Engin Zeydan

Energy-efficient routing for correlated data in wireless sensor networks

In this paper, we investigate the reduction in the total energy consumption of wireless sensor networks using multi-hop data aggregation by constructing energy-efficient data aggregation trees. We propose an adaptive and distributed routing algorithm for correlated data gathering and exploit the data correlation between nodes using a game theoretic framework. Routes are chosen to minimize the total energy expended by the network using best response dynamics to local data. The cost function that is used for the proposed routing algorithm takes into account energy, interference and in-network data aggregation. The iterative algorithm is shown to converge in a finite number of steps. Simulations results show that multi-hop data aggregation can significantly reduce the total energy consumption in the network.

Cross layer interference mitigation using a convergent two-stage game for ad hoc networks

In this paper, we concentrate on convergence issues of a two stage game namely on joint beamforming and channel allocation in an ad hoc network. Maximization of the received signal-to-interference-plus-noise (SINR) ratios between two communicating nodes under constant transmit power is considered. We propose a convergent sequential distortionless beamforming (SDRB) and cooperative channel allocation (CCA) algorithm which we call as SDRB_CCA, to mitigate the interference in the network. In this algorithm, a suboptimum beamforming algorithm is performed in PHY layer and a cooperative (or non-greedy) channel allocation is assigned based on the definition of potential games in MAC layer in an iterative manner. The payoff of each channel selection includes the interference received at each node as well as the interference that this selection will cause on the other nodes. Simulation results supported our analytical results in the sense that SDRB_CCA converges at the expense of decrease in average rate compared to the optimum joint iterative beamforming and greedy channel allocation (O_JIBGCA) algorithm especially in over-loaded scenarios.

Joint Iterative Channel Allocation and Beamforming Algorithm for Interference Avoidance in Multiple-Antenna Ad Hoc Networks

In this paper, we consider the problem of interference suppression by performing a joint iterative beamforming [1] and channel allocation (JIBCA) strategy for wireless nodes under contracted quality-of-service (QoS) constraints in an ad hoc network. The objective is to maximize the signal to interference plus noise ratios (SINRs) between two communicating nodes under constant transmit power considering the interference from other nodes in the network. For this purpose, the interference impaired network is modeled as a noncooperative joint beamforming and channel allocation game, in which the payoff includes the maximization of the target SINR and the limiting factor is related to the interference caused by other nodes. The proposed JIBCA algorithm is shown to give better SINR efficiency both with the assumptions of perfect and imperfect channel information availability at the transmit/receive units over the network. It is also shown through simulation results that the JIBCA algorithm converges to Nash equilibriums (NE) and results in SINR efficiency improvement.

Efficient routing for correlated data in wireless sensor networks

In this paper, we propose an efficient routing solution for correlated data collection in wireless sensor networks. Our proposed routing metric considers both the interference distribution as well as the data correlation when establishing routes. An iterative, distributed solution based on local information is proposed using a game theoretic framework. Routes are chosen to minimize both the interference impact of nodes in their neighborhood and the joint entropy of multiple sources relayed through common nodes.

Joint iterative beamforming and power adaptation for MIMO ad hoc networks

In this paper, we present distributed cooperative and regret-matching-based learning schemes for joint transmit power and beamforming selection for multiple antenna wireless ad hoc networks operating in a multi-user interference environment. Under the total network power minimization criterion, a joint iterative approach is proposed to reduce the mutual interference at each node while ensuring a constant received signal-to-interference and noise ratio at each receiver. In cooperative and regret-matching-based power minimization algorithms, transmit beamformers are selected from a predefined codebook to minimize the total power. By selecting transmit beamformers judiciously and performing power adaptation, the cooperative algorithm is shown to converge to a pure strategy Nash equilibrium with high probability in the interference impaired network. The proposed cooperative and regret-matching-based distributed algorithms are also compared with centralized solutions through simulation results.

Iterative Beamforming and Power Control for MIMO Ad Hoc Networks

We present a distributed joint power control and transmit beamforming selection scheme for multiple antenna wireless ad hoc networks. Under the total network power minimization criterion, a joint iterative beamforming and power control algorithm is proposed to reduce mutual interference at each node. Total network transmit power is minimized while ensuring a constant received signal-to-interference and noise(SINR) at each receiver. First, transmit beamformers are selected from a predefined codebook to minimize the total power in a cooperative fashion. We also study the interference impaired network as a noncooperative beamforming game. By selecting transmit beamformers judiciously and performing power control, convergence of noncooperative beamformer games are guaranteed throughout the iterations. The noncooperative distributed algorithm is compared with centralized and cooperative solutions through simulation results.

Differential Space-Frequency Group Codes for MIMO-OFDM

In recent years, coherent space-frequency (SF) coded multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems have attracted great attention. However, obtaining perfect channel estimates for frequency-selective channels with lots of taps is challenging and computationally complex. In this paper, we present a transmission scheme that uses differential space-frequency group codes (DSFC) for MIMO-OFDM systems. Our proposed scheme is based on the theory of space-frequency group codes. We use the group properties of space-frequency codes that has recently been investigated and obtain a differential transmission rule incorporated with subcarrier allocation method that allows data to be sent without channel estimates at the transmitter or receiver. Recently proposed noncoherent space-frequency codes using MIMO-OFDM have exponential computational complexity with code rate in frequency-selective channels. Compared to existing noncoherent space-frequency codes, our proposed code design is computationally more efficient and is easier to implement. We also demonstrate that the presence of additional resolvable channel taps does not monotonically improve the performance of DSFCs, which shows that obtaining full space-frequency diversity order for increasing number of channel taps decreases the performance of the receivers with lack of channel state information (CSI). This result is completely different from the coherent case of space frequency group codes in which additional channel taps increase the BER performance due to the exploitation of frequency diversity present in MIMO-OFDM frequency-selective channels.

Seamless mobile data offloading in Heterogeneous Wireless Networks based on IEEE 802.21 and user experience

The increase on smartphone usage has brought the burden of data traffic with it. Operators are looking for cost-effective solutions to overcome the problem of 3G infrastructure for high contention traffic scenarios. Several schemes were offered to save the moment, and they brought some extra costs including deploying femtocell or WiMax, LTE, LTE-Advanced systems along with their expensive equipment. On the other hand, operators are expanding their networks with 802.11 technologies such that they can exploit the free-band communication. Meaning the data traffic can handover between WLAN and UMTS interchangeably. By using NS-2 simulator, we implemented IEEE 802.21 WGs Media Independent Handover (MIH) module by combining with Channel Quality Indicator (CQI) values collected from user equipment (UE) and observed a recovered throughput for both medium. We found that there is a tradeoff among energy efficiency, delay tolerance and cost. Furthermore, in this study, we integrated a Quality of Experience (QoE) metric during real-time handover decision process so that with this type of collaborative solution, an operator will be unique in terms of user happiness and heterogeneous network management.

Bottleneck throughput maximization for correlated data routing: a game theoretic approach

In this paper, we propose an efficient bottleneck throughput maximizing routing framework for correlated data gathering in wireless sensor networks. Our proposed routing metric exploits the the data correlation present in sensor networks. For throughput-maximizing correlation aware routing, a game theoretic framework is developed for a local solution of the NP-complete optimization problem. The proposed throughput maximization algorithm selects the best routes to increase the bottleneck throughput of each source in the network using best response dynamics. Numerical results corroborates predicted throughput gains.

Unitary and Non-Unitary Differential Space-Frequency Coded OFDM

In this paper, we present the code design structure of unitary and non-unitary differential space-frequency group codes (DSFCs) for multiple-input multiple-output (MIMO)- orthogonal frequency division multiplexing (OFDM) systems based on optimal coherent space-frequency (SF) group codes. Under the assumption that the transmitter knows only the delay profile of the channel, a differential transmission rule incorporated with subcarrier allocation is obtained that allows data to be sent without channel estimates at the transmitter or receiver. The differential encoding/decoding is performed in the frequency domain within each single OFDM symbol. Therefore, proposed DSFCs can be successfully decoded even for a rapidly fading channel which may change independently from one OFDM symbol to another. Unitary and nonunitary DSFCs, that are constructed based on design criteria, are compared with recently published techniques in the literature and shown to inherit coding gain of optimal coherent SF codes. Due to design structure and energy constraints, our nonunitary DSFCs do not blow up or diminish during the differential encoding.