Power efficient wireless technologies are being developed to combat the finite battery power in wireless portable computing devices. This paper investigates energy efficiency, throughput and packet delay for non- persistent and p-persistent CSMA, two protocols popularly applied in current wireless networks. We find that the non-persistent CSMA can be configured to obtain maximum probability of success of message transmission with energy-efficiency and throughput greater than a p-persistent system, when more than two nodes are ready to transmit at the same time slot. However, we also observe that the p-persistent system has a lower packet delay as compared to a non-persistent system. The comparisons between both the protocols have been presented using a specific transmission model and substantiated by simulations. Packet collisions over the medium are the main challenge facing the designer of MAC protocols. In this paper, we investigate energy efficiency in carrier sense multiple access (CSMA) protocols that can be applied to wireless packet switched networks. We consider a system of N active nodes employing the p-persistent CSMA scheme on a slotted shared channel, where each node senses the channel persistently in every time slot. If the node finds the channel to be idle, it transmits a packet of fixed length, K time slots with a probability p = 1−q starting from the next time slot.
[...] Three different plots have been shown in the figure, one depicting the performance of a p-persistent system equation where is assumed, and other two representing non-persistent systems using different formulations as depicted by equations and (16). Figure 3. Plots of Energy efficiency vs. number of Nodes . Figure.4 shows the Throughput per unit energy spent as a function of the number of contenders from by the same systems defined by and(16). Figure 4. Plots of Throughput per unit energy spent vs. [...]
[...] In a p-persistent system that considers a maximum of two sensors contending for each slot, this value of p is constant for all the slots, as shown by the probability distribution But if we consider a non-persistent system, then the optimized probability of each slot getting sensed for maximum rate of successful transmission is given by pr* where .K . For N nodes contending to transmit on the channel in K time slots, the flow graph with the states defined as above is shown in Fig.1. [...]
[...] Therefore, from an energy consumption standpoint, each node is assumed to alternate between two states: 1)a carrier-sense state, with an energy consumption of Ecs per time slot and a transmit state, with Et per time slot. Now, in order to optimize our transmission model to obtain maximum rate of successful transmissions, we utilize the same model with an optimal non-persistent CSMA distribution Development of the Optimal Distribution The optimal probability distribution is defined in terms of a recursive function fs which in turn is related to the probability of success when stations compete. [...]
[...] The non-persistent system thus mapped provides an advantageous higher energy efficiency and throughput but a high packet delay too along with a maximum rate of successful transmission under the fact that the number of contenders for each slot may vary to any value>=2. If the statistics of imperfections and energy consumption characteristics of transceivers of varying complexities are known, the analysis presented here can be very precise and useful in selecting right complexity for optimum energy efficiency. References: Iyappan Ramachandran, Sumit Roy, “Analysis of throughput and Energy [...]
[...] Energy-Efficiency Analysis Energy efficiency is the fraction of the total energy spent by a node used for the successful transmissions. Considering the CSMA protocol behavior, an expression for the mean energy spent by one node (the tagged node), to transmit one packet successfully is to be computed. We see from Fig.1, that the system comprises of the following states: IDLE: The channel is idle and all nodes are waiting to transmit. TXsucc: The tagged node has successfully captured the channel and its transmission is successful, i.e. [...]
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