Patent Publication Number: US-2013238682-A1

Title: Signal-equalizing system and method for multi-rate signal

Description:
BACKGROUND 
     1. Technical Field 
     The disclosure relates to signal-equalizing systems and, more particularly, to a signal-equalizing system for multi-rate signal and a signal-equalizing method adapted for the system. 
     2. Description of Related Art 
     An equalizer is utilized for reducing distortion in the course of transmission of a signal. However, the equalizer compensates one single rate signal to obtain low distortion, when a multi-rate signal is transmitted, the conventional compensation method of equalization does not satisfy multi-rate signal. 
     Therefore, what is needed is a signal-equalizing system for multi-rate signal to overcome the described shortcoming. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a signal-equalizing system for multi-rate signal in accordance with an exemplary embodiment. 
         FIG. 2  is a block diagram of a control unit of the system of  FIG. 1 . 
         FIG. 3  is a flowchart of signal-equalizing method adapted for the system of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a schematic view of a signal-equalizing system for multi-rate signal in accordance with an exemplary embodiment. The signal-equalizing system for multi-rate signal (hereinafter “the system  1 ”) includes a storage unit  10  and a control unit  20 . Each multi-rate signal can be transmitted in a number of different transmission rates. 
     The storage unit  10  stores the functions performed by the control unit  20 . The storage unit  10  further stores a number of compensation methods of equalization and a number of groups of equalizer parameters. 
     In the embodiment, the number of compensation methods of equalization is equal to three, that is, an average value compensation method, a minimum value compensation method, and a maximum value compensation method. When all differences among all transmission rates of the multi-rate signal are greater than a first preset value and channel loss in the course of transmission of the multi-rate signal is greater than a second preset value, the average value compensation method is set to obtain low distortion, thereby making sure there is a reliable transmission. When all differences among all transmission rates of the multi-rate signal are greater than the first preset value and channel loss in the course of transmission of the multi-rate signal is less than the second preset value, the minimum value compensation method is set to obtain low distortion, thereby making sure there is a reliable transmission. When all differences among all transmission rates of the multi-rate signal are less than the first preset value and channel loss in the course of transmission of the multi-rate signal is less than the second preset value, the maximum value compensation method is set to obtain low distortion, thereby making sure there is a reliable transmission. 
     The average value compensation method is defined as compensating the transmission rate of the multi-rate signal for an average value of channel loss values of all transmission rates of the multi-rate signal. The minimum value compensation method is defined as compensating the transmission rate of the multi-rate signal for the minimum value among the channel loss values of all transmission rates of the multi-rate signal. The maximum value compensation method is defines as compensating the transmission rate of the multi-rate signal for the maximum value among the channel loss values of all transmission rates of the multi-rate signal. 
     Taking a formula which is well known to illustrate how to obtain a group of equalizer parameters, y(n)=a*x(n)−b*x(n−1)−c*x(n−2) . . . , wherein y(n) represents a signal amplitude value after an equalizer compensates, variable a, b, c . . . represent equalizer parameters, and x(n) represents an amplitude value of the current output signal. Each multi-rate signal defines a time period, the time period is equal to the time between transmission of the current signal and transmission of a next signal, for example, 5 seconds, thus, x(n−1) represents an amplitude value of the output signal 5 seconds ago, x(n−2) represents an amplitude value of the output signal 10 seconds ago. The output signal during each time period is compensated by the compensation method. When the group of equalizer parameters is calculated according to the formula to obtain the lowest distortion by comparing an amplitude value of the multi-rate signal before transmitting with after the equalizer compensating, the group of equalizer parameters is optimal. 
     The control unit  20  is configured for controlling the system  10  to select a compensation method adapted for a current transmission of multi-rate signal from the compensation methods of equalization, calculating all the number of groups of equalizer parameters adapted for the current transmission of multi-rate signal, and acquiring one group of equalizer parameters which possesses the lowest distortion for the multi-rate signal according to calculating results. As shown in  FIG. 2 , the control unit  20  further includes a receiving module  100 , a selecting module  101 , a loading module  102 , a determination module  103 , a timing module  104 , an evaluation module  105 , and an output module  106 . All modules perform corresponding functions as shown in  FIG. 3 . 
       FIG. 3  is a flowchart of signal-equalizing method adapted for the system of  FIG. 1 . 
     In step S 10 , the storage control module  100  stores the number of compensation methods of equalization, the number of groups of equalizer parameters, and at least one multi-rate signal. For example, the multi-rate signal is a serial attached SCSI (SAS) differential one which can be transmitted in two transmission rates, for example, 6 Gbit/s and 1.5 Gbit/s. 
     In step S 11 , the selecting module  101  selects a multi-rate signal from the at least one multi-rate signal in response to user input and acquires all transmission rates and the time period of the multi-rate signal. When the multi-rate signal is selected, the transmission rates and the time period of the multi-rate signal are correspondingly generated. The multi-rate signal may be a SAS one or a SATA one. If the storage control module  100  stores a multi-rate signal, the procedure does not perform the step by the selecting module  101 . 
     In step S 12 , the loading module  102  loads output documents of a signal simulation software, wherein the output documents include the amplitude values of output signals during each time period and channel loss values of all transmission rates of the multi-rate signal, and the signal simulation software is used to simulate and analyze signal transmission of to obtain the amplitude values of output signals during each time period. 
     In step S 13 , the determination module  103  selects a compensation method based on channel loss in the course of the multi-rate signal transmitted and differences among all transmission rates of the multi-rate signal from the number of compensation methods of equalization. 
     In step S 14 , the calculating module  104  calculates a compensation value during each time period based on channel loss values of all transmission rates of the multi-rate signal and the selected compensation method. For example, the multi-rate signal is a SAS differential one which includes two transmission rates, for example, 6 Gbit/s and 1.5 Gbit/s, when the SAS differential signal is transmitted via 6 Gbit/s, the channel loss value is 9 dB, and when the SAS differential signal is transmitted via 1.5 Gbit/s, the channel loss value is 3 dB. The determination module  103  selects the average value compensation method based on the channel loss values of the SAS differential signal and differences between the two rates, and the calculating module  104  calculates the compensation value during each time period which is equal to 6 dB((9+3)/2). 
     In step S 15 , the calculating module  104  further compensates the compensation value for the output signals during each time period and calculates the signal amplitude values of all the number of groups of equalizer parameters after the equalizer compensates by the formula. 
     In step S 16 , the evaluation module  105  compares an amplitude value of the multi-rate signal before transmitting with after the equalizer compensates for each group of equalizer parameters to obtain a distortion and evaluates one group of equalizer parameters which distortion is lowest, the group of equalizer parameters is optimal for the multi-rate signal. 
     In step S 17 , the output module  106  outputs the optimal group of equalizer parameters of the multi-rate signal. 
     Although the present disclosure has been specifically described on the basis of the exemplary embodiment thereof, the disclosure is not to be construed as being limited thereto. Various changes or modifications may be made to the embodiment without departing from the scope and spirit of the disclosure.