The worldwide utilization of wireless devices such as two-way radios, pagers, portable televisions, personal computers (PCs), personal communication systems (PCSs), personal digital assistants (PDAs), cellular telephones or mobile telephones, Bluetooth® devices, satellite radio receivers, Satellite Positioning systems (SPSs) such as Global Positioning System (GPS), also known as NAVSTAR, and automotive telematic systems is growing at a rapid pace. As a result, current trends are calling for the incorporation of as many features as possible into these wireless devices. As one example, there is currently a demand to incorporate SPS services into a broad range of these electronic devices and systems.
The SPS systems, including systems for processing GPS signals, include various hardware and software components generally designed to accomplish the task of geographically locating a GPS receiver as quickly as possible to the highest degree of accuracy possible. GPS systems have become remarkably capable since the very first GPS units became available. Advances in semiconductor technology and microprocessor technology have helped make this improved capability possible. In addition, consumer and government demand for small, fast, GPS-capable devices (for example, E911-compliant cell phones) have helped drive GPS system design improvements.
As used herein GPS capability is the capability to receive and process GPS signals, and further, to use the processed GPS signals to generate accurate position information. More and more devices include GPS availability. Therefore, manufacturers of a wide variety of products desire or require the ability to insert GPS hardware and software into their product designs. Of course, it is desirable for the GPS hardware to use as little semiconductor die space as possible, and for the GPS hardware and software system to be as economical as possible in its demands for memory and power.
Designing GPS systems within these constraints usually forces a series of choices among speed, size, power usage, etc. Most existing GPS system designs thus embody a set of tradeoffs. Most existing GPS systems provide little or no flexibility once designed. For example, they are not readily reconfigurable to process or store data differently under different conditions in order to perform most efficiently at any given time. Typically, the amount of memory made available to a GPS system (either in a stand-alone GPS system, or in another system such as a cell phone) is highly dependent on factors such as the type of signal processing performed and on the absolute limit of memory available.
Another disadvantage of many existing GPS systems is that they rely much of the time on other systems for aiding data in order to provide a position within acceptable time limits. For example, a GPS system in a cell phone may constantly require time aiding, and possibly other aiding, from the cellular network in order to perform effectively. Existing GPS systems may not be capable of acquiring GPS signals within a required time without aiding. This may be acceptable if the time information is always available and if the provision of the time information does not impact other system performance aspects. However, a system that is designed to rely on aiding to meet performance requirements is not capable of performing satisfactorily without aiding, and further is not flexible enough to perform well in both aided and unaided situations.