Study Of Throughput Evaluation Modelling And Network Performance In WLAN-over-fiber Distributed Antenna System

Distributed Antenna Systems (DASs) using radio-over-fiber (RoF) links have been long recognized as a commonly used infrastructure solution due to its transparency, broad bandwidth and low attenuation features. In this theis, we aimed at the wide application request of the wireless access solutions in large-scale in-building scenarios. Several key technologies are discussed in this paper, such as the throughput modelling and network performance in WLAN-over-fiber distributed antenna systems. Efficient evaluation mechanism and solving methods are provided. The innovative works of the thesis are listed as follows:1. In simulcast distributed antenna systems with RoF links, IEEE 802.11 Distributed cooperation function (DCF) protocol will face greater challenges compared to the tranditional wireless environment. In this thesis, we take into account the inter-RAU hidden node problem and different fiber length effect in the performance analysis of a simulcast WLAN-RoF-DAS and derive a new two-dimensional Markov chain analytical model to evaluate the IEEE 802.11 DCF performance in terms of network throughput. Both basic access mode and RTS/CTS access are considered in this thesis. Using simulation and experiment method, the effect of different user number, different fiber length difference are discussed in the proposed system. With the developed model, the investigations can greatly assist the network designer to evaluate the network performance quickly and choose a better access mode easily.2. In order to solve the the inter-RAU hidden nodes problems and the access fairness problem, two promising methods for alleviating collisions in the uplink are provided for simulcast DAS architecture. The fist one is a new MAC protocol-adaptive PCF mechanism. The adaptive PIFS parameter is provided to consider the fiber length effect. Another method is a detection-swithcing (D-S) assisted DCF method based on the popular Basic mode. Both methods are discussed under different user number, different network payload, different fiber length and different fiber length differnet. The adaptive PCF and D-S methods were compared with DCFs in basic-access and RTS/CTS modes. It is shown that both of the two methods are promising mechanisms for simulcast RoF-DASs. The two methods can achieve 25.61% and 36.76% throughput improvement via RTS/CTS mode respectively.3. D-MIMO system can achieve a improvement of system capacity and throughput performance with large antenna separation. However there are some limits of D-MIMO system, such as the fiber-length difference effect and received power imbalance problem. The results show that MIMO signals can maintain high throughput performance when the fiber length difference between the two RAUs was under 100m (0.5μs) but fell quickly when the fiber length difference was greater than this. Then, with regard to the effect of power imbalance of MIMO signals in a RoF-based DAS, results indicate that the throughput performance drops in specific positions when the received power imbalance is above 12-15dB. The DAS architecture inherently provides dynamic resource allocation and effective management of network elements. Both the analysis of fiber-length difference effect and the received power imbalance problem can greatly assist the CU to make allocation decisions.