Zadoff Chu (ZC) sequences are a principal manifestation of spread spectrum in modern cellular systems including LTE and 5G NR, largely displacing PN and Walsh sequences which were the mainstays of 3G cellular (WCDMA and cdma2000) and the 2G-era IS-95. ZC sequences are complex sequences with unit amplitude and particular phase shifts, as opposed to Walsh and PN codes which are real and binary valued, most commonly $\pm1$ when used in communication systems. ZC sequences have a number of remarkable and desirable properties that we define in the next section. Because of these properties, they are used for many key functions in current cellular systems, and are likely to be prevalent in future cellular systems as well. In LTE and 5G NR, they are widely used for a number of important initial access and overhead channel functions that are often overlooked by engineers who focus on data transmission. For example, ZC sequences are used for initial access in both the downlink (synchronization) and uplink (random access), uplink control information, uplink channel sounding, and for the reference symbols (pilots) used for fine-grained channel estimation. It is not an exaggeration to say that most types of signals other than the data transmissions in modern cellular standards utilize ZC sequences.

翻译：Zadoff-Chu（ZC）序列是现代蜂窝系统（包括LTE和5G NR）中扩频技术的主要体现形式，在很大程度上取代了曾是3G蜂窝（WCDMA和cdma2000）及2G时代IS-95核心技术的PN序列和Walsh序列。与通信系统中常取值为$\pm1$的实值二进制Walsh码和PN码不同，ZC序列是具有单位幅度和特定相位偏移的复数序列。ZC序列拥有多项卓越且理想的特性（详见后文定义）。正是凭借这些特性，它们被应用于当前蜂窝系统的诸多关键功能，并极有可能在未来蜂窝系统中继续广泛使用。在LTE和5G NR中，ZC序列被广泛应用于初始接入和开销信道等核心功能——这些功能常被专注于数据传输的工程师所忽视。例如，ZC序列用于下行链路（同步）和上行链路（随机接入）的初始接入、上行控制信息传输、上行信道探测，以及用于精细信道估计的参考符号（导频）。毫不夸张地说，现代蜂窝标准中除数据传输信号外，绝大多数信号类型均采用ZC序列。