Ghazanfar Ali Safdar

Interference Mitigation in Cognitive-Radio-Based Femtocells

Femtocell architecture involves the use of two separate layers-the macrocell and femtocell layers. In this architecture, the former is the conventional cellular network, whereas the latter incorporates a range of shorter range cells. Femtocells are designed to coexist alongside macrocells, providing spatial frequency reuse, higher spectrum efficiency, and cover areas where macrocells cannot. Femtocells positioned in the macrocell considerably improve the indoor coverage and provide better user experience. However, interference between the two layers is imminent; therefore, ways to manage it must be employed to efficiently avoid problems such as coverage holes in the macrocells. Essential limits of capacity and attainable data rates also mainly depend on the interference faced by a femtocell network. Recently, cognitive radio (CR), which has the ability to sense its environment and accordingly alter its characteristics, e.g., transmission parameters, has been merged with femtocells to exploit the capabilities of the former in the latter. CR-enabled femtocells in a two-tier network can sense the environment and opportunistically allocate both licensed and unlicensed frequency bands to user equipments to avoid interference. This paper examines interference mitigation in femtocells using CR and provides comprehensive survey of different CR-enabled interference mitigation schemes. Presented schemes such as power control, spectrum access, antenna, and joint schemes are classified before they are compared for pros and cons. Finally, tradeoffs and cost of using CR in femtocells are highlighted with some insight into future research issues and challenges.

Interference Mitigation in D2D Communication Underlaying LTE-A Network

The mobile data traffic has risen exponentially in recent days due to the emergence of data intensive applications, such as online gaming and video sharing. It is driving the telecommunication industry as well as the research community to come up with new paradigms that will support such high data rate requirements within the existing wireless access network, in an efficient and effective manner. To respond to this challenge, device-to-device (D2D) communication in cellular networks is viewed as a promising solution, which is expected to operate, either within the coverage area of the existing eNB and under the same cellular spectrum (in-band) or separate spectrum (out-band). D2D provides the opportunity for users located in close proximity of each other to communicate directly, without traversing data traffic through the eNB. It results in several transmission gains, such as improved throughput, energy gain, hop gain, and reuse gain. However, integration of D2D communication in cellular systems at the same time introduces new technical challenges that need to be addressed. Containment of the interference among D2D nodes and cellular users is one of the major problems. D2D transmission radiates in all directions, generating undesirable interference to primary cellular users and other D2D users sharing the same radio resources resulting in severe performance degradation. Efficient interference mitigation schemes are a principal requirement in order to optimize the system performance. This paper presents a comprehensive review of the existing interference mitigation schemes present in the open literature. Based on the subjective and objective analysis of the work available to date, it is also envisaged that adopting a multi-antenna beamforming mechanism with power control, such that the transmit power is maximized toward the direction of the intended D2D receiver node and limited in all other directions will minimize the interference in the network. This could maximize the sum throughput and hence, guarantees the reliability of both the D2D and cellular connections.

A Survey of QoS-aware Web Service Composition Techniques

process of aggregating services with disparate functionalities into a new composite service in order to meet increasingly complex needs of users. Service composition process has been accurate on dealing with services having disparate functionalities, however, over the years the number of web services in particular that exhibit similar functionalities and varying Quality of Service (QoS) has significantly increased. As such, the problem becomes how to select appropriate web services such that the QoS of the resulting composite service is maximized or, in some cases, minimized. This constitutes an NP-hard problem as it is complicated and difficult to solve. In this paper, a discussion of concepts of web service composition and a holistic review of current service composition techniques proposed in literature is presented. Our review spans several publications in the field that can serve as a road map for future research.

On the Usage of History for Energy Efficient Spectrum Sensing

Spectrum sensing is one of the most challenging issues in cognitive radio networks. It provides protection to primary users (PUs) from interference and also creates opportunities of spectrum access for secondary users (SUs). It should be performed efficiently to reduce number of false alarms and missed detection. At the same time, spectrum sensing should be energy efficient to ensure the longevity of cognitive radio devices. This work presents a novel scheme which investigates the usage of history for energy efficient spectrum sensing in infrastructure cognitive radio networks. The presented scheme employs an iteratively developed history processing database. It is shown that usage of history helps predicting PU activity and results into reduced spectrum scanning by SUs thereby improving the sensing related energy consumption.

Spectrum sharing security and attacks in CRNs: a review

Cognitive Radio plays a major part in communication technology by resolving the shortage of the spectrum through usage of dynamic spectrum access and artificial intelligence characteristics. The element of spectrum sharing in cognitive radio is a fundamental approach in utilising free channels. Cooperatively communicating cognitive radio devices use the common control channel of the cognitive radio medium access control to achieve spectrum sharing. Thus, the common control channel and consequently spectrum sharing security are vital to ensuring security in the subsequent data communication among cognitive radio nodes. In addition to well known security problems in wireless networks, cognitive radio networks introduce new classes of security threats and challenges, such as licensed user emulation attacks in spectrum sensing and misbehaviours in the common control channel transactions, which degrade the overall network operation and performance. This review paper briefly presents the known threats and attacks in wireless networks before it looks into the concept of cognitive radio and its main functionality. The paper then mainly focuses on spectrum sharing security and its related challenges. Since spectrum sharing is enabled through usage of the common control channel, more attention is paid to the security of the common control channel by looking into its security threats as well as protection and detection mechanisms. Finally, the pros and cons as well as the comparisons of different CR-specific security mechanisms are presented with some open research issues and challenges.

Providing security and energy efficiency in wireless ad-hoc sensor networks through Secure Cluster-Head Election (SEC-CH-E)

Data sensed and transferred between sensor nodes should be secure and preserve battery life. Some algorithms, such as LEACH (Low Energy Adaptive Clustering Hierarchy), have been proposed to efficiently organize sensor nodes into clusters, where a cluster-head, is elected to represent that cluster. To save energy, the cluster-head coordinates the cluster and forwards data generated within the cluster. Despite preserving energy, in practice LEACH lacks security features. A Secure Cluster Head Election algorithm (SEC-CH-E) that improves the original LEACH algorithm by adding security features as well as bringing increasing energy savings is proposed. The algorithm takes into account wireless sensor networks constraints such as the limited radio range and power limitations when electing secure cluster-head nodes, which are factors unaccounted for in LEACH. It is shown that these factors have profound energy implications. The superiority of Sec-CH-E performance is assessed by looking at the energy remaining in the network and the fraction of dead nodes.

Reduced Early Handover for Energy Saving in LTE Networks

Long-term evolution (LTE) facilitates users with high data rate at the cost of increased energy consumption. eNodeBs are main energy hungry elements in LTE networks. Since power consumption directly affects the operational expenditure, thus the provision of cost effective services with adequate quality of service (QoS) has become a major challenge. This letter exploits the phenomenon of handover and presents a novel hybrid idea of reduced early handover with bandwidth expansion to achieve improved energy saving in LTE networks. Through system level simulations, the effectiveness of the proposed scheme is demonstrated. It is shown that the proposed energy saving scheme achieves around 35% energy efficiency compared to benchmark and other state of the art while still maintaining acceptable level of radio link failure.

A Novel Learning-Based Spectrum Sensing Technique for Cognitive Radio Networks

Spectrum sensing is one of the most challenging issues in Cognitive Radio (CR) networks. It should be performed efficiently to reduce number of false alarms and missed detections. This paper presents a novel approach, which employs collective intelligence developed via learning agents, for spectrum sensing in CR networks. The approach is used to share the sensed information, then digest it and make intelligent decisions about the presence or absence of primary users (PUs), by exploiting the accumulated history. The usage of history thus results in reduced sensing, subsequently requiring minimum activity in the common control channel (CCC), to help secondary users (SUs) exchange information and switch to the chosen empty space(s). Paper provides implementation of the proposed approach based on maxminfunctions integrated with a probabilistic decision making process. The performance analysis of the proposed approach shows that the usage of accumulated history by CR nodes results in reduced spectrum sensing by fine tuning the scan threshold.

Analysis of time correlated channel model for simulation of packet data networks

Performance of any communication system is ultimately determined by the characteristics of the medium, i.e., the channel utilized. A communication channel may be wired, where there is a constrained physical connection between the transmitter and receiver, or wireless where the physical constraint is missing. Wired channels differ significantly from wireless channels which can change their state in very short time span and are thus unreliable in behaviour. Wireless network protocol simulators that operate at a packet level are computationally intensive and the addition of accurate channel fading models must add as little complexity as possible. The need for channel modelling is emphasized in this paper whereas as limitations of uncorrelated channel models have been highlighted. Paper describes benefits of time correlated channel modelling and provides validation of such a model for simulation of burst errors. Results presented also prove that both Doppler frequency and velocity are inversely proportional to channel invariance for small scale fading models.

Euclidean Geometry Axioms Assisted Target Cell Boundary Approximation for Improved Energy Efficacy in LTE Systems

Long Term Evolution (LTE) facilitates users with high data rate at the cost of increased energy consumption. The base station, also known as eNodeB, is the main energy hungry elements in LTE networks. Since power consumption directly affects the operational expenditure, thus the provision of cost-effective services with adequate quality of service has become a major challenge. This paper investigates reduced early handover (REHO) scheme aimed at increased energy efficiency in LTE systems. REHO, compared to standard LTE A3 event, initiates early handover, thereby resulting into reduced energy consumption. Axioms of Euclidean geometry are employed to estimate the target cell boundary towards calculation of the time difference