WO2009037364A1

WO2009037364A1 - Wireless communications system, device and method for compensation of power losses

Info

Publication number: WO2009037364A1
Application number: PCT/ES2007/000527
Authority: WO
Inventors: Emilio Tejedor Escobar
Original assignee: Terminales De Telecomunicaciones Terrestre, S.L.
Priority date: 2007-09-19
Filing date: 2007-09-19
Publication date: 2009-03-26

Abstract

The present invention, a wireless communications system, device and method for compensation of power losses, concerns a device, a method and a system which enable wireless communications networks to be used on the basis of standards for cabled networks thereby solving the problems associated with signal fading due to adverse atmospheric conditions.

Description

WIRELESS COMMUNICATIONS SYSTEM, DEVICE AND METHOD FOR COMPENSATION OF POWER LOSSES

OBJECT OF THE INVENTION

The present invention, wireless communications system, device and method for compensation of loss in power, refers to a wireless radio frequency communications system, a device and a method that solve the losses that occur in the power of a radioelectric signal in both directions of the communication (descending path and ascending path) due to the atmospheric conditions in said radio path.

In particular, the invention focuses on a device, a method and a communication system that provides a wireless extension to the cable installations, so that the wireless section is completely transparent to the user equipment in relation to the variations in the level of the signal.

The present invention has its scope in the field of telecommunications, and in particular in wireless broadband subscriber loop technologies.

STATE OF THE TECHNIQUE

Wired networks are infrastructures designed to offer data and video services, currently being fully extended throughout the world. The high volume of them and the need to promote competitiveness among different vendors have led to an effort in standardization, resulting in the following standards:

- Standards for digital television: DVB (Digital Video Broadcasting, Digital Video for Broadcasting), ISDB (Integrated Services Digital Broadcasting, Digital Transmission of Integrated Services) and ATSC (Advanced Television System Comitee, Advanced Television Systems Committee).

- Standards for voice and data services: DOCSIS (Data Over Cable Service Interface Specification) or EuroDOCSIS. Communications based on these standards must be transported through fixed wired networks, for example HFC (Hybrid Fiber Coaxial, Hybrid Fiber and Coaxial) networks composed of fiber and coaxial cable.

The existing competitiveness in this market has led to a large supply of equipment and a rapid evolution in technology, offering an increase in functionality at low cost. This competitiveness and the good price-performance ratio have made wireless technology manufacturers and telecommunications operators start designing products and deploying networks respectively, taking into account wireless technologies.

However, wireless technologies are not as standardized as wired. Specifications have only been defined for mobile systems, initially oriented to voice communications, and for fixed access networks such as WIMAX (Worldwide Interoperability for Microwave Access, World Interoperability for Microwave Access), and Wi-Fi (Wireless Fidelity, Wireless fidelity), while LMDS system operators (Local Multipoint Distribution Service) use proprietary and customized solutions.

Thus, wireless radio equipment has not been designed to process standards-based communications for fixed networks. It is for this reason that wireless radio equipment has the disadvantage of having to cope with the atmospheric changes that occur and that affect the signal when it is being transmitted through the air. This variation in the power of the signal due to atmospheric changes is of great importance when the frequency of the signal increases. This is due to the sensitivity of high frequency signals to heavy rain. But also this variation in the power of the signal due to atmospheric changes, affects smaller frequency ranges.

The characteristics of the wireless physical medium, the air, cause some signal distortions that do not occur in cable networks. The most important distortions that occur in the signals are:

Greater intermodulation distortion,

Phase noise, and - Variability of the signal dependent on atmospheric conditions.

In the state of the art some solutions are known that attempt to solve the previous technical problem and perform an equalization of the signal in the receiver.

Thus, for example, the European patent application EP0851618A2 describes a method for controlling multipoint remote stations. In the aforementioned patent application, the use of a near pilot signal in frequency is proposed on the way down to the carriers. The pilot signal is measured at the receiver to estimate the losses along the way and set an appropriate gain through an automatic gain control that compensates for the previous losses.

In this way the signal is sent to the demodulator once it has been compensated. The gain to be applied to the received signal is set to the signal to be transmitted by means of the same automatic gain control.

US patent application US2002 / 0145968A1 describes a procedure similar to the previous one. In this case, a multipoint wireless system delivers OFDM (Orthogonal Frequency Division Multiplexing Division Multiplexing by Orthogonal Frequency Division) signals. These OFDM signals incorporate a pilot signal responsible for determining the losses along the way. An automatic gain control in each remote station is responsible for measuring the said pilot signal sent together with the main signal to determine in this way the losses in the radio path. The transmitter adjusts its gain according to the value provided by the previous automatic gain control.

Finally, US patent US6011980 describes a wireless telecommunications equipment with a transmitting part and another receiving part, which uses the data signal to estimate the losses along the way. The power of the received signal is compared with the desired one and the difference of the signal is used as input to an automatic gain control in the receiver. In the transmitting part an amplifier is used, governed by a closed loop power control, which is fed successively with the aforementioned signal difference.

As described, some solutions adopted make use of pilot signals in order to measure the losses of the signal that occur in the radio path. However, this solution has some disadvantages. On the one hand, these types of solutions are technically complicated and therefore expensive. Filters and devices are necessary to extract the near pilot tone in frequency to the data signal. Therefore, it is not an optimal solution in terms of costs since the fact of having to process a pilot tone implies the need for additional devices such as selective filters, oscillators, etc.

On the other hand, the fact of using pilot signals results in spectral inefficiency, due to the fact that the pilot tone has to be inserted inside the working frequency band, and therefore a fraction of the width is spent of band, a very scarce resource.

These solutions have a lower availability, since by increasing the number of circuits a less robust system is obtained, and also if redundant architectures are chosen to solve these problems of lack of robustness, an even more expensive system is obtained

Another of the solutions adopted consists in carrying out a complex processing of the radiofrequency signal to compensate for the losses in the path, performing a demodulation and an analysis of the demodulated signal to estimate the variations of the losses in the path. Therefore they require a "digital portion" in the system. This limits the applicability of its solutions, since in the case of the American application US2002 / 0145968A1 the use of pilot tones is required within an OFDM signal and in the case of the US patent US6011980 the demodulated I-Q signal is analyzed.

The present invention solves the aforementioned drawbacks as follows:

To avoid the use of a pilot tone, the present system makes use of the carriers so that the entire spectrum is available to the user, giving the design flexibility.

- Without the need to perform a complex processing of the radio frequency signal,

The present invention uses radio frequency broadband detectors and therefore does not require the demodulation of the signals, making it technologically agnostic and being able to work in intermediate units (such as repeaters) that do not normally have demodulation hardware. DESCRIPTION OF THE INVENTION

The present invention, wireless communications system, device and method for

The compensation of power losses refers to a method, a device and a system that make it possible for wireless communications based on standards for wired broadband systems to be transported continuously in wireless networks and working in various frequency bands .

A wired system typically consists of a header (CMTS Cable Modem Termination System) and a number of cable modems (CM) located at the subscriber's premises. In the case of the DOCSIS specification, it is determined that the power transmitted by the CM can only be corrected by a "ranging response" packet sent from the CMTS in response to a "ranging request" packet sent from the CM.

Since the wired networks are highly stable in relation to the loss of power, the standards were designed only to deal with small and sporadic variations in power. However, signal variations due to atmospheric conditions can be very large in the long term and relatively large in the short term when transported through high-frequency wireless networks.

Thus, in wireless networks conceived as an extension of wired networks, it may be that the cable modem loses its connection with the CMTS due to the following reasons:

- The rain is so intense that it causes the signal to be outside the dynamic range of the device,

- Although the power level is within the dynamic range, the rate of change is so high that the CMTS cannot correctly receive the CM signals and therefore cannot send the adjustment message.

The latter happens when the CM signal reaches the CMTS with ± 6dB of difference with respect to the expected level of the signal. When the received energy changes so fast, the CM sends ranging messages insistently and the CMTS considers it unstable, not sending any response message from ranging and finally disconnecting to the CM after a time limit is reached. The CM must be restarted and registered in the network. In ordinary wireless systems the CM has to address these two effects if no correction mechanisms are implemented in the radio devices; The higher the frequency or the longer the link, the more severe these effects are.

An object of the present invention is to ensure that a wireless network can deliver a signal that remains constant regardless of atmospheric conditions, and for this purpose a device, a method and a system have been developed.

Currently, variations in the signals in the wireless radio path are compensated in the subscriber equipment, the cable modem (CM). That is, for the receiver, an internal gain control compensates for variations in the level of the signal by increasing or decreasing its gain. On the transmitter side, the modem cable does not perform any action and requires the header that indicates to the modem cable the magnitude and the sign in the correction value of the power to be transmitted. This is the main reason for the weakness of the applications currently in use.

In particular, a first object of the invention refers to a communications system that compensates for attenuation due to heavy rain, automatically changing the gain of some elements of the network in the descending path and in the ascending path. The network elements of the wireless communication system collaborate to maintain an approximately constant signal level at the input of the cable modem receiver and at the input of the CMTS receiver, thus freeing the modem cable and the CMTS from compensation for loss of high and / or fast value on the way.

A second object of the present invention is a device that performs automatic compensation both in the ascending path and in the descending path in some network elements. This device, by means of two automatic controls, increases the level of the signal in the ascending path to a value defined by the losses in the descending path.

A third object of the present invention refers to a method by which it is possible to compensate the losses in the radio path. The procedure monitors the signal level in the descending path to measure losses in the radio path and to compensate for such losses both in the descending path and in the ascending path; in this way the gain of the radio device increases or decreases to provide the modem cable with a constant signal level. The number of signals (or carriers) present in the system in the downward path may change during the life of the system. The operator can add more carriers if the traffic demand increases. If the carrier load changes, the radio must be informed to take into account that change in the calculations of the device that compensates for the variations in the signal.

The device and method is not implemented in the base station since both the device and the method are based on measuring the signals in the downward direction, and the base station is the generator of this signal. Therefore, at this point the level of the signal cannot change due to rain or other effects.

DESCRIPTION OF THE FIGURES

To complete the description that is being made and in order to help a better understanding of the characteristics of the invention, according to a preferred example of practical implementation thereof, a set of figures in the accompanying part is attached as an integral part of said description. where, as an illustration and not limitation, the following has been represented:

Figure 1.- Shows a schematic block diagram of the transparent communication system in wireless power.

Figure 2.- Shows a block diagram of an automatic gain control responsible for compensating the losses in power of the signal in the radio path.

DESCRIPTION OF A PREFERRED MODE OF EMBODIMENT

According to Figure 1, the communications system object of the present invention refers to a radio frequency system, intended to provide "triple play" services (television services, video services and data services) in a wide range of frequencies.

The system must be transparent in power providing a constant signal level both to the header 2 (CMTS) in the ascending path, and to the cable modem (CM) 8 in the descending path.

This system consists of the following elements: Base Station 3 (BST Base Station Transceiver); designed to increase and transmit the modulated signal from a multiservice header (DOCSIS, EuroDOCSIS, encapsulated E1 / T1 / E3 / STM1, ATM lines, etc., and also DVB-C, DVB-T) to the users of the network, as well as Receive and send the signals that come from the users.

- Outdoor Units 7 (ODU Outdoor Unit), are remote transceivers used to provide connection to one or more client devices with the wireless network. The ODU has an internal coaxial type F type for the remote network. It is equipped with an automatic internal gain control.

If necessary, active signal repeaters 5 (OAR Outdoor Active Repeater) will be used, which are a bidirectional unit designed to illuminate dark areas

(those with an obstacle that prevents the direct line between the base station and the user's equipment), and extending the coverage beyond the limits of the base station in a transparent manner to the superior services. It is also equipped with an automatic internal gain control.

The CMTS 2 is connected to an IP network 1 and communicates with the modem cable through the described wireless system. Between the base station 3 and the repeaters 5, the physical medium can be affected by the atmospheric conditions 4, as well as between the repeaters 5 and the outdoor units 7, the transmission medium can also be affected by atmospheric conditions 6.

The radio device of the base station 3 emits a constant signal level in the downward direction regardless of the atmospheric conditions 4 and 6. This makes the signal arrive with a power Pu to the ODU 7.

If it rains, there will be a loss Lr 4 of the signal on the way from the base station 3 to the repeater 5 and Lu 6 on the way from the repeater 5 to the ODU 7. If the gain in the repeater 5 is Gr and the gain in ODU 7 is Gu, the power received in cable modem 8 is (not considering cable losses):

- Before: Pcm = Pu + Gu

- After: Pcm = Pu + Gu - Lr - Lu In the previous case, a single carrier has been taken into consideration but if the operator adds more carriers, the detector will read more power, in which case the gain in the transmitter could be reduced even if the power received by the carrier has not really decreased.

5 To avoid this malfunction the system has to be informed of changes in

The load of carriers in the downward direction. For this, a global parameter, called the load coefficient (A), is sent together with the signal to give a measure of the capacity of use.

The load coefficient is equal to:

_in _ number of carriers used total number of carriers

Thus, when all carriers are present, A is equal to OdB, and if only half of the carriers are present, the value of A is 3dB (ie, half power). And so on.

Therefore, the above equations can be rewritten as:

15 - Before: Pcm = A x (Pu + Gu) / A, where (Pu + Gu) / A is the power received per carrier under ideal atmospheric conditions

- After: Pcm = [A x (Pu + Gu) / A] - Lr - Lu

Without the use of the present invention, the cable modem, assuming the load coefficient a constant, must increase the power transmitted in the amount of Lr + Lu + E _TX . Being

20 E _T χ the difference in losses in the descending and ascending path, and this difference is due to the difference in frequency in the descending and ascending path; E and _x can be estimated as 1 or 2dB in a wireless system that works at 28 GHz.

With the device and method of the present invention, the cable modem will have to compensate only the E _τx previously mentioned. The device and method have to be implemented in all the wireless network elements beyond the base station (repeaters if necessary and outdoor units) to work correctly. The device responsible for compensating the loss of power of the signal is an automatic control of bidirectional gain that, as already mentioned, is implemented in some of the network elements of the system (network units and repeaters if necessary) and that It is shown in Figure 2.

Automatic bidirectional gain control consists of a signal level detector

9, two gain controls one on the downward path 12 and one on the upward path 10 and a microprocessor 11 that governs the device. These components work together according to the method described below.

The power received in the downward path is measured by the detector 9, assuming constant the output power of the base station 3.

The microprocessor 11 monitors the variations in the power level. If the power of the radio frequency signal emitted by the base station 3 is constant, these variations are considered due to time disturbances.

The microprocessor 11 acts in the gain control in the downward direction 12 to compensate for variations in gain in the power variations, keeping the power delivered to the output of the constant receiver.

The microprocessor then acts in the gain control in the ascending path 10, providing the same compensation in gain as that applied in the gain control in the descending path 12.

The entire system works to provide the modem cable 8 with a constant signal level, regardless of the working frequency and the length jumps. The outdoor units 7 monitor the received signal either from the repeater 5 or from the base station 3 and compensate for the fading section between the repeater 5 - base station 3 to the outdoor units 7, increasing by this amount the signals in the descending and ascending path. The repeaters 5, if necessary, measure the power of the level of signal received from the base station 3, calculate the power losses between the base station 3 and the repeater 5, and amplify the signals in the descending path and in the ascending path .

Claims

1. Device for compensating the losses in power of a signal in the radio path in a wireless communication system in a bidirectional manner characterized in that it comprises:

- at least one detector of the level of said signal,

- at least one gain control on the downward path,

- at least one gain control on the upward path, and

- at least one microprocessor that governs said gain controls.

2. Device according to claim 1, characterized in that said level detector measures the power of the signal in the downward path.

3. Device according to claim 1 or 2, characterized in that said microprocessor processes the values obtained from said detector.

Device according to claim 1 or 3, characterized in that said microprocessor acts on said gain controls in the upward and downward path depending on said value of said signal level calculated on said detector.

5. Device, according to claim 1, characterized in that it knows the load of carriers downwards of said signal.

6. Device according to claim 1, characterized in that the network elements of said wireless communication system are arranged in the receivers

7. Device according to claim 6, characterized in that said network elements are repeaters and / or outdoor units.

Device according to claim 1, characterized in that said wireless communication system follows the standard of wired systems.

9. Device according to claim 8, characterized in that said standard in DOCSIS.

10. Method for compensating the losses in power of a signal in the radio path in a wireless communication system in a bidirectional manner characterized in that it comprises the following steps:

- Measure the power of the signal received in the descending path,

- Monitor the variations of said power in the descending path,

- Compensate for said variations in power of said signal in the downward direction with variations in gain and

- Compensate said variations in power of said signal with variations in gain in the upstream signal.

Method according to claim 10, characterized in that it is applied in the receivers of the network elements of said wireless communication system.

12. Method according to claim 11, characterized in that said network elements are repeaters and / or outdoor units.

13. Wireless communication system, of the type comprising at least one base station, at least one outdoor unit, at least one modem cable and / or at least one repeater, characterized in that it performs in said outdoor units and / or in said repeaters compensation of power losses bidirectionally.

14. System according to claim 13, characterized in that said compensation is performed by the device according to claim 1.

System according to claim 13 characterized in that said compensation is performed by the method according to claim 10.