Abstract:
The present invention relates to a server used to transmit Ethernet data signals from an Ethernet network to multiple cable TV network clients or receive Ethernet data signals from the multiple cable TV network clients, the server comprising multiple APs (access points), wherein the APs synchronously start a downlink transmission or an uplink transmission, and wherein during the downlink transmission the APs convert the Ethernet data signals into encoded and modulated RF signals and transmit the encoded and modulated RF signals to the multiple cable TV network clients, and during the uplink transmission the encoded and modulated RF signals from the cable TV network clients and convert the encoded and modulated RF signals into the Ethernet data signals.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to the technology of data communication through cable access network, and more particularly to a Headend apparatus for data transmission over cable access network. 
       BACKGROUND OF THE INVENTION 
       [0002]    Historically, Cable TV (CATV) is a type of unidirectional medium for broadcasting, and one objective of its design is to provide analogy video broadcast channels to maximum number of subscribers under a minimum cost. Recently, it has been widely recognized that a high potential of capacity is provided for bidirectional data communication by the coaxial cable broadband technology, and various cable network systems have been developed and implemented. Among those well known technologies, DOCSIS is one standard which is developed and widely adopted in North America, in which a type of dedicated cable modem (CM) must be used at the client ends, and a cable modem termination system (CMTS) must be employed at the server ends (front ends). Meanwhile, along with the rapid development of the home network technology, many kinds of cable home networks are also developed, which utilize the coaxial cable of the CATV network, for example, MoCA (Multimedia over COAX Alliance), HCNA (Home Cable Network Access), and PLC (Power Line communication), etc. 
         [0003]    On the other hand, thanks to the maturation of WiFi technology, the cost of WiFi compliant hardware and software is reduced a lot, which provides another possibility for access technology in the hybrid fiber coaxial cable network. In this field, one published Chinese patent No. CN1620132 discloses a system for integrating CATV with network communication, wherein IEEE802.11 signal is modulated and transmitted over the coaxial cable network of CATV at bandwidth of 0-65 MHz. This patent application is characterized in that the IEEE802.11 standard digital signal is first modulated from 2.4 GHz to 0-65 MHz by OFDM (Orthogonal Frequency Division Multiplex), QAM (Quadrature Amplitude Modulation), or QPSK (Quadrature Phase-Shift Keying), and then transmitted through the coaxial cable of CATV network. However, in this disclosed solution, there is only one channel in the cable. Therefore it still can not meet the real demands of high rate bandwidth data transmission. 
         [0004]    Therefore, it is desirable to develop an improved cable access network, which overcomes drawbacks of the prior arts. 
       SUMMARY OF THE INVENTION 
       [0005]    In an aspect, a server used to transmit Ethernet data signals from an Ethernet network to multiple cable TV network clients or receive Ethernet data signals from the multiple cable TV network clients is provided. The server comprises multiple APs (access points), wherein the APs synchronously start a downlink transmission or an uplink transmission, and wherein during the downlink transmission the APs convert the Ethernet data signals into encoded and modulated RF signals and transmit the encoded and modulated RF signals to the multiple cable TV network clients, and during the uplink transmission the APs receive the encoded and modulated RF signals from the cable TV network clients and convert the encoded and modulated RF signals into the Ethernet data signals. 
         [0006]    In another aspect, a server used to convert Ethernet data signals into encoded and modulated RF signals when transmitting Ethernet data signals from an Ethernet network to multiple cable TV network clients or convert the encoded and modulated RF signals into Ethernet data signals when receiving Ethernet data signals from the multiple cable TV network clients is described. The server comprises multiple APs (access points), wherein a load balance mechanism is used to the APs to choose an AP to connect a client according to the load information of each AP. 
         [0007]    In a third aspect, a server used to transmit Ethernet data signals from an Ethernet network to multiple cable TV network clients or receive Ethernet data signals from the multiple cable TV network clients is described. The server comprises multiple APs (access points), wherein there is at least one backup AP in the server used to monitor the work status of the other APs when the other APs work properly or to replace a broken down AP when the AP breaks down. 
         [0008]    In still another aspect, a client used to receive encoded and modulated RF signals from multiple APs in a cable TV network or transmit the encoded and modulated RF signals to an Ethernet network via the cable TV network is provided. The client comprises at least one modem which is used to receive synchronization information from the multiple APs to know the synchronous start of downlink transmission or an uplink transmission at the multiple APs, during the downlink transmission the modem being used to translate the encoded and modulated RF signals from the multiple APs into Ethernet data signals and during the uplink transmission the modem being used to translate the Ethernet data signals into the encoded and modulated RF signals. 
         [0009]    In a further embodiment, a system comprising multiple APs and multiple clients is described. Wherein the APs synchronously start a downlink transmission or an uplink transmission, and wherein during the downlink transmission the APs convert the Ethernet data signals into encoded and modulated RF signals and transmit the encoded and modulated RF signals to the multiple cable TV network clients, and during the uplink transmission the APs receive the encoded and modulated RF signals from the cable TV network clients and convert the encoded and modulated RF signals into the Ethernet data signals; the multiple clients are used to receive synchronization information from the multiple APs to know the synchronous start of downlink transmission or an uplink transmission at the multiple APs, during the downlink transmission the multiple clients being used to translate the encoded and modulated RF signals from the multiple APs into Ethernet data signals and during the uplink transmission the multiple clients being used to translate the Ethernet data signals into the encoded and modulated RF signals. 
         [0010]    In another aspect, a system used to transmit Ethernet data signals between an Ethernet network and a cable TV network is described. The system includes multiple APs and multiple clients, wherein the powers and the transmission rates of the transmission signals sent out from the multiple APs and the multiple clients are adaptable. 
         [0011]    In an aspect, a method used by a server to transmit data signals from an Ethernet network to multiple cable TV network clients or receive data signals from the multiple cable TV network clients is described, with the server including multiple APs. The method comprises steps of synchronously start a downlink transmission or an uplink transmission among all APs, wherein during the downlink transmission, the APs convert the Ethernet data signals into encoded and modulated RF signals and send out the encoded and modulated RF signals to the multiple cable TV clients; and during the uplink transmission, the APs ( 20 ) receive the encoded and modulated RF signals from the multiple cable TV clients ( 40 ) and convert the encoded and modulated RF signals into Ethernet data signals. 
         [0012]    These and other aspects, features and advantages will become apparent from the following description of non-limiting exemplary embodiments, which is to be read in connection with the accompany drawings. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0013]      FIG. 1  is a diagram illustrating the frame structure of a system for bidirectional data communication through CATV access network in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0014]    As illustrated in  FIG. 1 , it is an embodiment showing a system infrastructure for access to the internet through existing CATV cable network. Here the internet refers to Ethernet. At the server end of the system as shown by sign  100 , during the downlink transmission (from the server end  100  to the client end  100 ′), a Headend apparatus  10  is provided between the internet and the CATV network. Said Headend apparatus  10  comprises multiple access points  20  (AP 1 , . . . AP n ). The access points  20  are used to transform the Ethernet network signal received via a switch  12  into WiFi RF signal. The WiFi RF signals from the multiple access points  20  are combined together with CATV signal by a splitter  30 . Here the splitter  30  represents a set of power splitters and band splitters. Then the splitter  30  is connected to a cable  50 . The APs  20  in the embodiment provide data switching function over DataLink Layer of the OSI (Open System Interconnect) Reference Model. As shown in the  FIG. 1 , each client  40 , for example client  2 , at the remote client end  100 ′ of the CATV network, is provided with a splitter  60  for separating WiFi RF signal from analogy video signal of CATV, and transmitting relevant signals to modem  70  and the TV receiver  90  at client  2  respectively. Here, the splitter  60  can be replaced by power splitters and/or band pass filters. Finally, the data signal is translated by the modem  70  and sent to a PC  80  at client  2 . In this embodiment, client  2  is used just for explanation. Other clients  40  at the client end  100 ′ may have basically the same devices as client  2 . Of course, other devices known by those skilled in the art may be used too. 
         [0015]    During the uplink transmission (from the client end  100 ′ to the server end  100 ), data signal from the PC  80  at client  2  is first translated by modem  70  into WiFi RF signal and then transmitted by the splitter  60  to cable  50 . Finally the WiFi RF signal is translated by the associated AP  20  in the headend  10  into Ethernet signal and sent to the Ethernet network by the switch  12 . 
         [0016]    Accordingly, the following features will be implemented in the system for access to the internet through cable network of the embodiment to provide higher bandwidth capacity and better performance. 
         [0017]    Time Division and Synchronization 
         [0018]    In the above embodiment, there are several APs in the Headend  10  with each AP  20  being associated with one communication channel. When an AP  20  is receiving a weak signal from a modem  70  while another AP  20  is sending out a much stronger signal to the client  100 ′, the signal to be received by the AP  20  will be submerged by the signal to be sent out by the other AP  20 . To solve this problem, all APs  20  in the Headend  10  should work synchronously both during the uplink transmission (from the client end  100 ′ to the server end  100 ) and during the downlink transmission (from the server end  100  to the client end  100 ′), so that they can send out signals synchronously and receive signals synchronously. Because if the synchronization mechanism is used, when an AP  20  is sending out a strong signal through a channel, the others are also sending out signals via other channels. While when an AP  20  is receiving a weak signal the others may receive signals that are not very strong or no signal to receive. So the weak signal won&#39;t be submerged by the stronger one. To guarantee the synchronization of all APs  20 , a lot of methods can be used. For example, the APs  20  in the Headend  10  can be connected in a bus topological structure. One AP  20  serves as the master AP, and the others serve as slave AP. The master AP will send out a synchronization signal and/or a synchronization message to all slave APs to make all APs  20  work synchronously. At the same time, each AP  20  should send out a synchronization information to the modems  70  at the client end  100 ′ to synchronize the modems  70 . 
         [0019]    To implement the synchronization mechanism, TDMA (Time Division Multiple Access) method is necessary. In the present embodiment, the whole timeslots of each AP are separated into downlink transmission and uplink transmission. The APs  20  in the Headend  10  and the modems  70  communicate with each other during the respective uplink transmission or downlink transmission accordingly. 
         [0020]    Asymmetry 
         [0021]    In the system as shown in  FIG. 1 , the uplink and downlink transmission of the above embodiment system will employ different modulation methods (e.g. QAM, QPSK, BPSK, etc.) to support different data rates on Physical Layer of OSI (Open System Interconnect) Reference Model. The downlink and the uplink may have different transmitting power. 
         [0022]    The reason using asymmetry policy is that in the present cable TV access network, the distance between the Headend  10  and the modems  70  at the client end is long, so the signal attenuation is large. And also in this kind of system, the downlink transmission from the Headend  10  to multiple clients  40  at the client end  100 ′ and the uplink transmission from the multiple clients  40  at the client end  100 ′ to the Headend  10  are different. 
         [0023]    For example, at the client end  100 ′, within 5 MHz-2.5 GHz frequency domain, the signal power is weak, while the noise is decreased with the increase of the frequency. At the same time there is no signal transmitting sources with frequency band between 110 MHz and 862 MHz (CATV broadcast frequency band), and the power of signals at the receivers is mainly under 60 dBuV, and this facilitates the receipt of high frequency signals (for example, 800-1200 MHz), because the high frequency signals won&#39;t be affected much by the low power signals such as 60 dBuV signals. Meanwhile, at the Headend  10  (APs  20 ), the signal power within the frequency domain of 5 MHz-2.5 GHz is strong. Because the frequency band between 110 MHz and 800 MHz is full of transmitters (for example, digital TV, analog TV, etc.), the frequency band between 800 MHz and 1200 MHz is affected heavily even if the filters is used. So the transmitting power at the client end should be stronger than the transmitting power at the APs  20  of the Headend  10 , so as to decrease the effect of high noise caused by strong signal power to an AP  20 . While at the client end, the receiving devices at the frequency band of 50 MHz to 800 MHz usually don&#39;t perform filtering, so a over-high frequency signal (for example, 800-1200 MHz) may block the receipt of signal at the receiving devices. So the signal should not be very strong. If at the same time the attenuation is very high, the transmitting power at the APs of Headend should be strengthened to keep the transmitting power at the modem  70  of the client to be at a higher level. And thus the transmitting power of APs  20  at Headend  10  will be larger than the transmitting power of the modem  70  at client end. For example, when the attenuation of the cable is 70 dB, the downlink signal power is set up to 115 dBuV, and QAM64 (Quadrature Amplitude Modulation) is used, to get the optimal performance; at the same time, the uplink signal sent by modem is set up to 105 dBuv, and QAM16 or PSK (Phase Shift Keying) is used. In this case, Downlink power is larger than uplink power. Another example, when the attenuation of the cable is 50 dB, the downlink signal output by an AP  30  is set up to 100 dBuV, and QAM64 should be used, to get the optimal performance with lower power consumption; at the same time, the uplink signal output by modem  70  is also set up to 105 dBuV, QAM64 should be used. In this case, downlink power is weaker than uplink power. 
         [0024]    Backup 
         [0025]    In the Headend apparatus  30 , there is at least one backup AP  21  to monitor all the other APs  20 . When in the normal communication mode, the backup APs  21  only monitor the other APs  20 . And when there is an AP  20  breaks down, one of the backup APs  21  will turn from the monitoring status into working status to replace the broken down AP  20 . For example, the back up APs  21  can monitor all the other APs  20  through the synchronization frames sent by other APs  20  which operate in the normal communication mode. When all the monitored APs  20  under the monitoring domain send synchronization frames at the normal interval, the backup APs  21  will just stay in the backup status and don&#39;t send any synchronization frames. Once it is found that some AP  20  doesn&#39;t send out any synchronization frames for a period longer than a pre-defined timeout threshold, which is an indication that there is some problem with the specific AP  20 , one of the backup APs  20  will turn from the monitoring status into the communication status, and send the synchronization information on the cable access network to announce it is capable of communicating with the Modem  60 . In this way, the system will continue to provide normal communication functionality to the Modems in the network when some of the APs  20  have problems, and as a result, a more stable network is ensured. 
         [0026]    Load Management and Balance 
         [0027]    This mechanism means that the traffic load of the network can be shared by many APs in the same cable access network. 
         [0028]    Basically, there are some non-overlapping channels in Wi-Fi system and we denote the number of non-overlapping channels as n. In the cable access network with the same coverage, n APs can be deployed and each of them can operate in one of the non-overlapping channels. In the synchronization frame sent by an AP, the remained uplink bandwidth for further allocation will be encapsulated. Accordingly, the Modems  70  under this coverage will check all available channels to inspect the synchronization information sent by each AP  20 , select an AP  20  with the largest available uplink bandwidth for allocation, tune into the chosen AP&#39;s channel and send registration frame to associate with the chosen AP. When this load assignment and balance method is deployed, the available network bandwidth can be greatly increased for a group of Modems. 
         [0029]    Secondly, this function can be implemented by the APs  20  in the headend  10 . The entire traffic load can be coordinated by the APs  20  in the headend  10 , and the overloaded or unsuitable AP will reject it when a modem  70  tries to associate with the AP  20  (e.g. a modem  70  tries to connect APs when it is powered on), then the modem  70  selects another channel to try again circularly. 
         [0030]    For example, because there are three or more non-overlapping channels within the current 802.11 compliant WiFi solutions (For example, at least channel  1 ,  6  and  11 ), modems  70  at the client end will know the load condition of these three channels and choose a channel according to above load management and balance mechanism respectively to make sure the channels they use don&#39;t overlapping and have no interference. 
         [0031]    In the above embodiment, there can be a management server in the system to maintain and mange the whole access network system. It can provide user management, network line maintenance, network facility maintenance, failure management, performance management, topology management, configuration management, security management and failure/alarm management. 
         [0032]    Although the embodiments which incorporates the teachings of the present invention has been shown and described in detail here, those skilled in the art can readily revise many other varied embodiments that still incorporate these teachings. For example, the principle of the invention can also be used in MoCA (Multimedia over COAX Alliance) systems. It is noted that modifications and variations can be made by persons skilled in the art in light of the above teachings. It is to be understood that those units or devices described in the embodiments can be integrated in different ways have the similar effects.