Adaptive antenna system by ESP32-PICO-D4 and its application to web radio system

Abstract: Adaptive antenna technique has an important role in the IoT environment in order to establish reliable and stable wireless communication in high congestion situation. Even if knowing antenna characteristics in advance, electromagnetic wave propagation in non-line-of-sight environment is very complex and unpredictable, therefore, the adjustment the antenna radiation for the optimum signal reception is important for the better wireless link. This article presents a simple but effective adaptive antenna system for Wi-Fi utilizing the function of a highly integrated component, ESP32-PICO-D4. This chip is a system-in-chip containing all components for Wi-Fi and Bluetooth application except for antenna. Together with SP3T RF switch and dielectric antennas and high-resolution audio DAC, completed web-radio system is made in the size of 50 x 50 mm.

Keywords: beam switching, adaptive antenna, system-in-chip, ESP32, web-radio

Specifications table
Hardware name Web radio with adaptive antenna Subject area • Engineering and Material Science Hardware type • Electrical engineering and computer science Open Source License Creative Commons Attribution-Share Alike license Cost of Hardware 30USD Source File Repository https://osf.io/rf8d7/

1. Hardware in context 1.1 Introduction The recent drastic increase of IoT edge device leads to high congestion in the wireless communication. One solution for this issue is an adaptive beamforming. Adaptive beamforming and adaptive antenna techniques already have a long history and its effectiveness are well confirmed, nevertheless, they are rarely adapted for consumer product due to cost and circuit complexity.
   Recently, the significant progress of semiconductor integrated circuit technology has enabled RF transceiver for Wi-Fi and Bluetooth in one package and eventually very powerful dual-core processor, flash memory for storage, SRAM for main memory and all peripherals are integrated into single package. The main chip of this article, ESP32-PICO-D4 is one kind of such a highly integrated chip. By using this chip, not only RF transceiver implementation but also fully programmable system is easily realized.
   This article presents a simple but effective adaptive antenna system for Wi-Fi utilizing programmability of the chip. Together with SP3T RF switch and dielectric antennas and high-resolution audio DAC, completed web-radio system is made in the size of 50 x 50 mm. As demonstrated in this article, the circuit will select one antenna for maximum RSSI to a given access point in the initial boot process and move to start the web radio system. The web radio system is based on two sophisticated codes [9][10] and station preset and selection can be made through a web browser. The application of the implementation of adaptive antenna selection introduced in this article is not limited a web radio system but also various IoT application is expected.

1.2 Comparison to previously published designs ESP32 series have a lot of users all over the world but the author could not find this type of application, combining with RF SP3T switch in the literature. The adaptive antenna system is widely reported in various articles but the two-chip configuration consisting of the system-on-chip and SP3T switch is the simplest implementation.

1.3 Comparison to commercial instruments The adaptive antenna is not novel technology but rarely applied to consumer product from the viewpoint of cost. ESP32-PICO-D4 is a very recent chip (released on Aug. 2016) and at the moment of submission, just one simple prototyping board (Espressif’s genuine board, ESP32-PICO-KIT V3) can be found on the market. The circuit in this article costs just $30 even including audio DAC, which is quite competitive to established commercial products. 2. Hardware description.

2.1 System overview

Fig.1 Block diagram of the whole system

Figure 1 shows the whole system block diagram. The main processor is ESP32-PICO-D4, which is a system-in-package component. ESP32-PICO-D4 contains all components required for Wi-Fi and Bluetooth application except for antenna just in 7 x 7 mm package. The programming environment is well organized by Espressif, the manufacturer of ESP32-PICO-D4 and released on GitHub [1]. Table 1 denotes the summary of ESP32-PICO-D4 specifications. Together with RF part, the high-performance main processor is able to support complex applications.

Table 1 Brief summary of ESP32-PICO-D4 speficiation[2] Items Specification Main Processor 32bit LX6 Dual core 240 MHz Containing RF radio WiFi Bluetooth SRAM 520 kB Flash Memory 4 MB Package size 7 x 7 mm

As shown in Fig. 1, the system has four peripherals including CP2102 USB serial in

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