WLAN 802.11ad Tutorial
This WLAN 802.11ad tutorial covers basic 11ad features, 802.11ad channels, 802.11ad spectrum mask, 802.11ad modulation coding rates, 802.11ad frame types and provide link to 802.11ad physical layer.
WLAN 802.11ad standard has been developed as next version of 802.11ac standard. This standard is also referred WiGig. The IEEE 802.11ad supports very high data rate (about 7 Gbps) at shorter distances(about 1-10 meters) at the frequency of 60GHz.
This standard takes care of high data rate requirement in various WLAN usage models such as video streaming, HDTV, rapid upload and download, backhaul connectivity and more. It delivers high data rate due to higher bandwidth support on the order of about 2.16 GHz. It supports legacy wifi networks at 2.4 GHz as well as 5 GHz.
802.11ad channels
Following table-1 mentions country wide frequency allocations of 802.11ad.
Table-1: WLAN-11ad Country wide Frequency allocations:
| Country/Region | Frequency range |
|---|---|
| US and canada | 57.05 to 64.00 GHz |
| European union | 57.00 to 66.00 GHz |
| South Korea | 57.00 to 64.00 GHz |
| Japan | 57.00 to 66.00 GHz |
| Australia | 59.40 to 62.90 GHz |
| China | 59.00 to 64.00 GHz |
Following are the 11ad channel-1, channel-2, channel-3 and channel-4 used in WLAN 802.11ad. The table-2 mentions frequency range as well as RF center frequency used for these channels. The bandwidth for all the channels is about 2.16GHz wide.
Table-2: WLAN-11ad Channels:
| 802.11ad channel number | RF Center frequency | RF Frequency range |
|---|---|---|
| 11ad Channel-1 | 58.32 GHz | 57.24 to 59.40 GHz |
| Channel-2 | 60.48 GHz | 59.40 to 61.56 GHz |
| Channel-3 | 62.64 GHz | 61.56 to 63.72 GHz |
| Channel-4 | 64.80 | 63.72 to 65.88 GHz |
WLAN 802.11ad frame types
The figure-1 depicts different physical layer frame formats. As shown in the figure, there are four different PHY modes. They are control, single carrier, low power single carrier and OFDM.
802.11ad frame consists of three parts preamble, header and payload.
The preamble is known data pattern which helps in front end synchronization at the receiver.
The front end synchronization covers time, frequency and channel correction modules.
The header contains information useful to decode the rest of the packet i.e. payload.
Modulation and coding scheme of the payload is carried by the header.
Following are the supported 802.11ad modulation code rates.
Control packet header = {1 bit(diff.detector initialization, 4 bits(scrambler init., 10 bits(length), 1 bit(packet type),
5 bits(training length), 1 bit (turnaround), 2 bits(reserved), 16 bits(HCS) }
Single carrier header = {7 bits(scrambler init.), 5 bits(MCS), 18 bits(Length), 1 bit(add.PPDU),
1 bit(packet type), 5 bits(training length), 1 bit(aggregation), 1 bit(beam tracking request),
4 bits(last RSSI), 1 bit(turnaround), 4 bits(reserved), 16 bits(HCS) }
OFDM header = {7 bits(scrambler init), 5 bits(MCS), 18 bits(length), 1 bit(add. PPDU), 1 bit(packet type),
5 bits(training length, 1 bit(aggregation), 1 bit(bram tracking request), 1 bit(tone pairing type),
1 bit (DTP indicator), 4 bits( Last RSSI), 1 bit(turn around), 2 bits(reserved), 16 bis( HCS) }
STF stands for Short Training Field and CEF stands for Channel Estimation Field.
802.11ad modulation-code rate
Following tables 3 to 5 mentions modulation code rate information for these different physical layer modes. This information is mapped to MCS index which is carried in the header part of the 802.11ad packet. This MCS index indicates the modulation/code rate of the data payload/control information.
Table-3:Modulation code rate for control PHY
| MCS Index | Modulation | Code rate | Data rate |
|---|---|---|---|
| MCS-0 | DBPSK | 1/2 | 27.5 Mbps |
Table-4:Modulation code rate for Single Carrier PHY
| MCS Index | Modulation | NCBPS | Repetition | Code rate | Data rate(Mbps) |
|---|---|---|---|---|---|
| MCS-1 | π/2 BPSK | 1 | 2 | 1/2 | 385 |
| MCS-2 | π/2 BPSK | 1 | 1 | 1/2 | 770 |
| MCS-3 | π/2 BPSK | 1 | 1 | 5/8 | 962.5 |
| MCS-4 | π/2 BPSK | 1 | 1 | 3/4 | 1155 |
| MCS-5 | π/2 BPSK | 1 | 1 | 13/16 | 1251.25 |
| MCS-6 | π/2 QPSK | 2 | 1 | 1/2 | 1540 |
| MCS-7 | π/2 QPSK | 2 | 1 | 5/8 | 1925 |
| MCS-8 | π/2 QPSK | 2 | 1 | 3/4 | 2310 |
| MCS-9 | π/2 QPSK | 2 | 1 | 13/16 | 2502.5 |
| MCS-10 | π/2 16QAM | 4 | 1 | 1/2 | 3080 |
| MCS-11 | π/2 16QAM | 4 | 1 | 5/8 | 3850 |
| MCS-12 | π/2 16QAM | 4 | 1 | 3/4 | 4620 |
Table-5:Modulation code rate for OFDM PHY
| MCS Index | Modulation | Code rate | NBPSC | NCBPS | NDBPS | Data rate(Mbps) |
|---|---|---|---|---|---|---|
| MCS-13 | SQPSK | 1/2 | 1 | 336 | 168 | 693.00 |
| MCS-14 | SQPSK | 5/8 | 1 | 336 | 210 | 866.25 |
| MCS-15 | QPSK | 1/2 | 2 | 672 | 336 | 1386.00 |
| MCS-16 | QPSK | 5/8 | 2 | 672 | 420 | 1732.50 |
| MCS-17 | QPSK | 3/4 | 2 | 672 | 504 | 2079.00 |
| MCS-18 | 16-QAM | 1/2 | 4 | 1344 | 672 | 2772.00 |
| MCS-19 | 16-QAM | 5/8 | 4 | 1344 | 840 | 3465.00 |
| MCS-20 | 16-QAM | 3/4 | 4 | 1344 | 1008 | 4158.00 |
| MCS-21 | 16-QAM | 13/16 | 4 | 1344 | 1092 | 4504.50 |
| MCS-22 | 64-QAM | 5/8 | 6 | 2016 | 1260 | 5197.50 |
| MCS-23 | 64-QAM | 3/4 | 6 | 2016 | 1512 | 6237.00 |
| MCS-24 | 64-QAM | 13/16 | 6 | 2016 | 1638 | 6756.75 |
Table-6:Modulation code rate for Low Power Single carrier(SC) PHY
| MCS Index | Modulation | Effective Code rate | Coding Scheme | NCPB | Data rate(Mbps) |
|---|---|---|---|---|---|
| MCS-25 | π/2 BPSK | 13/28 | RS(224,208)+Block code(16,8) | 392 | 626 |
| MCS-26 | π/2 BPSK | 13/21 | RS(224,208)+Block code(12,8) | 392 | 834 |
| MCS-27 | π/2 BPSK | 52/63 | RS(224,208)+SPC(9,8) | 392 | 1112 |
| MCS-28 | π/2 QPSK | 13/28 | RS(224,208)+Block code(16,8) | 392 | 1251 |
| MCS-29 | π/2 QPSK | 13/21 | RS(224,208)+Block code(12,8) | 392 | 1668 |
| MCS-30 | π/2 QPSK | 52/63 | RS(224,208)+SPC(9,8) | 392 | 2224 |
| MCS-31 | π/2 QPSK | 13/14 | RS(224,208)+Block code(8,8) | 392 | 2503 |
WLAN 802.11ad Spectrum Mask
Figure-2 depicts 802.11ad spectrum mask. The X-axis is frequency and Y-axis is decibels relative to teh signal level at band center(dBr). This spectrum mask is approved by the ITU-WPA5. This 802.11ad spectrum mask is different compare to lower frequency masks provided in other wireless standards. The breakpoins in the mask are at -17 dBr level. This is for single carrier as well as OFDM modulation types. Out of band rejections are kept higher to make it easy for RF circuit designs for these WiGig 60 GHz transmitters. Usually 10dBm is used as maximum allowed transmit power. It varies slightly country by country. The transmit spectrum mask will be measured on the data packets greater than 10 µs without the training fields.
This 11d spectrum mask measurements have been carried with RBW of 1MHz. The nominal bandwidth used is 1830.47 MHz for OFDM PHY and 1760 MHz for single carrier PHY.
WLAN 802.11ad physical layer
The 802.11ad Physical layer helps encode the MAC layer data packet suitable to be transmitted over 802.11ad air interface. There four different physical layer used in the transmitter. Hence physical layer modules are different in each of them. In general physical layer composed of scrambler, LDPC encoder or RS encoder used as FEC techniques, modulation, interleaver, guard insertion, spectrum shaping and RF up conversion. IFFT is included in the OFDM Phy version. Refer WLAN 802.11ad physical layer for detailed description of each of these physical layer transmitters and their functional modules.
11ad device conformance testing
Refer 11ad conformance testing page which covers RF and PHY layer testing as per 11ad standard. This conformance tests are useful for 11ad device testing.
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