Macrocell Network Research Articles

Optimal Overlay Cognitive Spectrum Access With F-ALOHA in Macro-Femto Heterogeneous Networks

The 5th generation (5G) wireless networks are conceived in the form of heterogeneous networks (HetNets), where small cells are deployed over the conventional macrocell networks to improve the spectral efficiency. In HetNets, the interference between different tiers is the main bottleneck for achieving high spectral efficiency. Many spectrum access schemes have been proposed to manage the cross-tier interference. Unfortunately, the optimal spectrum access scheme remains unknown. In this paper, we propose an F-ALOHA based cognitive spectrum access scheme for macro-femto HetNets, where the femtocells can access the idle macro-tier spectrum with a certain probability. Therefore, besides the degrees of freedom from the conventional spectrum deployment and co-tier spectrum access, the proposed scheme obtains a new degree of freedom from cross-tier spectrum access for interference management and spectral efficiency optimization. Simulation results will show that the proposed scheme outperforms existing F-ALOHA based spectrum access schemes in terms of the area spectral efficiency (ASE). More importantly, it is observed that the maximum ASE is achieved when the number of active links per unit area, which governs the interference level, reaches a certain value. The advantage of the proposed scheme comes from its ability to offload the traffic between two tiers through the cross-tier spectrum access probability, which flexibly manages the cross-tier interference.

Heterogeneous Networks in Shared Spectrum Access Communications

We investigate an advanced two-phase shared spectrum access communication scheme as an efficient approach to enhance the spectral utilization of a network. In the first phase, we devise a spectrum-sharing policy based on demands, fairness, and so on, which utilizes a priority scheme in fulfilling operators’ demands, and envision a secure operator-specific information sharing policy where no critical information is exchanged between the operators. In the second phase, a macro cell network (MCN) benefits through offloading services offered by small cell network (SCN). This allows the MCN to satisfy its users’ capacity demands, improve its quality of services and coverage under Nakagami fading channel. As a repayment, the SCN is rewarded with licenses to share and operate on the spectrum originally owned by the MCN. We devise a density division-based shared spectrum access model, where the density of the licensee’s SCN deployment is exploited as network resources. A fair division of the densities of the licensee operator’s small cell base stations into fractions of licensed small cell base stations serving its own users and offloading small cells is presented. Unlike most of the previous research works that considered Poisson point process (PPP) to model the distribution of the network entities even when PPP modeling is not accurate for the networks, where the number of MCN/SCN base stations is definite and the number of MCN/SCN base stations in disjoint areas is not independent, we employ a more realistic network model known as binomial point process to perform an analytical analysis of the cumulative interference and performance of the system. Furthermore, we analyze the rate coverage and outage performances considering a wide range of values for path-loss exponent and fading severity parameter of Nakagami fading.

A power-controlled interference management mechanism for femtocell-based networks

Femtocell deployment is one of the promising solutions to meet the increasing demands on wireless services and applications. Based on deploying Femtocells within the already-existing Macrocells, Femtocells can improve indoor coverage and increase both spectral efficiency and data rate. This improvement can be achieved by reusing the available spectrum assigned for the Macrocells, and being closer to the users. However, Femtocell deployment faces many challenges. One of the most challenging issues is the interference management issue. In this paper, a power-control channel assignment algorithm to manage the interference between Femtocell and Macrocell networks is proposed. The proposed algorithm allows frequency reuse among Femtocell users (FUEs) to provide better throughput performance. Simulation results have shown an improvement in throughput by up to 90% compared to previous schemes.

Mitigating ICI at cell edges in cognitive-femtocell networks through fractional frequency reuse

In this paper, we consider a situation where femtocells are deployed over the existing macrocell network and share the same frequency spectrum with macrocells where we focus only on downlink situation. It is essential to implant femtocell at cell edges due to the fact that the number of outage user is large because of their position which is far away from macrocell base station MBS located at macrocell centre, more precisely at 0, 0 coordinates. In general, the uncoordinated deployment of femtocell creates the potential for severe interference to co-located femtocells, especially in dense deployment, resulting in large inter cell interference ICI effect on the users located at cell edges. Here, we propose dynamic FFR algorithm at cell edges to overcome all possible difficulties in the networks. Frequency reuse is an approach to increase the signal to interference plus noise ratio SINR and channel capacity Bits/s/Hz. The bit error rate BER is also evaluated by maximal ratio combining MRC diversity technique for accurate transmission over multipath fading dispersive channels. The simulation results conclusively validate the superior performance of the network model in interference mitigation, precisely in high density FAP scenarios.

An Automated Dynamic Offset for Network Selection in Heterogeneous Networks

Complementing traditional cellular networks with the option of integrated small cells and WiFi access points can be used to further boost the overall traffic capacity and service level. Small cells along with WiFi access points are projected to carry over 60 percent of all theglobal data traffic by 2015. With the integration of small cells on the radio access network levels, there is a focus on providing operators with more control over small cell selection while reducing the feedback burden. Altogether, these issues motivate the need for innovative distributed and autonomous association policies that operate on each user under the network operator’s control, utilizing only partial information, yet achieving near-optimal solutions for the network. In this paper, we propose a load-aware network selection approach applied to automated dynamic offset in heterogeneous networks (HetNets). In particular, we investigate the properties of a hierarchical (Stackelberg) Bayesian game framework, in which the macro cell dynamically chooses the offset about the state of the channel in order to guide users to perform intelligent network selection decisions between macro cell and small cell networks. We derive analytically the utility related to the channel quality perceived by users to obtain the equilibria, and compare it to the fully centralized (optimal), the full channel state information and the non-cooperative (autonomous) models. Building upon these results, we effectively address the problem of how to intelligently configure a dynamic offset which optimizes network’s global utility while users maximize their individual utilities. One of the technical contributions of the paper lies in obtaining explicit characterizations of the dynamic offset at the equilibrium and the related performances in terms of the price of anarchy. Interestingly, it turns out that the complexity of the algorithm for finding the dynamic offset of the Stackelberg model is $\mathcal {O}(n^4)$ (where $n$ is the number of users). It is shown that the proposed hierarchical mechanism keeps the price of anarchy almost equal to $1$ even for a low number of users, and remains bounded above by the non-cooperative model.

An Isotropic SPPP Model for Femtocells Networks with Outage Probability Constraints

Femtocells have been considered as a cost-effective solution to unload traffic from already overburdened macrocell networks in 4G cellular networks. The severe interference in spectrum-sharing macro and femto networks may cause User-equipment (UE) to experience outage. We derive an utmost isotropic Spatial Poisson point process (SPPP) density for Femtocell access points (FAPs) under the UEs’ outage constraints. Based on the derived isotropic SPPP density, we propose a distributed transmit probability self-regulation scheme for an FAP to adapt its transmit probability per Transmission time interval (TTI). The scheme adjusts the homogeneous distributed FAPs in practice deployment to the proposed isotropic one. Simulation results show that the derived density can fulfill the outage probability constraints of UEs while accommodating the maximum femtocells. The self-regulation scheme can adapt the femtocell transmit probabilities to provide reliable downlink service, for even a large number of femtocells per cell site.

Exploiting Device-to-Device Communications to Enhance Spatial Reuse for Popular Content Downloading in Directional mmWave Small Cells

With the explosive growth of mobile demand, small cells in millimeter wave (mmWave) bands underlying the macrocell networks have attracted intense interest from both academia and industry. MmWave communications in the 60 GHz band are able to utilize the huge unlicensed bandwidth to provide multiple Gbps transmission rates. In this case, device-to-device (D2D) communications in mmWave bands should be fully exploited due to no interference with the macrocell networks and higher achievable transmission rates. In addition, due to less interference by directional transmission, multiple links including D2D links can be scheduled for concurrent transmissions (spatial reuse). With the popularity of content-based mobile applications, popular content downloading in the small cells needs to be optimized to improve network performance and enhance user experience. In this paper, we develop an efficient scheduling scheme for popular content downloading in mmWave small cells, termed PCDS (popular content downloading scheduling), where both D2D communications in close proximity and concurrent transmissions are exploited to improve transmission efficiency. In PCDS, a transmission path selection algorithm is designed to establish multi-hop transmission paths for users, aiming at better utilization of D2D communications and concurrent transmissions. After transmission path selection, a concurrent transmission scheduling algorithm is designed to maximize the spatial reuse gain. Through extensive simulations under various traffic patterns, we demonstrate PCDS achieves near-optimal performance in terms of delay and throughput, and also superior performance compared with other existing protocols, especially under heavy load.

Ameliorated Resource Allocation in Two-Tier Femtocell–Macrocell Networks with Six Directional Antennas for Macrocells

Femtocells are deployed in the coverage area of traditional macrocell networks and can provide high data rates and good quality of service with low transmission power. In order to achieve the high spectral efficiency, allocated resources to the femtocells should be from the same licensed spectrum band of the macrocell network. Therefore, interference management is an important challenge in two-tier femtocell---macrocell networks. Previously, it was shown that cross-tier interference from macrocell to femtocell can be reduced by using directional antennas in macrocell tier. In this paper, we propose a new spectrum partitioning approach by dividing the spectrum to four sub-bands and then allocating them to different sectors of the macrocell with six directional antennas in a proper manner to reduce interferences. Therefore, first, we calculate the interference from the adjacent macrocells in different sectors. Then, based on the results of interference analysis, we propose a sub-band exchanging allocation strategy for improving the macrocells' and femtocells' performance. Moreover, we analyze the downlink outage probability of the two-tier femtocell---macrocell network based on the orthogonal-frequency-division-multiple-access. Finally, simulation and theoretical results demonstrate that the proposed cellular network achieves lower downlink outage probability of femtocell and macrocell in comparison with the previous cellular model and consequently, system throughput increases substantially.

Qualitative analysis for coverage probability and energy efficiency in cognitive‐femtocell networks under macrocell infrastructure

The network coverage and energy efficiency issues in heterogeneous cognitive-femtocell networks over the macrocell network is studied. Cognitive functions in wireless network nodes are serviceable with the macrocell infrastructure to achieve a balance between two desirable but incompatible features: coverage and energy efficiency. There are two basic but related aspects of cognitive radios (CRs) in the context of wireless communications: optimum CRs for energy efficiency and the act of the functioning of CRs with energy efficiency. To fully utilise the cognitive capability, a dual-tier network architecture is assumed where both the macrocell and the femtocell have a bearing on the cognitive capability. Owing to the salient features of femtocells, they can improve the coverage and enhance the spectrum efficiency by reutilising the frequency spectrum allocated to the macrocell, although, the resulting intercell interference accompanied by the same frequency coverage cannot be underestimated. The effectiveness of the scheme is verified by extensive Matlab simulation.

On the Spectral Efficiency of Multiuser Scheduling in RF-Powered Uplink Cellular Networks

This paper characterizes the spectral efficiency of an uplink radio frequency (RF)-powered macrocell network considering harvest-then-transmit protocol such that the macrocell users transmit in the uplink while replenishing the energy from their serving base station (BS) in the downlink. Using the theory of order statistics, a tractable mathematical framework is developed to derive the uplink spectral efficiency and the downlink power consumption resulting due to wireless energy transfer. The framework captures the impact of the locations of the users that are selected for uplink transmission, their channel statistics for information and energy transfer, and different user selection schemes. We first analyze the performance of state-of-the-art greedy and round-robin scheduling schemes in RF-powered cellular networks. Closed-form expressions for the minimum power outage probability (i.e., the probability that the selected user is unable to harvest sufficient power for uplink transmission) are also derived. We then develop modified versions of the conventional user selection schemes that improve the spectral efficiency on a given uplink transmission channel with zero power outage probability (i.e., probability of outage due to insufficient amount of harvested power). The developed schemes are shown to outperform the conventional user scheduling schemes in terms of the throughput and energy harvesting time with a trade-off in fairness among users. The accuracy of the expressions is validated via Monte-Carlo simulations. Numerical results highlight the trade-offs associated with the various user selection schemes as a function of network parameters.

Handling interference in self-organizing femtocell networks through frequency-polarization diversity

The next generation heterogeneous networks are expected to offer higher data-rate and better QoS to the customers by leveraging smaller cells like femtocells and making use of orthogonal frequency division multiple access. However, uncoordinated dense deployment of femtocells in macrocell network pose unique challenges involving cross-tier interference and resource management which results in significant degradation of the system performance. As part of addressing these challenges for the successful integration of both technologies, this paper proposes the deployment of a self-organizing femtocell network that employs an opportunistic smart frequency reuse technique ---cross polarized complementary frequency allocation (CPCFA). It exploits the frequency and polarization diversity to mitigate interference in two-tier femto-macro networks. In this work, a strategy combining the adoption of reverse frequency allocation and orthogonal polarized transmission is analyzed as a potential solution for maximizing spectral efficiency and minimizing interference in the existing heterogeneous networks. Focus of the current work is on downlink transmission where the traffic is high and the deployment of femtocell is more beneficial. The results of analytic and simulation studies prove that CPCFA increases the scope for an easily implementable, remarkable opportunity in the context of two-tier femto-macro network that can substantially increase the system capacity as well as cell coverage without additional network complexities.

Resource allocation in integrated femto–macrocell networks based on location awareness

This study presents an efficient fractional frequency reuse scheme for macrocell network which uses six directional antennas to cover the outer region and analyses the performance. Cross-tier interference between macrocell and femtocell networks leading to throughput and outage probability degradation is a major issue in two-tier networks when femtocells are deployed in co-channel with macrocells. In this study, the received interference from the macrocell network to femtocell network is analysed. Then, based on the degree of received interference, an algorithm for orthogonal resource allocation to femtocells with low cross-tier interference is presented. According to the introduced scheme, macrocell uses all resource blocks along with a portion of the spectrum allocated to femtocell while both networks operate simultaneously. Closed-form expressions for downlink throughput and outage probability of femtocells are also attained as well as the throughput of macrocell network. The results demonstrate that the proposed hierarchical cellular network achieves higher throughput and lower outage probability for femtocell when compared to other hierarchical macro–femto cellular networks.

Performance Analysis of Preemption-Based Call Admission Scheme for Macrocell Users in Multi-Operator LTE Picocellular–Macrocellular Networks

A heterogeneous network (HetNet) is one of the core features that have been introduced in the LTE-advanced standardization to meet the predicted requirements for higher data rates and capacity. An integrated picocellular–macrocellular networks is part of such HetNets. Most previous works have concentrated on solving the picocellular–macrocellular networks challenges, including optimal picocell deployment, interference coordination, cell association methods and frequency resource allocations. However, the resource allocation control issue for LTE macrocells integrated with underlying picocells owned by different operators that can allow macrocell user (MU) accommodation has not been investigated deeply. Therefore, this paper proposes and analyzes a new resource allocation control framework called a preemption-based call admission control scheme (PCAC) for integrating independent underlying picocells with macrocell networks. The proposed scheme aims to utilize the resource blocks (RBs) of picocells efficiently to improve MU performance by allowing its MU visitors to utilize unused picocell RBs without any degradation for picocell users. A developed simulation model and a multi-dimensional continuous-time Markov chain (CTMC) model are used to model and analyze the proposed PCAC. The analytical model developed considers a limited-size buffer to store MUs, buffer time out and resource reservation. The MU connection-level performance metrics, including dropping and blocking probabilities, are derived and studied. The results indicate that better connection-level parameters for MUs and higher throughputs are achieved by using the proposed PCAC.

Exploiting Device-to-Device Communications in Joint Scheduling of Access and Backhaul for mmWave Small Cells

With the explosive growth of mobile data demand, there has been an increasing interest in deploying small cells of higher frequency bands underlying the conventional homogeneous macrocell network, which is usually referred to as heterogeneous cellular networks, to significantly boost the overall network capacity. With vast amounts of spectrum available in the millimeter wave (mmWave) band, small cells at mmWave frequencies are able to provide multi-gigabit access data rates, while the wireless backhaul in the mmWave band is emerging as a cost-effective solution to provide high backhaul capacity to connect access points (APs) of the small cells. In order to operate the mobile network optimally, it is necessary to jointly design the radio access and backhaul networks. Meanwhile, direct transmissions between devices should also be considered to improve system performance and enhance the user experience. In this paper, we propose a joint transmission scheduling scheme for the radio access and backhaul of small cells in the mmWave band, termed D2DMAC, where a path selection criterion is designed to enable device-to-device transmissions for performance improvement. In D2DMAC, a concurrent transmission scheduling algorithm is proposed to fully exploit spatial reuse in mmWave networks. Through extensive simulations under various traffic patterns and user deployments, we demonstrate D2DMAC achieves near-optimal performance in some cases, and outperforms other protocols significantly in terms of delay and throughput. Furthermore, we also analyze the impact of path selection on the performance improvement of D2DMAC under different selected parameters.

Joint Dimensioning of Outdoor Heterogeneous Radio Access Networks (HetNet) using Monte Carlo Simulation

Abstract The experienced mobile traffic increase in the recent years made traffic capacity the bottleneck instead of the coverage constraints, calling for significantly higher density of the base stations. Heterogeneous radio access networks (HetNet) provide a possible solution to this problem, combining various wireless technologies. In this paper we investigated the joint dimensioning of the co-existent radio access networks, the relation between the required macro and small cell densities to meet a certain traffic demand, and compared the two main, competing technological solutions, namely small cells and Wi-Fi, suitable to complement an LTE (macrocell) network.

Pendekatan Teori Permainan Potensial untuk Manajemen Interferensi pada Jaringan Makro-Femto

In the present paper, a dynamic resource allocation scheme in orthogonal frequency-division multiple access (OFDMA) femtocells is proposed. In the proposed scheme, each femto base station dynamically selects the most appropriate subset of resource blocks (RBs) in a decentralized manner in order to mitigate the downlink cross- and co-tier interference. A game theoretic approach is used to model the interactions among autonomous entities, where each player attempts to maximize its own utility by choosing the best subset of RBs among the available RBs. The proposed utility function captures the cooperative behavior to manage the cross- and co-tier interference, which can be formulated as a potential game and demonstrated to converge to a Nash equilibrium. The simulation results show that the proposed scheme guarantees the convergence to Nash equilibrium and facilitates the femtocells to improve the throughput where the average 50% of user throughput above 7.3 Mbps, while minimizing the cross-tier interference to the macrocell network.

Impact of a small cell on the RF-EMF exposure in a train.

The deployment of a miniature mobile-phone base station or small cell in a train car significantly improves the coverage and the capacity of a mobile network service on the train. However, the impact of the small cell on the passengers’ exposure to radio-frequency electromagnetic fields (RF-EMF) is unknown. In this study, we assessed experimentally the RF-EMF exposure of a mobile-phone user who is either connected to the outdoor macrocell network or to an in-train small cell, while traveling on the train, by means of the absorbed-dose concept, which combines the base station downlink exposure with the mobile-phone uplink exposure. For Global System for Mobile Communications (GSM) technology at 1800 MHz, we found that by connecting to a small cell, the brain exposure of the user could realistically be reduced by a factor 35 and the whole-body exposure by a factor 11.

English

Nowadays LTE (Long Term Evaluation) network becomes more popular and main issue regarding LTE network is indoor coverage. In LTE spectrum is limited so to increase spectral efficiency most of the operator deploy single frequency network but this also increase level of interference. Femtocell deployment inside Macrocell network can reduce indoor coverage issue but unplanned placing of Femtocells as per user requirements may create interference between Femtocells which is called as “Co-tier interference” which may have an impact on the overall performance of Femtocells. Avoiding such interference is very important for Femtocells to work properly. Hence this research survey seeks to analyze various techniques used for Co-tier interference reduction in LTE Femtocell networks are discussed in this review paper.

Wireless Sensor Network Aided Cognitive Femtocell Networks

Abstract The radio spectrum is underutilized and salient application of cognitive radio (CR) is to capitalize the spectrum resources more effectively by opportunistically utilizing radio spectrum not utilized by primary networks, referred to as spectrum holes. When facilited by a sensor network, the cognitive femtocell will be able to use frequencies other than the macrocell network and also, enhance its power to cover macrocell edge areas. The foremost objectives of the wireless sensor network routing protocol design are stabilized network energy consumption and extending the entire network lifespan. In this paper, we analyze the effectiveness of Low Energy Adaptive Clustering Hierarchy (LEACH) protocol in cluster-head selection. It takes node's residual energy and position information into account, the selection method of the threshold for electing cluster-head is optimized, normal nodes select the optimal cluster-head based on the cost function which improves optimal cluster-head selection strategy. Finally, the effectiveness of the scheme is verified by extensive matlab simulation.

Uplink spectrum resource allocation in heterogeneous networks (small cell/macrocell)

Small cells are expected to increase network capacity, extend the macrocell coverage and to add edge-based intelligence. These advantages are achieved by overlaying macrocell networks with the small cells, resulting in a two-tier network. However, the average capacity of the network is reduced due to interference generated by the two-tier configuration. Conventional small cells are configured to have either an open or closed access scheme. Small cells with a hybrid access scheme or partially open access scheme are known for their flexibility and improved performance achieved through their interference-mitigating ability and adaptive resource allocation capabilities. In a hybrid access scheme, resource allocation is a vital issue in the design of small cells networks. In this paper, we propose an uplink resource allocation technique to enhance hybrid small cell capacity in orthogonal frequency division multiple access (OFDMA) two-tier cellular networks. In particular, we investigate a new possibility available for developing an optimal scheme for OFDMA hybrid access small cells. We formalize the problem as an optimization problem for an uplink resource allocation that partitions the bandwidth for both subscribed or unsubscribed users. Moreover, we propose a convex optimization model for the gradient of the capacity difference between closed access and hybrid access capacity. We present two schemes, firstly an optimal scheme and secondly a scheme that is the simple version of the optimal scheme. Numerical results show the effectiveness of the proposed bandwidth resource allocation, where the simple solution shows inferior performance than the optimal solution with a small margin while the optimal solution has a more mathematical complexity disadvantage due to the mathematical functions it employs. Numerical results also show the convergence and effectiveness of the proposed uplink bandwidth resource allocation scheme.