Feedback Solution for Blind Symbol Timing Recovery in Bandlimited Optical Intensity Channels

Gappmair, Wilfried; Schlemmer, Harald

doi:10.1109/cobcom55489.2022.9880656

Cited by 4 publications

(6 citation statements)

References 16 publications

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“…In this case, the signal parts of r ( t ) and z ( t ) are the same, whereas the noise component is determined by n ( t ) = w ( t ) ⊗ q ( t ) representing a zero-mean non-white Gaussian process. Under the assumption that the symbol timing has been reliably recovered and corrected, e.g., by one of the algorithms proposed in [ 10 , 11 , 12 ], the T -spaced samples at the output of the receiver filter are obtained as

where

, and sinc( x ) =

.…”

Section: Signal and Channel Modelmentioning

confidence: 99%

“…Of course, synchronization of carrier frequency and phase need not be considered in case of intensity modulation, whereas the recovery of the symbol timing is still of paramount importance since this is a pre-requisite for many other estimation and detection procedures. This problem has been tackled in a couple of papers recently published by the author in [ 10 , 11 , 12 ].…”

Section: Introductionmentioning

confidence: 99%

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Non-Data-Aided SNR Estimation for Bandlimited Optical Intensity Channels

Gappmair

2023

Sensors

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Powerful and reliable estimation of transmission parameters is an indispensable task in each receiver unit—not only for radio frequency, but also for optical wireless communication systems. In this context, the signal-to-noise ratio (SNR) plays an eminent role, especially for adaptive scenarios. Assuming a bandlimited optical intensity channel, which requires a unipolar waveform design, an algorithm for SNR estimation is developed in this paper, which requires no knowledge of the transmitted data. This non-data-aided approach benefits to a great extent from the fact that very long observation windows of payload symbols might be used for the estimation process to increase the accuracy of the result; this is in striking contrast to a data-aided approach based on pilot symbols reducing the spectral efficiency of a communication link. Since maximum likelihood, moment-based or decision-directed algorithms are not considered for complexity and performance reasons, an expectation-maximization solution is introduced whose error performance is close to the Cramer-Rao lower bound as the theoretical limit, which has been derived as well.

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where

, and sinc( x ) =

.…”

Section: Signal and Channel Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Non-Data-Aided SNR Estimation for Bandlimited Optical Intensity Channels

Gappmair

2023

Sensors

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“…Performing an impulse response expressed by

, the corresponding output is given by

. Under the assumption that the symbol timing has been reliably recovered by properly selected estimation or synchronization algorithms [ 21 , 22 , 23 ], it is required that

exhibits an impulse response such that the signal component of

vanishes at integer multiples of the symbol period, which is satisfied only if

for all

. In this respect, it is to be noticed that the first-order derivative of squared raised cosine or double jump functions fulfills this pre-requisite [ 7 ], i.e.,

.…”

Section: Signal and Channel Modelmentioning

confidence: 99%

“…After having synchronized symbol timing and clocking, e.g., by implementation of one of the recovery algorithms investigated in [ 21 , 22 , 23 ], the T -spaced samples at the output of the dual-filter concept are furnished by

and

…”

Section: Signal and Channel Modelmentioning

confidence: 99%

“…Performing an impulse response expressed by ( ) q t  , the corresponding output is given by ( ) ( ) ( ) z t q t r t     . Under the assumption that the symbol timing has been reliably recovered by properly selected estimation or synchronization algorithms [21][22][23], it is required that ( ) q t  exhibits an impulse response such that the signal component of ( ) z t  vanishes at integer multiples of the symbol period, which is satisfied only if ( )…”

Section: Furthermore By Introduction Ofmentioning

confidence: 99%

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Novel Results on SNR Estimation for Bandlimited Optical Intensity Channels

Gappmair

2023

Sensors

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In a previous work of the author about non-data-aided estimation of the signal-to-noise ratio (SNR) for bandlimited optical intensity channels, a couple of limitations have been identified in terms of error performance and computational complexity. In the current paper, these deficiencies are avoided by the introduction of a second receiver filter with specific properties that is operated in parallel to the receiver filter normally used in this respect. Although not initially intended, the concept is also applied to data-aided SNR estimation by deriving a maximum likelihood algorithm and the Cramer–Rao lower bound (CRLB) as the theoretical limit of the error performance. In the next step, the dual-filter framework is used in the context of SNR estimation without knowledge about data symbols. The most significant benefit of this method is that the number of payload data employed for the estimation procedure might be selected arbitrarily long without impacting the spectral efficiency of the link. Since the computation of the true CRLB was out of scope due to complexity reasons, an asymptotic variant for very low SNR values is analyzed, which ends up in a closed-form solution. Furthermore, an algorithm based on first- and second-order moments of the samples at the dual-filter output is investigated, which turned out to be very attractive in terms of error performance and computational complexity.

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Dual-Filter Architecture for Blind Feedback Recovery of the Symbol Timing in Bandlimited Optical Intensity Channels

Gappmair

Schlemmer

2023

Electronics

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Reliable recovery of transmission parameters is of paramount importance not only for radio frequency receivers, but also for optical wireless communication solutions. This paper discusses a feedback algorithm for recovering the symbol timing in the context of a bandlimited optical intensity link. The link is determined by a PAM scheme and pulse shaping with squared raised cosine or double jump functions. When preambles or pilot sequences are not available to the receiver, non-data-aided (blind) recovery concepts are useful for tracking smaller variations of the timing error affecting the payload data. The current state-of-the-art solution uses a Gardner detector with two samples per symbol, although this introduces a non-negligible amount of inter-symbol interference resulting in an error floor. To avoid this drawback, the authors propose a dual-filter approach which includes an appropriately designed filter operated in parallel to the receiver filter. Despite the additional complexity of the dual-filter architecture, the recovery loop is very simple and requires only one sample per symbol, representing the lowest degree of complexity in this respect. Open-loop characteristic, jitter performance, and acquisition behavior of the suggested recovery loop are investigated.

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Feedback Solution for Blind Symbol Timing Recovery in Bandlimited Optical Intensity Channels

Cited by 4 publications

References 16 publications

Non-Data-Aided SNR Estimation for Bandlimited Optical Intensity Channels

Non-Data-Aided SNR Estimation for Bandlimited Optical Intensity Channels

Novel Results on SNR Estimation for Bandlimited Optical Intensity Channels

Dual-Filter Architecture for Blind Feedback Recovery of the Symbol Timing in Bandlimited Optical Intensity Channels

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