This paper proposes a nonlinear distortion suppression scheme for optical direct FM Radio-on-Fiber system. This scheme uses the interaction between the nonlinearities of DFM-LD and OFD to suppress a 3rd order intermodulation distortion. We theoretically analyze the carrier to noise-plus-distortion ratio (CNDR) and show a controlling method in the MZI type OFD to realize the proposed suppression scheme.

The statistical behavior of the amplitude probability distribution of intermodulation distortion interference in multichannel optical-cable TV systems was experimentally investigated. In multichannel transmission, the non-linearity of a laser diode (LD) or an electrical amplifier can cause intermodulation distortion (composite-second-order beat; CSO, composite-triple-beat; CTB, etc. ). Even though it has been discussed as laser-clipping distortion, intermodulation distortion is usually distortion from AM-VSB carriers. The statistical analysis and evaluation of the distortion in transmitted channel is in controversial. We evaluated the distortion in 20 frequency-division-multiplexed 16-QAM channels, with each carrier carrying 80 Mbps for an optical cable TV system. We first enumerated the distortion components causing interference in each transmission channel so as to identify the intermodulation products. Then, in selected channels, we precisely measured the power of each kind of distortion and the amplitude distributions of the intermodulation distortion from sinusoidal and digital-modulated carriers on cable TV as a function of optical modulation depth (OMD) of LD. And we clarified how the probability distribution function (PDF) changed as the OMD increased. Also, the BER performance of a 16-QAM signal was measured and compare to the intermodulation behavior of the different distortion sources. We found evidence that the amplitude distribution of intermodulation distortion from digital carriers differs from that of thermal noise. Experimental results showed that the PDF of the intermodulation distortion changed when the ratio of intermodulation distortion among all undesired signals varied with the OMD. The BER performance varied with intermodulation of both analogue and digital carriers even when the carrier to interference noise power ratio (CIR) is the same.

The statistical behavior of the amplitude probability distribution of intermodulation distortion interference in multichannel optical-cable TV systems was experimentally investigated. In multichannel transmission, the non-linearity of a laser diode (LD) or an electrical amplifier can cause intermodulation distortion (composite-second-order beat; CSO, composite-triple-beat; CTB, etc. ). Even though it has been discussed as laser-clipping distortion, intermodulation distortion is usually distortion from AM-VSB carriers. The statistical analysis and evaluation of the distortion in transmitted channel is in controversial. We evaluated the distortion in 20 frequency-division-multiplexed 16-QAM channels, with each carrier carrying 80 Mbps for an optical cable TV system. We first enumerated the distortion components causing interference in each transmission channel so as to identify the intermodulation products. Then, in selected channels, we precisely measured the power of each kind of distortion and the amplitude distributions of the intermodulation distortion from sinusoidal and digital-modulated carriers on cable TV as a function of optical modulation depth (OMD) of LD. And we clarified how the probability distribution function (PDF) changed as the OMD increased. Also, the BER performance of a 16-QAM signal was measured and compare to the intermodulation behavior of the different distortion sources. We found evidence that the amplitude distribution of intermodulation distortion from digital carriers differs from that of thermal noise. Experimental results showed that the PDF of the intermodulation distortion changed when the ratio of intermodulation distortion among all undesired signals varied with the OMD. The BER performance varied with intermodulation of both analogue and digital carriers even when the carrier to interference noise power ratio (CIR) is the same.

The architecture and control procedure for a direct conversion receiver are investigated for a linear modulation scheme. The proposed design techniques maintain receiver linearity despite various types of signal distortion. The techniques include the fast gain control procedure for receiving a control channel for air interface connection, DC offset canceling in both analog and digital stages, and 2nd-order intermodulation distortion canceling in an analog down-conversion stage. Experimental and computer simulation results on PHS (Personal Handy-phone System) parameters, showed that required linear modulation performance was achieved and thus the applicability of the proposed techniques was demonstrated.

This paper describes amplification with improved linearity by employing a linearizing circuit in an input circuit of an internally-matched Ku-band high power amplifier. The linearizing circuit is composed of series L, C, R and an FET with grounded source and drain, and is connected between the input signal line and ground. This linearizing circuit was applied to a Ku-band 10 W output power amplifier utilizing a 25.2 mm gate-width double-doped Heterojunction FET. The power amplifier demonstrated a 8 dB reduction of the third-order intermodulation at about 6 dB output power backoff point from the 2 dB output compression point.

Since an orthogonal multi-carrier signal has large peak power, intermodulation distortion occurs due to the non-linearity of the power amplifier. This distortion severely deteriorates the performance of the multi-carrier system. Especially when carriers are modulated by information bits which produce the same phase shift or the alternative phase shift, the modulated signal has maximum peak power at the input of the amplifier. In order to avoid these phase shifts (code sequences), we propose a code reversal technique which suppresses the maximum peak power of multi-carrier signals for intermodulation compensation. This method utilizes the reversal codes which are added to the original information bits. We also show the effectiveness of the code reversal technique combined with error correction coding and examine the optimum operating point of the amplifier.

This paper describes the design, fabrication, and performance of a GaAs FET linearizer with a large source inductance, focusing mainly on (a) a mechanism of positive gain and negative phase deviations for input power, (b) stability considerations, and (c) a dependence on load impedance. In addition, in an application to the linearized amplifier, it is shown that an improvement can be achieved for adjacent channel leakage power (ACP) and third order intermodulation distortion (IM3) with the use of the linearizer.

Optical Feedering between Base Stations and Control Station is an effective technique for future microcellular mobile communication systems. The use of Laser Diode (LD) in such a system leads to the generation of intermodulation products, which consequently affect a system performance and ultimately restrain the maximum number of users that the system can serve. The problem becomes further intensified in case of CDMA system which is a candidate for future cellular mobile and personal communication systems. In this paper LD's Nonlinearity compensation technique for Direct Sequence spread spectrum CDMA signals in optical communication system is presented. This technique involves the implementation of a nonlinear block herein after called Post Nonlinearity Recovery Block (PNRB). This block is designed to exhibit the characteristics inverse to those of LD. The block is designed theoretically by deriving the complete expressions for Transfer functions. Some useful results of theoretical investigation of a proposed scheme have been presented, which form the basis for the experimental test system. The work is novel because, (i) Compensation analysis has been carried out for DS-CDMA signals for the first time, and (ii) Compensation has been proposed on the control station instead of base station, which is different from the conventional techniques and offers several additional advantages. Performance of the system with and without PNRB is evaluated by Intermodulation Distortion (IMD) and SNR Analysis. The results show that LDs' nonlinearity distortion level can be compensated to a remarkable extent.

This paper describes the performance of a predistorter implementation to a superluminescent diode (SLD) in fiber-optic wireless systems under the optical reflection. SLD intensity noise and 3rd-order intermodulation distortion (IM3) are experimentally compared with those of DFB-and FP-LD. It is observed that the IM3 of SLD has ideal 3rd characteristics and output noise remains unchanged against the number of optical connectors. It is also found that the predistorter reduces IM3 by 8 dB. Receiver sensitivity of the system is discussed from the view point of overall design. the BER performance of an SLD with predistorter using a π/4-QPSK signal as a subcarrier is also described theoretically and experimentally.

This paper presents a potential FM double modulation technique for subcarrier optical transmission in order to improve the input dynamic range. The proposed theory of FM double modulation is presented. The BER performance and input dynamic range are shown theoretically and experimentally compared with conventional direct intensity modulation. It was found that the dynamic range could be experimentally improved by 20dB compared with the conventional method by using FM double modulation. The proposed technique achieved an input dynamic range of 60 dB even when using a commercial Fabri-Perot LD.

Atmospheric optical communication (AOC) system using subcarrier PSK modulation is proposed and its superiority to OOK modulation in the presence of scintillation is discussed theoretically. An experimental AOC setup with a subcarrier modulated by 155.52(Mb/s) DPSK at light wave-length λ=0.83(µm) over an 1.8(km) outdoor path is employed to show the performance. Theoretical and experimental results are compared under scintillation in clear weather and a good agreement is observed. Finally, AOC systems using subcarrier M-ary PSK and multiple subcarriers are proposed and discussed.

This paper describes a fiber-optic microcell radio system with a spectral delivery switch to meet traffic demands. Optical link performance is discussed from the view points of link loss and noise figure aimed at system design. The theoretical carrier-to-noise ratio (CNR) performance is shown as a function of the input electrical power of the laser and the received optical power. Improvement of dynamic range defined by both CNR and intermodulation distortion is proposed by using the frequency modulation (FM) technique. The experimental results using the proposed technique indicate that the performance is much better than that of conventional methods. Moreover, economical diversity planning delivery methods over fibers are presented. This strategy will provide more cost effective and flexible networks.