Junji Namiki

Optical fiber feeder for microcellular mobile communication systems (H-O15)

The authors investigate the feasibility of using an optical fiber feeder for microcellular mobile communication systems. The optical feeder enables compact and low-cost base stations, easy radio channel control, and flexible mobile communication systems. Basic transmission characteristics were investigated through optical transmission experiments. Using these results, it is estimated that the optical feeder can transmit 880 telephone channels for digital TDM systems and 2000 channels for analog FDM systems through 20 km of optical fiber. Furthermore, two kinds of novel techniques that enlarge dynamic range of the optical feeder are reported. >

Feasibility studies on an optical fiber feeder system for microcellular mobile communication systems

The optical fiber feeder system is a wideband and low-loss radio signal feeder system for use between a base station (BS) and micro-base stations (micro-BSs). This system can realize very compact micro-BSs and easy radio channel assignment control in the BS. Calculations and experiments confirmed that the optical feeder can transmit a 1.5 GHz band digital mobile telephone signal, composed of five carriers (pan-European GSM-type eight-channel TDM), through 20 km of optical fiber with more than 75 dB CNR and less than -80 dBc intermodulation distortion.<<ETX>>

Block demodulation for short radio packet

The demodulation of phase-modulated signals is performed primarily by synchronous detection which has excellent characteristics. Thus, to regenerate a reference carrier wave that is identical with the transmitted one, a pure carrier should be received for a fixed time as a preamble before the data. Therefore, in digital radio terminals which are expected to appear, if a single extremely short information data burst has to be transmitted, it would possibly require the addition of a long preamble. If the relative carrier frequency offset is large in a low-speed transmission system, then a longer preamble is necessary. This paper proposes a demodulation system for phase-modulated signals which allows a shorter preamble or eliminates the need for it completely. The proposed system is based on the recent rapid progress in the speed, capability, and price of the microprocessors which obviates immediate demodulation, but makes it practical to store a data sequence of a fixed length without any demodulation. In addition, it is possible to realize the demodulation with batch processing by a block demodulation system. In such a system the complete transmitted burst signal containing no preamble can be demodulated with the optimum carrier phase. If this system is used merely as a frequency offset detector, it can complete the detection more than 5 times faster than a phase-locked system under the same noise conditions.

Preambleless demodulator for satellite communications

A high-performance demodulator capable of demodulating packetized data without preamble sequence in a very low bit-energy-to-noise (Eb/NO) environment is described. The design uses newly developed algorithms for estimating precise input carrier phase and frequency on the basis of a near-maximum-likelihood (ML) estimation strategy. Performance obtained through experiments satisfies a 2.5-dB Eb/NO requirement to demodulate 512-b packetized data at 1*10/sup -2/ packet loss probability. An experimental system that has been built to evaluate system performance, along with very small aperture terminal (VSAT) system parameters, is presented. The results are quite satisfactory, giving prospects for future VSAT applications.<<ETX>>

Upstream-FDMA/downstream-TDM optical fiber multiaccess network

The upstream-frequency-division-multiple access/downstream-time-division multiplexing (UFDMA/DTDM) optical multiaccess network is discussed. The system design for the proposed network is outlined. In this network, superluminescent diodes, which have a wide optical spectrum linewidth, are used as transmitter light sources in the network terminators to avoid optical beat interference. The carrier to noise ratio (CNR) and the dispersion power penalty are calculated to determine the channel capacity. For example, in the 1.5 mu m wavelength region. 800 Mb/s downstream channel capacity and 1.5 Mb/s upstream channel capacity are applicable for 32 network terminators and a 10 km optical fiber.<<ETX>>

Non-stop subscriber radio coexisting with 4 approximately 6 GHz band long haul digital microwave radio

The author proposes that subscriber radio should be operated in coexistence with high capacity long haul-digital microwave system in 4-6 GHz bands, where it is easy to obtain systems immune to rainfall attenuation and with relatively high system gain. The required modifications for the existing long haul system are to strengthen the transmitter out-of-band emission suppression and to adopt cochannel radio-frequency allocation. Coexistence with local distribution radio can be allowed in the vacant band gaps between adjacent channels in the cochannel scheme.<<ETX>>

Block demodulation for short radio packet: Block demodulation for short radio packet

The demodulation of phase-modulated signals is performed primarily by synchronous detection which has excellent characteristics. Thus, to regenerate a reference carrier wave that is identical with the transmitted one, a pure carrier should be received for a fixed time as a preamble before the data. Therefore, in digital radio terminals which are expected to appear, if a single extremely short information data burst has to be transmitted, it would possibly require the addition of a long preamble. If the relative carrier frequency offset is large in a low-speed transmission system, then a longer preamble is necessary. This paper proposes a demodulation system for phase-modulated signals which allows a shorter preamble or eliminates the need for it completely. The proposed system is based on the recent rapid progress in the speed, capability, and price of the microprocessors which obviates immediate demodulation, but makes it practical to store a data sequence of a fixed length without any demodulation. In addition, it is possible to realize the demodulation with batch processing by a block demodulation system. In such a system the complete transmitted burst signal containing no preamble can be demodulated with the optimum carrier phase. If this system is used merely as a frequency offset detector, it can complete the detection more than 5 times faster than a phase-locked system under the same noise conditions.