Hyung Yun Kong

General expression for pdf of a sum of independent exponential random variables

In order to evaluate exactly the performance of some diversity schemes, the probability density function (pdf) of a sum of independent exponential random variables (r.v.s) must be known. This paper proposes a simple method to find it by using characteristic function., The resultant pdf is successfully applied to formulate the closed-form BER expression of 2 Tx-J Rx transmit diversity as well as the outage probability of repetition coding.

Exact outage probability of cognitive two-way relaying scheme with opportunistic relay selection under interference constraint

In this study, the authors analyse the outage performance of a cognitive two-way relaying system under an interference constraint. In the proposed protocol, the best relay which is chosen by an opportunistic relay selection strategy, combines the received packets using XOR operation and then forwards the combined packet to two secondary sources. The authors derive an exact closed-form expression of outage probability over flat and block Rayleigh fading channels. Various Monte-Carlo simulations are presented to verify the theoretical analyses and to compare the performance of the proposed protocol with that of the two-way relaying protocol without network coding.

LLR-Based Decode-and-Forward Protocol for Relay Networks and Closed-Form BER Expressions

Decode-and-forward cooperative communications protocol (DFP) allows single-antenna users in wireless medium to obtain the powerful benefits of multi-antenna systems without physical antenna arrays. So far, only signal-to-noise ratio (SNR) or square amplitude of path gain has been used to evaluate the reliability of received signals for relays to decide whether to forward the decoded data so as to prevent unsuccessful detection at the relays. In this paper, we propose using log-likelihood ratio (LLR) as an alternative to SNR in the conventional DFP. Closed-form BER expressions for different versions of DFP are also derived and verified by Monte-Carlo simulations. A variety of numerical results reveal the significant superiority of LLR-based DFP to SNR-based DFP regardless of threshold level and relay position under flat Rayleigh fading channel plus additive white Gaussian noise (AWGN).

Performance Analysis of Two-Way Hybrid Decode-and-Amplify Relaying Scheme with Relay Selection for Secondary Spectrum Access

In this paper, we propose and analyze the outage probability of a two-way hybrid decode-and-amplify relaying scheme with relay selection for secondary spectrum access. In this scheme, a secondary network is co-located and uses the same spectrum as the primary network. The primary network is comprised of two primary terminals that attempt to transmit signals to one another; the secondary network is comprised of M secondary transmitter-receiver pairs (ST-SR). One of the secondary transmitters chosen to cooperate with the primary network uses a hybrid decode-and-amplify forward technique in order to relay primary and secondary signals. We derive expressions for the outage probability of the primary network as well as the secondary network over a Rayleigh fading channel. Simulation results are presented to verify theoretical analyses and to compare the performance of the proposed protocol to that of a two-way direct transmission protocol.

Performance Analysis of Incremental Amplify-and-Forward Relaying Protocols with Nth Best Partial Relay Selection Under Interference Constraint

In this paper, we investigate two incremental amplify-and-forward relaying protocols in cognitive underlay networks. In the proposed protocols, whenever the secondary destination cannot receive the secondary source’s signal successfully, it requests a retransmission from one of M secondary relays. In the first protocol, we assume that a secondary relay with the Nth best channel gain to the secondary source is used to forward the received signal to the secondary destination. In the second protocol, relying on the quality of channels between the secondary relay and secondary destination and between the secondary relay and primary user, the Nth best relay is chosen for the retransmission. We derive exact closed-form expressions of the outage probability and average number of time slots for both protocols over Rayleigh fading channel. Finally, these mathematical expressions are then verified by Monte Carlo simulations.

Ergodic and outage capacity of interference temperature-limited cognitive radio multi-input multi-output channel

In this study, we consider a cognitive radio multi-input multi-output (CR-MIMO) system in which the cognitive radio (CR) users are allowed to access the spectrum of the licensed primary users, provided that interference power received at the primary receiver is less than a certain threshold. The authors investigate the effect of the MIMO diversity on such multi-constraint CR-MIMO systems. They consider peak interference power constraint at the primary receiver and peak transmit power constraint at the CR transmitter. In MIMO systems, the allowable transmit power is distributed over the transmit-antennas. The power allocation problem of such CR systems is studied under both sum power and interference constraints. The authors show that the equal power allocation does not improve the ergodic capacity but improves the outage capacity over the single-input single-output (SISO) system. Transmit antenna selection (TAS) which is a special case of power allocation is also investigated. The authors show that, under the peak interference and transmit power constraint, selecting a single transmit-antenna and allocating all the power to the selected best antenna achieves the same performance as the optimal power allocation (OPA). The authors evaluate ergodic capacity and outage capacity for both power allocation- and antenna selection-based schemes. The closed-form expressions of the outage probabilities are also derived. Results show that both OPA and TAS significantly improves the capacities over the SISO system.

Distributed switch and stay combining for selection relay networks

We propose an efficient combination of distributed switch and stay and selection relay that offers the best performance at high SNRs compared to conventional selection relay schemes and to incremental relaying schemes in conjunction with selection relay. Our results, in terms of bit error probability, confirm the benefit of the proposed scheme at high SNR regime. We also show that the high-SNR performance of the proposed scheme with more than two relays is dominated by the decode- and- forward relaying link.

Performance analysis of hybrid decode-amplify-forward incremental relaying cooperative diversity protocol using SNR-based relay selection

In this paper, we propose a hybrid decode-amplify-forward incremental cooperative diversity protocol using SNR-based relay selection. In the proposed protocol, whenever destination unsuccessfully receives the sources signal, one of relays that exploit hybrid decode-amplify-forward technique is chosen to retransmit the signal. We derive approximate closed-form expressions of outage probability and average channel capacity. MonteCarlo simulations are presented to verify the theoretical results and compare the performance of the proposed protocol with the direct transmission protocol and conventional incremental relaying protocols.

Performance Analysis of Incremental Selection Decode-and-Forward Relaying over Rayleigh Fading Channels

Selection decode-and-forward (DF) relaying and incremental relaying were introduced as efficient relaying protocols to increase capacity and performance of cooperative diversity networks. This paper proposes an incremental relaying in conjunction with selection DF and provides its performance in terms of outage probability and bit error probability. Our proposed protocol offers a good trade off between performance and channel resource with an appropriate given threshold. Simulations are performed to confirm our theoretical analysis.

Performance Analysis of M-PAM and M-QAM with Selection Combining in Independent but Non-Identically Distributed Rayleigh Fading Paths

A compact expression for pdf of SC combiner on independent but not necessarily identical distributed Rayleigh fading channels is derived. Using this expression, new exact-closed form expressions for average SER and average BER of M-PAM and M-QAM are studied. The proposed mathematical analysis is verified by various simulation results which demonstrate the accuracy of the theoretical approach.