Showing papers on "Co-channel interference published in 2011"

Capacity Analysis of a Multi-Cell Multi-Antenna Cooperative Cellular Network with Co-Channel Interference

Abstract: Characterization and modeling of co-channel interference is critical for the design and performance evaluation of realistic multi-cell cellular networks. In this paper, based on alpha stable processes, an analytical co-channel interference model is proposed for multi-cell multiple-input multi-output (MIMO) cellular networks. The impact of different channel parameters on the new interference model is analyzed numerically. Furthermore, the exact normalized downlink average capacity is derived for a multi-cell MIMO cellular network with co-channel interference. Moreover, the closed-form normalized downlink average capacity is derived for cell-edge users in multi-cell multiple-input single-output (MISO) cooperative cellular networks with co-channel interference. From the new co-channel interference model and capacity formulas, the impact of cooperative antennas and base stations on cell-edge user performance in the multi-cell multi-antenna cellular network is investigated by numerical methods. Numerical results show that cooperative transmission can improve the capacity performance of multi-cell multi-antenna cooperative cellular networks, especially in a scenario with a high density of interfering base stations. The capacity performance gain is degraded with the increased number of cooperative antennas or base stations.

On the Degrees of Freedom of $K$-User SISO Interference and X Channels with Delayed CSIT

Abstract: The $K$-user single-input single-output (SISO) AWGN interference channel and $2\times K$ SISO AWGN X channel are considered where the transmitters have the delayed channel state information (CSI) through noiseless feedback links. Multi-phase transmission schemes are proposed for both channels which possess novel ingredients, namely, multi-phase partial interference nulling, distributed interference management via user scheduling, and distributed higher-order symbol generation. The achieved degrees of freedom (DoF) values are greater than the best previously known DoFs for both channels with delayed CSI at transmitters.

Interference Mitigation Through Limited Transmitter Cooperation

Abstract: Interference limits performance in wireless networks and cooperation among receivers or transmitters can help mitigate interference by forming distributed MIMO systems. Earlier work shows how limited receiver cooperation helps mitigate interference. The scenario with transmitter cooperation, however, is more difficult to tackle. In this paper we study the two-user Gaussian interference channel with conferencing transmitters to make progress towards this direction. We characterize the capacity region to within 6.5 bits/s/Hz, regardless of channel parameters. Based on the bounded-gap-to-optimality result, we show that there is an interesting reciprocity between the scenario with conferencing transmitters and the scenario with conferencing receivers and their capacity regions are within a bounded gap to each other. Hence, in the interference-limited regime, the behavior of the benefit brought by transmitter cooperation is the same as that by receiver cooperation.

Performance Analysis of Dual-Hop AF Systems With Interference in Nakagami- $m$ Fading Channels

Abstract: In this letter, we investigate the performance of dual-hop channel state information-assisted amplify-and-forward relaying systems over Nakagami-m fading channels in the presence of multiple interferers at the relay. Assuming integer fading parameter m, we derive closed-form expressions for the exact outage probability and accurate approximation for symbol error rate of the system. Furthermore, we look into the asymptotical high signal to noise ratio regime, and characterize the diversity order achieved by the system. All the analytical results are validated via Monte Carlo simulations.

System and method for co-channel interference measurement and managed adaptive resource allocation for wireless backhaul

Abstract: A system, method, and software are provided for measuring co-channel interference in a wireless network with particular application for management of resource allocation for Non Line of Sight (NLOS) wireless backhaul in MicroCell and PicoCell networks. Given the difficulty of predicting the mutual interference between multiple links, DownLink and UpLink co-channel interference are characterized between each Hub and each Remote Backhaul Module Unit periodically during active service. Beneficially, the co-channel interference metrics are used as the basis for intelligently and adaptively managing network resources to substantially reduce interference and increase the aggregate data capacity of the network e.g. by grouping of interfering and/or non-interfering links, and managing resource block allocations accordingly, i.e. assigning common resource blocks preferentially to weakly interfering links or groups of links and allocating different resource blocks or orthogonal channels to strongly interfering links or groups of links.

On the Ergodic Capacity of Correlated Rician Fading MIMO Channels With Interference

Abstract: An asymptotic approach to derive the ergodic capacity achieving covariance matrix for a multiple-input multiple-output (MIMO) channel is presented. The method is applicable to MIMO channels affected by separately correlated Rician fading and co-channel interference. It is assumed that the number of transmit, receive and interfering antennas grows asymptotically while their ratios, as well as the SNR and the SIR, approach finite constants. Nevertheless, it is shown that the asymptotic results represent an accurate approximation in the case of a finitely many antennas and can be used to derive the ergodic channel capacity. This is accomplished by using an iterative power allocation algorithm based on a water-filling approach. The convergence of a similar algorithm (nicknamed frozen water-filling) was conjectured in a work by Dumont Here, we show that, in the Rayleigh case, the frozen water-filling algorithm may not converge while, in those cases, our proposed algorithm converges. Finally, numerical results are included in order to assess the accuracy of the asymptotic method proposed, which is compared to equivalent results obtained via Monte-Carlo simulations.

Wireless device and method of operation

Abstract: A wireless device has at least first and second radio systems. A first of the radio systems provides an indication for a second of the radio systems that it is transmitting or is about to transmit. The actual interference caused by transmissions by the first radio system to operation of the second radio system is measured, and/or the likely interference caused by transmissions by the first radio system to operation of the second radio system is estimated. The behaviour of at least one of the first and second radio systems is modified in order to reduce the interference depending on the measured actual interference or estimated likely interference.

Enhancement of in-device coexistence interference avoidance

Abstract: A method, system and device are provided for avoiding in-device coexistence interference between different radio technologies deployed in adjacent bands on the same device by reporting uplink buffer status information to the radio network and configuring LTE and non-LTE components to provide an in-device coexistence operation mode where non-LTE components use radio resources during the non-LTE on-intervals and during off-intervals inserted into the LTE on-intervals in response to predetermined trigger events.

When Alamouti codes meet interference alignment: Transmission schemes for two-user X channel

Abstract: Interference alignment increases transmission rate in terms of multiplexing gain for X channel. In this paper, we propose a fixed-rate transmission scheme over a two-user X channel where each of the two double-antenna transmitters has independent messages for each of the two double-antenna receivers. Each transmitter encodes symbols using Alamouti codes followed by beamformers that align interference at unintended receivers. The receiver removes the aligned interference and decouples symbols using interference cancellation followed by symbol-by-symbol decoding. Our analysis shows that the proposed scheme achieves a diversity gain of 2 at the maximum node-to-node symbol-rate of 2 over 3.

Interference Channels With Arbitrarily Correlated Sources

Abstract: Communicating arbitrarily correlated sources over interference channels is considered in this paper. A sufficient condition is found for lossless transmission of a pair of correlated sources over a discrete memoryless interference channel. With independent sources, the sufficient condition reduces to the Han-Kobayashi achievable rate region for interference channels. For sources with a special correlation structure, the proposed region reduces to the known achievable region for interference channels with common information. Moreover, the proposed coding scheme is optimal for transmitting such set of correlated sources over a class of deterministic interference channels as defined in El Gamal and Costa, 1982.

Fixed Gain Amplify-and-Forward Relaying with Co-Channel Interference

Abstract: We investigate the outage probability and the average bit error rate (BER) of a dual-hop fixed gain relaying system in the presence of co-channel interference and thermal noise at the relay and the destination. Our analysis assumes Rayleigh fading for the source-relay and relay-destination channels and Rician fading for the interfering channels. We present new closed-form/series expressions for the outage probability and the average BER. The achievable diversity order is also studied. It is further shown through numerical results that the Rician K-factor of the interfering channel has a negative effect on the overall outage probability and BER, yet this effect is very small.

Performance of Multihop Relay Systems with Co-Channel Interference in Rayleigh Fading Channels

Abstract: In this letter we investigate the effect of co-channel interference on the performance of multihop transmission systems that employ amplify-and-forward relays and operate in a Rayleigh fading environment. We assume that an arbitrary number of interferers with arbitrary powers are present at each relay node and derive useful bounds for important performance measures, such as the outage probability and the average symbol error probability of various digital modulation schemes.

Distributed Adaptation of Quantized Feedback for Downlink Network MIMO Systems

Abstract: This paper focuses on quantized channel state information (CSI) feedback for downlink network MIMO systems. Specifically, we propose to quantize and feedback the CSI of a subset of BSs, namely the feedback set. Our analysis reveals the tradeoff between better interference mitigation with large feedback set and high CSI quantization precision with small feedback set. Given the number of feedback bits and instantaneous/long-term channel conditions, each user optimizes its feedback set distributively according to the expected SINR derived from our analysis. Simulation results show that the proposed feedback adaptation scheme provides substantial performance gain over non-adaptive schemes, and is able to effectively exploit the benefits of network MIMO under various feedback bit budgets.

The Ergodic Capacity of Phase-Fading Interference Networks

Abstract: We identify the role of equal strength interference links as bottlenecks on the ergodic sum capacity of a K user phase-fading interference network, i.e., an interference network where the fading process is restricted primarily to independent and uniform phase variations while the channel magnitudes are held fixed across time. It is shown that even though there are K(K-1) cross-links, only about K/2 disjoint and equal strength interference links suffice to determine the capacity of the network regardless of the strengths of the rest of the cross channels. This scenario is called a minimal bottleneck state. It is shown that ergodic interference alignment is capacity optimal for a network in a minimal bottleneck state. The results are applied to large networks. It is shown that large networks are close to bottleneck states with a high probability, so that ergodic interference alignment is close to optimal for large networks. Limitations of the notion of bottleneck states are also highlighted for channels where both the phase and the magnitudes vary with time. It is shown through an example that for these channels, joint coding across different bottleneck states makes it possible to circumvent the capacity bottlenecks.

Improper Gaussian signaling on the two-user SISO interference channel

Abstract: On a single-input-single-out (SISO) interference channel (IC), under non-cooperative setting, every user maximizes its own transmit date rate by transmitting proper (symmetric) complex Gaussian symbols with full power. However, the efficiency of such equilibrium is low. In particular, the resulting interference saturates the sum rate in high SNR regime, yielding degrees-of-freedom zero. Fortunately, through cooperation among transmitters, it is possible to restore the degrees-of-freedom by the user of improper complex Gaussian signaling. In this paper, we study the impact of improper signaling on the 2-user SISO-IC. In particular, we analyze the efficiency of improper signaling in extreme SNR regimes and the performance of some particular simple improper transmit strategies.

Review of spectrum sensing in cognitive radio

Abstract: The frequency spectrum bandwidth used in modern wireless systems is limited while the number of wireless systems is rapidly increasing. In order to alleviate the spectrum scarcity, secondary systems can opportunistically access the temporarily unused licensed bands of primary systems which are known as spectrum holes or white spaces, by altering their transmitting parameters so that the interference is minimal to primary user while coordinating access to this channel with other cognitive radio (CR) users in the vicinity. Spectrum sensing is necessary to enable dynamic spectrum access without interfering with primary users. This optimizes the use of available radio frequency spectrum while minimizing interference to other licensed or unlicensed users by detecting and utilizing only the white spaces. This paper explores various sensing methods, their performance, applicability and effectiveness under different transmission conditions and advantages and disadvantages incorporated with each sensing method.

Rate-limited transmitter-cooperation in Wyner's asymmetric interference network

Abstract: We study Wyner's asymmetric interference network (soft-handoff model) when each transmitter has local, rate-limited side-information about the messages of the J transmitters to its left and the J transmitters to its right. We distinguish two scenarios. In Scenario A the neighbors of Transmitter k can have different, individual, side-information about Message M k . In Scenario B they all have the same side-information about M k . For both scenarios we derive the asymptotic multiplexing gain per-user, that is, the limiting ratio of the multiplexing gain divided by the number of users K when K → ∞.

Retrospective interference alignment

Abstract: In this paper, we explore the possibility of achieving interference alignment with delayed CSIT when the transmitters are distributed. Our main contribution is an interference alignment scheme, called retrospective interference alignment, that is specialized to settings with distributed transmitters. With this scheme we show that the interference channel with 3 users with only delayed channel state information at the transmitters can achieve 9/8 DoF, while the the 2 user X channel is able to achieve 8/7 DoF. We also consider another setting where delayed channel output feedback is available to transmitters. In this setting the 3 user interference channel and the 2 user X channel are shown to achieve 6/5 and 4/3 DoF, respectively.

Unified Spectral Efficiency Analysis of Cellular Systems with Channel-Aware Schedulers

Abstract: Spectral efficiency is a key characteristic of cellular communications systems, as it quantifies how well the scarce spectrum resource is utilized. It is influenced by the scheduling algorithm as well as the signal and interference statistics, which, in turn, depend on the propagation characteristics. In this paper we derive analytical expressions for the short-term and long-term channel-averaged spectral efficiencies of the round robin, greedy Max-SINR, and proportional fair schedulers, which are popular and cover a wide range of system performance and fairness trade-offs. A unified spectral efficiency analysis is developed to highlight the differences among these schedulers. The analysis is different from previous work in the literature in the following aspects: (i) it does not assume the co-channel interferers to be identically distributed, as is typical in realistic cellular layouts, (ii) it avoids the loose spectral efficiency bounds used in the literature, which only considered the worst case and best case locations of identical co-channel interferers, (iii) it explicitly includes the effect of multi-tier interferers in the cellular layout and uses a more accurate model for handling the total co-channel interference, and (iv) it captures the impact of using small modulation constellation sizes, which are typical of cellular standards. The analytical results are verified using extensive Monte Carlo simulations.

Parameterized cancellation of partial-band partial-block-duration interference for underwater acoustic OFDM

Abstract: Despite that underwater acoustic channels are well known to contain various interferences, research on interference mitigation in underwater acoustic communications has been very limited. In this paper, we deal with a wideband orthogonal frequency division multiplexing (OFDM) transmission in the presence of an external interference which occupies partially the signal band and whose time duration is shorter than the OFDM block. We parameterize the unknown interference waveform by a number of parameters assuming prior knowledge of its frequency band and time duration, and develop an iterative receiver, which couples interference detection via a generalized likelihood-ratio-test (GLRT), interference reconstruction and cancellation, channel estimation, and data detection. In addition to simulation results, we verify the receiver performance using data sets collected from two experiments. In both time-invariant and time-varying channels, the proposed iterative receiver achieves robust performance in the presence of unknown interference.

Enhanced In-Device Coexistence Interference Avoidance Using Predetermined Downlink Channel

Abstract: A method, system and device are provided for avoiding in-device coexistence interference between different radio technologies deployed in adjacent bands on the same device by allocating a non-interfering downlink signaling channel for downlink reception of interference avoidance instructions at the UE device. In operation, a user equipment device detects IDC interference and sends an IDC indication message to the radio network to get an appropriate solution, but instead of waiting at the current frequency to receive the IDC response from the radio network, the user equipment device moves to a non-interfering downlink signaling channel for downlink reception of interference avoidance instructions.

Method and apparatus for reducing co-channel interference

Abstract: A method for providing co-channel interference information by a network node includes receiving information for at least one user equipment (UE) connected to an adjacent network node, determining a co-channel interference list for user equipment (UE) connected to the network node wherein the co-channel interference list is based on the received information and transmitting the co-channel interference list to a UE connected to the network node.

Performance of interference-limited dual-hop non-regenerative relays over rayleigh fading channels

Abstract: This paper studies the performance of a dual-hop non-regenerative relay fading channel in an interference-limited environment. The relay and destination nodes are corrupted by co-channel interference. New closed-form expressions for the probability density function and cumulative distribution function of the output signal-to-interference ratio are derived. Analytical expressions for the outage probability of both the channel-state-information-assisted relay and the fixed-gain relay channels are derived and the obtained numerical results are compared. Monte-Carlo simulations are performed to verify the obtained theoretical results.

A downlink power control scheme for interference avoidance in femtocells

Abstract: Femtocells being small low powered base stations provide sufficient increase in system capacity along with better indoor coverage However, the dense deployment of femtocells face the main challenge of co channel interference with macrocell users In this paper, this interference problem is addressed by proposing a novel downlink power control algorithm for femtocells The proposed algorithm gradually reduces the downlink transmit power of femtocells when they are informed about a nearby macrocell user under interference This information is given to the femtocells by the macrocell base station through a unidirectional downlink broadcast channel Simulation results show that the algorithm causes the macrocell to accommodate large number of femtocells within its area, whereas at the same time protecting the macrocell users from any harmful interference

Coexistence and Mutual Interference between Mobile and Broadcasting Systems

Abstract: The ever increasing demand for multimedia wireless communication systems is a key feature of more advanced markets. The buzzword of personal communications, meant to provide "access to anyone, anywhere, at anytime" to the wanted service, implies that spectrum demands are dramatically increasing in most developed markets. To cope with these needs, and in order to exploit the released spectrum resulting from the Digital Switchover, the last World Radiocommunication Conference (WRC-07) allocated on a co-primary basis the upper part of the UHF band to mobile services as from 2015. This will cause potentially harmful mutual interference between TV and mobile radio services, that needs to be carefully analyzed. In this paper we present a study of the co-channel interference problem, proposing a methodology to take into account the mutual interference between a LTE mobile network and a DVB-T system and highlighting the different behaviour of the two radio links.

Interference Alignment by Opportunistic User Selection in 3-User MIMO Interference Channels

Abstract: In this paper, we propose a practical interference alignment technique based on an opportunistic user selection in a three-user MIMO interference channel where no information is allowed to be shared among transmitters. In the proposed scheme, the user whose interference signals from other transmitters are most aligned with each other is selected at each transmitter. The proposed opportunistic interference alignment (OIA) is shown to achieve notable sum rate compared to conventional opportunistic user selection schemes. In addition, the proposed OIA significantly reduces not only the amount of feedback information but also computational complexity.

Interference channel with binary fading: Effect of delayed network state information

Abstract: We investigate the fundamental limits of communication over binary interference channels with finite states and with delayed network state information at the transmitters. Our results include a novel achievability strategy that systematically utilizes the stale network state information available at the nodes. We also derive new bounds on the capacity region of such networks.

System and Method for Reducing In-Band Interference for a Shared Antenna

Abstract: An interference compensation circuit for suppressing in-band or nearby out-of-band interference in a shared antenna communication system. The communication system can include a first communication device having a transmitter for transmitting signals within a first frequency band and a second communication device having a receiver for receiving electromagnetic signals within a second frequency band. The second frequency band can be adjacent or overlapping the first frequency band. The communication system also can include an interference compensation circuit that receives samples of the signals transmitted by the transmitter and generate an interference compensation signal in response to adjusting amplitude, phase, and/or delay of the samples. The interference compensation signal can suppress interference imposed on the receiver by the signals transmitted by the transmitter when applied to a signal receive path of the receiver.

Performance analysis of fixed-gain AF dual-hop relaying systems over Nakagami-m fading channels in the presence of interference

Abstract: This article presents an analytical investigation on the performance of interference-limited fixed-gain amplify-and-forward dual-hop relaying systems over Nakagami-m fading channels. Assuming the fading parameter m of the two hop channels being integer, we derive a closed-form expression of the cumulative distribution function of a new type of random variables involving a number of independent gamma random variables, based on which, the outage performance and symbol error rate of the system are examined, and two important performance metrics at the high signal-to-noise ratio regime, namely, diversity order and coding gain, are characterized. Moreover, expressions of the general moments of the end-to-end signal-to-interference-and-noise ratio are derived and then applied in the analysis of the ergodic capacity of the system. In addition, the impact of interference power distribution on the ergodic capacity of the system is studied with the aid of a majorization result. Our findings suggest that the diversity of the system is limited by the hop experiencing severer fading, and co-channel interferences do not reduce the diversity order of the system, instead, they degrade the outage performance by affecting the coding gain of the system.

Usable speech processing: a filterless approach in the presence of interference

Abstract: A speech signal is commonly corrupted by non-stationary interference in different environments. The interference distributes itself nonuniformly over the temporal regions of the signal. This makes certain segments more speech dominant and hence, “usable” for speech processing applications like speaker identification and speech recognition. The main part of this paper examines the detection of usable segments in a co-channel environment having two interfering speakers. A method based on determining the Target-to-Interferer Ratio to detect the usable portions in which one speaker is very dominant over the other is discussed. A short discussion of additive noise distortion follows. Experimental results are presented.