Özgür Özdemir

ML performance analysis of digital relaying in bi-directional relay channels

The research challenges to enhance the throughput of communication networks revealed the concept of network coding which is based on the idea of coding at packet level. The bi-directional relay channel in which two user terminals exchange independent information with the help of a relay terminal is among the prominent applications of network coding in wireless cooperative communications. In this paper, maximum likelihood (ML) performance analysis of digital relaying based bi-directional communication is presented. The three stage communication scenario is considered where the first and second stages are allotted to the transmissions of the users and after demodulation the relay broadcasts the network encoded packet obtained by a bit-wise XOR operation to the users in the third stage. The average bit error rate of this scheme with ML detection is derived for Rayleigh fading channels under noncoherent BFSK and coherent BPSK signaling. Simulation results are also presented to validate the theoretical analysis. Analytical and simulation results show that digital relaying based three stage bi-directional communication scheme with ML detection not only outperforms the noncooperative system that involves direct transmissions between user terminals but also prevents the diversity level reduction due to error propagation. Copyright

Link adaptive relaying with noncoherent BFSK and DPSK modulations in multiple access relay channels

Network coding has recently received significant attention as an innovative approach to improve the throughput of wireless communication systems. The multiple access relay channel (MARC), in which multiple users communicate with a common destination via a relay, is one of the important network coding applications for wireless cooperative communications. In this paper, link adaptive relaying (LAR) approach which combats performance degradation due to error propagation in digital relaying based wireless networks has been applied to the MARC model with noncoherent binary frequency shift keying (BFSK) and differential binary phase shift keying (DPSK) signalings which are among the prominent techniques for eliminating the need for channel estimation by training sequences. Simulation results for Nakagami-m fading channels have shown that the proposed MARC model with LAR scheme outperforms the noncooperative system that involves direct transmissions and overcome the diversity gain reduction due to error propagation.

Side effect of metenolone enanthate on rats heart in puberty: Morphometrical study

The aim of this study was the investigation of effects of the metenolone enanthate (ME) that is used among athletes as doping and muscle amplifier, on hearts of male and female rats that are in puberty using morphometrical methods. A total of 36 rats which were divided into three separate groups (Experiment, ME; vehicle, PO; control, C) each consisting of 6 male and 6 female rats were used. 0.5 mg/kg metenolone enanthate was applied intraperitoneally into experiment subjects 5 times a week over a period of 4 weeks. At the end of experiment, rats were euthanized and their hearts were cut at the level of musculus papillaris after the fixation in formalin. Hearts were taken out and embedded in paraffin wax. Photos were taken at cut surfaces, and thickness, diameters and surface area levels were measured. Left ventriculus mass (LVM) and left ventriculus mass index (LVMI) were calculated. In the study LVM (p<0.005) and LVMI (p<0.05) were found to be significantly higher in the ME group in females whereas left ventricular lumen diameter (LVLD) were found to be significantly lower (p<0.05). Thus left ventricular hypertrophy development was observed. LVM and LVMI were found to be similar in ME and C groups among male rats and the highest level of these data were found in the group. LVM and LVMI were higher among females (p<0.006). In conclusion, it has been shown that the adverse effects of ME on heart were developing starting from puberty and resulting with the enlargement of the heart and left ventricular hypertrophy and especially among females this condition was more evident. It has also been discussed that the continuous use of drugs may further enhance this condition.

Differential network coding in wireless networks

In this paper a three-terminal communication scenario where two users exchange information by employing differential binary modulation and network coding via a relay is considered. The transmission is divided into three slots in time where the first and second slots are allocated to the transmission of differential encoded data of the users. After demodulation, the relay broadcasts the bit-wise XOR-ed and differential encoded packet to the users in the third slot. The optimum detector and a simplified decision algorithm are derived based on the maximum likelihood rule. The numerical results for Rayleigh fading show that both of the proposed algorithms provide full diversity order. The simulations also demonstrate that the proposed differential network coded transmission not only offers a sum-rate gain of up to 4/3 compared to classical bi-directional relaying with four communication slots but also provides better BER performance as the signal to noise ratio increases.

SNR-based antenna selection schemes for cooperative relay networks in wireless channels

In this paper, two different antenna selection models based on signal-to-noise ratio (SNR) have been proposed in order to reduce the end-to-end bit error rate (BER) of decode and forward (DF) relaying cooperative system where source and destination terminals contain single antenna while relay terminal has multiple antennas. Specifically, by using instantaneous and average SNR of source-to-destination, source-to-relay and relay-to-destination links, optimal decision rules are derived theoretically for antenna selection at the relay terminal. Later, BER expressions of considered system have been derived for two antenna selection models over Rayleigh fading channels. Theoretical and simulation results show the validity of proposed mathematical analysis and point out the confirmation of theoretical results.

Antenna selection for decode and forward based MIMO cooperative networks

In this paper, a cooperative system structure that utilizes decode and forward (DF) method with antenna selection based on the signal to noise ratio (SNR) have been proposed. In order to decrease performance degradation due to error propagations in DF based wireless cooperative networks and increase the error performance of the system, selection combining (SC), classical maximal ratio combining (MRC), cooperative-maximal ratio combining (C-MRC) and link adaptive regeneration (LAR) techniques have been utilized at destination. Error performance analyses of the considered structures are investigated using optimal decision rules determined theoretically for the corresponding relaying strategy.

Network coded noncoherent cooperative communications

In recent years, network coding has received significant attention as an innovative approach that improves the spectral efficiency of wireless communication systems. The Multiple Access Relay Channel (MARC) where multiple users communicate with a common destination via a relay, is one of the important network coding applications in wireless cooperative communications. In this paper, error performance of MARC system non-coherent BFSK technique is studied. This technique, which employs training sequences, is a prominent approach for decreasing the system complexity and cost by eliminating the need for channel estimation. The numerical results for Rayleigh fading channels have shown that proposed approach provides full diversity gain.

Exact BER Performance Analysis of Link Adaptive Relaying with Noncoherent BFSK Modulation

Link adaptive relaying (LAR) is one of the most popular techniques developed for mitigating error propagation in decode and forward (DF) based cooperative wireless networks which employs soft power scaling approaches at the relay nodes. On the other side, frequency shift keying (FSK) is a prominent technique for eliminating the need for channel estimation by training sequences which increases complexity of the system and causes reduction in the transmission rate in proportional to the number of users involved in the network. In this paper, performance of an LAR scheme with noncoherent binary FSK (BFSK) signaling is investigated by deriving exact closed form bit error rate expressions in Rayleigh fading channels.

Mitigating error propagation in multiple access relay channels

Network coding has recently received significant attention as an innovative approach that improves the spectral efficiency of wireless communication systems. The multiple access relay channel (MARC) where multiple users communicate with a common destination via a relay, is one of the important network coding applications in wireless cooperative communications. In this paper, selective relaying (SR) and maximum likelihood (ML) detection approach which combat performance degradation due to error propagation in digital relaying based wireless networks have been applied to the MARC model. Simulation results for Rayleigh fading channels show that both SR and ML detection schemes outperform the noncooperative system that involves direct transmissions and overcome the diversity gain reduction due to error propagation.Network coding has recently received significant attention as an innovative approach that improves the spectral efficiency of wireless communication systems. The multiple access relay channel (MARC) where multiple users communicate with a common destination via a relay, is one of the important network coding applications in wireless cooperative communications. In this paper, selective relaying (SR) and maximum likelihood (ML) detection approach which combat performance degradation due to error propagation in digital relaying based wireless networks have been applied to the MARC model. Simulation results for Rayleigh fading channels show that both SR and ML detection schemes outperform the noncooperative system that involves direct transmissions and overcome the diversity gain reduction due to error propagation.

Error performance analysis of decode and forward based cooperative systems with relay selection

In this paper, error performance analysis of a cooperative system with relay selection that utilizes decode and forward (DF) method is considered. The source-relay, relay-destination and source-destination links are modeled as Nakagami-m distributed random variables. The effects of the cooperative maximal ratio combining (C-MRC) used to decrease performance degradation due to error propagation in DF based wireless cooperative networks and classical maximal ratio combining (MRC) methods on error performance of the system are investigated with computer simulations. It has been shown that C-MRC technique provides significant performance improvement with respect to the MRC method.