Showing papers on "Co-channel interference published in 1978"

A heuristic technique for assigning frequencies to mobile radio nets

Abstract: In preparing or revising an RF channel plan for a group of mobile radio nets operating in the same region, the order in which the nets are assigned channels can be crucial to success. One well-known principle for selecting such an assignment sequence is to rank the channel requirements of the various nets in descending order of "assignment difficulty." This paper describes an easily automated heuristic assignment technique in which the channel requirements that prove themselves to be "difficult," through repeated failures to be assigned channels, rise rapidly toward the top of the list of requirements. The heuristic technique is useful in solving complex frequency-assignment problems that involve cochannel, adjacent-channel, spurious and intermodulation interference; nonrepetitive zone structures; fixed pre-existing frequency assignments; and frequency-resource lists that contain gaps and vary from zone to zone.

Co-Channel Interference of Spread Spectrum Systems in a Multiple User Environment

Abstract: This paper considers the mutual interference problem of several users employing the same spread spectrum technique in selected multiple user environments. The spread spectrum techniques consist of pseudo noise (PN), time division multiple access/PN, synchronous and asynchronous frequency hopping (FH). The environment consists of a desired transmitter-receiver pair located in an area where there are M interfering users distributed in accordance with a specified probability density function. Both coherent phase-shift-keyed-and noncoherent frequency-shift-keyed modulations are considered. The general relationship between the probability of bit error of PN and FH systems is derived which is independent of the signal modulation and distribution of users. The degradation of the communication system performance (average probability of bit error) of the desired link as a function of the total number of interfering users within the considered area is investigated. The analysis shows that the mutual interference problem is less severe with users employing synchronous FH than with the other spread spectrum techniques. The comparison between asynchronous FH and PN is highly dependent on the relative location of interferers to the desired link and the time duty factor of the hopping.

Automatic channel selection

Abstract: HF and VHF radio channels which are subject to time-varying propagation aalies and to interference are arranged in groups according to frequency band Within each group are several channels, each spaced sufficiently close so that they experience essentially the same propagation The several channels in each group are continuously measured to find which channels have the least ambient energy levels, then one of those channels is selected in a random manner to transmit data

Effects of Thermal Noise, Filtering and Co-Channel Interference on the Probability of Error in Binary Coherent PSK Systems

Abstract: An analytical method for evaluating the bit error probability in Binary Coherent Phase Shift Keying (BCPSK) systems is presented. The system impairments considered are additive Gaussian noise, intersymbol interference and co-channel interference. The method is based on the power series expansion of the characteristic function of the interferences. Each characteristic function is expanded in a power series and its coefficients are averaged analytically with respect to the random phase and the bit timing alignment. Numerical examples are given to illustrate the method and to provide design data for system designers.

A simple mathematical model of co-channel and adjacent channel interference in land mobile radio

Abstract: A simple mathematical model is used to predict co-channel and adjacent channel interference effects in land mobile radio, valid for flat urban terrain. Results obtained, although oversimplified compared with real-life mobile radio systems, yield insights into the properties of differing types of modulation.

Radio interference bucker apparatus

Abstract: An apparatus for intercepting radio waves emitted from a relatively local interference radio-wave-emitting source and processing the same so that they may be fed into the antenna terminal of a radio wave receiver for accomplishing substantially interference-free reception of distant radio wave stations. An antenna suited for only local reception provides the interfering radio wave energy to the bucker apparatus. Therein it is amplified a selected amount and the phase thereof altered by a continuously adjustable delay means to accomplish the desired cancellation of interference by phase opposition of the interfering signal from the bucker with respect to the interfering signal as it is received at the antenna terminal of the radio wave receiver.

Periodic switching diversity effect on co-channel interference performance of a digital FM land mobile radio

Abstract: The effect of periodic switching diversity on the bit error rate (BER) performance of a binary frequency-shift keying (FSK) system in the presence of co-channel interference is described. The distribution of the signal-to-interference energy ratio per bit presented to the FM detector is found and the diversity effect on the BER performance in a Rayleigh fading environment is analyzed. The diversity effect on the BER performance in a Manchester-coded FSK system with limiter-discriminator detection is verified by laboratory simulation tests using a Rayleigh fading simulator.

Spread Spectrum Interference to Voice Communications Systems

Abstract: A computer s im u la t io n model d eve lop ed f o r d e t e r ­ mining th e manner in which u n d e s ire d spread spectrum s i g n a l s a f f e c t th e perform ance o f c o n v e n t io n a l narrow­ band AM and FM v o i c e communications system s i s o u t ­ l in e d . D ir e c t s e q u e n c e , freq uency-hopp in g and h y b rid , fr e q u e n c y -h o p p in g /d ir e c t s e q u e n c e , spread spectrum in t e r f e r e n c e s i g n a l s were modeled. Using a r t i c u l a t i o n index as th e measure o f perform ance, com parisons are made between system performance f o r d ir e c t s e q u e n c e i n t e r f e r e n c e and w h ite Gaussian n o i s e . System p e r ­ formance f o r freq uency-hopp in g o r fr eq u en cy -h o p p in g / d ir e c t s e q u e n c e in t e r f e r e n c e i s compared w ith th a t fo r p u lsed in t e r f e r e n c e .

A Preliminary Estimate of the Effects of Spread–spectrum Interference on TV

Abstract: The report examines the conditions under which spread–spectrum, land–mobile radio, and television can share spectrum. After a preliminary assessment, the report concludes that the interference caused by a constant amplitude, spread–spectrum system should be comparable to that caused by a conventional, narrowband, FM, land mobile signal of same total power, provided the spread–spectrum signal has an rf bandwidth less than 2 MHz. With spectrum spreads greater than 6 MHz, the spread–spectrum system should have some acivantage because of the out–of–band rejection capabilities of a TV receiver. A limited number of laboratory measurements are also described that support the conclusions of the report.

The Fadeogram, A Sonogram-Like Display of the Time-Varying Frequency Response of HF-SSB Radio Channels

Abstract: A method is presented for displaying the time-varying transfer characteristic of communication channels, and is illustrated by showing in detail the behavior of an HF-SSB radio channel during one minute periods, under the various fading characteristics classified by USAEL. It is also demonstrated how this method aided study of the causes of errors in data received by digital modems.