Interference (wave propagation)

About: Interference (wave propagation) is a research topic. Over the lifetime, 26086 publications have been published within this topic receiving 321110 citations.

Adaptive spread spectrum FH-MFSK transmitter and receiver

Abstract: The present invention relates to a transmitter, a receiver and techniques for use in a frequency-hopping, multilevel frequency shift keyed (FH-MFSK) radio system which permits the selective concurrent transmission of one or two encoded frequencies per time slot of the transmitted sequence for improving reception at a receiver experiencing interference from the system transmitters above a predetermined interference threshold level. An alternative arrangement permits all transmitters and receivers to communicate with one another by transmitting a separate one of multiple frequencies in a separate one of an equal number of multiple frequency subbands forming the system frequency band during each time slot for providing flexibility in system design. Combinations of the two arrangements can also be employed.

Single-step superresolution by interferometric imaging

Abstract: The use of vertical-cavity surface-emitting laser (VCSEL) arrays for implementation of incoherent source superresolution is presented. The method uses an interferometer setup to obtain superresolution in a single step. The novelty of the method relies on the use of a VCSEL array as the light source, which provides a set of coherent sources which are mutually incoherent. The technique accomplishes the transmission of several spatial frequency bands of the object’s spectrum in parallel by use of spatial multiplexing that occurs because of the tilted illumination of the source array. The recording process is done by interference of each frequency band with a complementary set of reference plane waves. After the reconstruction process, the resolution of any optical system can approach the natural λ/2 limit. The benefit of our system is improved modulation speed and hence more rapid image synthesis. Moreover, any desired synthetic coherent transfer function can be realized at ultrafast rates if we simply change the electrical drive of the VCSEL array.

Transmit beamforming for spectral coexistence of satellite and terrestrial networks

Abstract: Herein, we study transmit beamforming techniques in an underlay cognitive mode for the coexistence of satellite and terrestrial networks with the satellite forward link as primary and the terrestrial downlink as secondary. Since geostationary satellite terminals have predetermined propagation characteristics so that they always point towards the geostationary satellite, the interference received by the satellite terminals from the terrestrial Base Station (BS) is confined in an angular sector. Based on this a priori knowledge, we propose transmit beamforming techniques at the BS to maximize the Signal to Interference plus Noise Ratio (SINR) towards the desired Secondary User (SU) and to mitigate the interference towards the primary satellite terminals. Different types of Linearly Constrained Minimum Variance (LCMV) techniques have been proposed for our considered scenario where the exact locations and the number of satellite terminals within a specific angular sector are not known while designing the beamformer. Furthermore, an optimization problem is formulated for maximizing the SU rate and it is shown that the worst case SU rate depends on the Primary User (PU) distance, PU interference threshold and the angular separation of the desired SU from the region of interest.

Method and apparatus for eliminating interference using transmission delay and code multiplexing in digital radio system

Abstract: At a transmitter side, signals are providcd with a delay difference with a plurality of branches, coded multiplexed by spectrum spreaders and a combination unit, and transmitted by single antenna. At a receiver side, the signals are received by a single antenna, and diversity branches are extracted and separated by first and second spectrum de-spreaders. They are subject to linear combination so that the mean square of the decision error signals is minimized. The output passes through an adaptive matched filter and an adaptive equalizer so as to provide an output from which interference waves are eliminated. Thus, interference is eliminated and diversity gain for a signal is ensured, while reducing the scale and cost of a system without using a plurality of antennae.

Effective Carrier Sensing in CSMA Networks under Cumulative Interference

Abstract: This paper proposes and investigates the concept of a safe carrier-sensing range that can guarantee interference safe (also termed hidden-node-free) transmissions in CSMA networks under the cumulative interference model. Compared with the safe carrier-sensing range under the commonly assumed but less realistic pairwise interference model, we show that the safe carrier-sensing range required under the cumulative interference model is larger by a constant multiplicative factor. The concept of a safe carrier-sensing range, although amenable to elegant analytical results, is inherently not compatible with the conventional power threshold carrier-sensing mechanism (e.g., that used in IEEE 802.11). Specifically, the absolute power sensed by a node in the conventional mechanism does not contain enough information for it to derive its distances from other concurrent transmitter nodes. We show that, fortunately, a carrier-sensing mechanism called Incremental-Power Carrier-Sensing (IPCS) can realize the carrier-sensing range concept in a simple way. Instead of monitoring the absolute detected power, the IPCS mechanism monitors every increment in the detected power. This means that IPCS can separate the detected power of every concurrent transmitter, and map the power profile to the required distance information.