Image Processing Reference
In-Depth Information
FIGURE .
Measured spectrum of an IEEE .b WLAN PCMCIA card. (From Matheus, K.
Industrial
Information Technology Handbook
. Ed. R. Zurawski, CRC Press, Boca Raton, FL, . With permission.)
µscanbeused.FortheIEEE.bPHY-payload(consistingoftheMACheaderandthe
user data) a . and Mbps complementary code keying (CCK) modulation is used. he CCK
employs a variation of M-ary orthogonal signaling (complex Walsh/Hadamard functions) with
eight complex chips in each spreading code word. For the . Mbps modulation rate bits are
mapped onto eight chips and for Mbps bits are mapped onto eight chips.
OFDM: The orthogonal frequency division multiplexing (OFDM) physical layer was originally
designed for different GHz bands (also referred to as IEEE .a) but has now been
adopted also for the . GHz band (as part of IEEE .g). The parameters of the IEEE
. OFDM PHY had at the time of standardization been harmonized with those of HIPER-
LAN/.
∗
Seven modi are defined ranging from BPSK with rate R
=
/ FEC (lowest modulation
rate with Mbps) to -QAM with rate R
/ FEC (highest modulation rate with Mbps,
see also Table .). The OFDM technique is based on a -point IFFT/FFT, while only
using of the subcarriers ( for user data, for pilot carriers). The subcarrier spacing is
∆
f
=
. MHz. Note that full OFDM symbols always have to be transmitted.
This means that they possibly have to be filled up with dummy bits. To transmit one OFDM
symbol
t
sym
=
MHz
/
=
=
/
∆
f
+
/
×
/
∆
f
=
µs are needed, with the latter part representing the time
∗
Originally, HIPERLAN/ was intended to be the WLAN technology for the European market while IEEE . was the
pendant for North America. Owing to delays in the development, HIPERLAN/ lost the chance to establish itself on the
market, despite its better overall network performance (from which the user would have had the advantage of higher user-
data rates). Publications on HIPERLAN/ are, e.g., [KJSWW,TM,Eurb,GL,HZ,LLM
+
,LMP
+
,MKJST,
Eura,Eurb,KYW,Mat].