As the rapid development of network technology, Internet has become an integral part of our lives. With the popularity of smart mobile devices, surfing the Internet anytime, anywhere has become a kind of necessity for the modern life. How to combine the coming mobile communication technologies with other existent technologies to support modern networking services in mobile networks is one of the major issues.
The 4G LTE-A (Long Term Evolution - Advanced) standard developed by 3GPP organization is the main trend of the future wireless mobile communication industry. The 4G LTE-A standard adopts small cell as well as unlicensed spectrum (5.8GHz LTE-U) to offload heavy traffic from licensed band to unlicensed band. Such major technology is known as Licensed Assisted Access (LAA) technology. On the other hand, the development of IEEE 802.11 standard has been matured everywhere. All IEEE 802.11 products use CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) with request-to-send/clear-to-send (RTS/CTS) protocol to solve contention and hidden-node problems. Therefore, the LTE-U shall have the new mechanism to coexist with pervasive IEEE 802.11 products. In other words, how to avoid the effects of operating LAA on unlicensed band, where there are IEEE 802.11 products, is the research objective of this thesis.
The Listen-Before-Talk (LBT) procedure is the main procedure for LAA to accomplish fair and friendly coexistence with other operators or technologies operating over unlicensed spectrum. However, lacking the Layer 2 RTS/CTS protocol with the other existing systems, it is uneasy to solve the hidden-node problem (HNP). Intuitively, the drawback of hidden-node problem may be the advantage of exposed node problem (ENP) where the transmitters which are not hidden to each other can simultaneously transmit if corresponding receivers are hidden nodes to each other. In order to fully understand the essential problem of coexistence issue between LAA and Wi-Fi systems, we have done the thorough analyses on hidden-node and exposed-node probabilities by means of mathematical approach. Analytical results surprisingly reveal that the exposed-node probability is as high as 39.33%. In order to avoid the collision caused by the HNP and retrieve the bandwidth which is being sacrificed by the ENP, this thesis aims to propose the compliance solution(s) for LBT mechanism in order to optimize the overall system performance.
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