Wireless technology dominates our lives these days, yet most of us do not notice until it isn’t there. We take our smartphones and Wi-Fi connections for granted and simply expect them to work. Wireless services have become like electricity. How can we live without them? Here is a look at the dominant wireless technologies like LTE, 5G, and Wi-Fi and how they are continuing to improve.
The wireless technologies we all use daily are cellular LTE and Wi-Fi. LTE is gradually morphing into 5G and Wi-Fi continues to get better. The common theme behind the recent and coming improvements is faster data rates and increased capacity. Video demand is the primary reason for the need for more speed. Wireless standards continue to meet that expectation.
Wi-Fi. The IEEE 802.11 working group and the Wi-Fi Alliance over the years have given us a continuous upgrade path for our wireless LANs. New standards are always in the works and WLANs continue to get faster and serve more users. Many users have still not upgraded from the breakthrough 802.11n version that first incorporated MIMO. The next logical upgrade step is 802.11ac. This version called Wave 1 uses the 5 GHz band only and makes use of three spectral streams, 20/40/80 MHz channels, and 256QAM to achieve data rates to 1.3 Gb/s. The Wave 2 version of 802.11ac uses four spatial streams, channel bonding, and up to 160 MHz bandwidth, and introduces multi-user MIMO. This serves more users and boosts data rate to a peak of 1.7 Gb/s.
Now the 802.11ax standard has come along to provide an even more aggressive upgrade. This standard has not been finally ratified but, as usual, chip companies have already implemented it. Final approval is expected in 2019. 11ax uses either 2.4 or 5 GHz channels, switches from OFDM to OFDMA, adds 1024QAM with FDD, and uses narrower subcarriers. OFDMA permits multi-user MIMO, so it adds capacity as well as greater speed. Speeds peak at 7 Gb/s under ideal conditions. This standard also supports mesh networking.
Broadcom’s new Max WiFi devices (BCM43684, BCM43694, BCM 4375) for 11ax promise to improve download speeds by four times, upload speeds by six times, better coverage by four times, and battery life by seven times over the current 802.11ac. Chip company Quantenna Communications’ new QSR10R-AX chip packages three 4×4 MIMO 11ax radios on a chip, making it easier to implement mesh access points (APs).
A somewhat forgotten technology is WiGig or the 802.11ad standard that uses the 60 GHz band. Speeds to 7 Gb/s are possible, but the range is restricted to about 10 meters with line-of-site coverage and no wall penetration. It uses a phased array with beamforming to achieve its coverage. WiGig has been around for several years now but not been widely deployed. Wireless virtual reality headsets are said to be one possible application.
A new wireless LAN technology on the horizon is visible light communications. Also known as LiFi, this developing LAN technology uses visible light as the carrier. The data stream modulates standard LEDs in light fixtures. Data rates as high as several hundred Mb/s have been demonstrated but lower rates are more typical. One form of implementation is an LED light bar, designed to replace fluorescent tubes, that incorporates the LiFi circuitry. The range is short and there is no wall penetration making this type of LAN very secure. Dongles containing a photodetector are currently used on laptops or other computers to link to the network.
LTE. Long Term Evolution is our current 4G worldwide cellular standard. Like other good wireless standards it has been continuously improved through a series of upgrade Releases by the Third Generation Partnership Project (3GPP). Virtually all major carriers implement it and follow the upgrade path. Currently many carriers are incorporating the LTE Advanced version as defined by 3GPP Release 10. LTE-A adds carrier aggregation (CA) and higher-level 8×8 MIMO. CA allows operators to combine up to five 20 MHz channels (contiguous or non-contiguous) into one channel as a way to boost data rate. Along with higher MIMO, the potential maximum data rate is 1 Gb/s. The next upgrade is to Release 13, LTE-Advanced Pro that permits up to 32 CA, making LTE speeds even faster. It makes one wonder why we need 5G. LTE will be with us for decades to come, even when 5G arrives.
And let’s not forget that LTE is increasingly being used for some IoT/M2M applications, thanks to the new LTE-M and NB-IoT standards. New LTE-M (Cat 1) modules are available from Link Labs and Gemalto.
5G. The Third Generation Partnership Project (3GPP) is still working on 5G, but concurrently companies are testing 5G New Radio (NR) equipment. And we should see a first draft (Release 15) during 2018.
The goals for 5G are a user capacity of x100 existing LTE capability, downlink data rates up to 10 Gb/s, and a latency of less than 10 ms. Here are the highlights of the proposed 5G standard to meet these goals.
- Spectrum. The major carriers will use their below-6 GHz spectrum licenses. The 3.5 GHz Citizens Broadband Radio Service (CBRS) now used by the military may see some 5G usage on a shared basis. The major trend is to build out a network in the millimeter wave bands. In the United States, the 28 GHz and 39 GHz bands will be the new operational space. AT&T, T-Mobile, and Verizon have committed to this spectrum.
- Small Cells. A dense collection of small cells will supplement traditional LTE basestations. These miniature cell sites will attach to light poles, the sides of buildings, and on other structures. Getting permissions to install the small cells is turning out to be a major problem and will no doubt slow implementation of full 5G networks. Providing power and backhaul are related issues.
- Modulation. Some form of OFDMA with different subcarrier bandwidths from LTE’s current 15 kHz to 30-240 kHz. Adaptive modulation to 256QAM.
- Duplexing. Time division duplexing (TDD) rather than frequency division duplexing (FDD) that requires twice the spectrum.
- Coding. New channel coding includes low-density parity check (LDPC) for data and polar coding for control.
- Antennas. Massive, multi-user MIMO and agile beamforming antennas.
Multiple Antennas are the Solution
Wi-Fi, LTE, and 5G all have one thing in common. Their increases in data rate and user capacity have come primarily from advanced antenna techniques. With spectrum limited and most technologies up against Shannon’s law, it would seem that data rates should have topped out long ago. Antenna technology like MIMO, phased arrays, and agile beamforming and steering have made it possible to continue to boost data rates while accommodating more users with the same or less spectrum.
MIMO. Multiple input, multiple output is a system of multiple transmitters, receivers, and antennas for boosting data rate and adding reliability to a wireless system. Data is divided into separate serial streams that modulate transmitters on the same frequency band. Spatial diversity creates different signal paths with unique spectral characteristics that allow multiple receivers and advanced signal-processing techniques to separate and reproduce the data streams. The result is an increase in data rate by a factor of the number of paths created.
An enhancement to MIMO is multiple-user MIMO or MU-MIMO. This permits two or more simultaneous data streams to serve different users. Different antennas are assigned to each user so they get maximum data rates. MU-MIMO is still not widely implemented but the most recent standards 802.11ac/ax have adopted it. Both AP/routers and mobile terminals must support the technology for it to be useful.
MIMO is the key technology for all new Wi-Fi, LTE, and 5G products. But it has also initiated the need for fast, low-cost testing solutions. Over-the-air (OTA) testing is a must. One solution is National Instruments massive MIMO test system.
This is National Instruments’ system at the University of Bristol for testing massive 128 MIMO systems.
Phased Arrays. Another antenna technology that makes the modern wireless systems possible is the phased array. This is a matrix of multiple antennas such as tiny dipoles or patches spaced by at least one half wavelength and driven by multiple transmitters. By controlling the phase and amplitudes of the signals applied to the antennas, it is possible to combine the beams of each antenna so that the electromagnetic waves mix in an additive or subtractive way. The result is narrow beams that focus the signal and provide gain. In addition to this beamforming, control of the signals to the antennas can make the beam steerable in azimuth, elevation, or both.
On the receive side, the multi-element array feeds the signals to LNAs and individual phase shifters. The resulting signals are combined to form the composite signal. Agile beamforming and steering let the antenna focus on individual clients.
Multiple companies are now addressing the phased array. Analog Devices’ AD9371 dual RF transceiver is making it easier to build phased arrays with beamforming. This IC shown below includes two transmitters and two receivers that operate at frequencies up to 6 GHz. It supports FDD and TDD operation. When combined with the phase shifters and amplifiers/attenuators, this transceiver provides most of the circuitry to build large MIMO and beamforming phased arrays.
Analog Devices’ AD9371 dual transceiver operates up to 6 GHz and is finding a home in some 5G products.
A fully integrated phased-array device is Anokiwave’s AWA-0134, a 256-element electronically scanned antenna for 5G applications. The IC operates in the 28 GHz band and contains four each sets of power amplifiers (PAs), low noise amplifiers (LNAs), plus related phase shifters, attenuators, and switches; 64 of these chips go to operate the 256-element array. Anokiwave has a family of chips that support four radiating elements with 5-bit phase control and 5-bit gain control. ICs are available for the 26, 28, and 39 GHz 5G bands.
The Anokiwave AWA-0134 contains PAs, LNAs, phase shifters, attenuators, and switches that simplify phased-array construction to meet MIMO and beamforming requirements.
Ethertronics recently announced its next-generation Wi-Fi Active Steering platform, based on the EC477 Active Steering Processor and the EC624 Active Steering Antenna Switch. This solution doubles throughput, range, and efficiency for high-performance 802.11ax/802.11ac systems and has been optimized for current Wi-Fi access point and client solutions. The technology implemented in the EC477/EC624 family provides support for up to 8x8 MIMO in 802.11 applications as well as performance and scalability for next-generation 802.11ax applications (Fig. 4).
The Ethertronics Active Steering antenna is designed for 802.11/ac and 802.11ax Wi-Fi devices.
Movandi, a venture-backed startup, has a new RFIC front-end called BeamX that integrates RF, antenna, beamforming, and control algorithms into a modular 5G millimeter wave solution targeted for Customer Premises Equipment (CPE), small-cell, and base-station applications. Movandi has 28 and 39 GHz versions.
Now, what is the design solution for integrating 5G mmWave antennas into a handset with existing antennas for LTE cellular with MIMO, Wi-Fi, Bluetooth, and GPS?