|Homepage / Publications & Opinion / Silicon.com
Peter Cochrane's Uncommon Sense: Wireless everything
Like moving from two people having a conversation in a quiet room to a cocktail party where everyone is talking at once?
Communicating wirelessly is attractive, for all kinds of reasons. But, asks Peter Cochrane, have we considered the next steps that have to be taken?
The past five years have seen an unusual transition in the number of wireless devices I own. I have the usual range of radios and televisions as well as VHS, DVD, tape and other disk recorders but I have also installed or inherited a wireless controlled garage door, security system, weather monitor, door bell, intercom, and LAN. Of course, I also have mobile and cordless phones, walkie-talkies and numerous remote controls for toys and other pieces of IT including a myriad of infrared wireless devices. Suddenly, I am now in possession of more transmitters than receivers.
This change has mostly gone unnoticed as people use their key fob to unlock their car at a distance or use a remote for hi-fi and TV. What is really invisible is the radiation of energy across a broad range of frequencies. The planning and policing of radio is a complex task on a par with organising road transport systems. There have to be rules, regulation and control otherwise we would suffer interference and very poor quality service. Sometimes this is experienced when atmospheric conditions cause unexpected interference, with signals propagating from one country to another in an unintended manner.
Today, countries agree spectrum allocations (and channel frequencies) for broadcast, amateur and emergency services, remote control, military applications, cordless and mobile phones. But there are now devices and modes of operation that threaten this approach for the future. We have principally avoided interference by allocating specific frequencies of operations separated in the same way that the different radio channels on your FM radio are allocated. With the arrival of far more short-range transmitters it is becoming increasingly difficult to avoid interference and the violation of agreed allocations.
It is not unusual to install a wireless LAN (802.11 Wi-Fi) and achieve 'right first time' operation. Sterling service over long periods is the norm but short and unexplained periods of downtime are sometimes experienced. The usual culprit is an imported and powerful cordless phone creating interference. It is extremely difficult to track down such devices and they can be a nuisance to all in the vicinity. In the defence of the purchaser it is not at all clear they are the culprit.
I see this situation getting worse as increasing numbers of wireless devices are produced. Just about every electrical and IT appliance radiates some energy and it is difficult to locate where interference originates. This is especially true if it involves correlating the activity of yourself, your children, spouse and others and what device they are using at a given time.
This is a problem that is going to accelerate with the arrival of Bluetooth and more strains of wireless LAN, as well as RFID tags and plastic cards and other passive devices that will also contain transmitters in future. So it is imperative that we start thinking about solutions and engineering technology to adapt to an increasingly wireless population.
We have to adopt new modes of signalling beyond carving up frequency space with individual services allocated specific channels. We have to move in a direction of allowing everyone to use all of the frequency space all of the time. The transition is almost the same as moving from two people having a conversation in a quiet room to a cocktail party where everyone is talking at once.
The electronics to operate in 'cocktail party' mode and filter out the desired signal by using the equivalent of a wireless sieve at the receiver are now available. Paradoxically, wireless communication started with spark transmitters generating signals spanning all frequencies. The interference problem was gross as the nearest transmitter to your receiver dominated. It was the arrival of electronics in the early 1900s that allowed electronic filtering to give us the channel selection we enjoy today. It has provided the foundation for all our entertainment and telecommunications services.
We now stand to reverse history through electronic sophistication only made commercially possible by recent advances in chip technology. We can create complex digital signals that occupy a broad swath of frequency space and still filter them out at the receiver.
Understanding the detail is not easy and is probably easiest to conceive of as thousands of micro-radio channels broadcast in parallel all at the same time. Each signal is allocated different time and micro-frequency relationships that can only be unscrambled by an a priori knowledge embedded in selected receivers.
Another way of looking at this is to see a conversation broken into channels occupying the space currently allocated to BBC Radio channels 1, 2, 3, 4, and 5. A listener would need a receiver capable of selecting all of these channels at the same time to extract and recover the conversation.
This is a very simplistic explanation but not so far from the truth. Such 'spread spectrum' systems were originally developed towards the end of WWII for secret communications beyond the detection capabilities of the enemy. It is now used in the latest generations of mobile phone and wireless LAN and is the mode of operation most likely to be ideal for the future.
Adopting this technology as the dominant mode for the future would mean the disassembling today's radio spectrum rules in terms of frequency and power allocations. It would require new rules focused on the allocation of codes for the transmission and reception of signals for given applications, and necessary power limitations for different classes of device.
For you and me as users, the big breakthrough will be an interference free future and an unrestricted ability to communicate when and how we wish.
This column was typed on an Apple G4 laptop and transmitted to silicon.com via a wireless LAN using a spread spectrum signal.