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The high data rates enabled by free-space optical communication links and additional factors, such as the unregulated spectrum, make them an attractive solution in future geostationary feeder link applications with capacities beyond one Terabit per second. However, optical links through the atmosphere are heavily affected by atmospheric turbulence, leading to significant scintillation. Transmitter diversity is an effective way to improve the signal quality of optical links. Transmitter diversity with Phase-Division in Bit-Time is a novel scheme for mitgating interference and thus enabling the use of equal wavelengths for multiple transmitters. This paper will evalute the Phase-Division in Bit-Time transmitter diversity scheme and present measurement results from a lab testbed.

For some free-space laser communications (lasercom) links impacted by atmospheric-induced scintillation, the principle of reciprocity provides knowledge of a remote terminal's received intensity fluctuations based on measurements of the local terminal's received intensity fluctuations. We evaluate a reciprocity-enhanced technique using optical switching between multiple spatially-diverse transmit apertures to mitigate against atmospheric-induced scintillation. Experimental bit-error rate measurements are presented to quantify the expected performance of this approach in comparison to standard static diversity approaches. We investigate system constraints of this reciprocity-enhanced transmitter diversity approach, and identify candidate optical switches and digital logic for implementation.

For realizing high-speed implant communications, ultra-wideband (UWB) transmission is one of the promising candidates. In this paper, an UWB transmitter diversity antenna was presented, and then the fundamental performances were numerically and experimentally evaluated. In addition, this paper discussed the path loss performance in an implant communication link a living animal. Consequently, the communication performance improvement by the implant side polarization diversity with the antenna developed in this study was evaluated and discussed. Our evaluation results demonstrated that the developed antenna can improve the communication performance by 7 dB to establish an outage rate of 0.01.

In this research work, we have presented an iterative joint source channel decoding- (IJSCD-) based wireless video communication system. The anticipated transmission system is using the sphere packing (SP) modulation assisted differential space-time spreading (DSTS) multiple input-multiple output (MIMO) scheme. SP modulation-aided DSTS transmission mechanism results in achieving high diversity gain by keeping the maximum possible Euclidean distance between the modulated symbols. Furthermore, the proposed DSTS scheme results in a low-complexity MIMO scheme, due to nonemployment of any channel estimation mechanism. Various combinations of source bit coding- (SBC-) aided IJSCD error protection scheme has been used, while considering their identical overall bit rate budget. Artificial redundancy is incorporated in the source-coded stream for the proposed SBC scheme. The motive of adding artificial redundancy is to increase the iterative decoding performance. The performance of diverse SBC schemes is investigated for identical overall code rate. SBC schemes are employed with different combinations of inner recursive systematic convolutional (RSC) codes and outer SBC codes. Furthermore, the convergence behaviour of the employed error protection schemes is investigated using extrinsic information transfer (EXIT) charts. The results of experiments show that our proposed R a t e − 2 / 3 SBC-assisted error protection scheme with high redundancy incorporation and convergence capability gives better performance. The proposed R a t e − 2 / 3 SBC gives about 1.5 dB E b / N 0 gain at the PSNR degradation point of 1 dB as compared to R a t e − 6 / 7 SBC-assisted error protection scheme, while sustaining the overall bit rate budget. Furthermore, it is also concluded that the proposed R a t e − 2 / 3 SBC-assisted scheme results in E b / N 0 gain of 24 dB at the PSNR degradation point of 1 dB with reference to R a t e − 1 SBC benchmarker scheme.

Transmitter diversity is an effective fading mitigation scheme in an optical geostationary satellite feeder uplink. We quantify the performance of the scheme over a slow fading channel where the atmospheric turbulence causes scintillation and wandering of the optical beam resulting in deep fades at the satellite receiver. For given atmospheric conditions and residual beam pointing jitter, we optimize the transmit power of each beam to obtain the minimum overall power scintillation index and achieve a bit error rate gain of 0.46dB considering intensity modulation and direct detection.

Current satellite communication systems based on RF technology are often limited by the available spectrum. Free-Space Optical Communication Links are a promising solution to overcome this bottleneck. The available spectrum enables Terabit-per-Second data rates, and the point-to-point nature of FSO links makes spectrum regulation unnecessary. Therefore, the use of optical links is investigated in a number of scenarios, as e.g. for GEO feeder links serving multimedia applications. Transmitter Diversity might be a solution to overcome atmospheric impacts on the ground-to-satellite transmission in an optical GEO feeder link application. Transmitter Diversity can e.g. be implemented by using various spectral channels. Despite the virtually unlimited bandwidth available in atmospheric transmission windows, practical implementations of an optical GEO feeder link need to use available hardware, namely fiber amplifiers in the C- and L-band – Therefore, a more efficient use of the available spectrum will enable in a higher system throughput. In this paper, we present a bandwidth efficient transmitter diversity scheme, called "phase-division in bit-time". It is based on Intensity Modulation with Direction Detection, and makes use of phase modulation for the transmitters to mitigate the impact of atmospheric phase distortions on the quality of the received signal.

Providing high data rates is one of the drivers in visible light communication (VLC) systems. This paper introduces a VLC system that employs angle diversity transmitters with beam steering to provide high data rates. In this work, red, yellow, green, and blue (RYGB) laser diodes (LD) are used as transmitters to obtain a high modulation bandwidth. Two types of RYGB LDs units are used in this paper: angle diversity transmitters (ADT) RYGB LDs light unit (for illumination and communication) and RYGB LDs light unit (for illumination). In addition, a four branch angle diversity receiver (ADR) is used where we study the delay spread and SNR. The proposed system was compared to the normal VLC system. A data rate up to 22.8 Gb/s was achieved using simple on-off-keying (OOK) modulation.

Optical geostationary orbit (GEO) satellites are one of the means to provide high speed internet and broadband services to even remote areas on the globe. However, the optical beam, as it propagates through the atmosphere, is affected by the atmospheric index of refraction turbulence and pointing errors due to beam wander and mechanical vibrations on the platform which result in fading, hence loss of signal. We present transmit diversity as a fading mitigation technique and use wavelength division to minimize cross interference between the transmitted signals. Optical single sideband (OSSB) scheme is used to increase spectral efficiency (SE) of the system. We demonstrate a scheme where an OSSB signal is produced using commercially available optical filter with tunable bandwidth and center frequency. For a 32Gbps data signal modulated using amplitude shift keying (ASK), we measure the required minimum 6dB and 20dB bandwidths of the optical filter to be 12GHz and 24GHz, respectively. Also, the offset of the filter from the carrier is found to be -11GHz and +10GHz to produce an error free lower and upper OSSB signal, respectively. The SE of the OSSB signal is found to be 1.34 bit/s/Hz. Moreover the stability of the optical filters and carrier ensure reliable signal generation making the OSSB a potential candidate to be used in future free space optical links.

Optical links to geostationary (GEO) satellites suffer from atmospherically-induced beam wander which leads to pointing errors at the satellite causing deep fades. In this paper, we show the benefit of transmitter diversity in reducing the fades caused by beam wander. We derive an analytical expression for the reduction of overall scintillation index for a given number of transmitted beams with Gaussian profile in a multiple-input single-output (MISO) system considering solely the effect of beam wander. The transmitted power, beam divergence angle and pointing jitter are kept as free parameters as in the real situation. Moreover, the optimized ratio of transmitted powers between multiple beams is obtained through simulations for a two-fold transmitter diversity to obtain minimum overall power scintillation index (PSI).

The performance of constellation rotation scheme in the presence of channel estimation error for space-time coding is investigated. The optimal combining equations with constellation rotation are presented. The simulation results show that the constellation rotation provides the better BER performance in a low variance of channel estimation error for varying signal-to-noise ratio (SNR).

Optical links between ground stations and geostationary orbit (GEO) satellites suffer from the atmospherically induced phase piston and intensity fluctuations. This aggravates stable signal detection in the uplink scenario. In this work transmitter diversity is studied as a fading mitigation technique in GEO satellite feeder uplinks. A single sideband scheme is used as a spectrally efficient frequency division technique compatible with intensity modulation and direct detection. A spectral efficiency of 0.56 bit/s/Hz with twofold diversity gaining 2.3 dB at BER = 10-3 was obtained by simulation.

The performances of a PCTH-based communication UWB system with diversiform modulation schemes are compared on the classic AWGN channel propagation and the realistic IEEE-UWB channel model. By employing different versions of modulation at the transmitters, the performances of an optimal receiver and a Rake receiver with various combining schemes are studied in this paper. The numerical results for several compared cases illustrate the tradeoff between transmitter diversity and receiver complexity. It is shown that the actual performance of the PAM-PCTH scheme can be better in both kinds of channel propagation. We also find that the PCTH-based UWB system with the Rake receiver has better performance than the conventional proposal for overcoming the multipath propagation effects in the UWB indoor environment.

To improve the performance of the time domain synchronous -orthogonal frequency division multiplexing (TDS-OFDM) system, an efficient space-time-frequency coding scheme is proposed. The block coding is employed in both time and frequency dimensions simultaneously and proved to be a quasi-orthogonal design. The performance improvement of TDS-OFDM system with this method is theoretically analyzed and computer simulated, showing its superior performance in the presence of both time and frequency selective environments. Comparing to the pure space-time or space-frequency coding scheme with straightforward implementations, the proposed implementation scheme reduces the computational load by about 70% in TDS-OFDM system.

Studies have shown that transmit and receive diversity employing a combination of multiple transmit-receive antennas (given ideal channel state information (CSI) and independent fading between antenna pairs) will potentially yield maximum achievable system capacity. In this paper, the concept of a layered super-orthogonal turbo transmit diversity (SOTTD) for downlink direct-sequence code-division multiple-access (CDMA) systems is explored. This open-loop transmit diversity technique improves the downlink performance by using a small number of antenna elements at the base station and a single antenna at the handset. In the proposed technique, low-rate super-orthogonal code-spread CDMA is married with code-division transmit diversity (CDTD). At the mobile receiver, space-time (ST) RAKE CDTD processing is combined with iterative turbo code-spread decoding to yield large ST gains. The performance of the SOTTD system is compared with single- and multiantenna turbo-coded (TC) CDTD systems evaluated over a frequency-selective Rayleigh fading channel. The evaluation is done both by means of analysis and computer simulations. The performance results illustrate the superior performance of SOTTD compared to TC CDTD systems over practically the complete useful capacity range of CDMA. It is shown that the performance degradation characteristic of TC CDTD at low system loads (due to the inherent TC error floor) is alleviated by the SOTTD system.

Space-time coded orthogonal frequency division multiplexing (OFDM) transmitter diversity techniques have been shown to provide an efficient means of achieving near optimal diversity gain in frequency-selective fading channels. For these systems, knowledge of the channel parameters is required at the receivers for diversity combining and decoding. In this paper, we propose a low complexity, bandwidth efficient, pilot-symbol-assisted (PSA) channel estimator for multiple transmitter OFDM systems. The pilot symbols are constructed to be nonoverlapping in frequency to allow simultaneous sounding of the multiple channels. The time-varying channel responses are tracked by interpolating a set of estimates obtained through periodically transmitted pilot symbols. Simulations are used to verify the effectiveness of the proposed estimator and to examine its limitations. It is also shown that the PSA channel estimator has a lower computational complexity and better performance than a previously proposed decision-directed minimum mean square error MMSE channel estimator for OFDM transmitter diversity systems.

The aim of paper is to design SCFDMA system using SFBC and receiver diversity which provides satisfactory performance over fast fading channel environment. The performance evaluation will be checked through MATLAB R2009b simulator. There are comparisons of performance among 1x1 SCFDMA system, 2x1 SCFDMA system using SFBC, 1x2 SCFDMA system using receiver diversity and 2x2 SCFDMA system using SFBC and receiver diversity. We describe design of SCFDMA system using transmitter diversity technique and receiver diversity technique. We have compared the performance of these systems with the conventional SCFDMA system. The main focus is on design of SCFDMA system using SFBC and receiver diversity which enables desired system to combat detrimental effects of fast fading.

To improve the transmission performance of terrestrial digital multimedia/television broadcasting (DMB-T) system, the performance of an efficient space-frequency transmitter diversity scheme is introduced in this article. This scheme maintains the original transmitter branch and the network structure is simple to upgrade. DMB-T system is an important candidate for Chinese digital television terrestrial broadcasting (DTTB) standard. The system was simulated over both slow and fast fading DTTB channels. Simulation results show that the introduced transmitter diversity scheme can efficiently improve the system performance in fading environments

We investigate the performance of a hybrid direct-sequence/frequency-hopping (DS/FH) scheme for spread spectrum systems over Rayleigh fading channels. In this hybrid scheme, the users are divided into a number of groups, where each group of users use one of a cyclic FH sequences designed to eliminate signal collisions among different groups. To improve the user-capacity, we assign to each user within a group a different DS sequence. Given this arrangement, our results show significant performance improvements relative to conventional DS/FH systems that employ randomly generated hopping sequences. The proposed frequency-hopping scheme is then investigated in a space-time convolutionally-coded system with two transmit and one receive antennas

A Wiener LMS channel estimation and tracking algorithm for OFDM systems with transmitter diversity was proposed. The algorithm used Wiener prediction technology to improve the ability of tracking channel. The simulation results show that the algorithm achieved reliable channel estimation. The performance is improved greatly compared with conventional algorithm LMS algorithm and decision directed algorithm proposed by LiYe and this improvement is obvious under fast varying channel.

Orthogonal Frequency Division Multiplexing (OFDM) technique has been applied broadly in the transmission of high speed data in wireless communication. Transmitter diversity can be used with OFDM systems for performance improvement in a fading environment. In this paper, we investigate transmitter diversity for OFDM systems in high speed wireless data applications, and propose a low complexity channel estimation approach for transmitter diversity OFDM systems.

Space-time block-coded orthogonal frequency division multiplexing (OFDM) transmitter diversity techniques have been shown to be efficient means of achieving near-optimal diversity gain in frequency-selective fading channels. However, these known techniques all require a cyclic prefix to be added to the transmitted symbols, resulting in bandwidth expansion. In this paper, iterative space-time and space-frequency block-coded OFDM transmitter diversity techniques are proposed that exploit spatial diversity to improve spectral efficiency by eliminating the need for a cyclic prefix.

Bu çalışmada, frekans seçici hızlı sönümlemeli kanallarda telsiz iletişim için bir uzay-zaman-frekans çeşitlemesi yöntemi önerilmiştir. Önerilen yöntem, OFDM tekniğini kullanarak frekans seçici kanalı uygun hale getirdikten sonra sırasıyla dik uzay-frekans ve dik uzay-zaman blok kodlama uygulayarak uzay-zaman-frekans çeşitlemesi sağlamaktadır. Elde edilen sistemin başarımını arttırmak üzere sisteme uygun bu kafes kodlama tekniği araştırılmış ve uygun kafes yapısının oluşturulması için yeni kriterler ortaya çıkarılmıştır. Oluşan sistemin başarımını, bilgisayar benzetimleriyle incelenmiş ve var olan yöntemlerle karşılaştırılmıştır. This work is concerned with a transmitter diversity technique for wireless communications over frequency selective fading channels. The proposed technique utilizes orthogonal frequency division multiplexing (OFDM) to transform a frequency selective fading channel into multiple flat fading subchannels on which space-frequency processing is first applied and then additional space-time coding is applied in order to increase the diversity. In order to improve the performance of the system, a convenient trellis coding scheme is investigated and design criteria are established. Performance of the proposed space-time-frequency OFDM (STF-OFDM) transmitter diversity technique has been examined by computer simulations and compared with existing schemes. IEEE TUBITAK Istanbul Teknik Universitesi Aselsan Profilo Telr@ TURCom Sgi Datacore Divit Publisher's Version WOS:000225861200017