Changes between Version 16 and Version 17 of WARPLab/Examples/OFDM

Timestamp:

Nov 2, 2015, 3:39:52 PM (9 years ago)

Author:

chunter

Comment:

--

WARPLab/Examples/OFDM

@@ -87 +87 @@
 == CFO, Phase Error, and SFO ==
 
+Typically, a transmitter and receiver are each clocked independently. This independence manifests in three different degradations that must be dealt with by a wireless receiver:
+
+ * [https://en.wikipedia.org/wiki/Carrier_frequency_offset Carrier Frequency Offset (CFO)] - The center frequency of the transmitter will not perfectly match the center frequency of the receiver. Unless corrected, this will de-orthogonalize the OFDM subcarriers and cause inter-carrier interference (ICI). CFO is typically corrected in the time domain via multiplication with a digital carrier whose frequency negates the CFO estimate.
+ * Phase Error - Even after CFO is corrected in the time domain, there is typically a residual phase error component that must be corrected in the frequency domain.
+ * Sampling Frequency Offset (SFO) - The temporal duration of a sample is slightly different at the receiver and transmitter due to different sampling clocks. Over the course of a reception, the relative sample periods will drift apart from one another. This manifests as larger phase error for the outer subcarriers.
+
 At the [https://warpproject.org/trac/browser/ResearchApps/PHY/WARPLAB/WARPLab7/M_Code_Examples/wl_example_siso_ofdm_txrx.m#L27 top of the script], there are three control variables that toggle three different recovery systems: {{{DO_APPLY_CFO_CORRECTION}}}, {{{DO_APPLY_PHASE_ERR_CORRECTION}}}, {{{DO_APPLY_SFO_CORRECTION}}}. In this section, we will explore what happens when different combinations of these recovery systems are enabled or disabled. For reference, here is an example output from the design when all three recovery systems are activated: