Umesh Phuyal

Energy-Aware Resource Allocation for Cooperative Cellular Network Using Multi-Objective Optimization Approach

Energy consumption in wireless communication system is rapidly increasing due to growing wireless multimedia access. Combating adverse effects of excessive energy consumption demands for energy-aware system design, leading to a new research paradigm called green communication. In this paper, we propose user selection and power allocation schemes for a multi-user, multi-relay cooperative cellular system in order to minimize the cost of transmission. In the proposed schemes, the cost function is first formulated to optimize the weighted sum powers of base and relay stations. It is then extended to a more general multi-objective scheme which jointly optimizes the sum power and throughput keeping a balance between them. In both of the schemes, quality-of-service is guaranteed in terms of end-to-end signal-to-noise ratio. To make the proposed schemes realistic, we assume the presence of estimation errors in channel state information. An algorithm to enhance fairness among users in these schemes is also presented. Simulation results are presented to confirm the performance of proposed schemes in terms of energy efficiency, system throughput, outage probability, and fairness to end users.

Controlling access overload and signaling congestion in M2M networks

Access overload and signaling congestion are serious issues in machine-to-machine (M2M) networks. These issues can be caused by (i) external events triggering a large number of M2M devices to connect or disconnect all at once, (ii) recurring application events that are synchronized to the exact time (e.g., hour), and (iii) malfunctioning of M2M application or server. It is vital to control access overload and signaling congestion in order to prevent the network from a complete collapse. This paper investigates a few mechanisms to prevent this issue.

Some research issues in cognitive radio networks

The cognitive radio (CR) technology will allow a group of potential users to identify and access available spectrum resources provided that the interference to the users for whom the band has been licensed is kept below a prescribed level. However, this research area is at a very immature stage because various research challenges have to be addressed and solved. In this paper our objective is to present an overview of some research issues for CR networks. Specifically, we present some research and development in CR networks with focus on i) information- theoretic aspects, ii) spectrum sensing, iii) link adaptation, iv) advanced transceiver design, and v) admission control. We also discuss some important research problems related to these specific topics that needs to be addressed before deployment of CR systems in practice.

Power Loading for Multicarrier Cognitive Radio with MIMO Antennas

We propose a power loading scheme for multicarrier cognitive radio (CR) network employing multiple-input multiple-output (MIMO) antennas.We allocate power to different transmitting antennas within different subcarriers maximizing the total system capacity while maintaining the interference to primary user within a prescribed limit. We formulate this as a convex optimization problem and use numerical methods to solve for optimal power allocation. We also compare the performance of power loading scheme proposed in this paper to conventional uniform power loading scheme with and without interference constraint. Simulation results show that the capacity of MIMO CR using our proposed power loading scheme increases significantly with increase in interference temperature limit and the number of transmit antennas. However, we also confirm that if we include interference constraint in the conventional uniform power loading schemes, the capacity does not increase proportionally with increase in number of transmit antennas as those schemes do not take the instantaneous channel condition between cognitive user transmitter and primary user receiver into account.

Joint Zero-Forcing Based Precoder Design for QoS-Aware Power Allocation in MIMO Cooperative Cellular Network

We study a cellular system scenario where multiple data streams originating from a base station (BS) targeted to multiple cell-edge mobile stations (MSs) are transmitted via pre-installed cooperative relay stations (RSs) with multiple antennas. Our objective is to guarantee quality-of-service (QoS) in terms of predefined signal-to-noise ratio at such users within the transmit power budgets at BS and RSs while minimizing total transmit power. We propose a novel precoder design method for power allocation between multiple data streams at BS and RS by using joint zero-forcing strategy in order to avoid multiuser interference (MUI) in the signal received by MSs via both the direct and relay links. We also propose low-complexity suboptimal power allocation algorithm. We focus on analyzing the significance of direct link transmission in providing QoS to cell-edge MSs specially when RS is not situated directly between BS and MSs. Simulation results show that considering direct link and using the proposed scheme in such case significantly improves system outage performance compared to existing schemes in the literature which do not consider direct link.

Energy-aware user selection and power allocation for cooperative communication system with guaranteed quality-of-service

Energy consumption in wireless communication system is rapidly increasing due to the growth in wireless multimedia access. Combating the adverse effects of excessive energy consumption demands for energy-aware system design called green communication, which has become the major focus of many researchers recently. In this paper, we propose user selection and power allocation schemes for a multi-user multi-relay cooperative cellular system in order to minimize the cost of transmission. In the proposed schemes, the cost function is first formulated with the objective of optimizing the sum power consumption. Then it is extended to a more general multi-objective optimization scheme which jointly optimizes the sum power and throughput. The former scheme makes the system energy efficient, while the latter scheme keeps a balance between energy efficiency and throughput. In both of the schemes, quality-of-service is guaranteed in terms of end-to-end signal-to-noise ratio. Numerical results are also presented to confirm the system performance enhancement with the proposed schemes.

Green resource allocation with QoS provisioning for cooperative cellular network

Relay-based cooperative transmission in cellular network has been an area of tremendous research recently. Transmission via relays introduces power consumption at both the source and relay stations which may lead to less efficient system in terms of power consumption. Because of increasing energy cost for cellular systems and concern over environmental issues, an energy efficient design of resource allocation scheme in cooperative cellular network is of prime importance. In this paper, we propose a novel resource allocation scheme in order to maximize the energy aware system performance. The proposed low-complexity scheme allocates powers for base station and relay by using a strategy that minimizes required transmit power per unit achieved throughput and at the same time guarantees a predefined quality of service (QoS) which is specified in terms of minimum end-to-end data rate required by each user. Simulation results show that proposed scheme outperforms existing power allocation schemes by decreasing required power to guarantee the QoS without increasing system outage penalty, which is essential for green communication systems.

QoS Guaranteed Resource Allocation in Cooperative Cellular Network with MIMO-Based Relays

Relay-based cooperative transmission in cellular wireless networks has been an area of tremendous research recently. Since MIMO technique has been shown to increase the spectral efficiency significantly, relays with MIMO antennas seem to be potential candidate for future cooperative cellular system in order to achieve reliable transmission, high system throughput and extended network coverage. In this paper, we study a cellular system scenario where quality of service (QoS) of multiple data streams originating from a base station (BS) targeted to multiple mobile stations (MSs) is guaranteed by using pre-installed relay stations (RSs) with MIMO antennas. We propose a low-complexity algorithm to design precoder matrices at BS and RS by using joint zero-forcing strategy to avoid multiuser interference in the signal received at the MSs via both the direct path (BS-MS) and the relay path (BS-RS-MS). The proposed algorithm guarantees a predefined signal-to-noise ratio at each user within the transmit power constraint at BS and with the minimal sum transmit power of BS and RS. Simulation results show that proposed algorithm outperforms the singular value decomposition (SVD)-based scheme existing in the literature by keeping the outage probability lower. Moreover, the performance of proposed algorithm compared to that of SVD-based scheme is further improved when the RS is not situated directly between the BS and the MSs.

Joint power and subcarrier allocation in multi-hop OFDMA network: A cross-layer approach

Resource wastage due to loss of a packet in a multi-hop wireless network greatly depends on number of hops the packet has already traveled. Hence, consideration of hop-count information is crucial while optimizing overall resource utilization of such network. Therefore, we propose a cross-layer resource allocation approach for an orthogonal frequency division multiple access based multi-hop network which jointly allocates subcarriers and transmit power prioritizing packets with higher hop-counts. Simulation results show that the proposed scheme is capable of minimizing network-wide resource wastage significantly without degradation in goodput and system outage performance.

Cross-layer resource allocation approach for multi-hop distributed cognitive radio network

In multi-hop distributed cognitive radio network, link layer resource allocation must consider the information about number of hops packets have already traveled in the network in order to optimize the overall resource utilization. The loss of a packet after traveling some hops results in waste of all the resources allocated to it in previous hops. The existing resource allocation schemes may not provide optimal resource utilization in such network as this issue has been greatly ignored. Therefore, in this paper, we propose a scheme to allocate transmit power to different packets favoring those which have traveled more hops before reaching a particular node. We present a cross-layer approach in which link layer gets the hop-count information from network layer module. Distributed implementation is possible with the proposed scheme because each node can access this information. We formulate the power allocation problem as a convex optimization problem and obtain its analytical solution by using Lagrangian duality. Simulation results show that the proposed scheme is capable of minimizing wastage of network resources used by packets in their previous hops without any degradation in throughput and outage performance.