Network Coding Tree Algorithm for Multiple Access System

Network coding is famous for significantly improving the throughput of networks. The successful decoding of the network coded data relies on some side information of the original data. In that framework, independent data flows are usually first decoded and then network coded by relay nodes. If appropriate signal design is adopted, physical layer network coding is a natural way in wireless networks. In this work, a network coding tree algorithm which enhances the efficiency of the multiple access system (MAS) is presented. For MAS, existing works tried to avoid the collisions while collisions happen frequently under heavy load. By introducing network coding to MAS, our proposed algorithm achieves a better performance of throughput and delay. When multiple users transmit signal in a time slot, the mexed signals are saved and used to jointly decode the collided frames after some component frames of the network coded frame are received. Splitting tree structure is extended to the new algorithm for collision solving. The throughput of the system and average delay of frames are presented in a recursive way. Besides, extensive simulations show that network coding tree algorithm enhances the system throughput and decreases the average frame delay compared with other algorithms. Hence, it improves the system performance

Uplink Age of Information of Unilaterally Powered Two-way Data Exchanging Systems

We consider a two-way data exchanging system where a master node transfers energy and data packets to a slave node alternatively. The slave node harvests the transferred energy and performs information transmission as long as it has sufficient energy for current block, i.e., according to the best-effort policy. We examine the freshness of the received packets at the master node in terms of age of information (AoI), which is defined as the time elapsed after the generation of the latest received packet. We derive average uplink AoI and uplink data rate as functions of downlink data rate in closed form. The obtained results illustrate the performance limit of the unilaterally powered two-way data exchanging system in terms of timeliness and efficiency. The results also specify the achievable tradeoff between the data rates of the two-way data exchanging system.Comment: INFOCOM 2018 AOI Wkshp, 6 page

Age of Information in a Multisource Ber/Geo/1/1 Preemptive Queueing System

This work studies the information freshness of the vehicle-to-infrastructure status updating in Internet of vehicles, which is modeled as a multi-source Ber/Geo/1/1 preemptive queueing system with heterogeneous service time. We pay attention to both the distribution and average of AoI. To fully track the per-source AoI evolution, a Markov two-dimensional (2D) age process is introduced. The first element of the 2D age process stands for the instantaneous per-source AoI, while the second represents whether an update of the concerned source is being served and its current age. A complete framework and detailed analyses on the per-source AoI are presented based on the Markovity of the 2D age process. By studying the state transition probabilities, stationary equations, and stationary distribution of the 2D age process, analytical expressions of the probability mass function and average of per-source AoI are derived. Numerical results validate the accuracy of the theoretical analyses