License Assisted Access (LAA) LTE (LAA-LTE) is a new type of LTE that aggregates the licensed LTE bands with the unlicensed bands via carrier aggregation. To operate in unlicensed bands, LAA-LTE adopts the listen-before-talk policy and designs its channel access mechanism similar to WLAN's DCF. This paper considers an LAA-LTE eNB coexisting withasymmetric hiddenWi-Fi APs where the eNB can detect the APs while the APs cannot, which is caused by the asymmetric CCA thresholds. The behavior of such a network is modeled by a joint Markov chain (MC), using which steady-state probabilities, throughput, and channel access delay are derived analytically. An extensive evaluation confirms that the proposed analysis correctly models the dynamics of LAA-WLAN coexistence, and identifies important design guidelines for fair coexistence as follows. First, LAA-LTE should enable channel access priority class 4 to exploit its large contention window (CW). Second, LAA-LTE should re-design its CW doubling policy to restore the balance between LAA-LTE and WLAN in throughput and channel access delay. Third, to protect Wi-Fi, the maximum CW stage should be used more times by increasing the retry count.

In this paper, we study a contention-based beam search procedure for directional communication in a Millimeter wave (mmWave) cellular network. A beam search procedure is required for directional alignment/spatial synchronization between the base station (BS) and a user Equipment (UE) to get beamforming (BF) gain in the mmWave communication. We propose a beam search procedure, which is performed by BS and multiple UEs to establish physical link based on contention in the initial access phase, without any prior knowledge and feedback channel. The proposed scheme enables multiple UEs to perform beam search procedures with the BS simultaneously. Also that enables the BS to select multiple UEs and corresponding beam pairs that can maximize the achievable sum rate.