Block demodulation for short radio packet

Abstract

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...

Earth satellite communication systems with low orbits, and effects of the doppler shift

“…(11) into Eq. (12), we can obtain the following condition: (13) From here, if, for example, the orbit at an altitude of 1000 km is considered, then from Fig. 4, Lax is nearly 2.1 X Thus if we take the camer frequency of 2 GHz, Q = 100, and f = l/a, then W, should have the wide bandwidth of nearly 40 MHz for camer correction.…”

A study of the communication systems using the low-altitude nongeostationary satellites

“…The configulation of a receiver with a block demodulator is shown in Figure 5-B [ 5 ] . The received signal is first multipled by the fixed reference signal whose frequency is the same as that of transmitted one and filtered by a Low-Pass-Filter with bandwidth B.…”

Spread spectrum demodulator using block signal processing

“…The received SS signal is demodulated quasicoherently [5][6] [8], and sampled. The quantized signal is once stored in memory.…”

“…Applying SS techniques to the radio networks, therefore, the data transmission efficiency will be extremely degraded by the data loss due to the initialacquisition of PN-code. By the way, PSK demodulator using block signal processing has been actively studied in satellite communication systems [5][6] [7]. In land mobile communications, however, it will not be easy to estimate the carrier offset against interference, multipath, and collision with other signals.…”