Hyunduk Kang

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.

Coexistence between 802.22 and 802.11af over TV white space

Using OPNET simulation we evaluate performance of 802.22 system operating over TV white space when 802.11af system coexist with 802.22 system at a given geo-location considering co-channel interference. To do that, we consider coexistence scenario that 802.11af system is located near 802.22 base station (BS) or customer-premises equipment (CPE). We compare upstream and downstream performance of 802.22 system. Upstream performance of 802.22 system is heavily degraded when 802.11af system exists near 802.22 CPE due to significant loss of upstream MAP data at 802.22 CPE.

Analysis of asynchronous FFH-MA systems with a hard-limited combining in Rayleigh fading

The bit error rate (BER) performance of the asynchronous fast frequency hopping multiple access (AFFH-MA) system with multiple hops per symbol is investigated considering the noncoherent M-ary frequency shift keying (MFSK) modulation and hard-limited linear combiner in Rayleigh fading. We present a method for the accurate evaluation of the BER of the AFFH-MA system, and verify the analytic works by Monte Carlo simulations.

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.

Dynamic priority scheduling for heterogeneous cognitive radio networks

In cognitive radio networks (CRNs), secondary networks (SNs) are regulated in order to prevent them from accessing a channel if primary networks (PNs) are currently occupying the channel. However, there not exists any regulation how to coordinate the channel access among multiple heterogeneous SNs. In this paper, we consider a centralized approach to explicitly coordinate the channel accesses among SNs coexisting in the same CRN; these SNs can exchange channel information through a coexistence manager (CM). We propose a channel access scheduling scheme that differentiates the quality-of-service (QoS) by assigning priority values and provides a certain level of fairness by taking the queue waiting time into consideration. Through various simulations, we show that the proposed scheme achieves the QoS differentiation among contending SNs while improving both the throughput and fairness performance in CRNs.

Making the Best out of Spectral Efficiency; Studies on The Introduction of Open-Spectrum Policy

Open spectrum policy mostly deals with the shared-use of spectrum resources which again utilizes the orthogonality in different spectral domains - geography, space, power, frequency and time. Among these, temporal share of the spectrum, known as CR or cognitive radio technology, allows secondary licensees to opportunistically access the spectrum during the absence of the first. This paper provides the analysis on the performance of CR implementations in IEEE 802.22 WRAN system, in terms of the spectrum utilization rate, along with simulation results. Also discussed are the regulatory issues in introducing open spectrum policies into the market, centered on the reuse of spectrum resources.

A multi-channel assignment for wireless networks with a limited number of channels

In multi-channel wireless networks, the interferences due to simultaneous transmissions of neighboring nodes can be reduced by assigning different non-overlapping orthogonal channels to sender-receiver pairs that may interfere with each other. However, if the number of non-overlapping channels is smaller than that of interfering nodes, we cannot avoid assigning the same channels to adjacent interfering nodes. We propose a multi-channel assignment algorithm for wireless networks with a limited number of multi-channels. It attempts to minimize the geographically overlapped areas among interference circles (defined as “guard zones”) of neighboring nodes. Through extensive simulations, we show that the proposed algorithm improves the aggregate throughput performance by fully exploiting the multichannel diversity even though the number of non-overlapping channels is not sufficiently large.

Performance Analysis of Asynchronous FFH-MA Systems with a Linear-Combining Receiver in Rayleigh Fading

The performance of asynchronous fast frequency hopping-multiple access (AFPH-MA) systems with multiple hops per bit is investigated with a linear-combining receiver in Rayleigh fading. We present an accurate approximation method for evaluating the error probability by using the characteristic function, Taylor series, and Gauss-Chebyshev quadrature rule. We will show that the proposed method provides an accurate approximation, compared with a simple Gaussian approximation. The validity of proposed analytic works is verified through Monte Carlo simulations.

A channel allocation method for IEEE802.19.1 coexistence service to mitigate interferences among heterogeneous wireless networks

IEEE 802.19.1 is the world first standard that specifies coexistence methods by means of exchanging messages between 802.19.1 coexistence system and wireless systems registered to the coexistence system. We propose a channel allocation mechanism for 802.19.1 management service. The mechanism mainly depends upon channel classification where the CM manages channel availability information based on TV channel classification and events on channel set transitions. Based on coexistence scenario, we evaluate performance of interference mitigation between 802.11af APs and 802.22 BSs with 802.19.1 management service. We compare throughput at 802.11af STA and 802.22 CPE with 802.19.1 management service through OPNET simulation. It is demonstrated that significant throughput enhancement on CPE of 802.22 BS with 802.19.1 management service using the proposed mechanism.

Power control for cognitive users in coexistence with CSMA-based primary networks

Cognitive radio networks are an emerging paradigm for intelligent networks to resolve the spectrum under-utilization problem, as they allow cognitive users to utilize frequency bands assigned to primary users. In this paper, we consider the transmit power control of a secondary transmitter when a primary user accesses a wireless channel through a carrier sense multiple access (CSMA) mechanism. In this case, the transmit power of the secondary transmitter should be adjusted in order to prevent the transmissions of the primary user from being deferred under the CSMA mechanism.