Apparatus and method for digital data transmission using orthogonal codes

A ranging process for use in a distributed digital data communication system requiring frame synchronization of frames of code division multiplexed data transmitted to a central unit transceiver by a plurality of remote unit transceivers at physically different locations in a shared transmission media, comprising the steps:

• (1) transmitting data downstream from said central unit transceiver to said remote unit transceivers;
• (2) in each remote unit transceiver which has already achieved frame synchronization transmitting upstream frames each of which is separated from its neighboring frames by a small gap that represents less than 15% of the total duration of each said upstream frame interval, each upstream frame carrying interleaved, code division multiplexed data that has been encoded with error detection and correction bits, each said upstream frame being transmitted to said central unit transceiver using whatever transmit frame timing delay value each remote unit transceiver that has achieved frame synchronization previously determined was necessary to achieve frame synchronization such that each such upstream frame transmitted to said central unit transceiver arrives with its frame boundaries aligned in time with the frame boundaries of upstream frames transmitted by other remote unit transceivers that have also achieved frame synchronization;
• (3) in a remote unit transceiver that has not yet achieved frame synchronization selecting an initial value for a transmit frame timing delay, and then, without invitation from said central unit transceiver and regardless of whether other remote unit transceivers are or are not starting the frame synchronization process, determining the a transmit frame timing delay that will result in frame synchronization for upstream frame transmissions from said remote unit transceiver by transmitting from said remote unit transmitter to said central unit transceiver a ranging signal during each upstream frame with properties such that it can be detected in the presence of noise even if it arrives during reception of upstream frames transmitted by other remote unit transceivers that have already achieved frame synchronization, said transmission of said ranging signal carried out using a said initial transmit frame timing delay value;
• (4) in said central unit transceiver monitoring each gap in at least some of said upstream frames for a received upstream ranging signal, and transmitting data downstream to said remote unit transceiver that informs said remote unit transceiver whether or not said ranging signal has arrived at said central unit transceiver in an upstream frame gap;
• (5) continuing to adjust said transmit frame timing delay value in said remote unit transceiver until a message is received from said central unit tranceiver that the ranging signal has arrived in said small upstream frame gap;
• and
• (6) thereafter, if necessary, adjusting said transmit frame timing delay value in accordance with an instruction message from said central unit transceiver such that each said ranging signal arrives at a precise location in said small upstream frame gap.

A process for ranging in any digital data communication system requiring frame synchronization of frames transmitted over a shared transmission media by a plurality of physically distributed remote transceivers to a central transceiver such that all such frames arrive at said central transceiver with their frame boundaries aligned in time, comprising:

• (1) in each remote transceiver which has not achieved frame synchronization, receiving a downstream reference signal that marks a reference time which lies within a gap during each frame during which no transmission of payload data is allowed, and establishing a first trial and error delay value relative to said reference time for transmission of a ranging signal to said central transceiver and transmitting said ranging signal;
• (2) at said central transceiver listening for said ranging signals from said remote transceivers during each upstream frame and transmitting a status message to said remote transceivers that indicate if a ranging signal has been detected during said gap or not, and, if so, requesting transmission of a signature;
• (3) in each said remote transceiver which has not achieved frame synchronization, doing substantially all the processing necessary to achieve frame synchronization by receiving said status message and, if said status message indicates no ranging signal was received during said gap, adjusting said trial and error delay value and transmitting another ranging signal in response to the next reference signal received from said central transceiver, and continuing this receipt of a status message and trial and error adjustment until a status message is received indicating a ranging signal has been received during said gap and requesting transmission of a signature, and then holding the delay value steady at its then existing value and using said delay value to transmit a signature that identifies said remote transceiver;
• (4) in said central transceiver, listening for said signature and determining from it if more than one remote transceiver's ranging transmissions are being received during the same gap, and, if so, transmitting a downstream contention message so indicating and requesting each remote transceiver which has not achieved frame synchronization to execute a contention resolution protocol that will cause some of said remote transceivers to temporarily suspend further attempts to achieve frame synchronization, and if the signature indicates that only one remote transceiver's ranging transmissions are being received during said gaps, identifying the particular remote transceiver that sent said signature and sending a downstream fine tuning message indicating the identity of the remote transceiver to whom the fine tuning message is directed and by how much and in which direction to adjust that remote transceiver's trial and error delay value such that said ranging transmissions will be received at a predetermined reference time within each gap;
• (5) in each remote transceiver that is attempting to achieve frame synchronization, receiving said contention message or said fine tuning message, and, if a fine tuning message is received identifying the particular remote transceiver that sent said signature, adjusting said trial and error delay value in accordance with the fine tuning message and commencing transmissions of frames of upstream payload data using this value for said trial and error delay value as a time reference at which to start transmission of each upstream frame, and if a contention message is received, randomly deciding whether or not to continue ranging and, if a decision to continue ranging has been made, retransmitting said signature using the same value for said trial and error delay as was used for the last signature transmission from this remote transceiver;
• (6) in said central transceiver, monitoring said gaps for receipt of a signature, and, if only one remote transceiver's signature is received in said gap or gaps, identifying said remote transceiver and transmitting a fine tuning message to said remote transceiver identifying it and instructing it by how much and in which direction to adjust said trial and error delay value, and if more than one signature is received, repeating steps (4), (5) and (6) until only one signature is received and a fine tuning message has been sent to the remote transceiver having that signature, but if no signature has been received, sending a re-execution message requesting all remote transceivers that have not yet achieved frame synchronization to re-execute their contention resolution protocols to again randomly decided whether to continue ranging or to stop ranging which will cause some remote transceivers to resume the ranging process;
• (7) in any remote transceiver which has decided to continue ranging or resume ranging, retransmitting its signature using the same delay as was used the last time the signature was transmitted;
• and
• (8) if no more than a predetermined number of attempts have been made to achieve frame synchronization, repeating steps (6), (7) and (8) until frame synchronization has been achieved, but if more than a predetermined number of attempts have been made to achieve frame synchronization without success, repeating steps (1) through (8).

A method of achieving frame synchronization in a distributed digital data communications network implemented on a hybrid fiber coax cable TV network having a central transceiver coupled by an optical fiber link to an optical node which is directly coupled to one or more remote transceivers and is coupled by a plurality of coaxial cable links to a plurality of remote transceivers, comprising:

• transmitting a barker code or other reference signal, hereafter referred to as the reference signal, during every downstream frame of data transmitted from said central transceiver to said remote transceivers, said reference signal transmitted at a time relative to the beginning of each downstream frame established by a first delay value T.sub.cu ;
• at a remote transceiver directly coupled to said optical node, responding to receipt of said reference signal by transmitting a ranging signal at a first remote delay value in an attempt to cause said ranging signal to arrive at said central transceiver during a gap between frames which is some integer number of frames in the future following the frame during which said reference signal was transmitted where every downstream frame is followed by a gap during which no payload data is transmitted and every upstream frame is numbered and is the same size as the downstream frames and is followed by a gap also where the first and all subsequent downstream frames are offset in time from the first and all subsequent upstream frames, said first remote delay value set at an interval T.sub.ru which is equal to
• T.sub.near =T.sub.F -T.sub.u
• where the mathematical relationship that defines the gap which is an integer n frame times, T.sub.F, into the future to which all the remote transcievers attempt to align is given by
• TTA=T.sub.cu +T.sub.ru +2.times.T=constant=n.times.T.sub.F
• where
• TTA=the total turnaround time from the central transceiver to the farthest remote transceiver coupled by a coaxial cable to said optical node, and
• T.sub.ru =the delay imposed by the furthest remote transceiver from said central transceiver along said fiber optic link and coaxial cable link before transmitting said ranging signal;
• 2.times.T.sub.P =two times the propagation delay T.sub.P from said central transceiver to the furthest remote transceiver from said central transceiver along said fiber optic link and coaxial cable link;
• n.times.T.sub.F =an integer multiple of the frame interval T.sub.F ;
• and wherein there are three additional requirements imposed with respect to how much delay said central transceiver and said remote transceivers must be able to impose, the first of which is:
• T.sub.cu =(T.sub.d +T.sub.u)modulo T.sub.F
• where
• T.sub.d =the span of the network which is equal to the quantity (TTA.sub.2 -TTA.sub.1) where TTA.sub.2 is equal to the total turnaround propagation time for a signal to propagate from the central transceiver to the farthest remote transceiver and back and TTA.sub.1 equals the total turnaround propagation time for a signal to propagate from the central transceiver to the nearest remote transceiver and back and modulo T.sub.F equals the remainder of ##EQU1## and where T.sub.u equals the uncertain additional propagation delay caused by network expansion, the second requirement being:
• T.sub.far >T.sub.u
• where
• T.sub.far =the small possible T.sub.ru of the farthest remote transceiver which is equal to the smallest possible delay which can be imposed by the farthest remote transceiver, and where the third requirement is:
• T.sub.near <T.sub.F -T.sub.u
• where T.sub.near is equal to the maximum possible T.sub.ru of the nearest remote transceiver;
• and
• assuming said remote transceiver which had its delay value T.sub.ru set equal to T.sub.near =T.sub.F -T.sub.u does not hit any gap with its ranging signal, adjusting the delay value T.sub.cu of said central transceiver until the remote transceiver which had its delay value T.sub.ru set equal to T.sub.near =T.sub.F -T.sub.u does hit a gap with its ranging signal, thereby causing the condition T.sub.cu =(T.sub.d +T.sub.u) modulo T.sub.F to be true thereby indicating that the central transceiver has adjusted its delay value T.sub.cu adequately to compensate for the uncertain amount of propagation delay T.sub.u caused by network expansion.