Ha Nguyen Vu

Joint subcarrier matching and power allocation in OFDM two-way relay systems

A decode-and-forward two-way relay system benefits from orthogonal frequency division multiplexing (OFDM) and relay transmission. In this paper, we consider a decode-and-forward two-way relay system over OFDM with two strategies: A joint subcarrier matching algorithm and a power allocation algorithm operating with a total power constraint for all subcarriers. The two strategies are studied based on average capacity using numerical analysis by uniformly allocating power constraints for each subcarrier matching group. An optimal subcarrier matching algorithm is proposed to match subcarriers in order of channel power gain for both transmission sides. Power allocation is defined based on equally distributing the capacity of each hop in each matching group. Afterward, a modified water-filling algorithm is also considered to allocate the power among all matching groups in order to increase the overall capacity of the network. Finally, Monte Carlo simulations are completed to confirm the numerical results and show the advantages of the joint subcarrier matching, power allocation and water filling algorithms, respectively.

Optimal Throughput of Secondary Users over Two Primary Channels in Cooperative Cognitive Radio Networks

In this paper, we investigated the throughput of a cognitive radio network where two primary frequency channels (PCs) are sensed and opportunistically accessed by N secondary users. The sharing sensing member (SSM) protocol is introduced to sense both PCs simultaneously. According to the SSM protocol, N SUs (Secondary User) are divided into two groups, which allows for the simultaneous sensing of two PCs. With a frame structure, after determining whether the PCs are idle or active during a sensing slot, the SUs may use the remaining time to transmit their own data. The throughput of the network is formulated as a convex optimization problem. We then evaluated an iterative algorithm to allocate the optimal sensing time, fusion rule and the number of members in each group. The computer simulation and numerical results show that the proposed optimal allocation improves the throughput of the SU under a misdetection constraint to protect the PCs. If not, its initial date of receipt shall be nullified.

An optimal cooperative spectrum sensing method in cognitive radio network over Rayleigh fading channel

In cognitive radios, there exist two kinds of detection errors: missed-detection errors and false-alarm errors. These errors severely degrade sensing performance. In this paper, we aim to minimize the total detection probability by considering it as a target function for the optimization of sensing parameters in a Rayleigh fading environment. With this established target function, we perform a discrete difference operation and derive the closed — form expression of the optimal fusion rule for cooperative spectrum sensing. Furthermore, we derive an algorithm to optimize the energy detection threshold for the cognitive users for any fusion rule. A second algorithm that optimizes both the energy threshold and the fusion rule is also proposed so as to minimize the total error probability. Based on this algorithm, an optimal sensing method for a cooperative cognitive radio network is suggested.

Overlap cooperative spectrum sensing with energy comparing in cognitive radio networks

In cognitive radio network, cooperation multiple secondary users can improve the performance of spectrum sensing. However, the sensing process duration is generally increasing because the number of the local decisions needing to be sent to the fusion center. Most alternative works consider a general time frame structure in which all the cognitive radio users (CRs) sense the signal in the same time and then each user must waits for its turn to report its observation. Hence, there is a waste of the time here and this time consumed by waiting can contribute little to the performance of spectrum sensing. In this paper, we propose an overlap spectrum sensing, the CRs keep collecting and fusing the signal while another is reporting to FC. By making use of the waiting time for sensing, the new framework provides a much wider observing window for spectrum measurement, which results in a performance improvement of spectrum sensing. Besides, we also apply the energy comparing to choose the good CR to send its local decision in each reporting time slot. The sensing performances of this sensing strategy are analyzed and confirmed by the Monte-Carlo simulation results.

Optimal secondary throughput over two primary channels in cooperative cognitive radio networks

In this paper, we investigated the throughput of a cognitive radio network where two primary frequency channels (PCs) are sensed and opportunistically accessed by N secondary users. The sharing sensing member (SSM) protocol is introduced to sense both PCs simultaneously. The throughput of the network is formulated as a convex optimization problem. The numerical investigation shows that the proposed optimal allocation improves the throughput of the SU under a misdetection constraint to protect the PCs.

Adaptive Decode-and-Forward Cooperative Networks with Multiple Relay Nodes

We propose an adaptive cooperative scheme with a multi-relay node that achieves high bandwidth efficiency and achieves better SEP performance. In the proposed protocol, if the quality of the direct channel is better than that of the all channels from relays to destination, the source will transmit directly to the destination. Otherwise, the source broadcasts the signal and then a potential relay will be chosen to help the source. A re-transmission will also occur if the potential relay cannot be detected. The spectral efficiency is first derived by calculating the probability of each mode, i.e., direct and cooperation transmission. Subsequently, the SEP performance of M-PSK modulation for the scheme is analyzed by considering each event where the source transmits data to the destination. Finally, the obtained analytical results are verified through computer simulations.

A crosslayer design approach for multihop diversity schemes with feedback capabilities

Motivated by the recent works on multihop diversity, this paper presents a crosslayer approach to design a multihop transmission protocol for wireless adhoc networks. We consider a transmission protocol for a multihop wireless network that does not restrict its transmission range within one hop. In the crosslayer design approach, we adopt diversity gain in the physical layer, automatic request for retransmission (ARQ) in the data-link layer and optimal number of hops in the network layer. We focus on the optimal transmission-rate and minimum number of hops of a linear multihop network. An optimal automatic request for cooperation (ARC) based multihop protocol is proposed to maximize the end-to-end throughput and minimize the number of retransmission. In this optimal protocol, all succeeding relays of a transmitting terminal require to receive the packet and send feedback. Although it gives the optimal performance, the implementation complexity of such protocol is very high. To achieve a good complexity-performance tradeoff, a K-hop ARC based multihop protocol is further proposed, where only the K succeeding relay nodes receive the transmitted packet and send feedback. Simulation results are provided to show that the proposed protocols outperform the conventional multihop protocol and the multihop diversity protocol in terms of end-to-end throughput.