With the rapid growth of wireless data services, the continuous introduction of new vacation technology and market competition from WiMAX, UMTS faces challenges in real-time data services, large data volume services, and requires continuous evolving. LTE has a spectral use, which can be seamlessly interoperable with prior art and low network deployment and management costs. A new technique can survive in the market, depending on whether the end user's recognition of this technology is whether these technologies meet the expectations of the end users. Therefore, the operator will conduct a lot of testing network equipment and mobile terminals.
The LTE terminal RF test is not only to examine the terminal RF chip indicator, but also the terminal test, and investigate the performance of the whole machine.
The overall requirements of the LTE terminal RF indicator are:
● For the transmitter, on the one hand, it is possible to generate an LTE useful signal that meets the standard requirements, and on the other hand, the useless transmit and interference level are controlled within a certain level.
● For the receiver, it is required to receive and demodulate the useful signals to be reliably, accurately received under certain environmental conditions, and also require a certain interference signal.
The LTE terminal radio frequency test item is divided into 4 most, namely transmitter indicators, receiver indicators, performance requirements, and channel status information. Although the LTE signal structure is different from UMTS, the LTE terminal radio frequency test demand substantially comes from UMTS defined radio frequency requirements, only a small number of new test items. At receiver and performance statistics, the UMTS system is measured by BER and BLERs, while the LTE system is measured by throughput. In the performance test section, the channel structure for the LTE also increases the corresponding channel demodulation performance index. In addition, for the LTE terminal radio frequency test, there is a need for a variety of bandwidths supported by the terminal, and various RB configurations, and various modulation methods are tested, and the test amount is also very huge. The following is a brief description of this 4 most test items.
(1) In the transmitter indicator, include the following types of test items:
● Project related to transmit power
Such as the UE output power, power rollback (MPR), UE configuration output power, etc. These test items are mainly to examine whether the transmit power of the terminal meets the standard requirements. If the terminal transmit power is too large, it will cause interference to other channels or systems, and the transmit power will cause a reduction in system coverage. Power Retreat is a new test item, which will be analyzed later.
● Output power dynamic range
Such as output power, transmit shutdown power, switching time template, etc. These test items are mainly to examine whether the output power range of the terminal meets the standard requirements. If the output power and the shutdown power are too large, it will cause interference to other terminals and systems. The switching time template verifies whether the terminal can open or turn off its transmitter, otherwise it will cause interference to other channels or increase the transmission error of the uplink channel.
● Power control
Such as power control, relative power control, etc. The purpose of power control is to limit the interference level and compensation channel fading of the terminal, which is mainly to verify that the terminal can set its transmit power and the transmit power is within a certain tolerance range.
● Emission signal quality
Such as frequency error, error vector amplitude EVM, carrier leak, non-allocated RB band internal emission, EVM equalizer spectrum flatness, etc. Terminal transmit signal quality is a very important indicator for examining terminal transmitter modulation performance. We know that the OFDM system is sensitive to frequency offset and phase noise. The method of dividing the various subchannels is to utilize strict orthogonality between each subcarrier. The frequency offset and phase noise will deteriorate the orthogonal characteristics between the individual subcarriers, causing the performance of the LTE system to decrease. Therefore, the frequency error, EVM, carrier leak (IQ imbalance), etc. are indicators that the LTE terminal must be investigated.
● Output radio frequency spectrum emission
Such as occupying bandwidth, spectrum emission template, adjacent leakage power ratio (ACLR), transmitter stray radiation, etc. The useful spectrum emission of the terminal must strictly meet the standard requirements, and the out-of-band transmitting and stray emissions belong to useless launch, more need to be strictly limited, otherwise it will cause serious interference to other users.
● Transmit intermodulation
When the radio frequency signal power of two or more frequencies occurs simultaneously in the passive radio frequency device, the passive intermodulation product is generated, and generally three-order intermodulation is serious. The test principle of transmitting intermodulation is to set the terminal after large transmission power, and after configuring the interference signal, it is below the limit of the ratio (unit DBC) of the utterance signal and intermodulation product in the frequency band. This test project is mainly to verify the ability of the terminal to inhibit its intermodulation products.
(2) In the receiver indicator, include the following types of test items:
● Reference sensitivity level
The ability to examine the terminal receive small signals. If the terminal sensitive degree is too poor, the effective coverage of the eNodeB will be reduced.
● Input level
The ability to examine the terminal receive large signals. If the terminal input level is unqualified, the coverage of the near-end of the eNodeB will be reduced.
● Neighboring channel selectivity, blocking characteristics, stray response, intermodulation characteristics
The above types are the reception performance of the terminal in the case of an interference signal (single sound / double sound / modulation interference). If the terminal anti-interference ability is too bad, the end receiver performance will be reduced.
● stray radiation
Expected the ability of the receiver to suppress the pneumatic signal power generated or amplified in the receiver.
(3) In the performance requirements, including the following types of test items:
● The demodulation of the PDSCH channel.
● The demodulation of the PCFICH / PDCCH channel.
● The demodulation of the PHICH channel.
● The demodulation of the PBCH channel.
The performance test part is mainly to investigate the channel demodulation performance of the LTE terminal. Performance tests are visited by satisfying SNR (signal-to-noise ratio) under certain throughput conditions.
The calculation formula of the SNR is as follows:
The representation of the received energy on the formula, indicates white noise, and the formula is represented to receive the corresponding antenna port.
Performance test parts can be divided into single antenna ports and multi-antenna (diversity, spatial interleaving, mu-mimo) associated with UE performance test. Single antenna port performance is measured by satisfying the SNR under multipath fading conditions when a certain throughput requirement. Double antenna port performance is mainly to examine the MIMO performance (diversity, space multiplexing, MU-MIMO) of the terminal, and is also measured by SNR under multipath fading conditions when a certain throughput requires.
(4) In the channel status information, include the following types of test items:
● CQI in the Additive Gaussian Noise (AWGN) environment Report.
● Reporting CQI in the decline environment.
● Pre-encoded matrix indication (PMI) reported.
● Rank Indicator Report.
This part of the test project is mainly to examine the MIMO feedback performance of the terminal. The performance test of space multiplexing can be divided into open loop and closed loop. Open MIMO, there is no prior information of the channel; the closed-loop MIMO system is the receiver feeds back channel information to the transmitting end, and then performs pre-encoding, beam forming or antenna selection. The feedback method of closed-loop MIMO can be divided into full feedback and partial feedback.
The following is an analysis and description of some of the key test items for the LTE terminal RF test.
Power rollback
LTE signal structure and R99 (WCDMA) are different, and the downlink uses OFDM signals, and the SC-FDMA signal is used uplink. Although the power peak of the SC-FDMA signal is lower than the OFDM signal, when the power peak of the SC-FDMA signal is relatively high, it means that the radio frequency power amplifier of the terminal must have a high linear linear to ensure that the terminal transmit signal is not true. However, the use of linear radio power amplifiers can cause a significant increase in the cost of the transmitter, and even if the linear radio frequency amplifier is used, it will also reduce the efficiency of the entire system. The actual system is basically the system of peak power, most actual systems in order to ensure certain efficiency, usually use nonlinear power amplifiers to zoom in using nonlinear power amplifiers under certain output power backup conditions, so inspection power rollback test items It is necessary. When the power peak of the uplink signal is higher, the power is required to return to the linear zone of the amplifier. The more the resource block (RB) is, the higher the modulation method, the greater the power return value.
Carrier leak (IQ imbalance)
IQ imbalance has a significant impact on the results of the signal quality EVM. IQ imbalance is characterized by the IQ offset of the initial constellation, due to the DC offset due to the adjustment of the DSP. The IQ two signals are zoomed separately. Since the inconsistency of the device can cause the imbalance of I and Q road gain, so that the IQ amplitude is different, so that the original constellation map will become a rectangle, that is, the same frequency point The amplitude and phase of the signal change. However, there is no related test on the R99 specification, mainly by measuring EVM to measure the modulation quality of the signal. Due to the phase and frequency offset and sensitivity of OFDM technology, the performance of the transmitter modulation can be better measured by measuring IQ imbalance.
IQ origin offset is measured with relative carrier leakage power (IQ origin shift power). Depending on the UE transmit power, the relative carrier leakage power requirement is different from -10 dBc ~ -25dBc.
Spectrum flatness
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