Il-Gu Lee

Interference-aware self-optimizing Wi-Fi for high efficiency internet of things in dense networks

Wi-Fi is one of the candidate technologies for the Internet of Things (IoT), and today connects billions of devices world-wide in dense networks to offer Internet connectivity in a partially or fully automated manner. In order to provide seamless and high quality service, wireless local area networks (WLANs) can adopt dynamic channel access technologies such as dynamic bandwidth or channel hopping schemes in order to avoid interference for better link quality. However, in dense networks, the dynamic channel access leads to a higher probability of adjacent channel interference (ACI). The efficiency of IEEE 802.11-based WLANs using multi-channel and wide dynamic ranges is thus severely degraded by ACIs in dense networks. In this paper, we analyze the ACI effect on WLANs and propose an interference-aware self-optimizing (IASO) Wi-Fi design that incorporates a multi-channel multi-level carrier sense and adaptive initial gain control scheme. This scheme controls carrier sensing thresholds in each band for multi-level sensors, as well as initial gains for amplifiers. The proposed scheme reduces false carrier sensing and avoids saturation of amplifiers while simultaneously improving the dynamic range of the receiver. Our prototype evaluation results demonstrate that the proposed scheme can improve the dynamic range of the receiver by approximately 45dB and 30dB for a low data rate and a high data rate mode, respectively, compared with the conventional receiver designs. Furthermore, network emulation results demonstrate that the IASO Wi-Fi can improve the average throughput, latency, and energy efficiency by approximately 32% (24%), 41% (43%), and 13% (17%), respectively, compared with the conventional receiver designs (and channel hopping techniques) in dynamically varying interfered channel conditions.

Analysis of Power Consumption and Efficient Power Saving Techniques for MIMO-OFDM-Based Wireless LAN Receivers

In this paper, we express the power consumption for the wireless receiver employing multiple antenna technique as a closed form function of the number of antennas, time duration, power dissipation for carrier sensing and data decoding, and the probability of successful carrier sensing. Based on the analytical model, we show that when MAC level power save mode is combined with PHY level power save mode utilizing the correlation based carrier sensing indicator, the proposed cross layer power saving technique improves the power efficiency of the wireless receiver. In this paper, we show that the proposed cross layer method improves power at about 15% and 7% efficiency compared to MAC level and PHY level power save mode, respectively.

IAPS: Interference Aware Power Saving for High-Efficiency Wireless LANs in Dense Networks

Battery-driven circuit design for power saving wireless local area networks (WLANs) has become more and more important because mobile devices and applications are required to support high throughput in wide service coverage and, at the same time, exhibit long battery lifetime. However, in dense networks, multiple and dynamic channel access leads to a higher probability of co-channel and adjacent channel interference. Therefore, the energy efficiency of IEEE 802.11-based WLANs is severely degraded by such interference. In this letter, an interference-aware power saving (IAPS) mechanism is proposed. The IAPS incorporates a signal quality and interference measurement process for determining link quality based on the incoming signal from a receiver. In the IAPS, the signal field decoding process is used to determine the required link quality for the received signal, and a physical layer power saving control based on the estimated link quality and the required link quality is implemented. The proposed IAPS technique achieves 29% and 26% average energy efficiency improvement over the conventional scheme and the channel hopping scheme, respectively.

Robust wireless transmission utilizing PPDU-based aggregation technique for next generation wireless LANs

In this paper, we propose a robust transmission scheme using aggregated physical protocol data units (APPDU). The proposed method includes a media access control (MAC) layer control for determining the number of preambles to be inserted based on the feed-back reply signal from a receiver; the generation of a multi-preamble aggregation frame by inserting the determined number of preambles into frames received from an upper layer; a physical layer for forming the multi-preamble aggregation frame generated in a data processing unit by using a physical layer frame; and the transmission of the formed multi-preamble aggregation frame. The proposed technique obtains performance improvement of about 3 dB in terms of SNR and 35% in terms of throughput efficiency.

Persistent jamming in wireless local area networks: Attack and defense

Abstract Wireless local area networks (WLANs) can adopt channel hopping technologies in order to avoid unintentional interferences such as radars or microwaves, which function as proactive jamming signals. Even though channel hopping technologies are effective against proactive types of jamming, it has been reported that reactive jammers could attack the targets through scanning busy channels. In this paper, we demonstrate that reactive jamming is only effective against channel hopping WLAN devices in non-dense networks and that it is not effective in dense networks. Then, we propose a new jamming attack called “persistent jamming”, which is a modified reactive jamming that is effective in dense networks. The proposed persistent jamming attack can track a device that switches channels using the following two features, and it can attack the specific target or a target group of devices. The first feature is that the proposed attack can use the partial association ID (PAID), which is included for power saving in the IEEE 802.11ac/af/ah frame headers, to track and jam the targets. The second feature is that it is possible to attack persistently based on device fingerprints in IEEE 802.11a/b/g/n legacy devices. Our evaluation results demonstrate that the proposed persistent jamming can improve the attack efficiency by approximately 80% in dense networks compared with the reactive jamming scheme, and it can also shut down the communication link of the target nodes using 20xa0dBm of jamming power and a 125xa0ms response time. In order to defend against the persistent jamming attack, this paper proposes three defense mechanisms for anti-tracking and anti-jamming; a digital fingerprints predistortion, dynamic ID allocation, and dual channel friendly jamming. The experimental results demonstrate that the proposed defense mechanisms are feasible and effective to significantly decrease the device tracking success ratio of the persistent jamming attack.

AMONET: A method for detecting and mitigating the data rate degradation due to interference over wireless networks

Recently, wireless networking technologies have been evolving to support wider bandwidth, and longer radio range in denser networks. Therefore, there is a high probability that two or more networks will overlap and result in more co-channel interferences. To mitigate the interference, the centralized network system is a promising solution which is based on the conflicts information provided by the interference detection methods. However, in this paper, we reveal that the existing Passive Interference Detection method (PIE) is not accurate and may cause dramatic throughput decrease in dynamically interfered networks because it is based on a single data rate criterion. Moreover, we propose and implement AMONET, which is a centralized detection method considering the data rate degradation due to interference (DRDI). Our simulation results demonstrate that the proposed scheme can improve aggregate throughput by 2.68x gains in the interfered wireless links over distributed coordination function (DCF), while PIE achieves 1.8x gains over DCF.

Interference-Aware Self-Optimizing Carrier Sensor for High Efficiency Wireless LANs in Dense Networks

Wireless local area networks (WLANs) can adopt dynamic channel access technologies such as dynamic bandwidth or channel hopping schemes in order to avoid interference for better link quality. However, in dense networks, the dynamic channel access leads to a higher probability of adjacent channel interference (ACI). The efficiency of IEEE 802.11-based WLANs using multi-channel and wide dynamic ranges is thus severely degraded by ACIs in dense networks. In this paper, we analyze the ACI effect on WLANs and propose an interference-aware self-optimizing carrier sensor design that incorporates a multichannel multi-level carrier sense and adaptive initial gain control scheme. This scheme controls carrier sensing thresholds in each band for multi-level sensors, as well as initial gains for amplifiers. The proposed scheme reduces false carrier sensing and avoids saturation of amplifiers while simultaneously improving the dynamic range of the receiver. Our prototype evaluation results demonstrate that the proposed scheme can improve the dynamic range of the receiver by approximately 45 dB and 30 dB for a low data rate and a high data rate mode, respectively, compared with the conventional receiver designs. Furthermore, network emulation results demonstrate that the proposed scheme can improve the average throughput and latency by approximately 32% (24%) and 41% (43%), respectively, compared with the conventional receiver designs (and channel hopping techniques) in dynamically varying interfered channel conditions.

Run Away If You Can: Persistent Jamming Attacks against Channel Hopping Wi-Fi Devices in Dense Networks

Wireless local area networks (WLANs) can adopt channel hopping technologies in order to avoid unintentional interferences such as radars or microwaves, which function as proactive jamming signals. Even though channel hopping technologies are effective against proactive types of jamming, it has been reported that reactive jammers could attack the targets through scanning busy channels. In this paper, we demonstrate that reactive jamming is only effective against channel hopping Wi-Fi devices in non-dense networks and that it is not effective in dense networks. Then, we propose a new jamming attack called “persistent jamming”, which is a modified reactive jamming that is effective in dense networks. The proposed persistent jamming attack can track a device that switches channels using the following two features, and it can attack the specific target or a target group of devices. The first feature is that the proposed attack can use the partial association ID (PAID), which is included for power saving in the IEEE 802.11ac/af/ah frame headers, to track and jam the targets. The second feature is that it is possible to attack persistently based on device fingerprints in IEEE 802.11a/b/g/n legacy devices. Our evaluation results demonstrate that the proposed persistent jamming can improve the attack efficiency by approximately 80% in dense networks compared with the reactive jamming scheme, and it can also shut down the communication link of the target nodes using 20 dBm of jamming power and a 125 ms response time.

Development of 3.6 Gbps RF Transceiver for Wireless Nomadic Local Area Networks

We present high data rate wideband transceiver design and experimental evaluation for 3.62 Gbps wireless transmission systems in this paper. The present system provides high definition moving picture and contents in a real-time wireless environment at home, offices or class rooms of universities. Also, the present platform provides a test platform for the Giga level high throughput wireless communication system using the OFDM method and the multiple antennas.