Investigation on iterative multiuser detection physical layer network coding in two-way relay free-space optical links with turbulences and pointing errors

Physical layer network coding (PNC) improves the throughput in wireless networks by enabling two nodes to exchange information using a minimum number of time slots. The PNC technique is proposed for two-way relay channel free space optical (TWR-FSO) communications with the aim of maximizing the utilization of network resources. The multipair TWR-FSO is considered in this paper, where a single antenna on each pair seeks to communicate via a common receiver aperture at the relay. Therefore, chip interleaving is adopted as a technique to separate the different transmitted signals at the relay node to perform PNC mapping. Accordingly, this scheme relies on the iterative multiuser technique for detection of users at the receiver. The bit error rate (BER) performance of the proposed system is examined under the combined influences of atmospheric loss, turbulence-induced channel fading, and pointing errors (PEs). By adopting the joint PNC mapping with interleaving and multiuser detection techniques, the BER results show that the proposed scheme can achieve a significant performance improvement against the degrading effects of turbulences and PEs. It is also demonstrated that a larger number of simultaneous users can be supported with this new scheme in establishing a communication link between multiple pairs of nodes in two time slots, thereby improving the channel capacity

Free Space Optical Wireless Communication with Physical Layer Network Coding

Terrestrial free-space optical (FSO) communications is an emerging low-cost, licensefree and high-bandwidth access solution for a number of applications including the “last mile” access network. However, for a transmission range from a few meter to longer than 1 km, a number of atmospheric phenomena, such as rain, haze, fog, snow, scintillation and pointing errors become a major performance limiting factors in FSO systems resulting in link deterioration and ultimately complete link failure. Relay-assisted technique is capable of mitigating the signal fading and maintain acceptable performance levels. In this thesis, a two-way relay (TWR) channel technique is adopted to increase system spectral efficiency, which in turn boosts the network throughput. This is achieved by using a physical layer network coding (PNC) technique, where network coding (NC) is applied at the physical layer. It takes advantage of the superimposition of the electromagnetic waves, and embraces the interference, which was typically deemed as harmful, by performing the exclusive-OR mapping of both users’ information at the relay. Therefore, the main contribution of this thesis is to study the design of the TWR-FSO communication system that embraces PNC technique for the full utilization of network resources based on the binary phase shift keying (BPSK) modulation. Moreover, error control coding (ECC) in conjunction with interleaving can be employed in FSO communications to combat turbulence-induced fading, which can enhance the performance of the proposed TWR-FSO PNC system. A comparative study between convolutional code (CC) and bit-interleave coded modulation with iterative decoding (BICM-ID) code are carried out. The result shows that the BICM-ID code outperforms the CC for TWR-FSO based PNC over strong turbulence regime by ~10dB of SNR to achieve a BER of 10-4 . However, the number of users that can be simultaneously transmitted to the relay is considered the main constraint in PNC system. Therefore, to overcome this challenge, a new scheme that integrates the iterative multiuser detection (I-MUD) technique with the PNC system over RF and FSO links are introduced as another achievement. The results show that the I-MUD offers improved performance about 8, and 22dB of SNR to get a BER of 10-4 over RF and FSO channels, respectively, for number of simultaneously users equal to 14 with respect to TWR-PNC system

BICM-ID with Physical Layer Network Coding in TWR Free Space Optical Communication Links

Physical layer network coding (PNC) is a promising technique to improve the network throughput in a two-way relay (TWR) channel for two users to exchange messages across a wireless network. The PNC technique incorporating a TWR channel is embraced by a free space optical (FSO) communication link for full utilization of network resources, namely TWR-FSO PNC. In this paper, bit interleaved coded modulation with iterative decoding (BICM-ID) is adopted to combat the deleterious effect of the turbulence channel by saving the message being transmitted to increase the reliability of the system. Moreover, based on this technique, comparative studies between end-to-end BICM-ID code, non-iterative convolutional coded and uncoded systems are carried out. Furthermore, this paper presents the extrinsic information transfer (ExIT) charts to evaluate the performance of BICM-ID code combined with the TWR-FSO PNC system. The simulation results show that the proposed scheme can achieve a significant bit error rate (BER) performance improvement through the introduction of an iterative process between a soft demapper and decoder. Similarly, Monte Carlo simulation results are provided to support the findings. Subsequently, the ExIT functions of the two receiver components are thoroughly analysed for a variety of parameters under the influence of a turbulence-induced channel fading, demonstrating the convergence behaviour of BICM-ID to enable the TWR-FSO PNC system, effectively mitigating the impact of the fading turbulence channel

Investigating the Impact of Mobility and Traffic Loads on Energy Consumption of MANETs

In Mobile Ad-hoc Networks (MANETs), the energy allocated per node are used for both data transmission and broadcasting control packets. Therefore the network lifetime depends on the nodes’ battery lifetime. The lifetime of the network will be reduced significantly if mobility and traffic loads increase in each node as more power is utilized than expected. This paper investigates the energy consumption of mobile nodes for different speeds and traffic loads. We observed that the higher the mobility of nodes, the more the energy it consumes. In particular, a node spends up to 95%of its energy when moving at the speed of 20m/s. In addition, the power consumption of a node increases when the traffic load on the network grow because nodes will need more power for processing

Performance evaluation of IDMA implementation with physical layer network coding

Physical layer network coding (PNC) technique has been adopted in recent works for increasing the system throughput in a two way relay channel (TWRC) where two users exchange their information via an intermediate node. In this paper, we investigate the effectiveness of increasing numbers of users for PNC technique where multiple pairs of users swap their information simultaneously through a single relay node for TWRC. This scheme uses interleave division multiple access (IDMA) for multiuser detection at the receiver. Moreover, a common chip level interleaver is shared for each pair of users instead of using a distinct chip level interleaver as in traditional IDMA. In addition, channel coding is integrated with the newly proposed scheme to achieve more reliable communications. The performance of the proposed system is investigated for the TWRC in terms of the bit error rate (BER)

Physical layer network coding with two-way relay free space optical communication link

Physical layer network coding (PNC) is a promising technique used to improve the network throughput in a wireless two-way relay (TWR) channel. In this paper, the PNC technique is embraced for a TWR-free space optical (FSO) communication link for the full utilization of network resources. Such a scheme is particularly useful in situations where multiple nodes wish to exchange their information but there is no direct link between them. Compared with a traditional relay-assisted FSO link, the new scheme uses two phases in a round loop for a TWR transmissions link. We present simulation results for the bit error rate (BER) performance of the proposed system considering the effect of both the atmospheric turbulence and the path loss using subcarrier intensity modulation binary phase shift keying (SIM-BPSK). The result shows that for the TWR FSO link based PNC technique under an atmospheric channel with a weak fading strength of 0.3, a BER of 10-4 is achieved at a signal-to-noise ratio (SNR) of ~25dB

Iterative multiuser detection with physical layer network coding for multi-pair communications

The physical layer network coding (PNC) technique has been utilized for increasing the system throughput in a two-way relay channel (TWRC) where the two users exchange their information via a relay node. In this paper, we investigate the effectiveness of increasing the number of users for the PNC technique where multiple pairs of users swap their information simultaneously through a single relay node for TWRC. This scheme relies on the iterative multiuser technique for detection of users at the receiver. Moreover, a common chip-level interleaver is shared for each pair of users wanting to exchange information. The performance of the proposed system is evaluated in term of bit error rate (BER) for iterative manner compared without iterative detection and the system shows the ability to increase the number of users. Moreover, the new scheme offers improved performance about 10 dB of signal to noise ratio (SNR) compared to the scheme without iterative detection to achieve a target BER of 10-3 over Rayleigh fading channel

Forward error correction with physical layer network coding in two-way relay free space optical links

Physical layer network coding (PNC) is a promising technique to improve the network throughput in a wireless two-way relay (TWR) channel. The PNC is embraced for TWR with free space optical (FSO) communication link, TWR-FSO, for full utilization of network resources. In this paper, forward error correction (FEC) is employed with TWR-FSO PNC system. The convolutional code (CC) is considered to combat the deleterious effect of FSO turbulence channel to increase the system reliability. The performance of end-to-end (E2E) CC with TWR-FSO PNC scheme is examined in terms of bit error rate (BER) under the influence of turbulence-induced channel fading. The results show that the proposed scheme can achieve a significant BER performance improvement through the introduction of CC joint with PNC mapping, which enables the system to effectively mitigate the impact of channel