Mohammud Z. Bocus

An Approximation of the First Order Marcum Q-Function with Application to Network Connectivity Analysis

An exponential-type approximation of the first order Marcum Q-function is presented, which is robust to changes in its first argument and can easily be integrated with respect to the second argument. Such characteristics are particularly useful in network connectivity analysis. The proposed approximation is exact in the limit of small first argument of the Marcum Q-function, in which case the optimal parameters can be obtained analytically. For larger values of the first argument, an optimization problem is solved, and the parameters can be accurately represented using regression analysis. Numerical results indicate that the proposed methods result in approximations very close to the actual Marcum Q-function for small and moderate values of the first argument. We demonstrate the accuracy of the approximation by using it to analyze the connectivity properties of random ad hoc networks operating in a Rician fading environment.

Iterative successive interference cancellation for quasi-synchronous block spread CDMA based on the orders of the times of arrival

Recently, a block spreading code division multiple access (BS-CDMA) technique was presented, whereby user-specific precoding along with orthogonal spreading codes is used to achieve multiuser interference- (MUI-) free reception when all users arrive at the base station simultaneously. In practice, however, imperfect synchronization destroys the orthogonality among users, and MUI occurs. To mitigate the MUI in BS-CDMA due to quasisynchronous reception, this paper proposes an iterative successive interference cancellation (SIC) receiver, where cancellation of interfering signals is ordered according to the times of arrival (TOA) of the signals from different users. The ordering criterion is justified through analysis and simulation on the average signal-to-interference-plus-noise ratio (SINR) of different users, where it is shown that in a quasisynchronous BS-CDMA system, ordering with regard to increasing TOA is equivalent to ordering with respect to decreasing average SINR, when practical channels such as the exponentially decaying channel is considered. The proposed SIC receiver is shown to achieve a performance close to a system with synchronous reception for only two iterations. In addition, an algorithm to determine the detection order of different blocks is proposed such that parallel detection of the signals from different users with reduced latency can be achieved.

Per-Subcarrier Antenna Selection for H.264 MGS/CGS Video Transmission Over Cognitive Radio Networks

In this paper, the problem of efficiently allocating wireless resources to support multiple scalable video sequences over a downlink cognitive radio network is addressed. We consider the coarse grain scalable (CGS) and medium grain scalable (MGS) extension of the H.264 standard as the encoding method and propose to perform a per-subcarrier transmit antenna selection such that spatial diversity is exploited. We formulate the problem of optimally allocating subcarriers and antennas among secondary users as a binary integer program, where optimality is defined in terms of the aggregate visual quality of received video sequences of all cognitive users. The proposed formulation caters to the staircase rate-distortion characteristics of CGS/MGS sequences and avoids allocating more resources than are necessary to attain a given visual quality. However, due to the high computational complexity involved in solving this hard integer program using discrete programming solvers, we reduce the resource allocation problem to a subset-sum problem. Although it remains -hard in general, we present two efficient methods to solve this subset-sum problem based on its structure. Simulation results demonstrate that the methods proposed lead to a solution that is close to the optimal. Moreover, we demonstrate that having multiple antennas at the cognitive base station reduces the outage probability of secondary users.

Resource allocation for OFDMA-based cognitive radio networks with application to H.264 scalable video transmission

Resource allocation schemes for orthogonal frequency division multiple access- (OFDMA-) based cognitive radio (CR) networks that impose minimum and maximum rate constraints are considered. To demonstrate the practical application of such systems, we consider the transmission of scalable video sequences. An integer programming (IP) formulation of the problem is presented, which provides the optimal solution when solved using common discrete programming methods. Due to the computational complexity involved in such an approach and its unsuitability for dynamic cognitive radio environments, we propose to use the method of lift-and-project to obtain a stronger formulation for the resource allocation problem such that the integrality gap between the integer program and its linear relaxation is reduced. A simple branching operation is then performed that eliminates any noninteger values at the output of the linear program solvers. Simulation results demonstrate that this simple technique results in solutions very close to the optimum.

Location, location, location: Border effects in interference limited ad hoc networks

Wireless networks are fundamentally limited by the intensity of the received signals and by their inherent interference. It is shown here that in finite ad hoc networks where node placement is modelled according to a Poisson point process and no carrier sensing is employed for medium access, the SINR received by nodes located at the border of the network deployment/operation region is on average greater than the rest. This is primarily due to the uneven interference landscape of such networks which is particularly kind to border nodes giving rise to all sorts of performance inhomogeneities and access unfairness. Using tools from stochastic geometry we quantify these spatial variations and provide closed form communication-theoretic results showing why the receivers location is so important.

Cognitive antenna selection relay for green heterogeneous healthcare networks

This article presents the latest progress on green healthcare research in heterogeneous networks (HetNet), where devices are capable of switching between multiple radio access technologies (RAT) and each RAT operates on a different frequency channel. After outlining the design features and challenges of a medical service paradigm for green cognitive medical body area networks (MBAN), measurements are made to investigate the turn-on characteristics of a power amplifier (PA) in terms of excess energy consumption and turn-on delay. We then present a multi-mode PA architecture for an MBAN relay system. An energy-efficient PA switch/stay mechanism is also presented. This allows the proposed PA architecture to operate given a transmission outage probability and transmission delay constraint. Antenna selection between two heterogeneous RATs is exploited to improve the transmission reliability. Both measurement and numerical results are provided to corroborate the performance of the proposed architecture and its switch/stay mechanism.

Network Connectivity in Non-Convex Domains With Reflections

Recent research has demonstrated the importance of boundary effects on the overall connection probability of wireless networks but has largely focused on convex deployment regions. We consider here a scenario of practical importance to wireless communications, in which one or more nodes are located outside the convex space where the remaining nodes reside. We call these “external nodes” and assume that they play some essential role in the macro network functionality e.g. a gateway to a dense self-contained mesh network cloud. Conventional approaches with the underlying assumption of only line-of-sight (LOS) or direct connections between nodes fail to provide the correct analysis for such a network setup. To this end we present a novel analytical framework that accommodates for the non-convexity of the domain and explicitly considers the effects of non-LOS nodes through reflections from the domain boundaries. We obtain analytical expressions in 2D and 3D which are confirmed numerically for Rician channel fading statistics and discuss possible extensions and applications.

Joint Call Admission Control and Resource Allocation for H.264 SVC Transmission Over OFDMA Networks

This paper aims to combine adaptive subcarrier allocation and bit loading with the transmission of the H.264 SVC (Scalable Video Coding) encoded video sequences in order to increase the number of supported users in the system and provide the best quality of service (QoS) to the subscribers. We initially assume that the number of calls at the base station can be supported, and present an integer program (IP) formulation of the problem that considers the frequency selective nature of the channel, bit error rate requirement and the discrete rate requirements of the different layers of the medium grain scalable (MGS) video. It is shown how the IP can be extended to perform call admission control (CAC). Due to the complexity involved with IP, a sub-optimal scheme is then presented. Results demonstrate that our proposed scheme performs better than systems with a fixed resource allocation strategy by supporting more users and by always achieving acceptable QoS. Furthermore, the low complexity of the proposed CAC schemes makes it suitable for practical application.

Linear Equalizers for Quasi-Synchronous Block Spreading CDMA Systems

Recently, a block spreading code division multiple access (BS-CDMA) technique was presented whereby user-specific precoding along with orthogonal spreading codes are used to achieve multi-user interference (MUI) free when all users arrive at the base station simultaneously. In practice however, imperfect synchronization destroys the orthogonality among users and MUI occurs. This paper investigates the design of linear frequency domain equalizers to reduce the MUI in a quasi-synchronous BS-CDMA system. An optimal frequency domain linear minimum-mean squared error (LMMSE) equalizer is derived. Further simplification leads to a novel sub-optimal equalizer with reduced computational complexity. It is shown through simulation that the proposed equalizers effectively suppress the error floor due to quasi-synchronous reception when channel coding is applied.

Outage performance analysis of relay selection in SWIPT systems

In this paper, we investigate the performance of relay selection for simultaneous wireless information and power transfer (SWIPT) systems. In particular, we consider a relay network consisting of both energy harvesting (EH) and non-EH relays. We further assume amplify-and-forward relaying and power-splitting at the EH units. We study the scenarios for both the battery-less and battery-equipped relays. The diversity and coding gains for the battery-less scenario are derived through the outage probability analysis. Our analysis indicates that the relay selection schemes achieve full diversity gain for SWIPT. We corroborate our analysis through simulations and compare the performance of the battery-less and battery-equipped relay scenarios. Moreover, we investigate the effects of the powersplitting on the system performance through simulations.