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Feedback reduction scheme for downlink multiuser diversity
Jaewoo So,Cioffi, J.M. IEEE 2009 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.8 No.2
<P>A group random access-based feedback scheme is proposed for multiuser diversity systems, where users are divided into several feedback groups according to their measured channel states. Different random access probabilities and number of feedback minislots are assigned to each feedback group. Each user competes to send a feedback message through random access if its scheduling metric exceeds a threshold. The base station jointly controls the random access probabilities, the thresholds, and the number of feedback minislots to adjust the feedback load. The proposed feedback scheme shows a good system capacity with limited feedback resources regardless of the number of users.</P>
( Jaewoo So ) 한국인터넷정보학회 2017 KSII Transactions on Internet and Information Syst Vol.11 No.3
This paper proposes an opportunistic reporting-based sensing-reporting-throughput optimization scheme that maximizes the spectral efficiency of secondary users (SUs) in cooperative cognitive radio networks with a soft combining rule. The performance of cooperative spectrum sensing depends on the sensing time, the reporting time of transmitting sensing results, and the fusion scheme. While longer sensing time and reporting time improve the sensing performance, this shortens the allowable data transmission time, which in turn degrades the spectral efficiency of SUs. The proposed scheme adopts an opportunistic reporting scheme to restrain the reporting overhead and it jointly controls the sensing-reporting overhead in order to increase the spectral efficiency of SUs. We show that there is a trade-off between the spectral efficiency of SUs and the overheads of cooperative spectrum sensing. The numerical results demonstrate that the proposed scheme significantly outperforms the conventional sensing-throughput optimization schemes when there are many SUs. Moreover, the numerical results show that the sensing-reporting time should be jointly optimized in order to maximize the spectral efficiency of SUs.
Multiuser Diversity in a MIMO System With Opportunistic Feedback
Jaewoo So,Cioffi, J.M. IEEE 2009 IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY Vol.58 No.9
<P>An opportunistic feedback protocol with multiple thresholds and multiple access probabilities is proposed for multiuser diversity in multiple-input-multiple-output (MIMO) broadcast channels. Users compete to report the channel state information (CSI) via contention-based feedback channels if their scheduling metric exceeds a threshold. The users are divided into two classes according to their scheduling metric. For each class, the users have different random access probabilities and different chances to access feedback minislots. The performance of the proposed feedback protocol is evaluated in a MIMO system with zero-forcing (ZF) receivers in terms of the sum-rate capacity, the feedback load, and fairness. The simulation results show that the proposed feedback protocol significantly reduces the feedback load without sacrificing the sum-rate capacity too much. The proposed feedback protocol can be operated with existing scheduling algorithms without modification.</P>
Performance Analysis of VoIP Services in Mobile WiMAX Systems with a Hybrid ARQ Scheme
So, Jaewoo The Korea Institute of Information and Commucation 2012 Journal of communications and networks Vol.14 No.5
This paper analyzes the performance of voice-over-Internet protocol (VoIP) services in terms of the system throughput, the packet delay, and the signaling overhead in a mobile WiMAX system with a hybrid automatic repeat request (HARQ) mechanism. Furthermore, a queueing analytical model is developed with due consideration of adaptive modulation and coding, the signaling overhead, and the retransmissions of erroneous packets. The arrival process is modeled as the sum of the arrival rate at the initial transmission queue and the retransmission queue, respectively. The service rate is calculated by taking the HARQ retransmissions into consideration. This paper also evaluates the performance of VoIP services in a mobile WiMAX system with and without persistent allocation; persistent allocation is a technique used to reduce the signaling overhead for connections with a periodic traffic pattern and a relatively fixed payload. As shown in the simulation results, the HARQ mechanism increases the system throughput as well as the signaling overhead and the packet delay.
( Jaewoo So ) 한국인터넷정보학회 2015 KSII Transactions on Internet and Information Syst Vol.9 No.1
Spectrum sensing is a key component of cognitive radio. The prediction of the primary user status in a low signal-to-noise ratio is an important factor in spectrum sensing. However, because of noise uncertainty, secondary users have difficulty distinguishing between the primary signal and an unauthorized signal when an unauthorized user exists in a cognitive radio network. To resolve the sensitivity to the noise uncertainty problem, we propose an entropy-based spectrum sensing scheme to detect the primary signal accurately in the presence of an unauthorized signal. The proposed spectrum sensing uses the conditional entropy between the primary signal and the unauthorized signal. The ability to detect the primary signal is thus robust against noise uncertainty, which leads to superior sensing performance in a low signal-to-noise ratio. Simulation results show that the proposed spectrum sensing scheme outperforms the conventional entropy-based spectrum sensing schemes in terms of the primary user detection probability.
Cooperative Spectrum Sensing for Cognitive Radio Networks with Limited Reporting
( Jaewoo So ) 한국인터넷정보학회 2015 KSII Transactions on Internet and Information Syst Vol.9 No.8
Cooperative spectrum sensing increases the detection performance in a cognitive radio network, based on the number of sensing nodes. However, as the number of sensing nodes increases, the reporting overhead linearly increases. This paper proposes two kinds of cooperative spectrum sensing with limited reporting in a centralized cognitive radio network, a soft combination with threshold-based reporting (SC-TR) and a soft combination with contention-based reporting (SC-CR). In the proposed SC-TR scheme, each sensing node reports its sensing result to the fusion center through its own reporting channel only if the observed energy value is higher than a decision threshold. In the proposed SC-CR scheme, sensing nodes compete to report their sensing results via shared reporting channels. The simulation results show that the proposed schemes significantly reduce the reporting overhead without sacrificing the detection performance too much.
Jaewoo So,Srikant, R. IEEE 2015 IEEE communications letters Vol.19 No.6
<P>As the number of sensing nodes increases, cooperative spectrum sensing increases the detection probability of primary users at the cost of increased bandwidth of feedback channels. However, the excess feedback overhead of reporting sensing results may degrade the channel utilization of cognitive radio networks. This letter proposes cooperative spectrum sensing with a fixed number of feedback channels, where each sensing node opportunistically reports its sensing result to a fusion center via shared feedback channels only if its sensing result is greater than a threshold. The simulation results show that the proposed cooperative spectrum sensing increases the channel utilization with limited feedback overhead compared with the conventional cooperative spectrum sensing.</P>
Group-Based Multibit Cooperative Spectrum Sensing for Cognitive Radio Networks
So, Jaewoo,Sung, Wonjin IEEE 2016 IEEE Transactions on Vehicular Technology VT Vol.65 No.12
<P>In cooperative spectrum sensing (CSS), a multibit combination rule shows better sensing performance than one-bit hard combination rules at the sacrifice of the reporting overhead. To overcome the tradeoff between the sensing performance and the reporting overhead, we propose a novel group-based multibit CSS scheme with a limited reporting overhead. The proposed scheme adopts contention-based reporting to restrain the reporting overhead while achieving multiuser diversity with an increased number of secondary users (SUs). Moreover, SUs report one-bit sensing results to a fusion center instead of sending multibit quantization information, and the rest of the information is embedded in the time slot. The simulation results demonstrate that, as the number of SUs increases, the proposed scheme improves the sensing performance and the average throughput of SUs, whereas the conventional one-bit or multibit combination schemes show a tradeoff between the sensing performance and the throughput of SUs.</P>