In this paper, we consider a two-layer caching-aided network, where a single server consisting a library of N files connects with multiple relays through a shared noiseless link, and each relay connects with multiple users through a shared noiseless link. Each relay and user are equipped with a cache memory of M1 and M2 files, respectively. We design a caching scheme that exploits the spared transmission time resource by allowing the concurrent transmission between the two layers. It is shown that the caching scheme is order optimal and can further reduce the transmission delay compared to the previously known caching scheme. Also, we show that for the two-relay case, if each relay's caching size M1 equals to 0.382N , our scheme achieves the same delay as M1 = N , which implies that increasing M1 will not always reduce the transmission delay.

In this paper, we consider the coded-caching broadcast network with user cooperation, where a server connects with multiple users and the users can cooperate with each other through a cooperation network. We propose a centralized coded caching scheme based on a new deterministic placement strategy and a parallel delivery strategy. It is shown that the new scheme optimally allocate the communication loads on the server and users, obtaining cooperation gain and parallel gain that greatly reduces the transmission delay. Furthermore, we show that the number of users who parallelly send information should decrease when the users' caching size increases. In other words, letting more users parallelly send information could be harmful. Finally, we derive a constant multiplicative gap between the lower bound and upper bound on the transmission delay, which proves that our scheme is order optimal. Index TermsCache, cooperation, delay I. INTRODUCTIONDue to the continuous growth of traffic in the network and the growing needs for higher Internet speed from users, it's imperative to improve the performance of the network. One of the promising directions to improve the quality of service is to utilize the cache memories in the network. In [1] Maddah-Ali and Niesen proposed a novel scheme, namely coded caching scheme, to improve the transmission efficiency of each transmission. It obtains a global caching gain by creating multicasting opportunities for different users. This new class of caching system has attracted significant interests [2]- [7].To further improve the quality of service, one can combine caching with user cooperation. It is particularly common and useful in fog network [8], where the edge users can carry out some amount of communication. This can include, for example, device-to-device (D2D) networks and ad-hoc networks. In [9], coded caching schemes were proposed for a D2D noiseless network with the absence of server. In [10], the caching problem on a two-user D2D wireless network with the presence of a server was studied. In [12], a maximum distance separable (MDS) coded caching scheme was proposed to reduce the communication load in highly-dense wireless networks considering device mobility.In this paper, we study a K-user (K ≥ 2) coded-caching broadcast network with user cooperation. In this network, a server connects with all users through a noiseless shared link, and the users can communicate with each other through a noiseless cooperation network. The cooperation network is parameterized by a positive integer α max ∈ {1, . . . , K/2 }, denoting the maximum number of users allowed to parallelly send data in the cooperation network. For example, when α max equals to 1, the cooperation network operates as a simple shared link connecting with all users, which is easy and low-cost to implement in fog network. The main contributions are summarized below.• We propose a novel coded caching scheme that fully exploits user cooperation and optimally allocates communication loads between the server and users. The sche...

No abstract

Setting greenhouse gas emission target is a critical step to meet the challenge of climate change. While the debate on global and national carbon emission targets has dominated every major climate change conference, little is known about how the firms set emission targets. Using a dataset on S&P 500 companies in the United States, we investigate the determinants of firm-level climate change mitigation targets, including target adoption and target metric (intensity target vs. absolute target). We find that companies with larger size, higher growth, better innovation, weaker capital constraint, and higher government pressure are more likely to establish emission targets. Further, firm growth has a negative (positive) and significant association with the use of absolute (intensity) target. This may be due to the fact that intensity target can better accommodate growth than absolute target. Policymakers and corporate managers may resort to those determinant factors in designing climate change policies to induce desirable firm-level target-setting behaviors.

No abstract