Over the past century, we’ve wired and rewired the world countless times, evolving from copper cable to fiber optics and beyond. But this cycle will soon come to an end as rapid-fire wireless innovations consistently deliver faster, cheaper, and more reliable communication.
ONE TREND AT A TIME The telephone business is still mostly wired, but the cell-phone phenomenon continues to chip it away. The balance may in fact shift drastically, now that cellular service has passed wired phone service in terms of number of subscribers. And let’s not forget the wired to cordless phone movement inside the home. I’ve never seen any figures, but I would guess that more than half of all home phones are cordless.The next frontier in communications, computer networking movement, began in the 1970s with wired systems. Long-distance networking used domestic telephone lines with 300- and 1200-baud modems and special “fast” dedicated 56-kbit/s lines. Local-area networks (LANs) were invented later. Ethernet came along in 1973 using the large RG-8/U coax cable, which was followed by smaller cables like RG-58/U. Finally, unshielded twisted pair (UTP) first served as telephone wire before improved versions like CAT5 and CAT6 became the norm.
The LAN trend is now wireless. It started with the 802.11 standard in the 1990s, but didn’t take off until 802.11b arrived around 1997. Quickly after that, we got the faster 11a and 11g versions. Today, the super-fast 11n version dominates.
Wired Ethernet networks haven’t disappeared, they just got faster—first 100 Mbits/s, then 1 Gbit/s, and today reaching 10 Gbits/s. The faster versions consist of fiber, though wireless is still the trend. As enterprise networks expand, the extensions are wireless for greater flexibility and convenience. Work continues within the IEEE for even faster wireless LAN links.
Wireless reigns in home networks. Early home net adopters went for UTP Ethernet and other wired technologies like cable TV coax, powerline, and phone-line systems. Some of them are still around, but better than 80% of all home PC networks use Wi-Fi. While 11n can deliver up to about 300 Mbits/s over 100 m in a home or enterprise environment, a faster version beyond 1 Gbit/s is the goal.
Incidentally, Wi-Fi gave us something else: broadband wireless access through hotspots. When we’re in hotels, airports, cafes, convention centers, and other public places, we can easily connect to the Internet for e-mail and other applications with our laptops. You can even connect via a cell-phone plug-in card in your laptop. All laptops today come with Wi-Fi built in, and soon many will include WiMAX, making broadband wireless available in most major cities.
Wired remains solid in metropolitan-area networks (MANs) and wide-area networks (WANs), which are mostly fiber anyway (see “Wired Won’t Go Down Without A Fight” at www.electronicdesign.com, ED Online 19068). Fiber is super-fast, and lots of unlit fiber is still available. Fiber networks will continue to form the backbone of our connectivity, especially to the Internet.
But wireless trends are making their mark within MANs. Wireless links using microwave and free-space optical systems are already in use. Even faster links should emerge as equipment is developed for the millimeter bands.
And consider the most common wired MAN of all—the cable TV network. Its main distribution uses fiber and then drops to homes by coax. Most homes get their TV by cable, and most high-speed broadband Internet access in the U.S. hooks up via cable systems. Now we’re seeing WiMAX broadband wireless technology begin to attack this market.
WiMAX promises a high-speed wireless Internet connection to rival cable TV and DSL services as carriers like Clearwire, Sprint Nextel, and TowerStream roll out their new systems. WiMAX won’t kill the wired systems, but it brings needed competition, and rural areas with no broadband service can join the 21st century. We may even get Internet Protocol Television (IPTV) this way.
The cell-phone world was all voice until the late 1990s and early 2000s. That’s when data services and the so-called 2.5G period arrived. GPRS was added to GSM TDMA phones, and 1xRTT was added to cdma2000 phones. EDGE and EV-DO came later with higher speeds.
Since then, we’ve moved into the 3G era with WCDMA on GSM networks, which have been further updated with EDGE and HSDPA/HSUPA/ HSPA+. In the cdma2000 world (EV-DO), Rev. A has been added. Future 4G services will use Long Term Evolution (LTE) and, less likely, Ultra Mobile Broadband (Fig. 1). WiMAX will see a parallel path worldwide, though it isn’t expected to play a role in cell-phone service in the U.S.
Consider another cellular trend. Today, more than 200,000 of the cell-phone sites in the U.S. use a wired backhaul system to the main telephone system. That technology, the popular T1 digital line, carries 24 calls. Increasing subscriber capacity and expanding cell-phone data use requires more and faster backhaul.
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To solve that problem, more expensive leased T1 lines and even faster T3 (44-Mbit/s) lines were added. Even ATM (asynchronous transfer mode) and fiber have been used in a few places. Beyond that, engineers have looked at microwave backhaul and fiber.
In the future, wireless backhaul will expand. But the real solution may lie in the use of Ethernet and Internet Protocol (IP) backhaul, including the use of multiprotocol label switching (MPLS) to provide quality of service (QoS) over the IP networks. That could be either wired or wireless. In any case, backhaul is one of the most critical issues for cell-phone carriers.
The industrial networking world is making the shift to wireless as well. Because of reliability and maintenance issues, wireless has never been too popular in connecting sensors to control systems and in connecting end actuators (motors, pumps, solenoids, etc.) to the system. Today, though, wireless solutions are more reliable and secure than ever.
Industrial networks are widely adopting Wi-Fi, plus wireless sensor technology like ZigBee. Also, mesh networks help to interconnect a wide range of sensors and extend the system’s range and reliability. All sorts of wireless links, both proprietary and standard, are replacing the older wired industrial networks using Modbus, the Profibus Device bus, HART, and dozens of other technologies.
Machine-to-machine (M2M) wireless has grown along these same lines. M2M uses the cellular system to implement an enormous range of monitoring and control functions in virtually every industry (Fig. 2). Tiny GSM or CDMA cell-phone transceivers are buried inside truck fleets and cargo carriers for asset tracking. They also monitor remote tank farms, connect to security systems, and monitor vending machines.
M2M has been one of the most “silent” wireless movements, but it’s growing by double-digit percentages every year. The applications seem to be endless, and costs continue to drop.
MAKING IT HAPPEN Certainly, the wired to wireless movement will march on. Within that trend, at any given time, the wireless world is in transition from one technology to another or from an older technology to an improved technology. Buried even further within those shifts is the never-ending quest for higher data rates. While security and QoS are still part of the change, nothing else matters as much as speed in all segments of wireless.Technology developments like orthogonal frequency- division multiplexing (OFDM), multiple-input multiple-output (MIMO), and software-defined radio (SDR), as well as regulatory conditions, have smoothed the path from wired to wireless.
OFDM is a modulation technique that takes a high-speed serial data signal, divides it into multiple slower data streams, and uses them to modulate many adjacent narrow channels over a broad bandwidth. The modulation on each channel is usually binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), or some quadrature amplitude modulation (QAM) variant.
The result is a very broadband signal that’s very spectrally efficient, producing very high bit/ hertz rates. Because the signal is spread over a wide band, it’s also more tolerant of multipath cancellation and fading, which is a common problem in microwave frequencies. And, OFDM can be adapted to create an efficient access method (orthogonal frequency-division multiple access, or OFDMA) for many subscribers in the same band. OFDM is so good that it is gradually replacing most other more traditional wireless methods, including the vaunted CDMA spreadspectrum method.
The fastest Wi-Fi standards all use OFDM, with 802.11a/g producing data rates to 54 Mbits/s in a 20-MHz band. The broadband wireless standard WiMAX (802.16) is also OFDM (Fig. 3). 3GPP’s forthcoming LTE 4G cell-phone standard is based on OFDM as well. The most common form of short-range Ultra Wideband (UWB) networking, WiMedia, is based on OFDM. Broadcast HDRadio uses OFDM. All mobile TV technologies for cell phones (MediaFLO, DVB-H, etc.) are based on a coded OFDM.
Another technique that’s helping push wireless, MIMO, uses multiple transceivers and antennas on the same band to transmit different and coded parallel data streams to enable faster and more reliable wireless services. It has been adopted in the latest 802.11n Wi-Fi, as well as in forthcoming WiMAX applications. LTE also provides for a MIMO component. The overall result is greater data speeds and better link reliability under multipath conditions.
To make both OFDM and MIMO practical, SDR techniques are applied. SDR replaces traditional wireless circuits with software on DSPs or DSP-programmed FPGAs. OFDM and MIMO aren’t possible with older wireless circuits, but both are easier with DSP.
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Wireless standards have also aided the wired to wireless transition. Today, every wireless technology is established by a standard. The biggest contributor in this department, the IEEE, has standardized Wi-Fi (802.11), WiMAX (802.16), and other short-range wireless technologies like the personal-area-networking (PAN) standards for Bluetooth (803.15.3), ZigBee (802.15.4), and many others.
Both the 3GPP and 3GPP2 set cell-phone standards. Each group also develops standards that are ultimately adopted by the ITU. For instance, 3GPP developed the GSM, GPRS, EDGE, WCDMA, and now the LTE standards, while 3GPP2 handles cdma2000, 1xRTT, EV-DO, and UMB.
Standards provide interoperability between products of different companies. The related industry forums, alliances, and consortia ensure this interoperability with certification testing. While proprietary wireless technologies do occasionally succeed in niche markets, the largest adoption comes when firm national or international standards exist. Spectrum availability certainly plays into the wireless phenomenon. The electromagnetic spectrum is finite, and it ultimately could limit the wireless transition. Countries regulate the spectrum and allocate it to various standards and services. In highly developed areas like Europe, Asia, and the U.S., spectrum is scarce.
But thanks to technology with greater spectral efficiency, advances are being made. Pushing into the higher frequencies like the millimeter bands (30 to 300 GHz) gives us even more spectrum to use. The mm bands are tougher to deal with, but again, semiconductor technology advances are giving us devices that perpetuate the wireless trend.
In the U.S., the Federal Communications Commission is phasing out the older UHF TV spectrum from 698 to 806 MHz. Known as the 700-MHz band, this spectrum was recently auctioned off for new wireless services. Most of it will be used for expanded cell-phone services with faster data capabilities, such as those available from LTE. WiMAX will get new spectrum, as will the new broadcast mobile TV services that are just beginning (see “Some Interesting Wireless Trends,” Drill Deeper 19069).
WHAT WE NEVER HAD BEFORE Perhaps no other aspect of the wired to wireless transition has benefited more than personal and business communications. Of course, spearheading it all is the cell phone. Research firm ABI says that “as mobile usage in business grows, it challenges the value of fixed-line communications.” Today, the cell-phone business dominates wireless, both commercial and personal. Data services like texting, e-mail, and Internet access continue to grow at double-digit rates, and projections show that it will eventually exceed voice in most carriers’ networks.GPS navigation and other location technologies have no doubt added a new dimension to the cell-phone age. With a GPS receiver and increasingly with our cell phones, we can immediately find where we are. Also, emergency services can find us thanks to the E911 capability built into every new phone. With reliable navigation and location technology, new locationbased services are expected to flourish.
Some phones use internal GPS receivers with assistance from nearby cell sites (called Assisted-GPS) to pinpoint a handset location. Other handsets use a triangulation method with three nearby cell sites to locate a handset. Called uplink-time difference of arrival (U-TDOA), this method doesn’t require an internal GPS receiver. A newer hybrid approach from TruePosition combines the A-GPS and U-TDOA methods with new algorithms to greatly improve location accuracy to less than 25 m.