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Efficient Model for OFDM based IEEE 802.11 Receiver with Autocorrelation technique And…
Figure 8. Circular CORDIC rotation
CORDIC is based on the common rotation equations.The vector rotation is given as
x’=xcos(φ)–ysin(φ) (2)
y’=ycos(φ)+xsin(φ) (3)
x’=cos(φ)[x–y tan(φ) ] (4)
y’=cos(φ)[y+x tan(φ) ] (5)
x i+1 = cos(tan -1 (±2 -i ))·[x i –y i· d i · 2 -i ] (6)
y i+1 =cos(tan -1 (±2 -i ))·[y i +x i·d i .2 -i ] (7)
x i+1 =K i·[x i – y i · d i · 2 -i ] (8)
y i+1 =K i·[y i +x i · d i · 2 -I ] (9)
z i+1 =z i -d i·arctan(2 -i ) (10)
where Ki = Cos ( Tan ֿ¹ 2.exp(-i)) = 0.60725 and di= ±1
So to reach an expected angle, a series of iterations are required to be performed and in this design the
number of iterations are 8 and in every iteration the new values of x, y and z depend upon the previous values of
the same.
According to [8] [9], the CORDIC processor can be configured to work as circular, hyperbolic and
linear rotations for both vectoring and rotational modes. The circular vectoring mode is used to calculate coarse
Carrier Frequency Offset (CFO) estimation and fine CFO estimation. The circular rotation mode is used to
correct coarse CFO of the broadcast preamble, and to correct received section C and received OFDM symbols.
The linear vectoring mode is used to calculate the division in the channel estimation stage.
Figure 9. Operation of CORDIC Algorithm
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