WARP Project Forums - Wireless Open-Access Research Platform

The OFDM Reference Design PHY implements 2-antenna MIMO. The Tx and Rx blocks each use a single FFT core to compute the transforms of both streams. The FFT cores processed interleaved symbols for the two streams. The even/odd buffers de-interleave the symbols so they can be processed in parallel after the transforms.

The Alamouti STBC scheme improves reliability; it does not increase the data rate (i.e. it adds "diversity gain", not "multiplexing gain").

The PHY in the OFDM Reference Design does not implement sampling frequency offset estimation/correction. It does implement carrier frequency offset estimation and correction.

The PHY in the OFDM Reference Design supports 3 modes:
-SISO (1 Tx antenna, 1 Rx antenna)
-Alamouti (2 Tx antennas, 1 Rx antenna)
-Multiplexing (2 Tx antennas, 2 Rx antennas)

The Alamouti mode uses the extra spatial path for diversity (reliability) gain. The multiplexing mode uses the extra spatial paths for multiplexing (rate) gain. All 3 modes use simple zero-forcing equalization and soft-decision Viterbi decoding in the receiver.

I want to upgrade Reference MIMO to Alamouti 2x2 (2 Tx antennas, 2 Rx antennas).
For you, How I make it ? what 's i need to research ?

Extending the OFDM Reference Design to 2x2 Alamouti is feasible, but this is a big design project. 2-antenna Rx for Alamouti usually means maximal ratio combining (MRC) processing in the Rx. This means computing channel estimates for both Rx antennas, then using those estimates during the equalization process to weight the symbols received on each antenna.

I would *strongly* encourage you to build this scheme with WARPLab first, *especially* if you have limited experience with FPGA design (i.e. modifying the System Generator model). I would suggest starting with the SISO and MIMO OFDM example scripts included with WARPLab. These provide a good foundation to build a custom 2x2 STBC script.

What 's difference between Encoding of ref SISO and FEC of ref MIMO ?

The OFDM Reference Design PHY uses the same convolutional code and Viterbi decoder for all waveforms. The waveform controls which encoded bits are transmitted on which antennas (SISO sends all bits on 1 antenna, Alamouti sends all bits on both antennas, multiplexing sends half of bits on each antenna). The Rx PHY reconstructs a single bit sequence for every waveform, then passes this bit sequence to the Viterbi decoder. The decoder does not care what waveform provided the encoded bits.

I don't understaind what difference between SISO of Reference Design and Multiplexing mode in design ?

SISO Tx/Rx creates/consumes a single stream of I/Q samples. Multiplexing Tx/Rx creates/consumes two parallel streams of I/Q samples.

The PHY in the OFDM Reference Design uses the same logic blocks for SISO and Multiplexing modes. In SISO mode these blocks are idle half the time, since there are half as many samples to create/consume. The multiplexing mode achieves 2x the datarate of the SISO mode.

why write address have values ?
16    48    32    0    24    56    40    8    20    52    36    4    28    60    44    12    18    50    34    2    26    58    42    10    22    54    38    6    30    62    14    17    49    33    1    25    57    41    9    21    53    37    5    29    61    45    13    19    51    35    3    27    59    43    11    23    55    39    7    31    63    47    15

In the OFDM Reference Design Tx PHY the IFFT core is configured with "Bit/Digit Reversed Order" for "Output Ordering". Internally the IFFT implementation uses the bit reversed indexes for more efficient computation. The IFFT core can be configured to output transform results in that order, or to buffer the results and output them in "natural" order. In the Tx PHY the IFFT outputs are written to RAMs anyway, so it doesn't matter what order the IFFT produces samples - each sample is written to the specified index (in whatever order), then the RAMs are unloaded to the antenna interfaces in natural order. The cyclic prefix is added by reading the cyclic prefix samples twice from the RAMs.

Hi !
I have Ideal for  upgrade Reference have alamouti 2x2. But i think my upgarade not optimization with reference design .
Can you have me some idel for optimize ! Because i delete MODE MIMO,SISO,and Alamouti2x1 in desgin.


1/ In alamouti2x1 mode I copy block Channel Estimation & pilot in reference using for detection Channel !




2/ I write block equalize with zero-forcing

 


design:
https://drive.google.com/drive/folders/ … sp=sharing
I want to be check design with warplab ! I'm detect signal in Tx and transmit it with warplab and I use it for check Rx !  so how to up to 40Mhz in Warplab ?

Last edited by boyheyt (2018-Jan-16 14:06:17)

Thanks you !