Pilot-aided Equalization Research Articles

Likelihood-Based Selection Radius Directed Equalizer With Time-Multiplexed Pilot Symbols for Probabilistically Shaped QAM

Probabilistically shaped (PS) quadrature amplitude modulation (QAM) recently established itself as the solution to adopt for state-of-the-art coherent transponders. This in turn has drawn attention to the rework of conventional digital signal processing (DSP) algorithms, which are not optimal for QAM-PS. In this context, we propose a novel pilot-aided equalization technique based on the ubiquitous radius directed equalizer (RDE). Our solution employs both payload and time-multiplexed pilot symbols for the adaptive filters update. The payload symbols are treated on the basis of the likelihood of their correct blind assignment. We show that this approach is at the same time able to reduce the global pilot overhead (POH) required by the DSP chain and to provide greatly improved performance in the tracking ability of the equalizer in the event of fast state of polarization rotations. We describe a simulation environment in which we model accurately static and dynamic polarization-related impairments. We test our algorithm over different shaped modulation formats and in the presence of transceiver impairments and demonstrate its superior performance with respect to standard feed-forward implementations in all the scenarios considered.

Infinite-length pilot aided equalization

A single carrier pilot-assisted transmission scheme is considered in this letter. Specifically, we focus on the case of synchronous transmission where one pilot symbol is periodically inserted in the transmitted sequence on a time-division multiplexing basis. A new equalization scheme, where the knowledge of pilot symbols is exploited by the equalizer to generate an estimate of the noise affecting the symbol to be detected, is introduced and analyzed. The criterion used to compute the equalizer coefficients is the minimization of the mean-square error (MSE). The main result of our analysis is that the optimal pilot aided equalizer (PAE) can be decomposed as the cascade of a minimum MSE (MMSE) linear equalizer (LE) and a data-aided noise estimation filter. This result completes and extends the noise-predictive view of decision feedback equalization to general data-aided equalization. The performance of the proposed PAE is compared to that of theMMSE-LE and that of theMMSE decision feedback equalizer both for static and for fading channels.

Iterative Equalization Technique for Double-Selective Channel Estimation in OFDM Systems

In OFDM based mobile communication systems, channel variation during one symbol period introduces intercarrier interference (ICI). Conventional pilot-aided equalization mitigates the ICI at the price of band inefficiency. On the other hand, the blind or semi-blind equalization method, which utilizes the known statistic properties of the transmitted data, will raise system complexity. In this letter, without bandwidth-consuming pilots, a novel channel estimation and tracking method based on an iterative equalization technique (IET) is proposed. The proposed approach successfully achieves a good compromise between bandwidth efficiency and system complexity, and its validity is demonstrated by numerical simulations, especially for fast fading channel.