Bit-Level Spreading Sequence Hopping for Orthogonality
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Solution Overview
Problem
In wireless systems like WCDMA and CDMA2000, high Doppler channels and the near-far problem compromise the orthogonality of bit-level spreading sequences, leading to interference and performance penalties, especially in scenarios where base stations transmit to mobile stations with varying distances and power levels.
Innovation Solution
Assigning a unique bit-level spreading sequence to each slot of a time interval using a sequence-hopping pattern, which can be generated through cyclic, pseudo-random, or intelligent processes, to maintain orthogonality and reduce near-far interference by changing the spreading sequence from slot to slot.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed bit-level spreading sequence is used for control signals across all slots, then the system complexity is low and implementation is simple, but orthogonality is compromised in high Doppler channels leading to near-far interference
Solution Approach 1:
The patent applies dynamics by making the bit-level spreading sequence time-varying through sequence hopping. Instead of using a fixed sequence, the system dynamically changes the spreading sequence assigned to each mobile station across different time slots according to a hopping pattern. This dynamic adaptation maintains orthogonality in high Doppler channels where channel conditions change rapidly, resolving the contradiction between reliability and complexity by introducing manageable temporal variation.
Solution Approach 2:
The patent implements periodic action through sequence hopping patterns that periodically change the bit-level spreading sequences assigned to mobile stations. The sequences hop according to predetermined periodic patterns, ensuring that orthogonality is maintained over time while providing a structured, predictable approach that limits complexity. This periodic reassignment of sequences addresses the orthogonality maintenance requirement without requiring continuous complex adaptation.
2Reliability
If sequence hopping is implemented to maintain orthogonality in high Doppler channels, then reliability of control signals improves, but the complexity of sequence assignment and management increases
Solution Approach 1:
The patent applies preliminary action by pre-defining sequence hopping patterns and assigning them to mobile stations before transmission begins. The base station and mobile stations have predetermined knowledge of which sequences will be used in which time slots, eliminating the need for real-time complex sequence selection. This pre-planned approach maintains control signal separation through sequence hopping while significantly reducing the operational complexity of sequence management.
Solution Approach 2:
The patent uses copying by having multiple mobile stations use identical or related sequence hopping patterns. Instead of requiring unique complex sequences for each station, the system can copy proven effective hopping patterns across different users, simplifying the management burden at the base station while maintaining the orthogonality benefits of sequence hopping for control signal separation.
3Ease of operation
If the same spreading sequence is used for all mobile stations, then the system is easy to implement, but near-far interference occurs when mobile stations are at different distances from the base station
Solution Approach 1:
The patent applies local quality by assigning different bit-level spreading sequences to different mobile stations through sequence hopping. Each mobile station receives a locally optimized sequence assignment that is tailored to its specific channel conditions and distance from the base station. This localized differentiation eliminates near-far interference while maintaining reasonable implementation complexity through the use of structured hopping patterns rather than completely arbitrary sequence assignments.
Data Source
AI summary
A method and apparatus for code multiplexing one or more control signals onto a shared control channel. According to the present invention, a control signal for transmission from a base station to a mobile station terminal is repeated in each slot of a predetermined time interval. The control signal in each slot is spread using a bit-level spreading sequence, where the bit-level spreading sequence varies from slot to slot according to a predefined sequence-hopping pattern. The spread control signals generated for transmission to each mobile station terminal are then combined and spread using a common channelization code.