Kamran Arshad

Interference Management in Femtocells

Increase in system capacity and data rates can be achieved efficiently in a wireless system by getting the transmitter and receiver closer to each other. Femtocells deployed in the macrocell significantly improve the indoor coverage and provide better user experience. The femtocell base station called as Femtocell Access Point (FAP) is fully user deployed and hence reduces the infrastructure, maintenance and operational cost of the operator while at the same time providing good Quality of Service (QoS) to the end user and high network capacity gains. However, the mass deployment of femtocell faces a number of challenges, among which interference management is of much importance, as the fundamental limits of capacity and achievable data rates mainly depends on the interference faced by the femtocell network. To cope with the technical challenges including interference management faced by the femtocells, researchers have suggested a variety of solutions. These solutions vary depending on the physical layer technology and the specific scenarios considered. Furthermore, the cognitive capabilities, as a functionality of femtocell have also been discussed in this survey. This article summarises the main concepts of femtocells that are covered in literature and the major challenges faced in its large scale deployment. The main challenge of interference management is discussed in detail with its types in femtocells and the solutions proposed over the years to manage interference have been summarised. In addition an overview of the current femtocell standardisation and the future research direction of femtocells have also been provided.

Collaborative Spectrum Sensing Optimisation Algorithms for Cognitive Radio Networks

The main challenge for a cognitive radio is to detect the existence of primary users reliably in order to minimise the interference to licensed communications. Hence, spectrum sensing is a most important requirement of a cognitive radio. However, due to the channel uncertainties, local observations are not reliable and collaboration among users is required. Selection of fusion rule at a common receiver has a direct impact on the overall spectrum sensing performance. In this paper, optimisation of collaborative spectrum sensing in terms of optimum decision fusion is studied for hard and soft decision combining. It is concluded that for optimum fusion, the fusion centre must incorporate signal-to-noise ratio values of cognitive users and the channel conditions. A genetic algorithm-based weighted optimisation strategy is presented for the case of soft decision combining. Numerical results show that the proposed optimised collaborative spectrum sensing schemes give better spectrum sensing performance.

Order-Statistic Based Spectrum Sensing for Cognitive Radio

Spectrum sensing for cognitive radio is challenging. In this letter, a spectrum sensing method based on quintiles of Order-Statistics is proposed. We derive the test statistic and evaluate the performance of the proposed method by Monte Carlo simulations. Simulation results show that order statistics based sensing considerably outperforms both energy detection and anderson darling based sensing in an Additive White Gaussian Noise (AWGN) channel; especially in a lower signal to noise ratio region.

A Survey of the Challenges, Opportunities and Use of Multiple Antennas in Current and Future 5G Small Cell Base Stations

Small cell base stations (SBSs) and multiple antennas are seen as fundamental technologies in the emergence of the next generation [i.e., 5th generation (5G)] of cellular wireless technology. This paper provides a comprehensive survey of literature relating to the applications and challenges associated with using multiple antennas in SBSs. The use of multiple antenna techniques in conventional wireless base stations has undergone much study and is widespread. With heterogeneity in current networks and a furthering of this theme together with greater densification expected in 5G systems, their use in SBSs is at an evolutionary stage. In this paper, unique design challenges associated with size, cost, and performance in SBSs are presented. We present a clear understanding of this increasingly important research area, identifying a clear classification of use and design guidelines. We present a state-of-the-art review of the literature to show how researchers are using and considering the use of multiple antennas in small cells. Attention is given to current generation networks, and with SBSs being a dominant technology necessary for 5G, we also provide insights into the design challenges in such possible future networks.

Collaborative Spectrum Sensing for Cognitive Radio

Today’s wireless communication systems follow fixed spectrum assignment policies which leads to overall inefficient spectrum use. Further, spectrum scarcity is an issue for operators with emerging mobile services and large number of users with even higher capacity requirements. This inefficiency and scarcity in spectrum usage necessitates a new paradigm for communications such as utilising available spectrum opportunistically. Cognitive Radio (CR) is an enabling technology having potential to increase spectrum utilisation and provide desired interference protection to licenced users. This can be done by detection of spectrum opportunities by secondary users. Due to channel fading and shadowing a single user can not make a reliable decision and collaboration of and among users is required. In this paper, it has been demonstrated that for improved detection performance decision fusion algorithm for collaborative spectrum sensing must have information about channel and the mean SNR of all secondary users. Using Monte Carlo simulations it is concluded that for optimum performance it is not necessary that all users collaborate with each other.

A downlink power control scheme for interference avoidance in femtocells

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

Dynamic Spectrum Allocation Algorithm with Interference Management in Co-Existing Networks

This work addresses analytically the impact of multi-cell, multi-operator interference on the overall radio resources when multiple operators co-exist and share a common pool of spectrum. We propose a centralised dynamic spectrum allocation (DSA) scheme that is able to measure the interference level and interact dynamically to minimise interference and enhance spectrum utilisation while maintaining a satisfactory level of QoS. Furthermore, a concise system model and framework able to describe the interaction among different operators is presented.

Resource management for QoS support in cognitive radio networks

Cognitive radio technology is a key enabler to reuse a finite, scarce, and expensive resource: the radio spectrum. Guaranteeing required levels of QoS to cognitive users and ensuring necessary protection to incumbent users are the two main challenges in opportunistic spectrum access. This article identifies the main requirements and challenges for QoS support in cognitive radio networks. A framework for a twofold cognitive manager is presented; one part managing spectrum availability on longer timescales and the other handling resource management on shorter timescales. This article gives particular focus to the functionalities of the latter cognitive manager related to resource management. Finally, we present a few key scenarios and describe how QoS can be managed with the proposed approach without disturbing the communications of incumbent users.

LTE-Advanced Radio Access Enhancements: A Survey

Long Term Evolution Advanced (LTE-Advanced) is the next step in LTE evolution and allows operators to improve network performance and service capabilities through smooth deployment of new techniques and technologies. LTE-Advanced uses some new features on top of the existing LTE standards to provide better user experience and higher throughputs. Some of the most significant features introduced in LTE-Advanced are carrier aggregation, enhancements in heterogeneous networks, coordinated multipoint transmission and reception, enhanced multiple input multiple output usage and deployment of relay nodes in the radio network. Mentioned features are mainly aimed to enhance the radio access part of the cellular networks. This survey article presents an overview of the key radio access features and functionalities of the LTE-Advanced radio access network, supported by the simulation results. We also provide a detailed review of the literature together with a very rich list of the references for each of the features. An LTE-Advanced roadmap and the latest updates and trends in LTE markets are also presented.

Mobility driven energy detection based spectrum sensing framework of a cognitive radio

A cognitive radio opportunistically accesses spectrum bands under the constrain that it does not interfere with the licensed users. Cognitive radio performs spectrum sensing to find spectrum opportunities. Although a large number of spectrum sensing algorithms are available in literature; majority of them addressed static cognitive radios. In this paper, we study the energy detection based local spectrum sensing in the presence of user mobility. We show that CR mobility improves spectrum sensing performance by exploiting spatial diversity. We propose a framework for local spectrum sensing in which a cognitive radio do multiple spectrum measurements and makes a decision about the existence of the licensed user. An optimal fusion rule based on likelihood ratios is derived and based on test statistics a suitable detector and functional architecture of a cognitive radio is proposed. A closed form expression for the number of spectrum measurement cycles is also derived in this paper under given performance constraints.