What Is a Direct-Conversion Receiver?

The electromagnetic signals received by the antenna are sent to the receiver. The ideal receiver suppresses all unwanted noise, including other signals, without adding any noise or interference to the desired signal. Regardless of the form or format of the signal, it can be transformed to suit the characteristics required by the signal processor detection circuit, and then sent to the intelligent user interface. ^[1]

The receiver has two basic constituent structures, one is a superheterodyne structure, and the other is a direct conversion structure.

The so-called super - heterodyne receiver

The main function of the receiver is to

IEEE 802.16d. 2004 and IEEE 802.16e. 2005 defined receiver test requirements including:

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Receiver classification

1. Navigation receiver. This type of receiver is mainly used for navigation of moving carriers. It can give the position and speed of the carrier in real time. This type of receiver generally adopts C / A code pseudo-range measurement, and the single-point real-time positioning accuracy is low, generally ± 25mm, and ± 100mm when SA is affected. This type of receiver is cheap and widely used. According to different application fields, this type of receiver can be further divided into: vehicle type-used for vehicle navigation and positioning; marine type-used for ship navigation and positioning; aviation type-used for aircraft navigation and positioning. Because the aircraft runs fast, the receivers used in aviation are required to be able to adapt to high-speed motion. Space-borne type-used for satellite navigation and positioning. Because the speed of the satellite is as high as 7km / s or higher, the requirements for the receiver are higher.

2. Geodesic receiver. Geodesic receivers are mainly used for precision geodetic surveys and precision engineering surveys. High positioning accuracy. The structure of the instrument is complex and the price is relatively expensive. Timing receivers This type of receiver mainly uses the high-precision time standards provided by GPS satellites for timing, and is often used for time synchronization in observatories and radio communications.

Receiver carrier frequency classification

1. Single frequency receiver. The single frequency receiver can only receive the L1 carrier signal, and measure the carrier phase observation value for positioning. As the effect of ionospheric delay cannot be effectively eliminated, the single-frequency receiver is only suitable for precise positioning of short baselines (<15km).

2. Dual frequency receiver. The dual-frequency receiver can receive L1 and L2 carrier signals simultaneously. The difference in the ionosphere delay due to the dual frequency can eliminate the influence of the ionosphere on the delay of the electromagnetic wave signal, so the dual frequency receiver can be used for precise positioning up to several thousand kilometers.

Receiver has channel classification

1.Multi-channel receiver

2.Sequential Channel Receiver

3.Multi-channel multi-use channel receiver

Receiver working principle classification

1. Code-dependent receiver. Code-correlation receivers use pseudo-correlation techniques to obtain pseudorange observations.

2. Square receiver. The square receiver uses the carrier signal squaring technique to remove the modulation signal to restore the complete carrier signal. The phase difference between the carrier signal generated in the receiver and the received carrier signal is measured by a phase meter, and the pseudo-range observation is measured. .

3. Hybrid receiver. This instrument is a combination of the advantages of the above two receivers, and can obtain both code phase pseudorange and carrier phase observations.

4. Interference receiver. This receiver uses GPS satellites as radio sources and uses interferometry to determine the distance between two stations.