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Exploring 5G RF Technology

Exploring 5G RF Technology

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Exploring 5G RF Technology

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  1. FR1 is usually called sub-6 GHz and FR2 is the 5G millimeter wave (mmWave) frequency range. 1

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  3. In general, some key technologies contribute to 5G’s performance: Spectrum sharing Carrier aggregation Massive MIMO and antenna array systems Higher-order modulation can enhance data rate, which is not the main factor contributing to 5G’s performance. As shown in the previous table, the highest order of modulation scheme of both FR1 and FR2 is 256 QAM, which is identical to LTE-Advanced. To transition to a full 5G implementation, mobile network operators manage their spectrum allocations dynamically via dynamic spectrum sharing, which is an intelligent way to allocate spectrum between air interface standards, such as 3G, LTE, or 5G, in order to reduce spectrum waste and optimize end-user experience [1]. 3

  4. The ultimate aim of 5G NR is to natively support licensed, shared, and unlicensed spectrum simultaneously, providing more efficient use of the limited spectrum we have available [1,3]. For example, sharing spectrum allocations across FR1 and FR2 can double the coverage area of new 5G mid- and high-band base stations while delivering MB/s of data indoors and all the way to the cell edge. 4

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  6. Carrier aggregation (CA) combines multiple signals into one data channel to enhance data rates in the system with optimized usage of available bandwidth. 5G NR expands this trend, utilizing CA in both FR1 and FR2, supporting up to 16 component carriers, which is much more than that of 4G (5 component carriers). Using CA of LTE and 5G NR is known as dual connectivity. In dual connectivity, carrier aggregation mode, both LTE carriers and 5G NR carriers are simultaneously utilized. CA brings about a large number of merits for 5G NR, such as increased data rates and throughputs for both UL and DL. 6

  7. Dual connectivity in Non-Standalone (NSA) 5G allows combining of carrier aggregated LTE and carrier aggregated NR spectrum. However, carrier aggregation of LTE-5G carriers is not allowed [4]. As shown above, the carrier aggregation of (f2-f6) is not allowed. Although carrier aggregation has an interband scenario, which only allows (4G-4G) or (5G-5G) combinations. 7

  8. Massive MIMO is the backbone of 5G, helping carriers achieve an increase in network capacity and data rates while minimizing expenses. Massive MIMO reduces energy consumption by targeting signals to individuals through beamforming, which is a technique focusing the signal from multiple antennas into a single intense beam. As shown above, regarding the two terminals, the energy they need for communication is merely the two blue beams. To put it another way, the yellow section is unnecessary and wasted. 8

  9. This focused signal technique also helps reduce interference between users in the network. According to Shannon Theorem: low interference brings high SNR, thereby enhancing data rate. Therefore, in some ways, that’s why massive MIMO canachieve an increase in network capacity and data rates. To bring these merits, massive MIMO technology uses extensive antenna array system, which combines the RF transmit and receive chains into each array unit and typically are composed of 16, 32, 64, or more array elements. The idea of using such large antenna arrays is to exploit the concept of spatial multiplexing. Spatial multiplexing delivers multiple parallel streams of data within the same resource block of spectrum. 9

  10. By substantially expanding the total number of virtual channels, massive MIMO increases capacity and data rates without additional towers and spectrum. We can also infer that wider bandwidth brings a higher data rate, as shown below: 10

  11. In LTE, with 5 component carriers for CA (carrier aggregation), the signal bandwidth is 100 MHz at most. Nevertheless, thanks to the availability of a vast amount of unused bandwidth, using the mmWave spectrum would support channel bandwidth up to 400 MHz, thereby enabling gigabit data rates. There’re some non-line-of-sight challenges, which can be mitigated through massive MIMO utilizing multiple antennas to focus the transmitting and receiving signals into smaller regions of space, bringing vast improvements in throughput and energy efficiency. The more data streams, the higher the data rate, and the more efficient use of radiated power. 11

  12. Even before the advent of 5G, 4G LTE has provided a large number of improvements in spectral efficiency. The introduction of higher-order advancements in modulation, such as 64 and 256 QAM, as well as MIMO and beamforming, pushing the limits of peak data rates up to 2 gigabits per second. LTE’s addition of CA has also provided mobile network operators with an option to enhance bandwidth by combining several component carriers, thereby providing as much as 140 MHz of usable spectrum. 5G takes this one step further, allowing for larger CC bandwidths. In FR1 spectrum, 100 MHz can be achieved. In FR2, 400 MHz can be achieved. If the mobile network operator owns enough spectrum licenses, 800 MHz can be achieved in FR2 as well. 12

  13. Basically, we can divide 5G frequency bands into three distinct ranges: Low band: 410 MHz ~ 1 GHz Mid band: 1 GHz ~ 7 GHz High band: 24 GHz ~ 100 GHz (mmWave) FR1 FR2 According to their performances of capacity, area coverage, and data rate, we can summarize as the table: 13

  14. The foundation of 5G lies in these technical pillars: Extension of OFDM, which is a method of encoding more digital data onto multiple carrier frequencies MIMO, which involves using a large number of antennas simultaneously so as to enhance data speeds and reduce errors Beamforming, which combines RF signals from multiple antennas to produce a stronger signal focused towards a specific device or receiver Small cell, which places a large number of cell sites densely to enhance the available capacity. 14

  15. With a cyclic prefix on each side of the data, a receiver can better tolerate synchronization errors and prevent intersymbol interference. As shown below, with a cyclic prefix on each side of the data, the intersymbol interference can be reduced much. Cylic Prefix Data 15

  16. So the 3GPP chooses CP-OFDM as the waveform for 5G downlink and uplink for modulation schemes up to 256-QAM [2]. OFDM suffers from huge large peak-to-average power ratios (PAPRs). A peak in the signal power occurs when all, or most, of the sub-carriers, align themselves in phase. 16

  17. High PAPR requires high linearity requirements for PA, increasing current consumption. Consequently, for uplink (i.e., a user to base station), NR offers user equipment the option of using discrete Fourier transform spread OFDM (DFT-S-OFDM) to lower PAPR. 17

  18. Many of today’s LTE MIMO base stations consist of up to 8 antennas, which enables the base station to transmit 8 streams to 8 individual users simultaneously. [1]. The move to massive MIMO exponentially increases the number of antennas, up to 16, 32, 64, 128, or even more. These collections of antennas are called antenna array. 18

  19. They help focus energy into smaller regions of space through beamforming to bring tremendous improvements in throughput and radiated energy efficiency. 19

  20. In addition to enhancing cellular capacity and efficiency, massive MIMO uses narrow beamwidth to avoid interference from each data stream. In terms of UEs, thanks to distinct radiation patterns, each UE would not receive the signal from other antennas of a base station. In other words, there would be less interference during the reception. 20

  21. Beamforming uses multiple antennas to control the direction of an electromagnetic wave by appropriately weighting the magnitude and phase of an individual antenna in an array of multiple antennas, providing significant advantages to 5G. Since beamforming technique is used in massive MIMO, the two terms are used interchangeably occasionally. As mentioned earlier, the propagation loss of mm-wave is exceptionally high due to [5]: High path loss High atmospheric attenuation High penetration loss Foliage loss Rain attenuation Beamforming, or massive MIMO, allows the base station to deliver RF energy to the UE efficiently and precisely. Also, this technique can reduce interference during transmission, thereby increasing SNR and data rate. After all, the high data rate is the main demand for 5G applications. By taking advantage of the multiple paths of massive MIMO and beamforming, the spatial channel between the antenna elements and the UE can be characterized and digitally encoded and decoded to help mitigate signal loss, even when there is limited line-of-sight [1]. 21

  22. Carrier aggregation (CA) is a technique combining two or more carriers into one channel to enhance data rate by widening bandwidth. In 4G, CA was a pivotal contributor to increasing data throughput, which is also crucial in 5G. In 5G NR, there’s another option called dual connectivity. 22

  23. 5G, especially FR2, brings numerous RF components thanks to massive MIMO. Consequently, some suppliers are creating a System In a Package (SiP) approach to reduce the number of RF components despite the additional increased cost. As a result, the RFFE is turning into a complicated and highly integrated SiP. All in all, Gallium Nitride (GaN) has three significant advantages: Low current consumption High power capability Wide frequency bandwidth As mentioned earlier,the highest order of modulation scheme of both FR1 and FR2 is 256 QAM, which is identical to LTE-Advanced. Nevertheless, 5G, especially FR2, must have higher Peak-Average-Ratio (PAPR) than that of 4G. Indeed, 5G adopts DFT-s-OFDM for uplink to reduce PAPR, in both FR1 and FR2. However, according to the formula: PAPR is proportional to the number of subcarriers. The channel bandwidth of FR2 can be up to 400 MHz, which brings numerous subcarriers and high PAPR. It’s well known that high PAPR requires high linearity, which causes high current consumption. But, with low current consumption and high- power capability, GaN technology can achieve high linearity without extremely high current consumption. Due to high channel bandwidth, GaN is suitable for 5G as well. 23

  24. As a result, GaN is the most suitable technology for enabling high effective isotropic radiated base station power (EIRP), such as base station [1]. As shown below, compared to other semiconductor technologies, GaN has lower total power dissipation to attain the identical EIRP targets. 24

  25. Both SAW and BAW filters have dominated the mobile device filter market for a large number of years. Since FR1 in 5G uses the same spectrum as 4G, SAW and BAW filters would dominate the mobile device market in FR1 as well. Nevertheless, compared to 4G, 5G FR1 can possess more component carriers and broader bandwidth in the implementation of CA, which increases current consumption and temperature. 25

  26. Heat negatively affects the filter performance and causes a frequency shift in both out-of-band and passband. Thus, compared to 4G, 5G FR1 filters need higher frequency stability. 26

  27. Reference [1] 5G RF for dummies, Qorvo [2] From Waveforms to MIMO: 5 Things for 5G New Radio [3] What can we do with 5G NR Spectrum Sharing that isn’t possible today? Qualcomm [4] 5G Interview Questions 50 Questions on Spectrum [5] Millimetre wave frequency band as a candidate spectrum for 5G [6] How new is the 5G New Radio? 27

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