Research On System Throughput Enhancement Considering Fronthaul Capacity Limitation In C-RAN

With the popularity of mobile devices, people like to upload and download high-definition video and files from Internet. As a result, the network demands high-bandwidth, low latency, low power consumption and high throughput. Due to limited spectrum, fixed base station, high energy consumption, the network can not guarantee QoS. A new green radio accesses network architecture named Cloud-Radio Access Network(C-RAN)will effectively improve the spectrum utilization, reduce system energy consumption and enhance the user experience. The C-RAN network consists of a BBU pool consisting of many baseband unit (BBU), fronthaul which made up of a high-speed optical transport network, and large-scale distributed remote radio unit (RRH). By the way, the fronthaul is used to connect RRH and BBU pool and transmit the IQ signal between them. Also the load of fronthaul is obviously increased in contrast to the traditional link.Meanwhile, C-RAN has some problems, such as high transmission load of fronthaul and limited computing resources. So how to make full use of C-RAN system resources to improve throughput needs to be studied. To solve these problems, the current mainstream research compressed transmission signal, offloaded data transmission and cached calculation results. However, how to reduce the load on the forward link, reducing the business delay and thus improve the throughput remain to be studied in detail. Therefore, this paper focuses on computing offloading and optimization of cache allocation. The main contents are as follows:First, a computing offloading algorithm for RRH with limited computational resource is proposed. The core idea of this algorithm is that RRH receives the uplink transmission request of the mobile device, and then offloading the task in the fronthaul to the edge network according to the information about channel state and its remaining computing resources. The algorithm effectively improves the throughput of the network and guarantees the demand of the delay-sensitive task, and enhances the user experience. The algorithm consists of the following steps: First, the RRH receives the uplink transmission request from the mobile terminal in the cell.The RRH then chooses the channel for each mobile device in order to maximize the throughput of the system. In the end, the algorithm achieves Nash equilibrium in finite time, which is close to maximizing the system throughput. The simulation results show that the proposed algorithm achieves better performance than the existing algorithm, reduces the network delay and improves the system throughput.Secondly, a delay-optimized cache allocation algorithm is proposed.The core idea of this algorithm is that the cache architecture of C-RAN network is divided into three buffer layers (BBU layer, RRH layer and user device layer). C-RAN optimizes the allocation of the content blocks of the entire network to each cache layer according to the capacity, delay and other information about each cache layer, thereby reducing the network delay and improving the throughput of the system. The algorithm includes the following steps: First, the system obtains the optimal cache location of each content block according to the popularity of the content blocks in the network and the delay of each buffer layer to the user equipment. The cache then selects the content block storage according to the remaining capacity.Then, according to the state of the transmission channel and the delay of the network, it constantly changes the allocation of the cache until the network to achieve the optimal system throughput. The simulation results show that the algorithm proposed in this paper can reduce the delay of the network and improve the throughput of the network obviously, compared with the random buffer allocation algorithm.