Search

In this paper, we develop a queueing analysis for opportunistic decode-and-forward (DF) relay networks. It is assumed that the networks undergo Nakagami-m fading and that the external arrival process follows a Poisson distribution. By selecting the best relay according to the opportunistic relaying scheme, the source first transmits its signal to the best relay which then attempts to decode the reception and forwards the output to the destination. It is assumed that each relay operates in full-duplex mode, i.e., it can receive and transmit signals simultaneously. The communication process throughout the network can be modeled as a queueing network which is structured from sub-systems of M/G/1 and G/G/1 queueing stations. We invoke the approximate analysis, so-called method of decomposition, to analyze the performance behavior of the considered relay network. The whole queueing network is broken into separate queues which are then investigated individually. Based on this approach, the end-to-end packet transmission time and throughput of the considered relay network are quantified in comparison with the networks with partial relay selection (PRS).

In this study, the authors analyse the impact of channel estimation error (CEE), feedback delay (FD), and co-channel interference (CCI) on the performance of multiple-input multiple-output (MIMO) systems deploying maximum ratio transmission (MRT). In particular, the authors derive closed-form expressions for the ergodic capacity and the symbol error rate (SER) as well as the outage probability (OP). In addition, to reveal the effect of CEE, FD and CCI on the MIMO-MRT system, the authors adopt more simplified and tractable formulas in terms of asymptotic expressions for the ergodic capacity, SER and OP. The analysis shows that the system performance is degraded considerably under imperfect transmission conditions such as CEE, FD and CCI. However, the authors can compensate part of this degradation by deploying MRT transmission with a large number of antennas at the transmitter and receiver. Finally, the selected examples exhibit consistency between analytical results and Monte Carlo simulations.

In this paper, we investigate the effect of feedback delay on outage probability (OP) and symbol error rate (SER) of cognitive amplify-and-forward (AF) relay networks with beamforming transmission in Rayleigh fading environment. It is assumed that the secondary transmitter and the secondary receiver are equipped with multiple antennas, whereas the relay and the primary user comprise of a single antenna. Furthermore, in this system, the secondary users use the underlay scheme in which the secondary transmitter and the relay can coexist with the primary user as long as their interference caused to the primary receiver is below a predefined threshold. Through our analysis, numerical results are provided to show the level of degradation of cognitive AF relay systems in proportion to the degree of feedback delay. In addition, we also present the effect of the number of antennas at the secondary transceiver on the performance of the considered system.

In this paper, we study the performance of cognitive amplify-and-forward (AF) relay networks where the secondary users opportunistically access M licensed bands of the primary users over Nakagami-m fading channels. In order to enhance the accuracy of spectrum sensing and strongly protect the primary users from being interfered by the secondary transmission, collaborative spectrum sensing is deployed among the secondary transmitter, secondary relay, and secondary receiver. In particular, an analytical expression for the capacity of the considered network is derived. Numerical results are provided to show the influence of the arrival rate of the primary users on the channel utilization of licensed bands. Finally, the impact of the number of the licensed bands, channel utilization of the primary users, false alarm probability, and transmission distances on the capacity of the considered system are investigated.

In this paper, we study the use of transmit antenna selection (TAS) and maximal ratio combining (MRC) for a cognitive multiple-input multiple-output (MIMO) amplify-andforward (AF) relay network. We focus on the scenario that each of the source and relay selects only a single antenna which maximizes the instantaneous signal-to-noise ratio (SNR) to transmit and forward the signal while the receiver combines the signals from all receive antennas. Utilizing TAS, the considered cognitive network not only offers advantages such as achieving full diversity order with low transmit complexity but also reduces the interference induced to the primary transmission as compared to maximum ratio transmission (MRT). This in turn becomes beneficial for the secondary network when this network operates under the interference power constraint of the primary receiver. In particular, we derive expressions for the outage probability and symbol error rate (SER) of the network to evaluate the system performance. We also develop an asymptotic analysis for the outage probability and the SER to obtain diversity and coding gain. With the tractable asymptotic expressions, the effect of network parameters such as the number of antennas, the transmission distances, and the interference power constraint of the primary receiver on the system performance are readily revealed.

In this paper, we study the use of adaptive modulation (AM) for a dual-hop multiple-input multiple-output (MIMO) network with transmit antenna selection (TAS) at the transmitter and maximal ratio combining (MRC) at the receiver. Our system deploys incremental amplify-and-forward (AF) relaying with AM to forward the source signal. A switching policy for selecting between the relaying and the direct communications is utilized to maximize spectrum efficiency. In particular, we derive expressions for the outage probability, spectrum efficiency, and bit error rate (BER) for the considered system over Nakagamim fading. The considered network not only takes advantage of TAS transmission such as achieving full diversity order with low transmit complexity but also inherits the beneficial feature of AM such as spectrum efficiency improvement.

Motivated by a realistic scenario for cognitive radio systems, we model the underlay cognitive radio network (CRN) under interference power constraint imposed by the primary network as an M/G/1/K queueing system. The respective embedded Markov chain is provided to analyze several key queueing performance measures. In particular, the equilibrium probabilities of all states are derived and utilized to evaluate throughput, blocking probability, mean packet transmission time, mean number of packets in the system, and mean waiting time of an underlay CRN with Nakagami-m fading channels.

In this paper, we study the performance for the primary and secondary transmissions in cognitive radio networks where the amplify-and-forward (AF) secondary relay helps to transmit the signals for both the primary and secondary transmitters over independent Nakagami-m fading. First, we derive exact closed-form expressions for outage probability and symbol error rate (SER) of the primary network. Then, we derive an exact closed-form expression for outage probability and a closed-form expression of a tight upper bound for SER of the secondary network. Furthermore, we also make a comparison for the performance of the primary system with and without the help of the secondary relay.

In this paper, we examine the performance of multiple-input multiple-output cognitive amplify-and-forward (AF) relay systems with maximum ratio transmission (MRT). In particular, closed-form expressions in terms of a tight upper bound for outage probability (OP) and symbol error rate (SER) of the system are derived when considering channel estimation error (CEE) and feedback delay (FD) in our analysis. Through our works, one can see the impact of FD and CEE on the system as well as the benefits of deploying multiple antennas at the transceivers utilizing the spatial diversity of an MRT system.

In this paper, we investigate the performance of multiple-input multiple-output (MIMO) systems deploying maximum ratio transmission (MRT). Our analysis takes into account not only imperfect channel estimation at the receiver and feedback delay at the transmitter, but also includes co-channel interference (CCI). In particular, we first derive the statistical properties of the signal-to-interference-plus-noise ratio (SINR). Next, we obtain a closed-form expression for outage probability and an approximation for capacity. Finally, we show the consistency between analytical results and Monte-Carlo simulations. Our results indicate that the system performance is improved considerably in proportion to the number of transceiver antennas. Conversely, the outage probability increases, and the capacity decreases significantly with the severity of channel estimation error, feedback delay, and CCIs.