast security are proposed. This letter analyzes the security of a scheme proposed in [1] for securely establishing a shared, secret key in a large, dynamic group. We show that it fails to provide forward and backward security.

A novel power spectral density accumulation (PSDA) method for estimating the bandwidth of the clutter spectra is proposed, based on a priori knowledge of the shape of the clutter spectra. The comparison of the complexity and the performance between the PSDA method and the general ones is presented. It is shown that the PSDA method is effective for the short-time clutter data in the practical application.

In positioning systems NLOS (Non-Line of Sight) errors always cause remarkable positive bias and directly increase range measurement errors. In this paper, a new method is proposed to calibrate NLOS errors in positioning systems by using the relationship between mean excess delay and delay spread measured at a mobile station. The computer simulations showed that the proposed calibration technique effectively reduces the positioning error caused by urban NLOS environment.