Mirza Golam Kibria

Resource Allocation Optimization for Users with Different Levels of Service in Multicarrier Systems

We optimize the throughput of a single cell multiuser orthogonal frequency division multiplexing system with proportional data rate fairness among the users. The concept is to support mobile users with different levels of service. The optimization problem is a mixed integer nonlinear programming problem, which is computationally very expensive. We propose a novel and efficient near-optimal solution adopting a two-phase optimization approach that separates the subcarrier and power allocation. In the first phase, we relax the strict proportional data rate requirements and employ an iterative subcarrier allocation approach that coarsely satisfies desired data rate proportionality constraints. In the second phase, we reallocate the power among the users in an iterative way to further enhance the adherence to the desired proportions by exploiting the normalized proportionality deviation measure. The simulation results show that the proposed solution exhibits very strong adherence to the desired proportional data rate fairness while achieving higher system throughput compared to the other existing solutions.

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.

Throughput Enhancement of Multicarrier Cognitive M2M Networks: Universal-Filtered OFDM Systems

We consider a cognitive radio (CR) network consisting of a primary cellular system and a secondary cognitive machine-to-machine (M2M) system, and study the throughput enhancement problem of the latter system employing universal-filtered orthogonal frequency division multiplexing (UF-OFDM) modulation. The downlink transmission capacity of the cognitive M2M system is thereby maximized, while keeping the interference introduced to the primary users (PUs) below the prespecified threshold, under total transmit power budget of the secondary base station (SBS). The performance of UF-OFDM-based CR system is compared to the performances of OFDM-based and filter bank multicarrier (FBMC)-based CR systems. We also propose a near-optimal resource allocation method separating the sub-band and power allocation. The solution is less complex compared to optimization of the original combinatorial problem. We present numerical results that show that for given interference thresholds of the PUs and maximum transmit power limit of the SBS, the UF-OFDM-based CR system exhibits intermediary performance in terms of achievable capacity compared to OFDM- and FBMC-based CR systems. Interestingly, for a certain degree of robustness of the PUs, the UF-OFDM performs equally well as FBMC. Furthermore, the percentage rate-gain of UF-OFDM-based CR system increases by a large amount when UF-OFDM modulation with lower sidelobes ripple is employed. Numerical results also show that the proposed throughput enhancing method despite having lower computational complexity compared to the optimal solution achieves near-optimal performance.

An Efficient Algorithm for Weighted Sum-Rate Maximization in Multicell OFDMA Downlink

This paper considers coordinated linear precoding for rate optimization in downlink multicell, multiuser orthogonal frequency- division multiple access networks. We focus on two different design criteria. In the first, the weighted sum-rate is maximized under transmit power constraints per base station. In the second, we minimize the total transmit power satisfying the signal-to-interference-plus-noise-ratio constraints of the subcarriers per cell. Both problems are solved using standard conic optimization packages. A less complex, fast, and provably convergent algorithm that maximizes the weighted sum-rate with per-cell transmit power constraints is formulated. We approximate the nonconvex weighted sum- rate maximization (WSRM) problem with a solvable convex form by means of a sequential parametric convex approximation approach. The second- order cone formulations of an objective function and the constraints of the optimization problem are derived through a proper change of variables, first-order linear approximation, and hyperbolic constraints transformation. This algorithm converges to the suboptimal solution while taking fewer it- erations in comparison to other known iterative WSRM algorithms. Numerical results are presented to demonstrate the effectiveness and superiority of the proposed algorithm.

Partitioned Vector Quantization for MU-MIMO Downlink Broadcasting

A practical and efficient vector quantization called partitioned vector quantization (P-VQ) based non-linear precoder for MIMO downlink broadcasting channels has been analyzed in this paper. P- VQ has been found to be an efficient way of reducing the memory requirements and search complexity in conventional VQ systems, especially for large MIMO. Simulation results reveal that P-VQ technique can enhance the overall quantization performance in terms of achieved capacity, bit error rate (BER) at a cost of reasonable additional complexity under certain feedback budgets. Tomlinson-Harashima precoding (THP), a power and complexity efficient precoding technique along with data dependent vector perturbation (VP) has been employed to meet the power constraint requirements of our system. Least-square (LS) channel estimation is performed at the user terminals to acquire their channel state information (CSI).

Feedback Bits Allocation for Interference Minimization in Cognitive Radio Communications

This letter studies the limited feedback cognitive radio system, where the primary users (PUs) are interfered by the secondary transmitter (ST) due to the imperfect beamforming. We propose allocating the feedback bits among multiple PUs to minimize the maximum interference caused by the ST, by exploiting the heterogeneous average channel gains. In addition, we study the problem of minimizing the total feedback bits under a predefined interference threshold at the PUs. The solutions with low complexity are proposed for the studied problems, and the performances of bit allocations are analyzed. Simulation results validate our analysis and demonstrate that the proposed solutions work very well in terms of minimizing the maximum interference caused by the ST and minimizing the total feedback bits under predefined interference threshold at the PUs for limited feedback CR system.

Empirical investigation of IEEE 802.11ad network

The IEEE 802.11ad standard allows wireless devices to operate in the unlicensed spectrum band of 60 GHz. By utilizing the channel with 2.16 GHz width, the devices are able to transmit at multi-Gigabit data rates that potentially satisfy demanding requirements of quality of services. Additionally, the advent of off-the-shelf IEEE 802.11ad device motivates research efforts to exploit this 60 GHz opportunity for applications. Although much has been understood from the previous works, there is still a lack of insight into building IEEE 802.11ad networks, especially the ones with multi-Gigabit links. Address the issue, this work investigates the feasibility of multi-Gigabit IEEE 802.11ad networks, as well as, the factors that influence network performance in a typical office environment. By experimental study with off-the-shelf IEEE 802.11ad hardware, we can identify the conditions that the TCP and UDP throughput of IEEE 802.11ad link reach multi-Gigabit levels. Moreover, we show and discuss the negative effects of both co-channel and adjacent channel interference on the IEEE 802.11ad networks performance.

Outage Analysis of Offloading in Heterogeneous Networks: Composite Fading Channels

Small cells deployment is one of the most significant long-term strategic policies of the mobile network operators. In heterogeneous networks (HetNets), small cells serve as offloading spots in the radio access network to offload macro users (MUs) and their associated traffic from congested macrocells. In this paper, we perform analytical analysis and investigate how the radio channel propagation impairments such as multipath fading, shadowing, and small cell base station density affect MUs’ offloading to small cells network (SCN). In particular, we exploit composite fading channels in our evaluation when an MU is offloaded to SCN with varying small cell base station density in the stochastic geometry HetNets framework. We derive the expressions for service outage probability (equivalently service coverage probability) of the MU in macro cell network and SCN under two different composite fading scenarios, viz., Nakagami-Lognormal channel fading and time-shared (combined) shadowed/unshadowed channel fading. We propose efficient approximations for the probability density functions of the channel fading (power) for the aforementioned composite fading distributions that do not have closed-form expressions employing Gauss–Hermite integration and finite exponential series, respectively. Finally, the service outage probability performance of MU with and without offloading services is analyzed under various system parameters and channel fading conditions.

An Enhancement of Multipath TCP Performance in Lossy Wireless Networks

Multipath TCP (MPTCP) is an evolvable technology for bandwidth aggregation on a mobile device. MPTCP naturally and concurrently exploits wireless links via different interfaces (i.e., Wi-Fi and cellular) for data transferring. Theoretically, the MPTCPs aggregated throughput is better or at least equals to the TCP throughput over a link. However, our investigation of MPTCP performance in a lossy wireless environment shows that the theoretical statement does not always hold. Specifically, the aggregation benefit of MPTCP (i.e., in a comparison to TCP) becomes negative when the loss over a link surpasses specific levels. In this paper, we focus on finding the negative region of MPTCPs aggregation benefit by experimental study. Additionally, we propose a loss-aware disabling mechanism to bypass the negativity. The mechanism temporarily switches a wireless link to a backup mode when an observed loss value reaches a threshold. We integrate the mechanism with a state-of-the-art MPTCP implementation and compare the two MPTCPs in various lossy conditions. The evaluation results confirm the effectiveness of the newly proposed mechanism in terms of enhancing goodput and saving resources.

Resource allocation in shared spectrum access communications for operators with diverse service requirements

In this paper, we study inter-operator spectrum sharing and intra-operator resource allocation in shared spectrum access communication systems and propose efficient dynamic solutions to address both inter-operator and intra-operator resource allocation optimization problems. For inter-operator spectrum sharing, we present two competent approaches, namely the subcarrier gain-based sharing and fragmentation-based sharing, which carry out fair and flexible allocation of the available shareable spectrum among the operators subject to certain well-defined sharing rules, traffic demands, and channel propagation characteristics. The subcarrier gain-based spectrum sharing scheme has been found to be more efficient in terms of achieved throughput. However, the fragmentation-based sharing is more attractive in terms of computational complexity. For intra-operator resource allocation, we consider resource allocation problem with users’ dissimilar service requirements, where the operator supports users with delay constraint and non-delay constraint service requirements, simultaneously. This optimization problem is a mixed-integer non-linear programming problem and non-convex, which is computationally very expensive, and the complexity grows exponentially with the number of integer variables. We propose less-complex and efficient suboptimal solution based on formulating exact linearization, linear approximation, and convexification techniques for the non-linear and/or non-convex objective functions and constraints. Extensive simulation performance analysis has been carried out that validates the efficiency of the proposed solution.