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

Hello RGW,

Thanks for ur feed back. However, after reading ur replies, I am more at loss than before. FYI, We are not at the design stage yet. We are doing feasibility - to see if it is even possible to reach our goal, as I have defined earlier.

1) You did not answer my 1st question about TSS (Transmitted Signal Strength), and then about RSS (Received Signal Strength). I want to know where such information is given; it is not in the datasheet.

2) You have sent 2 links to some software examples. I have downloaded both. There are only code files - NO Documentation. How can we do evaluation? I am looking for detailed description, flow charts, state diagram and block diagrams etc. to understand what is needed to be done. Code writing comes later. At this stage, we are evaluating if we can use TI's transceivers. We are also evaluating ST-Micro and some others. Obviously, we will select the ICs where we find documentation. Once again, there is no App Note at TI's website for CC110L.

3) You have written : "Accuracy of RSSI signal is specified in the datasheet". Can u please point out where? I could not find. The only info I found was about RSSI status etc.

4) Further, u have given a generic answer to the "objects attenuating...". That is what I want to know. Someone with experience using these ICs for indoor applications would have some idea about how much ISM signal attenuates per wall between Tx and Rx units. For example, I know the indoor signal range of 2.4GHz WiFi signal based on my experience.

5) About Omnidirectional antenna, u have given some details about the donut shape of the radiation pattern. But I am looking for a solution for this problem, because I have no experience. Can we use 2 antennas mounted at 90 deg. to each other? I am hoping someone in the community has experience using moving Tx unit.

6) You have sent the Range Estimator. Thanks. But I cannot use it because I don't know the objects between Tx and Rx units in commercial buildings. I hope someone has experience and give me some estimate.

Looking forward to get some answers. Thanks.

Hi,

1. Transmitted Signal Strength is roughly the output power level  in dBm + antenna gain. The output power levels that can be achieved are in the datasheet.

2. There are many application notes associated with CC110L, CC1101. Please refer to  https://www.ti.com/product/CC110L#tech-docs

3. Refer to section 5.18.2 in the CC110L datasheet

4. Refer to the Range Estimator. It is impossible to say in a general term what a wall attenuates ? How thick is the wall ? Wall material ? Frequency of operation ? All these parameters effect the total attenuation and these are summarized in the Range Estimator tool and in the app: note https://www.ti.com/lit/pdf/SWRA479A

5. Refer to DN035 for a selection of antennas that can be used: https://www.ti.com/lit/pdf/swra351

6. The objects between the Tx and Rx unit have to be estimated in a rough manner in order to calculate the necessary link budget. The range estimator calculates a realistic pragmatic range and not an optimist range. 

Hope this helps a bit more.

Hello RGW,

Thanks for all the info supplied by u. Below are my replies to all items.

1) Transmitter Signal Strength - I understand now.

2) I have reviewed all App Notes from the CC110L link sent by u. I had already looked at these notes, and did not find what I am looking, as I wrote in my original question. Is there a standard protocol/process to create a link between the two CC110L transceivers, or similar transceivers? For example, I don't even know what format is used for the Beacon packet.        

2.1) I found an Antenna Diversity Note in the CC110L notes section, which is very useful. I also found another app note  AN085 at TI site by doing my own search - very useful. Together, these two notes gave answer to the Antenna donut problem pointing out by u. Thanks.

3) I had read section 5.18.2 in the CC110L datasheet before even starting this discussion. That section has a link "RSSI" Status Register. When I click on it, it takes me to Table  5-70 on page 77. That table has only one row. It does not have any information about the RSSI value stored anywhere in the datasheet. Please review that section yourself.

4, 6) Range Estimator App Report seems to be helpful. It is very long, so I will take time to review and understand it.

5) Antenna Selection Guide is also helpful. I have downloaded.

Thanks a lot.

Not too sure if this will work as you intend. 

If you are standing in a (flat) field without anything around you could probably estimate the distance but on an airport the signal will reflect off a lot of surfaces. In addition the probability is very high that something is between the sender and receiver (wall, humans, other luggage, the list is long) meaning that the RSSI will have a rather large variation in time, even with a fixed location. 

Before you continue with this I would get a couple of EMs (it doesn't matter if it's CC1101 or something else), use SmartRF Studio and send packet with one device and receive them with another one and check the RSSI variation etc.  

Hello TheGhostOf,

Thanks for ur reply. I am getting more and more aware of the fact that it is very difficult to accurately estimate the distance between the luggage bag and the Remote - with all these variations. If not (unable), then if the passenger pings the luggage suitcase and get a response, that validates that the bag has arrived at the airport, and is not lost. And if it does not come out at the luggage belt, airline employees can go and search it. I hope at least this much is feasible to do.

However, I have few other questions that I asked earlier to RGW. If anyone has past experience creating a RF link, please share that info. I did not find the DESCRIPTION of the basic process anywhere on TI site. This is the very first step in the project.

Thanks.

Hello RGW,

Thanks for ur reply. During past few days, I have done lot of research on my project. I will first reply to ur suggestion,  then discuss other issues.

1) Link Budget is not an issue. Using the combination of CC110L+ CC1190 (as I wrote originally) with 27dBm Tx power and -120dBm receiver sensitivity, I should get 147dBm budget, which is enough. Our range at airports is not too long.

2) The main problem is the unknown obstructions, that may reduce the range by an unknown amount. You have suggested to perform a test, but TI engineers have already done a comprehensive test. I have read the Application Report SWRA479A (thanks for sending me all those links). In this report, after doing extensive testing inside a High rise building, TI has published Table 3, that lists the attenuation for all commonly used building materials. The important ones to me are 8" concrete (25dB) and 1/2" drywall (0.3dB). We can use these numbers in our estimation. We have the  Tx Power, and RSSI (measured value) at the receiver CC110L. So, I don't need to repeat the same test.

3) I have also learned from articles about the Friis equation, that there is 6dB Free Space Path Loss (FSPL or simply FSL)when u double the distance. This could be a useful number for our estimation. However, there is an assumption in Friis equation - it works for large distances (between the Tx and Rx) where the small spherical area of the RF signal sphere is almost a Plane Surface compared to the antenna aperture size. The equation fails miserably at smaller distances. For example, I calculated the loss at 1m, 2m, 3m, 6m etc. And the loss came as 27.7, 33.7, 37 and 43 dB. At 0.1 meter loss comes out as 7dB. These numbers are useless for our project. We are dealing with distances from 1m to about 300m at the most.

4) This leads me to a question for u and the community. Is there a formula to calculate the FSL (signal attenuation) for shorter distances where Friis equation fails? Or a way to modify the Friis?

5) If I find a formula, I can estimate the distance at the same elevation (floor of the airport) assuming there are no objects in the path of the signal. There may be 2-3 dry walls in between, the loss should not significantly affect the estimated distance. However, if the luggage bag is at a lower or higher floor from the passenger, the loss will be 25 dB/floor. And there is no way for me to estimate that distance. Can anybody suggest a solution?

Besides above, my previous questions still remain unanswered, especially about the RSSI register, and the basic design process to follow. And also about the Beacon. The only thing I could find in the data sheet is the Packet Format, which has a Preamble of 0101... pattern.

I hope you or someone in the community can provide further help. Thanks.

Hello Community experts,

I am still waiting for someone to reply my above questions.

Besides these, I have discovered an issue in the Application Report SWRA479A. On page 3, paragraph "2.2 Link Budget", TI application engineers have calculated the Link Budget. They have included the Antenna Gains at sending and receiving ends. This is for an IDEAL dipole antenna, which I assume has no losses. As I started evaluating 915MHz antennas, I found that every antenna has losses in it. All manufacturers have defined antenna EFFICIENCY in their datasheets. This ranges from 35% to 60%. (There may be other antennas with higher efficiencies, which I have not found yet). This fact is really alarming. Does it mean the link budget will reduce significantly? Because the efficiency for TX and Rx antennas has be to included in the budget equation. Can any RF expert answer my question - How to modify the Link Budget equation?

Thanks.

Hello Community,

I am surprised that no one has answered my previous questions yet. I expect TI having RF application engineers who know how to use ICs made by TI. And my questions are very basic - needed for creating any RF link using Transceivers.

As I continue my study of RF, I came across an important parameter in the CC1190 datasheet which is ambiguous. On page 2 in the Table for Absolute Max. Ratings, it states: "Input RF level" to be 10dBm. The datasheet does not state the Pin. There are two possible pins where this max. 10 dBm can be applicable: Pin PA_IN, or LNA_IN. If it is PA_IN, then I can limit the output power from the CC110L to CC1190 to 10 dBm and everything is fine. But if the requirement is at LNA_IN, then the system won't work. Because - at the Antenna end, received power (RSSI) is coming from another CC1190 at the other end in my RF Link, which is transmitting 27 dBm. The losses would be small for most cases (especially for smaller distances on the same floor of the airport).

I hope someone will soon answer my questions. Thanks. 

Hi,

1) I can comment on the RSSI question:

The CC110L RSSI value is given in dBm with a ½-dB resolution (from Section 5.18.2 of the datasheet). You may also find the following App Note useful for additional information: 

SWRA114 (RSSI Interpretation and Timing): https://www.ti.com/lit/swra114

2) Regarding the CC1190 maximum input power rating:

The maximum input to the LNA (LNA_IN) of the CC1190 is +10 dBm. The following App Note might help with developing a solution for this if using the CC110L standalone, but unfortunately the CC1190 does not have this flexibility; it would be limited to the lowest output power possible when using the CC1190 or you would need to add a switch to bypass the CC1190: 

SWRA147 (Close-In Reception with CC1101): https://www.ti.com/lit/swra147

3) Because the CC110L supports less features than the CC1101, the CC1101 TI.com page has more Application Notes available. Whilst not all are applicable to the CC110L, they are still worth being aware of: https://www.ti.com/product/CC1101#tech-docs

Regards,

Zack

Hello Zack,

Thanks for ur reply. I am addressing each item one by one.

1) RSSI - I have read section 5.18.2 many times. I have to make this ASSUMPTION now - using my common sense, because this info is not provided anywhere in the datasheet of CC110L.

      The received (measured) signal power level is read and stored in the Rx FIFO; then based on the LNA gain, the estimated        value of RSSI is calculated by the CC110L (not by me in my code) and stored in the RSSI register. My code can read this value and apply Offset etc, as written further in section 5.18.2. 

     PLEASE VERIFY IF MY ASSUMPTION IS CORRECT. The App Note DN505 (or any other App Note even under CC1101) does not give this basic info.

    Another confusing info in the datasheet. Please see this: "Table 5-70. 0x34 (0xF4): RSSI - Received Signal Strength Indication"

It seems there are two addresses shown for the RSSI register: 0x34 and 0xF4. Can anyone clarify this info.

2) CC1190 - Max. Input Power level = 10dBm. This is a vague statement. Zack, u have replied that LNA_IN is +10dBm. How did u come up with this answer? Is there a document where this info is written? Or u made an assumption? Because, what u wrote contradicts info in the datasheet.

    On page 11, row 6 of the Table shows Receiver sensitivity to be -112dBm. On 1st page, right side column states -120dBm High sensitivity at 1.2 KBaud rate, 915 MHz using CC1190 along with CC110L.

Therefore, it is evident that a gain of -6dBm is achieved using CC1190. And the only way it could be possible if the LNA of the CC1190 is utilized. Moreover, if I the user has to bypass the LNA (as suggested by you), then why would I use CC1190 at first place? And why would TI manufacture this IC? The whole purpose is to increase the RANGE.

I hope someone at TI can escalate all my issues to the higher level Manager etc. and get correct answers. Otherwise, the new customers like me will NOT be able to use these ICs - loss of big new business.

Thanks again.

1) You requested the accuracy of the RSSI; you do not need to compute anything apart from the procedure outlined in Section 3 of DN505/Section 5.18.2 of the CC110L datasheet (subtracting the RSSI offset, which varies according to the register settings) to produce an absolute power estimate of the received signal. Your assumption is what is stated in those documents. Please rephrase your question if you require more detail.

Regarding the RSSI register address (and all of the Status register addresses), from Section 5.7 of the CC110L datasheet:

For register addresses in the range 0x30 - 0x3D, the burst bit is used to select between status registers when burst bit is one, and between command strobes when burst bit is zero (see Section 5.8). Because of this, burst access is not available for status registers and they must be accessed one at a time. The status registers can only be read.

The replies by Siri in the following threads also give some additional context for this: 

• https://e2e.ti.com/support/wireless-connectivity/sub-1-ghz-group/sub-1-ghz/f/sub-1-ghz-forum/625860/cc1101-device-id-read-out-as-0x1f-different-from-the-specification 
• https://e2e.ti.com/support/wireless-connectivity/other-wireless-group/other-wireless/f/other-wireless-technologies-forum/318124/question-about-rssi-register-address-in-cc2500 - this is also relevant to the CC110L, as the mechanism involving the required burst bit to access the STATUS registers is the same (and, in fact, the address is the same for the RSSI register).

2) The main use of the CC1190 is to extend the range, i.e. it is not designed for applications where the RX and TX devices are close to one another (this is not contradictory). The receiver (LNA) has a maximum signal power it can handle before it saturates and then a maximum input power rating which, if this is exceeded, could damage the chip. As with any receiver, transmitting at "high" power close enough to the receiver will at best cause saturation (such as transmitting +27 dBm with minimal attenuation at distances that would exceed +10 dBm received signal power). The CC1190 is not a "smart" device, so has less capabilities for close-in performance compared to the CC1101.

SWRA147 was written to address the use-case of improving close-in performance; either you would need to work around this by using an RF switch to bypass the CC1190 for close-in scenarios that risk exceeding the CC1190 maximum input power rating, or not use the CC1190, to enable the solutions described in SWRA147. Whether or not the CC1190 is required is dependent on the requirements (it sounds like it is a trade-off between reduced range and improved close-in reception in this use-case).

I am not sure what is contradictory about stating that LNA_IN has a maximum input power rating level of +10 dBm?

Regards,

Zack

Hello Zack,

I really appreciate ur help answering my questions. Here are my responses.

1) RSSI Calculations - Ur reply gives me answers. And I also understand the RSSI register address dilemma. I did not know that address is only 6 bits; and since RSSI is a status register and it is READ only, I need to set bits 7-8 to 11. This converts RSSI register's address from 0x30 to 0x3F. now I can proceed further.

2) CC110L + CC1190 Combo - After reading ur answer and reading SWRA147 (DN010), I understand what is not written anywhere in the datasheet. I am relatively new to RF design, so I could not have known the underlying issues with LNA saturation etc. Well, thanks a lot for the info.

3) New Item #1 - Yesterday, I searched for 863-928 MHz Omnidirectional antennas on Digi-Key site. I found out that the Efficiency range of these antennas is only 35% - 46%, and gain 1.5dBi. (There are antenna with up to 60% efficiency, but we cannot use those bigger antennas, especially in the Remote Control.) So, we have to live with this limitation.

To calculate the Received Power, we need to take into consideration the efficiencies of both Tx and Rx antennas. Assuming I use CC1190 with 27dBm output, with 46% efficiency, the radiated power should be 0.46x27 = 12.42dBm. Am I correct? Since I am new to RF, I have difficulty calculating these dB and dBm values. In simple terms, the Pr should be:

Pr = ((Pt x eff.t) + Ant-t Gain + Ant-r Gain) x eff.r

Pt = Transmitted power; eff.t = Transmitter Antenna efficiency and so on.

I am not sure if my above assumption is correct. If I go by that equation, the received power comes = 7.09 dBm, which is < 10 dBm. Can u please help me with this?

4) New Item #2 - I also found an Antenna (small size that is designed for both 868 and 915 MHz, but only 35% eff.). It is made by TE Connectivity, part number 2195835. That made me think if it is possible to design CC110L + CC1190 combo for both frequencies in each device. More specifically, I don't know if the RF filters (using inductors and capacitors) can be designed.

I would be very thankful if u answer above questions.

3) For this you can refer to:

• Section 2.2 of SWRA479 (Achieving Optimum Radio Range): https://www.ti.com/lit/swra479
• Section 2.2.1 of SWRA496 (CC-Antenna-DK2 and Antenna Measurements Summary): https://www.ti.com/lit/swra496
• Section 4.1 of SWRA328 (DN031 - CC-Antenna-DK Documentation and Antenna Measurements Summary): https://www.ti.com/lit/swra328

The antenna gain figures (G_T and G_R) should already account for the antenna efficency (stated as a mean antenna efficiency), given in dBi. The TX Output Power/RX Sensitivity are the power(s) supplied to the relevant antenna, so the antenna efficiency is not (and should not be) included in that part of the calculation.

This is already accounted for in the Range Estimation Tool as the fields "Mean Effecitive Gain (MEG) of Tx antenna" and "Mean Effecitive Gain (MEG) of Rx antenna", so you can select the closest gain value to the antenna you are considering (there are "fixed gain" options in the list, -1 dB to -10 dB, that you can use for this purpose). We strongly recommend using this tool instead.

You can use the "Link Margin" field to calculate the minimum and maximum expected ranges.

As an aside, when working in dB you would need to convert the efficiency (percentage) into dB as well. A good reference is: https://www.rohde-schwarz.com/us/applications/db-or-not-db-educational-note_230850-15534.html 

4) The CC110L + CC1190 can be used for the 868 MHz and 915 MHz, but only one band per design. This is because of the required SAW filter to pass regulatory requirements, which will be designed for either 868 MHz or 915 MHz, and the required impedance matching networks.

You can refer to the following App Notes:

• SWRA356 (AN094 - Using the CC1190 Front End with CC1101 under EN 300 220): https://www.ti.com/lit/swra356

• SWRA361 (AN096 - Using CC1190 Front End with CC1101 under FCC 15.247): https://www.ti.com/lit/swra361

and the Reference Designs for each frequency band:

• CC1101-CC1190EM 868MHz (SWRR075): https://www.ti.com/lit/zip/swrr075
• CC1101-CC1190EM 915MHz (SWRR077): https://www.ti.com/lit/zip/swrr077

Depending on the antenna, you may also need to match the antenna to either 868 MHz or 915 MHz - you would need to check the manufacturer's datasheet. 

Regards,

Zack

Hello Zack,

Thanks a lot for spending so much time to answer my questions. Now, I am in a much better position to move forward.

I will contact the Antenna manufacturers and verify what u have written above in ur answer for 3); specifically do they include efficiency in their Antenna gain values. If I have further questions, I will give you trouble again.

Thanks.