The important features that a telematics system should include are position awareness, two-way communications ability and speech recognition.
In most current designs of telematics units, these separate functions are performed by separate modules. For example, a Global Positioning System (GPS) module usually connects to a main processor by a serial interface. The main processor fuses the GPS data with information from other motion sensors, such as the vehicle's odometer, and a gyro or compass to produce a robust position in both the presence and absence of GPS signals. The GPS module has its own reference oscillator, RAM, ROM and CPU. The main processor also has its clock oscillator, RAM, ROM and CPU.
There is an opportunity to reduce costs by integrating the GPS and dead-reckoning processing onto a single IC. For example, Philips' SAF3100 Telematics Processor combines most of the essential functions required for telematics into a single IC. The most important features are the CPU (MIPS R3000 compatible, running at 68 MHz), 12-channel GPS baseband correlator block, real-time clock and small-parameter RAM, both powered by an independent battery source, along with general-purpose RAM, dual 14-bit A/Ds, timer counters and bus communications (UARTs, I2C, CAN bus).
To complete a basic telematics system, an RF front end for the GPS system has to be added as well as a cell phone module suited to the type of network required (CDMA, PCS) plus antennas for GPS and cell phone, and controlling software.
Even with GPS and dead-reckoning functions running, a good proportion of the IC's resources such as the CPU cycles, embedded RAM and battery-backed RAM should be kept free for application software to be integrated with the drivers; otherwise, the system becomes simply an overpriced GPS sensor. However, if there is sufficient spare capacity, this IC can function as, for example, the central processor of a midrange or high-end car radio, while still carrying out its positioning and communications functions.
With integration, there is less duplication of components, such as crystals, and more economy of scale by rolling all the RAM and ROM together, smaller pc-board footprint and greater reliability in service because there are fewer interconnects and solder joints.
A GPS receiver for automotive use is normally a tracking receiver-that is, it continually receives and decodes GPS signals, tracking as many satellites as are visible or as many as it has channel hardware to track. It uses the orbital parameters (ephemeris) of each tracked satellite to calculate the receiver's position. Such a receiver is a collaboration between a hardware part and a software part.
The hardware part usually operates at RF, IF and the 1.023-MHz GPS chip rate, whereas the software part operates at a scale of 1 kHz or slower. The dividing line between hardware and software can be moved in either direction. If less hardware is used, then the receiver should be less expensive (lower total silicon area), but the software will need to function at a higher rate, making the problems of integrating application-layer control code more difficult.
If more hardware is used, the silicon area, and therefore cost, increases but the software task becomes easier, such that a smaller, simpler CPU might be used. A common compromise is to use hardware for the RF and IF sections, and to implement correlators and their associated integrators in hardware. The correlator outputs are then read by software at intervals of 1 millisecond (or longer) and the control loops are closed by software. All the higher-level functions-data extraction, decoding and checking; position and time calculation-are done purely in software.
Fortunately, most application software running on this type of platform is designed to run user interfaces and is thus keyed to human response times. As a result, a latency of a few hundred microseconds is not usually noticed.
Besides integrating functions in the baseband section of the receiver, cost savings can be made in the RF section. A typical GPS radio receiver section would contain a number of components: an IC, usually made in a bipolar or BiCMOS process; a surface-wave filter (SWF) to band-limit the input RF signal from the antenna; perhaps two separate IF filters, each made of 10 passive components; components for a voltage-controlled oscillator (VCO) such as varactor diodes; and a stable clock reference such as a temperature-compensated crystal oscillator (TCXO). Modern silicon-on-insulator processes can integrate high-Q, high-frequency inductors on-chip. This makes it possible to replace the SWF by an on-chip bandpass filter, and to be fabricated the VCO entirely on-chip. A change in circuit topology away from single-ended IF to full quadrature allows the IF frequency to be set close to 0 Hz. In this band, it is quite feasible to replace the external IF filters with an on-chip active filter, saving a handful of passive components. By adding a temperature sensor to the IC, it becomes possible to replace the TCXO by a simple crystal. All of this leads to reduced bill of materials, helping to make the telematics receiver affordable.
By using four ICs-an SAF3100 Telematics Processor, a UAF1572 GPS front end, a TJA1050 CAN-bus transceiver and a flash ROM-a complete telematics system can be built.