Low TCP Throughput Over LTE on "lena-radio-link-failure"

[Andy]

Hello,

   As I understand that applying TCP over LTE might experience throughput issues contributed by RLC UM buffer overflow and/or HARQ, I would like to fix these problems by correctly addressing them on the code. However, it seems like these fixes do not work. Could some experts enlighten me on what I should do now?

   * My research so far: 

a) The default value (8.3e-5) of the inter-packet interval (double interPacketInterval) of UDP is derived from the DataRate (98.6 Mbps). Should I tinker with the "Interval" to other values like "0.001", "0.00001", the TxOffered/throughput of UDP will be around 0.

b) This indicates the inter-packet interval is of utmost importance to maintain the TxOffered/throughput. As both OnOffHelper and BulkSendHelper of TCP do not support the interval feature, I resorted to apply the RLC UM buffer (1024 * 1024 by default) and the HARQ. However, they do not work.

   * Note: The enclosed code is altered from "lena-radio-link-failure.cc" which contains the following modifications:

1. Header files to include the Flow Monitor.

2. Channel bandwidths from 5 MHz to 20 MHz.

3. Enabled HARQ.

4. Changed the DLPort to 80 and commented out the UPPort.

5. Increased the data rate to 98.6 Mbps (Works only on UDP).

6. Commented out the DL and UL port changes and the default UDP code worked fine with the expected TxOffered (98.6 Mbps).

7. Replaced the UDP code to the TCP one with "OnOffHelper" and the throughput was almost 0 Mbps (Sent only 224 packets within 60 seconds).

8. From 7., replaced the UDP code to the BulkSendHelper... The result is identical to 7. for the same sent number of 224 packets.

9. Uplink disabled for simplicity purposes.

10. Flow Monitor code.

Please enlighten me on what I should do to rectify the TCP throughput issue.

Thanks! Much appreciated!

Regards,

Andy