Wireless Systems Design

Combining Bluetooth And Wi-Fi Makes Sense

Nowadays, people are increasingly exposed to wireless technologies that promise to improve life while providing a world of new possibilities. Right now, this trend is spotlighting two technologies: Bluetooth and Wireless Fidelity (Wi-Fi). Bluetooth and Wi-Fi are the vanguards of two very well-consolidated systems, which captured people's attention in recent years. These systems continue to grow at very impressive rates. Bluetooth expands the cellular functionality by making it possible to connect accessories and interact with devices that are less mobile and more complex like computers. In contrast, Wi-Fi releases the computer user from the Ethernet cable, thereby allowing portability.

Clearly, Bluetooth and Wi-Fi are both oriented to the consumer market. As a result, their products need to be small and attractively and ergonomically designed. They also must boast longer battery life and the ability to work at high speeds anywhere in the world. Some of these consumer needs are fulfilled by operation in the worldwide license-free spectrum, such as the 2.4-GHz Industrial Scientific Medical (ISM) band. In most countries, Bluetooth and Wi-Fi can be used without having to get cumbersome and explicit permission. But this advantage also is exploited by many other technologies, such as microwave ovens. As a result, some protective provisions need to be taken to avoid negative user experiences.

To reduce the time that the radio signal suffers interference, Bluetooth makes use of frequency hopping. In contrast, Wi-Fi uses spread-spectrum techniques. It also relies on the automatic scaling of speed, which makes the system more robust. For Bluetooth, a 1-MHz-bandwidth Gaussian Frequency Shift Keying (GFSK) modulator is specified. In contrast, Wi-Fi systems include a variety of modems based on a variant of Phase Shift Keying (PSK) and Quadrature Amplitude Modulation (QAM) with a wider bandwidth occupancy (22 MHz).

Compared to Wi-Fi, the speed and power requirements of target Bluetooth applications are smaller. For instance, speech and music can be easily and reliably transferred using the 1-Mbps Bluetooth radio. Clearly, this kind of traffic also can be sent over 54-Mbps Wi-Fi links. In the packet-switching nature of Wi-Fi systems, however, latency control is absent and collisions aren't uncommon. In the audio arena, Wi-Fi just isn't positioned to achieve the Quality of Service that's offered by Bluetooth.

Furthermore, most Bluetooth-enabled devices are expected to be in the virtual sphere of a 10-m radius. As a result, there's no need to transmit at high power (typically 0 dBm). In contrast, portable computers with enabled Wi-Fi functionality may be several meters (100 m) from the network access point. They also may find themselves in severely obstructed areas that require higher transmission power (up to 30 dBm).

Obviously, adding Wi-Fi functionality to a cellular phone would make the phone a "computer access point" for the cellular systems. But one must take into account the current capacity that's made available by cellular operators. Because this capacity is still far from being a fast Ethernet, it doesn't seem cost effective to have a high-speed link between the phone and the computer. This link would be sub-used by the traffic level to/from the cellular network.

Today, dial-up networking with General Packet Radio Service (GPRS) systems is well served using a Bluetooth link. With the deployment of future cellular networks and ongoing technology development, one could make a more compelling case for higher-speed solutions either in the phone-computer link or embedded in computers. In peer-to-peer connectivity, for example, a phone transfers local files to another phone or computer. Here, the use of a higher transfer rate is attractive and Wi-Fi may fit well. Of course, ongoing Bluetooth developments also are addressing the needs for shorter transfer times.

Computers may indeed benefit from Bluetooth functionality. Think about the wireless desktop that connects all of the peripherals to the CPU without cables. The master topology of Bluetooth makes it ideal to enable such a scenario. If a 100-MB file transfer is planned between two laptops, however, Wi-Fi's peer-to-peer high-speed link is a better choice.

From a business perspective, a combined Bluetooth and Wi-Fi solution in portable/desktop computers would be quite attractive. Users would then have the best of both technologies without sacrificing performance. The trick is to find a cost-effective combination of the technologies. The industry must exploit commonalities in terms of radio spectrum, operation modes, and design. It can then take advantage of the two technologies' increasing customer base.

Eventually, the limits between the Bluetooth and Wi-Fi worlds will begin to blur. In the computer arena, this trend will lead to the creation of a single, wireless, universal port for connectivity. It will be as ubiquitous as the present electrical plug, but without the need for cables or adapters. Such advantages are being spawned by the sharing and universal properties of the radio channel, which is always available. If that channel is exploited intelligently, it can deliver services that greatly empower the end user.

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