Content for TR 38.877 Word version: 18.1.0
5 Feasibility study
5.1 General
5.2 Wideband RF architectures
5.2.1 RF Front end
5.2.1.1 General
5.2.1.2 Beam former and PA
5.2.1.3 Receiver front end
5.2.1.4 Summary
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5 Feasibility study p. 13
5.1 General p. 13
According to the definition in clause 6.1, a multi-band FR2-1 RIB is a RIB that transmits in two or more FR2-1 bands using common active components. In this clause, the feasibility of an FR2-1 multi-band solution is considered. The feasibility is examined taking into account technology challenges and emerging solutions. It is possible that not all parts of the BS are multi-band but that some advantage can be gained by implementing some parts as multi-band. For example one potential advantage of a multiband PA might be that power can be distributed between the supported bands offering more flexibility to optimize the power available for each, this requires only a multi-band PA.
The evaluation considers whether the proposed set of FR2-1 requirements is likely to be achievable with present or future implementation possibilities. The study does not aim to conclude on whether a multi-band FR2 solution is more optimal or effective (considering complexity, power, weight etc.) than other possibilities, for example mounting individual radio panels for each band within a BS enclosure.
When discussing the feasibility of wideband components/systems the multi-band bandwidth as a percentage of the carrier frequency should be considered.
Note that this is generally called fractional BW but in [2] the term fractional BW is already defined to mean something specific so is best avoided to prevent confusion.
Fractional bandwidth (FBW) is defined for a single operating band as shown below:
-
Fractional bandwidth (FBW) is defined in [2] as
FBW=200∙(FFBWhigh - FFBWlow) / (FFBWhigh + FFBWlow) %,
- where FFBWhigh is highest supported frequency within supported operating band, for which fractional bandwidth support was declared, and FFBWlow is lowest supported frequency within supported operating band, for which fractional bandwidth support was declared.
-
Percentage bandwidth (PBW) is defined in this study as
PBW=200∙(FPBWhigh - FPBWlow) / (FPBWhigh + FPBWlow) %,
- where FPBWhigh is highest supported frequency, for which percentage bandwidth support was declared, and FPBWlow is lowest supported frequency, for which percentage bandwidth support was declared.
| Frequency group, NR operating band pairing (lowest, highest) | Frequency range | Percentage bandwidth |
|---|---|---|
| 26 GHz (n258) | 24250 MHz - 27500 MHz | 12.6% |
| 28 GHz (n257) | 26500 MHz - 29500 MHz | 10.7% |
| 28 GHz (n261) | 27500 MHz - 28350 MHz | 3% |
| 39 GHz (n260) | 37000 MHz - 40000 MHz | 7.8% |
| 40 GHz (n259) | 39500 MHz - 43500 MHz | 9.6% |
| 48 GHz (n262) | 47200 MHz - 48200 MHz | 2.1% |
| 24-29 GHz (n257/n258/n261) | 24250 MHz - 29500 MHz | 19.5% |
| 37-48 GHz (n260/n259/n262) | 37000 MHz - 48200 MHz | 26.3% |
| 26+28 GHz (n258, n261) | 24250 MHz - 28350 MHz | 15.6% |
| 28+39 GHz (n257/n261, n260) | 26500 MHz - 40000 MHz | 40.6% |
| 26+40 GHz (n258, n259/n262) | 24250 MHz - 48200 MHz | 66.1% |
| 28+40 GHz (n257/n261, n259/n262) | 26500 MHz - 48200 MHz | 58.1% |
5.2 Wideband RF architectures p. 14
5.2.1 RF Front end p. 14
5.2.1.1 General p. 14
Feasibility for RF front ends can be considered by looking at existing component capabilities which could be used for multi-band FR2 products now but also by studying literature for the direction of future capabilities.
5.2.1.2 Beam former and PA p. 14
There are a number of components available today which offer sufficient band widths to cover at least some of the FR2 multi-band options. In [24] a wide band beamformer and PA was presented which covered 24 to 29.5 GHz (bands n257/n258/n261). The performance of which can be seen in Table 5.2.1.2-1 and Figure 5.2.1.2-1.
| Parameter | Beamformer |
|---|---|
| Frequency Range | 24-29.5 GHz |
| Tx OP1dB/OIP3 | 21 / 25 dBm |
| Tx Pdiss/Ch @ 12dBm Pout | 300 mW |
| Pout @3% EVM w/ 64QAM | 12 dBm |
| Rx Single Channel NF | 4 dB |
| Rx Pdiss | 130 mW |
| Instantaneous Bandwidth | 1600 MHz |
Figure 5.2.1.2-1: PA bias optimized for P1dB for 24GHz (left), and 28GHz (right)
(⇒ copy of original 3GPP image)
(⇒ copy of original 3GPP image)
It is considered feasible that multi-band beamformer IC covering 24-29.5GHz and associated bands can be achieved.
Looking further ahead the results of academic studies in [25] a 24-42 GHZ wideband PA was presented which exhibited flat P1dB of 17.8 to 19.6dBm, within 1.6dB from Psat, and flat PAEP1dB of 36.6 to 44.3% over 24 to 40GHz, verifying the truly wideband large-signal matching.
In [26] the hybrid N/PMOS allowed the 26-39GHz PA deep Class-AB biasing and device cascade, substantially increasing PA Pout and efficiency.
These PAs across different frequency groups are summarized in the following Table 5.2.1.2-2. It can be seen that some recent study shows PA covering 26-39GHz, 24-42GHz with average output power around 10dBm,PAEP1dB larger than 30%.
| Frequency | [25] 24 -42GHz PA | [26] 26 -39GHz PA |
|---|---|---|
| Authors and year of publication | Fei Wang,2020 | J Park,2022 |
| Technology | 45nm SOI CMOS | 45nm SOI CMOS |
| Gain (dB) | 20.5 | 18.9 |
| S21BW-3dB(GHz) | 25.8-43.4 | 25.3-42.0 |
| P1dBBW-1dB(GHz) | 22.0-37.0 | 25.0-37.0 |
| PAEp1dB BW-1dB(GHz) | 24.0-41.2 | 29.9-33.6 |
| P1dB(dBm) | 17.8-19.6 | 16.3-18.4 |
| Pavg(dBm) | 8.4-11.3 | 10.8-12.3 |
| PAEP1dB(%) | 36.6-44.3 | 29.9-34.9 |
These papers indicate that PAs covering frequency ranges from 26 to 40GHz or more are at least technically feasible in the research environment and may become available in the longer term.
It should be noted PAs with wide percentage bandwidths may not be capable of operating with signals that broad. For instance, while the PA may cover 50% bandwidth, its instantaneous bandwidth, i.e. maximum signal bandwidth, is usually restricted to a few hundred MHz due to limitations with bias networks and memory effects.
5.2.1.3 Receiver front end p. 16
In [27] a 27-41GHz RX was designed and a proof-of-concept mm-Wave four-input-four-output MIMO RX array was implemented in a 45-nm CMOS SOI process with a total chip size of 3.6 mm×6.5 mm.
In [28] a 24.25-to-71GHz phased-array receiver is was introduced, which covering the whole FR2 frequency band 3GPP have defined by now. A harmonic-selection technique is was proposed to extend the operating bandwidth with low power consumption. The LNA can be configured into either operating Mode 1 covering 24 to 44GHz or operating Mode 2 covering 44 to 71GHz.
Paper [29] presented a 22-44 GHz 2×2 phased-array receive beamformer. The RX channel includes a LNA, a 5-bit vector modulator (VM) phase shifter, an attenuator, and a variable gain amplifier (VGA). The phased-array channel results in a peak gain of 26.3 dB and a 3-dB bandwidth of 20.5-44 GHz. The measured NF is 3-3.6 dB at 22-44 GHz with an IP1dB of -27.5 to -24.5 dBm.
For phase-array receive beamformer, these good performance receivers across different frequency groups are summarized in the following Table 5.2.1.3-3. They achieved low NF in a wide bandwidth.
| Frequency | [29] 22-44 GHz | [27] 27-41GHz | [28] 24-71GHz |
|---|---|---|---|
| Authors and year of publication | Li Gao,2020 | Min-Yu Huang,2019 | Jian Pang,2022 |
| Tech. | 45nm CMOS SOI | 45nm CMOS SOI | 65nm CMOS Bulk |
| BW(GHz) | 22-44 | 27-41 | 24.25-71 |
| Gain(dB) | 26.2 | 36/element | / |
| NF(dB) | 3-3.6 | 4.3-6.3 | 3.6-8.0 (at 24.25-35GHz) 4.0-7.6(at 35-44GHz) |
| Gain Tuning(dB) | 16 | 15 | / |
| Phase Shift Res(°) | 11.25 | / | / |
| Phase/Gain RMS Error(° /dB) | 6/1.9 | / | / |
| IP1dB(dBm) | -25.4 | -34/-27.3 | -17.6 (at 28GHz) -20.9(at 39GHz) |
| IIP3(dBm) | -18 | / | / |
| Pdc(mW) | 112 | / | / |
5.2.1.4 Summary p. 17
It has been shown that:
- Multi-band beamformer IC with common active RF components with 19.5% percentage bandwidth in frequency range 24-29 GHz which includes n257/n258/n261 is technically feasible.
- For RF front-end, TRX chips covering 24-29.5GHz. 27-41GHz RX are shown. A harmonic-selection technique is proposed to extend the receiver's operating bandwidth up to 24.25-71GHz.
