Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1997-12-23
2001-10-16
Chin, Wellington (Department: 2664)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S335000
Reexamination Certificate
active
06304561
ABSTRACT:
FIELD OF THE INVENTION
This invention reI general to wireless communications and, more particularly to a method and apparatus for regulating the effective noise figure of a CDMA receiver in a base station. The regulation may be effected to control the blossoming/breathing or wilting functions of a CDMA communication system.
BACKGROUND OF THE INVENTION
In a CDMA wireless system the activation or deactivation of-a cell/sector affects the network. The sudden activation of the cell/sector causes a sudden increase in the total forward link power. This may temporarily degrade the forward link performance of the network and possibly cause the calls in other cells/sectors close to the activating cell/sector to be dropped due to the sudden increase of channel interference from the activating cell/sector. In addition, the sudden deactivation of a cell/sector will result in calls in the cell/sector being dropped. To avoid this problem, when a cell/sector is activated in a CDMA wireless system, the transmitted power of the transmitter at the base station is increased gradually, while the effective noise figure of the receiver at the base station is gradually decreased accordingly. This allows the users in the neighboring cells/sectors who are subject to the interference from the activating cell/sector to have enough time to handoff to the activating cell/sector. The synchronized gradual increase of the transmitted power and decrease in the receiver effective noise figure is known as “blossoming”. Similarly, the synchronized gradual decrease in the transmitted power and increase in the receiver effective noise figure is known as “wilting”. This occurs when a cell/sector is deactivated. Wilting allows the users in the deactivating cell/sector to have enough time to handoff to neighboring cell/sectors, rather than being dropped. During normal operation of the cell/sector the balance between the forward link handoff boundary and the reverse link handoff boundary must be constantly maintained. This operation, known as “breathing”, is also effected by balancing the transmitted power and the effective noise figure at the receiver. In order to keep the handoff boundaries balanced, for every one dB change in transmitted power there must be an opposing one dB change in the receiver effective noise figure.
The implementation of the receiver blossoming, breathing and wilting functions has been traditionally effected in the analog chain of the receiver at the RF or at the analog IF stages by degrading its noise figure. Practically, this is traditionally effected by altering a variable attenuator located at the RF section or the early stages of the IF section, prior to any channel separation. The drawbacks of this approach are:
1. inaccurate control due to gain and/or noise figure instability (over temperature, aging, non-linearity, etc.)
2. this method is not suitable for effecting noise power regulation on a channel by channel basis in a multichannel CDMA receiver in which the channels share the same RF section and early stages of IF section.
Thus, there is a need in the industry to provide a CDMA receiver capable to implement the blossoming, breathing and wilting functions while alleviating the difficulties associated with prior art methods.
SUMMARY OF THE INVENTION
The present invention provides a CDMA receiver including an input for receiving an RF signal, an analog signal processing stage for processing the RF signal and a plurality of channels connected to the analog signal processing stage. The RF signal includes a plurality of components separable from one another, where each channel receives a signal derived from a respective component of the RF signal. Each channel includes an effective noise figure regulation unit operative to generate a noise signal and introduce the noise signal into the signal derived from the respective component of the RF signal, for regulating an effective noise figure of the signal derived from the respective component of the RF signal.
The effective noise figure regulation may be effected in the analog processing unit or the digital processing unit of each channel. In a specific embodiment the channels of the receiver process independent CDMA signals separated by frequency. Most preferably, the effective noise figure regulation unit is located in the digital processing unit of the channel. The effective noise figure regulation unit includes a source of noise, such as a synthesized pseudo-random noise that is injected in the signal path. For easier control it is preferred to inject the signal at the digital baseband stage. At the baseband stage, the noise can be injected in the signal before or after the channel select filter. To determine the amount of noise to inject into the signal path for a given effective noise figure change, a power detector is used to measure the actual receiver noise power. Based on the information supplied by the power detector, the noise source can be controlled to effectively regulate the receiver effective noise figure degradation.
In a specific embodiment the effective noise figure can be defined as
SNR
i
SNR
o
where SNRi is the signal to noise ratio at the antenna port and SNR
o
is the signal to noise ratio at the CDMA modem input port.
An important advantage of this arrangement is the ability to regulate the effective noise figure on a channel by channel basis. Since each channel of the CDMA receiver has an independent effective noise figure regulation unit, the amount of noise introduced in the signal path of each channel may vary from one channel to another.
REFERENCES:
patent: 5267262 (1993-11-01), Wheatley, III
patent: 5559790 (1996-09-01), Yano et al.
patent: 5675581 (1997-10-01), Soliman
patent: 5729571 (1998-03-01), Park et al.
patent: 5781542 (1998-07-01), Tanaka et al.
patent: 5870425 (1999-02-01), Piaget et al.
Jin Xin
McGowan Neil
Nielsen John
Stanier Jeff
Yang Hong-Kui
Chin Wellington
Nortel Networks Limited
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