1. Field of the Invention
The present invention relates to processing signals transmitted via a communication system, and more particularly, to methods and devices for detection of co-channel interference (CCI) in a Digital Video Broadcasting (DVB) system.
2. Description of the Prior Art
Due to sharing the same frequency band with a conventional television broadcasting system such as the National Television System Committee (NTSC) system, the Digital Video Broadcasting (DVB) system may encounter the problem of co-channel interference (CCI). To counter the effect of the CCI signal, CCI filters are essential in the receiver of the DVB system.
A well-designed CCI filter can effectively eliminate the interference; however, when CCI is absent or negligible, the information carried by subcarriers may be filtered out and hence the performance of the receiver will deteriorate. Since the occurrence of the CCI is volatile in the DVB system, enabling the CCI filter continuously may degrade the system performance when CCI is absent or negligible. Therefore, a novel mechanism of detecting CCI occurrence should be devised to control the operation of the CCI filter according to the existence of CCI to thereby improve the system performance.
It is therefore one of the objectives of the claimed invention to provide methods and devices for processing signals transmitted via a communication system to solve the above-mentioned problems.
According to one embodiment of the claimed invention, a method for processing signals transmitted via a communication system is disclosed. The method comprises: measuring a first parameter associated with a signal power of a first frequency band of a received signal; measuring a second parameter associated with a signal power of a second frequency band of the received signal, wherein the first frequency band and the second frequency band are overlapped; comparing the first parameter with the second parameter to generate a comparison result; and detecting whether co-channel interference (CCI) exists in the communication system according to the comparison result in order to generate a detection result.
In addition to the method mentioned above, a device for processing signals transmitted via a communication system is further disclosed according to one embodiment of the claimed invention. The device comprises: a first evaluation unit for measuring a first parameter associated with a signal power of a first frequency band of a received signal; a second evaluation unit for measuring a second parameter associated with a signal power of a second frequency band of the received signal, wherein the first frequency band and the second frequency band are overlapped; a comparator, coupled to the first evaluation circuit and the second evaluation circuit, for comparing the first parameter with the second parameter to generate a comparison result; and a decision unit, coupled to the comparator, for detecting whether CCI exists in the communication system according to the comparison result in order to generate a detection result.
According to yet another embodiment of the claimed invention, a device for processing signals transmitted via a communication system is provided. The device includes: a decision logic, for detecting whether co-channel interference (CCI) exists in the communication system to generate a detection result in a frequency domain; and a controller, coupled to the decision unit, for generating an output signal by selectively enabling or disabling a CCI filtering operation for filtering out the CCI of a received signal according to the detection result.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
Certain terms are used throughout the description and following claims to refer to particular components. As one skilled in the art will appreciate, manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following description and in the claims, the terms “include” and “comprise” are used in an open-ended fashion, and thus should be interpreted to mean “include, but not limited to . . . ”. Also, the term “couple” is intended to mean either an indirect or direct electrical connection. Accordingly, if one device is coupled to another device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections.
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To detect the CCI signal, measuring the signal power of the received signal is an efficient manner to determine whether the CCI occurs. As known to those skilled in the art, in the frequency domain, the greater is the absolute value of a signal component at a specific frequency, the stronger the signal power of the signal component at the specific frequency is. In general, the signal power is estimated by computing a root mean square of a plurality of signal components over a frequency band. However, in this embodiment, a parameter indicative of the signal power is simply estimated by means of computing the summation of the absolute values of frequency components of a specific signal (e.g., DVB signal or CCI signal) over a specific frequency band.
Hence, for detecting the CCI occurrence, the first evaluation circuit 150 is configured to output a parameter MAGCCI, which is associated with the signal power of the CCI signal having signal components in the range 220 shown in
MAG
CCI=Σs=0˜L Σk=0˜kmax Aabs(Ys,k) (1)
MAG
DVB=[Σs=0˜L Σk=CCI
where,
MAGCCI: parameter associated with the signal power of the CCI signal;
MAGDVB: parameter associated with the signal power of the received DVB signal;
Ys,k: kth FFT output of the sth OFDM symbol;
s: OFDM symbol index;
k: subcarrier index;
L: observed OFDM symbol length;
N: FFT sampling points (for 2K mode, N=2048; for 4K mode, N=4096; for 8K mode, N=8192);
Aabs( ): a simplified absolute value function;
Kmax: maximum subcarrier index (for 2K mode, Kmax=1704; for 4K mode, Kmax=3408; for 8K mode, Kmax=6816); and
CCI_idx: subcarrier index mainly affected by CCI.
Since the FFT output is a complex number, the absolute value of the kth FFT output of the sth OFDM symbol (i.e., Ys,k) can be directly obtained through computing the square root of Re(Ys,k) and Im(Ys,k), i.e., √{square root over ((Re(Ys,k))2+(Im(Ys,k))2)}{square root over ((Re(Ys,k))2+(Im(Ys,k))2)}. Please note that Re(Ys,k) and Im(Ys,k) respectively represent the real part and imaginary part of Ys,k. However, to simplify the computational complexity, the present invention employs a simplified absolute value function Aabs(.) to obtain an approximate value of above-mentioned square root of Re(Ys,k) and Im(Ys,k). For example, in one implementation, regarding a complex number A+Bi, Aabs(A+Bi) can be easily obtained using max {|A|, |B|}+½ min {|A|,|B|}. However, this is for illustrative purposes only, and is not meant to be a limitation of the present invention. Other computation algorithms can also be employed to define this simplified absolute value function, depending upon design requirements. Furthermore, if the first and second evaluation circuits 150 and 160 are equipped with powerful computation capability, a more complicated absolute value function can be employed for obtain parameters more accurately indicating the signal power of the DVB signal and CCI signal. This also obeys the spirit of the present invention.
The comparator 170 then compares the two parameters MAGDVB and MAGCCI to generate a comparison result R by estimating a ratio of MAGCCI to MAGDVB, as below:
R=MAG
CCI
/MAG
DVB (3)
The decision unit 180 is implied to detect the CCI existence according to the comparison result R to generate a detection result. The decision rule is as follows:
If R (i.e., MAGCCI/MAGDVB)≦CCI_thrd, then CCI is absent;
If R (i.e., MAGCCI/MAGDVB)>CCI_thrd, then CCI exists.
If the comparison result R is not greater than or equal to a predetermined threshold CCI_thrd, the decision unit 180 accordingly determines the absence of CCI and generates a detection signal to the controllable CCI filter 130 for turning off the CCI filter 130. Otherwise, if the comparison result R is greater than the predetermined threshold CCI_thrd, the decision unit 180 determines that CCI occurs and therefore generates a detection signal to the controllable CCI filter 130 for turning on the CCI filter 130. Through the detection result R generated by the decision unit 180, an output signal is outputted from the CCI filter 130 by selectively enabling or disabling a CCI filtering operation for filtering out the CCI.
Here please note that the first parameter MAGCCI, and the second parameter MAGDVB are respectively parameters associated with a power intensity of a specified signal band (i.e., signal band of CCI signal or DVB signal); these two parameters do not express the precise signal power of the aforementioned signal band. The parameter R is also a parameter for illustrating only. The magnitude of these three parameters MAGCCI, MAGCCI, and R are not meant to be limitations of the present invention.
By using the CCI detection mechanism described above, the present invention can provide an efficient manner to control the CCI filtering operation by detecting the existence of the CCI, and therefore can achieve better signal performance. It should be noted the present invention is not restricted to be employed in the DVB system. For example, it can also apply to any communication system that uses OFDM technique.
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Please note that the circuit configuration respectively shown in
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.