Proposed Diversity Scheme Research Articles

Code-Time Diversity for Direct Sequence Spread Spectrum Systems

Time diversity is achieved in direct sequence spread spectrum by receiving different faded delayed copies of the transmitted symbols from different uncorrelated channel paths when the transmission signal bandwidth is greater than the coherence bandwidth of the channel. In this paper, a new time diversity scheme is proposed for spread spectrum systems. It is called code-time diversity. In this new scheme, N spreading codes are used to transmit one data symbol over N successive symbols interval. The diversity order in the proposed scheme equals to the number of the used spreading codes N multiplied by the number of the uncorrelated paths of the channel L. The paper represents the transmitted signal model. Two demodulators structures will be proposed based on the received signal models from Rayleigh flat and frequency selective fading channels. Probability of error in the proposed diversity scheme is also calculated for the same two fading channels. Finally, simulation results are represented and compared with that of maximal ration combiner and multiple-input and multiple-output systems.

Code-time diversity for direct sequence spread spectrum systems.

Time diversity is achieved in direct sequence spread spectrum by receiving different faded delayed copies of the transmitted symbols from different uncorrelated channel paths when the transmission signal bandwidth is greater than the coherence bandwidth of the channel. In this paper, a new time diversity scheme is proposed for spread spectrum systems. It is called code-time diversity. In this new scheme, N spreading codes are used to transmit one data symbol over N successive symbols interval. The diversity order in the proposed scheme equals to the number of the used spreading codes N multiplied by the number of the uncorrelated paths of the channel L. The paper represents the transmitted signal model. Two demodulators structures will be proposed based on the received signal models from Rayleigh flat and frequency selective fading channels. Probability of error in the proposed diversity scheme is also calculated for the same two fading channels. Finally, simulation results are represented and compared with that of maximal ration combiner (MRC) and multiple-input and multiple-output (MIMO) systems.

A New Diversity Combining Scheme Based on Interleaving Method for Time-of-arrival Estimation of Chirp Signal

A new diversity combining scheme is proposed for time-of-arrival (TOA) estimation of chirp signal in dense multipath channel. In the multipath channel, the performance of TOA estimation using conventional correlation matrix-based diversity combining scheme is degraded due to the lack of de-correlation effect. To increase the de-correlation effect, the proposed diversity scheme employs interleaving method based on the property of de-chirped signal. As a result, the proposed scheme increases de-correlation effect and also reduces the noise of TOA estimation. Finally, the diversity achieved from the proposed scheme improves TOA estimation performance. The de-correlation effect is analyzed mathematically. The estimation accuracy of the proposed diversity scheme is superior to that of conventional diversity scheme in multipath channel.

A subcarrier modulation based optical wireless communication system employing transmission diversity

In this paper, we propose an optical wireless communication service for indoor environment. To seamlessly cover the target area and keep the received signal power strength at an acceptable level, we send the signal from multiple diffused optical emitters and achieve possible transmit diversity. With the proposed diversity scheme, the effective coverage range of the proposed system can be significantly enlarged with a guaranteed BER performance. Simulation results show a 13.4 m2 area can be effectively covered by two optical emitters with optical emitter spacing of 3 m and average transmit optical power of 28 dBm.

MVDR‐combining‐aided diversity and spatial multiplexing for MIMO multi‐cellular networks with cochannel interference

ABSTRACTTwo multiple‐input multiple‐output (MIMO) schemes (a diversity scheme and a spatial multiplexing scheme) that employ the minimum variance distortionless response (MVDR) combining are proposed for multi‐cellular networks with cochannel interference. With the receive diversity provided by the MVDR combining, the proposed diversity scheme can be benefited by both the transmit diversity and the receive diversity, also, the proposed spatial multiplexing scheme can be benefited by both the receive diversity and the spatial multiplexing. The proposed MIMO schemes do not require the space‐time coding or the successive interference cancellation, thus they can result in less computational complexity than space‐time block code (STBC) and vertical‐Bell Labs layered space‐time (V‐BLAST). We show that the capacity of the proposed diversity scheme is close to or larger than that of STBC for the noise‐corrupted case and is much larger than that of STBC for the interference‐corrupted case. We also show that the capacity of the proposed spatial multiplexing scheme can be much larger than that of V‐BLAST for the interference‐corrupted case and the noise‐corrupted case, and the proposed spatial multiplexing scheme can achieve good compromise between diversity and spatial multiplexing. Copyright © 2011 John Wiley & Sons, Ltd.

A Simple Multiphase Coding Technique for Transmit Diversity in Continuous Fading Channels

We propose a simple constellation-precoding technique for coherent phase-shift keying (PSK) modulation. The constellation of coded symbols is designed for a multiple-input-multiple-output (MIMO) system in frequency-nonselective Nakagami-m fading channels. Such a signaling mechanism, which is composed of the precoding technique and orthogonal pulse shaping, is shown to provide error performance and bandwidth efficiency comparable with those of the conventional space-time block codes (STBCs). We present a low-complexity coherent receiver, error bounds, and a code-search criterion for the considered system, which can alternatively operate with or without full channel-state information (CSI). Numerical and simulation results are provided to verify the significant performance improvement obtained by the proposed diversity scheme over Nakagami-m fading. The proposed approach is shown to be more robust against the decrease of adjacent fading sample correlation than the conventional STBCs while continuous fading is considered. For certain wireless environment limitations such as full CSI absence and fast fading, the scheme provides an alternative solution to mitigate the fading effects at the cost of low implementation complexities.

Diversity in Radar Sensor Networks: Theoretical Analysis and Application to Target Detection

We study a diversity scheme based on waveform design and space-time adaptive processing to improve the detection performance of radar sensor networks in the presence of certain types of interference. To reduce the interference between radar sensors and maximize the signal-to-interference-plus-noise ratio, we use an orthogonality criterion to design waveforms for radar sensors. Besides, performance of radar sensor networks depends largely on clutter which is extended in both angle and range and is spread in Doppler frequency. By using the space-time adaptive processing, effects of clutter can be suppressed. We also propose a receiver for diversity combining and, as an application example, we investigate the detection performance of radar sensor networks using the proposed diversity scheme. Simulation results for both non-fluctuating targets and fluctuating targets show that the performance of the proposed scheme is superior to that of the single radar with the spatial-temporal diversity only.

リアウィンドウ貼付形高感度ダイバーシチアンテナ

A sensitive antenna attached to the rear window of a car has been designed for diversity reception of digital terrestrial television broadcasting. The proposed antenna efficiently utilizes heat wires located on the rear window and the antenna elements to improve the directive gain in the horizontal direction. The field tests show that the proposed antenna using heat wires gives an antenna gain of 2.5 dB compared to the conventional rear-window half-wavelength dipole antenna. By computer simulation, we also show that the proposed diversity scheme, which is composed of two wire antennas with heat wires, can improve the gain in the front direction.

SIR weighting combining diversity for digital mobile communications

AbstractDiversity reception is a powerful technique to reduce the degradation of transmission quality caused by fading. One of the techniques, postdetection maximal‐ratio combiner (MRC), is not necessarily effective under cochannel interference, because received signal strength used as the weighting factor is not relative to the instantaneous signal‐to‐interference power ratio (SIR). The paper proposes an SIR estimation method using the matched filter and a diversity scheme using the estimated SIR as the weighting factor. The performance is evaluated theoretically and by means of computer simulations. The results show that the proposed SIR estimation method can estimate the accurate instantaneous SIR and that the BER characteristics of the proposed diversity scheme under cochannel interference realize better performances than those of MRC. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 85(7): 53–60, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/ecja.1111

SIR Weighting Combining Diversity Using Matched Filter for Personal Communication Systems

We propose a novel SIR weighting postdetection combining diversity scheme with a new accurate SIR estimation method. The SIR is estimated and used as the weighting factor to compensate severe cochannel interference, one of the most important issues for PCS in terms of frequency utilization. The improvement offered by the proposal depends on SIR estimation accuracy. The SIR is, in this paper, estimated by a matched filter where the auto-correlation between received signal and unique word is calculated. Computer simulations confirm that the SIR of each diversity branch can be estimated easily and accurately by the proposed SIR estimation method. The proposed diversity scheme achieves a performance very close to that of ideal SINR weighting diversity under Rayleigh fading with severe cochannel interference. When average SIR = 10 dB and the number of branches (L)=4, the proposed diversity scheme lowers the required Eb/N0 by 5 dB at BER = 1×10-3 compared to conventional maximal ratio combining diversity. This paper also presents the unique word length required to realize adequate performance, i.e., robustness against high-pitch Rayleigh fading.

Logical and diversity combining in FH/SSMA packet radio networks

We propose the logical and diversity combining in slotted frequency-hopped spread spectrum multiple access (FH/SSMA) packet radio networks. The proposed diversity scheme employs the symbol-by-symbol logical AND operation between the currently received packet and the previously combined packet. Our results show that the proposed low-complexity diversity combining scheme provides a significant performance improvement over existing diversity combining schemes.

Performance of multi-level QAM with post-detection maximal ratio combining space diversity for digital land-mobile radio communications

A new type of post-detection maximal ratio combining for space diversity receivers in digital land-mobile communications is proposed. The combining scheme is designed for multilevel quadrature amplitude modulation (QAM) and employs a pilot-symbol-aided fading estimator. It is realized at baseband using a digital signal processing (DSP) technique to simplify the receiver hardware. Computer simulation and laboratory experiments confirm that the proposed diversity scheme achieves a performance very close to that of ideal maximal ratio combining. >