Level Of Multiple Access Interference Research Articles

THE STUDY OF THE CROSS-CORRELATION PROPERTIES OF COMPLEX SIGNALS ENSEMBLES OBTAINED BY FILTERED FREQUENCY ELEMENTS PERMUTATIONS

Context. The relevance is to study the cross-correlation properties of the developed complex signals ensembles of large volume with a low level of multiple access interference, thereby increasing the efficiency of using a limited radio frequency range. The Object of Research is a method of bandpass filtering with permutations, which allows forming complex signals ensembles of large volume. Objective. The Objective is to determine the optimal cross-correlation properties for the formation of complex signals ensembles of large volume with a low level of multiple access interference. Method. The work has the study results of cross-correlation properties of complex signals ensembles obtained by applying the filtered elements permutation method. The formation of complex signals ensembles is based on pseudo-random sequences with improved cross-correlation properties in the time domain. Bandpass filtering is applied to such sequences, and the number of filter bands is determined based on the calculation of the frequency spectrum utilization coefficient. The filter band optimal width determination is based on a comparison of the maximum emissions of the side lobes values of the of cross-correlation function of signals from the elements number in the involved sequences. The signals obtained by frequency bands allocating are characterized by a difference in form in the minimal similarity condition. In order to reduce the multiple access interference impact, the frequency components transfer obtained by spectral filtering to the common frequency range is carried out. After that, the signals are transferred using the full search method. As a result, it was obtained all possible combinations of signal pairs permutations. The use of permutations in the complex signals ensemble formation can significantly increase the ensemble volume. The signals generated by frequency filtering, to which the transfer to the common frequency band and their subsequent permutation was applied, are subjected to correlation analysis based on the calculation of the maximum emissions values of the side lobes of the cross-correlation function. Comparative characteristic of cross-correlation properties of developed signals with known signals prove that signals generated based on pseudo-random sequences with improved cross-correlation properties have a much larger ensembles volume, are formed on the basis of simple algorithms that don’t require significant computing resources and have satisfactory cross-correlation characteristics. The use of bandpass filtering method with permutation allows the formation of large-volume ensembles whose signals differ inform, and the combination of different frequency bands reduces the vulnerability to multiple access interference. Results. Due to the software implementation of the bandpass filtering method with permutations, the comparison of crosscorrelation properties of nonlinear sequences, M-sequences, multiphase signals and developed signals based on sequences with improved cross-correlation properties was performed. In estimating the levels of maximum emissions of side lobes of the cross-correlation function, it was found that the generated signals obtained by bandpass filtering with permutations deteriorate cross-correlation characteristics by increasing the pulse duration proportional to the decrease in signal frequency band, but their value satisfies the minimal similarity condition, used in cognitive telecommunications systems. Conclusions. The study of the signals cross-correlation properties proves the effectiveness of the developed bandpass filtering with permutations method. The generated signals have cross-correlated characteristics no worse than ensembles based on known signals. At this level of maximum emissions of the side lobes of the cross-correlation function of the developed signals is 7–12% less than the known signals. Thus, the method of bandpass filtering with permutations can be used to increase the efficiency of radio frequency resource use of both existing and advanced cognitive telecommunication networks of wireless access based on systems with code division multiplexing.

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.

Performance Analysis of ZCC-Optical-CDMA over SMF for Fiber-To-The-Home Access Network

To provide a sustainable fiber-to-the-home (FTTH), several multiplexing techniques have been developed for this purpose. The correlation features are the main obstacle behind the network performance limitation, which imposes to a high level of multiple access interference. However, the development of multiplexing techniques helps to overcome these limitations, such as optical-code division multiple access (Optical-CDMA). Optical-CDMA is considered as one of the most powerful solutions for FTTH. This paper aims to enhance FTTH network performance by applying Zero cross-correlation code (ZCC) with Optical-CDMA with maximum link single-mode fiber. In the simulation, the system performance is demonstrated in terms of bit error rate, Q-Factor and eye diagram measurements.

Расширение словаря псевдослучайного кода с помощью двойной корреляционной обработки сигнала

The aim of research is the adaptation of code division multiple access (CDMA) technics for a radio frequency identification systems based on surface acoustic waves technology. The object of this research is a pseudo-random code of CDMA systems. The question of increasing the pseudo-random code vocabulary size, while maintaining good correlation characteristics is under consideration. The criterion for quality of pseudo-random code is the level of multiple access interference (MAI). This criterion is estimated by the maximum level of aperiodic correlation function between each pair of code words. The solution of the problem is achieved by signal processing and does not affect coding issues. A code is generated with necessary vocabulary size and a minimum level of MAI is achieved by using dual correlation processing. The concept of dual correlation processing is to seek a correlation function for two weakly dependent information features of the code. An additional informational sign is the amplitude spectrum of a code word. The correlation characteristics of the code after processing are modeled.

Optical Code Division Multiple Access for FTTH system

Many multiple access techniques have been proposed and demonstrated to provide flexible solutions for FTTH network configurations. The performance of this system suffers because of the correlation properties that contribute to a high level of Multiple Access Interference (MAI), low system capacity (users), and lower transmission rate. In this paper, we have proposed Optical CDMA (OCDMA) as a configuration solution for FTTH networks to improve the performance of this type of network. Full Text: PDF References. Z. Mateusz, M. Mariusz, On cost of the uniformity in FTTH network design, Conference on Transparent Optical Networks (2017), 87-90 CrossRef CEDRIC F. LAM, Passive Optical Networks- Principles and Practice, first ed., British Library, USA, 2007. DirectLink M.K. Abdullah, W.T. P'ng, P.W. Lau, E.R. Tee, FTTH access network protection using a switch, Asia Pacific Conference on Communications (APCC), 3(2003) 1219–1222. CrossRef J. Ronnakorn, S. Napat, L. Somkiat, Design and implement of GPON-FTTH network for residential condominium, Conference on Computer Science and Software Engineering, (2017), 333-339. CrossRef M. BOUREGAA, M. CHIKH-BLED, Comparative Study of Optical Unipolar Codes for Incoherent DS-OCDMA system, International Journal of Hybrid Information Technology, 6 (2013) 225-236. CrossRef M. BOUREGAA, M. CHIKH-BLED, The performance of a DS-OCDMA system using Orthogonal Optical Codes (OOC), European Scientific Journal, 9 (2013), 322-335 CrossRef M. Iwase, Y. Ishikawa, T. Komatsu, J. Kasahara, N. Hattori, M. Miura, N. Nakamura, K. Odaka, Optical transceiver modules for gigabit Ethernet PON FTTH systems, Furukawa Review, 28 (2005) 8-10. DirectLink

Cooperative MIMO relay beamforming in overloaded DS/CDMA multicast networks

A new beamforming scheme is proposed for multi-input multi-output (MIMO) non-regenerative relays in an overloaded synchronous direct sequence code division multiple access (DS-CDMA) network in which the number of users is larger than the processing gain. In this scheme, several transmitters multicast their data to their groups of receivers through MIMO relays and DS-CDMA technique is utilised to decrease the level of multiple access interference (MAI) at the relays and the receivers. At the relays, the data of transmitters are despread, beamformed and re-spread. The aim of the beamformer is to minimise the total relays transmission power subject to the signal to interference and noise ratio (SINR) constraints at the receivers. This optimisation problem is an indefinite quadratic (non-convex) programming. Semi-definite programming (SDP) and second-order cone programming (SOCP) are two existing methods to solve the problem. However, they, respectively, suffer from high computational complexity and performance degradation when the number of antennas or users increase. To effectively mitigate these deficiencies, we propose a novel DC (difference of two convex functions) programming method. Our simulation results demonstrate the computational advantage of the proposed DC programming over SDP, while a better performance over SOCP is achieved. Moreover, the superiority of the proposed MIMO-CDMA scheme over other multiplexing schemes is shown by several scenarios.

Iterative channel estimation for multiuser fibre‐wireless uplink exploiting semi‐correlated ternary signals

A novel design of ternary signal sets is proposed for estimation of multiuser fibre-wireless (Fi-Wi) uplink channels. The design overcomes the current limitation in the maximum number of users that the system can accommodate by separating the signals in a set into subsets. The signals are uncorrelated between subsets, but correlated within subsets, thus forming a semi-correlated ternary pseudo-random signal (SC-TPRS) set. An iterative channel estimator based on the SC-TPRS scheme is then proposed for joint estimation of the Fi-Wi uplink channel. The computational complexity associated with the existing and the proposed estimators is derived and it is shown that the latter incurs substantially lower computational cost than the former. Numerical results show that despite using signals which are a few hundred times shorter, the proposed scheme can improve estimation accuracy dramatically over the existing scheme at low signal-to-noise ratios. The proposed scheme has a further advantage of allowing the designer to optimise the Fi-Wi system under the constraint of maximum permissible level of multiple access interference, since the amount of interference can be tuned by adjusting the number and size of the ternary signal subsets.

Investigation of slotted aloha under nakagami fading with synchronized and asynchronous cochannel cells

The throughput performance of slotted ALOHA (S-ALOHA) in a cellular system and Nakagami fading environment is studied. Based on the signal capture model, the effects of multiple access interference (MAI) from in-cell users and of cochannel interference (CCI) from cochannel cells are quantified analytically. Especially considered are the cases when asynchronism of cochannel cells is present, for which an approximation of the interference distribution is successfully applied to get a highly precise expression of the system throughput. Our study shows that, though the MAI level and capture effect determine the basic behavior of the S-ALOHA, CCI significantly reduces the throughput of S-ALOHA and asynchronous CCI introduces an especially severe impairment. Our analytical framework is also able to incorporate additional channel conditions and system parameters like lognormal shadowing and the cellular cluster size.

Dynamic spreading gain control in multiservice CDMA networks

In this paper, we consider a direct-sequence code division multiple access (DS-CDMA) network consisting of a single radio access point and a collection of wireless terminals. The network offers two classes of service: class-1 (real-time) and class-2 (reliable). We are interested in studying the effect of dynamic spreading gain control (SGC) on the dynamics of multiple access interference (MAI), spectral efficiency, and the quality of service (QoS) experienced by each service class. We first consider a time-slotted system in which class-2 terminals operate in a random access fashion. We show that under optimal (throughput maximizing) dynamic SGC: (1) the optimal retransmission probability is equal to one, and (2) the optimal spreading gain increases linearly, or equivalently, the transmission rate decreases inverse linearly, as the MAI level increases. We then model the system as a continuous-time finite-source queueing system with processor sharing, and obtain an explicit (closed-form) expression for the stationary distribution of the number of active class-1 and class-2 terminals, that is, the MAI level. This distribution is used to derive expressions for various QoS measures and define a capacity or admissible region. The results obtained by simulation and analysis are in extremely close agreement. This work contributes to a better understanding of the relationships between QoS, multiple access interference, and allocation of radio resources in DS-CDMA networks.

Identification of active users in synchronous CDMA multiuser detection

The level of multiple access interference (MAI) in code division multiple access (CDMA) communication systems is a time-varying parameter related to the number of active users. Almost all existing multiuser detection schemes were designed based on a priori information of the active users. In many situations, however, the multiuser receiver does not know the number of active users, and the receiver designed for the detection of all users may lead to poor performance. To develop a more efficient detection scheme in practical applications, we propose a two-stage detection structure consisting of preprocessing (identification) and postprocessing (detection). In the preprocessing, we apply the subspace concept and a method based on the multiple signal classification (MUSIC) algorithm to identify the active users while requiring only a priori knowledge of all of the users' signature sequences. The proposed preprocessor is shown to be asymptotically near-far resistant, and to have the ability to identify the active users in a simple and reliable way. While in the detection process, as we efficiently use the active users' information in every observation interval, the performance is clearly improved compared to the conventional structure without identification. Moreover, the effect of imperfect identification on the decorrelating detector is also extensively analyzed. Though the decorrelating detector's inherent near-far resistant characteristic is impaired by imperfect identification, the proposed structure still outperforms the conventional structure in the general near-far environment.