10月31日，在新主楼第三会议室举行了本学期第一次实验室Workshop，这次Workshop有三位同学为我们报告了他们研究工作的最新进展，内容如下：

报告人：佘昌洋
题目: A Tool in Optimizing Resource Allocation for Tactile Internet  

摘要：Tactile internet requires ultra-low latency and ultrahigh reliability, which bring new challenges to the design of mobile systems. Recent studies focus on air interface technologies to reduce transmission delay, but the queueing delay is largely overlooked. In this workshop, we illustrate how to use effective bandwidth as a tool for optimizing resource allocation to ensure the ultra-low delay bound imposed on each short packet. To reflect the performance for a concrete system, we consider energy efficiency (EE) as the goal for optimization and take vehicle collision avoidance as an example application. We optimize transmit power and bandwidth allocation to maximize the EE under the constraint of required delay bound and its violation probability, while effective bandwidth is employed to characterize the requirement. To validate that effective bandwidth can be applied in short delay regions, we compare the distributions of queueing delay respectively derived with effective bandwidth and with an M/D/1 model. Simulation and numerical results show that the stringent requirement on delay and reliability can be satisfied with the optimized policy for the considered typical application of tactile internet. Moreover, the EE of the system achieved by the optimized policy when serving the traffic with ultra-short delay bound is close to that when serving delay tolerant traffic.

报告人：刘栋
题目：Cache-enabled Heterogeneous Cellular Networks: Comparison and Tradeoffs  

摘要：Caching popular contents at base stations (BSs) is a promising way to unleash the potential of cellular heterogeneous networks (HetNets), where backhaul has become a bottleneck. In this paper, we compare a cache-enabled HetNet where a tier of multi-antenna macro BSs is overlaid by a tier of helper nodes having caches but no backhaul with a conventional HetNet where the macro BSs tier is overlaid by a tier of pico BSs with limitedcapacity backhaul.We resort stochastic geometry theory to derive the area spectral efficiencies (ASEs) of these two kinds of HetNets and obtain the closed-form expressions under a special case. We use numerical results to show that the helper density is only 1/4 of the pico BS density to achieve the same target ASE, and the helper density can be further reduced by increasing cache capacity. With given total cache capacity within an area, there exists an optimal helper node density that maximizes the ASE.

报告人：陈彬强
题目：基于存储的D2D通信进行负载转移的能耗（Energy Costs for Traffic Offloading by Cache-enabled D2D Communications）  

摘要：Device-to Device(D2D) communications can offload the traffic and boost the throughput of cellular networks. By caching files at users, content delivery traffic can be offloaded via D2D links, if a helper user are willing to send the cached file to the user who requests the file. Yet it is unclear how much energy needs to be consumed at a helper user to support the traffic offloading. In this presentation, I will firstly give a holistic introduction to D2D communications and then introduce a usercentric proactive caching policy that can control the energy cost for a helper user to convey a file, and then optimize the caching policy to maximize the offloaded traffic. To reduce the energy during transmission, the optimal transmit power is derived to minimize the energy consumed by a helper to send a file. Then the relationship between traffic offloading and energy cost with the optimized caching policy and transmit power is showed by numerical and simulation results, which demonstrate that a significant amount of traffic can be offloaded with affordable energy costs.