Most previous works in the literature have focused on the cache hit probability and/or the communication cost and assume that the download of content is instantaneous. In [1], the placement of content encoded using a maximum distance separable (MDS) code to small BSs was investigated and it was shown that a careful placement allows to significantly reduce the backhaul rate. In [2], for the scenario where content is stored directly in the mobile devices, the repairing of the lost data when a device storing data leaves the network was considered. Assuming instantaneous repair, the communication cost of data download and repair was investigated. In [3], [4], a repair scheduling where repair is performed periodically was introduced and analytical expressions for the overall communication cost of content download and data repair as a function of the repair interval were derived. Using these expressions, the overall communication cost entailed by storing content using MDS codes, regenerating codes, and locally repairable codes was evaluated in [4] and it was shown that storing content using erasure correcting code can reduce the overall communication cost with respect to the scenario where content is downloaded solely from the BS. For the scenario where content is stored in small BSs, the expected file download delay has been minimized over the cache content placement, assuming that content is cached using ideal MDS rateless codes. However, while the mobile devices are spread randomly over an area, no mobility of the mobile devices is considered in the analysis. Mobility of the devices, assuming a random walk, is then considered in Monte Carlo simulations.
The novelty of project lies in the fact that for the first time the advantage of distributed caching for wireless content delivery has been analysed in terms of latency, that is a performance measure of very practical interest.
The main achieved scientific objective consists in showing that coded distributed caching can greatly improve the performance in terms of content download delay with respect to the case where content is downloaded from the BS, provided that the BS broadcasts the network information frequently enough. Interestingly, the results of the project also show that the performance improves when the length of the code increases. In particular, simple replication is very inefficient and much better performance are achieved using larger codes (of the same rate).
References:
[1] V. Bioglio, F. Gabry, and I. Land, “Optimizing MDS codes for caching at the edge,” in Proc. IEEE Global Commun. Conf. (GLOBECOM), San Diego, CA, 2015.
[2] J. Pääkkönen, C. Hollanti, and O. Tirkkonen, “Device-to-device data storage for mobile cellular systems,” in Proc. IEEE Global Commun. Conf. (GLOBECOM), 2013.
[3] J. Pedersen, A. Graell i Amat, I. Andriyanova, and F. Brännström, “Repair scheduling in wireless distributed storage with D2D communication,” in Proc. IEEE Inf. Theory Work. (ITW), Jeju Island, Korea, 2015.
[4] J. Pedersen, A. Graell i Amat, I. Andriyanova, and F. Brännström, “Distributed storage in mobile wireless networks with device-to-device communication,” IEEE Trans. Commun., vol. 64, no. 11, pp. 4862–4878, Nov. 2016.
[5] A. Piemontese and A. Graell i Amat, “MDS-coded distributed storage for low delay wireless content delivery,” in Proc. Int. Symp. Turbo Codes & Iterative Inform. Proc. (ISTC), Brest, France, Sep. 2016.
[6] A. Piemontese and A. Graell i Amat, “MDS-coded distributed caching for low delay wireless content delivery,” submitted to IEEE Trans. Commun.. Available on arXiv.
