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Can You Schedule Me Now: A Detailed Analysis of How Enodebs Schedule Multiple Devices in a Commercial LTE Network
Signals Research Group, LLC, Dec 2010
With 2x10MHz or 2x20MHz of spectrum and an unloaded network, LTE can deliver incredibly high individual user data rates. At a minimum the data rates should be 8x higher than what is possible with HSPA+ (4x with MIMO) and 16x the data rates achieved with EV-DO Rev A. If LTE is to be a key differentiator that it must also support a large number of users, each consuming a more modest amount of bandwidth. This requirement is especially important for applications, such as VoIP. Unfortunately, while today’s LTE networks deliver very high individual data rates, they do not necessarily do so in an efficient manner. Without the proper test equipment, these inefficiencies could go unnoticed until the network started experiencing higher volumes of traffic.
For this research project the publisher collaborated with Sanjole, a leading supplier of LTE and Mobile WiMAX test equipment. By using its WaveJudge 4900 LTE Analyzer the publisher was able to analyze how some of today’s commercial eNodeB schedulers assign network resources at a 1ms sub-frame level across multiple devices that are simultaneously requesting network resources.
Key Conclusion. The publisher conclude that while the performance of an individual device can be stellar, work remains before they can make a similar claim about the overall performance of an LTE network, especially a network that is supporting lots of subscribers – something that has yet to occur. Further, it is possible to demonstrate that the user experience is being impacted in the form of higher latency and lower data rates, even in lightly loaded network. It is just that the user isn’t aware it is occurring.
In summary, the WaveJudge solution captures everything that the eNodeB sends and receives. Although it obviously isn’t seeing the actual data, it does capture how much data is being sent in each sub-frame – both downlink and uplink – for each device that is connected to the eNodeB. Further, it is also possible to “see” the frame structure of the control channel overhead, which is buried within each sub-frame. Examples of data that the publisher collected and analyzed include:
- Downlink/uplink throughput in each sub-frame – by device and combined throughput
- Percentage of resource blocks (RBs) used/not used in each sub-frame
- Modulation type assigned in each sub-frame – by device
- Amount of data sent in each RB – by device
- “Fairness” of the scheduler to serve all devices
- Percentage of network resources used for overhead
- OFDMA versus SC-FDMA
- Availability of MIMO (Rank Indicator 1 and Rank Indicator 2) – by device
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