CDM-TDM Hybrid Control Channel Multiplexing
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Solution Overview
Problem
Current wireless communication systems face inefficiencies in control channels, particularly in CDMA systems, where peak power requirements are often unattainable, and there is a need for more efficient control channels that can reach multiple mobile stations while optimizing system capacity and reducing interference.
Innovation Solution
The implementation of Code Division Multiplexing (CDM) and Time Division Multiplexing (TDM) techniques to encode and combine symbol streams, allowing for efficient transmission to multiple mobile stations, thereby reducing peak power requirements and enhancing system capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If Time Division Multiplexing (TDM) is used to multiplex control channels for multiple mobile stations, then the control channel can reach multiple mobile stations, but the peak power requirements become unattainable and system capacity is reduced
Solution Approach 1:
The patent combines TDM and CDM techniques to multiplex control channels. Multiple mobile station command sequences are first time-division multiplexed into separate time slots, then code-division multiplexed using orthogonal covering codes. This hybrid approach allows the control channel to reach multiple mobile stations while reducing peak power requirements compared to pure TDM, because the orthogonal codes provide signal separation that reduces the need for high peak power in each time slot.
Solution Approach 2:
The patent creates a composite multiplexing scheme by combining two different multiplexing techniques (TDM and CDM) into a unified control channel structure. The command sequences for multiple mobile stations are processed through both time-division and code-division multiplexing layers, creating a composite signal structure that leverages the advantages of both methods while mitigating their individual disadvantages, particularly the high peak power requirement of TDM.
2Productivity
If Code Division Multiplexing (CDM) is used to transmit control channels to multiple mobile stations, then system capacity increases, but interference increases and quality of service for delay-sensitive services deteriorates
Solution Approach 1:
The patent segments the control channel transmission by allocating separate orthogonal covering codes to different mobile stations. Each mobile station's command sequence is encoded with a unique orthogonal code, which segments the overall signal into orthogonal components. This segmentation reduces interference between different mobile station commands while maintaining high system capacity, as orthogonal codes provide perfect separation in ideal conditions.
Solution Approach 2:
The patent applies different orthogonal covering codes to different portions of the control channel signal corresponding to different mobile stations. Each mobile station receives commands with a specific local code assignment optimized for its channel conditions and service requirements, allowing tailored signal quality for each user while maintaining overall system capacity.
3Reliability
If the control channel uses high power transmission to ensure reliability, then the control channel can reach multiple mobile stations reliably, but system capacity is reduced due to increased interference
Solution Approach 1:
The patent uses orthogonal covering codes to create coded versions of control channel commands for multiple mobile stations. Each command sequence is copied and encoded with a unique orthogonal code, allowing the same control information to be transmitted to multiple mobile stations simultaneously with reliable detection through correlation with the known orthogonal codes, without requiring high power transmission.
Data Source
AI summary
An apparatus includes a first encoder for receiving a plurality of symbol streams for respective ones of a plurality of mobile stations and encoding each of the symbol streams with one of a plurality of covering sequences to form a plurality of covered sequences. The apparatus further includes a summer for summing the plurality of covered sequences to form a first Code Division Multiplexed (CDM) signal. In addition, the apparatus includes a second encoder for covering the first CDM signal with a covering sequence to form a first covered CDM signal. A system and method for multiplexing plurality of symbol streams are also provided.