Simulating complex biological models consisting of multiple ordinary differential equations can aid in the prediction of the pharmacological/biological responses; however, they are often hampered by the availability of reliable kinetic parameters. In the present study, we aimed to discover the properties of behaviors without determining an optimal combination of kinetic parameter values (parameter set). The key idea was to collect as many parameter sets as possible. Given that many systems are biologically stable and resilient (BSR), we focused on the dynamics around the steady state and formulated objective functions for BSR by partial linear approximation of the focused region. Using the objective functions and modified global cluster Newton method, we developed an algorithm for a thorough exploration of the allowable parameter space for biological systems (TEAPS). We first applied TEAPS to the NF-κB signaling model. This system shows a damped oscillation after stimulation and seems to fit the BSR constraint. By applying TEAPS, we found several directions in parameter space which stringently determines the BSR property. In such directions, the experimentally fitted parameter values were included in the range of the obtained parameter sets. The arachidonic acid metabolic pathway model was used as a model related to pharmacological responses. The pharmacological effects of nonsteroidal anti-inflammatory drugs were simulated using the parameter sets obtained by TEAPS. The structural properties of the system were partly extracted by analyzing the distribution of the obtained parameter sets. In addition, the simulations showed inter-drug differences in prostacyclin to thromboxane A2 ratio such that aspirin treatment tends to increase the ratio, while rofecoxib treatment tends to decrease it. These trends are comparable to the clinical observations. These results on real biological models suggest that the parameter sets satisfying the BSR condition can help in finding biologically plausible parameter sets and understanding the properties of biological systems.

China is beset by environmental problems. This study focused on addressing China's environmental problems by using a language grid to provide a Japanese environmental education program, "manufacturing soap from waste oil," to Chinese students at home and evaluating their practice. The teaching and work experiments comprised observations of the knowledge-transfer process under a multilingual environment and the students 'work during experimental activities, respectively. The results show that a better training effect was obtained by the family groups who performed both teaching and work experiments than by the student groups who performed the teaching experiment only.

In this paper, an adaptive codebook precoding scheme is proposed for time-varying multiple-input multiple-output (MIMO) channels with feedback delay. The proposed scheme updates its codebook on the basis of the spherical cap codebook (SCC) approach. In contrast with the conventional radius calculation for SCC, the proposed scheme does not need additional feedback of the cap radius or offline radius calculation, but only adapts the radius according to a previously selected codeword. In addition, the Kalman filter using the differential model as its process equation is employed to predict MIMO channels and to select a suitable codeword from the codebook. Since the Kalman filter does not require information on the maximum Doppler frequency, the proposed scheme, which is a combination of the self-adaptive SCC and the Kalman filter, can work well even when the maximum Doppler frequency is not exactly known. Computer simulations under 4-by-4 MIMO channels with 2 data streams and a 6-bit codebook demonstrate that the proposed scheme can improve the system capacity in the same way as the conventional scheme does, which needs exact information on the maximum Doppler frequency in contrast to the proposed scheme. When the different channel model is used, it is shown that the proposed self-adaptive SCC can still provide considerable capacity gain, while the conventional scheme can not do so.

Applications of millimeter-wave (mm-wave) to high mobility wireless communication scenarios such as high speed trains (HSTs) have been discussed. In the HST scenarios, not only phase noise but also Doppler shift should be considered. In previous works, our proposed iterative phase noise compensation method was evaluated with a dynamic channel model with high Doppler shift. The efficacy of the iterative method, employing symbol level decision directed channel estimation (SDDCE), was demonstrated with the dynamic channel model. However, parameters of the channel model need to be obtained further for the HST environments. In this paper, we construct a linear HST environment, and analyse the propagation characteristics of the HST scenario with a ray tracing method at 60 GHz band. With the simulation, we obtain the received power, the K factor of the Rician model, delay spread, and angular spread characteristics of the HST environment. It is shown that the K factor is large when the distance between the transmit (Tx) and receive (Rx) antennas is short, and that when the distance between the Tx and Rx is large, the level of fading becomes large, which is much different from the indoor environment. We also complete the dynamic channel model with the obtained statistical parameters, which can simulate the dynamic channel fluctuation due to the Doppler shift.

OFDM transmission schemes are adopted in the integrated services digital broadcasting-terrestrial (ISDB-T), the downlink of long term evolution (LTE), etc. In most cases, there are not many delayed paths in the propagation environments, i.e., the wireless channels are likely to be sparse. In addition, when the receiver moves rapidly, the accuracy of channel estimation deteriorates significantly. In order to alleviate the deterioration, the iterative channel estimation scheme with the tap selection and the least mean squares (LMS) algorithm has been studied. For further improvement of the channel estimation accuracy, this paper investigates a channel estimation scheme employing the optimization method with L1-norm regularization, called fast iterative shrinkage-thresholding algorithm (FISTA), and proposes an iterative receiver employing such a channel estimation scheme for OFDM systems. For evaluating the performance of the proposed scheme, computer simulations are conducted under the condition of ISDB-T with the scattered pilots (SP)-OFDM signal. It is shown that the proposed method has much better accuracy in the estimation of the sparse channel impulse response than the conventional method.

Recent demand for capacity increase in mobile communications urges the development of both multiple- input multiple-output (MIMO) and small cells. However, overlapping coverage areas between neighboring small cells results in interference-limited networks, where the capacity of the network is severely degraded without superior intercell interference management (IIM) techniques. As one of the superior IIM techniques, the power control intercell interference coordination (ICIC) optimizes downlink transmit powers in the network. This paper proposes an IIM scheme consisting of both neural networks (NNs) power control on the transmitter side and interference cancellation (IC) on the receiver side. Computer simulations examine networks of MIMO systems with the power optimization using some ICIC algorithms: NN, the greedy search, the belief propagation (BP), and the maximum power, combined with IC on the receiver side. In addition, the deep learning, a breakthrough technique for NN with multi-layer structures, is also applied to mobile communications. The results show that the performance of NN is very close to that of the greedy search and superior to that of BP. Complexity of NN is much less than that of BP, and thus NN is suitable for IIM. It is also demonstrated that employing IC provides high capacity gain.

As a signal detection method for multiple-input multiple-output (MIMO) communications, this paper proposes multi-stream constrained search (MSCS) that achieves very good trade-off between computational complexity and bit error rate (BER) performance. The proposed method sets a minimum mean-squared error (MMSE) detection result to the starting point. From this point, MSCS searches for signal candidates in multi-dimensions of the noise enhancement from which the MMSE detection suffers. In the search, some streams of the signal candidates are fixed at constellation points. Among the obtained signal candidates, the detected signal is selected as the one that minimizes the log likelihood function. Furthermore, this paper proposes stream selection-MSCS (S-MSCS) that selects the constrained streams under the criterion of small equivalent amplitudes of channels caused by the MMSE detection. Setting the number of patterns of constrained streams to just one can reduce complexity, and selecting the constrained streams on the basis of the equivalent amplitude can maintain excellent BER performance. Computer simulations under 8 × 8 MIMO channel conditions with 16QAM demonstrate that S-MSCS can maintain only 0.5 dB degradation of the average BER performance from the maximum likelihood detection (MLD), while reducing the computational complexity to about one third of that of QR decomposition with M algorithm (QRM)-MLD.

The performance of 30 Gbps super high bit rate mobile communications is evaluated by computer simulation using channel data collected in 11 GHz band 24×24 MIMO outdoor propagation experiments, and the feasibility of 11 GHz band 30 Gbps transmission is verified. To achieve the super high bit rate mobile communications, 10 Gbps transmission using 11 GHz band 8×16 MIMO has been verified in outdoor transmission experiments. In addition, channel measurement and analysis have been conducted in 11 GHz band 24×24 MIMO radio propagation experiments. Although 24×24 MIMO transmission is expected to achieve a bit rate exceeding 30 Gbps, transmission experiments have not yet been performed due to the hardware limitations. In this paper, computer simulations based on 24×24 MIMO-OFDM eigenmode transmission are conducted by utilizing channel data measured using an 11 GHz band 24×24 MIMO channel sounder. This paper shows that throughput exceeding 30 Gbps is achieved in 11 GHz band mobile environments, and clarifies the requirements for the average signal-to-noise ratio, channel conditions, and accuracy of channel state information to achieve 30 Gbps throughput over a real 11 GHz band 24×24 MIMO channel.

This paper proposes an automatic prosodic labeling technique for constructing speech database used for speech synthesis.In the corpus-based Japanese speech synthesis, it is essential to use annotated speech data with prosodic information such as phrase boundaries and accent types.However, manual annotation is generally time-consuming and expensive.To overcome this problem, we propose an estimation technique of accent types and phrase boundaries from speech waveform and its transcribed text using both language and acoustic models.We use conditional random field (CRF) for the language model, and HMM for the acoustic model which has shown to be effective in prosody modeling in speech synthesis.By introducing HMM, continuously changing features of F0 contours are modeled well and this results in higher estimation accuracy than conventional techniques that use simple polygonal line approximation of F0 contours.

This paper proposes interference suppression schemes by linear combining for wireless multiuser relay communications. Interference from base stations and relays in neighboring cells degrades bit error rate (BER) performance of mobile stations (MSs) near cell boundaries. To suppress such interference for half-duplex relay systems, the proposed methods linearly combine received signals of the first and second phases at MS. Without channel state information (CSI) feedback, weight coefficients for the linear combining are first evaluated under the minimum mean-squared error (MMSE) criterion and then estimated by the recursive least-squares (RLS) algorithm. The MMSE combining requires information on preamble symbols of all MSs for channel estimation whereas the RLS-based linear combining requires only information on those of the target MS. In addition to the preamble symbols, the RLS algorithm can use detected symbols, which performs the decision-directed estimation. Computer simulations for orthogonal frequency-division multiplexing (OFDM) transmission under two-cell and frequency selective fading conditions are conducted. It is demonstrated that the RLS-based linear combining with the decision-directed estimation is superior to the RLS-based linear combining using only the preamble and can slightly outperform the MMSE combining with imperfect CSI under low average Eb/N0when the number of preamble symbols is as small as four.

This paper proposes an approximate block diagonalization (BD) method that does not require feedback of channel state information (CSI) by using the second-order statistics of channels for multiuser MIMO mobile communications. On the assumption that an incidence angle (angle-of-arrival) distribution in the uplink channel is the same as an angle-of-departure distribution in the downlink channel, the proposed scheme estimates the autocorrelation matrix of the downlink channel from the average and variance of incidence angles in the uplink. Since the proposed scheme uses the estimate of the autocorrelation matrix of the downlink channel, it performs eigenvalue decomposition of the estimated autocorrelation matrix whereas the conventional BD precoding performs singular value decomposition of the channel matrix. To verify the effectiveness of the proposed scheme, computer simulations are conducted. It is shown that the proposed scheme, which does not need CSI feedback, is little inferior in the channel capacity to the conventional BD precoding that requires CSI feedback.

This paper presents detailed results of 11 GHz band outdoor transmission experiments employing 8 × 16 MIMO-OFDM for 10 Gbps super high bit rate mobile communications. Super high bit rate mobile communications have been studied for future mobile communications, and to verify the feasibility, outdoor transmission experiments were performed. A mobile station (MS) with 8 transmitter antennas traveled along a measurement course while a base station (BS) with 16 receiver antennas stored the received signals, and then the throughput performance levels were evaluated by demodulating them in an off-line mode. This paper introduces specifications and a hardware configuration for the 11 GHz band 8×16 MIMO-OFDM experimental system with a signal bandwidth of 400 MHz. In addition, it presents the SNR distribution and delay spread that are calculated from the received signals in the measurement course used in the outdoor experiments. The experimental results show that for 11.8 Gbps transmission with 8 streams, 64QAM, and the coding rate of 3/4, throughput of greater than 10 Gbps is achieved in an 11 GHz band outdoor mobile environment.

Joint signal detection and channel estimation based on the expectation-maximization (EM) algorithm has been investigated for orthogonal frequency-division multiplexing (OFDM) mobile communications over fast- fading channels. In order to make the signal detection suitable for the iterative EM-based receiver with multiple antennas, this paper proposes spatial removal from the perspective of a message- passing algorithm on factor graphs. The spatial removal performs the channel estimation of a targeted antenna by using detected signals that are obtained from the received signals of all antennas other than the targeted antenna. It can avoid the repetitive use of unreliable received signals for consecutive signal detection and channel estimation. Computer simulations under fast-fading conditions demonstrate that appropriate application of the spatial removal can exploit such a removal effect and the spatial diversity, resulting in improvement of the packet error rate (PER).

ABSTRACT We develop an efficient hard detector for multiple‐input multiple‐output (MIMO) channels, which adaptively combines maximum‐likelihood detection (MLD) and minimum‐mean‐square error with a successive interference canceler together. Unlike the conventional joint combination scheme, which may suffer from considerable degradation in bit‐error‐rate (BER) performance over correlated channels and where only one data stream is detected by MLD, our proposed scheme adaptively controls the number of data streams to be detected by MLD based on an analytical characterization of reliability for the detection. Simulation results illustrate that near‐optimal BER performance can be obtained at much lower computational complexity by the proposed method as compared with existing techniques, regardless of the spatial correlation of the MIMO channels. Copyright © 2012 John Wiley & Sons, Ltd.

To maintain good transmission performance of orthogonal frequency-division multiplexing (OFDM) mobile communications over fast-fading channels, iterative maximum a posteriori (MAP) receivers that iterate channel estimation and signal detection on the basis of the expectation-maximization (EM) algorithm have been investigated. In order to make such a MAP receiver more robust against time-variant channels, this paper derives channel estimation with subcarrier removal from the perspective of a message-passing algorithm on factor graphs. The subcarrier removal estimates the channel frequency response by using the detected signals of all subcarriers other than that of a targeted subcarrier. This modification can avoid the repetitive use of incorrectly detected signals for the channel estimation. Computer simulations under fast-fading conditions demonstrate that the EM-based MAP receiver performing the subcarrier removal can improve the packet error rate (PER) drastically.

Super high bit-rate mobile communications have been investigated to achieve more than 10 Gbps bit-rate. This paper studies an experimental system that can achieve 5 Gbps throughput by using 11 GHz band radio frequency (RF) circuits and 4×4 MIMO-OFDM with 400 MHz wide bandwidth, of which feasibility is verified. The experimental system consists of (i) 11 GHz band RF circuits, (ii) FPGA boards with 800 MHz sampling DAC or ADC, and (iii) CPU boards that perform MIMO-OFDM transmission and reception processing in offline mode. The RF circuits employ a direct conversion method. Since IQ imbalance and phase noise in the RF circuits degrade transmission performance, this paper compensates for them by digital signal processing. The experimental system evaluates the transmission performance in 5 Gbps 4×4 MIMO-OFDM employing turbo detection, and it is shown that performance degradation of the experimental system to the simulation results can be limited to less than 1 dB by the compensation method for imperfection of the RF circuits. In addition, it is clarified that the turbo detection with two iterations can improve 6.0 dB at SNR to achieve 5 Gbps throughput.

This paper proposes a low-complexity signal detection algorithm for spatially correlated multiple-input multiple-output (MIMO) channels. The proposed algorithm sets a minimum mean-square error (MMSE) detection result to a starting point, and searches for signal candidates in multi-dimensions of the noise enhancement from which the MMSE detection suffers. The multi-dimensional search is needed because the number of dominant directions of the noise enhancement is likely to be more than one over the correlated MIMO channels. To reduce computational complexity of the multi-dimensional search, the proposed algorithm limits the number of signal candidates to O(NT) where NTis the number of transmit antennas. Specifically, the signal candidates, which are unquantized, are obtained as the solution of a minimization problem under a constraint that a stream of the candidates should be equal to a constellation point. Finally, the detected signal is selected from hard decisions of both the MMSE detection result and unquantized signal candidates on the basis of the log likelihood function. For reducing the complexity of this process, the proposed algorithm decreases the number of calculations of the log likelihood functions for the quantized signal candidates. Computer simulations under a correlated MIMO channel condition demonstrate that the proposed scheme provides an excellent trade-off between BER performance and complexity, and that it is superior to conventional one-dimensional search algorithms in BER performance while requiring less complexity than that of the conventional algorithms.

This article describes the development and application of a modified grouping genetic algorithm (GGA) used to identify sets of optimal ambulance locations. The GGA was modified to consider a special case with only two groups, and the reproduction and mutation schemes were modified to operate more efficiently. It was applied to a case study locating ambulances from a fixed set of alternative locations. The sites were evaluated using data of emergency medical services (EMS) calls summarised over census areas and weighted by network distance. Census areas serviced by the same selected location defined ambulance catchments. The results indicated alternative sites for ambulances to be located, with average EMS response times improved by 1 min 14 s, and showed the impacts of having different numbers of ambulances in current locations and in new locations. The algorithmic developments associated with the modified GGA and the advantages of using census areas as spatial units to summarise data are discussed.

This paper proposes a new coherent detector that exploits the real zero (RZ) concept for signal recovery. The detector recovers the complex envelope consisting of in-phase (I) and quadrature (Q) components of linear quadrature amplitude modulation (QAM). The received signal before amplification is processed by RZ conversion, after which the converted signal can be amplified by a severely distorted amplifier. The RZ conversion combines the modulated received signal with a sinusoidal wave whose frequency is slightly outside the modulated frequency band, and the resultant signal is amplified to a saturated level. Next, the IQ detection applies the RZ concept to the IQ signal recovery. It utilizes a time to digital converter (TDC) for RZ timing estimation. A linear interpolation type TDC is introduced. Computer simulations demonstrate the effectiveness of the proposed detector. It is shown that error vector magnitude (EVM) of the recovered complex envelope is around -30 to -40 dB for a narrowband signal.

This paper proposes a precoding scheme for downlink multiuser MIMO-OFDM systems. The proposed precoding employs the minimum bit error rate (BER) criterion and estimates precoding matrices to minimize total BER of mobile stations by the steepest descent algorithm. As the cost function of the proposed scheme, an upper bound of the total BER is derived from the pairwise error probability (PEP) and is averaged with respect to channel state information (CSI) errors. Thus, the proposed scheme can be robust to imperfect CSI. Computer simulations under a frequency-selective fading condition demonstrate that the proposed precoder is more robust to the CSI errors than the zero-forcing (ZF) precoder, and that it is superior in BER to the conventional scheme.

This paper proposes an iterative receiver employing multiuser detection (MUD) and channel estimation for uplink MIMO-OFDM interleave-division multiple access (IDMA). IDMA can perform low-complexity MUD by employing a low-rate channel code and an individual interleaver for each user, and is expected to improve spectrum efficiency in mobile communications. However, an excellent channel estimator has not been proposed in the uplink MIMO-OFDM IDMA. This paper proposes the iterative receiver that repeats a joint processing of MUD and channel estimation by exploiting log-likelihood ratios of coded bits (bit LLRs) which channel decoders of all users provide. The receiver employs soft decision-directed channel estimation (SDCE) using the bit LLRs during data symbols, in addition to initial channel estimation (ICE) using known preambles. To improve an accuracy of the channel estimation, it performs tap selection (TS) that extracts only dominant paths from a channel impulse response estimated by ICE or SDCE. Moreover, this paper evaluates transmission performances of the proposed receiver, and shows that the receiver can achieve an excellent performance in 4-by-4 MIMO-OFDM IDMA with four users.

This paper proposes a peak-to-average power ratio (PAPR) reduction method that maintains an effect of linear precoding by block diagonalization (BD) for multiuser (MU) MIMO-OFDM systems. In the downlink MU-MIMO-OFDM, BD orthogonalizes multiple signals of all users by the linear precoding using channel state information, but the transmitted signal still has high PAPR due to OFDM characteristics. Therefore, BD suffers from waveform distortion caused by a nonlinear transmit power amplifier, especially when the number of transmit antennas is set large enough for the orthogonalization. This paper proposes BD transmission selected mapping (BD-SLM) that can reduce PAPR while maintaining the BD effect. BD-SLM performs the phase shift to modulation signals of all users before the linear precoding. From several phase sequences, it selects a phase sequence that minimizes the peak of the time-domain signals at all transmit antennas. Computer simulations demonstrate that BD-SLM can drastically reduce PAPR in 16 × 4 MIMO-OFDM with four users, and that it can alleviate the performance degradation even when the power amplifier causes nonlinear distortion.

This paper proposes a low-complexity algorithm to calculate log likelihood ratios (LLRs) of coded bits, which is necessary for channel decoding in coded MIMO-OFDM mobile communications. An approximate LLR needs to find a pair of transmitted signal candidates that can maximize the log likelihood function under a constraint that a coded bit be equal to either one or zero. The proposed algorithm can find such a pair simultaneously, whereas conventional ones find them individually. Specifically, the proposed method searches for such candidates in directions of the noise enhancement with the MMSE detection as a starting point. First, an inverse matrix which the MMSE weight matrix includes is obtained and then the power method derives eigenvectors of the inverse matrix as the directions of the noise enhancement. With some eigenvectors, one-dimensional search and hard decision are performed. From the resultant signals, the transmitted signal candidates to be required are selected on the basis of the log likelihood function. Computer simulations with 4×4 MIMO-OFDM, 16QAM, and a half-rate convolutional code demonstrate that the proposed algorithm requires only 1.0 dB more Eb/N0than that of the maximum likelihood detection (MLD) in order to achieve packet error rate of 10-3, while reducing the complexity to about 0.2% of that of MLD.

This paper proposes methods that can reduce peak- to-average power ratio (PAPR) while maintaining performance improvement by linear precoding for the eigenmode MIMO- OFDM transmission. In the eigenmode MIMO-OFDM system, a transmitter performs linear precoding using channel state information (CSI), and thus excellent transmission performance can be achieved. However, the transmitted signal still has high PAPR because of OFDM characteristics. To reduce such PAPR, this paper enhances selected mapping (SLM) and partial transmit sequence (PTS) which are known as PAPR reduction methods for OFDM. The enhanced methods, which are referred to as eigenmode transmission SLM (EM-SLM) and eigenmode transmission PTS (EM-PTS), can be applied to the eigenmode MIMO- OFDM without any performance degradation. Computer simulations demonstrate that in 4times4 MIMO-OFDM, the proposed methods can drastically reduce PAPR, and thus they can alleviate performance degradation due to nonlinear amplification.

This paper proposes an iterative OFDM millimeterwave receiver employing low-complexity decision-directed phase noise compensation (DD-PNC) to alleviate degradation due to the phase noise. High bit-rate OFDM transceivers based on the single-chip Si RF-CMOS IC technology in the 60-GHz millimeter-wave band have been extensively studied for wireless personal area network (WPAN) systems, and the relatively large phase noise in the phase locked loop (PLL) synthesizer severely degrades transmission performance. The proposed OFDM receiver iterates DD-PNC and decision-directed channel estimation (DDCE) by exploiting the output of the channel decoder. DDPNC estimates the phase noise each sampling time by using the decoder output, and then it removes the estimate from a time-domain received signal. In addition, DDCE estimates a channel impulse response by using the compensated received signal. Computer simulations demonstrate that in the 64QAM modulation with the coding rate of 3/4, the proposed receiver with DD-PNC and DDCE can perfectly remove the phase noise of -85 dBc/Hz at 1 MHz offset, and that it can alleviate the degradation of the channel estimation due to the phase noise.

This paper applies iterative multiuser detection employing new channel estimation to multicarrier interleave- division multiple access (MC-IDMA), known as OFDM-IDMA, which is expected to improve spectral efficiency in mobile communications. The MC-IDMA transmitter uses both a low-rate channel code and an individual chip interleaver for each user. The MC-IDMA receiver, which this paper investigates, repeats the iterative multiuser detection and soft decision-directed channel estimation (SDCE) by exploiting log-likelihood ratios (LLRs) of the coded bits which the MAP-based channel decoders for all users provide. SDCE estimates channel impulse responses of all users by the LMS algorithm, which aims to minimize the mean squared error between the received signal and its replica. This paper investigates the performance of MC-IDMA employing SDCE and compares it with those of three MC-CDMA techniques. Computer simulations demonstrate that MC-IDMA employing SDCE outperforms time-spread MC-CDMA and frequency-spread MC-CDMA, and that it can achieve almost the same bit error rate performance as chip-interleaved MC-CDMA while requiring lower complexity.

This paper proposes a minimum BER (MBER) based precoder that is robust to imperfect channel state information (CSI) for MIMO-OFDM mobile communications. The proposed MBER precoding aims to minimize BER of the maximum likelihood detection (MLD), on the condition that the transmitter can obtain only imperfect CSI owing to channel estimation and quantization errors of the feedback CSI. The proposed scheme controls its precoding parameters under a transmit power constraint by minimizing an upper bound of BER which is derived from the pairwise error probability and then averaged with respect to the CSI error. Computer simulations demonstrate that the proposed precoding method outperforms a conventional nonrobust MBER precoder and a conventional robust power allocation MBER precoder.

This paper proposes joint maximum a posteriori (MAP) detection and spatial filtering for MIMO-OFDM mobile communications, which can maintain excellent receiver performance even over interference-limited channels. The proposed joint processor consists of a log likelihood generator and a MAP equalizer. The log likelihood generator suppresses cochannel interference by spatially filtering received signals and provides branch metrics of transmitted signal candidates. Using the branch metrics, the MAP equalizer generates log likelihood ratios of coded bits and performs channel decoding based on the MAP criterion. In the first step, the log likelihood generator performs spatio-temporal filtering (STF) of the received signals prior to the fast Fourier transform (FFT) and is referred to as preFFT-type STF. For further improvement, in iterative steps, the generator performs spatial filtering (SF) of the received signals posterior to FFT and is referred to as postFFT-type SF. Estimation of both tap coefficients of the spatial filters and channel impulse responses employs the recursive least squares (RLS) with smoothing. The reason for making a switch from preFFT-type STF into postFFT-type SF is that preFFT-type STF outperforms postFFT-type SF with a limited number of preamble symbols while postFFT-type SF outperforms preFFT- type STF when data symbols can be reliably detected and used for the parameter estimation. Computer simulations demonstrate that the proposed joint processing can achieve excellent BER performance under interference-limited channel conditions and that it can outperform the conventional joint processing of preFFT-type STF and the MAP equalizer.

This paper proposes a new MIMO-OFDM preceding method that minimizes BER of the maximum likelihood detection (MLD). Conventional MIMO precoding methods can approximately minimize BER of the minimum mean square error (MMSE) based detector by using singular value decomposition (SVD) of the channel matrices. However, they cannot minimize BER of MLD because the orthogonalization does not increase the Euclidean distance between a pair of channel-distorted replicas of transmitted signals. To optimize the Euclidean distance effectively, the proposed method controls its precoding parameters by minimizing the upper bound of BER based on the pairwise error. Computer simulations demonstrate that the proposed precoding method outperforms the MMSE precoder and the conventional minimum BER (MBER) precoder that assumes the precoding matrix structure similar to the solution of the weighted MMSE precoder.

This paper proposes low-complexity blind detection for orthogonal frequency division multiplexing (OFDM) systems with the differential space-time block code (DSTBC) under time-varying frequency-selective Rayleigh fading. The detector employs the maximum likelihood sequence estimation (MLSE) in cooperation with the blind linear prediction (BLP), of which prediction coefficients are determined by the method of Lagrange multipliers. Interpolation of channel frequency responses is also applied to the detector in order to reduce the complexity. A complexity analysis and computer simulations demonstrate that the proposed detector can reduce the complexity to about a half, although it suffers a loss of 2.5 dB in Eb/N0at BER of 10-3owing to the complexity reduction when the prediction order and the degree of polynomial approximation are 2 and 1, respectively, with the normalized Doppler frequency of 1.6 times 10-2.

This paper proposes a new channel estimation method for the expectation-maximization (EM) algorithm applied to an OFDM receiver. Conventional schemes using the EM algorithm assume the random walk model as a process equation of a channel impulse response, and thus have insufficient tracking ability to fading fluctuation over fast fading channels. To improve the tracking ability, the proposed channel estimation method employs the differential model having the first and higher order differentials of the channel impulse response with respect to time. Computer simulations under the fast fading condition demonstrate that the proposed method is much superior in packet error rate to the conventional schemes employing the random walk model.

This paper proposes a MIMO-OFDM transmission scheme employing subcarrier-block phase hopping that can reduce peak-to-average power ratio (PAPR) while simultaneously improving transmission performance with low numerical complexity. As a conventional scheme for achieving these objectives, a combination of the enhanced selected mapping (ESLM) and the subcarrier phase hopping for space division multiplexing (SPH-SDM) has been proposed. To reduce the complexity furthermore and to increase feasibility of hardware implementation, the proposed scheme enhances SPH-SDM by introducing subcarrier-block phase hopping based on the partial transmit sequence (PTS). It divides the overall subcarriers into blocks and rotates phases of the complex signals which IFFT generates from the subcarriers of each block. Computer simulations demonstrate that the proposed scheme can drastically reduce PAPR and improve the packet error rate (PER) in comparison with the standard MIMO-OFDM, and that it can achieve almost the same performance as SPH-SDM with ESLM while achieving half as low complexity as that of the conventional one.

This paper proposes a maximum likelihood (ML) detector with spatial-temporal filters prewhitening cochannel interferences for MIMO-OFDM mobile communications. The proposed detector consists of several branch metric generators and an ML detector using metrics which the generators produce. In the branch metric generator, the spatial-temporal filter for received signals suppresses interfering signal components while prewhitening them. Subtracting replica signals from the filter's outputs and squaring the result yield the metrics. Coefficients of the filters and channel impulse responses for the replicas are estimated by using the eigenvalue decomposition (EVD) of an autocorrelation matrix of both the received and transmitted signals. To select appropriate eigenvectors for the branch metric generators, the proposed detector adopts a channel capacity criterion, and avoids prohibitive complexity by using a fast search algorithm. Another problem is that it requires a large amount of computational complexity for channel tracking because it performs parameter estimation using the nonrecursive EVD. To solve such a problem, the recursive EVD is applied, which can track the time-varying fading channel while simultaneously reducing the complexity. Computer simulations demonstrate that the proposed scheme can maintain an excellent BER performance in correlated channels and track the fast fading channel with reduced complexity.

This paper proposes a parallel recursive least square (P-RLS) channel estimator for the iterative maximum a posteriori (MAP) receiver. The targeted system is the low-density-parity-check (LDPC) coded multiple-input-multiple-output (MIMO) and orthogonal frequency-division multiplexing (OFDM) system. The proposed estimator, which can be theoretically derived from the message-passing algorithm, can track a fast fading channel, and allows the parallel implementation of the whole receiver. A simplified version of P-RLS (SP-RLS) that can reduce the computational complexity is also proposed. Compared to the RLS with smoothing and removing (SR-RLS), P-RLS can reduce the computational time by parallelization, and SP-RLS can further reduce the computational time and complexity. Computer simulations show that SP-RLS achieves almost the same packet error rate (PER) performance as that of P-RLS. It also achieves almost the same PER performance as that of SR-RLS with double iterations. Even in this case, the computational time and complexity of SP-RLS are smaller than those of SR-RLS.

This paper proposes novel channel estimation methods for an iterative maximum a posteriori (MAP) receiver. The targeted systems are low-density parity-check (LDPC)-coded multiple-input-multiple-output (MIMO) and orthogonal frequency-division multiplexing (OFDM) mobile communications. By reconsidering the joint processing of the iterative MAP receiver from the viewpoint of the message-passing algorithm in the factor graph, this paper theoretically derives the recursive least squares (RLS) algorithm with smoothing and removing (SR-RLS). The computational complexity of SR-RLS is about two to three times larger than that of the original RLS algorithm. Computer simulations under fast multipath fading conditions show that the MAP receiver using the proposed SR-RLS channel estimator outperforms the one using the conventional RLS channel estimator.

This paper proposes a new blind adaptive equalizer based on maximum-likelihood sequence estimation (MLSE) for frequency selective mobile radio channels. A conventional blind MLSE equalizer with a single fractionally spaced transversal filter can cope with timing offset, but it suffers from a performance degradation due to the ambiguity of blind channel estimation. To avoid this ambiguity, this paper proposes a different type of fractional sampling in which separate symbol-spaced channel estimations are performed in the respective fractional sampling phases. The estimation employs a recursive form using the Moore-Penrose generalized inverse matrix. The equalizer combines the separate channel estimation errors, and provides the sum for the Viterbi algorithm processor as the branch metric, which tremendously reduces the probability that the correct solution is turned into an ambiguous false solution. Computer simulation demonstrates the effectiveness of the proposed equalizer on frequency selective fading channels.

This paper proposes a MIMO-OFDM transmission scheme that combines the subcarrier phase hopping for space division multiplexing (SPH-SDM) with an enhanced selected mapping (ESLM). SPH-SDM randomizes the subcarrier phases within an OFDM symbol and makes subcarrier components of the received signal uncorrelated in order to improve BER performance of a MIMO-OFDM coded system. The phase patterns are adjusted so that they can not only randomize the subcarrier phase hopping but also reduce the peak-to-average power ratio (PAPR). In contrast to conventional PAPR reduction techniques for OFDM such as the selected mapping (SEM), ESLM employs roughly quantized IFFT processing for selecting the phase pattern in order to reduce the numerical complexity, and modulates the pilot subcarriers so as to inform the receiver of the selected phase pattern. Computer simulation shows that SPH-SDM with ESLM can increase the frequency diversity gain by channel coding, while simultaneously reducing PAPR by a suboptimum phase pattern

This paper proposes a suboptimal maximum likelihood detection (MLD) algorithm for multiple-input multiple-output (MIMO) communications. The proposed algorithm regards transmitted signals as continuous variables in the same way as a common method for the discrete optimization problem, and then searches candidates of the transmitted signals in the direction of a modified gradient vector of the metric. The vector enhances components in the gradient that are likely to cause the noise enhancement from which the zero-forcing (ZF) or minimum mean square error (MMSE) algorithms suffer. This method sets the initial guess to the solution by the ZF or MMSE algorithms, which can be recursively calculated. Also, the proposed algorithm requires the same complexity order as that of the ZF algorithm. Computer simulations demonstrate that it is superior in BER performance to conventional suboptimal algorithms of which complexity order is equal to that of ZF.

This paper proposes a maximum likelihood detection (MLD) method for the differential space-time block code (DSTBC) in cooperation with blind linear prediction (BLP) of fast frequency-flat fading channels. The method, which linearly predicts the fading complex envelope, determines the linear prediction coefficients by the method of Lagrange multipliers, and does not use decision-feedback nor require information on channel parameters such as the maximum Doppler frequency in contrast to conventional ones. Computer simulations under a fast fading condition demonstrate that the proposed method with a proper degree of polynomial approximation can be superior in BER performance to a conventional method that estimates the coefficients by the RLS algorithm using a training sequence.

This paper proposes two new types of maximum a posteriori probability (MAP) receivers for multiple-input-multiple-output and orthogonal frequency-division multiplexing mobile communications with a channel coding such as the low-density parity-check code. One proposed receiver employs the expectation-maximization algorithm so as to improve performance of approximated MAP detection. Differently from a conventional receiver employing the minimum mean-square estimation (MMSE) algorithm, it applies the recursive least squares (RLS) algorithm to the channel estimation in order to track a fast fading channel. For the purpose of further improvement, the other proposed receiver applies a new adaptive algorithm that can be derived from the message passing on factor graphs. The algorithm exploits all detected signals but one of targeted time, and can gain a considerable advantage over the MMSE and RLS. Computer simulations show that the first proposed receiver is superior in channel-tracking ability to the conventional receiver employing the MMSE. Furthermore, it is demonstrated that the second proposed receiver remarkably outperforms both the conventional and the first proposed ones.

This paper proposes a new blind algorithm effective for multiuser detection with an adaptive array antenna. The conventional blind algorithm, known as the constant modulus algorithm (CMA), has two major drawbacks: (i) the convergence speed is not sufficiently fast for usual applications in mobile communications, and (ii) the algorithm is very likely to lock on the path with the largest received power, which means the signal with the second largest power can hardly be extracted. This paper introduces the recursive least squares algorithm for CMA (RLS-CMA) in order to speed the convergence up, and additionally introduces the concept of the orthogonal projection into CMA so as to extract signals with weak power. The proposed CMA with orthogonal projection (CMA-OP) sequentially calculates the weight vector of each user under a constraint that the weight vector should be orthogonal to the estimated array response vectors of previously extracted users. Computer simulation demonstrates that the proposed scheme can operate properly in the Rayleigh fading channels under the two-user condition.

This paper proposes a frame synchronization method for adaptive array antennas (AAA) in digital mobile communications, which can achieve excellent performance even in severe asynchronous co-channel interference environments, in contrast to the conventional correlator-based methods. The proposed scheme that is based on maximum a posteriori (MAP) estimation utilizes the AAA's outputs of which interference signal components are drastically suppressed. Computer simulations show that the proposed scheme can operate properly even in interference-rich fading environments, and that it can significantly improve the synchronization performance.

This paper proposes a new correction technique for the LInear amplification with Nonlinear Components (LINC) transmitters. The technique, which is based on the minimum mean squared error (MMSE) criterion, estimates the gain and phase imbalance between the two amplifier branches. With information on the estimation, the imbalance is compensated by controlling the amplitude and phase of the input signal that is fed into one of the two amplifiers. Computer simulations with the QPSK modulation demonstrate that this method can calibrate the balance and sufficiently suppress the out-of-band distortion spectra.

This paper proposes a new maximum likelihood OFDM receiver for multipath fading environment with large delay spread. The large delay difference over the guard interval (GI) duration of the OFDM signal generally results in intersymbol interference (ISI) between temporally adjacent symbols and interchannel interference (ICI). Both of them spread over a large number of subcarriers. The new OFDM receiver consists of equalizers for both ISI and ICI and an accurate channel impulse response estimator. Furthermore, it introduces a temporal-window technique for the FFT-window in order to suppress the ICI, which is very effective for reducing the complexity of ICI equalization by maximum likelihood sequence estimator (MLSE). Computer simulation is conducted in order to verify the performance of the proposed OFDM receiver, and its effectiveness is shown.

This paper proposes an interference cancellation technique for DS-CDMA downlink mobile communication systems. The proposed scheme, referred to as orthogonal successive interference canceller (OSIC), is a low complexity version of the decorrelating decision-feedback detector (DDFD) proposed by Duel-Hallen (1993), which is achieved by using an orthogonal filter bank. A lower complexity scheme that takes into consideration only the subset of strongest active users at the OSIC is also proposed. For coherent detection of the OSIC under fading channels, the fixed AR model predictive and the higher order predictive channel estimation are employed. Computer simulations show that the proposed schemes with these two channel estimation techniques can achieve excellent BER performances under both AWGN and flat Rayleigh fading channels.

In this paper, we propose two VLSI applicable approaches to improving performance of soft-output Viterbi algorithm (SOVA)-based turbo decoders. In the first approach, a pseudo-median filter is employed to modify the soft outputs of each SOVA-based constituent decoder. Compared with conventional SOVA-based turbo decoders, an extra coding gain of 0.2 dB can be achieved for a wide range of target bit-error-rate (BER). In the second approach, an easily obtainable variable and a simple mapping function are used to avoid the complex computation of the scaling factor for extrinsic information in SOVA-based turbo decoders. An extra coding gain of 0.3 to 0.5 dB can be obtained in general. This approach does not require signal-to-noise ratio (SNR) related information while the original method does. The hardware overhead and the extra latency for both approaches are negligible.

This paper presents a low-power bit-serial Viterbi decoder chip with the coding rate r=1/3 and the constraint length K=9 (256 states). This chip has been implemented using 0.5 /spl mu/m three-layer metal CMOS technology and is targeted for high speed convolutional decoding for next generation wireless applications such as wide-band CDMA mobile systems and wireless ATM LANs. The chip is expected to operate at 20 Mbps under 3.3 V and at 2 Mbps under 1.8 V. The add-compare-select (ACS) units have been designed using bit-serial arithmetic, which has made it feasible to execute 256 ACS operations in parallel. For trace-back operations, we have developed a novel power-efficient trace-back scheme and an application-specific memory, which was designed considering that 256 bits should be written simultaneously for write operations but only one bit needs to be accessed for read operations. We have estimated that the chip dissipates only 10 mW at 2 Mbps operation under 1.8 V.

This paper presents some results of field tests for our proposed interference cancelling equalizer (ICE) to assess the feasibility of path division multiple access (PDMA). PDMA exploits the different properties of propagation paths between a desired and a co-channel interference (CCI) signal to discriminate them. The focus of this paper is on the case where the desired and CCI signals actually come from the same direction, in which case an adaptive array antenna based on space division multiple access (SDMA) cannot resolve the desired and CCI signals. The field trial results show that even in a negative range of average carrier-to-interference ratio (CIR), the ICE can achieve excellent CCI cancellation performances.

We propose a new private network-to-network interface (PNNI) aggregation algorithms for hierarchical ATM networks. Standard PNNI routing provides a scalable hierarchical routing capability to support a large ATM network, and its hierarchy mechanism can decrease the network complexity significantly. However, in order to support effective QoS-based routing across foreign subnetworks, the topology aggregation mechanism, representing the lower level network topology to higher level, becomes a key issue. PNNI specification defines general notions of this aggregation mechanism, leaving enough opportunities for subnetwork administrators to choose the amount of aggregated information that they advertise. So far, no feasible PNNI compliant algorithms have been proposed. We propose a new three step aggregation scheme to solve the problem. We evaluated the proposed scheme, based on large-scale simulations with different network topologies, traffic scenarios, and performance metrics. The proposed scheme delivers good network performance while significantly reducing the network complexity.

Efficient support for scalable multipoint-to-multipoint (mpt-mpt) communication in ATM has recently become a hot topic of discussion at the ATM Forum. Previously, we presented a new class of efficient switch algorithms for point-to-multipoint (pt-mpt) ABR service that deliver high performance in terms of fairness and link utilization and are significantly simpler to implement than other proposed protocols. However, the more challenging problem of providing bidirectional mpt-mpt ABR service has not been addressed before. While a number of key issues have been resolved in unidirectional pt-mpt ABR service, no satisfactory solution for multipoint-point (mpt-pt) ABR service is known. In this paper, we propose new efficient mpt-pt ABR mechanisms that can interoperate with existing standards for ABR service and provide a truly transparent and scalable solution to multipoint communication in ATM. We present simulation results to illustrate that our proposed ABR schemes provide high link utilization and fair bandwidth allocation in a mpt-pt connection for heterogeneous sources with different data rates.

This paper proposes a growable switch architecture with multiple modules comprising a CORE module to support highspeed switching and EDGE modules with large buffers, providing a large number of traffic classes. For open-loop traffic such as CBR and VBR, the proposed switch uses a weighted fair queueing scheduler at each EDGE buffer module based on the equivalent bandwidth allocated by the call admission control (CAC). On the other hand, for best effort class services (e.g., ABR and UBR), closed-loop control using adaptive rate control at the actual source and at the virtual source queue of the input EDGE module is proposed to avoid internal congestion and to achieve fair throughput performance among the flows competing on the same link. Simulation results show that the proposed architecture achieves ATM switches having hundreds of Gbps capacity, while providing a large number of QoS classes with high throughput and fair sharing of bandwidth by all flows.

We present a simulation study of the TCP performance in ATM networks with available bit rate (ABR) service and unspecified bit rate (UBR) service with early packet discard (EPD) schemes. We focus our study in a LAN environment using some benchmark network configurations proposed in the ATM Forum. Our simulation results show the following: (1) with UBR service and EPD schemes, TCP suffers significant performance degradation in terms of fairness and requires relatively large switch buffer even with a small number of active virtual connections over a LAN configuration, and (2) for the same set of network configurations and with ABR service using explicit rate feedback schemes, TCP achieves a good performance in terms of fairness and link utilization, and requires a relatively small switch buffer.

The basic performance of a multiple co-channel interference canceler assisted by channel estimation and diversity is clarified. It is assumed that the receiver knows the unique-word or identification code of each interfering signal. A simplified Viterbi algorithm for multiple co-channel interference cancellation is proposed and the error performance is clarified.

New congestion control schemes using the adaptive rate control for ATM LANs are presented. It is preferable for hosts in LANs to be able to send bursts at the same speed as the interface link speed in a lightly loaded condition, and as the network load increases, to reduce their traffic rate adaptively in order to avoid network congestion. The authors propose to apply such a rate control concept for two different traffic classes in the ATM LANs. For the first traffic class requiring no bandwidth reservation, i.e. a best effort service class, a combination of the end-to-end adaptive peak rate control with the link-by-link backpressure control is proposed. For the second traffic class, requiring the bandwidth reservation for the burst transmission, i.e. a guaranteed burst service class, a combination of the adaptive peak rate control with the fast bandwidth reservation (FRP) is proposed. It is shown through simulations that, in the first class traffic, cell loss is avoided by the backpressure, while the unfairness problems caused by the backpressure in a heavy load situation are resolved with the adaptive rate control. In the second class traffic, the network throughput characteristics are shown to be improved in the heavily loaded situations, owing to the fact that the adaptive rate control reduces the bandwidth reservation blocking probability.>

The authors propose a burst level bandwidth reservation scheme which is appropriate for an asynchronous transfer mode (ATM) network that supports the transfer of high-speed burst traffic. The proposed scheme utilizes multiple links and multiple paths in a network to transfer individual bursts, thereby increasing network efficiency. As the link and path selection is implemented on a burst-by-burst basis, instead of the cell-by-cell basis used in the conventional multilink approach, the proposed scheme does not require a cell-by-cell distributor and out-of-order cell delivery is avoided, which was the disadvantage of the conventional cell-by-cell multilink approach. Performance evaluation showed that the delay and blocking probability characteristics are greatly improved, as the number of links between each pair of adjacent nodes and the number of source-destination paths increase. For example, around 40% link utilizations are achieved with 16 multiple links, while the conventional single-link schemes yield only to 1% link utilization to guarantee the same quality requirements. It is shown that the proposed scheme works well if the round-trip propagation delay is less than about 10% of the burst duration.>

The authors propose a call admission control scheme based on a method of estimating cell loss quality for individual bursty traffic sources. The estimate is expressed in terms of virtual cell loss probability, which may be defined by two traffic characteristic parameters alone: peak and mean rate. The approach is suitable for the estimation of real cell loss probability in heterogeneous and homogeneous traffic models when burst length is larger than buffer capacity. The concept of virtual cell loss probability is extended to the individual call level so as to be able to estimate the quality of service (QOS) provided to individual calls. A virtual bandwidth method is used to develop a practical call admission control system. Quality is ensured by combining a traffic clustering scheme, with a scheme for assigning individual clusters to subcapacities of a link. Priority levels are presented in terms of the class of QOS required, i.e., deterministic or statistical, and the allocation of virtual bandwidth is discussed in terms of both QOS class and traffic characteristics.>

A new type of carrier recovery circuit suitable for coherent detection in digital land-mobile radio transmission is studied experimentally. A dual-mode carrier recovery (DCR) circuit is proposed that adaptively selects one of two phase locked-loop operation modes: the conventional mode or the adaptive carrier-tracking (ACT) mode. The ACT mode digitally controls the reference phase, and enables instantaneous phase tracking in burst signal operation and/or in a fast fading environment. The DCR coherent demodulator performance is identical to that of conventional coherent detection in the low-CNR region, and to that of differential detection in the high CNR region where the ACT mode is selected.>

The authors discuss and propose a very-high-speed and high-capacity packet-switching (HPS) architecture for a future broadband ISDN (integrated-services digital network). The HPS network accommodates various communication services, such as voice, high-speed data, high-speed still picture, and video services. The proposed architecture has three significant principles: a high-speed oriented simple network protocol, separation of signaling and network control from data transfer, and hardware switching. These principles provide fast- and high-throughput transmission for data packets and reliable transmission and processing for call-control packets. The HPS protocol structure is addressed, which provides high flexibility for various communications services as well as high-speed capability. A 3-Gb/s capacity and building-block-structured packet-switching system architecture, using bus- and loop-type switch fabric, is also presented.>

Wigner distribution (WD) can provide for high frequency- or time- resolution, but its nonlinear property poses problems when applied to signals with multiple frequency components. This paper proposes an alternative to WD with improved performance for such signals, based on a consideration why WD offers high resolution. The observed data is first converted to analytic signals, which are then subjected to Fourier transform after squaring. Experimental results revealed its superiority over WD for multi-component signals.

A new switching architecture for broadband ISDN, "Synchronous Composite Packet Switching (SCPS)," is proposed and evaluated. It efficiently integrates circuit and packet switching functions on a single switching system and accommodates very high speed-up to several tens of Mbit/s-communication services, such as very high speed bursts of data, still picture, and motion video, as well as 64 kbit/s or less voice and data services. The SCPS system comprises plural switch modules and plural Very high speed synchronous loops. In the SCPS system, messages on plural circuit switched channels are assembled into quasi-packets, called "composite packets," and switched synchronously between switch modules, maintaining complete time transparency and short absolute delay time. A system parameter design to obtain high system efficiency and appropriate system modularity is explained, and an example for a very large capacity transit switch of 4 Gbit/s throughput is presented. System implementation problems to realize the SCPS principle, such as efficient implementation of the composite packet assembling and loop transmission functions, are investigated and an experimental system constructed for circuit switching part is presented. The most remarkable characteristic of the SCPS is that it efficiently integrates64 \times nkbit/s circuit switching with packet switching. Moreover, the SCPS system retains compatibility with existing networks and the possibiliy of evolution toward a future broadband ISDN. On the basis of the above investigations and experimental system construction, the authors conclude that the SCPS is one of the most practical switching architectures for the coming broadband ISDN era.

Digital mobile radio transmission techniques and integrated circuit devices have been developed for application to a digital portable transceiver utilizing narrow-band GMSK modulation and ADM voice coding. Design and performance of a quadrature type GMSK modulator and a single-chip coherent demodulator as the GMSK modem are described. To overcome slow fading, encountered in portable applications, switching diversity using a jitter detection type sensor is Proposed and shown to be effective. An experimental Portable transceiver, developed to demonstrate hardware feasibility, is also described.

Spectrum efficiency ofM-ary PSK land-mobile radio is discussed theoretically. The spectrum efficiency ηT(erlangs/Hz·m2) is defined as spatial traffic density per system bandwidth, and is shown to be consistent with the conventional ones. The effect of multilevel modulation upon ηTis calculated. It is shown that ηTis optimal whenM=4, i.e. QPSK.

An optimum predetection Gaussian bandpass filter for differential detection of MSK is derived theoretically with numerical techniques. The optimum product of bandwidth(B)and bit duration(T), compromising the noise reduction effect with the intersymbol interference effect, is calculated at a given bit error rate (BER). It is shown that the optimumBTproduct is 1.21 with 4.02 dB degradation at 10-6BER where the degradation is defined as the increase inE_{b}/N_{0}relative to ideal coherent detection of MSK.