This paper investigates the potential of Non-Terrestrial Networks (NTNs) as a resilient complement to terrestrial 5G/6G infrastructure in Singapore. It focuses on scenarios where terrestrial networks are unavailable, such as during nationwide outages. Through link budget analysis and antenna modeling, the study evaluates the capabilities of High-Altitude Platforms (HAPs), Very Low Earth Orbit (VLEO), and Low Earth Orbit (LEO) satellites. The findings indicate that HAPs are well-suited for urban environments due to their compact antenna requirements and favorable beam characteristics, while VLEO and LEO systems provide wider coverage, making them ideal for maritime applications. The analysis offers insights into system design, cell sizing, and interference mitigation, supporting the integration of NTNs into future communication networks.

As an important role in achieving seamless world-wide coverage for the maritime communication, the VDE satellite component (VDE-SAT) aims to provide efficient services to a large number of ship terminals each with only a limited satellite coverage time, which requires efficient resource allocation strategies. In this paper, we investigate the downlink VDE-SAT system consisting of a low-earth orbiting (LEO) satellite communicating with multiple randomly distributed ship terminals. As the LEO satellite orbits the Earth at a fixed altitude and speed, ship terminals are served in a periodic manner with known but periodically time-varying channel gains from the satellite. By exploiting the periodic channel gain variations in the line-of-sight (LoS) dominant satellite-ship channels, we propose an angle partition based time division multiple access (TDMA) scheme to schedule downlink communications from the satellite to ship terminals based on the moving satellite's real-time position. Specifically, time resources allocated to different ship terminals are optimized via the partition of the satellite's azimuth angle range to maximize their minimum/common throughput. Simulation results verify the effectiveness of the proposed angle partition-based TDMA scheme and show its performance improvement over benchmark schemes.

This paper evaluates the performance of FASTAR code in Multimedia Broadcast Multicast Service (MBMS) System. It is demonstrated that FASTAR code, which is optimised for erasure channel through its overhead minimising degree distribution, can improve the system performance compared to the conventional systematic Raptor code. The system is simulated under the Evolved UMTS Terrestrial Radio Access (E-UTRA) network environment according to 3GPP LTE-A specifications. The extent of the improvement and its relation to the system parameters are also studied.

This paper presents the outage probability analysis of Joint Channel and Network Coding (JCNC) scheme in Multiple Access Relay Channel (MARC). In particular, the effect of using different interleaver patterns at different users is analysed. The motivation of this work is to show that despite its capability of achieving up to 2 dB gain in Packet Error Rate (PER), the corresponding outage probability improvement is only minimal (upper bounded at approximately 0.6 dB). This signifies that the improvement achieved by using different interleaver patterns is largely attributed by the ability of iteratively decodable codes to perform closer to the capacity limit compared to the conventional convolutional code with Soft Input Soft Output (SISO) decoder.

In this paper, a novel transmission scheme which incorporates network coding into rateless transmission over relay networks is proposed. This technique allows partial information about the upcoming message block to be transmitted during the current block transmission, hence reducing the required number of transmissions and improving the spectral efficiency. Different techniques for applying network coding to several fading models are discussed, and their relationships to an erasure channel model is explained. An optimisation of the network coding weight is given, and we show that by choosing the weight that minimizes the duration of the current block transmission and sending sufficient information about subsequent block, we can improve the overall performance.

In this paper, we propose a technique to improve the performance of Joint Channel and Network Coding (JCNC) scheme in Multiple Access Relay Channel (MARC). This technique is motivated by the observation that decoding quality is improved when channel output can be processed iteratively. Using different permutation patterns for different users, we enabled more scenarios that destination can apply iterative decoding, thereby achieving an improvement in the overall performance. The proposed scheme is evaluated for Gaussian channels and Rayleigh fading channels, and it is shown to perform well in both cases. A comparative study is also given, and it is shown that up to 3dB and 6dB gain from the original JCNC scheme is achievable in AWGN and Rayleigh fading channels respectively.

In this paper, a transmission strategy of fountain codes over cooperative relay networks is proposed. When more than one relay nodes are available, we apply network coding to fountain-coded packets. By doing this, partial information is made available to the destination node about the upcoming message block. It is therefore able to reduce the required number of transmissions over erasure channels, hence increasing the effective throughput. Its application to wireless channels with Rayleigh fading and AWGN noise is also analysed, whereby the role of analogue network coding and optimal weight selection is demonstrated.

In this paper, transmission of fountain code over cooperative networks is considered. While it is known that fountain code is optimal for sending data to multiple receivers, extra care is needed when it is used in cooperative networks. On one hand, the presence of relay node can help to improve the overall performance. On the other hand, multiple relay nodes introduce the problem of mutual interference, which can potentially degrade the performance. This work proposes an amplitude modulation scheme to address the above issue. By appropriately scaling the output signal at each node according to their unique identifier, separability of data from several transmitters at the destination can be achieved. A numerical analysis highlighting the advantage of the proposed scheme is then presented.

The problem of carrier and clock synchronization without a training sequence for a robust receiver working at low signal-to-noise (SNR) ratios is considered. Both short packet and long burst transmission scenarios are taken into account. A low-complexity iterative symbol timing and carrier synchronization algorithm making use of the extrinsic information from the soft- input soft-output (SISO) decoder is proposed. The non-data-aided (NDA) algorithms are used for initial synchronization. In order to solve the phase ambiguity problem inherent in the NDA phase synchronization algorithm, two SISO decoders denoted by I and Q decoders, respectively, along with a differential decoder are proposed. The simulation results show that the proposed iterative synchronizer and decoder can reach the ideal performance at very low SNR with an increased allowed residual frequency offset and [-pi,pi] phase uncertainty region.

We consider the problem of carrier frequency and phase synchronization at low SNR without a training sequence for short packet transmission. A low-complexity iterative joint symbol timing and carrier synchronization algorithm making use of the extrinsic information from the soft-input soft-output (SISO) decoder is proposed. The non-data-aided (NDA) algorithms are used for initial synchronization. The simulation results show that the frequency offset estimation is the most critical problem in low SNR region. The proposed low-complexity algorithm can reach the ideal performance with perfect synchronization in the absence of frequency offset at very low SNR. When the frequency offset exists, the proposed algorithm can work effectively and improve the performance significantly.

In this paper, we address the problem of multiple-input multiple-output (MIMO) spatial multiplexing (SM) systems in the presence of antenna fading correlation. It is well known that severe spatial correlations present at the transmitter and/or receiver can significantly compromise the performance of existing SM systems. Recent results showed that joint-over-antenna (JA) iterative detection schemes can improve the performance of SM systems in correlated channels as compared to schemes that detected the signals on an antenna-by-antenna basis. We extend this idea in this paper by incorporating a so-called antenna doping (AD) scheme into the SM system, in order to further counteract the detrimental effects of spatial correlation. Through simulations, we show that AD can improve the performance by 3-4 dB in severe spatial correlation as compared to non-doping systems. This improvement is explained with the aid of extrinsic information transfer (EXIT) charts, which illustrate the convergence behavior of the JA iterative detection with and without AD.

In this paper, an adaptive parallel interference cancellation (PIC) scheme is proposed for the asynchronous multicarrier direct sequence code division multiple access (MC-DS-CDM A) system. An adaptive MAI estimation algorithm is applied before the PIC stage to improve the accuracy of the MAI cancellation. The performance behaviour of our proposed detector is investigated and its analytic hit error probability is derived. The theoretical results agreed well with the simulations. It is shown that the adaptive PIC receiver outperforms the matched filter and the conventional PIC receiver for the MC-DS-CDMA system in a fading channel.

In this contribution we propose a novel M-ary coded modulation assisted genetic algorithm based multiuser detection (CM-GA-MUD) scheme for synchronous CDMA systems. The performance of the proposed scheme was investigated using quadrature-phase-shift-keying (QPSK), 8-level PSK and 16-level quadrature amplitude modulation (16QAM) when communicating over AWGN and narrowband Rayleigh fading channels. When compared with the optimum MUD scheme, the GA-MUD subsystem is capable or reducing the computational complexity significantly. On the other hand, the CM subsystem is capable of obtaining considerable coding gains despite being fed with sub-optimal information provided by the GA-MUD output.

A spatial diversity reception assisted multiuser code-division multiple-access detector based on genetic algorithms (GAs) is proposed. Two different GA-based individual-selection strategies are considered. In our first approach, the so-called individuals of the GA are selected for further exploitation, based purely on the sum of their corresponding figures of merit evaluated for the individual antennas. According to our second strategy, the GA's individuals are selected based on the concept of the so-called Pareto optimality, which uses the information from the individual antennas independently. Computer simulations showed that the GAs employing the latter strategy achieve a lower bit-error rate as compared to the former strategy. For a 15-user GA-assisted system employing a spreading factor of 31, a complexity reduction factor of 81 was achieved at a performance identical to that of the optimum multiuser detector using a full search.

Binary phase shift keying (BPSK) and quaternary phase shift keying (QPSK) were often used as the underlying modulation scheme for demonstrating the performances of the various multi-user detection and interference cancellation methods for direct sequence-code division multiple access (DS-CDMA) systems. On the other hand, M-level quadrature amplitude modulation (M-QAM) is fast becoming an attractive modulation technique for future wireless communications, due to its high spectral efficiency. Based on a fixed bit and chip rate, we study the performance of a decorrelator as well as a successive interference cancellation (SIC) scheme for an M-QAM-based DS-CDMA system.

The up-link transmissions of mobile stations are typically uncoordinated, which lead to asynchronous DS-CDMA systems. Provided that the propagation delay differences of users are less than one symbol duration, every bit of each user is interfered by two consecutive bits of every other user supported by the system which are overlapping with the bit of interest. This is only true, however, with the proviso of an identical channel bit rate for all the users. Hence the multiuser detector (MUD) must have knowledge of these two overlapping bits, in order to efficiently detect the desired bit (DB). Suboptimal MUDs have been proposed based on a truncated observation window, in which the overlapping 'edge' bits are tentatively estimated by some other means. Using a similar approach, a MUD is developed in this contribution which invokes genetic algorithms (GAs), in order to estimate the DBs within the truncated observation window as well as to simultaneously improve the edge bits error probability (EBEP). Computer simulations showed that by using GAs for improving the reliability of the edge bits, our proposed MUD can achieve a near-optimum EBEP performance, while imposing a lower complexity compared to that of the optimum MUD.

A novel multiuser code division multiple access (CDMA) receiver based on genetic algorithms is considered, which jointly estimates the transmitted symbols and fading channel coefficients of all the users. Using exhaustive search, the maximum likelihood (ML) receiver in synchronous CDMA systems has a computational complexity that is exponentially increasing with the number of users and, hence, is not a viable detection solution. Genetic algorithms (GAs) are well known for their robustness in solving complex optimization problems. Based on the ML rule, GAs are developed in order to jointly estimate the users' channel impulse response coefficients as well as the differentially encoded transmitted bit sequences on the basis of the statistics provided by a bank of matched filters at the receiver. Using computer simulations, we showed that the proposed receiver can achieve a near-optimum bit-error-rate (BER) performance upon assuming perfect channel estimation at a significantly lower computational complexity than that required by the ML optimum multiuser detector. Furthermore, channel estimation can be performed jointly with symbol detection without incurring any additional computational complexity and without requiring training symbols. Hence, our proposed joint channel estimator and symbol detector is capable of offering a higher throughput and a shorter detection delay than that of explicitly trained CDMA multiuser detectors.

The performance of Reed-Solomon (RS) coded direct-sequence code division multiple-access (DS-CDMA) systems using noncoherent M-ary orthogonal modulation is investigated over multipath Rayleigh fading channels. Equal gain combining (EGC) diversity reception is invoked and the related performance is evaluated for both uncoded and RS-coded DS-CDMA systems. 'Errors-and-erasures' decoding is considered, where the erasures are based on Viterbi's (1982) so-called ratio threshold test (RTT). The performance of the 'errors-and-erasures' decoding technique employing the RTT is compared to that of 'error-correction-only' decoding over multipath Rayleigh fading channels. The numerical results show that when using RTT-based 'errors-and-erasures' decoding, RS codes of a given code rate can achieve a higher coding gain than without erasure information.

The performance of Reed-Solomon (RS) coded direct-sequence code division multiple-access (DS-CDMA) systems using noncoherent M-ary orthogonal modulation is investigated over multipath Rayleigh fading channels. Diversity reception techniques with equal gain combining (EGC) or selection combining (SC) are invoked and the related performance is evaluated for both uncoded and coded DS-CDMA systems. "Errors-and-erasures" decoding is considered, where the erasures are based on Viterbi's (1982) so-called ratio threshold test (RTT). The probability density functions (PDF) of the ratio associated with the RTT conditioned on both the correct detection and erroneous detection of the M-ary signals are derived. These PDFs are then used for computing the codeword decoding error probability of the RS coded DS-CDMA system using "errors-and-erasures" decoding. Furthermore, the performance of the "errors-and-erasures" decoding technique employing the RTT is compared to that of "error-correction-only" decoding refraining from using side-information over multipath Rayleigh fading channels. As expected, the numerical results show that when using "errors-and-erasures" decoding, RS codes of a given code rate can achieve a higher coding gain than without erasure information.