Wi-Fi Direct, now part of Android smartphones, makes it possible for Wi-Fi devices to communicate directly without passing through an access point. Before starting actual data exchange, two devices should apparently find each other through a device discovery process, called find phase. After identifying the limitation of the legacy find phase, incurring long discovery delay, we propose a simple and efficient scheme, called Listen Channel Randomization (LCR), in order to expedite device discovery. Both the legacy find phase and LCR are evaluated with our elaborate Markov model and ns-3 simulations for comprehensive comparisons. Moreover, we have implemented a prototype of LCR in Android smartphone. Our experimental results reveal that LCR can significantly reduce the device discovery delay, yielding up to 72% delay reduction compared to the legacy find phase.

The emerging 60-GHz multigigabits per second wireless technology enables the streaming of high-quality “uncompressed” video, which has been impossible with other existing wireless technologies. To support such a resource-hungry uncompressed video streaming service with limited wireless resources, it is necessary to design efficient link adaptation policies selecting suitable transmission rates for the 60-GHz wireless channel environment, thus optimizing video quality and resource management. For proper design of the link adaptation policies, we propose a new metric, called expected peak signal-to-noise ratio (ePSNR), to numerically estimate the video streaming quality. By using the ePSNR as a criterion, we propose two link adaptation policies with different objectives considering unequal error protection (UEP). The proposed link adaptation policies attempt to 1) maximize the video quality for given wireless resources, or 2) minimize the required wireless resources, while meeting the video quality. From the link adaptation policies, we provide a distributed resource management scheme for multiple users to maintain satisfactory video streaming quality. Our extensive simulation results demonstrate that the newly proposed variable, i.e., ePSNR, well represents the level of video quality. It is also shown that the proposed link adaptation policies can enhance the resource efficiency while achieving acceptable quality of the video streaming.

With the proliferation of Wi-Fi equipped mobile devices such as smart phones, it becomes even more important to design and implement effective power management schemes for Wi-Fi interfaces so that the battery lifetime can be prolonged. In this paper, we propose an enhancement to the default 802.11 Power Save Mode (PSM), called M-PSM, which exploits additional power-saving opportunities by considering user mobility and detailed traffic condition when making the sleep/wakeup schedules for Wi-Fi interfaces. We have implemented M-PSM in the Madwifi device driver and demonstrated its effectiveness via experiments and trace-based simulations.

In the wireless data systems, automatic repeatrequest (ARQ) is used in order to reliably deliver packets to the upper layer while hybrid ARQ (HARQ) intends to improve the reliability over the air through the combination with other transmission techniques, e.g., modulation and channel coding. While the two functions are complementary to each other, it has been typically recognized as if they work independently at their corresponding layer. However, we note that the retransmission via ARQ is correlated with whether HARQ eventually delivers a packet successfully within a retransmission limit. Capturing this observation, we in this paper introduce a new ARQ feedback scheme called Cross-Layer ARQ (CL-ARQ). CL-ARQ makes use of the acknowledgement of HARQ internally. CL-ARQ not only allows ARQ to operate without explicit acknowledgement, but also improves the reliability combined with existing ARQ protocols. Especially, when the entities in charge of HARQ and ARQ are located far apart geographically, we show that CL-ARQ remarkably outperforms other schemes. Additionally, CL-ARQ is shown to resolve the stall problem, which occurs when the link capacity can not be fully utilized due to the limitation of ARQ window size. We evaluate the performance of CL-ARQ via both analysis and simulations.

While the IEEE 802.11 Wireless Local Area Network (WLAN) became a prevailing technology for the broadband wireless Internet access, new applications such as Internet Protocol (IP) telephony are fast emerging today. For the battery-powered IP phone devices, the standby time extension is a key concern for the market acceptance while today's 802.11 is not optimized for such an operation. In this paper, we propose a novel Idle Mode operation, which comprises paging, idle handoff, and delayed handoff. Under the idle mode operation, a Mobile Host (MH) does not need to perform a handoff within a predefined Paging Area (PA). Only when the MH enters a new PA, an idle handoff is performed with a minimum level of signaling. Due to the absence of such idle mode operation, both IP paging and Power Saving Mode (PSM) have been considered the alternatives so far even though they are not efficient. We develop a new analytical model to comparatively evaluate our proposed scheme. Our numerical results demonstrate that the proposed scheme outperforms the legacy alternatives with respect to power consumption, thus extending the standby time dramatically.