Patent Application
20150031310
The subject matter described herein relates to testing communications network equipment. More particularly relates to methods and systems for simulating per-UE Doppler shifts for testing air interface devices.
In mobile communications networks, fixed network equipment, such as evolved Node Bs (e-Node Bs) communicates with mobile UEs over the air interface. Because UEs move relative to the fixed network equipment, Doppler effects can cause frequency shifts in uplink signals transmitted from the UEs to the fixed network equipment. For example, if a UE is in a car moving towards or away from the e-Node B, Doppler shifts affect the frequency of the signals transmitted from the UE to the e-Node B and the reception of the signal from the e-Node B to the UE. Because multiple UEs may be present in an area served by an e-Node B, and the UEs may be moving at different speeds and directions, the Doppler effects on the signals to and from the UEs vary.
It is desirable to test the functionality and performance of air interface equipment in response to Doppler effects on signals to and from the UEs. However, conventional communications network test equipment is only capable of applying the same Doppler shift to a group of UEs. There is no ability to apply Doppler shifts on a per-UE basis. Thus, the test environment does not accurately reflect the real operating environment.
In light of these difficulties, there exists a need for methods, systems, and computer readable media for simulating per-UE Doppler shifts for testing air interface devices.
The subject matter described herein includes methods, systems, and computer readable media for simulating per-UE Doppler shifts. One exemplary method includes generating uplink signals to be transmitted from a plurality of different simulated UEs to an air interface device under test. The method further includes applying per-UE Doppler shifts to the signals, wherein applying per-UE Doppler shifts includes applying different Doppler shifts to at least some of the signals. The method further includes transmitting the signals to the air interface device under test.
The subject matter described herein for simulating per-UE Doppler shifts for testing air interface devices may be implemented in hardware, software, firmware, or any combination thereof. As such, the terms “function” or “module” as used herein refer to hardware, software, and/or firmware for implementing the feature being described. In one exemplary implementation, the subject matter described herein may be implemented using a computer readable medium having stored thereon computer executable instructions that when executed by the processor of a computer control the computer to perform steps. Exemplary computer readable media suitable for implementing the subject matter described herein include non-transitory computer-readable media, such as disk memory devices, chip memory devices, programmable logic devices, and application specific integrated circuits. In addition, a computer readable medium that implements the subject matter described herein may be located on a single device or computing platform or may be distributed across multiple devices or computing platforms.
Preferred embodiments of the subject matter described herein will now be explained with reference to the accompanying drawings, wherein like reference numerals represent like parts, of which:
The subject matter described herein includes methods, systems, and computer readable media for applying per-UE Doppler shifts to uplink signals to test an air interface device.
Network equipment test device 100 may be a multi-UE simulator that simultaneously simulates multiple UEs, such as long term evolution (LTE) or LTE advanced UEs. In the illustrated example, network equipment test device 100 includes an uplink signal generator 104 for generating uplink signals from simulated UEs to be transmitted to device under test 102. Uplink signal generator 104 may generate LTE, LTE advanced, and other uplink signals to test the functionality and performance of device under test 102. Uplink signal generator 104 may generate reference signals, control signals and data signals to simulated uplink transmissions by UEs.
Network equipment test device 100 further includes a plurality of per-UE Doppler shifters 106 for applying Doppler shifts to uplink signals on a per-UE basis. Because Doppler shifts are applied on a per-UE basis, different Doppler shifts can be applied to signals from different UEs. As a result, the test environment generated by network equipment test device 100 more accurately simulates a real network environment where Doppler shifts vary.
After subcarrier mapping, the entire uplink signal is in the frequency domain. However, the signal must be converted to the time domain before being transmitted over the air interface. Accordingly, the signal undergoes inverse fast Fourier transform 214 and cyclic prefix (CP) insertion 216 before the signal is provided to radio head 218 and then either transmitted wirelessly over the air interface to a device under test or over a simulated air interface using cables to the device under test. In conventional multi-UE simulators, the Doppler shift was applied either after CP insertion 216 or after processing by radio head 218. Such Doppler shift was applied to the entire signal such that all UEs were shifted the same. These two conventional methods for Doppler shifting are represented in
In order to avoid the shortcomings of wideband Doppler shifting, the subject matter described herein includes per-UE Doppler shifting of uplink signals.
Doppler shift to the uplink signal for each UE. The per-UE Doppler shifters 106 apply Doppler shifts to the time domain uplink signals prior to discrete Fourier transform and subcarrier mapping. In addition, per-UE Doppler shifts are also applied to the reference signal for each UE. Because Doppler shifts are applied on a per-UE basis, different Doppler shifts can be applied to signals from different UEs. For example, a signal for one UE may be Doppler shifted to indicate that the UE is traveling towards the device under test at a certain rate of speed. A Doppler shift for another UE may be applied to simulate the UE traveling away from the device under test at a certain speed. Applying per-UE Doppler shifts can be performed in software or hardware in the uplink signal chain of network equipment test device 100 without requiring a conventional wideband Doppler shifter.
An uplink signal for a single UE can be represented in the time domain by:
Acos(2πf t), (1)
where A is the amplitude and f is the frequency of the uplink signal. Applying a per-UE Doppler shift may be accomplished by changing the frequency of the uplink signal according to one of the Doppler shift equations, depending on whether the UE is being simulated as moving towards or away from the device under test. If the UE is being simulated as moving towards the device under test, the new frequency of the uplink signal for that UE may be calculated as follows:
f′=(V/(V−Vs))*f, (2)
where v is the velocity of light in air, vs is the velocity of the moving source (the UE being simulated), and f is the original frequency of the uplink signal. Thus, the time domain equation for the Doppler shifted source signal becomes:
Acos(2πf′t), (3)
where f′ is the Doppler shifted frequency for the uplink signal. To simulate different frequencies for different UEs, per-UE Doppler shifters 106 may use different values of vs to simulate different UE velocities when moving towards the device under test. Similarly, to simulate per-UE Doppler shifts when the UE is moving away from the device under test, per-UE Doppler shifters 106 may utilize the following equation to compute the Doppler shifted frequency of the uplink signal:
f′=v/(v+vs), (4)
where v is the speed of light in air, vs is the velocity of the moving source (the UE being simulated), and f is the original frequency of the uplink signal. Thus, by using equations 2-4, and varying the value of vs, per-UE Doppler shifters 106 may simulate per-UE Doppler shifts with different amounts and directions of frequency shift for different UEs.
It will be understood that various details of the subject matter described herein may be changed without departing from the scope of the subject matter described herein. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation.
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/859,771, filed Jul. 29, 2013; the disclosure of which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61859771 | Jul 2013 | US |
