UP-OFDMA Precoding for Constant Modulus Wireless Efficiency
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Solution Overview
Problem
Conventional OFDMA systems face performance degradation due to deep fades or nulls in user-specific channels, leading to reduced efficiency and the need for error-control coding or frequency hopping, while GMC-CDMA systems suffer from non-constant modulus transmissions and reduced bandwidth efficiency.
Innovation Solution
The implementation of unitary-precoded OFDMA (UP-OFDMA) techniques, which apply non-redundant unitary precoding across subcarriers to maintain constant modulus transmissions, allowing for high bandwidth and power efficiency, even with multiple subcarriers per user, and improving performance over conventional OFDMA and GMC-CDMA.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple subcarriers are assigned per user to support high data rate applications, then bandwidth efficiency is improved, but power efficiency deteriorates due to non-constant modulus signaling
Solution Approach 1:
The invention segments the transmission into blocks of information-bearing symbols and applies unitary precoding matrices to each block. This segmentation allows the system to maintain constant modulus signaling (for power efficiency) while still supporting multiple subcarriers per user (for high data rate) by processing symbols in manageable blocks with dedicated precoding matrices.
Solution Approach 2:
The invention changes the parameter of signal modulation from non-constant modulus to constant modulus by applying unitary precoding. This parameter change maintains the average power level while enabling multiple subcarriers per user, thus resolving the contradiction between bandwidth efficiency (multiple subcarriers) and power efficiency (constant modulus).
2Reliability
If error-control coding and frequency hopping are employed to robustify performance against channel fades, then reliability is improved, but device complexity increases
Solution Approach 1:
The invention applies unitary precoding matrices to information-bearing symbols before transmission as a preliminary action. This precoding prepares the signal in advance to be more robust against channel fades, eliminating the need for complex error-control coding and frequency hopping mechanisms while maintaining reliability.
Solution Approach 2:
The invention extracts and removes the need for complex error-control coding and frequency hopping by implementing unitary precoding. The precoding technique directly addresses channel fade issues through mathematical transformation of the signal, taking out the requirement for additional complexity-heavy error correction mechanisms.
Data Source
AI summary
Techniques are described for multicarrier multiple access wireless transmission, e.g. orthogonal frequency-division multiple access (OFDMA) transmissions, over frequency selective fading channels. The techniques are designed to maintain constant modulus transmissions for uplink while effectively mitigating intersymbol interference. Specifically, the techniques utilize non-redundant unitary precoding across OFDMA subcarriers to maintain constant modulus transmissions for uplink communications. For example, the techniques involve precoding a block of information symbols and assigning a different subcarrier for each symbol of the block. The subcarriers are selected to be equi-spaced and may be selected, for example, from a phase-shift keying constellation. The number of symbols per block is equal to the number of subcarriers assigned per user. Importantly, even with multiple subcarriers per user, the techniques enable constant modulus transmissions for uplink. Consequently, the techniques may achieve high power and bandwidth efficiency as well as improved performance over conventional OFDMA and GMC-CDMA transmissions.