Methods for assigning scrambling codes and reducing interference in telecommunications networks
Example methods use secondary scrambling codes in telecommunications networks. The secondary scrambling codes are assigned to mobile stations and channels used by mobile stations that are not adversely affected by the use of secondary scrambling codes. By assigning secondary scrambling codes additional users can utilize telecommunications networks with unique scrambling codes without reducing quality of service or increasing resource consumption. Example methods also reduce interference between mobile stations in the telecommunications networks.
1. A method of reducing interference in a multi-antenna wireless telecommunications network using primary and secondary scrambling codes, the method comprising:
selecting, by a base station, a candidate set of mobile stations among a plurality of candidate sets of mobile stations based on a code weight correlation associated with each candidate set; wherein
each candidate set includes at least a first mobile station assigned a primary scrambling code and at least a second mobile station assigned a secondary scrambling code, and
the code weight correlation associated with each candidate set is a correlation between code weights associated with mobile stations in the candidate set; and
allocating, by the base station, wireless communication resources to the mobile stations in the selected candidate set.
2. The method of claim 1 , wherein the selecting step selects the candidate set associated with a minimum code weight correlation among the code weight correlations.
3. The method of claim 1 , wherein the code weight correlation for each candidate set is an inner product of the code weights associated with the mobile stations in the candidate set.
4. The method of claim 1 , further comprising:
generating, by the base station, a sum rate metric for each candidate set based on a signal-to-interference and noise ratio (SINR) indicator received from the mobile stations within the candidate set, the sum rate metric being indicative of the code weight correlation for the candidate set; wherein
the selecting step selects the candidate set having a minimum code weight correlation based on the generated sum rate metrics.
5. The method of claim 4 , wherein the maximum sum rate metric corresponds to the minimum code weight correlation.
6. The method of claim 4 , further comprising:
determining, by the base station, an achievable rate based on the signal-to-interference and noise ratio (SINR) indicator for each of the plurality of mobile stations; and wherein
for each candidate set, the generating step generates the sum rate metric based on the determined achievable rate for each mobile station in the candidate set.
7. The method of claim 6 , wherein, for each of the plurality of mobile stations, the determining step determines the achievable rate by mapping the received SINR indicator to an achievable rate using a look-up table.
8. The method of claim 4 , wherein the SINR indicator is a channel quality indicator (CQI).
9. The method of claim 1 , wherein, for each candidate mobile station, the code weight is calculated to minimize SINR at the mobile station.
10. The method of claim 1 , wherein the allocating step comprises:
scheduling the mobile stations in the selected candidate set for concurrent or simultaneous transmission.
11. The method of claim 1 , further comprising:
first determining if a primary scrambling code is available for the first mobile station requesting network access;
assigning the first mobile station a primary scrambling code if the determining step determines that a primary scrambling code is available;
generating the secondary scrambling code if the determining step determines that a primary scrambling code is not available; and
assigning the first mobile station the generated secondary scrambling code if the determining step determines that a primary scrambling code is not available.
12. The method of claim 11 , further comprising:
second determining if the first mobile station is compatible with the secondary scrambling code, if the primary scrambling code is not available;
generating the secondary scrambling code if the second determining step determines that the first mobile station is compatible with the secondary scrambling code; and
assigning the first mobile station the generated secondary scrambling code if the second determining step determines that the first mobile station is compatible with the secondary scrambling code.
13. The method of claim 12 , wherein generating the secondary scrambling code includes applying an offset to the primary scrambling code such that some non-orthogonality exists between the primary scrambling code and the secondary scrambling code.