How do I design the RF front end for a narrowband IoT cellular module?

How do I design the RF front end for a narrowband IoT (NB-IoT) cellular module? NB-IoT uses a very narrow bandwidth (180 kHz, one LTE resource block) to achieve extreme coverage with a simplified RF front end compared to standard LTE: (1) NB-IoT RF specifications: bandwidth: 180 kHz (single PRB). Modulation: QPSK only (no higher-order modulation, simplifying the linear PA requirement). Data rate: 26 kbps DL, 62 kbps UL. TX power: 14-23 dBm (power class 3: 23 dBm, power class 5: 14 dBm, power class 6: 14 dBm). Receiver sensitivity: -141 dBm (with repetition coding, 20 dB enhanced coverage). MCL: 164 dB. Duplex: half-duplex FDD (TX and RX never simultaneous). Deployment modes: in-band (within LTE), guard-band (in LTE guard band), standalone (re-farmed GSM channel). (2) RF front end design: PA: since NB-IoT uses only QPSK (constant envelope), the PA linearity requirements are relaxed compared to standard LTE. A class AB PA with moderate efficiency is sufficient. Output power: +23 dBm (class 3) or +14 dBm (class 5/6). PAE: 30-40% is readily achievable with QPSK. No DPD is needed (the modulation has near-constant envelope). Filter: the filter bandwidth requirement is unique: the NB-IoT signal is only 180 kHz wide, but the filter must reject adjacent interferers. A SAW filter centered on the operating band is standard. The filter for each band is the same as the standard LTE band filter (the narrowband selectivity is done in the digital baseband, not the RF filter). Half-duplex simplification: no duplexer needed. TX/RX switch + single bandpass filter replaces the expensive duplexer. Switch: SOI CMOS T/R switch with > 25 dB isolation. This saves $0.50-1.00 per module compared to a duplexer-based design. LNA: NF < 3 dB. Gain: 15-20 dB. IP3: moderate (NB-IoT has less stringent blocking requirements). (3) Antenna: standard sub-GHz antenna (for Band 8 at 900 MHz: quarter-wave = 83 mm). For compact modules: chip antenna or PCB trace antenna (lower efficiency, suitable for short-range NB-IoT with repetition coding). NB-IoT operates on existing LTE bands (Band 8, 20, 28, etc.): the antenna design follows standard cellular antenna practice for the chosen band(s). (4) Module integration: highly integrated NB-IoT modules: Nordic nRF9160/nRF9151 (SiP with modem + MCU + GNSS). Quectel BC660K/BC950K (standalone module). Sierra Wireless HL7812. These modules contain the entire RF front end (PA, filter, switch, LNA, transceiver, modem) in a single package. The designer only needs to add the antenna and power supply.