Memory-efficient ADSL transmission in the presence of TCM-ISDN interferers

#This application claims priority under 35 U.S.C. Section 120 to U.S. patent application Ser. No. 10/342,059 filed Jan. 14, 2003. Said application herein incorporated by reference.

#Telephone companies offer customers a number of ways to transport data. One popular way is called Asymmetric Digital Subscriber Line (ADSL). In ADSL, a small portion of the frequency spectrum is used for communicating data from the customer to the central office, and a much larger portion of the frequency spectrum is used for communicating data from the central office to the customer.

#Discrete multi-tone (DMT) modulation is used within each portion of the frequency spectrum, i.e., data are carried on equally-spaced carrier signals. The combined number of carrier signals from both portions of the spectrum is implementation-dependent. ADSL implementations that comply with the ITU-T G.992.1 standard have 256 carrier signals, while implementations that comply with the ITU-T G.992.2 standard have 128 carrier signals. Future implementations are expected to have 512 or even 1024 carrier signals (see, e.g., ITU-T G.992.5).

#A better understanding of the present invention can be obtained when the following detailed description of the preferred embodiment is considered in conjunction with the following drawings, in which:

#FIG. 1 is a functional-block diagram of one ADSL modem embodiment;

#FIG. 2 is a schematic block diagram of the ADSL modem embodiment of FIG. 1;

#While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.

#Turning now to the figures, you will find a functional block diagram of one embodiment of an ADSL (“Asymmetric Digital Subscriber Line”) modem 100 in FIG. 1. A control and data bus conveys to modem 100 data that is to be transmitted. A multiplexer/synchronization controller 102 routes the data via two paths: a fast path, and an interleaved path. Data that needs to be sent with a low latency is routed through the fast path, while data that needs to be sent with a low error rate is routed through the interleaved path. The two data types may be intermixed and identified by a bus protocol.

#The fast path data is delivered to CRC (cyclic redundancy code) block 104, which aligns the data into frames and appends a CRC checksum value. The interleaved path data is delivered to an independent CRC block 106 for the same processing. CRC blocks 104 and 106 forward the data frames to scrambling and forward error correction (FEC) blocks 108 and 110, respectively.