Showing papers on "Co-channel interference published in 2002"

Delay-hopped transmitted-reference RF communications

Abstract: Previously, the authors have invented and experimented with a new radio communications scheme called delay-hopped transmitted-reference (DHTR) radio. This technique can function either as an impulse radio, or can employ a more traditional spread-spectrum carrier such as broadband noise. The DHTR method is well-suited to short-range transmissions in a high multipath environment, and, in contrast to time-modulated impulse radio, is easy to synchronize at the receiver. Finally, DHTR receivers and transmitters are not highly complex, and can be implemented in a cost-effective way.

Performance of MIMO systems with channel inversion

Abstract: The paper discusses channel inversion which is a spatial equalization technique when channel state information is available at the transmitter. Channel inversion is a straightforward concept without iterations and it might be useful when the data transmission is critical with time e.g. high data rate applications. We discuss performance degradation caused by channel estimation errors, clipping due to the limited range of the transmitted power and the effect of cochannel interference. These results give an insight into the technical constraints of this transmission technique and show how these critical issues can be limited or reduced.

Method and apparatus to reduce interference in a communication device

Abstract: An apparatus and method to reduce interference in a communication device particularly effective for second-order interference in direct conversion receiver from a co-located transmitter. This is accomplished by characterizing a transfer function of a transmission path from the transmitter to the receiver and applying this transfer function to the baseband signal from the transmitter to provide an estimation of interference to be expected in the received signal. The estimated interference is subtracted from the receiver baseband signal to reduce interference. Adaptive filtering can also be applied to further minimize interference dynamically.

Narrowband interference suppression in time-hopping impulse-radio systems

Abstract: Ultra-wideband (UWB) radio systems have drawn a lot of attention during the last few years. These systems use very low transmission power, spread over a bandwidth of several gigahertz. The very low transmission power and the large bandwidth used enable UWB radio systems to coexist with other narrowband systems over the same frequency band without interfering with the narrowband systems. Nevertheless, these narrowband systems may cause interference which jams the UWB receiver completely. Since standard narrowband interference suppression techniques are not applicable, techniques for interference suppression have to be developed. This paper presents novel narrowband interference suppression algorithms for UWB radio systems. Theoretical analysis of these algorithms reveal that they can eliminate the narrowband interference almost completely.

Adaptive equalizer system for short burst modems and link hopping radio networks

Abstract: A method for an adaptive equalization apparatus (500) in a multiple-link hopping radio system includes hopping among a plurality of radio links to receive variable-length bursts of radio signals on the plurality of radio links and equalizing amplitude and phase variations of a slow channel for each radio link from a received burst on the radio link. Further, the method includes storing the estimated tap coefficients pertinent to each radio link and using the tap weights of the current burst of the radio link to reliably pre-compensate the channel amplitude and phase distortion of a next received burst on the radio link.

Method and apparatus for reducing inter-channel interference in a wireless communication system

Abstract: Method and apparatus for reducing interference in a wireless communication system when the source of interference is a deterministic component of the system. In one embodiment, the receiver weights the transmitters according to when the source of interference is transmitted. Further, the transmitter may employ power boosting to overcome the source of interference. In one embodiment, a W-CDMA system transmits a sync channel concurrently with physical channels, wherein the sync channel is not orthogonal to the physical channels. The receiver may cancel the sync channel when receiving control or data information. Similarly, the receiver may weight the transmissions from multiple transmitters.

Method and apparatus for reducing interference in a wireless communication system

Abstract: Method and apparatus for reducing interference in a wireless communication system when the source of interference is a deterministic component of the system. In one embodiment, the receiver weights the transmitters according to when the source of interference is transmitted. Further, the transmitter may employ power boosting to overcome the source of interference. In one embodiment, a W-CDMA system transmits a sync channel concurrently with physical channels, wherein the sync channel is not orthogonal to the physical channels. The receiver may cancel the sync channel when receiving control or data information. Similarly, the receiver may weight the transmissions from multiple transmitters.

Methods and systems for reducing interference using co-channel interference mapping

Abstract: Methods of demodulating a received signal are disclosed in which an interference map containing information regarding a plurality of candidate co-channel interference sources is provided. The information in the interference map regarding the plurality of candidate interference sources may be used to identify any of the candidate co-channel interference sources that comprise a dominant interference source. The received signal may then be demodulated in a manner that cancels at least part of the contribution of any identified dominant interference source by using the information regarding any such interference source contained in the interference map.

A theoretical study on the effects of interference UWB multiple access impulse radio

Abstract: Ultra wide bandwidth impulse radio occupies huge bandwidth from near DC to up to a few GHz. This suggests that many coexisting communication systems working simultaneously at different regions of impulse radio's bandwidth cause interference. The effects of an arbitrary external interference as SNR and bit error rate degradation of multiple access UWB radio versus interference frequency is theoretically evaluated and pulse shape design for narrow band interference rejection is presented. Using doublet pulses, it is shown how narrow bandwidth interference is mitigated significantly. Effects of amplitude mismatches and gap time offset from the nominal value in a doublet pulse are investigated.

The downlink orthogonality factors influence on WCDMA system performance

Abstract: The large scale statistics of the downlink orthogonality factor (OF) is addressed in this paper for typical urban macrocellular environments for terminals with standard Rake receivers. It is found that the OF improves as the user moves closer to the BS and the OF is positively correlated with the shadow fading component of the radio channel. The mean value of the OF is typically larger for users dominated by own cell interference over other cell interference. These effects result in a larger excess capacity close to the BS, compared to scenarios where the OF is assumed to be constant within the cell.

Pilots for joint channel estimation in multi-user OFDM mobile radio systems

Abstract: This paper addresses the issue of pilot design for the purpose of channel estimation in the uplink of a mobile radio system applying OFDM. The pilots are designed based on the performance criteria SNR degradation for noise scenarios and variation coefficient for interference scenarios. Besides the method of randomly generating pilots and the design method based on the disjoint subcarrier approach, a novel method for designing pilots based on Walsh codes is presented in the paper. The pilots resulting from the aforementioned method exhibit a very good performance both in noise and in interference scenarios.

An interference suppressing OFDM system for ultra wide bandwidth radio channels

Abstract: The orthogonal frequency division multiplexing (OFDM) technique introduced here, termed interference suppressing OFDM (IS-OFDM), is a point-to-point physical link system for ultra wide bandwidth (UWB) radio channels which has the capability of suppressing narrow-band interference. System performance evaluation has been provided in the presence of narrow band interference, inter-symbol/inter-channel interference, or frequency selective fading. BER performance of the IS-OFDM is compared with an equivalent ordinary OFDM system. As shown, the IS-OFDM in a narrow band interference channel has a significant advantage over the ordinary OFDM which exhibits an error floor for every narrow band interference to signal ratio. Also, in an UWB indoor multipath channel the IS-OFDM has a significant advantage over the ordinary OFDM which, as shown, does not offer an acceptable performance for this type of channel.

Methods and apparatus for canceling co-channel interference in a receiving system using spatio-temporal whitening

Abstract: Methods and apparatus for canceling co-channel interference in a receiving system using spatio-temporal whitening. In some embodiments, a spatio-temporal interference canceling method, and apparatus for carrying out the method are provided which effectively cancel co-channel interference despite frequency offset between the desired signal and the interferer in a TDMA type system. Real and imaginary component values of the total received signal are used for virtual diversity branches, and a vector-valued auto regressive model is used to characterize the interference. In other embodiments, spatio-temporal interference whitening is used to improve timing estimates used for synchronization. The two uses of spatio-temporal whitening can be combined in one receiver. The invention is typically implemented in one or more programmed digital signal processors or application specific integrated circuits (ASICS), embodied in a receiving system.

MIMO Channel Capacity in Co-Channel Interference

Abstract: Recent information theory results have indicated that a large channel capacity exists for wireless systems with multiple transmit and receive antennas. With different assumptions of channel knowledge and interference knowledge at the transmitter, the channel capacity of multiple input multiple output (MIMO) systems has been studied under both spatially white and colored interference and noise. In this paper, we fix the total interference-plus-noise power and evaluate the outage capacity under two spatially colored interference environments: (1) a few high-data-rate interferers each with high power, (2) a large number of lowdata-rate interferers each with low power. The results show that MIMO capacity is larger with fewer high-data-rate interferers. We also assess the impact of an estimated channel and/or interference on capacity. In the case of 4 transmit and 4 receive antennas for the user of interest, 10 interferers, total-interference-to-noise ratio and signal-to-noise ratio are both 20dB, the results show that it is beneficial to estimate the channel and/or interference if the variance of estimation error is less than about 50% of the variance of true channel and/or interference.

Adaptive interference suppression for DS-CDMA

Abstract: We propose an adaptive scheme to reject multiuser interference using as little as 20-30 taps in direct-sequence code-division multiple-access systems employing arbitrary processing gains (31-400 considered here). We demonstrate that our receiver using this scheme does not require training signals, either initially when the desired user powers on in the presence of several strong interferers, or during transmission, as other users (possibly near-far interferers) gain access to the system. Moreover, knowledge of interfering users spreading codes, timing, or phase information is not required with our adaptive receiver.

Co-channel interference cancellation based on MIMO OFDM systems

Abstract: This article deals with the exploitation of multiple input multiple output (MIMO) systems for broadband wireless indoor applications. Two systems, the Wind-Flex and ubiquitous antenna, are considered. Both aim to increase the system capacity by different approaches, to increase the single link data rate and the number of users in the whole system, respectively. Computer simulation results show the effectiveness of both MIMO systems.

The most spectrum-efficient duplexing system: CDD

Abstract: The game to play in wireless communications, when it comes to increasing spectrum efficiency, is eliminating interference. Currently, all cellular systems use frequency-division duplexing in an attempt to eliminate interference from adjacent cells. The use of many technologies has limited the effects of interference, but two types of interference remain. These are adjacent base-to-home mobile interference and adjacent mobile-to-home base interference, Time-division duplexing has not been used for mobile cellular systems because it is even more susceptible to different forms of interference. Not only is TDD subject to adjacent base-to-home mobile interference and adjacent mobile-to-home base interference; it also has to battle additional adjacent base-to-home base interference, and adjacent mobile-to-home mobile interference. Therefore, TDD can only be used for small confined area systems. Code-division duplexing (CDD) is an innovative solution that can eliminate all four kinds of interference: adjacent base-to-home mobile, adjacent mobile-to-home base, adjacent base-to-home base, and adjacent mobile-to-home mobile in cellular systems. Eliminating each of these types of interference makes CDD the most spectrum-efficient duplexing system. This article elaborates on a set of smart codes that will make an efficient CDD system a reality.

A novel approach to in-band interference mitigation in ultra wideband radio systems

Abstract: Ultra wideband (UWB) radio transmission is a very important topic and, at present, a lot of work is devoted to increasing the use of this technology. In this regard, a crucial point is to evaluate performance loss induced by the in-band interference generated by concurrent services ("foreign services") to try to limit it. We present a novel algorithm to estimate and suppress an external interference in UWB systems so as to increase the SIR (signal-to-interference ratio) and thus to achieve performance near to that of interference-free UWB systems.

Method and apparatus for diversity combining and co-channel interference suppression

Abstract: A method and apparatus for controlling an antenna array for wireless communication are described. The method uses the statistical characteristics of the received signal noise in controlling the antenna array in order to achieve directional reception in a wireless communication system and suppress co-channel interference. Furthermore, the method can be used to power space-division multiple access and can be used in conjunction with multi-carrier modulation signaling.

Radio communication device for avoiding frequency collision among different radio control schemes

Abstract: A radio communication device is provided with a unit for acquiring a prediction information for a frequency, time or direction to be used by each one of the first radio control scheme of the radio communication device and a second radio control scheme of another surrounding radio communication device, and a unit for obtaining a predicted frequency, time or direction for which interferences between radio communications by the first radio control scheme and radio communications by the second radio control scheme are predicted to occur according to the prediction information, and control the radio communication unit to carry out radio communications by avoiding the predicted frequency, time or direction.

Radio frequency interference issues in impulse radio multiple access communication systems

Abstract: Impulse radio systems use very short pulses. Consequently, the spectrum of the transmitted signal spreads over several gigahertz and overlaps with RF bands occupied by other communication systems. As a result, radio frequency interference (RFI) affects the received signal. We present an analysis of the effects of RFI to a victim UWB receiver. Conditions for RFI cancellation for a large class of interfering signals are derived and it is shown that accurate frequency estimation of the interfering signal is necessary in order to provide interference cancellation. Finally, we give the level of accuracy that guarantees that the theoretical results hold in practice.

Adaptive co-channel interference cancellation in space-time coded communication systems

Abstract: A multi-input-multi-output, minimum mean squared error spatial filtering-based adaptive antenna arrays method is proposed to suppress co-channel interference (CCI) in space-time coded systems. It is shown that the proposed method can effectively suppress CCI while preserving the space-time structure, thereby significantly improving the system's interference suppression ability.

A novel adaptive antenna architecture - subcarrier clustering for high-speed OFDM systems in presence of rich co-channel interference

Abstract: For future high-speed orthogonal frequency division multiplexing (OFDM) wireless communications, two major system requirements will exist: broadband transmission and rich interference elimination. Because of its broadband nature and limited frequency allocations worldwide, interference from co-located wireless LAN operating in the same frequency band will become a serious deployment issue, since interference may have a large amount of multipath and also have similar levels of received power compared to the desired signal. This paper presents recent investigations in OFDM smart antenna systems, more specifically the signal properties in the frequency domain, for co-channel interference detection and rejection. A novel architecture is proposed in this paper, which is a complexity-reduced frequency-domain technique using subcarrier clustering. Research results are presented and show that the proposed architecture can achieve high performance with low complexity, within a rich multipath environment with low signal to noise plus interference ratio (SNIR).

Quadratic forms in complex Gaussian matrices and performance analysis of MIMO systems with co-channel interference

Abstract: We derive new results dealing with the distribution of the largest eigenvalue of certain quadratic forms in complex Gaussian matrices. These results are useful for the performance analysis of optimized multi-input-multi-output (MIMO) systems subject to co-channel interference.

Blind source separation technique for reduction of co-channel interference

Abstract: A technique for co-channel interference reduction that uses blind separation of source signals through independent component analysis (ICA) is given. An outline of an ICA-based BPSK receiver operating in a flat non-dispersive channel is presented. The performance of the receiver is evaluated through computer simulations which demonstrate the significant improvement of the receiver performance.

Space-time equalization and interference cancellation for MIMO OFDM

Abstract: The paper develops equalization techniques that facilitate aggressive frequency reuse in cellular OFDM systems. The initial focus is on the case of a single strong interfering base at the mobile. The interfering base is asynchronous in that its cyclic prefix is not time-aligned with the desired base's cyclic prefix. Various methods for combating the asynchronous, interfering base are developed, based on channel shortening ideas. The most promising method works to align the cyclic prefixes while holding all channel lengths equal to the cyclic prefix length or less. For the case of two receive antennas at the mobile, two sets of space-time filters are designed so that the respective channels at either output for either base are time-aligned with length no greater than the cyclic prefix length. As a result, standard frequency-domain equalization/interference suppression techniques (e.g., MMSE combining) can be applied to the outputs of the space-time filters on a per frequency bin basis to obtain symbol estimates for the desired base. Simulations are presented comparing the BER performance of the candidate techniques.

Reducing effects of self-created interference on broadband reception

Abstract: The invention relates to a method for reducing effects of self-created digital radio frequency interference on broadband reception. In the method a DVB-T (Digital Video Broadcasting - Terrestrial) signal is received at a broadband receiver (200). The received signal is demodulated in a demodulation process. Information (210) on frequencies of self-created digital radio frequency interference is provided for the broadband reception. The information has been generated based on prior measurements and stored to a memory prior to the receiving of the DVB-T signal. The information is used in the broadband reception so as to reduce the effects of the self-created digital radio frequency interference on the broadband reception.