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Draft-n router claims 300Mbps wireless speed

Posted: 09 Jan 2007 ?? ?Print Version ?Bookmark and Share

Keywords:Wi-Fi? 802.11? draft-n? Netgear? Marvell?

As the telecom industry's nirvana of triple-play customers (Internet, television, telephone) begins to close in on reality, the wireless hub becomes a bigger deal than ever. With the potential for so much data to distribute in a consumer environment, traditional Wi-Fi 802.11b/g solutions just lack the steam to get it all done.

Enter 802.11n (still in draft form) and proprietary extensions, and there exists the possibility of a fully wireless environment where you can surf the Web, chat on the VoIP phone and watch a bit of IP TV, all from a common pipe.

The Netgear WNR854T access point provides backward compatibility with 802.11b/g, but draft-n capability lets it deliver wireless connections at up to a raw claimed 300Mbps. Of course, such numbers are sure to depend on the wireless environment, as well as on using compatible gear on both ends of the connection. But in a word, the theoretical capability is nothing short of blazing, probably delivering about half the claimed peak data rate as usable bandwidth.

Security features
High speed is no good without high security, though, so the design hosts a full complement of firewalling (NAT, SPI), access control (WPA, WEP, MAC authentication) and even built-in denial-of-service prevention and intrusion detection.

Based almost completely on chips from Marvell for the core communications functions, the WNR854T uses that company's Top Dog MIMO technology. Here, the MIMO is a 2 x 3 topology that implements two transmit and three receive paths and various antenna diversity modes. Unlike competing products, which sprout an alien-like array of antennas, the WNR854T comes in an elegant white case, with all circuitry sealed up in the simple box enclosure.

Electronics are partitioned across two surface-mount assemblies, one the primary networking and router board for wireline and control aspects, the other tackling all wireless connectivity.

On the larger mainboard, key components start with the Marvell 88E6131 eight-port Gigabit switch, responsible for inter-facing to the broadband connection and for distribution to four hardwired Ethernet ports on the back panel of the WNR854T. Two Marvell transceivers serve ports one and two of the four-port wired Ethernet distribution array. But why those ports receive special treatment vs. ports three and four remains unclear from any documentation.

Marvell footprint
The Marvell 88F5180 provides the router's processor, interfacing to the switch chip and wireless data card and, presumably, providing all the networking-security features. A total of 8Mbytes of Intel NOR flash (part 28F640) and 32Mbytes total across two Nanya NT5DS8M16FS DDR SDRAM chips provide supporting memory for the 88F5180 processor. Marvell's footprint in the components even extends down to the switching regulators used to provide system power management.

The wireless data card plugs into a 123-pin card-edge connector tied back into the 88F5180. The pluggable card suggests the use of the same board in other end systems where connectivity features surrounding the wireless 802.11x capability may vary.

Netgear WNR854T

Netgear WNR854T's draft-n capability enables wireless connections at up to 300Mbps.
Click image to view teardown diagram

The wireless-card devices, again, come primarily from Marvell. The two primary ICs are a baseband/MAC (88W8361) and an 802.11x transceiver (88W8060). Also, 8Mbytes of EtronTech SDRAM support the baseband/MAC's memory needs local to the wireless card. An Atmel 4Kbyte E2PROM provides code storage. And a Marvell switching regulator tends to the local power needs.

To create the 2 x 3 MIMO air interface, there are two Fairchild RMPA2458 RF power amplifiers for the dual transmit paths and three individual receive inputs. For the two transmit channels, a simple GaAs SPDT switch from Skyworks toggles between transmit and receive modes. In the center receive-only channel, a similar switch is used either to listen to the center antenna or to ground it.

Fan-pattern antennas
The antenna assemblies are stuck to the inside of the case in a fan pattern and connect to the wireless card via three RF coax plugs. The antennas themselves are based on coaxial unbalanced-feed dipoles, where the center conductor is freed from the shield to radiate as one half of the antenna and the shield is connected to a metal feed tube that serves as the second radiating element. Such antennas are dead-simple to make and, accordingly, are quite cost-effective for consumer products.

While poking around for chip identification, it became clear that Netgear may be more of a branding play and marketing front for the core electronics design. The same circuit board is shown in a product brief from Taiwanese ODM SparkLAN, albeit with different end packaging and case design. It seems Netgear has taken the basic electronics platform from SparkLAN (which itself may be a Marvell reference design) and either reengineered or respecified the enclosure style and use of internal antenna elements.

- David Carey
President, Portelligent

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