3 Key Mobile Technologies Explained

Posted 05/24/2011 at 12:13pm | by The Maximum PC Staff

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In our last white paper roundup, we explained the technology behind three modern connectors. And while stuff like USB 3.0 and Light Peak is pretty exciting, we can't help but feel like technologies that speed up physical connections are a little behind the times. After all, isn't the future supposed to be wireless?

In that spirit, our new batch of whitepapers explores the wild world of wireless technologies, including 4G, Near Field Communication, and 802.11ac Wi-Fi. So keep reading, and educate yourself about this generation's wireless tech.

4G Wireless

How the next generation of mobile technology boosts performance

The statement “4G mobile technology has evolved beyond 3G” might score high on the “Duh” meter; but when we asked how this evolution manifested itself, we got different answers from different folks.

Mobile companies maintain that they’re rolling out 4G networks and handsets today, but the ITU-R (International Telecommunications Union Radiocommunication Sector) disagrees. That standards body maintains that the gear currently being advertised as 4G falls well short of its ideal, and that true 4G networks and devices lie a few years into the future. We’ll explain where 4G is today, how the networks have improved since 3G, and where the ITU-R wants the industry to go.

4G Today

Devices and services being marketed as 4G today are actually 3GPP LTE (Third-Generation Partnership Project Long-Term Evolution) and Mobile WiMAX (IEEE 802.16e). Both technologies represent major overhauls to prior networks, so they’re more advanced than 3G, but they’re not quite 4G. Sprint has chosen WiMAX, and Verizon and AT&T are moving ahead with LTE.

While each company evangelizes its own decision, the differences are nuanced. “In many ways, WiMAX and LTE are pretty comparable,” says Verizon’s Executive Director, Ecosystem Development Brian Higgins. “Both are OFDMA-based technologies, so they’re quite similar.”

OFDMA (Orthogonal Frequency-Division Multiple Access) changes the way the wireless spectrum is divvied up. CDMA (Code Division Multiple Access), which Verizon uses today, assigns each transmitter a code in order to multiplex the signals from many users over the same physical channel. OFDMA uses two-dimensional resource scheduling (in time and frequency) to dedicate an overlapping but non-interfering frequency range to each user so that multiple users can be supported in the same time slot. Verizon’s LTE service will divide the 700MHz frequency spectrum it purchased during the 2008 FCC auction into 10MHz channels.

“Within milliseconds,” says Higgins, “we’re making decisions on what chunk of frequency and what chunk of time we are going to allocate, and how many of those chunks, down to each individual user.” This allows the network to shift more bandwidth to more demanding requests in real time.

Both next-gen mobile technologies—3GPP LTE and Mobile WiMAX—rely on Orthogonal Frequency-Division Multiple Access (OFDMA) to make the most efficient use of the available wireless spectrum. OFDMA allocates time and frequency range to each user on a schedule, so that multiple users can be supported in the same slice of time.

Verizon augments OFDMA with MIMO (Multiple-Input, Multiple-Output) antenna technology at the downlink end. MIMO takes wireless communications’ greatest weakness—multipath signal propagation—and turns it into an advantage. Radio signals propagate as they bounce off buildings, mountains, and other physical obstacles. Instead of rejecting the multiple signals, MIMO antennas accept all of them and combine them into a single coherent data stream.

Higgins uses sound waves to illustrate how MIMO works. Imagine listening to someone speak at the opposite end of a furnished room. That person represents a single radio transmitter. As the sound waves emanate from his mouth, some bounce off the walls, windows, and furniture, while upholstery, curtains, and other materials absorb others. Your ears represent a radio receiver. “If you are someone who has just one ear,” says Higgins, “you’re going to have an ability to hear a conversation to a certain level. But if you have two ears—which is what you’re thinking about with MIMO—you have the ability to pick up different paths of sound coming across.”

Packet-switched networks mark another major improvement in LTE and WiMAX. In earlier networks, such as CDMA, the phone transmits to a base station, and that traffic is then sent through a T1 circuit to a mobile switching station. The data can then be converted to IP (Internet Protocol) packets, if needed. LTE and WiMAX networks can process all traffic using IPv6 and avoid the conversion step. Verizon, however, will continue using CDMA for voice traffic for now, reserving LTE for data traffic.

All of these changes combine to reduce latency in LTE and WiMAX networks: OFDMA allocates bandwidth more efficiently, MIMO improves signal quality, and packet-switched networks reduce conversion overhead. Verizon claims its LTE latency is in the 30-50ms range, compared to nearly 500ms on some 3G networks. This should render Verizon’s network sufficiently responsive for online gaming, VoIP, and other demanding applications.

Will the Real 4G Please Stand Up?

LTE can reach speeds of 100Mb/s downlink and 50Mb/s uplink, while WiMAX delivers up to 128Mb/s down and 56Mb/s up. These speeds hurtle past 3G standards, but they’re still far off the 4G purists’ target, which has led some to dub LTE and WiMAX “3.9G” technologies.

The ITU-R guideline for true 4G is known as IMT (International Mobile Telecommunications) Advanced. According to that standards body, wireless technologies must run at 1Gb/s for stationary users and 100Mb/s for moving connections. The IMT Advanced guideline also calls for significantly reduced latency: 10ms.

The ITU-R hasn’t identified a specification that meets its goals for IMT Advanced; instead, the next generations of LTE and WiMAX—LTE Advanced and IEEE 802.16e—are being designed to achieve those speeds.

While the ITU-R definition of 4G will push the industry toward even faster performance, carriers defend their “4G” designators. “We’re talking about doing basically an order of magnitude change in the capabilities of our wireless technology,” says Verizon’s Higgins. “To us, that’s a meaningful difference and is worthy of creating the right kind of brand around that, which is ‘4G.’ ”