• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.33 no.4A
• /
• pp.361-370
• /
• 2008

Cooperative relaying permits one or more relay to transmit a signal from the source to the destination, thereby increasing network coverage and spectral efficiency. The performance of cooperative relaying is often measured as outage probability. However, appropriate measure for the channel quality is outage capacity. Although the outage probability for cooperative relaying protocol has been analyzed before, very little research has been addressed for the outage capacity. This paper is the first of its kind to derive a closed-form analytical solution of outage capacity using fixed decode and forward relaying and amplify and forward relaying in dissimilar Rayleigh fading channels, considering channel coefficients known to the receiver side. The analytical results show a tradeoff between the SNR and the number of relays for specific outage capacity. A comparison between decode and forward relaying and amplify and forward relaying shows that decode and forward relaying outperforms amplify and forward relaying for a large number of relays.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.35 no.5C
• /
• pp.487-494
• /
• 2010

This paper presents an OFDM-based dual-hop multi-relay system with best relay selection maximizing the mutual information. For the system either with decode-and-forward (DF) relays or with amplify-and-forward (AF) relays, we derive a lower-bound on the outage probability and the diversity order achievable in frequency selective fading channels and provide the outage capacity from simulation. Performance evaluation shows that both DF and AF provide the same diversity order as in the lower-bound but DF of which the outage probability is much closer to the lower-bound provides a better outage capacity than AF. It is also observed that the SNR gain of DF over AF gets larger as either the number of resolvable multipaths or the number of relay candidates increases, which makes DF relaying more favorable to the OFDM-based multi-relay system.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.9 no.5
• /
• pp.31-37
• /
• 2009

In the two-way relay channel, the relay employ Amplify-and-Forward (AF) or Decode-and-Forward (DF) protocol, and broadcast the network-coded signal to both user. In the system, DF protocol provides maximum throughput at low signal to noise ratio(SNR). On the other hand, at high SNR, AF protocol provides maximum throughput. The paper propose active transmission scheme which employ Amplify-and-Forward or Decode-and-Forward protocol based on received SNR at the relay over Two-way relay channel. The optimal threshold is investigated numerically for switching the protocol. Through numerical results, we confirm that the proposed scheme outperforms conventional schemes over two-way relay channel.

• Journal of Communications and Networks
• /
• v.12 no.6
• /
• pp.616-623
• /
• 2010

In this paper, exact closed-form expressions for outage probability and bit error probability (BEP) are presented for multi-hop decode-and-forward (DF) relaying schemes in conjunction with cooperative diversity, in which selection combining technique is employed at each node. We have shown that the proposed protocol offers remarkable diversity advantage over direct transmission as well as the conventional DF relaying schemes with the same combining technique. We then investigate the system performance when different diversity schemes are employed. It has been observed that the system performance loss due to selection combining relative to maximal ratio combining is not significant. Simulations are performed to confirm our theoretical analysis.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.36 no.9A
• /
• pp.776-783
• /
• 2011

In this paper, assuming that the transmitter can exploit imperfect channel state information (CSI), the diversity-multiplexing tradeoff (DMT) functions of three adaptive decode-and-forward (DF) relay protocols, each of which uses multiple-antennas at the destination node, at the relay node, or at the source node are derived. When the imperfect CSI qualities for the source-relay link, the relay-destination link, and the source-destination link are subject to asymptotic conditions, the additional diversity gains attainable by exploiting the imperfect CSI at the transmitter for those three adaptive DF relay protocols are investigated.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.12 no.1
• /
• pp.81-108
• /
• 2018

In this paper, we derive the theoretical Symbol Error Probability (SEP) of cooperative systems with best relay selection for Nakagami-m fading channels. For Amplify and Forward (AF) relaying, the selected relay offers the best instantaneous Signal to Noise Ratio (SNR) of the relaying link (source-relay-destination). In cooperative networks using Decode and Forward (DF), the selected relay offers the best instantaneous SNR of the link between the relay and the destination among the relays that have correctly decoded the transmitted information by the source. In the second part of the paper, we derive the SEP when all participating AF and DF relaying is performed. In the last part of the paper, we extend our results to cognitive radio networks where there is interference constraints : only relays that generate interference to primary receiver lower than a predefined threshold T can transmit. Both AF and DF relaying with and without relay selection are considered.

• Journal of information and communication convergence engineering
• /
• v.11 no.4
• /
• pp.229-234
• /
• 2013

Diversity-multiplexing tradeoff (DMT) characterizes the fundamental relationship between the diversity gain in terms of outage probability and the multiplexing gain as the normalized rate parameter r, where the limiting transmission rate is give by rlog SNR (here, SNR denote the received signal-to-noise ratio). In this paper, we analyze the DMT and performance of an underwater network with a cooperative relay. Since over an acoustic channel, the propagation delay is commonly considerably higher than the processing delay, the existing transmission protocols need to be explained accordingly. For this underwater network, we briefly describe two well-known relay transmissions: decode-and-forward (DF) and amplify-and-forward (AF). As our main result, we then show that an instantaneous DF relay scheme achieves the same DMT curve as that of multiple-input single-output channels and thus guarantees the DMT optimality, while using an instantaneous AF relay leads at most only to the DMT for the direct transmission with no cooperation. To validate our analysis, computer simulations are performed in terms of outage probability.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.12A
• /
• pp.1260-1266
• /
• 2007

Error propagation of source-relay (S-R) link limits the performance of decode-and-forward (DF) relay and prohibits DF relay from achieving full diversity gain. In order to solve this problem, the proposed deployment strategy focuses on two objectives. One is to achieve full diversity gain, and the other is to minimize the used power of the DF relay system. In order to achieve full diversity, the error probability of S-R link should be lower than that of maximal ratio combining (MRC) at destination without error propagation since the error probability of the weaker link dominates the total error probability. The proposed strategy of relay positioning points out the range of the relay position for achieving full diversity, and the used power of the relay is minimized by this range. Analysis of error probability and simulation results prove that the two objectives are achieved by the proposed strategy of the relay position.

• The KIPS Transactions:PartC
• /
• v.14C no.7
• /
• pp.597-602
• /
• 2007

In conventional cooperative communication data rate is 1/2 than non cooperative protocols. In this paper, we propose a full data rate DF (Decode and Forward) cooperative transmission scheme. Proposed scheme is based on time division multiplexing (TDM) channel access. When DF protocol has full data rate, it can not obtain diversity gain under the pairwise error probability (PEP) view point. If it increases time slot to obtain diversity gain, then data rate is reduced. The proposed algorithm uses orthogonal frequency and constellation rotation to obtain both full data rate and diversity order 2. Moreover, performance is analyzed according to distance and optimized components that affect the system performance by using computer simulation. The simulation results revealed that the cooperation can save the network power up to 7dB over direct transmission and 5dB over multi-hop transmission at BER of $10^{-2}$. Besides, it can improve date rate of system compared with the conventional DF protocol.

• Journal of Communications and Networks
• /
• v.15 no.3
• /
• pp.266-275
• /
• 2013

The exact closed-form expressions for outage probability and bit error rate of spectrum sharing-based multi-hop decode-and-forward (DF) relay networks in non-identical Rayleigh fading channels are derived. We also provide the approximate closed-form expression for the system ergodic capacity. Utilizing these tractable analytical formulas, we can study the impact of key network parameters on the performance of cognitive multi-hop relay networks under interference constraints. Using a linear network model, we derive an optimum relay position scheme by numerically solving an optimization problem of balancing average signal-to-noise ratio (SNR) of each hop. The numerical results show that the optimal scheme leads to SNR performance gains of more than 1 dB. All the analytical expressions are verified by Monte-Carlo simulations confirming the advantage of multihop DF relaying networks in cognitive environments.