The fundamental communication problem in the wireless Internet of Things (IoT) is to discover a massive number of devices and to allow them reliable access to shared channels. Oftentimes these devices transmit short messages randomly and sporadically. This paper proposes a novel signaling scheme for grant-free massive access, where each device encodes its identity and/or information in a sparse set of tones. Such transmissions are implemented in the form of orthogonal frequency-division multiple access (OFDMA). Under some mild conditions and assuming device delays to be bounded unknown multiples of symbol intervals, sparse OFDMA is proved to enable arbitrarily reliable asynchronous device identification and message decoding with a codelength that is O(K(log K + log S + log N)), where N denotes the device population, K denotes the actual number of active devices, and log S is essentially equal to the number of bits a device can send (including its identity). By exploiting the Fast Fourier Transform (FFT), the computational complexity for discovery and decoding can be made to be sub-linear in the total device population. To prove the concept, a specific design is proposed to identify up to 100 active devices out of $2^{38}$ possible devices with up to 20 symbols of delay and moderate signal-to-noise ratios and fading. The codelength compares much more favorably with those of standard slotted ALOHA and carrier-sensing multiple access (CSMA) schemes.
翻译:事物无线互联网(IoT)的基本通信问题是发现大量装置,并允许它们可靠地进入共享的频道。这些装置往往随机和零星地传送短信息。本文件提出一个无赠与大规模访问的新信号计划,其中每个装置用零星的吨位来编码其身份和/或信息。这些传输是以矫形频率多功能访问(OFDMA)的形式实施的。在一些温和的条件下,假设装置延迟被捆绑的符号间隔的不为人知的多个倍数,DMA稀有的DMA证明能够任意可靠地进行非同步设备识别和信息解码,代码为O(K(log K+log S + log N)),其中每个装置用稀少的吨位表示其身份和/或信息。这些传输方式基本上相当于一个装置能够发送的位数(包括其身份 ) 。通过快速的 Fourierer变换(FFT),发现和解码的计算复杂性可以被任意地设定为亚值的超同步设备比值, 20个(LO) 和预质的标程图中, 可能将A 20个特定的缩图标标比。