Low-power Base Stations Research Articles

A Velocity and Transmission Environment Based Handover Algorithm for Heterogeneous Networks

Heterogeneous networks have attracted a lot of attention for supporting high data rate and high mobility wireless communications. Since the base station density in heterogeneous networks is much larger than that in homogeneous networks, and the deployment of low power base stations in heterogeneous networks may be unplanned, a mobile user may see a large number of base stations simultaneously. Thus handover management in heterogeneous networks is much more challenging than that in homogeneous networks. In this paper, we address these challenges and propose a heuristic handover algorithm for use in heterogeneous networks. The proposed algorithm uses estimates of user velocity (speed and direction) and the transmission environment to improve the handover performance, i.e., the handover rate and the handover failure rate. Simulation results show that the proposed algorithm performs better than the conventional scheme in typical scenarios of heterogeneous networks.

SCHEDULING FOR INTERFERENCE MITIGATION USING ENHANCED INTERCELL INTERFERENCE COORDINATION

Deployment of low power base station (pico) in macro cell is a key for providing high data rates. Cell range expansion is one of the features of LTE-advanced where low power base station in a heterogeneous network can increase their coverage area and neighboring cells can offload users to low power base station to reduce overload in macro cell. This presents a very challenging multi-user communication problem. Co-channel deployed Het-Net will experience interference between pico and macro. The main challenge of pico cells embedded into a macro cell is to let more users profit from the additional bandwidth introduced into the network. Enhanced Inter-cell Interference Coordination (eICIC) has been introduced to solve interference problem. Scheduling for eICIC is used to provide best solution for interference mitigation, overload in macro cell, fairness in resource usage by users. In this paper we have analyzed Round Robin scheduling for eICIC, results prove that fairness is maintained between users and throughput has been improved.

Analysis of an Adaptive Priority Based Resource Allocation Control for LTE-Advanced Communications with Type I Relay Nodes

Relaying is emerging as one of the key radio access techniques for LTE-Advanced (LTE-A) networks to fulfill the LTE-Advanced coverage and capacity requirements in a cost-efficient way. Relaying enables improved high data rate coverage for indoor environments or at the cell edge by deploying a low power base station. Type I in-band relaying supports a relaying mode where the backhaul link transmission is time-division multiplexed with the access link reception, whereas macro users share the same resources with the relays. Therefore, in LTE-A networks deployed with type I relay nodes, resource partitioning is required to support in-band relaying. Consequently, it is very important to know how to partition system resources to attain improved fairness and efficiency. The main contribution of this paper is to design and analyze a novel admission control with an adaptive resource partitioning (AC-ARP) scheme to facilitate the operation of fixed relay stations in the OFDMA-based relay enhanced LTE-Advanced networks in a more efficient way. Its analytical model using multi-dimensional continuous time Markov chains is derived and explained. In addition, its performance comparisons with conventional admission control with a fixed resource partitioning (AC-FRP) scheme is presented and discussed. We present numerical examples to demonstrate the performance of the proposed AC-ARP scheme, and we show that analytical and simulation results are in complete agreement. The results also indicate the superiority of AC-ARP because it is able to achieve a better balance between system utilization and QoS provisioning compared to the AC-FRP scheme.

Interference Alignment for Cooperative Femtocell Networks: A Game-Theoretic Approach

The use of small cells serviced by low-power base stations such as femtocells is envisioned to improve the spectrum efficiency and the coverage of next-generation mobile wireless networks. However, one of the major challenges in femtocell deployments is managing interference. In this paper, we propose a novel cooperative solution that enables femtocells to improve their achievable data rates, by suppressing intratier interference using the concept of interference alignment (IA). We model this cooperative behavior among the femtocells as a coalitional game in partition form and we propose a distributed algorithm for the coalition formation. The proposed algorithm allows the femtocell base stations to independently decide on whether to cooperate or not, while maximizing a utility function capturing both the gains and costs from cooperation. Using the proposed algorithm, the femtocells can self-organize into a stable network partition composed of disjoint femtocell coalitions and which constitutes the recursive core of the game. Inside every coalition, cooperative femtocells use advanced IA techniques to improve their downlink transmission rate. Simulation results show that the proposed coalition formation algorithm yields significant gains, in terms of average payoff per femtocell, reaching up to 30 percent relative to the noncooperative case for a network of N=300 femtocells.

Joint Base Station Association and Power Control via Benders' Decomposition

Heterogeneous cellular network (Hetnets), where various classes of low power base stations (BS) are underlaid in a macro-cellular network, is a promising technique for future green communications. These new types of BSs can achieve substantial improvement in spectrum-efficiency and energy-efficiency via cell splitting. However, mobile stations perceive different channel gains to different base stations. Therefore, it is important to associate a mobile station with the right BS so as to achieve a good communication quality. Oftentimes, the already-challenging BS association problem is further complicated by the need of transmission power control, which is an essential component to manage co-channel interference in many wireless communications systems. Despite its importance, the joint BS association and power control (JBAPC) problem has remained largely unsolved, mainly due to its non-convex and combinatorial nature that makes the global optimal solution difficult to obtain. This paper aims to circumvent this difficulty by proposing a novel algorithm based on Benders' Decomposition to solve the non-convex JBAPC problem efficiently and optimally. In particular, we endeavor to maximize the system revenue and meanwhile associate every served mobile station with the right BS with the minimum total transmission power. We first propose a single-stage formulation that captures the two objectives simultaneously. The problem is then transformed in a way that can be efficiently solved using the proposed joint BS Association and poweR coNtrol algorithm (referred to as BARN) that is derived from classical Benders' Decomposition. Finally, we derive a closed-form analytical formula to characterize the effect of the termination criterion of the algorithm on the gap between the obtained solution and the optimal one. For practical implementation, we further propose an Accelerated BARN (A-BARN) algorithm that can significantly reduce the computational time. By carefully choosing the termination criterion, both BARN and A-BARN are guaranteed to converge to the global optimal solution.

A Survey on Power Control Techniques in Femtocell Networks

Rapid increase in mobile data has raised the stakes on developing innovative new technologies and cellular topologies that can meet these demands in an energy efficient manner. One of the most interesting trends that will emerge from this cellular evolution is the femtocell networks. Femtocells are small, inexpensive, low power base stations that are generally consumer deployed, and are expected to significantly improve the coverage and capacity of the indoor users. Femtocell base stations (FBSs) have extensive auto configuration and self-optimization capability to enable simple plug-and-play deployment. The FBSs perform self-optimization function that continually adjusts the transmit power so the femtocell coverage does not leak into an outdoor area while sufficiently covering the indoor femtocell area. In this paper, different power control techniques in femtocell networks have been discussed and compared. The focus is on distributed power control techniques due to the decentralized nature of femtocell networks. The conclusion drawn from this review is that the distributed power control techniques using pilot power control schemes are simple and effective in optimizing the coverage of femtocells as well as reducing power consumption of the FBS. Furthermore a novel algorithm is still needed to perform power control optimization in femtocell networks. 

ICE: Intelligent Cell BrEathing to Optimize the Utilization of Green Energy

This letter proposes Intelligent Cell brEathing (ICE) to optimize the utilization of green energy in cellular networks by minimizing the maximal energy depleting rate of the low-power base stations powered by green energy. Minimizing the maximal depleting rate is an NP-hard problem. ICE is thus proposed to achieve low computational complexity. ICE, in each iteration, finds the energy dependent set and the vector of beacon power level decrements for low-power base stations in the set, and then shrinks the coverage area of these base stations by reducing their beacon power levels. The algorithm iterates until the optimal solution is found. ICE balances the energy consumptions among LBSs, enables more users to be served with green energy, and therefore reduces the on-grid energy consumption.

HopScotch-a low-power renewable energy base station network for rural broadband access

The provision of adequate broadband access to communities in sparsely populated rural areas has in the past been severely restricted. In this article, we present a wireless broadband access testbed running in the Scottish Highlands and Islands which is based on a relay network of low-power base stations. Base stations are powered by a combination of renewable sources creating a low cost and scalable solution suitable for community ownership. The use of the 5 GHz bands allows the network to offer large data rates and the testing of ultra high frequency "white space" bands provides expansive coverage whilst reducing the number of base stations or required transmission power. We argue that the reliance on renewable power and the intelligent use of frequency bands makes this approach an economic green radio technology which can address the problem of rural broadband access.

Inter-cell downlink co-channel interference management through cognitive sensing in heterogeneous network for LTE-A

Heterogeneous network for long term evolution advanced (LTE-A) creates severe interference. It is an urgent task to overcome the interference in macro cellular with low-power base stations (BSs), such as relay, pico, and femto called subnet nodes. In this paper, the cognitive interference model in interference zone (IZ) of the practical heterogeneous scenario is proposed. Based on investigation of interaction between the macro BS and subnet nodes in this model, the strategy framework of the cognitive critical ratio and power reward factor is set up for interference management aiming to get the maximum net saving power. The study of interference management is transformed into a multiple objective non-linear programming (MONLP) of the maximum saving power for the macro BS and subnet nodes. To facilitate the best compromise solution for both, the MONLP is changed into single objective programming and genetic algorithm (GA) is employed to obtain the global optimum solution. In addition, the practical implementation using the proposed algorithm in heterogeneous network for LTE-A is designed. Finally, numerical evaluation is used to test the applicability of the proposed algorithm, and system level simulation results demonstrate the effectiveness of the proposed interference management scheme.

Reducing Call Routing Cost for Femtocells

Femtocell is an effective solution to improve indoor coverage for cellular networks, where short-range and low-power Base Stations (BSs) called Femto BSs are deployed in small areas (e.g., buildings). We propose the Femto Private Branch Exchange (FPBX) to concentrate the traffic of the Femto BSs in a specific area, such as a campus or an enterprise with central or distributed locations. Through the FPBX, a normal cellular call between two Femto users can be replaced by a low-cost extension call. Therefore, the call routing cost can be significantly reduced. In this approach, the existing mobile network nodes are not modified. We analytically analyze the call routing performance for the FPBX approach, and develop simulation experiments to validate against the analytic model. Our study indicates that the FPBX approach can effectively reduces the call setup costs and the voice trunk costs among Femto users by slightly increasing the normal cellular call setup costs.

Autonomous component carrier selection: interference management in local area environments for LTE-advanced

Low-power base stations such as femtocells are one of the candidates for high-data-rate provisioning in local areas, such as residences, apartment complexes, business offices, and outdoor hotspot scenarios. Unfortunately, the benefits are not without new challenges in terms of interference management and efficient system operation. Due to the expected large number of user-deployed cells, centralized network planning becomes impractical, and new scalable alternatives must be sought. In this article we propose a fully distributed and scalable solution to the interference management problem in local areas, basing our study case on LTEAdvanced. We present extensive network simulation results to demonstrate that a simple and robust interference management scheme, called autonomous component carrier selection, allows each cell to select the most attractive frequency configuration; improving the experience of all users and not just the few best ones, while overall cell capacity is not compromised.

WiMAX femtocell: requirements, challenges, and solutions

Femtocells are low-power base stations operating in licensed spectrum, which are typically installed indoors in a house, small office, or home office by end users to provide exclusive or preferential access to a designated group of users as configured by the femtocell subscriber and/or the access provider. Femtocells have gained a lot of attention recently due to their advantages in terms of infrastructure cost saving and improved user experience in indoor environments. Several standards bodies, such as 3GPP, WiMAX Forum, and IEEE 802.16, have started to develop standard solutions to enable and optimize femtocells operation. However, there are some technical challenges to the success of femtocell technologies that need to be overcome before they can be deployed on large scales. This article presents an overview of WiMAX femtocell requirements, deployment models, and solutions in the near and long terms.

Effect of cell shape on design of CDMA systems for urban microcells

Placing antennas of low power base stations below surrounding buildings, as in urban microcells, makes propagation characteristics strongly dependent on the building environment. As a result, propagation in these urban microcells is nonisotropic, so that the assumption of circular cells used in planning of conventional cellular systems is no longer valid. Assuming circular cells leads to a more conservative system design, implying more base stations. This work investigates the effect of cell shape, due to non-isotropic propagation, on the out-of-cell interference and Erlang capacity of CDMA system. Propagation is described by measurement derived models for low antennas in a rectangular urban street grid. The analysis is done for soft handoff protocols