CDMA Forward Link Transmission Using Code-Space Expansion
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Solution Overview
Problem
CDMA2000 and WCDMA systems face capacity limitations and intra-sector interference issues, leading to signal degradation and reduced throughput in wireless communication systems.
Innovation Solution
Implementing time-sharing techniques for orthogonal codes, such as Walsh Codes, and code-combining soft/softer handoff across sectors to increase code-space dimensions on the downlink, allowing for earlier decoding and reduced intra-sector interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple carrier frequencies are used to transmit more data, then bandwidth and throughput are improved, but power allocation difficulty increases and signal degradation occurs
Solution Approach 1:
The data stream is segmented into multiple components that are transmitted on different carrier frequencies. Each component can be independently power-controlled, simplifying the power allocation problem while maintaining high throughput through parallel transmission.
Solution Approach 2:
The system dynamically allocates power and resources across multiple carriers based on channel conditions. This dynamic adaptation allows the system to optimize throughput while managing power distribution complexity through real-time adjustments rather than static allocation.
2Quantity of substance
If Quasi-Orthogonal Functions (QOF) are introduced to solve capacity problems, then code-space capacity is improved, but intra-sector interference increases
Solution Approach 1:
The patent converts the potentially harmful intra-sector interference into a beneficial signal combining opportunity. By using code-combining soft/softer handoff techniques, signals that would otherwise be interfering are combined constructively at the mobile station, improving capacity while neutralizing the interference problem.
Solution Approach 2:
The mobile station acts as an intermediary that receives and combines signals from multiple base stations using different codes. This intermediary combining process allows QOF-based capacity expansion while managing intra-sector interference through coordinated signal processing at the receiver.
3Quantity of substance
If WCDMA assigns extra PN codes to the same cell to solve capacity problems, then code-space capacity is improved, but intra-sector interference increases
Solution Approach 1:
The patent transforms the intra-sector interference caused by multiple PN codes into a beneficial diversity effect. Through code-combining techniques at the mobile station, the multiple coded signals are combined to improve capacity while the interference is converted into signal diversity that enhances reception reliability.
4Quantity of substance
If time-sharing techniques and code-combining are implemented, then code-space dimensions are increased and intra-sector interference is reduced, but system complexity increases
Solution Approach 1:
The patent merges time-sharing of orthogonal codes with code-combining soft/softer handoff techniques into a unified approach. This integration increases code-space dimensions by allowing multiple users to share codes temporally while the combining technique manages the complexity through coordinated signal processing across base stations and mobile stations.
Data Source
Figure 1A
Figure 1B
Figure 1C~1D
AI summary
A method for processing forward link channel signals generated by a CDMA base station includes time sharing by several mobile stations of spreading codes, which are orthogonal codes such as Walsh Code, and code-combining soft/softer handoff across sectors in the mobile station active set to increase dimensions on the CDMA2000 and WCDMA downlink while minimizing intra-sector interference. Since different parts of a packet or frame are transmitted to the user by the different base stations in the active set, earlier decoding and therefore early packet termination is enabled.