PERFORMANCE TO NEW THRESHOLDS

Transcription

1 10 ELEVATING RADIO ABSTRACT The advancing Wi-Fi and 3GPP specifications are putting pressure on power amplifier designs and other RF components. Na ose i s Linearization and Characterization Technologies elevate the performance of the entire RF signal chain. PERFORMANCE TO NEW THRESHOLDS

2 Page 1 of 7 Elevating Radio Performance to New Thresholds Next generation radio standards are pushing the limits of radio frequency (RF) systems. In the unlicensed world of IEEE Wi-Fi specifications, ac and 11ax are increasing MIMO layers, implementing wider channel bandwidths, and improving modulation to bring data rates to new levels. Specifically, bandwidths requirements of 160 MHz as well as 1024 QAM (10-bits/symbol Quadrature Amplitude Modulation) are being required by the ax specifications. Higher modulation schemes, such as 4096 QAM (12-bits/symbol), are under consideration. Given the cost conscience ethos of the Wi-Fi community, these specifications must be realized with low cost power amplifiers. In the licensed radio access systems defined by 3GPP, there are increasing requirements for multicarrier and multiband 4G (LTE) implementations. In addition, 3GPP is defining 5G as the next generation radio system with a targeted peak data rate of 5 Gbps to each mobile device. 5G has two licensed spectrum allocations; Sub 6 GHz and mmw (millimeter wave), specifically 28 GHz and 39 GHz. In the current 3GPP specifications, the component carrier for 5G is 100 MHz as opposed to 20 MHz used in 4G/LTE. For sub 6 GHz deployments, adaptive hybrid MIMO with up to 64 layers is being defined; for mmw, massive beamforming with many individual power amplifiers will be required to close the link between the mobile station and the base station. Once again, the performance of the RF chains and power amplifiers becomes a focus of the designs in order to meet the cost requirements of the mobile devices and performance metrics of base stations. The target market for Wi-Fi devices and smartphones is large. In 2016, over 1.4 billion smartphones shipped with LTE modems and over 3 billion Wi-Fi devices were shipped including smartphone, tablets, routers, computers, TV and other consumer electronics The Existing Radio Chain is Challenged The advancing Wi-Fi and 3GPP specifications are putting pressure on the power amplifier (PA) designs and other RF components. The higher data rates of Wi-Fi specifications manifest in both wider bandwidth and increasing the modulation rates from the currently common 256 QAM to as much as 4096 QAM. This is putting pressure on the cleanliness of the signal chain. This cleanliness, measured by the error vector magnitude (EVM), is a difficult objective for typical low-cost PAs used in Wi-Fi systems. In order to provide the higher rates promised by higher QAM, the power output and efficiency of the CMOS PAs must increase. The critical challenge of 1024 QAM or 4096 QAM is to meet EVM objectives with range on par with lower data rates while maintaining power efficiency Likewise, the increased bandwidth being required of 5G signals along with very strict out of channel emission requirements (ACLR) places a premium on the PA performance for mobile devices which typically use low cost PAs. At mmw carrier frequency implementations, the device Tx power to meet

3 Page 2 of 7 link level / coverage needs is challenged. This is a common problem for mobile devices, Customer Premises Equipment (CPE) and base stations as the power output and efficiency of PAs at these frequencies are very low. 5G will push bandwidths from the current 20MHz to 100MHz and up to 800MHz, representing a challenge for most power amplifiers to achieve inexpensively and efficiently The increased bandwidth requirements are impacting base-station designs as well. PAs used in both wideband 4G and 5G base-stations, (typically GaN, LDMOS or GaAs) are challenged to meet the ACLR and efficiency requirements being imposed by signal requirements of 100 MHz or more. What does NanoSemi Bring to Solve These Problems? Common to all of these requirements is the need to improve the performance of the signal chain, including the data converters, PAs and other system components. This is best done by linearization ith ad a ed digital sig al p o essi g. Na ose i i gs li ea izatio to e le els usi g a s a t lea i g app oa h hi h automatically characterizes the signal chain including the PAs. It identifies nonlinear components and other non-ideal impairments in dynamic system operation across the full signal chain of a radio and analyzes their impact on system performance. A corresponding mathematical model is created, including nonlinear transformations. This approach has the following benefits: Automatically characterizes and models the signal chain PA agnostic: GaN, LDMOS, GaAs, CMOS Works with any RF for mobile devices, customer premises equipment and base stations Unprecedented bandwidth with reduced sampling rate Improves EVM by max. 30 db Corrects ACLR by max. 40 db Figure 1: Na ose i s Algorith s sit ithi the ase a d pro essor a d hara terizes the e tire sig al hai Na ose i s app oa h is significantly different than existing linearization techniques which are based upon generalized memory polynomials (GMP) and envelope tracking (ET). Both DPD based upon GMP and ET suffer from increasing complexity as bandwidth increases, particularly when signal bandwidths exceed MHz (as is found in Wi-Fi and 5G signals). Also note that neither DPD based upon GMP nor

4 Page 3 of 7 ET a p ope l ha a te ize a e ti e sig al hai a d o l odif the PA eha io ; Na ose i s Linearization compensates the entire RF chain including filter and coupling effects. Bandwidth >100MHz Improve PA Efficiency Increase Average Power Envelope Tracking DPD based upon GMP NanoSemi Linearization Notes ET power supply must achieve switching frequencies >2-3X signal bandwidth ET and GMP optimized for linearizing low bandwidth signals GMP based DPD needs to back off further from Psat-PAPR Improve Linearity & ACLR ET introduces noise through switching power supply. Improve EVM Implementation Size RF Chain Characterization N/A N/A GMP becomes too large for bandwidth >40MHz: ET requires additional circuit blocks & highly linear switching power supply NS characterizes entire signal chain from data converter to PA; able to linearize non PA components Figure 2: Comparison of envelope tracking, traditional DPD based upon GMP a d Na ose i s linearization based upon wide band signals (>80MHz) For more information on Envelop Tracking, please see: What are the e efits of Na ose i s Li earizatio to Wi-Fi, LTE and 5G products? Benefits to Wi-Fi devices and access points: The benefits to the performance of Wi-Fi signals are significant. Traditionally Wi-Fi devices eschewed linearization due to the high bandwidth required of Wi-Fi signals. However, as shown below, linearization provides considerable benefits to Wi-Fi signals, allowing higher modulation rates, at higher power output and greater power efficiency. Figure 3 summarizes measured results, taken from a CMOS integrated transceiver where its digital to analog converter (DAC) and analog to digital converter (ADC) operated at MSPS and a Doherty GaAs PA at a carrier frequency of 5.5GHz.

5 Page 4 of 7 Figure 3: NanoSemi linearization significantly improves Wi-Fi Power Efficiency and Pout The significant improvement in EVM can be seen below where an uncorrected signal 160 MHz ax signal is compared to a corrected, linearized version. Notice how the 20 db EVM improvement has resulted in the signal with a significantly cleaner constellation. Also note that transmit power is higher by a factor of 12. Figure 4 is a measured result from a SiGe BiCMOS PA, driven at output power of 24dBm with power efficiency of 14.2%. Figure : Ho Na ose i s li earizatio lea s the sig al o stellatio, allo i g for higher QAM. The diagram on the left is an ax 160MHz signal without any linearization. The diagram on the right shows the same sig al pro essed ith Na ose i s linearization. The improved EVM allows for 4096 QAM at output power of 24dBm even with 160MHz. In a Smartphone or other Wi-Fi mobile device, higher data rates can be achieved at any given range and the improved PA efficiency results in less battery consumption. In a Wi-Fi access point, the improved PA performance and cleaner EVM leads to higher data rates over larger ranges.

6 Page 5 of 7 Figure 5: NanoSemi s linearization improves both Pout and EVM, yielding better rate to range performance due to higher power output and better EVM performance (free space propagation model). Benefits to LTE devices and Base Stations: For 3GPP Waveforms (LTE, 5G) the performance requirements are more stringent. Specifically, 3GPP puts constraints on adjacent channel performance as measured by the adjacent channel leakage ratio (ACLR), which is defined as the ratio of the transmitted power to the power in the adjacent radio channel. In addition, traditional approaches to LTE linearization were designed around the narrow 1.5, 5, 10, 15 or 20MHz component carriers. High bandwidths such as 80 or 100MHz LTE, multiband LTE and 5G wave forms require new approaches to achieve performance metrics without backing off the PA power output and efficiency. Newer base stations are pushing the limits on RF performance. GPP s 4.5G and 5G requirements include bandwidths in excess of 100MHz and massive MIMO with up to 64 PAs. Na ose i s implementation is inherently broadband. In addition, one receiver (either from a dedicated observation path or a regular receiver channel) can be shared among multiple transmitter channels, a capability which becomes increasingly important for large MIMO implementation. The combination of greater power efficiency, lower power consumption and the feedback receiver sharing reduces the radio subsystem power consumption. Specifically, for a 64x64 massive MIMO system:

7 Page 6 of 7 Compared to base-stations ithout a fo of DPD o li ea izatio, Na ose i s Li ea izatio is able to reduce the radio subsystem power consumption by 80%. Compared to GMP based DPD implementations, NanoSemi can reduce the power consumption by 33%. Upon request, NanoSemi can provide the details behind this analysis. Benefits to 5G devices and base-stations: 5G waveforms (still being finalized in 3GPP) are very broadband, with component carriers that are 100MHz wide vs. 20MHz for 4G. As stated in the introduction, there are two bands of operation for 5G; mmw (28GHz and 39GHz) and Sub 6GHz (e.g..5 GHz). As sho i the ta le elo, Na ose i s Linearization technologies are expected to improve the performance both mmw and sub 6GHz devices: Figure 6: NanoSemi s e efits to G De i es a d ase-stations. The wide band 5G signal presents challenges to PA performance and efficiency. Figure 7 shows the ACLR improvement on a 3.5 GHz m-mimo radio with 200MHz instantaneous bandwidth signal (10 20MHz LTE carriers). The resulting waveform s spectral characteristics are expected to be very similar to 2x 5G carriers. This testing was conducted with 64 GaN PAs, each operating at 35dBm. The measured ACLR of -51dBc exceeds 3GPP requirements.

8 Page 7 of 7 Figure 7: ACLR improvement of 25dB in a 200MHz OFDMA waveform (10x20MHz LTE). This is also indicative of a 2X100MHz 5G waveform. Conclusion The evolution of IEEE and 3GPP standards is putting greater pressure on radio systems. The radio chain is the interface between the modem and spectrum; therefore, improving the performance of the radio chain is critical to increasing the data rates, spectral and power efficiencies being required of standards su h as IEEE8. a a d GPP 5G. Na ose i s Li ea izatio a d Cha a te izatio te h i ues i p o e radio chain power efficiency and signal cleanliness at unprecedented bandwidths. The small implementation size is cost effective for integration into ASICs that support Wi-Fi or into LTE/5G chips for smartphones. For further information, please contact us through our web page: