Rohde&Schwarz R&S®WinIQSIM2™ Digital Standardss User Manual
IEEE 802.11 (a/b/g)
Digital Standard for
R&S®Signal Generators
Operating Manual
(;ÕÂá<)
1171528312
Version 18
Operating Manual
This document describes the following software options:
●
R&S®SMBV-K48
1415.8102.xx
●
R&S®SMU-K48
1161.0266.02
●
R&S®AMU-K48
1402.6706.02
●
R&S®SMATE-K48
1404.6703.02
●
R&S®SMJ-K48
1404.1001.02
This manual describes firmware version 4.70.108.xx and later of the R&S®SMBV100A.
© 2020 Rohde & Schwarz GmbH & Co. KG
Mühldorfstr. 15, 81671 München, Germany
Phone: +49 89 41 29 - 0
Fax: +49 89 41 29 12 164
Email: info@rohde-schwarz.com
Internet: www.rohde-schwarz.com
Subject to change – Data without tolerance limits is not binding.
R&S® is a registered trademark of Rohde & Schwarz GmbH & Co. KG.
Trade names are trademarks of the owners.
1171.5283.12 | Version 18 | IEEE 802.11 (a/b/g)
The following abbreviations are used throughout this manual: R&S®AMU200A is abbreviated as R&S AMU, R&S®SMATE200A is
abbreviated as R&S SMATE, R&S®SMBV100A is abbreviated as R&S SMBV, R&S®SMJ100A is abbreviated as R&S SMJ,
R&S®SMU200A is abbreviated as R&S SMU, R&S®WinIQSIM2TM is abbreviated as R&S WinIQSIM2; the license types
02/03/07/11/13/16/12 are abbreviated as xx.
ContentsIEEE 802.11 (a/b/g)
Contents
1 Preface.................................................................................................... 5
1.1 Documentation Overview............................................................................................. 5
1.2 Conventions Used in the Documentation...................................................................6
1.2.1 Typographical Conventions.............................................................................................6
1.2.2 Notes on Screenshots.....................................................................................................7
1.2.3 Naming of Software Options........................................................................................... 7
2 Introduction............................................................................................ 9
2.1 Physical Layer OFDM................................................................................................. 10
2.1.1 PLCP Format.................................................................................................................11
2.1.2 PLCP Preamble.............................................................................................................11
2.1.3 Signal Field................................................................................................................... 12
2.1.4 User Data...................................................................................................................... 12
2.2 Physical Layer CCK-PBCC.........................................................................................14
2.2.1 Long PLCP PPDU Format............................................................................................ 14
2.2.2 Short PLCP PPDU Format............................................................................................14
2.3 Data Spreading and Modulation CCK-PBCC............................................................ 15
2.3.1 1 Mbps Data Rate with DBPSK Modulation.................................................................. 16
2.3.2 2 Mbps Data Rate with DQPSK Modulation..................................................................16
2.3.3 5.5 Mbps Data Rate with CCK Modulation....................................................................17
2.3.4 11 Mbps Data Rate with CCK Modulation.....................................................................18
2.3.5 5.5 Mbps and 11 Mbps Data Rates with PBCC Modulation..........................................19
2.3.6 22 Mbps and 33 Mbps Data Rates with PBCC Modulation...........................................19
3 WLAN User Interface........................................................................... 21
3.1 General Settings for WLAN Signals.......................................................................... 22
3.2 PPDU/Sequence Configuration..................................................................................27
3.2.1 Standard 802.11a - OFDM............................................................................................ 27
3.2.2 Standard 802.11b/g - CCK - PBCC...............................................................................28
3.2.3 Settings......................................................................................................................... 29
3.3 MAC Header and FCS Configuration.........................................................................34
3.4 PPDU Graph.................................................................................................................37
3.5 Filter/Clipping Settings...............................................................................................38
3Operating Manual 1171.5283.12 ─ 18
ContentsIEEE 802.11 (a/b/g)
3.5.1 Filter Settings................................................................................................................ 38
3.5.2 Clipping Settings........................................................................................................... 39
3.6 Trigger/Marker/Clock Settings................................................................................... 40
3.6.1 Trigger In.......................................................................................................................41
3.6.2 Marker Mode................................................................................................................. 45
3.6.3 Marker Delay.................................................................................................................46
3.6.4 Clock Settings............................................................................................................... 47
3.6.5 Global Settings..............................................................................................................48
4 Remote-Control Commands............................................................... 49
4.1 General Commands.................................................................................................... 50
4.2 Filter/Clipping Settings...............................................................................................59
4.3 Trigger Settings...........................................................................................................63
4.4 Marker Settings........................................................................................................... 69
4.5 Clock Settings............................................................................................................. 74
4.6 PSDU Settings............................................................................................................. 76
List of Commands................................................................................85
Index......................................................................................................87
4Operating Manual 1171.5283.12 ─ 18
1 Preface
1.1 Documentation Overview
This section provides an overview of the R&S Signal Generator user documentation.
You find it on the product page at:
www.rohde-schwarz.com/manual/smbv100a
Quick start guide
Introduces the R&S Signal Generator and describes how to set up and start working
with the product. Includes basic operations, typical measurement examples, and general information, e.g. safety instructions, etc. A printed version is delivered with the
instrument.
Online help
PrefaceIEEE 802.11 (a/b/g)
Documentation Overview
Offers quick, context-sensitive access to the complete information for the base unit and
the software options directly on the instrument.
Operating manual
Separate manuals for the base unit and the software options are provided for download:
●
Base unit manual
Contains the description of all instrument modes and functions. It also provides an
introduction to remote control, a complete description of the remote control commands with programming examples, and information on maintenance, instrument
interfaces and error messages. Includes the contents of the quick start guide manual.
●
Software option manual
Contains the description of the specific functions of an option. Basic information on
operating the R&S Signal Generator is not included.
The online version of the operating manual provides the complete contents for immediate display on the Internet.
Service manual
Describes the performance test for checking the rated specifications, module replacement and repair, firmware update, troubleshooting and fault elimination, and contains
mechanical drawings and spare part lists.
The service manual is available for registered users on the global Rohde & Schwarz
information system (GLORIS, https://gloris.rohde-schwarz.com).
5Operating Manual 1171.5283.12 ─ 18
PrefaceIEEE 802.11 (a/b/g)
Conventions Used in the Documentation
Instrument security procedures manual
Deals with security issues when working with the R&S Signal Generator in secure
areas.
Basic safety instructions
Contains safety instructions, operating conditions and further important information.
The printed document is delivered with the instrument.
Data sheet and brochure
The data sheet contains the technical specifications of the software options, see "Digital Standards for Signal Generators - Data sheet" on the web site. It also lists the
options and their order numbers.
The brochure provides an overview of the instrument and deals with the specific characteristics.
Release notes and open source acknowledgment (OSA)
The release notes of the base units list new features, improvements and known issues
of the current firmware version, and describe the firmware installation.
The open source acknowledgment document provides verbatim license texts of the
used open source software. See the product page of the base unit, e.g. at:
www.rohde-schwarz.com/firmware/smbv100a
Application Notes, Application Cards, White Papers, etc.
These documents deal with special applications or background information on particular topics, see www.rohde-schwarz.com/application/smbv100a.
1.2 Conventions Used in the Documentation
1.2.1 Typographical Conventions
The following text markers are used throughout this documentation:
Convention Description
"Graphical user interface elements"
[Keys] Key and knob names are enclosed by square brackets.
Filenames, commands,
program code
Input Input to be entered by the user is displayed in italics.
All names of graphical user interface elements on the screen, such as
dialog boxes, menus, options, buttons, and softkeys are enclosed by
quotation marks.
Filenames, commands, coding samples and screen output are distinguished by their font.
6Operating Manual 1171.5283.12 ─ 18
Convention Description
Links Links that you can click are displayed in blue font.
"References" References to other parts of the documentation are enclosed by quota-
1.2.2 Notes on Screenshots
When describing the functions of the product, we use sample screenshots. These
screenshots are meant to illustrate as many as possible of the provided functions and
possible interdependencies between parameters. The shown values may not represent
realistic usage scenarios.
The screenshots usually show a fully equipped product, that is: with all options installed. Thus, some functions shown in the screenshots may not be available in your particular product configuration.
PrefaceIEEE 802.11 (a/b/g)
Conventions Used in the Documentation
tion marks.
1.2.3 Naming of Software Options
In this operating manual, we explicitly refer to options required for specific functions of
the digital standard.
The names of software options for signal generators vary in the name of the instrument, but the option name is identical. Therefore we use in this manual the placeholder
R&S SMx/AMU.
Example:
Naming for an option of the vector signal generator R&S SMBV100A, e.g:
●
R&S SMx/AMU-K99, stands for R&S SMBV-K99
The particular software options available for the corresponding instruments are listed
on the back of the title page.
7Operating Manual 1171.5283.12 ─ 18
PrefaceIEEE 802.11 (a/b/g)
Conventions Used in the Documentation
8Operating Manual 1171.5283.12 ─ 18
IntroductionIEEE 802.11 (a/b/g)
2 Introduction
The R&S Signal Generator provides you with the ability to generate signals in accordance with the Wireless LAN standards IEEE 802.11a, IEEE 802.11b and IEEE 802.11g.
(IEEE 802.11) standard WLAN.
IEEE 802.11 stands for a wireless LAN standard prepared by ANSI/IEEE Institute of
Electrical and Electronics Engineers). A brief description of the standard is given in the
following. For a detailed description see the corresponding ANSI/IEEE specifications.
In 1990, IEEE founded the work group 802.11 which issued a first version of the 802.11
standard in June 1997. This standard defines two transmission methods: an infrared
interface and radio transmission in the ISM band around 2.4 GHz.
Radio transmission can alternatively be carried out via frequency hopping spread spectrum (FHSS) or direct sequence spread spectrum (DSSS).
Originally, two data transmission modes were defined for the DSSS method.
●
1 Mbps data rate with DBPSK modulation
●
2 Mbps data rate with DQPSK modulation
Both modes spread the information data sequence with an 11-chip Barker sequence,
and operate with a chip rate of 11 Mcps.
In spring 1999, the standard was extended by an OFDM mode, 802.11a, in the 5 GHz
band. Soon afterwards, in summer 1999, the DSSS mode was extended, too. This
expansion to include the new data rates of 5.5 Mbps and 11 Mbps is defined in the
802.11b standard. A new modulation mode, complementary code keying (CCK), was
introduced (see following sections).
Standard 802.11g issued in 2003 extends standard 802.11b with higher transmission
rates. It includes the previous 802.11b standard and implements the OFDM transmission of standard 802.11a in the 2.4 GHz ISM band. In the physical layer, the packet
structure and modulation format of the OFDM modes are identical in 802.11g and
802.11a, only different transmission frequencies are used.
The 802.11 wireless LAN standard is a packet-oriented method for data transfer. The
data packets are transmitted and received on the same frequency in time division
duplex (TDD), but without a fixed timeslot raster. An 802.11 component can only transmit or only receive packets at any particular time.
The R&S Signal Generator simulates IEEE 802.11a-g WLAN at the physical on the
physical layer. Two simulation modes are offered:
In the framed mode a sequence of data packets with the frame structure defined by the
standard is generated. A MAC header and a frame check sequence can be activated.
In the unframed time mode a non-packet-oriented signal without frame structure is
generated, with the modulation modes and data rates defined by the IEEE 802.11.
The following list gives an overview of the options provided by the R&S Signal Generator for generating a IEEE 802.11a-g WLAN signal:
●
Physical Layer modes OFDM (IEEE.802.11a/g), and CCK/PBCC (IEEE.802.11b/g).
9Operating Manual 1171.5283.12 ─ 18
IntroductionIEEE 802.11 (a/b/g)
Physical Layer OFDM
●
Chip/Sample rate 20 Mcps (OFDM IEEE.802.11a/g), and 11 Mcps (CCK/PBCC
IEEE.802.11b/g).
●
PSDU bit rates 1Mbps, 2Mbps, 5.5Mbps and 11 Mbps (CCK/PBCC), 22Mbps
(PBCC), 6 Mbps, 9 Mbps, 12 Mbps, 18 Mbps, 24Mbps, 36 Mbps, 48 Mbps and 54
Mbps (OFDM).
●
PSDU Modulation DBPSK,DQPSK and CCK/PBCC (CCK/PBCC) and
BPSK,QPSK,16QAM or 64QAM (OFDM) (depending on specified PSDU bit rate).
●
Data scrambling can be activated or deactivated (CCK/PBCC) and initial scrambler
state can be set randomly or to a user-defined value (OFDM).
●
Clipping for reducing the crest factor.
To play back a signal from a waveform file created by the simulation software
R&S WinIQSIM2, the corresponding R&S WinIQSIM2 digital standard option must be
installed.
2.1 Physical Layer OFDM
The standard defines OFDM (orthogonal frequency division multiplex) with 52 carriers
as transmission method. The symbol rate of the modulation on the individual carriers is
250 kHz. A user data rate of up to 54 Mbps at a channel bandwidth of 20 MHz can be
obtained by combining 48 useful carriers for data transmission (4 carriers are used for
pilots) and using 64QAM for subcarrier modulation. With OFDM, the individual carriers
are superimposed mutually orthogonal, which, in the ideal case, does not cause any
intercarrier interference (ICI).
Table 2-1: Parameters of 802.11a/g OFDM modulation
Parameters Value
Number of data subcarriers 48
Number of pilot subcarriers 4
Total of subcarriers used 52
Subcarrier frequency spacing 0.3125 MHz (= 20 MHz/64)
IFFT/FFT period 3.2 µs
Guard interval duration 0.8 µs (TFFT /4)
Symbol interval 4 µs (TGI + TFFT)
PLCP preamble duration 16 µs
Subcarrier modulation BPSK OFDM
QPSK OFDM
16QAM OFDM
64QAM OFDM
Error correction code K = 7 (64 states) convolutional code
Code rates 1/2, 2/3, 3/4
10Operating Manual 1171.5283.12 ─ 18
IntroductionIEEE 802.11 (a/b/g)
Physical Layer OFDM
Parameters Value
Occupied bandwidth 16.6 MHz
Channel spacing 20 MHz
The table shows the main parameters of OFDM. 64-point IFFT is used to generate the
52 subcarriers. 12 of the 64 possible carriers are not used. One is the carrier in the
middle of the band, which would otherwise be impaired by the carrier leakage of the
I/Q modulator, the others are the remaining carriers at the upper and lower end of the
spectrum. The required subcarrier offset of 312.5 kHz is implicitly observed when the
time signal generated by the IFFT with a sampling rate of 20 MHz is output. These 20
MHz are also called 'kernel sample rate'. An OFDM symbol generated in this way
would have a period of 3.2 µs. To compensate for multipath propagation, a so-called
guard interval with a duration of 0.8 µs is attached to each symbol so that a total symbol interval of 4 µs is obtained.
Either BPSK, QPSK, 16QAM or 64QAM modulation can be used on the subcarriers.
Prior to the modulation, the raw data are convolutionally coded with code rates of ½ to
¾ being possible.
The frame structure can be seen in the figure below (also indicated in the "PPDU Configuration" dialog):
2.1.1 PLCP Format
The physical layer convergence protocol (PLCP) is a protocol layer between medium
access control and the actual physical transmission layer (PHY). It is mainly used to
adapt the different transmission formats of the 802.11 standards to the MAC layer
which is identical for all transmission methods. Moreover, this protocol informs the
receiver on the type of signal sent to allow for a correct demodulation.
The PLCP generates the PLCP protocol data unit (PPDU) frames which are physically
transmitted.
2.1.2 PLCP Preamble
Each frame starts with the PLCP preamble made up of 10 short and 2 long symbols.
The receiver uses the short symbols mainly for signal detection, AGC, coarse frequency adjustment and time synchronization. The long symbols are used to determine
the transmission function of the channel and to set the equalizer of the receiver accord-
11Operating Manual 1171.5283.12 ─ 18
ingly. The complete preamble is 16 µs long and thus corresponds to the duration of 4
normal OFDM symbols.
2.1.3 Signal Field
The signal field directly follows the preamble and consists of 24 bits which are used as
follows:
The first 4 bits inform on the data rate (RATE) of the following data section. This allows
the receiver to correctly set its demodulator. Following a reserved bit, 12 LENGTH bits
are sent. They contain the number of bytes transmitted in this frame. After a parity bit,
6 tail bits reset the convolutional coder to zero.
IntroductionIEEE 802.11 (a/b/g)
Physical Layer OFDM
With settings for 6 Mbps, the 24 bits are subjected to usual signal processing consisting of convolutional coding, interleaving, BPSK subcarrier modulation, pilot carrier generation and OFDM modulation and thus form exactly one OFDM symbol of 4 µs duration. Thanks to the use of the lowest data rate (6 Mbps), each receiver has the best
chance to obtain the information required for subsequent demodulation of the data section.
2.1.4 User Data
The user data in the data section of the frame is finally taken to the receiver. The data
section may have a variable length of OFDM symbols and can be transmitted with one
of the defined data rates between 6 and 54 Mbps. The data section of the frame is subdivided into the fields SERVICE, PSDU, TAIL and Pad bits.
The service field consists of 16 bits, the 7 LSBs transmitted first being 0. The allows
the receiver to draw conclusions as to the start value of the scrambler in the transmitter. The remaining 9 bits are reserved and, according to the current version of the standard, should also be set to 0.
The PSDU may have a user-selectable length of up to 2346 bytes. 6 tail bits follow to
reset the convolutional coder to zero. The data field must be filled with the full number
of OFDM symbols and is therefore rounded up. Additional bits that may be available
are set to 0 as pad bits.
A short description of the individual steps required to attain a valid 802.11a/g signal follows.
12Operating Manual 1171.5283.12 ─ 18
IntroductionIEEE 802.11 (a/b/g)
Physical Layer OFDM
Data from the source (usually the next higher protocol layer, here MAC) must first be
scrambled, i.e. multiplied with a PN sequence. A 127-bit code generated by the following generator polynomial is stipulated:
S(x) = x7 + x4 + 1
A feedback shift register generates the scrambling sequence. The start value of the
register for the data section should be randomly selected.
A subsequent convolutional coder adds redundancies to the bits thus scrambled (factor
of 2). The coder has 64 possible states (k = 7) and is described by the polynomials
g0=1338 and g1=1718. To obtain the data rates of 6 to 54 Mbps defined by the standard,
different channel code rates are required. Bits generated by the convolutional coder
are therefore punctured (i.e. omitted) depending on the setting so that 1/2, 2/3 or 3/4
code rates are attained. Increasing the redundancy by channel coding is generally
mandatory in case of OFDM modulations since complete subcarriers may be eliminated by frequency selective fading so that the loss of bits on the transmission path is in
many cases unavoidable.
To increase the performance of the convolutional coder, the coded data are interleaved
in the next step. Two interleaver stages ensure that the adjacent bits of the convolutional coder are first distributed to different subcarriers and then to higher- or lower-significant bits of the constellation used for subcarrier modulation. Long sequences of
defective bits can thus be avoided which significantly improves the faculties of the
Viterbi decoder in the receiver for a correction.
The next stage performs the actual modulation of the individual OFDM carriers.
Depending on the set data rate, the useful carriers are subjected to a uniform BPSK,
QPSK, 16QAM or 64QAM modulation. This is done by first calculating the I and Q
coefficients of each carrier. Gray coding is used to distribute the data bits to constellation points. All carriers from 26 to +26, except carriers -21, -7, 0, 7 and 21, are used for
the transmission of user data. Carrier number 0 (directly at the center frequency later
on) is not used and is always 0. The remaining 4 are BPSK-modulated pilots. The pilot
carriers change their phase with each symbol. The phase variation is determined by
the 127-bit PN sequence already defined as scrambling sequence.
The actual OFDM modulation is performed by inverse discrete Fourier transform (IFFT)
in the next step. A 64-point IFFT is carried out with the I and Q coefficients of the subcarriers obtained before. To ensure sufficient spacing of aliasing products, only 52 of
the 64 possible carriers are used. The result is a discrete complex time signal in the
baseband with modulated OFDM carriers. A guard field which corresponds to a periodic continuation of the same symbol is then appended before each OFDM symbol.
Multipath propagation can thus be easily compensated in the receiver.
Aliasing products are suppressed by oversampling, converting the discrete digital signal to an analog signal and subsequent filtering. In the last step, the baseband signal is
modulated onto the selected RF carrier and the complete signal is sent to the receiver
via the air interface.
13Operating Manual 1171.5283.12 ─ 18
2.2 Physical Layer CCK-PBCC
A distinction is made between the packet type (or PPDU format) with long or short
PLCP (physical layer convergence protocol).
2.2.1 Long PLCP PPDU Format
In 802.11, the data packet on the physical layer is referred to as PPDU (PLCP protocol
data units). A PPDU consists of three components; the PLCP preamble, the PLCP
header and the PSDU (PLCP service data unit), which contains the actual information
data (coming from higher layers).
The PLCP preamble and header are used for synchronization and signalling purposes,
and are themselves divided into fields.
The PLCP preamble consists of a synchronization field and a start frame delimiter
field. The standard specifies a fixed data content for both fields.
The PLCP header consists of the signal, service, length and CRC fields.
IntroductionIEEE 802.11 (a/b/g)
Physical Layer CCK-PBCC
The signal field determines the data rate used in the PSDU field. The rates 1 Mbps,
2 Mbps, 5.5 Mbps, and 11 Mbps can be selected; rates 22 MBps and 33 Mbps can be
used in the optional PBCC modes.
The service field also helps to differentiate the modulation modes (CCK or PBCC) used
for the higher data rates of 5.5 Mbps and 11 Mbps.
The length of the PSDU field is entered in µs in the Length field.
The CRC field contains a check sum of all the fields of the PLCP header.
The PLCP preamble and the PLCP header in the long PLCP PPDU format are both
DBPSK-modulated and transmitted at a data rate of 1 Mbps. The data rate and the
modulation of the PSDU component are defined by the signal and service fields in the
PLCP header.
The frame structure can be seen in the figure below (also indicated in the "PPDU Configuration" dialog):
2.2.2 Short PLCP PPDU Format
The basic structure of the short PLCP PPDU format is identical to that of the long
PLCP PPDU format. There is no difference in the PSDU component. The PLCP preamble and header are generated in an abbreviated form. In the short preamble, the
14Operating Manual 1171.5283.12 ─ 18
Data Spreading and Modulation CCK-PBCC
number of bits transmitted in the SYNC field is reduced from 128 to 56. In the short
header, however, the number of data bits transmitted remains unchanged, but the data
rate is doubled (to 2 Mbps). These measures halve the transmission periods of preamble and header in the short PLCP format, as compared to the long PLCP format.
The frame structure can be seen in the figure below (also indicated in the "PPDU Configuration" dialog):
2.3 Data Spreading and Modulation CCK-PBCC
IntroductionIEEE 802.11 (a/b/g)
The R&S Signal Generator simulates signals in accordance with 802.11 on the physical layer. In the standard, the data link layer or, to be more precise, the MAC sublayer
provides the input data for this layer The following graph illustrates the signal generation process.
Figure 2-1: Principle of 802.11b/g signal generation
Depending on the PLCP PPDU format used, the PLCP preamble and the PLCP
header are combined in the packet builder. The PSDU field of the packet is filled with
the input data of the physical layer block. In the next step, all the packet data is scrambled. The actual spreading and modulation of the data signal to the resulting chip rate
of 11 Mcps comes next.
However, the data rates and modulations of the individual fields of a packet can differ.
The PLCP preamble always has a data rate of 1 Mbps, and is DBPSK-modulated.
Besides the actual modulation, spreading to the resulting chip rate occurs.
The PLCP header is either treated exactly like the preamble (long PLCP PPDU format), or DQPSK-modulated at a data rate of 2 Mbps (short PLCP PPDU format). Data
rates (1 Mbps, 2 Mbps, 5.5 Mbps, 11 Mbps, etc) with different modulations can be used
for the data part of the packet, the PLCP service data unit (PSDU). The following table
gives an overview of the different combinations of data rates, modulations and spreading/coding methods.
15Operating Manual 1171.5283.12 ─ 18
IntroductionIEEE 802.11 (a/b/g)
Data Spreading and Modulation CCK-PBCC
Packet field Data rate Chip rate Spreading/coding
methods
Short PLCP preamble
Long PLCP preamble
Short PLCP header 2 Mbps 11 Mcps 11-chip Barker
Long PLCP header 1 Mbps 11 Mcps 11-chip Barker
PSDU 1 Mbps (long
PSDU 2 Mbps 11 Mcps 11-chip Barker
PSDU 5.5 Mbps 11 Mcps CCK DQPSK
PSDU 11 Mbps 11 Mcps CCK DQPSK
PSDU 5.5 Mbps 11 Mcps PBCC BPSK
PSDU 11 Mbps 11 Mcps PBCC QPSK
PSDU 22 Mbps 11 Mcps PBCC 8PSK
1 Mbps 11 Mcps 11-chip Barker
sequence
1 Mbps 11 Mcps 11-chip Barker
sequence
sequence
sequence
11 Mcps 11-chip Barker
PPDU)
sequence
sequence
Modulation
DBPSK
DBPSK
DQPSK
DBPSK
DBPSK
DQPSK
PSDU 33 Mbps 16.5 Mcps PBCC 8PSK
The individual combinations of spreading, coding and modulation are described below.
2.3.1 1 Mbps Data Rate with DBPSK Modulation
At a data rate of 1 Mbps, the already scrambled data stream is DBPSK-modulated
according to the table below. The resulting symbol sequence is then spread using the
11-chip Barker sequence.
Bit input Phase change
0 0
1 Pi
2.3.2 2 Mbps Data Rate with DQPSK Modulation
At a data rate of 2 Mbps, the already scrambled data stream is DQPSK-modulated
according to the table below. The resulting symbol sequence is then spread using the
11-chip Barker sequence.
16Operating Manual 1171.5283.12 ─ 18
Data Spreading and Modulation CCK-PBCC
Dibit pattern (d0,d1) (d0 is first in time) Phase change
00 0
01 pi/2
11 pi
10 3pi/2(-pi/2)
2.3.3 5.5 Mbps Data Rate with CCK Modulation
The standard specifies CCK modulation (complementary code keying) for a data rate
of 5.5 Mbps. To this end, in each modulation step, four successive bits (d0 to d3) are
taken from the data stream which is already scrambled. The phases φ1,φ2,φ3,φ4 are
determined by these four bits.
φ1 is determined by the data bits d0 and d1 according to the following table, which
specifies different phases for even and odd modulation steps:
IntroductionIEEE 802.11 (a/b/g)
Dibit pattern (d0,d1) (d0 is first
in time)
00 0 pi
01 pi/2 3pi/2(-pi/2)
11 pi 0
10 3pi/2(-pi/2) pi/2
Even symbols phase change Odd symbols phase change
The phase φ1 must be interpreted relative to the phase of the previous symbol.
The other three phases are determined as follows:
φ2 = (d2 - pi ) + pi/2
φ3= 0
φ4= d3 - pi
By means of these four phases, the CCK code word can now be determined; it is:
17Operating Manual 1171.5283.12 ─ 18
Data Spreading and Modulation CCK-PBCC
Example:
(d0 to d3) = (0110), the phase of the last symbol is 0, the current modulation step is
even:
φ1= pi/2
φ2= (1 - pi) + pi/2 = 3pi/2
φ3= 0
φ4= 0*pi = 0
The CCK code word is consequently:
j(pi/2+3pi/2+0+0),ej(pi/2+3pi/2+0),ej(pi/2+3pi/2+0)
c={e
c = (ej0, ej0, -e
jpi/2
, ej0, e
jpi/2
, ej0, e
jpi/2
) = (1, 1, 1, -j, 1, j, 1, j)
j(pi/2+0),ej(pi/2+3x/2+0),ej(pi/2+0)
,-e
The four data bits (d0 to d3) thus become the eight complex output chips (c0 to c7).
2.3.4 11 Mbps Data Rate with CCK Modulation
The standard also specifies CCK modulation (complementary code keying) for a data
rate of 11 Mbps. The modulation is basically the same as described for the 5.5 Mbps
data rate. In each modulation step, eight successive bits (d0 to d7) are taken from the
data stream, which is already scrambled. The phases φ1,φ2,φ3,φ4 are determined by
these eight bits.
IntroductionIEEE 802.11 (a/b/g)
j(pi/2+3pi/2),ejpi/2
,-e
}
φ1 is determined by the data bits d0 and d1 according to the following table, which
specifies different phases for even and odd modulation steps:
Dibit pattern (d0,d1) (d0 is first in
time)
00 0 pi
01 pi/2 3pi/2(-pi/2)
11 pi 0
10 3pi/2(-pi/2) pi/2
Even symbols phase change Odd symbols phase change
The phase φ1 must be interpreted relative to the phase of the previous symbol.
φ2 is determined by the data bits d2, d3, φ3 from d4, d5 and φ2 from d6, d7 according to
the following table:
Dibit pattern [di,d
00 0
01 pi/2
11 pi
10 3pi/2(-pi/2)
] (d0 is first in time) Phase change
(i+1)
18Operating Manual 1171.5283.12 ─ 18
Data Spreading and Modulation CCK-PBCC
2.3.5 5.5 Mbps and 11 Mbps Data Rates with PBCC Modulation
Packet binary convolutional coding (PBCC) can optionally be used instead of CCK
modulation for the 5.5 Mbps and 11 Mbps data rates. The following illustration provides
a schematic overview of this method. For details, refer to the standard.
Figure 2-2: Principle of PBCC modulation
IntroductionIEEE 802.11 (a/b/g)
2.3.6 22 Mbps and 33 Mbps Data Rates with PBCC Modulation
802.11g also defines the optional PBCC (ER-PBCC) modes using the extended 22
Mbps and 33 Mbps rates. In contrast to the 5.5 Mbps und 11 Mbps PBCC modes, a
rate 2/3 convolutional coder and 8PSK modulation are used. With 33 Mbps, also the
clock rate in the data section of the packet is increased to 16.5 Mcps.
19Operating Manual 1171.5283.12 ─ 18
IntroductionIEEE 802.11 (a/b/g)
Data Spreading and Modulation CCK-PBCC
20Operating Manual 1171.5283.12 ─ 18
WLAN User InterfaceIEEE 802.11 (a/b/g)
3 WLAN User Interface
The menu for setting the IEEE 802.11a-g WLAN digital standard is either called from
the baseband block or from the menu tree under "Baseband".
The menu is split into several sections for configuring the standard. The choice of simulation mode determines which displays and parameters are made available in the
lower section.
The upper section of the menu is where the IEEE 802.11a-g WLAN digital standard is
enabled. The default settings are called and the physical layer mode, the simulation
mode and the frame type are selected. Additional parameters for defining the signal
length and a graph outlining the signal structure are indicated.
A button leads to the submenu for loading and saving the IEEE 802.11a-g WLAN configuration.
The buttons of the lower menu section lead to submenus for configuring the PPDU and
for setting the filter, clipping and marker parameters.
21Operating Manual 1171.5283.12 ─ 18
General Settings for WLAN Signals
3.1 General Settings for WLAN Signals
In this section, the IEEE 802.11a-g WLAN digital standard is enabled and the basic signal structure is configured.
State
Activates the standard and deactivates all the other digital standards and digital modulation modes in the same path.
Remote command:
[:SOURce<hw>]:BB:WLAN:STATe on page 58
Set to default
Calls the default settings. The values of the main parameters are listed in the following
table.
Parameter Value
State Not affected by "Set to default"
WLAN User InterfaceIEEE 802.11 (a/b/g)
Standard 802.11g
Physical Layer Mode CCK
Simulation Mode Framed
Predefined Frames Data
Sequence Length 1 frame
Idle Time 0.1 ms
Filter Gauss (FSK), 0.50
Chip Rate Variation 11 Mcps
Clipping Off
PPDU Configuration (CCK)
PLCP P+H Format Long PLPC
PSDU Bit Rate (CCK/PBCC) 11 Mbps
Data Length 1024 bytes
PSDU Data Source PRBS 9
Scrambling On
Service Field Clock Bits Locked
MAC Header Off
FCS (checksum) Off
Remote command:
[:SOURce<hw>]:BB:WLAN:PRESet on page 53
22Operating Manual 1171.5283.12 ─ 18
WLAN User InterfaceIEEE 802.11 (a/b/g)
General Settings for WLAN Signals
Save/Recall
Calls the "Save/Recall" menu.
From the "Save/Recall" menu, the file select windows for saving and recalling IEEE
802.11a-g WLAN configurations and the file manager can be called.
IEEE 802.11a-g WLAN configurations are stored as files with the predefined file extension *.wlan. The file name and the directory are user-definable.
The complete settings in the "IEEE 802.11a-g WLAN" menu are saved and recalled.
"Recall IEEE 802.11a-g WLAN setting"
Opens the "File Select" window for loading a saved IEEE 802.11a-g
WLAN configuration.
The configuration of the selected (highlighted) file is loaded by pressing the "Select" button.
"Save IEEE 802.11a-g WLAN setting"
Opens the "File Select" window for saving the current IEEE 802.11a-g
WLAN signal configuration.
The name of the file is specified in the "File name" entry field, the
directory selected in the "save into" field. The file is saved by pressing
the "Save" button.
"File Manager"
Remote command:
[:SOURce<hw>]:BB:WLAN:SETTing:CATalog? on page 55
[:SOURce<hw>]:BB:WLAN:SETTing:LOAD on page 55
[:SOURce<hw>]:BB:WLAN:SETTing:STORe on page 56
[:SOURce<hw>]:BB:WLAN:SETTing:DELete on page 55
Calls the "File Manager".
The "File Manager" is used to copy, delete and rename files and to
create directories.
Generate Waveform File…
Calls the "Generate Waveform" menu. This menu is used to store the current WLAN
signal as ARB signal in a waveform file.
This file can be loaded in the "ARB" menu and processed as multicarrier or multisegment signal.
The file name is entered in the submenu. The file is stored with the predefined file
extension *.wv. The file name and the directory it is stored in are user-definable.
Remote command:
[:SOURce<hw>]:BB:WLAN:WAVeform:CREate on page 59
Standard
Selects the 802.11 standard.
The standard was expanded over the years adding additional features.
23Operating Manual 1171.5283.12 ─ 18
WLAN User InterfaceIEEE 802.11 (a/b/g)
General Settings for WLAN Signals
"802.11a"
"802.11b"
"802.11g"
Remote command:
[:SOURce<hw>]:BB:WLAN:STANdard on page 57
Physical Layer Mode
Selects the physical layer mode.
"OFDM"
"CCK"
The standard supports OFDM (orthogonal frequency division multiplexing). This modulation is defined by the IEEE 802.11a specification
in the 5 GHz frequency band.
The standard includes the modulation mode CCK (complementary
code keying) and the data rates 5.5 Mbps and 11 Mbps. PBCC
(packet binary convolutional coding) can optionally be used instead of
CCK modulation for the 5.5 Mbps and 11 Mbps data rates.
Standard 802.11g extends standard 802.11b with higher transmission
rates. 802.11g contains the previous 802.11b modes and also integrates the OFDM method used in 802.11a for frequencies in the 2.4
GHz band.
The OFDM (orthogonal frequency division multiplexing) physical layer
supports a frame-based transmission. The OFDM signal is divided
into 52 carriers. The symbol rate of the modulation on the individual
carriers is 250 kHz. A user data rate of up to 54 Mbps at a channel
bandwidth of 20 MHz can be obtained.
This is achieved by combining 48 useful carriers for data transmission
(4 carriers are used for pilots) and using 64QAM for subcarrier modulation. With OFDM, the individual carriers are superimposed mutually
orthogonal, which, in the ideal case, does not cause any intercarrier
interference (ICI).
The CCK (complementary code keying) physical layer mode is used
for the 5.5 Mbps and 11 Mbps data rates.
"PBCC"
Remote command:
[:SOURce<hw>]:BB:WLAN:MODE on page 52
Simulation Mode
Selects the simulation mode.
The PBCC (packet binary convolutional coding) physical layer can
optionally be used instead of CCK modulation and extents 802.11b to
higher data rates (22 Mbps).
24Operating Manual 1171.5283.12 ─ 18
WLAN User InterfaceIEEE 802.11 (a/b/g)
General Settings for WLAN Signals
"Framed"
"Unframed"
The "framed mode" is the standard operating mode which is also
used in the real system. Data packets with the frame structure
defined by the standard are generated.
Signals representing a sequence of frames (PLCP protocol data
units, referred to as PPDUs) and separated by a so-called idle time
can be configured in the framed mode. The user data is continued in
the consecutive frames, i.e. it is not repeated in each frame. Both the
duration of the idle time and the number of frames to be sent can be
user-selected.
The "unframed mode" is offered in addition. In this mode, a nonpacket-oriented signal without a frame structure is generated with the
modulations and data rates defined by 802.11a-g. This mode can be
used for simple tests for which only modulation and spectrum of the
test signal are of interest.
No PLCP preamble and no signal field are generated in the unframed
mode. The idle time is also omitted. The data field is identical to that
of the framed mode and also contains the service and tail bits. The
length limitation stipulated by the standard to the maximum PSDU
block length of 4095 bytes in the framed mode does not apply.
Operation is the same as in the framed mode, but only a limited number of setting parameters is available.
Remote command:
[:SOURce<hw>]:BB:WLAN:SMODe on page 57
Predefined Frames
(Framed Mode only) selects the frame type. The selection defines parameters of the
MAC layer, e.g. the bit fields of type and sub-type of the MAC Header.
"Data"
"RTS"
"CTS"
"ACK"
Remote command:
[:SOURce<hw>]:BB:WLAN:FFORmat on page 51
Frames containing useful data.
Request to send.
Clear to send.
Acknowledgement.
25Operating Manual 1171.5283.12 ─ 18
WLAN User InterfaceIEEE 802.11 (a/b/g)
General Settings for WLAN Signals
Sequence Length
Sets the sequence length of the signal in number of frames. A (physical layer) frame
consists of a PPDU burst including the subsequent idle time.
Remote command:
[:SOURce<hw>]:BB:WLAN:SLENgth on page 56
Idle time
(based on standard chip rate)
(This feature is available for Framed Mode only).
Sets the idle time, i.e. the time between two PPDU bursts. Idle time is given in µs; the
packets can also be joined to each other directly with idle time 0. Please note that the
idle time refers to the chip rate as defined in the standard (11 Mcps for 802.11b/g CCK/
PBCC and 20 Mcps for 802.11a/g OFDM). Only at this chip rate does the idle period
correspond exactly to the time set. If the chip rate is doubled, for instance, the real idle
time is halved.
Remote command:
[:SOURce<hw>]:BB:WLAN:ITIMe on page 51
PPDU Configuration
(This feature is available for Framed Mode only).
Calls the menu for configuration of the PPDU. The menu differs for the physical layer
modes.
The menu is described in Chapter 3.2, "PPDU/Sequence Configuration", on page 27.
Remote command:
n.a.
Sequence Configuration
(This feature is available for Unframed Mode only).
Calls the menu for configuration of the signal in unframed modes.
The menu is described in Chapter 3.2, "PPDU/Sequence Configuration", on page 27.
Remote command:
n.a.
Filter/Clipping
Calls the menu for setting the filter parameters and the clipping. The current setting is
displayed next to the button.
The menu is described in section Chapter 3.5, "Filter/Clipping Settings", on page 38.
Remote command:
n.a.
Trigger - Marker
Calls the menu for selecting the trigger source, for configuring the marker signals and
for setting the time delay of an external trigger signal (see Chapter 3.6, "Trigger/
Marker/Clock Settings", on page 40).
The currently selected trigger source is displayed to the right of the button.
26Operating Manual 1171.5283.12 ─ 18
WLAN User InterfaceIEEE 802.11 (a/b/g)
PPDU/Sequence Configuration
Remote command:
n.a.
Execute Trigger
This feature is available for Trigger Source Internal only.
Executes trigger manually. A manual trigger can be executed only when an internal
trigger source and a trigger mode other than "Auto" have been selected.
Remote command:
[:SOURce<hw>]:BB:WLAN:TRIGger:EXECute on page 64
Clock
Calls the menu for selecting the clock source (see Chapter 3.6, "Trigger/Marker/Clock
Settings", on page 40).
Remote command:
n.a.
3.2 PPDU/Sequence Configuration
In framed mode, a frame consists of a PPDU (PLCP protocol data unit) and the idle
time. The data packet on the physical layer is referred to as PPDU. A PPDU consists
of three components; the PLCP preamble, the PLCP header and the PSDU (PLCP service data unit), which contains the actual information data (coming from higher layers).
The PLCP preamble and header are used for synchronization and signaling purposes,
and are themselves divided into fields.
The details of the PPDU structure depend on the selected standard or, more precisely,
on the physical layer mode (see below).
In unframed mode, the signal can be configured via the "PSDU bit rate" and "PSDU
modulation" parameters, as in the framed mode. However, a preamble or header is not
generated; only a continuous PSDU block is generated, the length of which can be varied by using the "Sequence Length" parameter. There is no restriction of the maximum
PSDU block length to 4095 bytes as in the framed mode. Moreover, the data stream
can be scrambled before the modulation ("Scrambling Mode" parameter).
3.2.1 Standard 802.11a - OFDM
In the upper section of the menu, the parameters of the data part (PSDU) are set. In
the middle section, the parameters of the scrambler and interleaver are set. A graph in
the lower sections illustrates the structure of the PPDU (framed mode) or the unframed
sequence (unframed mode).
●
Framed mode:
27Operating Manual 1171.5283.12 ─ 18
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