As a concept, there is nothing new about GPS. What has changed is the way the consumer uses information about location. The means by which they want to access information is also changing.
Five years ago, GPS was only embedded in top-end vehicles, but with the availability of cheap and sturdy handheld after-market personal navigation devices (PNDs), the number of consumers who own such devices has increased.
Perhaps it's not surprising that the next step in GPS evolution would bring it out of the car and onto the street, or even inside buildings. In other words, PND functionality is coming to the mobile phone. If GPS in handsets is going to be a success, it is vital that designs are sufficiently intelligent to handle the challenging mobile environment—both in terms of the technological hurdles and the penetration of the mobile handset market. This means that GPS has to be low power, low cost and able to deliver on performance.
|Figure 1: Users of GPS-enabled cellphones should have the same experience, whether out standing out in the open countryside or inside a building.|
The performance of conventional GPS is generally recognized to be good enough. Unfortunately, the same cannot be said for power and cost in cellphone applications. As a first step in dealing with this, a radical shake-up of conventional GPS architecture is required. An obvious approach to bringing down costs and power is to integrate GPS technology into an existing RF platform.
It is clear to see that a software based GPS solution ported onto a chip that already has mobile real estate bought and paid for is going to bring the cost down substantially. Implementing GPS through software embedded on another platform means that it takes up to 80 percent less area than hardware-based solutions. This method is likely to ultimately have a cost-adder of less than $1.
A software implementation of GPS in conjunction with existing RF silicon will also have an effect on power requirements. But even given the advantages brought by re-engineering GPS architecture, more improvements on the cornerstones of successful implementations in mobile handsets can be done.
What does it mean when we talk about performance for GPS? A key indicator has traditionally been TTFF (time to first fix), the time it takes for a GPS receiver to acquire a signal from the satellite. In the past, TTFF has commonly been a minute or more in tough environments.
With a rework of the software algorithms involved, the TTFF terminology can be eliminated completely, and just simply ask the question that the consumer is asking: “Is the positioning information available on demand, at any time and in any place?” The answer should be “yes.”
|Figure 2: CSR integrates GPS technology into an existing RF platform with its BlueCore Host Software to bring down costs and power.|
Performance, power issues
If GPS is used on a mobile phone, the user should have the same experience, whether they are standing outside in the open countryside or inside a building. Unfortunately, this has not been the case until recently, and ensuring an excellent QoS when used deep indoors is a new issue for designing location services for mobile phones.
Power is also a serious issue in designing GPS for handsets. Most consumers would not choose to sacrifice talk time on a mobile phone for time with the GPS functionality, so it's important to use every trick in the book to keep power down.
Fortunately, the way that the user will use GPS in a mobile handset is inherently different to the way it might be used in a car. For instance, using a PND to go from points A to B in a car normally means that the GPS functionality is constantly working to track a signal to give real-time location of a vehicle traveling up to 113kph.
If, for example, that vehicle were to go into a tunnel, a typical GPS system would use a significant amount of power and brute force in a bid to acquire a signal that it is never going to be successful in finding.
Now, instead of being in a car in a tunnel, let us switch to an equivalent scenario—being deep inside a building. Rather than searching in vain for a signal, it's far more sensible and power-efficient if the handset uses cellular trilateration to calculate its position.
The eGPS software can switch off the GPS radio, thus saving power. Instead of being in a particularly power-hungry scenario, indoor positioning now represents a situation where GPS capability consumes virtually no power. to power is critical when designing GPS into a mobile platform.
In a mobile phone, GPS is not the only feature available, and it's highly likely that the consumer will use GPS in short bursts, for example, to find their way to the theater or to locate the nearest Italian restaurant. For this reason, it doesn't make sense to have GPS switched on all the time.
The approach to this power issue is to have the GPS jump into action when required and switched off completely when it's not in use, therefore bringing the power usage to less than one percent of battery life.
Where GPS hasn't worked in the past is when old technology gets shoehorned into a mobile phone. Rather than result in a workable – if slightly compromised – solution, this approach can actually hamper the performance of other functions in the phone, causing interoperability issues with other wireless technologies and exceptional power requirements, as well as being an overall costly solution to implement.
GPS functionality in cellphones is something that the consumer really wants. In this respect, having the technology embedded in mobiles seems almost inevitable.
Consumers have already warmed to having GPS technology in the car, and they now want to be able to take GPS out on the street. Product designers now need to ensure that they are taking the correct approach to the design challenges that GPS raises with care to ensure that the end-user can appreciate the benefits.
By taking care of the core components of success for designing in mobile phones—size, performance and cost—there's a greater chance of location-based services being adopted by the masses.
Matthew Phillips is senior vice president for the mobile handset connectivity business unit at CSR plc