Wireless Systems Design

Cut The Cord On Gaming

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Ever play "cat's cradle" as a kid? Think back to that convoluted web of string. That's what your living room quickly resembles when your kid and several of his or her friends take delivery of the latest Gamecube/PS-2/X-Box games. The TV is on one side of the room, the couch is on the other, and there's a no-man's land of tangled wires in between. A better way must exist, whether you're coming from a logic perspective or a desire to avoid face-plants into the carpet.

You may have seen wireless keyboards and mice. These devices use low-bandwidth, unidirectional 27-MHz technology. Though this technology works adequately in single-user, home-office environments, it's unsuitable for gamepads or joysticks. Gamepads include "rumble packs" that give tactile feedback to gamers when their car hits a wall, for example, or their robot takes a missile strike. This feedback requires two-way communication and performance that 27-MHz devices cannot deliver.

Due to this shortcoming and a number of other limitations, the 27-MHz technology is simply unsuitable for gaming. It has a range of only 2 m, latency of over 70 ms (one node), and support for only two nodes. In addition, the spectrum is not available worldwide. The bandwidth of 2.4 kbps also is way too slow for gaming. According to game device manufacturers, a maximum latency of 20 ms is the minimum that will be accepted for game controllers. Lastly, a user cannot locate more than two 27-MHz devices within range of each other because they'll cause mutual interference. The gaming story ends here for 27 MHz.

If it's not 27 MHz, then, what is the solution? It may seem easy and effective to just change the frequency and go bidirectional. In the U.S., portable phones that operate on the 433- and 900-MHz bands are popular. The range on these bands goes out to 10-50 m, and bandwidth is a respectable 200 kbps. However, latency is limited to 30 ms (two nodes), and you hit the wall at four nodes. Here again, the bands aren't available worldwide. Plus, interference between devices is still a problem—though less so than for 27 MHz.

So what about Bluetooth, which is finally coming into its own as the wireless technology du jour? Presumably, Bluetooth does what it was designed to do well. That is, it enables wireless cable replacement. But it's overpriced and overkill for the human-interface-device (HID) market, where low latency and low prices rule. With its huge protocol stack and logic requirements, a Bluetooth gamepad would be expensive and hard on batteries. The Bluetooth latency problem can be solved—at the expense of extremely short battery life. Obviously, this is not an acceptable tradeoff for portable devices. The final issue is that unavoidable 1.25- to 2.5-sec. latency to reconnect if the Bluetooth device disconnects or times out.

Despite these pitfalls, we may begin to see Bluetooth PC gamepads at some point. This won't occur until OEMs start widely integrating Bluetooth into PCs, which I don't see happening on a mass scale for the next three to four years. But it is unlikely that Bluetooth will ever appear in standalone game machines, such as Gamepad/PS-2/X-Box.

At Cypress, we spent considerable time trying to develop chips for wireless-HID devices that would implement Bluetooth. Our team focused on mice, keyboards, and gamepads. We finally concluded that Bluetooth is simply not the appropriate technology for these applications. In fact, we couldn't find a suitable wireless-HID technology. No existing technology could overcome the limitations that we'd been encountering.

We did succeed, however, in becoming well-acquainted with the requirements for a working wireless-HID technology. Our conclusion was that the ideal technology must operate in a band that is available worldwide. It must allow as many as seven active nodes to coexist without interference. It also has to be easy on battery life. To accommodate most living rooms, the hypothetical technology should have a range of up to 10 m. At the same time, it should let users feel every bump and crash. For convenience, it will preferably be plug and play. Most importantly for gaming, the winning technology must be fast and cheap.

A POTENTIAL SOLUTION
A solution has arrived that meets these requirements: WirelessUSB. Currently, it's a two-chip solution including a BiCMOS transceiver and a CMOS baseband chip, which handles packet framing, error checking, and any real-time operations. Very few external components are required, making the total system cost in high volume well under $5—a small price to pay for being able to safely traverse your living room. Of course, major game manufacturers take time to commit to new technologies. But third-party developers are already working on WirelessUSB gaming solutions. By the next holiday season, the market should be offering keyboards, mice, and wireless gamepads.

Clearly, gaming is evolving into a wireless form. Within the next couple of years, new designs will come online and other wireless-HID technologies will emerge. The result will be console game systems that are completely wireless. While young gamers wonder why they were ever otherwise, parents will rejoice at being able to cross the room safely.

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