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15 January 2015

MU-MIMO: the scramble to catch up with Qualcomm and Quantenna

Just as Broadcom, Marvell and MediaTek-owned Ralink all unveiled 4×4 Multiuser MIMO (MU-MIMO) WiFi chips at the CES event last week, Qualcomm and Quantenna smugly demonstrated the advantages of coming to market a year earlier.

As their rivals showed new chips, the early movers were able to boast actual devices from customers committed to deploying their MU-MIMO technologies this year. This is a David and Goliath fight at the front, with tiny start-up Quantenna, heavily focused on WiFi broadcast, up against Qualcomm Atheros.

Qualcomm showed off design wins at Amped Wireless, Buffalo, D-Link, NEC, TP-Link, TrendNet and Xiaomi, all of which have committed to using the technology.

Meanwhile, Broadcom finally showed its hand with a chip based around a different design philosophy from the early ones, and claiming to be four times faster than an ordinary SU-MIMO implementation (rather than three times faster, as claimed by Qualcomm).

Marvell and Mediatek’s Ralink also put their hat in the ring with chips that made similar claims and seemed very similar in conceptual design to Broadcom’s, with the new entrants focusing on portraying their rather belated efforts as leapfrogging the early movers.

The difference in approach, and speed, may prove important in determining whether Broadcom will achieve the coup it has often pulled off in WiFi – lingering at the back until just the right moment to catch the market at the best moment in terms of the volumes:margin ratio.

In November, an analysis by Manny Patel, director of WLAN business development at Broadcom, described the Qualcomm approach as ‘N minus 1’, suggesting that it was configured to best perform simultaneously with three client devices and designed for 1×1 WiFi. Patel said at the time that Broadcom would do better at supporting clusters of four devices simultaneously.

The difference appears to be in the mathematical model of how each spatial stream can best be used. When a designer assumes that the clients are 1×1 antenna clients, as Patel insisted Qualcomm does, it has to use one of the antennas to help the others form beams. However, when speaking to 2×2 clients, which is increasingly the case in smartphones, then it is easier to form beams, since there are twice as many spatial streams being received.

This argument will run and run, no doubt, but Qualcomm was not restricting its CES WiFi efforts to 11ac, also showing off its new 802.11ad 60GHz technology, from its acquisition of Wilocity last year. Although it only works with line of sight – so within the same room – the chip was demonstrated transferring a 122MB movie from a rental kiosk to a tablet in just two seconds.

WiGig, or 60GHz WiFi, is clearly a technology lead that buying Wilocity has earned Qualcomm, but in terms of near term mass markets, it will be more important to see whether the Atheros unit has achieved a sufficient headstart in Wave 2 11ac (MU-MIMO) to dent Broadcom’s previously unassailable lead in WiFi, which it has held for a decade.

If Broadcom genuinely has pursued a different technical philosophy (and we’re not sure Qualcomm would agree that it has) then there are many small details which may affect real world performance. Questions such as how much processing power do the chips have, what kind of overhead is there in calculating MU-MIMO beams, and how quickly can they switch to a less congested air channel when they meet interference, will be pertinent, as will the fact that, when a device is speaking back to the AP, it has to do this sequentially since these are not MU-MIMO clients.

Meanwhile, 11ac pioneer Quantenna, which has had its SU-MIMO devices selected by many of the US home gateway operators such as AT&T, launched its own MU-MIMO chip back in May 2013, though to date this has only thrown up one public design win, at Linksys, and a demonstration of interoperability with MediaTek MU-MIMO chips. At CES, however, Quantenna was maintaining its technical lead over the big guns, demonstrating what it calls its 10G WiFi platform, an 8×8 MU-MIMO chip with 160Mhz channel support, which it said even provides a benefit to 1×1 clients.

Broadcom’s MU-MIMO offering is the BCM 4366, targeted at retail routers, wireless cable/DSL/PON gateways and set-top boxes, and it claims it is optimized for the delivery of broadcast quality video around a home. The chip is coupled with the BCM47094 network processor system-on-chip to improve video streaming performance. This chips could help Broadcom steal some of the home media gateway business which Quantenna initially won with AT&T and other tier ones.

Marvell launched a very similar system to Broadcom’s with a 4×4 802.11ac Wave 2 WiFi SoC, the AP3200 Reference Platform, built around its 88W8964 chip. This is aimed at enterprise access points, smart gateways, multi-room carrier-grade video distribution and SMB routers. The Armada-395 SoC also integrates a dual-core host CPU running at 1.8GHz.

And finally MediaTek released its MT7615, MU-MIMO chip operating in both 2.4GHz and 5GHz channels, which it says is best for delivering 4K video around a home or office environments. It is designed with MediaTek’s 4x4x4 (4Transmitter, 4Receiver and 4Spatial Streams), and combines with MediaTek’s MT7623 Quad Core ARM-based network processing unit.