• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.14 no.4
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• pp.45-50
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• 2014

In this paper, we proposed a method using the user mobile device to overcome the interference constraint without building a cooperative communication system. In addition, in order to mitigate interference, we apply the user mobile device selection method, and then exploit power allocation scheme in the user mobile device. The proposed protocol is analyzed in the Rayleigh fading environment, and the performance system is evaluated in terms of the bit error rate and the outage probability. The simulation results showed that when the proposed transmission algorithm is applied, the interference can be mitigated. Further, network overload problems can be solved in the weak channel interference. Therefore, we can increase the network capacity without additional relay.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.11
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• pp.5335-5353
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• 2019

The definition of the bandwidth efficiency (BE) of cognitive cooperative network (CCN) is the ratio between a number of the licensed slot(s) or sub-channel(s) used by the unlicensed users to transmit a single data packet from the unlicensed transmitter to unlicensed destination, and from unlicensed relay(s) to unlicensed destination. This paper analyzes and improves the BE in the underlay CCN with a new reactive relay selection under interference and power constraints. In other words, this paper studies how unlicensed cooperative users use the licensed network slot(s) or sub-channel(s) efficiently. To this end, a reactive relay selection method named as Relay Automatic Repeat Request (RARQ) is proposed and utilized with a CCN under interference and power constraints. It is shown that the BE of CCN is higher than that of cooperative transmission (CT) due to the interference and power constraint. Furthermore, the BE of CCN is affected by the distance of the interference links which are between the unlicensed transmitter to the licensed destination and unlicensed relay to the licensed destination. In addition, the BE for multiple relays selection over a CCN under interference and power constraints is also analyzed and studied, and it is shown that the BE of CCN decreases as the number of relays increases.

• Journal of Communications and Networks
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• v.6 no.1
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• pp.26-34
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• 2004

A blind interference canceller in the presence of subchipspaced multipath channels for direct-sequence code division multiple access (DS-CDMA) down-link system is considered. This technique is based on combining the existing blind interference canceller with a technique that involves assigning subchip-tap spacing to the Rake receiver. The proposed receiver minimizes the receiver’s output energy subject to a constraint in order to mitigate the multiple access interference (MAI) along each multipath component, and then suboptimally combining all the multipath components. Moreover, it is able to mitigate the mismatch problem when subchip-spaced multipath components arrive at the blind interference canceller. It is known that optimal combining techniques perform a decorrelation operation before combining, which requires both knowledge and computational complexity. In the following, we have adopted a simpler but suboptimum approach in the combining of the suppressed signals at the output of our proposed receiver. Computer simulation results verify the effectiveness of the proposed receiver to handle subchip-spaced multipath components and still suppresses MAI significantly.

• Journal of Communications and Networks
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• v.18 no.4
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• pp.639-648
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• 2016

Next-generation (4G) systems are designed to support universal frequency reuse (UFR) to achieve best use of valuable spectra. However, it leads to undesirable interference level near cell borders. To control this, 4G systems adopt techniques, such as network multiple-input multiple-output (MIMO) and inter-cell interference coordination (ICIC), to improve cell-edge throughput. Network MIMO aims at mitigating inter-cell interference towards cell-edge users (CEUs) through multi-cell cooperation, where each collaborative base station serves both cell-center users (CCUs) and CEUs, including other cells' CEUs, under a power constraint. The present ICIC strategies cannot be directly applied to network MIMO because they were designed in absence of multi-cell coordination. In the presence of network MIMO, this paper investigates antenna orientations in ICIC and the method of power management. Results show that a proper antenna orientation can improve the cell-edge capacity and meantime lower the interference to CCUs. Capacity inconsistency between CCUs and CEUs is detrimental to mobile communications. Simulation results show that the proposed power management for ICIC in network MIMO systems can achieve a uniform data rate regardless users' position.

• ETRI Journal
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• v.38 no.6
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• pp.1153-1162
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• 2016

This paper addresses the resource allocation (RA) problem in multi-cell cognitive radio networks. Besides the interference power threshold to limit the interference on primary users PUs caused by cognitive users CUs, a proportional fairness constraint is used to guarantee fairness among multiple cognitive cells and the impact of imperfect spectrum sensing is taken into account. Additional constraints in typical real communication scenarios are also considered-such as a transmission power constraint of the cognitive base stations, unique subcarrier allocation to at most one CU, and others. The resulting RA problem belongs to the class of NP-hard problems. A computationally efficient optimal algorithm cannot therefore be found. Consequently, we propose a suboptimal RA algorithm composed of two modules: a subcarrier allocation module implemented by the immune algorithm, and a power control module using an improved sub-gradient method. To further enhance algorithm performance, these two modules are executed successively, and the sequence is repeated twice. We conduct extensive simulation experiments, which demonstrate that our proposed algorithm outperforms existing algorithms.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.9
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• pp.2120-2133
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• 2013

In this paper, we address the problem of linear minimum mean-squared error (MMSE) transmitter design for the cognitive radio (CR) multi-user multiple-input single-output (MU-MISO) broadcasting channel (BC), where the cognitive users are subject to not only a sum power constraint, but also a interference power constraint. Evidently, this multi-constraint problem renders it difficult to solve. To overcome this difficulty, we firstly transform it into its equivalent formulation with a single constraint. Then by utilizing BC-MAC duality, the problem of BC transmitter design can be solved by focusing on a dual MAC problem, which is easier to deal with due to its convexity property. Finally we propose an efficient two-level iterative algorithm to search the optimal solution. Our simulation results are provided to corroborate the effectiveness of the proposed algorithm and show that this proposed CR MMSE-based scheme achieves a suboptimal sum-rate performance compared to the optimal DPC-based algorithm with less computational complexity.

• IEIE Transactions on Smart Processing and Computing
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• v.3 no.5
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• pp.285-297
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• 2014

This paper presents the results of an investigation into bi-directional communication in spectrum sharing-based cognitive radio (Bi-CR) systems. A Bi-CR system can increase the spectral efficiency significantly by sharing the spectrum and through the bi-directional use of spatial resources for two-way communication. On the other hand, the primary user experiences more interference from the secondary users in a Bi-CR system. Satisfying the interference constraint by simply reducing the transmission power results in performance degradation for secondary users. In addition, secondary users also experience self-interference from echo channels due to full duplexing. These imperfections may weaken the potential benefits of the Bi-CR system. Therefore, a new way to overcome these defects in the Bi-CR system is needed. To address this need, this paper proposes some novel power allocation schemes for the Bi-CR system. This contribution is based on two major analytic environments, i.e., noise-limited and interference-limited environments, for providing useful analysis. This paper first proposes an optimal power allocation (OPA) scheme in a noise-limited environment and then analyzes the achievable sum rates. This OPA scheme has an effect in the noise-limited environment. In addition, a power allocation scheme for the Bi-CR system in an interference-limited environment was also investigated. The numerical results showed that the proposed schemes can achieve the full duplexing gain available from the bi-directional use of spatial resources.

• Journal of Satellite, Information and Communications
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• v.8 no.4
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• pp.47-52
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• 2013

In this paper, The existing interference alignment algorithms were analyzed in Rayleigh fading channel environment. The interference alignment techniques are divided to two parts. First thing is Iterative-method, another is Linear-method. Iterative method needs local channel info, but it has the constraint of iteration. On the other hand Linear-method must have global channel info, but has free of iteration and better performance. This paper evaluates the performance of interference alignment algorithms in Rayleigh fading channel of outdoor environment and WLAN channel based on IEEE 802.11n of indoor environment.

• Journal of Communications and Networks
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• v.13 no.5
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• pp.456-462
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• 2011

This paper investigates the outage behavior of peak interference power limited cognitive radio (CR) networks with multiple transmit antennas. In CR-multi-input single-output (MISO) channel, the total transmit power is distributed over the transmitantennas. First, we use the orthogonal space-time codes (STC) to achieve the transmit diversity at CR-receiver (rx) and investigate the effect of the power distribution on the interference power received at the primary-receiver (P-rx). Then, we investigate the transmit antenna selection (TAS) scheme in which the CR system selects the best transmit antenna and allocates all the power to the selected best antenna. Two transmit antenna selection strategies are proposed depending on if feedback channel is available or not. We derive the closed form expressions of outage probability and outage capacity of all schemes with arbitrary number of transmit-antennas. We show that the proposed schemes significantly improve the outage capacity over the single antenna systems in Rayleigh fading environment. We also show that TAS based scheme outperforms the STC based scheme when peak interference power constraint is imposed on the P-rx only if a feedback channel from CR-rx to CR-transmitter is available.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.1
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• pp.18-34
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• 2014

It is widely believed that cognitive radio (CR) networks have an opportunistic nature and therefore can only support best-effort traffics without quality-of-service (QoS) guarantees. In this paper, we propose a centralized CR network that adopts interference averaging techniques to support QoS guaranteed traffics under interference outage constraints. In such a CR network, a CR user adaptively adjusts its transmit power to compensate for the channel loss, thereby keeping the receive signal power at the CR base station (BS) at a constant level. The closed-form system capacity of such a CR network is analyzed and derived for a single cell with one CR BS and multiple CR users, taking into account various key factors such as interference outage constraints, channel fading, cell radius, and locations of primary users. The accuracy of the theoretical results is validated by Monte Carlo simulations. Numerical and simulation results show promising capacity potential for deploying QoS-guaranteed CR networks in frequency bands with fixed primary receivers. Our work can provide theoretical guidelines for the strategic planning of centralized CR networks.