About 802.11b/g DSSS/CCK/PBCC Modulation Analysis

89601B7RC 802.11b/g DSSS Direct sequence spread spectrum. The data transmission scheme (sometimes referred to as a "'modulation" scheme) used in 802.11b WLANs. DSSS uses a radio transmitter operating at a fixed centre frequency, but using a relatively broad range of frequencies, to spread data transmissions over a fixed range of the frequency band. 802.11a and 802.11g (when not operating in 802.11b mode) use Orthogonal Frequency Division Multiplexing (OFDM)./CCK complementary code keying/PBCC packet binary convolutional code Modulation Analysis adds Wireless Local Area Network (WLAN WLAN - Wireless Local Area Network: A system that includes the distribution system (DS), access points (APs), and portal entities. It is also the logical location of distribution and integration service functions of an extended service set (ESS). A WLAN system contains one or more APs and zero or more portals in addition to the DS.) - Direct Sequence A process of spectrum spreading where the digital information stream is multiplied, using an exclusive OR technique, by a high speed pseudorandom code (spreading sequence) to generate a spread spectrum signal. Spread Spectrum (DSSS) signal analysis to your 89600 VSA application software for IEEE Institute of Electrical and Electronics Engineers. A US-based membership organisation that includes engineers, scientists, and students in electronics and related fields. The IEEE developed the 802 series wired and wireless LAN standards. Visit the IEEE at http://www.ieee.org Std 802.11b and IEEE Std 802.11g modulated signals.

IEEE Std 802.11b

Wireless LAN Local Area Network: A communications network that serves users within a local geographical area, typically over distances of around 100m. Wireless LANs use wireless communicaitons to network devices so there is no need for data cabling. Medium Access Control and Physical Layer specification. Higher-Speed Physical Layer Extension in the 2.4 GHz Gigahertz: A frequency measurement which equals one billion hertz. Band

IEEE Std 802.11g

Wireless LAN Medium Access Control and Physical Layer specification. Further Higher-Speed Physical Layer Extension in the 2.4 GHz Band

The original IEEE 802.11 standard defined direct sequence spread spectrum (DSSS) signals with data rates at 1Mb/sec and 2Mb/sec in the 2.4 GHz Industrial Scientific and Medical (ISM Industrial, scientific and medical) frequency band. The IEEE 802.11b-1999 standard extends this with complementary code keying (CCK) modulation at 5.5 Mb/sec and 11 Mb/sec. In addition, 802.11b defines an optional packet binary convolutional code (PBCC) mode at 5.5 Mb/sec and 11 Mb/sec, and defines an optional shorter preamble.

The IEEE 802.11g-2003 standard adds the ability to use 802.11a OFDM Orthogonal Frequency Division Multiplexing: OFDM employs multiple overlapping radio frequency carriers, each operating at a carefully chosen frequency that is Orthogonal to the others, to produce a transmission scheme that supports higher bit rates due to parallel channel operation. OFDM is an alternative tranmission scheme to DSSS and FHSS. formatted signals in the 2.4 GHz ISM band A range of radio frequencies that are assigned for use by unlicensed users of Industrial, Scientific and Medical equipment but which is also used by many other wireless devices, including 802.11, 802.11b and 802.11g devices, by Bluetooth and by microwave ovens. The Internationally-recognised ISM band sits within the 2.4GHz - 2.5GHZ frequency range. In the US, two further ISM bands exist, in the 902MHz range and the 5.725GHz - 5.875GHz range., defines additional optional 802.11b-compatible PBCC modes at 22 Mb/sec and 33 Mb/sec, and defines an optional 802.11b-compatible "DSSS-OFDM" mode that is a combination of the 802.11a OFDM format with an 802.11b-compatible preamble.

In "802.11b/g DSSS/CCK/PBCC" mode, the VSA will support automatic detection, demodulation, and de-scrambling of the four mandatory 802.11b signal formats (1, 2, 5.5, and 11 Mb/sec), as well as detection and demodulation of the optional 802.11b and 802.11g PBCC formats. The VSA will detect but not demodulate the optional DSSS-OFDM format (the 802.11b-compatible preamble will be demodulated, but the 802.11a-compatible data will not be demodulated). The 802.11a/g/j/p OFDM mode can be used to demodulate the OFDM segment of the burst. The VSA will automatically detect, demodulate, de-spread, and de-scramble both the standard 802.11b preamble and the optional short 802.11b preamble, in order to detect the expected burst length and modulation type.

The following table shows a comparison of the data rates with mandatory and optional modulation formats for the WLAN IEEE std 802.11 versions a, b, and g:

WLAN IEEE Std 802.11 Data Rate Comparison Chart
	802.11b @ 2.4 GHz		802.11g @ 2.4 GHz		802.11a @ 5 GHz
Data Rate	Mandatory	Optional	Mandatory	Optional	Mandatory	Optional
1 Mbps	Barker	----	Barker	----	----	----
2 Mbps	Barker	----	Barker	----	----	----
5.5 Mbps	CCK	PBCC	CCK	PBCC	----	----
6 Mbps	----	----	OFDM	DSSS-OFDM	OFDM	----
9 Mbps	----	----	----	OFDM, DSSS-OFDM	----	OFDM
11 Mbps	CCK	PBCC	CCK	PBCC	----	----
12 Mbps	----	----	OFDM	DSSS-OFDM	OFDM	----
18 Mbps	----	----	---	OFDM, DSSS-OFDM	----	OFDM
22 Mbps	----	----	----	PBCC	----	----
24 Mbps	----	----	OFDM	DSSS-OFDM	OFDM	----
33 Mbps	----	----	----	PBCC	----	----
36 Mbps	----	----	----	OFDM, DSSS-OFDM	----	OFDM
48 Mbps	----	----	----	OFDM, DSSS-OFDM	----	OFDM
54 Mbps	----	----	----	OFDM, DSSS-OFDM	----	OFDM

The following figure shows the IEEE STD 1) abbrevation for "standard" or 2) Selective Transmit Diversity: A transmit diversity technique using multiple base stations to originate the signal and provide spatial diversity on the downlink. In STD, the transmitter selection is based on a QoS measurement made at the mobile station. See also transmit diversity, TDTD and TSTD. 802.11b PPDU PLCP Protocol data unit frame with Long preamble:

$image\PPDUlong_wmf.jpg$

The following figure shows the IEEE STD 802.11b PPDU frame with Short preamble:

$image\PPDUshort_wmf.jpg$