The exponential growth in indoor data traffic necessitates a massive deployment of small cells, and emphasizes the importance of interference coordination and suppression to realize the full potential of this densification. To be effective however, interference coordination and suppression requires strict time synchronization between the cells. This paper deals with distributed runtime synchronization for Beyond 4G femtocells. A simple random scheduling solution for the clock distribution messages is proposed, as well as different clock update mechanisms. Simulation results for a dense cell scenario with two stripes of apartments show that a 'multiplicative clock update' exhibits an initial large time divergence among neighbor cells, but is able to achieve a lower long-term error floor than 'additive clock update'. Practical implications of the residual time misalignment on the Beyond 4G system design are also addressed.

No abstract

Network synchronization is a fundamental enabler of interference mitigation techniques that are required in ultradense deployment of small cells as targeted by upcoming 5th Generation (5G) wireless system. In this paper, we experimentally evaluate the possibility of acheiving in a distributed manner (i.e. without any external high precision reference clocks) a tight time alignment in a network of small cells. We are considering a software defined radio (SDR) network of 8 nodes, where each node adopts the Universal Software Radio Peripheral N200 (USRP N200) radio boards by Ettus Research, and the ASGARD software platform. Experimental results demonstrate the possibility of synchronizing the timing of the multiple nodes with a few μs precision, despite of the occurrencies of beacon losses.

The Interference Rejection Combining (IRC) receiver can significantly boost the network throughput in scenarios characterized by dense uncoordinated deployment of small cells, as targeted by future 5th generation (5G) radio access technology. This paper presents an experimental study on the potential benefit of IRC receiver in real deployment scenarios. The study is carried out using a software defined radio (SDR) testbed network with four cells, each featuring one Access Point (AP) and one User Equipment (UE) with two antennas. The testbed network was placed in an indoor office and open hall scenarios, respectively. In each scenario, the cells were arranged to characterize the propagation in different spatial configurations. Using the obtained propagation data, we analysed the cases of closed and open subscriber group for the respective scenarios, to compare the achievable throughput with IRC and Maximum Ratio Combining (MRC) receivers. Different frequency reuse schemes were also considered. The throughput results confirm the effectiveness of the IRC receiver in improving the network throughput with respect to the MRC receiver, under the assumption of single stream (rank 1) transmission. Results show average gains up to around 40% and outage gains up to 70% over the MRC receiver. The combination of the IRC receiver and frequency reuse achieves a favourable trade-off between the network throughput and fairness. Overall, due to the direct propagation, the open hall open subscriber group scenario is benefiting the most from the ability of the IRC receiver to cancel a strong dominant interferer.

Next generation wireless networks aim at a significant improvement of the spectral efficiency in order to meet the dramatic increase in data service demand. In local area scenarios user-deployed base stations are expected to take place, thus making the centralized planning of frequency resources among the cells, a non-viable solution. Cognitive Radio (CR) and Dynamic Spectrum Access (DSA) are the research paradigms which are expected to provide the network nodes the capabilities for an autonomous and efficient selection of the spectrum resources. In this paper we present the first experimental activities with the Autonomous Component Carrier Selection (ACCS) algorithm, a distributed solution for interference management among small neighboring cells. A preliminary evaluation of the algorithm performance is provided considering its live execution on a software defined radio network testbed. The obtained experimental results confirm the performance trends obtained from prior simulation studies. The analysis in dynamic environment conditions also allowed identifying the utilization of static thresholds in the decision making process, as a critical aspect for the optimization of network capacity. I.