Louis E. Frenzel
December 13, 2011
The end of the world on December 21 this year notwithstanding—at least according to some superstitions—the wireless world keeps moving ahead with many impressive developments on all fronts. In fact, wireless has become the go-to communications link of modern times (see “Expect Eight Wireless Trends In 2012”).
Of all the different forms of wireless, cellular dominates. In a short time, the smart phone has become our number one consumer electronic device, and many users can’t seem to function without one. Also, wireless connections have enabled our growing infatuation with tablets. The wireless field is changing so fast that few can keep pace with its developments.
An LTE World
Everyone is adopting Long-Term Evolution (LTE) not only for cellular service but also for other broadband wireless services. As a very broad and complex standard of the Third Generation Partnership Project (3GPP) and the International Telecommunications Union (ITU), it uses orthogonal frequency-division multiplexing (OFDM) in usually 10- or 20-MHz bands and supports a wide range of multiple-input multiple-output (MIMO) variations.
LTE can deliver speeds of up to 100 Mbits/s downlink and 50 Mbits/s uplink under ideal conditions depending on the carrier configuration. In the U.S., access is via frequency-division duplex (FDD) that uses two bands for separate uplinks and downlinks. A time-division duplex (TDD) version is also available but is used primarily in China.
Time-Division LTE (TD-LTE) is more spectrum-efficient as it requires only a single band. That’s why it’s being widely adopted in areas where spectrum is an issue. India, Japan, and countries in Latin America will be using TD-LTE, and there’s no doubt it will ultimately find its way to the U.S.
For example, Clearwire’s huge WiMAX network shared by Sprint is expected to convert to TD-LTE sometime in the future. The conversion from WiMAX, which is a TDD technology, to TD-LTE is generally easy and inexpensive.
The state of LTE adoption is highly variable at this time. Operators in the U.S. have spent the past few years upgrading their systems to more advanced 3G technologies like HSPA. Both AT&T and T-Mobile have built impressive HSPA networks capable of speeds up to 21 and 42 Mbits/s.
On the other hand, Verizon, with its cdma2000/EV-DO networks maxed out, started the conversion to LTE last year and is far ahead of everyone. Verizon LTE is now available in most of the major U.S. markets and will continue aggressively. Sprint and partner Clearwire will stay with their WiMAX systems for now but are expected to move to TD-LTE in the future. New entrants like MetroPCS and LightSquared are also slowly building out their LTE networks.
One of the main factors in the LTE rollout besides the capital equipment expense of new LTE gear is the shortage of handsets. A high percentage of LTE today is by way of dongles and modems rather than handsets because of the multimode and band fragmentation problems. LTE phones must maintain backward compatibility with older technologies like GSM/WCDMA/HSPA or cdma2000/EV-DO on multiple bands in different countries. It is difficult and expensive to make a smart phone with such wide ranging coverage.
Altair Semiconductor’s FourGee 3100/6202 chipset supports both FDD LTE and TD-LTE on virtually all bands. The RF chip covers from 700 to 2700 MHz and provides automatic dynamic handover between FDD and TDD in more than 12 standard bands. Handset vendors can select one chipset for multiple smart-phone versions depending on operator specifications, country, and spectrum (Fig. 1).
LTE is the preferred wireless technology. Virtually all cellular systems ultimately will use LTE, and most broadband wireless access will be LTE. Even the public safety sector is considering a transformation from its narrowband mobile radios to some kind of LTE-based system.
In a recent report, research firm IHS indicated that LTE would account for 10% of all global wireless subscribers by 2015. In 2011 there were 11.6 million LTE subscribers, and IHS expects that to grow to 62.8 million in 2012. Despite the massive increases, LTE is still a smaller percentage overall with older 2G and 3G technologies dominating.
While the LTE rollout has started, it is slow going. Massive growth is not expected until the 2013-2014 timeframe, when the inflection point is expected to occur. At that time, we may also see some networks begin the upgrade to the next level of LTE called LTE-Advanced. This next generation of LTE uses wider bands of 40, 80, and even 160 MHz of contiguous or non-contiguous spectrum and more complex MIMO configurations to hit a magical 1-Gbit/s downlink speed.
Wi-Fi
Virtually every laptop, tablet, and smart phone includes Wi-Fi. This ubiquitous wireless service boasts millions of hot spots and home access points (APs) around the world. Despite the maturity and already widespread adoption of this wireless local-area network (WLAN) technology, many new developments are in the works. These developments will extend its usefulness and functionality beyond its initial intentions.
A good example is the increasing use of Wi-Fi on board airliners. No longer can you escape e-mail while you’re in the air. You not only can access your e-mail but also connect to the Internet to take your mind off of being stuck in a middle seat. American, Alaska, Delta, Southwest, United/Continental, and U.S. Airways offer Wi-Fi now, and service is growing.
Another significant development is the increased adoption of MIMO in 802.11n APs and client devices. Now, 2×2 MIMO in APs is giving way to 3×3 and 4×4 configurations to extend the range and speed of connected laptops and cell phones. While speed is important, the range and link reliability really are pushing users to adopt MIMO models.
The Wireless Broadband Alliance estimates that at the end of 2011, there were over a million worldwide hot spots. That will roughly double in 2012 and the number is expected to rise 350% by 2015.
In addition to the desirability of MIMO 802.11n is Marvell’s transmit beamforming technology. This signal processing method focuses the beam of an AP signal to extend the range and speed of a remote client using 2×2 or 4×4 MIMO APs.
The AP queries a remote client with Wi-Fi. If the client has the beamforming option in 11n, it sends a channel matrix feedback signal that lets the transmitter form its beam appropriately. The beam forming focuses the beam and provides significant gain over a standard antenna and channel.
This results in longer range and higher data rates. Even if the client does not have the beamforming option, the transmitter can still zoom in and boost range and data rate. Marvell’s 88W8764 4×4 and 88W8797 2×2 AP chips have the transmit beamforming option.
Progress is also being made on the two latest versions of Wi-Fi, designated 802.11ac and 802.11ad. The 802.11ac standard uses the 5-GHz unlicensed Wi-Fi band (5.18 to 5.85 GHz) but deploys wider-bandwidth channels (80 MHz or 160 MHz), higher-count MIMO up to 8×8, plus higher levels of modulation (up to 256-state quadrature amplitude modulation, or 256QAM) to achieve longer ranges and higher data rates from about 400 Mbits/s to well over 1 Gbit/s depending upon the MIMO configuration, bandwidth, and modulation.
Beamforming is also a part of this standard to further boost range and data rate. The IEEE task group has the draft form of the standard now, and final approval is expected in late 2012 or early 2013.
Chip companies are already preparing IC for 11ac products. One of the first (if not the first) is Quantenna with its QAC2300 chipset. This baseband chip and RF chip support up to four spatial streams. The chipset implements the Draft 11ac specification in a 4×4 format with baseband beamforming and can achieve a data rate to 1.7 Gbits/s. It targets APs, wireless routers, and high-end consumer electronics products primarily for streaming HD video. A reference design and development kit are available now (Fig. 2).
The IEEE 802.11ad standard uses the 60-GHz unlicensed radio spectrum from 57 to 64 GHz. The basis for this standard is sponsored by the WiGig Alliance. It uses OFDM modulation or a single-carrier format to achieve data rates to 7-Gbit/s. Also, it uses an antenna array to achieve active beamforming.
Wilocity, the 60-GHz radio pioneer, has developed the transceiver. It’s now available as a product that includes the Atheros Qualcomm 802.11n chip (Fig. 3). In addition to standard LAN duties, the new radio chips are expected to be used in TV sets, video equipment, remote storage units, and docking stations.
But that’s not all. Wi-Fi is also seeking to penetrate the machine-to-machine (M2M) and home monitor and control network spaces. Typically M2M is associated with cellular networks, but almost any wireless technology can be adapted. Home monitoring and control now uses mostly Z-Wave and ZigBee. Wi-Fi may be an even better option now that its chips are less expensive and consume less power than ever before.
Broadcom’s Wireless Internet Connectivity for Embedded Devices (WICED, pronounced “wik-id”) platform combines the Broadcom BCM4319 wireless LAN media access controller (MAC)/baseband/radio chip with an embedded processor in a module that can be built into almost any home product like home appliances, consumer electronics, or special products built for cloud-based services. The key to this module and related reference design is the unique Wi-Fi networking library and software application stack.
The complete development kit contains a software debugger, compiler, and test board. Other content is available in an easy-to-use software development and applications library with an innovative application programming interface (API) that reduces development complexity required to access and utilize advanced Wi-Fi capabilities.
Also available is a Serial-to-Wi-Fi API that enables high-speed TCP/IP throughput of greater than 20 Mbits/s that enables advanced applications and support for key I/O interfaces, including USB, UART, SPI and SDIO. Its built-in support for Wi-Fi Direct and Wi-Fi Protected Set-up allows end users to get connected simply and securely. Look for it to really stimulate the adoption of more Wi-Fi home networks that can potentially control and monitor devices with any laptop, tablet, or smart phone with the right app.
Finally, another role for Wi-Fi is cellular network offload (see “Spectrum And Backhaul Inhibit Wireless Growth,” p. xx). Cellular operators are beginning to use a system that shifts some of the data load on the network to their Wi-Fi networks. Since most smart phones have Wi-Fi anyway, a connection can still be made if a hot spot is nearby.
For example, while trying to access a YouTube video on your iPad via the cellular network, you could get automatically bumped off to your own home network or some nearby AP. The reduced traffic on the cellular network will make it faster and reserve capacity for more users and/or faster data to those needing it.
This is a work in process, but most of the major carriers are using it in some form or at least testing it. The IEEE’s new 802.11u standard protocol supports external authentication, authorization, and accounting that will make such transfers and connections faster, easier, and automatic.
Ultra-Low-Power Wireless
One sector that’s really taking off is very low-power short-range wireless. These technologies essentially serve low-data-rate, short-range applications that benefit from very long battery life. How long that battery lasts depends on the radio and other circuits. Applications include medical monitoring, health and fitness monitoring, human interface devices (HIDs, or PC peripherals like keyboards, mice, and game controllers), toys and games, and wireless audio.
One of the most popular technologies is Bluetooth Low Energy (BLE). As part of the latest Bluetooth SIG 4.0 standard, it specifies a simpler radio interface with energy-saving design to make long battery life a standard outcome. It still uses the adaptive frequency-hopping scheme of Bluetooth but uses only 40 2-MHz channels instead of 79 1-MHz channels. Modulation is still Gaussian frequency shift keying (GFSK) but with a modulation index of 0.5 that saves power.
Data rate is 1 Mbit/s peak and actual rate is usually lower, typically about 200 kbits/s. Packets are shorter in the 8- to 27-byte range again to save power by only transmitting short bursts. A key characteristic of BLE is lower latency and setup time, down from about 100 ms in standard Bluetooth to 3 to 6 ms in BLE. With low duty cycle transmission and a sleep mode, power consumption is very low.
While the BLE v4.0 feature is included in some standard Bluetooth chips and some multifunction chips, Nordic Semiconductor makes a BLE-only chip, designated the mRF8001, for strictly low-power applications. Nordic has a whole line of low-power radios that operate in the 2.4-GHz unlicensed band. The nRF24L series is for proprietary protocols (Fig. 4).
A special version called the nRF24AP2 uses the popular ANT+ protocol, which is designed for very low-power wireless sensor networks to collect, store, and transfer sensor data. An embedded computer or even a smart phone gathers data from multiple wireless sensors and then transfers it to a PC for tracking and presentation. The ANT+ protocol is widely used in sports, wellness, and home health areas.
Another potential application for BLE is TV/electronic remote control. Most remote controls are still infrared (IR), but there has been a movement to create an RF remote. Some designs use the 802.15.4 standard and ZigBee to produce remote controls based on the Radio Frequency for Consumer Electronics (RF4CE) standard.
Now serious consideration is being given to BLE and other low-power wireless options. TV giant Philips has created a dual IR/RF design using the Nordic lower-power transceivers that’s expected to find a place in smart TVs, over-the-top (OTT) boxes like Roku, and standard set-top boxes (STBs).