In this letter, we introduce new parameters for classifying digitally modulated unknown QAM and PSK signals. Our two parameters for the classification are the variance of magnitude ratios and the mean of mod 2π phase differences. The gain adjustments of amplitudes are not required for the classification. Five different types of QAM constellations and three different types of PSK constellations are tested and the characteristics of our classification parameters are investigated in various SNR environments. Simulation results demonstrate the effectiveness of our proposed technique.

In this letter, we propose a polarity decision carrier recovery algorithm that is useful for carrier acquisition in high order QAM. The PD (Phase Detector) output and its variance characteristic are mathematically derived and the simulation results are presented. The proposed algorithm shows enhanced acquisition performance especially for large frequency offset.

This paper proposes a simple adaptive channel estimation scheme for orthogonal frequency division multiplexing (OFDM) in order to realize high-rate wireless local area networks (LANs). The proposed estimator consists of simple frequency-domain FIR filters, which are adaptively selected according to the difference vector between adjacent subcarriers and channel amplitude of the subcarrier. No precomputation or matrix signal processing is required in the derivation of these characteristics. Computer simulations show that the packet error rate performance of the proposed scheme is superior to that of the least-squares scheme by 1.1 dB in terms of required Eb/N0 at PER=0.1 in AWGN channels. They also show, for the same criterion, a 0.7 dB improvement in a frequency selective fading channel with delay spread values of 100 ns.

In this paper, a transceiver VLSI architecture is proposed for high speed digital CATV modems, which can perform both the QAM and the VSB transmissions. The proposed architecture of all-digital dual-mode QAM/VSB receiver consists of digital AGC, digital demodulator, fractionally spaced blind equalizer and DFE, digital carrier recovery, and symbol timing recovery. Finite word-length simulation results show that the proposed architecture can achieve an SNR 29 dB for both the 64-QAM mode and 8-VSB mode when the 10 bit ADC input signal SNR is 36 dB, and there are 6 kHz of carrier frequency offset, 110 ppm of symbol rate offset, and -82 dBc carrier phase-jitter at 10 kHz away from the nominal carrier frequency.

A deterministic simulation method is investigated for rate 3/4 trellis-coded (TC) 16PSK, TC-16QAM and TC partially overlapped (PO) 12QAM schemes. The BER performance of these schemes are evaluated on realistic channels with the same transmisson parameters, and are compared with BER values obtained from a distance spectrum expression. The results of this study show that the BER values obtained by the deterministic simulation coincide well with those from the distance spectrum method, and that TC-16PSK is superior to both TC-16QAM and TC-PO-12QAM in terms of BER performance over linear and nonlinear channels. The BER degradation caused by a nonlinear amplifier and the BER difference between two mapping methods ( Gray code and natural binary code mapping) are also clarified.

This paper gives laboratory as well as the results of field experiment and describes the implementation of a system developed to evaluate and demonstrate multimedia multimode time division multiple access (MTDMA). The equipment has been developed with the radio transmission technology for future public land mobile telecommunication systems (FPLMTS/IMT-2000) in mind. To meet FPLMTS/IMT-2000 requirements the system employs the following techniques: a hybrid multiplex modulation system consisting of quadrature phase shift keying (QPSK) and 16-ary quadrature amplitude modulation (16QAM), a high data transmission bit rate of 2 Mbit/sec for QPSK, 4 Mbit/sec for 16QAM, and diversity combining and adaptive equalization technique. For the diversity adaptive equalization technique, we used a decision feedback equalizer (DFE) consisting of one feedback (FB) transversal filter and two feed-forward transversal (FF) filters. The output signals from two branches of space diversity reception antennas are then fed to the two FF filters of the DFE. For middle-speed mobile radio communication for a micro-cellular pedestrian environment, a QPSK modulation system is selected to obtain wide coverage, while for a pico-cellular indoor office environment, the delay spread is small, and a 16QAM modulation system is selected to achieve a high bit rate. The results given here of laboratory and field experiments show the technical feasibility of MTDMA for future public land mobile telecommunication systems.

A slow frequency-hopping/16-ary quadrature amplitude modulation (slow-FH/16QAM) system based on time-division-multiple-access (TDMA) is appropriate for third-generation land mobile cellular communications because of its high immunity to interference. The system uses 16QAM for high spectral efficiency and slow-FH and forward-error-correction (FEC) for high-quality transmission. To reduce sensitivity to interference, the system uses an improved decoding scheme based on a minimum Euclidean-distance which is effective when the interference level is dispersed by FH. The bit error rate (BER) of the system due to interference has been evaluated in a previous study, both theoretically and by computer simulation. Although computer-simulated results showed that the system improved the BER, the hardware feasibility was not considered. This paper presents a hardware implementation of the system and the results of experimental transmission using equipment we developed to verify the system and to confirm the BER performance. The laboratory experimental results indicated that the system could provide high-quality transmission over a channel that has frequency-selective fading and co-channel interference. This system provided an Eb/N0 of 9 dB with space diversity and one of 15 dB without it, when BER=10-3 and fd=120 Hz. Field experiments were also conducted in a suburban area of Tokyo to demonstrate the BER performance. The results meant that the system could lower sensitivity to vehicle velocity more than a system without FH and that the BER performance of the system was improved notably against that of a system without FH, especially at low vehicle velocity.

This paper presents a technique to transmit 16QAM signals in mobile radio environments by using extended symbol-aided estimation (ESAE) method for compensating the multipath fading effect. The main results of this paper are the symbol error rate (SER) performance analyses for BPSK and 16QAM systems using the proposed estimation method under Rician fading. The analytical results demonstrate better performance of the proposed systems compared with those of the conventional systems under fast and severe fading, especially in the region of high signal to noise ratio.

A system combining multicarrier modulation and adaptive modulation in which a suitable level of quadrature amplitude modulation (QAM) is selected for each subcarrier and time-slot, is proposed for high-bit-rate and high-quality digital land mobile communications. The advantages of the system are a mode in which information cannot be transmitted under adverse propagation conditions and a buffer memory to limit a transmission delay time. If the allowable delay time is small, such as in voice and video transmissions, the system tends to have a poor bit error rate (BER) because of the forcible QAM-level selection. Our new selection scheme improves the BER for small transmission delay time. Suitable distribution of the delay time among subcarriers is obtained by using the scheme where the QAM-level of each subcarrier is chosen collectively using the number of data bits stored in memory. Computer simulation of the systems BER performance showed that the system could provide a noticeable BER improvement over frequency-selective fading channels as well as flat Rayleigh fading channels. The QAM-level selection scheme was also effective for a low maximum Doppler frequency and a small memory size. The system could thus attain about 25-fold improvement in BER at Es/N030 dB compared to the multicarrier/16QAM system. It also attained about 60-fold and 3. 5-fold improvement in BER at fd=10Hz compared with the system with multicarrier/16QAM and without the QAM-level selection scheme, respectively.

This paper proposes a new method for estimating route outage probability in non-regenerative repeater digital microwave radio systems. In this method, the route outage probability is estimated by various means, including path correlation of fading occurrence and C/N degradation corresponding to the number of non-regenerative repeater stations with and without demodulator devices. In the conventional method, the path correlation is treated as 0 and the C/N degradation is taken as a constant value on each path. To confirm the proposed method's effectiveness, a field test is carried out in which 16QAM signals pass through two non-regenerative repeater stations. The results obtained are in good agreement with the estimated outage probability.

A new Neural Network Equalizer (NNE), employing multilayer feedforward neural network, is proposed as a compensation method for nonlinear and multipath distortion that arises from FTTA (Fiber To The Air) system. If a signal in a channel is affected by nonlinear distortion, the conventional Decision Feedback Equalizer (DFE) finds difficulty in perfect compensation of it. To compensate for nonlinear distortion as well as multipath distortion, an equalizer, employing neural network, is investigated. A new neural network equalizer, yielding a cubic function as unit output function, is proposed in order to compensate the nonlinear distortion effectively. We also propose an initial weights of neural network for preventing from local minimum. Computer simulation results show that the compensation performance of the new NNE is superior to the conventional DFE and the conventional NNE.

In bandlimited QPSK and QAM transmission systems, phase jitter occurs in the output of a carrier recovery circuit that uses a fourth-power multiplier. To analyze the phase jitter, an exact expression was derived for the autocorrelation function and power spectral density for the case in which bandlimited Gaussian noise and a QPSK or QAM signal with random modulation and arbitrary waveform are simultaneously applied to the fourth-power multiplier. Using this expression, the rms phase jitter of the recovered carrier in root-cosine-rolloff transmission systems for QPSK, 16QAM, 64QAM and 256QAM was calculated. It was shown that the conventional theories for rectangular waveforms are special cases of our theory.

A blind equalization algorithm which makes use of the Stop" region of the Stop-and-Go algorithm is proposed. By adaptively updating the tap weights at the Stop region as well, it is intended to improve the convergence property of the Stop-and-Go algorthm. The performance of the proposed algorithm is compared with the conventional Stop-and-Go algorithm using various communication channels. Simulation results indicate the improvement of the convergence speed while maintaining or possibly lowering the residual error.

This paper proposes a new block coded quadrature amplitude modulation (BC-QAM) scheme, which is designed by an optimization technique based on simulated annealing. Simulated annealing is an effective nonlinear optimization technique and can be applied to both the discrete and the continuous optimization problems. In this paper, the simulated annealing technique is used to design the optimum BC-QAM signal, which minimizes the upper bound on the bit error rate (BER) in a Rayleigh fading channel. The computer simulation shows that the proposed BC-QAM can improve the BER performance. This paper also proposes a simplified design method to reduce the number of variables to be optimized. The proposed simplified method optimizes the in-phase and quadrature components of the BC-QAM signal separately. The computer simulation also shows that the BC-QAM designed by the simplified method gives little degradation on the BER performance, although the simplified method can significantly reduce the number of optimization variables.

The use of existing metallic local line facilities is being studied for providing "video on demand (VOD)" services to residential subscribers across asymmetric digital subscriber lines (ADSL). ADSL carries a high-rate channel in the downstream direction from a central office (CO) to the subscriber, and a low-rate channel in both directions on an existing 2-wire pair. Audio and video signals are compressed by the moving picture experts group's standardized algorithms (MPEG 1 and MPEG 2), and delivered to the subscriber in the high-rate channel. Control (demand and response) signals are transceived in the low-rate channel. This paper presents the line length coverage of ADSL systems given the environment of NTT's local networks. The bit rates in the downstream and upstream directions are assumed to be 1.6-9.2Mbit/s and 24kbit/s, respectively. Two types of ADSL systems are considered: transceiving ADSL signals using the plain old telephone service (POTS) line or the basic rate access (BRA; 320 kbaud ping-pong transmission system) line on the same 2-wire pair. 16-QAM, 32-QAM and 64-QAM are compared as transmission schemes. Intra-system crosstalk interference (interference between identical transmission systems) and inter-system crosstalk interference (interference between different transmission systems) with the existing digital subscriber lines (DSL) are estimated. It is shown that the inter-system crosstalk interference with BRA is most stringent, and ADSL with 16-QAM yields the best performance in NTT's local networks. This paper concludes that realizing ADSL with 16-QAM can achieve channel capacities of up to 9.2Mbit/s for fiber-in-the-feeder (FITF) access systems, but the possibility of applying ADSL to direct access systems is remote except for a restricted short haul use. Some comparisons regarding American local networks are also described.

In this work, we present an 8-state trellis code for bit interleaved 16-QAM and the BER performance on Rayleigh fading channel is evaluated. We analyze the BER and show that the effective code length and minimum productive distance are also important criterion for code design on bit interleaved system. We design the code by considering not only minimum Hamming distance but also the effective code length and minimum productive distance. As a result, we found that the scheme employing the code achieves good BER performance on Rayleigh fading channel even with the finite interleaving size.

This paper proposes a symbol rate controlled adaptive modulation/TDMA/TDD for future wireless personal communication systems. The proposed system controls the symbol rate according to the channel conditions to achieve wide dynamic range of the modulation parameter control as well as to improve the delay spread immunity. The main purpose of the proposed system is to increase the data throughput with keeping a certain transmission quality, especially in frequency selective fading environments. For this purpose, the proposed system predicts the C/N0 (carrier power-to-noise spectral density ratio) and the delay spread separately, and selects the optimum symbol rate that gives the maximum bit rate within a given bandwidth satisfying the required BER. The simulated results show that the proposed system can achieve higher transmission quality in comparison with the fixed symbol rate transmission system in both flat Rayleigh and frequency selective fading environments. The results also show that the proposed system is very effective to achieve higher bit rate transmission in frequency selective fading environments.

This paper proposes an adaptive modulation/TDMA scheme to achieve high capacity personal multi-media communication systems. TDMA is employed to cope with various bit rate for multi-media services. The modulation scheme is selected from 1/4-rate QPSK, 1/2-rate QPSK, QPSK, 16QAM and 64QAM according to the received C/IC (power ratio of the desired signal to the co-channel interference) and the delay spread. The spectral efficiency is evaluated by using the simulated bit error rate (BER) performance as well as the cumulative distribution of the C/IC with parameters of cell configurations. The results show that the spectral efficiency of the proposed scheme is 3.5 times higher than that of the conventional QPSK systems at the outage probability of 10%, and the effect is more remarkable at lower outage probability. The results also show that the proposed adaptive modulation is effective in improving delay spread immunity.

This paper gives field experimental results on 16-ary quadrature amplitude modulation/time division multiple access (16QAM/TDMA) and trellis coded 16QAM/TDMA systems for land mobile communications in order to evaluate its capability of achieving large capacity and high quality data transmission. Pilot symbol aided space diversity and symbol timing synchronization based on maximum likelihood (ML) estimation are applied to both 16QAM/TDMA and trellis coded 16QAM/TDMA to improve transmission quality. For the trellis coded 16QAM/TDMA, trellis coding with Viterbi decoding and 2-frame symbol interleaving are further employed. The field experiments were conducted in the Tokyo metropolitan area of Japan. The results show that 16QAM/TDMA and trellis coded 16QAM/TDMA are practical modulation/access schemes for land mobile communication systems.

The paper proposes a new multicarrier 16QAM system for high-quality and high-bit-rate transmission with high spectral efficiency in land mobile radio communications. The proposed system uses a multicarrier transmission scheme to provide immunity against frequency-selective fading distortion. It also uses pilot-symbol-aided 16QAM to increase spectral efficiency, and it combines space diversity and FEC with maximum likelihood decoding to improve the bit error rate (BER) performance. Computer simulation shows that a BER of less than 10-4 is obtained over frequency-selective fading channels with rms delay spread of less than 5.4µs. Using a bandwidth of 200kHz the proposed system can achieve high-quality transmission with a total information rate of 256kbit/s.