WirelessUSB is a state-of-the-art technology that enables simple, reliable and affordable wireless solutions that enable the user to "Cut the cord" and unwire life in every day applications. The WirelessUSB family consists of multiple integrated circuits (based on range and power). Each IC is 2.4GHz Direct Sequence Spread Spectrum (DSSS) Radio System-on-Chip (SoC). They all connect directly to a micro-controller enabling user programmability for customized solutions.
We have seen two 2.4GHz technologies become mainstream in the market, namely IEEE 802.11b/g (WiFi) and Bluetooth (for cell phones). WirelessUSB is the next technology that is taking off today, starting with the HID market space and expanding into Gamepads, Joysticks and simple N:1 star networks.
The SoC is designed to implement wireless devices operating in the worldwide 2.4 GHz Industrial, Scientific, and Medical (ISM) frequency band (2.400 GHz - 2.4835 GHz). It is intended for systems compliant with worldwide regulations covered by ETSI EN 301 489-1 V1.4.1, ETSI EN 300 328-1 V1.3.1 (European Countries); FCC CFR 47 Part 15 (USA and Industry Canada) and ARIB STD-T66 (Japan).
The radio and baseband are both code- and frequency-agile. Forty-nine spreading codes selected for optimal performance (Gold codes) are supported across 78 1 MHz channels yielding a theoretical spectral capacity of 3822 channels.
The DSSS baseband has three operating modes: 64 chips/bit Single Channel, 32 chips/bit Single Channel, and 32 chips/bit Single Channel Dual Data Rate (DDR). The simplified block diagram of the CYWUSB6934/35 is shown in Figure 1.
Figure 1: The CYWUSB6934/35 IC is a 2.4-GHz Direct Sequence Spread Spectrum (DSSS) Radio System-on-Chip (SoC).
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The Advantages of 2.4 GHz Technology
There are a few unlicensed radio frequency bands available to designers of wireless HIDs, including 27 MHz, which is the predominant technology for wireless keyboards and mice. Some companies use 47/49 MHz or 900 MHz in HID applications that require distances greater than two meters. All of these bands have one major problem in common, namely, that the particular frequencies available for each band differ for various regions of the world. Some would dismiss this as just a manufacturing issue, but it does restrict the volumes for a given bill of materials, and injects complexity into the manufacturing process that would not be present if the frequencies were unified.
Another problem that arises is that these spectrums tend to be very limited in bandwidth, and having multiple systems running in the same physical space can cause problems ranging from missed keystrokes to non-functioning systems.
The unlicensed 2.4 GHz Industrial, Scientific, and Medical (ISM) band suffers from none of these drawbacks however. Recently published studies have shown that coexistence with dissimilar systems is achievable for such devices as cordless telephones and wireless LANs. This is because the large number of frequencies available on the 2.4 GHz ISM band allows for devices to spread out; in addition, devices utilizing this band are required to use spread spectrum techniques. Finally, the ISM band is available globally, not just in North America, Japan or Europe.
Until recently, implementing a 2.4 GHz wireless system was prohibitively expensive for HID applications targeted at the consumer market. In 2002, 27 MHz solutions cost orders of magnitude less than their 2.4 GHz counterparts. In 2005 however, 2.4 GHz solutions aimed specifically at the lower-end markets have brought the price down enough to start competing against 27 MHz devices; and while cost parity with 27 MHz would be nice, the features and benefits that 2.4 GHz brings to the table far outweigh the delta in system cost for most designers and marketing groups.
27 MHz has long been a thorn in the side of product managers, with its limited range and performance, while 2.4 GHz was outside their reach for financial reasons. 900 MHz has solved some of the issues with 27 MHz, but the cost difference has been too wide to justify the additional cost, especially given its performance limitations, crowded spectrum environments, and the differing frequency availability for North America and Europe.
.A WirelessUSB system consists of a WirelessUSB Bridge and between one and two/three WirelessUSB HIDs (Human Interface Devices). The host PC is not aware of the wireless connection, since the interface to the host acts like a normal wired USB HID connection. Therefore, there is no special software required on the host PC in order to support WirelessUSB.
There are several applications for a wireless system that offers co-location and interference immunity with other technologies sharing the same band. Some of the applications specific to HID space and star networking space are given below.
Figure 2: WirelessUSB application mouse solution will help remove the clutter of cables.
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Human Input Devices Go To 2.4 GHz Band
The real appeal of 2.4 GHz for a designer is low latency, high throughput, and worldwide availability. But what's the appeal for the consumer? What benefits are they likely to see? When it really comes down to it, going wireless is about reducing the hassle of cables; once a device goes wireless, users don't want to go back. Some applications will get an upgrade to 2.4 GHz capabilities, while others, currently cable-bound, will finally go wireless en masse.
For wireless keyboards and mice, the upgrade to 2.4 GHz will mean greater range and more reliable usage. Users won't have to position the receiver in "just the right spot" or avoid large metal items to get a wireless desktop working. Migrating wireless keyboards and mice to 2.4GHz will also mean that the corporate market uptake will increase substantially by virtue of the fact that the new 2.4 GHz devices will be able to co-exist with each other in any environment.
An offshoot advantage of being able to operate in an extended range means keyboards and pointing devices may finally start appearing in advanced set top boxes for cable and dish systems. This will be welcomed by consumers as the user interface for these systems goes wireless instead of IrDA with each generation. 2.4 GHz could potentially become a catalyst for the next jump in television and computer convergence.
For applications like video game controllers, 2.4 GHz wireless freedom will help remove the clutter of cables and the interference with cordless telephones typically associated with 900 MHz game controllers. Figure 2 illustrates a typical mouse product application using WirelessUSB SoC chip.
WirelessUSB Interference immunity with Other 2.4 GHz Technologies
One of the performance challenges that exist for wireless devices is interference from other radio communication devices. Cypress' WirelessUSB 2.4GHz radio system on a chip solution shares the 2.4GHz unlicensed ISM band with several other technologies: 802.11b/g, Bluetooth, 2.4GHz cordless phones, microwave ovens, and other proprietary 2.4GHz devices. Therefore, it is important that WirelessUSB peacefully co-exist with these other technologies. Furthermore, WirelessUSB must not only be able to tolerate interference from other wireless technologies but it should not, in turn, cause excessive degradation to them.
Cypress has validated the interference immunity of the WirelessUSB based Keyboard and Mouse against devices operating in the frequency band 2.4 "2.5 GHz. WirelessUSB has been designed to peacefully co-exist with all other 2.4GHz technologies. DSSS, strong error correction, retransmission, and frequency agility make WirelessUSB robust to interference from other technologies, allowing WirelessUSB to work reliably at 10 meters in the typical wireless office as shown by the test system described in Figure 3. WirelessUSB LS also does not cause excessive interference to other 2.4GHz technologies. The wirelessUSB based mouse and keyboard worked flawlessly without any appreciable degradation of performance at 10-meter distance from the Laptop.
Figure 3: Signal comparison of wireless systems operating in the 2.4-GHz band).
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With so many choices in spectrums, solutions, and standards, it's easy to loose track of what is really important. The need to transition to a wireless world requires robustness, interference immunity, excellent co-location capabilities, and affordable system cost. The real challenge for designers is to go beyond wireless and identify the value proposition based on features that can be driven to the end consumer. The era where doing a simple 27MHz solution that 'just worked' are over. Consumers are demanding higher reliability, ease-of-use and intelligence in these products that not only make it wireless but also make their life easier. One quick example is the KISSBIND feature for mouse that gives users dynamic flexibility in using the same wireless mouse across multiple laptops/PCs with no additional requirements.