Recently, calibration methods of the ground-based weather radars with reference to spaceborne precipitation radars, such as the Global Precipitation Measurement (GPM) Dual-Frequency Precipitation Radar (DPR), have attracted lot of attention, because of their cost effectiveness and near real-time inputs. This paper describes evaluations for radar reflectivity factors (Z-factors) of S-band and C-band ground-based radars over the Indian region with reference to the GPM/DPR observations. By statistical analyses, using a matching program between the ground-based radar and the GPM/DPR, the S-band ground-based radar measurements at Cherrapunji, Meghalaya, India tended to be significantly underestimated. In this case, a mean bias in the Z-factors was 13.203dBZ was computed. On the other hand, the C-band ground-based radar at Shar, Sriharikota, India was well-corresponded with the GPM/DPR and the mean bias tended to be small (0.688 dBZ).

To enhance precipitation monitoring, this study attempts integration among Global Precipitation Measurement (GPM) products such as the Dual-Frequency Precipitation Radar (DPR) and the merged satellite precipitation product, and ground-based radars. Here, radar reflectivity and rainfall composites are produced using three ground-based radars in Fiji. Calibration correction factors of the ground-based radars are calculated with reference to the GPM/DPR in the radar reflectivity composite. In the rainfall composite, two types of correction factors are calculated. One is a factor of the ground radars with the GPM/DPR, and the other is a factor of the merged satellite precipitation product with the ground-based radars. For making the composite, a weighting function is implemented with consideration of a beam height in the ground-based radar. These techniques can be helpful for the precipitation monitoring, because it allows seamless monitoring from the ground-based radar's observation range to satellite observation areas.

A fast channel-estimation scheme for adaptive maximum-likelihood sequence-estimation (MLSE) equalizers called the orthogonal-transformed variable-gain least mean squares (OVLMS) algorithm is proposed. This algorithm requires only as many operations as the least mean squares algorithm in spite of its excellent performance. Furthermore, an operational complexity reduction method is proposed in which the orthogonal matrix is reconfigured as eigenvectors with valid eigenvalues. The OVLMS algorithm is theoretically analyzed and is shown to have both a fast acquisition and a good tracking performance. An equalizer using OVLMS (OVLMS-MLSE) experimentally attains a 5-dB improvement in bit-error rate (BER) performance at BER of 1.0/spl times/10/sup -4/ over coherent detection. The OVLMS-MLSE is found to be free of the degradation caused by sampling phase error. Finally, the OVLMS-MLSE equalizer is experimentally verified to synchronize within five symbols.

This paper describes the performance of a 256 QAM modem with 400 Mbit / s transmission capacity. A variety of novel techniques are introduced as ways to achieve good performance. Key techniques include 1) an accurate 256 QAM modulator employing a new monolithic multiplier IC, 2) a carrier recovery circuit which satisfies such requirements: good phase jitter performance and no false lock phenomenon, 3) a highly stable high-level decision circuit, and 4) a forward error correcting code. As an overall modem performance, BER characteristics and signatures are presented. The equivalent CNR degradations of 1 dB(at BER of 10-4) and 2 dB (at BER of 10-9)are obtained using a single Lee-error correcting code and a seven-tap baseband transversal equalizer. The residual bit errors are decreased below the order of 10-10. The performance of a 256 QAM multicarrier modem has given prospect for the development of 400 Mbit/s digital microwave radio system.

This paper presents topics related to the 256 QAM modem for high capacity digital microwave radio. Specifications for modem circuitry are derived from the allowable carrier-to-noise ratio degradation point of view. In this process, various degradation factors are categorized so that the same evaluation is possible. Two representative circuits, the automatic threshold control (ATC) and carrier recovery circuits, of particular importance for developing a 256 QAM modem, are presented. For the ATC circuit, the operation principle as well as the presence of the false-lock phenomenon and its evasion method are described. The prototype 256 QAM modem performance indicates the prospect of a 400 Mbit/s 256 QAM modem.

This paper describes the design and performance of the 16 QAM carrier recovery PLL for service-channel transmission using FSK additional modulation. When FSK additional modulation is applied, tracking phase error occurs and corrupts the 16 QAM signal. To reduce the phase error without widening the loop noise bandwidth is an important issue in the 16 QAM-FSK double modulation scheme. An analytical expression to estimate the peak phase error due to class 4 partial response FSK is established, By using the approximation formula, an optimization of the carrier recovery PLL is presented. Moreover, experiments and computer simulations are carried out for the 200 Mbit/s 16 QAM and 64 kbit/s SC double modulation system. As a result, it is demonstrated that a 0.1 dB 16 QAM equivalent power loss and an 8 dB frequency deviation margin of SC transmission performance can be obtained.

A novel long haul 5 GHz 16 QAM digital radio system, which has 200 Mbit/s transmission capacity within the 40 MHz interleaved channel allocation, is proposed and described. It is designed to be overbuilt on existing FDM-FM routes with an approximately 50 km repeater spacing. To achieve the 5 bit/s/Hz RF spectral efficiency, the 16 QAM modulation and Nyquist cosine roll-off spectral shaping techniques (\alpha = 0.5) are investigated. Then a new signal shaping filter, differential encoding and carrier recovery techniques are presented. Finally, the effects of TWT amplifier nonlinearity on a 16 QAM signal are experimentally investigated.