Kyung Geun Lee

A Path Selection Method in IEEE 802.16j Mobile Multi-hop Relay Networks

IEEE 802.16j mobile multi-hop relay (MMR) network provides an attractive solution for the coverage extension and throughput enhancement of IEEE 802.16e network. IEEE 802.16j MMR network needs a method for finding the RS route that minimizes the latency and maximizes the network throughput. In this paper, we propose a path selection method for IEEE 802.16j MMR network. The metrics designed for the path selection, such as link available bandwidth, signal-to-noise ratio (SNR) and hop count will be discussed. We demonstrate the performance improvement with numerical results.

CSPA: Channel Selection and Parameter Adaptation scheme based on genetic algorithm for cognitive radio Ad Hoc networks

The cognitive radio (CR) is evolved as the potential technology to solve the problem of spectrum scarcity and to meet the stringent requirements of upcoming wireless services. CR has two distinct features, the spectrum sensing and the parameter adaptation. The former feature helps the CR to find the vacant spectrum slots/channels in the radio band while the latter mechanism allows it to adjust the operating parameters (e.g. frequency band, modulation and power, etc.) accordingly. The primary user (PU) activity has serious effects on the overall performance of the cognitive radio network (CRN).The CR should vacate the channel if it detects the arrival of the primary user (PU) in order to avoid the interference. The channel eviction/switching phenomenon severely degrade the quality of service (QoS) of the CR user and it is perhaps the key challenge for the CRN. In this paper, we propose the dynamic channel selection and parameter adaptation (CSPA) scheme based on the genetic algorithm to provide better QoS for the CR by selecting a best channel in terms of the quality, the power and the PU activity. The CSPA deals with the problem of channel switchings and it provides better QoS to the CR user. Simulation results prove that CSPA outperforms the existing schemes in terms of channel switchings, average service time, power and throughput.

Spectrum sharing optimization with QoS guarantee in cognitive radio networks

In this paper, we propose an optimized spectrum sharing scheme based on the Hungarian Algorithm to guarantee the quality of service (QoS) for individual cognitive radio (CR) users belonging to different CR cells. The proposed scheme is most favorable for overlapping cells where the users are demanding channels for heterogeneous applications such as chatting, web browsing, or voice and video streaming. The spectrum sharing optimization with the QoS guarantee (SSO-QG) is an optimal scheme that can operate in throughput enhancement mode, high reliability mode and collision avoidance mode based on the weight assigned to the corresponding QoS parameters in accordance with the demands of different applications. Simulation results show that the proposed scheme outperforms the existing schemes in terms of forming the optimal sharing pattern and meeting the stringent QoS requirements fairly enough according to the demands of the cell. Moreover, it reduces collisions with primary users.

Fair, efficient, and power-optimized spectrum sharing scheme for cognitive radio networks

The cognitive radio network (CRN) is a promising solution to the problem of spectrum scarcity. To achieve efficient spectrum utilization, cognitive radio requires a robust spectrum sensing and spectrum sharing scheme. Therefore, spectrum sharing scheme plays a key role in achieving the optimal utilization of the available spectrum. The spectrum sharing in CRN is more challenging than traditional wireless network. The main factors besides throughput and fairness which need to be addressed in spectrum sharing of CRN are primary user (PU) activity, transmission power, and variations in the radio environment. In this article, we propose fair, efficient, and power-optimized (FEPO) spectrum sharing scheme that will incorporate all critical factors mentioned above to maximize the spectrum utilization. Simulation results show that FEPO scheme outperforms in terms of transmission power by reducing the number of retransmissions and guarantees required level of throughput and fairness. Moreover, periodic monitoring helps to reduce the number of collisions with PUs.

Reliable, Efficient, and Power Optimized Control-Channel Selection Scheme for Cognitive Radio Networks

This paper presents a centralized control-channel selection scheme for cognitive radio networks (CRNs) by exploiting the variation in the spectrum across capacity, occupancy, and error rate. We address the fundamental challenges in the design of the control-channel for CRNs: (1) random licensed users (LUs) activity and (2) the economical and vulnerability concerns for a dedicated control-channel. We develop a knapsack problem (KP) based reliable, efficient, and power optimized (REPO) control-channel selection scheme with an optimal data rate, bit error rate (BER), and idle time. Moreover, we introduce the concept of the backup channels in the context of control-channel selection, which assists the CRs to quickly move on to the next stable channel in order to cater for the sudden appearance of LUs. Based on the KP and its dynamic programming solution, simulation results show that the proposed scheme is highly adaptable and resilient to random LU activity. The REPO scheme reduces collisions with the LUs, minimizes the alternate channel selection time, and reduces the bit error rate (BER). Moreover, it reduces the power consumed during channel switching and provides a performance, that is, competitive with those schemes that are using a static control-channel for the management of control traffic in CRNs.

A Potential Game Approach Towards Distributive Interference Management in OFDMA-Based Femtocell Networks

This paper proposes a distributive interference management for OFDMA-based hierarchical macro/femto-cell networks. Specifically, the joint resource block (RB) and power allocation of the downlink case is modeled by the potential game (PG) approach, which is proved to exhibit pure and unique Nash Equilibrium (NE). In the designed PG, the femto base stations (HBSs) are the players, and the RB and power allocation are the set of actions that each player can perform. The utility function of the game is designed in a way such that it guarantees the existence of femto cells within macro cell. To this end, the utility function incorporates all the sources of interference, which include co-tier (femto-femto) and cross-tier (femto-macro), and also the reward of each player. The game is solved by exploiting the best response dynamics, which corresponds to the selection of RBs and power allocation by HBSs. In addition, particle swarm optimization is taken into account for the joint allocation task for each iteration of the game. Simulation results are presented in terms of the performance metrics, which include convergence, impact of varying RBs and fairness. For the sake of comparison, RB random allocation and non-cooperative power optimization game is considered.

Performance analysis of unstructured peer-to-peer schemes in integrated wired and wireless network environments

Concurrent with the development of wireless equipment, the development of P2P (peer-to-peer) file sharing schemes for integrated wireless and wired networks is also needed. However, research on P2P file sharing has mainly been done only for wired environments or only for ad hoc networks. In this paper, we evaluate existing P2P schemes and propose unstructured P2P caching schemes for integrated wired and wireless network environments. We analyze existing unstructured P2P schemes and propose two kinds of extended Freenet caching schemes: WDC (wireless dependent caching) and HNS (half node storing). We evaluate the performance of the proposed schemes through simulation. The performance of WDC is similar to wired Freenet, however it can save bandwidth of wireless links significantly by replicating files only at wired nodes. With the HNS scheme, although it utilizes more bandwidth than WDC, nodes keep only half of the files of wired Freenet, and both the number of hops for success and the failure rate decrease. Therefore, the WDC scheme is appropriate for bandwidth-limited wireless links or integrated environments with a low proportion of wireless nodes, while the HNS scheme can provide a smaller number of hops to success and higher success rate as compared to wired Freenet.

Peer-to-peer caching schemes for integrated wired and wireless network environments

In order to make the unstructured P2P Freenet appropriate for integrated wired and wireless network environments, we propose two kinds of Freenet caching schemes, WDC (Wireless Dependent Caching) and HNS (Half Node Storing), and evaluate their performance through simulation. The performance of WDC is similar to the original Freenet, however it can save bandwidth of the wireless link significantly by replicating files only at wired nodes. With the HNS scheme, although it utilizes more bandwidth than WDC, nodes keep half of the files of the original Freenet, and both the number of hops for success and failure rate decrease. Therefore, the WDC scheme is appropriate for extremely limited wireless link or low proportion of wireless node environments while the HNS scheme can provide a smaller number of hops to success and higher success rate than the original Freenet

Practical Considerations in Trunk Engineering for Cellular Service

We identify and address practical problems facing the engineers who are responsible for trunk engineering(determining optimal trunk requirements between switching systems in a telecommunications network) in a nation-wide cellular service. Currently, Erlang B formula is used to calculate the number of trunks to carry the estimated cellular traffic with given target grade of service(i. e. call block rate). However, our recent measurement at a nation-wide cellular service covering more than 15 million customers shows that the measured block rate is occasionally far greater than the expected block rate, as much as 8 times. Fearing this, it is a common practice for field engineers to assign far more trunks than dictated by the Erlang B formula. But the main problem is that there is no basis on how to assign more trunks. In this paper, we track the cause for excessive block rate by analyzing vast amount of call log to identify the characteristic of the recent cellular traffic. We introduce a simple but effective compensation method to adjust the Erlang B formula with random and non-random traffic. The second problem we address is that the Erlang B formula gives average block rate while the management of the cellular service demands the engineers to guarantee given upper limit to the block rate. We employ the concept of the confidence interval to guarantee given block rate with certain reliability. We develop a simulation program to derive an updated version of Erlang B table with the confidence interval and a simple heuristic method to compensate for the peakedness of contemporary cellular traffic.

Fast Parallel Radix Sort Using a Reconfigurable Mesh

In this paper, we present a parallel SIMD algorithm for radix sorting of N numbers of w bits each, taking O(w + N1/4) time with the VLSI area of O(N3/2 w2), 0 < w < N1/4. For w = log N, our algorithm improves a previous known solution on a similar architecture in time complexity by a factor of log N. Since our algorithm uses only radix sort for sorting of subsets and merging of them, no comparator is needed. Our algorithm satisfies the lower bound of AT2 complexity which mainly restricts the VLSI implementation of most sorting algorithms. The same result is obtained in another previously known solution, but it requires a comparator of size w.