This paper proposes a new method to estimate the channel impulse response for Orthogonal Frequency Division Multiplexing (OFDM) mobile radio transmission. The method employs the Recursive Least Squares (RLS) algorithm so as to exploit the correlations in frequency and time domains, and can improve the estimation accuracy. It is also applicable to both the regular and scattered pilot schemes. Computer simulations demonstrate effectiveness of the method applied to the scattered pilot scheme.

This paper proposes Coherent-HYBrid Direct-Sequence Fast-Frequency-Hopping (CHYB-DS-FFH) CDMA with Adaptive Interference Cancelling (AIC) for cellular mobile communications. The features of CHYB-DS-FFH are symbol-by-symbol frequency diversity and low chip-rate DS multiplexing both of which are based on a coherent FFH modulation and demodulation scheme. The combination of coherent FFH, space diversity, and AIC is very effective for reducing the performance degradation due to interference. Computer simulations demonstrate BER performance of a 2 hop 500-kHz-interval frequency hopping system using () a linear canceller or () a nonlinear canceller. Both systems employ the two branch space diversity reception of 10kb/s QPSK with FFH over a 1MHz system bandwidth. In quasi-static channels, the average BER performance is 10-2 with average Eb/N0 less than 8dB. In dynamic fading channels under full interference conditions, CHYB-DS-FFH with the linear adaptive interference canceller realizes a BER of 10-2 at the average Eb/N0 of 15dB with maximum Doppler frequency fD of 5Hz, whereas CHYB-DS-FFH with the non-linear adaptive interference canceller achieves the same BER at the average Eb/N0 of 15dB with fD, equal to 30Hz.

This paper proposes a new adaptive Interference Cancelling Equalizer (ICE) with a blind algorithm. From a received signal, ICE not only eliminates inter-symbol interference, but also cancels co-channel interference. Blind ICE can operate well even if training signals for the interference are unknown. First, training signal conditions for applying blind ICE are considered. Next, a theoretical derivation for blind ICE is developed in detail by applying the maximum likelihood estimation theory. It is shown that RLS-MLSE with diversity, which is derived for mobile radio equalizers, is also effective for blind ICE. Computer simulations demonstrate the 40kb/s QDPSK transmission performance of Blind ICE as a blind canceller with two branch diversity reception under Rayleigh fading in a single interference environment. The simulations assume synchronous training; the canceller is trained for the desired signal but not for the interference signals. Blind ICE can be successfully achieved at more than -10dB CIR values when average Eb/N0 is 15dB and a maximum Doppler frequency is 40Hz.

This paper proposes a scattered-pilot-OFDM reception scheme employing turbo inter-carrier interference (ICI) cancellation in the fast varying fading environments of mobile communications. In the OFDM transmission, the orthogonality among the subcarriers cannot hold due to large Doppler shift, and the OFDM signal suffers from severe degradation due to ICI. The proposed receiver carries out two modes: (i) a coherent detection (CD) mode, and (ii) a turbo ICI cancellation (TC) mode. Initially, the receiver performs the CD mode. When any decision errors are detected, it shifts from the CD mode to the TC one that carries out both the ICI cancellation and the channel estimation by using the decoder output (the log likelihood ratio). In addition, the iteration of the TC mode can improve the accuracy of the channel estimation and ICI cancellation ability. Computer simulations following specifications for the mobile reception mode in the digital terrestrial television broadcasting demonstrate that the receiver can effectively cancel ICI due to the fast varying fading, and that its average BER performance is much better than that of CD.

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 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 is 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 using 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 44 MIMO-OFDM, 16QAM, and convolutional codes (rate =1/2, 2/3) demonstrate that the proposed algorithm requires only 1.0 dB more Eb/N0 than 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 reviews recent progress in adaptive signal processing techniques for digital mobile radio communications. In Radio Signal Processing (RSP) , digital signal processing is becoming more important because it makes it relatively easy to develop sophisticated adaptive processing techniques, Adaptive signal processing is especially important for carrier signal processing in RSP. Its main objective is to realize optimal or near-optimal radio signal transmission. Application environments of adaptive signal processing in mobile radio are clarified. Adaptive equalization is discussed in detail with the focus on adaptive MLSE based on the blind algorithm. Demodulation performance examples obtained by simulations and experiments are introduced, which demonstrates the recent advances in this field. Next, new trends in adaptive array processing, interference cancelling, and orthogonalization processing are reviewed. Finally, the three automatic calibration techniques that are based on adaptive signal processing are described for realizing high precision transmission devices.

This paper proposes a new minimum BER (MBER) criterion precoding method 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 averaged with respect to the CSI error. In contrast with a conventional power allocation MBER precoding method that is also robust to the CSI error, the proposed scheme does not make any assumption on the precoding parameters so as to reduce complexity. Thus, it is expected to outperform the conventional scheme at the cost of higher complexity. Computer simulations demonstrate that the proposed precoding method outperforms a conventional nonrobust MBER precoder and the conventional robust power allocation MBER precoding method when the amount of the CSI error is not considerable.

This paper describes the formation of ultra-thin tantalum oxide capacitors, using rapid thermal nitridation (RTN) of the storage-node polycrystalline-silicon surface prior to low-pressure chemical vapor deposition of tantalum oxide, using penta-ethoxy-tantalum [(Ta(OC2H5)5) and oxygen gas mixture. The films are annealed at 600-900 in dry O2 atmosphere. Densification of the as-deposited film by annealing in dry O2 is indispensable to the formation of highly reliable ultra-thin tantalum oxide capacitors. The RTN treatment reduces the SiO2 equivalent thickness and leakage current of the tantalum oxide film, and improves the time dependent dielectric breakdown characteristics of the film.

This paper proposes a new signal peak power reduction technique, Peak Reduction based on Control Signal Insertion (PRCSI), for broadband mobile communications based on multi-channel signaling schemes. PRCSI reduces the peak power with a peak control signal that is generated symbol-by-symbol; no signal band expansion is incurred because the peak control signal is inserted into the transmission signal band. PRCSI can achieve 4 dB peak power reduction for 8-carrier signaling, while the Eb/N0 value required to achieve 10-3 average BER is 1 dB larger with PRCSI than without it. This BER performance degradation can effectively be compensated by the proper use of Trellis coding. The proposed technique is applied to OFDM transmission systems with large carrier number. The proposed technique can achieve 3-dB peak power ratio for 128-carrier OFDM signals with less than 1-dB performance degradation at the BER of 10-3.

Both available bit rate (ABR) service and unspecified bit rate (UBR) service with early packet discard (EPD) schemes have been considered for supporting data applications in ATM networks. Since transmission control protocol (TCP) is perhaps the most widely used transport layer protocol in existing data networks, the performance of TCP over ATM using ABR service and UBR service with EPD schemes is of great interest to ATM equipment vendors and service providers. In this paper, we present a simulation study of this interesting issue 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 good performance in terms of fairness and link utilization, and requires relatively small switch buffer.

Cell losses due to statistical multiplexing of bursty traffic in ATM networks tend to be in clusters rather than uniformly scattered. Since the quality of service for users is quite sensitive to such bursty losses, it is necessary to characterize the temporal behavior of cell loss. This paper reports results obtained from investigating overload period and underload period in an ATM multiplexer with heterogeneous burst traffic input, using a bufferless model. The overload period is defined as the time interval when the instantaneous bit rate exceeds the output link capacity. With the bufferless model, we assume that all the instantaneous bit rate exceeding the link capacity is lost, and the loss rate is called "virtual cell loss probability". The virtual cell loss probability during the overload period, average overload period and underload period durations are analyzed. Numerical results show that the cell loss probability in overload periods and the average duration of overload periods (normalized by burst duration) are not very sensitive to link load or average rate/peak rate ratio of the burst, and that they are approximately on the order of peak bandwidth/link capacity ratio for the multiplexed burst. Furthermore, it is also shown that the mean underload duration is simply given as the inverse of the overall cell loss probability multiplied by the constant value inherently determined by peak bandwidth and link capacity. With these observations, applications to the call acceptance control using these measures are also presented.

We propose a new QOS routing algorithm for finding a path that guarantees several quality of service (QOS) parameters requested by users, for ATM networks. It is known that a routing problem is NP-complete, if the number of additive QOS parameters, such as delay and cost, are more than or equal to two. Although a number of heuristic algorithms have been proposed recently to solve this problem, the appropriate choice of routing algorithms is still an open issue. In this paper, we propose a new heuristic routing algorithm, while being compliant with PNNI routing and signaling specification in the ATM Forum. The performance of algorithms is evaluated by simulation with a various network topologies and loading scenarios. This simulation results demonstrate that the proposed scheme improves the performance while reducing computational complexity.

The random deployment of small cell base stations (BSs) causes the coverage areas of neighboring cells to overlap, which increases intercell interference and degrades the system capacity. This paper proposes a new intercell interference management (IIM) scheme to improve the system capacity in multiple-input multiple-output (MIMO) small cell networks. The proposed IIM scheme consists of both an interference cancellation (IC) technique on the receiver side, and a neural network (NN) based power control algorithm for intercell interference coordination (ICIC) on the transmitter side. In order to improve the system capacity, the NN power control optimizes downlink transmit power while IC eliminates interfering signals from received signals. Computer simulations compare the system capacity of the MIMO network with several ICIC algorithms: the NN, the greedy search, the belief propagation (BP), the distributed pricing (DP), and the maximum power, all of which can be combined with IC reception. Furthermore, this paper investigates the application of a multi-layered NN structure called deep learning and its pre-training scheme, into the mobile communication field. It is shown that the performance of NN is better than that of BP and very close to that of greedy search. The low complexity of the NN algorithm makes it suitable for IIM. It is also demonstrated that combining IC and sectorization of BSs acquires high capacity gain owing to reduced interference.

Performance of self-synchronizing scrambler/descrambler in mobile radio transmission systems is discussed theoretically and experimentally. Multiple-error characteristics in descrambler processing are analyzed in detail.

This paper proposes complex form BandPass Sampling (BPS) that is suitable for the software radio. This BPS utilizes offset frequency sampling and quadrature component interpolation. Three types of BPS techniques are first reviewed, which shows effectiveness of the proposed BPS technique. The major advantages over the conventional BPS techniques are: i) free from the DC offset that is caused by the leak of the sampling clock harmonics into the received signal, and ii) reduction of alias by the complex number processing in the signal detection. Next, detailed description of the BPS operation shows that it requires real-time interpolation for the time alignment of the sampled quadrature component. Finally, computer simulation shows that the misalignment generates distortion, and that effective interpolation techniques can reduce the distortion level less than -60 dB even for wideband signals.

As a blind linear-interference-canceller for DS-CDMA mobile communications, the orthogonal matched filter (OMF) minimizes the power of the output while maintaining constant power of the desired signal in the output. This paper studies the extension of OMF to an RAKE receiver (OMF-RAKE), which adaptively controls the steering vectors that determine the constraint. It also applies the QR-RLS algorithm to estimate the OMF-RAKE parameters and investigates a hardware implementation that employs a systolic array. Computer simulations show that OMF-RAKE with the QR-RLS algorithm and the systolic array structure can reduce the computational complexity to about a half that of the conventional RLS-type algorithm without degrading the BER.

A blind technique for adaptive signal suppression in multipath DS-CDMA communication channels for the downlink is considered. Its performance is degraded when mismatch problem occurs when multipath components arrive with fractional-chip delays. In order to surmount this problem, Multiple Finger Expansion Optimal Filter (MFE-OF) was recently proposed to estimate the received desired signal subspace using fractionally delayed despreading fingers. However, MFE-OF requires much computational complexity for good performance. In this paper, a modification to the MFE-OF is introduced by utilizing decision-directed steering vector to reduce the number of fingers required by MFE-OF down to that of the conventional OMF-RAKE without much performance degradation. This modified receiver is called Decision-Directed Optimal Filter (DDOF). Computer simulation validates the effectiveness of the new receiver to increase the downlink capacity of DS-CDMA systems.

The transmission and processing of multimedia information requires a high-speed communications network infrastructure. This is especially true for the networks between the user's computer and the information highway. An Ethernet LAN is widely used for these networks, but it has limited throughput. Asynchronous Transfer Mode (ATM) LAN technology is a promising approach to overcome this limitation. We have developed a chip set which can be used to connect personal computers (PCs) and workstations (WSs) to a 156-Mbps ATM LAN. The advanced architecture, optimized performance and efficient buffer management enables a sustained more than 100 Mbps transfer speed to be obtained. The chip set is implemented in a 0.8 µm triple metal-layer CMOS process to integrate total 460 K transistors and consumes total 4 W at 5 V.

When the multipath delay difference exceeds the guard interval (GI), the performance of MIMO-OFDM transmission suffers severely from both the inter-symbol interference (ISI) from the adjacent OFDM symbols and the inter-carrier interference (ICI) within the same symbol. This paper therefore proposes a MIMO-OFDM receiver employing the low-complexity turbo equalization. The proposed receiver initially separates the data streams and suppresses ICI by linear processing. In the iterative processing, it cancels the other data streams as well as ISI and ICI. The MIMO-OFDM turbo equalizer consists of an ISI canceller, an ICI canceller, an optimal detection filter, and a MAP detector. The proposed receiver can improve the transmission performance by exploiting the log-likelihood ratio that the decoding process produces for canceling both ISI and ICI and separating of the spatially multiplexed streams. Computer simulations, which apply the wireless LAN to MIMO, demonstrate that the proposed receiver can provide excellent performance in the severe multipath channels where the delay difference is greater than GI.

This paper reviews various switch architectures for Asynchronous Transfer Mode, which have been proposed and developed so far in Japan. The switch fabrics can be classified, owing to the arrangement of switch matrices and buffer memories, into four categories, input buffer switch, output buffer switch, shared buffer switch and crosspoint buffer switch. Those switches have their own advantages and disadvantages, which require additional effort to implement the switches for the practical network. This paper introduces examples of each category switch fabric and additional technical modifications to make it practical. Other general issues to construct ATM switch fabrics, such as non-blocking characteristics and path assignment within a multi-stage switch network, are also addressed. Furthermore, future directions in the ATM switch fabric is discussed.