Showing papers on "Co-channel interference published in 1973"

Interference into Angle-Modulated Systems Carrying Multichannel Telephony Signals

Abstract: An investigation of interference between angle-modulated systems carrying multichannel telephony, which is directly applicable to existing satellite and terrestrial radio-relay systems, has been undertaken. This study includes a general solution for arbitrary narrow-band interference into an angle-modulated system with arbitrary modulation. The algorithm has been implemented on a digital computer to provide calculations of interference between two FDM/FM systems. The analysis is valid for all modulation indices, and may be applied to any PM, FM, or preemphasized FM baseband. A comparison of calculated results and experimental measurements shows good agreement. An extensive investigation, covering a wide range of modulation indices and basebands, has been conducted for the particular case of preemphasized FDM/FM signals. Wherever possible, a generalized presentation of interference results is given. Interleaving criteria are also presented for certain cases of interference involving two identical signals.

Effect of Co-Channel Interference on CPSK Carriers

Abstract: This paper investigates the problem of estimating the effects of interference to a coherent phase-shift-keyed (CPSK) digital carrier. Paralleling Saltzberg [1], the principal tool utilized is the CramerChernoff bounding technique. The interference effects can be characterized by equating the larger interferers to an equivalent coherent canceling sine wave and the remaining interferers to an equivalent incoherent source of thermal noise. Subject to an envelope constraint, any allocation of the interferers between a canceling sine wave and thermal noise is allowed. Conditions are developed for the case: 1) when all the interference should be allocated to thermal noise; and 2) when as much as possible of the interference should be allocated to a canceling sine wave. This provides insight into the formal procedure of equating interference as additional thermal noise.

A volterra series description of crosstalk interference in communications systems

Abstract: This paper studies a general description of interchannel and intra-channel crosstalk interference created in a communications system. This description is in the form of a Volterra series expansion of the interference signal in terms of the signal which produced the interference. From it we are able to precisely define the “intelligible” part of the crosstalk. This description also provides us with quantitative measures of the amount of crosstalk created in some communications channel by signals in another channel, as well as a measure (intelligible crosstalk ratio) of the amount of intelligible crosstalk produced. We then consider a particular model for the generation of intelligible crosstalk [or direct adjacent channel interference (DACI)] between two neighboring angle-modulated channels in which the signal in one channel adds to the signal of the second channel, the sum is filtered, and the filter output then passes through an AM-PM conversion device. Using our definition, a simple expression for the intelligible crosstalk ratio for this model is derived in terms of the filter characteristic. We observe that this crosstalk ratio exhibits a number of properties usually associated with DACI.

Binary and Quaternary PSK Radio Systems in a Multiple-Interference Environment

Abstract: The planning of a digital radio network requires an evaluation of the effect of quite a large number of interfering sources. These in turn are dependent upon many parameters, such as the network structure, channel arrangement, antenna patterns, and so on. This paper presents a performance analysis of a digital radio-relay system during fading periods. The possibility of attaining a required fading margin is analyzed when many co-channel and interchannel interferences are simultaneously present, both for long-haul and shorthaul radio relay systems. A comparison is presented between two possible techniques for the reusing of the same frequency band in each hop, by taking advantage of the cross-polarization discrimination (XPD). The reduction of the XPD expected during fading periods is also taken into account. Binary and quaternary coherent PSK modulations are considered, with realizable filters (of the Butterworth type), both at the transmitter and at the receiver. The error probability calculations were performed with a combined analytical and computer simulation approach. The results seem to indicate the feasibility of the frequency reuse technique.

Analysis of Radio Paging Errors in Multitransmitter Mobile Systems

Abstract: Many mobile telephone and personal paging systems require signaling simultaneously from multiple transmitters. This paper analyzes the factors that cause paging errors due to interference when the signaling format consists of audio tones sent simultaneously from two FM transmitters. The factors considered are: drift in carrier and modulation frequencies, and misequalization of land-line amplitude and audio delay. The following results are shown: 1) the interference errors are eliminated if the land lines are amplitude and phase equalized, 2)if the lines are not equalized but the modulation frequencies are equal, then the interference errors can be decreased by an order of magnitude if the transmitters are mistuned such that their difference carrier frequency is just greater than the modulation tone filter bandwidth in the receiver, and 3) if the modulation frequencies are slightly different, then the interference errors can be decreased somewhat by misequalizing the modulation indicies. It is then concluded that if the land lines are not equalized and the signaling tones are not exactly equal, the interference errors cannot be eliminated, but can be decreased by properly aligning the system.

Baseband Performance of a Pilot Diversity System with Simulated Rayleigh Fading Signals and Co-Channel Interference

Abstract: Using simulated Rayleigh-fading FM signals, the baseband performance of a diversity system that uses a separate pilot is studied. The effect of various RF/audio bandwidth expansion ratios is included. These results show an approach to a constant asymptotic baseband SNR for large expansion ratios, with diversity increasing this asymptote by 5 dB in the case of moderate to large interference and/or RF noise levels (9 to 15 dB below the carrier), to over 10 dB in the case of lower impairment levels (21 to 27 dB below the signal level). Assuming the usual hex-cell radio coverage plan, and a propagation law of the form r^{-n}, n = 3 or 4, bandwidth expansion ratios of about three to six seem to yield the most efficient RF spectrum utilization in many practical situations. The number of required channel subsets (cells) is strongly influenced by the propagation law ranging from about 19 for n = 3 , to about 7 for n = 4 .

Analysis of radio paging errors in multitransmitter mobile systems

Abstract: Many mobile telephone and personal paging systems require signaling simultaneously from multiple transmitters. This paper analyzes the factors that cause paging errors due to interference when the signaling format consists of audio tones sent simultaneously from two FM transmitters. The factors considered are: drift in carrier and modulation frequencies, and misequalization of land-line amplitude and audio delay. The following results are shown: 1) the interference errors are eliminated if the land lines are amplitude and phase equalized, 2)if the lines are not equalized but the modulation frequencies are equal, then the interference errors can be decreased by an order of magnitude if the transmitters are mistuned such that their difference carrier frequency is just greater than the modulation tone filter bandwidth in the receiver, and 3) if the modulation frequencies are slightly different, then the interference errors can be decreased somewhat by misequalizing the modulation indicies. It is then concluded that if the land lines are not equalized and the signaling tones are not exactly equal, the interference errors cannot be eliminated, but can be decreased by properly aligning the system.

Properties of mobile radio propagation above 400 MHz

Abstract: This paper begins with a discussion of multipath interference. The spatial description of the field impinging upon a mobile radio antenna is derived and the power spectrum and other properties of the signal envelope are considered. Next, large scale variations of the average signal are discussed. Measurements of observed attenuation on mobile paths over both smooth and irregular terrain are summarized. The paper concludes with a discussion of methods of predicting the area of coverage from a base station.

Baseband performance of a pilot diversity system with simulated Rayleigh fading signals and co-channel interference

Abstract: Using simulated Rayleigh-fading FM signals, the baseband performance of a diversity system that uses a separate pilot is studied. The effect of various RF/audio bandwidth expansion ratios is included. These results show an approach to a constant asymptotic baseband SNR for large expansion ratios, with diversity increasing this asymptote by 5 dB in the case of moderate to large interference and/or RF noise levels (9 to 15 dB below the carrier), to over 10 dB in the case of lower impairment levels (21 to 27 dB below the signal level). Assuming the usual hex-cell radio coverage plan, and a propagation law of the form r-n, n = 3 or 4, bandwidth expansion ratios of about three to six seem to yield the most efficient RF spectrum utilization in many practical situations. The number of required channel subsets (cells) is strongly influenced by the propagation law ranging from about 19 for n = 3, to about 7 for n = 4.