Digital RF Transceiver To Meet Needs of Emerging Spectrum

1. Digital RF Transceiver To Meet Needs of Emerging Spectrum Authors: Date: 2010-11-09 Alex Reznik, Tanbir Haque (InterDigital)

2. November 2010 Abstract • We outline a design approach for a digital RF Transceiver • The design is aimed at addressing many of the problems associated with radio operation in TVWS and other sub-1 GHz frequencies • We believe these developments to be of interest to 802.11 as it considers potential multichannel operation and new spectra below 1 GHz Alex Reznik, Tanbir Haque (InterDigital)

3. Motivation • The expanding scope of 802.11 • New spectrum: sub-1GHz (including TV bands), 60GHz, 3.6 GHz • MAC enhancements: 802.11ac • New regulatory environments (TV bands) • This brings about new challenges • Can a single chipset address multiple spectra efficiently? • Can a reasonable implementation support operation over non-contiguous bands? • 802.11 is structured to successfully address many of these challenges • Common MAC supporting multiple PHYs • Closely related PHY definitions • All these enable efficient single chipset implementations of MAC/PHYs over multiple spectra • However, RF remains a challenge • Multiple analog solutions requires to address multiple bands • Aggregation of discontinuous spectrum remains a major challenge • Operation at low frequencies (TVWS and other sub-1 GHZ) requires truly “wideband” radios • Digital RF technology can address these challenges • The idea is not new • But it is finally ready for prime-time Alex Reznik, Tanbir Haque (InterDigital)

4. Digital RF: Motivation and Goals • Evolving & emerging standards are pushing baseband (modem) logic gate count, memory and clock speed requirements ever higher • At the same time, proliferation of multi-band and multi-radio devices require access (often simultaneous) to an ever-growing range of spectrum • To achieve performance (speed) and reduce cost (die size) baseband chip designs will migrate into scaled IC process technologies. • Analog radio designs do not scale easily and have emerged as a major barrier to the evolution of multi-mode devices • Next generation radio architectures will employ digital logic building blocks to implement RF functions • The goal is to develop highly flexible “Digital” transceiver technology suitable for monolithic integration with the modem on scaled CMOS process technologies Alex Reznik, Tanbir Haque (InterDigital)

5. Why Digital? Technology Benefits Summary of radio technology needs & challenges DTRX features that address needs • Implements RF functions on digital logic blocks  monolithic integration with modem possible  reduces number of components in UE reference design • RF waveform agnostic transceiver chain  single chain supports multiple PHY/spectra • Inductor-less design  reduced overall die size/cost • Efficient wide band TX/RX chains  commercially viable BW aggregation (contiguous & non-contiguous) • Wide band TX/RX chains  single free running oscillator used  superior phase noise performance possible • Employs digital up/down conversion & channelization  superior EVM performance possible • Employs adaptive hardware resource management algorithms  reduces overall power consumption • High SNDR TX chain delivers better than -55dBc ACLR • Constant envelope transmit signal  use of efficient switch-mode PA possible • Simplified supply chain • Lower complexity device design • Shorter time to market • Reduced cost & size • Non-contiguous BW aggregation • Stringent spectral mask requirements in emerging spectra (e.g. TVWS) • Broadband sensing, fast frequency scanning • Variable & narrow duplex spacing FDD • Increased downlink waveform complexity • Increased uplink waveform PAR Alex Reznik, Tanbir Haque (InterDigital)

6. Digital Transmitter Concept Alex Reznik, Tanbir Haque (InterDigital)

7. Going Digital in the TX: Sigma Delta Modulation • Programmable all-digital sigma-delta modulator technology • Response is programmed by writing appropriate coefficients stored in memory • Power optimized design supplies improved coding efficiency for better overall TX efficiency • Noise optimized design supplies better noise free bandwidth to relax bandpass filter requirements 4th order, 1.5-bit sigma-delta modulator for TVWS low band 4th order, 1.5-bit sigma-delta modulator for TVWS high band Better than 65dB SNR available to support -55dBc ACLR required for TVWS operation Alex Reznik, Tanbir Haque (InterDigital)

8. Aggregating Multiple Bands for TX • Digital design approach leads to simple “aggregation” of spectra • Simultaneous transmission over multiple non-adjacent channels is possible while preserving efficiency & spectrum mask performance • Example: TV Band Tx Channel Capabilities of Existing prototype • Waveform may be 5, 10, 15 or 20 MHz OFDM • 4x6 MHz channels: • Contiguous or non-contiguous • 2x12 MHz channels: • Contiguous or non-contiguous • 1x24 MHz channel: • Time alignment between channels < 1uSec • Better than -55dBc ACLR performance supports TVWS spectral mask requirements • 50% < sigma-delta coding efficiency < 75% Alex Reznik, Tanbir Haque (InterDigital)

9. Going Digital in the RX: Banked ADCs Digital Signal Processing Unit ADC ADC Modem ADC ADC LNA ADC Input ADC ADC ADC Clock and power management unit t • Multiple ADC’s sample the input signal on different phases of the clock • High-rate sampling (115 Msps per ADC, 1840 Msps aggregate) for direct-to-digital conversion • Signal processing unit assembles the input signal and sends it to modem • Enables use of power-efficient small non-instrumentation grade ADCs • Clock and power management helps to reduce the overall power consumption Alex Reznik, Tanbir Haque (InterDigital)

10. Aggregating Multiple Bands for RX • As with digital TX, simultaneous reception of multiple bands is possible for continuous of discontinuous spectra • Commercially viable BW aggregation • Example: Existing prototype supports simultaneous reception of OFDM waveform with BW of 5, 10 or 20 MHz in TV Spectrum • 4x6 MHz channels & 2x12 MHz channels • Contiguous or non-contiguous • 1x24 MHz channel • EVM < 2% • Maximum power difference between Rx channels: 40 dB • Time alignment between Rx channels < 1 uSec • 5 db Noise Figure with LNA Alex Reznik, Tanbir Haque (InterDigital)

11. Near Term Design Targets Key Features RX Performance Targets • Single chip transceiver solution • 40nm CMOS process • Programmable solution supports • LTE bands 1, 3, 4, 6, 7, 9, 10, 11, 17 • WCDMA bands I, II, III, IV, V, VI, VIII, IX, X, XI • TVWS bands 512MHz ~ 698MHz • Chip (die) size < 10mm^2 • ADC Performance Numbers • 12 HW bits (9 ENOB) • Max single rate = 200 Msps • Max agg.rate (x16) = 3200 Msps • RX EVM < 2% • RX SNDR > 50dB • RX noise figure < 6dB • 80mW* < RX power < 180mW* • *determined by operating conditions TX Performance Targets • TX EVM < 2% • TX ACLR better than -55dBc • Peak output power ~ +17dBm • Transmitter power consumption < 150mW • SD modulator coding efficiency > 50% • Switch mode PA peak efficiency > 50% Alex Reznik, Tanbir Haque (InterDigital)

12. Digital Radio Summary • Overcomes the limitations suffered by analog solutions • Delivers higher bandwidth in a commercially viable manner • Delivers better performance (EVM, SNR) • Suitable for and leverages the benefits of smaller CMOS process nodes • Lower cost (size and power) radio solution possible • Monolithic integration of modem and digital radio is possible – this reduces the overall size and cost • Scalable transceiver design and adaptive power management algorithms reduce overall power consumption • Enables broadening of possibilities for 802.11 • Wide band digital radio makes BW aggregation commercially viable • Waveform agnostic, re-configurable digital radio eases the incorporation of new bands and standards • Superior TX spectral mask performance suitable for TVWS operation Alex Reznik, Tanbir Haque (InterDigital)