Serial Interference Cancellation Research Articles

Optimizing the Timeliness of Hybrid OFDMA-NOMA Sensor Networks with Stability Constraints

In this paper, we analyze the timeliness of a multi-user system in terms of the age of information (AoI) and the corresponding stability region in which the packet rates of users lead to finite queue lengths. Specifically, we consider a hybrid OFDMA-NOMA system where the users are partitioned into several groups. While users in each group share the same resource block using non-orthogonal multiple access (NOMA), different groups access the fading channel using orthogonal frequency division multiple access (OFDMA). For this system, we consider three decoding schemes at the service terminals: interfering decoding, which treats signals from other users as interference; serial interference cancellation, which removes signals from other users once they have been decoded; and the enhanced SIC strategy, where the receiver attempts to decode for another user if decoding for a previous user fails. We present the average AoI for each of the three decoding schemes in closed form. Under the constraint of the stable region, we find the minimum AoI of each decoding scheme efficiently. The numerical results show that by optionally choosing the decoding scheme and transmission rate, the hybrid OFDMA-NOMA outperforms conventional OFDMA in terms of both system timeliness and stability.

Broadband wireless access and IP technologies - VBLAST detection algorithm

MIMO technology was proposed as early as 1908 to cope with wireless channel fading. In 1995, Bell Labs was the first to discover the great potential of MIMO system in channel capacity, and in 1996, Foshini of Bell Labs first proposed a space-time coding scheme, i.e., the diagonal-Bell Labs hierarchical space-time model, which can obtain very high spectrum utilization, but due to the complexity of its structure, it is difficult to be applied in practice, and is now rarely investigated. 1998, P.W. Wolniansky et al. gave a simple and practical space-time coding scheme on this basis, i.e., the vertical-Bell Labs layered space-time model. In 1998, P.W. Wolniansky et al. gave a simple and practical space-time coding scheme on this basis, i.e., Vertical Bell Labs Layered Space-Time (V-BLAST, Vertical Bell Labs Layered Space-Time) model, which can obtain very high spectrum utilisation and is easy to implement, and therefore has received wide attention once it was proposed. In this paper, we focus on airtime layered codes as well as the ZF detection algorithm and the MMSE detection algorithm in VBLAST systems and improve them to further enhance the performance of the two detection algorithms through sequential serial interference cancellation.

Broadband wireless access and IP technologies - VBLAST detection algorithm

MIMO technology was proposed as early as 1908 to cope with wireless channel fading. In 1995, Bell Labs was the first to discover the great potential of MIMO system in channel capacity, and in 1996, Foshini of Bell Labs first proposed a space-time coding scheme, i.e., the diagonal-Bell Labs hierarchical space-time model, which can obtain very high spectrum utilization, but due to the complexity of its structure, it is difficult to be applied in practice, and is now rarely investigated. 1998, P.W. Wolniansky et al. gave a simple and practical space-time coding scheme on this basis, i.e., the vertical-Bell Labs layered space-time model. In 1998, P.W. Wolniansky et al. gave a simple and practical space-time coding scheme on this basis, i.e., Vertical Bell Labs Layered Space-Time (V-BLAST, Vertical Bell Labs Layered Space-Time) model, which can obtain very high spectrum utilisation and is easy to implement, and therefore has received wide attention once it was proposed. In this paper, we focus on airtime layered codes as well as the ZF detection algorithm and the MMSE detection algorithm in VBLAST systems and improve them to further enhance the performance of the two detection algorithms through sequential serial interference cancellation.

Hybrid Beamforming With Sub-Connected Structure for MmWave Massive Multi-User MIMO Relay Systems

In this paper, we investigate the hybrid beamforming design with sub-connected structure for millimeter-wave (mmWave) massive multi-user multiple-input multiple-output (MU-MIMO) amplify-and-forward (AF) relay systems. Considering the constant-modulus and block-diagonal constraints, an iterative algorithm is proposed to sequentially design the analog beamforming of the base station, relay, and users. Next, the relay baseband combiner is designed by transforming the highly complicated non-convex mutual information maximization problem into an easily tractable weighted minimum mean squared error one. To mitigate the inter-user interference, a successive serial interference cancellation based and a piecewise successive approximation based methods are developed for the uniform sparse distribution and dense distribution scenarios, respectively. Simulation results demonstrate that the two proposed hybrid beamforming schemes can achieve good performance in terms of sum-rate and energy efficiency, and outperform benchmarks significantly. In addition, the two proposed schemes are shown to be robust to imperfect channel state information (CSI), even though they are studied based on perfect CSI.

An Asynchronous Collision-Tolerant ACRDA Scheme Based on Satellite-Selection Collaboration-Beamforming for LEO Satellite IoT Networks

In this paper, an asynchronous collision-tolerant ACRDA scheme based on satellite-selection collaboration-beamforming (SC-ACRDA) is proposed to solve the avalanche effect caused by packet collision under random access (RA) high load in the low earth orbit (LEO) satellite Internet of Things (IoT) networks. A non-convex optimization problem is formulated to realize the satellite selection problem in multi-satellite collaboration-beamforming. To solve this problem, we employ the Charnes-Cooper transformation to transform a convex optimization problem. In addition, an iterative binary search algorithm is also designed to obtain the optimization parameter. Furthermore, we present a signal processing flow combined with ACRDA protocol and serial interference cancellation (SIC) to solve the packet collision problem effectively in the gateway station. Simulation results show that the proposed SC-ACRDA scheme can effectively solve the avalanche effect and improve the performance of the RA protocol in LEO satellite IoT networks compared with benchmark problems.

Effective capacity analysis of NOMA with transceiver hardware and SIC imperfections

In this paper, we study the performance of the non-orthogonal multiple access (NOMA) networks. By considering two practical factors of residual hardware impairments (RHIs) and imperfect serial interference cancellation (ipSIC), we adopt effective capacity as a metric to characterize the effects of latency on the performance of NOMA networks and derive the analytical expressions of the effective capacity for the near user (NU) and the far user (FU). For further insights, we provide asymptotic analysis by invoking high signal-to-noise ratio (SNR) slope and high SNR power offset. Numerous analytical and simulated results have shown that: (1) The effective capacities of NU and FU are positively proportional to the SNR at low SNR, while at high SNR, the effective capacities approach to the constants; (2) Comparing the two users of the considered NOMA network, the effective capacity of NU shows pronounced advantages under the requirements of low quality of service. (3) RHIs are detrimental to the effective capacities of both NU and FU, especially for the high SNR regime. (4) The effective capacity of NU is limited by ipSIC.

Сравнение декодеров группового сигнала с неортогональным множественным доступом, сформированного из сигнально-кодовых конструкций LTE

A comparative analysis of the performance of SL-SIC (Symbol Level - Serial Interference Cancellation) and CWL-SIC (Codeword Level-SIC) decoders of PD-NOMA (Power Doman - Non-Orthogonal Multiple Access) baseband signals in a system with two users is presented. Real signal code constructs (SCC) from the 3GPP LTE (Long Term Evolution of 3rd Generation Partnership Project) communication standard are used. The performance of CWL-SIC achievable in practice in real systems for all possible designs of a group PD-NOMA signal consisting of different pair combinations of noise-immune SCCs has been obtained. With the help of mathematical modeling, weighting power coefficients are obtained that provide the maximum average performance of the group signal for two user channels. The high efficiency of the CWL-SIC and the expediency of its use in real systems, especially in conditions of low signal-to-noise ratio, are shown.

The effect of quantized ETF, grouping, and power allocation on non-orthogonal multiple accesses for wireless communication networks

Nonorthogonal multiple access (NOMA) is a significant technology in radio resource sharing and it has been recognized as a favorable method in fifth-generation (5G) wireless networks to meet the requirements of system capacity, service latency, and user connectivity. Many schemes for NOMA have been proposed in the last few years. such as transmitter linear spreading-based NOMA as a code domain, as well as a linear minimum mean square error (LMMSE), parallel interference cancellation (PIC), and serial interference cancellation (SIC) with power allocation and grouping as a power domain at the receiver side for uplink NOMA. This work aims to evaluate the performance of multiple types of linear spreading-based NOMA schemes. Simulations are achieved for the error-rate performance evaluation of these NOMA schemes, received signal after detection, and received signal and effect of every user on the other. Evaluating the performance of these technologies with comparison is also achieved through using grouping and power allocation. Simulations are achieved for the sum rate and spectral efficiency. For the future, 5G NOMA development, an equiangular tight frame (ETF) is suggested for improving performance and suggests grouping with 64qam-quantized Grassmannian for improving performance favorite about grouping with Generalized welch-bound equality (GWBE)

Multi-user detection for CPM spread system with turbo in VDES

The multi-user detection technology uses the spread sequence, delay, amplitude and phase information of each user to jointly detect users, which can effectively suppress multiple access interference, It is one of the key technologies in satellite communication system to make full use of uplink spectrum resources and improve system performance and capacity. Continuous phase modulation spread signal can adapt to multi-user communication due to the random variation of spread sequence, which is gradually applied to satellite communication. QPSK-CPM spread modulation scheme is adopted in the random access channel of VHF data exchange system. Aiming at the multi-user detection problem of QPSK-CPM spread system, proposing a multi-user detection algorithm based on interference elimination joint Turbo iterative detection based on the characteristics of CPM spread sequence. Compared with the traditional serial interference cancellation algorithm, the algorithm can effectively eliminate the multiple access interference problem caused by user aliasing by using the characteristics of Turbo codes. The theoretical simulation shows that the algorithm has a good detection effect on multi-user aliased signals.

MMW-NOMA: An Uplink NOMA Communication System Based on the Node Pairing Algorithm of Maximum and Minimum Weight in Underwater Acoustic Networks

In orthogonal multiple access (OMA) communication systems, resources are allocated to numerous users based on time, frequency, or code domains. The low bandwidth of the underwater acoustic network limits the number of nodes that can be supported by the OMA system, due to limited resources. The innovative concept of nonorthogonal multiple access (NOMA) provides a solution that offers more nodes and increases spectral efficiency. As a promising technique, it optimizes power allocation through channel characteristics and adopts serial interference cancellation algorithms to decode the signal at the receiver. This paper introduces an underwater communication system based on the node pairing algorithm of maximum and minimum weight (MMW-NOMA). First, we build the system model in a UAN scenario. Second, we present the node pairing strategy. Third, we design a node replacement mechanism. Furthermore, we offer a power allocation algorithm. Finally, we compare the performance of MMW-NOMA with randomly paired NOMA (RP-NOMA) and orthogonal frequency division multiplexing (OFDM). Numerical results show that MMW-NOMA outperforms RP-NOMA and OFDM in throughput, mean square error, and energy efficiency. However, the complexity of MMW-NOMA is slightly higher than that of RP-NOMA but significantly lower than OFDM. These results show that MMW-NOMA achieves a reasonable trade-off between performance and complexity.

A Novel Approach for Cancelation of Nonaligned Inter Spreading Factor Interference in LoRa Systems

Long Range (LoRa) has become a key enabler technology for low power wide area networks. However, due to its ALOHA-based medium access scheme, LoRa has to cope with collisions that limit the capacity and network scalability. Collisions between randomly overlapped signals modulated with different spreading factors (SFs) result in inter-SF interference, which increases the packet loss likelihood when signal-to-interference ratio (SIR) is low. This issue cannot be resolved by channel coding since the probability of error distance is not concentrated around the adjacent symbol. In this paper, we analytically model this interference, and propose an interference cancellation method based on the idea of segmentation of the received signal. This scheme has three steps. First, the SF of the interference signal is identified, then the equivalent data symbol and complex amplitude of the interference are estimated. Finally, the estimated interference signal is subtracted from the received signal before demodulation. Unlike conventional serial interference cancellation (SIC), this scheme can directly estimate and reconstruct the non-aligned inter-SF interference without synchronization. Simulation results show that the proposed method can significantly reduce the symbol error rate (SER) under low SIR compared with the conventional demodulation. Moreover, it also shows high robustness to fractional sample timing offset (STO) and carrier frequency offset (CFO) of interference. The presented results clearly show the effectiveness of the proposed method in terms of the SER performance.

Dual Dynamic Scheduling for Hierarchical QoS in Uplink-NOMA: A Reinforcement Learning Approach.

The demand for bandwidth-intensive and delay-sensitive services is surging daily with the development of 5G technology, resulting in fierce competition for scarce radio resources. Power domain Nonorthogonal Multiple Access (NOMA) technologies can dramatically improve system capacity and spectrum efficiency. Unlike existing NOMA scheduling that mainly focuses on fairness, this paper proposes a power control solution for uplink hybrid OMA and PD-NOMA in dual dynamic environments: dynamic and imperfect channel information together with the random user-specific hierarchical quality of service (QoS). This paper models the power control problem as a nonconvex stochastic, which aims to maximize system energy efficiency while guaranteeing hierarchical user QoS requirements. Then, the problem is formulated as a partially observable Markov decision process (POMDP). Owing to the difficulty of modeling time-varying scenes, the urgency of fast convergency, the adaptability in a dynamic environment, and the continuity of the variables, a Deep Reinforcement Learning (DRL)-based method is proposed. This paper also transforms the hierarchical QoS constraint under the NOMA serial interference cancellation (SIC) scene to fit DRL. The simulation results verify the effectiveness and robustness of the proposed algorithm under a dual uncertain environment. As compared with the baseline Particle Swarm Optimization algorithm (PSO), the proposed DRL-based method has demonstrated satisfying performance.

Optimized Power Control in Internet of Vehicles Based on Serial Interference Cancellation and User Matching

With the significant advantages of 5G technique such as higher transmission rate and lower transmission delay, it is more in line with the requirements of the connected vehicle scenario. In addition, the serial interference cancellation (SIC) technology in 5G technology can further improve the communication quality compared to a single one-to-one multiplexing method. Taking the dynamic communication characteristics of Internet of Vehicles into consideration, the robust optimization problem is formulated, which attempts to maximization the total throughput of vehicle users under the changing channel gains. The channel uncertainty is formulated as probability constraints, and they are transformed to the deterministic form to achieve a convex optimization problem. And the Hungarian algorithm is introduced to allocate the available channels to the V2V pairs. With the proposed joint resource allocation algorithm, the maximum throughput can be obtained with the lower algorithm complexity. Also, the robustness against the changing channel gains is guaranteed and the outage probability of users is kept below the pre-given outage threshold.

Physical Layer Security Designs for 5G NOMA Systems With a Stronger Near-End Internal Eavesdropper

Serial interference cancellation (SIC) technology is the key to ensure a higher system capacity for NOMA. However, SIC may also introduce some critical security risks, since it requires near-end users (NU) demodulate far-end users’ (FU) signals and make the cancellations. It is hard to obtain positive secrecy rate in the presence of a stronger NU eavesdropper. To this end, this paper studies the security designs for a 5G NOMA system with a stronger NU internal eavesdropper. We first consider the two-user case and then extend our results to a multi-user case. After adjusting the order of SIC and employing a cooperative jammer, an optimal power allocation problem is built subject to users’ data rate and total power constraints. The global closed-form optimal solution is achieved for the two-user case, while a closed-form sub-optimal solution is obtained for the multi-user case. For better insight, the jamming gain is introduced to approximately measure the performance gain achieved. Simulation results show that positive secrecy rate is obtained while the users’ data rate are guaranteed.

Time-Varying Channel Equalization in Underwater Acoustic OFDM Communication System

In this paper, three time-varying channel equalization schemes are studied in the underwater acoustic (UWA) Orthogonal Frequency Division Multiplexing (OFDM) communication system. The equalization algorithms are the zero-forcing (ZF) equalization algorithm, and the minimum mean square error equalization (MMSE) algorithm and the serial interference cancellation (SIC) equalization algorithm. Among the schemes, there is a problem of needing a large amount of operation when obtaining the inversion of the channel matrix. Then, to reduce the computation complexity of channel matrix inversion, the band approximation of the channel matrix, the serial equalization and the LDLH decomposition are also studied. To evaluate the efficacy of the algorithms studied in this paper, numerical simulation and the field experiment are both conducted. The simulation results proof that each equalization algorithm can work appropriately under different time-varying conditions, and valid the reliability of each simplified algorithm under the same Doppler factor. The results of two sets of field experiment also prove that the simplified algorithm eliminates the influence of the residual narrow band Doppler to a certain extent, and a better effect is obtained while a channel estimation algorithm with higher accuracy is combined.

Low overhead NOMA receiver with automatic modulation classification techniques

Recently non-orthogonal multiple access (NOMA) technique has been proposed for boosting spectral efficiencies in 5G cellular networks. In NOMA the transmitter maps a predefined number of user symbols on to the same resources. The conventional receiver for NOMA is the well-known serial interference cancellation. To overcome the problem of high overhead signalling, a receiver with an automatic modulation classification (AMC) algorithm for a K-user NOMA which identifies the modulation scheme of users before symbol detection is proposed. First, a two-user NOMA (TU-NOMA) scheme is treated and the receiver is extended to more general cases. For evaluating the performance of the proposed receiver its bit error rate (BER) for TU-NOMA case has been driven and shown that this can be approximated as the sum of the demodulator BER and the AMC algorithm error probability. The simulation results show the BER degradation can be neglected if an enough number of symbols with sufficiently large SNR values are available.

MIMO Underwater Acoustic Communication in Shallow Water with Ice Cover

Although multiple-input multiple-output (MIMO) underwater acoustic (UWA) communication has been intensively investigated in the past years, existing works mainly focus on open-water environment. There is no work reporting MIMO acoustic communication in under-ice environment. This paper presents results from a recent MIMO acoustic communication experiment which was conducted in Bohai Gulf during winter. In this experiment, high frequency MIMO signals centered at 10 kHz were transmitted from a two-element source array to a four-element vertical receiving array at 1 km range. According to the received signal of different array elements, MIMO acoustic communication in under-ice environment suffers less effect from co-channel interference compared with that in open-water environment. In this paper, time reversal followed by a single channel decision feedback equalizer is used to process the experimental data. It is demonstrated that this simple receiver is capable of realizing robust performance using fewer hydrophones (i.e. 2) without the explicit use of complex co-channel interference cancelation algorithms, such as parallel interference cancelation or serial interference cancelation.

Deep Learning Network for Multiuser Detection in Satellite Mobile Communication System.

A multiuser detection (MUD) algorithm based on deep learning network is proposed for the satellite mobile communication system. Due to relative motion between the satellite and users, multiple access interference (MUI) introduced by multipath fading channel reduces system performance. The proposed MUD algorithm based on deep learning network firstly establishes the CINR optimal loss function according to the multiuser access mode and then obtains the best multiuser detection weight through the steepest gradient iteration. Multilayer nonlinear learning obtains interference cancellation sharing weights to achieve maximum signal-to-noise ratio through gradient iteration, which is superior than the traditional serial interference cancellation algorithm and parallel interference cancellation algorithm. Then, the weights with multiuser detection through multilayer network forward learning iteration are obtained with traditional multiuser detecting quality characteristics. The proposed multiuser access detection based on deep learning network algorithm improves the MUD accuracy and reduces the number of traditional multiusers. The performance of the satellite multifading uplink system shows that the proposed deep learning network can provide high precision and better iteration times.

Advancing High-Speed Transmissions over OCDMA Networks by Employing an Intelligently Structured Receiver for Noise Mitigation

We propose an intelligently structured receiver to achieve high-speed transmissions over optical code-division multiple access (OCDMA) networks. Employing spectral-amplitude coding (SAC) reduces multiuser interference (MUI) in OCDMA, but the network bit-rate is limited by phase-induced intensity noise (PIIN) coming from the incoherency of light sources. To mitigate PIIN, the receiver performs interference estimations and regenerations through consecutive stages. The MUI is removed by subtracting the estimated interference term from the received multiplexed signals. For PIIN variance, it is both dependent on and positively related to user number and bit-rate. Reducing the number of interference users allows the network to support transmissions with a higher speed under a given noise level. The proposed scheme has the advantages of all-optical signal processing and a compact structure. Additionally, the function of noise suppression is rarely studied in the existing MUI elimination schemes, such as serial interference cancellation (SIC) and parallel interference cancellation (PIC). The simulation results show the proposed receiver achieves significant increment in bit-rate than the conventional balanced detector in SAC–OCDMA networks.

Compressed sensing-based time-domain channel estimator for full-duplex OFDM systems with IQ-imbalances

In full-duplex orthogonal frequency-division multiplexing (OFDM) systems with in-phase and quadrature (IQ) imbalances, a time-domain least squares (TD-LS) channel estimator is proposed for estimating both the source-to-destination (intended) and the destination-to-destination (self-interference) channels. To further improve the performance, an adaptive orthogonal matching pursuit (OMP) is proposed and its sparsity is estimated by a threshold method. Finally, the full-duplex interference is removed using serial interference cancellation and sphere decoding is used to complete the maximum likelihood detection. Simulation results demonstrate that in terms of both the mean square error (MSE) and the bit error rate (BER), the proposed adaptive OMP performs better than the TD-LS by exploiting the sparse property of the channel. Additionally, compared to the gradient projection, the proposed adaptive OMP is better in the low and medium signal-to-noise ratio (SNR) regions and marginally worse in the high SNR region.