Telecommunications – Receiver or analog modulated signal frequency converter – Local control of receiver operation
Reexamination Certificate
1998-12-30
2001-11-06
Nguyen, Lee (Department: 2683)
Telecommunications
Receiver or analog modulated signal frequency converter
Local control of receiver operation
C455S234200, C375S345000
Reexamination Certificate
active
06314278
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to communication devices and, more particularly, to processing of received signals in mobile communication devices.
2. Description of the Related Art
Mobile communication devices can include a wide range of devices, including cellular telephones, personal communication devices, and cordless telephones. Such devices include a handset that receives transmitted communication signals from a base station or cell station. The transmitted signal comprises a baseband voice signal that was modulated onto a carrier frequency to produce a signal that can be transmitted over an assigned band of the radio frequency spectrum. At the receiving handset, the modulated signal is received. The handset must then remove the carrier frequency to retrieve the baseband voice signal. A similar sequence of processing occurs in sending a voice signal from the handset to the base station.
More recently, the processing of the received signal occurs in the digital domain, although the transmitted signal is received as an analog signal. Thus, the received signal must undergo an analog-to-digital (A/D) conversion process. As the mobile communication device is moved about, the received signal strength can vary. For proper digital conversion, it is necessary to maintain control over the signal magnitude. Therefore, processing of the received signal usually includes amplification of the received signal, determination of received signal strength, and received signal gain control. In addition, the demodulation of the received signal for removal of the carrier frequency requires internal generation of a signal at the carrier frequency. This typically is achieved using a master clock signal that is generated in the handset. Inaccuracy in the master clock signal or parts imperfection can cause a DC offset in the generated signal and also result in an offset in the demodulated signal, which can prevent proper demodulation of the received signal.
Gain control of the received signal is typically achieved with a calculation of signal power by a standard computation involving I and Q terms of the A/D conversion process. In particular, the signal power is determined to be equal to the sum of the I
2
and Q
2
terms, where I and Q are A/D conversion terms of the received signal. Under conditions of fading and spectrum noise that are typical for a mobile communications device, such a signal power calculation can be difficult and unreliable. The response time to variations in the received signal strength can be unsatisfactory, and oscillation of gain adjustment can occur, causing further problems in signal demodulation. Response time can be faster and production costs can be lower if the processing is kept as simple as possible.
It should be apparent that signal gain control and associated processing performance can be improved and costs minimized with careful processing schemes for the received signal in a mobile communications device. It also would be advantageous if such improved performance would extend to better determination of received signal strength and superior generation of the master clock signal for better demodulation of the received signal and removal of the carrier frequency from the received signal.
From the discussion above, it should be apparent that there is a need for a mobile communications device with improved processing of the received signal without complex processing requirements. The present invention fulfills this need.
SUMMARY OF THE INVENTION
The present invention provides superior gain control of a received signal, without complicated additional signal processing, by utilizing A/D circuitry to determine gain control adjustment of the received signal based on the A/D samples of the received signal, rather than on power I
2
and Q
2
calculations of the received signal or 2 signals I and Q. This technique can be used with a single input. Using the A/D samples for gain control better maintains the signal gain so as to ensure proper A/D processing, efficiently utilizes A/D circuitry that is already provided for digital signal processing, and can be accomplished with relatively simple signal processing decisions. The gain is controlled so as to ensure that the received signal does not cause excessive full scale magnitude signal levels in the A/D converter (ADC), a situation referred to as saturation of the ADC. The gain control based on ADC signal samples can be implemented in simple hardware circuitry or in signal processing software. In this way, a communications device constructed in accordance with the invention provides improved signal gain control and associated processing performance with minimized costs.
In one aspect of the invention, a communications device processes a received signal and adjusts gain by amplifying the received signal after first setting signal gain to a maximum level, then providing the amplified received signal to an analog-to-digital converter (ADC) that produces a predetermined number of ADC signal sample values in a single cycle of the received signal. Setting the signal gain to a maximum initial level will ensure that low power signals will not go undetected, and initially cause a number of ADC signal sample values to have full scale magnitude, indicating saturation of the ADC. Next, the device continues processing by determining the number of ADC signal sample values that indicate full scale magnitude of the received signal within a signal cycle. The device then adjusts the signal gain from the maximum level that causes the number of ADC signal sample values indicating full scale magnitude to be above a predetermined saturation threshold, so as to reduce the signal gain until the saturation threshold of full scale values is not exceeded during a signal cycle.
Other features and advantages of the present invention should be apparent from the following description of the preferred embodiment, which illustrates, by way of example, the principles of the invention.
REFERENCES:
patent: 5825319 (1998-10-01), Murden et al.
patent: 5917865 (1999-06-01), Kopmeiners et al.
Heller Ehrman White & McAuliffe
Nguyen Lee
Uniden America Corporation
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