ES2257183A1 - Impulsive noise suppression method used in radio communication systems, involves detecting peak of impulsive noise when transmitting information signal and replacing portions of affected information signal with zeros - Google Patents

Abstract

The method involves demodulating polarization of a transmitted signal carrying information using orthogonal polarization as monitoring polarization. When the monitoring polarization exceeds a certain threshold value, the peak of impulsive noise is then detected and portions of the affected information signal are then replaced with zeros. The detection of impulsive noise can be performed through analog or digital processing.

Description

Impulse noise suppression procedure by diversity of polarizations, for communication systems through radio waves

Technical sector

This procedure finds application in the Telecommunications sector More specifically in relation to the systems of transmission and reception of signals by waves Radioelectric Among these, more specifically in those with modulation system and digital transmission. And especially those with OFDM modulation (Orthogonal Frequency Division Multiplexing), such as digital radio and digital television land.

State of the art

To try to minimize the effects of noise impulsive over digital radio transmissions, have been proposed and to different methods, such as patents: WO2004002101, EP1361720, EP1309095 and EP1180851. These base their operation on the location of impulse noise peaks from one's own Information signal received. When, using different algorithms, they believe they have recognized a peak of impulsive noise, eliminate the corresponding signal portion.

Explanation of the procedure

Impulsive noise significantly damages the Transmission of radio communications. Its effect becomes more patent in which they use modulation and transmission systems digital, and with special virulence in those with OFDM modulation, like digital radio and digital terrestrial television.

Impulse noise cancellation systems existing, try to detect impulsive noise from the Information signal received. His way of acting consists of identify the impulse noise that is added to the signal of desired information. These methods have limited efficiency, since it is conditioned by the more or less correct Impulse noise identification.

The new procedure presented is applicable to radio wave communication systems, in which the signal transmission is done by a polarization mode determined (polarization of information reception), so that there is a polarization mode orthogonal to it (polarization monitoring) in which no transmission is made. Be tries to detect impulse noise in polarization of monitoring, taking advantage of the correlation between impulse noise components received in both polarizations

The advantage of this new procedure compared to the existing ones, it is able to detect the presence of impulsive noise in a more efficient way.

The operation of the procedure will consist of permanent observation of the amplitude of the signal received in monitoring polarization. When this amplitude exceeds a previously established threshold will be considered to be due to the  disturbance caused by a peak of impulsive noise. Then will act on the signal received in the reception polarization of information, replacing the affected signal segment with another of zero value There is another variant that involves replacing the section of signal affected by another that retains the same phase, but cutting its breadth

The threshold value will be determined from the thermal or background noise power, observed in polarization of monitoring.

The impulse noise detection in the monitoring polarization can be done from the signal continue demodulated, or sampling it previously.

Description of the drawings

Figure 1 shows in (1) a pair of antennas oriented independent receivers, according to horizontal polarization (H) that of receiving information and according to vertical polarization (V) monitoring.

The blocks indicated in (2) represent the stages of: Filtering and amplification in radiofrequency (RF). Transfer of the signal to intermediate frequency (FI), with its corresponding filtering and amplification sections. Y baseband demodulation, obtaining a complex signal with phase and quadrature components for each polarization S_ {H} (t) and S_ {V} (t).

The blocks indicated in (3) correspond to Low pass antialiasing filters, prior to the sampling stage.

In (4), both polarizations are sampled simultaneously with sampling period T, obtaining the signals discrete S_ {H} [n] and S_ {V} [n].

(5) is a block that evaluates whether the amplitude | S_ {V} [n] | is greater than X_ {0}.

The block (6) acts according to the evaluation made in (5): If the amplitude | S_ {V} [n] | is less than X_ {0}, the sample S_ {H} [n] remains unchanged. Yes by the opposite | S_ {V} [n] | is greater than X_ {0}, the sample S_ {H} [n] is replaced by a zero.

Block (7) is an analog / digital converter (A / D).

Detailed statement of the procedure

In (1), the information receiving antenna is arranged according to a polarization coincident with the signal of information that you want to receive; in this case it is the polarization H. The other antenna is the monitoring one and is arranged according to a polarization orthogonal to the previous one; in this course is polarization V. When a noise peak arises impulsive, antenna H will pick up that impulsive noise added to the information signal that you want to receive; while the antenna V will only pick up a peak of impulsive noise, which is found correlated with the one collected in H. Both antennas will collect also another type of disturbances, of smaller amplitude, as per example thermal or background noise, but this does not affect the exposed reasoning.

The signal from each antenna passes through the RF, FI and baseband demodulation stages, common in the radio signal receivers (2) and then filtered (3) and sampled  (4). Up to this point, they have collected and demodulated the polarizations H and V, separately and have been sampled simultaneously, obtaining complex signals S_ {H} [n] and S_ {V} [n].

Next, it is checked whether the amplitude of the value received at polarization V | S_ {V} [n] | exceeds certain threshold value X_ {0} (5). The decision to replace will be made the sample received in polarization H by a zero (6) if in the polarization V amplitude exceeded the threshold.

Finally (7), the A / D conversion of the resulting signal for polarization H and continues with the rest of the normal detection process.

There is another variant of this embodiment, which is that the measure of the amplitude of V is made from the signal continues | S_ {V} (t) |, without the need to sample V to get | S_ {V} [n] |.

Similarly, you can apply this method of impulse noise suppression, in case the transmission Be analog.

Application of the procedure to the industry

This procedure constitutes an improvement that you can add to the hardware and / or software of any receiver of a radio wave communication system, with the polarization conditions described in the explanation of procedure, to improve its behavior against noise impulsive. Specifically, it has special application in those OFDM modulation communication systems, such as digital radio and digital terrestrial television.

Claims (12)

1. Impulse noise suppression procedure due to polarization diversity, for radio wave communication systems. In which the transmitted signal has a specific polarization and the orthogonal polarization to it does not carry any information signal. Characterized because it uses the polarization that does not carry any information signal (monitoring polarization) to detect the impulse noise, indicating it to the receiving system so that, at the time it occurs, it invalidates the information received in the polarization of the transmitted signal ( polarization of information reception), since it is also affected by impulse noise. 2. Method according to claim 1, in the that the invalidation of the information received in the polarization of receiving information is done by replacing the part affected by another zero value. 3. Method according to claim 1, in the that the invalidation of the information received in the polarization of receiving information is done by replacing the part affected by another that retains the same phase, but by cutting its amplitude. 4. Method according to claim 1, in the that impulse noise detection takes place when the amplitude of the signal received in the monitoring polarization exceeds certain threshold value. 5. Method according to claim 4, in the that the measurement of the amplitude in the monitoring polarization be performed with continuous signal, without sampling of said Polarization. 6. Method according to claim 4, in the that the measurement of the amplitude in the monitoring polarization be performed with discrete signal, with sampling of said Polarization. 7. Method according to claim 4, in the that the determination of the threshold value be made based on the thermal or background noise power received in the polarization monitoring. 8. Method according to claim 1, in the that the signal modulation and transmission system be analogical. 9. Method according to claim 1, in the that the signal modulation and transmission system be digital. 10. Method according to claim 9, in the that the communication system uses OFDM modulation. 11. Method according to claim 10, in the that the communication system be the digital radio. 12. Method according to claim 10, in the that the communication system be digital television land.