The combination of multi radio and multi protocol solutions can accommodate two or more radios running different multi protocols on the same or different spectrum at the same time.
Today, the market is driven to design products with multiple RF protocols in a box called gateway. Wireless connection brings many different benefits, provides better user experience, and different protocols provide complementary advantages. Each IOT device can communicate with the Internet through different protocols, whether ZigBee, Bluetooth, Z-Wave or Sub-1GHz, or some proprietary protocols. Multi protocol (wireless) gateways play a crucial role in the Internet of things infrastructure because they collect data from sensor farms and push data to the Internet through Wi Fi, cellular or other wired and wireless networks.
The combination of multi radio and multi protocol solutions can accommodate two or more radios running different multi protocols on the same or different spectrum at the same time. This method provides more efficient and reliable data flow by using different protocols. Therefore, end users can make full use of this because they can connect multiple devices running on different RF bands and protocols through a single unit.
Key challenges in designing multi protocol compact rf hardware
- The emergence of multi protocol hardware is a response to the popularity of many different communication protocols. Therefore, OEMs face some key challenges in designing multi radio hardware
- Multi radio hardware needs a lot of time in antenna selection, layout, simulation, memory estimation, shell design, material and field test
- Precise impedance control to reduce interference, return loss, coexist between radios in the same location, so it can meet the requirements of FCC, CE and other regulatory agencies
- If two or more radios operate at the same time and share the same spectrum, there will be coexistence, which will lead to mutual interference
- The communication delay, distance, efficiency and reliability of multi radio hardware are measured
- Coexistence often affects the performance of devices, resulting in packet loss or data damage, burst and burst noise in audio, and reduced working range and coverage
- Due to different standards applicability, when multi radio hardware appears, compliance for different geographical regions will also be a challenge.
Considerations when developing firmware for multi radio hardware
Nowadays, the application of Internet of things is more and more complex, and the demand for storage capacity is also increasing. Let’s understand the challenges of hardware engineering solutions brought by memory and firmware:
- Developing user-friendly and flexible embedded applications requires complex state machines, powerful power optimization, memory density and CPU performance. RF SOC or module needs more flash and ram optimizations for optimal performance
- Providing over the air (OTA) firmware update requires sufficient flash memory to store boot loader and twice the size of application firmware, so as to keep the old firmware and buffer the new firmware, so as to make products competitive in today’s booming Internet of things market
- Real time management of multiple radios with various network architectures without loss of performance
- In the case of no power supply, flash can also retain the user configuration and security key content for many years, because in the life cycle of the product, the information in flash can be read and written thousands of times. In this case, the ram information can be written to read quickly, which enables the processor to work at such a high speed and perform edge processing
Based on the above challenges, let’s take a small example. A complex wearable / sensor / automation application may need 128kbram and 512KB flash memory provided by RF module. A relatively simple beacon application may only need 24 KB ram and 192 KB flash.
To address the above challenges in terms of multi radio hardware, memory, and firmware, let’s see how OEMs’ hardware expertise can be used to address these challenges to help improve overall product performance.
The standard approach starts with a product understanding of all RF requirements and other peripherals, listing all RF interface protocol frequencies, and then performing a task such as module or SOC selection, relative antenna selection, material identification of enclosure, module placement, and antenna. 2D floor planning will be carried out in the early stage of PCB design, which will help to understand the actual location and parameters of all RF modules in detail
Module or SOC selection: selection criteria include RF protocol, modulation technology, manufacturer, MCU / processor requirements based on driver code availability, ram, flash memory, OS, regulatory approval, maximum TX output power, receiver sensitivity, power supply and data rate to provide significant performance
Memory budget: for any RF module, memory budget is a very important parameter. Its definition or calculation is completely based on RF stack size, support for the number of devices and application business logic. Before finalizing the module / SOC, the memory related requirements should be well calculated and clarified
Antenna selection and placement: antenna selection is the most important factor in multi radio hardware, because the selection depends on frequency range, polarization, radiation pattern, gain, feed point impedance, VSWR and power handling capability, such as range coverage and space. For example, chip antenna vs PCB tracking antenna vs external antenna
In order to reduce the co-existence and interference between two modules in the same frequency, antenna layout plays an important role. In this case, the antennas should be placed perpendicular to each other. We are trying to carry out proper isolation between the two RF antennas according to the regulatory requirements, and the isolation between the two antennas should be equal to or greater than 30 dB. Sometimes, due to space constraints, it is impossible to achieve such isolation. In this framework, the interference and radiation patterns of all RF antennas need to be considered. We also need to study the transmit power of RF module or SOC according to the application requirements and performance.
RF simulation: in the early stage of product development, simulation is an effective strategy to predict radio problems. There are many kinds of simulation software, such as HFSS, CST, ads, etc., which should be used reasonably according to the type of problem.
Shell design and materials: to achieve the best results, try to use materials that can balance the environment, reliability and RF performance requirements to finally determine a plastic shell. Sometimes, cots enclosure may lead to placement challenges due to the pre-defined size and structure. In the custom design, we have the flexibility of PCB placement, and can get better isolation and antenna placement options. The selection of dielectric constant / permittivity of shell material plays an important role in RF performance. At 2.4GHz, good plastic materials are PC, ABS, PC + ABS and PVC. Sometimes we also need to choose a metal enclosure for outdoor and industrial applications. In this case, the choice of external antenna will be the key.
Design verification test: the design verification of RF interface is very important. It is necessary to define a set of verification test cases, such as antenna matching impedance and return loss, RF output power measurement, receiving sensitivity, indoor and outdoor distance test, worst-case RF environment in heavy traffic scenario, and use the analyzer for monitoring.
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