Showing papers on "Co-channel interference published in 1998"

Applications of space-time block codes and interference suppression for high capacity and high data rate wireless systems

Abstract: This paper presents a combined interference suppression and ML decoding scheme for space-time block codes that can effectively suppress interference from other co-channel users while providing each user with a diversity benefit. We consider a multiuser environment with K synchronous co-channel users, each is equipped with N transmit antennas and uses the space-time block coding. By exploiting the temporal and spatial structure of these codes, we develop a minimum mean-squared error (MMSE) interference suppression technique. Assuming that the receiver uses M/spl ges/K receive antennas, these technique will perfectly suppress the interference from the K-1 co-channel space-time users and provide a diversity order of N/spl times/(M-K+1) to each of the K users. Moreover, this MMSE solution tends itself to an adaptive implementation and does not require any explicit knowledge about the interference. In conjunction with this interference suppression technique, we show how space-time block codes can be used to increasing the capacity and/or data rate of wireless communication systems.

Digital interference suppression system for radio frequency interference cancellation

Abstract: A digital signal processing system that produces an adaptive cancellation arrangement which nulls out all types of concurrent interference and/or jamming signals received by Global Positioning System (GPS) or spread spectrum receiver (7) from diverse antennas. In the present arrangement, orthogonal components of the composite received signal are separated by the receive antenna arrangement (3) and adjusted in the digital network (5) between the antenna (3) and the receiver (7) in phase and amplitude to optimally cancel components. The arrangements can be synergistically combined with digital adaptive transversal filter technology which is primarily used to supplement suppression performance by reducing narrowband interference in the band. The orthogonal received signal components from the GPS satellite constellation and from interference sources are combined in the present arrangement to adaptively create a null that attenuates interference sources while slightly modifying the GPS received signals.

A New Approach to Interference Excision in Radio Astronomy: Real-Time Adaptive Cancellation

Abstract: Every year, an increasing amount of radio-frequency (RF) spectrum in the VHF, UHF, and microwave bands is being utilized to support new commercial and military ventures, and all have the potential to interfere with radio astronomy observations. Such services already cause problems for radio astronomy even in very remote observing sites, and the potential for this form of light pollution to grow is alarming. Preventive measures to eliminate interference through FCC legislation and ITU agreements can be effective; however, many times this approach is inadequate and interference excision at the receiver is necessary. Conventional techniques such as RF filters, RF shielding, and postprocessing of data have been only somewhat successful, but none has been sufficient. Adaptive interference cancellation is a real-time approach to interference excision that has not been used before in radio astronomy. We describe here, for the first time, adaptive interference cancellation in the context of radio astronomy instrumentation, and we present initial results for our prototype receiver. In the 1960s, analog adaptive interference cancelers were developed that obtain a high degree of cancellation in problems of radio communications and radar. However, analog systems lack the dynamic range, noised performance, and versatility required by radio astronomy. The concept of digital adaptive interference cancellation was introduced in the mid-1960s as a way to reduce unwanted noise in low-frequency (audio) systems. Examples of such systems include the canceling of maternal ECG in fetal electrocardiography and the reduction of engine noise in the passenger compartments of automobiles. These audio-frequency applications require bandwidths of only a few tens of kilohertz. Only recently has high-speed digital filter technology made high dynamic range adaptive canceling possible in a bandwidth as large as a few megahertz, finally opening the door to application in radio astronomy. We have built a prototype adaptive canceler that consists of two receivers: the primary channel (input from the main beam of the telescope) and a separate reference channel. The primary channel receives the desired astronomical signal corrupted by RFI (radio-frequency interference) coming in the sidelobes of the main beam. A separate reference antenna is designed to receive only the RFI. The reference channel input is processed using a digital adaptive filter and then subtracted from the primary channel input, producing the system output. The weighting coefficients of the digital filter are adjusted by way of an algorithm that minimizes, in a least-squares sense, the power output of the system. Through an adaptive-iterative process, the canceler locks onto the RFI, and the filter adjusts itself to minimize the effect of the RFI at the system output. We have designed the adaptive canceler with an intermediate frequency (IF) of 40 MHz. This prototype system will ultimately be functional with a variety of radio astronomy receivers in the microwave band. We have also built a prototype receiver centered at 100 MHz (in the FM broadcast band) to test the adaptive canceler with actual interferers, which are well characterized. The initial laboratory tests of the adaptive canceler are encouraging, with attenuation of strong frequency-modulated (FM) interference to 72 dB (a factor of more than 10 million), which is at the performance limit of our measurements. We also consider requirements of the system and the RFI environment for effective adaptive canceling.

Adaptive antenna arrays for orthogonal frequency division multiplexing systems with co-channel interference

Abstract: A technique for estimating parameters for adaptive antenna arrays in orthogonal frequency division multiplexing systems with co-channel interference is disclosed. Channel parameter estimation is preferentially performed using a two pass process that advantageously expands the temporal scope (relative to a single pass process) and considers past, present and future temporal channel estimations during parameter estimation. Channel parameters are estimated by processing the signals through fast Fourier transforms, temporal filters, and inverse fast Fourier transforms. The temporal filters optimize parameter estimation based upon instantaneous correlation of the received signals.

Mobile radio communication device provided with functions for detecting and informing interference

Abstract: A mobile radio communication device for performing communication with a base station comprises an interference detection measure for detecting occurrence of interference to the downlink frequency and/or the uplink frequency, and an interference informing measure for transmitting information about the occurrence of the interference to the base station. The base station which received the information about the interference assigns the mobile radio communication device new time slots or a new communication carrier frequency. The mobile radio communication device has a transmission system and two reception systems which are composing a post-detection selective space diversity system, and each of the two reception systems is composed of a double superheterodyne system, in the same way as general conventional mobile radio communication devices. Interference to the downlink frequency is detected utilizing the data error rate in the demodulated reception signal in one reception system, and interference to the uplink frequency is detected utilizing the field intensity of a radio wave having the uplink frequency received by an antenna of the other reception system. The detection and informing of interference is realized by addition of a simple circuit composed of a circulator, a high frequency amplifier, a mixer and a switch to a general conventional mobile radio communication device.

GPS receiver autonomous interference detection

Abstract: Interference presents a challenge in the use of GPS for an aircraft high precision approach, by posing a threat to the accuracy and integrity of the GPS navigation solution. Such interference may result from 'unintentional' sources (such as TV/FM harmonics, radar, MSS), or may result from hostile (jamming) efforts. This research focuses on algorithms for on-board interference detection and monitoring. Types of interference considered include coherent CW and broadband, pulsed and continuous. We study the effects of different types of interference on GPS receiver measurements. From simulation and bench test validation we present interference detection algorithms based on the observable effects of the various types of interference on the GPS receiver derived measurements. Interference detection is based on a combination of the following: test statistic-correlator output power, variance of correlator output power, carrier phase vacillation, and AGC control loop gain. The role and benefits of pseudolites in reducing the adverse effects of interference are also discussed.

Co-channel interference analysis of shadowed Rician channels

Abstract: This paper presents an exact analysis of co-channel interference (CCI) in a shadowed-Nakagami (desired)/shadowed-Rician (interfering) channel. Because a Rician distribution can be closely approximated by a Nakagami distribution (Nakagami 1960), the proposed analysis can be viewed as a close approximation of a shadowed-Rician (desired)/shadowed-Rician (interfering) model. The model provided in this paper includes many flexibilities-different Rice factors, different shadowing spreads, and different transmitted powers for desired and interfering signals. Therefore, it is a powerful tool for determining cell sizes and power levels in mixed micro/macro cellular systems.

Spectral optimization and joint signaling techniques for communication in the presence of cross talk

Abstract: A system and method for determining transmission characteristics for a communications channel and for transmitting data on the communications channel. This method may be used in communicating data when the channel is subject to interference from one or more other communications channels, including near-end cross talk (NEXT) and far-end cross talk (FEXT) from other channels carrying the same service and/or different services. The present ivention may be used in digital subscriber-line (xDSL) communications or in a variety of other applications, such as in well-logging and in systems involving multiple interfering radio transmitters. In a preferred embodiment, the invention comprises a method of determining an optimal transmit mask or power spectral density (PSD) function for use on the communications channel. The transmit function is preferably determined in response to the channel transfer function and the amounts of self-NEXT interference, self-FEXT interference, and uncorrelated interference such as AGN and interference from different-service communications channels.

Radio frequency planning and assignment in a discontiguous spectrum environment

Abstract: Techniques and systems for formalizing discontiguous spectrum frequency planning maximize system capacity while minimizing the potential for adjacent channel interference. Within the context of an overall system frequency plan, spatial separation can be used to offset overlap resulting from channelization mapping when additional frequencies are not available. Site by site modification and/or design can be used to prevent intermodulation products and/or adjacent channel interference effects. A variety of factors can be taken into account including, for example, control channel position and separation in a new spectrum, probability block utilization, threshold levels for adjacent channel interference, symmetric vs. non-symmetric adjacent channel interference, frequency plan type, Antenna Near Part (ANP) separation, intermodulation effects, local topography, frequency environment conditions, and site availability. These techniques are especially useful for (although not limited to) establishing a downbanded cellular (DBC) radio communication system by overlaying 30 kHz channelization on portions of the Specialized Mobile Radio (SMR) band having 25 kHz channelization.

Method and apparatus for detecting co-channel interference and selectively filtering the interference when detected

Abstract: A method and apparatus for detecting the presence of a co-channel interference signal and, in response to detecting such an interference signal, utilizing a co-channel interference rejection filter. Specifically, the present invention monitors the status information generated by the error detecting/correcting circuitry of a signal receiver such as a high definition television (HDTV) receiver. A counter is used to determine an error rate. While this first error rate is being determined, the filter is not used within the signal path of the receiver. The filter is then switched into the signal path of the receiver and a second error rate is determined. The first and second error rates are then compared and if the first error rate is the same or lower than the second error rate, the co-channel interference rejection filter is not utilized. Otherwise, the co-channel interference rejection filter is used in signal path of the receiver to remove an interference signal that is interfering with the proper demodulation of the received signal.

Co-channel interference detection network for an HDTV receiver

Abstract: A receiver for processing a VSB modulated signal containing terrestrial broadcast high definition television information and a pilot component includes an input analog-to-digital converter ( 19 ) for producing a datastream which is oversampled at twice the received symbol rate, and a digital demodulator ( 22 ; FIG. 3 ) with a data reduction network ( 330, 332 ) in a phase control loop. A segment sync detector ( 24 ; FIG. 4, 5 ) uses an abbreviated correlation reference pattern to recover a twice symbol rate sampling clock for the digital converter ( 19 ). A DC offset associated with the pilot component is removed ( 26 ; FIG. 6 ) from the demodulated signal before it is applied to an NTSC interference detection network ( 30 ; FIG. 7 ). The interference detection network includes a comb filter network ( 710, 718 ) responsive to a twice symbol rate sampled data datastream, and exhibits a sample delay dimensioned to avoid aliasing in the combed frequency spectrum (FIG. 8 ), thereby increasing the effectiveness of NTSC co-channel interference detection.

Co-channel interference reduction in wireless communications systems

Abstract: Co-channel interference with a desired signal in a receiver arrangement of a TDMA cellular radio communications system having two antennas and receivers for providing two received signals is reduced. Two sampled signals are derived from each of the two received signals by sampling the respective received signal at twice the symbol rate of the system and separating alternate samples at twice the symbol rate to produce the two sampled signals each with different samples at the symbol rate, providing a total of four sampled signals from the two antennas. These signals are linearly combined with respective weights to produce an output signal, the weights being determined to reduce co-channel interference with the desired signal represented by the output signal.

Interference minimization using automatic design of cellular communication networks

Abstract: This paper presents an automatic cellular network design algorithm which determines the location of transmitters with respect to co-channel interference (CCI). The proposed method is capable of maximizing the average CCI ratio in the planning region while optimizing the covered teletraffic demand. Additionally, we investigate how the proposed algorithm can be extended for locating micro- and macro-cells.

Fuzzy implementation of a Bayesian equaliser in the presence of intersymbol and co-channel interference

Abstract: The authors investigate the problem of channel equalisation in the presence of co-channel interference (CCI), intersymbol interference and additive white gaussian noise. The optimal Bayesian decision feedback equaliser decision function for this problem is derived and an elegant fuzzy implementation of the optimal solution is proposed. This fuzzy implemented equaliser is able to provide performance close to the optimal equaliser with a substantial reduction in computational complexity. The equaliser consists of a fuzzy equaliser with an input processing block for co-channel compensation. This preprocessor can be used under severe-to-moderate CCI and can be removed under low CCI conditions. Simulation studies demonstrate the performance of the fuzzy equaliser developed.

Binary signal design for approximately synchronized CDMA systems without detection sidelobe nor co-channel interference using auto- and cross-complementary codes

Abstract: For mobile cellular CDMA systems, co-channel interference in the uplink is the most serious problem, because the power control or the interference cancellation required increase the system's cost. From this view point, Suehiro (1993, 1994) proposed a method for signal design by applying the pseudo-periodic sequences concept on the periodic sequence set without cross-correlation. Using this method, we can design CDMA signals without co-channel interference when the system is approximately synchronized. Approximate synchronization is not difficult for uplink in cellular mobile systems, so this signal design method is useful. Another problem of multipath fading is also solved by the proposed method, because the filter output has no sidelobe in the small shift terms. A signal design method is proposed by using a complete complementary code. Using the proposed method, we can design binary CDMA signals for far wider shifts of without sidelobe nor co-channel interference. In fact, the length of shifts without the influence of multipath is 2/sup n/ for any n.

TDMA single antenna co-channel interference cancellation

Abstract: A demodulator, within a receiver attached to a single antenna, that cancels co-channel interference within a time division multiple access (TDMA) communication system is disclosed. The demodulator takes as input a series of received signals comprising an information signal and a co-channel interference signal, both using the π/4-differential quadrature phase shift keying (DQPSK) modulation protocol. During a training period, in which the information signals corresponds to a known SYNC word, the demodulator estimates the fading coefficients corresponding to the information and interference signals. After the completion of the training period, the demodulator uses these estimates to generate accurate estimations for future information and interference signals corresponding to future data received signals. Therefore, the information signal has been essentially separated from the co-channel interference signal and can be demodulated with a lower bit error rate (BER) than previous demodulation techniques under these circumstances.

System and method for channel assignment based upon interference and channel quality measurements

Abstract: A telecommunications system and method is disclosed for assigning channels based upon interference and channel quality measurements. The interference level measurements are carried out on the uplink of the cellular network. Channels are categorized in accordance with interference bands depending upon the interference levels. Incoming service is pre-assigned to a channel in the highest available interference band and a channel quality measurement (CQM) is conducted. The service is either continued (assigned) on the same channel, reassigned to a channel with lower interference or dropped if no other channel with lower interference is available based upon the channel quality measurement and the interference bands having available channels.

Measurement radio system for producing operating information for traffic radios

Abstract: A measurement radio system uses a measurement radio to scan active channels of a base station and produce operating information for the traffic radios servicing the active channels. The measurement radio can produce operating information, such as signal strength, bit error rate (BER), frame error rate (FER) and signal to interference ratio (C/I), which is used to determine whether to change the manner in which the traffic radio is servicing the active channel. For example, if the measurement radio can switch between different sets of antennas, the measurement radio can scan an active voice/data channel using a different set of antennas than the traffic radio is using to service the active channel and determine operating information related to the signal received over the active channel using the different set of antennas. The traffic radio can use the operating information to determine whether to hand off the active channel to the different set of antennas. The measurement radio can determine operating information, such as operating coefficients, parameters or settings, to change how the traffic radio services the active channel.

An interference detection method and an interference avoidance method

Abstract: A multiple access radio communication system connecting a base station and a plurality of subscriber stations in a TDMA system, which correctly detects the occurrence of an interference in an R-channel, used by the subscriber stations (21-24) to make a call request to the base station (1), and which changes the assigned slot of the R channel on detecting interference to avoid interference.

Method and apparatus for canceling co-channel interference

Abstract: A co-channel interference canceler and a method therefor. The co-channel interference canceler includes: an NTSC interference rejection filter (NRF) for removing co-channel interference from an input signal; a noise reducer for reducing noise by removing interference other than co-channel interference from the input signal; and a selection controller for determining whether or not co-channel interference exists in the signal output from the noise-reducer and selecting the NRF when such co-channel interference exists in the noise reduced signal. Therefore, the effect from interference other than the co-channel interference is minimized, so that the co-channel interference controller is reliably controlled.

Frequency reuse scheme with reduced co-channel interference for fixed cellular systems

Abstract: A new frequency reuse scheme which reduces co-channel interference in comparison with the conventional scheme is presented for use in fixed cellular or wireless local loop systems where the antennas of subscriber units are fixed and directional. The new scheme is evaluated in a three-sector cell plan employing frequency reuse numbers N = 4 and N = 7 as a function of the subscriber unit antenna directivity. It is shown that a substantial improvement is obtained with the new scheme compared to the conventional scheme if the subscriber unit antenna beam width is narrower than ~150 degrees. For the case of a 60 degree antenna beam width, for example, the improvement is > 7 dB in the signal to co-channel interference ratio averaged along the cell boundary for both N = 4 and N = 7 cases.

Weighting of interference according to its effect on digital communications services

Abstract: A prerogative for the proper weighting of interference to modern digital communication systems is the knowledge of the interference effect. The effect on communication services will depend on the type of interference (e.g. broadband or narrowband, pulse rate etc.). The paper starts by explaining the classical concept of pulse weighting to analog radio systems, introduces a concept for weighting of interference to digital communication systems and gives experimental results of weighting curves.

Performance comparison of multi-stage SIC and limited tree-search detection in CDMA

Abstract: A rich array of detector structures for CDMA, offering a multitude of trade-offs between performance and complexity have been proposed. In this paper we consider two detector structures that are based on very different principles but represent a similar level of detection complexity. Through simulations the performance of multi-stage successive interference cancellation schemes with either a hard-decision or a clipped soft-decision limiter are compared to similar complexity limited tree-search detectors. The performance is evaluated over single-path and multipath channels.

Co-channel interference canceler and method therefor

Abstract: A co-channel interference canceler and a method therefor. The co-channel interference canceler includes: a co-channel interference rejection filter for outputting a second input signal by removing co-channel interference from a first input signal; a first post processor for removing interference other than co-channel interference from the second input signal; a second post processor for removing interference other than co-channel interference from the first input signal; and a selection controller for selecting the output of the post processor which has less error by comparing the output of the first post processor with the output of the second post processor. Therefore, other interference such as ghost and phase noise included in an input signal are removed or reduced via the extra second post processor which is different from the first post processor of the signal path. The selection of the NRF is controlled using the signal from which other interference has been removed or decreased, thereby minimizing the effects of the other interference. As a result, error in selection of the NRF, which may be caused by the other interference, can be prevented, and selection of the NRF is reliably controlled.

Co-channel interference canceler in simulcast receiver and method thereof

Abstract: A device for canceling co-channel interference and a method thereof are provided. The device, in a simulcast receiver for receiving a high definition television (HDTV) signal having a digital format and an analog broadcasting TV signal, includes a detector for detecting a synchronous signal from the analog broadcasting TV signal and outputting a detection signal, a co-channel interference rejection filter for removing co-channel interference from a first input signal including co-channel interference and outputting a second input signal, and a selector for selecting either the first or second input signal according to the detection signal. Therefore, the presence or absence of co-channel interference can be accurately determined regardless of channel environment.

Procedure for reducing interference in the transmission of an electrical communication signal

Abstract: Through crosstalk on lines, interference from current transmission lines or line echoes, the useable signal is superimposed by different interference signals. The task is to find a procedure for reducing interference which, compared to the current state of the art, can be achieved with a smaller amount of computing input and is suited to both the reduction of quasi steady-state and non-steady interference. In this, the interference of a received signal is classified with regards to characteristics in the time range as a click, crackle, rumble or noise interference signal. The time range in which the interference occurs is marked. Depending on the interference type, interference blanking and/or an interpolation of the useable signal and/or a subtraction of the interference signal from the useable signal and/or a regeneration of the useable signal is carried out.

On the parameters optimization in handover algorithms

Abstract: This paper investigates the performance of handover algorithms used in microcellular F-TDMA radio networks such as GSM. A very general simulation tool has been developed within the framework of a cooperation between the University of Bologna and Italtel SpA. The tool allows the evaluation of network performance in the context of a multicell scenario taking log-normal shadowing, co-channel interference, user mobility, uplink and downlink power levels, cell sectorization and proper frequency planning into account; different handover algorithms can be investigated by considering not only power levels, but also several quantities related to the grade of service and transmission quality. In this paper, handover algorithms based on measured power levels and timing constraints are addressed; the average number of handovers per call is considered as performance measure in order to stress the impact of co-channel interference on the efficiency of the algorithm. Moreover, the concept of outage probability is introduced to investigate handover parameters optimization.

Experiments on coherent multistage interference canceller for DS-CDMA mobile radio

Abstract: A 3-stage coherent multistage interference canceller for DS-CDMA mobile radio was implemented and its performance in a frequency selective multipath fading channel is experimentally evaluated by using a multipath fading simulator. The implemented interference canceller applied pilot symbol-assisted channel estimation for data decision and replica generation of multiple access interference (MAI). The laboratory experiment demonstrated that, as is expected, the coherent multistage interference canceller can reduce the MAI to satisfactory levels in a multipath fading environment and thus, improving the bit error rate (BER) performance under multiuser environment.

Co-channel FM interference suppressed by using the amplitude-locked loop for digital communication

Abstract: An amplitude-locked loop (ALL) is a high-gain, high-bandwidth servo-loop similar to a phase-locked loop (PLL) but operating in the amplitude domain rather than the frequency domain. The ALL has been used in combination with a PLL (the FM 201/5) and some additional circuitry to achieve a major improvement in frequency modulation technology. This includes co-channel interference (CCI), multipath interference and threshold extension . This work is the natural extension of this approach to digital communication systems.

On the capacity of TDMA and CDMA for broadband wireless packet access

Abstract: Studies of the capacity of cellular systems, stated in terms of the admissible number of remote users, have generally been limited to voice telephony. We address the problem of comparing the interference-limited performance of CDMA and TDMA systems in a packet switched environment. The objective is to determine whether the capacity advantages claimed for circuit-switched CDMA still apply in a packet-switched environment, where the natural time diversity of bursty transmission may be a significant factor. Under a set of specific assumptions about the wireless environment (including path loss, shadow fading, multipath delay spread, co-channel interference, power control, coding), we evaluate the number of users which can be admitted to the system while maintaining some desired quality-of-service level. Four different classes of users with different characteristics and requirements are considered. The system capacity is found to significantly depend on the QoS objectives, which might be stated in terms of availability of some specified signal to interference level, packet loss rate, or mean tolerable delay. The main finding is that strict requirements imposed on the radio access level tend to favor CDMA, whereas if some form of packet recovery at the higher layers is allowed (implying a relaxed set of requirements on the radio interface), then a somewhat higher capacity may be achieved by TDMA.