测绘学专业英语翻译 - 图文-

1、 role in signal tracking and processing. In the architecture, dedicated hardware handles all aspects of convolution processing and multi-second integration and also has features to provide frequency discrimination and data bit extraction from the GPS navigation message (when necessary, all without t

2、he need for rapid interrupts. getting a GPS fix, or, if a separate DSP is used, then this adds cost and extra components. The system on a chip demands significant CPU resources, as discussed above, and usually requires a dedicated CPU, adding to the size, cost and power consumption. TESTS Dedicated

3、silicon engine , existing circuits I :r-l I I I The Global Locate IndoorGPS receiver has been tested in a large range of environments. These tests have been filmed, and the film is available on CD, please contact the author (fvandiggelen. This paper shows stills extracted from test video, along with

4、 explanations of what is being shown. Test procedure: The Indoor GPS receiver is shut down before every single fix is obtained. The receiver is then powered up and it performs a server-assisted (cold start and attempts to acquire satellites and compute a position. A laptop screen shows a highlighted

5、 column for each satellite that is acquired. The top row of each highlighted column shows the signal strength of the satellite signal that was acquired. Signal strength is shown in units of dBm. The second row of each column shows the Carrier to Noise ratio in units of dB-Hz. existing circuits ! FFT

6、approach r-l IF SAMPLE MEMORY (LARGE RAM it I I I DSP II DEVICE Drlver I i MODEM8 VOICE j I SOFTWARE CORRELATOR I GPS system on a chip FLASH , existing circuits DEVICE Driver j , I I ! Figure 6. Three approaches to emb dding GPS in cell-phones Figure 6 contrasts three different approaches to GPS in

7、cellphones. The dotted lines in the figure show the boundary between existing circuits in a typical cell-phone, and the additional circuitry that must be added for GPS. The first approach, “Dedicated silicon engine”, is the method used with the GL-16000. All signal processing is done in custom logic

8、 built into the chip. The second approach, “FFT approach”, is to perform correlations in DSP software (using an FFT. The third approach is to use a conventional “system on a chip” architecture common in standard GPS receivers. Of the three approaches, only the dedicated silicon engine performs all s

9、ignal processing without requiring significant resources from a microprocessor. The FFT approach requires a DSP. If this is the cell-phone DSP (as shown then problems can occur in maintaining a voice call while These tests demonstrated satellite acquisition even when signal strengths are -155 dBm (-

10、185 dBW, corresponding to Carrier to Noise ratios of 18 dB-Hz. Note that the receiver does not first have to be powered on outside (or somewhere where strong signals are available: initial acquisition occurs at these very low signal strengths. These weak signals are approximately 25dB (more than 300

11、 times lower than the weakest signal that can be acquired by standard GPS receivers. This performance can only be achieved because the receiver has over 16000 correlators, more than standard GPS, and can approximately 5 0 0 245 acquire and accumulate signals 500x faster. When signal strengths are st

12、rong (outside, or in a benign indoor environment the receiver does not have to integrate signals for very long, and first fixes occur in milliseconds. In deep urban canyons the Indoor GPS receiver acquired satellites and computed correct positions, even though the dynamic range of the satellites was

13、 as much as 20dB between the strongest and the weakest satellites acquired. This demonstrated that the so-called “near-far problem in urban canyons does not affect the Indoor GPS receiver. The tests are done in environments where traditional GPS does not work. The tests also focused on performance w

14、hen the antenna was in locations typical for cell-phones, namely in shirt- and pants pockets, and when held to a users ear. The body effect significantly affects the received signal strength, but the IndoorGPS receiver still acquired satellites and made correct position fixes in all these tests. In

15、the environment shown above we found the mean signal strength at the antenna to be around -146dBm (C/No 27dB-Hz. One of the goals of the tests was to evaluate performance with low signal strengths (in the closed steel trunk of a car while moving at high speed. This is because it is much easier to ma

16、ke Indoor GPS work in the laboratory (stationary than in the real world (moving. The results of these tests were collected on the laptop (also in the trunk and shown later back in the office. We found that the receiver achieved startup and fix in as little as 250 milliseconds, with accuracy sufficie

17、nt to tell which side of the highway we were on, even with the receiver in the closed trunk of the car, while the car was moving at 70mph. With the antenna inside the main body of a car, received signals are, not surprisingly, stronger than in a closed trunk, and time to first f i x is consistently

18、250 milliseconds. This was tested in several different cars. The tests include a parking-lot test, shown on the video. Note that we are not acquiring satellites outside the parking lot, and then driving inside (a common trick, rather the receiver is powered up with the car already inside the parking lot. When the car is under one floor of the parking lot, the receivers mean time-to-first fix was just