Showing papers on "Co-channel interference published in 2005"

Adaptive beam forming with multi-user detection and interference reduction in satellite communication systems and methods

Abstract: Satellite communications methods include receiving communications signals including co-channel interference at a space-based component from a plurality of wireless terminals in a satellite footprint over a satellite frequency band and reducing interference in the communication signals by (a) performing co-channel interference reduction on the communications signals to generate a plurality of interference reduced signals and (b) performing multiple access interference cancellation on the interference reduced signals. An interference reducing detector for a satellite communications system includes an interference reducer configured to perform co-channel interference reduction on communications signals to generate a plurality of interference reduced signals, and a detector configured to perform multiple access interference cancellation on the interference reduced signals. Satellite communications systems and satellite gateways including interference reducing detectors are also disclosed.

Single-antenna co-channel interference cancellation for TDMA cellular radio systems

Abstract: Co-channel interference cancellation is particularly challenging in the downlink of cellular radio systems because usually only one receive antenna is available at the mobile terminal. This tutorial provides an overview of promising a single-antenna co-channel interference cancellation techniques. Focus is on the downlink of time-division multiple access systems. The results may, however, be extended to related applications, including interference suppression in multiple-input multiple-output systems.

Examination of a simple pulse-blanking technique for radio frequency interference mitigation

Abstract: [1] Radiometry at L band can be adversely impacted by radio frequency interference (RFI) due to the presence of numerous sources, especially pulsed RFI from radars operating below 1400 MHz. RFI mitigation is very important to deal with this problem. A simple strategy for reducing pulsed RFI, termed “asynchronous pulse blanking” (APB), has been implemented in a digital receiver developed at Ohio State University. This paper presents results from a simulation of the APB algorithm. Several aspects of algorithm use and performance are reported, including means for choosing the algorithm's parameters and the robustness of the method in a realistic RFI environment. Effects of the blanking process on the final output are also examined.

A single antenna interference cancellation algorithm for GSM

Abstract: In mobile communication networks, system capacity is often limited by cochannel interference. Therefore, receiver algorithms for cancellation of cochannel interference have recently attracted much interest. At the mobile terminal, algorithms can usually rely only on one received signal delivered by a single receive antenna. In this paper, a novel low-complexity single antenna interference cancellation (SAIC) algorithm for real-valued modulation formats referred to as mono interference cancellation (MlC) is introduced which is well suited for practical applications. By using this algorithm in the mobile terminals, capacity of GSM networks can be improved by up to 40-60 %.

Downlink multicell MIMO-OFDM: an architecture for next generation wireless networks

Abstract: In this paper, we consider a multicell MIMO-OFDM TDD system where the emphasis is on the downlink for future data-intensive applications. We propose a MIMO scheme that can effectively combat co-channel interference with only local BS coordination and retain the high peak rate achievable for point-to-point single-cell communications. We describe several different levels of CSI availability at both the transmitter and the receiver that lead to different system architecture choices. The performance of rate-1 SFBC code (Shao et al. (2004)) with channel estimation is investigated via simulation; our results show that with pragmatic channel estimation schemes, multi-cell MIMO-OFDM is a good candidate for future high-rate applications.

Dynamic frequency hopping in cellular fixed relay networks

Abstract: This paper proposes a new interference management/avoidance technique for cellular fixed relay networks with aggressive channel reuse: dynamic frequency hopping with limited information (DFH-LI). It incorporates relaying with a combination of dynamic frequency hopping (DFH) and random frequency hopping (RFH). This technique results in enhanced high data rate coverage and decreased outage.

Adaptive beam-forming with interference suppression and multi-user detection in satellite systems with terrestrial reuse of frequencies

Abstract: Adaptive space-time signal processing comprising interference suppression and multi-user detection in a CDMA Mobile Satellite System (MSS) environment is presented. Optimum beam-forming, based on a Minimum Mean-Squared Error (MMSE) performance index, is used to maximize the signal-to-noise plus interference ratio of MSS links in an environment of significant terrestrial reuse of the satellite service link frequencies by Ancillary Terrestrial Components (ATCs). The technique substantially mitigates both ATC-induced co- channel interference and Multiple-Access Interference (MAI). At the satellite gateway, a pilot-based MMSE algorithm is used to adaptively form an optimum return-channel beam for each user by processing the raw antenna feed element signals provided to the satellite gateway by a satellite return feeder link. Following beam-forming, pilot signals are used to estimate the multi-user channels. The proposed Sequential ATC and MAI Interference Canceller (SAMIC) algorithm takes advantage of a priori known pilot signal information and invokes preliminary decisions to sequentially perform interference suppression followed by multi- user detection. The performance of the SAMIC algorithm is illustrated by simulation of a multi-beam geo-stationary satellite system containing a wide deployment of ATC over 50 major markets across the Continental United States (CONUS).

Performance analysis for impulse radio and direct-sequence impulse radio in narrowband interference

Abstract: The impact of narrowband interference (NBI) on two ultra wideband (UWB) systems is analyzed. The two systems are impulse radio (IR) and a variation of it, termed direct-sequence IR (DS-IR). The signal-to-noise ratio (SNR) at the decision device of a correlation receiver is computed for both systems, assuming that the NBI is wide sense stationary and that the channel is frequency-selective. The SNR is expressed by means of a simple equation involving the signal and the interference spectrum. Next, a statistical model for the interference is introduced, considering the interference as the sum of a given number of sinusoidal signals with random powers and frequencies. The bit-error rate of IR and DS-IR is derived. The results are then specialized and compared with simulations in three case studies of practical interest, where the NBI is a single jammer with deterministic power and frequency, a multitone signal with random frequencies, or a grid of interfering signals with random powers.

Interference Mitigation in Wireless Communications

Abstract: and our parents for their love for all these years. iii ACKNOWLEDGEMENTS This dissertation could not be completed without influences from several individuals, to whom I am grateful for their contributions, direct or indirect, to the completion of this research. First and foremost, I would like to acknowledge a tremendous debt of gratitude towards my advisor, Prof. Gordon Stüber, whose patience, understanding, and guidance to me cannot be overstated. In addition to his academic supervision, I am also grateful for his financial support throughout my study. Most of all, I have learned a lot more than research work through his loyalty to integrity as an academic professional. Next, I thank the reading committee members of my dissertation committee, Prof. Ye (Geofferey) Li and Prof. Mary Ann Ingram for their time, effort, and valuable suggestions necessary to complete this work. I also extend my thank to Prof. Douglas Williams and Prof. Alfred Andrew for having dedicated their valuable time to participate my dissertation committee, and having provided insightful comments and feedbacks for this research. I thank all other members of Wireless Systems Laboratory (WSL), past and present, Zajic, and Qing Zhao, in no particular order, for all the time and discussions we shared during my stay at WSL. Especially, I give thanks to Dr. Apurva Mody. His optimism in academic and personal life has always made me focus on the light at the end of the tunnel. I also thank Dr. Tom Pratt and Galib Asadullah for their dedicated collaboration on the GSM project. Lastly, I owe a debt of gratitude to my family for their love, support, and sacrifice along the path of my academic pursuits. For all this and much more, I dedicate this thesis to them. Thank God for showing me the beginning and the end of a segment of the path of my life.

MMSE transmit optimization with interference pre-compensation

Abstract: We address the problem of nonlinear transmitter design for a point-to-multipoint wireless downlink, where the transmitter is equipped with multiple antennas and each of the independent receivers has a single antenna. We show that the downlink with perfect interference pre-compensation (IPC) has the same normalize MSE achievable region under a sum power constraint as an equivalent uplink with perfect successive interference cancellation (SlC). Based on this duality, we propose a nonlinear downlink transmit framework for joint MSE optimization. The strategy is equivalent to MMSE-DFE with perfect detection in terms of normalized MSE and SINR. As application examples, we solve the problem of minimizing the total transmit power while maintaining individual normalized MSE targets. For practical use, we propose a transmit scheme based on Tomlinson-Harashima-precoding (THP), which has a very simple structure and can be considered as the downlink counterpart of MMSE-DFE. Furthermore, in order to reduce the preceding loss, a strategy which combines THP with signal constellation shaping is utilized to compensate the power enhancement caused by interference pre-subtraction.

Some properties of the capacity of MIMO systems with co-channel interference

Abstract: The mutual information of a multiple-input multiple-output (MIMO) system with co-channel interference is considered. Perfect channel information is assumed to be available to the receiver, but the transmitter has no channel information. It is theoretically proved that the worst interference condition is when the total power is equally distributed among all available interfering antennas. Moreover, equal-power interferers give worse performance than unequal-power interferers, and a smaller number of interferers each with larger power degrades performance less than a larger number of interferers each with lower power. Finally, it is shown that, for asymptotically large interference, when the number of interfering antennas, N/sub I/, is smaller than the number of receive antennas, N/sub R/, the system is equivalent to a reduced MIMO system with N/sub R/-N/sub I/ receive antennas. When N/sub I//spl ges/N/sub R/, the mutual information approaches zero as interference becomes asymptotically large.

Apparatus and method of canceling interference

Abstract: Briefly, a wireless communication device having a receiver includes a pilot signal interference canceller and a linear interference suppressor is provided. The pilot signal interference canceller and the linear interference suppressor jointly operate to cancel a pilot signal interference and other interference which are part of a received signal. A method for jointly cancel the interference by the pilot signal interference canceller and the linear interference suppressor is also provided.

Interference Environment Between High Altitude Platform Networks (HAPN), Geostationary (GEO) Satellite and Wireless Terrestrial Systems

Abstract: A new broadband telecommunication system has been recently proposed for provision of fixed, mobile and personal services adopting the use of high altitude platform stations placed in a fixed position in the stratospheric layer at heights from 15.5 to 30 km. The International Telecommunication Union (ITU) has allocated a pair of 300 MHz of spectrum in the V band for these services, which is already in use by geostationary satellite and wireless terrestrial systems as co-primary allocations. This paper addresses an in-depth co-channel interference analysis and proposes a C/I (carrier-to-interference) calculation model applicable to all the interference propagation paths as well as sharing criteria between HAPN, GEO satellite and wireless terrestrial systems extracted from simulations performed in urban, suburban and rural environments. By evaluating the interference density cumulative probability distribution functions, sufficient geographical separation distances between the ground stations are proposed which guarantee the harmonic co-existence between the three broadband systems. Maintaining the platform stable in the stratosphere is a key issue, and in this paper the effect of the three different stratospheric platform's movement models (ITU, HELINET, HALO) appearing in the literature, on C/I levels is estimated.

Remedial actions for interference in wireless LANs

Abstract: In a wireless network having an access point and at least one wireless end device, the access point is operable to differentiate between normal communications and interference from another device in order to capture a sample of the interference, determine whether the interference originates from a known type of device, and prompt remedial actions such as moving communications to a distant channel, increasing transmission power, changing data rate, and packet fragmentation based on whether the interference originates from a known type of device. Interference pulse duration may be used to at least initially narrow the possible sources of interference. Pulse period may be employed to differentiate between interference sources which exhibit similar pulse duration. If pulse duration and period are not sufficient to identify the interference source then other characteristics may be examined, such as pulse waveform, roll off and period in relation to local power frequency. In the case of microwave interference it is generally best to move to a distant channel. Increased transmission power and packet fragmentation can be used to maintain communications while scanning for a new channel.

Method and apparatus for minimizing co-channel interference by scrambling

Abstract: An approach is provided for minimizing co-channel interference in a communication system is disclosed Non-header portions of frames, which are transmitted over the communication system, are scrambled according to respective different scrambling sequences The above arrangement is particularly suited to a digital satellite broadcast and interactive system

Interference cancellation within wireless transceivers

Abstract: The receiver includes a Rake receiver for separating a received signal into multipath components, an interference selector for selecting interference symbols corresponding to interfering paths and subchannels, a synthesizer for synthesizing an interference signal from selected paths and estimated subchannel symbols, and a canceller for constructing a projection operator or a scale-invariant subtraction operator to cancel selected interference in multipath components of the received signal, or from the received signal itself. The interference canceller may use a sequence of symbol estimates to simultaneously cancel inter-channel interference and inter-symbol interference. Interference cancellers may be placed at one or more locations within the receiver chain.

Method for intersystem-interference cancellation between at least two radio transmission methods

Abstract: The method involves having, for the radio supply of a regarded spatial range both a first radio transmission procedure of a first network and a second radio transmission procedure of a first network. The first radio transmission procedure has a first frequency band and the second radio transmission procedure has a second frequency band for the radio transmission. Between the two frequency bands a protection distance to the interference suppression is provided such that assigned frequencies disallows use by either the first or second radio transmission procedure. On the part of the first network a live load determination is arranged, for participant radio transmissions needed for determining frequencies of the first and the second frequency band. On the first network a regulation is arranged by interference, so that the second frequency band on the first frequency band is exercised. In dependence of the live load and the determined interference an adaptive allocation is accomplished for frequencies for the protection distance.

Radio communications system, radio transmitter, radio receiver and radio communication method

Abstract: PROBLEM TO BE SOLVED: To provide a radio communications system and the like capable of effectively utilizing resources, assigned to information channels and control channels in radio communications of an orthogonal frequency division multiplexing (OFDM) scheme. SOLUTION: A radio transmitter 200, used in a radio communications system based on an OFDM scheme, includes a determination unit 216 configured to determine the spread factor and the amplitude to be set to a control channel, based on transmission signal quality information and an interference amount from information data; a multiplexing unit 212, configured to multiplex an information channel with the control channel having been code-spread, based on the determined spread factor and amplitude, and means 214 configured to modulate the multiplexed signal in the OFDM scheme and transmit the modulated signal by radio. A radio receiver, used in the present system, comprises a means configured to extract the control channel, by demodulating a received signal in the OFDM scheme and despreading the demodulated signal. COPYRIGHT: (C)2005,JPO&NCIPI

On inter-cell interference in OFDMA wireless systems

Abstract: Orthogonal Frequency Division Multiple Access (OFDMA) is a multiple access technique that is starting to be examined as an alternative to Code Division Multiple Access (CDMA) for cellular mobile systems. Until recently, OFDMA had received little attention for multicellular applications and as a consequence of this, few results are available on the impact of interference on OFDMA communications. In this paper, we study the behaviour of an OFDMA system with respect to the inter-cell interference. We show that due to the heterogeneous nature of the interference, interference estimation combined with soft-input channel decoders can be used to improve the performance of the system. We show through realistic simulations that OFDMA can cope with inter-cell interference even without estimating it. Moreover we evaluate the performance gains obtained for different interference estimation techniques and show that a low complexity algorithm can be used to achieve gains of up to 2 dB.

Shifted channel characteristics for mitigating co-channel interference

Abstract: Methods and apparatuses for minimizing co-channel interference in communications systems are disclosed. A method in accordance with the present invention comprises shifting a characteristic of the first signal with respect to a like characteristic of the second signal to mitigate co-channel interference, and transmitting the first signal and the second signal over different channels of the communication system.

Interference modeling and analysis in two-hop cellular network with fixed relays in FDD mode

Abstract: Relaying network is expected to play an important role in the future wireless network. This paper presents a scheme of two-hop cellular network with fixed relay nodes (FRN). Based on this scheme, co-channel interference and SIR received by BS and FRN are analyzed. Both the theoretical analysis and simulation results show that the SIR can be improved significantly when relays are employed in the network. We also show that the antenna height of FRN and the cell radius of BS and FRN influence SIR received by BS and FRN greatly.

Inter-symbol/inter-frame interference in time-hopping ultra wideband impulse radio system

Abstract: A closed-form expression for the intersymbol/inter-frame interference variance is derived in the context of a time-hopping ultra wideband impulse radio based system This enables us to theoretically analyze on the performance the influence of the time-hopping codes, of the rake receiver number of fingers, and of the guard-time size Simulations sustain our claims

Interference mitigation in mobile units having location transmitters

Abstract: A mobile device (10) for data communications has a radio circuit for data communications with a wireless network access point and a radio tag (32) for transmitting location-identifying radio signals. The radio circuit and the radio tag are co-located on a circuit board or are commonly powered. The operation of the radio circuit and the radio tag (32) are segregated in time to avoid interferences. Standard wireless network interface protocol functions are exploited to identify time intervals in which the radio circuit is inactive for data communications. These time intervals are used to operate the radio tag to transmit the location-identifying radio signals.

When does interference not reduce capacity in multi-antenna networks?

Abstract: Multi-user interference induces performance loss in terms of BER and channel capacity when present in a communication system. Nevertheless multi-user interference can be suppressed via signal processing techniques so to improve performance. In fact, the presence of this interference reduce the channel capacity region A. Carleial et al., (1975). In this work the conditions allowing perfect interference cancellation are derived so to arrive at the same capacity region of an interference-free network.

Mitigating intermodulation interference using channel power estimation and attenuation in a two-way radio communications system

Abstract: A method for maximizing intermodulation interference protection during a handoff between radio cell sites (300) includes scanning a plurality of radio channels (302) and measuring the signal power (307, 315) for at least one of the radio channels. One or more receiver attenuators (313) are then set based on the detection of intermodulation (IM) interference of the measured channel. The attenuators are then scaled (311) based on the degree of IM interference. If the attenuators cannot mitigate this interference below some predetermined level, the radio channel is changed (321) and the process begins again to ensure a high quality of communication with a cell site.

Spatio-Temporal Equalization for Space-Time Block Coded Transmission over Frequency Selective Fading Channel with Co-channel Interference

Abstract: In this paper, we propose a spatio-temporal equalizer for the space-time block coded transmission over the frequency selective fading channels with the presence of co-channel interference (CCI). The proposed equalizer, based on the tapped delay line adaptive array (TDLAA), performs signal equalization and CCI suppression simultaneously using the minimum mean square error (MMSE) method. It is to show that our scheme outperforms the previous two-stage combined adaptive antenna and delayed decision feedback sequence estimator (DDFSE) approach. We also show that performance can be further improved if the synchronization between the preceding and delayed paths is achieved.

Radio frequency interference mitigation with phase‐only adaptive beam forming

Abstract: [1] Connected radio interferometers are sometimes used in the tied array mode: signals from antenna elements are coherently added and the sum signal applied to a very long baseline interferometry (VLBI) back-end or pulsar-processing machine. Usually, there is no computer-controlled amplitude weighting in the existing radio interferometer facilities. Radio frequency interference (RFI) mitigation with phase-only adaptive beam forming is proposed for this mode of observation. Small phase perturbations are introduced in each of the antenna's signals. The values of these perturbations are optimized in such a way that the signal from a radio source of interest is preserved and RFI signals are suppressed. An evolutionary programming algorithm is used for this task. Computer simulations, made for both one-dimensional and two-dimensional array setups, show considerable suppression of RFI and acceptable changes to the main array beam in the radio source direction.

A novel approach to interference mitigation for UWB pulse radio

Abstract: A novel approach named adaptive modified receiving template waveform (AMRTW) is proposed in this paper. This new approach uses adaptive frequency estimator to give the estimating values of the interference frequency and the interference frequency band. Based on these estimating values, the receiving template signal is decomposed rationally by the adaptive template signal-analyzing unit. And the UWB receiver modifies the receiving template signal with removing some decomposing signal components that are close to the interfering spectrum from the receiving template signal. The simulation results of bit error rate performance show that this new method is efficient in interference mitigation for UWB pulse radio.

Comparison of two cyclostationary detectors for radio frequency interference mitigation in radio astronomy

Abstract: [1] Radio frequency interference (RFI) mitigation has become a significant issue for current and future radio telescopes. This paper presents a new scheme for removing radio frequency interference from astronomical data. It exploits a priori knowledge of the transmitters, namely, their cyclostationary statistical properties. Two real-time cyclostationary detectors are proposed and compared. Results on both synthetic and real data demonstrate the efficiency of this concept.

Reference antenna techniques for canceling radio frequency interference due to moving sources

Abstract: [1] We investigate characteristics of radio frequency interference (RFI) signals that can affect the excision potential of some interference mitigation algorithms. The techniques considered are those that modify signals from auxiliary reference antennas to model and cancel interference from an astronomical observation. These techniques can be applied in the time domain, where the RFI voltage is modeled and subtracted from the astronomy signal path (adaptive noise canceling), or they can be applied to the autocorrelated and cross-correlated voltage spectra in the frequency domain (postcorrelation canceling). For ideal receivers and a single, statistically stationary interfering signal, both precorrelation and postcorrelation filters can result in complete cancellation of the interference from the observation. The postcorrelation method has the advantage of being applied on tens or hundreds of millisecond timescales rather than tens or hundreds of nanosecond timescales. However, this can be a disadvantage if the RFI transmitter location is changing, since the cross-correlated power measurements which link the interference power in the astronomy and reference signal paths can decorrelate. If the decorrelation is not too severe, it can be allowed for, at the expense of a noise increase. The time domain adaptive cancelers are allowed to slightly vary their internal coefficients and adapt to changing phases during the integrations, which means that they avoid the decorrelation problem. However, the freedom to adapt also results in a noise increase. In this paper the ability of both types of cancelers to excise interference originating from a moving source is compared. The cancelers perform well on both observed and simulated data, giving complete cancellation.