Igor Kim

Distributed implicit interference alignment in 802.11ac WLAN network

Recently, the demand for wireless service is highly increased because of many smart devices. Many people want to access the internet by using 802.11 WLAN network as of free service. So, a lot of APs are deployed in many places such as home, office and store. Because anyone can install the AP in any place, APs or STAs are suffered the interference between them. This interference makes whole WLAN network performance to be poor quality. The main reason existing the interference is that a huge number of AP and STA is deployed. To solve this situation, 802.11 standard has established a new study group (SG), high efficiency wireless (HEW) local area network. This SG want to enhance the area throughput which is the average throughput in a specific area. We think average throughput is mainly effected by the inter cell interference which is the interference from other APs or STAs. And average throughput is proportional to the sum rate of each node in a specific region. In this paper, we develop three different downlink interference management approach which is so called distributed interference alignment algorithms. To apply these algorithms in the 802.11 WLAN, we think there are some key points which are distributed processing between nodes, only local channel state information usage, linear processing and IA adaptation possibility for the number of general users. Our algorithms displayed in this paper are followed by above assumptions. And we show the performance comparison between our algorithms.

Overlapping BSS interference mitigation among WLAN systems

Using OPNET simulation we evaluate performance of interference mitigation of wireless local area network (WLAN) systems by means of message exchange based approaches when basic service sets (BSSs) of WLAN systems are overlapped. To do that, we consider 802.11af systems that utilize registered location secure server (RLSS). RLSS provides channel schedule management (CSM) that enables 802.11af access points (APs) to schedule operating channel use in order to mitigate OBSS interference. We also consider 802.11af systems that take advantage of knowledge of neighbor discovery and radio environment information provided by 802.19.1 system, called 802.19.1 coexistence information service. In case of 802.11af system without 802.19.1 system, performance of OBSS interference mitigation is heavily affected by each OBSS APs radio environments based on awareness of co-channel sharing situation with harmful interference that initiates CSM. It is demonstrated that 802.19.1 coexistence information service enables 802.11af APs to facilitate the channel with negligible harmful OBSS interference.

Delay model of multicast protocols co-existing with legacy unicast in IEEE 802.11 wireless local area network

Reliable and QoS-aware multimedia delivery is one of the most important requirements to satisfy end user needs. IEEE 802.11 networks have become one of the most popular Internet access methods owing to their low-cost and fast connection speed. Multicasting is a transmission technique that can significantly increase network efficiency through the simultaneous delivery of the same multimedia content to multiple multicast group members. IEEE 802.11 describes several multicast protocols targeted to increase the robustness of audio and video delivery. Some researchers have investigated the performance of such multicast protocols in terms of their achievable throughput. However, for a better understanding of the suitability of the protocols for a QoS-aware multimedia transmission, an in-depth analysis of the achievable delay is needed. This study provides a detailed delay analysis and describes analytical models for estimating the average achievable delay of IEEE 802.11 multicast protocols co-existing with legacy stations. The proposed analytical models are compared against simulation results under various conditions and parameter configurations. The simulation results validate the accuracy of the proposed models.

Performance comparison of backoff protocols and their co-existence with legacy WLAN

This paper describes the performance analysis of several existing backoff algorithms in terms of achievable throughput and short-term fairness. Through the performance evaluations conducted by the event-driven simulator we show the tradeoff of the maximum achievable throughput and short-term fairness. According to our investigations controlling the growth rate of contention window (CW) can make notable steps towards improvement of short-term fairness. Performance evaluations in co-existence scenarios with the legacy IEEE 802.11 WLAN also indicate that none of the existing schemes can fairly co-exist with the legacy backoff.

Maximum throughput and fairness aware backoff considering co-existence with legacy WLAN

This work presents a new backoff algorithm, namely Maximum Throughput and Fairness aware Backoff (MTFB), for IEEE 802.11 wireless LANs. The algorithm adaptively adjusts the contention window (CW) size so that the maximum throughput and fairness can be maintained even with large number of active stations (STAs). In mixed environments with the legacy 802.11 devices the algorithm is able to keep the predefined achievable throughput ratio and provide harmonious co-existence. Performance evaluations conducted in the event-driven simulator validate the accuracy of the mathematical model and show that MTFB outperforms existing proposals.

Interference mitigation among neighbor APs using 802.19.1 coexistence service: Information service vs. management service

IEEE 802.19.1 coexistence system provide two types of coexistence service: information service vs. management service. Information service provides radio environment information that enables 802.11af APs to facilitate channels with its neighbor APs. Each AP determines its operating parameters by itself to mitigate interference using the information. On the other hands, with management service, coexistence manager (CM) determines optimum operating parameters for each AP based on its coexistence decision making. We propose an operating channel selection mechanism for 802.19.1 management service and evaluate performance of interference mitigation among neighbor 802.11af Wireless Local Area Network (WLAN) access points (APs). Using OPNET simulation we compare SNR, BER, and packet drop at 802.11af APs based on BSS coexistence scenario with two services. It is shown that performance of OBSS interference mitigation with management service is superior to that with information service.

Performance evaluation and enhancement of scheduled and polled block ACK multicast protocols

IEEE 802.11aa amendment introduces several protocols to increase the robustness of multimedia traffic delivery for multicast destinations. According to the recent investigations Block ACK protocol is the most efficient among them. However, it requires polling to each of the multicast group member which may cause significant overhead in the scenarios with large group size. Compared to the polling based Block ACK protocol the scheduled Block ACK protocol does not require individual polling to each group member. In this paper we compare two protocols in terms of scalability, achievable throughput, and delay in various scenarios. In addition, we introduce a frame error based RTS/CTS protection scheme which improves the performance of both schemes in hidden node scenarios. Performance evaluations show that the proposed protection scheme significantly alleviates the hidden node problem in scheduled Block ACK protocol.