The Environment
All the mesurements are taken near the UPC Campus. In the next image you can see an aereal view of this zone.
The yellow spot marks the position of the base station
Our mobile is mounted in a van, so we can trace different paths, with LOS, NLOS or a combination of both.
The Signal
One of our objectives is to prove or the location algorithms in a real environment. And, as far as possible,
to reproduce existing communication systems, like GSM or UMTS. At our last experiments we focused mainly in UMTS
standard.
All our location techniques start at the channel estimation. To perform this operation, we use a known sequence
(the midamble). Usually this sequence is sent by the base station and the mobile to detect all rays for a RAKE receiver.
The mobile only sends this sequence continuosly, because is the only part with importance to us. The rest of the sequence
is simply avoided. This doesn't mean a lack of realism, because the result would be exacly the same, but with a more complex system.
Signal characteristics:
- Sequence length: 256 chips
- Sampling frecuency: 5 Mchip per second
- Central Frecuency: 1.8 GHz
- Shaping pulse: 0.22 Root cosinus.
The signal power depends on the distance between the mobile and the base station. The power control is performed at the base station.
One important topic is the signal interference. To emulate this interference, white noise is added at the receiver. We
can ensure that the SNR at the receiver is so much higher than the typical SNR of a real UMTS scenario.
Depending of the type of measurements, and mainly, the pilot channel used, the typical SNR is determined.
The Base Station
Once the signal is received at the base station, it is demodulated, and sampled. Four TMS320C6701 Texas Ins. DSP
estimate the channel, the TOA and AOA and track the source with a Kalman Filter. All in real Time.
Because some bottlenecks of the system, it can perform 200 channel estimations per second and antenna.
All the results (channel, TOA, AOA and Kalman estimations) are stored in memory, and transmitted to a PC for futher off-line processing.
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