What are the RF requirements for a wireless capsule endoscopy device?

A wireless capsule endoscopy device (a pill-sized camera that the patient swallows to image the gastrointestinal tract) has demanding RF requirements because it must transmit high-quality images from deep inside the body while operating on a tiny battery within severe size constraints. The RF requirements include: operating frequency (typically 402-405 MHz MICS band for low tissue absorption, or proprietary frequencies in the 430-470 MHz UHF range used by some manufacturers; some designs use the ISM 915 MHz band), data rate (2-4 frames per second of VGA-resolution (320x240) images requires approximately 1-4 Mbps of raw data; with JPEG compression, this reduces to approximately 200-800 kbps over the RF link), transmit power (1-10 mW, limited by battery capacity and SAR considerations), antenna (a miniature antenna, typically a helical, meandered monopole, or loop antenna, integrated within the 11x26 mm capsule shell; the antenna must radiate through the capsule housing and surrounding tissue with typical efficiency of 0.1-1%), battery life (the capsule must operate for 8-12 hours to transit the entire GI tract; a typical battery is a silver oxide cell, 1.55V, 25-50 mAh, limiting total available energy), and body-worn receiver array (an external receiver vest with 8-16 patch antennas distributed over the patient's abdomen provides spatial diversity to maintain link quality as the capsule moves through the GI tract).