Multiple Access Interference Research Articles

Resource Allocation Based on User Pairing and Subcarrier Matching for Downlink Non-Orthogonal Multiple Access Networks

The traditional orthogonal multiple access (OMA) is unable to satisfy the needs of large number of smart devices. To increase the transmission rate in the limited spectrum resource, implementation of both non-orthogonal multiple access (NOMA) and successive interference cancelation (SIC) is essential. In this paper, an optimal resource allocation algorithm in NOMA is proposed to maximize the total system rate in a multi-sector multi-subcarrier relay-assisted communication network. Since the original problem is a non-convex problem with mixed integer programming which is non-deterministic polynomial-time (NP)-hard, a three-step solution is proposed to solve the primal problem. Firstly, we determine the optimal power allocation of the outer users by using the approach of monotonic discrimination, and then the optimal user pairing is determined. Secondly, the successive convex approximation (SCA) method is introduced to transform the non-convex problem involving central users into convex one, and the Lagrangian dual method is used to determine the optimal solution. Finally, the standard Hungarian algorithm is utilized to determine the optimal subcarrier matching. The simulation results show that resource allocation algorithm is able to meet the user performance requirements with NOMA, and the total system rate is improved compared to the existing algorithms.

Design of a Hybrid WDMA-Optical-CDMA over Multi-Mode Fiber Transmission System based on LG Modes for Short Haul-Local Area Network

Various optical communication technologies use Optical-Code Division Multiple Access (Optical-CDMA) as a channel access technique, which allows transmission of different users simultaneously over the optical communication channel. Therefore, Optical-CDMA permits free undue interference transmission of several users. Whereas Wavelength-division multiple access (WDMA) is a technique that can be implemented on how the optical channel can be divided into subchannels. This paper proposes a Hybrid WDMA-Optical-CDMA over multi-mode fiber (MMF) transmission system for short haul-local area network. The WDMA system is carried out by using four Laguerre-Gaussian (LG) modes that operate over four main wavelengths (1551 nm, 1550 nm, 1549 nm and 1548 nm). Additionally, the Optical-CDMA system is carried out by using one dimension Zero Cross-Correlation (ZCC) code to overcome multiple access interference (MAI) between the four ZCC codes. The performance of our system is evaluated based on eye diagrams, Q-Factor and bit-error rates (BER) measurements.

WON-OCDMA System Based on MW-ZCC Codes for Applications in Optical Wireless Sensor Networks

The growing demand for extensive and reliable structural health monitoring resulted in the development of advanced optical sensing systems (OSS) that in conjunction with wireless optical networks (WON) are capable of extending the reach of optical sensing to places where fibre provision is not feasible. To support this effort, the paper proposes a new type of a variable weight code called multiweight zero cross-correlation (MW-ZCC) code for its application in wireless optical networks based optical code division multiple access (WON-OCDMA). The code provides improved quality of service (QoS) and better support for simultaneous transmission of video surveillance, comms and sensor data by reducing the impact of multiple access interference (MAI). The MW-ZCC code’s power of two code-weight properties provide enhanced support for the needed service differentiation provisioning. The performance of this novel code has been studied by simulations. This investigation revealed that for a minimum allowable bit error rate of , and when supporting triple-play services (sensing, datacomms and video surveillance, respectively), the proposed WON-OCDMA using MW-ZCC codes could support up to 32 simultaneous services over transmission distances up to 32 km in the presence of moderate atmospheric turbulence.

New Image Transmission Schemes for DST-Based MC-CDMA System

In recent years, one important research area for multimedia broadcasting is how to encrypt images over communication systems. However, wireless transmission is usually under many constraints and limitations like multipath fading, InterSymbol Interference and jitter especially for such applications require relatively high data rates compared to voice transmissions. Interleaving techniques with multicarrier code division multiple access system are used to combat multi-path fading environment. This paper proposes three new transmission schemes of encrypted images for downlink discrete sine transform-based multi-carrier code division multiple access (DST-MC-CDMA) system. For each one of them, two or three stages are added to the DST-MC-CDMA system to combat the wireless transmission problems. The three stages are called Randomization stage, Interleaving stage, and PIC stage. The randomization stage encrypts the image using a two dimensional chaotic map before the DST-MC-CDMA modulation. The interleaving stage interleaves the DST-MC-CDMA signal before the transmission. The stage of parallel interference cancellation is used to cancel the multiple access interference from the received image. The main aim is to clarify the received image by combating the wireless channel weaknesses. The results of the experiments reveal that the proposed schemes are superior to conventional one that uses only equalization. Moreover, a significant performance improvement in terms of the mean square error and peak to signal and noise ratio values when applying the proposed schemes is shown in the results.

Design, Calibration, and Evaluation of a Long-Range 3-D Infrared Positioning System Based on Encoding Techniques

Optical indoor positioning systems have experienced an increasing research interest during the last decade as they can provide 3-D centimeter accuracy using light emitting diode (LED) lighting. In the case of having several LEDs emitting simultaneously and a receiver (e.g., the tag to be localized), these systems face important challenges, such as very high dynamic ranges with low signal-to-noise ratios when the coverage area is increased, multiple access interference (MAI), multipath and near-far effects, calibration issues (misalignments in the receiver and other intrinsic parameters), and so on. Previous work have already shown the feasibility of using LED emitters in combination with quadrature angular diversity aperture (QADA) receivers to implement positioning systems. This work further introduces new design considerations, tested on an experimental setup, to enlarge the emitter–receiver range, thus increasing the total coverage, while dealing with the aforementioned challenges. The system applies encoding techniques to each transmitter to solve the multiple access problem. The performance of two different types of codes has been compared, as well as their influence on the final estimation of the receiver’s position: one based on Kasami sequences and another based on loosely synchronous (LS) codes, derived from complementary sets of sequences. At the receiver, the estimation of the incident point is constrained to angles at which the system can be linearized, and a specific calibration process for this type of sensor has also been defined and applied. The proposal has been finally validated with simulated and experimental results in a large space of $2 \times 2$ m2 (base), with a distance from transmitters to receiver of 3.4 m (height). The experimental tests at distances up to 4 m, carried out after the calibration process, achieve average absolute errors below 10 cm for $X$ and $Y$ axes and around 20 cm for $Z$ axis, and standard deviations below 4 cm for $X$ and $Y$ axes, and around 30 cm for $Z$ axis.

Performance evaluation of 120 GB/s hybrid FSO-SACOCDMA-MDM system using newly designed ITM-Zero cross-correlation code

Since last decade, Spectral Amplitude Coding Optical Code Division Multiple Access (SAC-OCDMA) system has become popular since it offers security, unlimited bandwidth and eliminates multiple access interference. On the other hand, Free Space Optics (FSO) provides last-mile access at a high data rate. We have designed a new zero cross-correlation code, which is named as an identity-type matrix ZCC code. The proposed code’s performance is evaluated by designing 120 GB/s Hybrid FSO-MDM (mode division multiplexing) and SAC-OCDMA system under atmospheric turbulence using the direct detection (DD) technique. Six channels, carrying 20 GB/s data each, are transmitted over the FSO channel. Two Laguerre Gaussian modes (LG 00 and LG 01) are used in MDM. The results of the simulation show that the performance of the proposed code is better in comparison to existing codes.

An Adaptive FH/MC-CDMA to Improve Channel Quality for Multiuser Using Variable Code-Based Carriers

The adaptive variable code-based carriers for multiusers in a common channel of communication is a technique of Multi-Carrier Code Division Multiple Access (MC-CDMA). It is an advanced mode of communication, where multiple users are communicating with different code and a different carrier. The proposed adaptive frequency hopping technique in MC-CDMA will give high signal to noise ratio value mitigating multiple access interference. Proposed adaptive technique detects multi-users with the help of matched filters. The simulation of the above system is done with correlated sub-carriers in the presence of realistic fading channels and even imperfect channel state information for recovering at the transmitter. The performance of an improved allocation algorithm for MC-CDMA system with adaptive frequency hopping is investigated. Imperfect channel state information at the base station does not affect the performance of the proposed technique due to the combined allocation algorithm and multi-user detector employment. The above combination mitigates multiple access interference efficiently, and increases the system capacity in a significant way compared to non-adaptive variable code-based carrier system. The results of the simulation confirm the above said performance factors with realistic correlated sub carriers that are faded with practical communication system parameters.

Reducing the Effects of Multiple Access Interference Signals Using Two Parallel Linear Antenna Array Based MVDR Beam former Technique

Reducing the Effects of Multiple Access Interference Signals Using Two Parallel Linear Antenna Array Based MVDR Beam former Technique

THE FORMATION METHOD OF COMPLEX SIGNALS ENSEMBLES BY FREQUENCY FILTRATION OF PSEUDO-RANDOM SEQUENCES WITH LOW INTERACTION IN THE TIME DOMAIN

Context. The problem of forming complex signal ensembles on the basis of frequency band filtering and research of their properties is considered. The object of research is the process of synthesis of signal ensembles based on frequency filtering of pseudo-random sequences of short video pulses with low interaction in the time domain.Objective. It is to form complex signal ensembles with satisfactory values of intercorrelation properties, which are close to the signals with minimal energy interaction. Method. The results of the application of forming complex signal ensembles method by frequency filtering of pseudo-random sequences with low interaction in the time domain are presented. As a result of the spectral band selection of the studied pseudorandom short video pulse sequences due to the use of bandpass filters based on the Chebyshev filter of the first kind, new samples of sequences with spectrum restriction are obtained. By applying intercorrelation analysis to the obtained sequence samples, the values of the maximum emissions of the side lobes of the cross-correlation functions (CCF) for all possible signal pairs are estimated. If the values of the maximum emissions of the side lobes of the CCF signals exceed the limit values, the sequence of the analyzed pair with a smaller value of the number of pulses is removed from the ensemble. In case of satisfactory value – the received signals are accepted for the signal ensemble formation with the minimum power interaction. Thus, a new set of values of the maximum emissions of the side lobes of the CCF is formed. This approach increases the number of signals in ensembles with satisfactory values of statistical characteristics with limited signal spectrum width, and the correlation properties of such sequences approach the signals with minimal energy interaction, which reduces the level of multiple access interference. As a result, complex signal ensembles obtained by frequency filtering should be used in cognitive radio systems with code division multiplexing.Results. Based on the software implementation of the method of forming complex signal ensembles by frequency filtering of pseudo-random sequences with low interaction in the time domain, signals with satisfactory values of statistical characteristics with limited signal spectrum width with intercorrelation properties close to signals with minimal energy interaction and higher ensemble volume were selected.Conclusions. The application of frequency filtering to pseudo-random sequences of short video pulses with a low level of crosscorrelation allows to obtain complex signal ensembles, which will be similar in correlation properties to sequences with minimal energy interaction. It will reduce the level of multiple access interference. The analysis revealed that the use of frequency filtering of sequences will slightly worsen the mutual correlation properties of signals, possibly due to suboptimal synthesis of values of maximum emission levels of side lobes of CCF signals, but, nevertheless, it is possible to use such signals in modern cognitive systems radio access multiple access with code division multiplexing.

Molecular Type Spread Molecular Shift Keying for Multiple-Access Diffusive Molecular Communications

In nano-networking, many nano-machines need to share common communication media, in order to achieve information exchange and data fusion. Multiple-access is an important technique for multiple nano-machines to send information to one access point (AP) or fusion center. Built on the Molecular Shift Keying (MoSK) modulation, this article proposes a novel Molecular Type Spread MoSK (MTS-MoSK) scheme for achieving multiple-access transmission in diffusion-based molecular communications (DMC). Correspondingly, two detection schemes are introduced and investigated, which are the Maximum Selection assisted Majority Voter Detection (MS-MVD) and Equal-Gain Combining Detection (EGCD). The error performance of the MTS-MoSK DMC systems with respectively the two detection schemes is analyzed, when both Multiple-Access Interference (MAI) and Inter-Symbol Interference (ISI) are taken into account. Furthermore, the performance of MTS-MoSK DMC systems is investigated and compared with the aid of analytical results as well as Monte-Carlo and particle-based simulations. Our studies and performance results show that MTS-MoSK constitutes a promising candidate for implementing multiple-access DMC, and MS-MVD has the potential to outperform EGCD in DMC.

Performance analysis of incoherent PPM‐OCDMA networks based on optimised modified prime code for multimedia applications

This study presents the design analysis and correlation properties of a new spreading code for the incoherent synchronous pulse position modulation-optical code division multiple access (PPM-OCDMA) networks. The proposed code called optimised modified prime code (OMPC), which refers to the modified prime codes (MPCs) family. Additionally, this new code designed at a higher code length, optimised code weight and good correlation characteristics to enhance communication security and improve the bit error rate (BER) performance. In this study, the proposed code is used as source code for different kinds of multimedia services such as data, voice, and video. Furthermore, the characteristics and correlation properties of the OMPC in comparison with the other MPCs families that utilised in the PPM-OCDMA networks are presented. Moreover, for the PPM-OCDMA networks, the effect of OMPC auto- and cross-correlation properties on the multiple access interference (MAI) was investigated. Consequently, the MAI is considered in the BER analysis and calculations. Finally, the results show that the proposed OMPC is better than the other existing codes with respect to the channel capacity and system performance.

An efficient 2D encoding/decoding technique for optical communication system based on permutation vectors theory

One dimensional encoding in optical communications has limitations in terms of the number of supported users and large bandwidth consumption. This study presents a new algorithm to generate two-dimensional (2D) encoding utilizing permutation vectors (PV) theory for incoherent multiple access network to suppress multiple access interference (MAI) and system complexity. The proposed code design approach is based on spectral/spatial techniques for code generation. All possible combinations of PV code-sets are obtained by utilizing all permutations of the vectors with the repetition of each vector weight (W) times. Furthermore, the 2D-PV code-set is constructed by combining two code sequences of the 1D-PV code. Furthermore, the transmitter–receiver architecture of the 2D-PV spectral/spatial (S/S) code based OCDMA system is presented. The Gaussian approximation is used to analyze the performance of the proposed OCDMA system with 2D- PV code by considering various noise sources (shot, thermal, and PIIN). Results indicate that the 2D-PV code provides increased cardinality by eliminating phase induced intensity noise (PIIN) effects with a minimum likelihood of interference between multiple user data. Simulation implementations validate the proposed system performance for an agreeable bit error rate (BER) of 10–9

Noncoherent Multiuser Chirp Spread Spectrum: Performance With Doppler Shift and Asynchronism

In this paper, we investigate multi user chirp spread spectrum with noncoherent detection as a continuation of our work on coherent detection in [1]. We derive the analytical bit error ratio (BER) expression for binary chirp spread spectrum (BCSS) in the presence of multiple access interference (MAI) caused by correlation with other user signals because of either asynchronism or Doppler shifts, or both, and validate with simulations. To achieve this we analyze the signal cross correlations, and compare traditional linear chirps with our recently-proposed nonlinear chirps introduced in [1] and with other nonlinear chirps from the literature. In doing so we illustrate the superior performance of our new nonlinear chirp designs in these practical conditions, for the noncoherent counterpart of [1].

A Performance Analysis of a Hybrid OCDMA-PON Configuration Based on IM/DD Fast-OFDM Technique for Access Network

The purpose of this article is to propose a new configuration based on OCDMA and Fast-OFDM techniques for access network applications. A hybrid intensity modulation with direct detection, fast orthogonal frequency-division multiplexing–code division multiplexing access (IM/DD Fast-OFDM-CDMA) system is analytically and numerically evaluated for an amplifier-free access network. Therefore, system performance is analytically investigated in terms of bit error rate/Q-factor as a function of simultaneous users, fiber length and launched optical power. Firstly, the proposed analytical model includes the overlapping effect among OFDM subcarriers, the peak-to-average power ratio (PAPR), and multiple access interference (MAI). Secondly, a simulation setup is performed, allowing four simultaneous users operating at 40 Gb/s in a passive optical network (PON) context. Furthermore, a power budget analysis is made between IM/DD Fast-OFDM-CDMA, all-optical IM/DD OFDM-CDMA (IM/DD AO-OFDM-CDMA) and OCDMA wavelength division multiplexing (OCDMA-WDM) configurations. It is shown that at 40 Gb/s and by using 2D-hybrid coding (2D-HC), the maximum achievable transmission-reach of IM/DD Fast-OFDM-CDMA is 142 km, which is 34 km and 60 km higher than those provided by the IM/DD AO-OFDM-OCDMA and OCDMA-WDM PON configurations, respectively.

Enhancement of reliability and security in spatial diversity FSO-CDMA wiretap channel

Abstract Due to atmospheric turbulence, the reliability and security of free space optical (FSO) communication will be affected seriously. In this paper, we propose a novel scheme of quasisynchronous spatial diversity free-space optical code division multiple access (FSO-CDMA) wiretap channel based on gamma-gamma distribution. Considering multiple access interference, shot noise, thermal noise and background noise, performances of bit error rate (BER) and physical-layer security are analyzed theoretically. The physical-layer security of quasisynchronous spatial diversity FSO-CDMA wiretap channel is evaluated by secrecy capacity and interception probability. Closed-form expression of interception probability is obtained. In order to compare the performances between conventional spatial diversity FSO-CDMA and the proposed scheme, Optisystem simulation is carried out. The results indicate that quasisynchronous spatial diversity FSO-CDMA scheme can improve the reliability and physical-layer security simultaneously.

Simultaneous Excitation Systems for Ultrasonic Indoor Positioning

The ultrasonic technology is a tool for indoor positioning systems (IPSs) and has been extensively used in many applications. In ultrasonic IPSs (UIPSs), the use of a chirp signal (in which the frequency varies with time) is widespread due to its capability to obtain high-range resolution through its time-frequency characteristic. It also provides an opportunity to design effective waveform diversity which has always been the key to mitigating multiple-access interference (MAI) in multi-user UIPSs. To explore this, we analyze the chirp signal from the signal design perspective, with the goal of developing a precise and efficient UIPS for multi-user environments. To achieve this, three waveform diversity design schemes are proposed in which all the benefits of the classical chirp, such as high-range resolution, are retained while all the transmitters can transmit chirp signals simultaneously. In each scheme, a linear chirp is divided into two linear sub-chirps with diverse durations and/or bandwidths. This process is optimized by selecting the concatenated sub-chirps that generate a waveform which has a high-range resolution and relatively low interference in the same scheme. Initially, the effectiveness of the proposed schemes is evaluated for five simultaneous excitation signals using several metrics and experimental results are then presented for the ultrasonic indoor positioning.

THE STUDY OF ENSEMBLE PROPERTIES OF COMPLEX SIGNALS OBTAINED BY TIME INTERVAL PERMUTATION

The results of statistical analysis of cross-correlation properties of complex signals’ ensembles, were obtained due to time interval permutations are presented in this paper. The essence of the method is to apply the division of short videopulse sequences at the level of intervals with low interaction in the time domain with different numbers of pulses. By applying the cross-correlation analysis, the maximum emission values of the side lobes of the cross-correlation functions are calculated and its total average value is determined. Based on the obtained values, a series is formed in which the first position is occupied by a time interval in which the value of the maximum emissions of the side lobes of the cross-correlation function has an average value. The determination of the following time intervals is based on the analysis of the rating series and the arrangement of values is carried out in accordance with the selected total average value. Thus, a new average range of the maximum emission values of the side lobes of the cross-correlation function is formed. The average range increases the number of ensembles with satisfactory cross-correlation properties for use in radio communication systems with code division multiplexing, and minimal interaction between signals in the time domain reduces multiple access interference.

Research on the system performance of SAC-FBGs codec scheme

The theory of codec based on non-coherent frequency domain codec (FBGs) and non-coherent spectral domain codec (SAC-FBGs) of light-brain grating is theoretically analyzed and its transmission performance is verified. The codec scheme with better performance is compared. An optical quadrature cyclic shift code with a code length N of 13, code weight ω of 4, and self-correlation λ of 1 is used to implement codec schemes using FBGs codec and SAC-FBGs codec, respectively. Based on multiple access interference, signal to interference ratio (SIR) and bit error rate (BER) are discussed separately. From experimental results, it can be concluded that under the condition that the optical orthogonal codes are identical and the number of concurrent users is the same, the signal to interference ratio of the OCDMA system obtained by using the SAC-FBGs coding and decoding scheme is higher than that of the OCDMA system obtained by using the FBGs coding and decoding scheme. The SIR has increased by nearly two orders of magnitude, and the multiple-site interference BER has decreased by 20 or even 100 orders of magnitude. The experiment verifies that the transmission performance of the same optical orthogonal code using the SAC-FBGs coding and decoding scheme is obviously higher than that of the system transmission performance using the FBGs coding and decoding scheme.

Construction and performance analysis of a new SAC-OCDMA code based on Latin square matrix

In this paper a family of novel spreading code called Latin square code (LSC) is proposed for spectral amplitude coding-optical code division multiple access (SAC-OCDMA) system. The main feature of the proposed code is the zero cross-correlation which eliminates both multiple access interference (MAI) and phase induced intensity noise (PIIN). The code construction can be easily accomplished using Latin square matrix (LSM) for any weight and number of users. The simplicity in the construction code has made it a compelling candidate for future OCDMA applications. SAC-OCDMA system employing direct decoding is mathematically analyzed and then numerically simulated using Matlab and OptiSystem respectively. The results show the improvement given by the LSC code to the SAC-OCDMA system compared to the other codes such as: ZCC (zero cross-correlation) and MMS (modified multiservice) by allowing high cardinality and improving BER. Furthermore, the transmission quality, so that the BER does not exceed the value of $10^{-9}$, is ensured by the LSC code with a lower effective source power of -14.5 dBm, a bit rate of 4.6 Gb/s and a cardinality exceeding ZCC and MMS by 1.7 and 1.22 times respectively. The simulation results validate the mathematical analysis and show that the system makes it possible to increase the transmission distance without affecting QoS (quality of service)

Full-duplex cooperative NOMA system under impacts of residual SI and MAI

ABSTRACT In this paper, we investigate the performance of a downlink cooperative non-orthogonal multiple access (C-NOMA) system with full-duplex decode-and-forward relaying, where a NOMA user with better channel operates as a full-duplex (FD) relay to assist other NOMA-user to forward its messages to the base station (BS). Specifically, we derive the exact expressions of the system performances in terms of outage probability and ergodic capacity for two users over the Nakagami- fading channels for the case with the direct link from the BS to users. We then analyse the impacts of residual self-interference (SI) due to imperfect self-interference cancellation in the FD mode and multiple access interference (MAI) due to imperfect co-channel interference cancellation (CCIC) on the system performance. Simulation results are provided to verify the theoretical analysis and demonstrate the advantages of the FD-C-NOMA system over the FD non-cooperative NOMA (FD-NC-NOMA) system and the half-duplex C-NOMA (HD-C-NOMA) one.