• ETRI Journal
• /
• v.41 no.5
• /
• pp.626-636
• /
• 2019

A novel algorithm for joint user selection and optimal power allocation for Stackelberg game-based revenue maximization in a downlink non-orthogonal multiple access (NOMA) network is proposed in this study. The condition for the existence of optimal solution is derived by assuming perfect channel state information (CSI) at the transmitter. The Lagrange multiplier method is used to convert the revenue maximization problem into a set of quadratic equations that are reduced to a regular chain of expressions. The optimal solution is obtained via a univariate iterative procedure. A simple algorithm for joint optimal user selection and power calculation is presented and exhibits extremely low complexity. Furthermore, an outage analysis is presented to evaluate the performance degradation when perfect CSI is not available. The simulation results indicate that at 5-dB signal-to-noise ratio (SNR), revenue of the base station improves by at least 15.2% for the proposed algorithm when compared to suboptimal schemes. Other performance metrics of NOMA, such as individual user-rates, fairness index, and outage probability, approach near-optimal values at moderate to high SNRs.

• Journal of Information Processing Systems
• /
• v.12 no.2
• /
• pp.295-309
• /
• 2016

Spectrum sensing is an essential function that enables cognitive radio technology to explore spectral holes and resourcefully access them without any harmful interference to the licenses user. Spectrum sensing done by a single node is highly affected by fading and shadowing. Thus, to overcome this, cooperative spectrum sensing was introduced. Currently, the advancements in multiple antennas have given a new dimension to cognitive radio research. In this paper, we propose a multiple energy detector for cooperative spectrum sensing schemes based on the evidence theory. Also, we propose a reporting mechanism for multiple energy detectors. With our proposed system, we show that a multiple energy detector using a cooperative spectrum sensing scheme based on evidence theory increases the reliability of the system, which ultimately increases the spectrum sensing and reduces the reporting time. Also in simulation results, we show the probability of error for the proposed system. Our simulation results show that our proposed system outperforms the conventional energy detector system.

• Proceedings of the IEEK Conference
• /
• 1998.06a
• /
• pp.42-45
• /
• 1998

Adaptive array antenas have emerged as a useful technique to enhance the cell capacity of mobile communications. In this research, to analyze the noncoherent CDMA systems employing adaptive array antennas, we modeled the transmitting signal of CDMA systems using M-ary orthogonal modulation. And we induced the conditional probability density function about the decision variable, the output of 2D-RAKE receiver and mean symbol error prabability through statistical analysis about MAI(Multiple Access Interference), SI(Self Interference) and Noise. Also, we analyzed the charateristics of adaptive array antenna for noncoherent CDMA systems using M-ary orthogonal modulation according to the distance between the array elements, doppler frequency and AOS(Angle of Spread).

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.18 no.9
• /
• pp.1077-1082
• /
• 2007

This paper presents the analysis of the potential ultra-wideband(UWB) interference to WiMAX at 3.5 GHz bands and the mitigation method using transmit power control(TPC) of UWB system. UWB interference effect is evaluated with WiMax's outage probability over UWB density when multiple UWB systems and single WiMAX receiver distribute in unit area of 1$km^2$, When UWB distribution density is 20$devices/km^2$ and the dynamic range of TPC is 30 dB, UWB interference effect with TPC is decreased by 42 % rather than that without mitigation scheme. Finally, we describe that the proposed TPC is an effective method to mitigate UWB interference to WiMAX.

• Journal of Communications and Networks
• /
• v.12 no.2
• /
• pp.174-180
• /
• 2010

Automatic Repeat reQuest (ARQ) is a very effective technique against transmission error at the medium access control (MAC) layer. An erroneous MAC protocol data unit can be typically retransmitted within a given limit. In order to improve the IP-level performance, which directly affects the user-perceived quality-of-service (QoS), we propose a new truncated ARQ strategy, called MAC service data unit-based ARQ (S-ARQ), where the finite number of opportunities for retransmissions are shared by multiple fragments out of an IP datagram. We describe how SARQ can be implemented in a practical system, and then propose another variant of S-ARQ employing a functionality called early detection of failure. Basically, we evaluate the performance of SARQ in two different manners. First, assuming i.i.d. error process, we analyze both the probability of the delivery failure and the average delay of IP datagram. Then, we assess the performance of S-ARQ via simulation over a 2-state Markov channel.

• Journal of Internet Computing and Services
• /
• v.9 no.5
• /
• pp.153-163
• /
• 2008

Almost literature has so far proposed the modifications to IEEE 802.11 DCF MAC protocol to improve system throughput and average delay. Jitter(variance in packet delays) is, however, considered as an important QoS parameter for real-time streaming service which is popularized increasingly. Unfortunately, legacy access protocol for WLAN can't support the jitter. This paper proposes two schemes modifying the DCF MAC protocol to reduce the average value of jitter for multimedia frames arrived at received nodes. The one scheme, referred to as DCW-DCF(Decreasing Contention Window-DCF), reduces CW(Contention Window) size by half whenever a transmitted frame collided against other frames and back-off happens. Also, it increase initial CW size according as the link utilization and the collision probability increase. The other scheme, referred to as D-DIFS(Differential-DIFS), assigns different values to DIFS. That is, the DIFS interval is deceased as the number of back-off for a frame increases. In this paper, the two schemes are evaluated through simulation using ns2 and simulation results show that the proposed schemes are effective for improving the jitter property of standard WLAN.

• Journal of Aerospace System Engineering
• /
• v.10 no.4
• /
• pp.98-104
• /
• 2016

This research describes the functional requirements of anti-ship ballistic missile (ASBM) defense systems, which depend on the threat characteristics of the ASBM. Recently, China has carried out a training launch of the DF-21D strategic countermeasures for the placement of Korean terminal high-altitude air defense (THAAD). The ASBM is being used as a primary means of attacking aircraft carriers, using an anti-access/area denial (A2/AD) strategy. Considering the missile technology connection between China and North Korea, there is a very high probability that North Korea already owns an ASBM. From this point of view, work with Aegis operational concepts provided implications for an ASBM threat. Utilizing quality function deployment (QFD) based on the operational concepts, the functional requirement were calculated.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.39C no.9
• /
• pp.757-766
• /
• 2014

To compensate signal loss due to the channel blockage in satellite communication link, we propose a cooperative communication scheme for OTM(On-The-Move) terminal in next generation satellite communication systems. The proposed scheme configures cooperation subnet with adjacent OTM terminal with the help of ground communication equipment. Shared data is spread by orthogonal spreading code, then the spread sequences are transmitted simultaneously. The receiver combines the power of received signals by EGC(Equal gain combining). The OTM terminal blockage channel is modeled by 2-state Markov chain. We evaluate the bit error rate according to the blockage channel of the channel state for the performance analysis of the proposed scheme. As a result, the proposed scheme shows better BER performance than traditional scheme with the help of subset members. In particular, the proposed scheme shows superior performance as the channel block probability is higher. However, as the number of subset members is increasing, there is a constraint because of the higher multiple access interference.