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Abstmct-A PSK group modem which modulates and demodulates multiple PSK signals en bloc will play an important role in realizing a cost-effective satellite communications system based on the narrowband multicarrier PSK/FDMA technique. This paper briefly discusses its possible applications, and presents a developed PSK group modem including its algorithm, hardware design, and implementation. In the algorith'm, filtering of respective PSK signals is effectively carried out by digital signal processing techniques applied to the digital transmultiplexer. Furthermore, in order to compensate for the ,difference between the operation timing of the PSK group modem and the symbol timing of each input/output data signal, digital signal processings based on a table-look-up method using ROM and a rate-conversion filter with adaptive weighting are proposed for the modulator and demodulator, respectively. An experimental 4-phase PSK group modem has been developed, and experiments have been conducted under various conditions. The measured performance of the developed hardware is also demonstrated.

SUMMARYThe 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 phaselocked system under the same noise conditions. . IntroductionThe demodulation of the phase-modulated signals is performed mainly by coherent detection which has excellent characteristics. During detection, however, a reference carrier is needed which is identical with the transmitted one. Therefore, to regenerate a 47 reference carrier at the receiver side, usually a pure carrier wave is transmitted as a preamble from the transmitter side for a fixed period before the information signal. Then, as soon as the reference carrier is available at the receiver side, the transmission of the phase-modulated signal may begin.In digital radio terminals expected to appear in the near future, the transmission of single extremely short information data bursts would possibly require the addition of a long preamble. Particularly, in lowspeed digital SCPC (Single Channel per Carrier) transmission systems, the relative carrier frequency drift (the ratio 6f/R of the carrier frequency drift 6f and the data symbol rate R) exceeds even the value of 1/8 to 1/16, which results in a slower carrier regeneration time and thus requires a longer preamble. Therefore, it is desirable here that the duration of the nonused carrier wave be shorter or eliminated completely from the demodulation process of the phasemodulated signal. For digital transmission the need for timing information is natural and the system must be designed to ensure that the timing information is independent of the radio frequency instabilities. Specifically , if a radio network in star configuration consists of a master and several slave stations, and the slave clocks are synchronized to the master, or the s...

A PSK group modem which modulates and demodulates multiple PSK signals en bloc will play an important role in cost-effective satellite communications systems based on the narrow-band multicarrier PSWFDMA technique. This paper describes the development of a PSK group modem, including its algorithm, hardware design and implementation. In the algorithm, PSK signals are efficiently filtered by digital signal processing applied to the digital transmultiplexer. Furthermore, in order to compensate for the difference between the operation timing of the PSK group modem and the symbol timing of each inputloutput data signal, digital signal processing based on a table-look-up method using ROM and a rate-conversion filter with adaptive weighting are proposed for the modulator and demodulator, respectively. An experimental four-phase PSK group modem has been developed, and experiments have been conducted under various conditions. The measured performance of the developed hardware is also demonstrated.