Showing papers on "Co-channel interference published in 1990"

Method of monitoring cellular radio channels to avoid adjacent and co-channel interference

Abstract: A method to enhance the quality of cellular radio service is disclosed. Only those channels that have a reduced likelihood of co-channel or adjacent channel interference are allocated. This technique, in addition, allows information to be provided to the operating company of drawbacks with the currently engineered RF environment. In particular, the base station will scan for RSSI readings on its channel and channels adjacent to it. If a RSSI measurement above a predetermined threshold is detected, it is assumed that the base station is intercepting a signal from a mobile that is presently being served by another voice channel on an adjacent cell. If this base station were selected to process a call, it may interfere with the call that is already in progress on the current channel or a call that is in progress on an adjacent channel. The base station will inform the controller when it detects a RSSI reading above the predefined threshold indicating that the possibility for co-channel and adjacent interference exists. It will also inform the controller when the detected RSSI reading has gone back below the predefined threshold indicating that the possibility for co-channel and adjacent interference has ceased. If an idle voice channel reports the possibility of co-channel or adjacent interference, it will not be chosen to process a call until all other voice channels that are not reporting interference are in use. When the voice channel reports that the possibility for co-channel or adjacent channel interference has ceased, it will be returned to its normal priority level to be selected to process a call.

On the spectral efficiency of CPM systems over real channel in the presence of adjacent channel and cochannel interference: a comparison between partial and full response systems

Abstract: In all the new radio systems to be designed-for example, local radio networks or portable communication systems-a crucial point is determination of the actual spectral efficiency obtainable. To this end, the fundamental role played by adjacent and cochannel interference must be considered. The computer program implemented allows general analysis of continuous phase modulation (CPM) systems with limiter-discriminator detection and symbol-by-symbol regeneration, the combined effects of intersymbol interference, noise, and adjacent channel or cochannel interference have been tested to give the design criteria of the transmission system. To emphasize the role played by interference, an ideal multipath-free channel has been considered: with reference to a binary case, Gaussian minimum-shift keying (GMSK) systems have been investigated and compared with full-response CPM systems to obtain a suitable tradeoff between spectral efficiency (connected to channel spacing at radio frequency) and signal-to-noise ratio with fixed bit-error probability. The numerical results presented emphasize the performance obtainable with full- and partial-response techniques for varying system parameters such as phase deviation index, receiver filter bandwidth, and spectral efficiency. >

Communication system that avoids co-channel interference

Abstract: Co-channel user (129) interference on trunked radio communication systems cannot be compensated for in the same way as conventional radio systems because the communication unit does not know what frequency it will be assigned to until it begins transmitting. Placing an additional receiver (119) in the coverage area (125) of the co-channel user (129) and sending information of recent co-channel usage to the controller (101) allows the controller (101) to decide which channel has the least likelihood of co-channel interference so that it may be assigned.

Method and apparatus for reducing co-channel interference in an HDTV receiver

Abstract: NTSC co-channel interference is reduced in an HDTV receiver by developing an interference signal that is representative of the high energy components in the NTSC signal and subtracting the interference signal from the received HDTV signal to produce an enhanced HDTV signal for processing.

Evaluation of diversity schemes in TDMA digital mobile radio

Abstract: Diversity receiver structures are discussed in the context of a digital mobile radio system using time division multiple access (TDMA). Both selection diversity and combining diversity are considered. Simulation results are presented, with reference to the European GSM (Groupe Speciale Mobile) system, taking into account frequency selective Rayleigh fading and cochannel interference. Receiver structures and simulation results provide useful information for a performance/complexity tradeoff. It is shown that an estimate of signal quality, based on the TDMA preamble processing, can substantially improve the performances in any of the examined schemes, particularly in the interference-limited environment. >

High power broadcasting skywave transmitters interference analysis for navigation and communication systems

Abstract: The operation of high-power broadcasting transmitters (Tx) can strongly interfere with collocated and even remote radio communication and navigation systems on broad frequency ranges. In these cases, extensive analysis and computation method developments are essential in order to assess the feasibility of reliable operation of indispensable radio communication links. The magnitudes of the interference effects are computed, based on specifications of 500 kW skywave Tx parameters and the important airborne VHF radio navigation and communication systems. The critical interference (i.e. desensitization or blocking of the victim airborne receivers) and other interference modes are analyzed using semiempirical state-of-the-art computation methods. Limits for victim receiver distances and frequency intervals for no-interference situations and optimal reception conditions are obtained. >

Narrowband interference identification and rejection applied to baseband radio signals

Abstract: Describes a system for identifying narrowband interference (e.g. CW and FEK) in a 3 kHz HF radio channel. The system is able to detect and eliminate such interference under severe HF channel conditions of frequency selective fading and noise. This signal processing technique can enhance the performance of broadband (3 kHz) HF radio systems subject to narrowband interference, and an example of this is presented. The performance of the currently implemented algorithm is outlined and the application of the technique to different signal formats is discussed. The system uses a programmable finite impulse response (FIR) filter implemented on a digital signal processor to remove unwanted interference. The signal processor also performs the spectrum analysis of the baseband 3 kHz radio channel and makes the decisions on the structure of the interference to enable rejection to take place. >

Adjacent and co-channel interference avoidance

Abstract: A method to enhance the quality of cellular radio service is disclosed. Only those channels that have a reduced likelihood of co-channel or adjacent channel interference are allocated. This technique, in addition, allows information to be provided to the operating company of drawbacks with the currently engineered RF environment. In particular, the base station will scan for RSSI readings on its channel and channels adjacent to it. If an RSSI measurement above a predetermined threshold is detected, it is assumed that the base station is intercepting a signal from a mobile that is presently being served by another voice channel on an adjacent cell. If this base station were selected to process a call, it may interfere with the call that is already in progress on the current channel or a call that is in progress on an adjacent channel. The base station will inform the controller when it detects an RSSI reading above the predefined threshold indicating that the possibility for co-channel and adjacent interference exists. It will also inform the controller when the detected RSSI reading has gone back below the predefined threshold indicating that the possibility for co-channel and adjacent interference has ceased. If an idle voice channel reports the possibility of co-channel or adjacent interference, it will not be chosen to process a call until all other voice channels that are not reporting interference are in use. When the voice channel reports that the possibility for co-channel or adjacent channel interference has ceased, it will be returned to its normal priority level to be selected to process a call.

The theoretical performance of optimal time-dependent filters for co-channel interference rejection

Abstract: Using the performance criterion of mean-square-error, periodically time-dependent and almost periodically optimal time-dependent filters (OTDF) are shown to be theoretically superior to time-independent optimal filters for suppressing cochannel interference in digital communications. The time-dependent filter is shown to be capable of exploiting the spectral correlation properties of digital communication signals to provide superior performance. The mathematical framework of the OTDF is formulated, and its performance for extracting various modulated signals in noise and for extracting these signals in interference is examined. The performance of the OTDF is described in terms of mean-square error. Examples that demonstrate the theoretical performance advantage of the optimal time-independent filter over the time-independent optimal filter for digitally modulated signals are presented. >

Performance of equalization techniques in a radio interference environment

Abstract: The performance of equalization techniques for digital radio systems in the presence of sinusoidal and modulated interference signals is investigated. Linear and nonlinear equalizers as well as synchronous and T/2-spaced structures are considered. It is shown that synchronous decision-feedback equalizers are powerful countermeasure devices for radio channels affected by both selective fading and sinusoidal interferers. It is also demonstrated that T/2-spaced linear and nonlinear equalizers can significantly improve the adjacent channel interference margin, especially in the case of multicarrier interleaved frequency arrangements. >

The error probability performance of Gray encoded QPSK scheme with co-channel interference in a slow fading indoor channel

Abstract: A theoretical analysis of the error performance of a Gray encoded quadrature phase shift keying (QPSK) scheme in the presence of thermal Gaussian noise and a fading cochannel interference signal in a slow fading indoor wireless channel is presented. The exact error probability expression is presented in a closed form with the error manifesting the combined effect of noise and interference. The system model and the underlying assumptions are specified, and the problem is formulated. The expressions for the bit and symbol error rates are derived. The performance plots and conclusions are presented. It is shown that the exact bit error ratio and the symbol error can be expressed in a closed form. >

Calculate interference digital microwave links

Abstract: A method is developed for determining interference into digital radio systems from other digital radio systems. Interference from FDM-FM (frequency division multiplexing/frequency modulation) systems can also be calculated. Once the algorithm for the receiver is found, all that is required to be known of the transmitter is its spectrum characteristics, i.e., amplitude versus frequency characteristics. Essentially, the digital receiver is defined as being a Butterworth filter with a cut-off characteristic related to the symbol rate. Initially it is important to be able to calculate the co-channel C/I (carrier/interference) relationship. This is normally done by using mathematical formulae and complementary error functions. The authors give values for the C/N (carrier/noise ratio) for various modulation schemes and then show how to translate that to a C/I value to be added to the faded signal level. The C/N's for various modulation schemes are given. >

A cositable ground radio for Have Quick and SATURN

Abstract: When transceivers are closely situated, reception by one radio can be prevented by nearby transmissions from another. Classical filtering techniques are difficult to employ when the radios are operating in the Have Quick mode which employs slow frequency hopping throughout the 225 to 400 MHz UHF band. They are even more challenging when the SATURN fast frequency hopping system is used. The author examines the effects of desensitization, cross modulation, broadband noise, spurious output, and intermodulation products with a SATURN ground radio recently developed by ESD. It predicts both the Have Quick and SATURN performance which can be obtained when four radios are used in an MCE or TRC-87 shelter. >

Measurement techniques for narrowband interference to loran; technical rept. sep 89-oct 90

Abstract: The paper represents follow-on work to a previous paper, where the authors primarily considered the problems of cross-rate and skywave interference. Here they also discuss the issue of interferene to LORAN, but now specifically address the problems associated with narrow band interference such as power line carrier (PLC) and Navy FSK interference, and present theory and measurement techniques for detection. Specifically, they introduce a model that simplifies the exact calculation of the LORAN spectrum and predicts the effects of interference on observed Time Delay (TD) or Time Of Arrival (TOA). They derive equations that relate amplitudes of interference relative to LORAN signal strength to peak variations in observed TD and TOA (for synchronous or near synchronous interference), and to rms variations (for non-synchronous or wideband interference). Furthermore, they consider various techniques in detecting interfering signals within the LORAN band in the presence of strong LORAN signals, and present methods to determine if the interference is synchronous, near synchronous or non-synchronous. Finally, they give examples showing ana lysis methods for typical types of existing narrowband interference sources, including Naval communications stations, time dissemination signals, and power line carriers.

The effect of shadowing on GMSK land mobile radio system

Abstract: Gaussian-filtered minimum-shift keying (GMSK) is proposed as effective digital modulation for mobile radio systems. The performance for GMSK is analyzed. Cochannel interference probabilities are evaluated for mobile radio systems operating in an environment where the fading is mitigated by adopting diversity reception. The protection ratio of the modulation and the cochannel interference probabilities are used to calculate the reuse distance and the number of channel sets needed for a cellular system. The conclusion is that the number of channel sets needed increases rapidly with the increase of standard deviation as the interference probability is fixed. With a high standard deviation users will suffer high interference and it is suggested that a greater reuse distance be used. For a given interference probability, a high protection ratio required by the modulation scheme will also increase reuse distance. >

Interference-Related Studies of Slant-Path Attenuation and Bistatic-Hydrometeor Scatter

Abstract: Co-channel interference may be caused by bistatic scattering of electromagnetic waves from hydrometeors The degradation of a wanted signal on a slant-path link due to interference depends on the signal-to-interference ratio, and thus also on the concurrent attenuation on the wanted path To investigate these propagation effects, concurrent measurements of bistatic scattering and attenuation have been performed in the 30-GHz band in a realistic scenario Statistical data are presented for several geometries, to make the results more generally applicable

Coding for multicarrier digital radio systems

Abstract: The authors investigate the performance of systems which combine the techniques of multicarrier transmission and block-coded modulation. Coding of the subchannels in multicarrier systems is made jointly, i.e. the codewords are formed by the symbols simultaneously transmitted on the different subchannels. With respect to separate encoding of the subchannels, this technique leads to significantly better performance in the presence of multipath fading and narrowband tone interference and adjacent channel interference. Simulations made using a multipath fading channel and tone interference confirmed that coding is significantly more effective than in single-carrier systems. >