D. K. Kothari

Optimal resource allocation techniques for Cooperative AF and DF wireless networks

Optimal resource allocation for cooperative amplify and forward and decode & forward wireless relay networks in which multiple source to destination pairs are assisted by relays is investigated here. Power and bandwidth are the resources which are allocated to sources and relays in the centrally controlled network by the access point or base station. The issue of resource allocation is very stringent to handle in wireless network with users having time varying different channels and wide range of QoS requirements Three joint resource allocation strategies are developed based on (1) maximization of the total data rate of all users (2) constrained resource allocation to all the users (3) Utility based allocation. Simulation results show the comparison among the data-rate achieved by different techniques of resource allocation. The movement of the relay as well as the relaying protocol also affect the resource allocation and total data rate in the multi-user dynamic network. We have also presented the result of AF & DF protocol as well as vertical & horizontal movements of relay with respect to Source-Destination plane.

Resource allocation techniques for cooperative AF wireless networks — Efficiency fairness trade-offs

Resource allocation is one of the critical problem in cooperative communication systems. The approach to allocate resources to maximize total network throughput favours sources with good channel condition. On the other hand, max-min fair technique suffers from the loss of efficiency to a larger extent. Looking at futuristic wireless applications, the demand of users vary on wider spectrum. Allocation of a fixed amount of resources cannot satisfy such requirements. In this context, satisfaction of the user is more important criteria compared to common achievable targeted data rate. The user satisfaction is represented in term of utility based on some network performance criteria. This paper presents the concept of utility based resource allocation. The utility is defined as a function of data rate achieved by the user in the cooperative mode. Extensive simulation is carried out considering different utility functions that resemble the satisfaction of the user for variable data rate applications. The results show with the proposed utility based allocation significant fairness can be achieved with vary nominal decrease in efficiency. We have also investigated the efficiency-fairness trade-off for each of the utility function.

Optimization of 2.5 Gbps WDM-FSO link range under different rain conditions in Ahmedabad

This paper describe design and simulation of Wavelength Division Multiplexing (WDM) based Free Space Optical (FSO) link for different rain conditions in Ahmedabad and analyses the performance of the system by using parametric optimization. Here OptiSystem is used as simulation tool to simulate the link for the data-rate of 2.5 Gbps and wavelength of 1550 nm. The minimum value of Bit Error Rate (BER) achieved is greater or equal to 10-9 for optimized link range. The optimized link range for light rain, medium rain and heavy rain is achieved as 15.6 km, 6.1 km and 3 km.

Bit error rate analysis of the K channel using wavelength diversity

Abstract. The presence of atmospheric turbulence in the free space causes fading and degrades the performance of a free space optical (FSO) system. To mitigate the turbulence-induced fading, multiple copies of the signal can be transmitted on a different wavelength. Each signal, in this case, will undergo different fadings. This is known as the wavelength diversity technique. Bit error rate (BER) performance of the FSO systems with wavelength diversity under strong turbulence condition is investigated. K-distribution is chosen to model a strong turbulence scenario. The source information is transmitted onto three carrier wavelengths of 1.55, 1.31, and 0.85  μm. The signals at the receiver side are combined using three different methods: optical combining (OC), equal gain combining (EGC), and selection combining (SC). Mathematical expressions are derived for the calculation of the BER for all three schemes (OC, EGC, and SC). Results are presented for the link distance of 2 and 3 km under strong turbulence conditions for all the combining methods. The performance of all three schemes is also compared. It is observed that OC provides better performance than the other two techniques. Proposed method results are also compared with the published article.

Performance of free space optical link using wavelength diversity over K turbulence channels

In this paper, authors have applied the wavelength diversity techniques over K turbulence channel to reduce the outcome of atmospheric turbulence on the received signal. The information signal was transmitted onto the three wavelength channels 1550 nm, 1310 nm, and 850 nm. At the receiver end, Optimal Combining (OC) and Selection Combining (SC) diversity schemes have been deployed to combine multiple carriers. Mathematical analysis is carried out to calculate the outage probability for both the schemes. The simulations are done for the link distances of 2.5 km and 3 km for both the schemes. The achieved results demonstrate that the wavelength diversity improve the performance of the FSO communication link, but at a significant escalation of the systems complication and budget.

Efficiency–Fairness Trade-Off Approaches for Resource Allocation in Cooperative Wireless Network

Optimum resource allocation problem of cooperative wireless communication is discussed in this paper. Looking at the variety in services offered in wireless network and time-varying nature of the channel, it is need of the time to go for dynamic resource allocation which not only improves the performance but also enhances reliability, coverage, and user satisfaction in cooperative network. Efficiency and fairness are two different perspectives of resource allocation which are very difficult to achieve at the same time. We have presented three approaches for performing trade-off between efficiency and fairness in systematic manner. First approach is based on converting the data rate achieved by the user in terms of utility and then maximizes the total utility of all the users. It is shown that a properly design utility function is able to result any desired trade-off. Second approach is based on putting the restrictions of minimum resources that must be assigned to the user and maximum resources that can be given to the user. The resources that assign to any user vary between this limit. The minimum and maximum are determined by the parameters A (0 1). In the third approach, E-F function is presented which is able to provide trade-off based upon the values of E (1 < E ≤ 2) and F (0 ≤ F ≤ 1). In all the three cases, the total resources available for distribution are kept constant. Fairness is measured by Jain’s fairness Index, and loss of efficiency is measured in terms of price of fairness.

Mitigation of Fog and Rain Effects in Free-Space Optical Transmission Using Combined Diversity

Free-Space Optics (FSO) have been emerging communication field because of several advantages like cost-effective, higher bandwidth, and license free. It is basically line of sight communication and more suitable for last mile connectivity. Signal degradation occurs mostly due to atmospheric interference like rain, fog, etc. Diversity is an efficient solution to overcome these effects. In this paper, we have applied the concept of combined diversity (spatial and wavelength) with help of two receiver antenna to mitigate effects of fog and rain attenuation over transmission. An Equal Gain Combining for array gain enhancement applied at the receiver side. Results also demonstrated improvement in BER performance under strong turbulence.

Partner selection and resource exchange in cooperative network

Resource sharing for improved performance is a key factor in practical realization of cooperative communication networks. This paper presents a choice of suitable partner for optimizing the resources and thereby, strengthening the cooperation in the wireless network. Nodes in the network forms a pair to compensate for each others deficiency. These paired nodes share the resources owned by them amongst the pair and hence naturally remain in cooperation. This is achieved without the need of any outside stimulation like pricing, credit or reputation index. Exchanging the resources is an attractive technique to achieve mutual benefits and encourage cooperation among the nodes. In the proposed work nodes cooperating by exchanging bandwidth with relaying power. Simulation results show that the source node can increase its data rate in the range of 71% to 97% by assigning some fraction of its bandwidth to relay. The relay also earn benefit by getting additional bandwidth in terms of increase in its data rate from 12.5% to 97 % Based on this, an algorithm is developed for partner selection. The algorithm produces sub-optimal results as it considers the benefit of source and relay individually. It is found that in this framework, the sub-optimal procedure is more suitable.

Power Efficient Strategy for Enhancing Link Capacity in Cooperative Network

of wireless channel, other nodes in the vicinity are also able to receive the signal which is actually not intended for them. One or more of these intermediate nodes, process the signal and transmits it towards the destination. The destination can combine both the signals- one from source and another from relay. There are many hurdles in the path of cooperation in wireless network. Resource allocations, security, stimulating and sustaining cooperation are the major issues which offer the challenge to the research community now a day. Out of these, resource allocation issue is undertaken in this paper. In cooperative scenario, duplication of transmission takes place due to retransmission by one or more relays, which, in turn leads to the inefficient utilization of resources, increased traffic and increased interference. These issues can be handled by allocating the resources to the nodes based on the distance and channel condition between the pair of nodes.

Power minimization algorithm in multi source multi relay cooperative wireless network

Ever increasing demand of data rate with limited available spectrum has compel and motivate the researcher to find novel solutions which enable to cater the demands of future wireless networks. One such solution is cooperative communication in which the inherent broadcasting nature of wireless channel is exploited by adding the flavors of cooperation to it. The node who overhears the communication cooperate with the source of information and retransmit it towards destination is the key concept of cooperation. If many cooperators retransmit with uncontrolled power, it results in wastage of power and increased interference in the network. To achieve the fruits of cooperation, it is, therefore, very essential to choose the appropriate partner (relay) and adequate power level for all the pairs of source-relay in the network. Relay assignment and power minimization algorithm for multisource multi relay scenario is presented in this paper. The approach taken in this paper ensures that each pair of source-relay consumes minimum power, at the same minimizing the overall power consumption of the network.