Maximizing Gazelle Data Throughput

[jcondon]

I'm looking to maximize the throughput using Gazelle on the nRF51.

Assuming zero retransmissions, I believe the theoretical max should be (1/TimeslotPeriod)*PayloadSize which would be 35.5kBps (284kbps) for my current settings.

Setup:

• One nRF51 Dongle as Device
• One nRF51 Dongle as Host
• SDK 8.1
• Very Close Range (RSSI ~ -51dBm)

Radio Parameters:

• Data Rate = 1Mbps
• Timeslot period = 900uS
• Sync Lifetime = 40 timeslots
• Packet Size = 32 bytes
• Timeslots per Channel (see below)
• 15 channels randomly generated per FCC 15.427 requirements
• Ch Selection Policy = USE_CURRENT

Transmit Code:

while(nrf_gzll_ok_to_add_packet_to_tx_fifo(PipeNum) && buf->getCount() > 0){
   TxCount = buf->getCount();
   PayloadLen_Tx = ( TxCount > NRF_GZLL_CONST_MAX_PAYLOAD_LENGTH )?NRF_GZLL_CONST_MAX_PAYLOAD_LENGTH:TxCount;
   buf->pop( NRF_TxBuf, PayloadLen_Tx); // Move the Tx bytes to byte array

   result = nrf_gzll_add_packet_to_tx_fifo( this->PipeNum, NRF_TxBuf, PayloadLen_Tx);	
   if(result == false){
       TxErrCnt++;
    }
       Tx_ErrCode = nrf_gzll_get_error_code();
       nrf_gzll_reset_error_code();
 }

Results:

My throughput seems to be dependent on number of timeslots per channel. Here are my results:

• 5 slots/ch -> 7.2 kBps (57.6 kbps)
• 4 slots/ch -> 9.0 kBps (72.0 kbps)
• 3 slots/ch -> 11.2 kBps (89.6 kbps) *bounces between 10.5 and 11.7 kBps
• 2 slots/ch -> 11.7 kBps (93.6 kbps) *Looses Sync periodically
• 1 slots/ch -> Not Stable

Is there anything I can do to improve throughput?

Thanks!

[Brian]

Hey guys, I have a similar setup (code below on device side), with the Gzll parameters printed out below: However, I'm only able to get a throughput of 41kpbs. What might I be missing here? Thanks!

    while(ImageTxIdx < ImageDataSize){

      if(nrf_gzll_ok_to_add_packet_to_tx_fifo(PIPE_NUMBER)) {

          for(uint8_t i=0;i<32;i++)
            data_payload[i] = ImageData[ImageTxIdx++];

          ret = nrf_gzll_add_packet_to_tx_fifo(PIPE_NUMBER, data_payload, 32);

          if(ret == false){
            TxErrCnt++;
            SEGGER_RTT_printf(0, "TxErrCnt:%d\n", TxErrCnt);
          }                                                                                                       
      }
    }

//device

nrf_gzll_get_datarate: 2

nrf_gzll_get_timeslot_period: 600

NRF_GZLL_CONST_MAX_PAYLOAD_LENGTH: 32

nrf_gzll_get_timeslots_per_channel: 2

nrf_gzll_get_sync_lifetime: 30

nrf_gzll_get_channel_table_size: 5

nrf_gzll_get_tx_power: 1

//host

nrf_gzll_get_datarate: 2

nrf_gzll_get_timeslot_period: 600

NRF_GZLL_CONST_MAX_PAYLOAD_LENGTH: 32

nrf_gzll_get_timeslots_per_channel: 2

nrf_gzll_get_sync_lifetime: 30

nrf_gzll_get_channel_table_size: 5

nrf_gzll_get_tx_power: 1