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ANALYSIS OF THE FUNDAMENTAL LIMITATIONS OF THE M AXIMUM DATA RATE IN THE LTE-ADVANCED NETWORK
Alexander S. Konstantinov,
Moscow Technical University of Communication and Informatics (MTUCI), Moscow, Russia, blackcron@gmail.com
Alexander V. Pestryakov,
Moscow Technical University of Communication and Informatics (MTUCI), Moscow, Russia, a.v.pestryakov@mail.ru
Keywords: LTE-Advanced, Noise Figure, Y-factor, SINR, the Shannon limit, throughput, Error Rate.
In order to adequately assess the LTE-Advanced data rate, it is necessary to perform testing in real-world conditions using certified measuring equipment and taking into account the influence of the environment. The main factors limiting the communication chanel data rate are the bandwidth and the ratio of signal power to noise power. In order to correctly interpret the test results, it is necessary to take into account all the noise components, including the contribution of the measuring equipment. A correct estimate of the degree of influence of the deviation of the temperature conditions from the declared in the datasheet on the noise parameters (DANL, Displayed Average Noise Level) of the measuring receiver is possible only on the basis of the results of the preliminary measurements of the noise parameters of the receiver itself under the same conditions, since the documentation gives one worst value of the DANL for a range of temperatures at specific frequencies. This will reveal additional factors contributing to the degradation of data rate, with a view to their subsequent elimination.
Для цитирования:
Константинов А.С., Пестряков А.В. Анализ фундаментальных ограничений максимальной скорости передачи информации в сети LTE-Advanced // T-Comm: Телекоммуникации и транспорт. 2017. Том 11. №12. С. 60-63.
For citation:
Konstantinov A.S., Pestryakov A.V. (2017). Analysis of the fundamental limitations of the maximum data rate in the LTE-Advanced network. T-Comm, vol. 11, no.12, рр. 60-63.
Introduction
The need for ultra-high data rates in mobile communication networks is due to the rapid growth in the use of various services: streaming video, high-speed upload of user content to social networks, ultra-high quality video communication in real time and many others. The use of these services in the modem world often takes place outside of any premises, and this imposes restrictions on the use of a familiar networking standard, Wi-Fi and other si alio nan,' solutions. Faster time to market for new custom mobile devices, all with big screens, big processing power and increasing memory capacity, dictates certain requirements to the speed of transfer of the full amount of information from one device to another when the user wants to replace its own equipment regardless of the location. The development of transport systems and the introduction of ultra-fast public transport will also impose conditions on the quality of services while moving at speeds constituting a few hundred kilometers per hour. To meet the need of users operators implement the new standards and use new technologies to ensure stable and high-quality communication in conjunction with high speed rate of data transmission. The most modern mobile communication standard that provides compatibility with previous generation mobile communication systems today is LTE-Advanced, This standard is updated periodically, introduced the use of new technologies and improved algorithms for radio resource management, which should ensure the smooth operation of user equipment in different environmental conditions guaranteed by the standard speeds. However, obtained in practice, the speed is always lower than the values obtained in the laboratory.
The main factors influencing the data rate
Specification 3GPP TS 36.306 [1) (release 13.3.0, September 2016) identified 20 categories for user equipment with support for data rate in a downlink to 3.133248 Gbit/s for 256QAM and 15 categories for user equipment support data rate in uplink to 1.198208 Gbit/s using 64QAM, These values are given for eases using antenna schemes M1MO 8x8 in downlink and MIMO 4x4 in uplink.
In accordance with the Shannon-Hartley theorem tells the maximum rale ai which information can be transmitted over a communications channel of a specified bandwidth in the presence of noise, the parameters, ceteris paribus influencing the speed of transmission are the channel bandwidth and the ratio of signal power to noise in the channel [2]:
C = W ■ log J H——•]• B\ W-N)
where
C - maximum throughput in bps;
W—bandwidth in Hz;
p
!_ — Signal to Interference Noise Ratio (SINR).
N
To maximize the bandwidth in LTE-Advanced, the technology of combining carriers from different frequency bands (Carrier Aggregation) is introduced. And lo optimize the SINR is unambiguous there is no solution - every developer of communications systems sees the optimization of this parameter on its own. The most popular solutions today are: increase the transmit-
ter power; increase the receiver sensitivity; use of error-correcting coding; use of Bcamforming; use of Coordinated Multi Point (CoMP); use of different antenna Transmission Modes (TM) for the respective terms of service; use of a cyclic prefix.
The influence of the measuring system
To measure the contribution of a particular technology or solution to the resulting signal-to-noise ratio, measuring equipment contributing its share of noise is used, which complicates the process of interpreting the measurement results. Spectrum analyzers used as measuring equipment have a specified noise figure level specified in the documentation [41 for the temperature range, But such information is incomplete because it indicates only the worst value corresponding to the highest value of the temperature at which the Noise Figure (NF) of analyzer was measured. Since taking measurements in real conditions requires taking into account the specific ambient temperature, in order to take into account the effect of the measuring system on the results obtained, it is necessary to correctly determine the values of the system's NF.
The evaluation of the impact measurement system
Studies have been conducted in measuring NF using flic following methods: when connected agreed load mechanical calibration kit to the spectrum analyzer input and the use of the noise generator. During the experiments, we used spectrum analyzer Rohde&Schwarz FSW and noise generator Keysight 346C. The studies were conducted at a frequency of 1 GHz at an ambient temperature of 297.15 K. This frequency was chosen for the convenience of comparing the values obtained with the values given in the FSW specifications for the NF.
The measurements of the first method DANL in the band I Hz when attenuator is switched off and the preamplifier is switched on made -165.44 dBm. In the FSW specification for the same frequency and under the same conditions, but for the temperature range from 278.15 to 313.15 K., only one guaranteed value of DANL = (-165) dBm is specified. Since the noise level increases with increasing temperature, this value is given for the worst case - for the temperature T = 313.15 K. We calculate the NF by the well-known formula [3J:
№ = £-io.igi^-Jl-io.iog,„(e)
J , (i)
where
L - measured DANL,
k- Boltzmann constant,
B - the equivalent noise bandwidth of a Normal filter with corrective factor 1.065 [3J.
As a result of calculation we get NF = 8.16 dB.
The measurements of the second method we use the method of Y-factor. Measure the DANL value when connected to the noise generator turned off and on states - in the band of I Hz attenuator is switched off and the preamplifier is switched on DANLoff = -164.54 dBm and DANLon = -158.31 dBm. Calculate Y-faclor by the well-known formula [3]:
Y =-158.31 - (-164.54) = 6.23 dB.
7T>
At I GHz the 346C has a claimed value of the ENR = 14.75 dB (Excess Noise Ratio) [5]. Calculate the value of NF by the well-known formula [3]:
(EHR)
NF = 10■lg
10
10'
(2)
The calculation produces a value NF = 9.7 dB.
Compare the measured by formulas (1) and (2) values with those specified in the documentation [4]. To recalculate the DANL value into the NF value in the Rohde & Schwarz calculator, it is proposed to use the formula (1). As a result, we obtain for DANL = (-165) dBm one value NF = 11.22 dB, corresponding to temperature T — 313.15 K.
When comparing the measured values of the NF with the worst-case declared in the specification, the discrepancy is 1.5 to 3.06 dB. At the decision of the majority of measuring problems the approach taking into account the worst values of parameters of the measuring equipment allows to conduct tests adequately. But when measuring the maximum data rate in the LTE-Advanced in real conditions, it is necessary to take into account the NF of the measuring receiver (spectrum analyzer) al a specific ambient temperature, so as not to miss additional factors |6, 7].
w 11
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iooai<i->io'icii»»t f • yv' 69.189 6
// //
I //
//
/
7 1 1
-32 * !S I 0 a f4 j*
Figure 1. Dependency charts of maximum bandwidth (y, Mbps) " from SINR (x, dB)
To make a clear estimate of the discrepancies obtained in the experiment, let us estimate the difference in the maximum Shannon throughput for the value of the NF = 11.22 dB declared in the datasheet for FSW and calculated above for T = 297.15 K, which is closest to the claimed value, NF = 9.7 dB, taking into
account the change in the power level of thermal noise with temperature changes, all other conditions being equal in the 20 MHz bandwidth (with a temperature change of 313.15 - 297.15 = 16 K the thermal noise power will change 1.05 times). Dependency charts are shown in Figure 1, where yellow plot is the plot with the real noise contribution FSW (at T = 297.15 K), and blue plot is the plot with the noise contribution FSW declared in the datasheet.
It can be seen from the charts that for SINR = 10 dB, the difference in the maximum throughput is more than 7.7 Mbps, and this is when testing with one antenna (it is possible to use Ml MO schemes with the number of antennas up to 8x8 in the downlink) and without manipulation use modulation types from QAM-4 to QAM-256). We also take into account that initially the minimum from the range of the values obtained in the experiment was taken as the discrepancy with the declared discrepancy in the datasheet.
Summary
The obtained values are of great importance in the testing of LTE-Advanced data rate, because here one of the most difficult is the question of the criteria for evaluating the results of measurements. Each manufacturer of radio equipment offers its own approach to solving this issue. However, the 3GPP specifications already describe a bandwidth measurement technique for assessing the network's ability to provide subscribers with user traffic (F/TS! TS 136.521-1 V14.3.0, Annex G). The bandwidth is estimated by the error rate (FR, Error Rate), which is calculated by the number of messages sent by the receiver to the transmitter on the feedback loop about the acknowledgment of the delivery of each sub frame (ACK - in case of successful decoding; NACK -in case of unsuccessful decoding; DTX - ¡n case of a break in the transfer):
_ NACK + DTX ~ NACK + DTX + ACK
ER = 0.01 corresponds to 99% of the maximum throughput of the channcl. For testing in the specifications, recommendations are given for setting the parameters of the reference channels on the transmitting side in accordance with ETSI TS 136.141 V14.4.0, Annex A. But when testing using a spectrum analyzer without considering the actual NF of the analyzer itself, it is impossible to interpret correctly the results obtained, because the decrease in the number of ACKs (hence, a decrease in the measured throughput value) can occur both due to the inlluence of external factors, and due to the influence of the NF of the measuring equipment. This makes it impossible to detect and then eliminate additional influencing factors.
Thus, when testing the throughput, it is necessary to correctly estimate the number of ACKs transmitted by the receiver through the feedback loop. It is the number of ACKs that will make it possible to draw a conclusion about the full use of network resources, all other things being equal. However, it is only possible to calculate the ACK messages correctly when the NF of the measuring equipment itself is taken into account in actual operating conditions, taking into account the influence of the ambient temperature. Only then it will be possible to detect and then eliminate additional factors contributing to the degradation of the maximum data rate in the LTE-Advanced.
w
References
1.3GPP TS 36.306, release 13.3.0, September 2016.
2. Proakis J,G. (¡995). Digital Communications (Third Edition). McGraw Hill, New York, (in Russian)
3. Rauscher C., Janssen V., Minihold R. (2001). Fundamentals of Spectrum Analysis, Rohde & Schwarz, 221 p. (in Russian)
4. FSW Signal and Spectrum Analyzer Specifications, Rohde&Schwarz, release 21.00, February 2017,
5. Keysight 346A/B/C Noise Source Operating and Service Manual, Keysight, release 3, May 2017.
6. Konstantinov A.S. Pestryakov A.V. (2017). Assessment of the adequacy of the measurement of the maximum speed of reception and transmission in LTF,-Advanced in real-time. Retrieved from http://ieeexplorc. ieee. org/document/7 99 7532.
7. Konstantinov A.S. Pestryakov A.V. (2017). Oeenka adekvatnosti izmereniya predelnyh skorostey priema b peredechi informatsii v seti LTE-Advanced v rezhimc realnogo vremcni. Sistems of signal sinchro-nization, generating and processing. No. I. Pp. 26-27. (in Russian)
АНАЛИЗ ФУНДАМЕНТАЛЬНЫХ ОГРАНИЧЕНИЙ МАКСИМАЛЬНОЙ СКОРОСТИ ПЕРЕДАЧИ ИНФОРМАЦИИ В СЕТИ LTE-ADVANCED
Константинов Александр Сергеевич, Московский Технический Университет Связи и Информатики (МТУСИ),
Москва, Россия, blackcron@gmail.com
Пестряков Александр Валентинович, Московский Технический Университет Связи и Информатики (МТУСИ),
Москва, Россия, a.v.pestryakov@mail.ru
Дннотация
Для адекватной оценки пропускной способности сети LTE-Advanced необходимо проводить тестирование в реальных условиях эксплуатации, используя поверенные средства измерения и принимая во внимание влияние окружающей среды. Основными факторами, ограничивающими пропускную способность в канале связи, являются ширина полосы пропускания и отношение мощности сигнала к мощности шума. Для правильной интерпретации результатов тестирования необходимо учитывать все составляющие шума, включая вклад измерительного оборудования. Корректная оценка степени влияния отклонения температурных условий от заявленных в технической документации на шумовые параметры измерительного приемника возможна только на основании результатов предварительных измерений шумовых параметров самого приемника при тех же условиях, поскольку в документации приводится одно наихудшее значение среднего уровня собственных шумов для диапазона температур на конкретных частотах. Это позволит обнаружить дополнительные факторы, дающие вклад в деградацию пропускной способности, с целью их последующего устранения.
Ключевые слова: LTE-Advanced, коэффициент шума, Y-фактор, С/Ш, предел Шеннона, пропускная способность, Error Rate. Литература
1. 3GPP TS 36.306, версия 13.3.0 от сентября 2016 г.
2. Прокис Дж. Цифровая связь. Пер. с англ. / Под ред. Д. Д. Кловского. М.: Радио и связь, 2000. 800 с.
3. Раушер К., Йанссен Ф., Минихольд Р. Основы спектрального анализа. Пер. с англ. С. М. Смольского / Под ред. Ю. А. Гребенко. М.: Горячая линия-Телеком, 2006. 224 с.
4. FSW Signal and Spectrum Analyzer Specifications, Rohde&Schwarz, версия 21.00 от февраля 2017 г.
5. Keysight 346A/B/C Noise Source Operating and Service Manual, Keysight, версия 3 от мая 2017 г.
6. Konstantinov A.S. Pestryakov A.V. (2017). Assessment of the adequacy of the measurement of the maximum speed of reception and transmission in LTE-Advanced in real-time. Retrieved from http://ieeexplore.ieee.org/document/7997532/.
7. Константинов А.С., Пестряков А.В. Оценка адекватности измерения предельных скоростей приема и передачи информации в сети LTE-Advanced в режиме реального времени // Системы синхронизации, формирования и обработки сигналов. 2017. №1. С. 26-27.
Информация об авторах:
Константинов Александр Сергеевич, аспирант кафедры "Радиооборудования и Схемотехники", Московский Технический Университет Связи и Информатики, Москва, Россия
Пестряков Александр Валентинович, декан факультета "Радио и Телевидение", заведующий кафедрой "Радиооборудования и Схемотехники", д.т.н., профессор, Московский Технический Университет Связи и Информатики, Москва, Россия
T-Comm Vol.11. #12-2017
