Here's an interesting article. We have discussed the doubling of IEEE 802.11 bit rates already, but it wasn't clear at the time how it was going to be accomplished. I had guessed that so-called space-time codes (ST codes) would have to be used, because more traditional techniques had already been used in the existing 802.11 standards. Turns out, there are two approaches competing in the standards process (nothing new for IEEE): 1. Just double the channel bandwidth. Current 802.11a,b,g use 20 MHz bandwidths. So go to 40 MHz. 2. Use ST codes, in what they are nowadays calling MIMO (multiple input, multiple output). This is where you transmit the signal on the same channel, but from different antennas at slightly different times. Then, receive with multiple antennas and reconstitute the original by applying the appropriate phase shifts. You can achieve very impressive b/s/Hz numbers this way. (It's also possible, at the cost of b/s/Hz, to use only one transmit *or* only one receive antenna, in a compromised version of this technique.) ST codes can be implemented with both single frequency and OFDM techniques. When used with OFDM, each of the subcarriers is assumed to experience even loss throughout. With single frequency modulation, of course, this assumption would be impossible. So from what I've read, ST codes with single frequency modulation can actually achieve higher spectral efficiency, although at the cost of receiver complexity. The goal is to provide at least 100 Mb/s in the WLAN. When combined with the 802.11 wireless MAC, the usable throughput is approximately cut in half. But with ST codes, a new MAC is needed anyway, so that might change. Bert ------------------------------------ IEEE pushes WLANs to 'nth' degree Patrick Mannion Jul 05, 2004 (9:00 AM) URL: http://www.commsdesign.com/showArticle.jhtml?articleID=3D22103634 MANHASSET, N.Y. - The IEEE 802.11n task group will start sorting through 61 proposals for next-generation wireless LANs in Portland, Ore., next week. The record-setting number of proposals indicates the importance of the work: a technology stake in the delivery of high-rate streaming audio, video and data in a consumer-centric wireless world. One of the latest entities entering the looming standards battle is Interuniversity Microelectronics Center (IMEC), the European research center, which will present its smart-antenna technology to the so-called TGn task group. TGn will define a WLAN standard that supports transmission rates between 100 and 200 Mbits/second, at least double the rate of current 802.11g/a WLAN standards. The many proposals fall into two broad camps. One, led by Atheros, advocates using a 40-MHz bandwidth. Intel, Matsushita, Philips and Sony join Atheros in this camp, which calls itself TG nSynch. The competing World Wide Spectrum Efficiency (WWiSE) group, with Airgo as its leader, is sticking with a 20-MHz bandwidth. Standing with Airgo are Broadcom, Conexant, Mitsubishi, Motorola, STMicroelectronics and Texas Instruments. "One side [TG nSynch] is interested in doubling the bandwidth to 40 MHz and doing more simplistic things on the coding side and pushing to get 2x to 3x the rates they have now," said Matthew Shoemake, president of ultrawideband startup WiQuest Communications Inc., and ex-chairman of the TGn. "The other side [WWiSE] would like to stay with 20-MHz bands and use more advanced coding techniques in combination with the MIMO [multiple-input, multiple-output] techniques." The standards-setting process is proceeding as usual, said Colin Macnab, vice president of communications at Atheros Communications Inc. (Sunnyvale, Calif.), who described group formation as likely "at a fairly late stage of development." Robust enough? Both Shoemake and Macnab said they were aware of the spectral-efficiency advantages of the single-channel MIMO approach, but also cited the cost and power issues associated with multiple RF front ends. Further, Macnab questioned the robustness of the WWiSE group's spatial-multiplexing techniques. IMEC said a mix of spatial-division multiplexing, spatial-division multiple access and space-time block coding is at the core of its technology. Liesbet Vanderperre, director of wireless-design technology, said IMEC's 5-GHz MIMO-OFDM proposal balances capacity, robustness and throughput. The technology is essentially neutral and can be applied across either camp, she said. Copyright 2003 CMP Media ---------------------------------------------------------------------- You can UNSUBSCRIBE from the OpenDTV list in two ways: - Using the UNSUBSCRIBE command in your user configuration settings at FreeLists.org - By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word unsubscribe in the subject line.