Changes between Version 25 and Version 26 of WARPLab/Examples/OFDM
- Timestamp:
- Nov 3, 2015, 10:42:32 AM (8 years ago)
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WARPLab/Examples/OFDM
v25 v26 119 119 || [[Image(Cn_PEy_Sy_phaseError.png,width=400)]][[BR]]1. Phase Error Estimates and SFO Correction Matrix || [[Image(Cn_PEy_Sy_constellations.png,width=400)]] [[BR]]2. Rx Constellation || [[Image(Cn_PEy_Sy_evm.png,width=400)]] [[BR]]3. Error Vector Magnitude (EVM)[[BR]] and effective SNR || 120 120 121 By disabling time-domain CFO correction, we have increased the burden on the phase error correction system. In effect, the residual CFO to be corrected is now considerably larger. This can be observed by comparing "Phase Error Estimates" plot in this section with the equivalent plot presented in [#scenA Scenario A]. The number of 2π wraps is considerably larger than the previous scenario where time-domain CFO correction was enabled. Ultimately, however, phase error recoverycan only go so far. By the time the system is applying phase corrections in the frequency domain, ICI has already occurred because the transmitter's IFFT operation is not aligned to the receiver's FFT operation. This can be observed in the "EVM and SNR" plots where the effective SNR is a couple of dB worse than the previous case.121 By disabling time-domain CFO correction, we have increased the burden on the phase error correction system. In effect, the residual CFO to be corrected is now considerably larger. This can be observed by comparing "Phase Error Estimates" plot in this section with the equivalent plot presented in [#scenA Scenario A]. The number of 2π wraps is considerably larger than the previous scenario where time-domain CFO correction was enabled. Ultimately, however, phase error correction can only go so far. By the time the system is applying phase corrections in the frequency domain, ICI has already occurred because the transmitter's IFFT operation is not aligned to the receiver's FFT operation. This can be observed in the "EVM and SNR" plots where the effective SNR is a couple of dB worse than the previous case. 122 122 123 123 === Scenario C === #scenC … … 130 130 || [[Image(Cn_PEn_Sy_phaseError.png,width=400)]][[BR]]1. Phase Error Estimates and SFO Correction Matrix || [[Image(Cn_PEn_Sy_constellations.png,width=400)]] [[BR]]2. Rx Constellation || [[Image(Cn_PEn_Sy_evm.png,width=400)]] [[BR]]3. Error Vector Magnitude (EVM)[[BR]] and effective SNR || 131 131 132 When both CFO recovery and Phase Error Recoveryare disabled, there is nothing to counteract the differing center frequencies of the transmitter and receiver. The result is a received constellation that "spins" around the complex plane. The speed of this spin is CFO. The "beat patterns" of high and low EVM are caused by the receive constellation periodically aligning to the transmitted constellation as it rotates around the complex plane.132 When both CFO correction and Phase Error correction are disabled, there is nothing to counteract the differing center frequencies of the transmitter and receiver. The result is a received constellation that "spins" around the complex plane. The speed of this spin is CFO. The "beat patterns" of high and low EVM are caused by the receive constellation periodically aligning to the transmitted constellation as it rotates around the complex plane. 133 133 134 134 === Scenario D === #scenD … … 141 141 || [[Image(Cy_PEy_Sn_phaseError.png,width=400)]][[BR]]1. Phase Error Estimates and SFO Correction Matrix || [[Image(Cy_PEy_Sn_constellations.png,width=400)]] [[BR]]2. Rx Constellation || [[Image(Cy_PEy_Sn_evm.png,width=400)]] [[BR]]3. Error Vector Magnitude (EVM)[[BR]] and effective SNR || 142 142 143 Finally, we have re-enabled both time-domain CFO recovery and phase error recovery. We have disabled SFO recovery. As the sample clocks drift over the duration of the reception, EVM begins to increase on the outer subcarriers.143 Finally, we have re-enabled both time-domain CFO correction and Phase Error correction. We have disabled SFO correction. As the sample clocks drift over the duration of the reception, EVM begins to increase on the outer subcarriers. 144 144 145 145 == Limitations ==