1. Adaptive Roaming between LTE and Wi-Fi 1 Daeguil Science high school, Daegu, Republic of Korea. 2 Daegu Gyeongbuk Institute of Science and Technology, Daegu, Republic of Korea. Abstract Introduction. Methods Results Discussion References (3GPP Release 8/ Category 5) Peak download rates up to 299.6 Mbit/s and upload rates up to 75.4 Mbit/s depending on the user equipment category (with 4x4 antennas using 20 MHz of spectrum). Five different terminal classes have been defined from a voice centric class up to a high end terminal that supports the peak data rates. All terminals will be able to process 20 MHz bandwidth. Low data transfer latencies (sub- 5 ms latency for small IP packets in optimal conditions), lower latencies for handover and connection setup time than with previous radio access technologies. Improved support for mobility, exemplified by support for terminals moving at up to 350 km/h (220 mph) or 500 km/h (310 mph) depending on the frequency band. (http://en.wikipedia.org/wiki/LTE_(telecommunication)) ■ Purpose of the research ■ Background Knowledge MAC Layer Power Control PHY Layer Wi-Fi transmit RF power with normal 15dBm. (FCC, CE, KC Regulation: <20dBm in ISM Band) FMDA, TDMACSMA-CA Recently, according to high smartphone distribution rate, the amount of used wireless data is increased. Smartphone can use Wi-Fi and cellular system for data communication. In detail, Wi-Fi include 802.11b, g, a, n, and ac and cellular system include 3G, LTE, and LTE-A in accordance with communication speed. One of the advantage of Wi-Fi is free by using ISM(industrial scientific and medical) band. On the other hand, cellular system is not but it has wide coverage rage and stable communication. Base mechanism of smartphone associated with roaming between Wi-Fi and cellular system is that if Wi-Fi is detected than data communication carry out by Wi-Fi or else, smartphone use cellular system. In this situation cannot meet various user’s demand. For example, one user receive bad service such as low speed, long delay when connect with weak Wi-Fi access point although user has enough capacity for cellular communication. As well a participant or traveler is interested in long battery life. In this case, energy efficiency communication method is preferred. In this research deal with method of roaming to meet various need and propose roaming strategy. We also carry out real test by using network test equipment and Samsung Galaxy Note2 and just consider LTE and 802.11n. Because these are most widely used. LTE and Wi-Fi are most widely used wireless communication method in the smartphone. Until now, Wi-Fi has been preferred because of free. But these days, LTE has a variety of payment system and there are various user demands such as fast data speed, long battery life, and short delay. Therefore we need efficient roaming strategy between LTE and Wi-Fi with consideration for these demands. This research purposed new roaming strategy considering user type and their needs. To reliability for this strategy, we carry out real measurement LTE and Wi-Fi throughput, power consumption, and delay depending on receive signal sensitivity. We look forward to this research will be one step to advance of smartphone. Keyword: Wi-Fi, LTE, Roaming, Smartphone. Long battery life: In this case, we can divide two application types. One is most downlink application and another is most uplink application. If you use most downlink application, we do better to use the Wi-Fi. On the other hand, when you use most uplink application, than LTE is better until -65dBm. After -65dBm, Wi-Fi is better. Fast network speed: As you can see, until down link -73dBm and uplink -68dBm, LTE and Wi-Fi are almost same performance. But after that LTE offer better fast network speed. This test scenario is special case. Because Wi-Fi client device is just one and we use LG U+ LTE network in particular space. If the number of Wi-Fi client device is increased, Wi-Fi speed will be down. Also, LTE speed will be down in the downtown. So, we will more study for generalization. There is tow way. One is making special MAC protocol. For example, Wi-Fi AP(access point) inform number of its client in the beacon frame and LTE base station inform allocated speed to client. Another way is heuristic method. Considering many scenario, we can fine optimal point. Norman, Terry. "The road to LTE for GSM and UMTS operators." Analysys Mason Ltd., White Paper (2009). Bianchi, Giuseppe. "Performance analysis of the IEEE 802.11 distributed coordination function." Selected Areas in Communications, IEEE Journal on 18.3 (2000): 535-547.