• Journal of Communications and Networks
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• v.11 no.5
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• pp.464-472
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• 2009

In this paper, we propose a packet scheduling algorithm for cellular relay networks by considering relay selection, variation of channel quality, and packet delay. In the networks, mobile users are equipped with not only cellular but also user relaying radio interfaces, where base station exploits adaptive high speed downlink channel. Our proposed algorithm selects a user with good cellular channel condition as a relay station for other users with bad cellular channel condition but can get access to relay link with good quality. This can achieve flexible packet scheduling by adjusting transmission rates of cellular link. Packets are scheduled for transmission depending on scheduling indexes which are calculated based on user's achieved transmission rate, packet utility, and proportional fairness of their throughput. The performance results obtained by using computer simulation show that the proposed scheduling algorithm is able to achieve high network capacity, low packet loss, and good fairness in terms of received throughput of mobile users.

• ETRI Journal
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• v.35 no.2
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• pp.336-339
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• 2013

To enhance the symbol error rate (SER) performance of the two-way relay channels with physical layer network coding, this letter proposes a relay selection scheme, in which the relay with the maximal minimum distance between different points in its constellation among all relays is selected to assist two-way transmissions. We give the closed-form expression of minimum distance for binary phase-shift keying and quadrature phase-shift keying. Additionally, we design a low-complexity method for higher-order modulations based on look-up tables. Simulation results show that the proposed scheme improves the SER performance for two-way relay networks.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.16 no.3
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• pp.65-71
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• 2016

Cooperative relaying systems have been studied actively to improve the system performance effectively in wireless fading channels. Most of the cooperative relay studies are assumed fixed relay, recently the performance analysis of the cooperative relaying systems with spatially random relays considering the practical mobile environment are introduced. However the comparative studies for relay selection methods of incremental cooperative relay systems, the performance of which is influenced by the selection methods, have not been studied. Therefore we derive the performance of the system which has MRC(Maximal-ratio combining) with Max SNR(signal-to-noise ratio) selection or Max-min SNR selection, respectively. And the outage performances of the system with Max or Max-min selection method are compared for different transmit power allocation to the source and to the relays. The analytical results serve as useful tools for relay selection and power allocation to transmit nodes for opportunistic incremental relaying systems.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.6
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• pp.2831-2847
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• 2017

In this paper, a joint destination-relay selection and antenna mode selection scheme for full-duplex (FD) relay network is investigated, which consists of one source node, N FD amplify-and-forward (AF) relays and M destination nodes. Multiple antennas are configured at the source node, and beamforming technique is adopted. Two antennas are employed at each relay, one for receiving and the other for transmitting. Only one antenna is equipped at each destination node. In the proposed scheme, the best destination node is firstly selected according to the direct links between the source node and destination nodes. Then the transmit and receive mode of two antennas at each relay is adaptively selected based on the relaying link condition. Meanwhile, the best relay with the optimal Tx/Rx antenna configuration is selected to forward the signals. To characterize the performance of the proposed scheme, the closed-form expression of the outage probability is derived; meanwhile, the simple asymptotic expressions are also obtained. Our analysis shows that the proposed scheme obtains the benefits of multi-relay diversity and multi-destination diversity. Moreover, extra space diversity in the medium SNR region can be achieved due to the antenna selection at the relay. Finally, Monte-Carlo simulations are provided to consolidate the analytical results, and show the effectiveness of the proposed scheme.

• Journal of Broadcast Engineering
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• v.21 no.1
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• pp.105-108
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• 2016

In this paper, a cooperative jamming network with multiple relays and multiple eavesdroppers is investigated. Among the relays, one best relay is selected to amplify and forward the signal to destination through two phases. To confuse eavesdroppers, the destination transmits a jamming signal in the first phase and the source transmits jamming signal in the second phase. Secrecy rate of this system is derived, and based on the available channel state information (CSI), relay selection schemes are proposed, respectively. Numerical results show that the performance of the proposed relay selection scheme outperforms than that of random relay selection scheme.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.12 no.5
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• pp.17-23
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• 2012

Recently, for spectral efficiency and power saving, an incremental best relay selection of a cooperative diversity scheme is proposed. However during the best relay selection process, there may exist a delay between channel estimation and actual data transmission. Consequently, this delay causes outdated channel state information (CSI). We analytically derive the effect of the outdated CSI to an incremental best relay selection diversity scheme. It is noted that the system performance deteriorates with decreasing the value of the correlation coefficient sensitively. When the correlation coefficient reduces from 1 to 0.9, the most performance degradation is denoted. However, the performance degradation is diminished with decreasing the correlation coefficient.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.1A
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• pp.36-43
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• 2008

In this paper, we propose an optimal relay selection scheme for decode-and-forward relaying systems. The optimal relay selection minimizes the number of time slots used to relay source's signal and maximizes an end-to-end signal-to-noise ratio. However, decode-and-forward relaying systems require additional overhead for the optimal relay selection. Assuming independent and identically distributed Rayleigh fading channels, we provide exact and closed-form expressions for the outage probability of capacity and the bit error rate for decode-and-forward relaying systems with the optimal relay selection. It is shown that the analytic results are perfectly matched with the simulated ones. When the numbers of relay nodes are 2, 4, and 8, and the numbers of time slots for overhead are 1, 2, and 4, respectively, the proposed system achieves 1 dB, 2 dB, and 3 dB gains at 1% bit error rate, respectively, and 0.5 dB, 4 dB, and 12 dB gains at 1% outage probability for 1 bps/Hz, respectively, over the conventional decode-and-forward relaying system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.12
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• pp.2317-2323
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• 2015

In this paper, we analyze the performance of dual-hop amplify-and-forward (AF) relaying in cooperative networks with partial relay selection. An AF relay gain considered in this paper includes channel-noise-assisted relay gain. Leveraging a received signal-to-noise ratio (SNR) model, we derive exact closed-form expressions for the probability density function (pdf) and cumulative distribution function (cdf) of the end-to-end SNR. Moreover, an exact closed-form expression of the ergodic capacity for dual-hop AF relaying with channel-noise-assisted relay gain and partial relay selection is investigated. The analytical results shown in this paper are confirmed by Monte-Carlo simulations.

• Journal of electromagnetic engineering and science
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• v.11 no.2
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• pp.133-142
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• 2011

Coded cooperation that integrates channel coding in cooperative transmission has gained a great deal of interest in wireless relay networks. The performance analysis of coded cooperation protocol with multiple relays is investigated in this paper. We show that the diversity order achieved by the coded cooperation in a multi-relay wireless network is not only dependent on the number of cooperating relays but is also dependent on the code-rate of the system. We derive the code-rate bound, which is required to achieve the full diversity gain of the order of cooperating nodes. The code-rate required to achieve full diversity is a linearly decreasing function of the number of available relays in the network. We show that the instantaneous channel state information (CSI)-based relay selection can effectively alleviate this code-rate bound. Analysis shows that the coded cooperation with instantaneous CSI-based relay selection can achieve the full diversity, for an arbitrary number of relays, with a fixed code-rate. Finally, we develop tight upper bounds for the bit error rate (BER) and frame error rate (FER) of the relay selection based on coded cooperation under a Rayleigh fading environment. The analytical upper bounds are verified with simulation results.

• Journal of Communications and Networks
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• v.13 no.3
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• pp.240-249
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• 2011

Cooperative diversity protocols have attracted a great deal of attention since they are thought to be capable of providing diversity multiplexing tradeoff among single antenna wireless devices. In the high signal-to-noise ratio (SNR) region, cooperation is rarely required; hence, the spectral efficiency of the cooperative protocol can be improved by applying a proper cooperation selection technique. In this paper, we present a simple "cooperation selection" technique based on instantaneous channel measurement to improve the spectral efficiency of cooperative protocols. We show that the same instantaneous channel measurement can also be used for relay selection. In this paper two protocols are proposed-proactive and reactive; the selection of one of these protocols depends on whether the decision of cooperation selection is made before or after the transmission of the source. These protocols can successfully select cooperation along with the best relay from a set of available M relays. If the instantaneous source-to-destination channel is strong enough to support the system requirements, then the source simply transmits to the destination as a noncooperative direct transmission; otherwise, a cooperative transmission with the help of the selected best relay is chosen by the system. Analysis and simulation results show that these protocols can achieve higher order diversity with improved spectral efficiency, i.e., a higher diversity-multiplexing tradeoff in a slow-fading environment.