38,459 research outputs found

    An antenna switching based NOMA scheme for IEEE 802.15.4 concurrent transmission

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    This paper introduces a Non-Orthogonal Multiple Access (NOMA) scheme to support concurrent transmission of multiple IEEE 802.15.4 packets. Unlike collision avoidance Multiple Access Control (MAC), concurrent transmission supports Concurrent-MAC (C-MAC) where packet collision is allowed. The communication latency can be reduced by C-MAC because a user can transmit immediately without waiting for the completion of other users’ transmission. The big challenge of concurrent transmission is that error free demodulation of multiple collided packets hardly can be achieved due to severe Multiple Access Interference (MAI). To improve the demodulation performance with MAI presented, we introduce an architecture with multiple switching antennas sharing a single analog transceiver to capture spatial character of different users. Successive Interference Cancellation (SIC) algorithm is designed to separate collided packets by utilizing the spatial character. Simulation shows that at least five users can transmit concurrently to the SIC receiver equipped with eight antennas without sacrificing Packet Error Rate

    Cdma blind channel equalization: a weighted subsface a proach

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    This paper considers the problem of blind demodulation of multiuser information symbols in a direct-sequence code-division multiple access (DS-CDMA) environment. Channel estimation and symbol detection in the presence of both multiple access interference (MAI) and intersymbol interference (ISI) is carried out with second order statistics methods from the received data. This problem is similar to direction of arrival (DOA) estimation, where many solutions like the MUSIC algorithm orPeer ReviewedPostprint (published version

    Loosely synchronized spreading code aided network performance of quasi-synchronous UTRA-like TDD/CDMA systems

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    In this paper we investigate the achievable capacity of a UTRA-like Time Division Duplex (TDD) Code Division Multiple Access (CDMA) system employing Loosely Synchronized (LS) spreading codes. The family of operational CDMA systems is interference limited, suffering from Inter-Symbol-Interference (ISI), since the orthogonality of the spreading sequences is destroyed by the frequency selective channel. They also suffer from Multiple-Access-Interference (MAI) owing to the non-zero cross-correlations of the spreading codes. By contrast, the family of LS codes exhibits a so-called Interference Free Window (IFW), where both the auto-correlation and cross-correlation of the codes become zero. Therefore LS codes have the promise of mitigating the effects of both ISI and MAI in time dispersive channels. Hence, LS codes have the potential of increasing the capacity of CDMA networks. This contribution studies the achievable network performance in comparison to that of a UTRA-like TDD/CDMA system using Orthogonal Vari- MSO able Rate Spreading Factor (OVSF) codes

    Statistical Modeling of Bit-Error-Rates in Asynchronous Multicarrier CDMA and Direct-Sequence CDMA Systems

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    This paper presents a method for modeling the bit-error-rate (BER) probability density functions (pdf) of asynchronous Multicarrier Code Division Multiple Access (MC-CDMA) and Direct-Sequence Code Division Multiple Access (DS-CDMA) systems. An uplink channel is considered and it is assumed that the only channel distortion introduced by the channel is caused by the timing misalignments. Deterministic spreading sequences are used and the pdfs of each interferer'’s multiple access interference (MAI) are determined as a function of timing offset. A Nakagami-m distribution is fitted to the pdf of the total MAI power and the BER pdf is obtained directly from this Nakagami-m pdf. Both Walsh-Hadamard (WH) and Gold sequences are analyzed and the mean BERs are compared amongst the two multiple access systems for both sets of spreading sequences of varying lengths. The results suggest a higher resistance to MAI in the MC-CDMA technique for the considered environment

    Performance analysis of a 2-D time-wavelength OCDMA wavelength-aware receiver with beat noise

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    The effect of beat noise on two-dimensional time-wavelength optical code-division multiple-access systems utilising wavelength-aware receivers is examined. A derivation of a general formula for the bit error probability taking into consideration multiple access interference (MAI) and other noise sources is given. In addition, a comparison between the system performance of such a receiver and the traditional configuration is presented. Studies to date that have focused only on the MAI limited case showed that the wavelength-aware configuration yields a better performance when compared to the traditional receiver. When beat noise is considered, the numerical results reveal that the performance of wavelength-aware receiver is very sensitive to beat noise and is not superior over the traditional receiver

    ANALISA PARALLEL INTERFERENCE CANCELLATION (PIC) SEBAGAI TEKNIK PENANGANAN MULTIPLE ACCESS INTERFERENCE (MAI) PADA WiMAX

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    ABSTRAKSI: Fokus dari sistem komunikasi wireless (nirkabel) dewasa ini adalah menyediakan layanan dengan data rate (laju data) yang tinggi bahkan untuk layanan multimedia dan akses internet. Salah satu cara yang dapat dilakukan untuk mendukung hal tersebut adalah menggunakan teknik modulasi multicarrier. Sistem OFDM (Orthogonal Frequency Division Multiplexing) merupakan skema komunikasi multicarrier dimana antar frekuensi subcarriers saling orthogonal dan dapat saling overlapping.Karena kelebihan tersebut, sistem OFDM dipakai sebagai teknik modulasi dan akses jamak, lebih dikenal dengan OFDMA (Orthogonal Frequency Division Multiple Access), pada teknologi WiMAX (Worldwide Interoperability for Microwave Access), Broadband Wireless Access yang dianggap sebagai generasi selular keempat (4G). Performansi sistem multiuser Wimax sangat dipengaruhi salah satunya oleh efek Multiple Access Interference (MAI). Pada arah uplink system Orthogonal Frequency Division Multiple Access (OFDMA), Multiple Access Interference (MAI) terjadi karena perbedaan Carrier Frequency Offsets (CFO) dari user yang berbeda di receiver (penerima). Salah satu cara memperbaiki performansi system multiuser Wimax terkait efek MAI adalah menggunakan teknik multiuser detection (MUD). Ada beberapa jenis multiuser detection (MUD), seperti Successive Interference Cancellation (SIC), Parallel Interference Cancellation (PIC), Decorrelator, MMSE, dan lainnya.Pada tugas akhir ini performansi sistem dianalisa dengan menggunakan metode Parallel Interference Cancellation (PIC). PIC merupakan jenis multiuser detection sub optimum yang paling sederhana dalam pengaplikasiannya pada jaringan WiMAX yang menggunakan teknik OFDMA sebagai akses jamaknya. simulasi menunjukkan peningkatan performansi sistem. Hal ini ditunjukkan dengan adanya perbaikan SNR sebesar 6 dB untuk mencapai BER 10-3 pada kondisi jumlah user 4, kecepatan user 3 km/jam dan jumlah stage PIC yang digunakan adalah 2 stage dibandingkan dengan tanpa menggunakan PIC. Performansi sistem pun menurun seiring dengan pertambahan kecepatan user. Peningkatan pada nilai SNR ditunjukkan dengan metode dari Parallel Interference Cancellation (PIC) dibandingkan dengan kinerja tanpa menggunakan PIC.Kata Kunci : OFDM, OFDMA, WiMAX, PIC, MUDABSTRACT: The focus of the wireless communication system today is providing services with data rate is high even for multimedia services and Internet access. One way that can be done to encourage it is to use multicarrier modulation technique. OFDM (Orthogonal Frequency Division Multiplexing) system is a scheme where the multicarrier communication between mutually orthogonal frequency subcarriers and overlapping each other.Because of these advantages, OFDM systems are used as the modulation technique and multiple access, better known as OFDMA (Orthogonal Frequency Division Multiple Access), the WiMAX technology (Worldwide Interoperability for Microwave Access) Broadband Wireless Access is considered a fourth-generation wireless (4G). Wimax multiuser system performance is strongly influenced by the effects of one Multiple Access Interference (MAI). In the uplink direction systems Orthogonal Frequency Division Multiple Access (OFDMA), Multiple Access Interference (MAI) occurs because of differences Carrier Frequency Offsets (CFO) of different users at the receiver. One way to improve performance multiuser Wimax systems related MAI effect is to use the technique of multiuser detection (MUD). There are several types of multiuser detection (MUD), such as successive Interference Cancellation (SIC), Parallel Interference Cancellation (PIC), Decorrelator, MMSE, and more.In this final assignment system performance will be analyzed by using the method of Parallel Interference Cancellation (PIC). Parallel Interference Cancellation (PIC) is a type of sub-optimum multiuser detection is the simplest to apply in WiMAX networks using OFDMA as access techniques plurality. Simulations show the performance improvement system. This is demonstrated by the improvement of SNR by 6 dB to achieve BER of 10- 3 on the condition of the user 4, user speed of 3 km / h and the number of PIC stages are used compared with 2 stage without using the PIC. Any system performance declines with the increase speed of the user. The increase in SNR values shown by the method of Parallel Interference Cancellation (PIC) compared with the performance without using the PIC.Keyword: OFDM, OFDMA, WiMAX, PIC, MU

    Statistical Analysis of Interference in Asynchronous MC-CDMA Systems

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    Two major sources of interference affect asynchronous MC-CDMA systems, i.e. multiple access interference due to subcarriers with the same frequency (MAI) and multiple access interference due to subcarriers with different frequency (ICI). Both MAI and ICI are generally modelled as zero-mean Gaussian random variable and their power has been previously been derived in the case of uniformly distributed timing offsets. In this paper, we derive an expression of the conditional power of the MAI and ICI as a function of timing offset. The advantage is that the interference power can then be derived for various distributions of the timing offsets. We then apply the expression to calculating the MAI and ICI power for two different distributions of timing offsets, i.e. uniform distribution and Poisson distribution. Finally, we propose a statistical model for asynchronous MC-CDMA systems that will simplify the computer simulation process of these systems. It is based on modelling the asynchronous system with a synchronous system followed by additive noise representing the MAI and ICI. The model is validated by comparing the BER at the output of the asynchronous system and the model

    Noise suppression using optimum filtering of OCs generated by a multiport encoder/decoder

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    We propose a novel receiver configuration using an extreme narrow band-optical band pass filter (ENB-OBPF) to reduce the multiple access interference (MAI) and beat noises in an optical code division multiplexing (OCDM) transmission. We numerically and experimentally demonstrate an enhancement of the code detectability, that allows us to increase the number of users in a passive optical network (PON) from 4 to 8 without any forward error correction (FEC)
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