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Cc112x cc120x lrm

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Long Range Mode

PER vs Offset vs Input Power Level. 470 MHz, 7.8 kHz RX filter BW
PER vs Offset vs Input Power Level 868 MHz, 12.5 kHz RX filter BW

Long range mode uses 600 bps symbol rate, +/- 1.5 kHz frequency deviation, GFSK modulation. The CC1120 evaluation module includes a 32 MHz TCXO.

RX filter BW

600 bps symbol rate, +/- 1.5 kHz frequency deviation, GFSK modulation gives a 99% occupied bandwidth (OBW) of 3.4 kHz.

On the receiver side there is a channel filter, which is centered on the down-converted received RF frequency, i.e. the intermediate frequency (IF). The channel filter has a programmable bandwidth "RX filter BW". OBW of the transmitted signal has to be less than the RX filter bandwidth, but the frequency error of the transmitter and receiver into account also has to be taken into account.

If there is an error in the transmitter carrier frequency and the receiver LO frequency, there will also be an error in the IF frequency. For simplicity assume the frequency error in the transmitter and receiver is equal (same type of crystal). If the receiver has an error of –X ppm and the transmitter has an error of +X ppm the IF frequency will have an error of +2*X ppm (assuming low side LO injection). Conversely, if the receiver has an error of +X ppm and the transmitter an error of -X ppm the IF frequency will have an error of -2*X ppm.

RX filter BW has to be larger than the OBW plus the maximum frequency error due to crystal inaccuracies. Worst case scenario will be for the crystal TX and RX errors to be of opposite signs

RX filter BW > OBW + 4* XTALppm* fRF (Equation 1)

where

XTALppm is the total accuracy of the crystal including initial tolerance and temperature drift
fRF is the RF operating frequency


At 470 MHz operation a 7.8 kHz RX filter BW and the use of FB2PLL (Feedback to PLL) allows up to +/-8 ppm frequency error. From Equation 1: 3.4 kHz + 4 x 4 x 470 = 11 kHz < 7.8 x 1.5 kHz (RX filter BW +/-RX filter BW/4). See plot of "PER vs Offset vs Input Power Level. 470 MHz, 7.8 kHz RX filter BW"

At 868 MHz operation a 12.5 kHz RX filter BW and the use of FB2PLL (Feedback to PLL) allows up to +/-8 ppm frequency error. From Equation 1: 3.4 kHz + 4 x 4 x 868 = 17.3 kHz < 12.5 x 1.5 kHz (RX filter BW +/-RX filter BW/4). See plot of "PER vs Offset vs Input Power Level. 868 MHz, 12.5 kHz RX filter BW"

An increase in RX filter BW from 7.8 kHz to 12.5 kHz gives a theoretical degradation in sensitivity of 2.0 dB. Sync word detection has better sensitivity than receiving data, and a novel frequency offset compensation technique can therefore be implemented to improve sensitivity.

Frequency Compensation

  1. Packet format: 3 byte PREAMBLE + 4 byte SYNC_1 + 1 byte payload (no CRC) + 1 byte PREAMBLE + 4 byte SYNC_2 + data payload
  2. Receive mode is started with 12.5 kHz RX filter BW and FB2PLL enabled (i.e. wide enough to account for maximum frequency error caused by temperature drift and initial tolerance). After SYNC_1 is detected, register FREQOFF_EST gives the frequency offset between RX and TX units.
  3. The RX unit is put in IDLE mode, the RX filter BW is reduced to 7.8 kHz, the error in FREQOFF_EST is written to register FREQOFF, SYNC_2 is written to the chip, and then RX is re-started. Note: FREQOFF and SYNC_2 cannot be updated in RX and must be doen with the chip in IDLE mode.
  4. The TX unit transmits PREAMBLE, SYNC_1 and 1 byte payload (no CRC), goes to IDLE and re-starts TX with 1 byte PREAMBLE, SYNC_2 and data payload (Alternative is to write second preamble and SYNC_2 to TX FIFO and not re-start TX after SYNC_1 and 1 byte payload, but then CRC needs to be calculated in SW on the receiver side)

SYNC_1 = 0x2633D9CC
SYNC_2 = 0x930B51DE

Sensitivity Measurement Results

The table below gives 1% BER sensitivity figures. The sensitivity is the average of 12 evaluation modules.

Part number RF frequency [MHz] Modulation format Symbol rate [ksps] Frequency deviation [kHz] Programmed RX_BW [kHz] FB2PLL [yes/no] Sensitivity [dBm] Comment
CC1120 470 GFSK 0.6 1.5 7.8 yes -125 LNA = 0x03, Extended Data filter on
CC1120 868 GFSK 0.6 1.5 12.5 yes -122.3 LNA = 0x03, Extended Data filter on
CC1120 868 GFSK 0.6 1.5 7.8 yes -124 LNA = 0x03, Extended Data filter on.
Sensitivity when using 12.5 kHz RX filter BW for frequency compensation and 7.8 kHz for packet reception
CC1125 868 GFSK 0.6 1.5 5.0 yes -126.5 LNA = 0x03, Extended Data filter on.
Sensitivity when using 10 kHz RX filter BW for frequency compensation and 5.0 kHz for packet reception

The long range mode demo uses CC1120 where the minimum RX filter BW is 7.8 kHz. If the crystal error between RX and TX units is less than +/-8 ppm a lower RX filter BW than 7.8 kHz can be used. CC1125 allows down to 3.5 kHz RX filter BW. As an example, at 868 MHz operation, 600 bps symbol rate, +/- 1.5 kHz frequency deviation it is possible to use 10 kHz RX filter BW for frequency compensation and 5 kHz RX filter BW after the compensation.


Register Settings, HW and Demo SW

In the demo SW, frequency offset compensation is implemented for 868 MHz operation. For 470 MHz operation the RX filter BW is fixed at 7.8 kHz

Import the XML file into SmartRF Studio to see the register settings.
- The 868 MHz register settings use 12.5 kHz RX filter BW. Change register CHAN_BW to 0x50 (7.8 kHz) and SYNC3,2,1,0 to 0x930B51DE after doing the frequency compensation.
- The 470 MHz register settings use 7.8 kHz RX filter BW.

Register settings XML-files: Media:LongRangeMode_XML_files.zip

HW 868 MHz: TrxEB with CC1120EM 868-930 MHz modified with 32 MHz TCXO. See CC1120EM 868/915 MHz reference design. Antenna: W5017 from Pulse.

HW 470 MHz: TrxEB with CC1120EM 420-470 MHz modified with 32 MHz TCXO. See CC1120EM 420-470 MHz reference design. Antenna: ???? from Nearson. The antenna is trimable and has been tuned to 470-510 MHz operation

Long Range Demo User Guide: File:LRM Demo User Guide.pdf

Range Testing

More than 100 km range with CC1120+CC1190

114 km range test with the transmitter at Table Mountain in Cape Town and the receiver along the coast. CC1120+CC1190EM at 868 MHz in Long Range Mode

The limitation on range here is actually the curvature of the earth, further away you will be below the horizon looking from the 1000 m high Table Mountain...

25 km Range Test in Cape Town, South Africa

25 km range test with the transmitter at Table Mountain in Cape Town and the receiver along the coast. CC1120EM operating at 868 MHz, 1.2 kbps, +/-4 kHz deviation, +14 dBm output power

Video showing the range test: CC112x Range Test in Cape Town, South Africa

Long-Range Test Across the City of Oslo

Long-range test from the Holmenkollen ski jump to the water's edge by the Oslo Fjord. CC1120EM operating at 868 MHz, 1.2 kbps, +/-4 kHz deviation

Video showing the range test: Range test of CC1120 sub-1 GHz performance line

Kista Science Tower

CC1120 TX unit placed at floor 26 in the stairway. Data transmission could be received 16 floors below the TX unit. 470 MHz operation. Using long range demo SW with 600 bps, +/-1.5 kHz deviation, 7.8 kHz RX filter BW.

Dense Urban Environment

Range test in Oslo, Norway. CC1120EM with TCXO. Using long range demo SW with 600 bps, +/-1.5 kHz deviation, 7.8 kHz RX filter BW. Frequency offset compensation done on each packet.

Range test in Oslo, Norway. CC1120EM with TCXO. Using easy link demo SW with 802.15.4g: 50 kbps, +/-25 kHz deviation, 100 kHz RX filter BW.

Range test in Plano, Texas, USA. CC1125+CC1190EM with TCXO operating at 915 MHz. Using standard PER test SW with 300 bps, +/-1.0 kHz deviation, 3.8 kHz RX filter BW.