Effect of Primary Interference on Cognitive Relay Network

Cognitive relay network is a method for optimizing frequency spectrum utilization. What’s important in these networks is to transmit data such that none of primary and secondary users cause destructive interference to other users. Although primary interference affect cognitive network performance, but is neglected in former researches. In this paper, we show cognitive network performance by calculating outage probability. We consider both primary and secondary interference links. Finally, our study is corroborated by representative numerical example. Simulation results demonstrate that increasing interference threshold increase outage probability and increasing data transmit rate cause outage probability increase

Power allocation in wireless multi-user relay networks

In this paper, we consider an amplify-and-forward wireless relay system where multiple source nodes communicate with their corresponding destination nodes with the help of relay nodes. Conventionally, each relay equally distributes the available resources to its relayed sources. This approach is clearly sub-optimal since each user experiences dissimilar channel conditions, and thus, demands different amount of allocated resources to meet its quality-of-service (QoS) request. Therefore, this paper presents novel power allocation schemes to i) maximize the minimum signal-to-noise ratio among all users; ii) minimize the maximum transmit power over all sources; iii) maximize the network throughput. Moreover, due to limited power, it may be impossible to satisfy the QoS requirement for every user. Consequently, an admission control algorithm should first be carried out to maximize the number of users possibly served. Then, optimal power allocation is performed. Although the joint optimal admission control and power allocation problem is combinatorially hard, we develop an effective heuristic algorithm with significantly reduced complexity. Even though theoretically sub-optimal, it performs remarkably well. The proposed power allocation problems are formulated using geometric programming (GP), a well-studied class of nonlinear and nonconvex optimization. Since a GP problem is readily transformed into an equivalent convex optimization problem, optimal solution can be obtained efficiently. Numerical results demonstrate the effectiveness of our proposed approach

Communications over fading channels with partial channel information : performance and design criteria

The effects of system parameters upon the performance are quantified under the assumption that some statistical information of the wireless fading channels is available. These results are useful in determining the optimal design of system parameters. Suboptimal receivers are designed for systems that are constrained in terms of implementation complexity. The achievable rates are investigated for a wireless communication system when neither the transmitter nor the receiver has prior knowledge of the channel state information (CSI). Quantitative results are provided for independent and identically distributed (i.i.d.) Gaussian signals. A simple, low-duty-cycle signaling scheme is proposed to improve the information rates for low signal-to-noise ratio (SNR), and the optimal duty cycle is expressed as a function of the fading rate and SNR. It is demonstrated that the resource allocations and duty cycles developed for Gaussian signals can also be applied to systems using other signaling formats. The average SNR and outage probabilities are examined for amplify-and-forward cooperative relaying schemes in Rayleigh fading channels. Simple power allocation strategies are determined by using knowledge of the mean strengths of the channels. Suboptimal algorithms are proposed for cases that optimal receivers are difficult to implement. For systems with multiple transmit antennas, an iterative method is used to avoid the inversion of a data-dependent matrix in decision-directed channel estimation. When CSI is not available, two noncoherent detection algorithms are formulated based on the generalized likelihood ratio test (GLRT). Numerical results are presented to demonstrate the use of GLRT-based detectors in systems with cooperative diversity

PSO based power allocation for single and multi relay AF cooperative network

Wireless channels are generally suffering from fading. Diversity is the effective way to combat fading in wireless channels. But, the ultimate aim of diversity is to allow multiple antennas into the environment. Due to size and hardware complexity, many wireless devices are limited to one antenna. Cooperative communication is a new class of diversity, it allows single antenna users into a multi user environment to share their antennas and create virtual multiple antennas. In cooperative communication, the information is transmitted with the help of neighboring nodes, which are called relays. Cooperative diversity is based on different relaying schemes such as amplify-and-forward, decode-and-forward and coded cooperation. Cooperative transmission using relay gives better performance compared to direct transmission between the source and destination. The system performance enhances as the number of relays in the network increases and in addition the diversity order also increased. Power allocation is one of the major issues in a wireless cooperative communication for enhancing the system performance. In this work, a single and multi relay cooperative network is considered using amplify-and-forward relaying scheme. Considering the perfect channel state information (CSI), allocating power to source and relay using Particle Swarm Optimization (PSO) with minimizing as a constraint. The PSO algorithm maintains a group of particles, where each particle in the group gives a possible solution. PSO gives the best optimum value for a given problem by using objective function. Hence the implemented scheme of PSO base power allocation in cooperative network enhances the system performance

POWER ALLOCATION ALGORITHM FOR MIMO BASED MULTI-HOP COOPERATIVE SENSOR NETWORK

Cooperative transmission is a new breed of wireless communication systems that enables the cooperating node in a wireless sensor network to share their radio resources by employing a distributed transmission and processing operation. This new technique offers substantial spatial diversity gains as the cooperating nodes help one another to send data over several independent paths to the destination node. In recent times, an extensive effort has been made to incorporate these systems in the future wireless networks like LTE (Long Term Evolution), IEEE 802.16j (Mobile Multi-hop Relay (MMR) Networks) and IEEE 802.16m (Mobile WiMAX Release 2 or WirelessMAN-Advanced). But, there are few technical issues which need to be addressed before this promising technique is integrated into future wireless networks. Among them, managing transmission power is a critical issue, which needs to be resolved to fully exploit the benefits of cooperative relaying. Optimal Power Allocation, is one such technique that optimally distributes the total transmission power between the source and relaying nodes thus saving a lot of power while maintaining the link quality. In the first part of the thesis, mathematical expressions of the received signals have been derived for different phases of cooperative transmission. Average-Bit-error-rate (ABER), has been taken as a performance metric to show the efficiency of cooperative relaying protocols. In the second part of this Chapter, a multi-hop framework has been presented for the power allocation algorithm with Amplify-and-Forward relaying protocol. The efficiency of the power allocation algorithm has been discussed with different scenarios i.e. First for a three node (2-Hop) wireless network configuration and then for a four node (3-Hop) wireless network configuration. The transmission scenarios (2-Hop and 3-Hop) have been further categorized into multiple cases on the basis of channel quality between source-to-destination, source-to-relay, relay-to-relay and relay-to-destination links.fi=Opinnäytetyö kokotekstinä PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=Lärdomsprov tillgängligt som fulltext i PDF-format

Simulation and improvements for cooperative MAC (COMAC) protocol

Cooperative communication has been recently proposed for wireless sensor networks for achieving reliable, high data rate communication, eventually decreasing energy consumption at the nodes and extending the lifetime of the sensor network. The benefits of cooperation can be obtained by appropriate design of the medium access control (MAC) protocol. In this thesis, we present a cooperative MAC protocol that enables cooperation of multiple relays in a distributed fashion. It is shown that energy efficiency of the protocol significantly depends on cooperator selection and power assignment. We propose random and intelligent timer models for coordinating access of the cooperating nodes. Next, we consider the contention channel observed during the cooperator selection period and we propose a collision resolution mechanism. We consider two alternatives for cooperative transmissions, and compare the performances of code division based and time division based approaches. The cooperative MAC protocol is further improved by introducing sleep feature for the relay nodes, since the major sources of wasted energy for the cooperative system are idle listening and overhearing. We evaluate the cooperative MAC protocol with all the proposed enhancements in terms of energy efficiency, throughput, average delay and MAC overhead cost and demonstrate the performance improvements