Soonchul Park

Channel estimation based on path separation for DVB-T in long delay situations

A least square (LS) channel estimation with pilots uses interpolation to obtain the channel information for the positions of data subcarriers in orthogonal frequency division multiplexing (OFDM) systems. However, the interpolation introduces estimation errors in long delay channels that usually happen in single frequency networks (SFNs). In this paper, we propose an algorithm that estimates the accurate channel information by separating channel paths. The performance is compared with conventional algorithms for DVB-T in SFN conditions1.

An efficient mac protocol for data collection in underwater wireless sensor networks

One of the fundamental differences between the terrestrial radio frequency (RF) signal and underwater acoustic signal is long propagation delay. This paper is focused on a scheduling scheme for regional data collection in underwater acoustic sensor networks. Long propagation delay of the acoustic signal causes a serious problem for transmission scheduling. In this paper, we propose an efficient transmission scheduling algorithm using the property of long propagation delay for real-time data collection which is critical to tactical surveillance applications. We show through the simulation that the proposed scheme reduces total transmission time and increases the network efficiency significantly.

An efficient transmission scheme for underwater sensor networks

One of the fundamental differences between the terrestrial radio frequency (RF) signal and underwater acoustic signal is long propagation delay. This paper is contented with a MAC protocol for underwater sensor networks (USN) in which there are n sensor nodes in a transmission range W . Long propagation delay of the acoustic signal causes a serious problem for MAC protocol. If every sensor node has packet to transmit, there are n packets to be transmitted to the sink node. In this paper, we propose an efficient packet transmission scheduling algorithm for underwater acoustic communications with arbitrary values of n and W , using the property of long propagation delay.

A Fast Suboptimal Algorithm for Detection of 16-QAM Signaling in MIMO Channels

We develop a computationally efficient approximation of the maximum likelihood (ML) detector for 16 quadrature amplitude modulation (16-QAM) in multiple-input multiple-output (MIMO) systems. The detector is based on solving a convex relaxation of the ML problem by an affine-scaling cyclic Barzila-Borwein method for box constrained optimization. Simulation results in a random MIMO system show that this proposed approach outperforms the conventional decorrelator detector and is similar to the semidefinite relaxation (SDR) detector. However, we should note that the complexity of the proposed approach is less than that of those detectors. In the case of 8 antennas and 4 users, about 99% fewer computations are required than the SDR and ML detectors.

An Efficient Method for All-To-All Broadcast in Long Propagation Delay Wireless Networks

All-to-all broadcast refers to the process by which every node broadcasts its certain piece of information to all other nodes in the network. The all-to-all broadcasting time is very large due to the long propagation delay time in the long-delay environment like the airborne network and the underwater network. In this letter, we propose an efficient all-to-all broadcast method based on location information in long-delay single-hop wireless networks. We propose a matrix transformation and an algorithm to avoid conflictions in parallel transmissions and reduce all-to-all broadcasting time. The effectiveness of the proposed scheme is proved through simulations. KeywordsAll-to-all broadcast, wireless networks, propagation delay.

A Dynamic Resource Allocation Scheme for Fairness Guarantee using Cooperative Diversity in OFDMA Systems

Orthogonal Frequency Division Multiple Access (OFDMA) is a promising technique which can provide high capacity in the wireless environments. Also cooperative communications are effectively used to achieve cooperative diversity for high reliability. In this paper, we propose the pair-based OFDMA frame structure in which cooperative users transmit their blocks in turns for achieving cooperative diversity in OFDMA systems. In order to guarantee the fairness of users we also propose a dynamic resource allocation scheme based on cooperative communications. Through the proposed scheme, user fairness can be achieved by sharing the remained capacity of users near the base station (BS) with users who are farther from the base station. For this purpose, the center-located users select their partner whose channel suffers the lowest SNR to BS among their neighbor set. Based on the partner selection results, subchannels are assigned to cooperative and non-cooperative users. Through simulations in the IEEE 802.16e system environments, it is shown that the proposed scheme outperforms the non-cooperation based scheme in terms of user fairness.

A power allocation scheme maximizing a discrete capacity function of OFDMA system

In this paper, we propose an adaptive power allocation method for an orthogonal frequency division multiple access (OFDMA) system that employs an adaptive modulation and coding (AMC) scheme. Unlike the water-filling scheme that has been aimed to maximize a continuous capacity function, the proposed scheme is to maximize a discrete capacity function that more precisely characterizes the discrete AMC levels. In terms of complexity, numerical results show that the proposed scheme reduces the processing time by more than 80% comparing with greedy adaptive power allocation (APA), and shows as same performance as greedy APA.

An analysis of the efficient size of a MIMO system for full multiplexing in 16-QAM signaling

In this paper, we provide an analysis of an adequate dimension of multiple-input multiple-output (MIMO) system for full multiplexing in 16-QAM signaling. There are many results of small MIMO system with various schemes. However, because of the unrealistic complexity and meaningless required signal to noise ratio (SNR), results for large (over 20 data streams) MIMO systems can be hardly found. We obtain from our simulations the most efficient size of the MIMO system in a realistic SNR range for each given number of data streams. We also provide the computational complexity of each algorithm for MIMO systems with 20 or more data streams. We conclude from our simulations that the performance depends on the ratio of the number of receivers and the number of transmitters.

An efficient training sequence for channel estimation in ATSC 8VSB system

The authors propose a new training sequence for the channel estimation in frequency selective fading channels. The proposed training sequence has advantages from the points of complexity, sequence length and the channel estimation performance over the PN511 sequence used in the ATSC 8VSB system.

A Mathematical Derivation of a Resource Allocation Matrix for an OFDMA System

In this paper, a resource allocation matrix (RAM) for an orthogonal frequency division multiple access (OFDMA) system is derived to maximize overall data throughput under a strict condition for user fairness. The RAM identifies the most preferable allocation state of OFDMA sub-bands. It is subject to a user fairness condition such that one sub-band is allocated per user during an OFDMA time-slot, allowing each user an equal opportunity to use the sub-bands. The proposed resource allocation scheme using the RAM is evaluated in terms of throughput and user fairness by comparison with the Proportional Fairness (PF) scheme and the Max C/I scheme. Numerical results show that the proposed scheme has much higher throughput under the strict user fairness condition. Even though the PF and Max C/I are given an advantage of ignoring the user fairness condition, the throughput performance of the proposed scheme is quite comparable to that of the PF and Max C/I.