Systems for high-speed backplane applications using pre-coding
View Patent ↗In conventional Backplane Ethernet systems, data is transmitted over two pairs of copper traces in one direction using a PAM-2 scheme and a baud rate of 10.3125 GHz, giving an effective bit rate of 10.3125 Gbps. The rate at which data can be transmitted in Backplane Ethernet systems, while still being reliably received, is typically limited by ISI caused by the dispersive nature of the copper traces, frequency dependent transmission losses caused primarily by skin effect and dielectric loss of the copper traces, and cross-talk from adjacent communication lines. The present invention is directed to systems for overcoming these and other signal impairments to achieve speeds up to, and beyond, twice the conventional 10 Gbps limit associated with Backplane Ethernet systems.
1. A transmitter configured to manipulate an input data stream to properly format an output data stream for transmission over a channel, the transmitter comprising:
a scrambler configured to remove sequences of digital zero or digital one values from the input data stream to provide a scrambled data stream;
a forward error correction (FEC) encoder configured to generate and append redundant symbols to the scrambled data stream to provide a FEC encoded data stream, wherein the redundant symbols allow a receiver to detect and correct for errors that occur during transmission of the FEC encoded data stream;
a line code encoder configured to modulate the FEC encoded data stream using a pulse amplitude modulation (PAM) scheme having an order M greater than two to provide a modulated data stream; and
a pre-coder configured to perform channel pre-equalization and power limiting on the modulated data stream to provide a pre-coded data stream, wherein the pre-coder comprises an infinite impulse response (IIR) filter to perform channel pre-equalization.
2. The transmitter of claim 1 , further comprising a TX linear filter configured to adjust the pre-coded data stream to compensate for high-frequency attenuation of the channel.
3. The transmitter of claim 1 , wherein the IIR filter is configured to have a transfer function substantially equal to an inverse transfer function of the channel.
4. The transmitter of claim 1 , wherein the precoder further comprises a modulo M device configured to limit symbols of the pre-coded data stream to have an amplitude within the interval [0, 1, . . . , M−1].
5. The transmitter of claim 1 , wherein the FEC encoder is configured to generate the redundant symbols in accordance with a Reed Solomon encoding technique.
6. The transmitter of claim 1 , further comprising a training sequence generator configured to generate a sequence of training bits known to a receiving entity.
7. The transmitter of claim 6 , further comprising a second line code encoder configured to modulate the sequence of training bits.
8. The transmitter of claim 7 , further comprising a multiplexer configured to provide as output either the modulated sequence of training bits or the modulated data stream based on a select signal.
9. The transmitter of claim 1 , wherein the transmitter is further configured to perform an auto-negotiation process with a receiving entity to determine a FEC scheme to be used by the FEC encoder based on a signal-to-noise ratio (SNR) supported by the channel or a desired latency.
10. The transmitter of claim 1 , wherein the transmitter is further configured to perform an auto-negotiation process with a receiving entity to establish a master-slave relationship such that the transmitter and the receiving entity communicate with each other based on a common clock.
11. The transmitter of claim 1 , wherein the channel is disposed on a backplane.
12. The transmitter of claim 1 , wherein the channel comprises an optical fiber.
13. A receiver configured to manipulate a modulated data stream received over a channel to properly recover an output data stream, the receiver comprising:
a discrete time sampler configured to sample the modulated data stream to provide a sampled modulated data stream;
a decision feedback equalizer (DFE) with an inverse pre-coder configured to detect symbols within the sampled modulated data stream and perform a modulo M operation on the detected symbols to provide an inverse pre-coded symbol stream;
a line code decoder configured to demodulate the inverse pre-coded symbol stream to provide a demodulated data stream, wherein the inverse pre-coded symbol stream has been modulated in accordance with a pulse amplitude modulation (PAM) scheme having an order greater than two;
a forward error correction (FEC) decoder configured to detect and correct for errors in the demodulated data stream to provide an error corrected data stream; and
a de-scrambler configured to perform an inverse scrambling function on the error corrected data stream to provide the output data stream.
14. The receiver of claim 13 , further comprising a feed forward equalizer (FIT) configured to reduce pre-cursor intersymbol interference (ISI) on the sampled modulated data stream prior to the sampled modulated data stream being processed by the DFE with the inverse pre-coder.
15. The receiver of claim 13 , further comprising a cancellation summer configured to substantially cancel from the sampled modulated data stream near end cross talk (NEXT) noise prior to the sampled modulated data stream being processed by the DFE with the inverse pre-coder.
16. The receiver of claim 13 , wherein the channel comprises an optical fiber.
17. A receiver configured to manipulate a modulated data stream received over a channel to properly recover an output data stream, the receiver comprising:
a discrete time sampler configured to sample the modulated data to provide a sampled modulated data stream;
an inverse pre-coder with an extended slicer configured to detect symbols within the sampled modulated data stream and perform a modulo M operation on the detected symbols to provide an inverse pre-coded symbol stream;
a line code decoder configured to demodulate the inverse pre-coded symbol stream to provide a demodulated data stream, wherein the inverse pre-coded symbol stream has been modulated in accordance with a pulse amplitude modulation (PAM) scheme having an order greater than two;
a forward error correction (FEC) decoder configured to detect and correct for errors in the demodulated data stream to provide an error corrected data stream; and
a de-scrambler configured to perform an inverse scrambling function on the error corrected data stream to provide the output data stream.
18. The receiver of claim 17 , further comprising a feed forward equalizer (FFE) configured to reduce pre-cursor intersymbol interference (ISI) on the sampled modulated data stream prior to the sampled modulated data stream being processed by the inverse pre-coder with the extended slicer.
19. The receiver of claim 17 , further comprising a cancellation summer configured to substantially cancel from the sampled modulated data stream near end cross talk (NEXT) noise prior to the sampled modulated data stream being processed by the inverse pre-coder with the extended slicer.
20. The receiver of claim 17 , wherein the channel comprises an optical fiber.