Dynamic configuration of modulation and demodulation
A modulator and demodulator pair may switch configurations without introducing errors as a result of the switch. Different configurations may, for example, correspond to different symbol rates and/or different amounts of controlled inter-symbol interference (ISI) introduced to the transmitted signal. For example, a first configuration may use be a near-zero ISI configuration (e.g., using Nyquist signaling) and a second configuration may introduce a significant (e.g., amount that would result in errors above a desired threshold if demodulation relied on symbol-by-symbol slicing) but controlled amount of ISI (e.g., using partial response or faster-than-Nyquist-rate signaling). Switching between modulator/demodulator configurations may be needed to maintain a stable link in the case of dynamic channels. At any given time, a modulator and demodulator pair may, for example, switch to a configuration that provides maximal throughput for the current channel conditions.
1. A transmitter comprising:
a modulator circuit configured to operate in at least two configurations, including an inter-symbol correlated signaling configuration,
wherein said modulator circuit operates in one of the at least two configurations based on an indication of performance, and
prior to switching from one of the at least two configurations to another of the at least two configurations, the modulator circuit adds a different preamble to a last frame generated with the one of the at least two configurations.
2. The transmitter of claim 1 , wherein the at least two configurations further include a Nyquist-rate signaling configuration.
3. The transmitter of claim 1 , wherein said modulator circuitry is further configured to mark the last frame generated with the one of the at least two preambles, upon a decision to switch from the one of said at least two configurations to the other of said at least two configurations.
4. The transmitter of claim 1 , wherein said modulator circuit includes a framing circuit configured to:
detect start of frame indicators in frames processed by said framing circuit;
detect whether a frame is marked as the last frame of the one of said at least two configurations; and
upon detecting a start of frame indicator of the frame marked as the last frame of the one of said at least two configurations, add a last-frame-indicating preamble to said last frame as the different preamble.
5. The transmitter of claim 4 , wherein said last-frame-indicating preamble is a negated version of a preamble used for other frames.
6. The transmitter of claim 1 , wherein said indication of performance is an indication of demodulation performance from a receiver.
7. The transmitter of claim 6 , wherein the indication of demodulation performance is one or more of: received signal strength, mean square error, bit error rate, symbol error rate, amount of interference, signal-to-noise ratio, amount of nonlinear distortion, amount of phase noise.
8. The transmitter of claim 1 , wherein said modulator circuit is further configured to, in response to a decision to switch from a first of said configurations to a second of said configurations:
generate a start of frame flag synchronized to the start of a last frame generated with said first of said configurations;
generate an end of frame flag synchronized to the end of said last frame generated with said first of said configurations; and
generate a last frame flag synchronized with said start of frame flag and said end of frame flag.
9. The transmitter of claim 8 , wherein said start of frame flag, said end of frame flag, and said last frame flag propagate through a plurality of circuits included in said modulator circuit along with said last frame.
10. The transmitter of claim 9 , wherein, for said reconfiguration of said modulator circuit from said first configuration to said second configuration, reconfiguration of each of said plurality of said circuits included in said modulator circuit is synchronized with one or more of said start of frame flag, said end of frame flag, and said last frame flag.
11. The transmitter of claim 1 , wherein reconfiguration of said modulator circuit among different ones of said configurations comprises reconfiguration of taps coefficients of a pulse shaping filter of said modulator circuit.
12. The transmitter of claim 1 , wherein said inter-symbol correlated signaling configuration is a partial response signaling configuration.
13. The transmitter of claim 1 , wherein said inter-symbol correlated signaling configuration is faster-than-Nyquist-rate signaling configuration.
14. A receiver comprising:
a demodulator circuit configured to demodulate faster-than-Nyquist-rate signals in a first configuration;
said demodulator circuit being configured to demodulate Nyquist-rate signals in a second configuration; and
said demodulator circuit is configured to dynamically switch between said first configuration and said second configuration based on receiving a frame including a different preamble than preambles of other received frames.
15. The receiver of claim 14 , wherein said demodulator circuit is configured to:
measure demodulation performance for a received signal; and
trigger a reconfiguration of said demodulator circuit between said first configuration and said second configuration in response to said measured demodulation performance.
16. The receiver of claim 15 , wherein said demodulator circuit is configured to trigger a reconfiguration of a modulator circuit that generated said received signal in response to said measured demodulation performance.
17. The receiver of claim 16 , wherein said measured demodulation performance includes one or more of the following: received signal strength, mean square error, bit error rate, symbol error rate, amount of interference, signal-to-noise ratio, amount of nonlinear distortion, amount of phase noise.
18. The receiver of claim 14 , wherein said demodulator circuit is configured to trigger a reconfiguration of said demodulator circuit between said first configuration and said second configuration in response to an indication that a modulator circuit has been reconfigured.
19. The receiver of claim 18 , wherein said indication that a modulator circuit has been reconfigured comprises the different preamble which is a last-frame-indicating preamble.
20. The receiver of claim 19 , wherein said last-frame-indicating preamble is a negated version of a normal preamble.
21. The receiver of claim 20 , comprising a preamble phase detector configured to determine a phase of a received preamble.
22. The receiver of claim 21 , comprising a configuration controller that is configured to:
disable said preamble phase detector when a reconfiguration of said demodulator circuit is not expected to occur within a determined amount of time; and
enable said preamble phase detector in response to a determination that a reconfiguration of said demodulator circuit is to occur within a determined amount of time.