You can use this analysis to examine the data service performance of your network. Typically this will be for an HSPA network, probably working in conjunction with some legacy UMTS or GPRS areas.
Note that for this functionality to be available, you will need to have selected a template that includes Data Service Analysis when you create your Spotlight project.
8.2.1 Using the Data Service Analysis Page
2 The panel reports on the following issues:
Service Setup Failure Rate - Service is used to refer to the end-to-end connection between the UE and the core network. A Service Setup Failure is detected when the UE attempts - but fails - to get an IP address (for instance, if a PDP Context Activation procedure fails).
Service Drop Rate - A Service Drop is detected when the UE loses the end to end connection to the core network (for instance, after a Routing Area Update procedure failure).
Task Failure Rate - Task is used to refer to any data upload ordownload; for example, an FTP ‘put’ or ‘get’, browsing a web page or a ‘ping’ test. A failure is detected when the Task did not complete (for instance, if the UE failed to download a file in case of a FTP DL test).
Percentage of FTP or HTTP upload or download tasks below the absolute threshold value - This corresponds to Tasks for which the average throughput was less than a configurable threshold*.
Percentage of FTP or HTTP upload or download tasks below the composite threshold value - This corresponds to Tasks for which the average throughput was less than a technology dependant threshold*. The technology threshold is derived by Analyzer from a set of configurable technology thresholds based on the time the UE spent on each technology. *Make sure that you set the Data Service Analysis thresholds to suit yourrequirements before loading the data. To set the thresholds, from the top menu select Tools > Display Thresholds and go to the Data Service Analysis section.
As an example of how the composite threshold value is calculated, consider a data download Task where the UE spends 80% of the time in Cell_DCH R99 and 20% in HSPA. The composite throughput threshold is:
(80% x ApplicationLowTput_UMTS_DL_Threshold) + (20% x Application_LowTput_HSDPA_DL_Threshold)
Note the dropdown selector at the top of the left hand panel. This allows you to select one of several Analysis pages:
DSA Failures (the default page, shown above)
DSA All Services and Tasks2
From the DSA All Services and Tasks page, you can click on the Display All links to view the related Event Explorer view. The following example screenshot shows the Event Explorer view for the FTP DL link Display All 57 Tasks:
2 To better understand the situation, the user has sorted the table on the left by
Status. The Status codes are: D - Drop
C - Cancelled by user
I - Interrupted (unknown whether this failed or not) OK - Successful task
To identify worst/best performing tasks, you could also sort by Throughput. Scrolling down the left hand panel, you can see useful data service statistics. The information displayed depends on the task type (upload or download), as well as the technologies that the UE experienced during the task.
2 Once you find an interesting task (for instance, a low throughput task, or task
with multiple Radio Access Technologies), you can select the box next to it and complete the Drilldown section to define the data that will be included in the drilldown.
2 When the drilldown processing has completed, you will see a drilldown analysis
page similar to this:
If you want to return from a drilldown, go to the top of the left panel and click on the Event Explorer link.
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8.2.2 Example of a good HSPA+ task
In this HSPA+ example, we can see that the UE is in HSPA+ mode throughout, that 64QAM modulation usage is high throughout, and CQI, CPICH EcN0, and CPICH RSCP are all good, whereas frame usage, HSDPA codes and throughput are all erratic. Note also that the throughput does spike at > 10Mbps.
From these observations we can conclude that:
The radio conditions were good throughout this section of drive, allowing for maximum download data rate. In these conditions the UE could have achieved ~10 Mbps.
Although on average the throughput is about 4.5 Mbps, instantaneous throughput measurements are erratic, ranging from 0 to 10 Mbps. This behavior is symptomatic of a buffer filling / emptying somewhere along the data transmission chain. The cause could be that the FTP server cannot sustain more than 4 Mbps on average, resulting in ‘bursty’ data transmissions on the air interface.2
8.2.3 Example of a MIMO HSPA+ FTP download
There are three areas of interest in this example:
MIMO statistics
Modulation
TCP slow start MIMO statisticsNote that the application throughput is ~5 times lower than the HSDPA L1 data rate: this is because in this log files, there were 5 simultaneous FTP downloads. In this case, since the UE has been configured to MIMO during the task, the side panel also shows HSPA+ MIMO measurements statistics. HSPA+ can either be in MIMO mode or non-MIMO mode, and if in MIMO mode, it can be using 1 transport block (diversity mode) or 2 transport blocks (spatial multiplexing mode). These statistics are measured from the portion of the task where the UE is configured in MIMO mode:
MIMO configuration (%) - This is the ratio of: the number of HSDPA subframes received when MIMO was configured, to the total number of HSDPA subframes received.
MIMO CQI Average - This is the average of the CQI measurements sent whilst the UE is in MIMO mode.
Usage (% frames) - This is measured from subframes received in MIMO mode. It indicates the percentage of subframes in MIMO mode for which a single transport block was received, and the percentage for which two transport blocks were received.
NACK Rate (%) - In MIMO mode, this indicates the HSDPA NACK rate measured from subframes where a single transport block was received, and where two transport blocks were received.
Data Rx (%) - In MIMO mode, this indicates how much data wasreceived on a single transport block transmissions, and how much on two transport block transmissions.
TB Size Avg. (bits) - In MIMO mode, this indicates the average number of bits received per TTI.2
In this task we see the following:
In MIMO mode, spatial multiplexing was used 34.16% of the time.
The HSDPA NACK rate is high in MIMO mode and also significantly higher with spatial multiplexing than with diversity: possibly the Node B settings should be changed to reduce the NACK rate.
Although the UE received two transport blocks in MIMO mode 34.16 % of the time, it amounted to 48.80 % of the data received: spatial2 Modulation
A quick analysis of the HSDPA radio chart tells us that there is a situation involving modulation usage.
We can break down this task into three periods (labeled in the screenshot): 1 During this first period, the UE is configured for MIMO, during which the
UE sometimes benefits from MIMO spatial multiplexing configuration. The best modulation is then 16 QAM, because this 3GPP release 7 handset cannot use both MIMO and 64 QAM modulation at the same time.
2 During this second period, the UE is not configured for MIMO and uses 64 QAM.
3 During this third period, the radio conditions degrade to a point where the UE is virtually only using QPSK modulation. Eventually the RRC connection drops, and the data transfer fails.
2 TCP Slow Start
We can see that after most of the HSPA cell changes, the HSDPA data rate and the number of HSDPA codes allocated to the UE both drop to a low value and then slowly ramp up. This is a typical effect of TCP flow control after a
reconnection, known as TCP slow start.
8.2.4 Example of a problematic HSDPA task
This HSDPA example highlights three problems. These problems are presented in a declining order of importance (problem 1 being the most significant), based on the proportion of the call where these conditions were occurring.
Problem 1 – UE spends time in DCHR99 mode
Problem 2 – congestion causing low HSDPA frame usage2 Problem 1 – UE spends time in DCHR99 mode
Here we can see periods were the CPICH EcN0 is low and the UE is in Cell_DCH R99 mode. The downlink throughput achieved during these periods is very low compared to what can be achieved in HSDPA mode. The transition to Cell_DCH R99 mode could be caused by the poor radio conditions, or possibly the maximum number of concurrent HSDPA users has been reached on this site.
2 Problem 2 – congestion causing low HSDPA frame usage
In this case, although there are good radio conditions (high CPICH EcN0), HSDPA is being used and the UE is allocated a large number of HSDPA codes when scheduled, the frame usage is very low. This is likely to be the result of congestion.
2 Problem 3 – low modulation order
In this last case, there are periods of high throughput coinciding with good CPICH EcN0 and high 16QAM modulation usage, but there are also periods where the opposite is occurring. In the latter case, the low modulation order is likely to be responsible for the low throughput.
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8.2.5 Example of a reasonable LTE task
In this LTE example, there is a high (> 10 Mbps) throughput, CQI is at maximum throughout the call, spatial multiplexing usage is good at > 80%, and system bandwidth allocation is good at > 80% (40 Resource Blocks in this case). However, the frame usage is only ~50%, which is probably due to a bottleneck along the data transmission chain – that is, some equipment or data link cannot support a throughput higher than 10 Mbps.
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