285 research outputs found
An Improved Chevron Configuration for the Detection of Magnetic Field Vectors
A modified version of Chevron type Magnetoresistive Recording Heads (MRH) sensor is described. Two shielded ferromagnetic thin-film vertical-type MRH
are biased at the linear region simultaneously using a small piece of permanent magnet chip. The biasing rotates the magnetisation vector Ms of each MRH .
through 4S· with respect to their respective current vectors J resulting in an
effective Chevron orientation of 90·. This configuration is shown to be most
effective to detect field vectors in applications such as non-destructive detection
of grain structures and loss variation in electrical steels, and in packing more
bits of information in magnetic disc storage
Telecommunications in Malaysia: diversity in adversity
The telecommunications industry in Malaysia has experienced a tremendous transformation in just over a decade. The government-owned Jabatan Talikom, which hitherto operated the network, was incorporated in 1987 and subsequently privatized a few years later, with a majority share holding by the government. The regulatory aspects were spun off under the slim looking JTM. This marked the beginning of liberalization, and many new players entered the fray. This article reviews the telecommunications infrastructure and services available in Malaysia and briefly visits some of the telcos offering these services. Some pertinent issues affecting the industry are also discussed
Low Complexity Partial Transmit Sequence with Complex Gain Memory Predistortion in OFDM Systems.
In this paper the peak to average power ratio (PAPR) reduction and digital predistortion effects in orthogonal frequency division multiplexing (OFDM) systems are investigated. By applying a predistortion technique called complex gain memory predistortion (CGMP), power amplifier works at higher power efficiency. The proposed enhanced partial transmit sequence scheme is applied for PAPR reduction and integration with CGMP technique results in increasing in OFDM system efficiency and prolonged battery life. Simulation and results are examined with actual power amplifier and OFDM signal with quadrature phase shift keying (QPSK) modulation
A crest factor reduction scheme based on recursive optimum frequency domain matrix
One of the main imperfections in orthogonal frequency division multiplexing (OFDM) techniques is a peak-to-average power ratio (PAPR) or crest factor (CF). High crest factor signal forces a power amplifier in communication systems to back-off which leads to power efficiency degradation. Several techniques have been proposed in literature to mitigate the high peaks in OFDM signal; however most of them suffer from complexity and PAPR performance. In conventional SLM (C-SLM), increasing the number of inverse fast Fourier transform (IFFT) leads to excessive hardware resources requirement and increases system cost. In this paper a novel crest factor scheme based on recursive optimum frequency domain matrix is proposed which requires only two IFFT which results in significant reduction in the computational complexity. Simulation results show both the complexity and crest factor are reduced significantly compared to the conventional methods
Partial transmit sequence scheme with new phase sequence for PAPR reduction in OFDM systems
One of the effective methods used for reducing peak to average power ratio (PAPR) in OFDM systems is partial transmit sequence (PTS). In the conventional PTS (CPTS) several inverse fast Fourier transform (IFFT) operations and complicated calculation to obtain optimum phase sequence, increase the computational complexity of C-PTS. In this paper, we propose a technique to reduce the number of IFFT operations to half at the expense of a slight PAPR degradation. Simulations are performed with QPSK modulation with OFDM signal and Saleh model power amplifier. The effects of digital predistortion (DPD) to increase the linearity and efficiency of the Saleh model power amplifier (PA) are also examined
Providing Dynamic TXOP for QoS Support of Video Transmission in IEEE 802.11e WLANs
The IEEE 802.11e standard introduced by IEEE 802.11 Task Group E (TGe)
enhances the Quality of Service (QoS) by means of HCF Controlled Channel Access
(HCCA). The scheduler of HCCA allocates Transmission Opportunities (TXOPs) to
QoS-enabled Station (QSTA) based on their TS Specifications (TSPECs) negotiated
at the traffic setup time so that it is only efficient for Constant Bit Rate
(CBR) applications. However, Variable Bit Rate (VBR) traffics are not
efficiently supported as they exhibit nondeterministic profile during the time.
In this paper, we present a dynamic TXOP assignment Scheduling Algorithm for
supporting the video traffics transmission over IEEE 802.11e wireless networks.
This algorithm uses a piggybacked information about the size of the subsequent
video frames of the uplink traffic to assist the Hybrid Coordinator accurately
assign the TXOP according to the fast changes in the VBR profile. The proposed
scheduling algorithm has been evaluated using simulation with different
variability level video streams. The simulation results show that the proposed
algorithm reduces the delay experienced by VBR traffic streams comparable to
HCCA scheduler due to the accurate assignment of the TXOP which preserve the
channel time for transmission.Comment: arXiv admin note: substantial text overlap with arXiv:1602.0369
The FPBA algorithm with controlled capture ICC2001
Abstract-In this paper, we introduce a new mixed priority
scheme that utilizes the LESRTPL model [S] to control the
assignment of the transmitter power levels, assigned to each
priority class, whose contending over the wireless channel using
the FPBA algorithm [l] to capture the channel. The wireless
channel capture model includes Rayleigh fading, shadowing, and
path loss. The performance of the algorithm is evaluated using
simulation models. Results show that the new priority scheme
offers significant improvement to the throughput and the waiting
time of the different priority classes, especially to high priority
class packets
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