Co-channel Interference Levels Research Articles

Interbeam Interference Constrained Resource Allocation for Shared Spectrum Multibeam Satellite Communication Systems

Future Internet of Things should contain space segment and terrestrial segment. In addition, the multibeam satellite communication systems, especially working in S shared band, have gained more attention, which plays a significant role in providing direct-to-user satellite mobile services. Besides, due to the limited on-board resources, it is increasingly urgent to improve resource utilization. Taking the interbeam interference, channel conditions, delay factor, capacity, bandwidth utilization variance into consideration, a novel joint resource allocation algorithm is proposed in this paper. Interbeam interference coefficient matrix derived from frequency reuse is established to measure the level of co-channel interference. Moreover, the proposed algorithm can allocate resources flexibly according to specific traffic requirements and channel conditions. A novel joint power and bandwidth allocation algorithm is proposed by optimizing throughput and approximation problem of actual requirement. The optimal solution to this optimization problem can be obtained by golden section theory and subgradient iteration. The evaluation results demonstrate that the proposed algorithm can maximize the capacity, minimize the bandwidth utilization variance, and it can also allocate resource intelligently adapting to the user requirements and channel conditions.

Resource Optimization in Full Duplex Non-Orthogonal Multiple Access Systems

In this paper, we investigate a full duplex (FD) multi-user non-orthogonal multiple access (NoMA) communication system based on the optimization of received signal-to-interference-plus-noise ratio (SINR) per unit power. Since the communication system operates in the FD mode, co-channel interference (CCI) and self-interference (SI) dominate the system's performance. Accordingly, to combat the CCI, we adopt a game-theoretic approach and propose users' clustering algorithms and to suppress the SI, we formulate an optimization problem to maximize the power-normalized SINR (PN-SINR). While the user clustering optimization problem is constrained by: 1) the successive interference cancellation (SIC) constraint and 2) two binary constraints for the allocations of uplink (UL) and downlink (DL) users, the PN-SINR problem is constrained by: 1) total transmit power budget at the base station and UL users; 2) the fundamental condition for the implementation of successive interference cancellation in the NoMA; and 3) the minimum fairness condition for the UL users. The original PN-SINR problem is non-convex and hence is converted into an equivalent subtractive-form problem, after which we propose an iterative algorithm to find the optimal power allocation policy. Properties of all the proposed algorithms are thoroughly investigated and the numerical results are provided. Based on the channel conditions and suppression level of SI and CCI, the superiority of the proposed FD-NoMA system over half-duplex NoMA and FD orthogonal multiple access systems is verified.

Parallel Data Transmission in Indoor Visible Light Communication Systems

This paper presents an indoor visible light communication (VLC) system in conjunction with an imaging receiver with parallel data transmission (spatial multiplexing) to reduce the effects of the inter-symbol interference (ISI). To distinguish between light units (transmitters) and to match the light units used to convey the data with the pixels of the imaging receiver, we propose the use of subcarrier multiplexing (SCM) tones. Each light unit transmission is multiplexed with a unique tone. At the receiver, a SCM tone decision system is utilized to measure the power level of each SCM tone and consequently associate each pixel with a light unit. In addition, the level of co-channel interference (CCI) between light units is estimated using the SCM tones. Our proposed system is examined in two indoor environments taking into account reflective components (first and second order reflections). The results show that this system has the potential to achieve an aggregate data rate of 8 Gb/s with a bit error rate of 10–6 for each light unit, using simple on-off-keying (OOK).

QoS-Based Multi-criteria Handoff Algorithm for Femto-Macro Cellular Networks

The hierarchical coexistence of femtocells and macrocells is a promising approach for heterogeneous networks (HetNets), dealing mainly with indoor coverage issues and providing high data rates in cellular networks. As for any HetNet, mobility management with handoff issues on top, should be studied prior to hindering the successful deployment of these networks. The current study introduces a new handoff algorithm in hierarchical macro/femtocell HetNets based on the combination of quality of service metrics for efficient network selection including: received signal strength, co-channel interference level, and outage probability of each of femtocell and macrocell networks. The proposed algorithm first collects the measured three mentioned metrics based on mobile station (MS) location, then applies a dynamic weighting system to three-metric sets according to the significance of each metric to obtain one utility for each of femtocell and macrocell networks. The obtained utility is then used as a measure for determining handoff necessity. In order to evaluate the performance of the proposed approach, the paper then introduces analytical model of cell assignment probability for an MS moving from the serving macrocell base station to the target femtocell base station in a two-tier cellular network. The analytical and simulation results indicate the efficiency of the proposed handoff algorithm in comparison with the existing algorithms in terms of cell assignment probability, throughput, number of handoffs, and ping-pong rate.

Spatial filter decomposition for interference mitigation

This paper presents a two-part decomposition of a spatial filter having to optimize the reception of a useful signal in the presence of an important co-channel interference level. The decomposition highlights the role of two parts of the filter, one devoted to the maximization of the signal to noise ratio and the other devoted to the interference cancellation. The two-part decomposition is used in the estimation process of the optimal reception filter. We propose then an estimation algorithm that follows this decomposition, and the global spatial filter is finally obtained through an optimal-weighted combination of two filters. It is shown that this two-component-based decomposition algorithm overcomes other previously published solutions involving eigenvalue decompositions.

Cloud Transmission: System Performance and Application Scenarios

Cloud transmission (Cloud Txn) is a flexible multilayer system that uses spectrum overlay technology to simultaneously deliver multiple program streams with different characteristics and robustness for different services (mobile TV, HDTV, and UHDTV) in one radio frequency channel. Cloud Txn is a multilayer transmission system like layered-division multiplexing. The transmitted signal is formed by superimposing a number of independent signals at desired power levels to form a multilayered signal. The signals of different layers can have different coding, bit rate, and robustness. The upper layer system parameters are chosen to provide very robust transmission that can be used for high-speed mobile broadcasting. The bit rate is traded for powerful coding and robustness so that the signal-to-noise ratio (SNR) threshold at the receiver is in the range of ${-}{2}$ to ${-}{\rm 3}~{\rm dB}$ . The top layer is designed to withstand combined noise, co-channel interference and multipath distortion power levels higher than the desired signal power. The lower-layer signal can be a DVB-T2 signal or another new system to deliver HDTV/UHDTV to fixed receivers. The system concept is open to technological advances that might come in the future: BICM/non uniform-QAM, rotated constellations, time frequency slicing or MIMO techniques can be implemented in the Cloud Txn lower (high data rate) layer. The system can have backward compatible future extensions, adding more lower layers for additional services without impact legacy services. This paper describes the performance of Cloud Txn broadcasting system.

Interference Mitigation Techniques for Spectral Capacity Enhancement in GSM Networks

Random Frequency Hopping (FH) is a key feature of GSM networks that allows for capacity enhancement. The increased co-channel interference experienced in networks with tight frequency reuse schemes can be mitigated by adopting frequency hopping. Frequency hopping diversifies the interference signals over sparse transmitted bursts. This effect is called Interference Diversity. Interference Diversity allows the Forward Error Correcting codes (FEC) to easily correct the corrupted bits. Thus, frequency hopping allows the network operator to use a tighter frequency reuse scheme without exhibiting higher levels of co-channel interference. Discontinuous Transmission (DTX) is another interference mitigation method that utilizes the user’s silence frames to reduce the transmitted power, while Power Control (PC) links the transmitted handset power with its relative distance from the Base Station (BTS). In this work, we study the impact of random FH, DTX and PC on the Spectral Capacity of GSM cellular networks by means of combined link level and system level simulation. It is shown that a spectral capacity gain is obtained in a 3/9 reuse scheme that deploys PC, DTX and FH compared to a conventional 4/12 reuse scheme.

Experimental Investigations of Cochannel Interference Reduction Effect at High Elevation Base Station Using Beam Tilt and Orthogonal Polarization

This paper addresses the problem of cochannel interference (CCI) generated in a mixed cell architecture in microcellular systems. In this type of microcellular systems in which both microcells and macrocells coexist in the same geographical urban area, the base station antennas mounted on the rooftops of buildings to cover wide circular radio zones suffer severe CCI from the surrounding low base stations. A dielectric-loaded slotted-cylinder antenna (DSCA) is applied to horizontally polarized omnidirectional array antennas in a height-diversity configuration with the high gain of 8 dBi, which is comparable to that of a collinear antenna, to reduce the CCI. The measurements conducted in a suburban area clarify the reduction in the CCI for three techniques. The beam-tilt technique reduces the CCI level by approximately 10 dB for both collinear antennas and the DSCA array antennas. The use of horizontal polarization reduces the CCI level by approximately 13 dB for the DSCA array antennas with and without beam tilt. The combination of the beam tilt and horizontal polarization or the DSCA array antennas with beam tilt significantly reduces the CCI level by approximately 23 dB.

Non‐cooperative uplink interference protection framework for fair and energy efficient orthogonal frequency division multiple access networks

In this study, the authors consider a low complexity resource allocation scheme for reducing the uplink cochannel interference (CCI). The goal is to obtain improvements in energy efficiency by controlling the level of CCI affecting vulnerable mobile stations (MSs). This is done with a combined scheduler and a two layer power allocation scheme, which is based on non-cooperative game theory. The authors approach forces users with good propagation conditions to reduce transmission power, to protect users experiencing high levels of interference. Thus, the MSs’ uplink throughputs are equalised under the max–min fairness optimisation criterion. The scheme they propose works with minimum channel knowledge, since only base-mobile channel path gains are required for the optimisation process. Furthermore, they show analytically and by simulation that the power reductions applied to users with good propagation conditions provide an increase in energy efficiency and fairness in the system. In addition, the simulation results show that their scheme provides a higher fairness index and a comparable system energy efficiency to a centralised signal interference noise ratio balancing scheme.

A Distributed Approach to Interference Alignment in OFDM-Based Two-Tiered Networks

In this paper, we consider a two-tiered network and focus on the coexistence between two tiers at the physical layer. We target our efforts on a Long-Term Evolution Advanced (LTE-A) orthogonal frequency-division multiple-access (OFDMA) macrocell sharing the spectrum with a randomly deployed second tier of small cells. In such networks, high levels of cochannel interference between the macrocell base station and the small-cell base station (SBS) may largely limit the potential spectral efficiency gains provided by frequency reuse 1. To address this issue, we propose a novel cognitive interference alignment-based scheme to protect the macrocell from cross-tier interference while mitigating the co-tier interference in the second tier. Remarkably, only local channel state information (CSI) and autonomous operations are required in the second tier, resulting in a completely self-organizing approach for the SBSs. The optimal precoder that maximizes the spectral efficiency of the link between each SBS and its served user equipment is found by means of a distributed one-shot strategy. Numerical findings reveal nonnegligible spectral efficiency enhancements with respect to traditional time division multiple access (TDMA) approaches at any signal-to-noise ratio (SNR) regime. Additionally, the proposed technique exhibits significant robustness to channel estimation errors, achieving remarkable results for the imperfect CSI case and yielding consistent performance enhancements to the network.

Performance analysis of a cellular network using frequency reuse partitioning

In this paper, we propose an analytical model to evaluate the performance of Frequency Reuse Partitioning (FRP) based cellular systems. In an FRP scheme, a channel with a smaller reuse factor is assigned to Mobile Stations (MSs) located near the serving Base Station (BS), whereas a channel with a larger reuse factor is assigned to MSs located near the edge of a cell. In this manner, FRP can reduce the effect of Co-Channel Interference (CCI) and improve system throughput. In order to establish an analytical model for FRP based cellular systems, we introduce a model for traffic analysis using a two dimensional Markov chain and approximate CCI levels with the power sum of multiple log-normal random components in a multi-cell environment. The performance of the FRP based system is presented in terms of channel utilization, call blocking probability, outage probability and effective throughput. The analytical results are compared with computer simulations.

Interference-Adaptive Fast Dynamic Channel Allocation in TD-SCDMA System

This paper proposes a new priority metric for fast dynamic channel allocation (DCA) in TD-SCDMA system, which reallocates radio resource units (RUs) to bearer services in a cell. It allows for developing a new interference-adaptive fast DCA algorithm, which is more flexible with a non-uniform user distribution. It considers the relative transmission opportunities with respect to the residual capacity and co-channel interference levels for all users, which steadily varies in the real communication environment. The proposed fast DCA algorithm aims to fully utilize the physical resource available in the time-division duplexing (TDD)-based CDMA system subject to the various types of inter-cell interference, as opposed to most existing algorithms in which traffic load and quality of service cannot be jointly balanced among the multiple radio resource units in a flexible manner. The simulation results show that the proposed algorithm improves the outage performance while reducing the average system interference, achieving full utilization of the physical resource, i.e., 48 RUs in TD-SCDMA, over a wide range of acceptable outage performance.

A New Modeling Scenario and Analysis of Handoff Algorithms in Multisector Systems With Cochannel Interference

This paper introduces a novel analytical model for analyzing the performance of handoff algorithms based on absolute and relative signal strength measurements. The performance is analyzed in multicell and multisector environments where cochannel interference (CCI) is present. The model presented in this paper accounts for the distinct features of intersector handoff compared with intercell handoff. Numerical results show that the performance metrics are affected by the CCI level. The occurrence condition of unnecessary handoffs in multisector systems is also presented.

INTERFERENCE SUPRESSION OF THE LINEAR ANTENNA ARRAYS CONTROLLED BY PHASE WITH USE OF SQP ALGORITHM

The performance of mobile cellular radio networks is limited by the level of cochannel interference that can be tolerated. The use of antennas arrays is very helpful in enhancing the performance and capacity of the wireless communication system. This paper presents a method for antenna pattern synthesis that suppress multiple interfering narrow or wide band signals while receiving the desired signal by controlling only the phase. Excitation phases are computed using the Sequential Quadratic Programming (SQP) technique. This method transforms the nonlinear minimization (or maximization) problem to a sequence of quadratic subproblems, based on a quadratic approximation of the Lagrangian function. 252 Mouhamadou et al.

Channel assignment for cellular mobile networks with nonuniform cells – an improved heuristic algorithm

A heuristic sequential algorithm for fixed channel assignment in cellular mobile networks with nonuniform cells, i.e., cells of different sizes and shapes, is presented. The channel assignment is treated as a nonbinary constraints satisfaction problem. The algorithm uses both the co-channel and adjacent channel interference levels and the number of channel requirements per cell to define the corresponding sequence of assignment. The effects of intercell overlapping and complex propagation mechanisms on the channel assignment results are investigated too.

Performance Evaluation of a Virtual Queuing --- Channel Allocation Scheme for Microcellular Networks

This paper deals with the performance evaluation of a novel distributed channel allocation scheme that attains a high resource reuse in cellular networks. A suitable interference model has been envisaged. Resources are nominally assigned to cells with Fixed Channel Allocation (FCA), according to a given reuse distance. Whenever a channel demand from a mobile user does not find a free nominal resource in a cell, a channel is temporarily borrowed violating the reuse distance constraint, provided that the co-channel interference level is acceptable. As soon as a nominal channel becomes available in this cell, the borrowed resource is released (virtual queuing). The performance of the proposed channel allocation scheme has been evaluated considering both uniform and non-uniform traffic patterns. A performance analysis approach has been also developed and validated by simulations. Comparisons with the classical FCA scheme and other dynamic and borrowing channel allocation strategies have permitted to highlight the good performance of the proposed technique.

Radiowave propagation research in the tropics using a transportable multiparameter radar system

Although accurate models for Earth-space microwave propagation, based on extensive measured data, exist for temperate regions of the world, this is not the case for the tropics. With the proliferation of satellite communications in these areas, it has become important to test the validity of currently recommended techniques for calculating circuit availability and co-channel interference levels due to attenuation by precipitation and scattering from precipitation, respectively. Multiparameter radar measurements, employing both polarimetric and Doppler techniques and made over a significant period of time on a statistically-valid basis, provide an ideal tool for these investigations. The paper describes the design considerations for, and construction of such a radar. A selection of its data products are presented, illustrating its potential for radio propagation and meteorological research.

Interference Analysis of an in-Building Wireless Communication System Employing Vertical Frequency Reuse

The reception quality of an interference limited indoor wireless communication system employing vertical frequency reuse is analysed. Outage probability expressions are used to measure the level of cochannel interference. The received signals are assumed to suffer the effects of Rayleigh fading and log-normal shadowing and multiple cochannel interferers are included in the analysis. The expected reception qualities are studied in a range of buildings and the results show that typically a vertical reuse distance of 3 floors will not isolate cochannel floors sufficiently to allow reliable reception. For one building analysed, even a vertical reuse distance of five floors is not likely to result in sufficiently low levels of cochannel interference. When multiple interferers are considered, it is not a straight forward task to determine the number of cochannel interferers that contribute significant interference since this may depend on the propagation conditions in a particular building.

Increasing the capacity of GSM cellular radio using adaptive antennas

The capacity of mobile cellular radio networks can be considerably increased if a higher level of cochannel interference can be tolerated. An adaptive antenna combines the outputs of an array of elements to maximise the wanted signal and suppress interfering signals. The author proposes an adaptive antenna algorithm suitable for GSM and the urban multipath environment. The algorithm is based on iterative reference signal reconstruction from the GSM training sequence. The average error rate is obtained by simulation for four equal power interfering signals and an urban GSM multipath model. An adaptive antenna can only practically be deployed at the base station. Realising its gains in a real network on both the up and downlinks requires, for the downlink, a number of techniques. This is discussed and a concept of how the full capacity gains can be achieved in an evolutionary manner on both links is proposed. The concept is equally applicable to the DCS 1800 and DCS 1900 systems based on GSM.

Analysis of LEO, MEO, and GEO global mobile satellite systems in the presence of interference and fading

Several multisatellite and multispot systems have been recently proposed for provision of mobile and personal services with global coverage, adopting GEO or non-GEO (i.e., MEO, LEO) satellite constellations. The paper addresses an in-depth analysis of these constellations, evaluating both geometrical performance measures and cochannel interference levels caused by extensive frequency reuse. The geometrical analysis yields the statistics for coverage, frequency of satellite hand-overs, and link absence periods. The interference analysis is based on a general model valid for all access techniques, which is here applied to the case of FDMA. The outage probability as a function of the specification on carrier-to-interference power ratio is evaluated for four selected constellations. Several techniques are introduced for interference reduction in non-GEO systems, in which the satellites coverage areas may intersect: spot turnoff, intraorbital plane frequency division, and interorbital plane frequency division. The effects of Rice fading have also been analyzed by means of an analytic approximated method. The overall analysis allows a fair comparison between LEO, MEO, and GEO constellations. >