Abstract-Ultra-dense (UD) wireless networks where the number of remote radio heads (RRHs) could exceed the number of served users, and cloud radio access networks (CRAN) where joint signal processing is performed at a central processor (CP) are two promising network architectures for the emerging fifthgeneration (5G) wireless communication systems. By jointly employing a UD network with CRAN, a new appealing network solution is proposed, termed UD-CRAN, which is able to achieve ultra-high-throughput wireless connectivity with scalable deployment cost and processing complexity. In UD-CRAN, a millimeterwave (mmWave) wireless fronthaul is practically favorable to connect a CP with distributed RRHs for information exchange, due to its lower cost and higher flexibility to deploy compared to dedicated wired links from each RRH to the CP. However, unlike wired links, the mmWave fronthaul capacity is limited due to propagation loss, and thus needs to be properly shared among the RRHs. This motivates our study in this paper by considering the downlink transmission in a mmWave fronthaul enabled, orthogonal frequency division multiple access (OFDMA) based UD-CRAN. Due to the line-of-sight nature of mmWave links, we consider that the mmWave fronthaul is shared among the RRHs via time division multiple access (TDMA); while the RRHs jointly transmit to the users on orthogonal frequency subchannels using OFDMA. The joint resource allocation over the TDMA-based mmWave fronthaul and OFDMA-based wireless transmission is investigated to maximize the weighted sum rate of all users. Although the problem is combinatorial and nonconvex, we propose a Lagrange duality based solution, which can be efficiently computed with good accuracy. To further reduce the complexity, we also propose a greedy search based heuristic, which achieves close to optimal performance under practical setups. Finally, we compare the performance of proposed solutions with other benchmark schemes by simulations, which show significant throughput gains of the proposed joint resource allocation approach in mmWave fronthaul enabled UD-CRAN. Index Terms-Cloud radio access network, orthogonal frequency division multiple access, resource allocation, ultra-dense network, millimeter-wave fronthaul.
Stephen and Zhang REF applied millimeter-wave (mmWave) wireless fronthaul links and orthogonal frequency-division multiple-access-based access links.
Joint Millimeter-Wave Fronthaul and OFDMA Resource Allocation in Ultra-Dense CRAN
Computer Science Mathematics