CC1150-RTR1 datasheet(28/67 Pages) TI

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CC1150

SWRS037A

Page 28 of 60

14.3

Amplitude Modulation

CC1150 supports two different forms of

amplitude modulation: On-Off Keying (OOK)

and Amplitude Shift Keying (ASK).

OOK modulation simply turns on or off the PA

to modulate 1 and 0 respectively.

The ASK variant supported by the

CC1150

allows programming of the modulation depth

(the difference between 1 and 0), and shaping

of the pulse amplitude. Pulse shaping will

produce a more bandwidth constrained output

spectrum.

Note that the OOK/ASK pulse shaping feature

on the

CC1150 does only support output power

up to about -1 dBm.

The DEVIATN register has no effect when

using ASK/OOK.

15 Forward Error Correction with Interleaving

15.1

Forward Error Correction (FEC)

CC1150 has built in support for Forward Error

Correction (FEC) that can be used with

CC1101

at the receiver end. To enable this option, set

MDMCFG1.FEC_EN

to 1. FEC is only supported

in fixed packet length mode, i.e. when

PKTCTRL0.LENGTH_CONFIG=0.

FEC

employed on the data field and CRC word in

order to reduce the gross bit error rate when

operating

near

the

sensitivity

limit.

Redundancy is added to the transmitted data

in such a way that the receiver can restore the

original data in the presence of some bit

errors.

The use of FEC allows correct reception at a

lower Signal-to-Noise RATIO (SNR), thus

extending communication range. Alternatively,

for a given SNR, using FEC decreases the bit

error rate (BER). As the packet error rate

(PER) is related to BER by

length

packet

BER

PER

)

(

−

A lower BER can be used to allow longer

packets, or a higher percentage of packets of

a given length, to be transmitted successfully.

Finally, in realistic ISM radio environments,

transient and time-varying phenomena will

produce occasional errors even in otherwise

good reception conditions. FEC will mask such

errors and, combined with interleaving of the

coded data, even correct relatively long

periods of faulty reception (burst errors).

The FEC scheme adopted for

CC1150 is

convolutional coding, in which n bits are

generated based on k input bits and the m

most recent input bits, forming a code stream

able to withstand a certain number of bit errors

between each coding state (the m-bit window).

The convolutional coder is a rate 1/2 code with

a constraint length of m=4. The coder codes

one input bit and produces two output bits;

hence, the effective data rate is halved. This

means that in order to transmit at the same

effective data rate when using FEC, it is

necessary to use twice as high over-the-air

data rate.

15.2

Interleaving

Data received through real radio channels will

often

experience

burst

errors

due

interference and time-varying signal strengths.

In order to increase the robustness to errors

spanning multiple bits, interleaving is used

when FEC is enabled. After de-interleaving, a

continuous span of errors in the received

stream will become single errors spread apart.

CC1150 employs matrix interleaving, which is

illustrated

Figure

15.

The

on-chip

interleaving buffer is a 4 x 4 matrix. In the

transmitter, the data bits are written into the

rows of the matrix, whereas the bit sequence

to be transmitted is read from the columns of

the matrix and fed to the rate ½ convolutional

coder. Conversely, in a

CC1101 receiver, the

received symbols are written into the rows of

the matrix, whereas the data passed onto the

convolutional decoder is read from the

columns of the matrix.

When FEC and interleaving is used, at least

one

extra

byte

required

for

trellis

termination. In addition, the amount of data

transmitted over the air must be a multiple of

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