| 1. |
- Kim, Su Min, et al.
(author)
-
Distributed MAC Based on Adaptive Sensing Period Adjustment in Overlay Cognitive Radio Networks
- 2013
-
In: Proceedings of IEEE Asia-Pacific Wireless Communications Symposium (APWCS) 2013, Seoul, Korea.
-
Conference paper (peer-reviewed)abstract
- In this paper, we propose distributed MAC protocols based on adaptive sensing period adjustment in overlay cognitive radio (CR) networks. The proposed MAC protocols adjust the sensing period based on both primary sensing and secondary data channel information at each CR user. A user with the shortest adjusted sensing period accesses to the channel in a distributed manner through an exchange of RTS/CTS messages. We propose two kinds of sensing period adjustment (SPA) protocols: logarithmic SPA (LSPA) and exponential SPA (ESPA) protocols. Through Monte-Carlo simulations, we evaluate the performance of the proposed protocols in terms of spectral efficiency and collision probability. Numerical results show that the collision probability is the most dominant factor to determine the spectral efficiency. The proposed ESPA protocol efficiently reduces the collision probability with a moderate increase of the sensing period.
|
|
| 2. |
- Bang, I., et al.
(author)
-
Opportunistic user selection with adaptive jamming for secure communication in heterogeneous networks
- 2015
-
In: IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC. - : IEEE conference proceedings. - 9781479949120 ; , s. 42-46
-
Conference paper (peer-reviewed)abstract
- In this paper, we propose an opportunistic user selection criterion to obtain a multiuser diversity gain for secure communication. At the same time, we also propose a strategy for utilizing a small base station in heterogeneous networks as a helper or a jammer adaptively. Our approach is to maximize the secrecy achievable rate based on an analytically derived lower bound instead of the original objective function due to its complexity. Based on a simple proposed user selection criterion considering both macro and small base stations, we propose two jamming strategies according to knowledge of eavesdropper's channel: adaptive jamming and probabilistic jamming strategies. Through simulations in two scenarios, it is shown that our proposed user selection and jamming schemes provide a good performance gain in terms of secrecy achievable rate.
|
|
| 3. |
- Charalambous, Themistoklis, et al.
(author)
-
Relay-pair selection in buffer-aided successive opportunistic relaying using a multi-antenna source
- 2019
-
In: Ad hoc networks. - : ELSEVIER SCIENCE BV. - 1570-8705 .- 1570-8713. ; 84, s. 29-41
-
Journal article (peer-reviewed)abstract
- We study a cooperative network with a buffer-aided multi-antenna source, multiple half-duplex (HD) buffer-aided relays and a single destination. Such a setup could represent a cellular downlink scenario, in which the source can be a more powerful wireless device with a buffer and multiple antennas, while a set of intermediate less powerful devices are used as relays to reach the destination. The main target is to recover the multiplexing loss of the network by having the source and a relay to simultaneously transmit their information to another relay and the destination, respectively. Successive transmissions in such a cooperative network, however, cause inter-relay interference (IRI). First, by assuming global channel state information (CSI), we show that the detrimental effect of IRI can be alleviated by precoding at the source, mitigating or even fully cancelling the interference. A cooperative relaying policy is proposed that employs a joint precoding design and relay-pair selection. Note that both fixed rate and adaptive rate transmissions can be considered. For the case when channel state information is only available at the receiver side (CSIR), we propose a relay selection policy that employs a phase alignment technique to reduce the IRI. The performance of the two proposed relay pair selection policies are evaluated and compared with other state-of-the-art relaying schemes in terms of outage and throughput. The results show that the use of a powerful source can provide considerable performance improvements.
|
|
| 4. |
- Do, Tan Tai, et al.
(author)
-
Uplink Waveform Channel With Imperfect Channel State Information and Finite Constellation Input
- 2017
-
In: IEEE Transactions on Wireless Communications. - : IEEE Press. - 1536-1276 .- 1558-2248. ; 16:2, s. 1107-1119
-
Journal article (peer-reviewed)abstract
- This paper investigates the capacity limit of an uplink waveform channel assuming imperfect channel state information at the receiver (CSIR). Various realistic assumptions are incorporated into the problem, which make the study valuable for performance assessment of real cellular networks to identify potentials for performance improvements in practical receiver designs. We assume that the continuous-time received signal is first discretized by mismatched filtering based on the imperfect CSIR. The resulting discrete-time signals are then decoded considering two different decoding strategies, i.e., an optimal decoding strategy based on specific statistics of channel estimation errors and a sub-optimal decoding strategy treating the estimation error signal as additive Gaussian noise. Motivated by the proposed decoding strategies, we study the performance of the decision feedback equalizer for finite constellation inputs, in which inter-stream interferences are treated either using their true statistics or as Gaussian noise. Numerical results are provided to exemplify the benefit of exploiting the knowledge on the statistics of the channel estimation errors and inter-stream interferences. Simulations also assess the effect of the CSI imperfectness on the achievable rate, which reveal that finite constellation inputs are less sensitive to the estimation accuracy than Gaussian input, especially in the high SNR regime.
|
|
| 5. |
- Do, Tan Tai, et al.
(author)
-
Waveform domain framework for capacity analysis of uplink WCDMA systems
- 2015
-
In: EURASIP Journal on Wireless Communications and Networking. - : Springer. - 1687-1472 .- 1687-1499.
-
Journal article (peer-reviewed)abstract
- This paper investigates the capacity limit of an uplink WCDMA system considering a continuous-time waveform signal. Various realistic assumptions are incorporated into the problem, which make the study valuable for performance assessment of real cellular networks to identify potentials for performance improvements in practical receiver designs. An equivalent discrete-time channel model is derived based on sufficient statistics for optimal decoding of the transmitted messages. The capacity regions are then characterized using the equivalent channel considering both finite constellation and Gaussian distributed input signals. The capacity with sampling at the receiver is also provided to exemplify the performance loss due to a typical post-processing at the receiver. Moreover, we analyze the asymptotic capacity when the signal-to-noise ratio goes to infinity. The conditions to simultaneously achieve the individual capacities are derived, which reveal the impacts of signature waveform space, channel frequency selectivity and signal constellation on the system performance.
|
|
| 6. |
- Jang, Han Seung, et al.
(author)
-
Spatial Group Based Random Access for M2M Communications
- 2014
-
In: IEEE Communications Letters. - 1089-7798 .- 1558-2558. ; 18:6, s. 961-964
-
Journal article (peer-reviewed)abstract
- We expect that the number of machine-to-machine (M2M) devices will rapidly increase in the near future due to a growing demand for a wide range of M2M applications such as e-health, public safety, surveillance, remote maintenance and control, and smart metering. Therefore, the future cellular networks should accommodate a large number of M2M devices and their random access (RA) requests at a specific time instant. In this letter, we propose a novel RA scheme to effectively increase the number of available preambles for the future M2M communication environment. The proposed scheme provides additional preambles by spatially partitioning a cell coverage into multiple group regions and reducing cyclic shift size in RA preambles. As a result, the proposed RA scheme can accommodate a significantly larger number of machine nodes with much lower collision probability and shorter random access delay, compared to a conventional RA scheme.
|
|
| 7. |
- Kim, Su Min, et al.
(author)
-
Effects of Heterogenous Mobility on Rate Adaptation and User Scheduling in Cellular Networks With HARQ
- 2013
-
In: IEEE Transactions on Vehicular Technology. - 0018-9545 .- 1939-9359. ; 62:6, s. 2735-2748
-
Journal article (peer-reviewed)abstract
- In this paper, we investigate the effects of heterogeneous mobility on rate adaptation and user scheduling in cellular networks with hybrid automatic repeat request (HARQ). To this end, we first show the performance tradeoff between two extreme scheduling criteria: retransmission-oriented scheduling (ROS) and mixed scheduling (MS) criteria over time-correlated Rayleigh fading channels. Then, we propose an ROS-based joint rate adaptation and user scheduling (JRAUS) policy for cellular networks and compare it with the conventional and reference JRAUS policies. We also evaluate the system-level performance of the proposed ROS-based JRAUS policy in various user distribution and mobility scenarios. In particular, in an asymmetric user distribution and heterogeneous mobility scenario, which is the most general one in practice, the proposed JRUAS policy yields a throughput gain of 49% and a fairness gain of 155% over the conventional JRAUS policies. In this paper, we find that the rate adaptation is significant not only in a single point-to-point link but in multiuser systems with heterogeneous mobility as well.
|
|
| 8. |
- Kim, Su Min, et al.
(author)
-
On the Entropy Computation of Large Complex Gaussian Mixture Distributions
- 2015
-
In: IEEE Transactions on Signal Processing. - 1053-587X .- 1941-0476. ; 63:17, s. 4710-4723
-
Journal article (peer-reviewed)abstract
- The entropy computation of Gaussian mixture distributions with a large number of components has a prohibitive computational complexity. In this paper, we propose a novel approach exploiting the sphere decoding concept to bound and approximate such entropy terms with reduced complexity and good accuracy. Moreover, we propose an SNR region-based enhancement of the approximation method to reduce the complexity even further. Using Monte-Carlo simulations, the proposed methods are numerically demonstrated for the computation of the mutual information including the entropy term of various channels with finite constellation modulations such as binary and quadratic amplitude modulation (QAM) inputs for communication applications.
|
|
| 9. |
- Kim, Su Min, et al.
(author)
-
Sphere decoding inspired approximation method to compute the entropy of large Gaussian mixture distributions
- 2014
-
In: IEEE Workshop on Statistical Signal Processing Proceedings. - 9781479949755 ; , s. 264-267
-
Conference paper (peer-reviewed)abstract
- The computation of mutual informations of large scale systems with finite input alphabet and Gaussian noise has often prohibitive complexities. In this paper, we propose a novel approach exploiting the sphere decoding concept to bound and approximate such mutual information term with reduced complexity and good accuracy. Using Monte-Carlo simulations, the method is numerically demonstrated for the computation of the mutual information of a frequency- and time-selective channel with QAM modulation.
|
|
| 10. |
- Kim, Su Min, et al.
(author)
-
Virtual Full-Duplex Buffer-Aided Relaying in the Presence of Inter-Relay Interference
- 2016
-
In: IEEE Transactions on Wireless Communications. - : IEEE. - 1536-1276 .- 1558-2248. ; 15:4, s. 2966-2980
-
Journal article (peer-reviewed)abstract
- In this paper, we study virtual full-duplex (FD) buffer-aided relaying to recover the loss of multiplexing gain caused by half-duplex (HD) relaying in a multiple relay network, where each relay is equipped with a buffer and multiple antennas, through joint opportunistic relay selection (RS) and beamforming (BF) design. The main idea behind virtual FD buffer-aided relaying is that the source and one of the relays simultaneously transmit their own information to another relay and the destination, respectively. In such networks, interrelay interference (IRI) is a crucial problem, which has to be resolved like self-interference in the FD relaying. In contrast to previous work that neglected IRI, we propose joint RS and BF schemes taking IRI into consideration by using multiple antennas at the relays. To maximize average end-to-end rate, we propose a weighted sum-rate maximization strategy assuming that adaptive rate transmission is employed in both the source to relay and relay to destination links. Then, we propose several BF schemes cancelling or suppressing IRI in order to maximize the weighted sum-rate. Numerical results show that our proposed optimal, zero-forcing, and minimum mean square error BF-based RS schemes asymptotically approach the ideal FD relaying upper bound when increasing the number of antennas and/or the number of relays.
|
|
