Bit error rates for ultrafast APD based optical receivers: exact and large deviation based asymptotic approaches

This paper presents analytical results of the effects of jitter and inter symbol interference (ISI) on a millimeter-wave impulse radio (IR) transceiver, compared with performance of the developed 10-Gb/s W-band IR transmitter prototype. The compact and cost-effective IR transmitter consists of a pulse generator (PG) that creates a short pulse with a duration of <10 ps, a band-pass filter (BPF) that shapes the short pulse to the desired millimeter-wave pulse (wavelet), and a power amplifier (PA) which is deployed as an option. Jitters of the PG and ISI from the BPF are a great issue to make the IR transceiver robust and to obtain excellent performance. One analysis verified that, thanks to a novel retiming architecture, the random jitter and the data dependent jitter from the PG give only a small penalty of <0.5-dB increase in signal to noise ratio (SNR) for achieving a bit error rate (BER) of <10−12. The alternative analysis on the effect of ISI from the BPF indicated that using a Gaussian BPF enables transmission with a BER of <10−12 up to a data rate of 1.4 times as large as a bandwidth of the BPF, whereas the ISI analysis suggested that mismatching of the skirt characteristics of the developed BPF to those of a Gaussian BPF causes tail lobes following the wavelet, resulting in an on/off ratio of <15 dB and hence an SNR penalty of <6 dB.

The effect of dead space on the mean gain, the excess noise factor, and the avalanche breakdown voltage for Si and GaAs avalanche photodiodes (APDs) with nonuniform carrier ionization coefficients are examined. The dead space, which is a function of the electric field and position within the multiplication region of the APD, is the minimum distance that a newly generated carrier must travel in order to acquire sufficient energy to become capable of causing impact ionization. Recurrence relations in the form of coupled linear integral equations are derived to characterize the underlying avalanche multiplication process. Numerical solutions to the integral equations are obtained and the mean gain and the excess noise factor are computed. >

In this paper we analyze the performance of multiple-input multiple-output (MIMO) multiplexing for BPSK and square M-QAM under Rayleigh fading. We derive exact closed-form expressions of the bit error rate (BER) assuming channel prediction error. Our analysis indicates that prediction error degrades MIMO multiplexing BER much more than MIMO beamforming BER. This is not surprising since prediction error in MIMO multiplexing leads to eigenchannel interference, which has a much greater impact on BER than the imperfect beamforming coefficients that result from such errors. Our numerical results also reveal that non-uniform rate allocation between ordered eigenchannels dramatically improves the BER.

Current studies on modulation and detection schemes in molecular communication mainly focus on the scenarios with static transmitters and receivers. However, mobile molecular communication is needed in many envisioned applications, such as target tracking and drug delivery. Until now, investigations about mobile molecular communication have been limited. In this paper, a static transmitter and a mobile bacterium-based receiver performing random walk are considered. In this mobile scenario, the channel impulse response changes due to the dynamic change of the distance between the transmitter and the receiver. Detection schemes based on fixed distance fail in signal detection in such a scenario. Furthermore, the intersymbol interference (ISI) effect becomes more complex due to the dynamic character of the signal which makes the estimation and mitigation of the ISI even more difficult. In this paper, an adaptive ISI mitigation method and two adaptive detection schemes are proposed for this mobile scenario. In the proposed scheme, adaptive ISI mitigation, estimation of dynamic distance, and the corresponding impulse response reconstruction are performed in each symbol interval. Based on the dynamic channel impulse response in each interval, two adaptive detection schemes, concentration-based adaptive threshold detection and peak-time-based adaptive detection, are proposed for signal detection. Simulations demonstrate that the ISI effect is significantly reduced and the adaptive detection schemes are reliable and robust for mobile molecular communication.

Due to the stochastic nature of the impact-ionization process, the buildup time of an avalanche photodiode (APD) is also stochastic and can degrade its performance. In particular, when an APD is operated in an optical receiver, the APD's finite and stochastic buildup time gives rise to intersymbol interference (ISI) and limits the bandwidth of the communication system [1]. While the buildup time of an APD is dependent on the material (e.g., on k, the hole-to-electron ionization coefficient ratio) it also has a dependence on the applied electric field and its profile in time and space [2] as it governs the cascade of impact ionizations. Several approaches have been explored to model the buildup time in order to increase the gain-bandwidth product (GBP) of APDs, including GBPs for heterojunction multiplication regions [2,3]. However, all existing models focused, mainly, on optimizing the APD's structure. In particular, the effect of modulating the electric field on the impact ionization characteristics of APDs remains unexplored, and to the best of our knowledge, no analytical model for avalanche multiplication exists for APDs that are driven by a time-varying bias voltages. The modulation of the applied electric field to control the impact ionization process could be beneficial in communication systems since it opens up the possibility of increasing the GBP in a simple and efficient way. The optimization problem becomes that of finding the optimal electric-field profile, for a fixed mean gain, that maximizes the GBP. In this paper we outline the potential benefits of modulating the applied electric field on the performance of APDs. Our approach enables the calculation of the impulse response, gain and and excess noise factor, breakdown probability, as well as pulse duration time all under conditions of a dynamic field in the multiplication region.

By dividing the available spectrum into multiple bands, multi-band ultra-wideband (UWB) systems possess many advantages, such as the flexibility to eliminate possible interference and coexistence problems with available wireless standards. UWB channels have large delay spread, causing inter- symbol interference (ISI) in high rate systems. The RAKE receiver is often used to capture multipath energy, but it is incapable of ISI compensation, causing severe bit error rate (BER) degradation in practical UWB channels. This paper proposes an over-sampling multi-channel equalizer per sub-band for multi-band UWB. The performance of the proposed receiver is compared with the RAKE receiver through analytical and simulation studies. The proposed equalizer has been shown to be able to handle ISI under any channel conditions or data rate presented, with an acceptable BER. In addition, the rich multipath diversity of the UWB channels is harnessed by the over-sampling scheme, for output SNR improvement. one. Therefore, equalization receiver based on adaptive algorithms seems to be an effective way to recover the transmitted data. With this consideration, we propose an over-sampling multi-channel equalizer per sub-band for a multi-band UWB system, which provides more effective inter-symbol interference (ISI) suppression compared with the conventional RAKE receiver when operating in channels with large delay spread. Through detailed theoretical analysis and extensive simulations, we are able to show that the proposed 4-arm equalizer scheme is superior to a 4-arm conventional RAKE receiver in the presence of ISI at all signal-to-noise ratios (SNRs). Based on the method presented in (4), the simulated performance is shown to conform to analytical predictions. The RAKE receiver is incapable of ISI compensation, and a moderate level of ISI is shown to cause severe bit error rate (BER) degradation. The proposed over-sampling equalizer, on the other hand, is able to handle ISI under any channel conditions or data rate, with an acceptable BER. Over- sampling is shown to be able to achieve diversity gain, and improves the output SNR.

Visible light communication (VLC) enables high speed wireless communication along with fulfilling the illumination requirement in the indoor environment. In this paper, we investigate the performance of a VLC system under multiple reflection condition. We minimize the effect of intersymbol interference (ISI) by using orthogonal frequency division multiplexing (OFDM). Particularly the use of guard interval (GI) in OFDM is utilized to mitigate intersymbol interference. We performed simulation using MATLAB to demonstrate the performance of our proposed VLC system. Simulation results show that the use of guard interval significantly reduces the ISI and hence improves bit error rate (BER) performance.

This paper describes a method of obtaining the temporal and frequency response of avalanche photodiodes (APD) by performing simple noise measurements. From the measured noise spectrum and by using the Hilbert transformation technique, the complex transfer function of the detector is determined. response can then easily be calculated by means of fast Fourier transforming. The method has been applied on a high speed APD, with a bandwidth of ~2 GHz, and on a relatively slow APD, with a bandwidth of 0.2 GHz, to calculate the pulse response from a short optical pulse. The calculated pulse width for the fast APD was 215 psec, and the corresponding measured width was 210 psec, while for the slow APD the calculated and the measured widths both were 3.1 nsec. Also the shapes of the pulse responses showed excellent agreement. The method depends on the essentially identical frequency response of an APD and associated circuits for noise due to steady-state illumination and for a signal.

Free Space Optical (FSO) communication is an emerging technology to provide high bandwidth, secure and high quality communication. In this work we have determined the capacity of the Free Space Optical communication system with Multiple Input Multiple Output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) technique under weak atmospheric turbulence conditions. To model the weak turbulence condition of the atmosphere lognormal channel model is used throughout the work. The capacity of MIMO-OFDM FSO is evaluated in the presence of Inter Symbol Interference (ISI) and is compared with MIMO FSO with ISI. The capacity of MIMO-OFDM FSO system increases in comparison to MIMO in the presence of ISI. It is found that the effect of ISI is mitigated by using OFDM and the capacity is enhanced. Since MIMO uses spatial divervity to mitigate the fading caused by turbulence hence the capacity of both MIMO-OFDM FSO and MIMO FSO also increases as the number of receiving antennas is increased.

This paper presents a new design technique of high-speed interconnects with controlled intersymbol interference (ISI) to create efficient signaling over a band-limited channel. Performance of high-speed electrical links is limited by conductor loss, dielectric dispersion, and reflections in the board, package, and connector. These nonidealities result in significant ISI. In current systems, the effect of ISI is either mitigated through complex equalization, signal conditioning, and coding techniques, or through costly impedance control and manufacturing processes. In the proposed approach, instead of eliminating ISI, we shape the response of the channel into a set of channel characteristics with controlled ISI using simple passive structures in the board and the package. The resulting controlled ISI is exploited at the transmitter and receiver to simplify the architecture of the system and to achieve high data rates. The techniques to design interconnects with controlled ISI are reasonably simple to implement in conventional interconnect technologies. Simulation examples are given to demonstrate the validity and advantages of the design technique using duobinary and analog multitone (AMT) signaling methods.

In this paper, the influences of thermal and spectral variations on various structures of avalanche photodiodes (APDs) have been deeply investigated. The characteristics and performance of Silicon (Si), Gallium Arsenide (GaAs) and Indium Gallium Arsenide (InGaAs) avalanche photodiodes have been evaluated under effects of different temperature degrees. The impacts of different temperature levels on the band gap energy, detector responsivity, noise equivalent power (NEP), cut-off wavelength, dark current and the photocurrent are studied and analyzed in details. The signal to noise ratio (SNR) and Bit Error Rate (BER) of these APDs are also computed and measured under the influences of different temperature levels and spectral variations. The aim of this paper is to determine the most efficient avalanche photodiode achieving the best performance according to the maximum SNR and minimum BER at high temperature environments. The analysis of the proposed model is performed by MATLAB. It was found that the experimental measured results endorse the analytical computed results. Further, it was observed that the APD (InGaAs) provides performance better than other APD structures in terms of larger SNR and less BER at higher temperature levels. Also, the temperature has a slight effect on the performance of APD (GaAs). So, it is seemed to be stable more than other APD structures and recommended to be used in warm environments and for high temperature applications.

Discrete multitone modulation allows for a simple receiver structure if the impulse response of the communication channel is shorter than the cyclic prefix. In ADSL, a time-domain equalizer (TEQ) is used to fulfil this requirement. Without a TEQ, unwanted intercarrier interference (ICI) and intersymbol interference (ISI) occur. In this paper, quadratic forms are developed to calculate the contributions of ICI and ISI to the desired signal. Based on these expressions, a new method for calculating the TEQ coefficients, which minimizes the effects of ICI, ISI, and additive noise, is derived. Simulations in the context of ADSL compare the performance of this new algorithm with one that is state of the art.

Intersymbol Interference (ISI) is one of the major bottlenecks in Molecular Communication via Diffusion (MCvD) systems resulting in degraded system performance. This paper first introduces two new families of linear channel codes to minimize the effect of ISI: linear Zero Pad Zero Start (ZPZS) and linear Zero Pad (ZP) codes, ensuring that every codeword is devoid of consecutive bit-1s. Subsequently, the ZPZS linear and ZP linear codes are combined to form a binary ZP code, aiming for a higher code rate compared to the linear ZP codes, which can be decoded with a simple Majority Location Rule (MLR) algorithm. Additionally, a linear Leading One Zero Pad (LOZP) code is proposed, which relaxes the zero padding constraints considering the placement of bit-1s in the codeword as an important metric to have an improved code rate than the ZP code. Finally, a closed-form expression is deduced to compute the expected ISI for the proposed codes and to demonstrate that the expected ISI is a function of the average bit-1 density of the codewords in a code. To compare the ISI and BER performance with average bit-1 density of the proposed codes, two types of MCvD channel are considered: (i) channel without refresh, where the previously transmitted bits persist for a longer duration and (ii) channel with refresh, where the channel is cleared after each successful reception of the message. The ISI comparison, across different sequence distributions for a given length and weight, shows that the linear LOZP code exhibits superior resilience against ISI in a channel with refresh due to the placement of bit-1s at the initial positions, whereas the ZP code performs better in channel without refresh by reducing the average bit-1 density of the code. The asymptotic upper bound of the code rate is derived for the proposed codes, which depicts that a trade-off exists between the ISI and code rate. The simulation results show that the proposed family of ZP and linear LOZP codes can improve the Bit Error Rate (BER) performance by controlling the bit-1 locations and the average bit-1 density of the code, specifically where the ISI is more pronounced over the channel noise, thus providing a better reliability compared to the conventional error correcting codes at different data rate regimes.

In this paper, we are going to discuss the error in determining the actual intersymbol interference noise (ISI) due to different circuit simulation methodology, while using a standard circuit simulator. In this paper, we have compared three different methods to predict accurately ISI noise. All three methods show that errors caused by circuit simulation can make the eye worst. We have also shown a method which allows one to determine that error and calculate the actual range of ISI noise. As we move towards sampling mVolt signals at the receiver end (Bhattacharyya, 2004 and Bhattacharyya, 2005), one needs to minimize the error that arises due to circuit simulation methodology. This is essential, in order to predict the actual performance of the interconnect.

The use of a spectrally sliced (SS) broad-band source provides a cost effective alternative to laser diode sources for wavelength-division multiplexing (WDM). In this paper the performance of direct detection p-i-n diode intensity modulated SS systems is analyzed using the saddlepoint approximation. Using this approach, based on moment generating functions, the effects of pulse distortion, intersymbol interference (ISI) and nonideal modulator extinction ratios have been included in the analysis of SS systems for the first time. The presence of ISI error floors as the product of optical bandwidth and bit time decreases is demonstrated using a model that agrees with previous work in the case of low bit rate, widely spaced channels. In addition, comparisons with recent experimental results from the literature are made with good agreement. Subsequently, the use of an integrate and dump filter where the integration time starts after the beginning of a bit is investigated and shown to produce significant enhancements to bit-error rate performance. Furthermore, it is shown that a modulator extinction ratio of 20 dB will suffice for 10/sup -9/ bit-error rate (BER) in most cases, with 30 dB offering a performance close to that possible with an ideal modulator. Finally, the likely system power for an SS system is presented.