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So whats the way to drive the error probability down and get cleaner plots? Becoz any paarameter I change does not buy me much gain and at this stage I am starting to get clueless about what may be going wrong. Also does the WARP hardware become a factor? I mean if the boards are old, do they give worse performance???
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It has been clearly explained that changing TX_SCALE should only be used to restrict your TX samples to the DAC's dynamic range, not to adjust TX gain.
To increase TX power, you must adjust the TX gain by sending WARPLab commands to the corresponding RF interface on the WARP board, using wl_interfaceCmd() routine, with the 'tx_gains' as command parameter.
murphpo wrote:
Hello Admin, which parameter in the OFDM example helps me increase tx power? I guess its TX_SCALE but the bad thing is that it has a threshold of [-1,1] so as to not cause problems at the ADC/DAC.
The MAX2829 Tx path has a variable gain amplifier (VGA) with ~30 dB range. You can adjust the Tx gain in WARPLab with:
wl_interfaceCmd(nodes, 'RF_ALL', 'tx_gains', BB_GAIN, RF_GAIN);
Refer to the docs for the param value ranges.
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Hi admin,
I want to do path loss measurements (of course including the free-space and Ethernet cables) in an office environment using 'wl_example_siso_txrx' m file in warp v3.
As we know the path loss "at a given distance d" is given by: PL(d)[dB]=P_TX[dB]+G_TX[dB]+G_RX[dB]-P_RX(d)[dB]. where, P_RX [dBm] is obtained from your sheets to be=(200/3069)*RSSI_D –(155/2), RSSI_D is obtained from the code, both P_TX[dB]+G_TX[dB] 'togother' controlled manually from RF_GAIN, and G_RX is controlled manually from RxGainRF. (1)Are the steps correct or there is something wrong?? (2) what are the best values of the RF or BB Gains to be 'manually' adjusted??
Thanks
Malik
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The RSSI signal is proportional to Rx power in dB. The RSSI signal shifts with changes to the Rx LNA gain (i.e. Rx RF gain). Refer to the MAX2829 datasheet (top-center plot on pg 16) for the actual curves of RSSI vs Rx power for each LNA gain setting.
The WARP v3 RF interfaces sample the RSSI signal with a 10-bit ADC. We have calibrated the digital-RSSI-to-Rx-power mapping for 802.11 waveforms in the 802.11 Reference Design. Refer 802.11 design file wlan_mac_low.c for the mapping table.
You can also approximate the RSSI-to-Rx-power mapping with 3 linear fits, one per RSSI-vs-LNA-gain curve. The formula you mentioned above is an example of the linear fit for one LNA setting.
The ideal Tx gain settings depend on your Tx waveform. Wideband waveforms tend to have higher peak-to-average-power and require reducing the Tx gain to minimize clipping in the PA. Narrowband waveforms can typically tolerate higher Tx gain settings.
The ideal Rx gain settings depend on the Tx signal and channel. You should select Rx gains which avoid clipping in the Rx I/Q signals. The AGC core automates this, but requires your Tx waveform include a preamble. Refer to our WARPLab examples for typical preamble+waveform Tx signals.
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Hi Admin,
Regarding the tx_gains: (RF_GAIN: Must be integer in [0:63] for approx [0:31]dB RF gain), is there any mapping formula or relationship between the RF_GAIN in 'integers' to the RF_GAIN in 'dB'??? Otherwise how can I obtain the gain in dB at, for example integer 28????. The same of course for BB_GAIN in rx_gains.
Many thanks
Malik
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The mapping of the gain settings for RX and TX are on pg 15 and pg 17, respectively, of the Maxim MAX2829 Datasheet.
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Hello,
Could you please advise me on this. I tried to roughly calculate the RF power transmitted from the Warp board using the information on page 17 of MAX2829 data sheet. For the TX RF gain of "30" we used in our simulation, this is given by the output power figure on page 17 of the data sheet as -20dBm. Does this power includes the base-band and AGC gains or we have to add these on top of the -20dBm value we got from this figure to know the transmitted power from the board?.
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For transmit power, there is no base-band or AGC. You are explicitly setting the transmit power. The baseband / RF gains are part of the receive power settings and the AGC will automatically set those values for you based on the input signal so that the amplitude of the received waveform is in a "reasonable" range. However, if you look at the RF sub-system of the WARP v3 hardware, you can see that beyond the MAX 2829, there is a power amplifier that is used to boost the transmit power.
If you are interested in transmit power, you should look at the 802.11 Tx characterization. From this, you can see the measured output transmit power vs set transmit power. Also, if you look in the code, you can see the conversion of transmit power to TX gain settings (constants are here).
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Hi Welsh,
Actually I am tracking your discussion about the transmitter power but I am now confused. Please give me a straight and direct answer on this (if I put TXBBgain and TXRFgain =3 and 30 respectively in the wl_example_siso.m, what would be the transmitted power in dBm ???). Please give me a number
Thanks in advance
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Actually I am tracking your discussion about the transmitter power but I am now confused. Please give me a straight and direct answer on this (if I put TXBBgain and TXRFgain =3 and 30 respectively in the wl_example_siso.m, what would be the transmitted power in dBm ???). Please give me a number
This is an incomplete question. The amplifier settings control the voltage gain applied by the MAX2829. The gain applied by each amplifier is defined in the MAX2829 datasheet.
Tx power is typically specified over a bandwidth of interest. Your baseband waveform design and the measurement bandwidth both affect the realized Tx power. This is why Erik directed you to the 802.11 characterization. That page provides a good example of mapping waveform+gains to realized Tx power. In the case of the 802.11 reference design the baeband waveform is the standard 20MHz-bandwidth 802.11 OFDM waveform. The Tx power values on that page reflect the realized Tx power measured over 20MHz bandwidth using WARP v3 hardware.
The wl_example_siso example transmits a simple sinusoid with amplitude ±0.6. At max Tx gains this signal will realize a waveform with ~20dBm power at the frequency of the sinusoid. This is an approximation- a few dB variation across time, temperature and hardware is normal. If you need a precise power value, you must measure it directly.
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Just a quick follow up since my original post only looked at the RF gains: For baseband gains, you can see that depending on whether we are using 2.4 GHz or 5 GHz, we tweak the baseband gain settings so that the mapping of RF gains to dBm is accurate. Therefore, if you are using an 802.11 waveform operating in 2.4 GHz and using a baseband gain of 1 (ie TXBBgain = 1), then an RF gain of 30 would equate to a power of 5 dBm (ie gain of 30 = (2 * 5 (power in dBm)) + 20;). This Tx power of 5 dBm for the same 802.11 waveform would required Tx gain settings of TXBBGain = 3; TXRFGain = 30 if it was being transmitted at 5 GHz.
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Thanks murphpo and welsh for your unlimited support,
My conclusion (from admin Mur.'s old replies (at 2014-Dec-15 09:57:12) and these replies, and also from Wel.) says that: From datasheet I obtained the PA gain to be 26 dB so, and for the same considered example, at 2.4 GHz, if I want to transmit 'around 0dBm from the board "after the PA", the fig. in datasheet of mid. p.g. 17 at -26dBm , it gives around TXRFgain=18 for TXBBgain=1. Therefore, the output power after the PA would be 0 dBm. Now if I use the tweak to get the same 0dBm for the 5GHz frequency this gives TXRFgain=18 for TXBBgain=3. Is this right?
Otherwise what are the values of TXRFgain and TXBBgain that would achieve the "0 dBm after the PA for both 2.4 and 5 GHz for the same wl_example_siso example"???
Many thanks
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