Ultra-wide Band is Ultra-fast 

Ir-DA, Blue-tooth, 802.11a Wi-Fi, and then 802.11b WLAN. Wireless LANs and PANs (personal area networks) couldn’t get better than this–or so we thought till the turn of this millennium. Fast forward to 2002 and enters yet another contender–UWB or Ultra-wide Band–with less hype and its share of supporters and critics. 

Ultra-what?



UWB is a RF (radio frequency) technology that transmits binary data–the 0s and 1s that are the digital building blocks of modern information systems. It uses low-energy and extremely short duration (in the order of pico seconds) impulses or bursts of RF energy over a wide spectrum of frequencies, to transmit data over short to medium distances, say about 15–100 m. Since it doesn’t need a dedicated radio frequency, it’s also called carrier-free, impulse or base-band radio. 

UWB is not a new technology. Dr. Gerald F Ross had demonstrated its potential in radar and communications in the early 1970s itself. However, its usage for wireless applications, particularly for WLANs and WPANs, began only in the late 1990s with several players like XtremeSpectrum, Time Domain, Multispectral Solutions, Aether Wire, Fantasma Network, IBM, Intel and Motorola. 

In amplitude modulation, the sine wave of the data is combined with the sine wave of the transmitter before transmission. Here the peak-to peak-voltage of the transmitted wave will change according to the data

Its significance lies in the fact that it transmits several times the data possible over current wireless technologies, using very low levels of power (in the order of a few milliwatts). Current UWB devices can transmit data up to 100 Mbps, compared to the 1 Mbps of Bluetooth and the 11 Mbps of 802.11b. It’s expected to reach around 500 Mbps by 2004. Also, this low power pulse can penetrate obstacles like doors, walls, metal etc, and suffers little or no interference from other narrow band frequencies. Hence, it is useful in densely built-up areas. It doesn’t require allocation of ‘precious’ or ‘paid for’ narrow-band spectrum, in use now. Supporters of UWB say that its electro-magnetic noise is only as much as that of a hair dryer or electric fan, and it doesn’t interfere with or hamper other RFs. Best of all, it costs a fraction of current technologies like Blue-tooth, WLANs and

Wi-Fi.

Back to basics



To understand UWB, we’ll first look at radio communication and how data is transmitted traditionally. All of us have dropped pebbles in a water pool at some point in our lives. Remember the ripples traveling outwards from the point where the pebble enters the water up to the boundary? 

Potential apps: Supporter speak Cellular services: It can emerge as a competitor to cellular services that currently use CDMA and TDMA technologies. Radars: The US military has already been using this technology for military radars and tracking systems for the last 15 years. Disaster rescue: Its earth and wall penetrating abilities makes it a good candidate for disaster rescue. By bouncing UWB pulses, rescuers can detect people through rubble, earth or even walls using equipment similar to radar. Construction and mineral exploration industries may also benefit. Personal tracking: Security personnel can use it to tag employees and visitors inside high security areas, give or deny permission to access certain areas etc. The US Navy is testing prototypes of this system to track its possessions overseas. Collision avoidance: Proponents believe that UWB technology can make intelligent auto-pilots in automobiles and other craft a reality one day.

Normal radio waves are sine waves or smoothly fluctuating waves like these ripples. Traditionally, radio communications stay within the allocated frequency band. We normally use a carrier wave to transmit data. The carrier wave is imprinted with data by modulating any of the following– amplitude, frequency or phase of the carrier wave. Three common ways of modulating a sine wave are AM (Amplitude Modulation), FM (Frequency Modulation) and PM (Pulse Modulation). Refer to the diagrams to understand how radio waves transmit data). 

What happens when you listen to news from an AM radio station, say an All India Radio medium wave station? The sine wave of the announcer’s voice is combined with the transmitter’s sine wave (carrier wave) to vary its amplitude, and then transmitted. In AM, the amplitude of the sine wave or rather its peak-to-peak voltage changes. FM stations and other wireless technologies including cordless phones, cell phones and WLANs use FM, where based on the information signal, the transmitter’s sine wave frequency changes slightly. In PM, the carrier or sine wave is turned on and off to send data. In its simplest form, it can be a kind of Morse code. (See diagrams for a basic idea of how narrow-band communications work). The receiver in each case is specially tuned to decode information in the carrier wave.

Usage of a carrier wave within a narrow band effectively means limiting amount of data that can be imprinted on to it. Hence the importance of

UWB.

Inner workings



UWB uses a kind of pulse modulation. To transfer data, a UWB transmitter emits a single sine wave pulse (called a monocycle) at a time. This monocycle has no data in it. On the contrary, it is the timing between monocycles (the interval between pulses) that determines whether data transmitted is a 0 or a 1. A UWB pulse typically ranges between .2 and 1.5 nanoseconds. If a monocycle is sent early (by 100 pico seconds), it can denote a 0, while a monocycle sent late (by 100 pico seconds) can represent a 1. Now, one pico second = one trillionth of a second. Hence, the quantity of data transmitted is on the high side.

In Pulse Modulation, the sine wave is turned on and off in a particular manner to transmit data

Spacing between monocycles changes between 25 to 1000 nanoseconds on a pulse-to-pulse basis, based on a channel code.

A channel code allows data to be detected only by the intended receiver. Since pulses are spaced and timing between pulses depends on the channel, it’s already in encrypted form and is more secure than conventional radio waves.

Now, visualize what happens when you heave a large rock into a small pond. It splashes out the water in one go (as seen with our naked eyes). If captured as a still photo, we’ll see the millions of water droplets that splash out in a fraction of a second and make the splash we see. If ripples are like normal transmission of data between wireless devices (as in blue-tooth or Wi-Fi), UWB promises to be the ‘huge rock’ in data transmission. Through several million monocycles, it uses a wide range of frequencies to transmit large amounts of data in one go.

Only a receiver specifically tuned to the transmitter can receive transmitted data. Hence, it is a comparatively more secure channel for data transmission. Moreover, by using some amount of modulation, sharp spiking and subsequent noise interference with other narrow band devices are reduced to minimal levels. Any other device into whose band UWB pulses might spill over, will at most, feel it as background noise as energy levels of the pulse are low.

Advantage UWB



Apart from low-power usage, inherent security and minimal noise generation, UWB doesn’t suffer from multi-path interference (where signals reach the receiver after traveling through two or more paths). Something similar happens when your car is at an intersection surrounded by tall buildings. Your radio might not give a clear reception as it’s receiving both direct signals and those that have bounced off the buildings. Often, the static disappears when you move ahead or backwards.

Hence, it can be used in densely built-up places, or where number of users are more than what is supported by Wi-Fi, Blue-tooth etc.

Huge bandwidth, large lobbies



Some players have come out with UWB prototypes. XtremeSpectrum claims to have created a chipset codenamed Trinity that offers 100 Mbps data rates and consumes only 200 milliwatts of power. Trinity will be priced around $ 20 per piece in groups of 100,000. Commercial production is expected in the first half of 2003.

The timing between the monocycles emitted by the UWB transmitter determines whether the data transmitted is a ‘0’ or a ‘1’

So far, while some players have given it a wide berth, others are lobbying hard for it. Those who have worked on competing

technologies like 2.5 G and 3 G are against it.

They claim that since UWB is spread across the spectrum, it could theoretically interfere with other electromagnetic waves and essential services dependent on these, like air traffic communications, mobile services, GPS, radio and TV signals. Also, rivals like Synad Technologies have developed the Mercury5G chipset that can operate on both 802.11a WLAN and 802.11b (Wi-Fi) standards and offers reasonably high throughputs.

Where does this leave UWB? It is undoubtedly a niche technology which holds promise in a wide area. But, its success depends on scoring against a handful of rival technologies in which companies have invested billions. Those who’ve invested their money will not hasten to consider an upstart rival, even if it offers better services. It seems that UWB will most probably succeed in WPANs as a means of delivering data-intensive applications like video. Imagine downloading the latest blockbuster on your portable player while tanking up at the petrol pump! But, this dream will take at least a year to materialize at the current pace of things.

Benoy George Thomas