Question: How to create an RF Link between two TI's CC110L+CC1190 Combo Transceivers

Wireless and IoT RF and Wireless
1

Hello Tech team,

I am working on my company’s patented project where an airline passenger needs to track his check-in Suitcase with a Remote Control. Since GPS and WiFi signals do not reach deep inside the airport buildings (especially underground areas), we are planning to use TI’s CC110L+CC1190 Combo transceivers at both ends using lower frequency 863-928 MHz ISM band. A battery powered Device comprising an MSPM0G3507ZR MCU, CC110L+CC1190 Combo and related circuitry will be installed inside the suitcase. Similar circuit will be installed in a Remote Control. The GOAL is to determine approximate distance and the (possible) direction of Suitcase location from the Remote Control when the passenger pushes a Button.

I have spent more than a week researching on the Internet, including TI.com website. But I did not find any Application Note etc. teaching the basics how to design the RF link.

I hope some tech expert in this field can answer my questions.

1) I have learned on ST Micro website that distance between two transceivers can be estimated using the RSSI (Received Signal Strength). For that, first I need to know how to configure CC110L to define the TSS (Transmitted Signal Strength). Is it the signal strength written in the data sheet? And then, how to compute RSS?

I assume CC110L (in the suitcase) would transmit/advertise a Beacon packet, which will have TSS stored in 1-2 bytes. When CC110L in the Remote detects the packet, it will store the packet in the Receiver FIFO. A few packets will be received/stored in the FIFO, then some sort of averaging would be done (by the software) to estimate the RSS. After that, based on the LNA Gain (I assume configured initially), RSS value could be calculated by the MCU. This is the basic process needed by every design. So, I am expecting TI to provide software/firmware and necessary documentation. Is there something available?

  1. How accurate would be the estimated distance based on RSS? I need to take into consideration the suitcase may be stationary inside, or slowly moving on the luggage belt. And also, there will be loss of signal based on the number of walls between the Suitcase and the Remote.

  2. The Orientation of the suitcase would not be fixed. It could be lying flat, or standing vertically. I assume the ISM band antenna would transmit Omni-directional RF signal, and suitcase orientation would not be an issue. Am I correct?

  3. Is it possible to estimate the direction of the suitcase from the Remote? Do I need to install accelerometer etc.?

Thanks. AB Singh

2

I see you also pinged the ti e2e forum: https://e2e.ti.com/support/wireless-connectivity/sub-1-ghz-group/sub-1-ghz/f/sub-1-ghz-forum/1389822/cc110l-question-how-to-create-an-rf-link-between-two-cc110l-cc1190-combo-transceivers

I’ve read a few studies over the years on using RSSI/etc for distance accuracy. Most end up being meters off, but in the “ball park”…

Regards,

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Hi absingh,

I can see many potential problems with implementing your idea that I suspect needs further consideration.

First, RSSI is going to be extremely unpredictable in such an environment with so many variables, to the point that I would think you would be hard-pressed to determine whether your device was 10m or 50m away with any consistency.

Second, I don’t think any single sub-GHz frequency band is legal everywhere in the world, so unless your device was guaranteed to be used only within specific regions of the world, it could potentially be transmitting illegally somewhere.

Thirdly, I suspect most airlines would not appreciate customers placing transceivers within their cargo compartments. I would recommend you have discussions with airlines, at least within the regions for which you expect these devices to be used, before spending significant resources in developing such a product.

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