OTFS系統使用零自相關序列進行隨機存取前置訊號偵測

Abstract

在上行高移動性多用戶環境中，隨機存取前置訊號偵測 (random access preamble detection; RAPD) 透過正交時頻空間 (orthogonal time-frequence space; OTFS) 系統進行競爭隨機存取程序被認為是一種可行的方法。在本論文中，設計了一種全新的前置訊號格式，該格式結合了少量循環字首 (reduced-cyclic-prefix; RCP) 的OTFS波形格式、可循環移位的零自相關序列，以及多個可擴展的前置訊號幀間隔，用以表示可請求的存取通道，並在線性時變 (linear time-varying; LTV)多重路徑通道中實現可靠的RAPD。 此外，本文亦提出一種基於相關功率測量 (correlation power measure; CPM) 的 RAPD 方法，用於在基地台接收端辨識多個提出存取請求的前置訊號序列。該基於CPM的RAPD系統，在多個非同步接收請求訊號經過已知LTV通道下，從理論上分析了其誤警、遺漏偵測和誤識別機率。當系統運作於具有非整數延遲與都卜勒頻移的隨機LTV通道時，相較於傳統RAPD系統，在限制誤警機率與平均遺漏偵測機率上限的前提下，能夠達成更小的平均誤識別機率，從而提供更高的可靠性。同時，基於CPM的RAPD系統亦可透過為前置訊號序列分配幾乎相同的時頻資源，實現可擴展的存取通道容量。

Random-access preamble detection (RAPD) is considered to enable the contention-based random-access procedure for rectangularly-pulsed orthogonal time frequency space (OTFS) systems operating on linear time-varying multipath (LTV) channels in uplink high-mobility multiple-access environments. Particularly, a new preamble signaling format is designed by adopting the reduced-cyclic-prefix OTFS waveform format, cyclically-shiftable zero-autocorrelation sequences, and multiple scalable preamble frame intervals to represent requestable access channels and enable reliable RAPD over LTV channels. A correlation-power-measure (CPM) -based RAPD approach is also developed to identify multiple requesting preamble signals at the base station receiver. The CPM-based RAPD system is analytically studied in terms of false alarm, outage, and false identification probabilities for asynchronous reception of multiple requesting signals over deterministic LTV channels. When operating over random LTV channels exhibiting fractional delay and Doppler shifts, the CPM-based RAPD system can provide higher reliability than conventional RAPD systems in the sense of achieving the smaller average false identification probability while constraining upper bounds to false alarm probability and average outage probability. Meanwhile, the CPM-based RAPD system can provide a scalable capacity of requestable access channels by allocating nearly the same spectral-temporal resource for preamble signaling.