• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.1A
• /
• pp.66-74
• /
• 2007

Cognitive Radio system can guarantee available channel whenever, wherever by sensing surrounding channel condition. Therefore, there is a strict rule that have to use allocated channel efficiently without any interference from incumbent User. In this paper, to avoid interference which can occur during uplink transmission in CR system, we propose reporter using scheme which informs incumbent user's situation to adjacent cell to limit channel usage. Therefore, we can use more channel in each cell without interference. With this scheme we can expect better throughput using more channel in a large space with same resource.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.37B no.11
• /
• pp.1050-1057
• /
• 2012

Super Wi-Fi is a newly emerging wireless Internet technology, which constitutes Wi-Fi networks using TV white space. A key technical challenge in the Super Wi-Fi applications is how to provide a seamless Internet service even when a Super WiFi user should give up the channel in use to the active incumbent user which is activated in the same service area, preventing from the service continuity in Super Wi-Fi. In this paper, we propose a channel handover method to support service continuity of Super Wi-Fi, in which an AP selects a new operational channel and provides the channel information for MSs. Therefore, the AP and the MSs can carry out seamless handover for Super Wi-Fi service. A performance evaluation shows that the proposed scheme is superior to the conventional Wi-Fi in channel mobility delay.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.48 no.6
• /
• pp.28-33
• /
• 2011

Recently, the investigation of the cognitive radio (CR) system is actively progressed as one of the methods for using the frequency resources more efficiently. In CR systems, when the frequency band allocated to the incumbent user is not used, the unused frequency band is assigned to the secondary user. Thus, the FFT input signals corresponding to the actually used frequency band by the incumbent user are assigned as '0'. In this paper, based on the fact that there are many '0' input signals in CR systems, a low-power FFT design method for NC-OFDM is proposed. An efficient zero flag generation technique for each stage is first presented. Then, to increase the utility of the zero flag signals, modified architectures for memory and arithmetic circuits are presented. To verify the performance of the proposed algorithm, 2048 point FFT with radix-24SDFstructureisdesignedusingVerilog HDL. The simulation results show that the power consumption of FFT is reduced considerably by the proposed algorithm.

• Journal of information and communication convergence engineering
• /
• v.9 no.2
• /
• pp.166-171
• /
• 2011

This paper investigates the design issues of spectrum sensing in the cognitive radio (CR) networks of opportunistic unlicensed spectrum access. The cognitive radios can perform a communication using the incumbent user spectrum band without the interference caused by the cognitive radio users. In this case, the cognitive radios must know the real-time radio environments of the incumbent user spectrum band using the spectrum sensing, beacon signal, and geo-location database access. Then in this paper, we are going to provide spectrum sensing issues which include the sensing techniques, the regulatory requirements, the analysis of DTV detection threshold, and main considerations associated with the spectrum sensing design in cognitive radio systems. Also, this paper introduces design trade-offs in order to optimize the sensing parameters such as sensing time and sensing complexity.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.13 no.9
• /
• pp.1891-1897
• /
• 2009

This paper describes the optimization of the spectrum sensing in terms of the throughput of the cognitive radio (CR)system. The conventional rapers do not describe the optimization problem of the spectrum sensing by considering the channel search and channel move of the CR system to be caused by the appearance of the incumbent user. However this paper evaluates the throughput of the CR user by considering the situations such as the channel search and channel move additionally. Also, this paper suggests the sensing structure being separated the data receiver from sensing receiver, and compares the sensing performance for the same receiver structure of sensing and communication with that for the separated sensing receiver in terms of the throughput of the CR user. The numerical result demonstrates that the performance of the throughput efficiency is improved by the proposed sensing receiver to be separated from the data communication path.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.34 no.2B
• /
• pp.178-187
• /
• 2009

Cognitive radio (CR) technology is to maximize the spectrum utilization by allocating the unused spectrums to the unlicensed users. In CR environment, it is strictly required for the unlicensed users not to interference with the licensed users. Thus, it is essential to rely on the scheduling algorithm to avoid the interference when utilizing spectrum holes that are changing in time and frequency. However, the existing scheduling algorithms that are applied for the wireless communication environment considering the licensed users only is not appropriate for CR environment. In this paper, we propose downlink scheduling algorithm based on probability of incumbent user presence for cognitive radio networks. With computer simulations, it is shown that the proposed scheduling algorithm outperforms the conventional scheduling algorithm.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.45 no.3
• /
• pp.27-33
• /
• 2008

In this paper, we propose a cognitive beamforming scheme for coexistence of CR (Cognitive Radio) and IR (Incumbent Radio) systems. In order to maintain the priority of the IR in spectrum utilization the proposed cognitive beamforming scheme needs to have the CR not cause any interference to the IR systems occupying the same frequency band at the same time. In addition the proposed scheme has to provide maximum channel gain to the CRU (CR User) in a boundary of satisfying the former criterion. For this purpose, the proposed scheme does not cause any interference to the IRU (IR User), while the CRU is served without additional radio resource consumption. From simulation, we confirmed that when using the proposed scheme the CRU does not interfere with the IRU and there is little bit error rate performance degradation of the CRU as compared to that of the ideal beamforming system, which does not consider the IR priority.

• Journal of information and communication convergence engineering
• /
• v.9 no.1
• /
• pp.27-31
• /
• 2011

This paper describes the optimization of spectrum sensing in terms of the throughput of a cognitive radio (CR) system. Dealing with the optimization problem of spectrum sensing, this paper evaluates the throughput of a CR system by considering such situations as the penalty time of a channel search and incumbent user (IU) detection delay caused by a missed detection of an incumbent signal. Also, this paper suggests a serial channel search scheme as the search method for a vacant channel, and derives its mean channel search time by considering the penalty time due to the false alarm of a vacant channel search. The numerical results suggest the optimum sensing time of the channel search process using the derived mean channel search time of a serial channel search in the case of a sensing hardware structure with single radio frequency (RF) path. It also demonstrates that the average throughput is improved by two separate RF paths in spite of the hardware complexity of an RF receiver.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.9C
• /
• pp.826-833
• /
• 2007

In this paper, we present an adaptive transmission system model to establish the baseline for wireless adaptive transmission using CR (Cognitive Radio) systems, and propose an adaptive transmission scheme based on IT (Interference Temperature) cognition for CR systems in the presented system environment. The proposed CR adaptive transmission scheme is the method that provides the CR user with the maximum transmit power in the range of not causing any interference to the incumbent user and guaranteeing the optimal throughput by applying CR-AMC (CR-Adaptive Modulation and Coding) in the given channel state. Simulation results show that in case of using the proposed CR adaptive transmission scheme, there is little degradation of BER performance, while causing no interference to the incumbent user. At the same time, the proposed scheme guarantees the optimal throughput to the CR user in the given channel state.

• Journal of Satellite, Information and Communications
• /
• v.10 no.2
• /
• pp.1-9
• /
• 2015

Recently, cognitive radio technology has been spotlighted for the efficient use of limited frequency technology. The most important part of CR is to protect the incumbent user's communications. Therefore, CR user should be sensing the currently using channel and another hopping channel for sudden appearance of the Incumbent User. In this paper, we propose the cooperative channel sensing to protect the IU considering each CR user's remained power and sensing-zone, sense the spectrum bands in a fairly distributed manner and share the results among the users within respective sensing zone. Sensing scheme including inband sensing and outband sensing is utilized. The inband sensing is in charge of current using channel scanning while the outband sensing mainly cares about other channels. The performance results by computer simulations show that our sensing scheduling scheme reduces the number of sensing nodes and saves energy need to channel sensing.