Case Study –Joining Maneuver

In this section, a simulator is programmed by the Borland C++ Builder (BCB) based on the two-level communication architecture. The simulator is used to simulate the executing conditions of the example of the joining maneuver.

Description for simulating communication architecture for AHS

In order to simulate the situation of communication transmission of AHS, a local network architecture is used to implement. A server is used as a monitor for displaying the status of AHS. Each computer represents one vehicle in AHS and has a specific IP (Internet Protocol) address in the local network architecture that makes vehicles can easily exchange information from others. In a real highway system, the AHS maybe not have the server. A server is set up for monitoring all the states of executing AHS-related maneuvers. In this case study, four computers are used: One is a server, and the others are vehicles.

Simulator and development environment

The simulator is an operating interface of vehicles and a monitoring interface of AHS.

The simulator provides a virtual environment of AHS. By operating the simulator in different computer simulates a real automated highway system. The user can test other maneuver protocols by programming the controller algorithm into the vehicle dynamic model, including longitudinal controllers and lateral controllers.

Figure 3.84 Environment information and systemic messages in the simulator

(Figure 3.84) shows the processes of running the simulator. The above of (Figure 3.84) shows the road situations. There are seven vehicles including vehicle A, vehicle B, and vehicle C. The memo in left-down of (Figure 3.84) shows the information according to the data format discussed before.

The variation of trajectory

In this section, in order to give an easy visualization of the variation of trajectory, the data generated by the simulator are shown via Matlab. The variation of trajectory includes the longitudinal trajectory and lateral trajectory shown in (Figure 3.85) and(Figure 3.86).

According to (Figure 3.85) and(Figure 3.86), the processes of executing joining maneuver can be easily observed. (Figure 3.85) shows that the vehicle A traces the longitudinal position of the preceding platoon (vehicle B). After forty-five time slots, the vehicle A achieves the goal. The vehicle A has a short space with vehicle B (about thirty units).

(Figure 3.86) shows that the vehicle A traces the lateral position of the preceding platoon (vehicle B). After twenty time slots, the vehicle A achieves the goal. Vehicle A and vehicle B run in the same lateral lane. In this thesis, the time slot of simulator is 0.5 second.

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Figure 3.85 Variation of longitudinal trajectory Figure 3.86 Variation of lateral trajectory 5. Transceiver for DSRC

(Figure 3.87) shows the architecture of the transceiver. In the transmitter, the modulated instruction is processed by the IF circuit and up-converted to an RF signal by an up-conversion mixer, amplified and sent to the antenna for transmission. In the receiver, the signal received by the antenna is amplified by a low-noise amplifier, then down-converted to an IF signal by a down-conversion mixer. The IF signal is demodulated and decoded to retrieve the instruction. The RF and LO signals are at 2.431 GHz and 2.43 GHz, respectively, rendering 1 MHz signal at the IF port.

DAC modulator encoder instruction

LO

PA Mixer DSP

(a)

Ant.

LNA Mixer

LO

LPF ADC demodulator decoder

instruction DSP

(b)

Ant.

Figure 3.87 Architecture of (a) transmitter and (b) receiver

(Figure 3.88) shows a low-noise amplifier circuit diagram. The source impedance and load impedance should be conjugate matched to achieve maximum power gain. In microwave circuits, power gain is more frequently specified than voltage gain.

(Figure 3.89) shows an example of balanced mixer which consists of two identical single-ended mixers connected to a 3-dB coupler.

Figure 3.88 LNA circuit Figure 3.89 Schematic of balanced mixer

With ideally matched diodes and 3-dB coupler, no LO signal will leak to the IF and RF ports, and the attenuation between the RF and the IF ports is insignificant.

(Figure 3.90) shows the local oscillator circuit diagram. In order to stabilize the local oscillator frequency, injection- locking oscillator is used. Fig.3.81 is the injection-locking oscillator circuit. At small injection signal, the locking range is related to the injection signal

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power is

0

2 _{free inj}

ext

f P

f Q P

 

where Pinj is the injection power, P0is the output power of the free-running oscillator, ffree is the free-running frequency, Qextis the external Q factor of the resonant circuit.

Figure 3.90 Local oscillator Figure 3.91 Injection-locking oscillator

The simulated and measured S parameters of LNA are shown in (Figure 3.92). The power gain is about 16 dB and the return loss is about -30 dB. The simulated IIP3 and OIP3 are 6.0928 dB and 21.7147 dB, respectively, the measured IIP3 and OIP3 are 4.5931 dB and 20.2642 dB, respectively.

Simulation results of conversion loss and return loss are shown in (Figure 3.93). At 2.43 GHz, the conversion loss is 7.4 dB, and return loss is 21.7 dB. The measured conversion loss is 10 dB and the measured RF return loss is 12 dB. The isolation between RF and LO is 15 dB.

(Figure 3.94) shows the measured ILO signal. Its output power is 8.5 dBm and its phase noise is -101 dBc/Hz at 100 KHz offset.

(a) (b)

Figure 3.92 S parameter of LNA, (a) input return loss, (b) power Gain, -- : simulated, - : measurement

Finally, LNA, mixer and ILO are integrated into a single circuit board. A 2.431 GHz RF signal is mixed with the LO signal to generate an IF signal. IF amplifier and bandpass filter are designed to get the desired frequency at 1 MHz. The measured spectrum is shown in (Figure 3.95).

In summary, key components of a typical RF front-end were designed and integrated to build a prototype of dedicated short-range communication (DSRC) transceiver. IF amplifier and filter were also designed to improve the IF signal. The RF front-end is designed in the ISM band at 2.431GHz and render 1 MHz IF signal. Injection-locking oscillator is used to stabilize the LO signal with PLL and crystal oscillator, respectively, as reference signal

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Figure 3.93 Simulated Figure 3.94 Measured Figure 3.95 Measured IF conversion loss and return spectrum of ILO spectrum after IF

loss of diode mixer, with PLL injection amplifier and bandpass

--: S11, -: S21 filter