wireless architecture. Some important research challenges as well as future research directions in designing the XaaS framework were discussed and presented.

[1]{}

C. Liang and F. R. Yu, “Wireless virtualization for next generation mobile cellular networks,” *IEEE Wireless Communications*, vol. 22, no. 1, pp. 61-69, Feb. 2015.

P. Rost, I. Berberana, A. Dekorsy, G. Fettweis, A. Maeder, H.Paul, V. Suryaprakash, M. Valenti, and D. Wübben, “Benefits and challenges of virtualization in 5G radio access networks,” *IEEE Communications Magazine*, vol. 53, no. 12, pp.75-82, December 2015.

Y. Duan, G. Fu, N. Zhou, X. Sun, N. C. Narendra, and B. Hu, “Everything as a service(XaaS) on the cloud: origins, current and future trends”, *in proc. of IEEE 8th International Conference on Cloud Computing*, New York, USA, June 2015.

H. Wen, P. K. Tiwary, and T. Le-Ngoc, “Wireless Virtualization,” Springer International Publishing, 2013.

D. Sabella, A. De Domenico, E. Katranaras, M. A. Imran, M. Di Girolamo, U. Salim, M. Lalam, K. Samdanis, and A. Maeder, “Energy efficiency benefits of RAN-as-a-Service concept for a cloud-based 5G mobile network infrastructure,” *IEEE Access*, vol.2, pp.1586-1597, 2014.

Z. Chang, K. Zhu, Z. Zhou, and T. Ristaniemi, “Service provisioning with multiple service providers in 5G ultra-dense small cell 