802.11n standard, final ratification by IEEE expected on Sep 11, 2009, increases the effective network capacity by up to 10x compared to legacy 802.11a/b/g. One of the key enhancements introduced in 802.11n is the use multiple spatial streams based on multiple input, multiple output (MIMO). MIMO refers to the number of transmit and receive antennas involved in exchanging wireless signals. The number of radios and antennas determines how many spatial streams of traffic can be sent simultaneously. 2×2 MIMO, for example, indicates two antennas at the transmit end and 2 antennas at the receive end, the minimum required by the draft 802.11n standard. Spatial multiplexing is a mandatory component of the 802.11n standard, and MIMO is required in order for spatial multiplexing to take place.
Most products, access points and client devices, introduced over the last couple of years support two spatial streams
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using a variety of antenna configurations, such as 2×2, 2×3, 3×3, in an access point (AP) or client device. Wi-Fi Alliance certification of 802.11n products based on draft 2.0 specification mandates two spatial streams support. Some of the Wi-Fi chipset vendors are now offering products with support for three and four spatial streams promising speeds up to 600 Mbps. Implementations requiring more than two RF antenna chains will need to be carefully architected to keep costs down while maintaining performance expectations.
While these continued improvements are welcomed by laptop manufacturers, handheld manufacturers have to deal with different set of requirements and challenges. Demand for dual-mode handhelds, especially the high end smart phones segment, is increasing rapidly with customers expecting their devices to offer an optimal balance of power consumption, price, performance and while shrinking the size and/or weight of the device. To address these prickly demands, recently the some of the chipset vendors introduced chipsets supporting 1×1 with single spatial stream (e.g. Atheros AR9281, Intel 5100, Marvell, Ralink etc.) targeting the handheld applications. Some in the industry call into question whether products designed with 1×1 will be considered 802.11n as they are not using MIMO, one of the key features of 802.11n.
Products using 1×1 single spatial stream do benefit from the other improvements in 802.11n standard such as channel bonding, packet aggregation to offer close to 100 Mbps. Handset manufacturers can benefit from the continued investments by the chipset manufacturers to optimize the performance and cost of the 802.11n handset solutions and delivering a product that offers higher performance to the end customers.
