Data communication has seen exponential growth recently, and it currently dominates wireless communication. As a result, proactive caching was developed to minimize peak traffic rates by storing content, in advance, at different nodes in the network. We consider proactive caching for a broadcast wireless network with one central hub such as a satellite (ST) and K associated mobile units (MUs) such as mobile mini-ground stations or end users. The ST has a library of files, and the MUs demands are assumed to be limited to this library, while the popularity of the library files changes over time. We assume that the MUs demands arrive at different times, and hence, asynchronous file delivery is necessary. We propose a new scheme that minimizes the files delivery sum rate and show that we can use the file delivery messages to proactively and constantly update the MU finite caches. We show that this mechanism reduces the downloaded traffic of the network. The proposed scheme uses index coding to jointly encode the delivery of different demanded files with the cache updates to other MUs to follow the changes in the files popularities. An offline optimization of the delivery sum rate of the scheme is proposed, where it requires knowledge of the files popularities across the whole transmission period. In particular, the problem is formulated as a linear program and the optimal caching is obtained numerically. Moreover closed form solutions to two special cases are derived and a lowerbound to the achievable delivery sum rate is developed. Numerical results show the benefits of the proposed scheme over conventional caching schemes, in terms of reducing the delivery sum rate.Index Terms-Coded caching, data communications, index coding, proactive caching.
I. INTRODUCTIONC ELLULAR traffic has shifted over the past decade from mainly locally generated instantaneous traffic (voice calls) to centrally generated delay-tolerant bulks of traffic (data driven communication) [1]. This necessitated the development of new information theoretic analysis and new algorithms for communication networks. One key characteristic of data communication is that the delay between the time of data generation and the time of data demand at the receivers is mostly large. This enables the data to be stored midway in different nodes along the path from the transmitter to the receiver to relieve pressure of congested links. Future expansions of future generation cellular networks are targeting satellite integration with terrestrial networks to increase coverage and availability. Satellite links have broadcast nature and introduces further delays; thus, strengthening the case for midway storage (or caching). Moreover, the shift from voice to data traffic contradicts the classical assumption of network analysis that messages are generally independent. This assumption is not accurate for data communication, especially in broadcast networks, where a piece of data is generally demanded by multiple users over time. Proactive caching is an efficient technique t...