Showing papers on "Co-channel interference published in 1979"

Contention interference detection by comparison of transmitted and received signal information

Abstract: When a plurality of transceivers share a common communication medium or radio frequency channel, then collision interference will result when two or more transceivers transmit simultaneously. In order to detect this simultaneous transmission, an interference detector apparatus compares the received information after demodulation to that of the transmitted information before modulation. The classification of the distorted signals into either of the two decoded output states permits this interference to be detected with a comparison. The output from the interference detector is used to interrupt the transmitter when collision interference is present on the medium. It is also used to inhibit the receiver from generating erroneous data during the interference duration.

The simulcasting technique: An approach to total-area radio coverage

Abstract: The simulcasting technique described provides total-area radio coverage on an automatic basis where the use of multiple transmitter and receiver sites is required to achieve acceptable communications coverage over rugged terrain or wide areas. In this technique the same audio information is simultaneously broadcast over several transmitters operating on a single nominal-carrier frequency. Special attention must be given to transmitter-frequency stability and audio envelope characteristics. A master tone-distribution system is essential when incorporating a continuous tone-controlled squelch system (CTCSS). Use of the simulcasting technique reduces effects of fading in a mobile environment through transmitter space diversity. An application of the simulcasting technique to a coordinated FM-UHF law-enforcement communications system in Orange County, CA, is described.

Contention interference detection in data communication receiver

Abstract: When a plurality of transmitters share a common communication medium or radio frequency channel, collision interference will result when two or more transmissions overlap in time. An interference detector apparatus is used to sense this simultaneous transmission. The use of code redundancy in transmitting data over the medium in conjunction with a code classifying decoder apparatus permits interference to be detected within the receiver. The interference detector signal interrupts its own transmitter or a plurality of transmitters, when collision interference is present on the medium. This truncation of transmission improves the channel capacity of the shared medium. The interference signal can also be used to inhibit a receiver from generating erroneous data during the interference duration.

Signal-to-Noise Ratio Statistics for Nondispersive Fading in Radio Channels with Cross Polarization Interference Cancellation

Abstract: The signal-to-noise ratio (SNR) statistics of a crosspolarized interference cancellation scheme is derived in terms of the statistics of nondispersive fading of the signals in the radio channels. The results are applied to certain digital radio channels subjected to nondispersive fading. It is found that error rates not exceeding 10-6could be maintained during 99 percent of the duration of a 30 dB fade in a 26.4 mi path. The method and data presented support the feasibility of cross polarization interference cancellation. They are applicable to the determination of SNR budget in the transmission system.

Significant Receiver Intermodulation (RIM) Products

Abstract: Results of measurements of receiver intermodulation products are reviewed. A large number of products were identified, many of which could result in degradation of performance of communications receivers collocated with transmitters using the same or adjacent tuning ranges. Probable mechanisms are described and suggestions provided for ranking the relative significance of the various interactions.

The effects of mobile radio channel bandwidth reduction on spectrum usage

Abstract: The paper discusses the implications of channel splitting and examines the objections which have been raised against reducing channel widths below 25 kHz. It shows that, although the intermodulation products multiply in number, with suitable planning procedures the increase, if anything, tends to improve the choice of frequencies to be allocated. This is particularly so in the case of two frequency operation. Reuse is examined in relation to various layout configurations and shows clearly that spectrum efficiency is improved as bandwidths are reduced.