Lauro joined Award Solutions in 2008, bringing over ten years of experience in the wireless telecommunication industry working with mobile cellular, broadband and satellite communications. Has a thorough knowledge and understanding of all standardized radio transmission technologies (i.e.: GSM, GPRS, EDGE, WCDMA, HSxPA, HSPA+,IS-95, cdma 1xRTT, 1xEV-DO) and non-standardized technologies (i.e.: Flash OFDM, I-Burst, etc.) as well as and their migration path to 4G and beyond (LTE and WiMAX).
Lauro has co-authored four different telecommunication books, has published 18 international refereed journal papers and over 30 international conference papers, all of them results of research in the wireless telecommunication area. Additionally, has presented over 20 different wireless related courses nationally and internationally to a diverse class of clients. Lauro has a thorough knowledge of mathematical analysis and hands-on experience on wireless and traffic engineering design, including Design, Planning, Performance & Optimization as well as computer simulation of mobile wireless networks. Through research and computer simulation techniques has helped a large base of clients (carriers, vendors, new start up companies) develop optimum technological solutions.
Currently, Lauro is one of the instructors at Award Solutions. His current focus is UMTS, HSPA/HSPA+ and LTE. He is also involved in the development of cutting edge training on optimization courses for LTE operators in the USA.
Lauro holds a Ph.D. in electrical engineering (EE) from King's College London, UK (the University of London), a MSc. In EE. and a B.EE from the National Polytechnic Institute, Mexico, all of them with specialty in telecommunications.
In this blog we will briefly describe general troubleshooting guidelines for downlink throughput in LTE networks with MIMO 2x2. The reader is advised to look for particular counters in their respective OEM’s documentation to address each of the fields explored below.
The general troubleshooting strategy is described below and the covered reasons for bad throughput are shown in the figure below.
Figure 1. Low Throughput causes in the Downlink for LTE networks.
Step 1: Identify cell with low DL (downlink) throughput
a) The first thing is to identify those cells with low throughput. This threshold is defined by your network policies and practices (it also depends on your design parameters). Reports should be run for a significant number of days so that data is statistically valid.
Step 2: Identify Downlink interference
a) Cells with downlink interference are those whose CQI values are low (an exception to this rule is when most traffic is at the cell edge –bad cell location-). Analyze the CQI values reported by the UE for
Typical values for transmit diversity oscillate between 7 and 8.
Typical values for MIMO one and two layers oscillate between 10 and 12.
b) If low CQI values are found after a CQI report is obtained, then downlink interference might be the cause of low throughput.
c) Common sources of interference in the 700 MHz band (LTE deployment in the USA) are: inter-modulation interference, cell jammers and wireless microphones
Step 3: BLER Values
a) Run a report for BLER in the cells identified. The BLER should be smaller or equal than 10%. If the value is larger, then, there is an indication of bad RF environment.
b) Typical causes of bad BLER are downlink interference, bad coverage (holes in the network, etc.)
Step 4: MIMO Parameters
a) Identify the transmission mode of your network. There are seven transmission modes as shown in the table below
b) Adjust the SINR thresholds for transition of transmission modes as recommended by the OEM. Request the Link Level simulations they used to set these thresholds and see if the conditions under which the values were calculated apply to your network. Otherwise, update them if the parameters are settable and not restricted.
Step 5: Low Demand
a) Run a report using the counters provided by the OEM to find
b) If the maximum number of RRC connections active per cell is close or equal to the maximum number of RRC connections supported, then. The cause for low throughput is load.
c) A high number of scheduled users per TTI does not necessarily mean that demand is the cause for low throughput.
Step 6: Scheduler Type
a) Find the scheduler types your OEM supports
b) Select the one that is more convenient for the type of cell you are investigating. Examples of schedulers are: round robin, proportional fairness, maximum C/I, equal opportunity, etc. OEMs allow you to switch the scheduler in your network but recommend one in particular.
c) The wrong scheduler may be the reason for bad throughput.
Step 7: CQI reporting parameters
a) Check if your network is using periodic or aperiodic CQI reporting (or both).
b) Verify the frequency in which the CQI reporting is carried out for periodic reporting as well as the maximum number of users supported per second.
c) If the value is too small compared with the maximum number of RRC active connections, then, increase the values of the parameters CQIConfigIndex as well as RIConfigIndex (deal with in future blog).
d) If your network is not using aperiodic CQI reporting, then enable it.
e) Slow frequencies of CQI reporting might yield bad channel estimations that prevent the eNodeB from scheduling the right amount of data and Modulation and Coding Schemes to UE.
Step 7: Other
a) Run a VSWR report or ask your OEM to run it for you.
b) High values of VSWR result in low throughput due to losses.
c) Check your backhaul capacity. Often times, the backhaul links are shared among multiple RATs. Make sure your backhaul is properly dimensioned.
At the end of this methodology, you will be able to determine if the reasons for low throughput in your cells is one of the following or a combination, thereof:
- BLER (bad coverage)
- Downlink Interference (Bad CQI)
- MIMO Parameters
- Scheduling algorithm
- Low Demand
- CQI reporting frequency
- Other (VSWR, Backhaul capacity)