PS Call Performance Issues

PS call performance optimisation aims to maximise the data throughput. Throughput depends very much on the round trip time (RTT, delay from mobile, typically through USB , connector to server and back). The lower the RTT the greater the potential for higher throughput. Normally RTT is around 200ms.

Also the radio resource efficiency for certain bit rate should be optimised, such that resources will only be allocated when needed, based on the throughput demand. This can be optimised with Dynamic Link Optimisation (DyLo) feature parameters.

It should be noted that there is no optimum parameters set to be used for all networks for maximising PS throughput, but every networks needs some local optimisation.

Throughput also varies with UEs types.

Below are the throughput and efficiency specific problems and solutions, although the common call performance issues also apply.

Behaviour	Problem	Description	Possible solutions
Low Throughput	The User bit rate is much less than the Radio Bearer bit rate either in DL or UL.	The reason for lower throughput problems in file transfer is in flow control between PC and UE which could mean that TCP parameter settings are not optimum, which may cause degradation to the throughput [10]	Measure throughput and RTT. Increase TCP Window Size - RWIN in case RTT is much more than 200ms and low throughput has been achieved. In Windows 2000 the default value is 17520 Bytes. There are many tools available to change the window size, for example DoctorTCP [13]. Optimal RWIN in client = 32660 B Optimal RWIN in server = 65535 B See more in reference [11].
Low Throughput	The User bit rate is much less than the Radio Bearer bit rate in bi-directional file.	When uploads and downloads are occurring simultaneously then the TCP ACKs (for the downloading) are competing with the upload traffic to get across the PPP link between the PC and UE. This competition in combination with the flow control instigated by the UE will delay the ACK. Depending on how big the extra delay is will depend on how much TCP will be forced to slow down.	Measure throughput and RTT Increase TCP Window Size - RWIN in case RTT is much more than 200ms and low throughput has been got. In Windows 2000 this has default value of 17620 Bytes. Optimal RWIN in client = 32660 B Optimal RWIN in server = 65535 B See reference [11].
Low Throughput	The User bit rate is much less than the Radio Bearer bit rate in bi-directional file.	PC has lots of data to send in uplink direction at a rate faster than the actual radio interface between UE and BTS (=64 kbit/s). To prevent overflow, UE turns flow control on towards PC to stop data flow. The problem is that this stops also TCP ACK for downlink data, sent in uplink direction. This causes downlink throughput reduction, because TCP session (=ftp) is not receiving ACKs so quickly. The phenomenon is bigger, if the DL data rate is faster than UL data rate.	Measure throughput and RTT Increase TCP Window Size- RWIN in case RTT is much more than 200ms and low throughput has been got. IWindows 2000 as default value of 17620 Bytes. Optimal RWIN in client = 32660 B Optimal RWIN in server = 65535 B See reference [11].
Low Throughput	The User bit rate is much less than the Radio Bearer bit rate either in DL or UL.	The reason for lower throughput problems in file transfer could be wrong parameters in server.	Tune TCP parameters in the Server: MSS = Maximum Segment Size (in bytes) = TCP payload MTU = Maximum Transmission Unit (in bytes) = IP packet size MTU = MSS + TCP Header (20 bytes) + IP Header (20 bytes) Optimal MTU in client and server =1460 Bytes
Low Throughput	The User bit rate is much less than the Radio Bearer bit rate in bi-directional file	There is Problem in FTP server	Change the FTP server. In general FTP server should be located right after the GGSN (not behind the public internet) so it would be recommended to have test FTP server located right to the GGSN. Make several FTP sessions instead of one to increase the throughput. Try with stream e.g. http//wwitv.com
Low Throughput	The User bit rate is much less than the Radio Bearer bit rate in bi-directional file	Bluetooth connection has been used between UE and PC.	Use USB connection instead of bluetooth.
Low Efficiency	BTS Power resources are wasted in case high bit rates are used but throughput is low.	Dynamic Link Optimisation (DyLo) parameters are not set optimum.	Adjust the PtxDLAbsMax parameter (default value 50 dBm as maximum link power, optimum setting between 35-37dBm) to trigger DyLo earlier.