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AWR Version 14
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AWR Version 13
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This example demonstrates a RAKE receiver for a Direct-Sequence Spread-Spectrum system.
The transmitted signal is assumed to be packetized and using a known preamble for training.
The propagation channel consists of two equal-power, independently Rayleigh fading paths, with time separation determined by the variable TapDelaySec (sec). Background noise is simulated by the AWGN block.
The signal power is fixed to 0 dBm, while the noise level is varied so that it results in an Eb/N0 at the source symbol level defined by the vector Eb_N0_span. The Eb/N0 experienced at the channel level is adjusted by the spreading factor.
The parameters used for defining the system are listed below:
- ChipRate: chip rate at the channel level,
- ChipsPerSym: spreading factor, number of chips used for each symbol,
- TapDelaySec: time separation between Rayleigh fading paths of the channel,
- BlkSz: length of packet in symbols,
- CorrSeqSz: length of training sequence,
- Eb_N0_span: set of Eb/N0 values to be swept during simulation.
A RAKE receiver with two paths is implemented. It estimats the channel coefficients, adjusts the received signal accordingly, and combines the two adjusted and appropriately delayed versions of the received signal.
A Correlation Receiver is provided for reference. This conventional implementation estimates only a single channel tap and uses it to correct for the effect of the propagation channel.
A series of graphs is provided to show BER results, output of the correlator used for channel estimation, estimated channel taps, output spectrum, transmitted and detected data for both receivers.
To get faster BER results, user can disable all measurements except those in the BER Graphs.
System Diagram - CDMA System
Graph - Output spectrum
Graph - Channel Estimates
Graph - With channel correction
Graph - Without channel correction
Graph - Correlator output
Graph - BER Graphs