Joint resource optimization for energy efficient full-duplex heterogeneous CRAN system

In this paper, we study a joint resource allocation algorithm for energy efficiency (EE) of a cloud radio access network (CRAN) with full-duplex (FD) remote radio heads (RRHs), which enable simultaneous uplink and downlink communications. To solve the joint optimization problem, we utilize a successive convex approximation (SCA) based joint antenna selection and power allocation (JASPA) algorithm. In addition, we present an improved multi-candidate remote radio heads (RRHs) user association (MCRUA) algorithm. The simulation results show that the proposed joint resource allocation algorithm has a fast convergence speed and a significant gain in the EE for FD CRAN. INTRODUCTION Cloud radio access network (C-RAN) has been considered by both the operators and the equipment vendors for fifthgeneration (5G) mobile networks to reduce both capital and operating expenditures [1], [2]. C-RAN has been shown to provide high spectral efficiency and energy efficiency (EE). In C-RAN, the baseband unit (BBU) is located in the center of a cell, and is connected to remote radio heads (RRHs) through optical transmission network. The BBU acts as a digital unit implementing the base station functionality from baseband processing to packet processing. The RRHs perform radio functions which include frequency conversion, amplification, and A/D and D/A conversion. The RRHs send/receive digitalized signals to/from the BBU pool via optical fiber, and antennas are equipped with RRHs to transmit/ receive radio frequency (RF) signals. The basic idea of the C-RAN is that the transmission distance between antennas and mobile users (MUs) is reduced, so that significant improvement to the EE are achieved. From the viewpoint of green information technology, the EE has recently attracted more attention. Thus, the resource allocation for EE maximization has attracted considerable attention. However, most existing works on resource allocation for the EE of C-RAN have been considered as the separated optimization problems operating on the traditional half duplex (HD) communication systems [3], [4]. Nowadays FD radios have emerged as an attractive solution to increase the throughput of wireless communication systems [5], [6]. FD transmission allows downlink and uplink transmission to occur simultaneously at the same frequency. FD radios have the potential to double the spectral efficiency of conventional HD communication systems. In this paper, we study a resource allocation algorithm to maximize the downlink EE in FD C-RAN by solving a joint optimization problem. To solve the complex joint optimization problem, we utilize a successive convex approximation (SCA) based joint antenna selection and power allocation (JASPA) algorithm [7]. Furthermore, we present an improved multicandidate RRHs user association (MCRUA) algorithm. This algorithm utilizes the tabu search technique [8], [9] to obtain the appropriate large-scale fading threshold (LSFT) for EE improvement. Finally, we present a joint resource allocation algorithm with fast convergence which is based on the Dinkelbach method [10] for solving nonlinear fractional problems. SYSTEM MODEL A C-RAN system with L hexagonal cells is considered. In each cell there are N FD RRHs and K MUs are uniformly distributed. The K MUs use single antenna HD mobile communication devices to have low hardware complexity. , U j K and , D j K users in the -th j cell are scheduled for simultaneous uplink and downlink transmissions, respectively, such that , , U j D j K K K   . We also assume that the n -th RRH in the j -th cell is equipped with jn M antennas and the total number of system antennas in the j -th cell is given by max 1 N jn n M M    . The channel vector between the RRHs in the l -th cell and the k -th MU in the j -th cell is denoted as 1/2 jkl jkl jkl  g Λ h where   T 1 diag [ , , ] jkl jkl jklN N     Λ I , jkln jkln ad    , and T T T 1 [ , , ] jkl jkl jklN   h h h . Here, jkln  represents the long-term path loss between the k -th MU in the j -th cell and the n -th RRH in the l -th cell. jkln d represents the distance between the k -th MU in the j -th cell and the n -th RRH in the l -th cell.  represents the Kronecker product, a is the path loss gain, and  is the path loss exponent. jkln h denotes an 1 ln M  small-scale fading channel vector which contains independent and identically distributed circularly symmetric complex Gaussian random variables with zero mean and unit variance. International Journal of Applied Engineering Research ISSN 0973-4562 Volume 13, Number 2 (2018) pp. 1233-1237 © Research India Publications. http://www.ripublication. com 1234 The minimum mean-square error channel estimation for the channel vector is given by 1 P, ˆ jkl jkl jk jk   g Λ Q y where   max 1 2 P 1 L jk jkl M l       Q Λ I and P, 1 L jk jkl lk l    y g z is max 1 M  received pilot signal. Here, the large-scale fading between the n -th RRH in the l -th cell and the k -th MU in the j -th cell is given by   1/2 2 P 1 L jkln jkln jkln l     