For decades, optical networks have provided larger bandwidths than could be utilized, but with the increasing growth of the global Internet traffic demand new optical transmission technologies are required to provide a much higher data rate per channel and to enable more flexibility in the allocation of traffic flow. Currently, researchers are investigating innovative elastic transceiver architectures capable of dynamically adapting the spectral efficiency to the transmission link properties. In this work, we address the problem of finding efficient strategies to enable variable transmission rate for light speed digital coherent systems. We consider three techniques: regular QAM formats, time-domain Hybrid QAM formats and Probabilistically Shaped QAM formats. The time-domain Hybrid QAM format is based on the transmission of alternated modulation formats. Within each time-division-multiplexing (TDM) frame, two regular M-QAMs with different spectral efficiencies (SE, [bit/s/Hz]) are assigned to different time slots. Using this method, any SE that falls between the SE of the two QAMs can be realized by appropriately designing the TDM frame length and the time slot occupancy ratio of the two QAMs. Attainment of the channel capacity bound requires that the signal points have a Gaussian probability distribution. In Probabilistic Shaping, symbols of a regular QAM constellation are assigned different probabilities of occurrence. By acting on symbol probabilities, Probabilistic Shaping varies the information rate ([bit/symbol]). Besides, it offers an SNR gain up to the ultimate shaping gain of 1.53 dB for the additive white Gaussian noise (AWGN) channel. In this thesis we investigate the effectiveness, in terms of BER/SNR performance, of regular QAM formats, time-domain Hybrid QAM formats and Probabilistically Shaped QAM formats, emulating the transmission of symbols through an AWGN channel. The data stream is encoded using a reference LDPC code and then modulated according to the desired modulation format.
Per decenni, le reti ottiche hanno fornito una banda maggiore di quella effettivamente utilizzabile. Tuttavia, il costante aumento del traffico Internet globale ha comportato la necessità di nuove tecnologie di trasmissione ottica, in grado di fornire un maggiore data rate per canale e di permettere una maggiore flessibilità nell’allocazione del flusso di traffico. Attualmente, la ricerca è impegnata nell’investigare nuove architetture di trasmissione, innovative ed elastiche, in grado di adattare dinamicamente l’efficienza spettrale alle proprietà del canale di trasmissione. In questo lavoro, consideriamo il problema di trovare strategie efficienti, in grado di consentire rate di trasmissione variabile per sistemi ottici coerenti. Esamineremo tre tecniche: i formati di modulazione regular QAM, time-domain Hybrid QAM e Probabilistically Shaped QAM. Il formato di modulazione time-domain Hybrid QAM è basato sulla trasmissione alternata di diversi formati QAM. In ogni frame TDM (time-division-multiplexing), due regular M-QAM aventi diverse efficienze spettrali (SE, [bit/s/Hz]) sono assegnate a time slots differenti. Utilizzando questo metodo, si può realizzare ogni SE compresa tra le efficienze spettrali delle due QAM, progettando in modo accurato la lunghezza del frame TDM e il rapporto di occupazione del time slot. La capacità di canale viene raggiunta considerando segnali con una distibuzione di probabilità gaussiana. Nel Probabilistic Shaping, ai simboli di una costellazione regular QAM vengono associate differenti probabilità di occorrenza. Agendo sulle probabilità dei simboli, il Probabilistic Shaping varia il tasso (rate) di informazione ([bit/simbolo]). Inoltre, esso offre un guadagno in SNR (shaping gain) che può raggiungere il limite di 1.53 dB nel caso di canale AWGN. In questa tesi investighiamo l’efficacia, in termini di prestazione BER/SNR, dei for- mati di modulazione regularss QAM, time-domain Hybrid QAM e Probabilistically Shaped QAM, simulando la trasmissione di simboli attraverso un canale AWGN. Il data stream è codificato con un codice LDPC di riferimento e poi modulato secondo il formato di modulazione desiderato.
Rate adaptive modulations for optical transmission systems
CAOBIANCO, SARA
2015/2016
Abstract
For decades, optical networks have provided larger bandwidths than could be utilized, but with the increasing growth of the global Internet traffic demand new optical transmission technologies are required to provide a much higher data rate per channel and to enable more flexibility in the allocation of traffic flow. Currently, researchers are investigating innovative elastic transceiver architectures capable of dynamically adapting the spectral efficiency to the transmission link properties. In this work, we address the problem of finding efficient strategies to enable variable transmission rate for light speed digital coherent systems. We consider three techniques: regular QAM formats, time-domain Hybrid QAM formats and Probabilistically Shaped QAM formats. The time-domain Hybrid QAM format is based on the transmission of alternated modulation formats. Within each time-division-multiplexing (TDM) frame, two regular M-QAMs with different spectral efficiencies (SE, [bit/s/Hz]) are assigned to different time slots. Using this method, any SE that falls between the SE of the two QAMs can be realized by appropriately designing the TDM frame length and the time slot occupancy ratio of the two QAMs. Attainment of the channel capacity bound requires that the signal points have a Gaussian probability distribution. In Probabilistic Shaping, symbols of a regular QAM constellation are assigned different probabilities of occurrence. By acting on symbol probabilities, Probabilistic Shaping varies the information rate ([bit/symbol]). Besides, it offers an SNR gain up to the ultimate shaping gain of 1.53 dB for the additive white Gaussian noise (AWGN) channel. In this thesis we investigate the effectiveness, in terms of BER/SNR performance, of regular QAM formats, time-domain Hybrid QAM formats and Probabilistically Shaped QAM formats, emulating the transmission of symbols through an AWGN channel. The data stream is encoded using a reference LDPC code and then modulated according to the desired modulation format.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/132003