Orthogonal variable spreading factor (OVSF) code assignment
The invention includes a system and methods for orthogonal variable spreading factor (OVSF) code assignment, de-allocation and code tree pruning. The invention also includes OVSF code identification and storage schemes. Embodiments are provided for code tree pruning, code assignment and de-allocation. These embodiments apply to both slotted and non-slotted code division multiple access systems.
1. A method for reassigning codes of an orthogonal variable spreading factor code tree in code division multiple access communications to a new call, the code tree having a plurality of codes at differing spreading factors and having a plurality of branches between the codes of different spreading factors, if a particular code of the code tree is assigned, a lower spreading factor code of the code tree connected to that code by one of the branches is blocked from assignment, if a code of the code tree is blocked, a code of the tree of a lower spreading factor connected to that code by one of the branches is blocked from assignment, the method comprising:
finding a code of a highest spreading factor in a time slot;
determining if a leftward code of the highest spreading factor code in the time slot is available;
relocating the new call into the leftmost available code in the time slot; and
repeating, for a next lower spreading factor, finding a code of the next lower spreading factor in the time slot, determining if a leftward code is available in the time slot, and relocating the new call to the leftward available code.
2. The method of claim 1 in wireless communications using multiple time slots, and further comprising:
for another time slot:
finding a code of a highest spreading factor in the other time slot;
determining if a leftward code of the highest spreading factor code in the other time slot is available;
relocating the new call into the leftmost available code in the other time slot; and
repeating, for a next lower spreading factor, finding a code of the next lower spreading factor in the other time slot, determining if a leftward code is available in the other time slot, and relocating the new call to the leftward available code in the other time slot.
3. The method of claim 2 wherein the other time slot is a time slot adjacent to the first time slot in a rightward direction.
4. The method of claim 1 further comprising:
stopping the method if the number of relocations reaches a predetermined number.
5. The method of claim 1 wherein the method is invoked when a predefined number of new call arrivals is received.
6. A method for reassigning codes of an orthogonal variable spreading factor code tree used in code division multiple access communications to a new call, comprising:
selecting a first code in the code tree of a highest spreading factor in a timeslot to be evaluated and assigning the first code to the new call;
searching a subsequent time slot if there are no available codes of that spreading factor in the first timeslot;
determining if the new call can be relocated to a different code in the spreading factor;
relocating the new call to the different code in the spreading factor, if possible;
selecting the next code in the spreading factor and repeating the determining; and
selecting a first code in the next lower spreading factor if there are no more codes in a current spreading factor, and repeating the determining.
7. The method according to claim 6 , wherein the first code is a leftmost code in the tree.
8. The method according to claim 7 , wherein the relocating includes relocating the new call to a code to the left in the tree.
9. The method according to claim 7 , wherein the relocating includes relocating the new call to a code to the right in the tree.
10. The method according to claim 6 , wherein the first code is a rightmost code in the tree.
11. The method according to claim 10 , wherein the relocating includes relocating the new call to a code to the left in the tree.
12. The method according to claim 10 , wherein the relocating includes relocating the new call to a code to the right in the tree.
13. The method according to claim 6 , wherein the searching is not performed, whereby the method only reassigns the new call to a code within a single timeslot.
14. The method according to claim 6 , wherein the method is performed for each new call.
15. The method according to claim 6 , wherein the method is performed periodically.
16. The method according to claim 6 , wherein the method limits the number of code reassignments to the new call.
17. The method according to claim 6 , further comprising:
evaluating a fragmentation parameter of the code tree; and
performing the method if the fragmentation parameter exceeds a threshold.