Multiple User Interference Research Articles

Coalitional game based sub-channel allocation for full-duplex-enabled mmWave IAB network in B5G

The combination of full-duplex communication (FDC) and millimeter wave integrated access and backhaul (mmWave IAB) is a highly implementable technique in beyond 5G era. However, the technical challenges such as sub-channel allocation and interference coordination must be effectively handled before the attractive benefits of the commercial implementation are enjoyed. In particular, the multiple user interference (MUI) is caused when the same sub-channel is shared by the concurrent links sourced from different transmitters, and the residual self-interference (RSI) is resulted from self-interference cancellation (SIC) in FDC. To this end, a coalitional game based sub-channel allocation mechanism is proposed for the full-duplex-enabled mmWave IAB network to maximize the total actual achievable rate. Firstly, the maximization problem of the sum actual achievable rate is formulated as an integer non-convex and non-linear optimization problem under the constriction of MUI and RSI, which is a non-polynomial hard (NP-Hard) problem, and it is intractable to obtain the optimal solution. Secondly, the formulated problem is transformed as a cooperative game, and a coalitional game based sub-channel allocation (CGSA) algorithm with lower computational complexity is proposed to obtain the sub-optimal solution. Thirdly, the properties of the proposed CGSA algorithm are discussed and analyzed from the aspects of stability and convergence, and it is proved that the final coalition partition formed by the proposed CGSA algorithm is Nash-stable. Fourthly, the proposed CGSA algorithm is compared with the reference algorithms under different scenarios, extensive simulations show that superiorities of the proposed CGSA algorithm are obvious including sum of achievable rate, number-ratio of user equipments with satisfied quality-of-service (QoS)requirement and iterations of algorithm convergence.

Novel technique to cancel MAI for OCDMA system

Abstract Code division multiple access in optical domain has a potential in next-generation long-haul transmission systems. However, multiple user interference is a snag in functioning of system employing OCDMA. A detailed analysis of multiple access interference (MAI) which causes a severe degradation in the system performance is done in this paper. An optimum MAI cancellation scheme has been proposed. This cancellation scheme depends not only on using the excellent correlation property of the double padded modified prime codes (DPMPC) as spreading sequence but also on employing minimum shift keying (MSK). The performance of the proposed cancellation scheme is compared with the existing techniques of FSK-OCDMA and PPM-OCDMA cancellation techniques. MSK-OCDMA cancellation technique achieves the lowest bit error rate of 10−20. It is also efficient in power. It achieves lowest bit error rate at same number of mean photon number when compared to the existing techniques. The investigations reveal that MSK-OCDMA cancellation technique outperforms FSK-OCDMA and PPM-OCDMA cancellation schemes.

Addressing Multi-User Interference in Vehicular Visible Light Communications: A Brief Survey and an Evaluation of Optical CDMA MAC Utilization in a Multi-Lane Scenario.

Visible Light Communications (VLC) are developing as an omnipresent solution for inter-vehicle communications. Based on intensive research efforts, the performance of vehicular VLC systems has significantly improved in terms of noise resilience, communication range, and latencies. Nevertheless, in order to be ready for deployment in real applications, solutions for Medium Access Control (MAC) are also required. In this context, this article provides an intensive evaluation of several optical CDMA MAC solutions and of their efficiency in mitigating the effect of Multiple User Interference (MUI). Intensive simulation results showed that an adequately designed MAC layer can significantly reduce the effects of MUI, ensuring an adequate Packet Delivery Ratio (PDR). The simulation results showed that based on the use of optical CDMA codes, the PDR can be improved from values as low as 20% up to values between 93.2% and 100%. Consequently, the results provided in this article show the high potential of optical CDMA MAC solutions in vehicular VLC applications, reconfirm the high potential of the VLC technology in inter-vehicle communications, and emphasize the need to further develop MAC solutions designed for such applications.

RIS Assisted Multiple User Interference Mitigation via an Accelerated Coordinate Descent Method

Reconfigurable intelligent surfaces (RIS) aided multiple user interference mitigation with constant modulus constraint (CMC) is the key issue in the multiple-input-multiple-output (MIMO) communication systems. Usually, the existing methods solve this problem by relaxation (relaxing CMC or cost function) or with designing phase, which either degrade the performance or need huge computational cost. To address this issue, a low-complexity Accelerated Coordinate Descent (ACD) method is proposed to design the phase. First, the problem is reformulated as a penalty quadratic function with CMC. Then, a Coordinate Descent (CD) algorithm is derived to obtain the solution, by transforming the problem into a decomposable problem with multiple one-dimensional subproblems. Finally, the ACD algorithm is derived by using the square iterative technique. Particularly, RIS discrete phase design is also considered due to practical hardware constraints. Compared with the existing methods, the proposed method has the following advantages: (1) The achievable rate per user is 0.64 bits/s/Hz higher than Pan et al. (2020) and ElMossallamy et al. (2021). (2) The computational cost is an order of magnitude lower than Pan et al. (2020) and ElMossallamy et al. (2021).

Satellite continuous-variable quantum key distribution systems using code-division multiple access

In this paper, we propose a novel architecture of the satellite continuous-variable quantum key distribution (CV-QKD) system that can not only support multiple users but also enhance the security. The satellite CV-QKD system is based on a code-division multiple access (CDMA) technique to simultaneously transmit multiple key streams from a trusted satellite to a ground station, which passively forwards these key streams to multiple users nearby via optical fibers. Our proposed architecture avoids using multiple ground stations that result in high costs. We analyze the performance of the proposed system under the negative impacts of atmospheric attenuation and atmospheric turbulence, as well as beam spreading and pointing error loss. Especially, the impact of multiple user interference is also considered in our analysis. The numerical results show that the proposed QKD system using CDMA can support multiple users, whose performance metrics such as quantum bit-error rate (QBER), sifted probability, and secret key rate meet the designed targets. The eavesdroppers suffer high QBER and low sifted probability, thus the security is guaranteed.

Joint design of transmit waveform and passive beamforming for RIS-assisted ISAC system

The joint design of the transmit waveform and passive beamforming is the key issue in the reconfigurable intelligent surface (RIS) assisted integrated sensing and communication (ISAC) systems. The existing methods are the joint waveform design without RIS or the sensing-first joint waveform design with RIS. Different from these methods, the fair sensing-communication joint waveform design with RIS is studied in this paper. For this purpose, we simultaneously optimize the waveform and RIS phase shifts to maximize the sensing Signal-to-Interference-and-Noise-Ratio (SINR) and minimize the communication Multiple User Interference (MUI). Due to the constant modulus (CM) constraint and the fractional programming form of the SINR expression, the resulted optimization problem is hard to solve. To address these issues, an Alternating Gradient-descent on Riemannian Manifold (AGRM) method is proposed. First, a dinkelbatch-GRM algorithm is derived to maximize SINR, by fixing the RIS phase shifts. Then, a GRM algorithm is given to mitigate MUI, while fixing the waveform. Finally, the overall AGRM algorithm is presented to solve the original problem. Simulation results show that the communication achievable rate and the sensing SINR of the proposed method are 2.33 bits/s/Hz and 5.6 dB higher than [17] and [30,31].

RIS-Aided Multiple User Interference Mitigation via Fast Successive Upper-Bound Minimization Method

Reconfigurable intelligent surfaces (RIS) aided multiple user interference mitigation with constant modulus constraint (CMC) is a key issue in the future 6G communication systems. Usually, the existing methods solve this problem either by relaxing the CMC with performance degrading or by relaxing the cost function with huge computational cost. To achieve a good trade-off between the performance and the complexity, a Fast Successive Upper-bound Minimization (FSUM) method is proposed. In the proposed method, the problem is first reformulated as a penalty quadratic function with CMC. Then, by efficiently finding the surrogate function, a FSUM algorithm is derived to obtain the solution. Compared with the existing methods, the proposed method can achieve 0.4 bits/Hz/s average sum-achievable rate gain enhancement.

Design and analysis of three-dimensional m-sequence bipolar OCDMA spectral amplitude code

This paper has been focused to utilize the m-sequence (matrix) code in spectral/time/spatial OCDMA domain in a bipolar mode (Three Dimensional modes). The scheme has elegantly incorporated the design of an encoder and decoder such that the system efficiently generates the code in three-dimensional bipolar mode. The decoder design is such that it effectively suppresses the multiple user interference (MUI) of three-dimensional code. System analyses are carried for defining the BER performance variation with users acceptability and received power. The observed results demonstrate that the cardinality of m- matrix three-dimensional bipolar code is larger than the existing 3D Pascal code, 2D-MDW, 3D-PDC, 2D-PDC, 1D-CWH and 1D-MS codes. The received power in proposed system is − 5.8 dBm lesser than the 3D Pascal Code at 10–18 BER and the users in system more than 210% can be accomplished as compared to 3D Pascal code.

Joint power control and user grouping for uplink power domain non-orthogonal multiple access

Orthogonal multiple access schemes based on assignment of communication resource blocks among multiple contenders, although widely available, still necessitate an upper limit on the number of concurrent users for minimization of multiple-user interference. The feature thwarts efforts to cater for pressing connectivity demands posed by modern-day cellular communication networks. Non-orthogonal multiple access, regarded as a key advancement towards realization of high-speed 5G wireless communication networks, enables multiple users to access the same set of resource blocks non-orthogonally in terms of power with controllable interference, thereby allowing for overall performance enhancement. Owing to the combinatorial nature of the underlying optimization problem involving user pairing/grouping scheme, power control and decoding order, the computational complexity in determining optimal and sub-optimal solutions remains considerably high. This work proposes three novel alternative approaches (Randomly, 2-Opt and Hybrid) for arriving at a near-optimal solution for the problem of user pairing/grouping. The algorithms not only offer reduced computational complexity but also outperform orthogonal multiple access and existing schemes reported in the literature for uplink non-orthogonal multiple access systems.

Simulative Comprehensive Analysis of 2D Algebraically Constructed Codes for Optical CDMA

In this manuscript, comprehensive analysis of distinct optical codes belonging to family of algebraically constructed codes has been demonstrated. Many optical codes belonging to algebraically constructed family such as Extended Reed-solomon codes (E-RS), Multi-level prime codes (MPC), Extended-multi level prime codes (E-MPC), and Variable-weight quadratic congruence codes (VWQCC), Bipolar/Unipolar codes are taken into consideration. The performance characteristics of these codes are examined through Hard-error limiting probability (HEP) equations. Investigations revealed that Bipolar/Unipolar code is the one algebraically developed code that has outperformed all the codes considered here even in the presence of Multi-user interference effect. It has been observed that this optical 2D Bipolar/Unipolar code shows minimum BER value with increasing user count. Hence Bipolar/Unipolar code is robust to multiple user interference affected OCDMA systems.

Topological Interference Management for MIMO Interference Broadcast Channels

In this paper, we investigate the topological interference management (TIM) for MIMO interference broadcast channels (IBC) under the fixed topology, where only topology information is needed to cancel the inter-cell interference (ICI). For the single user case, where the MIMO IBC network is reduced to the MIMO interference channel (IC) networks, we propose one novel TIM scheme by exploiting the solution to the corresponding SISO IC TIM based on topology information. And also, we present one theorem to characterize the achievable degrees of freedom (DoFs). For the multiple user case, assuming that each BS not only knows topology information but also knows the channel state information at transmitters (CSIT) within its own cell, we propose two novel TIM schemes, i.e., the virtual user compression-based scheme and the virtual base station extension-based scheme. For each scheme, we design transceivers to cancel both the ICI only based on the topology information by exploiting the solution to the corresponding SISO IC TIM and the multiple user interference (MUI) within its own cell based on the CSIT. Furthermore, we present one theorem to characterize the achievable DoF, respectively. Moreover, we prove that the DoF achieved by the virtual base station extension-based scheme is higher than or equal to that achieved by the virtual user compression-based scheme. Hence, the achievable DoF of MIMO IBC TIM is lower bounded by the optimal DoF attainable for the base station extension scheme. Furthermore, the numerical results show that our schemes can achieve significant performance gain against the traditional interference avoidance scheme.

Analysis and design of weighted MPC in incoherent synchronous OCDMA network

In this paper, a novel spreading code design in incoherent synchronous Optical Code Division Multiple Access networks is introduced. This new code is designed by remodeling and improvising the existing concept of Modified Prime Code (MPC) sequences. In addition, it has been generated at optimum code weight and sufficient code length with respect to the new MPC, Uniform Cross-Correlation MPC, Double Padded MPC and Enhanced MPC. The proposed new code is named as Weighted MPC (WMPC). The used technique to generate the WMPC sequences is based on XOR operation between code words of MPC and then rearranging between them. Such operation is performed to increase code weight. The proposed coding technique has a capability to provide better correlation results, higher throughput, minimum Multiple User Interference and good network performance. Furthermore, the auto and cross-correlation properties of WMPC sequences were investigated, where the results were compared with the correlation results of other Prime Codes family.

Performance analysis of 2-D optical prime codes for optical-CDMA

In this paper, comparative analysis of code performance of distinct optical 2-D codes belonging to the Prime code family have been examined. Various optical 2-D Prime codes such as Low-weight Prime sequence code (LW-PSC), Modified prime-hop code (MPHC), Extended prime-hop code (E-CHPC), Transposed-modified prime code (T-MPC), Transposed-sparse padded modified prime code (T-SPMPC) are considered. Hard-limiting Error Probability (HEP) equations of these codes are used to scrutinize the performance of these codes. Performance of one of the 2-D Prime codes, more specifically MPHC performs best in OCDMA systems where only Multi-user interference effect is considered. This optical 2-D MPHC code possesses very low BER value as compared to universally accepted standard with the increasing user count. MPHC provides robustness to multiple user interference affected OCDMA therefore very much apt for applications where simultaneous access of immense number of active user is required.

Uncoded integrated interleave division multiple access systems in presence of power interleavers

Interleaving is one of the most common methods known to eradicate the effects of multiple user interference. Removal of different interferences is one of the major challenges for advanced communication system designers. Several methods of interleaving have been proposed in literature and their performances have been analyzed on different communication systems to prove their worthiness in multiple user interference removal. One of such interleavers is power interleaver, which can be employed in communication systems as a means to control burst errors and reduce the multiple user interference. In this paper, performances of two different integrated interleave division multiple access (IIDMA) techniques i.e. SCFDM-IDMA and OFDM-IDMA have been analyzed. Novelty of this work is in the sense that the entire analysis has been performed in the presence of power interleavers for the above two IIDMA techniques as the conventional IDMA fails to mitigate the problems of inter-carrier and inter-symbol interferences. Hence, the two techniques in presence of power interleavers empower the idea of quality communication without any interference for future generation communication systems.

Performance of Different OCDMA Codes with FWM and XPM Nonlinear Effects

AbstractIn this paper, 1 Gb/s non-linear optical code division multiple access system have been simulated and modeled. To reduce multiple user interference multi-diagonal (MD) code which possesses the property of having zero cross-correlation have been deployed. The MD code shows better results than Walsh-Hadamard and multi-weight code under the nonlinear effect of four-wave mixing (FWM) and cross-phase modulation (XPM). The simulation results reveal that effect of FWM reduces when MD codes are employed as compared to other codes.

Performance analysis of SAC-OCDMA in free space optical medium using DDW code

Spectral amplitude coded Optical code division multiple access technique (SAC-OCDMA) has become a major area of research in optical communication. OCDMA allows multiple users to access a medium simultaneously without any contention. It has ability to operate asynchronously, provide privacy and security and reduce multiple user interference. In this paper performance of SAC-OCDMA with Diagonal double weight (DDW) code with FSO communication system is presented and compared under different conditions of rain and haze. 10 simultaneous users with 5Gbps data rate are evaluated in the system. Effect of transmitted power and beam divergence is also studied. Results have been formulated based upon eye diagrams and values of Q- factor and BER. Maximum distance covered is 10 Km with BER of 10−25 under clear weather. Simulation results show that DDW code is able to perform well at low power values also.

Channel Estimation and Demodulation for MIMO-OFDM System Under Fractional Timing Offset

For the channel offset caused by the time offset(TO) of the MIMO-OFDM system, we propose a new high-precision and low complexity new channel estimation algorithms, which is based on least squares(LS) method to solve the problem that we need to send a lot of pilot symbols to estimate the channel coefficient again when the fractional timing offset is present, which greatly reduces the complexity of the system. Meanwhile, we combine the new algorithm and Vectoring technology, so that it allows multiple transmitted signals through the down-link pre-coding matrix and the actual channel to each receiver, completely eliminating the multiple user interference caused by transmitted signals of multiple users and accurately extracting the signal of each user. Simulation experiments prove that the new algorithms have good estimation performance.

Distributed energy efficiency beamforming design in multiple‐input‐single‐output interference channels

Coordinated beamforming designs based on energy efficiency of multiple-user interference channels have attracted much attention. The optimisation problem has a fractional form, and is coupled among users, which makes it difficult to be solved directly. A beamforming design for energy-efficient communication in multiple-input–single-output interference channels is studied, and proposes an efficient distributed approach to solve it. A novel method is developed to transform the optimisation problem into a DC (difference of two convex/concave functions) structure. The transformed optimisation problem is approximated by using a separable structure across the users, and this approximated version is solved iteratively. Numerical results show the effectiveness of the authors’ proposed algorithm.

Joint Timing Synchronization and Channel Estimation Using Perfect Sequence in Uplink Time Domain Synchronous OFDMA

AbstractTime Domain Synchronous Orthogonal Frequency Division Multiple Access (TDS-OFDMA) is used in mobile broadband wireless access scheme in uplink transmission. This leads to multiple user interference due to timing offset and frequency offset. In this paper, the effect of timing offset and channel estimation in mobile broadband system is analysed. Time-space two dimensional structure is used in TDS-OFDMA and perfect sequence is used for guard interval to achieve perfect timing synchronization and channel estimation for each user. Simulations are performed for timing synchronization and channel estimation using perfect sequence under Urban channel, Indoor Office B channel and HIPER LAN-A channel. Simulation results show that the timing synchronization is achieved and channel estimation performance using perfect sequence is better than CAZAC and PN Sequences.

Multiple-users interference alignment base on two-tired heterogeneous networks

Multiple-users interference alignment base on two-tired heterogeneous networks