Most of the short range wireless technologies are addressing the growing Internet of Things (IoT) opportunity. Now there is a new one to add to the pile: HaLow is the name given by the Wi-Fi Alliance to one of the IEEE’s newer standards, 802.11ah. It is one of a growing number of wireless technologies that promise longer-range communication than what is currently available from standard Wi-Fi, Bluetooth, ZigBee, Z-Wave, and others.
The 802.11ah standard uses the 902 to 928 MHz Industrial Medical Scientific (ISM) license-free band in the U.S., plus similar bands just below 1 GHz in other countries. As you know, the lower frequencies inherently have a greater range for a given power and antenna than the traditional higher 2.4 and 5 GHz Wi-Fi bands. Better still is the fact that these lower frequencies do a better job of penetrating buildings, trees, and other obstacles, making them more reliable for communications.
This is good news as low power can be used over these lower frequencies enabling battery-operated equipment. While most Wi-Fi gear has a maximum range of 100 meters under ideal conditions, HaLow has a maximum reach up to a kilometer with the right antenna. Shorter ranges will probably be more typical.
The applications appropriate for 11ah are sensor networks and longer-range monitoring and control projects common in M2M cases. Other potential uses include home automation, smart grid, smart cities, wearables, and other IoT applications requiring low power and longer range connections. Additional uses will certainly be found.
Technical Details
As for the technical details, 11ah is said to be a scaled-down 802.11ac, meaning slower clock rates at the lower frequencies. The 11ah standard specifies channel bandwidths of 1, 2, 4, 8, and 16 MHz. Modulation is OFDM using 24 subcarriers in a 1 MHz channel and 52 subcarriers in the larger bandwidths. Modulation can be BPSK, QPSK, 16QAM, 64QAM, or 256QAM, providing for a wide range of data rates. 11ah rates won’t be anywhere near as high as for standard Wi-Fi, but such speeds typically won’t be needed for most IoT types of applications. Rates of 100kb/s to several Mb/s will do in most cases.
The technical details of the standard are being finalized now, and ratification is expected this year. The Wi-Fi Alliance says it will implement an 802.11ah testing and certification program by 2018. In the meantime, look for some early chips and applications.
Some Competition
The 11ah standard will no doubt find some uses, but it has a great deal of competition from other <1 GHz long range offerings. Known as low-power wide area networks (LPWAN), these include 802.11af, LoRa, Sigfox, Weightless, and 5by5.
The IEEE standard 802.11af was designed to use the TV white spaces or unused TV channels from 54 to 698 MHz. Channels are 6 MHz wide in the U.S. and 8 MHz wide in Europe. These channels are ideal for supporting long range and non-line of sight transmission. The standard employs cognitive radio technology to ensure no interference to local TV signals. The basestation queries a data base to see what channels are available locally for data transmission.
The modulation is OFDM using BPSK, QPSK, 16QAM, 64QAM, or 256QAM. The maximum data rate per 6 MHz channel is about 24 Mb/s. Up to four channels can be bonded to get higher rates. Data base query is part of the protocol to identify useable local channels. Even longer ranges are expected at the lower VHF TV frequencies. Just remember that at the lower frequencies antennas have to get bigger, and that may be a knockout factor.
LoRa (long range) is a product of Semtech. Typical operating frequencies are 915 MHz for the U.S., 868 MHz for Europe and 433 MHz for Asia. The LoRa physical layer (PHY) uses a unique form of FM chirp spread spectrum along with forward error correction (FEC). This spread spectrum modulation permits multiple radios to use the same band if each radio uses a different chirp and data rate. Typical range is 2 to 5 km, and up to 15 km is possible depending upon the location and antenna characteristics.
Sigfox is a wireless technology as well as a network service. Sigfox is a French company offering its wireless technology, as well as a local LPWAN for longer-range IoT or M2M applications. It operates in the 902 MHz ISM band but consumes very little bandwidth or power. Sigfox radios use a controversial technique called ultranarrowband (UNB) modulation, and only transmits short messages at low data rates occasionally.
Weightless is an open LPWAN standard and technology for IoT and M2M applications. It is sponsored by the Weightless SIG and is available in several versions (W, N, and P). The original version, Weightless-W, was designed to use the TV white spaces. Other versions operate in the ISM bands (< 1 GHz).
5by5 Wireless is a newer patented technology that also uses the UHF bands from 300 to 1,000 MHz. It provides full duplex service with a range up to 25 miles. Its goal is to provide reliable Internet connectivity for IoT and M2M applications.
All of these alternatives have their pros and cons, but they do compete with 11ah. No doubt all will find a niche. My bet is that 11ah will do well just because it is a variant of our beloved Wi-Fi.