258,730 research outputs found
Redundant RF system for space application
An S-band radio frequency subsystem is described including two transmitters, two receivers and two antennas. The subsystem is capable of connecting either transmitter or receiver to either antenna while permitting simultaneous operation of a transmitter and a receiver. Circulator switches provide selection of a specific transmitter and receiver for connection to either a high gain or low gain antenna. Transmitter output filters, receiver input filters, and diplexers are combined to prevent radiation or coupling or unwanted transmitter and receiver signals and to provide isolation, permitting simultaneous operation of the transmitter and receiver. The filter elements are designed of constant diameter coaxial elements to meet demanding rejection, loss, power-handling and environmental characteristics
Capacity Gain from Two-Transmitter and Two-Receiver Cooperation
Capacity improvement from transmitter and receiver cooperation is
investigated in a two-transmitter, two-receiver network with phase fading and
full channel state information available at all terminals. The transmitters
cooperate by first exchanging messages over an orthogonal transmitter
cooperation channel, then encoding jointly with dirty paper coding. The
receivers cooperate by using Wyner-Ziv compress-and-forward over an analogous
orthogonal receiver cooperation channel. To account for the cost of
cooperation, the allocation of network power and bandwidth among the data and
cooperation channels is studied. It is shown that transmitter cooperation
outperforms receiver cooperation and improves capacity over non-cooperative
transmission under most operating conditions when the cooperation channel is
strong. However, a weak cooperation channel limits the transmitter cooperation
rate; in this case receiver cooperation is more advantageous.
Transmitter-and-receiver cooperation offers sizable additional capacity gain
over transmitter-only cooperation at low SNR, whereas at high SNR transmitter
cooperation alone captures most of the cooperative capacity improvement.Comment: Accepted for publication in IEEE Transactions on Information Theor
Adaptive Molecule Transmission Rate for Diffusion Based Molecular Communication
In this paper, a simple memory limited transmitter for molecular
communication is proposed, in which information is encoded in the diffusion
rate of the molecules. Taking advantage of memory, the proposed transmitter
reduces the ISI problem by properly adjusting its diffusion rate. The error
probability of the proposed scheme is derived and the result is compared with
the lower bound on error probability of the optimum transmitter. It is shown
that the performance of introduced transmitter is near optimal (under certain
simplifications). Simplicity is the key feature of the presented communication
system: the transmitter follows a simple rule, the receiver is a simple
threshold decoder and only one type of molecule is used to convey the
information
Emergency locating transmitter
A transmitter generates three signals for sequential transmission. These signal are an unmodulated r.f. carrier, a r.f. carrier amplitude modulated by a first audio frequency waveform and a r.f. carrier amplitude modulated by a second audio frequency waveform which is distinguishable from the first and which may be employed as a means for identifying a particular transmitter. The composite, sequentially transmitted signal may be varied in terms of the individual signal transmission sequence, the duration of the individual signals, overall composite signal repetition rate and the frequency of the second audio waveform. Various combinations of signal variations may be employed to transmit different information
Automatic frequency control for FM transmitter
An automatic frequency control circuit for an FM television transmitter is described. The frequency of the transmitter is sampled during what is termed the back porch portion of the horizontal synchronizing pulse which occurs during the retrace interval, the frequency sample compared with the frequency of a reference oscillator, and a correction applied to the frequency of the transmitter during this portion of the retrace interval
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