fabianeckermann / cv2x-traffic-generator Goto Github PK

Issue Description

• Packets are failing the CRC checksum (srslte_bit_diff) in the srslte_pssch_decode function in pssch_ue. This causes num_decoded_tb to always equal 0 (even when num_decoded_sci is non-zero), or takes a very long time before a packet passes srslte_pssch_decode.

Setup Details

We have tried 2 different synchronization setups to fix this issue. We are using two NI 2901 USRPs.

1. Synchronization with 2 Keysight waveform generators. Both USRPs are connected to a signal generator at 10MHz and another at 1 Hz.
2. Synchronization with GPSDO using OctoClock clock distribution module

Expected Behavior

• num_decoded_tb to be a non-zero value during transmission of C-V2X packets.

Steps to reproduce the problem

• Add ERROR("Checksum error") error printing statements within the CRC checksum in pssch.ue/srslte_pssch_decode, i.e.:

1. Change # 1

  if (srslte_bit_diff(q->cb_crc_temp, &q->c_r[(K_r - L)], L) != 0) {
        ERROR("Checksum error");
        return SRSLTE_ERROR;
  }

2. Change # 2

  if (srslte_bit_diff(q->tb_crc_temp, &q->b[(B - SRSLTE_PSSCH_CRC_LEN)], SRSLTE_PSSCH_CRC_LEN) != 0) {
    ERROR("Checksum error");
    return SRSLTE_ERROR;
  }

• For waveform generator synchronization: Run ./pssch_ue and ./cv2x_traffic_generator -d UHD -a clock=external -n 5 -l 10 -s 0 on separate USRPs
• For OctoClock synchronization: Run ./pssch_ue and ./cv2x_traffic_generator -d UHD -a clock=gpsdo on separate USRPs