Frequency Allocation Scheme Research Articles

Ground-to-Air Communications Beyond 5G: A Coordinated Multipoint Transmission Based on Poisson-Delaunay Triangulation

This paper designs a novel ground-to-air communication scheme to serve unmanned aerial vehicles (UAVs) through legacy terrestrial base stations (BSs). In particular, a tractable coordinated multi-point (CoMP) transmission based on the geometry of Poisson-Delaunay triangulation is developed, which provides reliable and seamless connectivity for UAVs. An effective dynamic frequency allocation scheme is designed to eliminate inter-cell interference by using the theory of circle packing. For exact performance evaluation, the handoff probability of a typical UAV is characterized, and then the coverage probability with handoffs is attained. Simulation and numerical results corroborate that the proposed scheme outperforms the conventional CoMP scheme with three nearest cooperating BSs in terms of handoff and coverage probabilities. Moreover, as each UAV has a fixed and unique CoMP BS set, it avoids the real-time dynamic BS searching process, thus reducing the feedback overhead.

Resonant Manifold Multiplexers

This article presents a new compact multiplexer structure and its design approach, based on a novel resonant manifold. Different from typical transmission-line-based manifold multiplexers, the proposed manifold junction is formed of coupled resonators, so that the manifold also contributes to the filtering poles and selectivity in the passbands. The all-resonator configuration achieves a more compact footprint than the conventional manifold. This multiport filtering network can be represented by a single coupling matrix which can be obtained by using a robust optimization-based method. Tailored channel frequency allocation schemes are presented for the proposed multiplexers with a different number of channels. To validate the proposed concept, a triplexer and a five-channel multiplexer, both at X-band, are designed and tested using rectangular waveguide technology. Good agreements have been achieved between the measurement and simulations. Comparisons have been made with conventional multiplexers.

Enhancement of Cognitive Radio Spectrum with Proposed Cascade Filter Model

The use of the frequency spectrum has become an urgent necessity, especially in the advanced generations of communications and various types of transmitted data. The radio spectrum is not being exploited effectively, primarily due to the current strict frequency allocation scheme. Only few bands of the spectrum are heavily utilized, such as those used for wireless base stations. Many bands are either not used at all or are only used infrequently. This problem has been solved through cognitive radio (CR) technology. CR technology faces many challenges in finding the unused frequency spectrum, especially the presence of noise in the spectrum analysis. This paper proposes a filter model with two-stages to enhance the cognitive radio performance and perform a comparison between proposed filter with the traditional cognitive radio techniques, by the means of QPSK modulation. The comparison result based on parameters such as the probability of detection as well as the probability of failure and the cumulative error rates. High probability of detection is required to achieve better network performance. A proposed filter model in the CR method has successfully passed all tests and provided better performance than other filters.

An improved water-filling algorithm based on power allocation in network MIMO

Inter-Cell Interference (ICI) could affect the performance of the LTE-Advanced (LTE-A) system and can be evaluated according to the user’s Signal to Interference and Noise Ratio (SINR). Owing to this, the power and frequency allocation schemes can be utilized in order to attain an optimum trade-off within the obtained SINR and the resulting interference. In this study, power allocation was integrated into the Dynamic Fractional Frequency Reuse (DFFR) scheme and Network MIMO (NetMIMO) to reduce ICI and enhance the performance of LTE-A downlink. Moreover, this study focuses on the design and development of a novel power allocation algorithm, which is an extension to the previous Improved Water-Filling algorithm (IWF), namely, Low-Complexity Improved Water-Filling algorithm (LC-IWF). Results indicated a reduction in computations and enhancement in interference rejection performance in comparison to the existing algorithms by removing the Lagrange multiplier and water level. Moreover, simulation results revealed that the proposed algorithm enhances the throughput and fairness of up to 20% and 25%, respectively. Furthermore, the power consumption was reduced by 41% and the running time was 5–10 times faster than the IWF algorithm while attaining the best solution. The proposed power allocation algorithm provided a significant improvement in the performance of the NetMIMO LTE-A system, which can be extended for future 5G networks.

Air-to-Air Communications Beyond 5G: A Novel 3D CoMP Transmission Scheme

In this paper, a novel $3$D cellular model consisting of aerial base stations (aBSs) and aerial user equipments (aUEs) is proposed, by integrating the coordinated multi-point (CoMP) transmission technique with the theory of stochastic geometry. For this new $3$D architecture, a tractable model for aBSs' deployment based on the binomial-Delaunay tetrahedralization is developed, which ensures seamless coverage for a given space. In addition, a versatile and practical frequency allocation scheme is designed to eliminate the inter-cell interference effectively. Based on this model, performance metrics including the achievable data rate and coverage probability are derived for two types of aUEs: {\it i)} the general aUE (i.e., an aUE having distinct distances from its serving aBSs) and {\it ii)} the worst-case aUE (i.e., an aUE having equal distances from its serving aBSs). Simulation and numerical results demonstrate that the proposed approach emphatically outperforms the conventional binomial-Voronoi tessellation without CoMP. Insightfully, it provides a similar performance to the binomial-Voronoi tessellation which utilizes the conventional CoMP scheme; yet, introducing a considerably reduced computational complexity and backhaul/signaling overhead.

Joint Frequency and Power Control for Self–Organizing OFDMA Femtocell Networks

In this paper, distributed joint power and frequency allocation problem is studied. First, we present a distributed power update algorithm for the general wireless networks that eliminates the feasibility issue encountered in the well-known Foschini-Miljanic algorithm. Then, the proposed algorithm is extended by considering Orthogonal Frequency Division Multiple Access (OFDMA) femtocell networks in which each femto base station has more than one user. In addition, a frequency allocation scheme is developed in order to increase the maximum achievable signal-to-interference-plus-noise ratio (SINR). Subsequently, we present a joint frequency/power update algorithm by combining the proposed frequency allocation scheme with the power update algorithm. Convergence and optimality analyses of all the proposed algorithms are carried out and the theoretical results are illustrated with numerical results.

Uplink Performance Improvement for Downlink-Uplink Decoupled HetNets with Non-uniform User Distribution

In the heterogeneous networks (HetNets), the downlink-uplink decoupled (DUDE) user association is a very promising technology that can employ different association strategies for uplink and downlink. The DUDE mode has great potential for improving system capacity and frequency efficiency. However, interference between the DUDE user equipment (DUDE UE), macro user equipment (MUE) and small user equipment (SUE) still needs to be considered and properly tackled. Therefore, this paper presents an optimization scheme of frequency allocation and power control to improve the communication quality of users. Firstly, the multiple region frequency allocation (MRFA) scheme is proposed for non-uniform user distribution to alleviate interference among users and allocate spectrum resources equally to dense users. This scheme is modelled as a sub-region partition problem with maximum sum rate, which can disperse densely distributed users to different sub-bands for transmission. Secondly, the convergent power control (CPC) algorithm is considered to improve the transmission performance of each user. It can converge the transmit power to the optimal transmit power for reducing interference among co-channel users when there is no disturbance in the network. The CPC algorithm can also make the signal-to-interference-plus-noise-ratio (SINR) of each active user always greater than the target threshold until the end of communication by dynamically adjusting the transmit power of users. Simulation results show that the joint scheme of MRFA and CPC achieves a higher system throughput and better user performance than existing frequency allocation schemes or power control schemes.

A Novel Frequency Allocation Scheme for In Band Full Duplex Systems in 5G Networks

In band full duplex (IBFD) is an emerging transceiver technology that facilitates simultaneous transmission and reception on the same frequency to double spectral efficiency. Self-interference (SI) from its own transmitter is the biggest challenge in IBFD radios causing significant degradation to its receiver performance. SI cancellation (SIC) techniques proposed in literature involve considerable hardware and software complexities for practical realization of IBFD radios. In this letter, a hybrid cellular architecture is proposed composing of IBFD base station and legacy half duplex user equipments (UEs), thus avoiding complex SIC requirement at UE. A novel frequency allocation scheme is proposed for this hybrid architecture that allows sharing of carrier frequencies among UEs based on distance criteria. As the number of UEs increases, chances of finding UEs that satisfy the distance criteria also increase steadily. Simulation results reveal that the probability of 100% frequency reuse exceeds 0.9 for as few as 8 UEs itself, demonstrating the potential of the proposed idea.

Full-Duplex Cognitive Radio Using Guided Independent Component Analysis and Cumulant Criterion

Due to the ever-increasing wireless service requirements, the issues of a limited frequency resource and underutilized frequency allocation scheme as well as frequency crowd have come to become increasingly severe. It gives rise to being difficult to effectively eliminate the spectrum interference and fulfill an efficient spectrum access mechanism using the congested frequency band. For this purpose, this paper conceives a simultaneous transmission and sensing scheme based on the guided independent component analysis combined with the cumulant-based non-Gaussian criterion for fulfilling full-duplex cognitive radio (FD-CR). The philosophy of this proposed scheme is that the ICA based blind source separation principle is firstly utilized for blind separation of the observation mixtures, and then the separated signals are recognized through correlation processing and non-Gaussian criterion based on cumulant. In particular, the known secondary user signal is used as a signature signal for assisting ICA framework construction for blind extraction of signals. As a key component of machine learning, the ICA theory can contribute significantly to conquering the static sensing problem and residual self-interference influence in existing conventional cognitive radio systems. The simulation experiments and analysis corroborate the effectiveness of the proposed method and system design. In addition, the low complexity and performance enhancement of the proposed method are also validated by comparing with that of the two practical FD-CR schemes.

Fractional Frequency Reuse Scheme for Device to Device Communication Underlaying Cellular on Wireless Multimedia Sensor Networks.

Wireless multimedia sensor networks (WMSNs) have been improved with the increase of multimedia data. In WMSNs, a centralization problem can occur because of large-size multimedia data. It is necessary to consider device-to-device (D2D) communication. We focus on D2D WMSN based on cellular networks. Sensors in the D2D WMSN can non-orthogonally use a cellular link, which is a wireless communication channel between a sensor and an aggregator, and a D2D link, which is the channel between sensors. As a result, it has more complex interference environments than an ordinary system. Therefore, it is a key factor to manage the varying inter-cell interference effectively for throughput improvement. We propose an interference mitigation scheme that can be applied to D2D WMSN. In the proposed scheme, a cell is separated into six zones and orthogonal frequency is allocated to each zone for cellular links. The frequencies allocated to cellular links are reused by D2D links of neighboring zones. The simulation results show that the throughput of the proposed scheme increases two times compared to a static frequency allocation scheme.

Interference aware coordinated multiuser access in multi-band WLAN for next generation low power applications

With the new IEEE 802.11ah standard aimed at improving the existing WLAN standard for the machine-to-machine applications, there is a renewed interest from the research community to analyze and suggest improvements to the standard. With thousands of smart devices and sensors involved in an internet of things network, the interference from multiuser access becomes a serious issue. This paper presents an access point (AP) coordinated multiuser access mechanism for such applications, where the strategy to improve channel usage efficiency is based on analyzing interference present in the neighborhood. Interference experienced in such a system is a function of node location, transmitted power, traffic load and resource allocation. In our proposed system, each WLAN AP from the overlapping basic service sets employs multiple frequency sub-bands and associates user nodes to these sub-bands dynamically. We show that this proposed interference-aware dynamic frequency allocation (IDFA) scheme, which is based on neighborhood contention analysis, can significantly enhance the system throughput and improve the energy efficiency by about 30%. In dense user node deployments, the channel access efficiency of the IDFA multi-band scheme is 2–3 times higher than that of the single band legacy WLAN.

A Dynamic Inter-cellular Bandwidth Fair Sharing scheduler for future wireless networks

Due the limitation of the frequency spectrum, channel assignment remains a main challenge in future wireless networks. In this context, the Inter-cellular Scheduling Scheme consists in dynamically allocating/reallocating the bandwidth to the cells, adapting it to the inhomogeneous traffic distribution that appears in a multi-cell environment. More precisely, it dynamically selects the cell that experiences the highest difficulties and grants it supplementary radio resources borrowed from its neighboring under-loaded donor ones. In this paper, we introduce and explain the concept of minimal bandwidth, which corresponds to the minimal amount of radio resources that an under-loaded cell must keep in order to be protected from sudden and uneven high bit rates peaks. This minimal bandwidth guarantees a minimal service. The majority of the existing works on dynamic channel assignment neglects the use of this important parameter or consider it as a static one. In this context, we introduce a novel multicellular scheduler called Dynamic Inter-cellular Bandwidth Fair Sharing that dynamically computes the minimal bandwidth of a cell according to its ratio of used bandwidth and available bandwidth. In the first step, the proposed solution is applied to the channel assignment scheme Reuse 3 and compared to a state of the art inter-cellular scheduling strategy in order to underline the benefits of the dynamic minimal bandwidth adaptation. In the second step, we have applied our methodology to the Fractional Frequency Reuse (FFR) scheme and compared it to the four frequency allocation schemes, Reuse 1, Reuse 3, FFR and Soft Frequency Reuse (SFR), as well as to a reference Dynamic FFR (D-FFR) solution that does not take into consideration the needs of the cells in terms of minimal bandwidth while redistributing the radio resources. Simulation results show that although the D-FFR scheme enhances the performances of the overloaded cell, it deteriorates the performance of the neighboring under-loaded ones. On the contrary, our solution called FFRDIBFS improves the provided Quality of Service (QoS) of both the congested cells and the whole cellular network.

Recursive Frequency Allocation Scheme in Wireless Power Transfer and Magnetic Induction Communication Systems

Magnetic induction applications mostly rely on resonance for inducing maximum magnetic fields to system loads and hence for each resonant frequency dedicated circuits are required. Unfortunately, the frequency responses of such inductive systems manifest several peaks (frequency splitting) when their coupling coefficients are equal to or larger than critical coupling. Such frequency responses with several peaks are detrimental when the objective is to transfer maximum energy. Frequency splitting between inductive coils have been seen to date as detrimental to wireless power transfer and inductive communication systems. In this paper it is demonstrated that frequency splitting is a welcome phenomenon with advantage in the design of inductive filter banks and multi-frequency inductive systems. The centre frequencies of the filter banks result from split bands of inductive systems. This phenomenon is applied in conjunction with an innovative recursive algorithm to design inductive filter banks. The filters straddle both sides of the resonant frequency position and can be resolved individually.

Distributed spatial modulation with dynamic frequency allocation

This paper proposes a distributed implementation of spatial modulation (SM) using cognitive radios. In distributed spatial modulation (DSM), multiple relays form a virtual antenna array and assist a source to transmit its information to a destination. The source broadcasts its signal, which is independently demodulated by all the relays. Each of the relays then divides the received data in two parts: the first part is used to decide which one of the relays will be active, and the other part decides what data it will transmit to the destination. An analytical expression for symbol error probability is derived for DSM in independent and identically distributed (i.i.d.) Rayleigh fading channels. The analytical results are later compared with Monte Carlo simulations. Further, an instantaneous symbol error rate (SER) based selection combining is proposed to incorporate the direct link between the source and destination with existing DSM. Next, DSM implementation is extended to a cognitive network scenario where the source, relays, and destination are all cognitive radios. A dynamic frequency allocation scheme is proposed to improve the performance of DSM in this scenario. The frequency allocation is modeled through a bipartite graph with end-to-end SER as a weight function. The optimal frequency allocation problem is formulated as minimum weight perfect matching problem and is solved using the Hungarian method. Finally, numerical results are provided to illustrate the efficacy of the proposed scheme.

Analysis of Load Balancing and Interference Management in Heterogeneous Cellular Networks

To meet the current cellular capacity demands, proactive offloading is required in heterogeneous cellular networks (HetCNets) comprising of different tiers of base stations (BSs), e.g., small-cell BSs (sBSs) and conventional macro-cell BSs (mBSs). Each tier differs from the others in terms of BS transmit power, spatial density, and association bias. Consequently, the coverage range of each tier BSs is also different from others. Due to low transmit power, a fewer number of users are associated to an sBS as compared with mBS. Thus, inefficient utilization of small-cell resources occurs. To balance the load across the network, it is necessary to push users to the underloaded small cells from the overloaded macro-cells. In co-channel deployed HetCNets, mBSs cause heavy inter-cell interference (ICI) to the offloaded users, which significantly affects the network performance gain. To address this issue, we develop a tractable analytical network model abating ICI using reverse frequency allocation (RFA) scheme along with cell range expansion-based user association. We probabilistically characterize coverage probability and user rate while considering RFA with and without selective sBS deployment. Our results demonstrate that selective sBS deployment outperforms other deployment methods.

Coverage and Rate Analysis for Downlink HetNets Using Modified Reverse Frequency Allocation Scheme

The deployment of heterogeneous networks (HetNets) inevitably demands the design of interference management techniques to elevate the overall network performance. This paper presents a novel interference mitigation technique known as reverse frequency allocation (RFA), which provides an efficient resource allocation compared with the other state-of-the-art techniques. RFA reverses the transmission direction of interferers, thereby minimizing the cross-tier interference. Eventually, better coverage as well as increased data rates are achieved by providing complementary spectrum to the macro and pico users. In this paper, we present a tractable approach for modeling HetNets under the proposed RFA scheme. Specifically, we employ well known tools from stochastic geometry to derive closed-form expressions for the coverage probability and rate coverage in two-tier cellular network employing RFA and its variants. The modeling is performed using two approaches; first, where the base stations and users are modeled as independent Poisson point processes (PPPs) and second, the interference is approximated using the fluid model. It is shown that the results obtained from the PPP model are accurate for higher values of path loss exponents, while the results from fluid model are useful for smaller values of path loss exponents. The plausibility of model is validated through the Monte-Carlo simulations and the network performance is evaluated in terms of coverage probability, coverage rate, and outage capacity. The results demonstrate that 2-RFA yields outage capacity gains of 13% as compared with the soft fractional frequency reuse scheme, whereas, the performance gains can be further improved by 14% by employing the proposed variants of RFA.

Dynamic Frequency Resource Allocation in Heterogeneous Cellular Networks

Deployment of low power pico basestations within cellular networks can potentially increase both capacity and coverage. However, such deployments require efficient frequency allocation schemes for managing interference from the pico and macro basestations that are located within each other's transmission range. Partitioning the available frequencies between the various basestations avoids the problem of interference, but can lead to inefficient spectrum usage. In this paper, we introduce a distributed frequency allocation scheme that shares frequencies between macro and pico basestations, and guarantees a minimum average throughput to users. The scheme seeks to minimize the total number of frequencies needed to honor the minimum throughput requirements. We evaluate our scheme using detailed simulations and show that it performs on par with the centralized optimum allocation. Moreover, our proposed scheme outperforms a static frequency reuse scheme and the centralized optimal partitioning between the macro and pico basestations.

Resource Allocation for D2D Links in the FFR and SFR Aided Cellular Downlink

Device-to-device (D2D) communication underlying cellular networks, allows direct transmission between two devices in each other’s proximity that reuse the cellular resource blocks in an effort to increase the network capacity and spectrum efficiency. However, this imposes severe interference that degrades the system’s performance. This problem may be circumvented by incorporating fractional frequency reuse (FFR) or soft frequency reuse (SFR) in OFDMA cellular networks. By carefully considering the downlink resource reuse of the D2D links, we propose beneficial frequency allocation schemes, when the macrocell has employed FFR or SFR as its frequency reuse technique. The performance of these schemes is quantified using both the analytical and simulation results for characterizing both the coverage probability and the capacity of D2D links under the proposed schemes that are benchmarked against the radical unity frequency reuse scheme. The impact of the D2D links on the coverage probability of macrocellular users (CUs) is also quantified, revealing that the CUs performance is only modestly affected under the proposed frequency allocation schemes. Finally, we provide insights concerning the power control design in order to strike a beneficial tradeoff between the energy consumption and the performance of D2D links.

Decoupled Downlink-Uplink Coverage Analysis with Interference Management for Enriched Heterogeneous Cellular Networks

Heterogeneous cellular networks (HetCNets) offer a promising solution to cope with the current cellular coverage crunch. Due to the large transmit power disparity, while following maximum power received (MPR) association scheme, a larger number of users are associated with macro-cell BS (MBS) than small-cell BSs (SBSs). Therefore, an imbalance load arrangement takes place across the HetCNets. Hence, using cell range expansion-based cell association, we can balance the load across the congested MBS. However, using MPR association scheme, users' offloading leads to two challenges: 1) macro-cell interference, in which the MBS interferes with the offloaded users, and 2) coupled downlink-uplink cell association, in which a random user associates with a single tier's base station (BS) both in uplink (UL) and downlink (DL) directions. This paper aims to address these problems while considering a two-tier scenario consisting of small-cell and macro-cell tiers. For the MBS interference mitigation, we employ a reverse frequency allocation (RFA) scheme. Besides coupled DL-UL association (Co-DUA), this paper also highlights the notion of decoupled DL-UL association (De-DUA). In De-DUA, a random user associates with two different tiers' BSs, i.e., with one tier's BS in the DL direction and with the other tier's BS in the UL direction. Our results illustrate that, in comparison with the Co-DUA, De-DUA with RFA employment achieves a better coverage performance.

네트워크 코딩을 쓰는 언더레이 인지 무선 네트워크에서의 주파수 할당과 경로 선택 기법

In this paper, we propose frequency allocation and path selection scheme in underlay cognitive radio (CR) networks using network coding. In the proposed scheme, we choose the path with consideration of network coding and interference temperature in underlay CR networks and propose an optimization problem to maximize the system throughput of secondary users (SUs). Then, we represent the proposed optimization problem as the multi-dimensional multiple-choice knapsack problem and give the theoretical upper bound for the system throughput of SUs by using linear programming. Finally, we compute the system throughput of SUs by using brute-force search (BFS) and link quality first (LQF) scheme in underlay CR networks. Simulation results show that the system throughput of SUs with BFS is higher than that with LQF in underlay CR networks with and without application of network coding, respectively.