How to make the optimum design choices to meet coexistence requirements while achieving performance targets.
The termscoexistenceandinterferencedescribe the same connectivity issue from different perspectives.Interference设计Wi-Fi产品时是一个关键问题，特别是因为今天的家庭包括快速越来越多的不同无线设备，具有不同的无线通信协议。共存目标是：允许所有无线电，协议和标准运行，而不会导致同一连接环境中的问题。
Let’s explore the wireless environment of today’s connected home – where many devices and standards can interfere with Wi-Fi – and then examine some strategies Wi-Fi designers can employ to address and solve the primary types of Wi-Fi interference.
The evolving wireless home environment
Wireless connectivity is the easiest, most reliable and most cost-effective way to create a connected home or office — or a smart city. The number of wireless devices in the home is expanding with extraordinary speed: by 2022, the average home is projected to have up to 50 connected devices, including cell phones, TVs, computers, appliances, and smart thermostats (Figure 1).
这些设备中的许多都将通过Wi-Fi进行通信，而其他设备将使用蜂窝连接或本地区域的内容（IOT）网络（如ZigBee，蓝牙低能量（BLE）和线程。提供所需的连接，智能家庭正在移动到一个分布式Wi-Fi模型that includes access points throughout the home and support for more standards.
设备和不同的无线标准的增殖为潜在的共存和干扰问题创造了HotBed，这意味着Wi-Fi设计师可能必须解决几种类型的干扰。
图1.每间客房的无线室内架构与豆荚
三种类型的Wi-Fi干扰以及如何解决它们
三种主要类型的干扰可能会影响Wi-Fi系统：非Wi-Fi, adjacent channeland共同渠道(Figure 2).
图2. Wi-Fi干扰的三种模型
有两种主要方法可以解决Wi-Fi CPE单位内的共存和干扰（图3）：
- Establish coordination between the radios.防止一个无线电（Wi-Fi，蓝牙，Zigbee等）试图与另一个相同的时间避免潜力共同渠道interference。This can be achieved using a system-on-a-chip (SoC) solution that supports multiple standards and coordinates communication among them.
- 创造足够的隔离水平between potential sources of interference。This can be accomplished using RF filters and by managing the board layout and antenna design. Filters are the most cost-effective and scalable approach. They help with相邻的信道and非Wi-Fiinterference。
RF应用中使用了两个主要滤波器技术：散装声波（BAW）和表面声波（SAW）。BAW过滤器为家庭内的许多应用提供了最高的性能，并且特别适用于用于Wi-Fi和其他标准的较高频率。
- BAW filters have lower insertion loss, higher power handling, steeper skirts and a higher Q factor than SAW filters and are also more temperature-stable. BAW filters therefore enable more effective use of the full Wi-Fi spectrum, increasing capacity and range.
- Due to their higher performance, BAW filters provide better future-proofing for the stringent performance requirements of 802.11ac and 802.11ax (Wi-Fi 6) standards.
Figure 3. Ways to Address the Three Types of Wi-Fi Interference
解决干扰的考虑因素
在Wi-Fi系统中，寻址干扰的规范比其他参数更少于其他参数，例如吞吐量和范围。这意味着设计人员在选择RF组件时需要超越基本系统规格，并仔细考虑潜在的共存问题和解决方案。这些包括：
- How interference affects receive sensitivity and throughput
- How much isolation is needed
- Temperature stability
- 系统的插入损耗和整体链接预算
- 共存with other standards using Wi-Fi spectrum (Zigbee, Thread, Bluetooth, etc.)
敏感性及其对吞吐量的影响
Wi-Fi 6的目标是提供非常高的数据速率，可能达到每秒千兆。为了实现这种性能，802.11ax在整个发射过程中需要非常高的线性（低EVM）并接收RF链。它需要比前面的Wi-Fi标准更大的接收灵敏度，因此更为缩小灵敏度的干扰更大。共存过滤器已经广泛用于智能手机和其他客户端设备，以提供防止非Wi-Fi干扰所需的隔离;使用802.11ax，也会在Wi-Fi接入点中使用共存过滤器将更大的势在必行。
隔离：需要多少？
大多数天线设计可以在意外（干扰）和预期信号（无线）之间提供20-30dB之间的隔离。但是要获得良好的吞吐量，干扰信号不应超过-70至-90 dBc - 这意味着设计人员需要将另一个40-60 dB的隔离构建到Wi-Fi前端系统中。过滤器可以有效地帮助。
对于非Wi-Fiinterference, a BAW Wi-Fi coexistence filter provides isolation that protects receive sensitivity and prevents performance degradation. As shown in Figure 4, interference shifts the baseline packet error rate (PER) curve to the right; beyond a certain threshold, the receiver can no longer interpret the incoming data. A coexistence filter greatly improves sensitivity; the PER curve moves to the left.
图4.干扰如何影响接收（RX）路径上的吞吐量
温度：设备的性能，稳定性或灵敏度是多少？
并不是所有过滤器都是平等的。一个过滤器的频率uency response drifts as the temperature changes. If an LTE or other non-Wi-Fi interferer is close enough in frequency that it overlaps the temperature drift of the device, the Wi-Fi system will have no protection.
Temperature-compensated filters, which have much less temperature drift, are designed to counteract this problem and are an important component of high-performance Wi-Fi systems. As shown in Figure 5, temperature-compensated BAW filters offer an improvement in temperature stability over SAW filters. They also offer much higher Q factors than SAW – which is an important factor since SAW may not even be an option for 802.11ax due to the stringent linearity, throughput and performance requirements.
Figure 5. SAW versus BAW Thermal Drift
系统的插入损耗会影响盒子内的整体链接预算和热量
Lower insertion loss means a better link budget. BAW offers lower insertion loss than SAW at the higher frequency bandwidths used by Wi-Fi. This translates into higher output power and operating range, and better receive sensitivity. Decreasing the insertion loss by 0.5 dB translates to an 11% improvement in power-added efficiency, which also means an 11% improvement in thermal dissipation.
温度也对共信道共存产生了影响，因为它影响了系统余量。具有更多温度裕度的系统可以允许更高的容量。
共存with other standards (e.g., Zigbee, Thread, Bluetooth)
共存between Wi-Fi and other standards can be achieved by coordination (time multiplexing) or filters (frequency multiplexing). Key transceiver solutions use time multiplexing to support Wi-Fi and IoT standards that share the same spectrum. However, performance and throughput start to degrade as the number of devices increases, duty cycles increase, or airtime becomes more congested. A complementary approach of frequency multiplexing, using filters, can expand network capacity and improve reliability.
外带
在Wi-Fi产品设计中，共存和干扰是影响用户体验的重要问题，这些问题通常不会受到足够的关注。由于家庭内的设备和网络标准越来越多，并且由于向Wi-Fi 6（802.11ax）的转换需要更高的性能，因此干扰成为更大的关注。根据干扰类型，解决问题的方法包括BAW共存和BandEdge过滤器，以及互通多标准之间的通信的收发器。