OFDM's New Uses

By Steven J. Vaughan-Nichols

November 18, 2002

OFDM takes Wireless Networking at the Next Level -- but what happens after that? Part two covering the modulation scheme of once and future WLANs.

Now we understand how Orthogonal Frequency Division Multiplexing (OFDM) works. But that's not all there is to it.

Even in WLANs, OFDM isn't just IEEE 802.11a and IEEE 802.11g; it's also used in the European Telecommunications Standards Institute (ETSI)'s HiperLAN/2 (high-performance radio LAN 2) standard . In addition, Japan's Mobile Multimedia Access Communications (MMAC) WLAN broadband mobile technology uses OFDM.

Rajiv Laroia, Founder & CTO of Flarion, sees OFDM playing a major role in 4G networks. He believes that "Wireless systems originally architected for circuit-voice and then adapted for data, e.g., 3G, cannot cost-effectively provide the whole Internet experience to mobile users. Because OFDM can overcome signaling transmission barriers and increase transmission speeds," while dealing with "the unpredictable changes of the radio frequency environment, it is especially well suited for mobility applications in cellular networks."

Laroia certain hopes that is true, because Flarion intends to complete with existing 3G broadband mobile wireless technologies used in cell phones, PDAs, and other wireless communication devices. We can expect to see a war between OFDM and CDMA for dominance of the mobile broadband wireless access market in the next five to ten years.

On the other hand, Nogee comments that while "OFDM is less affected by multipath and requires much less linearity than CDMA, so in those ways, its better. But OFDM "shares" bandwidth completely differently than both CDMA and Time Division Multiple Access (TDMA), so it's far from a "drop-in" replacement for those technologies." Practically speaking, "There really isn't much of a battle here (today) since CDMA has more than 150 million worldwide subscribers and OFDM has none. Certainly OFDM works well for packet-based data, but the jury is still out with large numbers of voice customers. CDMA has proven itself with voice, and is very capable in data as well, and maybe even more important, in the mixture of the two. OFDM, however, certainly has potential."

Looking Ahead

Where is OFDM going? It's going a lot of places. With the advent of 802.11a and the forthcoming products based on the draft specification for 802.11g, it seems clear that it will have a large role to play in WLANs. It also seems a safe bet that it will play an important role in MANs. Whether it will be as important in digital TV or 4G is another question.

Nogee notes, for example that, "It looks like the Japanese are moving forward the fastest on 'standardizing' OFDM for a 4G technology, but that's probably not the final word. I might add that the Japanese have had an analog HDTV standard in place for 10 years now, and it looks like others are now moving toward a digital version instead, so 'first' doesn't always mean 'standard.'"

Edward Rerisi, Senior Analyst of Allied Business Intelligence adds, "As of today, we know of no major wireless operator going ahead with an OFDM platform for their mobile data delivery solution. However, there are many operators proceeding with CDMA. Even with the recent delays in 3G deployment worldwide, we do not see any operator moving ahead with an OFDM-only platform. There are exceptions to this. The black sheep, so to speak, of the wireless world is Nextel. They have not committed to either the CDMA or WCDMA routes. Instead, they may -- and I stress the word may -- decide to deploy OFDM for their 3G solution."

So there you have it. Will OFDM be important? Yes. Where will it be important and how important will it be? That's a question that only tomorrow can answer.

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