Symbol spaced adaptive MIMO equalization for ultra high bit rate optical communication systems
System and method for equalizing a high bit rate optical communication channel in a symbol spaced adaptive Multiple-In-Multiple-Out (MIMO) system, where the optical communication channel carries a signal that is sampled at a symbol rate. Accordingly, Anti Aliasing Filtering (which introduces distortions in the form of Deterministic Inter Symbol Interference D-ISI) is applied in a MIMO channel, in order to reduce the aliasing effect associated with symbol rate sampling. The Polarization Mode Dispersions introduced in the optical communication channel are solely compensated by a MIMO Equalizer, which ignores the Deterministic ISI (D-ISI) distortion. Then the Deterministic ISI (D-ISI) distortion is solely compensated by an independent Deterministic Equalizer (DE).
1. A symbol spaced adaptive MIMO equalization system for a high bit rate optical communication channel, carrying a signal that is sampled at a symbol rate, comprising:
a) a MIMO Equalizer (ME) for compensating random distortions introduced by said optical communication channel, while ignoring Deterministic ISI (D-ISI) distortion caused by the effect of reducing the bandwidth of said optical communication channel; and
b) an independent Deterministic Equalizer (DE) following said MIMO Equalizer (ME), for solely compensating said Deterministic ISI (D-ISI) distortion, wherein the error signal in said MIMO Equalizer (ME), being the difference between a novel desired response vector in said MIMO Equalizer (ME) and the vector outputs of said MIMO Equalizer (ME), is adapted to include the Deterministic ISI (D-ISI) distortion effect in said desired response vector.
2. A system according to claim 1 , in which the MIMO Equalizer (ME) compensates distortions according to one of the following criteria:
Least Mean Squares (LMS);
Zero Forcing (ZF);
Constant Modulus Algorithm (CMA).
3. A system according to claim 1 , in which the MIMO Equalizer (ME) is a Linear Equalizer (LE).
4. A system according to claim 1 , in which the Deterministic Equalizer (DE) is any type of correcting filter being capable of correcting Deterministic ISI (D-ISI) distortion.
5. A system according to claim 4 , in which the correcting filter includes:
a Maximum Likelihood Sequence Estimator (MLSE);
a Decision Feedback Equalizer (DFE).
6. A symbol spaced adaptive MIMO equalization system for a high bit rate optical communication channel, carrying a signal that is sampled at a symbol rate, comprising:
a) a MIMO Equalizer (ME) for compensating random distortions introduced by said optical communication channel, while ignoring Deterministic ISI (D-ISI) distortion caused by the effect of reducing the bandwidth of said optical communication channel; and
c) an independent Deterministic Equalizer (DE) following said MIMO Equalizer (ME), for solely compensating said Deterministic ISI (D-ISI) distortion,
wherein the error vector that is used by said independent Deterministic Equalizer (DE) for compensating the Deterministic ISI (D-ISI) distortion resulting from bandwidth reduction effect of the channel is modified to be:
e m ( n )= d ( n )* h AAF ( n )− y ( n )
where h AAF (n) is an equivalent impulse response of said bandwidth reduction.
7. A system according to claim 6 , in which the Deterministic ISI (D-ISI) distortion is caused by Anti-Aliasing Filtering (AAF).
8. A system according to claim 6 , in which the random distortion is PMD.