每个连续的wi - fi代提供了更高的data rates and more capacity, but also presents more challenging requirements for Wi-Fi product design. The Wi-Fi 5 standard used in many current products achieves up to 866 Mbps downlink data rates over a single RF channel, and up to 6933 Mbps using 160 MHz channels and eight simultaneous data streams. It offers 8x8 MU-MIMO (Multi-user Multiple Input Multiple Output) and uses 256 QAM (Quadrature Amplitude Modulation). It's a big step up from the previous Wi-Fi 4 standard, which supported only 600 Mbps maximum downlink data rates using 4x4 MIMO. The next generation, Wi-Fi 6, adds 1024 QAM and OFDMA (Orthogonal Frequency Division Multiple Access), to achieve even higher uplink and downlink speeds up to about 9600 Mbps.
为了构建符合新Wi-Fi的日益具有挑战性的挑战性要求的差异化产品，您需要最好的软件和最佳硬件组合。首先，您需要RF前端提供卓越的输出功率和范围，以及低电流消耗和高效率。其次，您需要在单个包中包含最佳共存和支持多个标准。在本文中，我们探索如何将软件和硬件策略结合起来实现这两个关键目标，并创建一流的Wi-Fi产品。
PA和数字预失真（DPD）
The PA is the most critical component of the RF radio in a Wi-Fi transmitter. The PA's performance affects range, coverage area, data rate, capacity and power consumption. Wi-Fi access points typically transmit between 100 mW and 1 W of RF output power. The PA must be able to generate this power with minimal non-linear distortion.
每个Wi-Fi的一代都需要PA线性的重大改进。为了满足此要求，必须使用新的更高线性的PA硬件，以及数字预失真（DPD），一种基于软件的方法，用于使用数字信号处理技术去除失真。虽然PA硬件提供了大部分的线性性改善，但DPD使得更小但基本的贡献。DPD使用软件模型来测量PA的非线性并使用启用软件的预失真算法创建逆信号，然后将PA输出信号线性化。
A widely used Wi-Fi PA linearity measurement is Error Vector Magnitude (EVM). EVM quantifies the performance of a digital communications channel, measuring the deviation of captured encoded data symbols from their ideal locations within the I/Q constellation. The PA must deliver acceptable EVM over the full operating range of power output and channel frequencies.
图1说明了最新Wi-Fi标准所需的越来越严格的EVM系统规范。
Figure 1: EVM System Specifications for Wi-Fi 4, 5, and 6
图2显示了典型的EVM PA测量，随着输出功率增加。如图所示，EVM劣化发生在11dBm高于11dBm以上的高输出功率水平。随着PA输出增加并进入增益压缩区域，出现导致EVM增加的非线性失真。
For a Wi-Fi 5 application, this PA needs to deliver output power above 16 dBm and therefore cannot meet the specification of 2.5% (-32 dB) EVM; its linear output power is insufficient for a Wi-Fi 6 transmitter design. Additional linearization is needed to meet the specification.
Figure 2: Example PA EVM % vs. Pout Measurement
As shown in Figure 3, using DPD with the PA provides this additional linearization, enabling the PA to meet the Wi-Fi 5 EVM specification of 2.5% (-32 dB).
Figure 3: Example PA EVM % vs. Pout Measurement – with and without DPD
非线性失真的一个主要影响是相邻的信道泄漏：在Wi-Fi频段外的频率传输。如图4所示，DPD大大减少了相邻的信道泄漏。
图4：示例PA输出频谱测量 - 有和没有DPD
Wi-Fi干扰的最佳解决方案 - 软件，硬件或两者？
Interference can occur inside a Wi-Fi device or between devices. For example, interference can occur between Wi-Fi and wireless signals from carriers such as AT&T and Verizon; there can also be interference between different wireless standards supported within an access point. The most common scenarios involve interference between Wi-Fi and Bluetooth or LTE, because those technologies are so widespread.
三种主要的干扰类型对于Wi-Fi产品设计很重要。
- 非Wi-Fi干扰。这涉及在Wi-Fi频带之外的频率运行的设备。当诸如LTE电话或无绳手机之类的设备时，它通常发生在Wi-Fi频谱中的噪声，干扰Wi-Fi接收。
- Adjacent channel interference。This occurs when Wi-Fi devices in close proximity operate in the same spectrum range but on different channels that overlap. These devices essentially talk over each other.
- 共同渠道干扰。设备在相同的频率上运行，但使用不同的无线电;每个客户端和接入点都竞争相同的通话时间。例如，共同信道干扰可能发生在2.4 GHz Wi-Fi和蓝牙，ZigBee或线程之间。同一设备上的不同无线电也会发生共同信道干扰。
必须使用诸如批量声波（BAW）Wi-Fi共存或BandEdge过滤器等硬件解决方案来寻址非Wi-Fi和相邻信道干扰，因为我们将在以下段落中讨论。通过使用软件和硬件的组合在RF无线电之间建立协调来解决共同信道干扰。通过使用将智能软件与芯片（SOC）相结合的解决方案，您可以消除大量的共同信道干扰。
The best solution for non-Wi-Fi and adjacent channel interference is filtering. BAW filters, along with intelligent software, effectively eliminate interference between Wi-Fi and adjacent frequencies, and also provides a scalable solution. They prevent devices such as cell phones from interfering with Wi-Fi reception, and they allow Wi-Fi access points to utilize the full Wi-Fi spectrum for transmissions without the risk of interfering with adjacent bands.
Interference can also occur within devices that have multiple antennas as well as multiple radios (e.g. Wi-Fi, Bluetooth, Zigbee, and Thread). Proper antenna isolation is paramount to mitigate the potential for coupling between antennas. Without proper isolation, a transmit signal from one antenna can generate increased noise at a receiver on the same device, negatively impacting the signal-to-noise ratio and desensitizing the receiver.
Currently, no software algorithms exist that can effectively increase antenna isolation or decrease desensitization. The only resolution is to add bandpass or notch filtering. Figure 5 shows two examples of front-end modules with embedded filters. Using integrated modules with embedded filters, as opposed to discrete components, is the best approach because it reduces the need for external tuning, requires less board space and simplifies design.
图5：Wi-Fi前端模块带嵌入式凸帘滤波器
外带
Hardware and software are equally important when designing a best-in-class Wi-Fi product. Cohesively integrating software and hardware can help you optimize RF front-end performance, maximizing output power and efficiency and minimizing power consumption. A combination of software and hardware also helps to increase linearity and meet interface requirements set by regional certifying bodies. Integrated front-end modules typically provide the best solutions. They help reduce design time and are typically engineered with enough headroom to meet regional requirements, increasing the likelihood that the final Wi-Fi product will achieve certification.