Jinhyung Oh

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.

Protocol design for interference alignment in 802.11 WLAN interfering network

Nowadays, a huge number of WiFi devices are distributed in anywhere place. Because tremendous WLAN devices are transmitting in ISM bands, the interference problem has emerged as an important issue. The simple method to solve the interference problem is to avoid to the other vacant operating channel. However, current ISM band might be already shortage because of operating many WiFi devices. So, the researches about interference management like interference alignment (IA) which multiple nodes can simultaneously transmit in the same frequency band without interfering each other have received much attention. Most of the IA algorithms have researched to just obtain the precoding and decoding vector. To operate the IA algorithms in the real system such as 802.11 WiFi network or LTE cellular network, however, the operational procedure to function IA transceiver design is also needed. So, we propose a novel IA functional sequence protocol with our IA developed algorithm and evaluate the throughput considering protocol overhead.

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.

MIMO/multi-channel RF transceiver for Cognitive Radio system

Cognitive Radio (CR) technology is one of the favorable technology to efficiently deploy the underutilized frequency spectrum. Currently, the Federal Communications Commission (FCC) allowed TV white space (TVWS) which should protect the licensed user communication to utilize for data communication. The first actual deployment of communication system operating on TVWS is implemented in our group. However, it operates in SISO and single-channel procedure. So, we will develop a second version test-bed operating various modes such as SIMO, 2×2 MIMO and multi-channel communications. From these diverse operation methods, we expect that data rate is enhanced. In this paper, we will introduce a CR RF transceiver which is equipped in our second version of test-bed based on ECMA-392 international standard.

A Distributed Interference Management for Crowded WLANs: Opportunistic Interference Alignment

Wireless local area networks (WLANs) are becoming denser and thus interference-limited due to heavy traffic from a number of adjacent access points (APs) and stations (STAs). We propose a novel interference management technique for overlapping basic service sets (OBSSs) in such WLANs, which intelligently applies an opportunistic interference alignment (OIA) concept to WLANs. Each BSS has an AP and multiple STAs, and operates with a carrier sensing multiple access (CSMA) protocol as commercial IEEE 802.11 WLANs. Both APs and STAs are assumed to have multiple antennas. Specifically, the proposed OIA framework consists of physical (PHY) and medium access control (MAC) layer techniques: transmit beamforming and opportunistic medium access, respectively. First, each STA performs transmit beamforming which minimizes generating interference to other BSSs at the PHY layer. Second, each STA sends packets to its serving AP only when its generating interference to other BSSs is smaller than a pre-determined threshold at the MAC layer. Through extensive simulations, we show that proposed OIA scheme significantly outperforms existing schemes in terms of system throughput. Note that the OIA scheme operates with a distributed manner based on local channel state information at each STA and does not require any coordination among BSSs, leading an easier implementation in practice.

Partial band interference alignment for overlapped WLAN channel allocation

Nowadays, the request for wireless services is greatly exploded to receive a good services from internet. So, many APs for WLAN are thoughtlessly deployed in various places. At this environments, inter-basic service set (BSS) interference might be happened. If the APs locating in same overlapped region are operated in the same channel, the CSMA/CA is well worked, that is multiple APs are operated by dividing the transmission time. However, if the APs placing in same overlapped area is worked in the partially overlapped bandwidth, CSMA/CA protocol cannot be functioned due to different transmit channel. At this case, each WLAN nodes are suffered partial band interference each other. In this paper, we suggest a new-typed procedure of the neighbor interfering AP discovery for implementing the IA and a novel IA algorithm for mitigating the partially overlapped subcarrier interference. By applying this proposed approach into IEEE 802.11 WLAN system, we expect the robust transmission and spectrally efficient gain. And we will verify the performance of our approach by suggesting the simulation result.

Performance comparison of cooperative downlink transmission schemes in IEEE 802.11ac: Interference alignment vs. MU-MIMO with TDMA

Recently, demand for high data rate of wireless service is increased due to full high definition (HD) video transmission and cloud services and so on. To enhance the capacity, many APs are installed in various places. Because of multiple APs are deployed in unplanned situation, interference between basic service set (BSS) is increased. To reduce the overlapped BSS (OBSS) interference of IEEE 802.11ac interfering broadcasting network, we suggest two cooperative transmission schemes which are interference alignment (IA) and multi-user multi-input and multi-output (MU-MIMO) with time division multiple access (TDMA). We can simultaneously transmit the data in the same time and frequency with IA, however, the required overhead of transmission for IA is considerably high. However, MU-MIMO with TDMA scheme needs lower overhead than IA because only channel state information (CSI) feedback of a desired link from AP to STA and AP Poll transmission which decides the timely transmission order for MU-MIMO with TDMA. Even though there are a few feedback quantity for MU-MIMO with TDMA, the average throughput will be reduced because the data should be transmitted by dividing the time. Therefore, we have observed the average throughput between IA and MU-MIMO with TDMA in IEEE 802.11ac interfering downlink network. And we also compare the performance between two cooperative downlink transmission schemes.

Measurement and analysis for 3.5GHz small-cell environment with time and spatial ratio

Recently, researches regarding spectrum sharing has been underway due to the insufficiency of spectrum resources. Basically, it is necessary to solve the temporal or spatial environment in order to share the frequency. In this paper, we will introduce to our own channel sounder and we use this system to generate path loss modelling based on time and space ratio.

A wireless channel sounding system for 3.5GHz band small-cell environmental measurements

Recently, 3.5GHz band is determined as mobile communications frequency in IMT-2020. Basically, TD-LTE in small-cell environment and downlink supplement in hotspot area can be utilized in 3.5GHz band. According to this latest trends, channel sounder for 3.5GHz band is harmoniously implemented by universal devices such as NI equipment for baseband and transceiver and self-developed modules which are high power amplifier, RF switch, timing module and antenna. From this channel measurement system, we obtain the various measurement parameters through real wireless channel measurement in urban and suburban areas for 3.5GHz band.

The practicality of interference alignment with measured IEEE 802.11ac wireless channels

Interference is known to cause the performance degradation of the wireless network. To solve the interference problem, cooperative transmission scheme such as interference alignment (IA) is required. Channel state information (CSI) among IA participation nodes should be essentially obtained to implement IA. By implementing the IA prototype with obtaining the real environment CSI, we can check the performance of our developed IA algorithms and compare the IA and non-IA case.