BRIEF DESCRIPTION OF THE DRAWINGS
The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:
FIG. 1A shows schematically a typical, known, point to multi-point communication system;
FIG. 1B shows data packets arriving in order at the receiver of FIG. 1A;
FIG. 2 shows schematically a typical, known, passive optical network (PON) communication system;
FIG. 3 shows a typical receiver unit used in a system as that of FIG. 1;
FIG. 4 shows a typical situation when a Ranging window is allocated for a new user to join the network;
FIG. 5 shows a commonly known packet structure;
FIG. 6 shows a typical existing Ranging method;
FIG. 7 shows a flow chart of a preferred embodiment of the Ranging method of the present invention;
FIG. 8 shows an exemplary propagation delay determination process following the method of FIG. 7.
DETAILED DESCRIPTION OF THE INVENTION
The present invention discloses a robust, periodic Ranging method, which requires no additional hardware for its implementation (except for the ability to receive data), and which can always guarantee successful Ranging. A preferred embodiment of the Ranging method of the present invention is described with reference to the flow chart shown. Each new user who wants to join the network transmits a Ranging packet (in the ranging window), which consists of a Header and a Payload (described in FIG. 5). After the start of a ranging window in step 702, the MAC optionally activates the AFE (i.e. sends the required control signals Reset AFE 310 and Reset CDR 316 to) in step 704, and optionally searches for a Preamble (step 706) of the Ranging packet. The “optional” term means that AFE activation may not be needed for some types of AFEs, or that the search for a Preamble is skipped. If no Preamble is found in a check step 708 or if a first timeout period TO1 is exceeded, the AFE checks if a “global” timeout TO3 is exceeded in step 709, and if NO, the process returns to step 704. If YES in step 709, the Ranging process is stopped (being unsuccessful). If a Preamble sequence is found in step 708, the AFE starts looking for a Delimiter of the Ranging packet in step 710. Ranging packet data (such as the abovementioned Preamble and Delimiter) is also referred to herein as “expected data”. If no Delimiter is found in a check step 712 or if a second timeout period TO2 is exceeded, the AFE checks if TO3 is exceeded in step 713, and if NO, the process returns to step 704. If YES in step 713, the Ranging process is also stopped (being unsuccessful). If a Delimiter is detected in step 712, the MAC receives the data, registers the user and estimates the user's propagation delay (to the receiver). In both cases of failure (YES) in steps 709 and 713, the ranging process needs to be restarted from step 702 in the next ranging window.
In an exemplary case, the Ranging packet is set as follows.
Guard time: 32 bits.
Preamble: 600 bits.
Delimiter: 20 bits.
TO1: 200 bits
TO2: 250 bits
TO3: Equal to the size of the ranging window.
FIG. 8 shows schematically an exemplary Ranging process. Since the arrival time of the Ranging packet is not known to the receiver, the receiver starts operating according to the Ranging method disclosed herein. First, it activates its AFE and start searching for a Preamble. In the figure, the Ranging packet of the single new user is shown as not having been found (not arrived) in a period up to TO1. Therefore, after TO1, the process is repeated for a second time, in which the Ranging packet is still not found. Therefore, after another TO1, the process is repeated for a third time. In this third “round” (still in the same ranging window) a Preamble of the ranging packet is found, so the receiver looks for a Delimiter. The Delimiter which follows the Preamble is found, so the ranging process ends successfully: the receiver can correctly receive the data, the user can register to the network and the propagation delay can be estimated.
The process described above and clearly illustrated in FIGS. 7 and 8 is “literative”, in a cyclical or “repetitive” sense. In contrast with prior art processes, which start once per ranging window, the process here repeats itself in a ranging window if a match between expected data and received data is not found. The iterative (repetitive) process in a ranging window ends only if the match is found or if predetermined timeouts are exceeded.
After the process described in FIG. 8 is done, the propagation delay determination can follow (i.e. the receiver or the user can calculate the difference between the sending time at the user and the arrival time). After this point, the Ranging process is done and both the receiver and the user are now in a Steady State mode or regime of operation. In steady state operation (after the propagation delay is known to the system), the arrival time of each packet is known to the system. For this reason the logic unit can supply control signals (i.e. Reset AFE 310 and Reset CDR 316) to both the AFE and to the CDR exactly when required (usually at the beginning of data packet). Note that these control signals can not be supplied with exact timing when in Ranging mode, because of the unknown propagation delay.
In summary, the method described herein enables to range and find the propagation delay with almost any existing system and AFE. No dedicated expensive hardware is required for the Ranging. The main idea is periodic trial and error. The receiver activates its AFE and CDR and searches for a special sequence (a Preamble and Delimiter). If it does not find such a sequence, the process (AFE activation and search) periodically start from the beginning. This process ends when finding the delimiter or after TO3 (unsuccessful). The method, by tuning certain parameters, can meet the requirement of almost any known AFE. It also proved itself as a very robust method in a noisy environment.
The disclosed ranging method requires cheaper and easier to implement AFE and CDR components. It is also more robust in case of noisy channels, when a high BER (Bit Error Rate) is expected.
All patents mentioned in this specification are incorporated herein in their entirety by reference into the specification, to the same extent as if each individual patent was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention.
While the invention has been described with respect to a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of the invention may be made. In particular, the Ranging process disclosed herein may work without step 704 (activate AFE) in cases where the AFE does not require activation (as there are different kinds of AFE). It may also work without step 706, directly searching for a Delimiter.
Patent Application
20080069562
