Coexistence of Wi-Fi and LTE-Unlicensed (LTE-U) technologies has drawn significant concern in industry. In this paper, we investigate the Wi-Fi performance in the presence of duty cycle based LTE-U transmission on the same channel. More specifically, one LTE-U cell and one Wi-Fi basic service set (BSS) coexist by allowing LTE-U devices to transmit their signals only in predetermined duty cycles. Wi-Fi stations, on the other hand, simply contend the shared channel using the distributed coordination function (DCF) protocol without cooperation with the LTE-U system or prior knowledge about the duty cycle period or duty cycle of LTE-U transmission. We define the fairness of the above scheme as the difference between Wi-Fi performance loss ratio (considering a defined reference performance) and the LTE-U duty cycle (or function of LTE-U duty cycle). Depending on the interference to noise ratio (INR) being above or below −62 dbm, we classify the LTE-U interference as strong or weak and establish mathematical models accordingly. The average throughput and average service time of Wi-Fi are both formulated as functions of Wi-Fi and LTE-U system parameters using probability theory. Lastly, we use the Monte Carlo analysis to demonstrate the fairness of Wi-Fi and LTE-U air time sharing.

With the exponential growth in mobile data traffic taking place currently and projected into the future, mobile operators need cost effective ways to manage the load of their networks. Traditionally, this has been achieved by offloading mobile traffic onto Wi-Fi networks due to their low cost and ubiquitous deployment. Recently, LTE operating in the unlicensed spectrum has drawn significant interests from mobile operators due to the availability of the unlicensed spectrum. However, the deployment of LTE networks in the unlicensed band poses significant challenges to the performance of current and future Wi-Fi networks. We discuss the LTE and Wi-Fi coexistence challenges and present analysis on performance degradation of the Wi-Fi networks at the presence of LTE.

We propose a wireless optical-mesh network based on optical code-division multiple-access (OCDMA)-coded free-space optical links. The performance of the proposed network under intermediate and strong turbulence channel conditions is investigated for synchronous and asynchronous OCDMA. We show that synchronous OCDMA using complementary Walsh-Hadamard codes operating at a raw bit rate of 622 Mb/s per user can achieve a bit-error rate of 10/sup -9/. This is achievable in channels with strong turbulence and high temporal correlation, or in channels with intermediate turbulence conditions; reasonable conditions based on channel characteristics inferred from the refractive index spectrum. For asynchronous OCDMA using optical orthogonal codes (OOCs), using a lower bound, we show that asynchronous OCDMA using OOCs cannot achieve acceptable performance for the same channel conditions, due to interference limitations.