Multiple access interference cancellation in Manchester-coded synchronous optical PPM-CDMA network

A new interference cancellation technique for direct-detection optical code- division multiple-access (OCDMA) network employing pulse-position modulation (PPM) is proposed in this paper. The multiple access interference (MAI) estimation is achieved by pre-reserving one of optical spreading code sequences at the receiver based on the correlation property of padded modified prime codes (PMPC). The estimated interference is then cancelled out after photo-detection process. Additionally, the transmitted signal is Manchester-coded to further improve the system performance. Based on this proposed interference canceller in a shot-noise limited regime, we have obtained an expression for the upper bound of the bit-error probability (BEP) taking into account effects of both MAI and shot-noise. This BEP is compared with that of a PPM-OCDMA without cancellation. Finally, the receiver structure of the proposed optical network unit (ONU) is fairly simple to compare with the conventional cancellation schemes.     

Performance analysis of a hybrid fiber Bragg grating-based spectral-amplitude-coding/successive interference cancellation for optical CDMA systems

Successive interference cancellation (SIC) scheme is proposed as a new technique that has the potential to reduce the interference and suppress the multiple-access interference (MAI) in spectral-amplitude-coding (SAC) optical-code-division-multiple access (OCDMA) systems. The proposed receiver-based on fiber Bragg gratings (FBGs) techniques. The performance of the proposed system is theoretically analyzed, taking into account various types of noise and interference, including both multiple-access interference (MAI) and receiver noise. Analytical results show that the proposed system offers significant improvement in terms of bit error rate and system capacity (number of users). We have tested our results with both modified prime codes (MPR) and modified quadratic congruence (MQC) codes. In addition, we have compared our proposed system with the corresponding one without cancellation. It has been shown that the proposed scheme gives a substantial increase in capacity.     

Estimation and cancellation of multi-user interference in synchronous fiber-optic PPM-CDMA system using Manchester coding

A multi-user interference estimation and cancellation technique is proposed for direct-detection fiber-optic code division multiple-access communication systems employing pulse-position modulation. In addition, Manchester codes are used in signaling the transmitted data to further improve the bit-error rate (BER). The multi-user interference of any user is estimated with the help of properties of modified prime code sequences. The estimated interference is canceled out from the received signal after the photo-detection process. We have used PIN photo-detector in our proposed system. An upper bound on the BER for the proposed system is derived and compared with a lower bound on the BER for the system without cancellation. In the presence of multiple users interference (MUI) and the Poisson shot noise model, our results clearly indicate that the performance, in terms of the BER, of the proposed system is significantly improved compared with that of the system without cancellation. The effect of thermal, dark current and surface leakage noise is insignificant compared to MUI and thus will not be considered in our calculation of BER.     

On the outage performance of multi-user NOMA system with adaptive SIC

The performance of non-orthogonal multiple-access (NOMA) is significantly determined by the successive interference cancellation (SIC) technique. However, the interference redundancy can happen during the NOMA receiver performing SIC. To tackle this issue, this paper proposes a novel adaptive successive interference cancellation (ASIC) method. Specifically, the decoding error is considered as interference during the SIC process, and an adaptive filter with various weights is introduced for detection error mitigation. For the multi-user downlink NOMA system, the outage probability is analyzed under conventional and the proposed SIC methods. Simulation results verify our analysis, which also demonstrate the superiority of the proposed ASIC method.     

Analysis of the method of division of spatial channels with successive interference cancellation in modern MIMO-OFDM cellular systems

We consider the problem of parallel data transmission via several spatial channels in modern high-throughput cellular systems employing the OFDM (Orthogonal Frequency Division Multiplexing) and antenna arrays at both ends of the communication system. Parallel data transmission in such MIMO (Multiple Input Multiple Output) systems is achieved by using the beamforming schemes in the transmitter and the special methods of the spatial-channel division in the receiver. Interference immunity of the scheme of the spatial-channel division by the maximum-likelihood criterion using the method of successive interference cancellation is analyzed. Probability of implementation of the stage of successive interference cancellation for the case of two spatial channels and various combinations of the coding schemes and modulations is obtained. We analyze the efficiency of a cellular communication system using horizontal coding and successive interference cancellation. Practical recommendations on choosing modulation and the code speed for each spatial channel, which ensure maximum interference immunity of a receiver with successive interference cancellation, are made.     

Analysis of interference cancellation techniques in OFDMA systems employing adaptive antenna arrays

We analyze the problem of interference cancellation in OFDMA cellular communication systems employing adaptive antenna arrays at the receiver and operating in the channels with frequency-selective fading and interference from the neighboring base stations. This problem is very important for modern broadband cellular systems operating with a low coefficient of multiple use of frequencies. Under such conditions of the network deployment, the system efficiency is restricted by the level of intrachannel interference from the neighboring base stations transmitting in the same frequency channel. In this work, we analyze different methods for measuring the interference characteristics and using them for spatial processing of received signals. Five different methods for signal processing in an adaptive antenna array of the receiver are discussed. Each approach (reception method) has its own interference immunity and complexity degree. Comparative analysis of the interference immunity of the considered receivers has been performed for different frequency-channel loads and different numbers of interfering stations. Recommendations for using the considered receivers are given.     

Full-duplex communication for future wireless networks: Dynamic resource block allocation approach

In this paper, we discuss a full-duplex (FD) communication scenario, where multiple FD user equipments (UEs) share same spectrum resources (or resource blocks) simultaneously. The FD eNodeB deploys digital precoding and successive interference cancellation with optimal ordering algorithm, to allow coexistence of multiple UEs in downlink and uplink, respectively. The sharing of same resource blocks, results in co-channel interference (CCI), in downlink of a UE, from uplink signals of other UEs. To mitigate the interference, a smart antenna approach is adopted. The approach includes using multiple antennas at UEs to form directed beams towards eNodeB and nulls towards other UEs. However, the approach fails when the UEs due to their mobility align themselves in the same direction with respect to the eNodeB (eNB). In this paper, we propose a dynamic resource block allocation (DRBA) algorithm for avoiding CCI due to mobility of UEs, sharing the spectrum resource, in a FD communication scenario. The proposed algorithm shows significant improvement of the quality of service (QoS) of the communication links.     

Reference signal design to mitigate co-channel interference in 5G OFDM systems with multiple numerologies

The 5G cellular technology is expected to support diverse services by flexible use of the allocated spectrum. It is achieved by allowing multiple subcarrier spacing and dynamically changing downlink (DL) and uplink (UL) transmissions based on the instantaneous traffic and latency requirements. The problem of mitigating co-channel interference (CCI) with different subcarrier spacings becomes more challenging, and the dynamic DL–UL configuration makes it further difficult. In this paper, a reference signal design to measure the CCI is proposed along with detailed mathematical analysis. Furthermore, novel algorithms to estimate the CCI are proposed which along with advanced receivers are used to effectively mitigate the interference. Simulations are performed to evaluate the performance of reference signal design and the proposed estimation algorithms. The results confirm the efficacy of the proposed methods.     

Fairness-aware resource allocation for D2D-enabled IoT in NOMA-based cellular networks with mutual successive interference cancellation

Device-to-device (D2D) communications and non-orthogonal multiple access (NOMA) are promising technologies to meet the growing demand for IoT-connected devices. However, they bring about new challenges including the co-channel interference, that can limit the performance improvement. To manage the co-channel interference, we address the problem of joint power allocation and sub-channel assignment for D2D-enabled IoT devices (IoTDs) underlaying a NOMA-based cellular network, in which the successive interference cancellation (SIC) decoding is enabled at the level of IoTDs and cellular user equipment (CUE)to increase the number of connected devices and the capacity. This problem is modeled as a mixed-integer nonconvex optimization problem which includes the concept of fairness with respect to the data rates of IoTDs. To solve the problem, a semi-distributed algorithm is developed, which is of polynomial time complexity. The proposed algorithm leverages the successive convex approximation and a heuristic approach. Evaluation results demonstrate the efficiency of the proposed scheme with respect to the sum rate, fairness, access rate and computational complexity.     

Optimization design of RIS-assisted high-capacity visible light communications based on HDMA

In this paper, a new non-orthogonal multiple access (NOMA) scheme is proposed for the reconfigurable intelligent surface (RIS) assisted high-capacity visible light communication (VLC) system, which is named hybrid domain multiple access (HDMA). HDMA enjoys the benefit of hybrid-domain signals, including the power domain, code domain, and frequency domain, where the message passing algorithm (MPA) and successive interference cancellation (SIC) detectors are jointly used at the HDMA receiver. Furthermore, to achieve a higher communication capacity for the VLC system, we proposed an optimization model by jointly optimizing the power allocation ratio and RIS reflection units. The simulation results verified the proposed scheme. By comparing the system capacity of different RIS allocation schemes and multiple access methods, the VLC system based on HDMA proposed in this paper can significantly improve its communication capacity.     

Multiuser interference cancellation in time-varying channels

In this letter, an adaptive time-reversal multichannel combiner is embedded within an iterative successive interference cancellation receiver. With the addition of matching pursuit, a sparse channel estimation technique, the combined receiver is shown to provide both temporal interference cancellation as well as spatial interference suppression in decoding simultaneous transmissions from separate users in a time-varying underwater acoustic environment. Experimental data collected during the KAM11 experiment illustrates that for a two-user multiple-access system, multiuser separation can be achieved.     

Interference Cancellation and FEC in S/CDMA Networks with PIN+OA Receiver

For reducing the effects of optical multiple access interference (OMAI) and receiver noise in code-division multiple access (OCDMA) networks with STM-1 input, use of parallel cancellation and forward error correcting (FEC)codes greatly improves the performance of the receiver..     

Novel family of prime codes for synchronous optical CDMA

In this paper we have proposed a novel prime spreading sequence family hereby referred to as “new-Modified Prime Code (n-MPC)” for direct-detection synchronous optical code-division multiple-access (OCDMA) networks. The new code has been applied to Overlapping Pulse-Position Modulation (OPPM) CDMA system and the performance of system is evaluated. In addition, we have analyzed the system throughput and also introduced a new interference cancellation technique which significantly improves the bit error probability (BEP) of OPPM-OCDMA systems.     

视听系统声干扰的自适应抵消

对一个用语音遥控的视听系统而言，视听系统本身所发出的声音常常造成语音识别的错误，本文所采用的自适应声干扰低消技术能有效地降低这种声干扰，基于自适应声干扰抵消最佳性能的分析，导出了抵消性能与权系数的个数以及混响时间的表达式，并实时地实现了带有１０２４个权系数的自适应声干扰抵消系统。在一般居室中，声干扰的抵肖可达２６ｄＢ。     

Performance analysis of electronic code division multiple access based virtual private networks over passive optical networks

A solution for implementing multiple secure virtual private networks over a passive optical network using electronic code division multiple access is proposed and experimentally demonstrated. The multiple virtual private networking capability is experimentally demonstrated with 40 Mb/s data multiplexed with a 640 Mb/s electronic code that is unique to each of the virtual private networks in the passive optical network, and the transmission of the electronically coded data is carried out using Fabry-Perot laser diodes. A theoretical scalability analysis for electronic code division multiple access based virtual private networks over a passive optical network is also carried out to identify the performance limits of the scheme. Several sources of noise such as optical beat interference and multiple access interference that are present in the receiver are considered with different operating system parameters such as transmitted optical power, spectral width of the broadband optical source, and processing gain to study the scalability of the network.     

基于水声信道传播时延排序的分层空时信号检测

基于分层空时编码的多输入多输出技术是一种极具潜力的高速水声通信技术, 但要实现这种潜力需要复杂的空时信号处理方法, 以抵消来自水声信道的多径干扰和异步到达干扰, 以及叠加在接收端的各层信号之间的干扰. 对低复杂度的空时信号处理方案进行了研究, 提出了一种基于子信道传播时延排序的有序连续干扰抵消信号检测算法, 利用子信道间的传播时延差, 实现可使差错概率最小的最佳检测排序; 给出了利用信道估计, 以极低的计算量确定排序的方法, 从而可以大幅降低信号检测的计算复杂度. 采用低复杂度的单载波频域均衡来抵消水声信道中的码间干扰和异步到达干扰. 仿真结果表明, 基于时延排序的信号处理算法可以获得检测性能的改善, 而且性能增益在高数据率时更加显著. 研究结果表明, 采用有效的信号处理方法可使水声信道中造成信号检测干扰的传播时延成为改善系统性能的有利因素.     

时域相位光码分多址系统性能分析

给出了时域相位光码分多址系统(OCDMA)的噪声模型,提出了由码间串扰(ISI)所引起的自差拍噪声(SB)概念.利用鞍点近似法分析了多址干扰(MAD、码间串扰、自差拍等噪声对系统性能的影响,给出了系统误码率公式.对最佳门限接收系统以及采用光硬件限幅器的系统性能进行了仿真研究.表明"1"码的误判概率是影响系统的决定性因素.也是开关键控(OOK)系统难以克服的主要问题.最后给出一种采用双编/解码器平衡检测系统的原理框图,分析其性能,并与传统OOK系统比较,结果表明其性能有较大的提高.     

水声正交频分复用异步多用户接入方法

水声信道传播时延大导致水声通信网中上行用户同步困难,因此需要接收端具备异步多用户检测能力。针对水声正交频分复用(OFDM)异步多用户系统提出一种基于滑动迭代的异步多用户接入方法,包括重叠截断、干扰消除、频域过采样、多用户信道估计与解码、以及干扰重构5个处理模块,并通过滑动迭代结构同时消除前向干扰和后向干扰影响。仿真结果表明,所提方法在不同异步到达时延,以及有、无信道估计误差下的误比特率均明显低于逐块解调异步接收算法。水池实验结果表明,滑动迭代异步接收算法在多径扩展18 ms、异步到达时延大于或等于循环前缀1.5倍时实现了两用户异步接入的可靠通信。      

Single-carrier frequency domain adaptive antenna array for uplink multi-user MIMO transmission in a cellular system

In this paper, single-carrier frequency domain adaptive antenna array (SC-FDAAA) for the uplink multi-user multiple-input multiple-output (MIMO) transmission in a cellular system is studied. By employing AAA weight control in frequency domain, the base station (BS) can suppress the multi-user interference (MUI) and therefore realize multi-user SC transmission. In addition, channel frequency selectivity can be exploited to obtain the frequency diversity (or the multi-path diversity). The frequency domain signal-to-interference-plus-noise-ratio (SINR) after weight control is investigated and the computational complexity of the proposed receiver is analyzed. In numerical simulations, cellular structure using the frequency reuse is assumed, and the effect of co-channel interference (CCI) is considered. The performance of the SC uplink multi-user MIMO transmission using SC-FDAAA is testified and compared with other multi-user detection schemes. The link capacity (maximum number of users/cell) and cellular link capacity (link capacity/frequency reuse factor) are also be evaluated.     

Multi-scale mapping algorithm for INI cancellation and a novel mixed-numerologies OFDM transceiver

OFDM with mixed-numerologies enhances the system flexibility effectively to meet the demands of diversified application scenarios. However, the coexistence of waveforms with different numerologies leads to serious inter-numerology interference (INI), and the corresponding relationship between the number of guard subcarriers and the power of INI needs to be considered for scheduling subcarriers. In this paper, we propose a multi-scale mapping (MSM) and INI cancellation (MSM-INIC) algorithm as well as the corresponding de-MSM algorithm for mixed-numerologies OFDM system. Based on the proposed algorithms, we provide a novel transceiver in the scenario of multi-path fading channel, in which subcarrier scheduling does not need to consider whether the guard band is allocated. In the proposed transmitter, an additional MSM-INIC module is employed to pre-compensate signal distortion for downlink, and in the receiver, a de-MSM module is applied to de-map the received signals for recovering the original numerologies. Furthermore, we reveal the inherent property of the mapped signals, and propose a low computational complexity de-MSM algorithm accordingly. Simulation results verify the superiority of the proposed transceiver in BER performance as well as spectrum efficiency even without any guard band.