Preventing Interference to DTV Broadcasting in Every Market From Unlicensed or Uncontrolled Clusters of Broadband Devices on Unoccupied DTV Channels

The threat of interference to licensed DTV by clusters of unlicensed and uncontrolled broadband devices (BDs) transmitting simultaneously on unoccupied DTV channels remains. DTV channels in major U.S. cities could be victimized by interference from unlicensed or uncontrollable clusters. This paper shows how and why interference by clusters of broadband devices would be significantly higher than interference by individual broadband devices or by interference from clusters of single-tone devices. This paper also provides a real-world assessment of the maximum interference that consumer-grade receivers can accept from clusters of broadband devices operating on unoccupied DTV channels. To prevent interference to DTV and to maximize spectral efficiency individual base stations would have to be licensed as part of a network, and portable unlicensed devices would have to be equipped with dual DTV tuners with GPS chips.     

A Unified Model for Interference Analysis in Unlicensed Frequency Bands

This paper presents a unified framework for interference characterizations and analysis in the unlicensed frequency bands and the like, where many narrowband heterogenous terminals coexist and share a common wideband channel using less-restrictive transmission etiquettes. Here, each transmitter/receiver pair makes his own decision regarding when to access the channel without any direct coordination with the other users. This is usually based on the local channel conditions at the receiver or/and the transmitter. Due to the nature of the wireless channel, communication in such environments is usually prone to arbitrary partial-band interference which can be generated anywhere in the space and frequency domains. In this paper, a new spatial-spectral interference model is introduced, where interferers can be of any power spectral density and are distributed according to a Poisson process in space and frequency domains. This basic model is extended to include the effects of channelization, where users are allowed only to transmit at a preassigned set of discrete frequencies. This is further extended to include also the effects of spectral-spatial guard zones, where the interferers can not exist in a given band nearby the victim receiver. Based on this multidimensional spatial-spectral Poisson model and the accurate conditional Gaussian analysis, explicit expressions are derived for average error rates of different communication systems.     

Interference Channels With Common Information

In this paper, the interference channel with common information (ICC), in which two senders need deliver not only private messages but also certain common messages to their corresponding receivers, is investigated. An achievable rate region for such a channel is obtained by applying a superposition coding scheme that consists of successive encoding and simultaneous decoding. It is shown that the derived achievable rate region includes or extends several existing results for the interference channels with or without common information. The rate region is then specialized to a class of ICCs in which one sender has no private information to transmit, and a class of deterministic interference channels with common information (DICCs). In particular, the derived rate region is found to be the capacity region for this class of DICCs. Last, the achievable rate region derived for the discrete memoryless ICC is extended to the Gaussian case, in which a numerical example is provided to illustrate the improvement of our rate region over an existing result.     

Interference Avoidance and Multiaccess Vector Channels

In this paper we present application of interference avoidance in the context of a general multiple access vector channel model. We show that this monotonically increases sum capacity, and discuss algorithms for code division multiple access (CDMA) codeword optimization based on this procedure. A greedy interference avoidance algorithm for multiaccess vector channels is presented in the paper, for which we discuss convergence to a class of codeword ensembles that satisfy a simultaneous water filling solution and maximize sum capacity. Numerical results obtained from simulations that corroborate our analytical results are also presented.     

The Capacity Region of Frequency-Selective Gaussian Interference Channels Under Strong Interference

This paper presents the capacity region of frequency-selective Gaussian interference channels under the condition of strong interference, assuming an average power constraint per user. First, a frequency-selective Gaussian interference channel is modeled as a set of independent parallel memoryless Gaussian interference channels. Using nonfrequency selective results, the capacity region of frequency-selective Gaussian interference channels under strong interference is expressed mathematically. Exploiting structures inherent in the problem, a dual problem is constructed for each independent memoryless channel, in which both mathematical and numerical analysis are performed. Furthermore, three suboptimal methods are compared to the capacity-achieving coding and power allocation scheme. Iterative waterfilling, a suboptimal scheme, provides close-to-optimum performance and has a distributed coding and power allocation scheme, which are attractive in practice.     

Matched-Transmission Technique for Channels With Intersymbol Interference

A new transmission scheme for channels with intersymbol interference named "matched-transmission (MT) technique" is proposed. An implementation of the MT system is presented and its relations with conventional techniques are described. It is shown that the partial response scheme is a special case of our new technique. The performance of the MT technique is discussed from the view point of the output signal-to-noise ratio and the system is shown to attain asymptotically the bound performance predicted by the information theory.     

Capacity Optimizing Power Allocation in Interference Channels

The interference channel is an essential model in both wireline and wireless communication systems. This article addresses transmit power allocation in interference channels with total transmit power constraint. The optimum power allocation maximizing the sum rate in two user interference channels can be derived analytically. However, the non-convexity of the optimization problem makes it prohibitively complex to obtain the optimum solution either analytically or numerically in general K user scenarios. After reviewing several conventional suboptimum power allocation schemes including equal power allocation, greedy power allocation and waterfilling power allocation, an iterative waterfilling algorithm is proposed and discussed. The performance of various power allocation schemes is evaluated through simulations, which suggests that the proposed iterative waterfilling outperforms other suboptimum power allocation schemes in certain scenarios.     

Successive Interference Cancellation and Alignment in K-User MIMO Interference Channels with Partial Unidirectional Strong Interference

Recently cellular networks have been densely and heterogeneously deployed indoors and outdoors to expand the network capacity,and thus the in-building propagation loss and the transmit power diversity of access points will exacerbate link heterogeneity and result in partial unidirectional strong interference.To make full use of the strong interference feature,we propose the successive interference cancellation and alignment(SICA)scheme in the K-user interference channel with partial unidirectional strong interference.SICA is designed to transmit two kinds of data streams simultaneously,the alignment streams and superposition streams.The alignment streams will follow the interference alignment criterion to maintain the optimal degrees of freedom(DoF)performance;the superposition streams are handled via successive interference cancellation at all the strongly interfered receivers to improve the overall achievable rate.The joint transceiver designs for SICA is modeled as a weighted sum rate(WSR)maximization problem,and then can be alternately solved for a local optimum according to the optimality equivalence between WSR and its corresponding weighted mean square error(WMMSE)problem.Simulation results have confirmed the sum rate improvement and DoF optimality of the proposed SICA scheme.     

Unlicensed TX

The pace of growth of licence-exempt devices is set to continue. DECT phones, car key-fobs, baby monitors, garage-door openers, wireless headsets, WLANs in home and offices, wireless alarms, anti-theft systems, RFID chips: are all examples of license-exempt devices. From the point of view of a spectrum regulator there are broadly two reasons why devices might be exempted from licensing. The first reason is the economic benefits of the exempted user are greater than those of alternative licensed use. The second reason is if the demand for spectrum in a given frequency band is less than the supply. The rules for management of licence-exempt devices are discussed in this paper     

MMSE Equalization of Interference on Fading Diversity Channels

Adaptive equalization is used in digital transmission systems with parallel fading channels. The equalization combines the diversity channels and reduces intersymbol interference due to multipath returns. When interference is present and correlated from channel to channel, the equalizer can also reduce its effect on the quality of information transfer, important applications for interference cancellation occur in diversity troposcatter systems in the presence of jamming, diversity high frequency (HF) systems which must cope with interfering skywaves, and space diversity line-of-sight (LOS) radio systems where adjacent channel interference is a problem. In this paper we develop the general formulation for minimum mean square error (MMSE) equalization of interference in digital transmission diversity systems. The problem formulation includes the use of available receiver decisions to assist in MMSE processing. The effects of intersymhol interference are included in the analysis through a critical approximation which assumes sufficient processor capability to reduce ISI effects to levels small enough for satisfactory communication. The analysis also develops he concept of additional implicit or intrinsic diversity which results from channel multipath dispersion. It shows how the MMSE processor sacrifices diversity to suppress interference even when the interference arrives in the main beams of the receiver antenna patterns. The condition of near synchronous same-path interference is also addressed. Because the spatial angle of arrival of the interference may result in delay differences between interference signals in different antenna channels, interference delay compensation may be required. We show that this effect is compensated for with a small number of appropriately spaced equalizer taps.     

Robust Frequency Hopping for Interference and Fading Channels

A robust frequency-hopping system with noncoherent detection, iterative turbo decoding and demodulation, and channel estimation is presented. The data modulation is the spectrally compact nonorthogonal continuous-phase frequency-shift keying, which strengthens the frequency-hopping system against multiple-access interference and multitone jamming. An analysis based on information theory provides the optimal values of the modulation index when there is a bandwidth constraint. The channel estimator, which is derived by applying the expectationmaximization algorithm, accommodates both frequency-selective fading and interference. Simulation experiments demonstrate the excellent system performance against both partial-band and multiple-access interference.     

Adjacent-Cell Interference in Direct-Sequence CDMA Forward Traffic Channels

Each transmission from a base station in a mobile cellular direct-sequence CDMA network is a source of interference for the receivers in the mobile handsets that are operating in adjacent cells. This interference can limit the capacity of the forward traffic channels. The effect of adjacent-cell interference on the performance of the handset receivers is evaluated for a mobile cellular CDMA network that employs quadriphase-shift-key spreading, convolutional coding, and soft-decision decoding. It is demonstrated that acceptable performance may not be possible for a fully loaded cellular network. Of particular interest in this paper are cellular networks in which the base stations are mobile and must be interconnected by wireless communication links. Such networks are important for military applications and certain civilian emergency communications services.     

Asynchronous Iterative Water-Filling for Gaussian Frequency-Selective Interference Channels

This paper considers the maximization of information rates for the Gaussian frequency-selective interference channel, subject to power and spectral mask constraints on each link. To derive decentralized solutions that do not require any cooperation among the users, the optimization problem is formulated as a static noncooperative game of complete information. To achieve the so-called Nash equilibria of the game, we propose a new distributed algorithm called asynchronous iterative water-filling algorithm. In this algorithm, the users update their power spectral density (PSD) in a completely distributed and asynchronous way: some users may update their power allocation more frequently than others and they may even use outdated measurements of the received interference. The proposed algorithm represents a unified framework that encompasses and generalizes all known iterative water-filling algorithms, e.g., sequential and simultaneous versions. The main result of the paper consists of a unified set of conditions that guarantee the global converge of the proposed algorithm to the (unique) Nash equilibrium of the game.     

Capacity of Interference Channels With Partial Transmitter Cooperation

Capacity regions are established for several two-sender, two-receiver channels with partial transmitter cooperation. First, the capacity regions are determined for compound multiple-access channels (MACs) with common information and compound MACs with conferencing. Next, two interference channel models are considered: an interference channel with common information (ICCI) and an interference channel with unidirectional cooperation (ICUC) in which the message sent by one of the encoders is known to the other encoder. The capacity regions of both of these channels are determined when there is strong interference, i.e., the interference is such that both receivers can decode all messages with no rate penalty. The resulting capacity regions coincide with the capacity region of the compound MAC with common information.     

多模干涉型集成光学器件研究进展

基于自镜像效应(SIE)的多模干涉(MMI)型集成光学器件是集成光学中具有广泛用途的重要器件。本文详细而系统地综述了近几年来MMI器在国内外的研究进展，特别是其在集成光学中的应用。     

Electromagnetic Interference Control Considerations Solenoid Operated Control Devices

Relay and solenoid controlled devices have historically been a common source of electromagnetic interference. The pulsed electrical energy resulting from actuation and deactuation generates broad frequency spectrum interference. Establishment of meaningful component and subsystem specifications and application of proper design techniques can minimize the interference generated by such devices and subsystems and can also minimize their susceptibility to other interference sources. This paper reviews the approaches which will significantly minimize electromagnetic interference problems.     

Effects of Measurement Devices on Conducted Interference Levels

Measurements of power line conducted interference voltages are commonly made throughout the 150 kHz to 30 MHz frequency range on military, industrial, and consumer equipment using line impedance stabilization networks (LISN) and, more recently, current probe techniques. This paper presents some brief background information concerning power line conducted interference measurements and the results of a study to assess the effects of LISN and current probe measurement devices on the level of measured conducted interference. A model is defined which facilitates prediction of the effects. The model concept allows the procedures described in this paper to be extended to equipment of other impedance definitions. A comparison of the calculated and empirical differences is made and suggests an analytical approach in sizing the effects upon the conducted interference levels.     

Evaluating the Use of Cross-Polarization Discrimination in Mitigating Interference from Unlicensed Devices onto DTV

This paper presents the results of the tests performed by the Communications Research Centre Canada (CRC) for determining cross-polarization discrimination of some consumer-grade UHF TV antennas that are available on the market. The test conditions were selected to resemble the situation when a UD (Unlicensed Device) transmitting antenna is operational in the vicinity of a TV receiving antenna. The results of this experiment will be helpful in evaluating the effectiveness of cross-polarization discrimination when it is used as a way of mitigating the interference effects from UD radiation onto DTV reception.      

Capacity of Cognitive Interference Channels With and Without Secrecy

Like the conventional two-user interference channel, the cognitive interference channel consists of two transmitters whose signals interfere at two receivers. It is assumed that there is a common message (message 1) known to both transmitters, and an additional independent message (message 2) known only to the cognitive transmitter (transmitter 2). The cognitive receiver (receiver 2) needs to decode messages 1 and 2, while the noncognitive receiver (receiver 1) should decode only message 1. Furthermore, message 2 is assumed to be a confidential message which needs to be kept as secret as possible from receiver 1, which is viewed as an eavesdropper with regard to message 2. The level of secrecy is measured by the equivocation rate. In this paper, a single-letter expression for the capacity-equivocation region of the discrete memoryless cognitive interference channel is obtained. The capacity-equivocation region for the Gaussian cognitive interference channel is also obtained explicitly. Moreover, particularizing the capacity-equivocation region to the case without a secrecy constraint, the capacity region for the two-user cognitive interference channel is obtained, by providing a converse theorem.