Performance limits of spectrally-efficient WDM direct-detection SSB Nyquist subcarrier modulation with signal-signal beat interference cancellation

Comparison of digital signal-signal beat interference compensation techniques in direct-detection subcarrier modulation systems

“…However, its digital hardware complexity is greatly increased due to the need to perform multiple (typically three or four) signal demodulation and modulation operations in the receiver DSP. Recently, we proposed and demonstrated an SSBI compensation scheme which is an updated version of the iterative scheme, combining single-stage linearization filter with noniterative SSBI estimation and cancellation [15]. Results of simulation and experimental studies indicated that it offers compensation performance matching the iterative scheme.…”

“…Figure 5 shows the receiver DSP design with the SSBI estimation and cancellation technique. A detailed description of the technique is given in [15]. Two copies of the detected DSB signal waveform VDD(n) are made with one being stored in memory and the other being passed through the single-stage linearization filter to partially eliminate the SSBI terms.…”

“…Its compensation performance can be further improved by iteratively repeating the linearization process or adding an extra linearization stage, techniques termed iterative linearization filter [13] and two-stage linearization filter [14], respectively. Alternatively, in order to maximize the potential compensation gain, especially at high values of optical signal-to-noise power ratio (OSNR), combined linearization and SSBI estimation and cancellation was proposed and investigated in [15] in which the SSBI is estimated from the symbol decisions and subtracted from the received signal waveform. The use of linearization in the latter scheme avoids the complexity of iterative signal demodulation and modulation stages, as proposed in [16][17][18].…”

Two-Stage Linearization Filter for Direct-Detection Subcarrier Modulation

“…The proposed two-stage linearization filter requires more than twice the DSP hardware compared with the single-stage linearization filter [12] due to the use of extra sideband filters and multipliers. However, since all the compensation is carried out before the SCM signal demodulation (DEMOD DSP), there is no need for additional SCM signal demodulation and modulation stages, and hence, its complexity is significantly lower than the previously proposed techniques in [10,13,14].…”

“…The single-stage linearization filter proposed in [12] can reduce SSBI with a very simple DSP structure, but cannot achieve the maximum compensation gain due to the introduction of extra beating interference by the technique itself; its compensation performance can be improved by repeating the single-stage linearization filter iteratively (four times or more) and using the stored received signal waveform [7]. A single-stage linearization filter combined with single-iteration SSBI cancellation [13,14] avoids the need for multiple iterations but still has the drawback of high dependency on the accuracy of symbol decision making.…”