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We present a study of DTN transport layer service, evaluating its performance during a file transmission from a Mars relay satellite towards Earth. The experiments are being held in a DTN Testbed designed and implemented for emulating and evaluating deep-space communications. Bundle Protocol truncates application data into bundles of different size and Licklider Transmission Protocol is used as the...
This paper considers optimizing the utilization of radio resources in a heterogeneous networks consisting of a WLAN and a CDMA network. We propose a joint admission control mechanism for multimedia traffic that exploits vertical handoff as an effective tool to enhance radio resource management while guaranteeing handoff user's QoS requirements. The network resources utilized by the vertical handoff...
Turbo codes has excellent error correcting performance in low SNR condition. The design of interleaver in Turbo codes directly affects the Turbo decoding performance. Based on analysing the design rules and types of interleaver, a random interleaver is designed by taking advantage of the ergodic property of m sequence. The simulation results show that applying this random interleaver can remarkably...
In pilot-aided OFDM systems, the minimum mean-square-error (MMSE) interpolator provides the optimum performance based on the channel statistics. And symbol timing offset (STO) introduces a linear phase rotation to data modulated on individual subcarriers. A MMSE channel estimator designed only using the wireless channel statistics performs only sub-optimally when subcarrier phase rotations due to...
The frequency selective channel estimation problem in orthogonal frequency division multiplexing (OFDM) systems is investigated using compressed sensing (CS). Based on minimizing mutual coherence of the measurement matrix in CS theory, a criterion of optimizing the pilot pattern for the CS-based channel estimation is proposed. Simulation results show that using the pilot pattern designed according...
High-speed parallel transmission is significant for the study of high-speed transmission. The high-speed serial transmission has high performance whereas costs large amount of hardware and calls for complex implementation. Reduction of data valid window, data and clock skew, and clock jitter are three crucial negative factors for high-speed parallel transmission. The paper analyses these factors,...
In this paper, ultra-wideband impulse radio(UWB-IR)system inside a vehicle is considered to construct internal vehicle wireless sensor network with better performance. In a vehicle, a direct path is likely to be blocked by the seat and passengers. The channel model characteristic in a vehicle is different from other wireless systems. When using UWB systems, other wireless systems in the same frequency...
To achieve diversity with a single antenna, a fractional sampling (FS) scheme in OFDM has been investigated. In addition, to obtain more diversity gain through FS, a sampling point selection (SPS) scheme has been proposed. However, it requires a large number of multiplication operations for the SPS. This leads to large power consumption and costs for additional circuits. In this paper, a low-complexity...
This paper discusses a multi-user access technique for Ultra-wideband Impulse Radio (UWB-IR) system in energy detection receiver. The UWB-IR system is modulated by On-Off shift Keying (OOK). As multi-users access scheme, the Code Division Multiple Access (CDMA) using the Optical Orthogonal Code (OOC) sequence is adopted. The integral interval and the sample energy threshold value are optimized to...
This paper examines radio wave propagation in underground and subway environments from the perspective of providing digital radio with multimedia and video enhanced services (DAB/DMB) as a continuity of the same services offered above ground. To this end, a preliminary simulation framework of a DAB/DMB transmission system inside a rectangular subway tunnel is proposed. First, the received power and...
This paper compares the performance of convolutional codes to that of LDPC block codes with identical decoding latencies. The decoding algorithms considered are the Viterbi algorithm and stack sequential decoding for convolutional codes and iterative message passing for LDPC codes. It is shown that, at very low latencies, convolutional codes with Viterbi decoding offer the best performance, whereas...
In order to reduce the system computation complexity and delay, we propose a scheme to decrease the iterative time of the carrier synchronization for low-density parity-check (LDPC) codes. The system will stop iteration if the log-likelihood ratio (LLR) message at the output of decoder satisfies the limitary conditions. Simulation results show that the proposed scheme is efficient and there is little...
Multi-input multi-output (MIMO) is an attractive solution to high data rate underwater acoustic communications (UAC) with limited bandwidth. However, the long delay spread characteristic of UAC channels makes the equalization challenging for those MIMO schemes. Although maximum likelihood sequence estimation (MLSE) is known to be optimum and is intensively used in many terrestrial wireless applications,...
The main targets for the next generation of mobile communication systems, with LTE as a main candidate, are increased data rates and improved spectrum efficiency. The transmission scheme for the LTE downlink is OFDM which enables the design of low complexity and high performance receivers, if the channel is time-invariant. However in high-mobility scenarios, where the channel is time-variant, the...
In asynchronous communication system, such as MANET or uplink of CDMA system, MAI (Multiple Access Interference) is a problem that cannot be ignored. To suppress the effect of MAI, this paper introduces a new mix-carrier method in asynchronous CDMA system. The proposed method uses both cosine and Chirp as carriers, by using frequency domain filter and Fractional Fourier domain filter at the receiver...
We show a direct comparison between silicon reconfigurable delay lines based on coupled resonator optical waveguides and photonic crystal waveguides. The structures are used to selectively delay the two orthogonally polarized channels of a RZ-PolDM-DQPSK format at 100 Gbit/s.
We propose a new concept for a comb filter based UWB receiver, where the delay of the analog delay element is shortened. The comb filter receiver can cope with the problems of low SNR, high interference levels, strong narrowband interference and multipath propagation in an excellent way. The main challenge for realization with real hardware is the analog delay element. With our new concept proposal,...
Visible light communication networks are currently constrained in range by the divergent source characteristics of the light emmiting diode (LED) and in achievable rate by the modulation bandwidth of the LED transmitter; however, as device advancements improve the limitation on rate becomes inter-symbol interference (ISI). The key contributor to ISI is the non-uniform time of arrival (TOA) of all...
Frequency domain equalization (FDE) has shown its ability to improve the performance of single carrier system. For DS-CDMA system, MMSE based FDE can obtain frequency diversity gain through undergoing more fading paths. Meanwhile, delay time-domain windowing technique has been introduced to suppress the noise power which perturbs the channel estimation. In this paper, we analysis the impact of delay...
Turbo codes are widely investigated due to its excellent error control ability since it was proposed and applied in the late 20 th century. But decoding algorithms for Turbo codes were complex, so there is large time delay in iteration processing course in order to obtain the excellent error control properties of turbo codes. This paper proposes an improved adaptive decoding algorithm through deeply...
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