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Qualcomm unveils MU-MIMO silicon

A bit of spectrum space-saving

A hyped and highly-anticipated feature of the next generation of WiFi kit, MU-MIMO (multi-user multiple in, multiple out), has taken a step towards commercial reality, with chip vendor Qualcomm announcing its first silicon to support the feature.

In today's MIMO, multiple spatial paths between transmitter and receiver are used to create a multiplexed signal to expand channel capacity. In MU-MIMO, as explained in detail here, a wireless access point can create devoted spatial streams to different users, reducing the impact of contention when there's lots of devices trying to access the network.

Qualcomm's initial chips (announcement here) handle four spatial streams at the base station side, and the company is claiming its technology will deliver between two and three times more network capacity compared to a non-MU-MIMO access point.

Its MU-MIMO implementation allows the base station to split its spatial streams not just to individual devices but to provide simultaneous transmission to groups of devices, the company says – a useful feature if multiple devices are accessing the same video content, for example.

In its “bare bones” implementation, MU-MIMO's pre-stream throughput is limited to the capacity of the end user device. Qualcomm wants to take that further, so as well as shipping four chipsets for various base station configurations (the QCA9980 and QCZ9982 for routers and gateways, and the enterprise-level QCA9990 and QCA9992), it's put the technology on all new Atheros 802.11ac client-side chipsets, as well as the Snapdragon 805 and 801 mobile processors.

The base station devices support three and four stream MU-MIMO. At the client side, the Atheros WCN3680 is a single stream device, while the QCA6174 (tablets and smartphones), QCA9378 (TVs and set-top-boxes) and QCA6574 (automotive applications) are all two-stream chips.

The chips claim maximum physical layer rates of up to 1.733 Gbps for routers and access points, and up to 867 Mbps at the client side. The usual caveats – chiefly that the channel capacity is rarely achieved in an end user application – should apply.

Qualcomm expects products based on its MU-MIMO silicon to reach the shelves in late 2014 or early 2015. ®

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